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Publisher: AGU   (Total: 17 journals)   [Sort by number of followers]

Showing 1 - 17 of 17 Journals sorted alphabetically
Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 30, SJR: 2.439, h-index: 91)
Geophysical Research Letters     Full-text available via subscription   (Followers: 136, SJR: 3.323, h-index: 185)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 15, SJR: 3.22, h-index: 136)
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J. of Geophysical Research : Atmospheres     Partially Free   (Followers: 138)
J. of Geophysical Research : Biogeosciences     Full-text available via subscription   (Followers: 30)
J. of Geophysical Research : Earth Surface     Partially Free   (Followers: 55)
J. of Geophysical Research : Oceans     Partially Free   (Followers: 53)
J. of Geophysical Research : Planets     Full-text available via subscription   (Followers: 115)
J. of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 49)
J. of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 132)
Paleoceanography     Full-text available via subscription   (Followers: 5, SJR: 3.067, h-index: 100)
Radio Science     Full-text available via subscription   (Followers: 38, SJR: 1.072, h-index: 59)
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Tectonics     Full-text available via subscription   (Followers: 16, SJR: 2.628, h-index: 96)
Water Resources Research     Full-text available via subscription   (Followers: 82, SJR: 2.661, h-index: 144)
Journal Cover Journal of Geophysical Research : Oceans
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   Published by AGU Homepage  [17 journals]
  • Spatial Variation of Diapycnal Diffusivity Estimated from Seismic Imaging
           of Internal Wave Field, Gulf of Mexico
    • Authors: Alex Dickinson; N. J. White, C. P. Caulfield
      Abstract: Bright reflections are observed within the upper 1000 m of the water column along a seismic reflection profile that traverses the northern margin of the Gulf of Mexico. Independent hydrographic calibration demonstrates that these reflections are primarily caused by temperature changes associated with different water masses that are entrained into the Gulf along the Loop Current. The internal wave field is analyzed by automatically tracking 1171 reflections, each of which is greater than 2 km in length. Power spectra of the horizontal gradient of isopycnal displacement, ϕεx, are calculated from these tracked reflections. At low horizontal wavenumbers (kx 
      PubDate: 2017-11-10T17:42:46.082098-05:
      DOI: 10.1002/2017JC013352
       
  • Atmospheric Inputs of Iron and Manganese to Coastal Waters of the Southern
           California Current System: Seasonality, Santa Ana Winds, and
           Biogeochemical Implications
    • Authors: A. Félix-Bermúdez; F. Delgadillo-Hinojosa, M.A. Huerta-Diaz, V. Camacho-Ibar, V. Torres-Delgado
      Abstract: The magnitude and temporal variability of mineral dust deposition and its associated Fe and Mn inputs to coastal waters of the California Current System (CCS) has been scarcely investigated. Here, we report a five-year time series (April 2010-December 2014) of mineral dust (Fdust), Fe (FFe) and Mn (FMn) fluxes to the coastal zone of the southern CCS. Atmospheric deposition displayed a strong seasonal trend, with lowest Fdust, FFe and FMn during the warm season (May-October), a period dominated by strong moisture-laden winds of oceanic origin. In contrast, the highest Fdust, FFe and FMn were recorded during the cool season (November-April), a period characterized by strong winds devoid of moisture coming from the mainland. Our analysis suggests that Santa Ana Wind events could contribute with ∼15, 20 and 24%, respectively, to the total annual input of dust, Fe and Mn to the region. Besides, atmospheric soluble Fe inputs are equivalent to between 11% (warm season) and 35% (cool season) of the dissolved Fe supplied by upwelling. Our calculations indicate that atmospheric Fe deposition could explain between ∼5% (warm season) and 15% (cool season) of primary production reported for the southern CCS, suggesting that this route could also be an important input of Fe for primary producers in this region. Finally, the average Fdust, FFe and FMn for the cool seasons showed a positive interannual trend that was significantly correlated with an intensification of drought conditions over the period 2010-2014 in northwest of Mexico and southwest of the United States.
      PubDate: 2017-11-10T17:41:14.800507-05:
      DOI: 10.1002/2017JC013224
       
  • Complementary Use of Glider Data, Altimetry, and Model for Exploring
           Mesoscale Eddies in the Tropical Pacific Solomon Sea
    • Authors: L. Gourdeau; J. Verron, A. Chaigneau, S. Cravatte, W. Kessler
      Abstract: Mesoscale activity is an important component of the Solomon Sea circulation that interacts with the energetic low latitude western boundary currents of the South tropical Pacific Ocean carrying waters of subtropical origin before joining the equatorial Pacific. Mixing associated with mesoscale activity could explain water mass transformation observed in the Solomon Sea that likely impacts El Niño Southern Oscillation dynamics. This study makes synergetic use of glider data, altimetry, and high-resolution model for exploring mesoscale eddies, especially their vertical structures, and their role on the Solomon Sea circulation. The description of individual eddies observed by altimetry and gliders provides the first elements to characterize the 3D structure of these tropical eddies, and confirms the usefulness of the model to access a more universal view of such eddies. Mesoscale eddies appear to have a vertical extension limited to the Surface Waters (SW) and the Upper Thermocline Water (UTW), i.e. the first 140-150 m depth. Most of the eddies are nonlinear, meaning that eddies can trap and transport water properties. But they weakly interact with the deep New Guinea Coastal Undercurrent that is a key piece of the equatorial circulation. Anticylonic eddies are particularly efficient to advect salty and warm SW coming from the intrusion of equatorial Pacific waters at Solomon Strait, and to impact the characteristics of the New Guinea Coastal Current. Cyclonic eddies are particularly efficient to transport South Pacific Tropical Water (SPTW) anomalies from the North Vanuatu Jet and to erode by diapycnal mixing the high SPTW salinity.
      PubDate: 2017-11-10T17:40:59.180883-05:
      DOI: 10.1002/2017JC013116
       
  • Estimation of Transmittance of Solar Radiation in the Visible Domain Based
           on Remote Sensing: Evaluation of Models Using In Situ Data
    • Authors: M. Laura Zoffoli; Zhongping Lee, Michael Ondrusek, Junfang Lin, Charles Kovach, Jianwei Wei, Marlon Lewis
      Abstract: The transmittance of solar radiation in the oceanic water column plays an important role in heat transfer and photosynthesis, with implications for the global carbon cycle, global circulation and climate. Globally, the transmittance of solar radiation in the visible domain (∼400 – 700 nm) (TRVIS) through the water column, which determines the vertical distribution of visible light, has to be based on remote sensing products. There are models centered on chlorophyll-a (Chl) concentration or Inherent Optical Properties (IOPs) as both can be derived from ocean color measurements. We present evaluations of both schemes with field data from clear oceanic and from coastal waters. Here, five models were evaluated: (1) Morel and Antoine [1994] (MA94), (2) Ohlmann and Siegel [2000] (OS00), (3) Murtugudde et al. [2002] (MU02), (4) Manizza et al. [2005] (MA05) and (5) Lee et al. [2005] (IOPs05), where the first four are Chl-based and the last one is IOPs-based, with all inputs derived from remote sensing reflectance. It is found that the best performing model is the IOPs05, with Unbiased Absolute Percent Difference (UAPD) ∼23%, while Chl-based models show higher uncertainties (UAPD for MA94: ∼54%, OS00: ∼133%, MU02: ∼56% and MA05: ∼39%). The IOPs-based model was insensitive to the type of water, allowing it to be applied in most marine environments; whereas some of the Chl-based models (MU02 and MA05) show much higher sensitivities in coastal turbid waters (higher Chl waters). These results highlight the applicablity of using IOPs products for such applications.
      PubDate: 2017-11-10T17:40:50.890562-05:
      DOI: 10.1002/2017JC013209
       
  • Early Spring Phytoplankton Dynamics in the Western Antarctic Peninsula
    • Authors: Kevin R. Arrigo; Gert L. van Dijken, Anne-Carlijn Alderkamp, Zachary K. Erickson, Kate M. Lewis, Kate E. Lowry, Hannah L. Joy-Warren, Rob Middag, Janice E. Nash-Arrigo, Virginia Selz, Willem van de Poll
      Abstract: The Palmer Long-Term Ecological Research program has sampled waters of the western Antarctic Peninsula (wAP) annually each summer since 1990. However, information about the wAP prior to the peak of the phytoplankton bloom in January is sparse. Here we present results from a spring process cruise that sampled the wAP in the early stages of phytoplankton bloom development in 2014. Sea ice concentrations were high on the shelf relative to non-shelf waters, especially toward the south. Macronutrients were high and non-limiting to phytoplankton growth in both shelf and non-shelf waters, while dissolved iron concentrations were high only on the shelf. Phytoplankton were in good physiological condition throughout the wAP, although biomass on the shelf was uniformly low, presumably because of heavy sea ice cover. In contrast, an early stage phytoplankton bloom was observed beneath variable sea ice cover just seaward of the shelf break. Chlorophyll a concentrations in the bloom reached 2 mg m−3 within a 100 to 150 km band between the SBACC and SACCF. The location of the bloom appeared to be controlled by a balance between enhanced vertical mixing at the position of the two fronts and increased stratification due to melting sea ice between them. Unlike summer, when diatoms overwhelmingly dominate the phytoplankton population of the wAP, the haptophyte Phaeocystis antarctica dominated in spring, although diatoms were common. These results suggest that factors controlling phytoplankton abundance and composition change seasonally and may differentially affect phytoplankton populations as environmental conditions within the wAP region continue to change.
      PubDate: 2017-11-10T17:40:43.091685-05:
      DOI: 10.1002/2017JC013281
       
  • Spume Drops:Their Potential Role in Air-Sea Gas Exchange
    • Authors: Edward C. Monahan; Allison Staniec, Penny Vlahos
      Abstract: After summarizing the time scales defining the change of the physical properties of spume and other droplets cast up from the sea surface, the time scales governing drop-atmosphere gas exchange are compared. Following a broad review of the spume drop production functions described in the literature, a sub-set of these functions is selected via objective criteria, to represent typical, upper-bound, and lower-bound production functions. Three complementary mechanisms driving spume-atmosphere gas exchange are described, and one is then used to estimate the relative importance, over a broad range of wind speeds, of this spume drop mechanism compared to the conventional, diffusional, sea surface mechanism in air-sea gas exchange. While remaining uncertainties in the wind dependence of the spume drop production flux, and in the immediate sea surface gas flux, preclude a definitive conclusion, the findings of this study strongly suggest that, at high wind speeds (>20 m s−1 for dimethyl sulfide and>30 m s−1 for gases such a carbon dioxide), spume drops do make a significant contribution to air-sea gas exchange.
      PubDate: 2017-11-10T17:40:36.961042-05:
      DOI: 10.1002/2017JC013293
       
  • Multidecadal fCO2 Increase Along the United States Southeast Coastal
           Margin
    • Authors: Janet J. Reimer; Hongjie Wang, Rodrigo Vargas, Wei-Jun Cai
      Abstract: Coastal margins could be hotspots for acidification due to terrestrial-influenced CO2 sources. Currently there are no long-term (>20 years) records from biologically important coastal environments that could demonstrate sea surface CO2 fugacity (fCO2) and pH trends. Here, multi-decadal fCO2 trends are calculated from underway and moored time series observations along the United States southeast coastal margin, also referred to as the South Atlantic Bight (SAB). fCO2 trends across the SAB, derived from ∼26 years of cruises and ∼9.5 years from a moored time series, range from 3.0 to 4.5 µatm y−1, and are greater than the open ocean increases. The pH decline related to the fCO2 increases could be as much as -0.004 y−1; a rate greater than that expected from atmospheric-influenced pH alone. We provide evidence that fCO2 increases and pH decreases on an ocean margin can be faster than those predicted for the open ocean from atmospheric influence alone. We conclude that a substantial fCO2 increase across the marginal SAB is due to both increasing temperature on the middle and outer shelves, but to lateral land-ocean interactions in the coastal zone and on inner shelf.
      PubDate: 2017-11-10T17:40:30.559046-05:
      DOI: 10.1002/2017JC013170
       
  • Modeling North Atlantic Nor'easters with Modern Wave Forecast Models
    • Authors: Will Perrie; Bechara Toulany, Aron Roland, Mathieu Dutour-Sikiric, Changsheng Chen, Robert C. Beardsley, Jianhua Qi, Yongcun Hu, Mike Casey, Hui Shen
      Abstract: Three state-of-the-art operational wave forecast model systems are implemented on fine-resolution grids for the Northwest Atlantic. These models are: (1) a composite model system consisting of SWAN implemented within WAVEWATCHIII® (the latter is hereafter, WW3) on a nested system of traditional structured grids, (2) an unstructured grid finite-volume wave model denoted ‘SWAVE’, using SWAN physics, and (3) an unstructured grid finite element wind wave model denoted as ‘WWM’ (for ‘wind wave model’) which uses WW3 physics. Models are implemented on grid systems that include relatively large domains to capture the wave energy generated by the storms, as well as including fine-resolution nearshore regions of the southern Gulf of Maine with resolution on the scale of 25 m to simulate areas where inundation and coastal damage have occurred, due to the storms. Storm cases include three intense midlatitude cases: a spring Nor'easter storm in May 2005, the Patriot's Day storm in 2007 and the Boxing Day storm in 2010. Although these wave model systems have comparable overall properties in terms of their performance and skill, it is found that there are differences. Models that use more advanced physics, as presented in recent versions of WW3, tuned to regional characteristics, as in the Gulf of Maine and the Northwest Atlantic, can give enhanced results.
      PubDate: 2017-11-03T10:35:27.212607-05:
      DOI: 10.1002/2017JC012868
       
  • A Model of Icebergs and Sea Ice in A Joint Continuum Framework
    • Authors: Irena Vaňková; David M. Holland
      Abstract: The ice mélange, a mixture of sea ice and icebergs, often present in front of outlet glaciers in Greenland or ice shelves in Antarctica, can have a profound effect on the dynamics of the ice-ocean system. The current inability to numerically model the ice mélange motivates a new modeling approach proposed here. A continuum sea-ice model is taken as a starting point and icebergs are represented as thick and compact pieces of sea ice held together by large tensile and shear strength, selectively introduced into the sea-ice rheology. In order to modify the rheology correctly, an iceberg tracking procedure is implemented within a semi-Lagrangian time-stepping scheme, designed to exactly preserve iceberg shape through time. With the proposed treatment, sea ice and icebergs are considered a single fluid with spatially varying rheological properties. Mutual interactions are thus automatically included without the need for further parametrization. An important advantage of the presented framework for an ice mélange model is its potential to be easily included within sea-ice components of existing climate models.
      PubDate: 2017-11-03T10:30:48.750792-05:
      DOI: 10.1002/2017JC013012
       
  • A Spectral Selective Attenuation Mechanism-Based Kpar Algorithm for
           Biomass Heating Effect Simulation in the Open Ocean
    • Authors: Jun Chen; Xiangguang Zhang, Xiaogang Xing, Joji Ishizaka, Zhifeng Yu
      Abstract: Quantifying the diffuse attenuation coefficient of the photosynthetically available radiation (Kpar) can improve our knowledge of euphotic depth (Zeu) and biomass heating effects in the upper layers of oceans. An algorithm to semi-analytically derive Kpar from remote sensing reflectance (Rrs) is developed for the global open oceans. This algorithm includes the following two portions: (1) a neural network model for deriving the diffuse attention coefficients (Kd) that considers the residual error in satellite Rrs, and (2) a three band depth-dependent Kpar algorithm (TDKA) for describing the spectral selective attenuation mechanism of underwater solar radiation in the open oceans. This algorithm is evaluated with both in situ PAR profile data and satellite images, and the results show that it can produce acceptable PAR profile estimations while clearly removing the impacts of satellite residual errors on Kpar estimations. Furthermore, the performance of the TDKA algorithm is evaluated by its applicability in Zeu derivation and mean temperature within a mixed layer depth (TML) simulation, and the results show that it can significantly decrease the uncertainty in both compared with the classical chlorophyll-a concentration-based Kpar algorithm. Finally, the TDKA algorithm is applied in simulating biomass heating effects in the Sargasso Sea near the Bermuda, with new Kpar data it is found that the biomass heating effects can lead to a 3.4°C maximum warming in the upper layers but could result in a 0.67°C maximum cooling in the deep layers.
      PubDate: 2017-11-02T10:47:08.275581-05:
      DOI: 10.1002/2017JC013101
       
  • Dynamical Evolution of Intense Ierapetra Eddies on a 22 Year Long Period
    • Authors: Artemis Ioannou; Alexandre Stegner, Briac Le Vu, Isabelle Taupier-Letage, Sabrina Speich
      Abstract: Considered as wind forced, the recurrent formation of Ierapetra eddy affects the Eastern Mediterranean Sea circulation. Even though this large, coherent and long-lived anticyclone has been extensively studied, there are only few quantitative information on its dynamical characteristics. The main goal of this study is to quantify the Ierapetra Eddies (IEs) intensity and examine their seasonal and interannual variability over a 22 year period (1993-2014). We choose the automatic eddy detection algorithm AMEDA to estimate the main IEs dynamical parameters such as their size, their intensities and their lifetimes. Applied to daily AVISO altimetric products, the AMEDA algorithm allows a full characterization providing additional information on vortex velocity profiles as well as on merging and splitting events. Among the years of observations, the IEs Rossby number experience a strong variability and could vary by a factor 4 (Ro=0.07-0.27). This is mainly due to the eddy velocity variations rather than size variations. Moreover, we found that after their formation IEs could re-intensify. This intensification process may lead to a doubling of the vortex intensity in less than four months. That extra input of energy coincides with the Etesian winds period. Such high intensities are not expected from large-scale anticyclones and require cyclogeostrophic corrections. Considering this ageostrophic part, the maximum values of the core vorticity were derived and we found that the IEs might sometimes exhibit a negative potential vorticity core. Evidences on the eddy intensity from two oceanographic campaigns suggest that the IEs are probably more intense than we even estimate.
      PubDate: 2017-11-02T10:40:48.390081-05:
      DOI: 10.1002/2017JC013158
       
  • A Lagrangian View of Spring Phytoplankton Blooms
    • Authors: Shinichiro Kida; Takamitsu Ito
      Abstract: The mechanisms of spring phytoplankton blooms are investigated from a Lagrangian framework by using a Lagrangian NPZD model that can track the movement and transfers of nutrient parcels in a turbulent environment. The model reveals that the onset of spring blooms depends on the cumulative euphotic age, which is the total time that inorganic nutrient is exposed to light before the photosynthetic conversion to phytoplankton biomass. A spring bloom, defined as a 10-fold increase of near-surface phytoplankton, occurs when this cumulative euphotic age is approximately μeff-1·ln⁡10, where μeff is the effective growth rate in the euphotic layer, regardless of the underlying mechanism. If the turbulent layer depth is shallower than the critical depth and turbulence is strong, nutrient parcels accumulate enough light exposure through multiple entries to the sun-lit zone near the surface. If turbulence is weak, as that considered in the critical turbulence theory, the accumulation of the light exposure depends on the residence time of the nutrients parcels near the surface. The spectral shape of the cumulative euphotic age can clearly distinguish these two modes of spring blooms. The spectrum shows a peak at the theoretical growth timescale when multiple entries become important, while it shows a maximum near age zero that decays with age when the near-surface residence time becomes important. Mortality increases the cumulative euphotic age necessary for a bloom but does not affect the spectral shape, suggesting that it does not alter the primary mechanism behind the accumulation of cumulative euphotic age.
      PubDate: 2017-11-02T10:35:23.361021-05:
      DOI: 10.1002/2017JC013383
       
  • A Bayesian-Based System to Assess Wave-Driven Flooding Hazards on Coral
           Reef-Lined Coasts
    • Authors: S.G. Pearson; C.D. Storlazzi, A.R. van Dongeren, M.F.S. Tissier, A.J.H.M. Reniers
      Abstract: Many low-elevation, coral reef-lined, tropical coasts are vulnerable to the effects of climate change, sea-level rise, and wave-induced flooding. The considerable morphological diversity of these coasts and the variability of the hydrodynamic forcing that they are exposed to make predicting wave-induced flooding a challenge. A process-based wave-resolving hydrodynamic model (XBeach Non-Hydrostatic, ‘XBNH') was used to create a large synthetic database for use in a “Bayesian Estimator for Wave Attack in Reef Environments” (BEWARE), relating incident hydrodynamics and coral reef geomorphology to coastal flooding hazards on reef-lined coasts. Building on previous work, BEWARE improves system understanding of reef hydrodynamics by examining the intrinsic reef and extrinsic forcing factors controlling runup and flooding on reef-lined coasts. The Bayesian estimator has high predictive skill for the XBNH model outputs that are flooding indicators, and was validated for a number of available field cases. It was found that, in order to accurately predict flooding hazards, water depth over the reef flat, incident wave conditions, and reef flat width are the most essential factors, whereas other factors such as beach slope and bed friction due to the presence or absence of corals are less important. BEWARE is a potentially powerful tool for use in early warning systems or risk assessment studies, and can be used to make projections about how wave-induced flooding on coral reef-lined coasts may change due to climate change.
      PubDate: 2017-11-02T10:25:30.556336-05:
      DOI: 10.1002/2017JC013204
       
  • Submesoscale Sea Ice-Ocean Interactions in Marginal Ice Zones
    • Authors: Georgy E Manucharyan; Andrew F Thompson
      Abstract: Signatures of ocean eddies, fronts and filaments are commonly observed within the marginal ice zones (MIZ) from satellite images of sea ice concentration, and in situ observations via ice-tethered profilers or under-ice gliders. Localized and intermittent sea ice heating and advection by ocean eddies are currently not accounted for in climate models and may contribute to their biases and errors in sea ice forecasts. Here, we explore mechanical sea ice interactions with underlying submesoscale ocean turbulence. We demonstrate that the release of potential energy stored in meltwater fronts can lead to energetic submesoscale motions along MIZs with sizes O(10 km) and Rossby numbers O(1). In low-wind conditions, cyclonic eddies and filaments efficiently trap the sea ice and advect it over warmer surface ocean waters where it can effectively melt. The horizontal eddy diffusivity of sea ice mass and heat across the MIZ can reach O(200 m2 s−1). Submesoscale ocean variability also induces large vertical velocities (order of 10 m day−1) that can bring relatively warm subsurface waters into the mixed layer. The ocean–sea ice heat fluxes are localized over cyclonic eddies and filaments reaching about 100 W m−2. We speculate that these submesoscale-driven intermittent fluxes of heat and sea ice can potentially contribute to the seasonal evolution of MIZs. With the continuing global warming and sea ice thickness reduction in the Arctic Ocean, submesoscale sea ice-ocean processes are expected to become increasingly prominent.
      PubDate: 2017-11-02T10:20:36.372046-05:
      DOI: 10.1002/2017JC012895
       
  • Velocity and Drag Evolution From the Leading Edge of a Model Mangrove
           Forest
    • Authors: Maria Maza; Katherine Adler, Diogo Ramos, Adrian Mikhail Garcia, Heidi Nepf
      Abstract: An experimental study of unidirectional flow through a model mangrove forest measured both velocity and forces on individual trees. The individual trees were 1/12th scale models of mature Rhizophora, including 24 prop roots distributed in a three-dimensional layout. Thirty-two model trees were distributed in a staggered array producing a 2.5-m long forest. The velocity evolved from a boundary layer profile at the forest leading edge to a vertical profile determined by the vertical distribution of frontal area, with significantly higher velocity above the prop roots. Fully-developed conditions were reached at the 5th tree row from the leading edge. Within the root zone the velocity was reduced by up to 50 percent and the TKE was increased by as much as 5-fold, relative to the upstream conditions. TKE in the root zone was mainly produced by root and trunk wakes, and it agreed in magnitude with the estimation obtained using the Tanino and Nepf (2008) formulation. Maximum TKE occurred at the top of the roots, where a strong shear region was associated with the change in frontal area. The drag measured on individual trees decreased from the leading edge and reached a constant value at the 5th row and beyond, i.e. in the fully-developed region. The drag exhibited a quadratic dependence on velocity, which justified the definition of a quadratic drag coefficient. Once the correct drag length-scale was defined, the measured drag coefficients collapsed to a single function of Reynolds number.
      PubDate: 2017-11-02T10:10:34.588222-05:
      DOI: 10.1002/2017JC012945
       
  • Seasonal Dynamics of Dissolved Organic Carbon Under Complex Circulation
           Schemes on a Large Continental Shelf: The Northern South China Sea
    • Authors: Feifei Meng; Minhan Dai, Zhimian Cao, Kai Wu, Xiaozheng Zhao, Xiaolin Li, Junhui Chen, Jianping Gan
      Abstract: We examined the distribution and seasonality of dissolved organic carbon (DOC) based on a large data set collected from the northern South China Sea (NSCS) shelf under complex circulation schemes influenced by river plume, coastal upwelling and downwelling. The highest surface values of ∼117 μmol L−1 were observed nearshore in summer suggesting high DOC supplies from the river inputs, whereas the lowest surface values of ∼62 μmol L−1 were on the outer shelf in winter due to entrainment of DOC-poor subsurface water under strengthened vertical mixing. While the summer coastal upwelling brought lower DOC from offshore depth to the nearshore surface, the winter coastal downwelling delivered higher surface DOC to the mid-shelf deep waters from the inner shelf fueled by the China Coastal Current (CCC) transporting relatively high DOC from the East China Sea to the NSCS. The intensified winter downwelling generated a cross-shelf DOC transport of 3.1 × 1012 g C over a large shelf area, which induced a significant depression of the NSCS DOC inventory in winter relative to in autumn. In addition to the variable physical controls, net biological production of DOC was semiquantified in both the river plume (2.8±3.0 μmol L−1) and coastal upwelling (3.1±1.3 μmol L−1) in summer. We demonstrated that the NSCS shelf had various origins of DOC including riverine inputs, inter-shelf transport and in situ production. Via cross-shelf transport, the accumulated DOC would be exported to and stored in the deep ocean, suggesting that continental shelves are a potentially effective carbon sink.
      PubDate: 2017-11-02T10:05:45.244839-05:
      DOI: 10.1002/2017JC013325
       
  • Nitrogen and Phosphorus Budgets in the Northwestern Mediterranean Deep
           Convection Region
    • Authors: Faycal Kessouri; Caroline Ulses, Claude Estournel, Patrick Marsaleix, Tatiana Severin, Mireille Pujo-Pay, Jocelyne Caparros, Patrick Raimbault, Orens Pasqueron de Fommervault, Fabrizio D'Ortenzio, Vincent Taillandier, Pierre Testor, Pascal Conan
      Abstract: The aim of this study is to understand the biogeochemical cycles of the northwestern Mediterranean Sea (NW Med), where a recurrent spring bloom related to dense water formation occurs. We used a coupled physical-biogeochemical model at high resolution to simulate realistic one-year period and analyze the nitrogen (N) and phosphorus (P) cycles. First, the model was evaluated using cruises carried out in winter, spring and summer and a Bio-Argo float deployed in spring. Then, the annual cycle of meteorological and hydrodynamical forcing and nutrients stocks in the upper layer were analyzed. Third, the effect of biogeochemical and physical processes on N and P was quantified. Fourth, we quantified the effects of the physical and biological processes on the seasonal changes of the molar NO3:PO4 ratio, particularly high compared to the global ocean. The deep convection reduced the NO3:PO4 ratio of upper waters, but consumption by phytoplankton increased it. Finally, N and P budgets were estimated. At the annual scale, this area constituted a sink of inorganic and a source of organic N and P for the peripheral area. NO3 and PO4 were horizontally advected from the peripheral regions into the intermediate waters (130-800 m) of the deep convection area, while organic matter was exported throughout the whole water column toward the surrounding areas. The annual budget suggests that the NW Med deep convection constitutes a major source of nutrients for the photic zone of the Mediterranean Sea.
      PubDate: 2017-11-02T09:55:38.222818-05:
      DOI: 10.1002/2016JC012665
       
  • Vulnerability of Coral Reefs to Bioerosion From Land-Based Sources of
           Pollution
    • Authors: Nancy G. Prouty; Anne Cohen, Kimberly K. Yates, Curt D. Storlazzi, Peter W. Swarzenski, Darla White
      Abstract: Ocean acidification (OA), the gradual decline in ocean pH and [CO32-] caused by rising levels of atmospheric CO2, poses a significant threat to coral reef ecosystems, depressing rates of calcium carbonate (CaCO3) production, and enhancing rates of bioerosion and dissolution. As ocean pH and [CO32-] decline globally, there is increasing emphasis on managing local stressors that can exacerbate the vulnerability of coral reefs to the effects of OA. We show that sustained, nutrient rich, lower pH submarine groundwater discharging onto nearshore coral reefs off west Maui lowers the pH of seawater and exposes corals to nitrate concentrations 50 times higher than ambient. Rates of coral calcification are substantially decreased, and rates of bioerosion are orders of magnitude higher than those observed in coral cores collected in the Pacific under equivalent low pH conditions but living in oligotrophic waters. Heavier coral δ15N values pinpoint not only site-specific eutrophication, but also a sewage nitrogen source enriched in 15N. Our results show that eutrophication of reef seawater by land-based sources of pollution can magnify the effects of OA through nutrient driven-bioerosion. These conditions could contribute to the collapse of coastal coral reef ecosystems sooner than current projections predict based only on ocean acidification.
      PubDate: 2017-11-01T09:00:02.056173-05:
      DOI: 10.1002/2017JC013264
       
  • The Global Mesoscale Eddy Available Potential Energy Field in Models and
           Observations
    • Authors: C. A. Luecke; B. K. Arbic, S. L. Bassette, J. G. Richman, J. F. Shriver, M. H. Alford, O. M. Smedstad, P. G. Timko, D. S. Trossman, A. J. Wallcraft
      Abstract: Global maps of the mesoscale Eddy Available Potential Energy (EAPE) field at a depth of 500m are created using potential density anomalies in a high-resolution 112.5° global ocean model. Maps made from both a free-running simulation and a data-assimilative reanalysis of the HYbrid Coordinate Ocean Model (HYCOM) are compared with maps made by other researchers from density anomalies in Argo profiles. The HYCOM and Argo maps display similar features, especially in the dominance of western boundary currents. The reanalysis maps match the Argo maps more closely, demonstrating the added value of data assimilation. Global averages of the simulation, reanalysis, and Argo EAPE all agree to within about 10%.The model and Argo EAPE fields are compared to EAPE computed from temperature anomalies in a dataset of “Moored Historical Observations” (MHO) in conjunction with buoyancy frequencies computed from a global climatology. The MHO dataset allows for an estimate of the EAPE in high-frequency motions that is aliased into the Argo EAPE values. At MHO locations, 15-32% of the EAPE in the Argo estimates is due to aliased motions having periods of 10 days or less. Spatial averages of EAPE in HYCOM, Argo, and MHO data, agree to within 50% at MHO locations, with both model estimates lying within error bars observations.Analysis of the EAPE field in an idealized model, in conjunction with published theory, suggests that much of the scatter seen in comparisons of different EAPE estimates is to be expected given the chaotic, unpredictable nature of mesoscale eddies.
      PubDate: 2017-10-27T12:05:48.293248-05:
      DOI: 10.1002/2017JC013136
       
  • Ocean-Forced Ice-Shelf Thinning in a Synchronously Coupled Ice-Ocean Model
    • Authors: James R. Jordan; Paul R. Holland, Dan Goldberg, Kate Snow, Robert Arthern, Jean-Michel Campin, Patrick Heimbach, Adrian Jenkins
      Abstract: The first fully synchronous, coupled ice shelf-ocean model with a fixed grounding line and imposed upstream ice velocity has been developed using the MITgcm (Massachusetts Institute of Technology general circulation model). Unlike previous, asynchronous, approaches to coupled modeling our approach is fully conservative of heat, salt, and mass. Synchronous coupling is achieved by continuously updating the ice-shelf thickness on the ocean time step. By simulating an idealized, warm-water ice shelf we show how raising the pycnocline leads to a reduction in both ice-shelf mass and back stress, and hence buttressing. Coupled runs show the formation of a western boundary channel in the ice-shelf base due to increased melting on the western boundary due to Coriolis enhanced flow. Eastern boundary ice thickening is also observed. This is not the case when using a simple depth-dependent parameterized melt, as the ice shelf has relatively thinner sides and a thicker central “bulge” for a given ice-shelf mass. Ice-shelf geometry arising from the parameterized melt rate tends to underestimate backstress (and therefore buttressing) for a given ice-shelf mass due to a thinner ice shelf at the boundaries when compared to coupled model simulations.
      PubDate: 2017-10-27T12:05:38.970936-05:
      DOI: 10.1002/2017JC013251
       
  • The Yermak Pass Branch: A Major Pathway for the Atlantic Water North of
           Svalbard'
    • Authors: Zoé Koenig; Christine Provost, Nathalie Sennéchael, Gilles Garric, Jean-Claude Gascard
      Abstract: An upward-looking Acoustic Doppler Current Profiler deployed from July 2007 to September 2008 in the Yermak Pass, north of Svalbard, gathered velocity data from 570 m up to 90 m at a location covered by sea-ice 10 months out of 12. Barotropic diurnal and semi-diurnal tides are the dominant signals in the velocity (more than 70% of the velocity variance). In winter, baroclinic eddies at periods between 5 and 15 days and pulses of one-to-two month periodicity are observed in the Atlantic Water layer and are associated with a shoaling of the pycnocline. Mercator-Ocean global operational model with daily and 1/12 degree spatial resolution is shown to have skills in representing low frequency velocity variations (>1 month) in the West Spitsbergen Current and in the Yermak Pass. Model outputs suggest that the Yermak Pass Branch has had a robust winter pattern over the last 10 years, carrying on average 31% of the Atlantic Water volume transport of the West Spitsbergen Current (36% in autumn/winter). However those figures have to be considered with caution as the model neither simulates tides nor fully resolves eddies and ignores residual mean currents that could be significant.
      PubDate: 2017-10-27T12:05:22.913434-05:
      DOI: 10.1002/2017JC013271
       
  • Regional Effects of the Mount Pinatubo Eruption on the Middle East and the
           Red Sea
    • Authors: Sergey Osipov; Georgiy Stenchikov
      Abstract: The 1991 eruption of Mount Pinatubo had dramatic effects on the regional climate in the Middle East. Though acknowledged, these effects have not been thoroughly studied. To fill this gap and to advance understanding of the mechanisms that control variability in the Middle East's regional climate, we simulated the impact of the 1991 Pinatubo eruption using a regional coupled ocean-atmosphere modeling system set for the Middle East and North Africa (MENA) domain. We used the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) framework, which couples the Weather Research and Forecasting Model (WRF) model with the Regional Oceanic Modeling System (ROMS). We modified the WRF model to account for the radiative effect of volcanic aerosols. Our coupled ocean-atmosphere simulations verified by available observations revealed strong perturbations in the energy balance of the Red Sea, which drove thermal and circulation responses. Our modeling approach allowed us to separate changes in the atmospheric circulation caused by the impact of the volcano from direct regional radiative cooling from volcanic aerosols. The atmospheric circulation effect was significantly stronger than the direct volcanic aerosols effect. We found that the Red Sea response to the Pinatubo eruption was stronger and qualitatively different from that of the global ocean system. Our results suggest that major volcanic eruptions significantly affect the climate in the Middle East and the Red Sea and should be carefully taken into account in assessments of long-term climate variability and warming trends in MENA and the Red Sea.
      PubDate: 2017-10-26T01:45:30.271784-05:
      DOI: 10.1002/2017JC013182
       
  • Interannual Variation in Offshore Advection of Amazon-Orinoco Plume
           Waters: Observations, Forcing Mechanisms, and Impacts
    • Authors: S. Fournier; D. Vandemark, L. Gaultier, T. Lee, B. Jonsson, M.M. Gierach
      Abstract: This study investigates sea surface salinity (SSS) and sea surface temperature (SST) variations in the tropical Atlantic east of the Lesser Antilles, a region where freshwater advection from the Amazon and Orinoco rivers, may potentially impact air-sea interaction. Observations are used to document later-summer variability and evaluate offshore riverine transport from 2010-2014. During the period 2010-2014, the largest difference in plume-affected areas, defined as the extent covered by SSS lower than 35.5 pss, is found between 2011 and 2014. Plume waters covered 92% of the study region in 2011 and 60% in 2014, with the average SSS in the study region being 2-pss lower in 2011. Lagrangian particle tracking based on satellite-derived ocean currents is used to diagnose the impact of the river plumes on SSS and SST from 2010 through 2014. Northward freshwater flux in summer 2014 was significantly weaker than fluxes in 2010-2013. This difference is not due to interannual discharge variability, but to significant changes in eddy-driven transport and cross-shore winds. In particular, the stronger cross-shore wind in May 2014 restricted offshore freshwater flow and lead to a smaller plume-affected area. Persistent SST gradients are often found near the plume edge, which may have implications for ocean-atmosphere coupling associated with atmospheric convection. SST in the study region was 1°C higher in 2010 than in other years, and is related to basin-scale ocean-atmosphere processes. Interannual variation in Amazon advective pathways and the associated SSS changes are also influenced by changes in the ITCZ position between 2011 and 2014.
      PubDate: 2017-10-25T13:06:03.796644-05:
      DOI: 10.1002/2017JC013103
       
  • Generation and Decay Mechanisms of Ningaloo Niño/Niña
    • Authors: Takahito Kataoka; Tomoki Tozuka, Toshio Yamagata
      Abstract: Using an ocean model, generation and decay mechanisms of warm/cool sea surface temperature anomalies (SSTAs) off Western Australia, or Ningaloo Niño/Niña, are investigated through the calculation of a mixed-layer temperature (MLT) balance taking the mixed-layer depth (MLD) variation into account. Since Ningaloo Niño/Niña develops owing to local air-sea interaction and/or remote forcing, events are classified into two cases based on alongshore wind anomalies and analyzed separately. It is revealed that the anomalous meridional advection associated with the stronger Leeuwin Current and the enhanced warming by the climatological shortwave radiation because of the shallower MLD generate warm SSTAs in the coastal region for both cases of Ningaloo Niño. On the other hand, the latent heat flux damps SSTAs only in a case without northerly alongshore wind anomalies. In the decay, larger sensible heat loss is important. Because of the reduced meridional temperature gradient, the meridional advection eventually damps SSTAs. The sensitivity change to the climatological shortwave radiation owing to MLD anomalies explains offshore MLT tendency anomalies for both cases throughout the events. The mechanisms for Ningaloo Niña are close to a mirror image of Ningaloo Niño, but differ in that the latent heat flux damps offshore SSTAs. The seasonal phase-locking nature of Ningaloo Niño/Niña is related to the seasonal variations of MLD and surface heat fluxes, which regulate the amplitude and sign of the sensitivity change to surface heat fluxes. It is also related to the seasonal variations of the Leeuwin Current and meridional temperature gradient through advection anomalies.
      PubDate: 2017-10-25T13:06:00.933989-05:
      DOI: 10.1002/2017JC012966
       
  • Regional Sea Level Variability and Trends, 1960–2007: A Comparison of
           Sea Level Reconstructions and Ocean Syntheses
    • Authors: M. Carson; A. Köhl, D. Stammer, B. Meyssignac, J. Church, J. Schröter, M. Wenzel, B. Hamlington
      Abstract: Several existing statistical and dynamical reconstructions of past regional sea level variability and trends are compared with each other and with tide gauges over the 48-yr period 1960–2007, partially pre-dating the satellite altimetry era. Evaluated statistical reconstructions were built from tide gauge data (TGR), and dynamical reconstructions from ocean data assimilation (ODA) approaches. Although most of the TGRs yield global-mean time series of sea level with trends deviating within only ±0.1 mm yr−1, the spatial anomalies of the trends deviate substantially between the reconstructions over the period predating altimetry. In contrast, TGRs match observed regional trend patterns fairly well during the satellite altimetry era. TGRs match tide gauge data better than ODA results; however, they exhibit less variability in the open ocean compared to altimetric data. Over the pre-altimetry period, all reconstructed regional sea level trend patterns deviate substantially from each other. In terms of detrended correlations in this earlier period, the reconstructions match tide gauges, and each other, much better in the Pacific than in the Atlantic. An ensemble of all TGR and ODA estimates provides some improvements in correlations and trends to both tide gauges and altimetry. Nevertheless, a lack of independent open-ocean sea surface height data predating altimetry makes impossible the validation of the ensemble for pre-altimetry open ocean sea level trends and variability. Estimating regional sea level changes prior to altimetry therefore remains an unsolved challenge.
      PubDate: 2017-10-25T13:05:57.20921-05:0
      DOI: 10.1002/2017JC012992
       
  • Implications of Future Northwest Atlantic Bottom Temperatures on the
           American Lobster (Homarus Americanus) Fishery
    • Authors: Jennie E. Rheuban; Maria T. Kavanaugh, Scott C. Doney
      Abstract: Sea surface temperatures of the northwest Atlantic have warmed dramatically over the last several decades, while benthic temperatures have increased at a slower pace. Here, we analyze a subset of the CMIP5 global Earth System model ensemble using a statistical downscaling approach to determine potential future changes in benthic temperatures on the northwest Atlantic continental shelf and slope (
      PubDate: 2017-10-25T13:05:39.93825-05:0
      DOI: 10.1002/2017JC012949
       
  • Thirty-Three Years of Marine Benthic Warming Along the US Northeast
           Continental Shelf and Slope: Patterns, Drivers, and Ecological
           Consequences
    • Authors: Maria T. Kavanaugh; Jennie E. Rheuban, Kelly M. A. Luis, Scott C. Doney
      Abstract: The US Northeast Continental Shelf is experiencing rapid warming, with potentially profound consequences to marine ecosystems. While satellites document multiple scales of spatial and temporal variability on the surface, our understanding of the status, trends and drivers of the benthic environmental change remains limited. We interpolated sparse benthic temperature data along the New England Shelf and upper Slope using a seasonally dynamic, regionally-specific multiple linear regression model that merged in situ and remote sensing data. The statistical model predicted nearly 90% of the variability of the data, resulting in a synoptic time series spanning over three decades from 1982-2014. Benthic temperatures increased throughout the domain, including in the Gulf of Maine. Rates of benthic warming ranged from 0.1 to 0.4 °C per decade, with fastest rates occurring in shallow, nearshore regions and on Georges Bank, the latter exceeding rates observed in the surface. Rates of benthic warming were up to 1.6 times faster in winter than the rest of the year in many regions, with important implications for disease occurrence and energetics of overwintering species. Drivers of warming varied over the domain. In southern New England and the mid-Atlantic shallow Shelf regions, benthic warming was tightly coupled to changes in SST, whereas both regional and basin scale changes in ocean circulation affect temperatures in the Gulf of Maine, the Continental Shelf and Georges Banks. These results highlight data gaps, the current feasibility of prediction from remotely sensed variables, and the need for improved understanding on how climate may affect seasonally-specific ecological processes.
      PubDate: 2017-10-25T13:05:33.463043-05:
      DOI: 10.1002/2017JC012953
       
  • Biogeochemical Impact of Snow Cover and Cyclonic Intrusions on the Winter
           Weddell Sea Ice Pack
    • Authors: J.-L. Tison; S. Schwegmann, G. Dieckmann, J.-M. Rintala, H. Meyer, S. Moreau, M. Vancoppenolle, D. Nomura, S. Engberg, L. J. Bloomster, S. Heindricks, C. Uhlig, A.-M. Luhtanen, J. de Jong, J. Janssens, G. Carnat, J. Zhou, B. Delille
      Abstract: Sea ice is a dynamic biogeochemical reactor and a double interface actively interacting with both the atmosphere and the ocean. However, proper understanding of its annual impact on exchanges, and therefore potentially on the climate, notably suffer from the paucity of autumnal and winter data sets. Here we present the results of physical and biogeochemical investigations on winter Antarctic pack ice in the Weddell Sea (R.V. Polarstern AWECS cruise, July-August 2013) which are compared with those from two similar studies conducted in the area in 1986 and 1992.The winter 2013 was characterized by a warm sea ice cover due to the combined effects of deep snow and frequent warm cyclones events penetrating southwards from the open Southern Ocean. These conditions were favorable to high ice permeability and cyclic events of brine movements within the sea ice cover (brine tubes), favoring relatively high chlorophyll-a (Chl-a) concentrations. We discuss the timing of this algal activity showing that arguments can be presented in favor of continued activity during the winter due to the specific physical conditions. Large-scale sea ice model simulations also suggest a context of increasingly deep snow, warm ice and large brine fractions across the three observational years, despite the fact that the model is forced with a snowfall climatology. This lends support to the claim that more severe Antarctic sea ice conditions, characterized by a longer ice season, thicker and more concentrated ice are sufficient to increase the snow depth and, somehow counter-intuitively, to warm the ice.
      PubDate: 2017-10-25T13:05:27.913958-05:
      DOI: 10.1002/2017JC013288
       
  • Internal Solitary Wave Reflection Near Dongsha Atoll, the South China Sea
    • Authors: Xiaolin Bai; Xiaofeng Li, Kevin G. Lamb, Jianyu Hu
      Abstract: Internal solitary wave (ISW) reflection is rarely observed in satellite images, even in the South China Sea (SCS), where the strongest and most energetic ISWs in the world have been observed. Compared to the large number of satellite images showing shoaling ISW in the SCS, fewer than 10 satellite images have been reported showing ISW reflection. In this study, we collect recent satellite images and implement a numerical model to analyze ISW reflection near Dongsha Atoll, in the SCS. Satellite observations show that the reflection appears to be associated with the large-amplitude ISWs generated by strong tidal currents in Luzon Strait. Numerical simulations show that ISWs break when reaching the sloping bottom. Part of ISW energy is reflected by mode-1 waves and their trailing mode-2 waves. The mode-1 waves have two types: long inertia-gravity waves and breaking ISW-induced short waves. They propagate quickly but induce weak vertical velocity and surface imprints. Mode-2 waves induce strong vertical velocity, showing visible signature in satellites. Horizontal distribution of the energy indicates that a maximum energy of about 2% of the incident energy is contained in a single reflected wave. This could explain why the reflected waves are rarely observed, because reflected waves must be sufficiently large to be detected in satellite images. Although individual wave's energy is small, in total up to 20% of the incident wave is reflected by the groups of mode-1 and mode-2 waves. This suggests that ISW reflection has a significant impact on energy distribution over the continental slopes.
      PubDate: 2017-10-21T04:55:40.933066-05:
      DOI: 10.1002/2017JC012880
       
  • Quantitative Assessment on Multiple Timescale Features and Dynamics of Sea
           Surface Suspended Sediment Concentration Using Remote Sensing Data
    • Authors: Zhou Zhou; Changwei Bian, Chenghao Wang, Wensheng Jiang, Rong Bi
      Abstract: Wind-waves, tidal currents and some other dynamic factors dominate the suspended sediment concentration (SSC) variations in shallow seas and it is difficult to quantitatively evaluate the effects of individual dynamic factors on SSC modulation. This work used the long-term Moderate Resolution Imaging Spectroradiometer (MODIS) and the high temporal-resolution Geostationary Ocean Color Imager (GOCI) remote sensing data to quantify the sea surface SSC variations on multiple timescales (intra-tidal, spring-neap, seasonal and long-term timescales) in the Bohai Sea, and further quantitatively evaluated the effects of corresponding dynamic factors on the SSC modulation. The results indicated that the monsoon associated wind-waves and stratification played the most important role in modulating SSC, with seasonal SSC variation of 8.1 mg/L in the Bohai Sea. The intra-tidal current variations played the secondary important role, causing SSC variation of 5.8 mg/L. The spring-neap tidal current variations led to SSC variation of 3.1 mg/L in the Bohai Sea. In the long run (2003-2014), the SSC of the Bohai Sea decreased slightly with SSC variation of 2.8 mg/L (decline rate: 0.23 mg/L/year), which may be caused by the weakening wind, decreasing sediment load from the Yellow River or the massive reclamation in recent decades. Probably due to the topography, sea bed sediment grain size and river plume, SSC variations in the southern Bohai Sea were more pronounced than those in the northern Bohai Sea.
      PubDate: 2017-10-16T08:19:27.255484-05:
      DOI: 10.1002/2017JC013082
       
  • Front-Eddy Influence on Water Column Properties, Phytoplankton Community
           Structure, and Cross-Shelf Exchange of Diatom Taxa in the Shelf-Slope Area
           Off Concepción (∼36-37°S)
    • Authors: Carmen E. Morales; Valeria Anabalón, Joaquim P. Bento, Samuel Hormazabal, Marcela Cornejo, Marco A. Correa-Ramírez, Nelson Silva
      Abstract: In eastern boundary current systems (EBCSs), submesoscale to mesocale variability contributes to cross-shore exchanges of water properties, nutrients, and plankton. Data from a short-term summer survey and satellite time series (January-February 2014) were used to characterize submesoscale variability in oceanographic conditions and phytoplankton distribution across the coastal upwelling and coastal transition zones north of Punta Lavapié, and to explore cross-shelf exchanges of diatom taxa. A thermo-haline front (FRN-1) flanked by a mesoscale anticyclonic intrathermocline eddy (ITE-1), or mode-water eddy, persisted during the study period and the survey was undertaken during a wind relaxation event. At the survey time, ITE-1 contributed to an onshore intrusion of warm oceanic waters (southern section) and an offshore advection of cold coastal waters (northern section), with the latter forming a cold, high chlorophyll-a filament. In situ phytoplankton and diatom biomasses were highest at the surface in FRN-1 and at the subsurface in ITE-1, whereas values in the coastal zone were lower and dominated by smaller cells. Diatom species typical of the coastal zone and species dominant in oceanic waters were both found in the FRN-1 and ITE-1 interaction area, suggesting that this mixture was the result of both offshore and onshore advection. Overall, front-eddy interactions in EBCSs could enhance cross-shelf exchanges of coastal and oceanic plankton, as well as sustain phytoplankton growth in the slope area through localized upward injections of nutrients in the frontal zone, combined with ITE-induced advection and vertical nutrient inputs to the surface layer.
      PubDate: 2017-10-16T08:17:54.155208-05:
      DOI: 10.1002/2017JC013111
       
  • Observations of Tidal Straining Within Two Different Ocean Environments in
           the East China Sea: Stratification and Near-Bottom Turbulence
    • Authors: Wei Yang; Hao Wei, Liang Zhao
      Abstract: Tidal straining describes the straining effect induced by the vertical shear of oscillatory tidal currents that act on horizontal density gradients. It tends to create tidal periodic stratification and modulate the turbulence in the bottom boundary layer (BBL). Here, we present observations of current, hydrology and turbulence obtained at two mooring stations that are characterized by two typical hydrological environments in the East China Sea (ECS). One is located adjacent to the Changjiang River's mouth, and the other is located over a sloping shelf which is far from the freshwater sources. Tidal straining induces a semidiurnal switching between stable and unstable stratification at both stations. Near-bottom high-frequency velocity measurements further reveal that the dissipation rate of turbulent kinetic energy (TKE) is highly elevated during periods when unstable stratification occurs. A comparison between the TKE dissipation rate (ε) and the shear production (P) further reveals that the near-bottom mixing is locally shear-induced most of the time except during the unstable stratification period. Within this period, the magnitude of dissipation exceeds the expected value based on the law of the wall by an order of magnitude. The buoyancy flux that calculated by the balance method is too small to compensate for the existing discrepancy between the dissipation and shear production. Another plausible candidate is the advection of TKE, which may play an important role in the TKE budget during the unstable stratification period.
      PubDate: 2017-10-16T08:15:50.192526-05:
      DOI: 10.1002/2017JC012924
       
  • Calibrating a Viscoelastic Sea Ice Model for Wave Propagation in the
           Arctic Fall Marginal Ice Zone
    • Authors: Sukun Cheng; W. Erick Rogers, Jim Thomson, Madison Smith, Martin Doble, Peter Wadhams, Alison L. Kohout, Björn Lund, Ola Persson, Clarence O. Collins, Stephen F. Ackley, Fabien Montiel, Hayley H. Shen
      Abstract: This paper presents a wave-in-ice model calibration study. Data used were collected in the thin ice of the advancing autumn marginal ice zone of the western Arctic Ocean in 2015, where pancake ice was found to be prevalent. Multiple buoys were deployed in seven wave experiments; data from four of these experiments are used in the present study. Wave attenuation coefficients are calculated utilizing wave energy decay between two buoys measuring simultaneously within the ice covered region. Wavelength is measured in one of these experiments. Forcing parameters are obtained from simultaneous in-situ and remote sensing observations, as well as forecast/hindcast models. Cases from three wave experiments are used to calibrate a viscoelastic model for wave attenuation/dispersion in ice cover. The calibration is done by minimizing the difference between modeled and measured complex wavenumber, using a multi-objective genetic algorithm. The calibrated results are validated using two methods. One is to directly apply the calibrated viscoelastic parameters to one of the wave experiments not used in the calibration and then compare the attenuation from the model with measured data. The other is to use the calibrated viscoelastic model in WAVEWATCH III® over the entire western Beaufort Sea and then compare the wave spectra at two remote sites not used in the calibration. Both validations show reasonable agreement between the model and the measured data. The completed viscoelastic model is believed to be applicable to the fall marginal ice zone dominated by pancake ice.
      PubDate: 2017-10-16T08:15:30.414719-05:
      DOI: 10.1002/2017JC013275
       
  • Persistent Shoreline Shape Induced From Offshore Geologic Framework:
           Effects of Shoreface Connected Ridges
    • Authors: Ilgar Safak; Jeffrey H. List, John C. Warner, William C. Schwab
      Abstract: Mechanisms relating offshore geologic framework to shoreline evolution are determined through geologic investigations, oceanographic deployments and numerical modeling. Analysis of shoreline positions from the past 50 years along Fire Island, New York, a 50 km long barrier island, demonstrates a persistent undulating shape along the western half of the island. The shelf offshore of these persistent undulations is characterized with shoreface-connected sand ridges (SFCR) of a similar alongshore length scale, leading to a hypothesis that the ridges control the shoreline shape through the modification of flow. To evaluate this, a hydrodynamic model was configured to start with the US East Coast and scale down to resolve the Fire Island nearshore. The model was validated using observations along western Fire Island and buoy data, and used to compute waves, currents and sediment fluxes. To isolate the influence of the SFCR on the generation of the persistent shoreline shape, simulations were performed with a linearized nearshore bathymetry to remove alongshore transport gradients associated with shoreline shape. The model accurately predicts the scale and variation of the alongshore transport that would generate the persistent shoreline undulations. In one location, however, the ridge crest connects to the nearshore and leads to an offshore-directed transport that produces a difference in the shoreline shape. This qualitatively supports the hypothesized effect of cross-shore fluxes on coastal evolution. Alongshore flows in the nearshore during a representative storm are driven by wave breaking, vortex force, advection and pressure gradient, all of which are affected by the SFCR.
      PubDate: 2017-10-15T10:41:57.752473-05:
      DOI: 10.1002/2017JC012808
       
  • The Effect of the Leeuwin Current on Offshore Surface Gravity Waves in
           Southwest Western Australia
    • Authors: Moritz Wandres; E.M.S. Wijeratne, Simone Cosoli, Charitha Pattiaratchi
      Abstract: The knowledge of regional wave regimes is critical for coastal zone planning, protection, and management. In this study, the influence of the offshore current regime on surface gravity waves on the southwest Western Australian (SWWA) continental shelf was examined. This was achieved by coupling the three dimensional, free surface, terrain-following hydrodynamic Regional Ocean Modelling System (ROMS) and the third generation wave model Simulating WAves Nearshore (SWAN) using the Coupled Ocean-Atmosphere-WaveSediment Transport (COAWST) model. Different representative states of the Leeuwin Current (LC), a strong pole-ward flowing boundary current with a persistent eddy field along the SWWA shelf edge were simulated and used to investigate their influence on different large wave events. The coupled wave-current simulations were compared to wave only simulations, which represented scenarios in the absence of a background current field. Results showed that the LC and the eddy field significantly impact SWWA waves. Significant wave heights increased (decreased) when currents were opposing (aligning with) the incoming wave directions. During a fully developed LC system significant wave heights were altered by up to ±25% and wave directions by up to ±20°. The change in wave direction indicates that the LC may modify nearshore wave dynamics and consequently alter sediment patterns. Operational regional wave forecasts and hindcasts may give flawed predictions if wave-current interaction is not properly accounted for.
      PubDate: 2017-10-15T10:41:38.51958-05:0
      DOI: 10.1002/2017JC013006
       
  • Characterization of the Deep-Water Surface Wave Variability in the
           California Current Region
    • Authors: Ana B. Villas Bôas; Sarah T. Gille, Matthew R. Mazloff, Bruce D. Cornuelle
      Abstract: Surface waves are crucial for the dynamics of the upper ocean not only because they mediate exchanges of momentum, heat, energy, and gases between the ocean and the atmosphere, but also because they determine the sea state. The surface wave field in a given region is set by the combination of local and remote forcing. The present work characterizes the seasonal variability of the deep–water surface wave field in the California Current region, as retrieved from over two decades of satellite altimetry data combined with wave buoys and wave model hindcast (WaveWatch III). In particular, the extent to which the local wind modulates the variability of the significant wave height, peak period, and peak direction is assessed. During spring/summer, regional–scale wind events of up to 10 m/s are the dominant forcing for waves off the California coast, leading to relatively short period waves (8-10 s) that come predominantly from the north–northwest. The wave climatology throughout the California Current region shows average significant wave heights exceeding 2 m during most of the year, which may have implications for the planning and retrieval methods of the Surface Water and Ocean Topography (SWOT) satellite mission.
      PubDate: 2017-10-15T10:41:05.616475-05:
      DOI: 10.1002/2017JC013280
       
  • The Global Mode-1 S2 Internal Tide
    • Authors: Zhongxiang Zhao
      Abstract: The global mode-1 S2 internal tide is observed using sea surface height (SSH) measurements from four satellite altimeters: TOPEX/Poseidon, Jason-1, Jason-2, and Geosat Follow-On. Plane wave analysis is employed to extract three mode-1 S2 internal tidal waves in any given 250 km by 250 km window, which are temporally coherent over a 20-year period from 1992–2012. Depth-integrated energy and flux of the S2 internal tide are calculated from the SSH amplitude and a conversion function built from climatological hydrographic profiles in the World Ocean Atlas 2013. The results show that the S2 and M2 internal tides have similar spatial patterns. Both S2 and M2 internal tides originate at major topographic features and propagate over long distances. The S2 internal tidal beams are generally shorter, likely because the relatively weaker S2 internal tide is easily overwhelmed by nontidal noise. The northbound S2 and M2 internal tides from the Hawaiian Ridge are observed to travel over 3500 km across the Northeast Pacific. The globally integrated energy of the mode-1 S2 internal tide is 7.8 PJ (1 PJ = 1015 J), about 20% that of M2 (36.4 PJ). The histogram of S2 to M2 SSH ratios peaks at 0.4, consistent with the square root of their energy ratio. In terms of SSH, S2 is greater than M2 in ≈ 10% of the global ocean and ≥50% of M2 in about half of the global ocean.
      PubDate: 2017-10-15T10:40:38.478001-05:
      DOI: 10.1002/2017JC013112
       
  • Oxygen in the Southern Ocean From Argo Floats: Determination of Processes
           Driving Air-Sea Fluxes
    • Authors: Seth M. Bushinsky; Alison R. Gray, Kenneth S. Johnson, Jorge L. Sarmiento
      Abstract: The Southern Ocean is of outsized significance to the global oxygen and carbon cycles with relatively poor measurement coverage due to harsh winters and seasonal ice cover. In this study, we use recent advances in the parameterization of air-sea oxygen fluxes to analyze nine years of oxygen data from a recalibrated Argo oxygen dataset and from air-calibrated oxygen floats deployed as part of the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project. From this combined dataset of 150 floats, we find a total Southern Ocean oxygen sink of -183 ± 80 Tmol yr−1 (positive to the atmosphere), greater than prior estimates. The uptake occurs primarily in the Polar-Frontal Antarctic Zone (PAZ, -94 ± 30 Tmol O2 yr−1) and Seasonal Ice Zone (SIZ, -111 ± 9.3 Tmol O2 yr−1). This flux is driven by wintertime ventilation, with a large portion of the flux in the SIZ passing through regions with fractional sea ice. The Subtropical Zone (STZ) is seasonally driven by thermal fluxes and exhibits a net outgassing of 47 ± 29 Tmol O2 yr−1 that is likely driven by biological production. The Subantarctic Zone (SAZ) uptake is -25 ± 12 Tmol O2 yr−1. Total oxygen fluxes were separated into a thermal and non-thermal component. The non-thermal flux is correlated with net primary production and mixed layer depth in the STZ, SAZ, and PAZ, but not in the SIZ where seasonal sea ice slows the air-sea gas flux response to the entrainment of deep, low oxygen waters.
      PubDate: 2017-10-15T10:40:25.628-05:00
      DOI: 10.1002/2017JC012923
       
  • An Assessment of State-of-the-Art Mean Sea Surface and Geoid Models of the
           Arctic Ocean: Implications for Sea Ice Freeboard Retrieval
    • Authors: Henriette Skourup; Sinéad Louise Farrell, Stefan Hendricks, Robert Ricker, Thomas W. K. Armitage, Andy Ridout, Ole Baltazar Andersen, Christian Haas, Steven Baker
      Abstract: State-of-the-art Arctic Ocean mean sea surface (MSS) models and global geoid models (GGMs) are used to support sea ice freeboard estimation from satellite altimeters, as well as in oceanographic studies such as mapping sea level anomalies and mean dynamic ocean topography. However, errors in a given model in the high frequency domain, primarily due to unresolved gravity features, can result in errors in the estimated along-track freeboard. These errors are exacerbated in areas with a sparse lead distribution in consolidated ice pack conditions. Additionally model errors can impact ocean geostrophic currents, derived from satellite altimeter data, while remaining biases in these models may impact longer-term, multi-sensor oceanographic time-series of sea level change in the Arctic. This study focuses on an assessment of five state-of-the-art Arctic MSS models (UCL13/04, DTU15/13/10) and a commonly used GGM (EGM2008). We describe errors due to unresolved gravity features, inter-satellite biases, and remaining satellite orbit errors, and their impact on the derivation of sea ice freeboard. The latest MSS models, incorporating CryoSat-2 sea surface height measurements, show improved definition of gravity features, such as the Gakkel Ridge. The standard deviation between models ranges 0.03-0.25 m. The impact of remaining MSS/GGM errors on freeboard retrieval can reach several decimeters in parts of the Arctic. While the maximum observed freeboard difference found in the central Arctic was 0.59 m (UCL13 MSS minus EGM2008 GGM), the standard deviation in freeboard differences is 0.03-0.06 m.
      PubDate: 2017-10-13T09:47:38.711864-05:
      DOI: 10.1002/2017JC013176
       
  • Surface Wave Dynamics in Delaware Bay and Its Adjacent Coastal Shelf
    • Authors: Tobias Kukulka; Robert L. Jenkins, James T. Kirby, Fengyan Shi, Robert W. Scarborough
      Abstract: This study presents a broad overview of surface gravity wave dynamics in Delaware Bay and the adjacent continental shelf by employing the wave model Simulating Waves Nearshore one-way coupled to the ocean model Regional Ocean Modeling System for a period from 2006-2012. The distributions of simulated wave statistics agree well with observations obtained from three wave buoys located on the shelf, in the bay near the open ocean, and about 35 km up the bay. A partitioning analysis to separate the two-dimensional wave height spectrum into wind-forced and swell parts reveals that waves on the shelf are predominantly remotely generated swell. Bathymetric refraction shelters the bay from energetic open ocean waves, which is supported by an idealized ray tracing analysis. Waves near the bay entrance are also refracted by oblique tidal currents, whose refraction characteristics critically depend on the detailed spatial distributions of the currents. Opposing tidal currents, flowing against the wave propagation direction, focus wave energy outside the bay entrance and in the deeper bay channels, where currents are relatively strong. A spectral partitioning analysis for waves in the bay indicates that less energetic wave fields are likely not directly forced by the wind. More energetic waves, on the other hand, are dominantly driven by winds and the wave response in the bay depends on the fetch-setting wind direction. Our results for wind-driven waves in the bay are consistent with previous fetch-limited observations, but we find a systematic bias between wind and wave directions due to bathymetric refraction.
      PubDate: 2017-10-13T09:47:20.862878-05:
      DOI: 10.1002/2017JC013370
       
  • Estimating Particulate Inorganic Carbon Concentrations of the Global Ocean
           From Ocean Color Measurements Using A Reflectance Difference Approach
    • Authors: C. Mitchell; C. Hu, B. Bowler, D. Drapeau, W. M. Balch
      Abstract: A new algorithm for estimating particulate inorganic carbon (PIC) concentrations from ocean color measurements is presented. PIC plays an important role in the global carbon cycle through the oceanic carbonate pump, therefore accurate estimations of PIC concentrations from satellite remote sensing are crucial for observing changes on a global scale. An extensive global dataset was created from field and satellite observations for investigating the relationship between PIC concentrations and differences in the remote sensing reflectance (Rrs) at green, red and near-infrared (NIR) wavebands. Three color indices were defined: two as the relative height of Rrs(667) above a baseline running between Rrs(547) and an Rrs in the the NIR (either 748 nm or 869 nm), and one as the difference between Rrs(547) and Rrs(667). All three color indices were found to explain over 90% of the variance in field-measured PIC. But, due to the lack of availability of Rrs(NIR) in the standard ocean color data products, most of the further analysis presented here was done using the color index determined from only two bands. The new two-band color index algorithm was found to retrieve PIC concentrations more accurately than the current standard algorithm used in generating global PIC data products. Application of the new algorithm to satellite imagery showed patterns on the global scale as revealed from field measurements. The new algorithm was more resistant to atmospheric correction errors and residual errors in sun glint corrections, as seen by a reduction in the speckling and patchiness in the satellite-derived PIC images.
      PubDate: 2017-10-13T09:45:49.03661-05:0
      DOI: 10.1002/2017JC013146
       
  • Characterization of Particle Backscattering of Global Highly Turbid Waters
           From VIIRS Ocean Color Observations
    • Authors: Wei Shi; Menghua Wang
      Abstract: Normalized water-leaving radiance spectra nLw(λ) at the near-infrared (NIR) from five years of observations (2012–2016) with the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) are used to derive the particle backscattering coefficients bbp(λ) for global highly turbid coastal and inland waters. Based on the fact that the absorption coefficient of sea water aw(λ) is generally much larger than those of the other constituents aiop(λ) at the NIR wavelengths in coastal and inland waters, a NIR-based bbp(λ) algorithm for turbid coastal and inland waters has been developed and used in this study. This algorithm can be safely used for highly turbid waters with nLw(745) and nLw(862) less than ∼6 and ∼4 mW cm−2 μm−1 sr−1, respectively. Seasonal and inter-annual variations of bbp(λ) in China's east coastal region, the Amazon River Estuary, the La Plata River Estuary, the Meghna River Estuary, the Atchafalaya River Estuary, and Lake Taihu are characterized and quantified. The coefficient bbp(λ) can reach over ∼3–4 m−1 in the Amazon River Estuary and China's east coastal region. The Amazon River Estuary is identified as the most turbid region in the global ocean in terms of bbp(λ) magnitude. bbp(λ) spectra in these five highly turbid regions are also seasonal- and regional-dependent. In the highly turbid waters of China's east coastal region and the Amazon River Estuary, bbp(λ) generally increases in wavelength from 410 to 862 nm, while it decreases in the La Plata River Estuary and Atchafalaya River Estuary. This is attributed to the different particle size distributions in these waters. The geophysical implication of the bbp(λ) spectral curvatures for different waters is discussed. To improve global bbp(λ) for both open oceans and coastal turbid waters, a new combined NIR- and Quasi-Analytical Algorithm (QAA)-based bbp(λ) algorithm is proposed and demonstrated.
      PubDate: 2017-10-13T09:45:40.783144-05:
      DOI: 10.1002/2017JC013191
       
  • Ra Tracer-Based Study of Submarine Groundwater Discharge and Associated
           Nutrient Fluxes into the Bohai Sea, China -A highly human-affected
           marginal sea
    • Authors: Jianan Liu; Jinzhou Du, Lixin Yi
      Abstract: Nutrient concentrations in coastal bays and estuaries are strongly influenced by not only riverine input but also submarine groundwater discharge (SGD). Here, we estimate the SGD and the fluxes of the associated dissolved inorganic nitrogen (DIN), phosphorus (DIP) and silicon (DSi) into the Bohai Sea based on a 226Ra and 228Ra mass balance model. This procedure shows that in the Bohai Sea the average radium activities (dpm 100 L−1) are 42.8 ± 6.3 (226Ra) and 212 ± 41.7 (228Ra) for the surface water and 43.0 ± 6.1 (226Ra) and 216 ± 38.4 (228Ra) for the near-bottom water. According to the 228Ra/226Ra age model, the residence time in the Bohai Sea is calculated to be 1.7 ± 0.8 yrs. The mass balance of 226Ra and 228Ra suggests that the yearly SGD flux into the whole Bohai Sea is (2.0 ± 1.3) × 1011 m3 yr−1, of which the percentage of submarine fresh groundwater discharge (SFGD) to the total SGD is approximately (5.1 ± 4.1) %. However, the DIN and DSi fluxes from SFGD constitute 29% and 10%, respectively, of the total fluxes from the SGD. Moreover, nutrient loads, which exhibit high DIN/DIP from SGD, especially the SFGD, may substantially contribute to the nutrient supplies, resulting in the occurrence of red tide in the Bohai Sea.
      PubDate: 2017-10-10T12:26:02.300982-05:
      DOI: 10.1002/2017JC013095
       
  • Impacts of Atmospheric Nitrogen Deposition on Surface Waters of the
           Western North Atlantic Mitigated by Multiple Feedbacks
    • Authors: P. St-Laurent; M.A.M. Friedrichs, R.G. Najjar, D.K. Martins, M. Herrmann, S.K. Miller, J. Wilkin
      Abstract: The impacts of Atmospheric Nitrogen Deposition (AND) on the chlorophyll and nitrogen dynamics of surface waters in the western North Atlantic (25–45°N, 65–80°W) are examined with a biogeochemical ocean model forced with a regional atmospheric chemistry model (Community Multi-scale Air Quality model, CMAQ). CMAQ simulations with year-specific emissions reveal the existence of a ‘hot-spot’ of AND over the Gulf Stream. The impact of the hot-spot on the oceanic biogeochemistry is mitigated in three ways by physical and biogeochemical processes. First, AND significantly contributes to surface oceanic nitrogen concentrations only during the summer period, when the stratification is maximal and the background nitrogen inventories are minimal. Second, the increase in summer surface nitrate concentrations is accompanied by a reduction in upward nitrate diffusion at the base of the surface layer. This negative feedback partly cancels the nitrogen enrichment from AND. Third, gains in biomass near the surface force a shoaling of the euphotic layer and a reduction of about 5% in deep primary production and biomass on the continental shelf. Despite these mitigating processes, the impacts of AND remain substantial. AND increases surface nitrate concentrations in the Gulf Stream region by 14% during the summer (2% on average over the year). New primary production increases by 22% in this region during summer (8% on average). Although these changes may be difficult to distinguish from natural variability in observations, the results support the view that AND significantly enhances local carbon export.
      PubDate: 2017-10-10T12:25:56.149325-05:
      DOI: 10.1002/2017JC013072
       
  • Surface Current Patterns in the Northeastern Chukchi Sea and Their
           Response to Wind Forcing
    • Authors: Ying-Chih Fang; Rachel A. Potter, Hank Statscewich, Thomas J. Weingartner, Peter Winsor, Brita K. Irving
      Abstract: We measured northeastern Chukchi Sea surface currents using high-frequency radar systems (HFR) during the ice-free periods of August to October from 2010–2014. We analyzed these data, along with regional winds, using Self-Organizing Maps (SOM) to develop a set of surface current-wind patterns. Temporal changes in the SOM patterns consist predominantly of two patterns comprising northeastward and southwestward surface currents. A third pattern represents a transitional stage established during the onset of strong northeasterly winds. These patterns are analogous to the first two eigenmodes of an empirical orthogonal function analysis of the HFR data. The first principal component (PC1) is significantly correlated (∼0.8) to that of the winds and is directly related to the time series of SOM-derived patterns. The sign of PC1 changes when the speed of local northeasterly winds exceeds ∼6 m s−1, at which point the northeastward surface currents reverse to the southwest. This finding agrees with previous models and observations that suggest this wind threshold is needed to overcome the pressure gradient between the Pacific and Arctic Oceans. The transitional stage is characterized by alongshore currents bifurcating in the vicinity of Icy Cape and wind-driven Ekman currents north of 71.5°N. Its development is a manifestation of interactions amongst the poleward pressure gradient, wind stress, and geostrophic flow due to the coastal setdown.
      PubDate: 2017-10-10T12:25:51.532747-05:
      DOI: 10.1002/2017JC013121
       
  • Nonhydrostatic Simulations of Tide-Induced Mixing in the Halmahera Sea: A
           Possible Role in the Transformation of the Indonesian Throughflow Waters
    • Authors: Taira Nagai; Toshiyuki Hibiya, Pascale Bouruet-Aubertot
      Abstract: The Indonesian Throughflow (ITF) waters are significantly transformed within the Indonesian Archipelago and consequently influence the large-scale ocean circulation such as Agulhas and Leeuwin Currents. Existing ocean general circulation models (OGCMs) are, however, incapable of reproducing the transformation of the ITF waters, since tidal forcing is neglected in such models. In the present study, we first conduct high-resolution non-hydrostatic three-dimensional numerical experiments focusing on the transformation of the ITF waters in the Halmahera Sea which is thought to be the most important bottleneck in simulating the ITF water-mass properties. It is shown that intensive vertical mixing induced by breaking of internal tides in the shallow regions in the Halmahera Sea dilutes the ITF waters, significantly reducing model biases found in the existing OGCMs. We next evaluate quantitatively the effect of tide-induced vertical mixing on the transformation of the ITF waters. It is shown that tide-induced vertical mixing dominates the transformation of the ITF waters, although some supplementary processes such as horizontal mixing associated with the sub-mesoscale eddies resulting from tidal interaction with land configurations cannot be ignored.
      PubDate: 2017-10-10T12:25:37.132792-05:
      DOI: 10.1002/2017JC013381
       
  • Towards Understanding the Diverse Impacts of Air-Sea Interactions on MJO
           Simulations
    • Authors: Joshua-Xiouhua Fu; Wanqiu Wang, Toshiaki Shinoda, Hong-Li Ren, Xiaolong Jia
      Abstract: The role of air-sea interactions on MJO simulations has long been recognized. However, the reasons for the variation of the impacts of air-sea coupling among different models are still elusive. In this study, we used NCEP GFS under different cumulus schemes and SST conditions to explore this issue. We focused on the Oct- and Nov-MJOs during the DYNAMO IOP. We show that the effects of SST-feedback on MJO simulations not only vary between these two MJO events, but are also very sensitive to the specifics of cumulus schemes and intra-seasonal SST forcing. The Oct-MJO basically reinvigorates over Indian Ocean in association with the arrival of global circumnavigating mode. The Nov-MJO is largely reinvigorated by a robust intra-seasonal SST anomaly over Indian Ocean. We found that SST-feedback is crucial for the existence of the Nov-MJO, but has little effect on the Oct-MJO. This finding raises the possibility that the occurrence of some MJO events may be rooted in air-sea interactions. These results suggest that the diverse impacts of air-sea coupling on MJO simulations can be attributed to at least the following three potential causes: (i), diverse nature of ocean responses to individual MJO events in nature; (ii), diverse behaviors of various cumulus parameterizations; and (iii), diverse intra-seasonal SST anomalies in coupled models. Either a too weak internal MJO mode in atmospheric models or a too weak intra-seasonal SST anomaly in coupled models would lead to the underestimation of the impacts of air-sea coupling on MJO simulations.
      PubDate: 2017-10-10T12:25:27.687704-05:
      DOI: 10.1002/2017JC013187
       
  • Rollover of Apparent Wave Attenuation in Ice Covered Seas
    • Authors: Jingkai Li; Alison L. Kohout, Martin J. Doble, Peter Wadhams, Changlong Guan, Hayley H. Shen
      Abstract: Wave attenuation from two field experiments in the ice-covered Southern Ocean is examined. Instead of monotonically increasing with shorter waves, the measured apparent attenuation rate peaks at an intermediate wave period. This ‘rollover' phenomenon has been postulated as the result of wind input and nonlinear energy transfer between wave frequencies. Using WAVEWATCH III®, we first validate the model results with available buoy data, then use the model data to analyze the apparent wave attenuation. With the choice of source parameterizations used in this study, it is shown that rollover of the apparent attenuation exists when wind input and nonlinear transfer are present, independent of the different wave attenuation models used. The period of rollover increases with increasing distance between buoys. Furthermore, the apparent attenuation for shorter waves drops with increasing separation between buoys or increasing wind input. These phenomena are direct consequences of the wind input and nonlinear energy transfer, which offset the damping caused by the intervening ice.
      PubDate: 2017-10-10T12:25:21.802714-05:
      DOI: 10.1002/2017JC012978
       
  • Mixed Layer Temperature Budget for the Northward Propagating Summer
           Monsoon Intraseasonal Oscillation (MISO) in the Central Bay of Bengal
    • Authors: M. S. Girishkumar; J. Joseph, V. P. Thangaprakash, P. Vijay, M. J. McPhaden
      Abstract: Composite analyses of mixed layer temperature (MLT) budget terms from near surface meteorological and oceanic observations in the central Bay of Bengal are utilized to evaluate the modulation of air-sea interactions and MLT processes in response to the summer monsoon intraseasonal oscillation (MISO). For this purpose, we use moored buoy data at 15°N, 12°N and 8°N along 90°E together with TropFlux meteorological parameters and the Ocean Surface Current Analyses Real-time (OSCAR) current product. Our analysis shows a strong cooling tendency in MLT with maximum amplitude in the central and northern BoB during the northward propagation of enhanced convective activity associated with the active phase of the MISO; conversely, warming occurs during the suppressed phase of the MISO. The surface mixed layer is generally heated during convectively inactive phases of the MISO primarily due to increased net surface heat flux into the ocean. During convectively active MISO phases, the surface mixed layer is cooled by the combined influence of net surface heat loss to the atmosphere and entrainment cooling at the base of mixed layer. The variability of net surface heat flux is primarily due to modulation of latent heat flux and shortwave radiation. Shortwave is controlled primarily by an enhancement or reduction of cloudiness during the active and inactive MISO phases and latent heat flux is controlled primarily by variations in air-sea humidity difference.
      PubDate: 2017-10-06T09:47:40.445012-05:
      DOI: 10.1002/2017JC013073
       
  • Global Tidal Impacts of Large-Scale Ice-Sheet Collapses
    • Authors: Sophie-Berenice Wilmes; J. A. Mattias Green, Natalya Gomez, Tom P. Rippeth, Harriet Lau
      Abstract: Recent studies show that the glaciers draining both the West Antarctic and the Greenland ice sheets are experiencing an accelerated ice loss, highlighting the possibility of large-scale ice-sheet retreat and sea-level rise in the coming centuries and millennia. These sea-level changes would vary spatially, and could significantly alter global tides as the latter are highly dependent on bathymetry (or water column thickness under ice shelves) and basin shape. This paper investigates how the principal semi-diurnal (M2) tidal amplitudes and energy dissipation respond to the non-uniform sea-level changes induced by complete ice-sheet collapses. The sea-level changes are calculated using gravitationally self-consistent sea-level theory, and the tides are simulated using an established tidal model. Results from the simulations show global and spatially heterogeneous changes in tidal amplitudes. In addition, pronounced changes in tidal energy dissipation occur in both the open ocean and in shelf seas, also altering the location of tidal mixing fronts. These changes have the potential to impact ocean mixing, and hence large-scale currents and climate patterns, and the contribution of shelf-sea to the global carbon cycle. The new results highlight the importance of considering changes in the tides in predictions of future climate and reconstructions of past climate phases such as the Last Interglacial.
      PubDate: 2017-10-06T09:47:17.784608-05:
      DOI: 10.1002/2017JC013109
       
  • On the Variability of the East Australian Current: Jet Structure,
           Meandering, and Influence on Shelf Circulation
    • Authors: Matthew Archer; Moninya Roughan, Shane Keating, Amandine Schaeffer
      Abstract: Given the importance of western boundary currents over a wide range of scales in the ocean, it is crucial that we understand their dynamics to accurately predict future changes. For this, we need detailed knowledge of their structure and variability. Here we investigate the jet structure of the East Australian Current (EAC), using observations from HF radars and moorings deployed at 30-31°S. Meandering, core velocity, width, and eddy kinetic energy (EKE) are quantified from 4 years of hourly 1.5 km resolution surface current maps (2012-2016), to obtain the most detailed representation of the surface EAC jet to date. The EAC flows predominantly over the 1000 m isobath 50 km offshore, but makes large amplitude displacements eastward every 65-100 days – the timescale associated with mesoscale eddy-shedding at the EAC separation. Smaller-amplitude, higher-frequency meanders occur every 20-45 days. Using a coordinate frame that follows the jet, we show core velocity and EKE exhibit seasonality in both magnitude and variance, being maximum in summer (1.55 m s−1 mean core velocity), minimum in winter (0.8 m s−1). However, it is the eddy-shedding timescale that dominates jet variability. As the EAC moves shoreward, shelf temperature and along-stream velocity vary linearly with jet movement, within ∼35 km of the core. The EAC is within this range 75% of the time, demonstrating its importance to the shelf circulation. Temperature and velocity fluctuations at the 70 m (100 m) isobath are more influenced by wind (EAC encroachment), with the strongest response occurring when wind and EAC act constructively.
      PubDate: 2017-10-06T09:47:01.512747-05:
      DOI: 10.1002/2017JC013097
       
  • On the ‘cal mode’ Correction to TOPEX Satellite Altimetry and its
           Effect on the Global Mean Sea-Level Time Series
    • Authors: B. D. Beckley; P. S. Callahan, D. W. Hancock, G. T. Mitchum, R. D. Ray
      Abstract: Comparison of satellite altimetry against a high-quality network of tide gauges suggests that sea-surface heights from the TOPEX altimeter may be biased by ±5 mm, in an approximate piecewise linear, or U-shaped, drift. This has been previously reported in at least two other studies. The bias is probably caused by use of an internal calibration-mode range correction, included in the TOPEX 'net instrument' correction, which is suspect owing to changes in the altimeter's point target response. Removal of this correction appears to mitigate most of the drift problem. In addition, a new time series based on retracking the TOPEX waveforms, again without the calibration-mode correction, also reduces the drift aside for a clear problem during the first two years. With revision, the TOPEX measurements, combined with successor Jason altimeter measurements, show global mean sea level rising fairly steadily throughout most of 24-year time period, with rates around 3mm/y, although higher over the last few years.
      PubDate: 2017-10-06T09:46:44.567761-05:
      DOI: 10.1002/2017JC013090
       
  • Impacts of the Tropical Pacific Cold Tongue Mode on ENSO Diversity Under
           Global Warming
    • Authors: Yang Li; Jianping Li, Wenjun Zhang, Quanliang Chen, Juan Feng, Fei Zheng, Wei Wang, Xin Zhou
      Abstract: The causes of ENSO diversity, although being of great interest in recent research, do not have a consistent explanation. This study provides a possible mechanism focused on the background change of the tropical Pacific as a response to global warming. The second empirical orthogonal function mode of the sea surface temperature anomalies (SSTA) in the tropical Pacific, namely the cold tongue mode (CTM), represents the background change of the tropical Pacific under global warming. Using composite analysis with surface observations and subsurface ocean assimilation datasets, we find ENSO diversity in its spatial structure appears closely associated with the CTM. A positive CTM tends to cool the SST in the eastern equatorial Pacific and warm the SST outside, as well as widen (narrow) zonal and meridional scales for El Niño (La Niña), and vice versa. Particularly in the positive CTM phase, the air-sea action center of El Niño moves west, resembling the spatial pattern of CP-El Niño. This westward shift of center is resulted from the weakened Bjerknes feedback (BF) intensity by the CTM. By suppressing the SSTA growth of El Niño in the eastern equatorial Pacific, the CTM is responsible for more frequent occurrence of CP-El Niño under global warming.
      PubDate: 2017-10-06T09:46:41.217909-05:
      DOI: 10.1002/2017JC013052
       
  • Characterization of Convective Plumes Associated With Oceanic Deep
           Convection in the Northwestern Mediterranean From High Resolution In-Situ
           Data Collected by Gliders
    • Authors: Félix Margirier; Anthony Bosse, Pierre Testor, Blandine L'Hévéder, Laurent Mortier, David Smeed
      Abstract: Numerous gliders have been deployed in the Gulf of Lions (Northwestern Mediterranean Sea) and in particular during episodes of open-ocean deep convection in the winter 2012–2013. The data collected represents an unprecedented density of in-situ observations providing a first in-situ statistical and 3D characterization of the important mixing agents of the deep convection phenomenon, the so-called plumes. A methodology based on a glider-static flight model was applied to infer the oceanic vertical velocity signal from the glider navigation data. We demonstrate that, during the active phase of mixing, the gliders underwent significant oceanic vertical velocities up to 18 cm.s−1.Focusing on the data collected by two gliders during the 2012–2013 winter, 120 small scale convective downward plumes were detected with a mean radius of 350∼m and separated by about 2∼km. We estimate that the plumes cover 27% of the convection area. Gliders detected downward velocities with a magnitude larger than that of the upward ones (-6 cm.s−1 versus +2 cm.s−1 on average). Along track recordings of temperature and salinity as well as biogeochemical properties (dissolved oxygen, fluorescence, turbidity) allow a statistical characterization of the water masses' properties in the plumes' core with respect to the 'background': the average downward signal is of colder (-1.8 × 10−3°C), slightly saltier (+4.9 × 10−4 psu) and thus denser waters (+7.5 × 10−4 kg.m−3). The plunging waters are also on average more fluorescent (+2.3 × 10−2 μg.L−1). The plumes are associated with a vertical diffusion coefficient of 7.0 m2.s−1 and their vertical velocity variance scales with the ratio of the buoyancy loss over the Coriolis parameter to the power 0.86.
      PubDate: 2017-10-06T09:46:38.786084-05:
      DOI: 10.1002/2016JC012633
       
  • Turbulence and Mixing in a Shallow Shelf Sea From Underwater Gliders
    • Authors: Larissa K. P. Schultze; Lucas M. Merckelbach, Jeffrey R. Carpenter
      Abstract: The seasonal thermocline in shallow shelf seas acts as a natural barrier for boundary-generated turbulence, damping scalar transport to the upper regions of the water column, and controlling primary production to a certain extent. To better understand turbulence and mixing conditions within the thermocline, two unique 12- and 17-day datasets with continuous measurements of the dissipation rate of turbulent kinetic energy (ε) collected by autonomous underwater gliders under stratified to well-mixed conditions are presented. A highly intermittent ε signal was observed in the stratified thermocline region, which was mainly characterized by quiescent flow (turbulent activity index below 7). The rate of diapycnal mixing remained relatively constant for the majority of the time with peaks of higher fluxes that were responsible for much of the increase in bottom mixed layer temperature. The water column stayed predominantly strongly stratified, with a bulk Richardson number across the thermocline well above 2. A positive relationship between the intensity of turbulence, shear and stratification was found. The trend between turbulence levels and the bulk Richardson number was relatively weak, but suggests that ε increases as the bulk Richardson number approaches 1. The results also highlight the interpretation difficulties in both quantifying turbulent thermocline fluxes, as well as the responsible mechanisms.
      PubDate: 2017-10-06T09:46:26.651964-05:
      DOI: 10.1002/2017JC012872
       
  • Physical Mechanisms Routing Nutrients in the Central Red Sea
    • Authors: Nikolaos D. Zarokanellos; Benjamin Kürten, James H. Churchill, Cornelia Roder, Christian R. Voolstra, Yasser Abualnaja, Burton H. Jones
      Abstract: Mesoscale eddies and boundary currents play a key role in the upper layer circulation of the Red Sea. This study assesses the physical and biochemical characteristics of an eastern boundary current (EBC) and recurrent eddies in the central Red Sea (CRS) using a combination of in situ and satellite observations. Hydrographic surveys in November 2013 (autumn) and in April 2014 (spring) in the CRS (22.15 − 24.1°N) included a total of 39 and 27 CTD stations, respectively. In addition, high-resolution hydrographic data were acquired in spring 2014 with a towed undulating vehicle (ScanFish). In situ measurements of salinity, temperature, chlorophyll fluorescence, colored dissolved organic matter (CDOM), and dissolved nitrate: phosphorous ratios reveal distinct water mass characteristics for the two periods. An EBC, observed in the upper 150 m of the water column during autumn, transported low-salinity and warm water from the south toward the CRS. Patches of the low-salinity water of southern origin tended to contain relatively high concentrations of chlorophyll and CDOM. The prominent dynamic feature observed in spring was a cyclonic/anticyclonic eddy pair. The cyclonic eddy was responsible for an upward nutrient flux into the euphotic zone. Higher chlorophyll and CDOM concentrations, and concomitant lower nitrate:phosphorous ratios indicate the influence of the EBC in the CRS at the end of the stratified summer period.
      PubDate: 2017-10-06T09:46:13.90477-05:0
      DOI: 10.1002/2017JC013017
       
  • Cold Front Driven Flows Through Multiple Inlets of Lake Pontchartrain
           Estuary
    • Authors: W. Huang C. Li
      Abstract: With in situ observations using acoustic Doppler current profilers (ADCPs) and numerical experiments using the Finite Volume Coastal Ocean Model (FVCOM), this study investigates atmospheric cold front induced exchange of water between Lake Pontchartrain Estuary and coastal ocean through multiple inlets. Results show that the sub-tidal hydrodynamic response is highly correlated with meteorological parameters. Northerly and westerly winds tend to push water out of Lake Pontchartrain, while south and east winds tend to produce currents flowing into it. For most cases, the sub-tidal water level is inversely correlated with the east wind, with the correlation coefficient being ∼ 0.8. The most important finding of this work is that, contrary to intuition, the cold front induced remote wind effect has the greatest contribution to the overall water level variation, while the local wind stress determines the surface slope inside the estuary. It is found that wind driven flow is roughly quasi-steady state: the surface slope in the north-south direction is determined by the north-south wind stress, explaining ∼ 83% of the variability but less so in the east-west direction (∼ 43%). In other words, the north-south local wind stress determines the water level gradient in that direction in the estuary while the overall water level change is pretty much controlled by the open boundary which is the "remote wind effect", a regional response that can be illustrated only by a numerical model for a much larger area encompassing the estuary.
      PubDate: 2017-10-06T09:45:49.894934-05:
      DOI: 10.1002/2017JC012977
       
  • A Meteoric Water Budget for the Arctic Ocean
    • Authors: Matthew B. Alkire; James Morison, Axel Schweiger, Jinlun Zhang, Michael Steele, Cecilia Peralta-Ferriz, Suzanne Dickinson
      Abstract: A budget of meteoric water (MW = river runoff, net precipitation minus evaporation, and glacial meltwater) over four regions of the Arctic Ocean is constructed using a simple box model, regional precipitation-evaporation estimates from reanalysis data sets, and estimates of import and export fluxes derived from the literature with a focus on the 2003-2008 period. The budget indicates an approximate/slightly positive balance between MW imports and exports (i.e., no change in storage); thus, the observed total freshwater increase observed during this time period likely resulted primarily from changes in non-MW freshwater components (i.e., increases in sea ice melt or Pacific water and/or a decrease in ice export). Further, our analysis indicates that the MW increase observed in the Canada Basin resulted from a spatial redistribution of MW over the Arctic Ocean. Mean residence times for MW were estimated for the Western Arctic (5-7 years), Eastern Arctic (3-4 years), and Lincoln Sea (1-2 years). The MW content over the Siberian shelves was estimated (∼14,000 km3) based on a residence time of 3.5 years. The MW content over the entire Arctic Ocean was estimated to be ≥ 44,000 km3. The MW export through Fram Strait consisted mostly of water from the Eastern Arctic (3237 ± 1370 km3 yr−1) whereas the export through the Canadian Archipelago was nearly equally derived from both the Western Arctic (1182 ± 534 km3 yr−1) and Lincoln Sea (972 ± 391 km3 yr−1).
      PubDate: 2017-10-06T09:45:45.510474-05:
      DOI: 10.1002/2017JC012807
       
  • A Bidirectional Subsurface Remote-Sensing Reflectance Model Explicitly
           Accounting for Particle Backscattering Shapes
    • Authors: Shuangyan He; Xiaodong Zhang, Yuanheng Xiong, Deric Gray
      Abstract: The subsurface remote sensing reflectance (rrs, sr−1), particularly its bidirectional reflectance distribution function (BRDF), depends fundamentally on the angular shape of the volume scattering functions (VSFs, m−1 sr−1). Recent technological advancement has greatly expanded the collection, and the knowledge of natural variability, of the VSFs of oceanic particles. This allows us to test the Zaneveld's theoretical rrs model that explicitly accounts for particle VSF shapes. We parameterized the rrs model based on HydroLight simulations using 114 VSFs measured in three coastal waters around the US and in oceanic waters of North Atlantic Ocean. With the absorption coefficient (a), backscattering coefficient (bb) and VSF shape as inputs, the parameterized model is able to predict rrs with a root mean square relative error of ∼ 4% for solar zenith angles from 0° to 75°, viewing zenith angles from 0° to 60°, and viewing azimuth angles from 0° to 180°. A test with the field data indicates the performance of our model, when using only a and bb as inputs and selecting the VSF shape using bb, is comparable to or slightly better than the currently used models by Morel et al. and Lee et al. Explicitly expressing VSF shapes in rrs modeling has great potential to further constrain the uncertainty in the ocean color studies as our knowledge on the VSFs of natural particles continues to improve. Our study represents a first effort in this direction.
      PubDate: 2017-10-06T09:45:21.045617-05:
      DOI: 10.1002/2017JC013313
       
  • Depth Dependence of Nearshore Currents and Eddies
    • Authors: Stephen M. Henderson; Joshua Arnold, H.T. Özkan-Haller, Stephen A. Solovitz
      Abstract: The three-dimensional (across-shore, alongshore, and vertical) structure of hourly-mean currents and 
      PubDate: 2017-09-30T16:50:43.068151-05:
      DOI: 10.1002/2016JC012349
       
  • Tidal Variability Related to Sea Level Variability in the Pacific Ocean
    • Authors: Adam T. Devlin; David A. Jay, Edward D. Zaron, Stefan A. Talke, Jiayi Pan, Hui Lin
      Abstract: Ocean tides are changing worldwide for reasons unrelated to astronomical forcing. Changes in tidal properties coupled with altered mean sea level (MSL) may yield higher peak water levels and increased occurrence of short-term exceedance events such as storm surge and nuisance flooding. Here we investigate the hypothesis that changes in relative sea-level are correlated with alterations in tidal amplitudes. Our approach focuses on the correlation between short-term (monthly to interannual) fluctuations in sea-level with changes in tidal properties of major ocean tides (M2, and K1; S2 and O1) at 152 gauges. Results suggest that sea-level variability is correlated to inter-annual tidal variability at most (92%) of tide gauges in the Pacific, with statistically significant rates between ±10 and ±500 mm per meter sea-level rise observed. These tidal anomalies, while influenced by basin-scale climate processes and sea-level changes, appear to be locally forced (in part) and not coherent over amphidromic or basin-wide scales. Overall, the Western Pacific shows a greater concentration of tide/sea level correlations at interannual time scales than the Eastern Pacific; 44% and 46% of gauges are significant in K1 and O1 in the west compared to 29% and 30% in the east, and 63% and 53% of gauges in the west are significant in M2 and S2 versus 47% and 32% in the east. Seasonal variation in tidal properties is less apparent in the empirical record, with statistically significant seasonal variations observed at only 35% of all gauges, with the largest concentrations in Southeast Asia.
      PubDate: 2017-09-30T16:50:32.608608-05:
      DOI: 10.1002/2017JC013165
       
  • Shelf Circulation Induced by an Orographic Wind Jet
    • Authors: Laura Ràfols; Manel Grifoll, Gabriel Jordà, Manuel Espino, Abdel Sairouní, Manel Bravo
      Abstract: The dynamical response to cross-shelf wind-jet episodes is investigated. The study area is located at the northern margin of the Ebro Shelf, in the Northwestern (NW) Mediterranean Sea, where episodes of strong northwesterly wind occur. In this case, the wind is channeled through the Ebro Valley and intensifies upon reaching the sea, resulting in a wind jet. The wind jet response in terms of water circulation and vertical density structure is investigated using a numerical model. The numerical outputs agree with water current observations from a High Frequency radar. Additionally, temperature, sea-level and wind measurements are also used for the skill assessment of the model. For the wind jet episodes, the numerical results show a well-defined two-layer circulation in the cross-shelf direction, with the surface currents in the direction of the wind. This pattern is consistent with sea-level set-down due to the wind effect. The comparison of the vertical structure response for different episodes revealed that the increase of stratification leads to an onshore displacement of the transition from inner shelf to mid-shelf. In general, the cross-shelf momentum balance during a wind-jet episode exhibits a balance between the frictional terms and the pressure gradient in shallow waters, shifting to a balance between the Coriolis force and the wind stress terms in deeper waters.
      PubDate: 2017-09-30T16:50:25.039539-05:
      DOI: 10.1002/2017JC012773
       
  • Interannual Variations of Surface Currents and Transports in the Sicily
           Channel Derived From Coastal Altimetry
    • Authors: Fatma Jebri; Bruno Zakardjian, Florence Birol, Jérôme Bouffard, Loïc Jullion, Cherif Sammari
      Abstract: A twenty-year coastal altimetry data set (X-TRACK) is used, for the first time, to gain insight into the long-term inter-annual variations of the surface circulation in the Sicily Channel. Firstly, a spectral along with a time/space diagram analysis are applied to the monthly means. They reveal a regionally coherent current patterns from track to track with a marked inter-annual variability that is unequally shared between the Atlantic Tunisian Current and Atlantic Ionian Stream inflows in the Sicily Channel and the Bifurcation Tyrrhenian Current outflow northeast of Sicily. Secondly, an empirical altimetry-based transport-like technique is proposed to quantify volume budgets inside the closed boxes formed by the crossing of the altimetry tracks and coastlines over the study area. A set of hydrographic measurements is used to validate the method. The inferred altimetry transports give a well-balanced mean eastward Atlantic Waters baroclinic flow of 0.4 Sv and standard deviations of 0.2 Sv on a yearly basis throughout the Sicily Channel and toward the Ionian Sea, which is fairly coherent with those found in the literature. Furthermore, the analysis allows to quantify the intrusions of Atlantic Waters over the Tunisian Shelf (0.12 +/- 0.1 Sv) and highlights two main modes of variability of the main surface waters path over the Sicily Channel through the Bifurcation Atlantic Tunisian Current and Atlantic Ionian Stream systems. Some physical mechanisms are finally discussed with regards to changes in the observed currents and transports.
      PubDate: 2017-09-28T14:35:30.202437-05:
      DOI: 10.1002/2017JC012836
       
  • Quantifying How Observations Inform a Numerical Reanalysis of Hawaii
    • Authors: B. S. Powell
      Abstract: When assimilating observations into a model via state-estimation, it is possible to quantify how each observation changes the modeled estimate of a chosen oceanic metric. Using an existing two-year reanalysis of Hawaii that includes more than 31 million observations from satellites, ships, SeaGliders, and autonomous floats, I assess which observations most improve the estimates of the transport and eddy kinetic energy. When the SeaGliders were in the water, they comprised less than 2.5% of the data, but accounted for 23% of the transport adjustment. Because the model physics constrains advanced state-estimation, the prescribed covariances are propagated in time to identify observation-model covariance. I find that observations that constrain the isopycnal tilt across the transport section provide the greatest impact in the analysis. In the case of eddy kinetic energy, observations that constrain the surface-driven upper ocean have more impact. This information can help to identify optimal sampling strategies to improve both state-estimates and forecasts.
      PubDate: 2017-09-27T14:26:28.185552-05:
      DOI: 10.1002/2017JC012854
       
  • Bottom Water Acidification and Warming on the Western Eurasian Arctic
           Shelves: Dynamical Downscaling Projections
    • Authors: P. J. Wallhead; R. G. J. Bellerby, A. Silyakova, D. Slagstad, A. A. Polukhin
      Abstract: The impacts of oceanic CO2 uptake and global warming on the surface ocean environment have received substantial attention, but few studies have focused on shelf bottom water, despite its importance as habitat for benthic organisms and demersal fisheries such as cod. We used a downscaling ocean biogeochemical model to project bottom water acidification and warming on the western Eurasian Arctic shelves. A model hindcast produced 14‒18 year acidification trends that were largely consistent with observational estimates at stations in the Iceland and Irminger seas. Projections under SRES A1B scenario revealed a rapid and spatially-variable decline in bottom pH by 0.10‒0.20 units over 50 years (2.5–97.5% quantiles) at depths 50–500 m on the Norwegian, Barents, Kara, and East Greenland shelves. Bottom water undersaturation with respect to aragonite occurred over the entire Kara shelf by 2040 and over most of the Barents and East Greenland shelves by 2070. Shelf acidification was predominantly driven by the accumulation of anthropogenic CO2, and was concurrent with warming of 0.1–2.7°C over 50 years. These combined perturbations will act as significant multistressors on the Barents and Kara shelves. Future studies should aim to improve the resolution of shelf bottom processes in models, and should consider the Kara Sea and Russian shelves as possible bellwethers of shelf acidification.
      PubDate: 2017-09-27T14:25:42.18878-05:0
      DOI: 10.1002/2017JC013231
       
  • Katabatic Wind-Driven Exchange in Fjords
    • Authors: Michael A. Spall; Rebecca H. Jackson, Fiammetta Straneo
      Abstract: The general issue of katabatic wind-driven exchange in fjords is considered using an idealized numerical model, theory, and observations. Two regimes are identified. For fjords narrower than a viscous boundary layer width, the exchange is limited by a balance between wind and friction in lateral boundary layers. For the nonlinear viscous parameterization used here, this boundary layer thickness depends on the properties of the fjord, such as stratification and length, as well as on the wind stress and numerical parameters such as grid spacing and an empirical constant. For wider fjords typical of east Greenland, the balance is primarily between wind, the along-fjord pressure gradient, and acceleration, in general agreement with previous two-layer nonrotating theories. It is expected that O(10%) of the surface layer will be flushed out of the fjord by a single wind event. Application of the idealized model to a typical katabatic wind event produces outflowing velocities that are in general agreement with observations in Sermilik Fjord. The presence of a sill has only a minor influence on the exchange until the sill penetrates over most of the lower layer thickness, in which cases the exchange is reduced. It is concluded that the multiple katabatic wind events per winter that are experienced by the fjords along east Greenland represent an important mechanism of exchange between the fjord and shelf, with implications for the renewal of warm, salty waters at depth and for the export of glacial freshwater in the upper layer.
      PubDate: 2017-09-27T14:25:25.891425-05:
      DOI: 10.1002/2017JC013026
       
  • Plankton Assemblage Estimated With BGC-Argo Floats in the Southern Ocean:
           Implications for Seasonal Successions and Particle Export
    • Authors: Mathieu Rembauville; Nathan Briggs, Mathieu Ardyna, Julia Uitz, Philippe Catala, Christophe Penkerc'ch, Antoine Poteau, Hervé Claustre, Stéphane Blain
      Abstract: The Southern Ocean (SO) hosts plankton communities that impact the biogeochemical cycles of the global ocean. However, weather conditions in the SO restrict mainly in situ observations of plankton communities to spring and summer, preventing the description of biological successions at an annual scale. Here, we use shipboard observations collected in the Indian sector of the SO to develop a multivariate relationship between physical and bio-optical data, and, the composition and carbon content of the plankton community. Then we apply this multivariate relationship to five biogeochemical Argo (BGC-Argo) floats deployed within the same bio-geographical zone as the ship-board observations to describe spatial and seasonal changes in plankton assemblage. The floats reveal a high contribution of bacteria below the mixed layer, an overall low abundance of picoplankton and a seasonal succession from nano- to microplankton during the spring bloom. Both naturally iron-fertilized waters downstream of the Crozet and Kerguelen Plateaus show elevated phytoplankton biomass in spring and summer but they differ by a nano- or microplankton dominance at Crozet and Kerguelen, respectively. The estimated plankton group successions appear consistent with independent estimations of particle diameter based on the optical signals. Furthermore, the comparison of the plankton community composition in the surface layer with the presence of large mesopelagic particles diagnosed by spikes of optical signals provides insight into the nature and temporal changes of ecological vectors that drive particle export. This study emphasizes the power of BGC-Argo floats for investigating important biogeochemical processes at high temporal and spatial resolution.
      PubDate: 2017-09-27T14:25:22.609943-05:
      DOI: 10.1002/2017JC013067
       
  • Interactions of Estuarine Shoreline Infrastructure With Multiscale
           Sea-Level Variability
    • Authors: Ruo-Qian Wang; Liv M. Herdman, Li Erikson, Patrick Barnard, Michelle Hummel, Mark T. Stacey
      Abstract: Sea-level rise increases the risk of storms and other short term water-rise events, because it sets a higher water level such that coastal surges become more easily to overtop and cause floods. To protect coastal communities, it is necessary to understand the interaction among multi-day and tidal sea-level variabilities, coastal infrastructure, and sea-level rise. We performed a series of numerical simulations for San Francisco Bay to examine two shoreline scenarios and a series of short and long-term sea-level variations. The two shoreline configurations include the existing topography and a coherent full-bay containment that follows the existing land boundary with an impermeable wall. The sea-level variability consists of a half-meter perturbation, with duration ranging from 2 days to permanent (i.e. sea-level rise). The extent of coastal flooding was found to increase with the duration of the High Water Level event. The nonlinear interaction between these intermediate scale events and astronomical tidal forcing only contributes ∼1% of the tidal heights; at the same time, the tides are found to be a dominant factor in establishing the evolution and diffusion of multi-day high water events. Establishing containment at existing shorelines can change the tidal height spectrum up to 5%, and the impact of this shoreline structure appears stronger in the low-frequency range. To interpret the spatial and temporal variability at a wide range of frequencies, Optimal Dynamic Mode Decomposition is introduced to analyze the coastal processes and an inverse method is applied to determine the coefficients of a 1-D diffusion wave model that quantify the impact of bottom roughness, tidal basin geometry, and shoreline configuration on the high water events.
      PubDate: 2017-09-26T12:51:43.861315-05:
      DOI: 10.1002/2017JC012730
       
  • Acoustic Tomography in the Canary Basin: Meddies and Tides
    • Authors: Brian D. Dushaw; Fabienne Gaillard, Thierry Terre
      Abstract: An acoustic propagation experiment over 308-km range conducted in the Canary Basin in 1997–1998 was used to assess the ability of ocean acoustic tomography to measure the flux of Mediterranean water and Meddies. Instruments on a mooring adjacent to the acoustic path measured the southwestward passage of a strong Meddy in temperature, salinity, and current. Over nine months of transmissions, the acoustic arrival pattern was an initial broad stochastic pulse varying in duration by 250 to 500 ms, followed eight stable, identified ray arrivals. Small-scale sound speed fluctuations from Mediterranean water parcels littered around the sound channel axis caused acoustic scattering. Internal waves contributed more modest acoustic scattering. Based on simulations, the main effect of a Meddy passing across the acoustic path is the formation of many early-arriving, near-axis rays, but these rays are thoroughly scattered by the small-scale Mediterranean water fluctuations. A Meddy decreases the deep-turning ray travel times by 10–30 ms. The dominant acoustic signature of a Meddy is therefore the expansion of the width of the initial stochastic pulse. While this signature appears inseparable from the other effects of Mediterranean water in this region, the acoustic time series indicates the steady passage of Mediterranean water across the acoustic path. Tidal variations caused by the mode-1 internal tides were measured by the acoustic travel times. The observed internal tides were partly predicted using a recent global model for such tides derived from satellite altimetry.
      PubDate: 2017-09-26T12:51:37.146453-05:
      DOI: 10.1002/2017JC013356
       
  • Eddy-Resolving Simulation of the Atlantic Water Circulation in the Fram
           Strait With Focus on the Seasonal Cycle
    • Authors: Claudia Wekerle; Qiang Wang, Wilken-Jon von Appen, Sergey Danilov, Vibe Schourup-Kristensen, Thomas Jung
      Abstract: Eddy driven recirculation of Atlantic Water (AW) in the Fram Strait modifies the amount of heat that reaches the Arctic Ocean, but is difficult to constrain in ocean models due to very small Rossby radius there. In this study we explore the effect of resolved eddies on the AW circulation in a locally eddy-resolving simulation of the global Finite-Element-Sea ice-Ocean-Model (FESOM) integrated for the years 2000–2009, by focusing on the seasonal cycle. An eddy-permitting simulation serves as a control run. Our results suggest that resolving local eddy dynamics is critical to realistically simulate ocean dynamics in the Fram Strait. Strong eddy activity simulated by the eddy-resolving model, with peak in winter and lower values in summer, is comparable in magnitude and seasonal cycle to observations from a long-term mooring array, whereas the eddy-permitting simulation underestimates the observed magnitude. Furthermore, a strong cold bias in the central Fram Strait present in the eddy-permitting simulation is reduced due to resolved eddy dynamics, and AW transport into the Arctic Ocean is increased with possible implications for the Arctic Ocean heat budget. Given the good agreement between the eddy-resolving model and measurements, it can help filling gaps that point-wise observations inevitably leave. For example, the path of the West Spitsbergen Current offshore branch, measured in the winter months by the mooring array, is shown to continue cyclonically around the Molloy Deep in the model, representing the major AW recirculation branch in this season.
      PubDate: 2017-09-26T12:51:13.347043-05:
      DOI: 10.1002/2017JC012974
       
  • The Importance of Freshwater to Spatial Variability of Aragonite
           Saturation State in the Gulf of Alaska
    • Authors: Samantha A. Siedlecki; Darren J. Pilcher, Albert J. Hermann, Ken Coyle, Jeremy Mathis
      Abstract: High latitude and subpolar regions like the Gulf of Alaska (GOA) are more vulnerable than equatorial regions to rising carbon dioxide (CO2) levels, in part due to local processes that amplify the global signal. Recent field observations have shown that the shelf of the GOA is currently experiencing seasonal corrosive events (carbonate mineral saturation states Ω, Ω
      PubDate: 2017-09-26T12:50:28.694705-05:
      DOI: 10.1002/2017JC012791
       
  • Remote Sensing Estimation of Phytoplankton Size Classes From Goci
           Satellite Measurements In Bohai Sea and Yellow Sea
    • Authors: Deyong Sun; Yu Huan, Zhongfeng Qiu, Chuanmin Hu, Shengqiang Wang, Yijun He
      Abstract: Phytoplankton size class (PSC), a measure of different phytoplankton functional and structural groups, is a key parameter to the understanding of many marine ecological and biogeochemical processes. In turbid waters where optical properties may be influenced by terrigenous discharge and non-phytoplankton water constituents, remote estimation of PSC is still a challenging task. Here, based on measurements of phytoplankton diagnostic pigments, total chlorophyll-a, and spectral reflectance in turbid waters of Bohai Sea and Yellow Sea during summer 2015, a customized model is developed and validated to estimate PSC in the two semi-enclosed seas. Five diagnostic pigments determined through high-performance liquid chromatography (HPLC) measurements are first used to produce weighting factors to model phytoplankton biomass (using total chlorophyll-a as a surrogate) with relatively high accuracies. Then, a common method used to calculate contributions of micro-, nano-, and picophytoplankton to the phytoplankton assemblage (i.e., Fm, Fn, and Fp) is customized using local HPLC and other data. Exponential functions are tuned to model the size-specific chlorophyll-a concentrations (Cm, Cn, and Cp for micro-, nano-, and picophytoplankton, respectively) with remote-sensing reflectance (Rrs) and total chlorophyll-a as the model inputs. Such a PSC model shows two improvements over previous models: 1) a practical strategy (i.e., model Cp and Cn first, and then derive Cm as C-Cp-Cn) with an optimized spectral band (680 nm) for Rrs as the model input; 2) local parameterization, including a local chlorophyll-a algorithm. The performance of the PSC model is validated using in situ data that were not used in the model development. Application of the PSC model to GOCI (Geostationary Ocean Color Imager) data leads to spatial and temporal distribution patterns of phytoplankton size classes (PSCs) that are consistent with results reported from field measurements by other researchers. While the applicability of the PSC model together with its parameterization to other optically complex regions and to other seasons is unknown, the findings of this study suggest that the approach to develop such a model may be extendable to other cases as long as local data are used to select the optimal band and to determine the model coefficients.
      PubDate: 2017-09-26T12:50:21.112213-05:
      DOI: 10.1002/2017JC013099
       
  • Global Ocean Vertical Velocity From a Dynamically Consistent Ocean State
           Estimate
    • Authors: Xinfeng Liang; Michael Spall, Carl Wunsch
      Abstract: Estimates of the global ocean vertical velocities (Eulerian, eddy-induced and residual) from a dynamically consistent and data-constrained ocean state estimate are presented and analyzed. Conventional patterns of vertical velocity, Ekman pumping, appear in the upper ocean, with topographic dominance at depth. Intense and vertically coherent upwelling and downwelling occur in the Southern Ocean, which are likely due to the interaction of the Antarctic Circumpolar Current and large-scale topographic features and are generally canceled out in the conventional zonally averaged results. These “elevators” at high latitudes connect the upper to the deep and abyssal oceans and working together with isopycnal mixing are likely a mechanism, in addition to the formation of deep and abyssal waters, for fast responses of the deep and abyssal oceans to the changing climate. Also, Eulerian and parameterized eddy-induced components are of opposite signs in numerous regions around the global ocean, particularly in the ocean interior away from surface and bottom. Nevertheless, residual vertical velocity is primarily determined by the Eulerian component, and related to winds and large-scale topographic features. The current estimates of vertical velocities can serve as a useful reference for investigating the vertical exchange of ocean properties and tracers, and its complex spatial structure ultimately permits regional tests of basic oceanographic concepts such as Sverdrup balance and coastal upwelling/downwelling.
      PubDate: 2017-09-21T14:15:39.140845-05:
      DOI: 10.1002/2017JC012985
       
  • Wind Speed and Sea State Dependencies of Air-Sea Gas Transfer: Results
           From the High Wind Speed Gas Exchange Study (HiWinGS)
    • Authors: B. W. Blomquist; S. E. Brumer, C. W. Fairall, B. J. Huebert, C. J. Zappa, I. M. Brooks, M. Yang, L. Bariteau, J. Prytherch, J. E. Hare, H. Czerski, A. Matei, R. W. Pascal
      Abstract: A variety of physical mechanisms are jointly responsible for facilitating air-sea gas transfer through turbulent processes at the atmosphere-ocean interface. The nature and relative importance of these mechanisms evolves with increasing wind speed. Theoretical and modeling approaches are advancing, but the limited quantity of observational data at high wind speeds hinders the assessment of these efforts. The HiWinGS project successfully measured gas transfer coefficients (k660) with coincident wave statistics under conditions with hourly mean wind speeds up to 24 m s−1 and significant wave heights to 8 m. Measurements of k660 for carbon dioxide (CO2) and dimethylsulfide (DMS) show an increasing trend with respect to 10-meter neutral wind speed (U10N), following a power-law relationship of the form: k660 co2~U10N1.68 and k660 dms~U10N1.33. Among seven high wind speed events, CO2 transfer responded to the intensity of wave breaking, which depended on both wind speed and sea state in a complex manner, with k660 co2 increasing as the wind sea approaches full development. A similar response is not observed for DMS. These results confirm the importance of breaking waves and bubble injection mechanisms in facilitating CO2 transfer. A modified version of the Coupled Ocean-Atmosphere Response Experiment Gas transfer algorithm (COAREG ver. 3.5), incorporating a sea state-dependent calculation of bubble-mediated transfer, successfully reproduces the mean trend in observed k660 with wind speed for both gases. Significant suppression of gas transfer by large waves was not observed during HiWinGS, in contrast to results from two prior field programs.
      PubDate: 2017-09-21T14:15:33.045912-05:
      DOI: 10.1002/2017JC013181
       
  • Wind-Driven Response of the Upper Ocean Along the U.S. West Coast to
           Tropical MJO Convection
    • Authors: Bradford S. Barrett; Alexander R. Davies, Jacob I. Rose
      Abstract: In this study, time-lagged composites of OSCAR upper ocean currents from February to May of 1993-2016 were binned by active phase of the leading atmospheric mode of intraseasonal variability, the Madden-Julian Oscillation (MJO). Seven days after the convectively active phase of the MJO is present in the tropical Indian Ocean, anomalously strong south-southeastward upper-ocean currents are seen along nearly the entire U.S. west coast. Seven days after the convectively active phase is present in the tropical western Pacific Ocean, upper-ocean current anomalies reverse along the U.S. west coast, with weaker southward flow. A physical pathway to the ocean was found for both of these phases: (a) tropical MJO convection modulates upper-tropospheric heights and circulation over the Pacific Ocean; (b) those anomalous atmospheric heights adjust the strength and position of the Aleutian Low and Hawaiian High; (c) surface winds change in response to the adjusted atmospheric pressure patterns; and (d) those surface winds project onto upper-ocean currents.
      PubDate: 2017-09-21T14:15:24.402277-05:
      DOI: 10.1002/2017JC013086
       
  • Occurrence and Turnover of Biogenic Sulfur in the Bering Sea During Summer
    • Authors: Cheng-Xuan Li; Bao-Dong Wang, Gui-Peng Yang, Zi-Cheng Wang, Jian-Fang Chen, Yang Lyu
      Abstract: The horizontal/geographical variations in dissolved dimethylsulfide (DMS), its precursor dimethylsulfoniopropionate (DMSPd and DMSPp), and chlorophyll a (Chl a), as well as the oceanographic parameters influencing the concentrations of dimethylated sulfur compounds, were investigated in the Bering Sea from July to August 2012. Similar to Chl a, the surface DMS and DMSPp levels, as well as DMS(P) production and consumption rates, exhibited a declining gradient from the central basin to the continental shelf, with high-value areas appearing in the central basin, the slope regions and Anadyr Strait but a low-value area occurring on the outer-middle continental shelf. Considerably high values of DMS and DMSP were measured in the saline Bering Sea Basin Deep Water (>2000 m) located at the southwest of the Bering Basin because of the release of resuspension in 2000 m depth and the DMSP production from endogenous benthic bacteria and cyanobacteria population. Chl a was positively correlated with DMSPp and DMS in the surface waters and the upper water of the basin, whereas significant negative correlations were found between DMS and nutrients (dissolved inorganic nitrogen (DIN), phosphorus, and silicate) in the inner shelf of the Bering Sea. DMS microbial consumption was approximately 6.26 times faster than the DMS sea-air exchange, demonstrating that the major loss of DMS in the surface water occurred through biological consumption relative to evasion into the atmosphere. Average sea-to-air DMS fluxes were estimated to be 4.66 μmol/(m2·d), and consequently oceanic biogenic DMS emission had a dominant contribution to the sulfur budget over the observational area.
      PubDate: 2017-09-21T09:55:31.026391-05:
      DOI: 10.1002/2017JC013299
       
  • Improving Estimation of Submarine Groundwater Discharge Using Radium and
           Radon Tracers: Application in Jiaozhou Bay, China
    • Authors: Yan Zhang; Hailong Li, Kai Xiao, Xuejing Wang, Xiaoting Lu, Meng Zhang, An An, Wenjing Qu, Li Wan, Chunmiao Zheng, Xunsheng Wang, Xiaowei Jiang
      Abstract: Radium and radon mass balance models have been widely used to quantify submarine groundwater discharge (SGD) in the coastal areas. However, the losses of radium or radon in seawater caused by re-circulated saline groundwater discharge (RSGD) are ignored in most of the previous studies for tracer-based models and this can lead to an underestimation of SGD. Here, we present an improved method which considers the losses of tracers caused by RSGD to enhance accuracy in estimating SGD and SGD-associated material loadings. Theoretical analysis indicates that neglecting the losses of tracers induced by RSGD would underestimate the SGD by a percentage approximately equaling the tracer activity ratio of nearshore seawater to groundwater. The data analysis of previous typical case studies shows that the existing old models underestimated the SGD by 1.9 ∼ 93%, with an average of 32.2%. The method is applied in Jiaozhou Bay (JZB), North China, which is experiencing significant environmental pollution. The SGD flux into JZB estimated by the improved method is ∼1.44 and 1.34 times of that estimated by the old method for 226Ra mass balance model and 228Ra mass balance model, respectively. Both SGD and RSGD fluxes are significantly higher than the discharge rate of Dagu River (the largest one running into JZB). The fluxes of nutrients and metals through SGD are comparable to or even higher than those from local rivers, which indicates that SGD is an important source of chemicals into JZB and has important impact on marine ecological system.
      PubDate: 2017-09-21T09:55:21.036761-05:
      DOI: 10.1002/2017JC013237
       
  • Out of the woods: Driftwood insights into Holocene pan-Arctic sea ice
           dynamics
    • Authors: Georgia M. Hole; Marc Macias-Fauria
      Abstract: The collation of 913 driftwood samples from across the western Arctic, with spatiotemporal distribution and available provenance data, enabled the production of a high-resolution proxy-based reconstruction of Holocene Arctic Ocean surface current and sea ice dynamics. Regionally bounded, driftwood-based sea ice reconstructions studies suggest spatiotemporally complex past Arctic sea ice extent and movement; however, a large-scale compilation of Holocene Arctic driftwood has not previously been developed. Sparse driftwood in the early Holocene (≥8.2 cal ka B.P.) deglacial period was followed by increased driftwood deposition in the warmer mid-Holocene (8.2–4.2 cal ka B.P.); characterized by an enhanced Transpolar Drift (TPD) ∼7 cal ka B.P., leading to sea ice loss through the Fram Strait. Driftwood incursion peaks show spatial E-W progression from the Eurasian Archipelagos to Greenland and the Canadian Arctic Archipelago, suggesting a progressive shift in the orientation of the TPD on centennial-millennial time scales and intermediate phases in the Arctic Oscillation. Late Holocene cooling (≤4.2 cal ka B.P.) is indicated by increased influx of probably North American Picea via a strengthened Beaufort Gyre (BG) which enhanced sea ice recirculation, starting in the western Arctic and progressing eastward. In recent millennia (
      PubDate: 2017-09-20T09:00:03.825457-05:
      DOI: 10.1002/2017JC013126
       
  • Probability Distribution of Turbulent Kinetic Energy Dissipation Rate in
           Ocean: Observations and Approximations
    • Authors: I. Lozovatsky; H.J.S. Fernando, J. Planella-Morato, Z. Liu, J.-H. Lee, S.U.P. Jinadasa
      Abstract: The probability distribution of kinetic energy dissipation rate in stratified ocean usually deviates from the classic lognormal distribution that has been formulated for and often observed in unstratified homogeneous layers of atmospheric and oceanic turbulence. Our measurements of vertical profiles of small-scale shear, collected in the East China Sea, northern Bay of Bengal, to the south and east of Sri Lanka, and in the Gulf Stream region show that the probability distributions of the dissipation rate in the pycnoclines (r ∼ 1.4 m is the averaging scale) can be successfully modeled by the Burr (type XII) probability distribution. In weakly stratified boundary layers, lognormal distribution of is preferable, although the Burr is an acceptable alternative. The skewness Skɛ and the kurtosis Kɛ of the dissipation rate appear to be well correlated in a wide range of Skɛ and Kɛ variability.
      PubDate: 2017-09-17T14:53:45.487025-05:
      DOI: 10.1002/2017JC013076
       
  • Seismic Oceanography in the Tyrrhenian Sea – Thermohaline Staircases,
           Eddies and Internal Waves
    • Authors: G.G. Buffett; G. Krahmann, D. Klaeschen, K. Schroeder, V. Sallarès, C. Papenberg, C. Ranero, N. Zitellini
      Abstract: We use seismic oceanography to document and analyze oceanic thermohaline finestructure across the Tyrrhenian Sea. Multichannel seismic (MCS) reflection data were acquired during the MEDiterranean OCcidental survey in April-May 2010. We deployed along-track expendable bathythermograph probes simultaneous with MCS acquisition. At nearby locations we gathered conductivity-temperature-depth data. An autonomous glider survey added in-situ measurements of oceanic properties. The seismic reflectivity clearly delineates thermohaline finestructure in the upper 2,000 m of the water column, indicating the interfaces between Atlantic Water/Winter Intermediate Water, Levantine Intermediate Water, and Tyrrhenian Deep Water. We observe the Northern Tyrrhenian Anticyclone, a near-surface meso-scale eddy, plus laterally and vertically extensive thermohaline staircases. Using MCS we are able to fully image the anticyclone to a depth of 800 m and to confirm the horizontal continuity of the thermohaline staircases of more than 200 km. The staircases show the clearest step-like gradients in the center of the basin while they become more diffuse towards the periphery and bottom, where impedance gradients become too small to be detected by MCS. We quantify the internal wave field and find it to be weak in the region of the eddy and in the center of the staircases, while it is stronger near the coastlines. Our results indicate this is because of the influence of the boundary currents, which disrupt the formation of staircases by preventing diffusive convection. In the interior of the basin the staircases are clearer and the internal wave field weaker, suggesting that other mixing processes such as double-diffusion prevail.
      PubDate: 2017-09-17T14:53:41.85555-05:0
      DOI: 10.1002/2017JC012726
       
  • CO2-Induced Ocean Warming of the Antarctic Continental Shelf in an Eddying
           Global Climate Model
    • Authors: Paul B. Goddard; Carolina O. Dufour, Jianjun Yin, Stephen M. Griffies, Michael Winton
      Abstract: Ocean warming near the Antarctic ice shelves has critical implications for future ice sheet mass loss and global sea level rise. A global climate model with an eddying ocean is used to quantify the mechanisms contributing to ocean warming on the Antarctic continental shelf in an idealized 2xCO2 experiment. The results indicate that relatively large warm anomalies occur both in the upper 100 m and at depths above the shelf floor, which are controlled by different mechanisms. The near-surface ocean warming is primarily a response to enhanced onshore advective heat transport across the shelf break. The deep shelf warming is initiated by onshore intrusions of relatively warm Circumpolar Deep Water (CDW), in density classes that access the shelf, as well as the reduction of the vertical mixing of heat. CO2-induced shelf freshening influences both warming mechanisms. The shelf freshening slows vertical mixing by limiting gravitational instabilities and the upward diffusion of heat associated with CDW, resulting in the build-up of heat at depth. Meanwhile, freshening near the shelf break enhances the lateral density gradient of the Antarctic Slope Front (ASF) and disconnect isopycnals between the shelf and CDW, making cross-ASF heat exchange more difficult. However, at several locations along the ASF, the cross-ASF heat transport is less inhibited and heat can move onshore. Once onshore, lateral and vertical heat advection work to disperse the heat anomalies across the shelf region. Understanding the inhomogeneous Antarctic shelf warming will lead to better projections of future ice sheet mass loss.
      PubDate: 2017-09-17T14:50:46.827575-05:
      DOI: 10.1002/2017JC012849
       
  • Effects of the Relaxation of Upwelling-Favorable Winds on the Diurnal and
           Semidiurnal Water Temperature Fluctuations in the Santa Barbara Channel,
           California
    • Authors: María F. Aristizábal; Melanie R. Fewings, Libe Washburn
      Abstract: In the Santa Barbara Channel, California, and around the Northern Channel Islands, water temperature fluctuations in the diurnal and semidiurnal frequency bands are intermittent, with amplitudes that vary on time scales of days to weeks. The cause of this intermittency is not well understood.We studied the effects of the barotropic tide, vertical stratification, propagation of coastal trapped waves, regional wind relaxations, and diurnal-band winds on the intermittency of the temperature fluctuations during 1992–2015. We used temperature data from 43 moorings in 10-200 m water depth and wind data from two buoys and one land station.Subtidal-frequency changes in vertical stratification explain 20–40% of the intermittency in diurnal and semidiurnal temperature fluctuations at time scales of days to weeks. Along the mainland north of Point Conception and at the Northern Channel Islands, the relaxation of upwelling-favorable winds substantially increases vertical stratification, accounting for up to 55% of the subtidal-frequency variability in stratification. As a result of the enhanced stratification, wind relaxations enhance the diurnal and semidiurnal temperature fluctuations at those sites, even though the diurnal-band wind forcing decreases during wind relaxation. A linear model where the background stratification is advected vertically explains a substantial fraction of the temperature fluctuations at most sites. The increase of vertical stratification and subsequent increase in diurnal and semidiurnal temperature fluctuations during wind relaxation is a mechanism that can supply nutrients to the euphotic zone and kelp forests in the Channel in summer when upwelling is weak.
      PubDate: 2017-09-17T14:50:38.779862-05:
      DOI: 10.1002/2017JC013199
       
  • Impact of the Mesoscale Dynamics on Ocean Deep Convection: The 2012-2013
           Case Study in the Northwestern Mediterranean Sea
    • Authors: Robin Waldman; Marine Herrmann, Samuel Somot, Thomas Arsouze, Rachid Benshila, Anthony Bosse, Jerome Chanut, Herve Giordani, Florence Sevault, Pierre Testor
      Abstract: Winter 2012-2013 was a particularly intense and well-observed Dense Water Formation (DWF) event in the Northwestern Mediterranean Sea. In this study, we investigate the impact of the mesoscale dynamics on DWF. We perform two perturbed initial state simulation ensembles from summer 2012 to 2013, respectively mesoscale-permitting and mesoscale-resolving, with the AGRIF refinement tool in the Mediterranean configuration NEMOMED12.The mean impact of the mesoscale on DWF occurs mainly through the high-resolution physics and not the high-resolution bathymetry. This impact is shown to be modest: the mesoscale doesn't modify the chronology of the deep convective winter nor the volume of dense waters formed. It however impacts the location of the mixed patch by reducing its extent to the west of the North Balearic Front and by increasing it along the Northern Current, in better agreement with observations. The maximum mixed patch volume is significantly reduced from 5.7 ± 0.2 to 4.2 ± 0.6 1013m3. Finally, the spring restratification volume is more realistic and enhanced from 1.4 ± 0.2 to 1.8 ± 0.2 1013m3 by the mesoscale.We also address the mesoscale impact on the ocean intrinsic variability by performing perturbed initial state ensemble simulations. The mesoscale enhances the intrinsic variability of the deep convection geography, with most of the mixed patch area impacted by intrinsic variability. The DWF volume has a low intrinsic variability but it is increased by 2-3 times with the mesoscale. We relate it to a dramatic increase of the Gulf of Lions eddy kinetic energy from 5.0 ± 0.6 to 17.3 ± 1.5cm2/s2, in remarkable agreement with observations.
      PubDate: 2017-09-17T14:50:31.520503-05:
      DOI: 10.1002/2016JC012587
       
  • Fingerprints of Sea-Level Rise on Changing Tides in the Chesapeake and
           Delaware Bays
    • Authors: Andrew C. Ross; Raymond G. Najjar, Ming Li, Serena Blyth Lee, Fan Zhang, Wei Liu
      Abstract: Secular tidal trends are present in many tide gauge records, but their causes are often unclear. This study examines trends in tides over the last century in the Chesapeake and Delaware Bays. Statistical models show negative M2 amplitude trends at the mouths of both bays, while some upstream locations have insignificant or positive trends. To determine whether sea-level rise is responsible for these trends, we include a term for mean sea level in the statistical models and compare the results with predictions from numerical and analytical models. The observed and predicted sensitivities of M2 amplitude and phase to mean sea level are similar, although the numerical model amplitude is less sensitive to sea level. The sensitivity occurs as a result of strengthening and shifting of the amphidromic system in the Chesapeake Bay and decreasing frictional effects and increasing convergence in the Delaware Bay. After accounting for the effect of sea level, significant negative background M2 and S2 amplitude trends are present; these trends may be related to other factors such as dredging, tide gauge errors, or river discharge. Projected changes in tidal amplitudes due to sea-level rise over the twenty-first century are substantial in some areas, but depend significantly on modeling assumptions.
      PubDate: 2017-09-17T14:50:26.116881-05:
      DOI: 10.1002/2017JC012887
       
  • Inconsistent subsurface and deeper ocean warming signals during recent
           global warming and hiatus
    • Authors: Hua Su; Xiangbai Wu, Wenfang Lu, Weiwei Zhang, Xiao-Hai Yan
      Abstract: Ocean heat content (OHC) evolutions calculated from the datasets (WOA, MyOcean, ORAS4, and SODA) was examined at different depth ranges in this study. According to the OHC changes, the subsurface and deeper ocean (SDO, 300-2000 m) heat content rapidly increased over the world's ocean basins during 1998-2013, indicating significant warming in the SDO during the recent global surface warming hiatus. Almost all the ocean basins warmed up, but with various contributions to the global SDO warming tied to the recent hiatus. The role of the Indian Ocean is particularly important as it has accounted for about 30% of global SDO heat uptake during the hiatus. The combined use of multiple datasets can reveal inconsistencies in SDO warming analysis results, and improve our understanding of the role of the SDO in the recent hiatus. The heat uptake in global SDO during the hiatus was about 2.37, 5.44, 3.75, and 2.44*1022 joules with trends of 0.40, 0.70, 0.77, and 0.48 W m−2 according to WOA, MyOcean, ORAS4, and SODA respectively, presenting obviously inconsistent SDO warming signals. MyOcean shows OHC overestimates in different ocean basins, while ORAS4 presents more reliable SDO OHC analysis. In general, the global SDO has sequestered a significant amount of heat – about 3.50*1022 joules with trends of 0.59 W m−2 on average among the four datasets – during the recent hiatus, demonstrating widespread and significant warming signals in the global SDO. There remain substantial uncertainties and discrepancies, however (especially in the PO and SO), in the available SDO warming information due to insufficient subsurface observation coverage and variations in the dataset generation techniques used among different researchers.
      PubDate: 2017-09-17T14:50:21.191054-05:
      DOI: 10.1002/2016JC012481
       
  • The 2004 Sumatra Tsunami in the Southeastern Pacific Ocean: New Global
           Insight From Observations and Modeling
    • Authors: A.B. Rabinovich; V.V. Titov, C.W. Moore, M.C. Eblé
      Abstract: The 2004 Sumatra tsunami was an unprecedented global disaster measured throughout the world oceans. The present study focused on a region of the southeastern Pacific Ocean where the ‘westward' circumferentially propagating tsunami branch converged with the ‘eastward' branch, based on data from fortuitously placed Chilean DART 32401 and tide gauges along the coast of South America. By comparison of the tsunami and background spectra, we suppressed the influence of topography and reconstructed coastal ‘spectral ratios' that were in close agreement with a ratio at DART 32401 and spectral ratios in other oceans. Findings indicate that even remote tsunami records carry spectral source signatures (‘birth-marks'). The 2004 tsunami waves were found to occupy the broad frequency band of 0.25-10 cph with the prominent ratio peak at period of 40 min related to the southern fast-slip source domain. This rupture “hot-spot” of ∼350-km was responsible for the global impact of the 2004 tsunami. Data from DART 32401 provided validation of model results: the simulated maximum tsunami wave height of 2.25 cm was a conservative approximation to the measured height of 2.05 cm; the computed tsunami travel time of 25h 35min to DART 32401, although 20 min earlier than the actual travel time, provided a favorable result in comparison with 24h 25min estimated from classical kinematic theory. The numerical simulations consistently reproduced the wave height changes observed along the coast of South America, including local amplification of tsunami waves at the northern stations of Arica (72 cm) and Callao (67 cm).
      PubDate: 2017-09-14T15:12:04.33762-05:0
      DOI: 10.1002/2017JC013078
       
  • Mapping of a Typhoon-Driven Coastal Upwelling by Assimilating Coastal
           Acoustic Tomography Data
    • Authors: Minmo Chen; Arata Kaneko, Ju Lin, Chuanzheng Zhang
      Abstract: A typhoon-driven upwelling event was observed with coastal acoustic tomography in Hiroshima Bay during September 2013. The tomography data were used to obtain state estimates from an ocean model, employing the ensemble Kalman filter (EnKF) for data assimilation. Hiroshima Bay was represented as a two-layer system with a fresh, near-surface layer overlaying a more saline, lower layer. Wind from the typhoon forced the surface layer southward, thus drawing the lower layer northward and causing upwelling. After the upwelling, these currents reversed for a period. During the upwelling, the total volume transports for the upper and lower layers were well balanced, showing continuity of the two layers. However, the total upper-layer volume transported northward during the reverse-flow period was significantly smaller than the total upper-layer volume transported southward during the upwelling, and significantly larger than the total lower-layer volume transported southward during the reverse-flow period. The downstream reductions of transported volume indicated mixing fractions of 24-30%, with water mixing at the interface of the upper and lower layers. Errors in state estimates were less than the changes in current and salinity associated with the upwelling.
      PubDate: 2017-09-14T15:11:54.653457-05:
      DOI: 10.1002/2017JC012812
       
  • Preparing for the Future Nankai Trough Tsunami: A Data Assimilation and
           Inversion Analysis From Various Observational Systems
    • Authors: I. E. Mulia; D. Inazu, T. Waseda, A. R. Gusman
      Abstract: The future Nankai Trough tsunami is one of the imminent threats to the Japanese coastal communities that could potentially cause a catastrophic event. As a part of the countermeasure efforts for such an occurrence, this study analyzes the efficacy of combining tsunami data assimilation (DA) and waveform inversion (WI). The DA is used to continuously refine a wave field model whereas the WI is used to estimate the tsunami source. We consider a future scenario of the Nankai Trough tsunami recorded at various observational systems, including ocean bottom pressure (OBP) gauges, global positioning system (GPS) buoys, and ship height positioning data. Since most of the OBP gauges are located inside the source region, the recorded tsunami signals exhibit significant offsets from surface measurements due to coseismic seafloor deformation effects. Such biased data are not applicable to the standard DA, but can be taken into account in the WI. On the other hand, the use of WI for the ship data may not be practical because a considerably large precomputed tsunami database is needed to cope with the spontaneous ship locations. The DA is more suitable for such an observational system as it can be executed sequentially in time and does not require precomputed scenarios. Therefore, the combined approach of DA and WI allows us to concurrently make use of all observational resources. Additionally, we introduce a bias correction scheme for the OBP data to improve the accuracy, and an adaptive thinning of observations to determine the efficient number of observations.
      PubDate: 2017-09-14T15:11:51.485222-05:
      DOI: 10.1002/2017JC012695
       
  • Diurnal Critical Latitude and the Latitude Dependence of Internal Tides,
           Internal Waves and Mixing Based on Barcoo Seamount
    • Authors: Robin Robertson; Jihai Dong, Paul Hartlipp
      Abstract: Vertical mixing is a key issue in ocean circulation modeling today. Mixing, particularly tidal mixing, is poorly represented in ocean and climate models, which generally ignore critical latitude effects. Critical latitude is the latitude where the inertial frequency equals the tidal frequency and differs for each tidal constituent. Critical latitudes strongly influence generation and propagation of internal tides. Using a model, latitude effects on tidal interactions with a seamount were examined by varying the latitude from 20°-38°, through the range of the diurnal critical latitudes. The diurnal critical latitudes were found to strongly influence propagation of the diurnal internal tides, the magnitude of the semidiurnal tides, the energy in the harmonic and higher frequencies, the barotropic mean flow, and the diffusivities. The strongest effects occurred between the K1 and O1 critical latitudes. Here, the semidiurnal tides, harmonics and high frequencies were enhanced, barotropic mean velocities weakened, energy at the harmonics and higher frequencies increased, and diffusivities increased. Spectral techniques indicate that most of these impacts are the result of non-linear wave-wave interactions and resonant phenomena with the prominent mechanism harmonic transfers. There was no evidence of parametric subharmonic instabilities. The semidiurnal tides indicated a resonant response at 20oS, which is near the latitude for the combined M2 and K1 tidal period, ∼19oS.
      PubDate: 2017-09-14T15:11:46.920357-05:
      DOI: 10.1002/2016JC012591
       
  • Erosion and Accretion on a Mudflat: The Importance of Very Shallow-Water
           Effects
    • Authors: Benwei Shi; James R. Cooper, Paula D. Pratolongo, Shu Gao, T. J. Bouma, Gaocong Li, Chunyan Li, S.L. Yang, YaPing Wang
      Abstract: Understanding erosion and accretion dynamics during an entire tidal cycle is important for assessing their impacts on the habitats of biological communities and the long-term morphological evolution of intertidal mudflats. However, previous studies often omitted erosion and accretion during very shallow-water stages (VSWS, water depths 0.2 m (i.e., probe submerged) are considered. These findings suggest that the magnitude of bed-level changes during VSWS should not be neglected when modeling morphodynamic processes. Our results are useful in understanding the mechanisms of micro-topography formation and destruction that often occur at VSWS, and also improve our understanding and modeling ability of coastal morphological changes.
      PubDate: 2017-09-14T15:11:14.379536-05:
      DOI: 10.1002/2016JC012316
       
  • Unexpected Covariant Behavior of the Aegean and Ionian Seas in the Period
           1987-2008 by Means of a Nondimensional Sea Surface Height Index
    • Authors: M. Reale; S. Salon, A. Crise, R. Farneti, R. Mosetti, G. Sannino
      Abstract: In this work we use a set of recent multi-year simulations to develop a simplified sea surface height index (SSH). The index characterizes the dynamics of Ionian upper layer circulation and its links with sea surface height and salinity in the Southern Adriatic and Aegean Seas during the period 1987-2008. The analysis highlights a covariant behavior between Ionian Sea and Aegean Sea associated with a mutual zonal exchange of water masses with different salinity characteristics. Our analysis confirms that the variability observed in the period 1987-2008 in the upper layer circulation of the Ionian was driven by the salinity variability in the Southern Adriatic and Aegean Sea. This study supports and reinforces the hypothesis that two observed BiOS-like reversals reflect the existence of multiple equilibrium states in the Mediterranean Thermohaline circulation in the Eastern Mediterranean and that a complete characterization of observed variability needs to take into account a fully coupled Adriatic-Ionian-Aegean System.
      PubDate: 2017-09-14T15:10:54.236009-05:
      DOI: 10.1002/2017JC012983
       
  • Size Distribution and Dispersion of Droplets Generated by Impingement of
           Breaking Waves on Oil Slicks
    • Authors: C. Li; J. Miller, J. Wang, S. S. Koley, J. Katz
      Abstract: This laboratory experimental study investigates the temporal evolution of the size distribution of subsurface oil droplets generated as breaking waves entrain oil slicks. The measurements are performed for varying wave energy, as well as large variations in oil viscosity and oil-water interfacial tension, the latter achieved by premixing the oil with dispersant. In situ measurements using digital inline holography at two magnifications is applied for measuring the droplet sizes, and Particle Image Velocimetry (PIV) for determining the temporal evolution of turbulence after wave breaking. All early (2-10s) size distributions have two distinct size ranges with different slopes. For low dispersant to oil ratios (DOR), the transition between them could be predicted based on a turbulent Weber (We) number in the 2-4 range, suggesting that turbulence plays an important role. For smaller droplets, all the number size distributions have power of about -2.1, and for larger droplets, the power decreases well below -3. The measured steepening of the size distribution over time is predicted by a simple model involving buoyant rise and turbulence dispersion. Conversely, for DOR 1:100 and 1:25 oils, the diameter of slope transition decreases from ∼1mm to 46µm and 14µm respectively, much faster than the We-based prediction, and the size distribution steepens with increasing DOR. Furthermore, the concentration of micron-sized droplets of DOR 1:25 oil increase for the first ten minutes after entrainment. These phenomena are presumably caused by the observed formation and breakup oil micro-threads associated with tip streaming.
      PubDate: 2017-09-14T15:10:48.849115-05:
      DOI: 10.1002/2017JC013193
       
  • Air-Sea CO2 Exchange in the Ross Sea, Antarctica
    • Authors: Hans B. DeJong; Robert B. Dunbar
      Abstract: Although the Ross Sea is one of the most productive regions in Antarctica, it is not clear to what extent this region is an atmospheric CO2 sink. We calculate instantaneous CO2 flux rates with in situ pCO2 and wind speed data from 20 cruises in the Ross Sea. In addition, we estimate annual CO2 fluxes into the Ross Sea with nutrient budgets from a late summer cruise. We find that the Ross Sea is a lesser atmospheric CO2 sink (-7.5±0.5 Tg C yr−1, -1.3±0.1 mol C m−2 yr−1) than previously reported (-13 Tg C yr−1, -1.7 to -4.2 mol C m−2 yr−1). One exception is Terra Nova Bay (TNB) in the western Ross Sea, with CO2 flux rates (-4.8±0.3 mol C m−2, January-March) that are 3-4 times greater than the Ross Sea mean. The majority of the CO2 flux into TNB occurs during the late summer with instantaneous CO2 flux rates up to -246 mmol C m−2 d−1. These extraordinary CO2 flux rates are caused by the unique coupling of strong katabatic winds and low surface pCO2 values. Although strong katabatic winds deepen the mixed layer and entrain CO2 rich water from below, late season net community productivity maintains low surface water pCO2 levels. While TNB only covers ∼1% (3600 km2) of the Ross Sea continental shelf, extraordinary air-to-sea CO2 fluxes during the late summer may be regular features in many of the major sea ice production polynyas (148,000 km2 combined), including Antarctic Bottom Water formation regions.
      PubDate: 2017-09-14T15:10:40.305185-05:
      DOI: 10.1002/2017JC012853
       
  • The Dynamics of Cuba Anticyclones (CubANs) and Interaction With the Loop
           Current/Florida Current System
    • Authors: Vassiliki Kourafalou; Yannis Androulidakis, Matthieu Le Hénaff, HeeSook Kang
      Abstract: Mesoscale anticyclonic eddies along the northern Cuban coast (CubANs) have been identified in the Straits of Florida, associated with the northward shift of the Florida Current (FC) and the anticyclonic curvature of the Loop Current (LC) at the western entrance of the Straits. The dynamics of CubAN eddies and their interaction with the LC/FC system are described for the first time using satellite, drifter and buoy data and a high resolution model. It is shown that the evolution of CubANs to the south of the FC front complements the evolution of cyclonic eddies to the north of the FC, advancing previous studies on synergy between FC meandering and eddy activity. Two types of CubAN eddies are characterized: a) a main anticyclonic cell (type “A”) within the core of the LC during retracted phase conditions, associated with the process of LC Eddy (LCE) shedding from an extended LC, and b) an individual, distinct anticyclonic eddy that is released from the main LC core and is advected eastward, along the northern Cuban coast (type “B”). There are also mixed cases, when the process of LCE shedding has started, so a type “A” CubAN is being formed, in the presence of one or more eastward progressing type “B” eddies. CubAN evolution is associated with an increased mixed layer and weaker stratification of the upper ocean along the eddy's track. The cyclonic activity along the Cuban coast and wind-induced upwelling events also contribute to the evolution and fate of the CubAN eddies.
      PubDate: 2017-09-14T15:10:34.540315-05:
      DOI: 10.1002/2017JC012928
       
  • Spatio-temporal variations of mesoscale eddies in the Sulu Sea
    • Authors: Yinghui He; Ming Feng, Jieshuo Xie, Junliang Liu, Zhiwu Chen, Jiexin Xu, Wendong Fang, Shuqun Cai
      Abstract: Mesoscale eddies have been observed in the Sulu Sea, but their characteristics have not been well described. This study investigates the eddy population in the Sulu Sea using 22 years of satellite altimeter data with high spatiotemporal resolution. On average, there are approximately 1.6 eddies observed in the Sulu Sea each day and 1.8 eddy tracks generated each month. Two of the main eddy genesis regions are west of Negros Island and the Zamboanga Peninsula. The mean radius, lifespan and propagation speed of the eddies are 76.6 km, 32 days and 4.5 cm/s, respectively. The eddy radius and amplitude are generally large in the central Sulu Sea but small on its margin. The mean eddy kinetic energy and vorticity generally monotonically decrease from south to north, consistent with the distributions of background current kinetic energy. Over the seasonal cycle, there are more cyclonic eddies during boreal winter, and they tend to have a larger amplitude and radius than the other 3 seasons, while there are more anti-cyclonic eddies during boreal summer, and they tend to have a larger amplitude and radius than the other 3 seasons. The instability of the mean current and the island gap wind jets are the two key eddy genesis mechanisms in the Sulu Sea.
      PubDate: 2017-09-11T12:16:04.498208-05:
      DOI: 10.1002/2017JC013153
       
  • Estimation of melt pond fractions on first year sea ice using compact
           polarization SAR
    • Authors: Haiyan Li; Will Perrie, Qun Li, Yijun Hou
      Abstract: Melt ponds are a common feature on Arctic sea ice. They are linked to the sea ice surface albedo and transmittance of energy to the ocean from the atmosphere and thus constitute an important process to parameterize in Arctic climate models and simulations. This paper presents a first attempt to retrieve the melt pond fraction from hybrid-polarized compact polarization (CP) SAR imagery, which has wider swath and shorter revisit time than the quad-polarization systems, e.g. from RADARSAT-2 (RS-2). The co-polarization (co-pol) ratio has been verified to provide estimates of melt pond fractions. However, it is a challenge to link CP parameters and the co-pol ratio. The theoretical possibility is presented, for making this linkage with the CP parameter C22/C11 (the ratio between the elements of the coherence matrix of CP SAR) for melt pond detection and monitoring with the tilted-Bragg scattering model for the ocean surface. The empirical transformed formulation, denoted as the ‘compact polarization and quad-pol' (‘CPQP') model, is proposed, based on 2062 RS-2 quad-pol SAR images, collocated with in situ measurements. We compared the retrieved melt pond fraction with CP parameters simulated from quad-pol SAR data with results retrieved from the co-pol ratio from quad-pol SAR observations acquired during the Arctic-Ice (Arctic-Ice Covered Ecosystem in a Rapidly Changing Environment) field project. The results are shown to be comparable for observed melt pond measurements in spatial and temporal distributions. Thus, the utility of CP mode SAR for melt pond fraction estimation on first year level ice is presented.
      PubDate: 2017-09-11T12:15:27.626346-05:
      DOI: 10.1002/2017JC013248
       
  • Acidification mediated by a river plume and coastal upwelling on a
           fringing reef at the east coast of Hainan Island, Northern South China Sea
           
    • Authors: Xu Dong; Haining Huang, Nan Zheng, Aijun Pan, Sumin Wang, Cheng Huo, Kaiwen Zhou, Hui Lin, Weidong Ji
      Abstract: We investigated the dynamics of carbonate system which was greatly modulated by a river plume and coastal upwelling in July 2014 and July 2015 at the east coast of Hainan Island where a fringing reef distributes inshore. By using a three end-member mixing model, we semi-quantitatively estimated the removal of dissolved inorganic carbon (DIC) mediated by biological production in the river plume and upwelled water to be 13±17 μmol kg−1 and 15±16 μmol kg−1, respectively. The enhanced organic production was mainly responsible for these DIC consumptions in both two regimes, however, nearly a half of DIC removal was attributed to biocalcification in the plume system while it was negligible in the upwelling system. Furthermore, the modeled results over reefs revealed that river plume and coastal upwelling were two major threats of acidification to coral communities at the east coast of Hainan Island during cruises. In comparison, the biological contribution to acidification was limited for balancing between organic production and biocalcification during July 2014 cruise whereas the acidification was greatly intensified by organic degradation during July 2015 cruise. It was verified that naturally local acidification (physical and biological processes) played a major role in great pH decreases on a short-term scale, leading to coastal waters more vulnerable to anthropogenic “ocean acidification” (uptake of atmospheric CO2) by reducing buffering capacity of waters. Finally, effects of acidification associated with other local threats on a fringing reef was further depicted with a conceptual model.
      PubDate: 2017-09-08T14:15:40.477212-05:
      DOI: 10.1002/2017JC013228
       
  • On the dynamics of the Sri Lanka Dome in the Bay of Bengal
    • Authors: Jessica M. Burns; Bulusu Subrahmanyam, V. S. N. Murty
      Abstract: East of Sri Lanka, in the Northern Indian Ocean, a cold dome, known as the Sri Lanka Dome (SLD), develops during southwest monsoon season (June-September). The SLD first forms around May, matures in July and decays around September, in association with the strong cyclonic wind stress curl. In this study, the structure and dynamics of SLD in response to the climatic events such as the Indian Ocean Dipole (IOD) are examined. Our results reveal that these climatic events modulated the subsurface temperature variability in the thermocline at ∼100 m depth, whose signature was also evident in the satellite derived Sea Surface Height (SSH) anomaly in the SLD region. We find that the mechanisms for the formation of SLD are consistent with previous research, and there is year-to-year variability in the SLD dynamics. This study also reveals that the atmospheric parameters including vertical wind shear and mid-tropospheric relative humidity are high over the SLD region and adjacent southern Bay of Bengal and show an upward (increasing) trend over the decades. This has impacted the atmospheric parameters over the northern Bay of Bengal over the decades and as a consequence the total number of monsoon depressions (June-September) decreased over the decades from 1980 to 2015, as reported by the India Meteorological Department, New Delhi. Thus the new insight emerged from this study is the variability in the cyclogenesis and the occurrence of total number of monsoon depressions over northern Bay of Bengal over the decades are much related to the SLD dynamics.
      PubDate: 2017-09-08T14:00:26.159195-05:
      DOI: 10.1002/2017JC012986
       
  • Climatology and Decadal Variations in Multicore Structure of the North
           Pacific Subtropical Mode Water
    • Authors: Cong Liu; Shang-Ping Xie, Peiliang Li, Lixiao Xu, Wendian Gao
      Abstract: The pycnostad of the North Pacific subtropical mode water (STMW) often displays multiple vertical minima in the potential vorticity profile. Argo profile data from 2004 to 2015 are used to investigate inter-annual to decadal variations of the multicore structure. Climatologically, about 24% pycostads of STMW have multicore structure, and most of them distribute in the region west of 150°E. STMW cores are classified into three sub-modes—the cold, middle and warm ones with potential temperatures of 16.0°∼17 °C, 17°∼18 °C and 18°∼19.5 °C, respectively. The Kuroshio Extension (KE) varies between stable and unstable states. The unstable KE with large meanders increases the subsurface stratification and shoals the winter mixed layer east of 150°E with warmer temperatures. There, the dominant STMW type varies from the cold single type in stable KE years (making up 72% of the profiles with STMW) to the middle single one (53%) in unstable years. The variation of the dominant STMW type in the region east of 150°E subsequently affects the multicore structure of STMW west of 150°E. In a broad region between 130°E and 180°E, profiles with STMW are fewer in unstable years but the proportion of multicore profiles increases among STMW profiles. This might be due to the split recirculation gyre with a chaotic KE.
      PubDate: 2017-09-08T13:51:13.646264-05:
      DOI: 10.1002/2017JC013071
       
  • Satellite observed salinity distributions at high latitudes in the
           Northern Hemisphere: A Comparison of four products
    • Authors: Cynthia Garcia-Eidell; Josefino C. Comiso, Emmanuel Dinnat, Ludovic Brucker
      Abstract: Global surface ocean salinity measurements have been available since the launch of SMOS in 2009 and coverage was further enhanced with the launch of Aquarius in 2011. In the polar regions where spatial and temporal changes in sea surface salinity (SSS) are deemed important, the data has not been as robustly validated because of the paucity of in situ measurements. This study presents a comparison of four SSS products in the ice-free Arctic region, three using Aquarius data and one using SMOS data. The accuracy of each product is assessed through comparative analysis with ship and other in situ measurements. Results indicate RMS errors ranging between 0.33 and 0.89 psu. Overall, the four products show generally good consistency in spatial distribution with the Atlantic side being more saline than the Pacific side. A good agreement between the ship and satellite measurements were also observed in the low salinity regions in the Arctic Ocean, where SSS in situ measurements are usually sparse, at the end of summer melt seasons. Some discrepancies including biases of about 1 psu between the products in spatial and temporal distribution are observed. These are due in part to differences in retrieval techniques, geophysical filtering, and sea ice and land masks. The monthly SSS retrievals in the Arctic from 2011 to 2015 showed variations (within ∼1 psu) consistent with effects of sea ice seasonal cycles. This study indicates that spaceborne observations capture the seasonality and interannual variability of SSS in the Arctic with reasonably good accuracy.
      PubDate: 2017-09-08T13:10:46.811984-05:
      DOI: 10.1002/2017JC013184
       
  • Effects of topography and Earth's rotation on the oblique interaction of
           internal solitary-like waves in the Andaman Sea
    • Authors: Kenji Shimizu; Keisuke Nakayama
      Abstract: High-resolution three-dimensional MITgcm simulations and an extended Miles theory are used to investigate the oblique interaction of internal solitary-like waves (ISWs) in the Andaman Sea. Oblique solitary-wave interaction is well-studied in various fields of physics; however, this process in the ocean has seldom been investigated, despite the observations of its surface signature by remote sensing and potential 4-fold increase of ISW amplitude by the development of a (Mach) stem. This study confirms the development of stem-like ISWs under realistic oceanic conditions. The modeled interaction is found to be approximately consistent with the Miles theory extended to unequal incident-wave amplitudes and small-but-finite incident angles. Although topography does not appear to affect the process in the deep part of the Andaman Sea, substantial topographic amplitude variation along the wave trough needs to be adjusted before comparisons with the theory. Earth's rotation has a small effect on ISW propagation due to the low latitude (≈9°N), but it does slow down the growth of stem-like ISWs. Potential observation of the process by the next-generation wide-swath satellite altimeter is discussed.
      PubDate: 2017-08-30T12:30:41.252892-05:
      DOI: 10.1002/2017JC012888
       
  • Spectral decomposition of internal gravity wave sea surface height in
           global models
    • Authors: Anna C. Savage; Brian K. Arbic, Matthew H. Alford, Joseph K. Ansong, J.Thomas Farrar, Dimitris Menemenlis, Amanda K. O'Rourke, James G. Richman, Jay F. Shriver, Gunnar Voet, Alan J. Wallcraft, Luis Zamudio
      Abstract: Two global ocean models ranging in horizontal resolution from 1/12° to 1/48° are used to study the space- and time-scales of sea surface height (SSH) signals associated with internal gravity waves (IGWs). Frequency-horizontal wavenumber SSH spectral densities are computed over seven regions of the world ocean from three simulations of the HYbrid Coordinate Ocean Model (HYCOM) and two simulations of the Massachusetts Institute of Technology general circulation model (MITgcm). High-wavenumber, high-frequency SSH variance follows the predicted IGW linear dispersion curves. The realism of high-frequency motions (>0.87cpd) in the models is tested through comparison of the frequency spectral density of dynamic height variance computed from the highest resolution runs of each model (1/25° HYCOM and 1/48° MITgcm) with dynamic height variance frequency spectral density computed from 9 in-situ profiling instruments. These high-frequency motions are of particular interest because of their contributions to the small-scale SSH variability that will be observed on a global scale in the upcoming Surface Water and Ocean Topography (SWOT) satellite altimetry mission. The variance at supertidal frequencies can be comparable to the tidal and low-frequency variance for high-wavenumbers (length scales smaller than ∼50km), especially in the higher resolution simulations. In the highest resolution simulations, the high-frequency variance can be greater than the low-frequency variance at these scales.
      PubDate: 2017-08-30T12:30:37.79542-05:0
      DOI: 10.1002/2017JC013009
       
  • Modeling Arctic sea-ice algae: Physical drivers of spatial distribution
           and algae phenology
    • Authors: Giulia Castellani; Martin Losch, Benjamin A. Lange, Hauke Flores
      Abstract: Algae growing in sea ice represent a source of carbon for sympagic and pelagic ecosystems, and contribute to the biological carbon pump. The biophysical habitat of sea ice on large scales and the physical drivers of algae phenology are key to understanding Arctic ecosystem dynamics and for predicting its response to ongoing Arctic climate change. In addition, quantifying potential feedback mechanisms between algae and physical processes is particularly important during a time of great change. These mechanisms include a shading effect due to the presence of algae, and increased basal ice melt. The present study shows pan-Arctic results obtained from a new Sea Ice Model for Bottom Algae (SIMBA) coupled with a 3D sea-ice–ocean model. The model is evaluated with data collected during a ship-based campaign to the Eastern Central Arctic in summer 2012. The algal bloom is triggered by light, and shows a latitudinal dependency. Snow and ice also play a key role in ice algal growth. Simulations show that after the spring bloom, algae are nutrient-limited before the end of summer and finally they leave the ice habitat during ice melt. The spatial distribution of ice algae at the end of summer agrees with available observations, and it emphasizes the importance of thicker sea-ice regions for hosting biomass. Particular attention is given to the distinction between level ice and ridged ice. Ridge-associated algae are strongly light-limited, but they can thrive towards the end of summer, and represent an additional carbon source during the transition into polar night.
      PubDate: 2017-08-30T12:30:32.289063-05:
      DOI: 10.1002/2017JC012828
       
  • Moored observations of the Deep Western Boundary Current in the NW
           Atlantic: 2004-2014
    • Authors: John M. Toole; Magdalena Andres, Isabela A. Le Bras, Terrence M. Joyce, Michael S. McCartney
      Abstract: A moored array spanning the continental slope southeast of Cape Cod sampled the equatorward-flowing Deep Western Boundary Current (DWBC) for a 10-year period: May 2004 - May 2014. Daily profiles of subinertial velocity, temperature, salinity and neutral density are constructed for each mooring site and cross-line DWBC transport time series are derived for specified water mass layers. Time-averaged transports based on daily estimates of the flow and density fields in stream coordinates are contrasted with those derived from the Eulerian-mean flow field, modes of DWBC transport variability are investigated through compositing, and comparisons are made to transport estimates for other latitudes. Integrating the daily velocity estimates over the neutral density range of 27.8 - 28.125 kg/m3 (encompassing Labrador Sea and Overflow Water layers), a mean equatorward DWBC transport of 22.8 x 106 m3/s ± 1.9 x 106 m3/s is obtained. Notably, a statistically-significant trend of decreasing equatorward transport is observed in several of the DWBC components as well as the current as a whole. The largest linear change (a 4% decrease per year) is seen in the layer of Labrador Sea Water that was renewed by deep convection in the early 1990s whose transport fell from 9.0 x 106 m3/s at the beginning of the field program to 5.8 x 106 m3/s at its end. The corresponding linear fit to the combined Labrador Sea and Overflow Water DWBC transport decreases from 26.4 x 106 m3/s to 19.1 x 106 m3/s. In contrast, no long-term trend is observed in upper-ocean Slope Water transport. These trends are discussed in the context of decadal observations of the North Atlantic circulation, and subpolar air-sea interaction/water mass transformation.
      PubDate: 2017-08-30T12:30:25.776048-05:
      DOI: 10.1002/2017JC012984
       
  • On the secular changes in the tidal constituents in San Francisco Bay
    • Authors: Isaac Rodríguez-Padilla; Modesto Ortiz
      Abstract: Secular changes up to 7% in amplitude, as well as phase advances of 13 minutes of time per century in the diurnal and semidiurnal tidal constituents have been found in previous investigations on the sea level record of San Francisco Bay, California. A numerical hydrodynamic model for barotropic tide is used to explore local causes that may contribute to the secular changes found in the tidal constituents. The results indicate that the morphological evolution of the seabed in the region of the ebb-tidal delta a major factor that contribute to explain the secular changes observed in the tidal constituents in San Francisco Bay, besides of minor contributions from river flow changes and sea-level rise.
      PubDate: 2017-08-30T12:30:23.164262-05:
      DOI: 10.1002/2016JC011770
       
  • The origins of the anomalous warming in the California coastal ocean and
           San Francisco Bay during 2014-2016
    • Authors: Yi Chao; John D. Farrara, Eric Bjorkstedt, Fei Chai, Francisco Chavez, Daniel L. Rudnick, Wendy Enright, Jennifer L. Fisher, William T. Peterson, Gregory F. Welch, Curtiss O. Davis, Richard C. Dugdale, Frances P. Wilkerson, Hongchun Zhang, Yinglong Zhang, Eli Ateljevich
      Abstract: During 2014 exceptionally warm water temperatures developed across a wide area off the California coast and within San Francisco Bay (SFB) and persisted into 2016. Observations and numerical model output are used to document this warming and determine its origins. The coastal warming was mostly confined to the upper 100 meters of the ocean and was manifested strongly in the two leading modes of upper ocean (0-100 m) temperature variability in the extra-tropical eastern Pacific. Observations suggest that the coastal warming in 2014 propagated into nearshore regions from the west while later indicating a warming influence that propagated from south to north into the region associated with the 2015-16 El Niño event. An analysis of the upper ocean (0-100 m) heat budget in a Regional Ocean Modeling System simulation confirmed this scenario. The results from a set of sensitivity runs with the model in which the lateral boundary conditions varied supported the conclusions drawn from the heat budget analysis. Concerning the warming in the SFB, an examination of the observations and the heat budget in an unstructured-grid numerical model simulation suggested that the warming during the second half of 2014 and early 2016 originated in the adjacent California coastal ocean and propagated through the Golden Gate into the Bay. The finding that the coastal and Bay warming are due to the relatively slow propagation of signals from remote sources raises the possibility that such warming events may be predictable many months or even several seasons in advance.
      PubDate: 2017-08-25T13:37:59.172569-05:
      DOI: 10.1002/2017JC013120
       
  • Late-summer biogeochemistry in the Mertz Polynya: East Antarctica
    • Authors: E. H. Shadwick; B. Tilbrook, K. I. Currie
      Abstract: A marked reconfiguration of the Mertz Polynya following the 2010 calving of the Mertz Glacier Tongue has been associated with a decrease in the size and activity of the polynya. We report observations of the oceanic carbonate (CO2) system in late summer 2013, the third post-calving summer season. Estimates of seasonal net community production (NCP) based on inorganic carbon deficits and the oxygen-argon ratio indicate that the waters on the shelf to the east of Commonwealth Bay (adjacent to the Mertz Glacier) remain productive compared to pre-calving conditions. The input of residual or excess alkalinity from melting ice is found to contribute to the seasonal enhancement of carbonate saturation state and pH in shelf waters. Mean rates of NCP in 2012-2013 are more than twice as large as those observed in the pre-calving summers of 2001 and 2008 and suggest that the new (post-calving) configuration of the polynya favours enhanced net community production and a stronger surface ocean sink for atmospheric CO2 due at least in part to the the redistribution of sea-ice and associated changes in summer surface stratification.
      PubDate: 2017-08-25T13:37:53.653519-05:
      DOI: 10.1002/2017JC013015
       
  • The role of wave-current interaction in Lake Erie's seasonal and episodic
           dynamics
    • Authors: Qianru Niu; Meng Xia
      Abstract: Although the significance of surface gravity waves has been consistently emphasized in previous limnetic studies, the roles of wave-current interactions in lake dynamics are not sufficiently understood due to the lack of high-resolution wave information. With a two-way coupled hydrodynamic and wave model system, this study investigated how the Lake Erie dynamics are impacted by the wave-induced surface and radiation stresses on the seasonal-mean and episodic scales. The results showed that the surface radiation stress was the same as or an order of magnitude larger than the wave-induced surface stress in the nearshore area (< 5 km offshore), while the latter prevailed in the offshore areas. By enhancing air-lake momentum and heat transfers, the wave-enhanced surface stress improved the model's skill in simulating hydrodynamics in the Central and Eastern Basins, and it was of greater importance (at least an order of magnitude larger) in modifying surges, offshore currents and thermal structures compared to those of the radiation stress. Nevertheless, the radiation stress played key roles in wave-induced nearshore currents, especially in the shallow Western Basin. Their significances reached O (0.01 to 0.1 m/s) on the seasonal and episodic scales, respectively, and could have similar importance in other shallow water environments.
      PubDate: 2017-08-25T13:37:40.037628-05:
      DOI: 10.1002/2017JC012934
       
  • Tidal and residual currents across the northern Ryukyu Island chain
           observed by ferryboat ADCP
    • Authors: Zhao-Jun Liu; Hirohiko Nakamura, Xiao-Hua Zhu, Ayako Nishina, Menghong Dong
      Abstract: Ferryboat Acoustic Doppler Current Profiler (ADCP) data from 2003 to 2012 are used to estimate the tidal and residual currents across the northern Ryukyu Island chain (RIC) between the islands of Okinawa and Amamioshima. In this region, the M2 tide current is the strongest tidal component, and the K1 tide current is the strongest diurnal tidal component. The corresponding maximum amplitudes are 40 and 34 cm s−1, respectively. After removal of the tidal currents, the mean volume transport, 1.5 ± 2.7 Sv, flows into the East China Sea (ECS) from the western North Pacific through four channels in this area. In an empirical orthogonal function (EOF) analysis performed to clarify the temporal and spatial variability of currents through the four channels, the first two EOF modes account for 71% and 18% of the total variance, respectively. The EOF1 mode shows a clear bottom-intensified mode through the deep channel, which is likely to be formed by the propagation of bottom-trapped long topographic Rossby wave caused by the impingement of westward propagating mesoscale eddies upon the eastern slope of the northern RIC. The EOF2 mode has significant seasonal variability and may be driven by the wind stress prevailing over the Kuroshio flow region around the northern RIC in October to November. This study provides observational evidence of the water exchanges across the northern RIC, which is essential for constructing a circulation scheme in the North Pacific subtropical western boundary region.
      PubDate: 2017-08-25T13:37:29.990654-05:
      DOI: 10.1002/2017JC012876
       
  • Three-dimensional tidal flow in a fjord-like basin with converging width:
           An analytical model
    • Authors: Lauren Ross; Huib de Swart, Erik Ensing, Arnoldo Valle-Levinson
      Abstract: A three-dimensional analytical model was used to understand tidal dynamics in deep and narrow (fjord-like) basins. This model allows the width of the basin to decay exponentially with along-channel distance from the mouth. Both the length scale of exponential convergence, Lb*, and the friction parameter, Aν* (vertical eddy viscosity), were the free parameters. Model results show amplification of the tidal amplitude toward the head of the basin. Amplification depends on the narrowing rate of the funnel-like width of the channel and on friction. Cross-channel variations in along-channel tidal ow are also sensitive to the friction parameter. A typical along-channel tidal ow distribution was found across the channel when the vertical eddy viscosity was characteristic of a basin with strong friction, or the Stokes number was larger than 0.1 (St > 0:1). Maximum along-channel tidal velocities (ranging from 0:25 to 0:5 m s−1 depending on width convergence strength) were located in the center of the basin and at the surface. Decreasing values of the Stokes number, St 
      PubDate: 2017-08-25T13:37:22.647655-05:
      DOI: 10.1002/2017JC012820
       
  • Mechanisms underlying recent decadal changes in subpolar North Atlantic
           Ocean heat content
    • Authors: Christopher G. Piecuch; Rui M. Ponte, Christopher M. Little, Martha W. Buckley, Ichiro Fukumori
      Abstract: The subpolar North Atlantic (SPNA) is subject to strong decadal variability, with implications for surface climate and its predictability. In 2004–2005, SPNA decadal upper-ocean and sea-surface temperature trends reversed from warming during 1994–2004 to cooling over 2005–2015. This recent decadal trend reversal in SPNA ocean heat content (OHC) is studied using a physically consistent, observationally constrained global ocean state estimate covering 1992–2015. The estimate's physical consistency facilitates quantitative causal attribution of ocean variations. Closed heat budget diagnostics reveal that the SPNA OHC trend reversal is the result of heat advection by midlatitude ocean circulation. Kinematic decompositions reveal that changes in the deep and intermediate vertical overturning circulation cannot account for the trend reversal, but rather ocean heat transports by horizontal gyre circulations render the primary contributions. The shift in horizontal gyre advection reflects anomalous circulation acting on the mean temperature gradients. Maximum covariance analysis (MCA) reveals strong covariation between the anomalous horizontal gyre circulation and variations in the local wind stress curl, suggestive of a Sverdrup response. Results have implications for decadal predictability.
      PubDate: 2017-08-25T13:37:11.655975-05:
      DOI: 10.1002/2017JC012845
       
  • Tsunami and shelf resonance on the Northern Chile Coast
    • Authors: Pablo Cortés; Patricio A. Catalán, Rafael Aránguiz, Giorgio Bellotti
      Abstract: This work presents the analysis of long waves resonance in two of the main cities along the northern coast of Chile, Arica and Iquique, where a large tsunamigenic potential remains despite recent earthquakes. By combining a modal analysis solving the equation of free surface oscillations, with the analysis of background spectra derived from in situ measurements, the spatial and temporal structures of the modes are recovered. Comparison with spectra from three tsunamis of different characteristics shows that the modes found have been excited by past events. Moreover, the two locations show different response patterns. Arica is more sensitive to the characteristics of the tsunami source, whereas Iquique shows a smaller dependency and similar response for different tsunami events. Results are further compared with other methodologies with good agreement. These findings are relevant in characterizing the tsunami hazard in the area, and the methodology can be further extended to other regions along the Chilean coast.
      PubDate: 2017-08-25T13:36:59.104883-05:
      DOI: 10.1002/2017JC012922
       
  • The warmer the ocean surface, the shallower the mixed layer: How much of
           this is true'
    • Authors: R. Somavilla; C. González-Pola, J. Fernandez
      Abstract: Ocean surface warming is commonly associated with a more stratified, less productive, and less oxygenated ocean. Such assertion is mainly based on consistent projections of increased near-surface stratification and shallower mixed layers under global warming scenarios. However, while the observed sea surface temperature (SST) is rising at mid-latitudes, the concurrent ocean record shows that stratification is not unequivocally increasing nor is MLD shoaling. We find that while SST increases at three study areas at mid-latitudes, stratification both increases and decreases, and MLD deepens with enhanced deepening of winter MLDs at rates over 10m decade−1. These results rely on the estimation of several MLD and stratification indexes of different complexity on hydrographic profiles from long term hydrographic time-series, ocean reanalysis and Argo floats. Combining this information with estimated MLDs from buoyancy fluxes and the enhanced deepening/attenuation of the winter MLD trends due to changes in the Ekman pumping, MLD variability reveals itself as a subtle interplay between circulation and atmospheric forcing at mid-latitudes. Besides, it is highlighted that the density difference between the surface and 200 m, the most widely used stratification index, should not be expected to reliably inform about changes in the vertical extent of mixing.
      PubDate: 2017-08-25T13:36:50.356715-05:
      DOI: 10.1002/2017JC013125
       
  • Pathways and supply of dissolved iron in the Amundsen Sea (Antarctica)
    • Authors: P. St-Laurent; P.L. Yager, R.M. Sherrell, S.E. Stammerjohn, M.S. Dinniman
      Abstract: Numerous coastal polynyas fringe the Antarctic continent and strongly influence the productivity of Antarctic shelf systems. Of the 46 Antarctic coastal polynyas documented in a recent study, the Amundsen Sea Polynya (ASP) stands out as having the highest net primary production per unit area. Incubation experiments suggest that this productivity is partly controlled by the availability of dissolved iron (dFe). As a first step toward understanding the iron supply of the ASP, we introduce four plausible sources of dFe and simulate their steady spatial distribution using conservative numerical tracers. The modeled distributions replicate important features from observations including dFe maxima at the bottom of deep troughs and enhanced concentrations near the ice shelf fronts. A perturbation experiment with an idealized drawdown mimicking summertime biological uptake and subsequent resupply suggests that glacial meltwater and sediment-derived dFe are the main contributors to the pre-bloom dFe inventory in the top 100m of the ASP. The sediment-derived dFe depends strongly on the buoyancy-driven overturning circulation associated with the melting ice shelves (the ‘meltwater pump') to add dFe to the upper 300m of the water column. The results support the view that ice shelf melting plays an important direct and indirect role in the dFe supply and delivery to polynyas such as the ASP.
      PubDate: 2017-08-25T13:36:28.518044-05:
      DOI: 10.1002/2017JC013162
       
  • Thermohaline staircases in the Amundsen Basin: Possible disruption by
           shear and mixing
    • Authors: John D. Guthrie; Ilker Fer, James H. Morison
      Abstract: As part of the 2013 and 2014 North Pole Environmental Observatories (NPEO) in the Amundsen Basin of the Arctic Ocean, two similar temperature microstructure experiments were performed with different results. In 2013, vertical fluxes were through a thermohaline staircase, and in 2014 the thermohaline staircase was largely absent. Here we investigate the reasons for this difference. The 2013 data set was characterized by an extensive thermohaline staircase, indicative of the diffusive convective type of double diffusion (DC), from 120-250 m depths. The staircase was absent above 200 m in 2014, even though analysis of density ratio, Rρ, still shows high susceptibility to DDC. In the depth range of interest, survey averaged Rρ = 3.8 in 2013 and Rρ = 3.6 in 2014, indicating that the temperature-salinity structure in the pycnocline was not the cause of the lack of a staircase in 2014. We propose that exceptionally weak turbulent mixing, even for the typically quiescent Arctic Ocean, allowed formation of the staircase in 2013. Average thermal diffusivity, KT, between 50 – 120 m is elevated in 2014, 2 x 10−5 m2s−1, compared to 2013, 1 x 10−6 m2s−1. However, vertical Atlantic Water (AW) DC heat fluxes in 2013 are remarkably consistent with turbulent heat fluxes in 2014. Similar data sets collected in 2007 and 2008 both resemble 2014, showing consistently higher mixing values compared to 2013. The suppression of turbulence during NPEO 2013 resulted from increased near-surface stratification, possibly caused by a different large-scale circulation pattern that year.
      PubDate: 2017-08-25T13:31:16.285431-05:
      DOI: 10.1002/2017JC012993
       
  • Lateral variability of subtidal flow at the mid-reaches of a macrotidal
           estuary
    • Authors: Lauren Ross; Arnoldo Valle-Levinson, Aldo Sottolichio, Nicolas Huybrechts
      Abstract: Transverse variations of tidal and subtidal ow were investi-gated in a macrotidal and convergent estuary. This was accomplished by combining data analysis of current velocities and water density with numericalmodeling at the mid-reaches of the Gironde Estuary (France). Nonlinear mech-anisms responsible for overtide generation and hence subtidal ows were foundto vary across the estuary and from neap to spring tides. Subtidal ows weredriven by a combination of internal asymmetry, tidal advective accelerations, nonlinear effects of water level variations, quadratic friction and river discharge. The quarter-diurnal overtide band (D4) in ow was generated by in-ternal asymmetry and tidal advective accelerations during neap tide. Theratio of quarter-diurnal to squared semidiurnal bands (D4/D22) was largest(>0.3) in sections of the channel showing subtidal outow. River dischargeincreased from neap to spring tides causing a subsequent increase of sea-ward subtidal currents. During spring tide D4 was generated by tidal advec-tive accelerations and quadratic friction combined with river discharge, ratherthan by internal asymmetry. The sixth-diurnal overtide (D6) in the ow wascomparable to D4 for both neap and spring tides. Largest D6/D23 ratios werefound in the shallowest cross-channel locations during both neap and springtides.
      PubDate: 2017-08-25T13:31:12.755533-05:
      DOI: 10.1002/2016JC012504
       
  • The influence of variable slope-water characteristics on dissolved oxygen
           levels in the northern California Current System
    • Authors: Scott M. Durski; John A. Barth, James C. McWilliams, Hartmut Frenzel, Curtis Deutsch
      Abstract: Observations have suggested a trend of decreasing dissolved oxygen (DO) and increasing spiciness in summertime mid-depth slope waters and bottom shelf waters along the United States west coast over the past 50 years, but they have also demonstrated a large amount of interannual and decadal variability. Shelf bottom water and slope water properties can be influenced by both local and remote effects, including changes in circulation or changes in the characteristics of the source waters supplying the region. A regional-scale, coupled physical biogeochemical model has been developed to simulate seasonal-to-decadal scale variability along the US west coast to discern the physical dynamics behind these spatial and temporal patterns. A simulation run from 1981 through 2006 with forcing that incorporates the larger scale interannual trends reproduces the development of low DO late in the upwelling season, the considerable interannual variability and the reported tendency towards a shoaling, more spicy and oxygen-depleted, northern California Undercurrent (CU). Whereas the trend in spiciness in the model results from increased influence of equatorial relative to subarctic source waters, the decreases in DO are found to additionally be a consequence of local biogeochemical processes. In order to better understand the interannual variability, years of the simulation were classified into four groups based on intensity of upwelling forcing and undercurrent strength. Slope water characteristics, shelf-slope exchange, and slope-basin exchange were compared across the four cases. Years with both strong upwelling and a strong undercurrent generated the most negative anomalies in slope-water DO late in the upwelling season.
      PubDate: 2017-08-25T13:31:01.991174-05:
      DOI: 10.1002/2017JC013089
       
  • Characterization of the structure and cross-shore transport properties of
           a coastal upwelling filament using three-dimensional finite–size
           Lyapunov exponents
    • Authors: João H. Bettencourt; Vincent Rossi, Emilio Hernández-García, Martinho Marta-Almeida, Cristóbal López
      Abstract: The three dimensional structure, dynamics and dispersion characteristics of a simulated upwelling filament in the Iberian upwelling system are analyzed using Lagrangian tools. We used a realistic regional simulation of the western Iberian shelf which is concomitant with an in-situ oceanographic campaign that surveyed the area. We compute 3d fields of finite–size Lyapunov exponents (FSLE) from 3d velocity fields and extract the field's ridges to study the spatial distribution and temporal evolution of the Lagrangian Coherent Structures (LCSs) evolving around the filament. We find that the most intense curtain-like LCSs delimit the boundaries of the whole filamentary structure whose general properties match well the observations. The filament interior is characterized by small dispersion of fluid elements. Furthermore, we identify a weak LCS separating the filament into a warmer vein and a colder filament associated with the interaction of a mesoscale eddy with the upwelling front. The cold upwelled water parcels move along the filament conserving their density. The filament itself is characterized by small dispersion of fluid elements in its interior. The comparison of LCSs with potential temperature and salinity gradient fields shows that the outer limits of the filament coincide with regions of large hydrographic gradients, similar to those observed, explaining the isolation of the interior of the filament with the surrounding waters. We conclude that the Lagrangian analysis used in this work is useful in explaining the dynamics of cross-shore exchanges of materials between coastal regions and the open ocean due to mesoscale processes.
      PubDate: 2017-08-25T13:30:51.311667-05:
      DOI: 10.1002/2017JC012700
       
  • Phytoplankton light absorption and the package effect in relation to
           photosynthetic and photoprotective pigments in the northern tip of
           Antarctic Peninsula
    • Authors: Amabile Ferreira; Áurea M. Ciotti, Carlos Rafael B. Mendes, Julia Uitz, Annick Bricaud
      Abstract: This study investigates the variability in the spectral absorption of phytoplankton in Antarctic waters. A large in situ dataset comprising phytoplankton pigments and hyperspectral absorption was measured in the northern tip of Antarctic Peninsula during 2013 and 2014 summers at several depths. A proxy of package effect was estimated from the phytoplankton absorption spectra, independently of chlorophyll-a. Variations in the concentration of photosynthetic and photoprotective pigments were discernible by changes in this metric but not in a*ph(λ). The fucoxanthin to chlorophyll-a ratio correlated positively to package effect due to an increase in cell size of phytoplankton (diatoms) and increasing fucoxanthin content per cell to maximize light-harvesting in depth. The package effect was found to covary inversely with photoprotective pigments relative to chlorophyll-a, partially due to their contribution to enhance absorption in the blue part of the spectrum. Using a cluster analysis (k-means algorithm) on the phytoplankton absorption spectra, we illustrate the capacity to identify a regular increase in the degree of package effect. This approach can be useful to classify the phytoplankton assemblages in Antarctic waters according to different degrees of pigment packaging, each one related to a specific pigment composition. Our results demonstrate the potential for this classification at different temporal and spatial scales from ocean color satellite data. This should improve our understanding of deviations in global bio-optical algorithms when applied to the Southern Ocean.
      PubDate: 2017-08-25T13:30:47.223097-05:
      DOI: 10.1002/2017JC012964
       
  • Variability of the Subtropical Mode Water in the Southwest Pacific
    • Authors: Denise Fernandez; Philip Sutton, Melissa Bowen
      Abstract: The variability of Subtropical Mode Water (STMW) in the Southwest Pacific is investigated using a 28-year-long time series (1986 to 2014) of high-resolution expendable bathythermograph data north of New Zealand (PX06) and a shorter time series, the Roemmich-Gilson monthly Argo optimal interpolation for the 2004-2014 period. The variability in STMW inventories is compared to the variability in air-sea heat fluxes, mixed layer depths and transport of the East Auckland Current (EAUC) to assess both the atmospheric and oceanic roles influencing the formation and decay of STMW. The STMW north of New Zealand has a short lifespan with little persistence of the water mass from one year to the next one. Deeper mixed layers and negative anomalies in surface heat fluxes are correlated with increased formation of STMW. The heat content of the STMW layer is anticorrelated with inventories, particularly during the El Niño years. This suggests that large volumes of STMW are coincident with cooler conditions in the prior winter and less oceanic heat storage. There is significant seasonal and interannual variability in STMW inventories, however there are no trends in STMW properties, including its core layer temperature over the last decade. The variability of the winter EAUC transport is highly correlated with the STMW inventories and thermocline depth in the following spring, suggesting ocean dynamics deepen the thermocline and precondition for deeper mixed layers.
      PubDate: 2017-08-25T13:30:43.802087-05:
      DOI: 10.1002/2017JC013011
       
  • The pelagic ecosystem in the northern California Current off Oregon during
           the 2014-2016 warm anomalies within the context of the past 20 years
    • Authors: William T. Peterson; Jennifer L. Fisher, P. Ted Strub, Xiuning Du, Craig Risien, Jay Peterson, C. Tracy Shaw
      Abstract: A warm anomaly in the upper ocean, colloquially named “the Blob”, appeared in the Gulf of Alaska during the calm winter of 2013-2014, spread across the northern North Pacific (NP) Ocean and shifted eastward and onto the Oregon shelf. At least 14 species of copepods occurred which had never been observed in shelf/slope waters off Oregon, some of which are known to have NP Gyre affinities, indicating that the source waters of the coastal “Blob” were likely of both offshore (from the west) and subtropical/tropical origin. The anomalously warm conditions were reduced during strong upwelling in spring 2015 but returned when upwelling weakened in July 2015 and transitioned to downwelling in fall 2015. The extended period of warm conditions resulted in prolonged effects on the ecosystem off central Oregon, lasting at least through 2016. Impacts to the lower trophic levels were unprecedented and include a novel plankton community composition resulting from increased copepod, diatom and dinoflagellate species richness and increased abundance of dinoflagellates. Additionally, the multi-year warm anomalies were associated with reduced biomass of copepods and euphausiids, high abundance of larvaceans and doliolids (indictors of oligotrophic ocean conditions), and a toxic diatom bloom (Pseudo-nitzschia) throughout the California Current in 2015, thereby changing the composition of the food web that is relied upon by many commercially and ecologically important species.
      PubDate: 2017-08-25T13:30:41.263614-05:
      DOI: 10.1002/2017JC012952
       
  • Fine-scale variability of isopycnal salinity in the California Current
           System
    • Authors: Sachihiko Itoh; Daniel L. Rudnick
      Abstract: This paper examines the finescale structure and seasonal fluctuations of the isopycnal salinity of the California Current System from 2007 to 2013 using temperature and salinity profiles obtained from a series of underwater glider surveys. The seasonal mean distributions of the spectral power of the isopycnal salinity gradient averaged over submesoscale (12–30 km) and mesoscale (30–60 km) ranges along three survey lines off Monterey Bay, Point Conception, and Dana Point were obtained from 298 transects. The mesoscale and submesoscale variance increased as coastal upwelling caused the isopycnal salinity gradient to steepen. Areas of elevated variance were clearly observed around the salinity front during the summer then spread offshore through the fall and winter. The high finescale variances were observed typically above 25.8 kg m−3 and decreased with depth to a minimum at around 26.3 kg m−3. The mean spectral slope of the isopycnal salinity gradient with respect to wavenumber was 0.19 ± 0.27 over the horizontal scale of 12–60 km, and 31% to 35% of the spectra had significantly positive slopes. In contrast, the spectral slope over 12–30 km was mostly flat, with mean values of −0.025 ± 0.32. An increase in submesoscale variability accompanying the steepening of the spectral slope was often observed in inshore areas; e.g., off Monterey Bay in winter, where a sharp front developed between the California Current and the California Under Current, and the lower layers of the Southern California Bight, where vigorous interaction between a synoptic current and bottom topography is to be expected.
      PubDate: 2017-08-25T13:30:30.634842-05:
      DOI: 10.1002/2017JC013080
       
  • Seasonal fluctuations of ichthyoplankton assemblage in the northeastern
           South China Sea influenced by the Kuroshio intrusion
    • Authors: D. Huang; X. Zhang, Z. Jiang, J. Zhang, I. Arbi, X. Jiang, X. Huang, W. Zhang
      Abstract: The distribution and assemblage of ichthyoplankton related to local hydrographic features, especially intrusion of the Kuroshio Current (KC) and Guangdong Coastal Current (GCC) in the northeastern South China Sea (NESCS) were investigated in this study. A total of 193 species of ichthyoplankton belonging to 141 genera and 66 families were recognized in summer 2015 and late-winter 2016. The ichthyoplankton assemblage was identified with distinct seasonal differences, and the differences were responded well with the oceanography conditions. In summer, the assemblages were identified into offshore and inshore groups, as controlled by the South China Sea Warm Current (SCSWC) in off-shelf, upwelling and the diluted water from the Pearl River in inshore. In winter, three groups were divided, representing the southwestern inshore, intrusion of the KC in the eastern offshore and the GCC in the northern inshore area, respectively. Furthermore, Sigmops gracilis and Vinciguerria sp.3 were probably brought into the NESCS by intrusion of the KC from the eastern Luzon Strait. In addition, high ichthyoplankton abundance was found in high chlorophyll a located in upwelling areas in the northern coastal area in summer and in the southwestern Taiwan Bank in winter, respectively. The nutrition outcropped by the upwelling together, and those brought from the Pearl River probably supported high food availability of the ichthyoplankton in the northern coast of the NESCS.
      PubDate: 2017-08-25T13:30:24.025498-05:
      DOI: 10.1002/2017JC012906
       
  • Seismic estimates of turbulent diffusivity and evidence of nonlinear
           internal wave forcing by geometric resonance in the South China Sea
    • Authors: W.F.J. Fortin; W.S. Holbrook, R.W. Schmitt
      Abstract: The Luzon Passage generates some of the largest amplitude internal waves in the global ocean as the result of coupling between strong tides, strong stratification, and topography. These internal waves propagate into the South China Sea (SCS) and develop into soliton-like internal wave pulses that are observed by moored instruments and satellite backscatter data. Despite the observation of these waves, little is known of the mechanisms related to their evolution into nonlinear wave pulses. Using seismic data, we find evidence that the geometry of bathymetric conditions between the Heng-Chun and Lan-Yu ridges drive nonlinear internal wave pulse generation. We produce three seismic images and associated maps of turbulent diffusivity to investigate structure around the two ridges and into the SCS. We do not observe large amplitude soliton-like internal waves between the ridges, but do observe one outside the ridges, a finding in accord with the interpretation that wave pulses form due to geometrical resonance. Additionally, we find no evidence for lee wave activity above the ridges in either the seismic images or associated turbulence maps, suggesting an unlikelihood of hydraulic jump driven generation around the ridges. Our results show increased levels of turbulent diffusivity (1) in deep water below 1000m, (2) associated with internal tide pulses, and (3) near the steep slopes of the Heng-Chun and Lan-Yu ridges as explored in this paper.
      PubDate: 2017-08-25T13:30:19.881429-05:
      DOI: 10.1002/2017JC012690
       
  • Turbulent mixing within the Kuroshio in the Tokara Strait
    • Authors: Eisuke Tsutsumi; Takeshi Matsuno, Ren-Chieh Lien, Hirohiko Nakamura, Tomoharu Senjyu, Xinyu Guo
      Abstract: Turbulent mixing and background current were observed using a microstructure profiler and acoustic Doppler current profilers in the Tokara Strait, where many seamounts and small islands exist within the route of the Kuroshio in the East China Sea. Vertical structure and water properties of the Kuroshio were greatly modified downstream from shallow seamounts. In the lee of a seamount crest at 200 -m depth, the modification made the flow tend to shear instability, and the vertical eddy diffusivity is enhanced by nearly 100 times that of the upstream site, to Kρ ∼ O(10−3)–O(10−2) m2 s−1. A one-dimensional diffusion model using the observed eddy diffusivity reproduced the observed downstream evolution of the temperature-salinity profile. However, the estimated diffusion time-scale is at least 10 times longer than the observed advection time-scale. This suggests that the eddy diffusivity reaches to O(10−1) m2 s−1 in the vicinity of the seamount. At a site away from the abrupt topography, eddy diffusivity was also elevated to O(10−3) m2 s−1, and was associated with shear instability presumably induced by the Kuroshio shear and near-inertial internal-wave shear. Our study suggests that a better prediction of current, water-mass properties, and nutrients within the Kuroshio requires accurate understanding and parameterization of flow-topography interaction such as internal hydraulics, the associated internal-wave processes, and turbulent mixing processes.
      PubDate: 2017-08-25T11:57:41.94591-05:0
      DOI: 10.1002/2017JC013049
       
  • A data assimilating model for estimating Southern Ocean biogeochemistry
    • Authors: A. Verdy; M.R. Mazloff
      Abstract: A biogeochemical Southern Ocean state estimate (B-SOSE) is introduced that includes carbon and oxygen fields as well as nutrient cycles. The state estimate is constrained with observations while maintaining closed budgets and obeying dynamical and thermodynamic balances. Observations from profiling floats, shipboard data, underway measurements, and satellites are used for assimilation. The years 2008–2012 are chosen due to the relative abundance of oxygen observations from Argo floats during this time. The skill of the state estimate at fitting the data is assessed. The agreement is best for fields that are constrained with the most observations, such as surface pCO2 in Drake Passage (44% of the variance captured) and oxygen profiles (over 60% of the variance captured at 200 m and 1000 m). The validity of adjoint method optimization for coupled physical-biogeochemical state estimation is demonstrated with a series of gradient check experiments. The method is shown to be mature and ready to synthesize in situ biogeochemical observations as they become more available. Documenting the B-SOSE configuration and diagnosing the strengths and weaknesses of the solution informs usage of this product as both a climate baseline and as a way to test hypotheses. Transport of Intermediate Waters across 32°S supplies significant amounts of nitrate to the Atlantic Ocean (5.57±2.94 Tmol yr-1) and Indian Ocean (5.09±3.06 Tmol yr-1), but much less nitrate reaches the Pacific Ocean (1.78±1.91 Tmol yr-1). Estimates of air-sea carbon dioxide fluxes south of 50°S suggest a mean uptake of 0.18 Pg C/yr for the time period analyzed.
      PubDate: 2017-08-15T02:12:16.88532-05:0
      DOI: 10.1002/2016JC012650
       
  • Space and time variability of the Southern Ocean carbon budget
    • Authors: Isabella Rosso; Matthew R. Mazloff, Ariane Verdy, Lynne D. Talley
      Abstract: The upper ocean dissolved inorganic carbon (DIC) concentration is regulated by advective and diffusive transport divergence, biological processes, freshwater and air-sea CO2 fluxes. The relative importance of these mechanisms in the Southern Ocean is uncertain, as year-round observations in this area have been limited. We use a novel physical-biogeochemical state estimate of the Southern Ocean to construct a closed DIC budget of the top 650 m and investigate the spatial and temporal variability of the different components of the carbon system.The dominant mechanisms of variability in upper ocean DIC depend on location and time and space scales considered. Advective transport is the most influential mechanism and governs the local DIC budget across the 10 day to 5-year timescales analyzed. Diffusive effects are nearly negligible. The large-scale transport structure is primarily set by up- and downwelling, though both the lateral ageostrophic and geostrophic transports are significant. In the Antarctic Circumpolar Current, the carbon budget components are also influenced by the presence of topography and biological hot spots. In the subtropics, evaporation and air-sea CO2 flux primarily balances the sink due to biological production and advective transport. Finally, in the subpolar region sea ice processes, which change the seawater volume and thus the DIC concentration, compensate the large impact of the advective transport and modulate the timing of biological activity and air-sea CO2 flux.
      PubDate: 2017-08-11T12:27:33.772047-05:
      DOI: 10.1002/2016JC012646
       
  • Characterising the chaotic nature of ocean ventilation
    • Authors: Graeme A. MacGilchrist; David P. Marshall, Helen L. Johnson, Camille Lique, Matthew Thomas
      Abstract: Ventilation of the upper ocean plays an important role in climate variability on interannual to decadal timescales by influencing the exchange of heat and carbon dioxide between the atmosphere and ocean. The turbulent nature of ocean circulation, manifest in a vigorous mesoscale eddy field, means that pathways of ventilation, once thought to be quasi-laminar, are in fact highly chaotic. We characterise the chaotic nature of ventilation pathways according to a nondimensional ‘filamentation number', which estimates the reduction in filament width of a ventilated fluid parcel due to mesoscale strain. In the subtropical North Atlantic of an eddy-permitting ocean model, the filamentation number is large everywhere across three upper ocean density surfaces — implying highly chaotic ventilation pathways — and increases with depth. By mapping surface ocean properties onto these density surfaces, we directly resolve the highly filamented structure and confirm that the filamentation number captures its spatial variability. These results have implications for the spreading of atmospherically-derived tracers into the ocean interior.
      PubDate: 2017-08-11T12:27:14.989634-05:
      DOI: 10.1002/2017JC012875
       
  • Characteristics and evolution of an Agulhas Ring
    • Authors: M. Casanova-Masjoan; J. L. Pelegrí, P. Sangrà, A. Martínez, D. Grisolía-Santos, M. D. Pérez-Hernández, A. Hernández-Guerra
      Abstract: A South Atlantic ring is studied through remote sensing altimetry, hydrographic stations and drifters' trajectories. The ring's core was characterized by warmer and saltier Indian Ocean waters. At the time of the cruise the ring's signature extended out 110 km and down to 2000 m, and its core absolute dynamic topography (ADT) exceeded the surrounding Atlantic Ocean waters in 0.4 m. The geostrophic velocities were anticyclonic with maximum velocities about 35 cm s−1 at 100 m and reaching negligible values near 4500 m. The rotational transport inside the ring was 33 Sv in the thermocline and intermediate layers. The drifters' data distinguishes a 30-km core revolving as a solid body with periodicity near 5 days and a transitional band that revolves with constant tangential velocity, resembling a Rankine vortex. The ADT data identifies the ring's track, showing that it was shed by the Agulhas Current retroflection in November 2009 and propagated northwest rapidly during the first two months (mean speed ca. 10 cm s−1) but slowed down substantially (3-4 cm s−1) between March and July 2010, when it was last detected. The altimetry data also outlines the evolution of the ring's core ADT, radius, vorticity and, through a simple calibration with the cruise data, rotational transport. In particular, the ring surface and mean vorticity decay with time scales of 373 and 230 days, respectively, indicating that most of the property anomalies contained by the ring are diffused out to the subtropical gyre before it reaches the western boundary current system.
      PubDate: 2017-08-11T12:27:03.280732-05:
      DOI: 10.1002/2017JC012969
       
  • Observing System Simulation Experiments for an array of autonomous
           biogeochemical profiling floats in the Southern Ocean
    • Authors: Igor Kamenkovich; Angelique Haza, Alison R. Gray, Carolina O. Dufour, Zulema Garraffo
      Abstract: This study uses Observing System Simulation Experiments (OSSEs) to examine the reconstruction of biogeochemical variables in the Southern Ocean from an array of autonomous profiling floats. In these OSSEs, designed to be relevant to the Southern Ocean Carbon and Climate Observation and Modeling (SOCCOM) project, the simulated floats move with oceanic currents and sample dissolved oxygen and inorganic carbon. The annual mean and seasonal cycle of these fields are then reconstructed and compared to the original model fields. The reconstruction skill is quantified with the reconstruction error (RErr), defined as the difference between the reconstructed and actual model fields, weighted by a local measure of the spatio-temporal variability. The square of the RErr is small (< 0.5) for 150 floats in most of the domain, which is interpreted to mean that the reconstruction skill is high. An idealized analytical study demonstrates that the RErr depends on the magnitude of the seasonal cycle, spatial gradients, speed of float movement, amplitude of mesoscale variability and number of floats. These factors explain a large part of the spatial variability in the RErr and can be used to predict the reconstruction skill of the SOCCOM array. Furthermore, our results demonstrate that an array size of 150 floats is a reasonable choice for reconstruction of surface properties and annual-mean 2000 m inventories, with the exception of the seasonal cycle in parts of the Indo-Atlantic, and that doubling this number to 300 results in a very modest increase in the reconstruction skill for dissolved oxygen.
      PubDate: 2017-08-11T12:26:56.258436-05:
      DOI: 10.1002/2017JC012819
       
  • Spatiotemporal changes in extreme sea levels along the coasts of the North
           Atlantic and the Gulf of Mexico
    • Authors: Marta Marcos; Philip L. Woodworth
      Abstract: Extreme sea levels along the densely monitored coasts of the North Atlantic Ocean and the Gulf of Mexico have been investigated using high frequency tide gauge measurements in the GESLA-2 data set (www.gesla.org). Our results, based on non-tidal residuals and skew surges in records since 1960, confirm that mean sea level (MSL) is a major, but not a unique, driver of extremes. Regionally-coherent linear trends and correlations with large scale climate patterns are found in extreme events, even after the removal of MSL. A similar conclusion, that MSL is a major but not the only driver of extremes, comes from a small number of long records starting in the mid-19th century. The records show slight increases in the intensity of extreme episodes at centennial time scales, together with multi-decadal variability unrelated to MSL. Objective statistical criteria have been used to investigate whether extreme sea level distributions are stationary or not, resulting in non-stationarity being favoured in many records, with or without accounting for changes in MSL. Extremes have been found to favour a non-Gumbel behaviour at many locations, with implications for the accuracy of return levels for coastal engineering.
      PubDate: 2017-08-11T12:26:53.64096-05:0
      DOI: 10.1002/2017JC013065
       
  • ENSO impact on surface radiative fluxes as observed from space
    • Authors: R. T. Pinker; S. A. Grodsky, B. Zhang, A. Busalacchi, W. Chen
      Abstract: We investigate the impact of El Niño - Southern Oscillation (ENSO) on surface radiative fluxes over the tropical Pacific using satellite observations and fluxes derived from selected atmospheric re-analyses. Agreement between the two in this region is important because re-analysis information is frequently used to assess surface energy budget sensitivity to ENSO. We found that during the traditional ENSO, the maximum variance of anomalous incoming solar radiation is located just west of the dateline and coincides with the area of largest anomalous SST gradient. It can reach up to ∼60 W/m2 and lags behind the Niño3 index by about a month, suggesting a response to anomalous SST gradient. The magnitude of longwave anomaly is only half that large, and varies in phase with the SST anomaly. Similar anomalies were derived from outputs: from the European Centre for Medium-Weather Forecasts Reanalysis Interim (ERA-I), from the Modern Era Retrospective Analysis version 2 (MERRA-2), from the NCEP/NCAR Re-analysis 1 (R1), and from the Japanese JRA55 re-analysis. Among the four re-analyses used, results from ERA-I are the closest to observations. We have also investigated the surface wind divergence/convergence and found that the main factor limiting eastward excursions of convection is the surface wind convergence. Due to the wind divergence pattern normally present over the eastern cold tongue, anomalous convection extends into the eastern equatorial Pacific only during the strongest warm events. Our analysis also considers the El Niño Modoki events, for which the radiation flux patterns are shifted westward following the SST pattern.
      PubDate: 2017-08-11T12:26:46.522423-05:
      DOI: 10.1002/2017JC012900
       
  • Assimilation of coastal acoustic tomography data using an unstructured
           
    • Authors: Ze-Nan Zhu; Xiao-Hua Zhu, Xinyu Guo, Xiaopeng Fan, Chuanzheng Zhang
      Abstract: For the first time, we present the application of an unstructured triangular grid to the Finite-Volume Community Ocean Model using the ensemble Kalman filter scheme, to assimilate coastal acoustic tomography (CAT) data. The fine horizontal and vertical current field structures around the island inside the observation region were both reproduced well. The assimilated depth-averaged velocities had better agreement with the independent acoustic Doppler current profiler (ADCP) data than the velocities obtained by inversion and simulation. The root mean square difference (RMSD) between depth-averaged current velocities obtained by data assimilation and those obtained by ADCPs was 0.07 m s−1, which was less than the corresponding difference obtained by inversion and simulation (0.12 m s−1 and 0.17 m s−1, respectively). The assimilated vertical layer velocities also exhibited better agreement with ADCP than the velocities obtained by simulation. RMSDs between assimilated and ADCP data in vertical layers ranged from 0.02 to 0.14 m s−1, while RMSDs between simulation and ADCP data ranged from 0.08 to 0.27 m s−1. These results indicate that assimilation had the highest accuracy. Sensitivity experiments involving the elimination of sound transmission lines showed that missing data had less impact on assimilation than on inversion. Sensitivity experiments involving the elimination of CAT stations showed that the assimilation with four CAT stations was the relatively economical and reasonable procedure in this experiment. These results indicate that, compared with inversion and simulation, data assimilation of CAT data with an unstructured triangular grid is more effective in reconstructing the current field.
      PubDate: 2017-08-11T12:26:43.623956-05:
      DOI: 10.1002/2017JC012715
       
  • Variability and wind forcing of ocean temperature and thermal fronts in
           the slope water region of the Northwest Atlantic
    • Authors: Ingrid Peterson; Blair Greenan, Denis Gilbert, Dave Hebert
      Abstract: Subsurface temperatures in the Slope Water region of the Northwest Atlantic from Argo profiling floats and on the adjacent continental shelf from ship-based measurements are compared with the latitudinal position of the Shelf-Slope Front (SSF) and the Gulf Stream North Wall (GSNW). The Slope Water and shelf temperature anomalies at 200 m depth are in agreement for the period, 2002-2015. For the period 1978-2015, shelf temperatures are significantly correlated with the SSF position, and to a lesser extent with the GSNW position. Annual SSF position anomalies near the Grand Banks at 50-55°W lead anomalies to the west at 65-75°W by 1-2 years. Wind stress curl is compared with the annual change in the SSF and GSNW latitudinal positions, rather than with the positions directly. Changes in the mean position of the SSF are related to the wind stress curl pattern in the mid-Atlantic, with an 8-month lag. It is suggested that a wind pattern favoring a southward shift of the SSF is associated with a southward shift of the zero-curl line near 40°W, resulting in an expanded subpolar gyre and enhanced flow of Labrador Current Water westward from the Tail of the Grand Banks. However changes in the GSNW position are related to an NAO-like wind stress curl pattern in the eastern Atlantic in the winter-spring period, in agreement with other studies. High sea surface temperatures in the Gulf of Maine and on the Scotian Shelf in recent years can be largely attributed to positive local onshore wind anomalies.
      PubDate: 2017-08-11T12:26:36.570759-05:
      DOI: 10.1002/2017JC012788
       
  • Iceland-Scotland Overflow Water transport variability through the
           Charlie-Gibbs Fracture Zone and the impact of the North Atlantic Current
    • Authors: Amy Bower; Heather Furey
      Abstract: The Charlie-Gibbs Fracture Zone (CGFZ), a deep and wide gap in the Mid-Atlantic Ridge near 52°N, is a gateway between the eastern and western subpolar regions for the Atlantic Meridional Overturning Circulation (AMOC). In 2010-2012, an eight-mooring array of current meters and temperature/salinity sensors was installed across the CGFZ between 500 m and the sea floor to measure the mean transport of westward-flowing Iceland-Scotland Overflow Water (ISOW), and investigate the impact of the eastward-flowing North Atlantic Current (NAC) on ISOW transport variability. The 22-month record mean ISOW transport through the CGFZ, -1.7 ± 0.5 Sv (95% confidence interval), is 30% lower than the previously published estimate based on 13 months of current-only measurements, -2.4 Sv ± 1.2 Sv [Saunders, 1994]. The latter mean estimate may have been biased high due to the lack of continuous salinity measurements, although the two estimates are not statistically different due to strong mesoscale variability in both data sets. Empirical Orthogonal Function analysis and maps of satellite-derived absolute dynamic topography show that weak westward ISOW transport events and eastward reversals, are caused by northward meanders of the NAC, with its deep-reaching eastward velocities. These results add to growing evidence that a significant fraction of ISOW exits the Iceland Basin by routes other than the CGFZ.
      PubDate: 2017-08-05T10:20:26.00191-05:0
      DOI: 10.1002/2017JC012698
       
  • Deriving colored dissolved organic matter absorption coefficient from
           ocean color with a neural quasi-analytical algorithm
    • Authors: Jun Chen; Xianqiang He, Bin Zhou, Delu Pan
      Abstract: The objective of this study is to develop an approach to estimate the gelbstoff absorption coefficient (ag) from remote sensing reflectance (Rrs). This approach includes two components: the inherent optical properties are semi-analytically derived from the Rrs by a neural quasi-analytical algorithm (NQAA), and then the derivations are semi-analytically extended to ag estimations using a band difference approach. This method is then evaluated with the various type of ocean color data including synthetic, field measured, and satellite-observed data. The results show that the method can produce an excellent quantitative agreement between the estimated and known ag in ocean waters with a wide range of optical properties, while significantly reducing the effects of residual error in SeaWiFS Rrs, primarily from the imperfect atmospheric correction algorithm on the retrieval of ag in the clear open oceans. Furthermore, with the application of this new algorithm, the SeaWiFS ag products exhibit more spatially and temporally uniform results than the band ratio approach-based ag retrieval algorithm. These results indicate that the new algorithm is an encouraging approach to process ocean color images for ag retrieval, although a greater number of independent tests with in situ and satellite data are required to further validate and improve this approach.
      PubDate: 2017-08-03T07:46:08.680167-05:
      DOI: 10.1002/2017JC013115
       
  • Upper ocean cooling and air-sea fluxes under typhoons: A case study
    • Authors: Henry Potter; William M. Drennan, Hans C. Graber
      Abstract: Direct observations of ocean temperatures and air-sea energy exchange underneath three typhoons and a tropical storm encountered in the Philippine Sea during the 2010 Pacific typhoon season are examined. Data are reported from two buoys at 180 km apart with ocean temperatures recorded to 150 m and wind speeds up to 26 m s−1. A detailed examination of the cold wakes is used to determine the mechanisms though which the ocean cools. The result show that net cooling varied between storms by two orders of magnitude, accounting for between 9 and 1000 MJ m−2 of heat loss, and were a result of entrainment, advection, and surface fluxes. In some cases a marked temperature increase below the mixed layer occurred due to entrainment of warm water across the thermocline. Mixed layer temperatures decreases ranged from 0.35 to 1.6°C and found to be well predicted by typhoon translation speed and wind speed. Of the mixed layer heat loss, 12 to 47% could be attributed to enthalpy fluxes, the upper range of which is much greater than previous reports and related to storm intensity. Results are discussed in terms of their relevance to tropical cyclone and climate modeling.
      PubDate: 2017-08-03T07:40:32.953782-05:
      DOI: 10.1002/2017JC012954
       
  • Nitrogen enrichment and speciation in a coral reef lagoon driven by
           groundwater inputs of bird guano
    • Authors: Ashly McMahon; Isaac R. Santos
      Abstract: While the influence of river inputs on coral reef biogeochemistry has been investigated, there is limited information on nutrient fluxes related to submarine groundwater discharge (SGD). Here, we investigate whether significant saline groundwater-derived nutrient inputs from bird guano drive coral reef photosynthesis and calcification off Heron Island (Great Barrier Reef, Australia). We used multiple experimental approaches including groundwater sampling, beach face transects, and detailed time series observations to assess the dynamics and speciation of groundwater nutrients as they travel across the island and discharge into the coral reef lagoon. Nitrogen speciation shifted from nitrate-dominated groundwater (>90% of total dissolved nitrogen) to a coral reef lagoon dominated by dissolved organic nitrogen (DON; ∼86%). There was a minimum input of nitrate of 2.1 mmol m−2 d−1 into the lagoon from tidally-driven submarine groundwater discharge estimated from a radon mass balance model. An independent approach based on the enrichment of dissolved nutrients during isolation at low tide implied nitrate fluxes of 5.4 mmol m−2 d−1. A correlation was observed between nitrate and daytime net ecosystem production and calcification. We suggest that groundwater nutrients derived from bird guano may offer a significant addition to oligotrophic coral reef lagoons and drive ecosystem productivity and the coastal carbon cycle near Heron Island. The large input of groundwater nutrients in Heron Island may serve as a natural ecological analogue to other coral reefs subject to large nutrient inputs from anthropogenic sources.
      PubDate: 2017-08-03T07:40:26.710949-05:
      DOI: 10.1002/2017JC012929
       
  • Coastal ocean circulation during Hurricane Sandy
    • Authors: Travis Miles; Greg Seroka, Scott Glenn
      Abstract: Hurricane Sandy (2012) was the second costliest tropical cyclone to impact the United States and resulted in numerous lives lost due to its high winds and catastrophic storm surges. Despite its impacts little research has been performed on the circulation on the continental shelf as Sandy made landfall. In this study integrated ocean observing assets and regional ocean modeling were used to investigate the coastal ocean response to Sandy's large wind field. Sandy's unique cross-shelf storm track, large size, and slow speed resulted in along-shelf wind stress over the coastal ocean for nearly 48 hours before the eye made landfall in southern New Jersey. Over the first inertial period (∼18 hours) this along-shelf wind stress drove onshore flow in the surface of the stratified continental shelf and initiated a two-layer downwelling circulation. During the remaining storm forcing period a bottom Ekman layer developed and the bottom Cold Pool was rapidly advected offshore ∼70 kilometers. This offshore advection removed the bottom Cold Pool from the majority of the shallow continental shelf and limited ahead-of-eye-center sea surface temperature (SST) cooling, which has been observed in previous storms on the MAB such as Hurricane Irene (2011). This cross-shelf advective process has not been observed previously on continental shelves during tropical cyclones and highlights the need for combined ocean observing systems and regional modeling in order to further understand the range of coastal ocean responses to tropical cyclones.
      PubDate: 2017-07-26T10:21:02.109276-05:
      DOI: 10.1002/2017JC013031
       
  • Predicting the consequence of natural and chemical dispersion for oil
           slick size over time
    • Authors: Marieke Zeinstra-Helfrich; Wierd Koops, Albertinka J. Murk
      Abstract: Application of dispersants aims to enhance the natural dispersion process in order to reduce the size of the slick and the amount of oil at the surface. This study presents an approach for modelling the development of the surface oil slick as a function of the wind speed, oil viscosity and dispersant application. We modelled the oil slick mass distribution across a transect through the slick over time taking into account the continuous entrainment of oil, resurfacing process of the different oil droplet size classes and horizontal transport. Outcomes show distinctively different oil slick features, depending on how favorable conditions are for dispersion. A large comet shaped slick is formed in the case of sub-optimal dispersion. Optimal dispersion yields a small surface oil slick, with a large mass of oil suspended. The benefit of dispersants is limited to in conditions with sub-optimal natural dispersion, with the exception of extremely unfavorable conditions in which the slick size would be increased.The oil slick length, fraction of oil still floating, lifetime of the slick and wind drift are highly influenced by wind speed and related mixing conditions, and to a lesser extent by oil properties. In the newly defined ‘Dispersability Factor' (DF) the oil slick properties and environmental conditions can be combined into one value that correlates with the simulation outcomes and therefore can be used as an indicator of favorability of natural dispersion and likelihood of added value of chemical dispersion.
      PubDate: 2017-07-26T10:20:26.873245-05:
      DOI: 10.1002/2017JC012789
       
  • The role of wind gusts in upper ocean diurnal variability
    • Authors: Donata Giglio; Sarah T. Gille, Aneesh C. Subramanian, San Nugyen
      Abstract: Upper ocean processes play a key role in air-sea coupling, with variability on both short and long timescales. The diurnal cycle associated with diurnal solar insolation and night-time cooling, may act, along with stochastic wind variability, on upper ocean temperatures and stratification resulting in a diurnal warm layer and a nonlinear rectified effect on longer timescales. This study describes diurnal changes in upper ocean temperature for a location in the equatorial Indian Ocean, using observations from the Dynamics of the Madden-Julian Oscillation field campaign, a high vertical resolution 1-D process model, and a diurnal cycling scheme [Large and Caron, 2015]. Solar forcing is the main driver of diurnal variability in upper ocean temperature and stratification. Yet, except during nighttime convection, winds with variability on the order of hours (here referred to as “wind gusts”) regulate how fast surface water is mixed to greater depths when daily mean winds are weak. Wind gusts are much stronger than diurnal winds. Even using stochastic wind gusts but no diurnal winds as input in a 1-D process model yields an estimate of diurnal temperature that compares well with observations.A new version of the Large and Caron [2015] scheme (LC2015) provides an estimate of upper ocean diurnal temperature that is consistent with observations. LC2015 has the advantage of being suitable for implementation in a climate model, with the goal to improve SST estimates, hence the simulated heat flux at the air-sea interface. Yet LC2015 is not very sensitive to the inclusion or omission of the high-frequency component of the wind.
      PubDate: 2017-07-24T17:07:33.301736-05:
      DOI: 10.1002/2017JC012794
       
  • The evolution of scaling laws in the sea ice floe size distribution
    • Authors: Christopher Horvat; Eli Tziperman
      Abstract: The sub-gridscale floe size and thickness distribution (FSTD) is an emerging climate variable, playing a leading-order role in the coupling between sea ice, the ocean, and the atmosphere. The FSTD, however, is difficult to measure given the vast range of horizontal scales of individual floes, leading to the common use of power-law scaling to describe it. The evolution of a coupled mixed-layer-FSTD model of a typical marginal ice zone is explicitly simulated here, to develop a deeper understanding of how processes active at the floe scale may or may not lead to scaling laws in the floe size distribution. The time evolution of mean quantities obtained from the FSTD (sea ice concentration, mean thickness, volume) is complex even in simple scenarios, suggesting that these quantities, which affect climate feedbacks, should be carefully calculated in climate models. The emergence of FSTDs with multiple separate power-law regimes, as seen in observations, is found to be due to the combination of multiple scale-selective processes. Limitations in assuming a power-law FSTD are carefully analyzed, applying methods used in observations to FSTD model output. Two important sources of error are identified that may lead to model biases: one when observing an insufficiently small range of floe sizes, and one from the fact that floe-scale processes often do not produce power-law behavior. These two sources of error may easily lead to biases in mean quantities derived from the FSTD of greater than 100%, and therefore biases in modeled sea ice evolution.
      PubDate: 2017-07-05T08:26:41.477368-05:
      DOI: 10.1002/2016JC012573
       
  • Impact of Sea Spray on the Yellow and East China Seas Thermal Structure
           during the passage of Typhoon Rammasun (2002)
    • Authors: Lianxin Zhang; Xuefeng Zhang, P. C. Chu, Changlong Guan, Hongli Fu, Guofang Chao, Guijun Han, Wei Li
      Abstract: Strong winds lead to large amounts of sea spray in the lowest part of the atmospheric boundary layer. The spray droplets affect the air-sea heat fluxes due to their evaporation and the momentum due to the change of sea surface, and in turn change the upper ocean thermal structure. In this study, impact of sea spray on upper ocean temperatures in the Yellow and East China Seas (YES) during typhoon Rammasun's passage is investigated using the POMgcs ocean model with a sea spray parameterization scheme, in which the sea spray-induced heat fluxes are based on an improved Fairall's sea spray heat fluxes algorithm, and the sea spray-induced momentum fluxes are derived from an improved COARE version 2.6 bulk model.The distribution of the sea spray mediated turbulent fluxes was primarily located at Rammasun eye-wall region, in accord with the maximal wind speeds regions. When Rammasun enters the Yellow sea, the sea spray mediated latent (sensible) heat flux maximum is enhanced by 26% (13.5%) compared to that of the interfacial latent (sensible) heat flux. The maximum of the total air-sea momentum fluxes is enhanced by 43% compared to the counterpart of the interfacial momentum flux. Furthermore, the sea spray plays a key role in enhancing the intensity of the typhoon-induced “cold suction” and “heat pump” processes. When the effect of sea spray is considered, the maximum of the sea surface cooling in the right side of Rammasun's track is increased by 0.5°C, which is closer to the available satellite observations.
      PubDate: 2017-06-09T06:48:46.329082-05:
      DOI: 10.1002/2016JC012592
       
  • Modeling postconvective submesoscale coherent vortices in the northwestern
           Mediterranean Sea
    • Authors: P. Damien; A. Bosse, P. Testor, P. Marsaleix, C. Estournel
      Abstract: For the first time, the formation of Submesoscale Coherent Vortices (SCVs) during intermediate and deep convection events is documented in a realistic high resolution (1 km) numerical simulation of the oceanic circulation in the northwestern Mediterranean Sea. Winter intermediate and deep convection leads to the formation of anticyclonic and cyclonic eddies with lifetimes exceeding one year. By focusing on three typical eddies, the main characteristics of such vortices are discussed. The anticyclonic eddies are typical of SCVs observed in deep convection areas so far. They are characterized by a small radius (∼ 6.5 km) and orbital peak velocities of about 7 cm/s located at great depth (∼ 1500 m) or intermediate depth (∼ 500 m). The cyclonic vortices show very similar characteristics, such as a high Rossby number (∼ 0.4), but with surface-intensified structures. The long lifetimes of both anticyclonic and cyclonic eddies reflect very slow diffusive processes between their core and their surroundings and a strong resistance to external perturbations. These long-lived eddies are found to participate in the spreading of a significant portion (from 15 to 35%) of the convected waters in the Gulf of Lions and contribute to the ventilation of the deep basin.
      PubDate: 2017-03-31T13:51:16.311955-05:
      DOI: 10.1002/2016JC012114
       
  • Physical and biogeochemical controls of the phytoplankton blooms in
           North-Western Mediterranean Sea: A multiplatform approach over a complete
           annual cycle (2012–2013 DEWEX experiment)
    • Authors: Nicolas Mayot; Fabrizio D'Ortenzio, Vincent Taillandier, Louis Prieur, Orens Pasqueron de Fommervault, Hervé Claustre, Anthony Bosse, Pierre Testor, Pascal Conan
      Abstract: The North Western Mediterranean Sea exhibits recurrent and significant autumnal and spring phytoplankton blooms. The existence of these two blooms coincide with typical temperate dynamics. To determine the potential control of physical and biogeochemical factors on these phytoplankton blooms, data from a multiplatform approach (combining ships, Argo and BGC-Argo floats, and bio-optical gliders) were analyzed in association with satellite observations in 2012-2013. The satellite framework allowed a simultaneous analysis over the whole annual cycle of in situ observations of mixed layer depth, photosynthetical available radiation, particle backscattering, nutrients (nitrate and silicate) and chlorophyll-a concentrations. During the year 2012-2013, satellite ocean color observations, confirmed by in situ data, have revealed the existence of two areas (or bioregions) with comparable autumnal blooms but contrasting spring blooms. In both bioregions, the ratio of the euphotic zone (defined as the isolume 0.415 mol photons m−2 d−1, Z0.415) and the MLD identified the initiation of the autumnal bloom, as well as the maximal annual increase in [Chl-a] in spring. In fact, the autumnal phytoplankton bloom might be initiated by mixing of the summer shallowing deep chlorophyll maximum, while the spring restratification (when Z0.415/MLD ratio became > 1) might induce surface phytoplankton production that largely overcomes the losses. Finally, winter deep convection events that took place in one of the bioregions induced higher net accumulation rate of phytoplankton in spring associated with a diatom-dominated phytoplankton community principally. We suggest that very deep winter MLD lead to an increase in surface silicates availability, which favored the development of diatoms.
      PubDate: 2017-03-31T13:50:32.70281-05:0
      DOI: 10.1002/2016JC012052
       
  • Influence of the phytoplankton community structure on the spring and
           annual primary production in the North-Western Mediterranean Sea
    • Authors: Nicolas Mayot; Fabrizio D'Ortenzio, Julia Uitz, Bernard Gentili, Joséphine Ras, Vincenzo Vellucci, Melek Golbol, David Antoine, Hervé Claustre
      Abstract: Satellite ocean color observations revealed that unusually deep convection events in 2005, 2006, 2010 and 2013 led to an increased phytoplankton biomass during the spring bloom over a large area of the North-Western Mediterranean Sea (NWM). Here we investigate the effects of these events on the seasonal phytoplankton community structure, we quantify their influence on primary production, and we discuss the potential biogeochemical impact. For this purpose, we compiled in situ phytoplankton pigment data from five ship surveys performed in the NWM and from monthly cruises at a fixed station in the Ligurian Sea. We derived primary production rates from a light-photosynthesis model applied to these in situ data. Our results confirm that the maximum phytoplankton biomass during the spring bloom is larger in years associated with intense deep convection events (+ 51%). During these enhanced spring blooms, the contribution of diatoms to total phytoplankton biomass increased (+ 33%), as well as the primary production rate (+ 115%). The occurrence of a highly productive bloom is also related to an increase in the phytoplankton bloom area (+ 155%), and in the relative contribution of diatoms to primary production (+ 63%). Therefore, assuming that deep convection in the NWM could be significantly weakened by future climate changes, substantial decreases in the spring production of organic carbon and of its export to deep waters can be expected. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-17T19:15:43.10201-05:0
      DOI: 10.1002/2016JC012668
       
  • Observations of flooding and snow-ice formation in a thinner Arctic sea
           ice regime during the N-ICE2015 campaign: Influence of basal ice melt and
           storms
    • Authors: Christine Provost; Nathalie Sennéchael, Jonas Miguet, Polona Itkin, Anja Rösel, Zoé Koenig, Nicolas Villacieros-Robineau, Mats A. Granskog
      Abstract: Seven ice mass balance instruments deployed near 83°N on different first-year and second-year ice floes, representing variable snow and ice conditions, documented the evolution of snow and ice conditions in the Arctic Ocean north of Svalbard in Jan-Mar 2015. Frequent profiles of temperature and thermal diffusivity proxy were recorded to distinguish changes in snow depth and ice thickness with 2 cm vertical resolution. Four instruments documented flooding and snow-ice formation. Flooding was clearly detectable in the simultaneous changes in thermal diffusivity proxy, increased temperature and heat propagation through the underlying ice. Slush then progressively transformed into snow-ice. Flooding resulted from two different processes; i) after storm-induced break-up of snow-loaded floes and ii) after loss of buoyancy due to basal ice melt. In the case of break-up, when the ice was cold and not permeable, rapid flooding, probably due to lateral intrusion of seawater, led to slush and snow-ice layers at the ocean freezing temperature (-1.88°C). After the storm the instruments documented basal sea-ice melt over warm Atlantic waters and ocean-to-ice heat flux peaked at up to 400 Wm−2. The warm ice was then permeable and flooding was more gradual probably involving vertical intrusion of brines and led to colder slush and snow-ice (-3°C). The N-ICE2015 campaign provided the first documentation of significant flooding and snow-ice formation in the Arctic ice pack as the slush partially refroze. Snow-ice formation may become a more-frequently observed process in a thinner-ice Arctic. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-14T03:35:35.750566-05:
      DOI: 10.1002/2016JC012011
       
  • Issue Information
    • Pages: 6965 - 6967
      PubDate: 2017-10-17T07:51:10.048165-05:
      DOI: 10.1002/jgrc.21932
       
 
 
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