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Publisher: American Geophysical Union (AGU)   (Total: 17 journals)

Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 26, SJR: 2.56, h-index: 69)
Geophysical Research Letters     Full-text available via subscription   (Followers: 54, SJR: 3.493, h-index: 157)
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J. of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 26)
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Paleoceanography     Full-text available via subscription   (Followers: 3, SJR: 3.22, h-index: 88)
Radio Science     Full-text available via subscription   (Followers: 3, SJR: 0.959, h-index: 51)
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Water Resources Research     Full-text available via subscription   (Followers: 106, SJR: 2.189, h-index: 121)
Journal Cover   Journal of Geophysical Research : Oceans
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   ISSN (Online) 2169-9291
   Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • Temporal variation and stoichiometric ratios of organic matter
           remineralization in bottom waters of the northern Gulf of Mexico during
           late spring and summer
    • Abstract: An improved extended optimum multi‐parameter (eOMP) analysis was applied to hydrographic (temperature and salinity), and water chemistry data, including dissolved oxygen (O2), nutrients (nitrate plus nitrite, phosphate, and silicate), dissolved inorganic carbon (DIC), and total alkalinity (TAlk) data collected during late spring and summer from 2006 to 2012 in bottom waters off the Louisiana coast, to explore the dynamics and stoichiometry of DIC production during the development and maintenance of summer hypoxia. Our analysis demonstrated that DIC in bottom water was relatively low from April to June, but increased significantly in July, peaked in August, and dropped slightly in September. Furthermore, DIC production resulted from both aerobic organic carbon (OC) respiration and denitrification, as well as substantial loss due to vertical mixing with surface water. The average summer gross OC respiration rate was estimated to be 0.19 g C m−2 d−1, with the highest values occurring in late summer when hypoxic conditions dominated. We also found that Corg/N/P/‐O2 remineralization ratios for aerobic respiration were generally consistent with the classic Redfield ratio (106/16/1/138) except individual C/N and C/P ratios were slightly lower, indicating that marine OC was the major source of the DIC production in the bottom water. This study quantified the role of temporal bottom‐water microbial respiration to seasonal DIC dynamics and provided a means for studying the stoichiometry of biogeochemical processes in coastal waters. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-25T17:44:47.081679-05:
      DOI: 10.1002/2015JC011453
  • Shelf/fjord exchange driven by coastal‐trapped waves in the Arctic
    • Authors: Mark E. Inall; Frank Nilsen, Finlo R. Cottier, Ragnhild Daae
      Abstract: In this article we show that the class of low frequency (sub‐inertial) waves known as coastal‐trapped waves (CTWs) are a significant agent of water volume exchange in a west Svalbard fjord, and by extension more widely along the west Svalbard and east Greenland margins where similar conditions prevail. We show that CTWs generated by weather systems passing across the sloping topography of the shelf break propagate into the fjord, steered by the topography of an across‐shelf trough. The CTWs have characteristic periods of ∼two days, set by the passage time of weather systems. Phase speeds and wavelengths vary seasonally by a factor of two, according to stratification: winter (summer) values are Cp = 0.25 ms−1 (0.5 ms−1) and λ = 40 km (84 km). CTW‐induced flow velocities in excess of 0.2 ms−1 at 100 m water depth are recorded. Observationally‐scaled CTW model results allow their explicit role in volume exchange to be quantified. Of the estimated exchange terms, estuarine exchange is weakest (Qest=0.62×103 m3s−1), followed by barotropic tidal pumping (Qbt=2.5×103 m3s−1), with intermediary exchange dominating (Qi=2.4×104 m3s−1). Oscillatory flows display greatest activity in the one to five day period band, and CTW activity is identified as the likely source of variability in the 40 to 60 hour period band. Within that band intermediary exchange driven by CTWs is estimated as QiCTW_ave=0.82×104 m3s−1; an exchange rate exceeding both barotropic and estuarine exchange estimates. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-23T18:27:05.842741-05:
      DOI: 10.1002/2015JC011277
  • Vertical scales and dynamics of eddies in the Arctic Ocean's Canada Basin
    • Abstract: A decade of moored measurements from the Arctic Ocean's northwestern Beaufort Gyre (collected as a component of the Beaufort Gyre Exploration Project) are analyzed to examine the range of mesoscale eddies over the water column, and the dynamical processes that set eddy vertical scales. A total of 58 eddies were identified in the moored record, all anticyclones with azimuthal velocities ranging from 10 cm/s to 43 cm/s. These are divided into three classes based on core depths. Shallow eddies (core depths around 120 m) are shown to be vertically confined by the strong stratification of the halocline; typical thicknesses are around 100 m. Deep eddies (core depths around 1200 m) are much taller (thicknesses around 1300 m) owing to the weaker stratification at depth, consistent with a previous study. Eddies centered around mid‐depths all have two cores (vertically aligned and separated in depth) characterized by velocity maxima and anomalous temperature and salinity properties. One core is located at the base of the halocline (around 200 m depth) and the other at the depth of the Atlantic Water layer (around 400 m depth). These double‐core eddies have vertical scales between those of the shallow and deep eddies. The strongly decreasing stratification in their depth range motivates a derivation for the quasi‐geostrophic adjustment of a nonuniformly stratified water column to a potential vorticity anomaly. The result aids in interpreting the dynamics and origins of the double‐core eddies, providing insight into transport across a major water mass front separating Canadian and Eurasian Water. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-23T18:26:54.008784-05:
      DOI: 10.1002/2015JC011251
  • Short‐term sea ice forecasting: An assessment of ice concentration
           and ice drift forecasts using the U.S. Navy's Arctic Cap Nowcast/Forecast
    • Authors: David A. Hebert; Richard A. Allard, E. Joseph Metzger, Pamela G. Posey, Ruth H. Preller, Alan J. Wallcraft, Michael W. Phelps, Ole Martin Smedstad
      Abstract: In this study the forecast skill of the U.S. Navy operational Arctic sea ice forecast system, the Arctic Cap Nowcast/Forecast System (ACNFS), is presented for the period Feb 2014 – June 2015. ACNFS is designed to provide short term, 1‐7 day forecasts of Arctic sea ice and ocean conditions. Many quantities are forecast by ACNFS; the most commonly used include ice concentration, ice thickness, ice velocity, sea surface temperature, sea surface salinity, and sea surface velocities. Ice concentration forecast skill is compared to a persistent ice state and historical sea ice climatology. Skill scores are focused on areas where ice concentration changes by ±5% or more, and are therefore limited to primarily the marginal ice zone. We demonstrate that ACNFS forecasts are skillful compared to assuming a persistent ice state, especially beyond 24 hours. ACNFS is also shown to be particularly skillful compared to a climatologic state for forecasts up to 102 hours. Modeled ice drift velocity is compared to observed buoy data from the International Arctic Buoy Programme. A seasonal bias is shown where ACNFS is slower than IABP velocity in the summer months and faster in the winter months. In February 2015 ACNFS began to assimilate a blended ice concentration derived from Advanced Microwave Scanning Radiometer 2 (AMSR2) and the Interactive Multisensor Snow and Ice Mapping System (IMS). Preliminary results show that assimilating AMSR2 blended with IMS improves the short‐term forecast skill and ice edge location compared to the independently derived National Ice Center Ice Edge product. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-23T18:26:40.532518-05:
      DOI: 10.1002/2015JC011283
  • Remote alongshore winds drive variability of the California Undercurrent
           off the British Columbia‐Washington coast
    • Authors: Richard E. Thomson; Maxim V. Krassovski
      Abstract: The California Undercurrent transports warm, salty, nutrient‐rich, oxygen‐depleted water along the continental slope from the equatorial Pacific to the Aleutian Islands. We use multi‐year acoustic Doppler current profiler records collected simultaneously at two mooring sites off Vancouver Island to detail the regional structure of the undercurrent and to show that much of its variability is attributable to the passage of remotely forced, coastal‐trapped waves. We also document two subsurface currents missed by earlier current measurements. The undercurrent becomes evident in spring, intensifies through summer and fall, and merges with the wind‐driven poleward surface flow in winter. During intensification at the southern mooring site (A1), the undercurrent shoals from 250±50 m in early summer to 150±50 m depth in late fall. At the northern site (BP2), 225 km to the northwest of A1, the current is weaker and maintains a year‐round depth of 150±50 m. Temporal variability in the undercurrent velocity attains highest coherence with winds along the southern Oregon‐northern California coast, with peak coherence occurring for “synoptic” (10‐40 day period) alongshore winds off Cape Blanco in southern Oregon. The undercurrent lag of 3±2 days relative to the Cape Blanco winds at synoptic periods is consistent with low mode, poleward propagating, coastally trapped waves. For periods > 40 days, the wind‐current coherence remains high for winds off the Oregon‐California coast but lags are often negative, indicating possible forcing by alongshore baroclinic pressure gradients. At interannual time scales, the undercurrent variations have links to climate‐scale processes in the equatorial Pacific. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-23T18:26:31.617-05:00
      DOI: 10.1002/2015JC011306
  • Time variability in the annual cycle of sea ice thickness in the
           Transpolar Drift
    • Abstract: The annual cycle of modal and mean sea ice thickness was derived from upward looking sonar ice thickness observations (1990‐2011) in Fram Strait. The average annual peak‐to‐trough amplitude of the mode of 0.54 m is superimposed on interannual variability with peak‐to‐trough amplitudes of 0.73 m on timescales of 6‐8 years, which again is superimposed on a long‐term trend of ‐0.55 m/decade over the observation period. The long‐term trend is stronger for April than for August, the average months of maximum and minimum modal thickness. As a result, the annual peak‐to‐trough modal thickness amplitude was reduced by 30% between the 1990s and the 2000s. The average annual peak‐to‐trough amplitude of the mean ice thickness of 1.20 m is also superimposed on interannual variability, with as much as 0.97 m thickness change over only 3 years. These two modes of variability are superimposed on a long‐term trend of ‐0.35 m/decade through the entire data set. In contrast to the modal thickness, the long‐term trend is weaker for the average month of maximum mean thickness (June), than for the average month of minimum (September). Therefore, the annual peak‐to‐trough amplitude of the mean ice thickness increased by 14% between the 1990s and the 2000s. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-19T10:44:56.994834-05:
      DOI: 10.1002/2015JC011102
  • Long‐term variations in global sea level extremes
    • Abstract: Decadal to multi‐decadal variations in sea level extremes unrelated to mean sea level changes have been investigated using long tide gauge records distributed worldwide. A state space approach has been applied that provides robust solutions and uncertainties of the time evolving characteristics of extremes, allowing for data gaps and uneven sampling, both common features of historical sea level time series. Two different models have been formulated for the intensity and for the occurrence of extreme sea level events and have been applied independently to each tide gauge record. Our results reveal two key findings: first, the intensity and the frequency of occurrence of extreme sea levels unrelated to mean sea level vary coherently on decadal scales in most of the sites examined (63 out of 77) and, second, extreme sea level changes are regionally consistent, thus pointing towards a common large scale forcing. This variability of extremes associated with climate drivers should be considered in the framework of climate change studies. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-19T10:44:51.553413-05:
      DOI: 10.1002/2015JC011173
  • Interannual variability of the Indonesian Throughflow transport: A revisit
           based on 30 year expendable bathythermograph data
    • Abstract: Based on 30‐year repeated expendable bathythermograph (XBT) deployments between Fremantle, Western Australia and the Sunda Strait, Indonesia from 1984 to 2013, interannual variability of geostrophic transport of the Indonesian Throughflow (ITF) and its relationships with El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are investigated. The IOD induced coastal Kelvin waves propagate along the Sumatra‐Java coast of Indonesia, and ENSO induced coastal Kelvin waves propagate along the northwest coast of Australia, both influencing interannual variations of the ITF transport. The ITF geostrophic transport is stronger during La Niña phase and weaker during El Niño phase, with the Niño3.4 index leading the ITF variability by 7 months. The Indian Ocean wind variability associated with the IOD to a certain extent offset the Pacific ENSO influences on the ITF geostrophic transport during the developing and mature phases of El Niño and La Niña, due to the co‐varying IOD variability with ENSO. The ITF geostrophic transport experiences a strengthening trend of about 1 Sv every 10 years over the study period, which is mostly due to a response to the strengthening of the trade winds in the Pacific during the climate change hiatus period. Decadal variations of the temperature‐salinity relationships need to be considered when estimating the geostrophic transport of the ITF using XBT data. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-19T10:43:50.982576-05:
      DOI: 10.1002/2015JC011351
  • Seasonal variability of nutrient concentrations in the Mediterranean Sea:
           Contribution of Bio‐Argo floats
    • Abstract: In 2013, as part of the French NAOS (Novel Argo Oceanic observing System) program, five profiling floats equipped with nitrate sensors (SUNA‐V2) together with CTD and bio‐optical sensors were deployed in the Mediterranean Sea. At present day, more than 500 profiles of physical and biological parameters were acquired, and significantly increased the number of available nitrate data in the Mediterranean Sea. Results obtained from floats confirm the general view of the basin, and the well‐known west‐to‐east gradient of oligotrophy. At seasonal scale, the north western Mediterranean displays a clear temperate pattern sustained by both deep winter mixed layer and shallow nitracline. The other sampled areas follow a subtropical regime (nitracline depth and mixed layer depth are generally decoupled). Float data also permit to highlight the major contribution of high frequency processes in controlling the nitrate supply during winter in the north western Mediterranean Sea, and in altering the nitrate stock in subsurface in the eastern basin. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-19T10:39:14.016906-05:
      DOI: 10.1002/2015JC011103
  • Do East Australian Current anticyclonic eddies leave the Tasman Sea?
    • Authors: Gabriela S. Pilo; Peter R. Oke, Tatiana Rykova, Richard Coleman, Ken Ridgway
      Abstract: Using satellite altimetry and high‐resolution model output we analyse the pathway of large, long‐lived anticyclonic eddies that originate near the East Australian Current (EAC) separation point. We show that 25‐30% of these eddies propagate southward, around Tasmania, leave the Tasman Sea, and decay in the Great Australian Bight. This pathway has not been previously documented owing to poor satellite sampling off eastern Tasmania. As eddies propagate southward, they often “stall” for several months at near‐constant latitude. Along the pathway eddies become increasingly barotropic. Eddy intensity is primarily influenced by merging with other eddies and a gradual decay otherwise. Surface temperature anomaly associated with anticyclonic eddies changes as they propagate, while surface salinity anomaly tends to remain relatively unchanged as they propagate. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-19T10:39:03.228381-05:
      DOI: 10.1002/2015JC011026
  • Internal lee wave closures: Parameter sensitivity and comparison to
    • Abstract: This paper examines two internal lee wave closures that have been used together with ocean models to predict the time‐averaged global energy conversion rate into lee waves and dissipation rate associated with lee waves and topographic blocking: the Garner (2005; “G05”) scheme and the Bell (1975; “B75”) theory. The closure predictions in two Southern Ocean regions where geostrophic flows dominate over tides are examined and compared to microstructure profiler observations of the turbulent kinetic energy dissipation rate, where the latter are assumed to reflect the dissipation associated with topographic blocking and generated lee wave energy. It is shown that, when applied to these Southern Ocean regions, the two closures differ most in their treatment of topographic blocking. For several reasons, pointwise validation of the closures is not possible using existing observations, but horizontally averaged comparisons between closure predictions and observations are made. When anisotropy of the underlying topography is accounted for, the two horizontally averaged closure predictions near the seafloor are approximately equal. The dissipation associated with topographic blocking is predicted by the G05 scheme to account for the majority of the depth‐integrated dissipation over the bottom 1000 meters of the water column, where the horizontally averaged predictions lie well within the spatial variability of the horizontally averaged observations. Simplifications made by the G05 scheme that are inappropriate for the oceanic context, together with imperfect observational information, can partially account for the prediction‐observation disagreement, particularly in the upper water column. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-19T10:38:43.204801-05:
      DOI: 10.1002/2015JC010892
  • A new application of conditional nonlinear optimal perturbation approach
           to boundary condition uncertainty
    • Authors: Qiang Wang; Mu Mu
      Abstract: The conditional nonlinear optimal perturbation (CNOP) approach was mainly used to investigate the effects of the uncertainties in initial condition and model parameters on model results. This study presents a new application of the CNOP approach to the investigation of the effects of boundary condition uncertainty. Specifically, we first give the general formulation of the CNOP approach for uncertainties of initial and boundary conditions and model parameters. The method is then applied to analyze the effects of nutrient perturbations at the bottom boundary of the water column on the modeled deep chlorophyll maximum (DCM) using an ocean ecosystem model. The results show that nutrient perturbations at the bottom boundary have significant impacts on the modeled DCM. Interestingly, the approach also reveals that nonlinear processes play important roles in the evolution of phytoplankton perturbations caused by nutrient perturbations at the bottom boundary. This implies that the CNOP approach is useful for investigating the effects of boundary condition uncertainty. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-19T10:38:01.196953-05:
      DOI: 10.1002/2015JC011095
  • A 1.5D anisotropic sigma‐coordinate thermal stress model of
           landlocked sea ice in the Canadian Arctic Archipelago
    • Authors: Y. Hata; L. B. Tremblay
      Abstract: We present a 1.5D thermal stress model that takes into account the effect of land confinement, which causes anisotropy in thermal stresses. To this end, we fix the total strain in the direction perpendicular to the coastline to its value at landlocked ice onset. This prevents thermal expansion in the direction perpendicular to the coastline and therefore induces larger thermal stresses in this direction. The simulated stresses best match the observations, when a Young's Modulus of 0.5 GPa and a relaxation time constant of 8 days are used. This simulation gives root mean square errors of 13.0 kPa and 13.1 kPa (∼15%) in the major and minor principal stresses, respectively. The simulated anisotropic component of thermal stress also generally agrees with observations. The optimal Young's Modulus is in the low range of reported values in the literature and the optimal relaxation time constant (8 days) is larger than the largest relaxation time constant reported in the literature (5 days). A series of experiments are done to examine the model sensitivity to vertical resolution, snow cover, and the parameterizations of Young's Modulus and viscous creep. Results show that a minimum of one and three layers in the snow and ice, respectively, is required to simulate the thermal stresses within 15% error of the value assessed with the higher resolution control simulation. This highlights the importance of resolving the internal snow and ice vertical temperature profile in order to properly model the thermal stresses of sea ice. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-19T10:32:02.401093-05:
      DOI: 10.1002/2015JC010820
  • Influence of varying upper ocean stratification on coastal
           near‐inertial currents
    • Authors: Sung Yong Kim; Alexander L. Kurapov, P. Michael Kosro
      Abstract: The influence of varying horizontal and vertical stratification in the upper layer [O (10) m] associated with riverine waters and seasonal atmospheric fluxes on coastal near‐inertial currents is investigated with remotely sensed and in‐situ observations of surface and subsurface currents, and realistic numerical model outputs off the coast of Oregon. Based on numerical simulations with and without the Columbia River (CR) during summer, the directly wind‐forced near‐inertial surface currents are enhanced by 30% to 60% when the near‐surface layer has a stratified condition due to riverine water inputs from the CR. Comparing model results without the CR for summer and winter conditions indicates that the directly wind‐forced near‐inertial surface current response to a unit wind forcing during summer are 20% to 70% stronger than those during winter depending on the cross‐shore location, which is in contrast to the seasonal patterns of both mixed layer depth and amplitudes of near‐inertial currents. The model simulations are used to examine aspects of coastal inhibition of near‐inertial currents, manifested in their spatial coherence in the cross‐shore direction, where the phase propagates upward over the continental shelf, bounces at the coast, and continues increasing upward offshore (toward surface) and then downward offshore at the surface, with magnitudes and length scales in the near‐surface layer increasing offshore. This pattern exhibits a particularly well‐organized structure during winter. Similarly, the ray paths of clockwise near‐inertial internal waves are consistent with the phase propagation of coherence, showing the influence of upper layer stratification and coastal inhibition. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-18T14:07:51.235153-05:
      DOI: 10.1002/2015JC011153
  • An ocean‐biology‐induced negative feedback on ENSO as derived
           from a hybrid coupled model of the tropical Pacific
    • Abstract: Biological conditions in the tropical Pacific Ocean (e.g., phytoplankton biomass) are strongly regulated by physical changes that are associated with the El Niño‐Southern Oscillation (ENSO). The existence and variation of phytoplankton biomass act to modulate the vertical penetration of the incoming sunlight into the upper ocean, which causes an ocean biology‐induced heating (OBH) effect on the climate system. Previously, the penetration depth of solar radiation in the upper ocean (Hp) has been defined to describe the related bio‐climate connections. An empirical model for interannual Hp variability that is parameterized in terms of its relationship with the sea surface temperature (SST) in the tropical Pacific was derived from remotely sensed ocean color data and is incorporated into a hybrid coupled model (HCM) to represent the OBH effects. In this paper, several HCM experiments are performed to demonstrate the bio‐feedback onto the ENSO, including a climatological Hp run (in which Hp is prescribed as only seasonally varying), interannual Hp runs (with different intensities of the interannually varying OBH effects), and a run in which the sign of the OBH effect is reversed. Significant modulating impacts on the interannual variability are found in the HCM and are characterized by a negative feedback between the ocean biology and the climate system in the tropical Pacific; the stronger the OBH feedback, the weaker the interannual variability. The processes that are involved in the feedback are analyzed. The SST is modulated indirectly by dynamic ocean processes that are induced by OBH. The significance and implication of the OBH effects are discussed in terms of their roles in ENSO variability and the model biases in the tropical Pacific. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-18T14:07:34.29084-05:0
      DOI: 10.1002/2015JC011305
  • Assessing changes in extreme sea levels along the coast of China
    • Authors: Jianlong Feng; Hans von Storch, Wensheng Jiang, Ralf Weisse
      Abstract: Hourly tide‐gauge data along the coast of China are used to evaluate changes in extreme water levels in the past several decades. Mean sea level, astronomical tide, non‐tidal component and the tide‐surge interaction was analyzed separately to assess their roles in the changes of extreme sea levels. Mean sea level at five tide gauges, Kanmen, Keelung, Zhapo, Xiamen and Quarrybay, show significant increasing trends during the past decades (1954‐2013) with a rate of about 1.4 – 3.5 mm/year. At Keelung, Kaohsiung and Quarrybay the mean high waters increased during 1954‐2013 with a rate from 0.6 to 1.8 mm/year, while the annual mean tidal range rose at the same time by 0.9 to 3.8 mm/year. In terms of storm surge intensities, there is interannual variability and decadal variability but five tide gauges show significant decreasing trends, and three gauges, at Keelung, Xiamen and Quarrybay, exhibited significant increases of extreme sea levels with trends of 1.5 – 6.0 mm/year during 1954‐2013. Significant tide‐surge interactions were found at all 12 tide gauges, but no obvious change was found during the past few decades. The changes in extreme sea levels in this area are strongly related to the changes of mean sea levels (MSL). At gauges, where the tide‐surge interaction is large, the astronomic tides are also an important factor for the extreme sea levels, whereas tide gauges with little tide‐surge interaction, the changes of wind driven storm surge component adds to the change of the extreme sea levels. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-18T14:06:43.199664-05:
      DOI: 10.1002/2015JC011336
  • Observational validation of the diffusive convection flux laws in the
           Amundsen Basin, Arctic Ocean
    • Authors: John D. Guthrie; Ilker Fer, James H. Morison
      Abstract: The low levels of mechanically‐driven mixing in many regions of the Arctic Ocean make double diffusive convection virtually the only mechanism for moving heat up from the core of Atlantic Water towards the surface. In an attempt to quantify double diffusive heat fluxes in the Arctic Ocean, a temperature microstructure experiment was performed as a part of the North Pole Environmental Observatory (NPEO) 2013 field season from the drifting ice station Barneo located in the Amundsen Basin near the Lomonosov Ridge (approx. 89.5°N, 75°W). A diffusive convective thermohaline staircase was present between 150‐250 m in nearly all of the profiles. Typical vertical heat fluxes across the high‐gradient interfaces were consistently small, O(10−1) W m−2. Our experiment was designed to resolve the staircase and differed from earlier Arctic studies that utilized inadequate instrumentation or sampling. Our measured fluxes from temperature microstructure agree well with the laboratory derived flux laws compared to previous studies, which could find agreement only to within a factor of two to four,. Correlations between measured and parameterized heat fluxes are slightly higher when using the more recent Flanagan et al. [2013] laboratory derivation than the more commonly used derivation presented in Kelley [1990]. Nusselt vs. Rayleigh number scaling reveals the convective exponent, η, to be closer to 0.29 as predicted by recent numerical simulations of single‐component convection rather than the canonical 1/3 assumed for double diffusion. However, the exponent appears to be sensitive to how convective layer height is defined. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-18T14:06:31.206508-05:
      DOI: 10.1002/2015JC010884
  • Regional dependence in the timing of onset of rapid decline in Arctic sea
           ice concentration
    • Abstract: Arctic sea ice concentration from satellite passive microwave measurements is analysed to assess the form and timing of the onset of decline of recent ice loss, and the regional dependence of the response. The timing of the onset is estimated using an objective method, and suggests differences of up to 20 years between the various subregions. A clear distinction can be drawn between the recent onset times of the Atlantic sector (beginning in 2003) and the much earlier onset times associated with the Pacific sector, where the earliest transition to rapid loss is found in 1992. Rates of decline prior to and following the transition points are calculated, and suggest that the post‐onset rate of loss is greatest in the Barents Sea, and weakest in the Pacific sector. Covariability between the seasons is noted in the SIC response, both at interannual and longer time scales. For two case regions, potential mechanisms for the onset time transitions are briefly analysed. In the Barents Sea, the onset time coincides with a redistribution of the pathways of ice circulation in the region, whilst along the Alaskan coast, the propagation of the regional signal can be traced in the age of the sea ice. The results presented here indicate a series of spatially self‐consistent regional responses, and may be useful in understanding the primary drivers of recent sea ice loss. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-18T14:06:17.844197-05:
      DOI: 10.1002/2015JC011187
  • Particle delivery to the benthos of coastal Lake Michigan
    • Authors: James T. Waples
      Abstract: A 2‐D non‐steady state model was applied to measured profiles of 234Th/238U and 90Y/90Sr disequilibria in a shallow (22 m) water column of coastal Lake Michigan. Downward fluxes of 234Th and 90Y were primarily driven by onshore horizontal advection. Concordance between 234Th and 90Y‐derived mass flux estimates from the water column could only be realistically achieved under a nuclide scavenging scenario dominated by direct sorption on bottom or near‐bottom sediment and vertical convection in the water column – not sinking particles. An estimated vertical 234Th/90Y flux ratio of ∼0.31 in the water column agreed with measured 234Th/90Y activity ratios on collected ejecta from bottom dwelling dreissenid mussels (0.26 ± 0.05) and not with water column particles (3.3 ± 1.3). A similar 238U/90Sr parent nuclide activity ratio of 0.30 ± 0.02 suggests that both 234Th and 90Y are scavenged in toto below the maximum sampling depth (17 m) and near the sediment/water interface. Determining the mechanism by which particles are transported to the bottom is important for understanding not only how benthos are supplied with water column material, but also how particle fluxes should be measured and calculated. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-18T14:05:45.141841-05:
      DOI: 10.1002/2015JC011297
  • Can we map the interannual variability of the whole upper Southern Ocean
           with the current database of hydrographic observations?
    • Abstract: With the advent of Argo floats, it now seems feasible to study the interannual variations of upper ocean hydrographic properties of the historically undersampled Southern Ocean. To do so, scattered hydrographic profiles often first need to be mapped. To investigate biases and errors associated both with the limited space‐time distribution of the profiles and with the mapping methods, we colocate the mixed layer depth (MLD) output from a state‐of‐the‐art 1/12° DRAKKAR simulation onto the latitude, longitude and date of actual in‐situ profiles from 2005 to 2014. We compare the results obtained after remapping using a nearest‐neighbor (NN) interpolation and an objective analysis (OA) with different spatio‐temporal grid resolutions and decorrelation scales. NN is improved with a coarser resolution. OA performs best with low decorrelation scales, avoiding too strong a smoothing, but returns values over larger areas with large decorrelation scales and low temporal resolution, as more points are available. For all resolutions OA represents better the annual extreme values than NN. Both methods underestimate the seasonal cycle in MLD. MLD biases are lower than 10 m on average but can exceed 250 m locally in winter. We argue that current Argo data should not be mapped to infer decadal trends in MLD, as all methods are unable to reproduce existing trends without creating unrealistic extra ones. We also show that regions of the subtropical Atlantic, Indian and Pacific Oceans, and the whole ice‐covered Southern Ocean, still cannot be mapped even by the best method because of the lack of observational data. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-18T14:02:28.367795-05:
      DOI: 10.1002/2015JC011115
  • Issue Information
    • PubDate: 2015-11-18T11:10:01.981277-05:
      DOI: 10.1002/jgrc.20866
  • Modeled ocean circulation in Nares Strait and its dependence on
           landfast‐ice cover
    • Abstract: Two simplified ocean simulations are used to study circulation and transport within Nares Strait. The simulations are similar, except that one included a coupled sea ice model that effectively established a landfast ice cover throughout the simulation year. Comparison between the ocean‐only and ocean‐ice simulations reveals a systematic change in the current structure, reminiscent of the seasonal shift under mobile and landfast ice previously observed in Nares Strait. A surface‐intensified jet, which carries low salinity water along the strait's centerline, develops within the ocean‐only simulation. The current structure under landfast ice is characterized by a subsurface jet located along the western side with low salinity surface water distributed along the eastern side of the strait. Intermediate salinity water is offset to the west in the ice‐ocean simulation relative to the ocean‐only simulation, while high salinity water (>34.8) is constrained to recirculations that are located north and south of a sill in Kane Basin. The simulations, combined with an idealized, semi‐analytical model, suggest that the structural shift is caused by the surface Ekman layer beneath the landfast ice and the associated eastward advection of near‐surface low salinity water and westward movement of the jet. Temporal variability in the ocean‐ice simulation is dominated by the remote response to the time‐dependent northern boundary conditions. In contrast, the ocean‐only simulation favors an instability and additionally responds to local surface wind forcing, which enhances the variability within the strait above that imposed at the boundaries. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-12T18:26:42.859222-05:
      DOI: 10.1002/2015JC011091
  • Topographic form stress in the Southern Ocean State Estimate
    • Abstract: We diagnose the Southern Ocean momentum balance in a six‐year, eddy permitting state estimate of the Southern Ocean. We find that 95\% of the zonal momentum input via wind stress at the surface is balanced by topographic form stress across ocean ridges, while the remaining 5\% is balanced via bottom friction and momentum flux divergences at the northern and southern boundaries of the analysis domain. While the time‐mean zonal wind stress field exhibits a relatively uniform spatial distribution, time‐mean topographic form stress concentrates at shallow ridges and across the continents that lie within the Antarctic Circumpolar Current (ACC) latitudes; nearly 40\% of topographic form stress occurs across South America, while the remaining 60\% occurs across the major submerged ridges that underlie the ACC. Topographic form stress can be divided into shallow and deep regimes: the shallow regime contributes most of the westward form stress that serves as a momentum sink for the ACC system, while the deep regime consists of strong eastward and westward form stresses that largely cancel in the zonal integral. The time‐varying form stress signal, integrated longitudinally and over the ACC latitudes, tracks closely with the wind stress signal integrated over the same domain; at zero lag, 88\% of the variance in the six‐year form stress time series can be explained by the wind stress signal, suggesting that changes in the integrated wind stress signal are communicated via rapid barotropic response down to the level of bottom topography. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-12T18:18:28.147357-05:
      DOI: 10.1002/2015JC011143
  • Influence of post‐Tehuano oceanographic processes in the dynamics of
           the CO2 system in the Gulf of Tehuantepec, Mexico
    • Abstract: This investigation reports, for the first time, results of CO2 system variables in the Gulf of Tehuantepec, located in the Mexican tropical Pacific. We quantified the post‐Tehuano concentration of dissolved inorganic carbon (DIC) and pH (April 2013). These values were used to calculate pCO2, aragonite saturation (ΩAr) and air‐sea CO2 fluxes (FCO2). The intense vertical stratification was found to contribute to the biogeochemical processes in surface waters (< 70 m). However, in post‐Tehuano conditions, high pCO2 (∼1000 µatm) and DIC concentrations (2200 µmol kg−1), as well as low ΩAr (∼1.1) and pH (∼7.5) remain in surface waters for a few days after Tehuano winds have weakened. We identified four oceanographic areas: a) a highly mixed region due to previous Tehuano events; b) coastal upwelling in the western region; c) mesoscale eddies; and d) a poleward surface coastal current. The first three promoted the influence of Subtropical Subsurface Water in the chemistry of surface waters, whereas the coastal current contributed to the horizontal advection of DIC. The calculated CO2 fluxes ranged from ‐2.3 mmol m−2 d−1 in areas with stratified waters, to over 25 mmol m−2 d−1 for mixed areas. Positive values indicate an ocean‐to‐atmosphere flux. Our findings suggest that the Gulf of Tehuantepec is a major source of CO2 into the atmosphere. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-11T18:38:10.225233-05:
      DOI: 10.1002/2015JC011249
  • DopSCAT: A mission concept for simultaneous measurements of marine winds
           and surface currents
    • Abstract: A radar scatterometer operates by transmitting a pulse of microwave energy towards the ocean's surface and measuring the normalized (per‐unit‐surface) radar backscatter coefficient (σº). The primary application of scatterometry is the measurement of near‐surface ocean winds. By combining σº measurements from different azimuth angles, the 10‐m vector wind can be determined through a Geophysical Model Function (GMF), which relates wind and backscatter. This paper proposes a mission concept for the measurement of both oceanic winds and surface currents, which makes full use of earlier C‐band radar remote sensing experience. For the determination of ocean currents, in particular, the novel idea of using two chirps of opposite slope is introduced. The fundamental processing steps required to retrieve surface currents are given together with their associated accuracies. A detailed description of the mission proposal and comparisons between real and retrieved surface currents are presented. The proposed ocean Doppler scatterometer can be used to generate global surface ocean current maps with accuracies better than 0.2 m/s at a spatial resolution better than 25 km (i.e. 12.5 km spatial sampling) on a daily basis. These maps will allow gaining some insights on the upper ocean mesoscale dynamics. The work lies at a frontier, given that the present inability to measure ocean currents from space in a consistent and synoptic manner represents one of the greatest weaknesses in ocean remote sensing. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-06T19:19:53.272875-05:
      DOI: 10.1002/2015JC011011
  • Near‐inertial ocean response to tropical cyclone forcing on the
           Australian North‐West Shelf
    • Authors: M. D. Rayson; G. N. Ivey, N. L. Jones, R. J. Lowe, G. W. Wake, J. D. McConochie
      Abstract: The Regional Ocean Modeling System (ROMS) was applied to the Australian North‐West Shelf (NWS) to hindcast the ocean response to four intense historical Tropical Cyclones (TC). While the four cyclones had very different trajectories across the NWS, all passed within 150 km of a long‐term vertical mooring located on the continental shelf in 125 m depth. The observed ocean response at this relatively shallow, Southern Hemisphere shelf site was characterized by the development of a peak in the counter‐clockwise (CCW) near‐inertial kinetic energy, mixed layer deepening and subsequent restratification. Strong near‐inertial isotherm oscillations were also observed following two of the cyclones. ROMS reproduced these features and also showed that the peak in the near‐inertial CCW kinetic energy was observed on the left side of each cyclone trajectory. The time rate of change of near‐inertial kinetic energy depended strongly on the storm Rossby number, i.e., defined based on the storm speed, the storm length scale and the Coriolis frequency. The shallow water depth on the NWS resulted in firstly, a more rapid decay of near‐inertial oscillations than in the deep ocean, and secondly a generation efficiency (the ratio of near‐inertial power to the rate of wind work) of up to 10%, smaller than found for cyclones propagating across deeper water. The total energy put into near inertial motions is nevertheless large compared to the background tidal energy. The rapid decay of near‐inertial motions emphsizes the importance of frictional effects in characterizing the response to cyclone forcing in shallow seas. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-06T19:18:59.343246-05:
      DOI: 10.1002/2015JC010868
  • On the flow of Atlantic water and temperature anomalies in the Nordic Seas
           toward the Arctic Ocean
    • Abstract: The climatic conditions over the Arctic Ocean are strongly influenced by the inflow of warm Atlantic water conveyed by the Norwegian Atlantic Slope Current (NwASC). Based on sea surface height (SSH) data from altimetry, we develop a simple dynamical measure of the NwASC transport to diagnose its spatio‐temporal variability. This supports a dynamical division of the NwASC into two flow regimes; the Svinøy Branch (SvB) in the southern Norwegian Sea, and the Fram Strait Branch (FSB) west of Spitsbergen. The SvB transport is well correlated with the SSH and atmospheric variability within the Nordic Seas, factors that also affect the inflow to the Barents Sea. In contrast, the FSB is influenced by regional atmospheric conditions around Svalbard and northern Barents Sea. Using a composite analysis, we further relate anomalous strong SvB flow events to temperature fluctuations along the core of Atlantic water. A warm composite anomaly is found to propagate northwards, with a tendency to amplify enroute, after these events. A roughly 12‐months delayed temperature signal is identified in the FSB. However, also in the Lofoten Basin interior a delayed temperature signal is found, which appears to originate from the NwASC. This study suggests that hydrographic anomalies both upstream from the North Atlantic, and locally generated in the Norwegian Sea, are important for the oceanic heat and salt transport that eventually enters into the Arctic. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-05T17:54:53.592188-05:
      DOI: 10.1002/2015JC011012
  • CO2 Sink/Source Characteristics in the Tropical Indonesian Seas
    • Authors: A. R. Kartadikaria; A. Watanabe, K. Nadaoka, N. S. Adi, H. B. Prayitno, S. Suharsono, M. Muchtar, I. Triyulianti, A. Setiawan, S. Suratno, E. N. Khasanah
      Abstract: Two distinct CO2 sink/source characteristics are found in the tropical Indonesian seas from the compilation of observed data for the period 1984‐2013. The western region persistently emits CO2 to the atmosphere, whereas the eastern region is dynamic and acts either as a small source or sink of CO2 to the atmosphere, depending on sites. The segregation is proximal to the Makassar Strait, which is located over the continental shelf and is one of the main routes of the Indonesian Throughflow (ITF). Lower salinity and higher silicate were found in the western region, suggesting a terrestrial influence in this area. Temperature has a limited influence in controlling different CO2 sink/source characteristics in the west and east. However, an SST change of ‐2.0°C during La Niña events effectively reduces the pCO2 difference between the atmosphere and surface seawater by 50% compared to normal year conditions. During La Niña events, higher wind speeds double the CO2 flux from the ocean to the atmosphere compared to that of a normal year. In the continental shelf area where the CO2 sink area was found, data of over 29 years show that the seawater pCO2 increased by 0.6‐3.8 μatm yr−1. Overall, the seawater pCO2 of the Indonesian Seas is supersaturated relative to the atmosphere by 15.9 ± 8.6 μatm and thus acts as a source of CO2 to the atmosphere. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-05T17:52:17.013493-05:
      DOI: 10.1002/2015JC010925
  • Accuracy of short‐term sea ice drift forecasts using a coupled
           ice‐ocean model
    • Authors: Axel J. Schweiger; Jinlun Zhang
      Abstract: Arctic sea ice drift forecasts of 6 hr to 9 days for the summer of 2014 are generated using the Marginal Ice Zone Modeling and Assimilation System (MIZMAS); the model is driven by 6‐hr atmospheric forecasts from the Climate Forecast System (CFSv2). Forecast ice drift speed is compared to drifting buoys and other observational platforms. Forecast positions are compared with actual positions 24 hr to 8 days since forecast. Forecast results are further compared to those from the forecasts generated using an ice velocity climatology driven by multi‐year integrations of the same model. The results are presented in the context of scheduling the acquisition of high‐resolution images that need to follow buoys or scientific research platforms. RMS errors for ice speed are on the order of 5 km/day for 24 hr to 48 hr since forecast using the sea ice model compared with 9 km/day using climatology. Predicted buoy position RMS errors are 6.3 km for 24 hr and 14 km for 72 hr since forecast. Model biases in ice speed and direction can be reduced by adjusting the air drag coefficient and water turning angle, but the adjustments do not affect verification statistics. This suggests that improved atmospheric forecast forcing may further reduce the forecast errors.The model remains skillful for 8 days. Using the forecast model increases the probability of tracking a target drifting in sea ice with a 10x10 km image from 60% to 95% for a 24‐hr forecast and from 27% to 73% for a 48‐hr forecast. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-05T17:52:04.061871-05:
      DOI: 10.1002/2015JC011273
  • A comparative assessment of coastal mean dynamic topography in Norway by
           geodetic and ocean approaches
    • Authors: Vegard Ophaug; Kristian Breili, Christian Gerlach
      Abstract: The ocean's mean dynamic topography (MDT) is the surface representation of ocean circulation. It may be determined by the ocean approach, using numerical ocean circulation models, or by the geodetic approach, where MDT is the height of the mean sea surface (MSS), or mean sea level (MSL), above the geoid. Using new geoid models, geodetic MDT profiles based on tide gauges, dedicated coastal altimetry products, and conventional altimetry are compared with six ocean MDT estimates independent of geodetic data. Emphasis is put on the determination of high‐resolution geoid models, combining ESA's fifth release (R5) of GOCE satellite‐only global gravity models (GGMs) with a regional geoid model for Norway by a filtering technique. Differences between MDT profiles along the Norwegian coast together with Taylor diagrams confirm that geodetic and ocean MDTs agree on the ∼3‐7 cm level at the tide gauges, and on the ∼5‐11 cm level at the altimetry sites. Some geodetic MDTs correlate more with the best‐performing ocean MDT than do other ocean MDTs, suggesting a convergence of the methods. While the GOCE R5 geoids are shown to be more accurate over land, they do not necessarily show the best agreement over the ocean. Pointwise monomission altimetry products give results comparable with the multimission DTU13MSS grid on the ∼5 cm level. However, dedicated coastal altimetry products generally do not offer an improvement over conventional altimetry along the Norwegian coast. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-05T17:51:06.355836-05:
      DOI: 10.1002/2015JC011145
  • Loitering of the retreating sea ice edge in the Arctic Seas
    • Authors: Michael Steele; Wendy Ermold
      Abstract: Each year, the arctic sea ice edge retreats from its winter maximum extent through the Seasonal Ice Zone (SIZ) to its summer minimum extent. On some days, this retreat happens at a rapid pace, while on other days, parts of the pan‐arctic ice edge hardly move for periods of days up to 1.5 weeks. We term this stationary behavior “ice edge loitering,” and identify areas that are more prone to loitering than others. Generally, about 20‐25% of the SIZ area experiences loitering, most often only one time at any one location during the retreat season, but sometimes two or more times. The main mechanism controlling loitering is an interaction between surface winds and warm sea surface temperatures in areas from which the ice has already retreated. When retreat happens early enough to allow atmospheric warming of this open water, winds that force ice floes into this water cause melting. Thus while individual ice floes are moving, the ice edge as a whole appears to loiter. The time scale of loitering is then naturally tied to the synoptic time scale of wind forcing. Perhaps surprisingly, the area of loitering in the arctic seas has not changed over the past 25 years, even as the SIZ area has grown. This is because rapid ice retreat happens most commonly late in the summer, when atmospheric warming of open water is weak. We speculate that loitering may have profound effects on both physical and biological conditions at the ice edge during the retreat season. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-05T17:50:54.547974-05:
      DOI: 10.1002/2015JC011182
  • Anatomizing one of the largest saltwater inflows into the Baltic Sea in
           December 2014
    • Abstract: In December 2014, an exceptional inflow event into the Baltic Sea was observed, a so‐called Major Baltic Inflow (MBI). Such inflow events are important for the deep‐water ventilation in the Baltic Sea and typically occur every 3‐10 years. Based on first observational data sets, this inflow had been ranked as the third largest since 100 years. With the help of a multi‐nested modeling system, reaching from the North Atlantic (8 km resolution) to the Western Baltic Sea (600 m resolution, which is baroclinic eddy resolving), this event is reproduced in detail. The model gave a slightly lower salt transport of 3.8 Gt, compared to the observational estimate of four Gt. Moreover, by using passive tracers to mark the different inflowing water masses, including an age tracer, the inflowing water masses could be tracked and their paths and timing through the different basins could be reproduced and investigated. The analysis is supported by the recently developed Total Exchange Flow (TEF) to quantify the volume transport in different salinity classes. To account for uncertainties in the modeled velocity and tracer fields, a Monte Carlo Analysis (MCA) is applied to correct possible biases and errors. With the help of the MCA, 95% confidence intervals are computed for the transport estimates. Based on the MCA, the “best guess” of the volume transport is 291.0±13.65 km3 and 3.89±0.18 Gt for the total salt transport. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-05T17:50:43.712203-05:
      DOI: 10.1002/2015JC011269
  • Reconstruction of a meteotsunami in Lake Erie on 27 May 2012: Roles of
           atmospheric conditions on hydrodynamic response in enclosed basins
    • Authors: Eric J. Anderson; Adam J. Bechle, Chin H. Wu, David J. Schwab, Greg E. Mann, Kirk A. Lombardy
      Abstract: On May 27, 2012, atmospheric conditions gave rise to two convective systems that generated a series of waves in the meteotsunami band on Lake Erie. The resulting waves swept three swimmers a half‐mile offshore, inundated a marina, and may have led to a capsized boat along the southern shoreline. Analysis of radial velocities from a nearby radar tower in combination with coastal meteorological observation indicates that the convective systems produced a series of outflow bands that were the likely atmospheric cause of the meteotsunami. In order to explain the processes that led to meteotsunami generation, we model the hydrodynamic response to three meteorological forcing scenarios: (i) the reconstructed atmospheric disturbance from radar analysis, (ii) simulated conditions from a high‐resolution weather model, and (iii) interpolated meteorological conditions from the NOAA Great Lakes Coastal Forecasting System. The results reveal that the convective systems generated a series of waves incident to the southern shore of the lake that reflected toward the northern shoreline and reflected again to the southern shore, resulting in spatial wave focusing and edge wave formation that combined to impact recreational users near Cleveland, OH. This study illustrates the effects of meteotsunami development in an enclosed basin; including wave reflection, focusing, and edge wave formation as well as temporal lags between the causative atmospheric conditions and arrival of dangerous wave conditions. As a result, the ability to detect these extreme storms and predict the hydrodynamic response is crucial to reducing risk and building resilient coastal communities. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-05T03:42:51.62664-05:0
      DOI: 10.1002/2015JC010883
  • Seasonal and interannual variability of fast ice extent in the
           southeastern Laptev Sea between 1999 and 2013
    • Authors: V. Selyuzhenok; T. Krumpen, A. Mahoney, M. Janout, R. Gerdes
      Abstract: Along with changes in sea ice extent, thickness and drift speed, Arctic sea ice regime is characterised by a decrease of fast ice season and reduction of fast ice extent. The most extensive fast ice cover in the Arctic develops in the southeastern Laptev Sea. Using weekly operational sea ice charts produced by Arctic and Antarctic Research Institute (AARI, Russia) from 1999 to 2013 we identified five main key events that characterize the annual evolution of fast ice in the southeastern Laptev Sea. Linking the occurrence of the key events with the atmospheric forcing, bathymetry, freezeup and melt onset, we examined the processes driving annual fast ice cycle. The analysis revealed that fast ice in the region is sensitive to thermodynamic processes throughout a season, while the wind has a strong influence only on the first stages of fast ice development. The maximal fast ice extent is closely linked to the bathymetry and local topography and is primarily defined by the location of shoals, where fast ice is likely grounded. The annual fast ice cycle shows significant changes over the period of investigation, with tendencies toward later fast ice formation and earlier breakup. These tendencies result in an overall decrease of the fast ice season by 2.8 day/year, which is significantly higher than previously reported trends. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-02T02:17:46.152568-05:
      DOI: 10.1002/2015JC011135
  • Surface boundary layer evolution and near‐inertial wind power input
    • Authors: B.F. Kilbourne; J.B. Girton
      Abstract: Deep weakly stratified surface layers in the Southern Ocean complicate the identification of the mixed‐layer base, which is critical in estimating the wind power input through the ocean surface. Typically used mixed‐layer depth criteria often ignore weak stratification, which traps momentum near the surface and significantly enhances the near‐inertial band wind power input. The thickness of the active mixing‐layer, the turbulent layer in contact with wind stress, is needed to accurately estimate wind power input. A fine‐density‐threshold criterion of 0.005 kg m-3, just above the noise floor of most autonomous instruments, was applied to observed profiles of potential density to estimate the thickness of the actively mixing‐layer. Vertical shear, Langmuir cells, and buoyant convection are investigated as possible mechanisms maintaining turbulence within the mixing‐layer. Over 90% of the observed variance of the mixing‐layer thickness is explained by either shear‐driven entrainment, which is simulated using the Price‐Weller‐Pinkel model, or by a parameterization of downwelling plumes due to Langmuir cell convergence. In general, surface buoyancy fluxes are too weak to drive mixed‐layer turbulence. Comparison of National Oceanographic Data Center (NODC) climatological mixed‐layer thickness to those determined using the 0.005 kg m-3 density threshold suggests a multiplicative seasonally varying correction of 1.5 to 3.5 should be applied to wind work estimates made using the NODC climatological mixed‐layer thickness in the Southern Ocean. This article is protected by copyright. All rights reserved.
      PubDate: 2015-11-02T02:12:41.432995-05:
      DOI: 10.1002/2015JC011213
  • Optical properties of melting first‐year Arctic sea ice
    • Authors: Bonnie Light; Donald K. Perovich, Melinda Webster, Christopher Polashenski, Ruzica Dadic
      Abstract: The albedo and transmittance of melting, first‐year Arctic sea ice were measured during two cruises of the Impacts of Climate on the Eco‐Systems and Chemistry of the Arctic Pacific Environment (ICESCAPE) project during the summers of 2010 and 2011. Spectral measurements were made for both bare and ponded ice types at a total of 19 ice stations in the Chukchi and Beaufort Seas. These data, along with irradiance profiles taken within boreholes, laboratory measurements of the optical properties of core samples, ice physical property observations, and radiative transfer model simulations are employed to describe representative optical properties for melting first‐year Arctic sea ice. Ponded ice was found to transmit roughly 4.4 times more total energy into the ocean, relative to nearby bare ice. The ubiquitous surface‐scattering layer and drained layer present on bare, melting sea ice are responsible for its relatively high albedo and relatively low transmittance. Light transmittance through ponded ice depends on the physical thickness of the ice and the magnitude of the scattering coefficient in the ice interior. Bare ice reflects nearly three‐quarters of the incident sunlight, enhancing its resiliency to absorption by solar insolation. In contrast, ponded ice absorbs or transmits to the ocean more than three‐quarters of the incident sunlight. Characterization of the heat balance of a summertime ice cover is largely dictated by its pond coverage, and light transmittance through ponded ice shows strong contrast between first‐ and multiyear Arctic ice covers. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-31T03:52:35.998512-05:
      DOI: 10.1002/2015JC011163
  • A simplified wave enhancement criterion for moving extreme events
    • Authors: Vladimir Kudryavtsev; Pavel Golubkin, Bertrand Chapron
      Abstract: An analytical model is derived to efficiently describe the wave energy distribution along the main transects of a moving extreme weather event. The model essentially builds on a generalization of the self‐similar wave growth model and the assumption of a strongly dominant single spectral mode in a given quadrant of the storm. The criterion to anticipate wave enhancement with the generation of trapped abnormal waves is defined as gr/ur2≈cT(ur/V)1/q, with r, u, V, radial distance, average sustained wind speed, and translation velocity, respectively. Constants q and cT follow the fetch‐law definitions. If forced during a sufficient timescale interval, also defined from this generalized self‐similar wave growth model, waves can be trapped and large amplification of the wave energy will occur in the front‐right storm quadrant. Remarkably, the group velocity and corresponding wavelength of outrunning wave systems will become wind speed independent and solely related to the translating velocity. The resulting significant wave height also only weakly depends on wind speed, and more strongly on the translation velocity. Compared to altimeter satellite measurements, the proposed analytical solutions for the wave energy distribution demonstrate convincing agreement. As analytically developed, the wave enhancement criterion can provide a rapid evaluation to document the general characteristics of each storm, especially the expected wave field asymmetry. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-30T22:28:45.519138-05:
      DOI: 10.1002/2015JC011284
  • Field evidence of beach profile evolution toward equilibrium
    • Authors: B. C. Ludka; R.T. Guza, W.C. O'Reilly, M.L. Yates
      Abstract: An equilibrium framework is used to describe the evolution of the cross‐shore profile of five beaches (medium grain size sand) in southern California. Elevations were observed quarterly on cross‐shore transects extending from the back beach to 8 m depth, for 3‐10 years. Transects spaced 100 m in the alongshore direction are alongshore‐averaged into nineteen 700‐900 m long sections. Consistent with previous observations, changes about the time average profile in many sections are captured by the first mode empirical orthogonal function (EOF). The first EOF poorly describes sections with hard substrate (less than roughly 80% sandy bottom), and also fails near the head of a submarine canyon and adjacent to an inlet. At the 12 well described sections the time‐varying amplitude of the first EOF, the beach state A, describes the well known seasonal sand exchange between the shoreline and offshore (roughly between 4‐7 m depth). We show that the beach state change rate dA/dt depends on the disequilibrium between the present state A and wave conditions, consistent with the equilibrium concepts of Wright and Short [1984]; Wright et al. [1985]. Empirically determined, optimal model coefficients using the framework of Yates et al. [2009a, 2011] vary between sections, but a single set of globally optimized values performs almost as well. The model implements equilibrium concepts using ad hoc assumptions and empirical parameter values. The similarity with observed profile change at five southern California beaches supports the underlying model equilibrium hypotheses, but for unknown reasons the model fails at Duck, N.C. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-30T18:13:38.654494-05:
      DOI: 10.1002/2015JC010893
  • Factors governing the deep ventilation of the Red Sea
    • Authors: Vassilis P. Papadopoulos, Peng Zhan, Sarantis S. Sofianos, Dionysios E. Raitsos, Mohammed Qurban, Yasser Abualnaja, Amy Bower, Harilaos Kontoyiannis, Alexandra Pavlidou, Mohamed Asharaf T.T; Nikolaos Zarokanellos, Ibrahim Hoteit
      Abstract: A variety of data based on hydrographic measurements, satellite observations, reanalysis databases, and meteorological observations are used to explore the interannual variability and factors governing the deep water formation in the northern Red Sea. Historical and recent hydrographic data consistently indicate that the ventilation of the near bottom layer in the Red Sea is a robust feature of the thermohaline circulation. Dense water capable to reach the bottom layers of the Red Sea can be regularly produced mostly inside the Gulfs of Aqaba and Suez. Occasionally, during colder than usual winters, deep water formation may also take place over coastal areas in the northernmost end of the open Red Sea just outside the Gulfs of Aqaba and Suez. However, the origin as well as the amount of deep waters exhibit considerable interannual variability depending not only on atmospheric forcing but also on the water circulation over the northern Red Sea. Analysis of several recent winters shows that the strength of the cyclonic gyre prevailing in the northernmost part of the basin can effectively influence the sea surface temperature (SST) and intensify or moderate the winter surface cooling. Upwelling associated with periods of persistent gyre circulation lowers the SST over the northernmost part of the Red Sea and can produce colder than normal winter SST even without extreme heat loss by the sea surface. In addition, the occasional persistence of the cyclonic gyre feeds the surface layers of the northern Red Sea with nutrients, considerably increasing the phytoplankton biomass. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-30T10:17:20.117386-05:
      DOI: 10.1002/2015JC010996
  • Intraseasonal variability of upwelling in the equatorial eastern Indian
    • Authors: Gengxin Chen; Weiqing Han, Yuanlong Li, Dongxiao Wang, Toshiaki Shinoda
      Abstract: By analyzing satellite observations and conducting a series of ocean general circulation model experiments, this study examines the physical processes that determine intraseasonal variability (ISV) of the equatorial eastern Indian Ocean (EIO) upwelling for the 2001‐2011 period. The ISV of EIO upwelling ‐ as indicated by sea level, thermocline depth and sea surface temperature (SST) ‐ is predominantly forced by atmospheric intraseasonal oscillations (ISOs), and shows larger amplitudes during winter‐spring season (November‐April) when atmospheric ISOs are stronger than summer‐fall (May‐October). The chlorophyll (Chl‐a) concentration, another indicator of upwelling, however reveals its largest intraseasonal variability during May‐October, when the mean thermocline is shallow and seasonal upwelling occurs. For both winter‐spring and summer‐fall seasons, the ISV of EIO sea level and thermocline depth is dominated by remote forcing from the equatorial Indian Ocean wind stress, which drives Kelvin waves that propagate along the equator and subsequently along the Sumatra–Java coasts. Local wind forcing within the EIO plays a secondary role. The ISV of SST, however, is dominated by upwelling induced by remote equatorial wind only during summer‐fall, with less contribution from surface heat fluxes for this season. During winter‐spring, the ISV of SST results primarily from shortwave radiation and turbulent heat flux induced by wind speed associated with the ISOs, and local forcing dominates the SST variability. In this season, the mean thermocline is deep in the warm pool and thus thermocline variability decouples from the ISV of SST. Only in summer‐fall when the mean thermocline is shallow, upwelling has important impact on SST. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-30T10:15:27.87789-05:0
      DOI: 10.1002/2015JC011223
  • Evidence of upwelling events at the northern Patagonian shelf break
    • Authors: Daniel Valla; Alberto R. Piola
      Abstract: The Patagonian shelf break marks a transition between relative warm‐fresh shelf waters and relative cold‐salty Subantarctic Water advected northward by the Malvinas Current. From early spring to late autumn, the outer shelf region is characterized by a band of high chlorophyll concentration that sustains higher trophic levels, including significant fisheries. We analyze time series of current and water mass property observations collected at two moorings deployed at the shelf edge at 41 and 43.8 ºS to investigate what mechanisms lead to temperature variability at the shelf break, and their role on the nutrient supply to the upper layer. The in‐situ data are combined with satellite‐derived observations of sea surface temperature and chlorophyll‐a to analyze a sharp cooling event at the outer shelf that lasted ten days and extended ∼ 500 km along the outer shelf. The event is consistent with upwelling of cold waters through the base of the mixed layer. The vertical velocity required to explain the observed cooling is 13 to 29 m·day−1. Satellite derived sea surface temperature reveal additional cooling events of similar characteristics. Seventy‐five percent of these events are concurrent with surface chlorophyll increase over a 5‐day period suggesting that cooling events observed at the shelf break are associated with nutrient fluxes that promote the growth of phytoplankton. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-30T10:15:11.131028-05:
      DOI: 10.1002/2015JC011002
  • Passive buoyant tracers in the ocean surface boundary layer: 2.
           Observations and simulations of microplastic marine debris
    • Authors: K. Brunner; T. Kukulka, G. Proskurowski, K. L. Law
      Abstract: This paper is the second of a two part series that investigates passive buoyant tracers in the ocean surface boundary layer (OSBL). The first part examines the influence of equilibrium wind‐waves on vertical tracer distributions, based on large eddy simulations (LES) of the wave‐averaged Navier‐Stokes equation. Motivated by observations of buoyant microplastic marine debris (MPMD), this study applies the LES model and the parametric one‐dimensional column model from part one to examine the vertical distributions of MPMD. MPMD is widely distributed in vast regions of the subtropical gyres and has emerged as a major open ocean pollutant whose distribution is subject to upper ocean turbulence. The models capture shear‐driven turbulence, Langmuir turbulence (LT), and enhanced turbulent kinetic energy input due to breaking waves (BW). Model results are only consistent with observations of MPMD profiles and the relationship between surface concentrations and wind speed if LT effects are included. Neither BW nor shear‐driven turbulence is capable of deeply submerging MPMD, suggesting that the observed vertical MPMD distributions are a characteristic signature of wave‐driven LT. Thus, this study demonstrates that LT substantially increases turbulent transport in the OSBL, resulting in deep submergence of buoyant tracers. The parametric model is applied to eleven years of observations in the North Atlantic and North Pacific subtropical gyres to show that surface measurements substantially underestimate MPMD concentrations by a factor of three to thirteen. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-30T10:14:34.445135-05:
      DOI: 10.1002/2015JC010840
  • The Gas Transfer through Polar Sea ice experiment: Insights into the rates
           and pathways that determine geochemical fluxes
    • Authors: A. Lovely; B. Loose, P. Schlosser, W. McGillis, C. Zappa, D. Perovich, S. Brown, T. Morell, D. Hsueh, R. Friedrich
      Abstract: Sea ice is a defining feature of the polar marine environment. It is a critical domain for marine biota and it regulates ocean‐atmosphere exchange, including the exchange of greenhouse gases such as CO2 and CH4. In this study, we determined the rates and pathways that govern gas transport through a mixed sea ice cover. N2O, SF6, 3He, 4He, and Ne were used as gas tracers of the exchange processes that take place at the ice‐water, and air‐water interfaces in a laboratory sea ice experiment. Observation of the changes in gas concentrations during freezing revealed that He is indeed more soluble in ice than in water; Ne is less soluble in ice, and the larger gases (N2O and SF6) are mostly excluded during the freezing process. Model estimates of gas diffusion through ice were calibrated using measurements of bulk gas content in ice cores, yielding gas transfer velocity through ice (kice) of ca. 5x10−4 m d−1. In comparison, the effective air‐sea gas transfer velocities (keff) ranged up to 0.33 m d−1 providing further evidence that very little mixed‐layer ventilation takes place via gas diffusion through columnar sea ice. However, this ventilation is distinct from air‐ice gas fluxes driven by sea ice biogeochemistry. The magnitude of keff showed a clear increasing trend with wind speed and current velocity beneath the ice, as well as the combination of the two. This result indicates that gas transfer cannot be uniquely predicted by wind speed alone in the presence of sea ice. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-30T10:14:21.946188-05:
      DOI: 10.1002/2014JC010607
  • Estimating wave orbital velocity through the azimuth cutoff from
           spaceborne satellites
    • Authors: Justin E. Stopa; Fabrice Ardhuin, Bertrand Chapron, Fabrice Collard
      Abstract: It has been long accepted that ocean wave conditions recorded from synthetic aperture radar (SAR) aboard satellites resolve large scale swells. SARs make use of its displacement to achieve fine resolution; however the random surface motions can reduce its nominal azimuthal resolution. Accordingly, the SAR spectral azimuth response mirrors the probability distribution of the radial velocity component of the scatters. This effect, quantified in a measure called the azimuth cutoff, is estimated by defining a scale based on the fitting of a Gaussian function to the radar cross section azimuth spectrum. The independent measure provides additional sea state information related to the root mean square surface orbital wave velocity. We use data recorded from the European Space Agency's ENVISAT advanced SAR in the C‐band spanning its lifetime 2003‐2012. Our purpose is to first establish the validity of the azimuth cutoff using both co‐located buoys and modeled wave data. Some systematic biases are corrected using other SAR derived parameters, improving the accuracy of the estimate. Despite our efforts, errors exist in the presence of swell, extreme wind waves, and related to the wave direction. Under the majority of the sea states the parameter is well behaved. As a final point, applications using the wave orbital velocities are described in terms of diagnosing a spectral wave model and the wave climate. As illustrated, the returned radar signal provides useful sea state information that resolves wind speeds, wave orbital velocities from the wind waves, and swells. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-30T10:13:52.882062-05:
      DOI: 10.1002/2015JC011275
  • Macroscale‐wide nutrient inversions in the subsurface layer of the
           Japan Sea during summer
    • Authors: Taketoshi Kodama; Haruyuki Morimoto, Yosuke Igeta, Tadafumi Ichikawa
      Abstract: The nutrient concentrations at depths of 0–200 m in the southern area of the Japan Sea were investigated at 97 stations during six cruises between June and October in 2013 and 2014. The nutrient concentrations at the surface were depleted to less than 0.1 µM, except for silicates, which remained at 0.8–5 µM, and increased below the nutricline, at depths of 20–125 m. The vertical profiles of nitrate, silicate, and/or phosphate concentrations between 131°30′E–139°40′E and 35°50′N–40°40′N showed a peak in the subsurface layer at 40, 71, and 6 stations, respectively, and nutrient inversions occurred at macroscale widths. The subsurface nutrient maximum occurred at depths of 20–150 m in waters at temperatures of 15–16°C and potential densities of 25.3–25.5 σθ, on average. The depths of the subsurface nutrient maximum were generally associated with a salinity maximum originating in the bottom water of the shallow Tsushima Strait. The nutrient inversions was disturbed by phytoplankton consumption, as indicated by the presence of the subsurface chlorophyll maximum at the same depth or below the salinity maximum at stations without nutrient inversions. Therefore, it was inferred that remineralization of nutrients near the bottom, from the East China Sea to the Tsushima Strait, and horizontal advection by the Tsushima Warm Current below the euphotic layer induced macroscale subsurface nutrient inversions in the southern Japan Sea. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-29T18:48:28.741425-05:
      DOI: 10.1002/2015JC010845
  • Whitecap lifetime stages from infrared imagery with implications for
           microwave radiometric measurements of whitecap fraction
    • Authors: Henry Potter; Geoffrey B. Smith, Charlotte M. Snow, David J. Dowgiallo, Justin P. Bobak, Magdalena D. Anguelova
      Abstract: Quantifying active and residual whitecap fractions separately can improve parameterizations of air‐sea fluxes associated with breaking waves. We use data from a multi‐instrumental field campaign on FLoating Instrument Platform (FLIP) to simultaneously capture the signatures of active and residual whitecaps at visible, infrared (IR) and microwave wavelengths using, respectively, video camera, mid‐IR camera, and a radiometer at 10 GHz. We present results from processing and analyzing IR images and correlating this information with radiometric time series of brightness temperature at horizontal and vertical polarizations TBH and TBV. The results provide evidence that breaking crests and decaying foam appear in mid‐IR as bright and dark pixels clearly distinguishing active from residual whitecaps. We quantify the durations of whitecap lifetime stages from the IR images and identify their corresponding signatures in TB time series. Results show that TBH and TBV vary in phase during the active and in anti‐phase during the residual whitecap stages. A methodology to distinguish active and residual whitecaps in radiometric time series without a priori IR information has been developed and verified with corresponding IR and video images. The method uses the degree of polarization P (the ratio between the sum and difference of TBV and TBH) to capture whitecaps as prominent spikes. The maximum and zero‐crossing of the first derivative of P serve to identify the presence of active whitecaps, while the minimum of dP marks the transition from active to residual whitecap stage. The findings have implications for radiometric measurements of active and total whitecap fractions. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-29T18:47:46.714422-05:
      DOI: 10.1002/2015JC011276
  • Future change in ocean productivity: Is the Arctic the new Atlantic?
    • Authors: A. Yool; E. E. Popova, A. C. Coward
      Abstract: One of the most characteristic features in ocean productivity is the North Atlantic spring bloom. Responding to seasonal increases in irradiance and stratification, surface phytoplankton populations rise significantly, a pattern that visibly tracks polewards into summer. While blooms also occur in the Arctic Ocean, they are constrained by the sea‐ice and strong vertical stratification that characterise this region. However, Arctic sea‐ice is currently declining, and forecasts suggest this may lead to completely ice‐free summers by the mid‐21st century. Such change may open the Arctic up to Atlantic‐style spring blooms, and do so at the same time as Atlantic productivity is threatened by climate change‐driven ocean stratification. Here we use low‐ and high‐resolution instances of a coupled ocean‐biogeochemistry model, NEMO‐MEDUSA, to investigate productivity. Drivers of present‐day patterns are identified, and changes in these across a climate change scenario (IPCC RCP8.5) analysed. We find a globally‐significant decline in North Atlantic productivity (>‐20%) by 2100, and a correspondingly significant rise in the Arctic (>+50%). However, rather than the future Arctic coming to resemble the current Atlantic, both regions are instead transitioning to a common, low nutrient regime. The North Pacific provides a counterexample where nutrients remain high and productivity increases with elevated temperature. These responses to climate change in the Atlantic and Arctic are common between model resolutions, suggesting an independence from resolution for key impacts. However, some responses, such as those in the North Pacific, differ between the simulations, suggesting the reverse and supporting the drive to more fine‐scale resolutions. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-26T18:36:05.982435-05:
      DOI: 10.1002/2015JC011167
  • Weakening of subduction in the Subtropical Mode Water formation region
           observed during 2003–2013
    • Authors: Ran Wang; Fei Yu, Feng Nan
      Abstract: Subduction plays an important role in the formation of the Subtropical Mode Water (STMW). Variation of subduction in the western North Pacific was studied using gridded monthly data from Argo float profiles. The results revealed that there exists a weakening trend of subduction in the STMW formation region (28° N ‐35° N, 142° E‐175° W) due to decreasing winter mixed layer depth (MLD) during 2003‐2013. In the STMW formation region, the mean subduction rate was about 64 m yr−1 and showed a decreasing trend at ‐3.44±2.47 m yr−2 during 2003‐2013. Meanwhile the late winter (March) MLD showed a decreasing trend at ‐4.02±2.41 m yr−1. Associated with the weakening subduction, the STMW volume had a similar decreasing trend in late winter. Diagnostic calculation indicated that change of the mixed layer temperature (MLT) is the key factor in determining the MLD variations in the STMW formation region. It is demonstrated that the increasing MLT tends to decrease oceanic density and stabilize the upper ocean. This oceanic processes act to weaken the vertical mixing and decrease the MLD, resulting in the weakening of subduction. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-23T05:55:11.316265-05:
      DOI: 10.1002/2015JC010967
  • Phenology of particle size distributions and primary productivity in the
           North Pacific subtropical gyre (Station ALOHA)
    • Authors: Angelicque E. White; Ricardo M. Letelier, Amanda L. Whitmire, Benedetto Barone, Robert R. Bidigare, Matthew J. Church, David M. Karl
      Abstract: The particle size distribution (PSD) is a critical aspect of the oceanic ecosystem. Local variability in the PSD can be indicative of shifts in microbial community structure and reveal patterns in cell growth and loss. The PSD also plays a central role in particle export by influencing settling speed. Satellite‐based models of primary productivity (PP) often rely on aspects of photophysiology that are directly related to community size structure. In an effort to better understand how variability in particle size relates to PP in an oligotrophic ecosystem, we collected laser diffraction based depth‐profiles of the PSD and pigment‐based classifications of phytoplankton functional types (PFTs) on an approximately monthly basis at the Hawaii Ocean Time‐series Station ALOHA, in the North Pacific subtropical gyre. We found a relatively stable PSD in the upper water column. However, clear seasonality is apparent in the vertical distribution of distinct particle size classes. Neither laser diffraction‐based estimations of relative particle size nor pigment‐based PFTs was found to be significantly related to the rate of 14C‐based PP in the light‐saturated upper euphotic zone. This finding indicates that satellite retrievals of particle size, based on particle scattering or ocean color would not improve parameterizations of present‐day bio‐optical PP models for this region. However, at depths of 100 ‐ 125 m where irradiance exerts strong control on PP, we do observe a significant linear relationship between PP and the estimated carbon content of 2 ‐ 20 μm particles. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-23T05:54:56.694881-05:
      DOI: 10.1002/2015JC010897
  • Southern Ocean eddy phenomenology
    • Abstract: Mesoscale eddies are ubiquitous features in the Southern Ocean, yet their phenomenology is not well quantified. To tackle this task, we use satellite observations of sea level anomalies and sea‐surface temperature as well as in‐situ temperature and salinity measurements from profiling floats. Over the period 1997 through 2010, we identified over a million mesoscale eddy instances, and were able to track about 105 of them over one month or more. The Antarctic Circumpolar Current (ACC), the boundary current systems, and the regions where they interact are hot‐spots of eddy presence, representing also the birth places and graveyards of most eddies. These hot‐spots contrast strongly to areas shallower than about 2000 m, where mesoscale eddies are essentially absent, likely due to topographical steering. Anticyclones tend to dominate the southern subtropical gyres, and cyclones the northern flank of the ACC. Major causes of regional polarity dominance are larger formation numbers and lifespans, with a contribution of differential propagation pathways of long‐lived eddies. Areas of dominance of one polarity are generally congruent with the same polarity being longer‐lived, bigger, of larger amplitude, and more intense. Eddies extend down to at least 2000 m. In the ACC, eddies show near surface temperature and salinity maxima, whereas eddies in the subtropical areas generally have deeper anomaly maxima, presumably inherited from their origin in the boundary currents. The temperature and salinity signatures of the average eddy suggest that their tracer anomalies are a result of both trapping in the eddy‐core and stirring. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-23T03:55:49.532273-05:
      DOI: 10.1002/2015JC011047
  • Global Cs‐band Envisat, RADARSAT‐2 and Sentinel‐1 SAR
           measurements in copolarization and cross polarization
    • Authors: A. Mouche; B. Chapron
      Abstract: Using co‐located ASCAT and ECMWF winds, a careful global analysis of ENVISAT and Sentinel‐1 synthetic aperture radar (SAR) measurements helps to refine, at medium resolution (tens of kilometers) and especially for HH configuration, a C‐band geophysical model function (GMF, i.e. C‐SARMOD) to analyze wind sensitivity for different incidence and azimuth angles. Results unify major findings from previous global and case studies for polarization ratio (PR, VV/HH), polarization difference (PD, VV‐HH), and cross‐polarization (CP). At lower level than standard 2‐scale predictions, PR increases with increasing incidence angle, and decreases with increasing wind speed. PR further exhibits a strong azimuthal modulation, with maximum values in downwind configurations. The PD azimuth modulation is found more pronounced for VV than HH (VV being larger than HH), reaching maximum values for wind speed about 10 m/s. CP signals decrease with incidence angle, but increase with wind speed, especially beyond 10 m/s, with no evidence of saturation. Remarkably, this also applies to HH crosswind measurements. This comparable high wind sensitivity for both CP and HH crosswind signals, with a clear departure from PD ones, can be related to the onset of vigorous breaking events, large enough to impact in‐ and out‐of‐plane local tilts. Considering that VV polarization best maximizes the polarized resonant contribution, combined CP and VV wide swath SAR observations can thus have the potential to efficiently map and contrast local directional aspects. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-23T03:53:41.988163-05:
      DOI: 10.1002/2015JC011149
  • Modeling the impact of tidal flows on the biological productivity of the
           Alboran sea
    • Abstract: The control of phytoplankton production by tidal forcing in the Alboran Sea is investigated with a high‐resolution ocean circulation model coupled to an ecosystem model. The aim of the modeling efforts was to elucidate the role of tides in sustaining the high biological productivity of the Alboran Sea, as compared with the rest of the Mediterranean sub‐basins. It is shown that tidal forcing accounts for an increase of phytoplankton biomass and primary productivity in the basin of about 40% with respect to a non‐tidal circulation, and about 60% in the western Alboran Sea alone. The tidal dynamics of the Strait of Gibraltar is shown to be the primary factor in determining the enhancement of productivity, pumping nutrients from depth to the photic zone in the Alboran Sea. Model results indicate that the biological implications of the propagating internal tides are small. These results imply that nutrient transports through the Strait of Gibraltar have to be parametrized in ocean models that do not resolve tides in order to properly represent the biochemical budgets of the Alboran Sea. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-23T03:53:30.307557-05:
      DOI: 10.1002/2015JC010885
  • The Canary basin contribution to the seasonal cycle of the Atlantic
           Meridional Overturning Circulation at 26°N
    • Abstract: This study examines the seasonal cycle of the Atlantic Meridional Overturning Circulation (AMOC) and its eastern boundary contributions. The cycle has a magnitude of 6 Sv, as measured by the RAPID/MOCHA/WBTS project array at 26° N, which is driven largely by the eastern boundary. The eastern boundary variations are explored in the context of the regional circulation around the Canary Islands. There is a three month lag between maximum wind forcing and the largest eastern boundary transports, which is explained in terms of a model for Rossby wave generated at the eastern boundary. Two dynamic processes take place through the Lanzarote Passage (LP) in fall: the recirculation of the Canary Current and the northward flow of the Intermediate Poleward Undercurrent. In contrast, during the remaining seasons the transport through the LP is southward due to the Canary Upwelling Current. These processes are linked to the seasonal cycle of the AMOC. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-23T03:53:16.599267-05:
      DOI: 10.1002/2015JC010969
  • Varying responses to Indian monsoons during the past 220 kyr recorded in
           deep‐sea sediments in inner and outer regions of the Gulf of Aden
    • Authors: Yuta Isaji; Hodaka Kawahata, Naohiko Ohkouchi, Nanako O. Ogawa, Masafumi Murayama, Kazuki Inoue, Kensaku Tamaki
      Abstract: Although the climate in the Arabian Sea is controlled primarily by the southwest monsoon, the southwest monsoon has little influence in the Gulf of Aden. To examine the different responses to monsoons between the Gulf of Aden and areas outside the gulf, a comprehensive data set of bulk organic and inorganic geochemistry, sea surface temperature, and δ15N of pheopigments was obtained from deep‐sea sediment cores recovered from inner and outer regions of the gulf. The results indicated that during the past 220 kyr, the influence of the southwest monsoon was stronger in the outer region of the gulf than in the inner region, which implies that the southwest monsoon trajectory has not changed substantially during that time period. Furthermore, influxes of O2‐depleted water from the Southern Ocean and the lateral advection of upwelled seawater also had limited influence in the inner region. In contrast, concentrations of lithogenic materials transported by the southwest monsoon were similar in the two regions. δ15N of pheopigments indicated that during the last glacial maximum, the southwest monsoon was weaker and the northeast monsoon was stronger than at present. A stronger southwest monsoon during interglacials enhanced primary productivity and may have caused anoxic conditions to develop in the Arabian Sea, as indicated by redox proxies in the outer region. Anoxic conditions also formed during MIS 3, but no increase in the primary productivity is indicated; therefore, another mechanism, such as an influx of O2‐depleted water from the Southern Ocean, may have been the cause. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-23T03:53:04.918872-05:
      DOI: 10.1002/2015JC010982
  • Regional sea level change in response to ice mass loss in Greenland, the
           West Antarctic and Alaska
    • Abstract: Besides the warming of the ocean, sea level is mainly rising due to land ice mass loss of the major ice sheets in Greenland, the West Antarctic and the Alaskan Glaciers. However, it is not clear yet how these land ice mass losses influence regional sea level. Here, we use the global Finite Element Sea‐ice Ocean Model (FESOM) to simulate sea surface height (SSH) changes caused by these ice mass losses and combine it with the passive ocean response to varying surface loading using the sea level equation. We prescribe rates of fresh water inflow, not only around Greenland, but also around the West Antarctic Ice Sheet and the mountain glaciers in Alaska with approximately present day amplitudes of 200 Gt/yr, 100 Gt/yr and 50 Gt/yr, respectively. Perturbations in sea level and in freshwater distribution with respect to a reference simulation are computed for each source separately and in their combination. The ocean mass change shows an almost globally uniform behavior. In the North Atlantic and Arctic Ocean mass is redistributed toward coastal regions. Steric sea level change varies locally in the order of several centimeters on advective timescales of decades. Steric effects to local sea level differ significantly in different coastal locations, e.g. at North American coastal regions the steric effects may have the same order of magnitude as the mass driven effect, whereas at the European coast, steric effects remain small during the simulation period. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-19T17:46:41.139479-05:
      DOI: 10.1002/2015JC011244
  • Using Lagrangian‐based process studies to test satellite algorithms
           of vertical carbon flux in the eastern North Pacific Ocean
    • Abstract: The biological carbon pump is responsible for the transport of ∼5‐20 Pg C yr−1 from the surface into the deep ocean but its variability is poorly understood due to an incomplete mechanistic understanding of the complex underlying planktonic processes. In fact, algorithms designed to estimate carbon export from satellite products incorporate fundamentally different assumptions about the relationships between plankton biomass, productivity, and export efficiency. To test the alternate formulations of export efficiency in remote‐sensing algorithms formulated by Dunne et al. [2005], Laws et al. [2011], Henson et al. [2011], and Siegel et al. [2014], we have compiled in situ measurements (temperature, chlorophyll, primary production, phytoplankton biomass and size structure, grazing rates, net chlorophyll change, and carbon export) made during Lagrangian process studies on 7 cruises in the California Current Ecosystem and Costa Rica Dome. A food‐web based approach formulated by Siegel et al. [2014] performs as well or better than other empirical formulations, while simultaneously providing reasonable estimates of protozoan and mesozooplankton grazing rates. By tuning the Siegel et al. [2014] algorithm to match in situ grazing rates more accurately, we also obtain better in situ carbon export measurements. Adequate representations of food‐web relationships and grazing dynamics are therefore crucial to improving the accuracy of export predictions made from satellite–derived products. Nevertheless, considerable unexplained variance in export remains and must be explored before we can reliably use remote sensing products to assess the impact of climate change on biologically‐mediated carbon sequestration. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-19T03:11:07.839882-05:
      DOI: 10.1002/2015JC011264
  • Empirical error functions for monthly‐mean Arctic sea‐ice
    • Abstract: Empirical error functions for 6 different low‐resolution Arctic sea‐ice drift products are presented on monthly time‐scales. To assess the error statistics of the Eulerian ice‐drift products, we use high‐resolution Lagrangian sea‐ice drift obtained from synthetic aperture radar (SAR) images. We processed the Lagrangian drift to Eulerian drift vectors and used them as a reference for the error assessment. Unlike sea‐ice buoy trajectory data traditionally used for that purpose, SAR offers a much larger number of data, which enables us to do a thorough assessment of the error statistics of the Eulerian products under different ice conditions. We find that the error statistics differ between the products and between the seasons. For some products the error is dependent on ice drift speed, while for others the error is rather dependent on ice concentration or on both. The summer ice drifts have roughly a two times larger error than the winter drifts, and show significant mean biases. The calculated empirical error functions allow us to derive uncertainty maps for the respective products. These maps can be used for model validation and data assimilation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-19T02:57:55.553911-05:
      DOI: 10.1002/2015JC011151
  • Arctic pathways of Pacific Water: Arctic Ocean model intercomparison
    • Abstract: Pacific Water (PW) enters the Arctic Ocean through Bering Strait and brings heat, fresh water and nutrients from the northern Bering Sea. The circulation of PW in the central Arctic Ocean is only partially understood due to the lack of observations. In this paper pathways of PW are investigated using simulations with six state‐of‐the art regional and global Ocean General Circulation Models (OGCMs). In the simulations PW is tracked by a passive tracer, released in Bering Strait. Simulated PW water spreads from the Bering Strait region in three major branches. One of them starts in the Barrow Canyon, bringing PW along continental slope of Alaska into the Canadian Straits and then into Baffin Bay. The other initiates in the vicinity of the Herald Canyon and transports PW along the continental slope of the East‐Siberian Sea into the transpolar drift, and then through Fram Strait and the Greenland Sea. The third branch begins near the Herald Shoal and the central Chukchi shelf and brings PW waters into the Beaufort Gyre. Models suggest that the spread of PW through the Arctic Ocean depends on the atmospheric circulation. In the models the wind, acting via Ekman pumping, drives the seasonal and interannual variability of PW in the Canadian Basin of the Arctic Ocean. The wind effects the simulated PW pathways by changing vertical shear of the relative vorticity of the ocean flow in the Canada Basin. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-16T03:30:57.993879-05:
      DOI: 10.1002/2015JC011299
  • Sea surface temperature and salinity product comparison against external
           in situ data in the Arctic Ocean
    • Authors: J.N. Stroh; Gleb Panteleev, Sergey Kirillov, Mikhail Makhotin, Natalia Shakhova
      Abstract: Sea‐surface temperature and salinity (SST/S) in the Arctic Ocean (AO) are largely governed by sea‐ice and continental runoff rather than evaporation and precipitation as in lower latitude oceans, and global satellite analyses and models which incorporate remotely‐observed SST/S may be inaccurate in the AO due to lack of direct measurements for calibrating satellite data. For this reason, we are motivated to validate several {satellite} sea‐surface temperature (SST) data products and SST/S models by comparing gridded data in the AO with oceanographic records from 2006–2013. Statistical analysis of product‐minus‐observation differences reveals that the satellite SST products considered have a temperature bias magnitude of less than 0.5°C compared to ship‐based CTD measurements, and most of these biases are negative in sign. SST/S models also show an overall negative temperature bias, but no common sign or magnitude of salinity bias against CTD data. Ice Tethered Profiler (ITP) near‐surface data spans the seasons of several years, and these measurements reflect a sea‐ice dominated region where the ocean surface cannot be remotely observed. Against this data, many of the considered models and products show large errors with detectable seasonal differences in SST bias. Possible sources of these errors are discussed, and two adjustments of product SST on the basis of sea‐ice concentration are suggested for reducing bias to within less than 0.01$^{\circ}$C of ITP near‐surface temperatures. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-16T03:30:10.627429-05:
      DOI: 10.1002/2015JC011005
  • The modulation of the seasonal cross‐shelf sea level variation by
           the cold pool in the Middle Atlantic Bight
    • Abstract: This study explores the influence of the cold pool in the Middle Atlantic Bight (MAB) to cross‐shelf sea surface slope by fitting an annual harmonic to temperature and salinity profiles from 1993 to 2012, and compares to the 20‐year‐averaged altimetry sea level anomaly (SLA). The consistency within bottom temperature, thermal steric height, total steric height and altimetry observation validates that the cold pool induces depressed sea level in the middle shelf overlapping with the dominant surface seasonal cycles. Temporally, the cold pool pattern is most apparent in July and August as a result of magnitude competition between the thermal and haline steric height. In addition, Ensemble Empirical Mode Decomposition (EEMD) is employed to reconstruct the altimetry SLA and reveals the middle‐shelf depression pattern from single year's SLA data. The locations of the SLA depression from 1993 to 2012 agree with the cold pool locations identified from in‐situ measurements, suggesting a promising application of altimetry SLA in the cold pool study. Conclusively, this study reveals the modulation of the cross‐shelf sea level variation by the cold pool, and contributes to the understanding of the sea level response to water masses on the continental shelf. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-15T10:16:46.12713-05:0
      DOI: 10.1002/2015JC011255
  • Reconstruction of the 236U input function for the northeast Atlantic
           Ocean—Implications for 129I/236U and 236U/238U‐based tracer
    • Abstract: A reconstruction of historical discharges of 236U into the Northeast Atlantic Ocean by nuclear installations is presented. The nuclear reprocessing facilities Sellafield (SF), Great Britain (GB) and La Hague (LH), France and potentially also the nuclear fuel processing installation Springfields (SP), GB represent the main contributors of 236U in the Northeast Atlantic Ocean. Because data on 236U releases is lacking, 236U discharges from SP and SF are estimated based on the U‐isotopic systematics found in the discharges from LH. The resulting reconstruction of 236U releases indicates that, until 2013, a total of (95±32) kg of 236U was discharged from SF, SP, and LH. In a second step, the reconstructed 236U releases are combined with 129I data from literature and oceanic and atmospheric box models are used to derive the 129I/236U and 236U/238U input functions that, for example, can be used to calculate tracer ages of Atlantic Waters in the Arctic Ocean. Our conceptual results show that the combination of 129I/236U and 236U/238U generally allows the estimation of tracer ages over the past approximately 25 yr if contributions of 236U from global fallout are considered. Finally, as a proof of concept, the new method is applied to calculate tracer ages of Arctic Ocean surface samples (collected in 2011/12) and the results are in good agreement with literature data. We conclude that the combination of 129I/236U with 236U/238U in a dual tracer approach provides a sensitive tool for the calculation of tracer ages and ventilation rates in the North Atlantic region. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-15T10:15:33.474372-05:
      DOI: 10.1002/2015JC011116
  • Modeling comprehensive chemical composition of weathered oil following a
           marine spill to predict ozone and potential secondary aerosol formation
           and constrain transport pathways
    • Authors: Greg T. Drozd; David R. Worton, Christoph Aeppli, Christopher M. Reddy, Haofei Zhang, Evan Variano, Allen H. Goldstein
      Abstract: Releases of hydrocarbons from oil spills have large environmental impacts in both the ocean and atmosphere. Oil evaporation is not simply a mechanism of mass loss from the ocean, as it also causes production of atmospheric pollutants. Monitoring atmospheric emissions from oil spills must include a broad range of volatile organic compounds (VOC), including intermediate‐ and semi‐volatile compounds (IVOC, SVOC), which cause secondary organic aerosol (SOA) and ozone production. The Deepwater Horizon (DWH) disaster in the northern Gulf of Mexico during Spring/Summer of 2010 presented a unique opportunity to observe SOA production due to an oil spill. To better understand these observations, we conducted measurements and modeled oil evaporation utilizing unprecedented comprehensive composition measurements, achieved by gas chromatography with vacuum ultra‐violet time of flight mass spectrometry (GC‐VUV‐HR‐ToFMS) . All hydrocarbons with 10 to 30 carbons were classified by degree of branching, number of cyclic rings, aromaticity, and molecular weight; these hydrocarbons comprise ∼50% of total oil mass.[Worton et al.] Such detailed and comprehensive characterization of DWH oil allowed bottom‐up estimates of oil evaporation kinetics. We developed an evaporative model, using solely our composition measurements and thermodynamic data, that is in excellent agreement with published mass evaporation rates and our wind tunnel measurements. Using this model we determine surface slick samples are composed of oil with a distribution of evaporative ages and identify and characterize probable sub‐surface transport of oil. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-15T10:14:18.693327-05:
      DOI: 10.1002/2015JC011093
  • Crossing sea state and rogue wave probability during the Prestige accident
    • Abstract: We discuss the crossing sea state and the probability of rogue waves during the accident of the tanker Prestige on 13 November 2002. We present newly computed hindcast spectra for every hour during that day at nearby locations, showing the development of a bimodal sea state with two wave systems crossing at nearly right angle. We employ four different nonlinear models capable of computing the phase‐resolved sea surface from the hindcast spectra, allowing us to estimate statistics for the occurrence of rogue waves. At the location and moment of the accident, the models give expected values for the kurtosis κ = 3.0119 ± 0.0078. The models coincide that the maximum crest elevation was about 5–6% larger than the expected maximum crest elevation in a Gaussian sea at the moment of the accident. We also conclude that the possible nonlinear interaction between the two crossing wave systems practically did not modify neither the kurtosis nor the largest crest elevation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-13T10:29:34.561939-05:
      DOI: 10.1002/2015JC011161
  • Salt precipitation in sea ice and its effect on albedo, with application
           to Snowball Earth
    • Authors: Regina C. Carns; Richard E. Brandt, Stephen G. Warren
      Abstract: During the initial freezing of the tropical ocean on Snowball Earth, the first ice to form would be sea ice, which contains salt within inclusions of liquid brine. At temperatures below −23°C, significant amounts of the salt begin to crystallize, with the most abundant salt being hydrohalite (NaCl·2H2O.) These crystals scatter light, increasing the ice albedo. In this paper we present field measurements of the albedo of cold sea ice and laboratory measurements of hydrohalite precipitation. Precipitation of salt within brine inclusions was observed on windswept bare ice of McMurdo Sound at the coast of Antarctica (78°S) in early austral spring. Salinity and temperature were measured in ice cores. Spectral albedo was measured on several occasions during September and October. The albedo showed a gradual increase with decreasing temperature, consistent with salt precipitation. Laboratory examination of thin sections from the ice cores showed that the precipitation process exhibits hysteresis, with hydrohalite precipitating over a range of temperatures between −28°C and −35°C but dissolving at about −23°C. The causes of the hysteresis were investigated in experiments on laboratory‐grown sea ice with different solute mixtures. All mixtures showed hysteresis, suggesting that it may be an inherent property of hydrohalite precipitation within brine inclusions rather than being due to biological macromolecules or interactions between various salts in seawater. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-11T23:34:46.339361-05:
      DOI: 10.1002/2015JC011119
  • Nonlinear subsidence at Fremantle, a long‐recording tide gauge in
           the Southern Hemisphere
    • Authors: W. E. Featherstone; N. T. Penna, M. S. Filmer, S. D. P. Williams
      Abstract: A combination of independent evidence (continuous GPS, repeat geodetic leveling, groundwater abstraction, satellite altimetry and tide gauge (TG) records) shows that the long‐recording Fremantle TG has been subsiding in a non‐linear way since the mid‐1970s due to time‐variable groundwater abstraction. The vertical land motion (VLM) rates vary from approximately −2 mm/yr to −4 mm/yr (i.e., subsidence), thus producing a small apparent acceleration in mean sea level computed from the Fremantle TG records. We exemplify that GPS‐derived VLM must be geodetically connected to the TG to eliminate the commonly used assumption that there is no differential VLM when the GPS is not co‐located with the TG. In the Perth Basin, we show that groundwater abstraction can be used as a diagnostic tool for identifying non‐linear VLM that is not evident in GPS time series alone. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-09T17:51:34.929008-05:
      DOI: 10.1002/2015JC011295
  • Spatial and temporal variations of the seasonal sea level cycle in the
           northwest Pacific
    • Abstract: The seasonal sea level variations observed from tide gauges over 1900‐2013 and gridded satellite altimeter product AVISO over 1993‐2013 in the northwest Pacific have been explored. The seasonal cycle is able to explain 60‐90% of monthly sea level variance in the marginal seas, while it explains less than 20% of variance in the eddy‐rich regions. The maximum annual and semi‐annual sea level cycles (30cm and 6cm) are observed in the north of the East China Sea and the west of the South China Sea respectively. AVISO was found to underestimate the annual amplitude by 25% compared to tide gauge estimates along the coasts of China and Russia. The forcing for the seasonal sea level cycle was identified. The atmospheric pressure and the steric height produce 8‐12cm of the annual cycle in the middle continental shelf and in the Kuroshio Current regions separately. The removal of the two attributors from total sea level permits to identify the sea level residuals that still show significant seasonality in the marginal seas. Both nearby wind stress and surface currents can explain well the long‐term variability of the seasonal sea level cycle in the marginal seas and the tropics because of their influence on the sea level residuals. Interestingly, the surface currents are a better descriptor in the areas where the ocean currents are known to be strong. Here, they explain 50‐90% of inter‐annual variability due to the strong links between the steric height and the large‐scale ocean currents. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-09T17:50:58.001427-05:
      DOI: 10.1002/2015JC011154
  • Inferred support for disturbance‐recovery hypothesis of North
           Atlantic phytoplankton blooms
    • Authors: Matthew J. Smith; Derek P. Tittensor, Vassily Lyutsarev, Eugene Murphy
      Abstract: Analyses of satellite‐derived chlorophyll data indicate that the phase of rapid phytoplankton population growth in the North Atlantic (the ‘spring bloom') is actually initiated in the winter rather than the spring, contradicting Sverdrup's Critical Depth Hypothesis. An alternative disturbance‐recovery hypothesis (DRH) has been proposed to explain this discrepancy, in which the rapid deepening of the mixed layer reduces zooplankton grazing rates sufficiently to initiate the bloom. We use Bayesian parameter inference on a simple Nutrient‐Phytoplankton‐Zooplankton (NPZ) to investigate the DRH and also investigate how well the model can capture the multiyear and spatial dynamics of phytoplankton concentrations and population growth rates. Every parameter in our NPZ model was inferred as a probability distribution given empirical constraints, this provides a more objective method to identify a model parameterisation given available empirical evidence, rather than fixing or tuning individual parameter values. Our model explains around 75% of variation in the seasonal dynamics of phytoplankton concentrations, 30% of variation in their population rates of change, and correctly predicts the phases of population growth and decline. Our parameter‐inferred model supports DRH, revealing the sustained reduction of grazing due to mixed layer deepening as the driving mechanism behind bloom initiation, with the relaxation of nutrient limitation being another contributory mechanism. Our results also show that the continuation of the bloom is caused in part by the maintenance of phytoplankton concentrations below a level that can support positive zooplankton population growth. Our approach could be employed to formally assess alternative hypotheses for bloom formation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-08T09:49:08.73033-05:0
      DOI: 10.1002/2015JC011080
  • Spatial variability of absorption coefficients over a biogeochemical
           gradient in a large and optically complex shallow lake
    • Abstract: In order to improve robustness of remote sensing algorithms for lakes, it is vital to understand the variability of inherent optical properties (IOPs) and their mass‐specific representations (SIOPs). In this study, absorption coefficients for particulate and dissolved constituents were measured at 38 stations distributed over a biogeochemical gradient in Lake Balaton, Hungary. There was a large range of phytoplankton absorption (aph(λ)) over blue and red wavelengths (aph(440)=0.11‐4.39 m−1, aph(675)=0.048‐2.52 m−1), while there was less variability in chlorophyll‐specific phytoplankton absorption (a*ph(λ)) in the lake (a*ph(440)=0.022±0.0046 m2 mg−1, a*ph(675)=0.010±0.0020 m2 mg−1) and adjoining wetland system, Kis‐Balaton (a*ph(440)=0.017±0.0015 m2 mg−1, a*ph(675)=0.0088±0.0017 m2 mg−1). However, in the UV, a*ph(350) significantly increased with increasing distance from the main inflow (River Zala). This was likely due to variable production of photoprotective pigments (e.g. MAAs) in response to the decreasing gradient of colored dissolved organic matter (CDOM). The slope of CDOM absorption (SCDOM) also increased from west to east due to larger terrestrial CDOM input in the western basins. Absorption by non‐algal particles (aNAP(λ)) was highly influenced by inorganic particulates, as a result of the largely mineral sediments in Balaton. The relative contributions to the absorption budget varied more widely than oceans with a greater contribution from NAP (up to 30%), and wind speed affected the proportion attributed to NAP, phytoplankton or CDOM. Ultimately, these data provide knowledge of the heterogeneity of (S)IOPs in Lake Balaton, suggesting the full range of variability must be considered for future improvement of analytical algorithms for constituent retrieval in inland waters. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-08T09:48:49.507472-05:
      DOI: 10.1002/2015JC011202
  • AMSR2 calibration: Intercomparison of RSS and JAXA brightness temperatures
    • Authors: Kyle. A. Hilburn; Chelle L. Gentemann
      Abstract: This study provides an intercomparison of two independent TB calibrations for the AMSR2 sensor. The Remote Sensing Systems (RSS) calibration is based on a radiative transfer model, a method used for all microwave sensors. The Japan Aerospace Exploration Agency (JAXA) calibration is based on pre‐launch measurements of the sensor characteristics. Over the full range of TB, differences between the two calibrations are as large as 3‐4 K and vary systematically with TB. This paper shows that the large TB differences are mostly due to large differences in the nonlinearity corrections used by RSS and JAXA, which are likely due to on‐orbit versus pre‐launch behavior. Despite the disagreement, both JAXA and RSS find nonlinearity corrections of 3 K or more. Such large nonlinearity complicates accurate intercalibration, and a major conclusion of this paper is that future radiometer designs should make strict nonlinearity requirements (0.1‐0.2%) a primary design consideration. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-08T09:48:39.011545-05:
      DOI: 10.1002/2015JC011368
  • An inversion model based on salinity and remote sensing reflectance for
           estimating the phytoplankton absorption coefficient in the Saint Lawrence
    • Abstract: The inversion of individual inherent optical properties (IOPs) is very challenging in optically complex waters and within the violet spectral range (i.e., 380‐450 nm) due to the strong light attenuation caused by chromophoric dissolved organic matter, non‐algal particulates and phytoplankton. Here, we present a technique to better discriminate light absorption contributions due to phytoplankton based on a hybrid model (QAA‐hybrid) that combines regional Saint Lawrence System estimates of IOPs derived from a quasi‐analytical algorithm (hereafter QAA‐SLE) and empirical relationships between salinity and remote sensing reflectance. Preliminary results in the Saint Lawrence System during May 2000 and April 2001 showed that QAA‐hybrid estimates of phytoplankton absorption coefficient at 443 nm have a smaller bias with respect to in situ measurements (root mean square deviation, RMSD = 0.156) than those derived from QAA‐SLE (RMSD = 0.341). These results were valid for surface waters (i.e., 0‐5 m depth) of the lower estuary with a salinity and chlorophyll‐a concentration range of 22‐28 psu and 2.1‐ 13.8 mg m−3, respectively. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-08T09:47:52.755239-05:
      DOI: 10.1002/2015JC011079
  • Silicon isotopic chemistry in the Changjiang Estuary and coastal regions:
           Impacts of physical and biogeochemical processes on the transport of
           riverine dissolved silica
    • Authors: A.Y. Zhang; J. Zhang, J. Hu, R.F. Zhang, G.S. Zhang
      Abstract: The dissolved silica (DSi) concentration and silicon isotopic composition (δ30Si) of surface water samples from the Changjiang Estuary was measured in summer and winter to study the behavior of DSi fluvial inputs into the estuary. The DSi concentration decreased away from the estuary and had a linear relationship with salinity, suggesting that mixing between river water and seawater is the dominant effect on DSi levels in the study area. Measured δ30Si in the Changjiang Estuary ranged from +1.48‰ to +2.35‰ in summer, and from +1.54‰ to +1.95‰ in winter. As a result of low light levels and abundant DSi riverine inputs, DSi remains relatively unaffected by biological utilization and fractionation in the near‐shore region, and the isotopic imprint of water from the Changjiang can still be detected up to a salinity level of 20 in summer. An obvious increase in δ30Si was observed beyond this salinity level, indicating a significant increase in biological utilization and fractionation of DSi in high salinity waters. Lower water temperatures and light levels that prevail over the winter lead to the reduced fractionation of DSi compared with that in summer. The fractionation factor (30ε) was estimated using a steady state model to the high salinity waters, yielding a value of −0.95‰, which is in agreement with previous results obtained for Skeletonema costatum in cultivation experiments. The results of this study suggest that silicon isotopes can be used to identify the impact of biological utilization on the behavior of DSi in highly dynamic estuarine environments. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-07T04:41:57.42008-05:0
      DOI: 10.1002/2015JC011050
  • Joint assimilation of Aquarius‐derived sea surface salinity and
           AVHRR‐derived sea surface temperature in an Ocean General
           Circulation Model using SEEK filter: Implication for mixed layer depth and
           barrier layer thickness
    • Authors: Abhisek Chakraborty; Rashmi Sharma, Raj Kumar, Sujit Basu
      Abstract: Sea surface salinity (SSS) from Aquarius mission and sea surface temperature (SST) from Advanced Very High Resolution Radiometer (AVHRR) for the years 2012‐2014 are assimilated into the global Massachusetts Institute of Technology General Circulation Model (MITGCM). Investigation of the impact of assimilation of these two datasets on simulated mixed layer depth (MLD) and barrier layer thickness (BLT) forms the core of our study. The method of assimilation is the Singular Evolutive Extended Kalman (SEEK) filter. Several assimilation runs are performed. Single parameter assimilation, as well as joint assimilation, is conducted. To begin with, the model simulated SST and SSS are compared with independent Argo observations of these two parameters. Use of latitudinally varying error variances, which is a novel feature of our study, gives rise to the significant improvement in the simulation of SSS and SST. The best result occurs when joint assimilation is performed. Afterward, simulated MLD and BLT are compared with the same parameters derived from Argo observations forming an independent validation dataset. Comparisons are performed both in temporal and spatial domains. Significant positive impact of assimilation is found in all the cases studied and joint assimilation is found to outperform single parameter assimilation in each of the cases considered. It is found that simulations of MLD and BLT improve up to 24% and 29% respectively when a joint assimilation of SSS and SST is carried out. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-06T10:17:01.770042-05:
      DOI: 10.1002/2015JC010934
  • Downward lee wave radiation from tropical instability waves in the central
           equatorial Pacific Ocean: A possible energy pathway to turbulent mixing
    • Authors: Yuki Tanaka; Toshiyuki Hibiya, Hideharu Sasaki
      Abstract: Turbulent mixing in the equatorial Pacific Ocean is an important process that controls diapycnal heat transport and hence affects the air‐sea interactions and global climate. It is recently shown that, in the eastern equatorial Pacific, strong mixing is induced in the thermocline by enhanced vertical shear associated with tropical instability waves (TIWs), which propagate westward along the equator at a speed of ∼0.5 m s−1 with a wavelength of ∼1000 km. In this study, using a high‐resolution ocean general circulation model, we show that the TIWs can play an important role in inducing turbulent mixing in the thermocline also in the central equatorial Pacific, although the thermocline is too deep to be directly affected by the vertical shear of the TIWs. The front of the TIW is clearly manifested as a narrow strip of strong convergence of horizontal surface flow, from which area downward and westward propagating internal waves are intermittently emanated. These internal waves can be interpreted as lee waves generated by the surface‐flow convergence zone, which acts like an inverted obstacle moving along the stratified ocean surface by inducing downward flow. The associated downward energy flux below the surface mixed layer increases as the TIW structure becomes deeper toward the central equatorial Pacific, so that the energy pathway to turbulent mixing in the thermocline can be created. The downward energy flux integrated over the entire equatorial Pacific and averaged during January 2011 amounts to ∼8.1 GW, occupying a significant fraction of the energy input to the TIWs. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-06T10:11:32.644537-05:
      DOI: 10.1002/2015JC011017
  • Backscattering by very small particles in coastal waters
    • Authors: Xiaodong Zhang; Deric J. Gray
      Abstract: The volume scattering and backscattering by very small particles (VSPs) of sizes  0.2 µm), accounting for 40‐80% of total backscattering at 532 nm, while only account for
      PubDate: 2015-10-06T10:11:21.506832-05:
      DOI: 10.1002/2015JC010936
  • Decadal variability in seawater pH in the West Pacific: Evidence from
           coral δ11B records
    • Authors: Gangjian Wei; Zhibing Wang, Ting Ke, Ying Liu, Wenfeng Deng, Xuefei Chen, Jifeng Xu, Ti Zeng, Luhua Xie
      Abstract: Long‐term seawater pH records are essential for evaluating the rates of ocean acidification (OA) driven by anthropogenic emissions. Widespread, natural decadal variability in seawater pH superimposes on the long‐term anthropogenic variations, likely influencing the OA rates estimated from the pH records. Here, we report a record of annual seawater pH estimated using the δ11B proxy over the past 159 years reconstructed from a Porites coral collected to the east of Hainan Island in the northern South China Sea (SCS). By coupling this time series with previously reported long‐term seawater pH records in the West Pacific, the decadal variability in seawater pH records and its possible driving mechanisms were investigated. The results indicate that large decadal variability in seawater pH has occurred off eastern Hainan Island over the past 159 years, in agreement with previous records. The Qiongdong upwelling system, which controls nutrient supplies, regulates surface water productivity, and is driven by the East Asian summer monsoon, is the primary control of this decadal variability, while terrestrial inputs appear not influence significantly. Meanwhile the impacts of the Pacific Decadal Oscillation (PDO) and the El Nino and Southern Oscillation (ENSO) systems on seawater pH off eastern Hainan Island is likely limited. In contrast, the PDO is the main factor to influence the decadal seawater pH variability offshore the East Australia, while the mechanism controlling the decadal seawater pH variability in Guam is not clear yet. Meanwhile, The rate of decrease in seawater pH estimated from coral records are significantly different in different regions and over different time spans, which may reflect a combination of natural decadal variability in seawater pH and long‐term variations. Therefore, understanding the mechanisms driving natural variability in seawater pH is important for improving estimates of ocean acidification rates driven by anthropogenic emissions. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-05T03:48:14.446356-05:
      DOI: 10.1002/2015JC011066
  • Effect of sea‐ice melt on inherent optical properties and vertical
           distribution of solar radiant heating in Arctic surface waters
    • Abstract: The inherent optical properties (IOP) of Polar Waters (PW) exiting the Arctic Ocean in the East Greenland Current (EGC) and of the inflowing Atlantic waters (AW) in the West Spitsbergen Current (WSC) were studied in late summer when surface freshening due to sea‐ice melt was widespread. The absorption and attenuation coefficients in PW were significantly higher than previous observations from the western Arctic. High concentrations of colored dissolved organic matter (CDOM) resulted in 50‐60% more heat deposition in the upper meters relative to clearest natural waters. This demonstrates the influence of terrigenous organic material inputs on the optical properties of waters in the Eurasian Basin. Sea‐ice melt in CDOM‐rich PW decreased CDOM absorption, but an increase in scattering nearly compensated for lower absorption, and total attenuation was nearly identical in the sea‐ice meltwater layer. This suggests a source of scattering material associated with sea‐ice melt, relative to the PW. In the AW, melting sea‐ice forms a stratified surface layer with lower absorption and attenuation, than well‐mixed AW waters in late summer. It is likely that phytoplankton in the surface layer influenced by sea‐ice melt are nutrient limited. The presence of a more transparent surface layer changes the vertical radiant heat absorption profile to greater depths in late summer both in EGC and WSC waters, shifting accumulation of solar heat to greater depths and thus this heat is not directly available for ice melt during periods of stratification. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-05T03:48:02.721213-05:
      DOI: 10.1002/2015JC011087
  • Seasonality of tropical Pacific decadal trends associated with the 21st
           century global warming hiatus
    • Abstract: Equatorial Pacific changes during the transition from a non‐hiatus period (pre‐1999) to the present global warming hiatus period (post‐1999) are identified using a combination of reanalysis and observed data sets. Results show increased surface wind forcing has excited significant changes in wind‐driven circulation. Over the last two decades, the core of the Equatorial Undercurrent intensified at a rate of 6.9 cm s−1 decade−1. Similarly, equatorial upwelling associated with the shallow meridional overturning circulation increased at a rate of 2.0 x 10−4 cm s−1 decade−1 in the central Pacific. Further, a seasonal dependence is identified in the sea surface temperature trends and in subsurface dynamics. Seasonal variations are evident in reversals of equatorial surface flow trends, changes in subsurface circulation, and seasonal deepening/shoaling of the thermocline. Anomalous westward surface flow drives cold‐water zonal advection from November to February, leading to surface cooling from December through May. Conversely, eastward surface current anomalies in June‐July drive warm‐water zonal advection producing surface warming from July to November. An improved dynamical understanding of how the tropical Pacific Ocean responds during transitions into hiatus events, including its seasonal structure, may help to improve future predictability of decadal climate variations. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-01T11:30:51.989715-05:
      DOI: 10.1002/2015JC010906
  • Effects of the interannual variability in chlorophyll concentrations on
           sea surface temperatures in the east tropical Indian Ocean
    • Authors: Jinfeng Ma; Hailong Liu, Pengfei Lin, Haigang Zhan
      Abstract: The effects of interannual variability in chlorophyll concentrations on sea surface temperatures in the east tropical Indian Ocean (ETIO) during two positive Indian Ocean Dipole (IOD) events (in the boreal fall of 1997 and 2006) are investigated; this is done through two ocean model experiments, one with and one without the interannual variability of chlorophyll concentrations. A comparison of the two chlorophyll perturbation experiments reveals that, in contrast to the cooling effects at the seasonal timescale, increased chlorophyll concentrations during positive IOD events leads to an increase in the sea surface temperatures within the ETIO. Although upward velocity is enhanced (with a cooling effect), this does not counterbalance the increase in solar heating caused by the increased chlorophyll concentrations. This interannual variability of chlorophyll concentrations in the ETIO could reduce the amplitude of the IOD by about 6%. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-01T10:57:20.876573-05:
      DOI: 10.1002/2015JC010862
  • Estimating diffusivity from the mixed layer heat and salt balances in the
           North Pacific
    • Authors: Meghan F. Cronin; Noel A. Pelland, Steven R. Emerson, William R. Crawford
      Abstract: Data from two National Oceanographic and Atmospheric Administration (NOAA) surface moorings in the North Pacific, in combination with data from satellite, Argo floats and glider (when available), are used to evaluate the residual diffusive flux of heat across the base of the mixed layer from the surface mixed layer heat budget. The diffusion coefficient (i.e., diffusivity) is then computed by dividing the diffusive flux by the temperature gradient in the 20‐m transition layer just below the base of the mixed layer. At Station Papa in the NE Pacific subpolar gyre, this diffusivity is 1 × 10−4 m2/s during summer, increasing to ∼3 × 10−4 m2/s during fall. During late winter and early spring, diffusivity has large errors. At other times, diffusivity computed from the mixed layer salt budget at Papa correlate with those from the heat budget, giving confidence that the results are robust for all seasons except late winter‐early spring and can be used for other tracers. In comparison, at the Kuroshio Extension Observatory (KEO) in the NW Pacific subtropical recirculation gyre, somewhat larger diffusivities are found based upon the mixed layer heat budget: ∼ 3 × 10−4 m2/s during the warm season and more than an order of magnitude larger during the winter, although again, wintertime errors are large. These larger values at KEO appear to be due to the increased turbulence associated with the summertime typhoons, and weaker wintertime stratification. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-01T10:56:40.796831-05:
      DOI: 10.1002/2015JC011010
  • Pairwise surface drifter separation in the western Pacific sector of the
           Southern Ocean
    • Authors: Erik van Sebille; Stephanie Waterman, Alice Barthel, Rick Lumpkin, Shane R. Keating, Chris Fogwill, Chris Turney
      Abstract: The Southern Ocean plays a critical role in global climate, yet the mixing properties of the circulation in this part of the ocean remain poorly understood. Here, dispersion in the vicinity of the Southern Antarctic Circumpolar Current Front, one of the branches of the Antarctic Circumpolar Current, is studied using ten pairs of surface drifters deployed systematically across the frontal jet and its flanks. Drifter pairs were deployed with an initial separation of 13m and report their position every hour. The separation of the pairs over seven months, in terms of their Finite Scale Lyaponuv Exponents (FSLE), dispersion, and diffusivity, is characterized and related to expected behavior from Quasi‐geostrophic (QG) and Surface Quasi‐geostrophic (SQG) theories. The FSLE analysis reveals two submesoscale regimes, with SQG‐like behavior at scales below 3.2km and mixed QG/SQG behavior at scales between 3.2km and 73km. The dispersion analysis, however, suggests QG‐like behavior for the smallest scales. Both dispersion and diffusivity appear isotropic for scales up to 500km. Finally, there is no clear indication of a cross‐jet variation of drifter dispersion. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-01T10:56:20.842918-05:
      DOI: 10.1002/2015JC010972
  • Impacts of tides on tsunami propagation due to potential Nankai Trough
           earthquakes in the Seto Inland Sea, Japan
    • Abstract: The impacts of tides on extreme tsunami propagation due to potential Nankai Trough earthquakes in the Seto Inland Sea (SIS), Japan, are investigated through numerical experiments. Tsunami experiments are conducted based on five scenarios that consider tides at 4 different phases, such as flood, high, ebb, and low tides. The probes that were selected arbitrarily in the Bungo and Kii Channels show less significant effects of tides on tsunami heights and the arrival times of the first waves than those that experience large tidal ranges in inner basins and bays of the SIS. For instance, the maximum tsunami height and the arrival time at Toyomaesi differ by more than 0.5 m and nearly 1 hr, respectively, depending on the tidal phase. The uncertainties defined in terms of calculated maximum tsunami heights due to tides illustrate that the calculated maximum tsunami heights in the inner SIS with standing tides have much larger uncertainties than those of two channels with propagating tides. Particularly in Harima Nada, the uncertainties due to the impacts of tides are greater than 50% of the tsunami heights without tidal interaction. The results recommend to simulate tsunamis together with tides in shallow water environments to reduce the uncertainties involved with tsunami modeling and predictions for tsunami hazards preparedness. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-01T10:56:11.187238-05:
      DOI: 10.1002/2015JC010995
  • Southern Bay of Bengal currents and salinity intrusions during the
           northeast monsoon
    • Authors: H. W. Wijesekera; T. G. Jensen, E. Jarosz, W. J. Teague, E. J. Metzger, D. W. Wang, S. U. P. Jinadasa, K. Arulananthan, L. R. Centurioni, H. J. S. Fernando
      Abstract: Shipboard velocity and hydrographic profiles collected in December 2013 along with drifter observations, satellite altimetry, global ocean nowcast/forecast products, and coupled model simulations were used to examine the circulation in the southern Bay of Bengal as part of ongoing international research efforts in the region. The observations captured the southward flowing East India Coastal Current (EICC) off southeast India and east of Sri Lanka. The EICC was approximately 100 km wide, with speeds exceeding 1 m s−1 in the upper 75 m. East of the EICC, a subsurface‐intensified 300‐km‐wide, northward current was observed, with maximum speeds as high as 1 m s−1 between 50 m and 75 m. The EICC moved low‐salinity water out of the bay and the subsurface northward flow carried high‐salinity water into the bay during typical northeast monsoon conditions during a time period when the central equatorial Indian Ocean was experiencing a westerly wind burst related to the Madden‐Julian Oscillation (MJO) event. While the northward subsurface high‐salinity flow has previously been observed during the southwest monsoon, it was observed during the northeast monsoon. The observations are consistent with northward high‐salinity subsurface flow in numerical model solutions. The analysis suggests that direct forcing along the equator may play a significant role for high‐salinity intrusions east of Sri Lanka. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-01T10:55:53.459824-05:
      DOI: 10.1002/2015JC010744
  • The source of the Leeuwin Current seasonality
    • Authors: K. R. Ridgway; J. S. Godfrey
      Abstract: The seasonal circulation around the southwestern boundary of Australia is documented using sea‐level anomalies from satellite altimetry. Results extrapolated to the coast agree closely with tide gauge observations indicating that seasonal altimeter fields are realistic. Monthly sea‐level maps identify an annual propagating wave along a waveguide extending along the shelf‐edge, from the Gulf of Carpentaria to southern Tasmania. The annual sea‐level pulse does not originate from the Pacific Ocean, as annual Pacific sea‐level variations are completely out of phase with signals south of the Indonesian archipelago. The presence of a phase discontinuity is demonstrated in annual sea‐level, temperature and salinity observations. The origin of the Leeuwin Current seasonality is in the Gulf of Carpentaria where monsoonal winds drive a massive build‐up of sea‐level from November to December. During December to February, a sea‐level ‘pulse' emerges from the region, and rapidly propagates poleward along the western and southern Australian boundary. In the broad shelf region centred at 19°S, an independent process forms a high sea‐level feature when a positive heat flux anomaly induces an annual increase in sea surface temperature which is rapidly mixed through the water column by the strong regional tides. In March the winds relax and switch to a downwelling favourable alongshore component. In this period the sea‐level pulse is essentially in a quasi‐static equilibrium with the annual propagating wind systems. The change in cross‐shelf sea‐level gradient along the 8000 km path‐length at the western and southern boundaries, drives the seasonal changes in the Leeuwin Current flow. This article is protected by copyright. All rights reserved.
      PubDate: 2015-10-01T10:55:16.834715-05:
      DOI: 10.1002/2015JC011049
  • Projected changes to Tasman Sea eddies in a future climate
    • Authors: E. C. J. Oliver; Terence J. O'Kane, N. J. Holbrook
      Abstract: The Tasman Sea is a hot spot of ocean warming, that is linked to the increased poleward influence of the East Australian Current (EAC) over recent decades. Specifically, the EAC produces mesoscale eddies which have significant impacts on the physical, chemical, and biological properties of the Tasman Sea. To effectively consider and explain potential eddy changes in the next 50 years, we use high resolution dynamically downscaled climate change simulations to characterize the projected future marine climate and mesoscale eddies in the Tasman Sea through the 2060s. We assess changes in the marine climate and the eddy field using bulk statistics and by detecting and tracking individual eddies. We find that the eddy kinetic energy is projected to increase along southeast Australia. In addition, we find that eddies in the projected future climate are composed of a higher proportion of anti‐cyclonic eddies in this region and that these eddies are longer lived and more stable. This amounts to nearly a doubling of eddy‐related southward temperature transport in the upper 200 m of the Tasman Sea. These changes are concurrent with increases in baroclinic and barotropic instabilities focussed around the EAC separation point. This poleward transport and increase in eddy activity would be expected to also increase the frequency of sudden warming events, including ocean temperature extremes, with potential impacts on marine fisheries, aquaculture and biodiversity off Tasmania's east coast, through direct warming or competition/predation from invasive migrating species. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-29T11:05:13.92737-05:0
      DOI: 10.1002/2015JC010993
  • Seismic reflection imaging of mixing processes in Fram Strait
    • Authors: Sudipta Sarkar; Katy L. Sheen, Dirk Klaeschen, J. Alexander Brearley, Timothy A. Minshull, Christian Berndt, Richard W. Hobbs, Alberto C. Naveira Garabato
      Abstract: The West Spitsbergen Current, which flows northward along the western Svalbard continental slope, transports warm and saline Atlantic water (AW) into the Arctic Ocean. A combined analysis of high‐resolution seismic images and hydrographic sections across this current has uncovered the oceanographic processes involved in horizontal and vertical mixing of AW. At the shelf break, where a strong horizontal temperature gradient exists east of the warmest AW, isopycnal interleaving of warm AW and surrounding colder waters is observed. Strong seismic reflections characterize these interleaving features, with a negative polarity reflection arising from an interface of warm water overlying colder water. A seismic‐derived sound speed image reveals the extent and lateral continuity of such interleaving layers. There is evidence of obliquely aligned internal waves emanating from the slope at 450–500 m. They follow the predicted trajectory of internal S2 tidal waves and can promote vertical mixing between Atlantic‐ and Arctic‐origin waters. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-24T11:12:19.912896-05:
      DOI: 10.1002/2015JC011009
  • Effect of subtropical mode water on the decadal variability of the
           subsurface transport through the Luzon Strait in the western Pacific Ocean
    • Authors: Kai Yu; Tangdong Qu, Changming Dong, Youfang Yan
      Abstract: Analysis of the 62‐year hindcast outputs from an eddy‐resolving ocean general circulation model shows a good correspondence of the Luzon Strait subsurface transport to the Pacific Decadal Oscillation (PDO) index on a decadal time scale, with the latter leading by about 5 years. The backward particle tracing experiments indicate that the part of the subsurface water in the Luzon Strait generated by the subduction processes come from the Subtropical Mode Water (STMW). The model results also show a strong PDO signal in the subduction rate, as well as the subsurface low potential vorticity (PV), in the formation region of the STMW, and these decadal signals can be traced all the way to the Luzon Strait as PV anomalies follow the subtropical gyre circulation in about 5 years. The PV anomalies from the STMW affect the subsurface net transport in the Luzon Strait through changing the subsurface density structure and then zonal velocity. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-24T11:09:37.073913-05:
      DOI: 10.1002/2015JC011016
  • Tilt of mean sea level along the Pacific coasts of North America and Japan
    • Abstract: The tilt of coastal mean sea level with respect to an equipotential surface is estimated using two fundamentally different approaches. The geodetic approach is based on tide gauge and GPS observations, and a model of the geoid. The ocean approach uses a high resolution, dynamically‐based ocean model to estimate mean dynamic topography. Along the Pacific coast of North America the two approaches give similar large scale profiles with a minimum at about 40°N and a maximum in the northern part of the Gulf of Alaska. Along the Pacific coast of Japan the geodetically determined coastal sea levels indicate an eastward drop of about 20 cm along the south coast and a further northward drop across Tsugaru Strait. Both of these features are reproduced by the ocean models. An analysis of the alongshore momentum balance suggests that alongshore wind stress acting over the inner shelf is the primary driver of the mean sea level profile along the coast of North America. Several large scale features are explained using arrested topographic wave theory. A similar momentum analysis, and an additional study of time variability of sea level and circulation, suggest that the Kuroshio is the main driver of the mean sea level tilt along the south coast of Japan. Discrepancies in the alongshore tilt of sea level estimated by the geodetic and ocean approaches along both coasts are discussed in terms of errors in the ocean and geoid models. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-24T10:40:19.646545-05:
      DOI: 10.1002/2015JC010920
  • Simulating complex storm surge dynamics: Three‐dimensionality,
           vegetation effect, and onshore sediment transport
    • Authors: Andrew Lapetina; Y. Peter Sheng
      Abstract: The 3D hydrodynamics of storm surge events, including the effects of vegetation and impact on onshore transport of marine sediment, have important consequences for coastal communities. Here, complex storm surge dynamics during Hurricane Ike are investigated using a three‐dimensional (3D), vegetation‐resolving storm surge‐wave model (CH3D‐SWAN) which includes such effects of vegetation as profile drag, skin friction, and production, dissipation, and transport of turbulence. This vegetation‐resolving 3D model features a turbulent kinetic energy (TKE) closure model, which uses momentum equations with vegetation induced profile and skin friction drags, a dynamic q2 equation including turbulence production and dissipation by vegetation, as well as vegetation‐dependent algebraic length scale equations, and a Smagorinsky type horizontal turbulence model. This vegetation model has been verified using extensive laboratory tests, but this study is a comparison of 2D and 3D simulations of complex storm surge dynamics during Hurricane Ike. We examine the value of 3D storm surge models relative to 2D models for simulating coastal currents, effects of vegetation on surge, and sediment transport during storm events. Comparisons are made between results obtained using simple 2D formulations for bottom friction, the Manning coefficient (MC) approach, and physics‐based 3D vegetation‐modeling (VM) approach. Lastly, the role that the 3D hydrodynamics on onshore transport and deposition of marine sediments during the storm is investigated. While both the 3D and 2D results simulated the water level dynamics, results of the physics‐based 3D VM approach, as compared to the 2D MC approach, more accurately captures the complex storm surge dynamics. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-24T10:39:55.209738-05:
      DOI: 10.1002/2015JC010824
  • PV dynamics: The role of small‐scale turbulence, submesoscales and
    • Authors: V.M. Canuto
      Abstract: The diabatic and frictional components of the PV fluxes J in the Haynes‐McIntyre conservation law have been studied with physical arguments, scaling laws and numerical simulations. We suggest a procedure that expresses J in terms of buoyancy and momentum fluxes by small scale turbulence SS, sub‐mesoscales SM and mesoscales M. We employ the latest parameterizations of these processes and derive analytic expressions of the diabatic and frictional J fluxes for arbitrary wind stresses; we then consider the case of an Ekman flow. Small scale turbulence: at z=0, down and up‐front winds contribute equally to the frictional component of J while the diabatic component is much larger than that of mesoscales. Sub‐mesoscales: the geostrophic contributions to both diabatic and frictional J have the same sign while the wind contributions have opposite signs. Their magnitude depends on the SM kinetic energy which is derived in terms of large scale parameters. Comparison with numerical simulations is limited since the ones available resolve M but not SM. They concluded that the field patterns of the J fluxes are very similar to those obtained without resolving M, in agreement with the present analysis; a second conclusion that the diabatic component of J is an order of magnitude larger than the frictional one, is also in accordance with present results. When wind stresses are accounted for, down‐front winds lower PV and up‐front winds increase it. The changes in Hoskins' criterion for the onset of symmetric instabilities are discussed This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-24T10:39:29.067645-05:
      DOI: 10.1002/2015JC011043
  • Observed enhanced internal tides in winter near the Luzon Strait
    • Authors: Junliang Liu; Yinghui He, Dongxiao Wang, Tongya Liu, Shuqun Cai
      Abstract: Seasonal characteristics and nonlinear interaction of internal tides (ITs) near the Luzon Strait in the northeastern South China Sea are investigated using 285‐day, in‐situ observation data. It is found that, ITs, which are dominated by the first mode wave throughout the year, are the strongest in subsurface layer. Baroclinic incoherent diurnal (semidiurnal) variance accounts for about 85.7% (78.3%) of diurnal (semidiurnal) ITs. The amplitude and seasonal variation of the diurnal ITs are more prominent than those that are semidiurnal, e.g., the largest kinetic energy densities of diurnal and semidiurnal baroclinic tidal currents are 2.81 and 0.83 KJ/m2 in winter, respectively. It is considered that there are two reasons for the significantly enhanced ITs in winter, (1) it may be due to the Kuroshio intrusion, and (2) the enhanced diurnal ITs may be due to the enhanced diurnal barotropic tidal currents, while the enhanced semidiurnal ITs may be caused by the strong nonlinear interaction between diurnal IT constituents O1 and K1 due to their high vertical shears in subsurface layer. Thus, harmonic semidiurnal constituent D2 with a similar frequency of constituent M2 is induced; it subsequently enhances the semidiurnal ITs in this subsurface layer, and the associated energy is carried downward to enhance the semidiurnal ITs in the upper and lower layers. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-21T11:16:53.812845-05:
      DOI: 10.1002/2015JC011131
  • Direct measurements of World Ocean tidal currents with surface drifters
    • Abstract: Velocities of surface drifters are analyzed to study tidal currents throughout the World Ocean. The global drifter dataset spanning the period 1979‐2013 is used to describe the geographical structure of the surface tidal currents at global scale with a resolution of 2 degrees. Harmonic analysis is performed with two semi‐diurnal, two diurnal and four inferred tidal constituents. Tidal current characteristics (amplitude of semi‐major axis, rotary coefficient, tidal ellipse inclination and Greenwich phase) are mapped over the World Ocean from direct observations. The M2 currents dominate on all the shallow continental shelves with magnitude exceeding 60 cm/s. They are also substantial (4‐5 cm/s) over the main deep topographic features such as the Mid‐Atlantic Ridge, the Southwest Indian Ridge and the Mariana Ridge. The S2 currents have amplitudes typically half the size of the M2 currents, with a maximum of about 30 cm/s. The K1 and O1 currents are important in many shallow seas. They are large in the vicinity of the turning latitudes near 30°N/S where they merge with inertial motions of the same frequency. They are also substantial in the South China Sea and Philippine Sea. Maps of rotary coefficients indicate that all tidal motions are essentially clockwise (anticlockwise) in the Northern (Southern) Hemisphere. The rotary coefficient of the tidal currents are compared with the theory of freely and meridionally propagating baroclinic inertia‐gravity waves. The Greenwich phase of the M2 constituent has large scale coherent propagation patterns which could be interpreted as the propagation of the barotropic tide. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-21T11:16:00.591509-05:
      DOI: 10.1002/2015JC010818
  • Eddy‐topography interactions and the fate of the Persian Gulf
    • Authors: C. Vic; G. Roullet, X. Capet, X. Carton, M. J. Molemaker, J. Gula
      Abstract: The Persian Gulf feeds a warm and salty outflow in the Gulf of Oman (northern Arabian Sea). The salt climatological distribution is relatively smooth in the Gulf of Oman, and the signature of a slope current carrying salty waters is difficult to distinguish hundreds of kilometers past the Strait of Hormuz, in contrast to other outflows of the world ocean. This study focuses on the mechanisms involved in the spreading of Persian Gulf Water (PGW) in the Gulf of Oman, using a regional primitive equation numerical simulation. The authors show that the dispersion of PGW occurs through a regime that is distinct from, for example, the one responsible for the Mediterranean outflow dispersion. The background mesoscale eddy field is energetic and participates actively to the spreading of PGW. Remotely formed eddies propagate into the Gulf of Oman and interact with the topography, leading to submesoscales formation and PGW shedding. Eddy‐topography interactions are isolated in idealized simulations and reveal the formation of intense frictional boundary layers, generating submesoscale coherent vortices (SCVs). Interactions take place at depths encompassing the PGW depth, thus SCVs trap PGW and contribute to its redistribution from the boundaries to the interior of the Gulf of Oman. The overall efficiency of these processes is confirmed by a strong contribution of eddy salt fluxes in the interior of the basin, and is quantified using particle statistics. It is found to be a highly dispersive regime, with an approximated eddy diffusivity of ∼1700 m2s−1. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-21T11:15:40.976464-05:
      DOI: 10.1002/2015JC011033
  • Infragravity‐wave modulation of short‐wave celerity in the
           surf zone
    • Authors: M. Tissier; P. Bonneton, H. Michallet, B.G. Ruessink
      Abstract: The cross‐shore evolution of individual wave celerity is investigated using two high‐resolution laboratory experiments on bichromatic waves. Individual waves are tracked during their onshore propagation and their characteristics, including celerity, are estimated. The intra‐wave variability in celerity is low in the shoaling zone, but increases strongly after breaking. It is maximum when the infragravity wave height to water depth ratio is the largest, that is to say close to the shoreline. There, the observed range of individual wave celerity can be as large as the mean celerity value. This variability can be largely explained by the variations in water depth and velocity induced by the infragravity waves. The differences in celerity are such that they lead to the merging of the waves in the inner surf zone for most of the wave conditions considered. Again, the location at which the first waves start merging strongly correlates with the infragravity wave height to water depth ratio. The consequences of these findings for celerity‐based depth‐inversion techniques are finally discussed. Surprisingly, accounting for the infragravity‐wave modulation of the velocity field in the celerity estimate does not significantly improve depth estimation in the surf zone. However, it is shown that the occurrence of bore merging decreases significantly the coherence of the wave field in the surf zone. This loss of coherence could hamper celerity estimation from pixel intensity time‐series, and explain, at least partly, the relatively poor performance of depth‐inversion techniques in the inner surf zone. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-21T11:12:21.222261-05:
      DOI: 10.1002/2015JC010708
  • Impact of local winter cooling on the melt of Pine Island Glacier,
    • Abstract: The rapid thinning of the ice shelves in the Amundsen Sea is generally attributed to basal melt driven by warm water originating from the continental slope. We examine the hypothesis that processes taking place on the continental shelf contribute significantly to the interannual variability of the ocean heat content and ice shelf melt rates. A numerical model is used to simulate the circulation of ocean heat and the melt of the ice shelves over the period 2006‐2013. The fine model grid (grid spacing 1.5 km) explicitly resolves the coastal polynyas and mesoscale processes. The ocean heat content of the eastern continental shelf exhibits recurrent decreases around September with a magnitude that varies from year to year. The heat loss is primarily caused by surface heat fluxes along the eastern shore in areas of low ice concentration (polynyas). The cold winter water intrudes underneath the ice shelves and reduces the basal melt rates. Ocean temperatures upstream (i.e., at the shelf break) are largely constant over the year and cannot account for the cold events. The cooling is particularly marked in 2012 and its effect on the ocean heat content remains visible over the following years. The study suggests that ocean‐atmosphere interactions in coastal polynyas contribute to the interannual variability of the melt of Pine Island Glacier. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-21T11:12:01.604814-05:
      DOI: 10.1002/2015JC010709
  • Characteristics, vertical structures, and heat/salt transports of
           mesoscale eddies in the southeastern tropical Indian Ocean
    • Authors: Guang Yang; Weidong Yu, Yeli Yuan, Xia Zhao, Fan Wang, Gengxin Chen, Lin Liu, Yongliang Duan
      Abstract: Satellite altimetry sea surface height measurements reveal high mesoscale eddy activity in the southeastern tropical Indian Ocean (SETIO). In this study, the characteristics of mesoscale eddies in the SETIO are investigated by analyzing 564 cyclonic eddy (CE) tracks and 695 anticyclonic eddy (AE) tracks identified from a new version of satellite altimetry data with a daily temporal resolution. The mean radius, lifespan, propagation speed and distance of CEs (AEs) are 149 (153) km, 50 (46) days, 15.3 (16.6) cm s−1, and 651 (648) km, respectively. Some significant differences exist in the eddy statistical characteristics between the new‐version daily altimeter data and the former weekly data. Mean vertical structures of anomalous potential temperature, salinity, geostrophic current, as well as heat and salt transports of the composite eddies, are estimated by analyzing Argo profile data matched to altimeter‐detected eddies. The composite analysis shows that eddy‐induced ocean anomalies are mainly confined in the upper 300 dbar. In the eddy core, CE (AE) could induce a cooling (warming) of 2ºC between 60 and 180 dbar and maximum positive (negative) salinity anomalies of 0.1 (‐0.3) psu in the upper 50 (110) dbar. The meridional heat transport induced by the composite CE (AE) is southward (northward), whereas the salt transport of CE (AE) is northward (southward). Most of the meridional heat and salt transports are carried in the upper 300 dbar. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-21T11:07:35.679475-05:
      DOI: 10.1002/2015JC011130
  • Influence of sea level rise on the dynamics of salt inflows in the Baltic
    • Abstract: The Baltic Sea is a marginal sea, located in a highly industrialized region in Central Northern Europe. Salt water inflows from the North Sea and associated ventilation of the deep exert crucial control on the entire Baltic Sea ecosystem. This study explores the impact of anticipated sea level changes on the dynamics of those inflows. We use a numerical oceanic general circulation model covering both the Baltic and the North Sea. The model sucessfully retraces the essential ventilation dynamics throughout the period 1961 to 2007. A suite of idealized experiments suggests that rising sea level is associated with intensified ventilation as salt water inflows become stronger, longer and more frequent. Expressed quantitatively as a salinity increase in the deep central Baltic Sea we find that a sea level rise of 1 m triggers a saltening of more than 1 PSU. This substantial increase in ventilation is the consequence of the increasing cross section in the Danish Straits amplified by a reduction of vertical mixing. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-15T03:06:56.807923-05:
      DOI: 10.1002/2014JC010642
  • Clusters, deformation, and dilation: Diagnostics for material accumulation
    • Authors: Helga S. Huntley; B. L. Lipphardt, Gregg Jacobs, A. D. Kirwan
      Abstract: Clusters of material at the ocean surface have been frequently observed. Such accumulations of material play an important role in a variety of applications, from biology to pollution mitigation. Identifying where clusters will form can aid in locating, for example, hotspots of biological activity or regions of high pollutant concentration. Here cluster strength is introduced as a new metric for defining clusters when all particle positions are known. To diagnose regions likely to contain clusters without the need to integrate millions of particle trajectories, we propose to use dilation, which quantifies area changes of Lagrangian patches. Material deformation is decomposed into dilation and area‐preserving stretch processes to refine previous approaches based on finite‐time Lyapunov exponents (FTLE) by splitting the FTLE into fundamental kinematic properties. The concepts are developed theoretically and illustrated in the context of a state‐of‐the‐art data‐assimilating predictive ocean model of the Gulf of Mexico. Regions of dilation less than one are shown to be much more likely (six times more likely in the given example) to be visited by particles than those of dilation greater than one. While the relationship is nonlinear, dilation and cluster strength exhibit a fairly good correlation. In contrast, both stretch and Eulerian divergence are found to be uncorrelated with cluster strength. Thus, dilation maps can be used as guides for identifying cluster locations, while saving some of the computational cost of trajectory integrations. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-07T07:30:48.713358-05:
      DOI: 10.1002/2015JC011036
  • Generation and propagation of internal tides and solitary waves at the
           shelf edge of the Bay of Biscay
    • Abstract: High frequency mooring data were collected near the northern shelf edge of the Bay of Biscay to investigate the generation and propagation of internal tides and internal solitary waves (ISWs). During spring tide, strong nonlinear internal tides and large amplitude ISWs are observed every semi‐diurnal tidal period. While onshore propagation was expected since the mooring is located shoreward of the maximum internal tidal generation location, both onshore and seaward traveling internal tides are identified. Within a tidal period at spring tide, three ISW packets are observed. Like internal tides, different ISW packets have opposite (seaward and shoreward) propagating direction. Based on realistic hydrostatic HYCOM simulations, it is suggested that advection by the barotropic tide affects wave generation and propagation significantly and is essential for the seaward traveling internal tides to appear shoreward of their generation location. A two‐layer idealized non‐hydrostatic model derived by Gerkema [1996] further confirms the effect of advection on the generation and propagation of internal tides. Moreover, the two‐layer model reproduces one seaward propagating ISW packet and one shoreward propagating ISW packet, indicating that the offshore and onshore traveling ISWs are excited by nonlinear steepening of the seaward and shoreward traveling internal tides, respectively. This article is protected by copyright. All rights reserved.
      PubDate: 2015-09-07T07:27:26.986261-05:
      DOI: 10.1002/2015JC010827
  • The effects of tides on the water mass mixing and sea ice in the Arctic
    • Authors: Maria V. Luneva; Yevgeny Aksenov, James D. Harle, Jason T. Holt
      Abstract: In this study we use a novel pan‐Arctic sea ice‐ocean coupled model to examine the effects of tides on sea ice and the mixing of water masses. Two 30‐year simulations were performed: one with explicitly resolved tides and the other without any tidal dynamics. We find that the tides are responsible for a ∼15% reduction in the volume of sea ice during the last decade and a redistribution of salinity, with surface salinity in the case with tides being on average ∼ 1.0‐1.8 practical salinity units (PSU) higher than without tides. The ice volume trend in the two simulations also differs: ‐2.09 x103 km3/decade without tides and ‐2.49 x103 km3/decade with tides, the latter being closer to the trend of ‐2.58 x103 km3/decade in the PIOMAS model, which assimilates SST and ice concentration. The three following mechanisms of tidal interaction appear to be significant: (a) strong shear stresses generated by the baroclinic clockwise rotating component of tidal currents in the interior waters; (b) thicker subsurface ice‐ocean and bottom boundary layers; and (c) intensification of quasi‐steady vertical motions of isopycnals (by ∼50%) through enhanced bottom Ekman pumping and stretching of relative vorticity over rough bottom topography. The combination of these effects leads to entrainment of warm Atlantic Waters into the colder and fresher surface waters, supporting the melting of the overlying ice. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-31T19:09:43.870742-05:
      DOI: 10.1002/2014JC010310
  • Wind wave source functions in opposing seas
    • Authors: Sabique Langodan; Luigi Cavaleri, Yesubabu Viswanadhapalli, Ibrahim Hoteit
      Abstract: The Red Sea is a challenge for wave modeling because of its unique two opposed wave systems, forced by opposite winds and converging at its center. We investigate the different physical aspects of wave evolution and propagation in the convergence zone. The two opposing wave systems have similar amplitude and frequency, each driven by the action of its own wind. Wave patterns at the centre of the Red Sea, as derived from extensive tests and intercomparison between model and measured data, suggest that the currently available wave model source functions may not properly represent the evolution of the local fields that appear to be characterized by a less effective wind input and an enhanced white‐capping. We propose and test a possible simple solution to improve the wave‐model simulation under opposing winds and waves condition. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-26T09:51:16.706333-05:
      DOI: 10.1002/2015JC010816
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