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

Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 21, SJR: 2.156, h-index: 61)
Geophysical Research Letters     Full-text available via subscription   (Followers: 42, SJR: 2.668, h-index: 142)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 3, SJR: 2.4, h-index: 109)
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J. of Geophysical Research : Biogeosciences     Full-text available via subscription   (Followers: 5)
J. of Geophysical Research : Earth Surface     Partially Free   (Followers: 22)
J. of Geophysical Research : Oceans     Partially Free   (Followers: 14)
J. of Geophysical Research : Planets     Full-text available via subscription   (Followers: 12)
J. of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 22)
J. of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 13)
Paleoceanography     Full-text available via subscription   (Followers: 4, SJR: 2.16, h-index: 82)
Radio Science     Full-text available via subscription   (Followers: 2, SJR: 0.527, h-index: 47)
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Tectonics     Full-text available via subscription   (Followers: 7, SJR: 2.16, h-index: 79)
Water Resources Research     Full-text available via subscription   (Followers: 123, SJR: 1.769, h-index: 110)
Journal Cover Journal of Geophysical Research : Oceans
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     ISSN (Online) 2169-9291
     Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • Is weaker Arctic sea ice changing the Atlantic water circulation?
    • Authors: Polona Itkin; Michael Karcher, Rüdiger Gerdes
      Pages: n/a - n/a
      Abstract: With a numerical model we test the sensitivity of the Arctic Ocean circulation at mid‐depth (212‐1200 m) to the change in the sea ice rheology parameter P* that controls the sea ice compressive strength. We show that the reduction of the sea ice strength via P* within commonly used envelope reduces the sea ice extent and consequently enhances the ocean surface heat loss in the marginal ice zone. This leads to cooling of the Atlantic water inflow into the Arctic Ocean. As a result Eurasian Basin and Amerasian Basin temperatures are in average cooled by 0.1 °C and 0.05 °C, respectively. An increased sea ice drift speed in the central Arctic leads to an enhanced circulation of the anticyclonic Beaufort Gyre of the Amerasian Basin, which in turn weakens the cyclonic Atlantic water circulation below and enhances the recirculation of the Atlantic water in the Eurasian Basin. Consequently the balance of the volume fluxes through the Arctic gateways changes. Fram Strait net outflow increases by 0.46 Sv, Barents Sea Opening net inflow increases by 0.19 Sv and Davis Strait net outflow decreases by 0.28 Sv. This can spread the effects of the sea ice strength change beyond the limits of the Arctic Ocean and into the deep water convection zones in the North Atlantic. These substantial effects should be considered also in the model optimization efforts where P* is commonly used as one of the tuning parameters to achieve better sea ice simulations, whereas the effects on the ocean circulation are rarely taken into account.
      PubDate: 2014-07-25T23:32:34.515752-05:
      DOI: 10.1002/2013JC009633
  • Variability of oceanic carbon cycle in the North Pacific from seasonal to
           decadal scales
    • Authors: Peng Xiu; Fei Chai
      Pages: n/a - n/a
      Abstract: Variability of upper‐ocean carbon cycle in the North Pacific during 1958‐2010 period is investigated using a physical‐biogeochemical model. Comparisons with in‐situ data from five different oceanographic environments in the South China Sea, Monterey Bay, North Pacific gyre, northwestern Pacific, and Gulf of Alaska indicate that the model usually captures observed seasonal and interannual variability in both sea surface pCO2 and sea‐air CO2 flux. Seasonal variability of pCO2 and CO2 flux in the North Pacific follows the change in sea surface temperature (SST) closely with high and low values in summer and winter, respectively. Total CO2 modifies pCO2 seasonal pattern in an opposite manner with respect to SST, and surface wind speed modifies the magnitude of CO2 flux variations. On interannual and decadal timescales, sea surface pCO2 is primarily controlled by anthropogenic CO2, followed by modulations by the El Niño‐Southern Oscillation and the Pacific Decadal Oscillation (PDO), while sea‐air CO2 flux is significantly regulated by the PDO and the North Pacific Gyre Oscillation (NPGO). We show that anthropogenic CO2 tends to amplify the influence on CO2 flux from the PDO but to damp the influence from the NPGO.
      PubDate: 2014-07-25T23:28:37.197242-05:
      DOI: 10.1002/2013JC009505
  • Insights on the OAFlux ocean‐surface vector wind analysis merged
           from scatterometers and passive microwave radiometers (1987 onward)
    • Authors: Lisan Yu; Xiangze Jin
      Pages: n/a - n/a
      Abstract: A high‐resolution global daily analysis of ocean‐surface vector winds (1987 onward) was developed by the Objectively Analyzed air‐sea Heat Fluxes (OAFlux) project. This study addressed the issues related to the development of the time series through objective synthesis of 12 satellite sensors (2 scatterometers and 10 passive microwave radiometers) using a least‐variance linear statistical estimation. The issues include the rationale that supports the multi‐sensor synthesis, the methodology and strategy that were developed, the challenges that were encountered, and the comparison of the synthesized daily‐mean fields with reference to scatterometers and atmospheric reanalyses. The synthesis was established on the bases that the low and moderate winds (
      PubDate: 2014-07-25T23:28:33.880999-05:
      DOI: 10.1002/2013JC009648
  • Role of the western tropical Pacific in the North Pacific regime shift in
           the winter of 1998/1999
    • Authors: Hyun‐Su Jo; Sang‐Wook Yeh, Ben P. Kirtman
      Pages: n/a - n/a
      Abstract: In this study we examine the role of the western tropical Pacific in the North Pacific regime shift during the winter (December‐January‐February) of 1998/99. The North Pacific regime shift in the winter of 1998/99 is characterized by a dipole‐like structure along 40°N where significant warming is prominent in the western and central North Pacific. This shift might have been associated with an abrupt warming in the western tropical Pacific after 1998/99, in the North Equatorial Current (NEC) bifurcation region (8°N‐18°N, 125°E‐160°E) in particular. The NEC bifurcation region experiences a regime shift from cooling to warming during the 1998/99. Consequently, the Kuroshio current, which originates in the NEC bifurcation region, could transport the anomalous warm water into the North Pacific. In addition, a sudden shift in the NEC bifurcation latitude to the south also contributes to the 1998/99 regime shift in the North Pacific. We suggest a possible mechanism that could have caused the regime shift in the NEC bifurcation region during the 1998/99. An abrupt deepening of the thermocline depth in the NEC bifurcation region from 1997/98 to 1998/99, which is associated with the biggest El Niño in 1997/98 and a subsequent La Niña event in 1998/99, plays a role in initiating the shift in the NEC bifurcation region. Subsequently, the frequent occurrence of the La Niña events after 1998/99 plays a role in maintaining the regime shift toward warming by sustaining a deepening of the thermocline depth.
      PubDate: 2014-07-25T23:18:28.213633-05:
      DOI: 10.1002/2013JC009527
  • Impact of assimilating surface salinity from SMOS on ocean circulation
    • Authors: A. Köhl; M. Sena Martins, D. Stammer
      Pages: n/a - n/a
      Abstract: In a pilot attempt, the GECCO2 synthesis system is being used to investigate the impact of SMOS sea surface salinity (SSS) observations on estimates of SSS and freshwater fluxes. The paper focuses on the period 2010 ‐ 2011, during which, in addition to traditional in situ and satellite observations, SMOS SSS is assimilated. A prior SMOS SSS error field is inferred through a comparison of the satellite data with in situ salinity data and reveals large biases (>1 g/kg) in the SMOS product near continents and in the Southern Ocean. Employing this error estimate in the assimilation procedure leads only to an insignificant impact of SMOS SSS on the estimated ocean state. However, when reducing the error artificially by a factor of 10, the SMOS data can be reproduced well in the interior ocean. In this case, the previously remaining positive model bias with respect to in situ salinity is changed to a negative bias while the misfit slightly increased. The clear freshening can be attributed to the SMOS bias with respect to in situ data. The associated increase in freshwater input in the tropical oceans enhances slightly the correspondence of the estimated fluxes to the independent satellite based estimate from HOAPS except for the South Pacific and South Atlantic. On short time scales, changes in the estimated surface salinity result primarily from changes in surface freshwater fluxes, while over longer periods ocean dynamics become increasingly more important for changing the near‐surface salinity.
      PubDate: 2014-07-25T23:18:24.675172-05:
      DOI: 10.1002/2014JC010040
  • Coherent sea level variability on the North Atlantic western boundary
    • Authors: P. R. Thompson; G. T. Mitchum
      Pages: n/a - n/a
      Abstract: Interannual to decadal sea level variability on the North Atlantic western boundary is surprisingly coherent over substantial distances stretching from the Caribbean to Nova Scotia. The physical mechanisms responsible for this basin‐scale, low‐frequency coherence are explored in a diagnosis of simulated ocean fields from GECCO, which reproduces the observations to good approximation. Coastal sea level variability on the western boundary is known to be influenced by meridional divergence in the boundary current resulting in a geostrophic tilting of the sea surface. This mechanism is found to be of leading order along some stretches of the boundary, but it does not account for the coherence spanning the western North Atlantic. Instead, the coherence along the entire boundary is accounted for by vertical divergence resulting in the uniform rise and fall of the sea surface west of the 295°E meridian. The vertical divergence is found to be due to net vertically integrated zonal transport across this meridian resulting from meridional variation in the Sverdrup transport over the basin interior.
      PubDate: 2014-07-25T05:04:30.969259-05:
      DOI: 10.1002/2014JC009999
  • Hurricane Sandy storm surges observed by HY‐2A satellite altimetry
           and tide gauges
    • Authors: Nan Chen; Guoqi Han, Jingsong Yang, Dake Chen
      Pages: n/a - n/a
      Abstract: Hurricane Sandy made landfall to the northeast of Atlantic City, New Jersey at 23:30 UTC on 29 October 2012 and caused large storm surges and devastating flooding along the New Jersey and New York coasts. Here we combine sea surface height measurements from the HaiYang‐2A (HY‐2A) satellite altimeter with coastal tide‐gauge data to study the features of the Hurricane Sandy storm surges. The HY‐2A altimeter captured the cross‐shelf profile of surge at the time of Sandy's peak surge, with a surge magnitude of about 1.83 m at the coast and a cross‐shelf decaying scale of 68 km. The altimetric surge magnitude agrees approximately with tide‐gauge estimate of 1.73 m at nearby Montauk. Further analysis suggests that continental shelf waves were generated during the passage of Sandy. The continental shelf wave observed by altimetry has a propagating speed of 6.5 m/s. The post landfall free shelf wave at Atlantic City observed by tide gauges has a propagating phase speed of 6.8 m/s and cross‐shelf e‐folding scale of 75 km. In contrast, the post landfall sea level oscillation at Montauk is not associated with a continental shelf wave. The study indicates that satellite altimetry is capable of observing and useful for understanding features of storm surges, complementing existing coastal tide gauges.
      PubDate: 2014-07-24T11:13:10.170918-05:
      DOI: 10.1002/2013JC009782
  • Ocean response to volcanic eruptions in Coupled Model Intercomparison
           Project 5 (CMIP5) simulations
    • Authors: Yanni Ding; James A. Carton, Gennady A. Chepurin, Georgiy Stenchikov, Alan Robock, Lori T. Sentman, John P. Krasting
      Pages: n/a - n/a
      Abstract: We examine the oceanic impact of large tropical volcanic eruptions as they appear in ensembles of historical simulations from eight Coupled Model Intercomparison Project Phase 5 models. These models show a response that includes lowering of global average sea surface temperature by 0.1‐0.3 K, comparable to the observations. They show enhancement of Arctic ice cover in the years following major volcanic eruptions, with long‐lived temperature anomalies extending to the mid‐depth and deep ocean on decadal to centennial timescales. Regional ocean responses vary, although there is some consistent hemispheric asymmetry associated with the hemisphere in which the eruption occurs. Temperature decreases and salinity increases contribute to an increase in the density of surface water and an enhancement in the overturning circulation of the North Atlantic Ocean following these eruptions. The strength of this overturning increase varies considerably from model to model and is correlated with the background variability of overturning in each model. Any cause/effect relation between eruptions and the phase of El Niño is weak.
      PubDate: 2014-07-24T07:30:27.173756-05:
      DOI: 10.1002/2013JC009780
  • Intraseasonal to interannual variability of the Atlantic meridional
           overturning circulation from eddy‐resolving simulations and
    • Authors: Xiaobiao Xu; Eric P. Chassignet, William E. Johns, William J. Schmitz, E. Joseph Metzger
      Pages: n/a - n/a
      Abstract: Results from two 1/12° eddy‐resolving simulations, together with data‐based transport estimates at 26.5°N and 41°N, are used to investigate the temporal variability of the Atlantic meridional overturning circulation (AMOC) during 2004‐2012. There is a good agreement between the model and the observation for all components of the AMOC at 26.5°N, whereas the agreement at 41°N is primarily due to the Ekman transport. We found that 1) both observations and model results exhibit higher AMOC variability on seasonal and shorter time scales than on interannual and longer time scales; 2) on intraseasonal and interannual time scales, the AMOC variability is often coherent over a wide latitudinal range, but lacks an overall consistent coherent pattern over the entire North Atlantic; and 3) on seasonal time scales, the AMOC variability exhibits two distinct coherent regimes north and south of 20°N, due to different wind stress variability in the tropics and subtropics. The high AMOC variability south of 20°N in the tropical Atlantic comes primarily from the Ekman transport of the near‐surface water, and is modulated to some extent by the transport of the Antarctic Intermediate water below the thermocline. These results highlight the importance of the surface wind in driving the AMOC variability.
      PubDate: 2014-07-24T05:08:31.908521-05:
      DOI: 10.1002/2014JC009994
  • Investigation of the causes of historical changes in the subsurface
           salinity minimum of the South Atlantic
    • Authors: Marlos Goes; Ilana Wainer, Natalia Signorelli
      Pages: n/a - n/a
      Abstract: In this study we investigate the sub‐surface salinity changes on decadal timescales across the Subtropical South Atlantic Ocean using two ocean reanalysis products, the latest version of the Simple Ocean Data Assimilation and the Estimating the Circulation and Climate of the Ocean, Phase II, as well as with additional climate model experiments. Results show that there is a recent significant salinity increase at the core of the salinity minimum at intermediate levels. The main underlying mechanism for this sub‐surface salinity increase is the lateral advective (gyre) changes due to the Southern Annular mode variability, which conditions an increased contribution from the Indian Ocean high salinity waters into the Atlantic. The global warming signal has a secondary but complementary contribution. Latitudinal differences at intermediate depth in response to large‐scale forcing are in part caused by local variation of westward propagation features, and by compensating contributions of salinity and temperature to density changes.
      PubDate: 2014-07-24T04:37:41.348152-05:
      DOI: 10.1002/2014JC009812
  • Low‐frequency ocean bottom pressure variations in the North Pacific
           in response to time‐variable surface winds
    • Authors: C. Petrick; H. Dobslaw, I. Bergmann‐Wolf, N. Schön, K. Matthes, M. Thomas
      Pages: n/a - n/a
      Abstract: One decade of time‐variable gravity field observations from the GRACE satellite mission reveals low‐frequency ocean bottom pressure (OBP) variability of up to 2.5 hPa centered at the northern flank of the subtropical gyre in the North Pacific. From a 145 year‐long simulation with a coupled chemistry climate model, OBP variability is found to be related to the prevailing atmospheric sea‐level pressure and surface wind conditions in the larger North Pacific area. The dominating atmospheric pressure patterns obtained from the climate model run allow in combination with ERA‐Interim sea‐level pressure and surface winds a reconstruction of the OBP variability in the North Pacific from atmospheric model data only, which correlates favourably (r=0.7) with GRACE ocean bottom pressure observations. The regression results indicate that GRACE‐based OBP observations are indeed sensitive to changes in the prevailing sea‐level pressure and thus surface wind conditions in the North Pacific, thereby opening opportunities to constrain atmospheric models from satellite gravity observations over the oceans.
      PubDate: 2014-07-24T03:56:24.495298-05:
      DOI: 10.1002/2013JC009635
  • Relative role of El Niño and IOD forcing on the southern tropical
           Indian Ocean Rossby waves
    • Authors: Soumi Chakravorty; C. Gnanaseelan, J. S. Chowdary, Jing‐Jia Luo
      Pages: n/a - n/a
      Abstract: The role of local air‐sea interactions over the tropical Indian Ocean (TIO) and remote forcing from the tropical Pacific Ocean in the formation and maintenance of southern TIO Rossby waves during El Niño and positive Indian Ocean Dipole (IOD) years is investigated. These Rossby waves are significantly intensified during the El Niño and IOD co‐occurrence years, as compared to those during pure El Niño or IOD years. Coupled ocean‐atmosphere model sensitivity experiments reveal that air‐sea coupled processes in the TIO are responsible for the Rossby wave formation and its maintenance from boreal summer to fall, while remote forcing from the Pacific intensifies and maintains these waves up to the following spring. During the co‐occurrence years, the Rossby waves are generated by both the persistent equatorial easterlies and off‐equatorial wind stress curl. During pure El Niño years, however, only off‐equatorial wind stress curl exists to drive weak Rossby wave. Asymmetric heating associated with IOD and the mean background vertical wind shear (in the northern hemisphere) during summer and fall excite two symmetric anticyclones in both sides of the equator as atmospheric Rossby wave response, which are responsible for the anomalous equatorial surface easterlies. In contrast, symmetric heat sink over the Maritime Continent in winter associated with El Niño induced subsidence and mean easterly vertical shear (in southern hemisphere) are responsible for strong anticyclone in the southern TIO, which supports off equatorial wind stress curl.
      PubDate: 2014-07-24T03:54:29.978818-05:
      DOI: 10.1002/2013JC009713
  • Quantifying uncertainty sources in the gridded data of sea surface CO2
           partial pressure
    • Authors: Guizhi Wang; Minhan Dai, Samuel S. P. Shen, Yan Bai, Yi Xu
      Pages: n/a - n/a
      Abstract: The bulk uncertainty in the gridded sea surface pCO2 data is crucial in assessing the reliability of the CO2 flux estimated from measurements of air‐sea pCO2 difference, because atmospheric pCO2 are relatively homogeneous and well defined. The bulk uncertainty results from three different sources: analytical error (Em), spatial variance (σs2), and the bias from undersampling (σu2). Common uncertainty quantification by standard deviation may mix up the different sources of uncertainty. We have established a simple procedure to determine these three sources of uncertainty using remote sensing‐derived and field measured pCO2 data. Em is constrained by the analytical method and data reduction procedures. σs2 is derived from the remotely sensed pCO2 field. σu2 is determined by spatial variance and the effective number of observations, considering, for the first time, the geometric bias introduced by pCO2 sampling. This approach is applied to 1°×1° gridded pCO2 data collected from the East China Sea. We demonstrate that the spatial distribution of these biases is uneven and that none of them follow the same spatial trend as the standard deviation. σs2 contributes the most to the uncertainty in gridded pCO2 data over those grid boxes with good sampling coverage, while σu2 dominates the total uncertainty in the grid boxes with poor sampling coverage. Application of this procedure to other parts of the global ocean will help to better define the inherent spatial variability of the pCO2 field and thus better interpolate and/or extrapolate pCO2 data, and eventually better constrain air‐sea CO2 fluxes.
      PubDate: 2014-07-24T03:52:59.457868-05:
      DOI: 10.1002/2013JC009577
  • A physically based parameterization of gravity drainage for sea‐ice
    • Authors: David W. ReesJones; M. Grae Worster
      Pages: n/a - n/a
      Abstract: We incorporate a physically‐derived parameterization of gravity drainage, in terms of a convective upwelling velocity, into a one‐dimensional, thermodynamic sea‐ice model of the kind currently used in coupled climate models. Our parameterization uses a local Rayleigh number to represent the important feedback between ice salinity, porosity, permeability and desalination rate. It allows us to determine salt fluxes from sea ice and the corresponding evolution of the bulk salinity of the ice, in contrast to older, established models that prescribe the ice salinity. This improves the predictive power of climate models in terms of buoyancy fluxes to the polar oceans, and also the thermal properties of sea ice, which depend on its salinity. We analyze the behaviour of existing fixed‐salinity models, elucidate the physics affecting ice growth and compare against our dynamic‐salinity model, both in terms of laboratory experiments and also deep‐ocean calculations. These comparisons explain why the direct effect of ice salinity on growth is relatively small (though not always negligible, and sometimes different from previous studies), and also highlight substantial differences in the qualitative pattern and quantitative magnitude of salt fluxes into the polar oceans. Our study is particularly relevant to growing first‐year ice, when gravity drainage is the dominant mechanism by which ice desalinates. We expect that our dynamic model, which respects the underlying physics of brine drainage, should be more robust to changes in polar climate and more responsive to rapid changes in oceanic and atmospheric forcing.
      PubDate: 2014-07-24T03:52:57.946899-05:
      DOI: 10.1002/2013JC009296
  • Effect of coastal‐trapped waves and wind on currents and transport
           in the Gulf of California
    • Authors: Manuel O. Gutiérrez; Manuel López, Julio Candela, Rubén Castro, Affonso Mascarenhas, Curtis A. Collins
      Pages: n/a - n/a
      Abstract: Subsurface pressure (SsP) observations from stations inside and outside of the Gulf of California (GC) are used to analyze the relationship between low‐frequency currents, temperature and transport inside the GC and intraseasonal coastal‐trapped waves (CTWs), which propagate poleward along the coast towards the GC. Correlation functions and coherences of SsP stations were consistent with intraseasonal CTWs splitting in two at the mouth of the gulf: one part enters the gulf, propagates around the gulf, and eventually, towards the mouth, and another part that appears to “jump” the mouth of the gulf and travels poleward along the west coast of the peninsula. The correlation and coherence estimates of SsP at Manzanillo with currents showed that downwelling CTWs generated along‐gulf current anomalies towards the head of the gulf at the mainland shelf of the mouth, whereas at Ballenas Channel sill (San Lorenzo sill) these waves generated current anomalies towards the mouth near the surface (bottom). At the San Lorenzo (SL) sill, downwelling CTWs increased the near‐bottom (˜400 m) temperature and reduced the bottom transport of deep, fresher, and colder water that flows towards the head of the gulf. Cross Calibrated Multiplatform winds were used to investigate their relationship with currents. The first empirical orthogonal function of the along‐gulf wind stress showed that wind blowing towards the head of the gulf generated a reduction of bottom transport towards the head of the gulf through the SL sill, and intensified surface geostrophic current fluctuations towards the head of the gulf. There was also significant correlation between inflow bottom transport and outflow surface geostrophic velocities averaged across the gulf, consistent with the exchange pattern for the northern gulf.
      PubDate: 2014-07-24T03:52:54.680997-05:
      DOI: 10.1002/2013JC009538
  • Simulated tomographic reconstruction of ocean current profiles in a
           bottom‐limited sound channel
    • Authors: Naokazu Taniguchi; Chen‐Fen Huang
      Pages: n/a - n/a
      Abstract: Tomographic reconstruction of the vertical current profile in a bottom‐limited sound channel requires solving a difficult ray identification problem. An approach to deal with this problem is a ray group method in which received arrival pulses are divided into several ray groups according to the characteristics of the arrival patterns. The method is validated using numerically simulated reciprocal acoustic transmission in a synthetic ocean in the Luzon Strait, where the Kuroshio Current has speeds as high as 1.2 m/s, for both narrowband and broadband signals. Four ray groups are found for the synthetic data; these are chosen based on arrival time. The differential travel time is determined by pairing up the reciprocal arrival peaks and then averaging the differential travel times within the selected time windows. Compared with the narrowband case, the estimated broadband differential travel time is more consistent with that computed from the current magnitude in the synthetic ocean. The vertical current profile is reconstructed from the broadband differential travel times by a generalized Tikhonov regularization approach. The data weighting matrix includes observation error in picking and pairing travel times and model parameter error due to path length uncertainty. The time series of the reconstructed current agrees with the synthetic ocean current; the fractional residual variance is 0.013 for the surface layer and 0.01 for the entire water column. The ray group method mitigates the ray identification problem in the bottom‐limited environment and could offer valuable data regarding the range‐integrated current velocity.
      PubDate: 2014-07-24T00:28:27.91725-05:0
      DOI: 10.1002/2014JC009885
  • Inversion of submesoscale patterns from a high‐resolution Solomon
           Sea model: Feasibility assessment
    • Authors: Lucile Gaultier; Bughsin' Djath, Jacques Verron, Jean‐Michel Brankart, Pierre Brasseur, Angelique Melet
      Pages: n/a - n/a
      Abstract: A high‐resolution realistic numerical model of the Solomon Sea, which exhibits a high level of variability at mesoscales and submesoscales, is used to explore new avenues for data assimilation. Image data assimilation represents a powerful methodology to integrate information from high‐resolution observations such as satellite sea surface temperature or chlorophyll, or high‐resolution altimetric sea surface height that will be observed in the forthcoming SWOT mission. The present study investigates the feasibility and accuracy of the inversion of the dynamical submesoscale information contained in high‐resolution images of sea surface temperature (SST) or salinity (SSS) to improve the estimation of oceanic surface currents. The inversion method is tested in the context of twin experiments, with SST and SSS data provided by a model of the Solomon Sea. For that purpose, synthetic tracer images are built by binarizing the norm of the gradient of SST, SSS or spiciness. The binarized tracer images are compared to the dynamical image which is derived from the Finite‐Size Lyapunov Exponents. The adjustment of the dynamical image to the tracer image provides the optimal correction to be applied on the surface velocity field. The method is evaluated by comparing the result of the inversion to the reference model solution. The feasibility of the inversion of various images (SST, SSS, both SST and SSS or spiciness) is explored on two small areas of the Solomon Sea. We show that errors in the surface velocity field can be substantially reduced through the inversion of tracer images.
      PubDate: 2014-07-23T12:15:48.067309-05:
      DOI: 10.1002/2013JC009660
  • Summer primary productivity and phytoplankton community composition driven
           by different hydrographic structures in the East/Japan Sea and the Western
           Subarctic Pacific
    • Authors: Jung Hyun Kwak; Sang Heon Lee, Jeomshik Hwang, Young‐Sang Suh, Hyun Park, Kyung‐Il Chang, Kyung‐Ryul Kim, Chang‐Keun Kang
      Pages: n/a - n/a
      Abstract: The East/Japan Sea (EJS) is a highly productive marginal sea in the northwest Pacific, consisting of three basins (Ulleung Basin: UB, Yamato Basin: YB, and Japan Basin: JB). To find causes of the reportedly high primary productivity in summer in the EJS, especially in the UB, we measured primary productivity, phytoplankton composition, and other environmental variables. The water column was strongly stratified in the EJS compared with the Western Subarctic Pacific (WSP). Integrated primary productivity was two times higher in the EJS (612 mg C m−2 d−1) than in the WSP (291 mg C m−2 d−1). The vertical distributions of physicochemical and biological factors confirmed that production in the subsurface chlorophyll maximum layer in the study regions was an important factor regulating primary productivity within the water column. While picoplankton (
      PubDate: 2014-07-23T09:03:04.906483-05:
      DOI: 10.1002/2014JC009874
  • Satellite views of the episodic terrestrial material transport to the
           southern Okinawa Trough driven by typhoon
    • Authors: Xianqiang He; Yan Bai, Chen‐Tung Arthur Chen, Yi‐Chia Hsin, Chau‐Ron Wu, Weidong Zhai, Zhiliang Liu, Fang Gong
      Pages: n/a - n/a
      Abstract: Using satellite‐derived water transparency (alias Secchi depth) images, we found clear signals of terrestrial material transport to the southern Okinawa Trough triggered by the Typhoon Morakot in August 2009. Three sources were identified: one is from the eastern coast of Taiwan, another is from the western coast of Taiwan, and the other is from the coast of mainland China. Carried by northward flows, typhoon‐triggered terrestrial materials from both sides of Taiwan's coasts were transported to the region northeast of Taiwan. Moreover, the terrestrial material from the coast of mainland China could cross the Taiwan Strait and be further transported to the region northeast of Taiwan. These typhoon‐induced terrestrial materials off northeastern Taiwan could then be transported to the southern Okinawa Trough along the western edge of the Kuroshio. In addition to the particulate terrestrial material transported, nutrients might also be transported to the Kuroshio main stream. A significant phytoplankton bloom was observed along the Kuroshio path for about 300 km off northeast of Taiwan. Our results indicate that episodic cyclone‐driven terrestrial material transport could be another source of mud in the southern Okinawa Trough.
      PubDate: 2014-07-22T13:10:56.738761-05:
      DOI: 10.1002/2014JC009872
  • Impacts of typhoon megi (2010) on the South China Sea
    • Authors: Dong Shan Ko; Shenn‐Yu Chao, Chun‐Chieh Wu, I‐I Lin
      Pages: n/a - n/a
      Abstract: In October 2010, typhoon Megi induced a profound cold wake of size 800 km by 500 km with sea surface temperature cooling of 8°C in the South China Sea (SCS). More interestingly, the cold wake shifted from the often rightward bias to both sides of the typhoon track and moved to left in a few days. Using satellite data, in situ measurements and numerical modeling based on the East Asian Seas Nowcast/Forecast System (EASNFS), we performed detailed investigations. To obtain realistic typhoon‐strength atmospheric forcing, the EASNFS applied typhoon‐resolving Weather Research and Forecasting (WRF) model wind field blended with global weather forecast winds from the U.S. Navy Operational Global Atmospheric Prediction System (NOGAPS). In addition to the already known impacts from the slow typhoon translation speed and shallow pre‐exiting ocean thermocline, we found the importance of the unique geographical setting of the SCS and the NE monsoon. As the event happened in late October, NE monsoon already started and contributed to the southwestward ambient surface current. Together with the topographicβ effect, the cold wake shifted westward to the left of Megi's track. It was also found that Megi expelled waters away from the SCS and manifested as a gush of internal Kelvin wave exporting waters through the Luzon Strait. The consequential sea level depression lasted and presented a favorable condition for cold dome development. Fission of the north‐south elongated cold dome resulted afterward and produced two cold eddies that dissipated slowly thereafter.
      PubDate: 2014-07-22T13:09:29.125478-05:
      DOI: 10.1002/2013JC009785
  • Transient modulation of Kuroshio upper layer flow by directly impinging
           typhoon Morakot in east of Taiwan in 2009
    • Authors: Zhe‐Wen Zheng; Quanan Zheng, Chia‐Ying Lee, Ganesh Gopalakrishnan
      Pages: n/a - n/a
      Abstract: This study deals with the modulation of the Kuroshio upper layer flow (KULF) in response to the passage of Typhoon Morakot in 2009, using Regional Oceanic Modeling System (ROMS) and in situ measurements from Argos drifters and Argo floats. The analysis of the simulated current fields near the typhoon track revealed an intermittency phenomenon of the KULF, which was almost shut down for at least 6 hours. The process begun 2 days prior to the approach of typhoon center due to blockage of the KULF by the steadily northerly winds, and lasted for more than 2 days, simultaneously shifting the Kuroshio main stream (KMS) path. When the Morakot gradually moved closely to the Kuroshio, the KMS shifted vertically from the surface layer to deeper layer of 50 – 100 m depth, and the maximum current speed in the KMS decreased from more than 1.3 m s−1 to less than 1.1 m s−1. When the Morakot center approached about 100 km to the original position of the Kuroshio, the KULF spread eastward for 1.5 degrees at 24°N. When the Morakot center moved to the original position of the KMS, the Kuroshio abruptly rushed with a maximum speed near 1.4 m s−1. Meanwhile, an offshore cool jet originating from southeastern tip of Taiwan was generated and extended northward along the Kuroshio. In the cool jet, the lowest temperature reached about 5°C lower than the ambient waters. Modeled current variations and the cool jet during the Morakot passage were validated by in situ measurements.
      PubDate: 2014-07-22T11:13:55.302629-05:
      DOI: 10.1002/2014JC010090
  • Assessing the temporal variability in extreme storm‐tide time series
           for coastal flood risk assessment
    • Authors: N. Quinn; M. Lewis, M. P. Wadey, I.D. Haigh
      Pages: n/a - n/a
      Abstract: The probability of extreme storm‐tide events has been extensively studied, however the variability within the duration of such events, and implications to flood risk, is less well understood. This research quantifies such variability during extreme storm‐tide events (the combined elevation of the tide, surge, and their interactions) at 44 national tide gauges around the UK. Extreme storm‐tide events were sampled from water level measurements taken every 15 minutes between 1993 and 2012. At each site, the variability in elevation at each time step, relative to a given event peak, was quantified. The magnitude of this time‐series variability was influenced both by gauge location (and hence the tidal, and non‐tidal residual characteristics) and the time relative to high water. The potential influence of this variability on coastal inundation was assessed across all UK gauge sites, followed by a detailed case study of Portsmouth. A two‐dimensional hydrodynamic model of the Portsmouth region was used to demonstrate that given a current 1 in 200 year storm‐tide event, the predicted number of buildings inundated differed by more than 30% when contrasting simulations forced with the upper and lower bounds of the observed time‐series variability. The results indicate that variability in the time‐series of the storm‐tide event can have considerable influence upon overflow volumes, hence with implications for coastal flood risk assessments. Therefore, further evaluating and representing this uncertainty in future flood risk assessments is vital, while the envelopes of variability defined in this research provides a valuable tool for coastal flood modellers.
      PubDate: 2014-07-22T00:22:00.513995-05:
      DOI: 10.1002/2014JC010197
  • On the nonquivalent barotropic structure of the Antarctic Circumpolar
           Current: An observational perspective
    • Authors: H. E. Phillips; N. L. Bindoff
      Pages: n/a - n/a
      Abstract: We examine the vertical structure of the horizontal flow and diagnose vertical velocities in the Antarctic Circumpolar Current (ACC) near the Kerguelen Plateau using EM‐APEX profiling floats. Eight floats measured horizontal velocity, temperature and salinity profiles to 1600 dbar, with a vertical spacing of 3‐5 dbar four times per day over a period of approximately 3 months. Horizontal velocity profiles show a complex vertical structure with strong rotation of the velocity vector through the water column. The distribution of rotation angles from 1247 profiles is approximately Gaussian and rotations of either sign are equally likely. Fourty percent of profiles with speed greater than 5cms‐1 have a depth‐integrated rotation of less than 15 degrees over 1300 dbar, while the other 60% demonstrate significantly stronger rotation. Consequently, most profiles do not conform to the equivalent barotropic model (deep flow parallel and proportional to the surface flow) used in simplified dynamical models and in Gravest Empirical Mode climatologies of the ACC. Nevertheless, since we find the mean rotation to be zero, an equivalent barotropic assumption is valid to first order. Vertical velocities inferred using conservation of mass and a gradient wind balance in natural coordinates have magnitudes on the order of 100 m/day. We find robust patterns of upwelling and downwelling phase‐locked to meanders in the flow, as found in earlier studies. With the advent of high‐resolution observations such as those presented here, and high‐resolution models, we can advance to a more complete understanding of the rich variability in ACC structure that is neglected in the equivalent barotropic model.
      PubDate: 2014-07-22T00:15:50.20928-05:0
      DOI: 10.1002/2013JC009516
  • Can we do better than the grid survey: Optimal synoptic surveys in
           presence of variable uncertainty and decorrelation scales
    • Authors: Sergey Frolov; Bartolame Garau, James Bellingham
      Pages: n/a - n/a
      Abstract: Regular grid (“lawnmower”) survey is a classical strategy for synoptic sampling of the ocean. Is it possible to achieve a more effective use of available resources if one takes into account a‐priori knowledge about variability in magnitudes of uncertainty and decorrelation scales? In this article, we develop and compare the performance of several path‐planning algorithms: optimized “lawnmower”, a graph‐search algorithm (A*), and a fully non‐linear Genetic Algorithm. We use the machinery of the best linear unbiased estimator (BLUE) to quantify the ability of a vehicle fleet to synoptically map distribution of phytoplankton off the central California coast. We used satellite and in‐situ data to specify covariance information required by the BLUE estimator. Computational experiments showed that two types of sampling strategies are possible: a sub‐optimal space‐filling design (produced by the “lawnmower” and the A* algorithms) and an optimal uncertainty‐aware design (produced by the Genetic Algorithm). Unlike the space‐filling designs that attempted to cover the entire survey area, the optimal design focused on revisiting areas of high uncertainty. Results of the multi‐vehicle experiments showed that fleet performance predictors, such as cumulative speed or the weight of the fleet, predicted the performance of a homogeneous fleet well; however, these were poor predictors for comparing the performance of different platforms.
      PubDate: 2014-07-21T23:57:12.291021-05:
      DOI: 10.1002/2013JC009521
  • Impacts of nonbreaking wave‐stirring‐induced mixing on the
           upper ocean thermal structure and typhoon intensity in the South China Sea
    • Authors: Yineng Li; Shiqiu Peng, Jia Wang, Jing Yan
      Pages: n/a - n/a
      Abstract: To investigate the effect of non‐breaking wave‐induced mixing caused by surface wave stirring on the upper ocean thermal structure (UOTS) and the typhoon intensity, a simple non‐breaking wave‐stirring‐induced mixing parameterization (WMP) scheme is incorporated into a regional coupled atmosphere‐ocean model for the South China Sea (SCS), which couples the Princeton Ocean Model (POM) to the Weather Research and Forecasting (WRF) model using the OASIS3 coupler. The results of simulating two selected typhoon cases indicate that the non‐breaking wave‐stirring‐induced mixing has significant impacts on UOTS and the typhoon intensity, and the incorporation of the simple WMP scheme in the coupled model helps to improve the simulation of UOTS and thus the typhoon intensity. In the case that the typhoon intensity is underestimated by the atmosphere model alone, the improvement of initial UOTS by the ocean model with the WMP included can deepen the initial thermocline depth, reduce the effect of SST cooling, and prevent the typhoon intensity from undesired weakening. In the case that the typhoon intensity is overestimated (with strong winds), including the WMP in the ocean model significantly enhances the total vertical mixing rate in the upper ocean, which in turn enhances the SST cooling and thus reduces the typhoon intensity as desired. The results obtained in this study make a contribution to the ongoing efforts of improving the typhoon intensity forecast using a regional atmosphere‐ocean coupled model by worldwide researchers and forecasters, especially for the typhoons in the SCS regions.
      PubDate: 2014-07-21T23:57:07.901348-05:
      DOI: 10.1002/2014JC009956
  • Impact of climate change on the Northwestern Mediterranean Sea pelagic
           planktonic ecosystem and associated carbon cycle
    • Authors: Marine Herrmann; Claude Estournel, Fanny Adloff, Frédéric Diaz
      Pages: n/a - n/a
      Abstract: The Northwestern Mediterranean Sea (NWMS) is biologically one of the most productive Mediterranean regions. NWMS pelagic planktonic ecosystem is strongly influenced by hydrodynamics, in particular by deep convection, that could significantly weaken under the influence of climate change. Here we investigate the response of this ecosystem and associated carbon cycle to the long‐term evolution of oceanic and atmospheric circulations. For that we developed a tridimensional coupled physical‐biogeochemical model and performed two groups of annual simulations under the climate conditions of respectively the XXth and the end of XXIst century. Our results suggest that the evolution of oceanic and atmospheric circulations does not modify the NWMS pelagic planktonic ecosystem and associated carbon cycle at a first order. However differences mainly induced by the deep convection weakening and the surface warming are obtained at a second order. The spring bloom occurs one month earlier. Resulting from the decrease in nutrients availability, the bottom up control of phytoplankton development and bacteria growth by the nitrogen and phosphorus availability strengthens and the microbial loop intensifies as the small‐sized plankton biomass increases. Carbon net fixation and deep export do not change significantly. The choice of the biogeochemical initial and boundary conditions does not change the representation of the ecosystem seasonal cycle, but the associated uncertainty range can be one order of magnitude larger than the predicted interannual and long term variabilities. The uncertainty range of long‐term trends associated to the physical forcing (hydrological, atmospheric, hydrodynamical and socio‐economic) is much smaller (
      PubDate: 2014-07-21T22:56:50.233667-05:
      DOI: 10.1002/2014JC010016
  • Zonal momentum budget along the equator in the Indian Ocean from a
           high‐resolution ocean general circulation model
    • Authors: Motoki Nagura; Michael J. McPhaden
      Pages: n/a - n/a
      Abstract: This study examines the zonal momentum budget along the equator in the Indian Ocean in a high‐resolution ocean general circulation model. Wyrtki Jets, wind‐driven eastward flows in the upper 100 m that appear typically twice per year in boreal spring and fall, are a prominent feature of the ocean circulation in this region. Our results indicate that nonlinearity associated with these jets is an important element of the zonal momentum budget, with wind driven eastward momentum advected downward into the thermocline. This advection results in annually averaged zonal currents that flow against the zonal pressure gradient in the upper 200 m, such that there is no mean subsurface undercurrent in the Indian Ocean as there is in the Pacific and Atlantic Oceans. Zonal momentum is further distributed along the equator by zonal advection, with eastward flow substantially enhanced in the eastern basin relative to the western basin. Meridional advection, though generally weak, tends to decelerate surface eastward flow along the equator. These results contrast with those from previous idealized wind‐forced model experiments that primarily emphasized the importance of vertical momentum advection. Also, beyond semiannual period fluctuations, significant momentum advection results from a broad range of interacting processes, spanning intraseasonal to interannual time scales. We conclude that proper simulation of zonal flows along the equator in the Indian Ocean, including their climatically relevant impacts on the mass and heat balance, requires accurate representation of nonlinearities that derive from a broad range of time and space scales.
      PubDate: 2014-07-21T14:11:56.157489-05:
      DOI: 10.1002/2014JC009895
  • ITCZ and ENSO pacing on East Asian winter monsoon variation during the
           Holocene: Sedimentological evidence from the Okinawa Trough
    • Authors: Xufeng Zheng; Anchun Li, Shiming Wan, Fuqing Jiang, Shuh Ji Kao, Cody Johnson
      Pages: n/a - n/a
      Abstract: Deep‐sea fan sediments provide an excellent geological archive for paleoenvironment reconstruction. Grain size, clay mineral and elemental (Ti, Fe, Ca) compositions were measured for a core retrieved from a submarine fan in the Okinawa Trough. Varimax‐rotated Principal Component Analysis (V‐PCA) on time‐evolution of grain size spectrum reveals that, since the Holocene, sediment was transported mainly by the benthic nepheloid layer (33%) and upper layers (33%) which is driven by the East Asian winter monsoon (EAWM). The intensification of the Kuroshio Current during the Holocene, masks the fluvial signal of the summer monsoon and obstructs clay minerals derived from the Yellow River, a major contributor prior to 12 ka BP. A new grain size index (GSI), which represents the EAWM well, exhibits a negative correlation with the δ18O record in Dongge Cave, China during the Holocene when sea level was relatively steady. This anticorrelation suggests the southward migration of the Intertropical Convergence Zone (ITCZ). The consistency among our records and rainfall records in Peru, Ti counts in the Cariaco Basin, monsoon records in Oman and the averaged summer insolation pattern at 30°N further support the ITCZ's impact on monsoon systems globally. Cross‐Correlation Analyses for GSI and log(Ti/Ca) against δ18O record in Dongge Cave reveal a decoupling between the East Asian winter and summer monsoon during 5500–2500 cal yr BP, with greater complexity in the last 2500 years. This can be attributed to exacerbated ENSO mode fluctuations and possibly anthropogenic interference superimposed on insolation and ITCZ forcing.
      PubDate: 2014-07-21T09:00:39.872357-05:
      DOI: 10.1002/2013JC009603
  • Seasonal migration of the Yellow Sea Bottom Cold Water
    • Authors: Bin Wang; Naoki Hirose, Boonsoon Kang, Katsumi Takayama
      Pages: n/a - n/a
      Abstract: The three‐dimensional motion of the Yellow Sea Bottom Cold Water (YSBCW) and the relevant dynamical factors are studied using a regional circulation model and the two‐way Lagrangian particle tracking method (PTM). The simulated results are in good agreement with hydrographic observations. The trajectories of the modeled particles show that the subsurface cold heavy water mass from the northern part of the Yellow Sea gradually sinks into deeper layers along the western slope of the Yellow Sea trough with a southward movement from spring to summer. The cold water mass gradually gathers speed from early March to July or August, and eventually reaches its southernmost location in late September or early October. Furthermore, sensitivity experiments demonstrate that tide‐induced residual currents under baroclinic conditions are the dominant factor driving deep circulation during summertime in the Yellow Sea. The summer southerly wind and strong surface solar radiation are the secondary factors influencing the southward migration. This study also proposes an improved delimitation for the YSBCW based on temperature statistics in the central basin (deeper than 40 m) between 35°N and 39°N in March with an increase in rate of approximately 0.7°C/month, which is more appropriate than the constants of the 8°C or 10°C isotherms frequently used.
      PubDate: 2014-07-21T08:40:29.803864-05:
      DOI: 10.1002/2014JC009873
  • Historical wave height trends in the South and East China Seas,
    • Authors: Lingli Wu; Xiaolan L. Wang, Yang Feng
      Pages: n/a - n/a
      Abstract: This study reconstructs 6 hourly significant wave heights (Hs) in the South and East China Seas for the period 1871–2010, using the Twentieth Century Reanalysis ensemble of mean sea level pressure (SLP) fields and a multivariate regression model to represent the Hs‐SLP relationship in each study area. The regression model was calibrated and validated using the ERA‐Interim reanalysis of Hs and SLP for the period 1981–2010. These reconstructions were found to reproduce reasonably well the seasonal mean and maximum Hs climates as represented by the ERA40 and ERA‐Interim wave reanalyses. For each study area, an ensemble of 56 members of 6 hourly Hs was reconstructed for each grid point. The regional mean series of the ensemble mean of the reconstructed consecutive monthly mean Hs was tested for temporal homogeneity, which identified a few discontinuities in the pre‐1946 period and led to the exclusion of the reconstructed Hs for 1871–1910 from trend analysis (due to data uncertainty and inhomogeneity). Each 6 hourly Hs time series for the period 1911–2010 was homogenized for the identified discontinuities, before being used to derive annual and seasonal mean and maximum Hs for trend analysis. The trend analysis results show that, in both study areas, the 1911–2010 wave height trends are dominantly negative, with the exception that the seasonal maximum significant wave heights seem to have increased in summer and spring in the central South China Sea and in summer in the East China Sea.
      PubDate: 2014-07-18T13:43:19.723092-05:
      DOI: 10.1002/2014JC010087
  • Mechanisms of the disappearance of sea surface temperature fronts in the
           subtropical North Pacific Ocean
    • Authors: Chunhua Qiu; Hiroshi Kawamura, Huabin Mao, Jiaxue Wu
      Pages: n/a - n/a
      Abstract: The disappearance mechanisms of subtropical sea surface temperature (SST) fronts occurring from May to August were examined quantitatively using a simple mixed‐layer model. Weekly 2.5° data sets were matched up between satellite and in situ observations, including cloud‐free SST from Advanced Microwave Scanning Radiometer‐Earth Observing System (AMSR‐E) and Global Temperature and Salinity Profile Program (GTSPP) data. A 1.5 mixed‐layer model used in this study assumed that the temporal variation of the SST gradient was controlled by the resultant effect among the net heat flux, temperature advection (including Ekman and geostrophic), and the temperature entrainment at the bottom of the mixed layer. The net heat flux was found to provide a dominant contribution to the weakening of the SST front (decreasing SST gradient), while the temperature advection and the bottom entrainment were relatively weak. Decomposition of the net heat flux revealed that the meridional gradient of the latent heat flux is a direct factor in the weakening of the SST front, while the shortwave radiation could have indirect effects. The meridional gradient of the latent heat flux is induced by southerly winds, which in turn causes the weakening and disappearance of the SST front. Comparison of weekly and monthly averaged SST gradient modeling results with in situ observations demonstrated that the weekly SST gradient in the model agrees closely with AMSR‐E observations, but there was a large difference between the monthly SST gradient in the model and in the observations.
      PubDate: 2014-07-18T13:36:47.042097-05:
      DOI: 10.1002/2014JC010142
  • Cross‐shore tracer exchange between the surfzone and
    • Authors: Kai Hally‐Rosendahl; Falk Feddersen, R. T. Guza
      Pages: n/a - n/a
      Abstract: Cross‐shore tracer exchange between the surfzone and inner‐shelf is examined using temperature and dye measurements at an approximately alongshore‐uniform beach. An alongshore‐oriented plume is created by releasing dye continuously for 4.5 h in a surfzone alongshore current. The plume is sampled for 13 h from the release point to 700 m downstream, between the shoreline and 250 m offshore (6 m water depth). Within the surfzone (≤2 m depth), water is relatively warm, and dye is vertically well mixed. On the inner‐shelf (3–6 m depth), alongshore currents are weak, and elevated temperature and dye co‐occur in 25–50 m wide alongshore patches. Within the patches, dye is approximately depth‐uniform in the warm upper 3 m where thermal stratification is weak, but decreases rapidly below 3 m with a strong thermocline. Dye and temperature vertical gradients are correlated, and dye is not observed below 18 °C. The observations and a model indicate that, just seaward of the surfzone, thermal stratification inhibits vertical mixing to magnitudes similar to those in the ocean interior. Similar surfzone and inner‐shelf mean alongshore dye dilution rates are consistent with inner‐shelf dye properties being determined by local cross‐shore advection. The alongshore‐patchy and warm inner‐shelf dye is ejected from the surfzone by transient rip currents. Estimated Stokes drift driven cross‐shore exchange is small. The transient rip current driven depth‐normalized heat flux out of the surfzone has magnitude similar to those of larger‐scale shelf processes. Dye recycling, from the inner‐shelf back to the surfzone, is suggested by relatively long surfzone dye residence times.
      PubDate: 2014-07-17T08:27:12.145058-05:
      DOI: 10.1002/2013JC009722
  • Extensive hydrogen supersaturations in the western South Atlantic Ocean
           suggest substantial underestimation of nitrogen fixation
    • Authors: Robert M. Moore; Markus Kienast, Michael Fraser, John J. Cullen, Curtis Deutsch, Stephanie Dutkiewicz, Michael J. Follows, Christopher J. Somes
      Pages: n/a - n/a
      Abstract: The nitrogen cycle is fundamental to Earth's biogeochemistry. Yet major uncertainties of quantification remain, particularly regarding the global oceanic nitrogen fixation rate. Hydrogen is produced during nitrogen fixation and will become supersaturated in surface waters if there is net release from diazotrophs. Ocean surveys of hydrogen supersaturation thus have the potential to illustrate the spatial and temporal distribution of nitrogen fixation and to guide the far more onerous but quantitative methods for measuring it. Here we present the first transect of high resolution measurements of hydrogen supersaturations in surface waters along a meridional 10,000 km cruise track through the Atlantic. We compare measured saturations with published measurements of nitrogen fixation rates and also with model‐derived values. If the primary source of excess hydrogen is nitrogen fixation and has a hydrogen release ratio similar to Trichodesmium, our hydrogen measurements would point to similar rates of fixation in the North and South Atlantic, roughly consistent with modeled fixation rates but not with measured rates, which are lower in the south. Possible explanations would include any substantial nitrogen fixation by newly discovered diazotrophs, particularly any having a hydrogen release ratio similar to or exceeding that of Trichodesmium; undersampling of nitrogen fixation south of the equator related to excessive focus on Trichodesmium; and methodological shortcomings of nitrogen fixation techniques that cause a bias toward colonial diazotrophs relative to unicellular forms. Alternatively, our data are affected by an unknown hydrogen source that is greater in the southern half of the cruise track than the northern.
      PubDate: 2014-07-16T11:55:20.416386-05:
      DOI: 10.1002/2014JC010017
  • Long‐term trends in the East Australian Current separation latitude
           and eddy driven transport
    • Authors: P. Cetina‐Heredia; M. Roughan, E. van Sebille, M. A. Coleman
      Pages: n/a - n/a
      Abstract: An observed warming of the Tasman Sea in recent decades has been linked to a poleward shift of the maximum wind stress curl, and a strengthening of the poleward flow along the coast of southeastern Australia. However, changes in the East Australian Current (EAC) separation latitude, as well as in the contribution of the EAC, the EAC extension and its eddy field to the total southward transport due to such a strengthening remain unknown. This study uses 30 years (1980–2010) of the Ocean Forecast for the Earth Simulator (OFES) sea surface height and velocity outputs to obtain a three decade long‐time series of (i) the EAC separation latitude, (ii) the southward transport along the coast of southeastern Australia (28°S–39°S), and (iii) the southward transport across the EAC separation latitude. A Lagrangian approach is implemented and the spin parameter Ω is used to provide a quantitative distinction between the transports occurring outside and inside (cyclonic and anticyclonic) eddies. Significant positive trends of the low pass southward transports indicate that the intensification of the poleward flow has occurred both within the EAC and in the EAC extension. In addition, a significant increase in southward transport inside and outside eddies is found. Importantly, the contribution of eddy driven transport has a large temporal variability and shows a sharp increase from 2005 onward. Finally our results show that the EAC has not penetrated further south but it has separated more frequently at the southernmost latitudes within the region where it typically turns eastward.
      PubDate: 2014-07-16T11:52:49.805696-05:
      DOI: 10.1002/2014JC010071
  • Southern Ocean jets and how to find them: Improving and comparing common
           jet detection methods
    • Authors: Christopher C. Chapman
      Pages: n/a - n/a
      Abstract: This study undertakes a detailed comparison of different methods used for detecting and tracking oceanic jets in the Southern Ocean. The methods under consideration are the gradient thresholding method, the probability density function (PDF) method, and the contour method. Some weaknesses of the gradient thresholding method are discussed and an enhancement (the WHOSE method), based on techniques from signal processing, is proposed. The WHOSE method is then compared to the other three methods. Quantitative comparison is undertaken using synthetic sea‐surface height fields. The WHOSE method and the contour method are found to perform well even in the presence of a strong eddy field. In contrast, the standard gradient thresholding and PDF methods only perform well in high signal‐to‐noise ratio situations. The WHOSE, PDF, and the contour methods are then applied to data from the eddy‐resolving Ocean General Circulation Model for the Earth Simulator. While the three methods are in broad agreement on the location of the main ACC jets, the nature of the jet fields they produce differ. In particular, the WHOSE method reveals a fine‐scale jet field with complex braiding behavior. It is argued that this fine‐scale jet field may affect the calculation of eddy diffusivities. Finally, recommendations based on this study are made. The WHOSE and gradient thresholding methods are more suitable for the study of jets as localized strong currents, useful for studies of tracer fluxes. The contour and PDF methods are recommended for studies linking jets to hydrographic fronts.
      PubDate: 2014-07-16T10:45:25.449486-05:
      DOI: 10.1002/2014JC009810
  • Ocean subsurface studies with the CALIPSO spaceborne lidar
    • Authors: Xiaomei Lu; Yongxiang Hu, Charles Trepte, Shan Zeng, James H. Churnside
      Pages: n/a - n/a
      Abstract: The primary objective of the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission is to study the climate impact of clouds and aerosols in the atmosphere. However, recent studies have demonstrated that CALIPSO also collects information about the ocean subsurface. The objective of this study is to estimate the ocean subsurface backscatter from CALIPSO lidar measurements. The effects of the lidar receiver's transient response on the attenuated backscatter were first removed in order to obtain the correct attenuated backscatter profile. The empirical relationship between sea surface lidar backscatter and wind speed was used to estimate the theoretical ocean surface backscatter. Then the two‐way atmospheric transmittance was estimated as the ratio between the corrected ocean surface backscatter and the theoretical one. The ocean subsurface backscatter was finally derived from the subsurface attenuated backscatter divided by the two‐way atmospheric transmittance. Significant relationships between integrated subsurface backscatter and chlorophyll‐a concentration and between integrated subsurface backscatter and particulate organic carbon were found, which indicate a potential use of CALIPSO lidar to estimate global chlorophyll‐a and particulate organic carbon concentrations.
      PubDate: 2014-07-16T10:32:25.066959-05:
      DOI: 10.1002/2014JC009970
  • Shelf water and chlorophyll export from the Hatteras slope and outer shelf
    • Authors: James H. Churchill; Glen G. Gawarkiewicz
      Pages: n/a - n/a
      Abstract: Using high‐resolution data acquired from a shipboard ADCP and a towed Scanfish equipped with a CTD and fluorometer, we examine the properties and transport of Middle Atlantic Bight (MAB) shelf water over a region of the Hatteras outer shelf and slope where MAB shelf water is commonly deflected offshore and entrained into the Gulf Stream. The data are from a period in early August 2004 when the seasonal pycnocline of the MAB is well developed and situated over a weakly stratified, near‐bottom shelf water mass commonly referred to as the cold pool. Our data show chlorophyll‐rich cold pool water carried rapidly southward over the slope and outer shelf, at a rate of up to 60 cm s−1, as part of the shelf‐edge frontal jet. This southward transport of chlorophyll‐rich cold pool water is shunted eastward and entrained into the Gulf Stream. However, the latitude band over which this export occurs varies significantly over the 7 day course of our study, a variation which is linked to an order 50 km shift in the latitude at which the Gulf Stream separates from the continental margin. The coupled rapid translation of the Gulf Stream frontal separation and the cold pool export zone is likely to have a significant impact on the movement and accumulation of biogenic material over the Hatteras slope and rise.
      PubDate: 2014-07-16T10:20:19.828531-05:
      DOI: 10.1002/2014JC009809
  • Issue Information
    • Pages: i - v
      PubDate: 2014-07-14T08:50:10.684468-05:
      DOI: 10.1002/jgrc.20351
  • Surface circulation in the Gulf of California in summer from surface
           drifters and satellite images (2004–2006)
    • Authors: M. F. Lavín; Rubén Castro, Emilio Beier, Carlos Cabrera, Victor M. Godínez, A. Amador‐Buenrostro
      Pages: n/a - n/a
      Abstract: Surface drifters released in the Gulf of California between June 2004 and August 2006 are used to describe the surface circulation in late spring and summer. In the June to September mean, there was a poleward coastal current on the shelf and slope of the mainland side of the Gulf, with mean speed ∼0.3 m/s; it reached the northern Gulf and joined the cyclonic circulation typical of this zone in summer. In the western half of the southern Gulf, the drifters presented recirculating currents that are due to mesoscale eddies that appear to dominate the surface circulation in summer. In June 2004, the coastal current presented an enhancement event with mean speed around 0.60 m/s and maximum ∼0.80 m/s. It took ∼20 days for a particular drifter to travel the 1000 km from the Gulf entrance to the head. This strengthening of the coastal current was apparent in chlorophyll a and SST satellite images, the drifters following closely the intrusion of warm, chlorophyll‐poor surface water from outside the Gulf. The drifters and the satellite images suggest that the current‐enhancement event lasted less than a month. This mesoscale event was linked with a mesoscale remote forcing in the tropical Pacific coast and with a mesoscale local forcing of the wind. These events seem to occur every year, and are probably important in carrying organisms and properties from the entrance to the whole length of the Gulf.
      PubDate: 2014-07-12T06:23:31.520902-05:
      DOI: 10.1002/2013JC009345
  • The nascent Kuroshio of Lamon Bay
    • Authors: Arnold L. Gordon; Pierre Flament, Cesar Villanoy, Luca Centurioni
      Pages: n/a - n/a
      Abstract: A northward flowing current, emanating from the North Equatorial Current (NEC) bifurcation at the Philippine margin, enters Lamon Bay along Luzon's eastern coast. There the NEC tropical water masses merge with subtropical water of the western North Pacific to form the Kuroshio. A northward flowing western boundary current is first observed near 16.5°N, marking the initiation of the Kuroshio. The current feeding into the nascent Kuroshio of Lamon Bay is bracketed by an anticyclonic dipole to its northeast and a cyclonic dipole to its southwest. Ship‐based observational programs in the spring seasons of 2011 and 2012 detect a shift of the Lamon Bay thermohaline stratification with marked enrichment of NEC tropical thermocline water in 2012 relative to a dominant western North Pacific subtropical stratification of 2011. Temperature‐salinity time series from moorings spanning the two ship‐based observations identify the timing of the transition as December 2011. The NEC bifurcation was further south in May 2012 than in May 2011. We suggest that the more southern bifurcation in May 2012 induced increased NEC thermocline water injection into Lamon Bay and nascent Kuroshio, increasing the linkage of the western North Pacific subtropical and tropical thermoclines. This connection was reduced in May 2011 as the NEC bifurcation shifted into a more northerly position and western North Pacific subtropical thermocline dominated Lamon Bay stratification.
      PubDate: 2014-07-10T12:51:12.752646-05:
      DOI: 10.1002/2014JC009882
  • Semidiurnal tidal currents in the deep ocean near the East Pacific Rise
           between 9° and 10°N
    • Authors: Xinfeng Liang
      Pages: n/a - n/a
      Abstract: Spatial and temporal variations of the semidiurnal tidal currents, especially the baroclinic components, in the deep ocean near a segment of the East Pacific Rise (EPR) are examined using observations from a set of current meter moorings. Over the ridge crest, the baroclinic semidiurnal tidal current is dominated by the zonal component and is coherent along the observed ridge segment. In the direction across the ridge crest, the baroclinic semidiurnal tidal current is not coherent and its magnitude decreases away from the ridge crest. Vertically, the baroclinic semidiurnal tidal current covaries in a few hundred meters near the seafloor. Both the semidiurnal kinetic energy (KE) and shear show significant subinertial temporal variations. By comparing with background forcings, the author found that the subinertial variation of the semidiurnal tides over the ridge crest is related to both the spring‐neap cycles and the eddy‐induced low‐frequency flows in the deep ocean, particularly their cross‐ridge components. The observation that the baroclinic tidal currents at the axial stations flowing perpendicularly to the ridge crest suggests that the baroclinic semidiurnal tides at the axial stations are generated locally. It is therefore probable that the subinertial variation of the baroclinic semidiurnal tides near the EPR is due to the eddy‐modulated internal tide generation. Since the mesoscale eddies in the eastern tropical Pacific vary with the state of the climate, the observed eddy‐modulated internal tide generation connects climate change and variability to the physical and biogeochemical dynamics in the deep ocean and implies an unexplored feedback mechanism potentially affecting the climate system.
      PubDate: 2014-07-10T12:37:07.914739-05:
      DOI: 10.1002/2013JC009522
  • Characteristics and dynamics of two major Greenland glacial fjords
    • Authors: David A. Sutherland; Fiammetta Straneo, Robert S. Pickart
      Pages: n/a - n/a
      Abstract: The circulation regimes of two major outlet glacial fjords in southeastern Greenland, Sermilik Fjord (SF) and Kangerdlugssuaq Fjord (KF), are investigated using data collected in summer 2009. The two fjords show similar flow patterns, with a time‐dependent, vertically sheared flow structure dominating over the background estuarine flow driven by buoyancy input. We show that this time‐dependent flow is consistent with circulation induced by density interface fluctuations at the fjord mouth, often referred to as intermediary circulation. One difference between the fjords is that the hydrographic and velocity structure below a surface modified layer is found to be three‐layer in KF in summer, compared to two‐layer in SF. Outside each fjord, large‐scale geostrophic currents dictate the stratification at the mouth, although the way in which these large‐scale flows impinge on each fjord is distinct. Combining the observations with estimates from existing theories, we find the magnitudes of the estuarine (Qe) and intermediary (Qi) circulation and show that Qi >> Qe, although along‐fjord winds can also be significant. We expect that the critical parameter determining Qi / Qe is the sill depth compared to the fjord depth, with shallower sills corresponding to weaker intermediary circulation. Finally, we discuss the implications of strong intermediary circulation on calculating heat transport to the glacier face and its potential feedbacks on the background circulation in these highly stratified estuaries.
      PubDate: 2014-05-29T10:27:47.923239-05:
      DOI: 10.1002/2013JC009786
  • Precessional forced extratropical North Pacific mode and associated
           atmospheric dynamics
    • Authors: Yue Wang; Ping Zhao, ZhiMin Jian, Dong Xiao, JunMing Chen
      Pages: n/a - n/a
      Abstract: Using transient accelerated simulations of the Community Climate System Model version 3 and an Earth system Model of Intermediate Complexity as well as equilibrium experiments of the Community Earth System Model, we identified a response of the extratropical air‐ocean coupled system to the precessional insolation changes at orbital timescales and named this extratropical response pattern as the North Pacific mode (NPM). Corresponding to the increased/decreased boreal winter/summer insolation at 22ka (relative to 10‐8ka), the NPM is characterized by a western warm‐eastern cold seesaw pattern of sea surface temperature (SST) over the extratropical North Pacific from November to April, a weakened winter Aleutian low and an anomalous anticyclonic circulation throughout the troposphere. This feature forms a barotropic warm‐ridge response of tropospheric temperature and geopotential height to the precessional insolation. At the surface, rainfall increases over East Asia and the Northwest Pacific, which indicates a weakened East Asian winter monsoon, while drier conditions appear over the Northeast Pacific and the western coasts of North America. Associated with a negative phase of NPM is a weaker warming over the equatorial Pacific during winter. The increased winter insolation at precessional band not only induces the in‐phase SST warming over the Northwest Pacific and the tropical Pacific, but also explains those extratropical atmospheric changes associated with NPM. The latter might be associated with the warm SST‐induced tropospheric downstream ridge response through transient eddy activities. Besides the vital role of air‐ocean interactions, the decreased summer insolation is also essential to the zonal SST seesaw of NPM at precessional band.
      PubDate: 2014-05-27T06:25:18.770305-05:
      DOI: 10.1002/2013JC009765
  • Biological and physical processes influencing sea ice, under‐ice
           algae, and dimethylsulfoniopropionate during spring in the Canadian Arctic
    • Authors: V. Galindo; M. Levasseur, C. J. Mundy, M. Gosselin, J.‐É. Tremblay, M. Scarratt, Y. Gratton, T. Papakiriakou, M. Poulin, M. Lizotte
      Pages: n/a - n/a
      Abstract: [1] This study presents temporal variations in concentrations of chlorophyll a (Chl a), particulate and dissolved dimethylsulfoniopropionate (DMSPp and DMSPd) in the sea ice and underlying water column in the Canadian Arctic Archipelago during the spring of 2010 and 2011. During both years, bottom‐ice Chl a, DMSPp and DMSPd concentrations were high (up to 1328 µg L-1, 15 000 nmol L-1, and 6000 nmol L-1, respectively) in May and decreased thereafter. The release of bottom ice algae and DMSPp in the water column was gradual in 2010 and rapid (8 days) in 2011. Bottom brine drainage during the pre‐snowmelt period in 2010 and a rapid loss of the snow cover in 2011 coinciding with rain events explain most of the difference between the two years. During both years, less than 13% of the DMSPd lost from the ice was detected in the water column, suggesting a rapid microbial consumption. An under‐ice diatom bloom developed in both years. In 2010, the bloom was dominated by centric diatoms while in 2011 pennates dominated, likely reflecting seeding by ice algae following the faster snow melt progression induced by rainfall events in 2011. Both under‐ice blooms were associated with high DMSPp concentrations (up to 185 nmol L-1), but pennate diatoms showed DMSPp/Chl a ratios twice higher than centrics. These results highlight the key role of snowmelt and precipitation on the temporal pattern of ice‐DMSP release to the water column and on the timing, taxonomic composition, and DMSP content of phytoplankton under‐ice blooms in the Arctic.
      PubDate: 2014-05-27T06:24:02.159445-05:
      DOI: 10.1002/2013JC009497
  • Seaglider observations of equatorial Indian Ocean Rossby waves associated
           with the Madden‐Julian Oscillation
    • Authors: Benjamin G. M. Webber; Adrian J. Matthews, Karen J. Heywood, Jan Kaiser, Sunke Schmidtko
      Pages: n/a - n/a
      Abstract: During the CINDY‐DYNAMO field campaign of September 2011 ‐ January 2012, a Seaglider was deployed at 80°E and completed 10 north‐south sections between 3 and 4°S, measuring temperature, salinity, dissolved oxygen concentration and chlorophyll fluorescence. These high‐resolution subsurface observations provide insight into equatorial ocean Rossby wave activity forced by three Madden‐Julian Oscillation (MJO) events during this time period. These Rossby waves generate variability in temperature O(1°C), salinity O(0.2 g kg‐1), density O(0.2 kg m‐3) and oxygen concentration O(10 µmol kg‐1), associated with 10 m vertical displacements of the thermocline. The variability extends down to 1000 m, the greatest depth of the Seaglider observations, highlighting the importance of surface forcing for the deep equatorial ocean. The temperature variability observed by the Seaglider is greater than that simulated in the ECCO‐JPL reanalysis, especially at depth. There is also marked variability in chlorophyll fluorescence at the surface and at the depth of the chlorophyll maximum. Upwelling from Rossby waves and local wind stress curl leads to an enhanced shoaling of the chlorophyll maximum by 10‐25 m in response to the increased availability of nutrients and light. This influence of the MJO on primary production via equatorial ocean Rossby waves has not previously been recognised.
      PubDate: 2014-05-26T04:27:03.501854-05:
      DOI: 10.1002/2013JC009657
  • From the subtropics to the equator in the Southwest Pacific: Continental
           material fluxes quantified using neodymium data along modeled thermocline
           water pathways
    • Authors: Mélanie Grenier; Catherine Jeandel, Sophie Cravatte
      Pages: n/a - n/a
      Abstract: The southwestern tropical Pacific, part of a major pathway for waters feeding the Equatorial Undercurrent, is a region of important geochemical enrichment through land‐ocean boundary exchange. Here we develop an original method based on the coupling between dynamical modeling and geochemical tracer data to identify regions of enrichment along the water pathways from the subtropics to the equator, and to allow a refined quantification of continental material fluxes. Neodymium data are interpreted with the help of modeled Lagrangian trajectories of an Ocean General Circulation Model. We reveal that upper and lower thermocline waters have different pathways together with different geochemical evolutions. The upper thermocline waters entering the Solomon Sea mainly originate from the central subtropical gyre, enter the Coral Sea in the North Vanuatu Jet and likely receive radiogenic neodymium from the basaltic island margins encountered along their route. The lower thermocline waters entering the Solomon Sea mainly originate from northeast of New Zealand and enter the Coral Sea in the North Caledonian Jet. Depletion of their neodymium content likely occurs when flowing along the Australian and Papua coasts. Downstream from the Solomon Sea, waters flowing along the Papua New Guinea margins near the Sepik river mouth become surprisingly depleted in their neodymium content in the upper thermocline while enriched in the lower thermocline. This coupled approach is proposed as strong support to interpret the origin of the equatorial Pacific natural fertilization through a better understanding of the circulation, important objectives of the international GEOTRACES and SPICE programs, respectively.
      PubDate: 2014-05-26T04:05:39.011215-05:
      DOI: 10.1002/2013JC009670
  • Interannual variations of Kuroshio transport in the East China Sea and its
           relation to the Pacific Decadal Oscillation and mesoscale eddies
    • Authors: Endro Soeyanto; Xinyu Guo, Jun Ono, Yasumasa Miyazawa
      Pages: n/a - n/a
      Abstract: Results of a data assimilative ocean model (JCOPE2) from 1993 to 2012 were used to examine the correlation between the Pacific Decadal Oscillation (PDO) index and interannual variations of the Kuroshio transport in the East China Sea (ECS) and the influences of mesoscale eddies on this correlation. In a period from 1993 to 2002, the Kuroshio transport estimated from the JCOPE2 reanalysis has a positive correlation with the PDO index. This well‐known correlation became weak or even disappeared when the analysis period was extended from 1993‐2002 to 1993‐2012. This occurs because the variation range of the PDO index became small during enhanced mesoscale eddy activity southeast of Taiwan in years after 2002. The eddies caused a larger variation in the Kuroshio transport in the years after 2002 than before 2002, and therefore changed the correlation between the PDO index and Kuroshio transport in the ECS. The influence of mesoscale eddies on the Kuroshio transport has strong regional dependence: the Kuroshio transport from the area east of Taiwan to the midway along the shelf break in the East China Sea depends mainly on eddies arriving from southeast of Taiwan, while transport from the midway along the shelf break to the Tokara Strait depends mainly on the eddies arriving from northeast of Okinawa Island. The combination of PDO‐related signals and eddy‐related signals determines the interannual variations of the Kuroshio transport in the ECS and sufficient attention must be paid to the spatial dependence of the Kuroshio transport in the ECS on eddies.
      PubDate: 2014-05-24T04:37:08.668037-05:
      DOI: 10.1002/2013JC009529
  • Linkage between the Pacific Decadal Oscillation and the low frequency
           variability of the Pacific Subtropical Cell
    • Authors: Lingya Hong; Liping Zhang, Zhaohui Chen, Lixin Wu
      Pages: n/a - n/a
      Abstract: The decadal variability of Pacific Subtropical Cell (STC) and its linkages with the Pacific Decadal Oscillation (PDO) are investigated in the present study based on a Simple Ocean Data Assimilation (SODA 2.2.4). It is found that, on decadal time scales, the western boundary and interior pycnocline transports are anticorrelated and the variation of the interior component is more significant, which is consistent with previous studies. The decadal variability of STC in the Northern Hemisphere is found to be strongly associated with PDO. Associated with a positive (negative) phase of PDO, the relaxation (acceleration) of the northeast trades slows down (spins up) the STC within a few years through baroclinic adjustment in conjunction with the subduction of the cold (warm) mixed layer anomalies in the extratropics. The cold (warm) water is then injected into the thermocline and advected further southwestward to the tropics along the isopycnal surfaces, leading to the slowdown (spin‐up) of STC due to zonal pressure gradient change at low latitude. Along with the STC weakening (strengthening), a significant warming (cold) anomaly appears in the tropics and it is advected to the mid‐latitude by the Kuroshio and North Pacific currents, thus feeding back to the atmosphere over the North Pacific. In contrast to the Northern Hemisphere, it is found the STC in the south only passively responds to the PDO. The mechanism found here highlights the role of the STC advection of extratropical anomalies to the tropics and horizontal gyre advection of the tropical anomalies to the extratropics in decadal variability of the STC and PDO.
      PubDate: 2014-05-24T04:37:06.521333-05:
      DOI: 10.1002/2013JC009650
  • Seismic observations from a Yakutat eddy in the northern Gulf of Alaska
    • Authors: Q. S. Tang; S. P. S. Gulick, L. T. Sun
      Pages: n/a - n/a
      Abstract: Recent works show that the seismic oceanography technique allows us to relate water column seismic reflections to oceanic finescale structures. In this study, finescale structures of a surface anticyclonic eddy have been unveiled by reprocessing two seismic transects acquired in the northern Gulf of Alaska using an 8‐km hydrophone streamer and 6600 cu in linear airgun array in September 2008. The eddy was a typical bowl‐like structure with around 55 km width and 700 m depth. It has two fringes around the eddy base and a spiral arm at the NE edge. The in situ sea surface temperature and salinity data from a shipboard thermosalinograph help to confirm our interpretations of a spiral arm shed from the warm eddy and the entrained cold water from elsewhere. Nearby the eddy and offshore the shelf‐break, there is a strong frontal feature, probably the Alaska Current. The eddy likely formed offshore Yakutat shelf and transported along the offshore shelf‐break by tracking the sea level anomalies. Its equivalent diameter of 65 km was measured using the along‐track altimeter and the seismic constraints. It was comparable with results from the representative conventional algorithms of eddy detection. Geostrophic velocities of the eddy were estimated from the dipping seismic reflections under the assumptions of approximate isopycnals and geostrophic balance. Measured water properties including sea surface temperature, salinity, and chlorophyll revealed that eddy translation transports coastal water to the pelagic regions. Structures synthesized from CTD profiles that sampled an earlier eddy suggest that thin striae around the base might be a common feature in Gulf of Alaska eddies.
      PubDate: 2014-05-24T04:21:50.176872-05:
      DOI: 10.1002/2014JC009938
  • Mindanao Current/Undercurrent measured by a subsurface mooring
    • Authors: Linlin Zhang; Dunxin Hu, Shijian Hu
      Pages: n/a - n/a
      Abstract: The mean structure and variability of the currents east of Mindanao are investigated through two‐year mooring observations at about 8ºN, 127º3'E from December 2010 to December 2012. The strong southward Mindanao Current (MC) exists in the upper 600 m with a maximum mean velocity of 73 cm/s and a standard deviation of 17 cm/s at 100 m. A northward mean flow is observed below 600 m to the depth deeper than 1000 m, which has been called the Mindanao Undercurrent (MUC) with a maximum mean velocity of about 10 cm/s at 950 m and a standard deviation of 19 cm/s. Further analysis with hydrographic data and an eddy‐resolving model outputs also suggests this northward mean current to be the MUC. Intraseasonal variability with a period of 60‐80 days is revealed through the whole water column from 200 m down to about 900 m. This intraseasonal variability appears to be closely related to subthermocline eddies, which translate westward and intensify near the Mindanao coast.
      PubDate: 2014-05-24T04:20:37.614635-05:
      DOI: 10.1002/2013JC009693
  • Improved mapping of sea ice production in the Arctic Ocean using
           AMSR‐E thin ice thickness algorithm
    • Authors: Katsushi Iwamoto; Kay I. Ohshima, Takeshi Tamura
      Pages: n/a - n/a
      Abstract: New and improved estimates of sea ice production in the Arctic Ocean are derived from AMSR‐E satellite and atmospheric reanalysis data for the period 2002–2011, at a spatial resolution of 6.25 km and using a newly‐developed fast‐ice mask. High ice production in the major coastal polynyas is well demonstrated. The total annual cumulative ice production in the major 10 polynya regions is about 1180 ±70km3. The interannual variability of the ice production for each polynya is presented during 2002–2011. No obvious relationship is noted between the ice production and the recent drastic reduction in the preceding summer Arctic sea ice extent. Most polynya regions exhibit maximum ice production in autumn (October – November), before areas offshore have been covered with consolidated pack ice. Sea ice production from October to November in the marginal ice zone of the Pacific Ocean sector is negatively correlated with summer ice extent there. The ice production from October to November of 2007 (a record minimum summer ice extent) was about twice as large as that in other years. The high ice production area shifted to higher latitudes i.e., towards the deep Canada Basin, due to the retreat of the summer ice edge. We speculate that the resultant increase in brine input could change the oceanic structure in the basin, specifically deepening the winter mixed layer.
      PubDate: 2014-05-23T23:50:57.633401-05:
      DOI: 10.1002/2013JC009749
  • Variation in the Kuroshio intrusion: Modeling and interpretation of
           observations collected around the Luzon Strait from July 2009 to March
    • Authors: Yaochu Yuan; Yu‐heng Tseng, Chenghao Yang, Guanghong Liao, Chun Hoe Chow, Zenghong Liu, Xiao‐Hua Zhu, Hong Chen
      Pages: n/a - n/a
      Abstract: This study analyzes the observed subtidal currents, 1/12˚ global HYCOM model results and the observed time series to interpret seasonal and interannual patterns in the behavior of the Kuroshio intrusion around the Luzon Strait (LS). The observations include current measurements conducted at mooring station N2 (20°40.441′ N, 120°38.324′ E) from July 7th, 2009 to March 31st, 2011, surface geostrophic currents derived from the merged absolute dynamic topography and the trajectory of an Argo float during the winter of 2010‐2011. Results from mooring station N2 confirmed the seasonal changes in the Kuroshio intrusion and the variation of the Kuroshio intrusion during El Niño event from July, 2009 to April, 2010 and La Niña even from June, 2010 to March, 2011. The strongest Kuroshio intrusion occurs in the winter, with successively weaker currents in spring, autumn and summer. Comparison of relative differences (Δmax(z)) in the maximum absolute value of monthly average zonal velocity components Umax (z) showed that the Kuroshio intrusion was stronger during the 2009‐2010 winter (El Niño) than the 2010‐2011 winter (La Niña). Furthermore, the relative differences (Δmax(z)) in deeper layers exceed those of the surface layer. Circulation patterns in surface geostrophic currents and the Argo float trajectory confirmed the results of mooring station N2. The Kuroshio intrusion velocity variation modeled using the 1/12˚ global HYCOM model resembled the observation on both seasonal to interannual scales. Modeled variation in the zonal mean velocity anomaly was also consistent with Niño3, Niño4 and North Equatorial Current (NEC) bifurcation latitude indices, indicating concurrent impacts of the ENSO influence. Monsoon winds strongly affect the seasonal variation while the weak upstream Kuroshio transport induced by El Niño, strongly affects the interannual variation, such as 2009‐2010 winter. In 2010‐2011 winter, the impact of winter monsoon forcing still exists in the LS. However, the stronger upstream Kuroshio transport during this period did not allow the Kuroshio to penetrate into the LS deeply. This explains why the 2009‐2010 winter Kuroshio intrusion (El Niño event) was stronger than that of the 2010‐2011 winter (La Niña event).
      PubDate: 2014-05-22T12:08:07.839022-05:
      DOI: 10.1002/2013JC009776
  • Connecting wind‐driven upwelling and offshore stratification to
           nearshore internal bores and oxygen variability
    • Authors: Ryan K. Walter; C. Brock Woodson, Paul R. Leary, Stephen G. Monismith
      Pages: n/a - n/a
      Abstract: This study utilizes field observations in southern Monterey Bay, CA to examine how regional scale upwelling and changing offshore (shelf) conditions influence nearshore internal bores. We show that the low‐frequency wind forcing (e.g., upwelling/relaxation time scales) modifies the offshore stratification and thermocline depth. This in turn alters the strength and structure of observed internal bores in the nearshore. An internal bore strength index is defined using the high‐pass filtered potential energy density anomaly in the nearshore. During weak upwelling favorable conditions and wind relaxations, the offshore thermocline deepens. In this case, both the amplitude of the offshore internal tide and the strength of the nearshore internal bores increase. In contrast, during strong upwelling conditions, the offshore thermocline shoals towards the surface, resulting in a decrease in the offshore internal tide amplitude. As a result, cold water accumulates in the nearshore (nearshore pooling), and the internal bore strength index decreases. Empirical orthogonal functions are utilized to support the claim that the bore events contribute to the majority of the variance in cross‐shelf exchange and transport in the nearshore. Observed individual bores can drive shock‐like drops in dissolved oxygen (DO) with rapid onset times, while extended upwelling periods with reduced bore activity produce longer duration, low DO events.
      PubDate: 2014-05-22T12:06:43.936813-05:
      DOI: 10.1002/2014JC009998
  • A modeling study of the processes of surface salinity seasonal cycle in
           the Bay of Bengal
    • Authors: V.P. Akhil; Fabien Durand, Matthieu Lengaigne, Jérôme Vialard, M.G. Keerthi, V.V. Gopalakrishna, Charles Deltel, Fabrice Papa, Clément de Boyer Montégut
      Pages: n/a - n/a
      Abstract: In response to the Indian Monsoon freshwater forcing, the Bay of Bengal exhibits a very strong seasonal cycle in sea surface salinity (SSS), especially near the mouths of the Ganges‐Brahmaputra and along the east coast of India. In this paper, we use an eddy‐permitting (~25 km resolution) regional ocean general circulation model simulation to quantify the processes responsible for this SSS seasonal cycle. Despite the absence of relaxation towards observations, the model reproduces the main features of the observed SSS seasonal cycle, with freshest water in the northeastern Bay, particularly during and after the monsoon. The model also displays an intense and shallow freshening signal in a narrow (~100 km wide) strip that hugs the east coast of India, from September to January, in good agreement with high‐resolution measurements along two ships of opportunity lines. The mixed layer salt budget confirms that the strong freshening in the northern Bay during the monsoon results from the Ganges‐Brahmaputra river discharge and from precipitation over the ocean. From September onward, the East India Coastal Current transports this freshwater southward along the east coast of India, reaching the southern tip of India in November. The surface freshening results in an enhanced vertical salinity gradient that increases salinity of the surface layer by vertical processes. Our results reveal that the erosion of the freshwater tongue along the east coast of India is not driven by northward horizontal advection, but by vertical processes that eventually overcome the freshening by southward advection and restore SSS to its pre‐monsoon values. The salinity‐stratified barrier layer hence only acts as a “barrier” for vertical heat fluxes, but is associated with intense vertical salt fluxes in the Bay of Bengal.
      PubDate: 2014-05-22T12:03:06.532129-05:
      DOI: 10.1002/2013JC009632
  • The vertical structure of the circulation and dynamics in Hudson Shelf
    • Authors: Steven J. Lentz; Bradford Butman, Courtney Harris
      Pages: n/a - n/a
      Abstract: Hudson Shelf Valley is a 20‐30 m deep, 5‐10 km wide v‐shaped submarine valley that extends across the Middle Atlantic Bight continental shelf. The valley provides a conduit for cross‐shelf exchange via along‐valley currents of 0.5 m s‐1 or more. Current profile, pressure, and density observations collected during the winter of 1999‐2000 are used to examine the vertical structure and dynamics of the flow. Near‐bottom along‐valley currents having times scales of a few days are driven by cross‐shelf pressure gradients set up by wind stresses, with eastward (westward) winds driving onshore (offshore) flow within the valley. The along‐valley momentum balance in the bottom boundary layer is predominantly between the pressure gradient and bottom stress because the valley bathymetry limits current veering. Above the bottom boundary layer the flow veers toward an along‐shelf (cross‐valley) orientation and a geostrophic balance with some contribution from the wind stress (surface Ekman layer). The vertical structure and strength of the along‐valley current depends on the magnitude and direction of the wind stress. During offshore flows driven by westward winds the near‐bottom stratification within the valley increases resulting in a thinner bottom boundary layer and weaker offshore currents. Conversely, during onshore flows driven by eastward winds the near‐bottom stratification decreases resulting in a thicker bottom boundary layer and stronger onshore currents. Consequently, for wind stress magnitudes exceeding 0.1 Nm‐2, onshore along‐valley transport associated with eastward wind stress exceeds the offshore transport associated with westward wind stress of the same magnitude.
      PubDate: 2014-05-22T04:19:48.675042-05:
      DOI: 10.1002/2014JC009883
  • Climate change projection in the Northwest Pacific marginal seas through
           dynamic downscaling
    • Authors: Gwang‐Ho Seo; Yang‐Ki Cho, Byoung‐Ju Choi, Kwang‐Yul Kim, Bong‐guk Kim, Yong‐jin Tak
      Pages: n/a - n/a
      Abstract: This study presents future climate change projections in the Northwest Pacific (NWP) marginal seas using dynamic downscaling from global climate models (GCMs). A regional climate model (RCM) for the Northwest Pacific Ocean was set up and integrated over the period from 2001 to 2100. The model used forcing fields from three different GCM simulations to downscale the effect of global climate change. MIROC, ECHAM, and HADCM were selected to provide climate change signals for the RCM. These signals were calculated from the GCMs using Cyclostationary Empirical Orthogonal Function analysis and added to the present lateral open boundary and the surface forcing. The RCM was validated by comparing hindcast result with the observation. It was able to project detailed regional climate change processes that GCMs were not able to resolve. A relatively large increases of water temperature were found in the marginal seas. However, only a marginal change was found along the Kuroshio path. Heat supply to the atmosphere decreases in most study areas due to a slower warming of the sea surface compared to the atmosphere. The RCM projection suggests that the temperature of the Yellow Sea Bottom Cold Water will gradually increase by 2100. Volume transports through major straits except the Taiwan Strait in the marginal seas are projected to increase slightly in future. Increased northeasterly wind stress in the East China Sea may also result in the transport change.
      PubDate: 2014-05-21T07:02:49.777515-05:
      DOI: 10.1002/2013JC009646
  • How well can we measure the ocean's mean dynamic topography from
    • Authors: R. J. Bingham; K. Haines, D. J. Lea
      Pages: n/a - n/a
      Abstract: Recent gravity missions have produced a dramatic improvement in our ability to measure the ocean's mean dynamic topography (MDT) from space. To fully exploit this oceanic observation, however, we must quantify its error. To establish a baseline, we first assess the error budget for an MDT calculated using a 3rd generation GOCE geoid and the CLS01 mean sea surface (MSS). With these products, we can resolve MDT spatial scales down to 250 km with an accuracy of 1.7 cm, with the MSS and geoid making similar contributions to the total error. For spatial scales within the range 133–250 km the error is 3.0 cm, with the geoid making the greatest contribution. For the smallest resolvable spatial scales (80–133 km) the total error is 16.4 cm, with geoid error accounting for almost all of this. Relative to this baseline, the most recent versions of the geoid and MSS fields reduce the long and short‐wavelength errors by 0.9 and 3.2 cm, respectively, but they have little impact in the medium‐wavelength band. The newer MSS is responsible for most of the long‐wavelength improvement, while for the short‐wavelength component it is the geoid. We find that while the formal geoid errors have reasonable global mean values they fail capture the regional variations in error magnitude, which depend on the steepness of the sea floor topography.
      PubDate: 2014-05-21T07:00:29.323757-05:
      DOI: 10.1002/2013JC009354
  • Observations of surface waves interacting with ice using stereo imaging
    • Authors: Alexander J. Campbell; Adam J. Bechle, Chin H. Wu
      Pages: n/a - n/a
      Abstract: A powerful Automated Trinocular Stereo Imaging System (ATSIS) is used to remotely measure waves interacting with three distinct ice types: brash, frazil, and pancake. ATSIS is improved with a phase‐only correlation matching algorithm and parallel computation to provide high spatial and temporal resolution 3‐D profiles of the water/ice surface, from which the wavelength, frequency, and energy flux are calculated. Along‐shore spatial frequency distributions show that pancake and frazil ices differentially attenuate at a greater rate for higher frequency waves, causing a decrease in mean frequency. In contrast, wave propagation through brash ice causes a rapid increase in the dominant wave frequency, which may be caused by non‐linear energy transfer to higher frequencies due to collisions between the brash ice particles. Consistent to the results in frequency, the wavelengths in pancake and frazil ices increase but decrease in brash ice. The total wave energy fluxes decrease exponentially in both pancake and frazil ice, whereas the overall energy flux remain constant in the brash ice due to thin layer thickness. The spatial energy flux distributions also reveal that wave reflection occurs at the boundary of each ice layer, with reflection coefficient decaying exponentially away from the ice interface. Reflection is the strongest at the pancake/ice‐free and frazil/brash interfaces; and the weakest at the brash/ice‐free interface. These high resolution observations measured by ATSIS demonstrate the spatially variable nature of waves propagating through ice.
      PubDate: 2014-05-19T01:25:52.50953-05:0
      DOI: 10.1002/2014JC009894
  • Surface energy budget of landfast sea ice during the transitions from
           winter to snowmelt and melt pond onset: The importance of net longwave
           radiation and cyclone forcings
    • Authors: B.G.T. Else; T.N. Papakyriakou, R. Raddatz, R.J. Galley, C.J. Mundy, D. G. Barber, K. Swystun, S. Rysgaard
      Pages: n/a - n/a
      Abstract: Relatively few sea ice energy balance studies have successfully captured the transition season of warming, snowmelt, and melt pond formation. In this paper, we report a surface energy budget for landfast sea ice that captures this important period. The study was conducted in the Canadian Arctic Archipelago from 10 May – 20 June, 2010. Over the first 20 days of the study we found that short periods (1‐3 days) of increased net radiation associated with low longwave loss provided most of the energy required to warm the snowpack from winter conditions. An extended period of low longwave loss (5 days) combined with the seasonal increase in incoming shortwave radiation then triggered snowmelt onset. Melt progressed with a rapid reduction in albedo and attendant increases in shortwave energy absorption, resulting in melt pond formation 8 days later. The key role of longwave radiation in initiating melt onset supports past findings, and confirms the importance of clouds and water vapor associated with synoptic weather systems. However, we also observed a period of strong turbulent energy exchange associated with the passage of a cyclone. The cyclone event occurred shortly after melt pond formation, but it delivered enough energy to significantly hasten melt onset had it occurred earlier in the season. Changes in the frequency, duration, and timing of synoptic‐scale weather events that deliver clouds and/or strong turbulent heat fluxes may be important in explaining observed changes in sea ice melt onset timing.
      PubDate: 2014-05-17T03:53:33.081419-05:
      DOI: 10.1002/2013JC009672
  • Ocean eddy freshwater flux convergence into the North Atlantic subtropics
    • Authors: Arnold L. Gordon; Claudia F. Giulivi
      Pages: n/a - n/a
      Abstract: For a quasi‐steady state condition the water vapor flux from the ocean to atmosphere typical of the salty subtropics, must be compensated by ocean processes that transfer freshwater into the evaporative regime. Observations of the North Atlantic subtropical sea surface salinity maximum region frequently reveal the presence of eddies with distinct salinity/temperature signatures of up to 0.2 psu/1°C, with horizontal scales of up to 200 km. Using the surface layer salinity and meridional velocity from the Simple Ocean Data Assimilation (SODA) re‐analysis data we find that the eddy flux can accomplish 50% to 75% of the required freshwater convergence into the subtropical regime, the rest being delivered by Ekman transport convergence, and therefore represents a significant component of the marine hydrological cycle. Interannual fluctuations of the eddy freshwater flux are reflected in sea surface salinity variability.
      PubDate: 2014-05-17T03:53:24.153772-05:
      DOI: 10.1002/2013JC009596
  • Evolution of a supercooled Ice Shelf Water plume with an
           actively‐growing sub‐ice platelet matrix
    • Authors: Natalie J. Robinson; Michael J. M. Williams, Craig L. Stevens, Patricia J. Langhorne, Tim G. Haskell
      Pages: n/a - n/a
      Abstract: We use new observations in Western McMurdo Sound, combined with longitudinal hydrographic transects of the sound, to identify a northward‐flowing Ice Shelf Water (ISW) plume exiting the cavity of the McMurdo‐Ross Ice Shelf. We estimate the plume's net northward transport at 0.4 ± 0.1 Sv, carving out a corridor approximately 35 km wide aligned with the Victoria Land Coast. Basal topography of the McMurdo Ice Shelf is such that the plume is delivered to the surface without mixing with overlying warmer water, and is therefore able to remain below the surface freezing temperature at the point of observation beneath first‐year ice. Thus the upper ocean was supercooled, by up to 50 mK at the surface, due to pressure relief from recent rapid ascent of the steep basal slope. The 70 m thick supercooled layer supports the growth and maintenance of a thick, semi‐rigid and porous matrix of platelet ice, which is trapped by buoyancy at the ice‐ocean interface. Continued growth of individual platelets in supercooled water creates significant brine rejection at the top of the water column which resulted in convection over the upper 200 m thick, homogeneous layer. By examining the diffusive nature of the intermediate water between layers of ISW and High Salinity Shelf Water, we conclude that the ISW plume must have originated beneath the Ross Ice Shelf and demonstrate that it is likely to expand eastward across McMurdo Sound with the progression of winter.
      PubDate: 2014-05-17T03:53:21.027839-05:
      DOI: 10.1002/2013JC009399
  • Enhanced particle scavenging in deep water of the Aleutian Basin revealed
           by 210Po‐210Pb disequilibria
    • Authors: Wangjiang Hu; Min Chen, Weifeng Yang, Run Zhang, Yusheng Qiu, Minfang Zheng
      Pages: 3235 - 3248
      Abstract: The high sedimentation rate but low primary production in surface ocean raised a question whether particles from local upper water column could support high deposition in the Aleutian Basin. Here we first present large 210Po‐210Pb disequilibria in deep water of the Aleutian Basin. Dissolved 210Po and 210Pb were depleted relative to 210Pb and 226Ra, respectively, in deep water below 1000 m, as well as decreased with depth, suggesting enhanced particle scavenging in the deep water. The 210Po residence times (1–2 a) in deep water were comparable to those in the upper water column, indicating that 210Po scavenging rates were high in deep water of the Aleutian Basin. The export fluxes of 210Po from the upper 100 m were estimated to be 0.2–0.8 Bq/m2/d, much lower than those in the deep water (7–8 Bq/m2/d). Similarly, POC export fluxes in deep water (24–80 mmolC/m2/d) were higher than those in the upper 100 m (∼1 mmolC/m2/d). Such a large discrepancy between the upper and deep water suggested that particles from local upper water column could not totally meet the enhanced scavenging in the deep water. Based on mass balance calculations, the extra fluxes of 210Pb and POC imported to deep water were estimated to be 8–12 Bq/m2/d and 22–79 mmolC/m2/d, respectively. The ratio of POC to particulate 210Pb (i.e., POC/PPb) in the extra source was estimated to be 6.5 mmol/Bq, which was lower than that in the Bering Shelf with a mean POC/PPb ratio of 10.9 mmol/Bq, implying that particles in the Bering Shelf could be a potential source for the enhanced particle scavenging in deep water of the Aleutian Basin. However, quantitative and detailed role of ridges and manganese from sediments in particle scavenging in the deep water was unclear, and further studies are necessary.
      PubDate: 2014-06-02T08:41:55.660391-05:
      DOI: 10.1002/2014JC009819
  • Tidal energy conversion in a global hot spot: On the 3‐D dynamics of
           baroclinic tides at the Celtic Sea shelf break
    • Authors: Vasiliy Vlasenko; Nataliya Stashchuk, Mark E. Inall, Joanne E. Hopkins
      Pages: 3249 - 3265
      Abstract: Globally, the Celtic Sea shelf break is ranked highest as an energetic “hot spot” of tidal energy conversion, therefore making it the most significant contributor to global internal tidal energy flux. In this paper, the three‐dimensional dynamics of baroclinic tides in the shelf‐slope area of the Celtic Sea was investigated numerically and using observational data collected on the 376th cruise of the RV “RRS Discovery” in June 2012. The time series recorded at a shelf break mooring showed that semidiurnal internal waves were accompanied by packets of internal solitary waves with maximum amplitudes up to 105 m, the largest internal waves ever recorded in the Celtic Sea, and ranking among the largest observed in the global ocean. The observed baroclinic wavefields were replicated numerically using the Massachusetts Institute of Technology general circulation model. A fine‐resolution grid with 115 m horizontal and 10 m vertical steps allowed the identification of two classes of short‐scale internal waves. The first classification was generated over headlands and resembles spiral‐type internal waves that are typical for isolated underwater banks. The second classification, generated within an area of several canyons, revealed properties of quasi‐planar internal wave packets. The observed in situ intensification of tidal bottom currents at the shelf break mooring is explained in terms of a tidal beam that was formed over supercritical bottom topography at the mooring location.
      PubDate: 2014-06-02T08:40:27.218238-05:
      DOI: 10.1002/2013JC009708
  • A modeling study of coastal circulation and landfast ice in the nearshore
           Beaufort and Chukchi seas using CIOM
    • Authors: Jia Wang; Kohei Mizobata, Xuezhi Bai, Haoguo Hu, Meibing Jin, Yanling Yu, Moto Ikeda, Walter Johnson, William Perie, Ayumi Fujisaki
      Pages: 3285 - 3312
      Abstract: This study investigates sea ice and ocean circulation using a 3‐D, 3.8 km CIOM (Coupled Ice‐Ocean Model) under daily atmospheric forcing for the period 1990–2008. The CIOM was validated using both in situ observations and satellite measurements. The CIOM successfully reproduces some observed dynamical processes in the region, including the Bering‐inflow‐originated coastal current that splits into three branches: Alaska Coastal Water (ACW), Central Channel branch, and Herald Valley branch. In addition, the Beaufort Slope Current (BSC), the Beaufort Gyre, the East Siberian Current (ESC), mesoscale eddies, and seasonal landfast ice are well simulated. The CIOM also reproduces reasonable interannual variability in sea ice, such as landfast ice, and anomalous open water (less sea ice) during the positive Dipole Anomaly (DA) years, vice versa during the negative DA years. Sensitivity experiments were conducted with regard to the impacts of the Bering Strait inflow (heat transport), onshore wind stress, and sea ice advection on sea ice change, in particular on the landfast ice. It is found that coastal landfast ice is controlled by the following processes: wind forcing, Bering Strait inflow, and sea ice dynamics.
      PubDate: 2014-06-04T12:01:30.854601-05:
      DOI: 10.1002/2013JC009258
  • Long‐term hydrological changes of the Aral Sea observed by
    • Authors: Wei Shi; Menghua Wang, Wei Guo
      Pages: 3313 - 3326
      Abstract: The Aral Sea has been shrinking since the former Soviet Union constructed irrigation projects to divert water from its main rivers in the 1960s. The diminishing of the Aral Sea is “one of the worst environmental disasters in the world” (from United Nations Secretary‐General Ban Ki‐moon). In this study, 33 years of satellite observations from Advanced Very High Resolution Radiometer (AVHRR) and 21 years of satellite altimetry sea level data from TOPEX/Poseidon, Jason‐1, and Jason‐2 are used to quantify the long‐term hydrological changes in the Aral Sea. A simple algorithm with AVHRR channels 1 and 2 albedo is developed to identify and discriminate the water pixels from land and cloud. Thus, monthly water coverage in the region can be reliably generated. The water coverage maps since 1981 show constant decline of the Aral Sea. The coverage dropped from ∼4.7–4.8 × 104 km2 in 1981 to about ¼ of this value in the recent years. In fact, drastic hydrological change was observed in the main Aral Sea during the 2000s. In the South Aral Sea, sea level shows a steady decrease from 35 m above sea level to
      PubDate: 2014-06-04T12:15:29.881942-05:
      DOI: 10.1002/2014JC009988
  • The contribution of the Weddell Gyre to the lower limb of the Global
           Overturning Circulation
    • Authors: Loïc Jullion; Alberto C. Naveira Garabato, Sheldon Bacon, Michael P. Meredith, Pete J. Brown, Sinhue Torres‐Valdés, Kevin G. Speer, Paul R. Holland, Jun Dong, Dorothée Bakker, Mario Hoppema, Brice Loose, Hugh J. Venables, William J. Jenkins, Marie‐José Messias, Eberhard Fahrbach
      Pages: 3357 - 3377
      Abstract: The horizontal and vertical circulation of the Weddell Gyre is diagnosed using a box inverse model constructed with recent hydrographic sections and including mobile sea ice and eddy transports. The gyre is found to convey 42 ± 8 Sv (1 Sv = 106 m3 s–1) across the central Weddell Sea and to intensify to 54 ± 15 Sv further offshore. This circulation injects 36 ± 13 TW of heat from the Antarctic Circumpolar Current to the gyre, and exports 51 ± 23 mSv of freshwater, including 13 ± 1 mSv as sea ice to the midlatitude Southern Ocean. The gyre's overturning circulation has an asymmetric double‐cell structure, in which 13 ± 4 Sv of Circumpolar Deep Water (CDW) and relatively light Antarctic Bottom Water (AABW) are transformed into upper‐ocean water masses by midgyre upwelling (at a rate of 2 ± 2 Sv) and into denser AABW by downwelling focussed at the western boundary (8 ± 2 Sv). The gyre circulation exhibits a substantial throughflow component, by which CDW and AABW enter the gyre from the Indian sector, undergo ventilation and densification within the gyre, and are exported to the South Atlantic across the gyre's northern rim. The relatively modest net production of AABW in the Weddell Gyre (6 ± 2 Sv) suggests that the gyre's prominence in the closure of the lower limb of global oceanic overturning stems largely from the recycling and equatorward export of Indian‐sourced AABW.
      PubDate: 2014-06-05T09:32:39.649182-05:
      DOI: 10.1002/2013JC009725
  • Global ocean current reconstruction from altimetric and microwave SST
    • Authors: C. González‐Haro; J. Isern‐Fontanet
      Pages: 3378 - 3391
      Abstract: Ocean currents are a key component to understanding many oceanic and climatic phenomena and knowledge of them is crucial for both navigation and operational applications. Currently, they are derived from Sea Surface Height (SSH) measurements provided by altimeters. However, distances between tracks and the limited number of available altimeters lead to errors in the accurate location of oceanic currents. In this study, we investigate the capability of Sea Surface Temperature (SST) observations to reconstruct surface currents at a global scale. The methodology we use consists of estimating the stream function by taking the phase from SST and the spectrum of SSH and then comparing it with altimetric measurements. Results reveal that SST provided by microwave radiometers can be used to retrieve ocean currents during winter near the major extratropical current systems, which are characterized by an intense mesoscale activity and the presence of strong thermal gradients. We have also found that surface ocean current reconstruction based on Surface Quasi‐Geostrophic approach can be improved if the information about the energy spectrum provided by altimeters is used. This points to the development of a new method of reconstructing ocean currents based on the combination of the phase of SST images with the energy spectrum derived from along‐track altimetric measurements.
      PubDate: 2014-06-05T09:36:06.59796-05:0
      DOI: 10.1002/2013JC009728
  • Characterization and variability of particle size distributions in Hudson
           Bay, Canada
    • Authors: Hongyan Xi; Pierre Larouche, Shilin Tang, Christine Michel
      Pages: 3392 - 3406
      Abstract: Particle size distribution (PSD) plays a significant role in many aspects of aquatic ecosystems, including phytoplankton dynamics, sediment fluxes, and optical scattering from particulates. As of yet, little is known on the variability of particle size distribution in marine ecosystems. In this study, we investigated the PSD properties and variability in Hudson Bay based on measurements from a laser diffractometer (LISST‐100X Type‐B) in concert with biogeochemical parameters collected during summer 2010. Results show that most power‐law fitted PSD slopes ranged from 2.5 to 4.5, covering nearly the entire range observed for natural waters. Offshore waters showed a predominance of smaller particles while near the coast, the effect of riverine inputs on PSD were apparent. Particulate inorganic matter contributed more to total suspended matter in coastal waters leading to lower PSD slopes than offshore. The depth distribution of PSD slopes shows that larger particles were associated with the pycnocline. Below the pycnocline, smaller particles dominated the spectra. A comparison between a PSD slope‐based method to derive phytoplankton size class (PSC) and pigment‐based derived PSC showed the two methods agreed relatively well. This study provides valuable baseline information on particle size properties and phytoplankton composition estimates in a sub‐arctic environment subject to rapid environmental change.
      PubDate: 2014-06-05T09:55:19.484954-05:
      DOI: 10.1002/2013JC009542
  • Improved transport estimate of the East Icelandic Current 2002–2012
    • Authors: Andreas Macrander; Héðinn Valdimarsson, Steingrímur Jónsson
      Pages: 3407 - 3424
      Abstract: The East Icelandic Current (EIC) is one of the major export pathways from the Iceland Sea north of Iceland, carrying mostly cold and fresh waters of Arctic origin. In this study, volume and freshwater transports are estimated using current profiles and salinity time series from a mooring deployed from 2011 to 2012 over the insular slope northeast of Iceland. These data are extended by hydrographic sections spanning the entire EIC four times per year. In combination with altimetry, geostrophic current profiles of the whole section are obtained for the period 2002–2012. The data are analyzed with respect to volume and freshwater transport variability and their relation to atmospheric forcing. The observations show a mean transport of 0.75 ± 0.08 Sv, and a mean freshwater transport of 3.4 ± 0.3 mSv in the upper 170 m. There is large interannual variability which appears to depend more on local conditions rather than large‐scale atmospheric forcing. The freshwater transport is small compared to the export in the East Greenland Current.
      PubDate: 2014-06-05T10:00:48.421615-05:
      DOI: 10.1002/2013JC009517
  • A multicomponent model of phytoplankton size structure
    • Authors: Robert J. W. Brewin; Shubha Sathyendranath, Gavin Tilstone, Priscila K. Lange, Trevor Platt
      Pages: 3478 - 3496
      Abstract: Size‐fractionated filtration (SFF) is a direct method for estimating pigment concentration in various size classes. It is also common practice to infer the size structure of phytoplankton communities from diagnostic pigments estimated by high‐performance liquid chromatography (HPLC). In this paper, the three‐component model of Brewin et al. (2010) was fitted to coincident data from HPLC and from SFF collected along Atlantic Meridional Transect cruises. The model accounted for the variability in each data set, but the fitted model parameters differed for the two data sets. Both HPLC and SFF data supported the conceptual framework of the three‐component model, which assumes that the chlorophyll concentration in small cells increases to an asymptotic maximum, beyond which further increase in chlorophyll is achieved by the addition of larger celled phytoplankton. The three‐component model was extended to a multicomponent model of size structure using observed relationships between model parameters and assuming that the asymptotic concentration that can be reached by cells increased linearly with increase in the upper bound on the cell size. The multicomponent model was verified using independent SFF data for a variety of size fractions and found to perform well (0.628 ≤ r ≤ 0.989) lending support for the underlying assumptions. An advantage of the multicomponent model over the three‐component model is that, for the same number of parameters, it can be applied to any size range in a continuous fashion. The multicomponent model provides a useful tool for studying the distribution of phytoplankton size structure at large scales.
      PubDate: 2014-06-06T11:06:55.954423-05:
      DOI: 10.1002/2014JC009859
  • Forcing mechanisms of intraseasonal SST variability off central Peru in
    • Authors: Serena Illig; Boris Dewitte, Katerina Goubanova, Gildas Cambon, Julien Boucharel, Florian Monetti, Carlos Romero, Sara Purca, Roberto Flores
      Pages: 3548 - 3573
      Abstract: The Sea Surface Temperature (SST) intraseasonal variability (40–90 days) along the coast of Peru is commonly attributed to the efficient oceanic connection with the equatorial variability. Here we investigate the respective roles of local and remote equatorial forcing on the intraseasonal SST variability off central Peru (8°S–16°S) during the 2000–2008 period, based on the experimentation with a regional ocean model. We conduct model experiments with different open lateral boundary conditions and/or surface atmospheric forcing (i.e., climatological or not). Despite evidence of clear propagations of coastal trapped waves of equatorial origin and the comparable marked seasonal cycle in intraseasonal Kelvin wave activity and coastal SST variability (i.e., peak in Austral summer), this remote equatorial forcing only accounts for ∼20% of the intraseasonal SST regime, which instead is mainly forced by the local winds and heat fluxes. A heat budget analysis further reveals that during the Austral summer, despite the weak along‐shore upwelling (downwelling) favorable wind stress anomalies, significant cool (warm) SST anomalies along the coast are to a large extent driven by Ekman‐induced advection. This is shown to be due to the shallow mixed layer that increases the efficiency by which wind stress anomalies relates to SST through advection. Diabatic processes also contribute to the SST intraseasonal regime, which tends to shorten the lag between peak SST and wind stress anomalies compared to what is predicted from an advective mixed‐layer model.
      PubDate: 2014-06-09T12:34:29.839579-05:
      DOI: 10.1002/2013JC009779
  • The oceanic response of the Turkish Straits System to an extreme drop in
           atmospheric pressure
    • Authors: Jeffrey W. Book; Ewa Jarosz, Jacopo Chiggiato, Şükrü Beşiktepe
      Pages: 3629 - 3644
      Abstract: Moorings across all four entry/exit sections of the Dardanelles Strait and the Bosphorus Strait simultaneously measured the response of the Turkish Straits System to the passage of a severe cyclonic storm that included an atmospheric pressure drop of more than 30 mbar in less than 48 h. The bottom pressure response at the Aegean Sea side of the Dardanelles Strait was consistent with an inverted barometer response, but the response at the other sections did not follow an inverted barometer, leading to a large bottom pressure gradient through the Turkish Straits System. Upper‐layer flow toward the Aegean Sea was reversed by the storm and flow toward the Black Sea was greatly enhanced. Bottom pressure across the Sea of Marmara peaked 6 h after the passage of the storm's minimum pressure. The response on the Dardanelles side was a combination of sea elevation and pycnocline depth rise, and the response on the Bosphorus side was an even greater sea elevation rise and a drop in pycnocline depth. The peak in bottom pressure in the Sea of Marmara was followed by another reverse in the flow through the Dardanelles Strait as flow was then directed away from the Sea of Marmara in both straits. A simple conceptual model without wind is able to explain fluctuations in bottom pressure in the Sea of Marmara to a 0.89–0.96 level of correlation. This stresses the importance of atmospheric pressure dynamics in driving the mass flux of the Turkish Strait System for extreme storms.
      PubDate: 2014-06-11T09:28:08.285507-05:
      DOI: 10.1002/2013JC009480
  • Annual primary production in Antarctic sea ice during 2005–2006 from
           a sea ice state estimate
    • Authors: Benjamin T. Saenz; Kevin R. Arrigo
      Pages: 3645 - 3678
      Abstract: Using the data‐bounded Sea Ice Ecosystem State (SIESTA) model, we estimate total Antarctic sea ice algal primary production to be 23.7 Tg C a−1 for the period July 2005–June 2006, of which 80% occurred in the bottom 0.2 m of ice. Simulated sea ice primary production would constitute 12% of total annual primary production in the Antarctic sea ice zone, and ∼1% of annual Southern Ocean primary production. Model sea ice algal growth was net nutrient limited, rather than light limited, for the vast majority of the sunlit season. The seasonal distribution of integrated ice algal biomass matches available observations. The vertical algal distribution was weighted toward the ice bottom compared to observations, indicating that interior ice algal communities may be under‐predicted in the model, and that nutrient delivery via gravity‐induced convection is not sufficient to sustain summertime algal biomass. Bottom ice algae were most productive in ice of 0.36 m thickness, whereas interior algal communities were most productive in ice of 1.10 m thickness. Sensitivity analyses that tested different atmospheric forcing inputs, sea ice parameterizations, and nutrient availability caused mean and regional shifts in sea ice state and ice algal production even when sea extent and motion was specified. The spatial heterogeneity of both ice state and algal production highlight the sensitivity of the sea ice ecosystem to physical perturbation, and demonstrate the importance of quality input data and appropriate parameterizations to models of sea ice and associated biology.
      PubDate: 2014-06-11T09:10:46.264334-05:
      DOI: 10.1002/2013JC009677
  • Variations of Luzon Undercurrent from observations and numerical model
    • Authors: Qingye Wang; Fangguo Zhai, Dunxin Hu
      Pages: 3792 - 3805
      Abstract: Significant intraseasonal variability (ISV) of about 45–80 days and seasonal variation of the Luzon Undercurrent (LUC) at 18°N are studied using direct current measurements and a high‐resolution global Hybrid Coordinate Ocean Model. The variations of the LUC are vertically coherent with those of Kuroshio Current both on intraseasonal and seasonal time scales. The ISV of the LUC is dominated by eddies with diameters of about 200–300 km and extending from sea surface to intermediate layer east of Luzon Island. The LUC becomes strong (weak) when cyclonic (anticyclonic) eddies occur. The eddies east of Luzon Island mainly originate from the bifurcation point (∼13°N) of the North Equatorial Current. These eddies propagate northwestward at a typical propagation speed of about 0.16 m s−1 along the east coast of Philippines, gradually strengthen and pass the Luzon coast, and continue northward to Luzon strait. On seasonal time scale, the LUC is strong (weak) in boreal winter (summer), and this variation is related to the seasonal evolution of large‐scale ocean circulation east of Philippines mainly controlled by local wind forcing.
      PubDate: 2014-06-16T10:16:53.282881-05:
      DOI: 10.1002/2013JC009694
  • Evidence that Agulhas Current transport is maintained during a meander
    • Authors: Greta M. Leber; Lisa M. Beal
      Pages: 3806 - 3817
      Abstract: In April 2010, full‐depth hydrographic and direct velocity measurements across a solitary meander in the Agulhas Current were collected at nominally 34∘S. During a second cruise in November 2011, a transect across the nonmeandering Agulhas Current was captured. These data provide the first full‐depth, in situ picture of the meandering Agulhas Current and allow us to investigate how the velocity structure and transport of the meandering current differs from its nonmeandering state. An analysis of the horizontal momentum equations show that the meander is in geostrophic balance. However, sampling bias causes large differences between geostrophic and direct velocity measurements during meandering, especially near the surface. As the current meanders offshore, its core speed weakens by more than 70 cm s−1 and its width broadens by almost 40 km. These two effects compensate so that the southwestward transport of the Agulhas current is largely unchanged during meandering. At the same time, the meander generates a strong inshore counterflow, which weakens the net Eulerian transport across the 300‐km line by almost 20 Sv.
      PubDate: 2014-06-17T17:41:50.98815-05:0
      DOI: 10.1002/2014JC009802
  • Wind‐driven spreading of fresh surface water beneath ice shelves in
           the Eastern Weddell Sea
    • Authors: Q. Zhou; T. Hattermann, O. A. Nøst, M. Biuw, K. M. Kovacs, C. Lydersen
      Pages: 3818 - 3833
      Abstract: Solar heated, fresh Antarctic Surface Water (ASW) is a permanent feature along the Eastern Weddell Sea (EWS) coast in summer down to a depth of roughly 200 m. Recently, ASW has been observed beneath the Fimbul Ice Shelf, suggesting that it might play an important role in basal melting. We propose that wind‐driven coastal downwelling is the main mechanism that spreads ASW beneath the ice shelf in this sector of Antarctica. We validate this hypothesis with observations, scaling analyses, and numerical modeling, along three principle lines: (i) data analyses of about 1500 salinity profiles collected by instrumented seals indicate that the observed freshening of the coastal water column is likely explained by the on‐shore Ekman transport and subsequent downwelling of ASW; (ii) an analytical model of the coastal momentum balance indicates that wind‐driven downwelling is capable of depressing the buoyant surface water to a depth similar to the ice shelf draft; and (iii) simulations from both idealized and regional eddy‐resolving numerical ice shelf/ocean models support our proposition. Our main conclusion is that wind‐driven spreading of ASW beneath the ice shelf occurs when downwelling exceeds the depth of the ice shelf base. Furthermore, our study adds to the understanding of the oceanic processes at the Antarctic Slope Front in the EWS, with possible implications for other sectors of Antarctica.
      PubDate: 2014-06-18T09:59:32.87815-05:0
      DOI: 10.1002/2013JC009556
  • Atmospheric NO2 dynamics and impact on ocean color retrievals in urban
           nearshore regions
    • Authors: Maria Tzortziou; Jay R. Herman, Ziauddin Ahmad, Christopher P. Loughner, Nader Abuhassan, Alexander Cede
      Pages: 3834 - 3854
      Abstract: Urban nearshore regions are characterized by strong variability in atmospheric composition, associated with anthropogenic emissions and meteorological processes that influence the circulation and accumulation of atmospheric pollutants at the land‐water interface. If not adequately corrected in satellite retrievals of ocean color, this atmospheric variability can impose a false impression of diurnal and seasonal changes in nearshore water quality and biogeochemical processes. Consideration of these errors is important for measurements from polar orbiting ocean color sensors but becomes critical for geostationary satellite missions having the capability for higher frequency and higher spatial resolution observations of coastal ocean dynamics. We examined variability in atmospheric NO2 over urban nearshore environments in the Eastern US, Europe, and Korea, using a new network of ground‐based Pandora spectrometers and Aura‐OMI satellite observations. Our measurements in the US and in Europe revealed clear diurnal and day‐of‐the‐week patterns in total column NO2 (TCNO2), temporal changes as large as 0.8 DU within 4 h, and spatial variability as large as 0.7 DU within an area often covered by just a single OMI pixel. TCNO2 gradients were considerably stronger over the coastal cities of Korea. With a coarse resolution and an overpass at around 13:30 local time, OMI cannot detect this strong variability in NO2, missing pollution peaks from industrial and rush hour activities. Observations were combined with air quality model simulations and radiative transfer calculations to estimate the impact of atmospheric NO2 variability on satellite retrievals of coastal ocean remote sensing reflectance and biogeochemical variables (i.e., chlorophyll and CDOM).
      PubDate: 2014-06-19T09:36:23.589456-05:
      DOI: 10.1002/2014JC009803
  • Analyzing the 2010–2011 La Niña signature in the tropical
           Pacific sea surface salinity using in situ data, SMOS observations, and a
           numerical simulation
    • Authors: Audrey Hasson; Thierry Delcroix, Jacqueline Boutin, Raphael Dussin, Joaquim Ballabrera‐Poy
      Pages: 3855 - 3867
      Abstract: The tropical Pacific Ocean remained in a La Niña phase from mid‐2010 to mid‐2012. In this study, the 2010–2011 near‐surface salinity signature of ENSO (El Niño‐Southern Oscillation) is described and analyzed using a combination of numerical model output, in situ data, and SMOS satellite salinity products. Comparisons of all salinity products show a good agreement between them, with a RMS error of 0.2–0.3 between the thermosalinograph (TSG) and SMOS data and between the TSG and model data. The last 6 months of 2010 are characterized by an unusually strong tripolar anomaly captured by the three salinity products in the western half of the tropical Pacific. A positive SSS anomaly sits north of 10°S (>0.5), a negative tilted anomaly lies between 10°S and 20°S and a positive one south of 20°S. In 2011, anomalies shift south and amplify up to 0.8, except for the one south of 20°S. Equatorial SSS changes are mainly the result of anomalous zonal advection, resulting in negative anomalies during El Niño (early 2010), and positive ones thereafter during La Niña. The mean seasonal and interannual poleward drift exports those anomalies toward the south in the southern hemisphere, resulting in the aforementioned tripolar anomaly. The vertical salinity flux at the bottom of the mixed layer tends to resist the surface salinity changes. The observed basin‐scale La Niña SSS signal is then compared with the historical 1998–1999 La Niña event using both observations and modeling.
      PubDate: 2014-06-19T09:20:35.987153-05:
      DOI: 10.1002/2013JC009388
  • Impact of vertical mixing on sea surface pCO2 in temperate seasonally
           stratified shelf seas
    • Authors: T. P. Rippeth; B. J. Lincoln, H. A. Kennedy, M. R. Palmer, J. Sharples, C. A. J. Williams
      Pages: 3868 - 3882
      Abstract: A key parameter in determining the exchange of CO2 across the ocean‐atmosphere interface is the sea surface partial pressure of carbon dioxide (pCO2). Temperate seasonally stratified shelf seas represent a significant sink for atmospheric CO2. Here an analytical model is used to quantify the impact of vertical mixing across the seasonal thermocline on pCO2. The model includes the impacts of the resultant dissolved inorganic carbon, heat, salt, and alkalinity fluxes on the solubility of CO2 and the effect of the inorganic carbon sink created by the primary production fuelled by the flux of limiting nutrient. The results indicate that diapycnal mixing drives a modest but continuous change in pCO2 of order 1–10 µatm d−1. In quantifying the individual impacts of the fluxes of the different parameters, we find that the impact of the fluxes of DIC and nitrate fluxes dominate. In consequence, both the direction and magnitude of the change in pCO2 are strongly dependent on the C:N uptake ratio in primary production. While the smaller impacts of the heat and salt fluxes tend to compensate for each other at midshelf locations, the heat flux dominates close to the shelf break. The analysis highlights the importance of the accurate parameterization of the C:N uptake ratio, the surface‐mixed layer depth, and the TKE dissipation rate within the seasonal thermocline in models to be used to predict the air‐sea exchange of carbon dioxide in these regimes. The results implicate storms as key periods of pCO2 perturbation.
      PubDate: 2014-06-20T12:21:19.203919-05:
      DOI: 10.1002/2014JC010089
  • Aquarius sea surface salinity in the South Indian Ocean: Revealing
           annual‐period planetary waves
    • Authors: Viviane V. Menezes; Marcio L. Vianna, Helen E. Phillips
      Pages: 3883 - 3908
      Abstract: A new milestone has been reached with the launch of two dedicated satellite missions to routinely measure the sea surface salinity (SSS) fields from space at global and regional scales. In the present work, a thorough analysis of the first 2 years of Aquarius SSS data in the South Indian Ocean is performed. This analysis is focused on three questions: How accurate is Aquarius SSS related to in situ data from the fresh Indonesian Throughflow and salty subtropical waters? Can Aquarius give a spatial context for the data measured by the RAMA mooring system? Are westward propagating annual‐period signals described in recent model simulations reproduced by Aquarius‐derived SSS? We find Aquarius observations to be highly correlated with those of Argo floats, with small disagreements occurring near oceanic fronts. Aquarius gives fresher SSS than in situ data in the tropical region due to rainfall effects, except in the eastern basin where the freshening seems to be related to sharp localized leakages of very fresh waters from the Indonesian seas that the Aquarius product is not able to properly resolve. Aquarius data are shown to reproduce quite well the annual cycle obtained from RAMA and Argo gridded data sets. The annual cycle in Aquarius is characterized by SSS propagating features with different characteristics west and east of the Ninety East Ridge. These features are strikingly different from sea surface height waves. Our results suggest that SSS annual propagation might be reflecting coupled ocean‐atmosphere dynamics and surface‐subsurface processes operating over the entire South Indian Ocean.
      PubDate: 2014-06-20T13:33:31.133066-05:
      DOI: 10.1002/2014JC009935
  • Eddies in the Red Sea: A statistical and dynamical study
    • Authors: Peng Zhan; Aneesh C. Subramanian, Fengchao Yao, Ibrahim Hoteit
      Pages: 3909 - 3925
      Abstract: Sea level anomaly (SLA) data spanning 1992–2012 were analyzed to study the statistical properties of eddies in the Red Sea. An algorithm that identifies winding angles was employed to detect 4998 eddies propagating along 938 unique eddy tracks. Statistics suggest that eddies are generated across the entire Red Sea but that they are prevalent in certain regions. A high number of eddies is found in the central basin between 18°N and 24°N. More than 87% of the detected eddies have a radius ranging from 50 to 135 km. Both the intensity and relative vorticity scale of these eddies decrease as the eddy radii increase. The averaged eddy lifespan is approximately 6 weeks. AEs and cyclonic eddies (CEs) have different deformation features, and those with stronger intensities are less deformed and more circular. Analysis of long‐lived eddies suggests that they are likely to appear in the central basin with AEs tending to move northward. In addition, their eddy kinetic energy (EKE) increases gradually throughout their lifespans. The annual cycles of CEs and AEs differ, although both exhibit significant seasonal cycles of intensity with the winter and summer peaks appearing in February and August, respectively. The seasonal cycle of EKE is negatively correlated with stratification but positively correlated with vertical shear of horizontal velocity and eddy growth rate, suggesting that the generation of baroclinic instability is responsible for the activities of eddies in the Red Sea.
      PubDate: 2014-06-20T12:25:36.8117-05:00
      DOI: 10.1002/2013JC009563
  • Seasonal variability of the East Greenland Coastal Current
    • Authors: Sheldon Bacon; Abigail Marshall, N. Penny Holliday, Yevgeny Aksenov, Stephen R. Dye
      Pages: 3967 - 3987
      Abstract: The East Greenland Coastal Current (EGCC) is characterized as cold, low‐salinity polar waters flowing equatorward on the east Greenland shelf. It is an important conduit of freshwater from the Arctic Ocean, but our present understanding of it is poor, outside of an assortment of measurements which stem mainly from summertime visits by research vessels. This manuscript first describes measurements from moored instruments deployed on the East Greenland shelf (∼63°N) between 2000 and 2004. The measurements are then used to show that a high‐resolution coupled ice‐ocean global general circulation model supports a realistic representation of the EGCC. The results show that the EGCC exists throughout the year and is stronger in winter than in summer. The model EGCC seawater transports are a maximum (minimum) in February (August), at 3.8 (1.9) × 106 m3 s−1. Freshwater transports, including modeled estimates of sea ice transport and referenced to salinity 35.0, are a maximum (minimum) in February (August) at 106 (59) × 103 m3 s−1. The model results show that wind and buoyancy forcing are of similar importance to EGCC transport. An empirical decomposition of the buoyancy‐forced transport into a buoyancy‐only component and a coupled wind and buoyancy component indicates the two to be of similar magnitude in winter. The model annual mean freshwater flux of ∼80–90 × 103 m3 s−1 approaches 50% of the net rate of Arctic freshwater gain, underlining the climatic importance of the EGCC.
      PubDate: 2014-06-25T09:18:31.600763-05:
      DOI: 10.1002/2013JC009279
  • Application of the Geostationary Ocean Color Imager (GOCI) to estimates of
           ocean surface currents
    • Authors: Hyun Yang; Jong‐Kuk Choi, Young‐Je Park, Hee‐Jeong Han, Joo‐Hyung Ryu
      Pages: 3988 - 4000
      Abstract: The Geostationary Ocean Color Imager (GOCI) can be utilized efficiently to observe subtle changes in oceanic environments under cloud‐free conditions because it receives ocean color images around the Korean Peninsula hourly, for 8 h a day. Here we investigated the applicability of the GOCI for estimating hourly variations in ocean surface currents, which provide significant information on seawater circulation for fisheries, shipping controls, and more. Ocean surface currents were deduced from eight images of GOCI‐derived total suspended matter (TSM) from highly turbid coastal waters and images of chlorophyll concentration (CHL) for relatively clear waters. The results showed that GOCI TSM‐derived ocean surface currents can effectively estimate and represent fast tidal currents, as well as flood and ebb tides on the west coast of Korea, in comparison with in situ measurements. GOCI‐derived CHL scenes successfully illustrated currents moving along boundaries where warm and cold seawaters mix, in addition to mesoscale currents such as the East Korea Warm Current (EKWC) in the East Sea of Korea. Satellite‐based sea surface temperature and sea surface height images supported the reliability of GOCI‐derived ocean surface currents in the East Sea.
      PubDate: 2014-06-26T12:26:51.13676-05:0
      DOI: 10.1002/2014JC009981
  • Mixing and remineralization in waters detrained from the surface into
           Subantarctic Mode Water and Antarctic Intermediate Water in the
           southeastern Pacific
    • Authors: B. R. Carter; L. D. Talley, A. G. Dickson
      Pages: 4001 - 4028
      Abstract: A hydrographic data set collected in the region and season of Subantarctic Mode Water and Antarctic Intermediate Water (SAMW and AAIW) formation in the southeastern Pacific allows us to estimate the preformed properties of surface water detrained into these water masses from deep mixed layers north of the Subantarctic Front and Antarctic Surface Water south of the front. Using 10 measured seawater properties, we estimate: the fractions of SAMW/AAIW that originate as surface source waters, as well as fractions that mix into these water masses from subtropical thermocline water above and Upper Circumpolar Deep Water below the subducted SAMW/AAIW; ages associated with the detrained surface water; and remineralization and dissolution rates and ratios. The mixing patterns imply that cabbeling can account for ∼0.005–0.03 kg m−3 of additional density in AAIW, and ∼0–0.02 kg m−3 in SAMW. We estimate a shallow depth (∼300–700 m, above the aragonite saturation horizon) calcium carbonate dissolution rate of 0.4 ± 0.2 µmol CaCO3 kg−1 yr−1, a phosphate remineralization rate of 0.031 ± 0.009 µmol P kg−1 yr−1, and remineralization ratios of P:N:–O2:Corg of 1:(15.5 ± 0.6):(143 ± 10):(104 ± 22) for SAMW/AAIW. Our shallow depth calcium carbonate dissolution rate is comparable to previous estimates for our region. Our –O2:P ratio is smaller than many global averages. Our model suggests neglecting diapycnal mixing of preformed phosphate has likely biased previous estimates of –O2:P and Corg:P high, but that the Corg:P ratio bias may have been counteracted by a second bias in previous studies from neglecting anthropogenic carbon gradients.
      PubDate: 2014-06-27T16:04:11.827323-05:
      DOI: 10.1002/2013JC009355
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