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

Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (21 followers)
Geophysical Research Letters     Full-text available via subscription   (41 followers)
Global Biogeochemical Cycles     Full-text available via subscription   (3 followers)
Journal of Advances in Modeling Earth Systems     Open Access   (2 followers)
Journal of Geophysical Research : Atmospheres     Partially Free   (18 followers)
Journal of Geophysical Research : Biogeosciences     Full-text available via subscription   (5 followers)
Journal of Geophysical Research : Earth Surface     Partially Free   (22 followers)
Journal of Geophysical Research : Oceans     Partially Free   (14 followers)
Journal of Geophysical Research : Planets     Full-text available via subscription   (12 followers)
Journal of Geophysical Research : Solid Earth     Full-text available via subscription   (21 followers)
Journal of Geophysical Research : Space Physics     Full-text available via subscription   (13 followers)
Paleoceanography     Full-text available via subscription   (4 followers)
Radio Science     Full-text available via subscription   (3 followers)
Reviews of Geophysics     Full-text available via subscription   (17 followers)
Space Weather     Full-text available via subscription   (3 followers)
Tectonics     Full-text available via subscription   (7 followers)
Water Resources Research     Full-text available via subscription   (81 followers)
Journal of Geophysical Research : Oceans    [16 followers]  Follow    
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     ISSN (Online) 2169-9291
     Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • Correction to “Examining the global record of interannual
           variability in stratification and marine productivity in the low‐and
           mid‐latitude ocean”
    • Authors: Apurva C. Dave
      Pages: n/a - n/a
      PubDate: 2014-03-21T11:07:11.705085-05:
      DOI: 10.1002/2013JC009723
       
  • Poleward ocean heat transports, sea ice processes, and Arctic sea ice
           variability in NorESM1‐M simulations
    • Authors: A. B. Sandø; Y. Gao, H. R. Langehaug
      Pages: n/a - n/a
      Abstract: Results from the NorESM1‐M coupled climate model were used to examine relationships between Arctic sea ice area and ocean heat transports through the primary Arctic gateways. Comparisons were made with two other models (CNRM‐CM5 and MRI‐CGM3) that are part of the CMIP5 archive which have the required outputs for calculating ocean heat transports. Based on an evaluation, NorESM1‐M was found to be best suited to study the effects of heat transports on sea ice area, and conclusions are based on results from this model. The Arctic Ocean was divided into two regions, the Barents Sea and the Central Arctic Ocean. The sea ice area variability was further analyzed in terms of frazil and congelation growth, top and bottom melting, and heat transports in the Barents Sea Opening (BSO) and the Fram Strait (FS). In the Barents Sea, increased heat transport in the BSO has a strong influence on sea ice area in terms of reduced congelation growth, while bottom melting is important for the variability in the Central Arctic Ocean. The negative trend in sea ice area is considerably greater in the Barents Sea than in the Central Arctic Ocean, despite the Central Arctic Ocean area being much larger, and reflects the major trend in the BSO heat transport. The model results in this study suggest that the ocean has stronger direct impact on changes in sea ice mass in terms of freezing and melting than the atmosphere, both in the mean and with respect to variability.
      PubDate: 2014-03-21T09:58:00.152081-05:
      DOI: 10.1002/2013JC009435
       
  • Formation of bottom water and its variability in the northwestern part of
           the Sea of Japan
    • Authors: Kiyoshi Tanaka
      Pages: n/a - n/a
      Abstract: The downslope descent of dense shelf water in the northwestern part of the Sea of Japan is investigated from a dynamical point of view, paying attention to the formation of bottom water in the winter of 2001. It is supposed that before 1980, the shelf water in Peter the Great Bay sometimes descended far down the continental slope, at least partly reaching depths in excess of 3000 m (the foot of the continental slope). After 1980, however, the shelf water did not descend as far; it either descended only moderately or not at all. In Winter 2001, however, the dense shelf water again descended to depths greater than 3000 m, resulting in the formation of bottom water. Descents of more than 3000 m are due to low temperatures coupled with high salinities, whereas the moderate descents of the late 20th century were purely related to the low temperature of the shelf water. It is estimated that over the continental slope, the shelf water becomes mixed with the ambient water in a ratio of about 1:9 for deep descents, whereas the ratio is about 1:5 for moderate descents. The formation of bottom water is greatly influenced by interannual atmospheric variability; thus in Winter 2001 a combination of the strengthened Siberian High (especially in its northern part) and the Aleutian Low advected very cold air into northeast Asia, producing dense shelf water and resulting in the formation of bottom water.
      PubDate: 2014-03-21T09:47:59.10982-05:0
      DOI: 10.1002/2013JC009456
       
  • Autonomous observations of solar energy partitioning in first‐year
           sea ice in the Arctic Basin
    • Authors: Caixin Wang; Mats A. Granskog, Sebastian Gerland, Stephen R. Hudson, Donald K. Perovich, Marcel Nicolaus, Tor Ivan Karlsen, Kristen Fossan, Marius Bratrein
      Pages: n/a - n/a
      Abstract: A Spectral Radiation Buoy (SRB) was developed to autonomously measure the spectral incident, reflected, and transmitted spectral solar radiation (350–800 nm) above and below sea ice. The SRB was deployed on drifting first‐year sea ice near the North Pole in mid‐April 2012, together with velocity and ice mass balance buoys. The buoys drifted southward and reached Fram Strait after approximately 7 months, covering a complete melt season. At the SRB site, snowmelt started on 10 June, and had completely disappeared by 14 July. Surface albedo was above 0.85 until snowmelt onset and decreased rapidly with the progression of snowmelt. Albedo was lowest on 14 July, when the observed surface was likely a mixture of bare ice and melt pond(s). The transmitted irradiance measured under the ice was largest in July, with a monthly average of 20 W m−2, compared to
      PubDate: 2014-03-21T09:33:54.470203-05:
      DOI: 10.1002/2013JC009459
       
  • Issue Information
    • Pages: i - vi
      PubDate: 2014-03-20T16:37:41.559427-05:
      DOI: 10.1002/jgrc.20347
       
  • Absorption and fluorescence of dissolved organic matter in the waters of
           the Canadian Arctic Archipelago, Baffin Bay, and the Labrador Sea
    • Authors: Céline Guéguen; Chad W. Cuss, Chase J. Cassels, Eddy C. Carmack
      Pages: n/a - n/a
      Abstract: The optical properties of dissolved organic matter (DOM) were investigated for the first time in the Canadian Arctic Archipelago (CAA), Baffin Bay (BB), and Labrador Sea (LS) as part of the International Polar Year Canada's Three Oceans project (C3O). The dynamics and composition of absorbing DOM (i.e., colored DOM, or CDOM) and fluorescent DOM (FDOM) were evaluated in several distinct water masses occupying the three regions: surface waters, Arctic outflow waters, West Greenland Intermediate waters (WGIW), upper Labrador Sea waters (uLSW), and Bottom Baffin Deep Water (BBDW). Four fluorescent components were identified by applying parallel factor analysis (PARAFAC) to 522 excitation emission matrix (EEM) spectra: three humic‐like and one protein‐like. The FDOM in surface waters of the CAA and BB differed considerably in character from those of the LS, with higher fluorescence intensity in the former. The fluorescence intensities of the two terrestrial humic‐like components (C1 and C3) were linearly correlated with apparent oxygen utilization (AOU) in the CAA Arctic outflow and the WGIW whereas only humic‐like C3 was significantly correlated with AOU in uLSW. These findings suggest that the humic‐like components were produced in situ as organic matter was bio‐oxidized. The slopes of the linear relationship between humic‐like intensity and AOU were significantly greater in the WGIW relative to the Arctic outflow waters, which implies that FDOM in the Arctic‐derived deeper layer was less prone to mineralization.
      PubDate: 2014-03-20T13:29:36.506961-05:
      DOI: 10.1002/2013JC009173
       
  • Mesoscale eddies in the South Atlantic Bight and the Gulf Stream
           Recirculation region: Vertical structure
    • Authors: Renato M. Castelao
      Pages: n/a - n/a
      Abstract: Sea level anomalies from altimeters are combined with decade‐long potential temperature and salinity profiles from Argo floats to investigate the vertical structure of mesoscale eddies in the South Atlantic Bight (SAB) and the Gulf Stream Recirculation region. Eddy detection and eddy tracking algorithms are applied to the satellite observations, and hydrography profiles from floats that surfaced inside eddies are used to construct three‐dimensional composites of cyclones and anticyclones. Eddies are characterized by large temperature and salinity anomalies at 500–1000 m depth and near the surface, and by small anomalies at 200–400 m below the surface at the depth of the North Atlantic Subtropical Mode Water. Anomalies associated with anticyclones are generally larger and found deeper in the water column compared to those due to the presence of cyclones. Geostrophic velocities around eddies generally exceed their translation speed in the top 1000 m of the water column. As such, these eddies can trap water in their interior as they propagate westward. Combining the volume of water inside eddies above their trapping depths with the number of eddies that propagate into the SAB each year, it is estimated that cyclones and anticyclones transport 3.5 ± 0.9 Sv and 4.1 ± 1.7 Sv onshore toward the Gulf Stream, respectively. The total volume transport of 7.6 ± 2.2 Sv represents an important fraction of previous estimates of the onshore transport in the Gulf Stream Recirculation gyre. Since eddies are characterized by large temperature and salinity anomalies, they also contribute significantly to the onshore transport of heat and salt.
      PubDate: 2014-03-20T13:28:36.341582-05:
      DOI: 10.1002/2014JC009796
       
  • Increasing carbon inventory of the intermediate layers of the Arctic Ocean
    • Authors: Ylva Ericson; Adam Ulfsbo, Steven vanHeuven, Gerhard Kattner, Leif G. Anderson
      Pages: n/a - n/a
      Abstract: Concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA), nutrients and oxygen in subsurface waters of the central Arctic Ocean have been investigated for conceivable time trends over the last two decades. Data from six cruises (1991‐2011) that cover the Nansen, Amundsen and Makarov Basins were included in this analysis. In waters deeper than 2000 m, no statistically significant trend could be observed for DIC, TA, phosphate or nitrate, but a small rate of increase in apparent oxygen utilization (AOU) was noticeable. For the individual stations, differences in concentration of each property were computed between the mean concentrations in the Arctic Atlantic Water (AAW) or the upper Polar Deep Water (uPDW), i.e. between about 150 and 1400 m depth, and in the deep water (assumed invariable over time). In these shallower water layers, we observe significant above‐zero time trends for DIC, in the range of 0.6 to 0.9 µmol kg‐1 yr‐1 (for AAW) and 0.4 to 0.6 µmol kg‐1 yr‐1 (for uPDW). No time trend in nutrients could be observed, indicating no change in the rate of organic matter mineralization within this depth range. Consequently, the buildup of DIC is attributed to increasing concentrations of anthropogenic carbon in the waters flowing into these depth layers of the Arctic Ocean. The resulting rate of increase of the column inventory of anthropogenic CO2 is estimated to be between 0.6 and 0.9 mol C m‐2 yr1, with distinct differences between basins.
      PubDate: 2014-03-20T05:22:35.457106-05:
      DOI: 10.1002/2013JC009514
       
  • Implications of fractured arctic perennial ice cover on thermodynamic and
           dynamic sea ice processes
    • Authors: Matthew G. Asplin; Randall Scharien, Brent Else, Stephen Howell, David G. Barber, Tim Papakyriakou, Simon Prinsenberg
      Pages: n/a - n/a
      Abstract: Decline of the Arctic summer minimum sea ice extent is characterized by large expanses of open water in the Siberian, Laptev, Chukchi and Beaufort Seas, and introduces large fetch distances in the Arctic Ocean. Long waves can propagate deep into the pack ice, thereby causing flexural swell and failure of the sea ice. This process shifts the floe size diameter distribution smaller, increases floe surface area, and thereby affects sea ice dynamic and thermodynamic processes. The results of Radarsat‐2 imagery analysis show that a flexural fracture event which occurred in the Beaufort Sea region on 06 September 2009 affected ~40,000 km2. Open water fractional area in the area affected initially decreased from 3.7% to 2.7%, but later increased to ~20% following wind‐forced divergence of the ice pack. Energy available for lateral melting was assessed by estimating the change in energy entrainment from longwave and shortwave radiation in the mixed‐layer of the ocean following flexural fracture. 11.54 MJ · m‐2 of additional energy for lateral melting of ice floes was identified in affected areas. The impact of this process in future Arctic sea ice melt seasons was assessed using estimations of earlier occurrences of fracture during the melt season, and is discussed in context with ocean heat fluxes, atmospheric mixing of the ocean mixed layer, and declining sea ice cover. We conclude that this process is an important positive feedback to Arctic sea ice loss, and timing of initiation is critical in how it affects sea ice thermodynamic and dynamic processes.
      PubDate: 2014-03-20T05:22:06.869805-05:
      DOI: 10.1002/2013JC009557
       
  • Dynamics of oxygen depletion in the nearshore of a coastal embayment of
           the southern Benguela upwelling system
    • Authors: Grant C. Pitcher; Trevor A. Probyn, Andre du Randt, Andrew. J. Lucas, Stewart Bernard, Haley Evers‐King, Tarron Lamont, Larry Hutchings
      Pages: n/a - n/a
      Abstract: Acquisition of high resolution time series of water column and bottom dissolved oxygen (DO) concentrations inform the dynamics of oxygen depletion in St Helena Bay in the southern Benguela upwelling system at several scales of variability. The bay is characterized by seasonally recurrent hypoxia (
      PubDate: 2014-03-20T05:20:03.487065-05:
      DOI: 10.1002/2013JC009443
       
  • Hindcasts of potential harmful algal bloom transport pathways on the
           Pacific Northwest coast
    • Authors: S.N Giddings; P MacCready, B.M Hickey, N.S Banas, K.A Davis, S.A Siedlecki, V.L Trainer, R.M Kudela, N.A Pelland, T.P Connolly
      Pages: n/a - n/a
      Abstract: Harmful algal blooms (HABs) pose a significant threat to human and marine organism health, and negatively impact coastal economies around the world. An improved understanding of HAB formation and transport is required to improve forecasting skill. A realistic numerical simulation of the US Pacific Northwest region is used to investigate transport pathways from known HAB formation hotspots, specifically for Pseudo‐nitzschia (Pn), to the coast. We show that transport pathways are seasonal, with transport to the Washington (WA) coast from a northern source (the Juan de Fuca Eddy) during the summer/fall upwelling season and from a southern source (Heceta Bank) during the winter/early spring due to the predominant wind driven currents. Interannual variability in transport from the northern source is related to the degree of wind intermittency with more transport during years with more frequent relaxation/downwelling events. The Columbia River plume acts to mitigate transport to the coast as the plume front blocks on‐shore transport. The plume's influence on along‐shore transport is variable although critical in aiding transport from the southern source to the WA coast via plume entrainment. Overall transport from our simulations captures most observed Pn HAB beach events from 2004‐2007 (characterized by Pseudo‐nitzschia cell abundance); however, numerous false positives occur. We show that incorporating phytoplankton biomass results from a coupled biogeochemical model reduces the number of false positives significantly and thus improves our Pn HAB predictions.
      PubDate: 2014-03-20T05:15:11.433027-05:
      DOI: 10.1002/2013JC009622
       
  • Seasonal overturning circulation in the Red Sea. 2: Winter circulation
    • Authors: Fengchao Yao; Ibrahim Hoteit, Larry J. Pratt, Amy S. Bower, Armin Köhl, Ganesh Gopalakrishnan, David Rivas
      Pages: n/a - n/a
      Abstract: The shallow winter overturning circulation in the Red Sea is studied using a 50‐year high‐resolution MITgcm (MIT general circulation model) simulation with realistic atmospheric forcing. The overturning circulation for a typical year, represented by 1980, and the climatological mean are analyzed using model output to delineate the three dimensional structure and to investigate the underlying dynamical mechanisms. The horizontal model circulation in the winter of 1980 is dominated by energetic eddies. The climatological model mean results suggest that the surface inflow intensifies in a western boundary current in the southern Red Sea that switches to an eastern boundary current north of 24 °N. The overturning is accomplished through a cyclonic recirculation and a cross‐basin overturning circulation in the northern Red Sea, with major sinking occurring along a narrow band of width about 20 km along the eastern boundary and weaker upwelling along the western boundary. The northward pressure gradient force, strong vertical mixing, and horizontal mixing near the boundary are the essential dynamical components in the model's winter overturning circulation. The simulated water exchange is not hydraulically controlled in the Strait of Bab el Mandeb; instead, the exchange is limited by bottom and lateral boundary friction and, to a lesser extent, by interfacial friction due to the vertical viscosity at the interface between the inflow and the outflow.
      PubDate: 2014-03-20T05:15:06.947652-05:
      DOI: 10.1002/2013JC009331
       
  • Observations and numerical modeling of the Pearl River plume in summer
           season
    • Authors: Jiayi Pan; Yanzhen Gu, Dongxiao Wang
      Pages: n/a - n/a
      Abstract: A cruise survey of the Pearl River plume during southeasterly and southwesterly winds, two typical wind patterns in summer in Guangdong coastal waters, is reported and the cruise data are analyzed to unveil the plume dynamics. The Kelvin number is derived from the in‐situ data, revealing that the Pearl River plume exhibits two different scales in response to the two kinds of the wind forcing. Numerical model simulations based on the regional oceanic modeling system (ROMS) with nesting‐domains are implemented to explore details of the plume dynamics, validated by cruise observations and tidal gauge sea level data. Modeling results suggest that there is a sub‐tidal, anti‐cyclonic recirculation bulge on the west side out of the estuary mouth under southeasterly winds, showing a re‐circulating plume in the near‐field. When the wind changes to the southwesterly, however, the re‐circulating plume vanishes. The distinct, supercritical tidal plume front occurs with southeasterly winds prevailing in spring tide due to the strong advection in the tidal plume. The tidal salt deficit flux can reach as high as 12.5% of the mean current flux, and illustrates the combined forcing of tide and wind.
      PubDate: 2014-03-18T14:03:24.590161-05:
      DOI: 10.1002/2013JC009042
       
  • Comparative hydrodynamics of 10 Mediterranean lagoons by means of
           numerical modeling
    • Authors: Georg Umgiesser; Christian Ferrarin, Andrea Cucco, Francesca De Pascalis, Debora Bellafiore, Michol Ghezzo, Marco Bajo
      Pages: n/a - n/a
      Abstract: A comparison study between ten Mediterranean lagoons has been carried out by means of the 3D numerical model SHYFEM. The investigated basins are the Venice and Marano‐Grado lagoons in the Northern Adriatic Sea, the Lesina and Varano lagoons in the Southern Adriatic Sea, the Taranto basin in the Ionian Sea, the Cabras Lagoon in Sardinia, the Ganzirri and Faro lagoons in Sicily, the Mar Menor in Spain and the Nador Lagoon in Morocco. This study has been focused on hydrodynamics in terms of exchange rates, transport time scale and mixing. Water exchange depends mainly on the inlet shape and tidal range, but also on the wind regimes in the case of multi‐inlet lagoons. Water renewal time, which is mostly determined by the exchange rate, is a powerful concept that allows lagoons to be characterized with a time scale. In the case of the studied lagoons the renewal time ranged from few days in the Marano‐Grado Lagoon up to one year in the case of the Mar Menor. The analysis of the renewal time frequency distribution allows identifying sub‐basins. The numerical study proved to be a useful tool for the inter‐comparison and classification of the lagoons. These environments range from a leaky type to a choked type of lagoons and give a representative picture of the lagoons situated around the Mediterranean basin. Mixing efficiency turns out to be a function of the morphological complexity, but also of the forcings acting on the system.
      PubDate: 2014-03-18T13:21:19.659207-05:
      DOI: 10.1002/2013JC009512
       
  • Wind‐forced interannual variability of the Atlantic meridional
           overturning circulation at 26.5°N
    • Authors: Jian Zhao; William Johns
      Pages: n/a - n/a
      Abstract: The observed Atlantic Meridional Overturning Circulation (AMOC) at 26.5°N shows interannual variability consisting of an increase from early 2004 to late 2005 and a following downtrend which reaches a minimum in the winter of 2009/2010. These interannual AMOC fluctuations are dominated by changes in the upper mid‐ocean geostrophic flow except during the winter of 2009/2010, when the anomalous wind‐driven Ekman transport also has a significant contribution. The physical mechanisms for the interannual changes of the AMOC are proposed and evaluated in a 2‐layer model. While the Ekman transport is linked to the North Atlantic Oscillation (NAO), the anomalous geostrophic transport involves the oceanic adjustment to surface wind forcing. In particular, the intensification and weakening of the southward interior geostrophic flow is modulated by the internal Rossby wave adjustment to the surface wind forcing. The Gulf Stream, on the other hand, is controlled by both topographic waves along the US coast and westward propagating planetary waves. Our study suggests that a large part of the observed AMOC interannual variability at 26.5°N can be explained by wind‐driven dynamics.
      PubDate: 2014-03-18T13:20:21.732104-05:
      DOI: 10.1002/2013JC009407
       
  • Exploring the mesoscale activity in the Solomon Sea: A complementary
           approach with a numerical model and altimetric data
    • Authors: L. Gourdeau; J. Verron, A. Melet, W. Kessler, F. Marin, B. Djath
      Pages: n/a - n/a
      Abstract: The Solomon Sea is an area of high level of eddy kinetic energy (EKE), and represents a transit area for the low latitude Western Boundary Currents (LLWBCs) connecting the subtropics to the equatorial Pacific and playing a major role in ENSO dynamics. This study aims at documenting the surface mesoscale activity in the Solomon Sea for the first time. Our analysis is based on the joint analysis of altimetric data and outputs from a 1/12° model simulation. The highest surface EKE is observed in the northern part of the basin and extends southward to the central basin. An eddy tracking algorithm is used to document the characteristics and trajectories of coherent mesoscale vortices. Cyclonic eddies, generated in the south basin, are advected to the north by the LLWBCs before merging with stationary mesoscale structures present in the mean circulation. Anticyclonic eddies are less numerous. They are generated in the southeastern basin, propagate westward, reach the LLWBCs and dissipate. The seasonal and interannual modulations of the mesoscale activity are well marked. At seasonal time scale, maximum (minimum) activity is in May‐June (September). At interannual time scale, the mesoscale activity is particularly enhanced during La Niña conditions. If instabilities of the regional circulations seem to explain the generation of mesoscale features, the modulation of the mesoscale activity seems to be rather related with the intrusion at Solomon Strait of the surface South Equatorial Current, rather than to the LLWBCs, by modulating the horizontal and vertical shears suitable for instabilities.
      PubDate: 2014-03-18T13:20:17.621218-05:
      DOI: 10.1002/2013JC009614
       
  • Influences of intratidal variations in density field on the subtidal
           currents: Implication from a synchronized observation by multiships and a
           diagnostic calculation
    • Authors: Zhongya Cai; Zhe Liu, Xinyu Guo, Huiwang Gao, Qiang Wang
      Pages: n/a - n/a
      Abstract: Using synchronous observational water temperature and salinity data collected simultaneously by 21 ships in summer and a three‐dimensional robust diagnostic model, we calculated the density‐driven current in Jiaozhou Bay (JZB), a semienclosed bay in the Yellow Sea. Special attention was paid to the influences of intratidal variations in temperature and salinity on the density‐driven current. The density‐driven current in JZB has a maximum speed of ∼0.1 m s−1 and is stronger than the tide‐induced residual current in some places. The density‐driven current is characterized by the intrusion of high‐density (low‐density) water in deep (shallow) areas. The results of the diagnostic model depend heavily on the observational data. For example, the density‐driven current calculated from nonsynchronous data obtained by one ship at the same 21 stations is not consistent with that calculated from synchronous data because the nonsynchronous data correspond to different tidal phases at different stations. The intratidal variations of the density field result in a false spatial variation of density in the nonsynchronous data, which induces a false density‐driven current that is of the same order as that calculated from the synchronous data. In contrast, the tidally averaged water temperature and salinity, which were used to remove intratidal variations from the synchronous data, diagnosed a density‐driven current consistent with that from synchronous data. We, therefore, conclude that it is not necessary to explicitly resolve the intratidal variations in density in the calculation of density‐driven current, but it is necessary to remove intratidal variations in the density field before the calculation.
      PubDate: 2014-03-18T08:58:24.666719-05:
      DOI: 10.1002/2013JC009262
       
  • Surf zone bathymetry and circulation predictions via data assimilation of
           remote sensing observations
    • Authors: G. W. Wilson; H. T. Özkan‐Haller, R. A. Holman, M. C. Haller, D. A. Honegger, C. C. Chickadel
      Pages: n/a - n/a
      Abstract: Bathymetry is a major factor in determining nearshore and surf zone wave transformation and currents, yet is often poorly known. This can lead to inaccuracy in numerical model predictions. Here bathymetry is estimated as an uncertain parameter in a data assimilation system, using the ensemble Kalman filter (EnKF). The system is tested by assimilating several remote sensing data products, which were collected in September 2010 as part of a field experiment at the U.S. Army Corps of Engineers Field Research Facility (FRF) in Duck, NC. The results show that by assimilating remote sensing data alone, nearshore bathymetry can be estimated with good accuracy, and nearshore forecasts (e.g., the prediction of a rip current) can be improved. This suggests an application where a nearshore forecasting model could be implemented using only remote sensing data, without the explicit need for in situ data collection.
      PubDate: 2014-03-17T10:23:06.019399-05:
      DOI: 10.1002/2013JC009213
       
  • Circulation around La Réunion and Mauritius islands in the
           south‐western Indian Ocean: A modeling perspective
    • Authors: Stéphane Pous; Pascal Lazure, Gaël André, Franck Dumas, Issufo Halo, Pierrick Penven
      Pages: n/a - n/a
      Abstract: The objective of this study is to document the circulation in the vicinity of La Réunion and Mauritius islands, i.e., within 500 km offshore, on the intraseasonal time scale, using a high‐resolution realistic modeling strategy. The simulated sea level anomalies, water mass properties, and large‐scale circulation compare favorably with satellite and in situ observations. Our high‐resolution simulation suggests that the currents around the islands are maximal locally, oriented southwestward, to the southeast of both islands which is not visible in low‐resolution satellite observations. It also highlights the high degree of variability of the circulation, which is dominated by westward propagating features. The predominant time scale of variability is 60 days. This coincides with the period of a barotropic mode of variability confined to the Mascarene Basin. The characteristics of the westward propagating anomalies are related to baroclinic Rossby waves crossing the Indian Ocean but only in the long‐wave resting ocean limit. Tracking those anomalies as eddies shows that they also have a meridional tendency in their trajectory, northward for cyclones and southward for anticyclones, which is consistent with previous studies. Sensitivity experiments suggest that they are predominantly advected from the east, but there is also local generation in the lee of the islands, due to interaction between the circulation and topography.
      PubDate: 2014-03-17T10:17:19.077174-05:
      DOI: 10.1002/2013JC009704
       
  • Internal tide generation in nonuniformly stratified deep oceans
    • Authors: M. S. Paoletti; Matthew Drake, Harry L. Swinney
      Pages: n/a - n/a
      Abstract: We present numerical and experimental studies of the conversion of tidal motions of an exponentially stratified fluid over two‐dimensional knife edge, Gaussian, and complex bottom topography to radiated internal waves in a model of the deep ocean. We compare the radiated internal wave power for cases of strong stratification, where the buoyancy frequency profile N(z) (proportional to the square root of the density gradient) is much larger than the tidal frequency ω, to the power radiated for weak stratifications. We consider particularly internal wave generation for topography below a turning depth ztd, where N(ztd )=ω; for zztd, although the radiated power in these waves is much weaker than in cases without turning depths. The radiated power is predicted well by prior analytical theory if the nonuniform stratification is averaged over depths spanning from the bottom boundary up to an effective height zeff. In the absence of a turning depth, we find zeff is approximately equal to the height of the topography, indicating that only the stratification for depths spanned by the topography is relevant. However, in the presence of a turning depth, the vertical scale of the internal tide becomes larger, and zeff increases approximately linearly with the turning depth height toward values comparable to the total fluid depth.
      PubDate: 2014-03-17T10:16:55.465513-05:
      DOI: 10.1002/2013JC009469
       
  • Horizontal and residual circulations driven by wind stress curl in Tokyo
           Bay
    • Authors: K. Nakayama; T. Shintani, K. Shimizu, T. Okada, H. Hinata, K. Komai
      Pages: n/a - n/a
      Abstract: This study investigates the horizontal and residual circulations in Tokyo Bay using field observations, numerical simulations, and theoretical analysis. Numerical simulations show that the observed deepening of isopycnals and associated anticyclonic horizontal circulation in the bay head are mainly driven by negative wind stress curl. The effects of river discharge, surface heat fluxes, and tides are found to be small. Under strong wind events, the wind stress curl over the bay head can be large enough to make the surface Ekman layer strongly nonlinear. Theoretical and numerical analyses show that, under large negative wind stress curl, the nonlinearity tends to induce positive pumping velocity (at the base of the surface mixed layer) that counteracts the Ekman pumping; however, the typical duration of wind events in the bay head is not long enough to induce positive pumping under negative wind stress curl. These results and historical wind data suggest that the average horizontal circulation and residual circulation immediately below the surface mixed layer in Tokyo Bay are, respectively, cyclonic and convergent in summer but anticyclonic and divergent in winter.
      PubDate: 2014-03-17T10:08:43.923659-05:
      DOI: 10.1002/2013JC009396
       
  • Seasonal overturning circulation in the Red Sea: 1. Model validation and
           summer circulation
    • Authors: Fengchao Yao; Ibrahim Hoteit, Larry J. Pratt, Amy S. Bower, Ping Zhai, Armin Köhl, Ganesh Gopalakrishnan
      Pages: n/a - n/a
      Abstract: The overturning circulation in the Red Sea exhibits a distinct seasonally reversing pattern and is studied using high‐resolution MITgcm (MIT general circulation model) simulations. In the first part of this study, the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results. The seasonal water exchange in the Strait of Bab el Mandeb is successfully simulated and the structures of the intruding subsurface Gulf of Aden intermediate water are in good agreement with summer observations in 2011. The model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the Gulf of Aden resulting from remote winds in the Arabian Sea and an upward surface slope from the Red Sea to the Gulf of Aden set up by local surface winds in the Red Sea. In addition during late summer, two processes associated respectively with latitudinally differential heating and increased salinity in the southern Red Sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation. Dynamically the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the Strait of Bab el Mandeb. Unlike some previous studies, the three‐layer summer exchange flows in the Strait of Bab el Mandeb do not appear to be hydraulically controlled.
      PubDate: 2014-03-17T04:14:27.055367-05:
      DOI: 10.1002/2013JC009004
       
  • Seasonality of floc strength in the southern North Sea
    • Authors: Michael Fettweis; Matthias Baeye, Dimitry Zande, Dries Eynde, Byung Joon Lee
      Pages: n/a - n/a
      Abstract: The suspended particulate matter (SPM) concentration in the high turbidity zones of the southern North Sea is inversely correlated with chlorophyll (Chl) concentration. During winter, SPM concentration is high and Chl concentration is low and vice versa during summer. This seasonality has often been associated with the seasonal pattern in wind forcing. However, the decrease in SPM concentration corresponds well with the spring algal bloom. Does the decrease of SPM concentration caused by changing wind conditions cause the start of algae bloom, or does the algae bloom decrease SPM concentrations through enhanced flocculation and deposition? To answer the question, measurements from 2011 of particle size distribution (PSD), SPM, and Chl concentrations from the southern North Sea have been analyzed. The results indicate that the frequency of occurrence of macroflocs has a seasonal signal, while seasonality has little impact upon floc size. The data from a highly turbid coastal zone suggest that the maximum size of the macroflocs is controlled by turbulence and the available flocculation time during a tidal cycle, but the strength of the macroflocs is controlled by the availability of sticky organic substances associated with enhanced primary production during spring and summer. The results highlight the shift from mainly microflocs and flocculi in winter toward more muddy marine snow with larger amounts of macroflocs in spring and summer. The macroflocs will reduce the SPM concentrations in the turbidity maximum area as they settle faster. Consequently, the SPM concentration decreases and the light condition increases in the surface layer enhancing algae growth further.
      PubDate: 2014-03-14T17:31:10.179275-05:
      DOI: 10.1002/2013JC009750
       
  • Evaluating Langmuir turbulence parameterizations in the ocean surface
           boundary layer
    • Authors: G. Sutherland; K. H. Christensen, B. Ward
      Pages: n/a - n/a
      Abstract: It is expected that surface gravity waves play an important role in the dynamics of the ocean surface boundary layer (OSBL), quantified with the turbulent Langmuir number ( La=u*/us0, where u* and us0 are the friction velocity and surface Stokes drift, respectively). However, simultaneous measurements of the OSBL dynamics along with accurate measurements of the wave and atmospheric forcing are lacking. Measurements of the turbulent dissipation rate ϵ were collected using the Air‐Sea Interaction Profiler (ASIP), a freely rising microstructure profiler. Two definitions for the OSBL depth are used: the mixed layer derived from measurements of density (hρ), and the mixing layer (hϵ) determined from direct measurements of ϵ. When surface buoyancy forces are relatively small, ϵ∝La−2 only near the surface with no dependency on La at mid‐depths of the OSBL when using hρ as the turbulent length scale. However, if hϵ is used then the dependence of ϵ with La−2 is more uniform throughout the OSBL. For relatively high destabilizing surface buoyancy forces, ϵ is proportional to the ratio of the OSBL depth against the Langmuir stability length LL. During destabilizing conditions, the mixed and mixing layer depths are nearly identical, but we have relatively few measurements under these conditions, rather than any physical implications. Observations of epsilon are compared with the OSBL regime diagram of Belcher et al. (2012) and are generally within an order of magnitude, but there is an improved agreement if hϵ is used as the turbulent length scale rather than hρ.
      PubDate: 2014-03-14T17:31:05.628238-05:
      DOI: 10.1002/2013JC009537
       
  • Model simulated volume fluxes through the Canadian Arctic Archipelago and
           Davis Strait: Linking monthly variations to forcing in different seasons
    • Authors: Youyu Lu; Simon Higginson, Shannon Nudds, Simon Prinsenberg, Gilles Garric
      Pages: n/a - n/a
      Abstract: The solution of a 10 year simulation of the Arctic Ocean, produced using a 6 km resolution coupled ocean and sea‐ice model, is analyzed to understand the variability, control, and forcing mechanisms of the volume fluxes through the Canadian Arctic Archipelago (CAA) and Davis Strait (DS). The analysis focuses on variability at monthly time scales. Analysis confirms the “control” of volume fluxes through the CAA, proposed in previous studies, by (1) variations of sea surface height (SSH) in the “upstream” regions and the relationship of this control to alongshore wind in the Beaufort Sea and (2) by SSH in the “downstream” region in Baffin Bay that may be related to wind stress in Baffin Bay and the northern Labrador Sea. The effectiveness of these control and forcing mechanisms vary for fluxes through different sections and for different seasons. Variation of the southward flux through DS is directly influenced by fluxes through Nares Strait (NS) and Barrow Strait (BS) in summer, fall, and winter. In spring, variations of the southward and northward fluxes through DS are closely related to each other and correspond to changes in the SSH along pathways of the Irminger Current, and the East and West Greenland Currents.
      PubDate: 2014-03-14T17:30:43.284991-05:
      DOI: 10.1002/2013JC009408
       
  • Modulation of Kuroshio transport by mesoscale eddies at the Luzon Strait
           entrance
    • Authors: Ren‐Chieh Lien; Barry Ma, Yu‐Hsin Cheng, Chong‐Ru Ho, Bo Qiu, Craig M. Lee, Ming‐Huei Chang
      Pages: n/a - n/a
      Abstract: Measurements of Kuroshio Current velocity at the entrance to Luzon Strait along 18.75°N were made with an array of six moorings during June 2012–June 2013. Strong positive relative vorticity of the order of the planetary vorticity f was observed on the western flank of the Kuroshio in the upper 150 m. On the eastern flank, the negative vorticity observed was about an order of magnitude smaller than f. Kuroshio transport near its origin is computed from direct measurements for the first time. Kuroshio transport has an annual mean of 15 Sv with a standard deviation of 3 Sv. It is modulated strongly by impinging westward propagating eddies, which are identified by an improved eddy detection method and tracked back to the interior ocean. Eight Kuroshio transport anomalies > 5 Sv are identified; seven are explained by the westward propagating eddies. Cyclonic (anticyclonic) eddies decrease (increase) the zonal sea level anomaly (SLA) slope and reduce (enhance) Kuroshio transport. Large transport anomalies of >10 Sv within O(10 days) are associated with pairs of cyclonic and anticyclonic eddies. The observed Kuroshio transport was strongly correlated with the SLA slope (correlation = 0.9). Analysis of SLA slope data at the entrance to Luzon Strait over the period 1992–2013 reveals a seasonal cycle with a positive anomaly (i.e., an enhanced Kuroshio transport) in winter and spring and a negative anomaly in summer and fall. Eddy induced vorticity near the Kuroshio has a similar seasonal cycle, suggesting that seasonal variation of the Kuroshio transport near its origin is modulated by the seasonal variation of the impinging mesoscale eddies.
      PubDate: 2014-03-14T05:50:20.10389-05:0
      DOI: 10.1002/2013JC009548
       
  • Seasonal to interannual variability in density around the Canary Islands
           and their influence on the Atlantic meridional overturning circulation at
           26°N
    • Authors: Aurélie Duchez; Eleanor Frajka‐Williams, Natalia Castro, Joël Hirschi, Andrew Coward
      Pages: n/a - n/a
      Abstract: The meridional interior flow obtained from the RAPID array is determined by horizontal density fluctuations at the eastern and western boundary of 26°N. The physical causes of these density variations are responsible for fluctuations in the Atlantic Meridional Overturning Circulation (AMOC) and through it, the meridional heat transport of the Atlantic. In this modeling study, a high‐resolution ocean model is used to investigate the source and origin of the AMOC variability associated with the density fluctuations at the eastern boundary. The AMOC in the model is in good agreement with the RAPID observations and appears to adequately represent the smaller scale features of variability around the Canary Islands. In this paper, we identify a robust relationship between the density structure south of the Canary Islands, the local wind stress curl (WSC) around these islands and the AMOC using an empirical orthogonal functions analysis, wavelet transform, and wavelet coherence. We find that the deep density fluctuations at the eastern boundary of 26°N arise from the pumping effect of the spatial pattern of WSC south of the islands. These deep density fluctuations drive the AMOC both on seasonal and interannual time scales, through their influence on the basinwide tilt of the thermocline. At seasonal time scales, the density fluctuations south of the islands are driven by the WSC and directly influence the AMOC. At interannual time scales, a significant coherence is found between the density fluctuation and the southward Upper Mid‐Ocean (UMO) transport although the origin of these density fluctuations is not explained by the direct pumping caused by the WSC.
      PubDate: 2014-03-13T13:05:21.365959-05:
      DOI: 10.1002/2013JC009416
       
  • Wind‐driven variability in sea surface temperature front
           distribution in the California Current System
    • Authors: Renato M. Castelao; Yuntao Wang
      Pages: n/a - n/a
      Abstract: Simultaneous satellite‐derived observations from 2002 to 2009 are used to quantify the relation between sea surface temperature (SST) fronts and ocean winds in the California Current System (CCS). An edge‐detection algorithm is applied to SST observations to generate monthly maps of frontal probabilities. Empirical orthogonal decompositions reveal that the seasonal evolution of fronts in the CCS is strongly related to the seasonal evolution of coastal alongshore wind stress. The seasonal development of SST fronts is remarkably different to the north and to the south of Cape Mendocino, however. While fronts to the north of the cape extend for hundreds of kilometers from the coast peaking during summer and fall, when upwelling winds are stronger off northern California and Oregon, the region to the south of Cape Mendocino is characterized by high frontal activity during spring in a much narrower band close to the coast. Throughout the region, anomalies in the intensity of upwelling‐favorable wind stress are followed by anomalies in frontal activity. The width and speed of the widening of the region of high frontal activity are also related to coastal alongshore wind stress. Interannual variability in the timing of the widening of the region of high frontal activity in the lee of Cape Blanco compared to the timing of the spring transition to upwelling‐favorable winds may be related to the wind stress curl distribution in the lee of the cape. Stronger upwelling‐favorable wind stress curl anomalies lead to early widening of the region of high frontal activity.
      PubDate: 2014-03-13T11:04:29.613982-05:
      DOI: 10.1002/2013JC009531
       
  • Propagation of uncertainty analysis of CO2 transfer velocities derived
           from the COARE gas transfer model using satellite inputs
    • Authors: Darren L. Jackson; Gary A. Wick
      Pages: n/a - n/a
      Abstract: A propagation of uncertainty method is developed to describe gas transfer uncertainties for carbon dioxide (CO2) using the National Oceanic and Atmospheric Administration‐Coupled Ocean Atmosphere Response Experiment (NOAA‐COARE) gas transfer model (COAREG). The uncertainty model assesses the impact uncertainties in satellite inputs to COAREG have on the resulting carbon dioxide gas transfer velocities. The model impact of 10 m temperature, 10 m specific humidity, 10 m wind speed, sea surface temperature, longwave and shortwave downward surface flux are investigated. Nine years of gas transfer velocities and their uncertainties were constructed and analyzed. The climatological mean transfer velocities were found to have standard errors of less than 15%. Spatial and temporal variations of the uncertainties from these inputs are presented and the percentage variance explained for each input was dominated by uncertainties in wind speed. Uncertainty due to the covariance between air temperature and wind speed and the uncertainties in the 10 m air temperature at low wind speed conditions were found to be significant. Additionally, the likelihood air temperature uncertainties affect the gas transfer uncertainty is greatest in regions where air temperature exceeds sea surface temperature. Buoyancy‐driven transfer in COAREG increases gas transfer velocities uncertainties under these conditions. These conditions most typically occur in regions along the equatorial cold tongue region east of South America and in the North Pacific and North Atlantic.
      PubDate: 2014-03-13T09:11:46.442003-05:
      DOI: 10.1002/2013JC009271
       
  • Observations of the space‐time structure of flow, turbulence, and
           stress over orbital‐scale ripples
    • Authors: Jenna Hare; Alex E. Hay, Len Zedel, Richard Cheel
      Pages: n/a - n/a
      Abstract: The spatial and temporal structure of flow, turbulence, and stress over equilibrium orbital‐scale sand ripples are investigated at turbulence‐resolving scales with a wide‐band coherent Doppler profiler (MFDop) and an oscillating tray apparatus. The oscillation period and horizontal excursion were 10 s and 0.5 m. A single trial was also executed at 0.6 m excursion. Ripple wavelength and amplitude were 25 and 2.2 cm. Ensemble‐averaged velocity profiles were acquired with 3 mm vertical resolution at 42 Hz. The spatial pattern of flow as a function of oscillation phase was determined by combining the phase‐averaged velocity measurements from trials with the MFDop at different positions relative to a particular ripple crest. The MFDop measurements are used to investigate the coevolution of the lee vortex, turbulent kinetic energy, Reynolds stress, and turbulence production as a function of phase. Shear stress is determined from the vertically integrated vorticity equation and the double‐averaged momentum equations. Friction factors obtained from the two methods are comparable and range from 0.1 to 0.2.
      PubDate: 2014-03-13T08:58:54.257213-05:
      DOI: 10.1002/2013JC009370
       
  • Simulation of subice shelf melt rates in a general circulation model:
           Velocity‐dependent transfer and the role of friction
    • Authors: Véronique Dansereau; Patrick Heimbach, Martin Losch
      Pages: n/a - n/a
      Abstract: Two parameterizations of turbulent boundary layer processes at the interface between an ice shelf and the ocean beneath are investigated in terms of their impact on simulated melt rates and feedbacks. The parameterizations differ in the transfer coefficients for heat and freshwater fluxes. In their simplest form, they are assumed constant and hence are independent of the velocity of ocean currents at the ice shelf base. An augmented melt rate parameterization accounts for frictional turbulence via transfer coefficients that do depend on boundary layer current velocities via a drag law. In simulations with both parameterizations for idealized as well as realistic cavity geometries under Pine Island Ice Shelf, West Antarctica, significant differences in melt rate patterns between the velocity‐independent and velocity‐dependent formulations are found. While patterns are strongly correlated to those of thermal forcing for velocity‐independent transfer coefficients, melting in the case of velocity‐dependent coefficients is collocated with regions of high boundary layer currents, in particular where rapid plume outflow occurs. Both positive and negative feedbacks between melt rates, boundary layer temperature, velocities, and buoyancy fluxes are identified. Melt rates are found to increase with increasing drag coefficient Cd, in agreement with plume model simulations, but optimal values of Cd inferred from plume models are not easily transferable. Uncertainties therefore remain, both regarding simulated melt rate spatial distributions and magnitudes.
      PubDate: 2014-03-12T12:52:35.234522-05:
      DOI: 10.1002/2013JC008846
       
  • Uncertainty in hurricane surge simulation due to land cover specification
    • Authors: Celso M. Ferreira; Jennifer L. Irish, Francisco Olivera
      Pages: n/a - n/a
      Abstract: Hurricane storm surge is one of the most costly natural hazards in the United States. Numerical modeling to predict and estimate hurricane surge flooding is currently widely used for research, planning, decision making, and emergency response. Land cover plays an important role in hurricane surge numerical modeling because of its impacts on the forcing (changes in wind momentum transfer to water column) and dissipation (bottom friction) mechanisms of storm surge. In this study, the hydrodynamic model ADCIRC was used to investigate predicted surge response in bays on the central and lower Texas coast using different land cover data sets: (1) Coastal Change Analysis Program for 1996, 2001, and 2006; (2) the National Land Cover Dataset for 1992, 2001, and 2006; and (3) the National Wetlands Inventory for 1993. Hypothetical storms were simulated with varying the storm track, forward speed, central pressure, and radius to maximum wind, totaling 140 simulations. Data set choice impacts the mean of maximum surges throughout the study area, and variability in the surge prediction due to land cover data set choice strongly depends on storm characteristics and geographical location of the bay in relation to storm track. Errors in surge estimation due to land cover choice are approximately 7% of the surge value, with change in surge prediction varying by as much as 1 m, depending on location and storm condition. Finally, the impact of land cover choice on the accuracy of simulating surges for Hurricane Bret in 1999 is evaluated.
      PubDate: 2014-03-12T12:49:34.857477-05:
      DOI: 10.1002/2013JC009604
       
  • Topographic scattering of the low mode internal tide in the deep ocean
    • Authors: Manikandan Mathur; Glenn S. Carter, Thomas Peacock
      Pages: n/a - n/a
      Abstract: We investigate the role of deep‐ocean topography in scattering energy from the large spatial scales of the low mode internal tide to the smaller spatial scales of higher modes. The complete Green function method, which is not subject to the restrictions of the WKB approximation, is used for the first time to study the two‐dimensional scattering of a mode‐1 internal tide incident on subcritical and supercritical topography of any form in arbitrary stratifications. For an isolated Gaussian ridge in a uniform stratification, large amplitude critical topography is the most efficient at mode‐1 scattering and small amplitude topography scatters with an efficiency on the order of 5‐10%. In a nonuniform stratification with a pycnocline, the results are qualitatively the same as for a constant stratification, albeit with the key features shifted to larger height ratios. Having validated these results by direct comparison with the results of nonlinear numerical simulations, and in the process demonstrated that WKB results are not appropriate for reasonable ocean predictions, we proceed to use the Green function approach to quantify the role of topographic scattering for the region of the Pacific ocean surrounding the Hawaiian Islands chain. To the south, the Line Islands ridge is found to scatter ~ 40% of a mode‐1 internal tide coming from the Hawaiian Ridge. To the north, realistic, small‐amplitude, rough topography scatters ~ 5‐10% of the energy out of mode‐1 for transects of length 1000‐3000km. A significant finding is that compared to large extents of small‐amplitude, rough topography a single large topographic feature along the path of a mode‐1 internal tide plays the dominant role in scattering the internal tide.
      PubDate: 2014-03-11T12:55:54.185158-05:
      DOI: 10.1002/2013JC009152
       
  • Cross‐shelf exchange in the northwestern Black Sea
    • Authors: Feng Zhou; Georgy Shapiro, Fred Wobus
      Pages: n/a - n/a
      Abstract: The transports of water, heat and salt between the northwestern shelf and deep interior of the Black Sea are investigated using a high‐resolution three‐dimensional primitive equation model. From April to August, 2005, both onshore and offshore cross‐shelf break transports in the top 20 m were 0.24 Sv on average, which is equivalent to the replacement of 60% of the volume of surface shelf waters (0 – 20 m) per month. Two main exchange mechanisms are studied: Ekman transport, and transport by mesoscale eddies and associated meanders of the Rim Current. The Ekman drift causes nearly uniform onshore or offshore flow over a large section of the shelf break, but it is confined to the upper layers. In contrast, eddies and meanders penetrate deep down to the bottom, but they are restricted laterally. During the strong wind events of April 15 – 22 and July 1 – 4, some 0.66×1012 and 0.44×1012 m3 of water were removed from the northwestern shelf respectively. In comparison, the single long‐lived Sevastopol Eddy generated a much larger offshore transfer of 2.84×1012 m3 over the period April 23 to June 30, which is equivalent to 102% of the volume of northwestern shelf waters. Over the study period, salt exchanges increased the average density of the shelf waters by 0.67 kg m‐3 and reduced the density contrast between the shelf and deep sea, while lateral heat exchanges reduced the density of the shelf waters by 0.16 kg m‐3 and sharpened the shelf break front.
      PubDate: 2014-03-11T12:39:52.162389-05:
      DOI: 10.1002/2013JC009484
       
  • Impact of a coastal‐trapped wave on the near‐coastal
           circulation of the Peru upwelling system from glider data
    • Authors: Alice Pietri; Vincent Echevin, Pierre Testor, Alexis Chaigneau, Laurent Mortier, Carmen Grados, Aurélie Albert
      Pages: n/a - n/a
      Abstract: Geostrophic alongshore velocity data from a glider repetitive section off the coast of Peru (14°S) are used to study the cross‐shore structure and temporal variability of the Peru current system during a five‐week period in April‐May 2010. Besides providing substantial information on the surface frontal jet associated with the Peru Coastal Current and the surfacing Peru‐Chile Undercurrent that flows poleward trapped on the continental shelf and slope, the glider data reveal the presence of an intense deep equatorward current, which transports up to ~ 2.5 sv. The dynamics of this current are investigated using an eddy‐resolving regional model. The variability of the vertically sheared alongshore flow are shown to be related to the passage of a poleward propagating coastal‐trapped wave likely of equatorial origin. Solutions from a two‐dimensional, linear, coastal wave model suggest that the alongshore current observed vertical structure is associated with the second and third baroclinic modes of the coastal‐trapped wave.
      PubDate: 2014-03-08T05:38:46.257474-05:
      DOI: 10.1002/2013JC009270
       
  • The anisotropic scattering coefficient of sea ice
    • Authors: Christian Katlein; Marcel Nicolaus, Chris Petrich
      Pages: n/a - n/a
      Abstract: Radiative transfer in sea ice is subject to anisotropic, multiple scattering. The impact of anisotropy on the light field under sea ice was found to be substantial and has been quantified. In this study, a large dataset of irradiance and radiance measurements under sea ice has been acquired with a Remotely Operated Vehicle (ROV) in the central Arctic. Measurements are interpreted in the context of numerical radiative transfer calculations, laboratory experiments, and microstructure analysis. The ratio of synchronous measurements of transmitted irradiance to radiance shows a clear deviation from an isotropic under‐ice light field. We find that the angular radiance distribution under sea‐ice is more downward directed than expected for an isotropic light field. This effect can be attributed to the anisotropic scattering coefficient within sea ice. Assuming an isotropic radiance distribution under sea ice leads to significant errors in light‐field modeling and the interpretation of radiation measurements. Quantification of the light field geometry is crucial for correct conversion of radiance data acquired by Autonomous Underwater Vehicles (AUVs) and ROVs.
      PubDate: 2014-01-22T09:12:41.790926-05:
      DOI: 10.1002/2013JC009502
       
  • Impact of Barents Sea winter air‐sea exchanges on Fram Strait dense
           water transport
    • Authors: Bengamin I. Moat; Simon A. Josey, Bablu Sinha
      Pages: n/a - n/a
      Abstract: Impacts of extreme Barents Sea air‐sea exchanges are examined using the HadCM3 coupled ocean‐atmosphere model. Variability in the Barents Sea winter air‐sea density flux is found to be a potentially significant factor in determining changes in the southward transport of dense water through Fram Strait. The density flux variability is primarily driven by the thermal term, FT, due to heat loss to the atmosphere. The other two terms (haline flux and ice formation) play a relatively minor role. The difference in ocean circulation between winters with extreme strong and weak Barents Sea surface density flux anomalies is analysed. This reveals an increase in strong winters of both the north‐westwards intermediate depth flow out of the basin and the east‐west deep flows north of Spitsbergen and south through the Fram Strait. A linear fit yields a Fram Strait southward transport increase of 1.22 Sv for an increase in FT of 1x10‐6 kg m‐2 s‐1. For the ten strongest Barents Sea surface density flux winters, the Fram Strait winter southward transport increases by 2.4 Sv. This compares with a reduction of 1.0 Sv for the corresponding weakest winters. Furthermore, the properties of the southwards flowing water are modified in strong density flux winters. In such winters, the Fram Strait water below 250 m is colder by up to 0.5 °C and fresher by 0.05 than the climatological winter mean.
      PubDate: 2014-01-22T09:10:17.22474-05:0
      DOI: 10.1002/2013JC009220
       
  • Energy dissipation in viscous‐plastic sea‐ice models
    • Authors: Amélie Bouchat; Bruno Tremblay
      Pages: n/a - n/a
      Abstract: In viscous‐plastic (VP) sea‐ice models, small deformations are approximated by irreversible viscous deformations, introducing a non‐physical energy sink. As the spatial resolution and the degree of numerical convergence of the models increase, linear kinematic features (LKFs) are better resolved and more states of stress lie in the viscous regime. Energy dissipation in this non‐physical viscous regime therefore increases. We derive a complete kinetic energy (KE) balance for sea ice, including plastic and viscous energy sinks to study energy dissipation. The main KE balance is between the energy input by the wind and the dissipation by the water drag and the internal stresses (dissipating respectively 87% and 13% of the energy input on an annual average). The internal stress term is mostly important in winter when ice‐ice interactions are dominant. The energy input that is not dissipated locally is redistributed laterally by the internal stresses in regions of dissipation by small scale deformations (LKFs). Of the 13% dissipated annually by the internal stress term, 93% is dissipated in friction along LKFs (14% in ridging, 79% in shearing) and 7% is stored as potential energy in ridges. For all time and spatial scales tested, the frictional viscous dissipation is negligible in the KE balance. This conclusion remains valid when the spatial resolution and the numerical convergence of the simulations are increased. Overall, the results confirm the validity, from an energetical point of view, of the VP approximation.
      PubDate: 2014-01-22T08:48:33.664204-05:
      DOI: 10.1002/2013JC009436
       
  • A two‐way nested simulation of the oceanic circulation in the
           southwestern Atlantic
    • Authors: Vincent Combes; Ricardo P. Matano
      Pages: n/a - n/a
      Abstract: This article presents the results of a high‐resolution (1/12˚), two‐way nested simulation of the oceanic circulation in the southwestern Atlantic region. A comparison between the model results and extant observations indicate that the nested model has skill in reproducing the best‐known aspects of the regional circulation, e.g., the volume transport of the ACC, the latitudinal position of the BMC, the shelfbreak upwelling of Patagonia and the Zapiola Anticyclone. Sensitivity experiments indicate that the bottom stress parameterization significantly impacts the mean location of the Brazil/Malvinas Confluence and the transport of the Zapiola Anticyclone. The transport of the Brazil Current strengthens during the austral summer and weakens during the austral winter. These variations are driven by the wind stress curl over the southwestern Atlantic. The variations of the transport of the Malvinas Current are out of phase with those of the Brazil Current. Most of the seasonal variability of this current is concentrated in the offshore portion of the jet, the inshore portion has a weak seasonality that modulates the magnitude of the Patagonian shelfbreak upwelling. Using passive tracers we show that most of the entrainment of deep waters into the shelf occurs in the southernmost portion of the Patagonian shelf and along the inshore boundary of the Brazil Current. Shelf waters are preferentially detrained near the Brazil/Malvinas Confluence. Consistent with previous studies, our simulation also shows that south of ~42˚S the Malvinas Current is composed of two jets, which merge near 42˚S to form a single jet farther north.
      PubDate: 2014-01-21T12:26:15.333396-05:
      DOI: 10.1002/2013JC009498
       
  • Ocean chlorophyll response to two types of El Niño events in an
           ocean‐biogeochemical coupled model
    • Authors: Kie‐Woung Lee; Sang‐Wook Yeh, Jong‐Seong Kug, Jong‐Yeon Park
      Pages: n/a - n/a
      Abstract: Based on a long term simulation of an ocean‐biogeochemical coupled model, we investigate the biogeochemical response to the two types of El Niño events, a Cold Tongue (CT)‐El Niño and a Warm Pool (WP)‐El Niño, in which a local maximum of anomalous sea surface temperature (SST) is located in the eastern and central tropical Pacific. Our model is able to reasonably simulate the characteristics of the biological variables in a way comparable to the observations. During the developing period, anomalous low chlorophyll appears in the eastern Pacific, while it appears in the central Pacific in the WP‐El Niño. The difference in the spatial‐temporal response of chlorophyll for the two types of El Niño events is mainly due to the eastward zonal advection of upper ocean currents, which plays a role in bringing nutrient‐poor water from the western Pacific. During the decaying period of the WP‐El Niño, anomalous high chlorophyll appears concurrently with anomalous low SST in the eastern Pacific. Conversely, anomalous high chlorophyll appears in the central Pacific prior to the decaying period of the CT‐El Niño. In particular, the anomalous low sea level from the northwestern Pacific shifts to the southern equatorial region during the decaying period of the CT‐El Niño. This drives anti‐cyclonic boundary currents which enhance the Equatorial Undercurrent, playing a role in the supply of nutrients to the central equatorial Pacific, resulting in an increase in chlorophyll concentration in the same region.
      PubDate: 2014-01-16T09:24:34.863599-05:
      DOI: 10.1002/2013JC009050
       
  • Subseasonal variations in salinity and barrier‐layer thickness in
           the eastern equatorial Indian Ocean
    • Authors: Kyla Drushka; Janet Sprintall, Sarah T. Gille
      Pages: n/a - n/a
      Abstract: The barrier layer, the layer between the bottom of the density‐defined mixed layer and the isothermal layer in the upper ocean, may play a role in air‐sea dynamics. In the present study, data from Argo profiling floats in the tropical Indian Ocean and a mooring at 90°E, 0°N are used to examine subseasonal variations in upper ocean salinity and barrier‐layer thickness (BLT) during boreal winter. In the eastern equatorial Indian Ocean, subseasonal variations in BLT are energetic. However, composites used to isolate the Madden‐Julian Oscillation (MJO) component of the subseasonal signal reveal that, on average, the MJO anomaly in BLT is negligible despite large swings in both the mixed‐layer depth and the isothermal‐layer depth. This discrepancy is likely due to (a) noise from other subseasonal processes; and (b) the diversity of individual MJO events: the thickness of the mixed layer and the isothermal layer are sensitive to wind and rain forcing, so even subtle differences in the phasing and strength of MJO‐related atmospheric anomalies can produce a very different effect on upper ocean stratification and hence on the thickness of the barrier layer. The effect of the barrier layer on the upper ocean response to MJO forcing is also evaluated. When the barrier layer is thick, entrainment cooling during the MJO is reduced, so the MJO drives a weaker sea surface temperature anomaly. This suggests that modulation of BLT can have significant consequences for the response of the upper ocean to the MJO, and hence, potentially, for feedbacks of the ocean onto the atmosphere on MJO timescales.
      PubDate: 2014-01-16T09:18:37.652511-05:
      DOI: 10.1002/2013JC009422
       
  • Driven around the bend: Spatial evolution and controls on the orientation
           of helical bend flow in a natural submarine gravity current
    • Authors: E. J. Sumner; J. Peakall, R. M. Dorrell, D. R. Parsons, S. E. Darby, R. B. Wynn, S. D. McPhail, J. Perrett, A. Webb, D. White
      Pages: n/a - n/a
      Abstract: Submarine channel systems transport vast amounts of terrestrial sediment into the deep sea. Understanding the dynamics of the gravity currents that create these systems, and in particular how these flows interact with and form bends, is fundamental to predicting system architecture and evolution. Bend flow is characterized by a helical structure and in rivers typically comprises inwardly directed near‐bed flow and outwardly directed near‐surface flow. Following a decade of debate, it is now accepted that helical flow in submarine channel bends can exhibit a variety of structures including being opposed to that observed in rivers. The new challenge is to understand what controls the orientation of helical flow cells within submarine flows and determines the conditions for reversal. We present data from the Black Sea showing, for the first time, the three‐dimensional velocity and density structure of an active submarine gravity current. By calculating the forces acting on the flow we evaluate what controls the orientation of helical flow cells. We demonstrate that radial pressure gradients caused by across‐channel stratification of the flow are more important than centrifugal acceleration in controlling the orientation of helical flow. We also demonstrate that non‐local acceleration of the flow due to topographic forcing and downstream advection of the cross‐stream flow are significant terms in the momentum balance. These findings have major implications for conceptual and numerical models of submarine channel dynamics, because they show that three‐dimensional models that incorporate across‐channel flow stratification are required to accurately represent curvature‐induced helical flow in such systems.
      PubDate: 2014-01-16T08:59:22.717945-05:
      DOI: 10.1002/2013JC009008
       
  • Deterioration of perennial sea ice in the Beaufort Gyre from 2003 to 2012
           and its impact on the oceanic freshwater cycle
    • Authors: R.A. Krishfield; A. Proshutinsky, K. Tateyama, W.J. Williams, E.C. Carmack, F.A. McLaughlin, M.‐L. Timmermans
      Pages: n/a - n/a
      Abstract: Time series of ice draft from 2003‐2012 from moored sonar data are used to investigate variability and describe the reduction of the perennial sea ice cover in the Beaufort Gyre (BG), culminating in the extreme minimum in 2012. Negative trends in median ice drafts and most ice fractions are observed, while open water and thinnest ice fractions (
      PubDate: 2014-01-16T08:57:42.124924-05:
      DOI: 10.1002/2013JC008999
       
  • Wind‐forced variability of the Antarctic Circumpolar Current south
           of Africa between 1993 and 2010
    • Authors: Ricardo Domingues; Gustavo Goni, Sebastiaan Swart, Shenfu Dong
      Pages: n/a - n/a
      Abstract: The variability of the Antarctic Circumpolar Current (ACC) system is largely linked to atmospheric forcing. The objective of this work is to assess the link between local wind forcing mechanisms and the variability of the upper‐ocean temperature and the dynamics of the different fronts in the ACC region south of South Africa. To accomplish this, in situ and satellite‐derived observations are used between 1993‐2010. The main finding of this work is that meridional changes in the westerlies linked with the Southern Annular Mode (SAM) drive temperature anomalies in the Ekman layer and changes in the Subantarctic Front (SAF) and Antarctic Polar Front (APF) transports through Ekman dynamics. The development of easterly anomalies between 35oS‐45oS during positive SAM is linked to reduced (increased) SAF (APF) transports and a warmer mixed layer in the ACC. The link between the changes in the wind stress and the SAF and APF transport variations occurs through the development of Ekman pumping anomalies near the frontal boundaries, driving an opposite response on the SAF and APF transports. The observed wind‐driven changes in the frontal transports suggest small changes to the net ACC transport. In addition, observations indicate that the SAF and APF locations in this region are not linked to the local wind forcing, emphasizing the importance of other factors (e.g. baroclinic instabilities generated by bottom topography) to changes in the frontal location. Results obtained here highlight the importance of repeat XBT temperature sections and their combined analysis with other in situ and remote sensing observations.
      PubDate: 2014-01-16T08:57:37.969381-05:
      DOI: 10.1002/2013JC008908
       
  • Regional impact of submarine canyons during seasonal upwelling
    • Authors: Thomas P. Connolly; Barbara M. Hickey
      Pages: n/a - n/a
      Abstract: A numerical model of the northern California Current System along the coasts of Washington and British Columbia is used to quantify the impact of submarine canyons on upwelling from the continental slope onto the shelf. Comparisons with an extensive set of observations show that the model adequately represents the seasonal development of near‐bottom density, as well as along‐shelf currents that are critical in governing shelf‐slope exchange. Additional model runs with simplified coastlines and bathymetry are used to isolate the effects of submarine canyons. Near submarine canyons, equatorward flow over the outer shelf is correlated with dense water at canyon heads and subsequent formation of closed cyclonic eddies, which are both associated with cross‐shelf ageostrophic forces. Lagrangian particles tracked from the slope to mid shelf show that canyons are associated with upwelling from depths of ~140‐260 m. Source depths for upwelling are shallower than 150 m at locations away from canyons and in a model run with bathymetry that is uniform in the along‐shelf direction. Water upwelled through canyons is more likely to be found near the bottom over the shelf. Onshore fluxes of relatively saline water through submarine canyons are large enough to increase volume‐averaged salinity over the shelf by 0.1‐‐0.2 psu during the early part of the upwelling season. The nitrate input from the slope to the Washington shelf associated with canyons is estimated to be 30–60% of that upwelled to the euphotic zone by local wind‐driven upwelling.
      PubDate: 2014-01-16T08:57:23.848232-05:
      DOI: 10.1002/2013JC009452
       
  • Water level effects on breaking wave setup for Pacific Island fringing
           reefs
    • Authors: J. M. Becker; M. A. Merrifield, M. Ford
      Pages: n/a - n/a
      Abstract: The effects of water level variations on breaking wave setup over fringing reefs are assessed using field measurements obtained at three study sites in the Republic of the Marshall Islands and the Mariana Islands in the western tropical Pacific Ocean. At each site, reef flat setup varies over the tidal range with weaker setup at high tide and stronger setup at low tide for a given incident wave height. The observed water level dependence is interpreted in the context of radiation stress gradients specified by an idealized point break model generalized for non‐normally incident waves. The tidally varying setup is due in part to depth‐limited wave heights on the reef flat, as anticipated from previous reef studies, but also to tidally dependent breaking on the reef face. The tidal dependence of the breaking is interpreted in the context of the point break model in terms of a tidally varying wave height to water depth ratio at breaking. Implications for predictions of wave‐driven setup at reef‐fringed island shorelines are discussed.
      PubDate: 2014-01-16T08:53:39.701338-05:
      DOI: 10.1002/2013JC009373
       
  • Interferometry of infragravity waves off New Zealand
    • Authors: Oleg A. Godin; Nikolay A. Zabotin, Anne F. Sheehan, John A. Collins
      Pages: n/a - n/a
      Abstract: Wave interferometry is a remote sensing technique, which is increasingly employed in helioseismology, seismology, and acoustics to retrieve parameters of the propagation medium from two‐point cross‐correlation functions of random wave fields. Here, we apply interferometry to yearlong records of seafloor pressure at 28 locations off New Zealand's South Island to investigate propagation and directivity properties of infragravity waves away from shore. A compressed cross‐correlation function technique is proposed to make the interferometry of dispersive waves more robust, decrease the necessary noise averaging time, and simplify retrieval of quantitative information from noise cross‐correlations. The emergence of deterministic wave arrivals from cross‐correlations of random wave fields is observed up to the maximum range of 692 km between the pressure sensors in the array. Free, linear waves with a strongly anisotropic distribution of power flux density are found to be dominant in the infragravity wave field. Lowest‐frequency components of the infragravity wave field are largely isotropic. The anisotropy has its maximum in the middle of the spectral band and decreases at the high‐frequency end of the spectrum. Highest anisotropy peaks correspond to waves coming from portions of the New Zealand's shoreline. Significant contributions are also observed from waves propagating along the coastline and probably coming from powerful sources in the northeast Pacific. Infragravity wave directivity is markedly different to the east and to the west of the South Island. The northwest coast of the South Island is found to be a net source of the infragravity wave energy.
      PubDate: 2014-01-15T12:26:55.667066-05:
      DOI: 10.1002/2013JC009395
       
  • An exceptional anticyclonic eddy in the South China Sea in 2010
    • Authors: Xiaoqing Chu; Huijie Xue, Yiquan Qi, Gengxin Chen, Qingwen Mao, Dongxiao Wang, Fei Chai
      Pages: n/a - n/a
      Abstract: The highest sea level near the Xisha Islands in recent 20 years occurred during August 2010. Satellite altimeter data indicated that the extreme event was largely due to an anticyclonic eddy, whose amplitude exceeded 20 cm and size exceeded 400 km on 11 Aug 2010. Cruise observations showed the eddy raised the center temperature by 7.7°C at 75 m and vertically extended to 500 m. Eddy tracking showed it had a life span of more than 8 months and propagated far from the south of Xisha Islands. Such strong and long‐lasting eddy that moved northward for such a long distance was observed for the first time in the South China Sea (SCS). Observational data from CTD/XBT and the reconstructed three‐dimensional temperature and salinity were used to explore the eddy's features and vertical structure. Our analyses show the 2010 summer monsoon and current in the western boundary of the SCS were largely altered after the 09/10 El Niño event. From May onwards, the wind blew northward and strengthened over the northwestern SCS. Such wind drove a strong northward current along the western boundary, which carried the eddy northward by advection from May to July. Energy budget showed, during the eddy northward propagation, the boundary current passed energy to the eddy, which led to the continuing growth of the eddy in both strength and size.
      PubDate: 2014-01-15T12:24:46.432392-05:
      DOI: 10.1002/2013JC009314
       
  • On the spatial structure and temporal variability of poleward transport
           between Scotland and Greenland
    • Authors: L. Chafik; T. Rossby, C. Schrum
      Pages: n/a - n/a
      Abstract: The flow north of warm subtropical water though the northeastern Atlantic is known to have many pathways that vary over time. Here we use a combination of upper ocean current measurements between Greenland and Scotland near 60°N and satellite altimetry to examine the space‐time variability of poleward transport. The high‐resolution scans of currents in the top 400 m show that the Reykjanes Ridge serves as a very effective separator of flow towards the Nordic and Labrador Seas, respectively. Whereas the Labrador Sea branch exhibits two mean flows to the north on the western slope of the Reykjanes Ridge, the eastern branch flows north in roughly equal amounts over the deep Maury channel and east of Hatton Bank including the Slope Current. There is also a well‐defined southward flow along the eastern slope of the Reykjanes Ridge. The satellite altimetric sea surface height (SSH) data show good overall agreement with geostrophically determined sea level difference from the repeat ADCP sections (1999‐2002), but are unable to resolve the fine structure of the topographically defined mean circulation. The altimetric data show that variations in poleward flow west and east of the Reykjanes Ridge are strongly anticorrelated. They further reveal that the two eastern sub‐branches also exhibit anticorrelated variability, but offset in time with respect to the Labrador Sea branch. Remarkably, all these variations cancel out for the entire Greenland‐Scotland section leaving a gradual decrease in sea level difference of about 0.06 m over the 1993 to the end of 2010 observation period.
      PubDate: 2014-01-15T12:15:56.015727-05:
      DOI: 10.1002/2013JC009287
       
  • The Indonesian Throughflow: Response to Indo‐Pacific climate
           variability
    • Authors: Janet Sprintall; Adèle Révelard
      Pages: n/a - n/a
      Abstract: The Indonesian Throughflow (ITF) is the only open pathway for inter‐ocean exchange between the Pacific and Indian Ocean basins at tropical latitudes. A proxy time series of ITF transport variability is developed using remotely‐sensed altimeter data. The focus is on the three outflow passages of Lombok, Ombai and Timor that collectively transport the entire ITF into the Indian Ocean, and where direct velocity measurements are available to help ground‐truth the transport algorithm. The resulting 18‐year proxy time series shows strong interannual ITF variability. Significant trends of increased transport are found in the upper layer of Lombok Strait, and over the full depth in Timor Passage that are likely related to enhanced Pacific trade winds since the early 1990s. The partitioning of the total ITF transport through each of the major outflow passage varies according to the phase of the Indian Ocean Dipole (IOD) or El Niño‐Southern Oscillation (ENSO). In general, Pacific ENSO variability is strongest in Timor Passage, most likely through the influence of planetary waves transmitted from the Pacific along the Northwest Australian shelf pathway. Somewhat surprisingly, concurrent El Niño and positive IOD episodes consistently show contradictory results from those composites constructed for purely El Niño episodes. This is particularly evident in Lombok and Ombai Straits, but also at depth in Timor Passage. This suggests that Indian Ocean dynamics likely win out over Pacific Ocean dynamics in gating the transport through the outflow passages during concurrent ENSO and IOD events.
      PubDate: 2014-01-15T12:05:41.153681-05:
      DOI: 10.1002/2013JC009533
       
  • Optical measurements of small deeply penetrating bubble populations
           generated by breaking waves in the Southern Ocean
    • Authors: Kaylan Randolph; Heidi M. Dierssen, Michael Twardowski, Alejandro Cifuentes‐Lorenzen, Christopher J. Zappa
      Pages: n/a - n/a
      Abstract: Bubble size distributions ranging from 0.5 to 125 μm radius were measured optically during high winds of 13 m s‐1 and large‐scale wave breaking as part of the Southern Ocean Gas Exchange Experiment. Very small bubbles with radii less than 60 µm were measured at 6‐9 m depth using optical measurements of the near forward volume scattering function and critical scattering angle for bubbles (˜80°). The bubble size distributions generally followed a power law distribution with mean slope values ranging from 3.6 to 4.6. The steeper slopes measured here were consistent with what would be expected near the base of the bubble plume. Bubbles, likely stabilized with organic coatings, were present for time periods on the order of 10‐100 s at depths of 6‐9 m. Here, relatively young seas, with an inverse wave age of approximately 0.88 and shorter characteristic wave scales, produced lower bubble concentrations, shallower bubble penetration depths, and steep bubble size distribution slopes. Conversely, older seas, with an inverse wave age of 0.70 and longer characteristic wave scales, produced relatively higher bubble concentrations penetrating to 15 m depth, larger bubble sizes and shallower bubble size distribution slopes. When extrapolated to 4 m depth using a previously published bubble size distribution, our estimates suggest that the deeply‐penetrating small bubbles measured in the Southern Ocean supplied ˜36% of the total void fraction and likely contributed to the transfer and supersaturation of low solubility gases.
      PubDate: 2014-01-10T05:56:20.734093-05:
      DOI: 10.1002/2013JC009227
       
  • Deep water circulation in the Luzon Strait
    • Authors: Wei Zhao; Chun Zhou, Jiwei Tian, Qingxuan Yang, Bin Wang, Lingling Xie, Tangdong Qu
      Pages: n/a - n/a
      Abstract: Deep water circulation in the Luzon Strait, which connects the Pacific deep circulation with the South China Sea throughflow, is investigated using a set of oceanographic observations combined with results from three numerical experiments. Both the in situ observations and the model show a deep water overflow in the Luzon Strait. Their results suggest that the deep Pacific water first flows into the Luzon Strait through the Bashi Channel (1.2 Sv, 1 Sv = 1×106 m3 s‐1) and the Taltung Canyon (0.4 Sv), then turns southward along the Luzon Trough, and finally enters the South China Sea primarily through two gaps in the Heng‐Chun Ridge. Overall, the mean transport of the Luzon Strait overflow is about 1.5 Sv. Results from numerical experiments suggest that strong diapycnal mixing in the South China Sea and Luzon Strait, which sustains the baroclinic pressure gradient across the Luzon Strait, is the primary driving mechanism of the deep circulation in the Luzon Strait.
      PubDate: 2014-01-10T05:56:14.16933-05:0
      DOI: 10.1002/2013JC009587
       
  • Coherent intraseasonal oceanic variations in the eastern equatorial Indian
           Ocean and in the Lombok and Ombai Straits from observations and a
           high‐resolution OGCM
    • Authors: Iskhaq Iskandar; Yukio Masumoto, Keisuke Mizuno, Hideharu Sasaki, Azhar K. Affandi, Dedi Setiabudidaya, Fadli Syamsuddin
      Pages: 615 - 630
      Abstract: Ongoing acoustic Doppler current profilers (ADCP) observation in the eastern equatorial Indian Ocean and a recent International Nusantara Stratification and Transport (INSTANT) experiment in the Indonesian Throughflow (ITF) straits have shown coherent intraseasonal oceanic variations in this region. The intraseasonal variations are dominated by 30–70 day variations, with a tendency for the observed currents in the eastern equatorial Indian Ocean to lead those at the Lombok and Ombai Straits. Phase speed of these eastward propagating signals estimated using lag correlation analysis does not correspond to one particular baroclinic mode, though it is in the range expected for the first two baroclinic modes. In this study, the dynamics underlying this intraseasonal coherency is evaluated using output from a high‐resolution ocean general circulation model developed for the Earth Simulator (OFES). The results from model simulation of January 2001 through December 2007 show that the first two baroclinic modes dominate the intraseasonal variations in this region. While the first and second baroclinic modes have comparable contribution to the intraseasonal oceanic variations in the eastern equatorial Indian Ocean and in the Ombai Strait, the intraseasonal oceanic variations in the Lombok Strait are dominated by the first baroclinic mode. Moreover, the analysis reveals that the intraseasonal variability at all mooring sites is mostly confined in the upper layer above ∼100 m depth. Both equatorial wind from the Indian Ocean and alongshore winds off Sumatra and Java play important roles in generating intraseasonal variations in the Lombok and Ombai Straits.
      PubDate: 2014-02-20T17:30:19.021116-05:
      DOI: 10.1002/2013JC009592
       
  • Oceanic heat delivery via Kangerdlugssuaq Fjord to the south‐east
           Greenland ice sheet
    • Authors: Mark E. Inall; Tavi Murray, Finlo R. Cottier, Kilian Scharrer, Timothy J. Boyd, Karen J. Heywood, Suzanne L. Bevan
      Pages: 631 - 645
      Abstract: Acceleration of the Greenland Ice Sheet (GrIS) tidewater outlet glaciers has increased the ice sheet's contribution to global sea level rise over the last two decades. Coincident increases in atmospheric temperatures around Greenland explain some of the increased ice loss, but warm Atlantic‐origin water (AW) is increasingly recognized as contributing to the accelerating ice‐mass loss, particularly, via the outlet glaciers of south‐east (SE) Greenland. However, there remains a lack of understanding of the variability in heat content of the water masses found to the east of Greenland and how this heat is communicated to the outlet glaciers of the GrIS. Here a new analysis is presented of ocean/GrIS interaction in which the oceanic heat flux toward the ice sheet in Kangerdlugssuaq Fjord (0.26 TW) is an order‐of‐magnitude greater than that reported for the other major outlet glacier of SE Greenland (Helheim). Heat delivered by AW to the calving front of Kangerdlugssuaq is equivalent to ∼10 m d−1 melt (i.e., 30–60% of the ice flow speed), and thus is highly significant. During the observational campaign in September 2010 warm Polar Surface Water (PSWw) melted a substantial volume of ice within the fjord; equivalent to 25% of the volume melted by AW alone. Satellite‐derived sea surface temperatures show large interannual variability in PSWw over the 20 year period 1991–2011. Anomalously warm PSWw was observed within the fjord prior to the well‐documented major ice front retreats of May 2004 and November 2010.
      PubDate: 2014-02-04T09:26:06.342972-05:
      DOI: 10.1002/2013JC009295
       
  • Impact of physical processes on the seasonal distribution of the fugacity
           of CO2 in the western tropical Atlantic
    • Authors: Nathalie Lefèvre; Domingos F. Urbano, Francis Gallois, Denis Diverrès
      Pages: 646 - 663
      Abstract: The fugacity of CO2 (fCO2) has been measured underway during three quasi‐synoptic cruises in the western tropical Atlantic in March/April 2009 and July/August 2010 in the region 6°S–15°N, 52°W–24°W. The distribution of fCO2 is related to the main features of the ocean circulation. Temperature exerts a dominant control on the distribution of fCO2 in March/April whereas salinity plays an important role in July/August due to the more developed North Equatorial Countercurrent (NECC) carrying Amazon water and to the high precipitation associated with the presence of the Intertropical Convergence Zone (ITCZ). The main surface currents are characterized by different fCO2. Overall, the NECC carries less saline waters with lower fCO2 compared to the South Equatorial Current (SEC). The North Equatorial Current (NEC) is usually characterized by CO2 undersaturation in winter and supersaturation in summer. Using empirical fCO2‐SST‐SSS relationships, two seasonal maps of fCO2 are constructed for March 2009 and July 2010. The region is a sink of CO2 of 0.40 mmol m−2d−1 in March, explained by the winter cooling in the northern hemisphere, whereas it is a source of CO2 of 1.32 mmol m−2d−1 in July. The equatorial region is a source of CO2 throughout the year due to the upwelling supplying CO2‐rich waters to the surface. However, the evolution of fCO2 over time, determined from all the available cruises in a small area, 1°S–1°N, 32°W–28°W, suggests that the source of CO2 has decreased in February‐March from 1983 to 2011 or has remained constant in October‐November from 1991 to 2010.
      PubDate: 2014-02-04T13:26:22.274968-05:
      DOI: 10.1002/2013JC009248
       
  • Temporal and spatial evolution of wave‐induced ripple geometry:
           Regular versus irregular ripples
    • Authors: Timothy Robert Nelson; George Voulgaris
      Pages: 664 - 688
      Abstract: Concurrent observations of inner shelf near bed hydrodynamics and acoustic imagery of the seabed are used to relate wave‐induced ripple geometry (wavelength and orientation) to near bed directional wave velocities. The observations were collected on the continental shelf of the South Atlantic Bight at water depths of 9.5 and 30 m off the coasts of South Carolina (median size 177 µm) and Georgia (388 µm), respectively. 2‐D spectral analysis techniques are performed on the imagery to automate detection of ripple wavelength, orientation, and irregularity. Our analysis shows that ripple irregularity is a time‐dependent process dependent on magnitude, direction, and duration of wave forcing. During energetic events, ripple geometry changes rapidly and the ripples align with the main wave direction. During periods of low energy, close to the critical conditions for initiation of sediment motion, ripple evolution occurs at a much slower rate often leading to irregularities such as terminations and bifurcations along the ripple crest. Under constantly changing wave direction, the rippled bed becomes highly disorganized. Six types of ripples are defined based on newly developed irregularity parameters: linear, bifurcating‐linear, linear‐bifurcating, bifurcating and cross, irregular, and disorganized beds. Ripple irregularity depends on the time history of the bed; ripples remain irregular until their wavelength and orientation attain a nearly equilibrium geometry. The observations collected provide significant information on the response of the seabed to wave forcing and identify processes that should be reproduced by any time‐dependent ripple prediction model. Ripple irregularity can only be predicted using such time‐dependent models.
      PubDate: 2014-02-04T00:03:02.988287-05:
      DOI: 10.1002/2013JC009020
       
  • Observations of flow variability through the Kerama Gap between the East
           China Sea and the Northwestern Pacific
    • Authors: Hanna Na; Mark Wimbush, Jae‐Hun Park, Hirohiko Nakamura, Ayako Nishina
      Pages: 689 - 703
      Abstract: The Kerama Gap, near the middle of the Ryukyu Island chain, is the deepest channel with a sill depth of 1050 m connecting the East China Sea (ECS) to the Northwestern Pacific. We measured the flow through the Kerama Gap from June 2009 to June 2011. The 2 year mean transport, 2.0 ± 0.7 Sv, is into the ECS from the Northwestern Pacific; it contributes about 11% of the mean Kuroshio transport in the ECS at the PN line. Subtidal standard deviation of the transport through the Kerama Gap is 3.2 Sv, comparable to that of the PN‐line Kuroshio transport (4.0 Sv), suggesting a significant effect of Kerama Gap transport on temporal variability of the Kuroshio transport in the ECS. Comparison with time series of satellite‐measured sea surface height maps reveals that temporal variability of the Kerama Gap transport is related to the arrival of mesoscale eddies from the east: high (low) transport into the ECS is associated with the presence of a cyclonic (anticyclonic) eddy south of the Kerama Gap.
      PubDate: 2014-02-04T16:21:49.040726-05:
      DOI: 10.1002/2013JC008899
       
  • Large‐scale impact of Saharan dust on the North Atlantic Ocean
           circulation
    • Authors: N. Serra; N. Martínez Avellaneda, D. Stammer
      Pages: 704 - 730
      Abstract: The potential for a dynamical impact of Saharan mineral dust on the North Atlantic Ocean large‐scale circulation is investigated. To this end, an ocean general circulation model forced by atmospheric fluxes is perturbed by an idealized, seasonally varying, net shortwave flux anomaly, as it results from remote sensing observations of aerosol optical thickness representing Saharan dust load in the atmosphere. The dust dynamical impact on the circulation is assessed through a comparison between perturbed and an unperturbed run. Results suggest that, following the dust‐induced shortwave irradiance anomaly, a buoyancy anomaly is created in the Atlantic offshore the African coast, which over the course of the time propagates westward into the interior Atlantic while progressively subducting. Changes in the large‐scale barotropic and overturning circulations are significant after 3 years, which coincides with the elapsed time required by the bulk of the buoyancy perturbation to reach the western boundary of the North Atlantic. Although small in amplitude, the changes in the meridional overturning are of the same order as interannual‐to‐decadal variability. Variations in the amplitude of the forcing lead to changes in the amplitude of the response, which is almost linear during the first 3 years. In addition, a fast, but dynamically insignificant, response can be observed to propagate poleward along the eastern boundary of the North Atlantic, which contributes to a nonlinear response in the subpolar region north of 40°N.
      PubDate: 2014-02-04T00:21:34.829834-05:
      DOI: 10.1002/2013JC009274
       
  • Impacts of canonical and Modoki El Niño on tropical Atlantic SST
    • Authors: Dillon J. Amaya; Gregory R. Foltz
      Pages: 777 - 789
      Abstract: The impacts of canonical and Modoki El Niño on tropical Atlantic sea surface temperature (SST) are quantified using composite analysis. Results show that El Niño Modoki fails to produce significant warming in the tropical Atlantic, in contrast to the well known warming following canonical El Niño events. El Niño Modoki instead induces significant cooling in the northeastern tropical Atlantic and near‐neutral conditions elsewhere in the tropical Atlantic. It is shown that the difference in SST response stems primarily from a much stronger Pacific/North American (PNA) teleconnection pattern and stronger atmospheric Kelvin wave response during canonical events compared to Modoki. The stronger PNA pattern and Kelvin waves during canonical events generate anomalously weak surface winds in the tropical North Atlantic, driving anomalously weak evaporative cooling and warmer SSTs. Past research has shown significant decadal variability in the frequency of noncanonical El Niños relative to canonical events. If such variability continues, it is likely that the impact of El Niño on tropical Atlantic SST will also fluctuate from one decade to the next.
      PubDate: 2014-02-07T16:17:25.294083-05:
      DOI: 10.1002/2013JC009476
       
  • A physical model of sea wave period from altimeter data
    • Authors: S. I. Badulin
      Pages: 856 - 869
      Abstract: A physical model for sea wave period from altimeter data is presented. Physical roots of the model are in recent advances of the theory of weak turbulence of wind‐driven waves that predicts the link of instant wave energy to instant energy flux to/from waves. The model operates with wave height and its spatial derivative and does not refer to normalized radar cross‐section σ0 measured by the altimeter. Thus, the resulting formula for wave period does not contain any empirical parameters and does not require features of particular satellite altimeter or any calibration for specific region of measurements. A single case study illustrates consistency of the new approach with previously proposed empirical models in terms of estimates of wave periods and their statistical distributions. The paper brings attention to the possible corruption of dynamical parameters such as wave steepness or energy fluxes to/from waves when using the empirical approaches. Applications of the new model to the studies of sea wave dynamics are discussed.
      PubDate: 2014-02-07T16:03:32.572741-05:
      DOI: 10.1002/2013JC009336
       
  • A simple turbulence model for stably stratified wall‐bounded flows
    • Authors: F. Karimpour; S. K. Venayagamoorthy
      Pages: 870 - 880
      Abstract: In this study, we present a simple zero‐equation (algebraic) turbulence closure scheme as well as the standard k‐ϵ model for stably stratified wall‐bounded flows. We do this by proposing a parameterization for the turbulent Prandtl number (Prt) for stably stratified flows under the influence of a smooth solid wall. The turbulent Prandtl number is the linking bridge between the turbulent momentum and scalar fluxes in the context of Reynolds‐averaged Navier‐Stokes (RANS) simulations. Therefore, it is important to use appropriate parameterizations for Prt in order to define the right level of momentum and scalar mixing in stably stratified flows. To date, most of the widely used parameterizations for Prt in stably stratified flows are based on data obtained from homogeneous shear flows experiments and/or direct numerical simulations (i.e., statistics are invariant under translations) and are usually formulated as functions of the gradient Richardson number (Rig). The effect of the wall boundary is completely neglected. We introduce a modified parameterization for Prt that takes into account the inhomogeneity caused by the wall coupled with the effects of density stratification. We evaluate the performance of the modified Prt by using a zero‐equation turbulence model for the turbulent viscosity that was proposed by Munk and Anderson (1948) as well as the standard k‐ϵ model to simulate a one‐dimensional stably stratified channel flow. Comparison of the one‐dimensional simulation results with direct numerical simulation (DNS) of stably stratified channel flow results show remarkable agreement.
      PubDate: 2014-02-12T05:48:45.98997-05:0
      DOI: 10.1002/2013JC009332
       
  • Modeling ice‐ocean interaction in ice‐shelf crevasses
    • Authors: James R. Jordan; Paul R. Holland, Adrian Jenkins, Matthew D. Piggott, Satoshi Kimura
      Pages: 995 - 1008
      Abstract: Ocean freezing within ice‐shelf basal crevasses could potentially act as a stabilizing influence on ice shelves; however, ice‐ocean interaction and ocean dynamics within these crevasses are as yet poorly understood. To this end, an idealized 2‐D model of an ice‐shelf basal crevasse has been developed using Fluidity, a finite‐element ocean model using an unstructured mesh. A simple model of frazil ice formation and deposition has been incorporated into Fluidity to better represent the freezing process. Model results show two different flow regimes, dependent on the amount of freezing in the crevasse: one driven by freezing at the top of the crevasse and the other by the ingress of meltwater from outside the crevasse. In the first, freezing at the top of the crevasse leads to the formation of an unstable overturning circulation due to the rejection of dense, salty water. In the second, a buoyant layer is formed along the sides and roof of the crevasse, stratifying the water column. Frazil ice precipitation is found to be the dominant freezing process at the top of the basal crevasse in the freeze‐driven case, with direct freezing being dominant in the melt‐driven case. In both cases, melting occurs lower down on the walls of the crevasse due to the strong overturning circulation. The freezing in ice‐shelf crevasses and rifts is found to be highly dependent upon ocean temperature, providing a stabilizing influence on ice shelves underlain by cold waters that is not present elsewhere.
      PubDate: 2014-02-12T05:45:57.623386-05:
      DOI: 10.1002/2013JC009208
       
  • Relating Lagrangian and Eulerian horizontal eddy statistics in the
           surfzone
    • Authors: Matthew S. Spydell; Falk Feddersen, R. T. Guza, Jamie MacMahan
      Pages: 1022 - 1037
      Abstract: Concurrent Lagrangian and Eulerian observations of rotational, low‐frequency (10−4 to 10−2 Hz) surfzone eddies are compared. Surface drifters were tracked for a few hours on each of 11 days at two alongshore uniform beaches. A cross‐shore array of near‐bottom current meters extended from near the shoreline to seaward of the surfzone (typically 100 m wide in these moderate wave conditions). Lagrangian and Eulerian mean alongshore velocities V are similar, with a midsurfzone maximum. Cross‐shore dependent Lagrangian (σL) and Eulerian (σE) rotational eddy velocities, estimated from low‐pass filtered drifter and current meter velocities, respectively, also generally agree. Cross‐shore rotational velocities have a midsurfzone maximum whereas alongshore rotational velocities are distributed more broadly. Daily estimates of the Lagrangian time scale, the time for drifter velocities to decorrelate, vary between 40 and 300 s, with alongshore time scales greater than cross‐shore time scales. The ratio of Lagrangian to apparent Eulerian current meter decorrelation times TL/TA varies considerably, between about 0.5 and 3. Consistent with theory, some of the TL/TA variation is ascribable to alongshore advection and TL/TA is proportional to V/σ, which ranges between about 0.6 and 2.5. Estimates of TL/TA vary between days with similar V/σ suggesting that surfzone Lagrangian particle dynamics vary between days, spanning the range from “fixed‐float” to “frozen‐field” [Lumpkin et al., 2002], although conclusions are limited by the statistical sampling errors in both TL/TA and V/σ.
      PubDate: 2014-02-12T16:53:26.709203-05:
      DOI: 10.1002/2013JC009415
       
  • Experimental observations of the splitting of a gravity current at a
           density step in a stratified water body
    • Authors: A. Cortés; F. J. Rueda, M. G. Wells
      Pages: 1038 - 1053
      Abstract: When a gravity current reaches the level of neutral buoyancy in a stratified water body it can separate from the sloping boundary as an intrusion. If there is a density gradient within the gravity current, then multiple intrusions can form in the stratified water body. Using a series of laboratory experiments in a two‐layered ambient stratification, we document how a gravity current splits in two upon reaching the sharp density step. Our laboratory observations stress the significance of the densimetric Froude number of the gravity current (Fr), as well as a measure of the ambient stratification (density Richardson number, Riρ), on determining how a gravity current intrudes into a two‐layered stratified ambient water. Gravity currents are more likely to detrain into two parts at a density step when they have a diffuse density interface (Fr > 1). However, gravity currents tend to intrude as a single intrusion when they have a sharp, more step‐like density profile (Fr 
      PubDate: 2014-02-12T16:01:14.226289-05:
      DOI: 10.1002/2013JC009304
       
  • Cyclogeostrophic balance in the Mozambique Channel
    • Authors: Pierrick Penven; Issufo Halo, Stéphane Pous, Louis Marié
      Pages: 1054 - 1067
      Abstract: Three methods are proposed for the inclusion of inertia when deriving currents from sea surface height (SSH) in the Mozambique Channel: gradient wind, perturbation expansion, and an iterative method. They are tested in a model and applied to satellite altimetry. For an eddy of 25 cm amplitude and 100 km radius, typical of Mozambique Channel rings at 18°S, the error made with geostrophy is 40% for the anticyclones and 20% for the cyclones. Inertia could reach one third of the pressure gradient. Geostrophy underestimates subsurface currents by up to 50 cm s−1, resulting in errors of 30–40%. The iterative method results in errors of 50% in Mozambique Channel rings. Geostrophic EKE reaches 1400 cm2 s−2, while it attains 1800 cm2 s−2 when inertia is added. Applied to the Gulf Stream, these methods confirm the hypothesis of Maximenko and Niiler [2006] that centrifugal accelerations should be the main cause for the difference observed between geostrophic and drifter EKE. This methodology should result in a net improvement for operational surface ocean currents.
      PubDate: 2014-02-12T16:11:47.991103-05:
      DOI: 10.1002/2013JC009528
       
  • Eddies and an extreme water mass anomaly observed in the eastern south
           Pacific at the Stratus mooring
    • Authors: Lothar Stramma; Robert A. Weller, Rena Czeschel, Sebastien Bigorre
      Pages: 1068 - 1083
      Abstract: In the tropical eastern South Pacific the Stratus Ocean Reference Station (ORS) (∼20°S, 85.5°W) is located in the transition zone between the oxygen minimum zone (OMZ) and the well‐oxygenated subtropical gyre. In February/March 2012, extremely anomalous water mass properties were observed in the thermocline at the Stratus ORS. The available eddy oxygen anomaly was −10.5 × 1016 µmol. This anomalous water was contained in an anticyclonic mode‐water eddy crossing the mooring site. This eddy was absorbed at that time by an anticyclonic feature located south of the Stratus mooring. This was the largest water property anomaly observed at the mooring during the 13.5 month deployment period. The sea surface height anomaly (SSHA) of the strong mode‐water eddy in February/March 2012 was weak, and while the lowest and highest SSHA were related to weak eddies, SSHA is found not to be sufficient to specify the eddy strength for subsurface‐intensified eddies. Still, the anticyclonic eddy, and its related water mass characteristics, could be tracked backward in time in SSHA satellite data to a formation region in April 2011 off the Chilean coast. The resulting mean westward propagation velocity was 5.5 cm s−1. This extremely long‐lived eddy carried the water characteristics from the near‐coastal Chilean water to the open ocean. The water mass stayed isolated during the 11 month travel time due to high rotational speed of about 20 cm s−1 leading to almost zero oxygen in the subsurface layer of the anticyclonic mode‐water eddy with indications of high primary production just below the mixed layer.
      PubDate: 2014-02-12T16:01:11.923515-05:
      DOI: 10.1002/2013JC009470
       
  • Determination of particulate organic carbon sources to the surface mixed
           layer of the Canada Basin, Arctic Ocean
    • Authors: Kristina A. Brown; Fiona McLaughlin, Philippe D. Tortell, Diana E. Varela, Michiyo Yamamoto‐Kawai, Brian Hunt, Roger Francois
      Pages: 1084 - 1102
      Abstract: Stable isotope ratios of particulate organic carbon (POC), together with other tracers, were analyzed in samples from the Canada Basin surface mixed layer in 2008 and 2009. Sampling was conducted during the end of the 2008 melt season and at the beginning of the 2009 freezeup under a variety of surface conditions, including open water, newly formed seasonal ice, and multiyear ice. In both years, POC exhibited a wide isotopic range (δ13C‐POC −24.5 to −31.1‰), with the most isotopically depleted material generally found in the central basin. Isotopically enriched material was found on the shelves, consistent with higher biological production and strongly correlated with in situ carbon‐uptake rates. In contrast, offshore in the central basin, there was no significant relationship between δ13C‐POC distributions and either chlorophyll a or aqueous CO2 concentrations, suggesting that in situ biological production was not the dominant control. Analysis of freshwater sources suggested that the sea ice melt contribution of POC to surface waters in the central Canada Basin exerted a negligible influence on δ13C‐POC distributions, and instead isotopically depleted POC in the surface waters of the central Canada Basin were sourced externally through advective transport of riverine organic matter. We show that alkalinity and meteoric water content can be used to distinguish POC inputs from North American and Russian rivers and our analysis suggests that Russian river inputs are the predominant source of 13C‐depleted organic matter to the mixed layer of the central Canada Basin.
      PubDate: 2014-02-15T03:58:57.477059-05:
      DOI: 10.1002/2013JC009197
       
  • Intensification and variability of the confluence of subtropical and
           subantarctic boundary currents east of New Zealand
    • Authors: D. Fernandez; M. Bowen, L. Carter
      Pages: 1146 - 1160
      Abstract: The confluence of subtropical and subantarctic boundary currents east of New Zealand creates strong fronts. The fronts have clear signatures in sea surface height (SSH) and sea surface temperature (SST) which make the confluence a good region to investigate the variability of the boundary currents of the South Pacific. Analysis of the 20 year time series of the SSH is used to investigate the location and strength of fronts, measured as the gradient in SSH (∇SSH), and the eddy kinetic energy (EKE) and their relationship to local and large‐scale wind forcing. The intensity of the ∇SSH and the EKE have increased at a rate of 0.02 cm km−1 and 32 cm2 s−2 decade−1, respectively. There is a significant correlation (r = 0.7, p 
      PubDate: 2014-02-18T21:07:37.868917-05:
      DOI: 10.1002/2013JC009153
       
  • Pulsed, cross‐shelf export of terrigenous dissolved organic carbon
           to the Gulf of Mexico
    • Authors: Cédric G. Fichot; Steven E. Lohrenz, Ronald Benner
      Pages: 1176 - 1194
      Abstract: The export of terrigenous dissolved organic carbon (tDOC) and other river‐borne material across the continental shelf boundary has important ramifications for biological productivity and the cycling of continentally derived bioelements in the ocean. Recent studies revealed the 275–295 nm spectral slope coefficient of chromophoric dissolved organic matter (CDOM), S275–295, is a reliable tracer for terrigenous dissolved organic carbon (tDOC) in river‐influenced ocean margins. Here an empirical algorithm for the accurate retrieval of S275–295 from ocean color was developed and validated using in situ optical properties collected seasonally in the northern Gulf of Mexico. This study also demonstrated S275–295 is a robust proxy for tDOC concentration in this environment, thereby providing a means to derive surface tDOC concentrations on synoptic scales and in quasi‐real time using remote sensing. The resulting tDOC‐algorithm was implemented using Aqua‐MODIS in a retrospective analysis of surface tDOC concentrations over the northern Gulf of Mexico between July 2002 and June 2013. Large pulses of tDOC were observed in continental‐slope surface waters off the Mississippi River delta, indicating cross‐shelf export of tDOC was sporadic and exhibited considerable interannual variability. Favorable winds following an anomalously high discharge from the Mississippi‐Atchafalaya river system always coincided with a major export event, and in general, cross‐shelf export was enhanced during years of anomalously high discharge. The tDOC‐algorithm will find applicability in the assessment of future climate‐ and human‐induced changes in tDOC export, in biogeochemical models of the continental shelf, and in the validation of high‐resolution coastal models of buoyancy‐driven shelf circulation.
      PubDate: 2014-02-20T17:30:27.495977-05:
      DOI: 10.1002/2013JC009424
       
  • Evolution of an oceanic anticyclone in the lee of Madeira Island: In situ
           and remote sensing survey
    • Authors: Rui M. A. Caldeira; Alexandre Stegner, Xavier Couvelard, Isabel B. Araújo, Pierre Testor, Alvaro Lorenzo
      Pages: 1195 - 1216
      Abstract: Island wakes are areas of a strong eddy activity influencing the availability and transport of organic matter in the ocean which, in turn impact biological productivity. Despite this, eddy formation in the lee of North Atlantic tropical islands is scarcely documented, except for the Canary Islands. Moreover, the occurrence of anticyclones leeward of Madeira has seldom been detected. During the summer of 2011, a multiplatform approach, combining satellite data with in situ measurements, was used to study an anticyclonic eddy generated in the lee of the Madeira Island. The main objective was to confirm recent numerical evidence suggesting that orographically perturbed winds can induce anticyclonic eddies leeward of Madeira, particularly during summer months. The high resolution sampling of the eddy's interior shows a strong downwelling of ≈100 m of the isopycnal layer below the mixed layer, typical of intrathermocline eddies. The 25 km radius of this anticyclonic structure exceeds the local deformation radius by a factor of 2. The vortex Rossby number remained moderate (Ro = 0.26) even if the relative core vorticity reached a finite value (ζ/f = −0.7). The occurrence of strong trade winds (10–15 m s−1) prior to the detection of the first surface eddy signatures (July 2011) concurrent with opposite flowing geostrophic currents, shows that the orographic wind forcing is the main mechanism for generating this mesoscale long‐lived eddy. After leaving the shelter of the island, the eddy traveled northwesterly following a perpendicular net Ekman transport pathway at a speed of 5 km/d, for at least 2 months. An interaction with a cyclonic partner generated in the area helped precipitate the northward trajectory. This study presents the first clear evidence of a wind‐induced mesoscale anticyclone in the lee of Madeira.
      PubDate: 2014-02-20T17:30:40.674241-05:
      DOI: 10.1002/2013JC009493
       
  • Impact of wind waves on the air‐sea fluxes: A coupled model
    • Authors: V. Kudryavtsev; B. Chapron, V. Makin
      Pages: 1217 - 1236
      Abstract: A revised wind‐over‐wave‐coupling model is developed to provide a consistent description of the sea surface drag and heat/moister transfer coefficients, and associated wind velocity and temperature profiles. The spectral distribution of short wind waves in the decimeter to a few millimeters range of wavelengths is introduced based on the wave action balance equation constrained using the Yurovskaya et al. (2013) optical field wave measurements. The model is capable to reproduce fundamental statistical properties of the sea surface, such as the mean square slope and the spectral distribution of breaking crests length. The surface stress accounts for the effect of airflow separation due to wave breaking, which enables a better fit of simulated form drag to observations. The wave breaking controls the overall energy losses for the gravity waves, but also the generation of shorter waves including the parasitic capillaries, thus enhancing the form drag. Breaking wave contribution to the form drag increases rapidly at winds above 15 m/s where it exceeds the nonbreaking wave contribution. The overall impact of wind waves (breaking and nonbreaking) leads to a sheltering of the near‐surface layer where the turbulent mixing is suppressed. Accordingly, the air temperature gradient in this sheltered layer increases to maintain the heat flux constant. The resulting deformation of the air temperature profile tends to lower the roughness scale for temperature compared to its value over the smooth surface.
      PubDate: 2014-02-20T17:30:07.379717-05:
      DOI: 10.1002/2013JC009412
       
  • Decadal variations of Pacific North Equatorial Current bifurcation from
           multiple ocean products
    • Authors: Fangguo Zhai; Qingye Wang, Fujun Wang, Dunxin Hu
      Pages: 1237 - 1256
      Abstract: In this study, we examine the decadal variations of the Pacific North Equatorial Current (NEC) bifurcation latitude (NBL) averaged over upper 100 m and underlying dynamics over the past six decades using 11 ocean products, including seven kinds of ocean reanalyzes based on ocean data assimilation systems, two kinds of numerical simulations without assimilating observations and two kinds of objective analyzes based on in situ observations only. During the period of 1954–2007, the multiproduct mean of decadal NBL anomalies shows maxima around 1965/1966, 1980/1981, 1995/1996, and 2003/2004, and minima around 1958, 1971/1972, 1986/1987, and 2000/2001, respectively. The NBL decadal variations are related to the first Empirical Orthogonal Function mode of decadal anomalies of sea surface height (SSH) in the northwestern tropical Pacific Ocean, which shows spatially coherent variation over the whole region and explains most of the total variance. Further regression and composite analyzes indicate that northerly/southerly NBL corresponds to negative/positive SSH anomalies and cyclonic/anticyclonic gyre anomalies in the northwestern tropical Pacific Ocean. These decadal circulation variations and thus the decadal NBL variations are governed mostly by the first two vertical modes and attribute the most to the first baroclinic mode. The NBL decadal variation is highly positively correlated with the tropical Pacific decadal variability (TPDV) around the zero time lag. With a lead of about half the decadal cycle the NBL displays closer but negative relationship to TPDV in four ocean products, possibly manifesting the dynamical role of the circulation in the northwestern tropical Pacific in the phase‐shifting of TPDV.
      PubDate: 2014-02-20T17:29:57.31405-05:0
      DOI: 10.1002/2013JC009692
       
  • Geostrophic and ageostrophic circulation of a shallow anticyclonic eddy
           off Cape Bojador
    • Authors: Simón Ruiz; Josep L. Pelegrí, Mikhail Emelianov, Ananda Pascual, Evan Mason
      Pages: 1257 - 1270
      Abstract: A shallow mesoscale anticyclonic eddy, observed south of the Canary Islands with satellite altimetry, has been intensively studied with multiparametric sampling. Hydrographic data from a CTD installed on an undulating Nu‐shuttle platform reveal the presence of a mesoscale anticyclonic eddy of ∼125 km diameter. The difference in sea level anomaly (SLA) between the interior and the edge of the eddy, as determined from altimetry, is ∼15 cm, which compares well with the maximum dynamic height differences as inferred using a very shallow reference level (130 m). Further, the associated surface geostrophic velocities, of about 35 cm s−1 in the northeast and southwest edges of the eddy, are in good agreement with direct velocity measurements from the ship. Deep rosette‐CTD casts confirm that the structure is a shallow eddy extending no deeper than 250 m before the fusion with another anticyclone. The SLA‐tendency (temporal rate of change of sea surface height) indicates a clear northwestward migration during the two first weeks of November 2008. Applying an eddy SSH‐based tracker, the eddy's velocity propagation is estimated as 4 km d−1. Use of the QG‐Omega equation diagnoses maximum downward/upward velocities of about ±2 m d−1. The instability of the Canary coastal jet appears to be the mechanism responsible for the generation of the shallow anticyclonic eddy.
      PubDate: 2014-02-22T17:42:01.701033-05:
      DOI: 10.1002/2013JC009169
       
  • Lagrangian simulations and interannual variability of anchovy egg and
           larva dispersal in the Sicily Channel
    • Authors: Luigi Palatella; Francesco Bignami, Federico Falcini, Guglielmo Lacorata, Alessandra S. Lanotte, Rosalia Santoleri
      Pages: 1306 - 1323
      Abstract: The interannual variability in the transport of anchovy eggs and larvae in the Sicily Channel, relatively to the period 1999–2012, is studied by means of numerical simulations of the Mediterranean Forecasting System (MFS) circulation model provided by INGV. Subgrid‐scale dynamics not resolved by the MFS model is parameterized in terms of kinematic fields. The latter affect small‐scale tracer relative dispersion, while leaving the mean large‐scale advection substantially unchanged. A Lagrangian Transport Index (LTI) can be defined to characterize the efficiency of the main currents, e.g., the Atlantic Ionian Stream, in connecting spawning and nursery areas to each other. In our case, this indicator comes from the first arrival time statistics of tracers traveling from a spawning area near Sciacca to a nursery area in proximity of Cape Passero. We observe, on the basis of LTI values, that there are years when the Lagrangian connectivity is very efficient (2004, 2008, 2012) and years when it is weak (2000, 2001, 2003, 2010). Lagrangian indicators like the LTI concur to explain observed fluctuations of larval density and, also, can be employed, more in general, in multivariate models of population dynamics.
      PubDate: 2014-02-24T14:10:11.258957-05:
      DOI: 10.1002/2013JC009384
       
  • Physical modeling of tidal resonance in a submarine canyon
    • Authors: K. E. Souëf; S. E. Allen
      Pages: 1324 - 1343
      Abstract: Current observations in submarine canyons poleward of 30° are usually dominated by the semidiurnal (M2) tidal frequency, which is superinertial at these latitudes. Observations from a submarine canyon at 44°N (the Gully, Nova Scotia) suggest that canyons can be dominated by the subinertial (K1) tidal frequency if length scales are correct for resonance of the K1 frequency. A model of the Gully was constructed in a tank on a rotating table and tidal currents generated to determine factors that influence resonance. Resonance curves were fit to measurements from the laboratory canyon for a range of stratifications, background rotation rates, and forcing amplitudes. Dense water was observed upwelling onto the continental shelf on either side of the laboratory canyon and traveled at least one canyon width along the shelf. Friction values measured in the laboratory were much higher than expected, probably due to upwelled water surging onto the shelf on each tidal cycle, similar to a tidal bore. By scaling observations from the laboratory to the ocean and assuming friction in the ocean is also affected by water traveling onto the shelf, a resonance curve for the ocean was created. Because of the broad resonance curve, the diurnal tide remains strong year round at the Gully, even as stratification at the shelf break changes. Dense water surging onto the shelf on tidal frequencies may affect friction and mixing at other nonresonant canyons.
      PubDate: 2014-02-24T12:16:30.326811-05:
      DOI: 10.1002/2013JC009612
       
  • Wave‐induced light field fluctuations in measured irradiance depth
           profiles: A wavelet analysis
    • Authors: Jianwei Wei; Marlon R. Lewis, Ronnie Dommelen, Christopher J. Zappa, Michael S. Twardowski
      Pages: 1344 - 1364
      Abstract: Rapid variations in the intensities of light are commonly observed in profiles of downwelling plane irradiance in the ocean. These fluctuations are often treated as noise and filtered out. Here an effort is made to extract the pertinent statistics to quantify the light field fluctuations from vertical profiles of irradiance measured under clear skies. The irradiance data are collected in oceanic and coastal waters using a traditional free‐fall downwelling plane irradiance sensor. The irradiance profiles are transformed into time‐frequency domain with a wavelet technique. Two signatures including the dominant frequency (
      PubDate: 2014-02-24T12:16:34.054942-05:
      DOI: 10.1002/2013JC009572
       
  • Pacific‐to‐Indian Ocean connectivity: Tasman leakage,
           Indonesian Throughflow, and the role of ENSO
    • Authors: Erik Sebille; Janet Sprintall, Franziska U. Schwarzkopf, Alex Sen Gupta, Agus Santoso, Matthew H. England, Arne Biastoch, Claus W. Böning
      Pages: 1365 - 1382
      Abstract: The upper ocean circulation of the Pacific and Indian Oceans is connected through both the Indonesian Throughflow north of Australia and the Tasman leakage around its south. The relative importance of these two pathways is examined using virtual Lagrangian particles in a high‐resolution nested ocean model. The unprecedented combination of a long integration time within an eddy‐permitting ocean model simulation allows the first assessment of the interannual variability of these pathways in a realistic setting. The mean Indonesian Throughflow, as diagnosed by the particles, is 14.3 Sv, considerably higher than the diagnosed average Tasman leakage of 4.2 Sv. The time series of Indonesian Throughflow agrees well with the Eulerian transport through the major Indonesian Passages, validating the Lagrangian approach using transport‐tagged particles. While the Indonesian Throughflow is mainly associated with upper ocean pathways, the Tasman leakage is concentrated in the 400–900 m depth range at subtropical latitudes. Over the effective period considered (1968–1994), no apparent relationship is found between the Tasman leakage and Indonesian Throughflow. However, the Indonesian Throughflow transport correlates with ENSO. During strong La Niñas, more water of Southern Hemisphere origin flows through Makassar, Moluccas, Ombai, and Timor Straits, but less through Moluccas Strait. In general, each strait responds differently to ENSO, highlighting the complex nature of the ENSO‐ITF interaction.
      PubDate: 2014-02-24T12:16:53.932257-05:
      DOI: 10.1002/2013JC009525
       
  • Finescale parameterizations of turbulent dissipation
    • Authors: Kurt L. Polzin; Alberto C. Naveira Garabato, Tycho N. Huussen, Bernadette M. Sloyan, Stephanie Waterman
      Pages: 1383 - 1419
      Abstract: This article (1) reviews and clarifies the basic physics underpinning finescale parameterizations of turbulent dissipation due to internal wave breaking and (2) provides advice on the implementation of the parameterizations in a way that is most consistent with the underlying physics, with due consideration given to common instrumental issues. Potential biases in the parameterization results are discussed in light of both (1) and (2), and illustrated with examples in the literature. The value of finescale parameterizations for studies of the large‐scale ocean circulation in the presence of common biases is assessed. We conclude that the parameterizations can contribute significantly to the resolution of large‐scale circulation problems associated with plausible ranges in the rates of turbulent dissipation and diapycnal mixing spanning an order of magnitude or more.
      PubDate: 2014-02-25T11:15:42.801218-05:
      DOI: 10.1002/2013JC008979
       
  • Caspian Sea surface circulation variability inferred from satellite
           altimeter and sea surface temperature
    • Authors: Murat Gunduz
      Pages: 1420 - 1430
      Abstract: Multiyear (1993–2007) satellite‐derived Sea Level Anomaly (SLA), Sea Surface Temperature (SST), and model‐derived mean dynamic topography were used together to analyze climatological and interannual variations of the Caspian Sea surface circulation. Constructed geostrophic currents are in good agreement with the known circulation features of the Caspian Sea, obtained from models and verified by some drifter observations. It is shown that the climatological surface circulation of the Middle Caspian Sea (MCS) is dominated by a basin‐wide cyclonic circulation in winter, switching to an anticyclonic circulation in summer. A dipole pattern (an anticyclonic eddy near 39.5°N and a cyclonic one near 38°N) exist in the Southern Caspian Sea (SCS) (stronger from September to January). Evaluation of the multiyear geostrophic velocities shows that the Caspian Sea surface circulation exhibits strong interannual variations, with the location and intensity of the circulation patterns changing from one year to another.
      PubDate: 2014-02-25T11:35:22.418025-05:
      DOI: 10.1002/2013JC009558
       
  • A mechanism for the latitudinal dependence of peak‐spectrum sea
           surface height variability
    • Authors: Xiaopei Lin; Yuqi Yin, Jiayan Yang
      Pages: 1431 - 1444
      Abstract: Previous studies have shown that the power spectrum of satellite‐observed sea surface height (SSH) variability peaks at a certain frequency (or a wave number) band at a given latitude. Lin et al. (2008) attributed this latitudinal dependence to the critical frequency of the first baroclinic mode Rossby waves in the tropical and subtropical oceans. Their study was based on the linear Rossby wave theory and focused on SSH variability in the tropical and subtropical oceans since the altimetry data do not adequately resolve lengths of baroclinic Rossby waves at and near the critical frequency in high latitudes. In this study, we expand their analysis to high‐latitude oceanic basins and to include nonlinear eddy effects, by using a linear wave model and a high‐resolution model output from the OGCM for the Earth Simulator (OFES). It is found that the linear wave mechanism by and large remains valid in the tropical and subtropical oceans. In higher latitudes as well as in some regions in the western tropical and subtropical oceans, other mechanisms, like nonlinear eddy, play more important role in determining the SSH variability.
      PubDate: 2014-02-25T11:44:38.196257-05:
      DOI: 10.1002/2013JC009642
       
  • Process modeling studies of physical mechanisms of the formation of an
           anticyclonic eddy in the central Red Sea
    • Authors: Changsheng Chen; Ruixiang Li, Larry Pratt, Richard Limeburner, Robert C. Beardsley, Amy Bower, Houshuo Jiang, Yasser Abualnaja, Qichun Xu, Huichan Lin, Xuehai Liu, Jian Lan, Taewan Kim
      Pages: 1445 - 1464
      Abstract: Surface drifters released in the central Red Sea during April 2010 detected a well‐defined anticyclonic eddy around 23°N. This eddy was ∼45–60 km in radius, with a swirl speed up to ∼0.5 m/s. The eddy feature was also evident in monthly averaged sea surface height fields and in current profiles measured on a cross‐isobath, shipboard CTD/ADCP survey around that region. The unstructured‐grid, Finite‐Volume Community Ocean Model (FVCOM) was configured for the Red Sea and process studies were conducted to establish the conditions necessary for the eddy to form and to establish its robustness. The model was capable of reproducing the observed anticyclonic eddy with the same location and size. Diagnosis of model results suggests that the eddy can be formed in a Red Sea that is subject to seasonally varying buoyancy forcing, with no wind, but that its location and structure are significantly altered by wind forcing, initial distribution of water stratification and southward coastal flow from the upstream area. Momentum analysis indicates that the flow field of the eddy was in geostrophic balance, with the baroclinic pressure gradient forcing about the same order of magnitude as the surface pressure gradient forcing.
      PubDate: 2014-02-25T11:05:25.043796-05:
      DOI: 10.1002/2013JC009351
       
  • Deep‐water dynamics and boundary mixing in a nontidal stratified
           basin: A modeling study of the Baltic Sea
    • Authors: Peter L. Holtermann; Hans Burchard, Ulf Gräwe, Knut Klingbeil, Lars Umlauf
      Pages: 1465 - 1487
      Abstract: Recent results from a tracer release experiment have shown that, similar to many lakes and ocean basins, deep‐water mixing in the Baltic Sea is largely determined by mixing processes occurring in the energetic near‐bottom region. Due to the complexity and small vertical extent of this region, however, previous modeling studies of the Baltic Sea have so far not been able to provide a numerically and physically sound representation of boundary mixing. Here we discuss first results from a nested high‐resolution simulation of the central Baltic Sea that aims at a realistic description of the turbulent bottom boundary layer with the help of new numerical techniques (adaptive coordinates) and state‐of‐the‐art turbulence modeling. Using a comprehensive data set from the Baltic Sea Tracer Release Experiment, we show that the model is able to reproduce the key dynamical processes (near‐inertial waves, topographic waves, and a rim current) with excellent accuracy. Boundary mixing triggered by these processes was found to result in simulated basin‐scale mixing rates in close agreement with observations, including a seasonal variability that has been emphasized in previous studies. These results may be relevant also for the description of mixing in large lakes and other stratified basins.
      PubDate: 2014-02-25T11:33:37.87533-05:0
      DOI: 10.1002/2013JC009483
       
  • Usable solar radiation and its attenuation in the upper water column
    • Authors: Zhongping Lee; Shaoling Shang, Keping Du, Jianwei Wei, Robert Arnone
      Pages: 1488 - 1497
      Abstract: A new radiometric term named as usable solar radiation (USR) is defined to represent the spectrally integrated solar irradiance in the spectral window of 400–560 nm. Through numerical simulations of optically deep waters covering a wide range of optical properties, it is found that the diffuse attenuation coefficient of downwelling USR, Kd(USR), is nearly a constant vertically for almost all oceanic waters (chlorophyll concentration under ∼3 mg m−3). This feature is quite contrary to the diffuse attenuation coefficient of the photosynthetic available radiation, K(PAR), which varies significantly from surface to deeper depths for oceanic waters. It is also found that the ratio of the photosynthetic utilizable radiation (PUR) to the product of USR and phytoplankton absorption coefficient at 440 nm approximates a constant for most oceanic waters. These results support the use of a single Kd(USR) for each water and each sun angle for accurate estimation of USR propagation, and suggest an efficient approach to estimate PUR(z) in the upper water column. These results further indicate that it is necessary and valuable for the generation of USR and Kd(USR) products from satellite ocean color measurements, which can be used to facilitate the studies of heat transfer and photosynthesis in the global oceans.
      PubDate: 2014-02-26T09:37:28.026073-05:
      DOI: 10.1002/2013JC009507
       
  • Frontogenesis and frontolysis of the subpolar front in the surface mixed
           layer of the Japan Sea
    • Authors: Ning Zhao; Atsuyoshi Manda, Zhen Han
      Pages: 1498 - 1509
      Abstract: The frontogenesis and frontolysis processes of the subpolar front (SPF) in the surface mixed layer of the Japan Sea are investigated using state‐of‐the‐art oceanic reanalysis data. The SPF experiences a 9 month weakening period from January to September, which shifts to a strengthening period in October. Our analysis shows that horizontal advection consistently contributes to the intensification of the SPF. After September, as the weakening effect of surface heat flux diminishes, horizontal advection becomes the dominant factor that contributes to changes in the SPF strength. Thus, the SPF enters a 3 month strengthening period. The geostrophic component of horizontal advection provides the most important contribution to strengthening the SPF, acting to intensify the SPF year‐round. Ekman advection also promotes SPF strengthening with a smaller but still important contribution. During the weakening period, SPF strength is largely controlled by heat flux. The heat flux, especially the shortwave radiation component, is the primary cause of the surface front disappearance in the summer.
      PubDate: 2014-02-28T14:35:20.55761-05:0
      DOI: 10.1002/2013JC009419
       
  • Comment on “Wave‐turbulence interaction and its induced mixing
           in the upper ocean” by Huang and Qiao
    • Authors: Lakshmi Kantha; Hitoshi Tamura, Yasumasa Miyazawa
      Pages: 1510 - 1515
      PubDate: 2014-02-27T11:56:36.803219-05:
      DOI: 10.1002/2013JC009318
       
  • Role of meso‐scale eddies on the variability of biogenic flux in the
           northern and central Bay of Bengal
    • Authors: P. J. Vidya; S. Prasanna Kumar
      Pages: n/a - n/a
      Abstract: Mesoscale cyclonic eddies (cold‐core) are though known to enhance the phytoplankton biomass in the Bay of Bengal, their contribution to the carbon export to the deep ocean are yet to be quantified. Using biogenic flux data obtained from the sediment traps, located at 17°27'N, 89°13'E (northern Bay of Bengal trap: NBBT) and 13°07'N, 84°24'E (central Bay of Bengal trap: CBBT), we explored the variability of biogenic flux in response to cyclonic eddies. Temporal variation of the biogenic flux at NBBT (1994‐1998) and CBBT (1993‐1996) showed four distinct peaks with no well‐defined seasonal pattern. The inverse relationship between the high flux events and sea surface height anomaly (SSHA) along with the dominant periodicity of 10‐15 weeks from the Chi‐square analysis of SSHA confirmed the role of eddies in the observed higher biogenic fluxes. During the eddy events, enhanced opal flux suggested eddy‐driven new production, while lower carbonate to opal ratio along with high organic carbon indicated large export via diatoms. Finally, we show that 42% of the total organic carbon collected at mid‐depth (˜1000m) in the Bay of Bengal is contributed by eddy‐driven processes via diatom bloom making it a regional sink for CO2.
      PubDate: 2013-10-19T02:59:08.704107-05:
      DOI: 10.1002/2013JC009060
       
 
 
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