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Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 24, SJR: 2.439, h-index: 91)
Geophysical Research Letters     Full-text available via subscription   (Followers: 96, SJR: 3.323, h-index: 185)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 12, SJR: 3.22, h-index: 136)
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J. of Geophysical Research : Earth Surface     Partially Free   (Followers: 47)
J. of Geophysical Research : Oceans     Partially Free   (Followers: 42)
J. of Geophysical Research : Planets     Full-text available via subscription   (Followers: 100)
J. of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 42)
J. of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 115)
Paleoceanography     Full-text available via subscription   (Followers: 6, SJR: 3.067, h-index: 100)
Radio Science     Full-text available via subscription   (Followers: 36, SJR: 1.072, h-index: 59)
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Journal Cover Journal of Geophysical Research : Oceans
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   Published by AGU Homepage  [17 journals]
  • Coherent motions and time scales that control heat and mass transfer at
           wind-swept water surfaces
    • Authors: D. E. Turney
      Abstract: Forecast of the heat and chemical budgets of lakes, rivers and oceans requires improved predictive understanding of air-water interfacial transfer coefficients. Here we present laboratory observations of the coherent motions that occupy the air-water interface at wind speeds (U10) 1.1 to 8.9 m/s. Spatio-temporal near-surface velocity data and interfacial renewal data are made available by a novel flow tracer method. The relative activity, velocity scales and time scales of the various coherent interfacial motions are measured, namely for Langmuir circulations, streamwise streaks, non-breaking wind waves, parasitic capillary waves, non-turbulent breaking wind waves, and turbulence-generating breaking wind waves. Breaking waves exhibit a sudden jump in streamwise interfacial velocity wherein the velocity jumps up to exceed the wave celerity and destroys nearby parasitic capillary waves. Four distinct hydrodynamic regimes are found to exist between U10 = 0 and 8.9 m/s, each with a unique population balance of the various coherent motions. The velocity scales, time scales and population balance of the different coherent motions are input to a first-principles gas transfer model to explain the waterside transfer coefficient (kw) as well as experimental patterns of temperature and gas concentration. The model mixes concepts from surface renewal and divergence theories, and requires surface divergence strength (β), the Lagrangian residence time inside the upwelling zone (tLu), and the total lifetime of new interface before it is downwelled (tLT). The model's output agrees with time-averaged measurements kw, patterns of temperature in infrared photographs, and spatial patterns of gas concentration and kw from direct numerical simulations. Several non-dimensional parameters, e.g. βtLu and τstLT where τs is the interfacial shear rate, determine the effectiveness of a particular type of coherent motion for affecting kw. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-19T10:26:45.800745-05:
      DOI: 10.1002/2016JC012139
  • Seasonal patterns of SST diurnal variation over the Tropical Warm Pool
    • Authors: Haifeng Zhang; Helen Beggs, Xiao Hua Wang, Andrew E. Kiss, Christopher Griffin
      Abstract: Five-year (2010 through 2014) Advanced Very High Resolution Radiometer (AVHRR) sea surface temperature (SST) data produced by the Australian Bureau of Meteorology have been validated against drifting buoy data and then used to study the seasonal patterns of the SST diurnal variation (DV) events over the Tropical Warm Pool region (TWP, 25°S–15°N, 90°E–170°E). The in-situ validation results illustrate the overall good quality of the AVHRR SST data set, although an average 0.19 K underestimation of the daytime measurements has been observed. The night-time observations are in good agreement with in-situ buoys with an average bias of 0.03 K and a 0.30 K standard deviation of the biases. This SST data set is then used to characterise the SST DV seasonal patterns, together with wind speeds, daily maximum solar shortwave insolation (SSImax) and latent heat flux (LHF). A double-peak seasonal pattern of SST DV is observed over the study region: the strongest DVs are found in March and October and the weakest in June. Sensitivity tests of DV to wind, SSImax, and LHF are conducted. The results indicate: (1) different morning and early afternoon winds (7 am to 2 pm local time, LT) affect DV by as much as 0.73 K when the half-daily (defined as 2 am to 2 pm LT in this study) average winds are fixed between 2-3 ms−1; (2) SSImax levels regulate DV less significantly (< 0.68 K) under fixed winds; and (3) LHF effects on DV are relatively weak (< 0.35 K). This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-19T10:26:34.038591-05:
      DOI: 10.1002/2016JC012210
  • Structure and dynamics of a subglacial discharge plume in a Greenlandic
    • Authors: Kenneth D. Mankoff; Fiammetta Straneo, Claudia Cenedese, Sarah B. Das, Clark G. Richards, Hanumant Singh
      Abstract: Discharge of surface-derived meltwater at the submerged base of Greenland's marine-terminating glaciers creates subglacial discharge plumes that rise along the glacier/ocean interface. These plumes impact submarine melting, calving and fjord circulation. Observations of plume properties and dynamics are challenging due to their proximity to the calving edge of glaciers. Therefore to date information on these plumes has been largely derived from models. Here we present temperature, salinity, and velocity data collected in a plume that surfaced at the edge of Saqqarliup Sermia, a mid-sized Greenlandic glacier. The plume is associated with a narrow core of rising waters approximately 20 m in diameter at the ice edge that spreads to a 200 m by 300 m plume pool as it reaches the surface, before descending to its equilibrium depth. Volume flux estimates indicate that the plume is primarily driven by subglacial discharge and that this has been diluted in a ratio of 1:10 by the time the plume reaches the surface. While highly uncertain, meltwater fluxes are likely two orders of magnitude smaller than the subglacial discharge flux. The overall plume characteristics agree with those predicted by theoretical plume models for a convection driven plume with limited influence from submarine melting. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-19T10:20:27.03883-05:0
      DOI: 10.1002/2016JC011764
  • Air pressure effects on sea level changes during the Twentieth Century
    • Authors: Christopher G. Piecuch; Philip R. Thompson, Kathleen A. Donohue
      Abstract: Interpretation of tide gauge data in terms sea level (η) and ocean dynamics requires estimates of air pressure (pa) to determine the ocean's isostatic response—the inverted barometer effect (ηib). Three gridded pa products (HadSLP2, NOAA-20CRv2, ERA-20C) are used alongside meteorological station pa and tide gauge η records to evaluate the contribution of ηib to η changes over the Twentieth Century. Agreement between gridded products is better during more recent periods and over regions with good historical data coverage, whereas it is worse for earlier time periods or in ocean areas with poor observational data coverage. Comparison against station data reveals the presence of systematic errors in the gridded products, for example, such that uncertainties estimated through differencing the gridded products underestimate the true errors by roughly $40\%$on interannual and decadal time scales. Notwithstanding such correlated errors, gridded products are still {useful} for interpretation of tide gauge data. Removing gridded estimates of ηib from η records reduces spatial variance in centennial trends across tide gauges by 10–30%, formal errors in centennial trends from individual gauges by ∼ 5%, and the temporal variance in detrended records by 10–15% on average (depending on choice of gridded product). Results here advocate for making the ηib correction to tide gauge records in studies of ocean circulation and global η over long, multidecadal and centennial time scales using an ensemble mean taken across several gridded ηib products. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-18T02:50:53.148746-05:
      DOI: 10.1002/2016JC012131
  • Mapping error in Southern Ocean transport computed from satellite
           altimetry and Argo
    • Authors: Michael Kosempa; Don P. Chambers
      Abstract: In an effort to better estimate transport dynamics in response to wind forcing (primarily the Southern Annual Mode), this study quantifies the uncertainty in mapping zonal geostrophic transport of the Antarctic Circumpolar Current from sparse temperature, salinity and sea surface height observations. To do this, we sampled an ocean state estimate at the locations of both Argo floats and the Jason-1 altimeter groundtrack. These sampled values were then optimally interpolated to create SSH and temperature/salinity grids with 1° resolution. The temperature, salinity and SSH grids were then combined to compute the zonal geostrophic transport and compared to that estimated from the full state estimate. There are significant correlations between the baroclinic and barotropic error contributions to the total transport error. The increase in Argo floats in the Southern Ocean is effective in reducing mapping error. However, that error improvement is not uniform. By analyzing systematic errors in transport time series, we find the transects that are most appropriate for analyzing the dynamics of ACC transport using Argo and altimetric gridded fields. Based on our analysis, we conclude region south of Tasmania is most appropriate, with lowest uncertainty. Using real-world data, we calculated zonal transport variability at a transect south of Tasmania. There is an insignificant trend (0.3 ± 0.4 Sv yr−1, 90% confidence) but significant low-frequency variability correlated with the Southern Annular Mode (0.53, p 
      PubDate: 2016-10-18T02:50:46.211771-05:
      DOI: 10.1002/2016JC011956
  • Projecting nuisance flooding in a warming climate using generalized linear
           models and Gaussian processes
    • Authors: Alexander Vandenberg-Rodes; Hamed R. Moftakhari, Amir AghaKouchak, Babak Shahbaba, Brett F. Sanders, Richard A. Matthew
      Abstract: Nuisance flooding corresponds to minor and frequent flood events that have significant socio-economic and public health impacts on coastal communities. Yearly-averaged local mean sea level can be used as proxy to statistically predict the impacts of sea level rise (SLR) on the frequency of nuisance floods (NF). In this study, we use Generalized Linear Models (GLM) and Gaussian Process (GP) models combined to (i) estimate the frequency of NF associated with the change in mean sea level, and (ii) quantify the associated uncertainties via a novel and statistically robust approach. We calibrate our models to the water level data from eighteen tide gauges along the coasts of United States, and after validation, we estimate the frequency of NF associated with the SLR projections in year 2030 (under RCPs 2.6 and 8.5), along with their 90% bands, at each gauge. The historical NF-SLR data is very noisy, and shows large changes in variability (heteroscedasticity) with SLR. Prior models in the literature do not properly account for the observed heteroscedasticity, and thus their projected uncertainties are highly suspect. Among the models used in this study the Negative Binomial Distribution GLM with GP best characterizes the uncertainties associated with NF estimates; on validation data ≈ 93% of the points fall within the 90% credible limit, showing our approach to be a robust model for uncertainty quantification. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-18T02:50:23.747946-05:
      DOI: 10.1002/2016JC012084
  • Processes of multibathyal aragonite undersaturation in the Arctic Ocean
    • Authors: J.G. Wynn; L.L. Robbins, L.G. Anderson
      Abstract: During three years of study (2010-2012), the western Arctic Ocean was found to have unique aragonite saturation profiles with up to three distinct aragonite undersaturation zones. This complexity is produced as inflow of Atlantic- and Pacific-derived water masses mix with Arctic-derived waters, which are further modified by physiochemical and biological processes. The shallowest aragonite undersaturation zone, from the surface to ∼ 30 m depth is characterized by relatively low alkalinity and other dissolved ions. Besides local influence of biological processes on aragonite undersaturation of shallow coastal waters, the nature of this zone is consistent with dilution by sea-ice melt and invasion of anthropogenic CO2 from the atmosphere. A second undersaturated zone at ∼ 90-220 m depth (salinity ∼31.8–35.4) occurs within the Arctic Halocline and is characterized by elevated pCO2 and nutrients. The nature of this horizon is consistent with remineralization of organic matter on shallow continental shelves bordering the Canada Basin and the input of the nutrients and CO2 entrained by currents from the Pacific Inlet. Finally, the deepest aragonite undersaturation zone is at greater than 2000 m depth and is controlled by similar processes as deep aragonite saturation horizons in the Atlantic and Pacific Oceans. The comparatively shallow depth of this deepest aragonite saturation horizon in the Arctic is maintained by relatively low temperatures, and stable chemical composition. Understanding the mechanisms controlling the distribution of these aragonite undersaturation zones, and the timescales over which they operate will be crucial to refine predictive models. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-13T03:46:18.997671-05:
      DOI: 10.1002/2016JC011696
  • Gulf Stream variability and a triggering mechanism of its large meander in
           the South Atlantic Bight
    • Authors: Xiangming Zeng; Ruoying He
      Abstract: The Gulf Stream (GS) variability has an important impact on coastal circulation, shelf ecosystem, and regional weather and climate systems. Here we focus on the variability of the GS south of Cape Hatteras in the South Atlantic Bight (SAB). Statistical analysis on the 21-year satellite altimetry data reveals that the GS path in the SAB has two patterns: weakly and strongly deflected. The strongly deflected pattern is more likely to occur in winter. Over the last two decades, the largest GS offshore meander occurred in November 2009-April 2010. Realistic ocean hindcast simulation and adjoint sensitivity analysis are used to investigate the triggering mechanisms for this extreme event. Our analyses show that a net increase of relative vorticity near the Charleston Bump was generated by strong interaction between increased GS velocity and local bathymetry, pushing the GS further offshore by virtue of conserving the potential vorticity. Quantitative vorticity analysis confirms this finding. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-13T03:46:11.526959-05:
      DOI: 10.1002/2016JC012077
  • Impact of an upgraded model in the NCEP Global Ocean Data Assimilation
           System: The tropical Indian Ocean
    • Authors: Hasibur Rahaman; David Behringer, Stephen G. Penny, M Ravichandran
      Abstract: The National Centers for Environmental Prediction (NCEP) and the Indian National Centre for Ocean Information Services (INCOIS) produces global ocean analysis based on the Global Ocean Data Assimilation System (GODAS). This study shows how upgrades to the forward model simulations from MOM4p0d to MOM4p1 impact ocean analyses over the tropical Indian Ocean in GODAS. Three experiments were performed with same atmospheric forcing fields:(i) using MOM4p0d (GODAS_p0), (ii) using MOM4p1 (GODAS_p1), both using observed temperature and synthetic salinity, and (iii) using MOM4p1 (GODAS_p1S) assimilating both observed temperature and observed salinity. Validation with independent observations show significant improvement of sub-surface temperature and salinity in the new analysis using MOM4p1 versus MOM4p0d. There is also improvement in the upper ocean current of the equatorial Indian Ocean. The impact of observed salinity on the upper ocean surface current is marginal, but there is significant improvement in the sub-surface current. The seasonal and inter-annual variability of the Wyrtki jet and the equatorial undercurrent is improved in GODAS_p1 versus GODAS_p0. All analyses reproduced the Indian Ocean dipole, with the GODAS_p1S simulated sea surface temperature (SST) the most accurate. The temperature inversion over the north Bay of Bengal (BoB) is reproduced only in GODAS_p1S. The mean sea level over BoB and equatorial Indian Ocean improved in GODAS_p1S as compared with AVISO observation. The combined model upgrade and assimilation of observed salinity led to reduced root mean square deviation and higher correlation coefficient values in the sea level anomaly (SLA) when compared with satellite observations. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-13T03:45:59.559059-05:
      DOI: 10.1002/2016JC012056
  • Observations of open-ocean deep convection in the northwestern
           Mediterranean Sea: Seasonal and interannual variability of mixing and deep
           water masses for the 2007–2013 period
    • Authors: L. Houpert; X. Durrieu de Madron, P. Testor, A. Bosse, F. D'Ortenzio, M.N. Bouin, D. Dausse, H. Le Goff, S. Kunesch, M. Labaste, L. Coppola, L. Mortier, P. Raimbault
      Abstract: We present here a unique oceanographic and meteorological dataset focus on the deep convection processes. Our results are essentially based on in situ data (mooring, research vessel, glider, and profiling float) collected from a multi-platform and integrated monitoring system (MOOSE: Mediterranean Ocean Observing System on Environment), which monitored continuously the northwestern Mediterranean Sea since 2007, and in particular high-frequency potential temperature, salinity and current measurements from the mooring LION located within the convection region.From 2009 to 2013, the mixed layer depth reaches the seabed, at a depth of 2330m, in February. Then, the violent vertical mixing of the whole water column lasts between 9 and 12 days setting up the characteristics of the newly-formed deep water. Each deep convection winter formed a new warmer and saltier '“vintage” of deep water. These sudden inputs of salt and heat in the deep ocean are responsible for trends in salinity (3.3+/-0.2 *10−3/yr) and potential temperature (3.2+/-0.5 *10−3°C/yr) observed from 2009 to 2013 for the 600-2300m layer.For the first time, the overlapping of the 3 “phases” of deep convection can be observed with secondary vertical mixing events (2-4 days) after the beginning of the restratification phase, and the restratification/spreading phase still active at the beginning of the following deep convection event. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-13T03:43:19.995887-05:
      DOI: 10.1002/2016JC011857
  • Dissipation of wind waves by pancake and frazil ice in the autumn Beaufort
    • Authors: W. Erick Rogers; Jim Thomson, Hayley H. Shen, Martin J. Doble, Peter Wadhams, Sukun Cheng
      Abstract: A model for wind-generated surface gravity waves, WAVEWATCH III®, is used to analyze and interpret buoy measurements of wave spectra. The model is applied to a hindcast of a wave event in sea ice in the western Arctic, October 11-14 2015, for which extensive buoy and ship-borne measurements were made during a research cruise. The model, which uses a viscoelastic parameterization to represent the impact of sea ice on the waves, is found to have good skill—after calibration of the effective viscosity—for prediction of total energy, but over-predicts dissipation of high frequency energy by the sea ice. This shortcoming motivates detailed analysis of the apparent dissipation rate. A new inversion method is applied to yield, for each buoy spectrum, the inferred dissipation rate as a function of wave frequency. For 102 of the measured wave spectra, visual observations of the sea ice were available from buoy-mounted cameras, and ice categories (primarily for varying forms of pancake and frazil ice) are assigned to each based on the photographs. When comparing the inversion-derived dissipation profiles against the independently derived ice categories, there is remarkable correspondence, with clear sorting of dissipation profiles into groups of similar ice type. These profiles are largely monotonic: they do not exhibit the “roll-over” that has been found at high frequencies in some previous observational studies. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-13T03:35:53.941718-05:
      DOI: 10.1002/2016JC012251
  • Chromophoric and fluorescent dissolved organic matter in and above the
           oxygen minimum zone off Peru
    • Authors: A.N. Loginova; S. Thomsen, A. Engel
      Abstract: As a result of nutrient upwelling, the Peruvian coastal system is one of the most productive regions in the ocean. Sluggish ventilation of intermediate waters, characteristic for the Eastern Tropical South Pacific (ETSP) and microbial degradation of a high organic matter load promotes deoxygenation at depth. Dissolved organic matter (DOM) plays a key role in microbial respiration and carbon cycling, but little is known on DOM distribution and cycling in the ETSP. DOM optical properties give important insights on DOM sources, structure and biogeochemical reactivity. Here, we present data and a conceptual view on distribution and cycling of chromophoric (CDOM) and fluorescent (FDOM) DOM in and above the oxygen minimum zone (OMZ) off Peru. Five fluorescent components were identified during PARAFAC analysis. Highest intensities of CDOM and of the amino acid-like fluorescent component (C3) occurred above the OMZ and coincided with maximum chl a concentrations, suggesting phytoplankton productivity as major source. High intensities of a marine humic-like fluorescent component (C1), observed in subsurface waters, indicated in situ microbial reworking of DOM. FDOM release from inner shelf sediment was determined by seawater analysis and continuous glider sensor measurement and included a humic-like component (C2) with a signature typical for terrestrially derived humic acids. Upwelling supplied humic-like substances to the euphotic zone. Photo-reactions were likely involved in the production of a humic-like fluorescent component (C5). Our data show that variable biological and physical processes need to be considered for understanding DOM cycling in a highly dynamic coastal upwelling system like the ETSP off Peru. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-13T03:30:53.767001-05:
      DOI: 10.1002/2016JC011906
  • Decomposition of thermal and dynamic changes in the South China Sea
           induced by boundary forcing and surface fluxes during 1970‒2000
    • Authors: Jun Wei; Paola Malanotte-Rizzoli, Ming-Ting Li, Hao Wang
      Abstract: Based on a fully-coupled, high-resolution regional climate model, this study analyzed three-dimensional temperature and momentum changes in the South China Sea (SCS) from 1970 to 2000, during which period the climate shifts from a decadal La Niña-like condition (before 1976/77) to a decadal El Niño-like condition afterward. With a set of partially-coupled experiments, sea surface temperature (SST) and kinetic energy (KE) changes during this period are first decomposed into two components: those induced by lateral boundary forcing and those induced by atmospheric surface fluxes. The results showed that the total SST and KE changes show an increasing trend from 1970 to 2000. The two decomposed components together determined 96% and 89% of the SST and KE changes respectively, implying their dominant roles on the SCS's surface variability. Spatially, a sandwich pattern of air-sea forcing relationship is revealed in the SCS basin. The increased KE, represented by a cyclonic flow anomaly in the northern SCS, was induced by enhanced cold water intrusion from Pacific into the SCS via the Luzon Strait (boundary forcing). This cold-water inflow, however, resulted in SST cooling along the northern shelf of the SCS. The maximal SST warming occurred in the central SCS and was attributed to the wind-evaporation-SST (WES) positive feedback (surface forcing), in which a southwestward wind anomaly is initialized by SST gradients between the northern and southern SCS. This wind anomaly decelerates the southwestly summer monsoons and in turn increases the SST gradients. Over the shallow Sunda shelf, which is far from the Luzon Strait, the SST/KE variability appeared to be determined primarily by local air–sea interactions. Furthermore, analyses on subsurface components indicated that the subsurface temperature changes are primarily induced by internal ocean mixing, which becomes significantly important below the thermocline. The enhanced subsurface flow is driven by the Luzon Strait inflow as well, and exits the SCS via the Mindoro-Sibutu passage. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-07T10:30:51.901249-05:
      DOI: 10.1002/2016JC012078
  • Interannual and interdecadal variability of the North Equatorial
           Countercurrent in the Western Pacific
    • Authors: Xiao Chen; Bo Qiu, Yan Du, Shuiming Chen, Yiquan Qi
      Abstract: Interannual and longer timescale variations of the North Equatorial Countercurrent (NECC) in the western Pacific are investigated using the multi-decade (1960-2014) hindcast by the Ocean general circulation model for the Earth Simulator (OFES). The OFES-simulated sea level and upper ocean circulation changes show favorable comparisons with available tide gauge data and repeat hydrographic surveys along the 137ºE meridian. An empirical orthogonal function (EOF) analysis reveals that the low-frequency NECC variability is dominated by two distinct modes. The first mode fluctuates interannually and shows strengthening and southward migration of the NECC concurrent with the development of El Niño events. Unlike the extra-tropical western Pacific Ocean circulation variability controlled by wind forcing west of the dateline, the interannual NECC variations are forced by equatorial wind forcing cumulative across the entire Pacific basin. The second mode of the NECC variability has a inter-decadal timescale and is characterized by NECC's progressive weakening in strength, migrating poleward, and broadening in width over the past 50 years. These long-term changes in NECC are caused by the corresponding changes in the trade wind system that weakened and expanded poleward in the past half a century across the Pacific basin. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-06T10:15:26.106931-05:
      DOI: 10.1002/2016JC012190
  • Long-term decrease in phosphate concentrations in the surface layer of the
           southern Japan Sea
    • Authors: Taketoshi Kodama; Yosuke Igeta, Mizuki Kuga, Shoko Abe
      Abstract: To identify possible causes for the long-term trends in nutrient concentrations in the southern Japan Sea (JS), we studied nutrient concentrations that were obtained by the Japan Meteorological Agency. Our evaluation shows that phosphate concentrations declined in the surface layers in summer (0–20 m and 21–50 m depth) and winter (0–20 m, 21–50 m, and 51–100 m depth) over the last 40 years, while no significant linear trend was observed for nitrate concentrations. The declining trend in the phosphate concentration was quantified as 1.8–3.3 nM year−1. The increase in atmospheric nutrient deposition to the JS could not explain the decline in phosphate concentration. In addition, the mixed layer depth during winter did not demonstrate any significant trend, and an increase in phosphate concentrations was not observed in any layers; therefore, the decrease in nutrient supply from deep JS water was not considered a major possible cause for the decline in the phosphate concentration. In contrast, the phosphate concentration in the surface of the southern JS during winter showed a significant positive correlation with the concentration in the 21–50 m depth layer of the saline East China Sea (ECS) water in the preceding summer, and the surface water of the southern JS was almost entirely replaced by water originating from the ECS during May–October. Therefore, it is concluded that the declining trend in the phosphate concentrations in the southern JS is caused by horizontal advection of ECS water. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-05T10:26:00.060089-05:
      DOI: 10.1002/2016JC012168
  • Winter ocean-ice interactions under thin sea ice observed by IAOOS
           platforms during N-ICE2015: Salty surface mixed layer and active basal
    • Authors: Zoé Koenig; Christine Provost, Nicolas Villacieros-Robineau, Nathalie Sennéchael, Amélie Meyer
      Abstract: IAOOS (Ice Atmosphere Arctic Ocean Observing System) platforms, measuring physical parameters at the atmosphere-snow-ice-ocean interface deployed as part of the N-ICE2015 campaign, provide new insights on winter conditions North of Svalbard. The three regions crossed during the drifts, the Nansen Basin, the Sofia Deep and the Svalbard northern continental slope featured distinct hydrographic properties and ice-ocean exchanges. In the Nansen Basin the quiescent warm layer was capped by a stepped halocline (60 and 110 m) and a deep thermocline (110 m). Ice was forming and the winter mixed layer salinity was larger by ∼0.1 g/kg than previously observed. Over the Svalbard continental slope, the Atlantic Water (AW) was very shallow (20 m from the surface) and extended offshore from the 500 m isobath by a distance of about 70 km, sank along the slope (40 m from the surface) and probably shed eddies into the Sofia Deep. In the Sofia Deep, relatively warm waters of Atlantic origin extended from 90 m downward. Resulting from different pathways, these waters had a wide range of hydrographic characteristics. Sea-ice melt was widespread over the Svalbard continental slope and ocean-to-ice heat fluxes reached values of 400 Wm−2 (mean of ∼150 Wm−2 over the continental slope). Sea-ice melt events were associated with near 12-hour fluctuations in the mixed-layer temperature and salinity corresponding to the periodicity of tides and near-inertial waves potentially generated by winter storms, large barotropic tides over steep topography and/or geostrophic adjustments. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-05T10:25:57.729296-05:
      DOI: 10.1002/2016JC012195
  • Time series measurements of transient tracers and tracer derived transport
           in the deep western boundary current between the Labrador Sea and the
           subtropical Atlantic Ocean at Line W
    • Authors: John N. Smith; William M. Smethie, Igor Yashayev, Ruth Curry, Kumiko Azetsu-Scott
      Abstract: Time series measurements of the nuclear fuel reprocessing tracer, 129I and the gas ventilation tracer, CFC-11 were undertaken on the AR7W section in the Labrador Sea (1997-2014) and on Line W (2004-2014), located over the US continental slope off Cape Cod, to determine advection and mixing time scales for the transport of Denmark Strait Overflow Water (DSOW) within the Deep Western Boundary Current (DWBC). Tracer measurements were also conducted in 2010 over the continental rise southeast of Bermuda to intercept the equator-ward flow of DSOW by interior pathways. The Labrador Sea tracer and hydrographic time series data were used as input functions in a boundary current model that employs transit time distributions to simulate the effects of mixing and advection on downstream tracer distributions. Model simulations of tracer levels in the boundary current core and adjacent interior (shoulder) region with which mixing occurs were compared with the Line W time series measurements to determine boundary current model parameters. These results indicate that DSOW is transported from the Labrador Sea to Line W via the DWBC on a time scale of 5-6 y corresponding to a mean flow velocity of 2.7 cm/s while mixing between the core and interior regions occurs with a time constant of 2.6 y. A tracer section over the southern flank of the Bermuda rise indicates that the flow of DSOW that separated from the DWBC had undergone transport through interior pathways on a time scale of 9 y with a mixing time constant of 4 y. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-05T10:25:55.624726-05:
      DOI: 10.1002/2016JC011759
  • CMIP5 earth system models with biogeochemistry: An assessment for the
           southwest Pacific Ocean
    • Authors: Graham J. Rickard; Erik Behrens, Stephen M. Chiswell
      Abstract: An assessment is made of the ability of CMIP5 models to represent the seasonal biogeochemical cycles over the late twentieth century in the southwest Pacific Ocean. In particular, sea surface temperature (SST), surface chlorophyll a, nitrate, phosphate, silicate, and the depth of the seasonal thermocline, are examined to quantify the physical-biogeochemical capabilities of each model; the result is a “ranking” estimate enabling model ensemble generation. The better/less ranked ensembles we refer to as inner/outer, respectively. The ensembles then allow less well observed variables such as iron and vertically integrated primary production to be assessed. The assessment establishes model output confidence limits for setting bounds on future model scenario ecosystem change projections. By the end of the twenty first century under Representative Concentration Pathways (RCP) RCP4.5 and/or RCP8.5 our best estimates suggest that there will be average domain wide increases in SST and surface iron, but average decreases in surface chlorophyll a, nitrate, and phosphate, accompanied by relatively large decreases in the depth of the seasonal thermocline (all changes realised by both ensembles). On the other hand, for surface silicate the inner ensemble suggests general declines, and vice versa for the outer ensemble. For integrated primary production the ensembles predict declines in subtropical water, but elsewhere generally less significant changes. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-05T10:25:53.513578-05:
      DOI: 10.1002/2016JC011736
  • Observations and Modeling of a Tidal Inlet Dye Tracer Plume
    • Authors: Falk Feddersen; Maitane Olabarrieta, R. T. Guza, D. Winters, Britt Raubenheimer, Steve Elgar
      Abstract: A 9 km-long tracer plume was created by continuously releasing Rhodamine WT dye for 2.2 h during ebb tide within the southern edge of the main tidal channel at New River Inlet, NC on May 7, 2012, with highly obliquely incident waves and alongshore winds. Over 6 h from release, COAWST (coupled ROMS and SWAN, including wave, wind, and tidal forcing) modeled dye compares well with (aerial hyperspectral and in situ) observed dye concentration. Dye first was transported rapidly seaward along the main channel and partially advected across the ebb-tidal shoal until reaching the offshore edge of the shoal. Dye did not eject offshore in an ebb-tidal jet because the obliquely incident breaking waves retarded the inlet-mouth ebb-tidal flow and forced currents along the ebb shoal. The dye plume largely was confined to 
      PubDate: 2016-10-04T10:25:55.161221-05:
      DOI: 10.1002/2016JC011922
  • The Beaufort Gyre intensification and stabilization: A model-observation
    • Authors: Jinlun Zhang; Michael Steele, Kay Runciman, Sarah Dewey, James Morison, Craig Lee, Luc Rainville, Sylvia Cole, Richard Krishfield, Mary-Louise Timmermans, John Toole
      Abstract: A model–observation synthesis is conducted to investigate changes in the upper ocean circulation and stratification in the Canada Basin (CB) of the Arctic Ocean. Results show that the Beaufort Gyre (BG) has been generally intensifying during 1992–2015 in conjunction with changes in sea ice and the upper ocean including increasing sea surface height (SSH), sea ice and ocean speed, Ekman transport convergence and downwelling, and freshwater content, decreasing ice thickness and upper ocean salinity, shoaling summer halocline and mixed layer, and deepening winter halocline and mixed layer. Increasing Ekman transport convergence draws more water from surrounding areas into the CB, thus lowering SSH in those areas and raising SSH in the CB. The rate of change in the CB began to decrease in 2008 and the BG circulation appears to be stabilizing, if not relaxing slightly. This is reflected in the general plateauing of SSH, the intensity of the sea ice and ocean circulation, and various measures of the CB thermohaline stratification. The BG intensification and subsequent stabilization appear to have been strongly controlled by atmospheric changes in the CB characterized by generally increasing anticyclonic wind circulation and sea level pressure (SLP) before 2008 and falling wind strength and SLP to below-average levels in some years after 2008. Changes in SLP are highly correlated with changes in ocean surface stress curl and downwelling. Since 2008, the magnitude of the stress curl and downwelling in much of the CB has declined, contributing to BG stabilization. The general leveling-off of sea ice thickness also contributes to the stabilization by limiting melt water input to the CB that increases freshwater content. Temperatures in the Near Surface Temperature Maximum layer trended upward slightly over 1992–2015, which is closely correlated with decreasing sea ice thickness. Upper ocean heat content increased over the study period mainly due to strong temperature increases in the summer Pacific Water layer. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-04T10:25:53.440564-05:
      DOI: 10.1002/2016JC012196
  • Impact of model resolution for on-shelf heat transport along the West
           Antarctic Peninsula
    • Authors: Jennifer A Graham; Michael S Dinniman, John M Klinck
      Abstract: The flux of warm deep water onto Antarctic continental shelves plays a vital role in determining water mass properties adjacent to the continent. A regional model, with two different grid resolutions, has been used to simulate ocean processes along the West Antarctic Peninsula. At both 4 km and 1.5 km resolution, the model reproduces the locations of warm intrusions, as shown through comparison with observations from instrumented seals. However, the 1.5 km simulation shows greater on-shelf heat transport, leading to improved representation of heat content on the shelf. This increased heat transport is associated with increased eddy activity, both at the shelf-break and in the deep ocean off-shore. Cross-shelf troughs are key locations of on-shelf heat transport. Comparison of two troughs, Belgica and Marguerite, shows differing responses to increased resolution. At higher resolution, there is an increased on-shelf volume transport at Belgica Trough, but not at Marguerite Trough. This is likely related to the differing structure of the shelf-break jet between these two locations. The increased heat flux at Marguerite Trough is attributed to increased heat content in the on-shelf transport. Increased eddy activity off-shelf may lead to greater cross-front heat transport, and therefore increased heat available above the continental slope. While these simulations differ in their magnitude of heat transport, both show similar patterns of variability. Variations in wind stress lead to variations in speed of the shelf-break jet, and therefore on-shelf heat transport. These results demonstrate the importance of model resolution for understanding cross-shelf transport around Antarctica. This article is protected by copyright. All rights reserved.
      PubDate: 2016-10-04T10:20:53.977797-05:
      DOI: 10.1002/2016JC011875
  • Recurrent Replenishment of Labrador Sea Water and Associated Decadal-Scale
    • Authors: Igor Yashayaev; John W. Loder
      Abstract: Winter convective overturning in the Labrador Sea reached an “aggregate” maximum depth of 1700m in 2015 – the deepest since 1994 – with the resulting Labrador Sea Water (LSW) “year class” being one of the deepest and thickest observed outside of the early 1990s. Argo float, annual survey and moored measurements in recent decades provide an unprecedented view of important seasonal, interannual and longer-term LSW variability in the Labrador Sea region. During the 2002-2015 “Argo” era, the average winter LSW pycnostad volume was about 70% larger in relatively strong convection years than in relatively weak ones. However, the winter-to-fall LSW disappearance volume was 180% larger, pointing to a factor of 2.8 difference in the potential LSW export rates from the region between relatively strong and weak convection years. Intermittently recurrent deep convection is contributing to predominant decadal-scale variations in intermediate-depth temperature, salinity and density in the LS, with implications for decadal-scale variability across the subpolar North Atlantic and potentially in the Atlantic Meridional Overturning Circulation. Comparison of the LS ocean heat content changes and cumulative surface heat losses during the fall-winter cooling seasons indicates that anomalously strong winter atmospheric cooling, associated at least in part with the North Atlantic Oscillation, is continuing to be a major forcing of the recurrent convection. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-30T03:45:42.867176-05:
      DOI: 10.1002/2016JC012046
  • Tidal distortion caused by the resonance of sexta-diurnal tides in a
           micro-mesotidal embayment
    • Authors: Dehai Song; Yuhan Yan, Wen Wu, Xiliang Diao, Yang Ding, Xianwen Bao
      Abstract: Double high water and double-peak flood current were observed in Daya Bay (DYB), China, which is a shallow, mixed, mainly semidiurnal-tide dominated bay with a micro- to meso-tidal range. Harmonic analysis reveals that the quarter- and especially the sexta-diurnal constituents are getting much stronger as tides propagating into the bay. The astronomical tides induced tidal asymmetry is yet dominant at the bay entrance, but overtaken by the sexta-diurnal tides at the end of the bay. Both the M4 and M6 tide meet the requirement proposed in previous studies, but still unable to produce a double high water alone. Therefore the conditions to produce a double high water between a fundamental tide and its higher harmonics need to be revisited. Analytical solutions were obtained in this paper, which fit the numerical solutions very well. Modelling result indicates M6 alone with M2 can produce the double high water in DYB, but limited in some regions; while the combination of M2, M4 and M6 tides would enhance the capability. The amplification of sexta-diurnal tides in DYB is dominated by resonance, and followed by shoaling effect. Bottom friction damped M6 a lot, and largely confined its amplification. However, the quadratic friction and other nonlinear processes are just responsible for about 10% of the total M6 increase. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-30T03:40:43.680092-05:
      DOI: 10.1002/2016JC012039
  • Century-scale perspectives on observed and simulated Southern Ocean sea
           ice trends from proxy reconstructions
    • Authors: Will Hobbs; Mark Curran, Nerilie Abram, Elizabeth R. Thomas
      Abstract: Observations show that Southern Ocean sea ice extent has increased since 1979, whereas global coupled climate models simulate a decrease over the same period. It is uncertain whether the observed trends are anthropogenically forced or due to internal variability, and whether the discrepancy between models and observations is also due to internal variability or indicative of a significant deficiency in the models. The length of the passive microwave satellite record hampers research into this question, which is too short to resolve multidecadal variability. Here, we use a number of proxies for regional seasonal sea ice extent around the Antarctic region to reconstruct sea ice extent for the full 20th century, which we compare with CMIP5 model simulations. We find that for the East Antarctic, Amundsen and Bellingshausen Seas, models and reconstructions agree that there has been a decrease in sea ice extent since the early 1970s, but this decrease is small compared to the simulated internal variability of the system. The Ross Sea is a confounding factor, with a significant increase in sea ice since 1979 that is not captured by climate models; however, existing proxy reconstructions of this region are not yet sufficiently reliable for formal change detection. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-30T03:36:08.469928-05:
      DOI: 10.1002/2016JC012111
  • Laboratory simulation of the geothermal heating effects on ocean
           overturning circulation
    • Authors: Fei Wang; Shi-Di Huang, Sheng-Qi Zhou, Ke-Qing Xia
      Abstract: Motivated by a desire to understand the geothermal heating effects on ocean circulation, a large-scale circulation generated and sustained by thermal forcing at the surface subject to a small amount of heating from the bottom boundary is investigated through laboratory experiments, motivated by understanding the geothermal heating effects on ocean circulation. Despite its idealization, our experiments demonstrate that the leading order effect of geothermal heating is to significantly enhance the abyssal overturning, in agreement with the findings in ocean circulation models. Our experiments also demonstrate that geothermal heating cannot influence the poleward heat transport due to the strong stratification in the thermocline. Our study further reveals that the ratio of geothermal-flux-induced turbulent dissipation to the dissipation due to other energies is the key parameter determining the dynamical importance of geothermal heating. This quantity explains why the impact of geothermal heating is sensitive to the deep stratification, the diapycnal mixing and the amount of geothermal flux. Moreover, it is found that this dissipation ratio may be used to understand results from different studies in a consistent way. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-30T03:36:06.617896-05:
      DOI: 10.1002/2016JC012068
  • Effects of mesoscale eddies on the volume transport and branch pattern of
           the Kuroshio east of Taiwan
    • Authors: Xiaomei Yan; Xiao‐Hua Zhu, Chongguang Pang, Linlin Zhang
      Abstract: Using satellite altimeter data and a long‐term altimetric transport index for the Kuroshio inflow northeast of Taiwan, the effects of mesoscale eddies on the Kuroshio volume transport (KVT) at the East Taiwan Channel and the branching pattern of the Kuroshio east of Taiwan are investigated at scales from those of individual events to interannual timescales. Both anticyclonic and cyclonic eddies are found to be able either to strengthen or weaken the KVT, depending on the relative strength of mass convergence and divergence produced upstream and downstream of the eddies. The major factor influencing the intensity of the Kuroshio inflow is the meridional location of the eddies. For single eddy events, the KVT is significantly correlated with the latitude of the eddy's center, the correlations being 0.44 and ‐0.48 for anticyclonic and cyclonic eddies, respectively. For dipole eddy events, when the direction angle falls in the interval 40°‐150° (240°‐300°), the KVT anomaly tends to be positive (negative). Furthermore, low KVT events generally correspond to the formation of the Ryukyu Current branch, which is also generated from strong mass divergence produced by the eddies. In addition, on interannual time scales, the variation of KVT is closely related to the relative number of anticyclonic to cyclonic eddies west of 125°E, with a correlation of 0.5. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-28T03:32:07.999989-05:
      DOI: 10.1002/2016JC012038
  • Weakest winter South China Sea western boundary current caused by the
           2015–2016 El Niño event
    • Authors: Ruixiang Zhao; Xiao‐Hua Zhu
      Abstract: During the winter of 2015–2016, the strongest El Niño event of the 21st century occurred. At the same time, volume transport (VT) time series of the South China Sea western boundary current (SCSWBC) exhibited a minimum value of 3.7 Sv (1 Sv = 1 × 106 m3 s−1) toward the southwest, indicating the weakest strength ever recorded in boreal winter (from November to February). The South China Sea (SCS) cyclonic gyre, inferred from the satellite‐derived surface absolute geostrophic current, was significantly reduced. It was considered that the weakened wind stress curl (negative anomaly) over the SCS resulting from an anticyclone over the Philippine Sea played an essential role. The anticyclone arose from a Rossby‐wave response to a negative sea surface temperature anomaly in the northwest Pacific. This idea is further supported by composite analysis, which shows that during El Niño (La Niña) winter, negative (positive) wind stress curl anomalies prevail in the Philippines Sea and the SCS; thus, the wind stress curl over the SCS is reduced (strengthened), leading to a weaker (stronger) SCS cyclonic gyre and SCSWBC. The mean VT of SCSWBC is 4.7 Sv (5.6 Sv), which is smaller (larger) than 5.2 Sv in normal years. This study provides robust observational evidence from long‐term in situ volume transport monitoring that El Niño can have a significant impact on the SCSWBC through an atmosphere‐bridged teleconnection. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-28T03:31:49.945392-05:
      DOI: 10.1002/2016JC012252
  • Pressure field induced in the water column by acoustic‐gravity waves
           generated from sea bottom motion
    • Authors: Tiago C. A. Oliveira; Usama Kadri
      Abstract: An uplift of the ocean bottom caused by a submarine earthquake can trigger acoustic‐gravity waves that travel at near the speed of sound in water and thus may act as early tsunami precursors. We study the spatio‐temporal evolution of the pressure field induced by acoustic‐gravity modes during submarine earthquakes, analytically. We show that these modes may all induce comparable temporal variations in pressure at different water depths in regions far from the epicenter, though the pressure field depends on the presence of a leading acoustic‐gravity wave mode. Practically, this can assist in the implementation of an early tsunami detection system by identifying the pressure and frequency ranges of measurement equipment and appropriate installation locations. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-28T03:27:02.815803-05:
      DOI: 10.1002/2016JC011742
  • Vernal distribution and turnover of dimethylsulfide (DMS) in the surface
           water of the Yellow Sea
    • Authors: Cheng‐Xuan Li; Gui‐Peng Yang, Bao‐Dong Wang, Zong‐Jun Xu
      Abstract: The spatial and interannual variations of dimethylsulfide (DMS) and its precursors, dissolved and particulate dimethylsulfoniopropionate (DMSP), were discussed on the basis of field observations in the surface waters of the Yellow Sea during spring 2007. Maxima of dimethylated sulfur compounds and low chlorophyll a concentrations were found in the central southern Yellow Sea, whereas low concentrations of DMS and DMSP were detected at the boundary between the northern and southern parts of the Yellow Sea. This frontal region is influenced by active water currents, air–sea interface exchanges, and biological turnover. The horizontal variations in DMS production and consumption rates showed a decreasing tendency from the coastal to offshore areas mainly due to the complicated biological features. DMS positively correlated with dissolved CH4 and CO2 but negatively correlated with nutrients (nitrite and phosphate). Particulate DMSP concentrations and DMS production rates positively correlated with dinoflagellate abundances but negatively correlated with diatom cell densities. DMS and DMSP concentrations, as well as DMS production and consumption rates, exhibited approximately 2.0‐2.8 fold increases from 2005 to 2012. This finding was likely caused by shifts in the phytoplankton communities from diatoms to dinoflagellates and the increases in abundances of zooplankton and bacteria. Average sea‐to‐air DMS fluxes were estimated to be 8.12 ± 1.24 µmol·(m−2·d−1), and DMS microbial consumption was approximately 1.68 times faster than the DMS sea–air exchange. These findings imply that biological consumption, relative to ventilation, is a predominant mechanism in DMS removal from the surface water. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-28T03:21:26.848701-05:
      DOI: 10.1002/2016JC011901
  • Assessing controls on cross‐shelf phytoplankton and suspended particle
           distributions using repeated bio‐optical glider surveys
    • Authors: Fernanda Henderikx Freitas; David A. Siegel, Libe Washburn, Stuart Halewood, Erik Stassinos
      Abstract: Characterizing the space/time variability of bio‐optical properties is essential to understanding the mechanisms that control cross‐shelf phytoplankton and suspended particle distributions in coastal waters. Approximately 400 high‐resolution cross‐shelf sections of bio‐optical properties collected with an oceanographic glider in the coastal Santa Barbara Channel, California, revealed complex relationships among optical properties and environmental conditions. Surface waves were found as a proximate control on suspended sediment variability for both inner and mid‐shelves. Increases in phytoplankton abundances attributed to horizontal advection and upwelling events were observed only on episodic time scales. The lack of all‐encompassing linear relationships between environmental forcings and changes in cross‐shelf phytoplankton highlight the challenge of decoupling bio‐optical signals from their controlling processes in coastal zones where phytoplankton distributions are patchy, and where nearshore and offshore phytoplankton populations and suspended sediments often occupy the same portion of the water column. Clear relationships between runoff and productivity were not observed. Temporal variability of suspended particles and phytoplankton distributions were roughly independent from each other during stratified conditions. Synchronous increases in phytoplankton and suspended sediments were observed when associated with strong upwelling events that may induce mixing and promote productivity. The repeated glider sections illustrated many processes regulating phytoplankton and particle transport in the innershelf and showed the difficulty in establishing general connections between high‐frequency changes in optical properties and potential environmental forcings in a complex coastal environment. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-26T18:15:30.835054-05:
      DOI: 10.1002/2016JC011781
  • Scales and dynamics of submesoscale coherent vortices formed by deep
           convection in the northwestern Mediterranean Sea
    • Authors: Anthony Bosse; Pierre Testor, Loïc Houpert, Pierre Damien, Louis Prieur, Daniel Hayes, Vincent Taillandier, Xavier Durrieu de Madron, Fabrizio d'Ortenzio, Laurent Coppola, Johannes Karstensen, Laurent Mortier
      Abstract: Since 2010, an intense effort in the collection of\textit{in situ} observations has been carried out in the northwestern Mediterranean Sea thanks to gliders, profiling floats, regular cruises and mooring lines. This integrated observing system enabled a year‐to‐year monitoring of the deep waters formation that occurred in the Gulf of Lions area during 4 consecutive winters (2010‐2013). Vortical structures remnant of wintertime deep vertical mixing events were regularly sampled by the different observing platforms. These are Submesoscale Coherent Vortices (SCVs) characterized by a small radius (∼5‐8 km), strong depth‐intensified orbital velocities (∼10‐20 cm s−1) with often a weak surface signature, high Rossby (∼0.5) and Burger numbers O(0.5‐1). Anticyclones transport convected waters resulting from intermediate (∼300 m) to deep (∼2000 m) vertical mixing. Cyclones are characterized by a 500‐1000 m thick layer of weakly stratified deep waters (or bottom waters that cascaded from the shelf of the Gulf of Lions in 2012) extending down to the bottom of the ocean at ∼2500 m. The formation of cyclonic eddies seems to be favored by bottom‐reaching convection occurring during the study period or cascading events reaching the abyssal plain. We confirm the prominent role of anticyclonic SCVs and shed light on the important role of cyclonic SCVs in the spreading of a significant amount (30%) of the newly‐formed deep waters away from the winter mixing areas. Since they can survive until the following winter, they can potentially have a great impact on the mixed layer deepening through a local preconditioning effect. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-26T02:57:39.972444-05:
      DOI: 10.1002/2016JC012144
  • Laboratory experiments on diffusive convection layer thickness and its
           oceanographic implications
    • Authors: Shuang‐Xi Guo; Sheng‐Qi Zhou, Ling Qu, Yuan‐Zheng Lu
      Abstract: We studied the thickness of diffusive convective layers that form when a linearly stratified fluid is subjected to heating from below in the laboratory. The thickness of the bottom convecting layer is much larger than subsequent layers. These thicknesses are systematically identified and used to examine the available convecting layer thickness parameterizations, which are consisted of the measured heat flux F (or thermal buoyancy flux qT), initial stratification N, density ratio Rρ, thermal diffusivity κT, etc. Parameterization with an intrinsic length scale (qT3κTN8)1/4 is shown to be superior. Including the present laboratory convecting layer thicknesses and those observed in oceans and lakes, where layer thickness ranges from 0.01 to 1000 m, the parameterization is updated as H=C(Rρ−1)2(qT3κTN8)1/4, where C=38.3 for the bottom convective layer and 10.8 for the subsequent layers. Different prefactors are proposed to be attributed to different convective instabilities induced by different boundary conditions. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-22T09:55:55.381865-05:
      DOI: 10.1002/2016JC012172
  • Teleconnection between the North Indian Ocean high swell events and
           meteorological conditions over the Southern Indian Ocean
    • Authors: P G Remya; S Vishnu, B Praveen Kumar, TM Balakrishnan Nair, B Rohith
      Abstract: The link between North Indian Ocean (NIO) high swell events and the meteorological conditions over the Southern Indian Ocean (SIO) is explored in this article, using a combination of in‐situ measurements and model simulations for the year 2005. High waves, without any sign in the local winds, sometimes cause severe flooding events along the south‐west coast of India, locally known as the Kallakkadal events and cause major societal problems along the coasts. In‐situ observations report ten high swell events in NIO during 2005. Our study confirm that these events are caused by the swells propagating from south of 30°S. In all cases, 3‐5 days prior to the high swell events in NIO, we observed a severe low pressure system, called the Cut‐Off Low (COL) in the Southern Ocean. These COLs are quasi‐stationary in nature, providing strong (∼25 ms−1) and long duration (∼3 days) surface winds over a large fetch; essential conditions for the generation of long period swells. The intense equator ward winds associated with COLs in the SIO trigger the generation of high waves, which propagate to NIO as swells. Furthermore, these swells cause high wave activity and sometimes Kallakkadal events along the NIO coastal regions, depending on the local topography, angle of incidence and tidal conditions. Our study shows that such natural hazards along the NIO coasts can be forecasted at least 2 days in advance if the meteorological conditions of the SIO are properly monitored. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-21T19:10:44.497883-05:
      DOI: 10.1002/2016JC011723
  • Measurement and modeling of oil slick transport
    • Authors: Cathleen E. Jones; Knut‐Frode Dagestad, Øyvind Breivik, Benjamin Holt, Johannes Röhrs, Kai Håkon Christensen, Martine Espeseth, Camilla Brekke, Stine Skrunes
      Abstract: Transport characteristics of oil slicks are reported from a controlled release experiment conducted in the North Sea in June 2015, during which mineral oil emulsions of different volumetric oil fractions and a look‐alike biogenic oil were released and allowed to develop naturally. The experiment used the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) to track slick location, size, and shape for ∼8 hours following release. Wind conditions during the exercise were at the high end of the range considered suitable for radar‐based slick detection, but the slicks were easily detectable in all images acquired by the low noise, L‐band imaging radar. The measurements are used to constrain the entrainment length and representative droplet radii for oil elements in simulations generated using the OpenOil advanced oil drift model. Simultaneously released drifters provide near‐surface current estimates for the single biogenic release and one emulsion release, and are used to test model sensitivity to upper ocean currents and mixing. Results of the modeling reveal a distinct difference between the transport of the biogenic oil and the mineral oil emulsion, in particular in the vertical direction, with faster and deeper entrainment of significantly smaller droplets of the biogenic oil. The difference in depth profiles for the two types of oils is substantial, with most of the biogenic oil residing below depths of 10 m, compared to the majority of the emulsion remaining above 10 m depth. This difference was key to fitting the observed evolution of the two different types of slicks. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-21T18:35:26.123817-05:
      DOI: 10.1002/2016JC012113
  • Tsunami generation and associated waves in the water column and seabed due
           to an asymmetric earthquake motion within an anisotropic substratum
    • Authors: Amirhossein Bagheri; Stewart Greenhalgh, Ali Khojasteh, Mohammad Rahimian, Reza Attarnejad
      Abstract: In this paper, closed‐form integral expressions are derived to describe how surface gravity waves (tsunamis) are generated when general asymmetric ground displacement (due to earthquake rupturing), involving both horizontal and vertical components of motion, occurs at arbitrary depth within the interior of an anisotropic sub‐sea solid beneath the ocean. In addition, we compute the resultant hydrodynamic pressure within the seawater and the elastic wavefield within the seabed at any position. The method of potential functions and an integral transform approach, accompanied by a special contour integration scheme, are adopted to handle the equations of motion and produce the numerical results. The formulation accounts for any number of possible acoustic‐gravity modes and is valid for both shallow and deep water situations as well as for any focal depth of the earthquake source. Phase and group velocity dispersion curves are developed for surface gravity (tsunami mode), acoustic‐gravity, Rayleigh, and Scholte waves. Several asymptotic cases which arise from the general analysis are discussed and compared to existing solutions. The role of effective parameters such as hypocenter location and frequency of excitation are examined and illustrated through several figures which show the propagation pattern in the vertical and horizontal directions. Attention is directed to the unexpected contribution from the horizontal ground motion. The results have important application in several fields such as tsunami hazard prediction, marine seismology and offshore and coastal engineering. In a companion paper we examine the effect of ocean stratification on the appearance and character of internal and surface gravity waves. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-21T18:35:21.897982-05:
      DOI: 10.1002/2016JC011944
  • Enhanced turbulence driven by mesoscale motions and flow‐topography
           interaction in the Denmark Strait Overflow plume
    • Authors: Janin Schaffer; Torsten Kanzow, Kerstin Jochumsen, Klas Lackschewitz, Sandra Tippenhauer, Victor M. Zhurbas, Detlef Quadfasel
      Abstract: The Denmark Strait Overflow (DSO) contributes roughly half to the total volume transport of the Nordic overflows. The overflow increases its volume by entraining ambient water as it descends into the subpolar North Atlantic, feeding into the deep branch of the Atlantic Meridional Overturning Circulation. In June 2012 a multi‐platform experiment was carried out in the DSO plume on the continental slope off Greenland (180 km downstream of the sill in Denmark Strait), to observe the variability associated with the entrainment of ambient waters into the DSO plume. In this study we report on two high‐dissipation events captured by an autonomous underwater vehicle (AUV) by horizontal profiling in the interfacial layer between the DSO plume and the ambient water. Strong dissipation of turbulent kinetic energy of O(10‐6) W kg‐1 was associated with enhanced small‐scale temperature variance at wavelengths between 0.05 and 500 m as deduced from a fast‐response thermistor. Isotherm displacement slope spectra reveal a wavenumber‐dependence characteristic of turbulence in the inertial‐convective subrange (k1/3) at wavelengths between 0.14 and 100 m. The first event captured by the AUV was transient, and occurred near the edge of a bottom‐intensified energetic eddy. Our observations imply that both horizontal advection of warm water and vertical mixing of it into the plume are eddy‐driven and go hand in hand in entraining ambient water into the DSO plume. The second event was found to be a stationary feature on the upstream side of a topographic elevation located in the plume pathway. Flow‐topography interaction is suggested to drive the intense mixing at this site. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-21T11:10:38.629141-05:
      DOI: 10.1002/2016JC011653
  • Wind‐driven export of Weddell Sea slope water
    • Authors: A.J.S. Meijers; M.P. Meredith, E.P. Abrahamsen, M.A. Morales Maqueda, D.C. Jones, A.C. Naveira Garabato
      Abstract: The export of waters from the Weddell Gyre to lower latitudes is an integral component of the southern subpolar contribution to the three‐dimensional oceanic circulation. Here, we use more than 20 years of repeat hydrographic data on the continental slope on the northern tip of the Antarctic Peninsula and five years of bottom lander data on the slope at 1000 m to show the intermittent presence of a relatively cold, fresh westward‐flowing current. This is often bottom intensified between 600‐2000 dbar with velocities of over 20 cms−1, transporting an average of 1.5±1.5 Sv. By comparison with hydrography on the continental slope within the Weddell Sea and modelled tracer release experiments we show that this slope current is an extension of the Antarctic Slope Current that has crossed the South Scotia Ridge west of Orkney Plateau. On monthly to interannual timescales the density of the slope current is negatively correlated (r >0.6 with a significance of over 95%) with eastward wind stress over the northern Weddell Sea, but lagging it by 6‐13 months. This relationship holds in both the high temporal resolution bottom lander time series and the 20+ year annual hydrographic occupations and agrees with Weddell Sea export variability observed further east. We compare several alternative hypotheses for this wind‐stress/export relationship and find that it is most consistent with wind‐driven acceleration of the gyre boundary current, possibly modulated by eddy dynamics, and represents a mechanism by which climatic perturbations can be rapidly transmitted as fluctuations in the supply of intermediate‐level waters to lower latitudes. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-21T11:00:30.892787-05:
      DOI: 10.1002/2016JC011757
  • Direct observations of the Antarctic Slope Current transport at 113°E
    • Authors: B. Peña‐Molino; M. S. McCartney, S. R. Rintoul
      Abstract: The Antarctic Slope Current (ASC), defined here as the region of westward flow along the continental slope off Antarctica, forms the southern limb of the subpolar gyres. It regulates the exchange of water across the shelf break, and provides a path for interbasin westward transport. Despite its significance, the ASC remains largely unobserved around most of the Antarctic continent. Here we present direct velocity observations from a 17‐month current meter moored array deployed across the continental slope between the 1000 and the 4200 m isobaths, in the southeastern Indian Ocean near 113°E. The observed time‐mean flow consists of a surface intensified jet associated with the Antarctic Slope Front (ASF) and a broader bottom intensified westward flow that extends out to approximately the 4000 m isobath and is strongest along the upper slope. The time‐mean transport of the ASC is ‐29.2 Sv. Fluctuations in the transport are large, typically exceeding the mean by a factor of 2. They are mainly due to changes in the northward extent of the current over the lower slope. However, seasonal changes in the wind also drive variations in the transport of the ASF and the flow in the upper slope. Both mean and variability are largely barotropic, thus invisible to traditional geostrophic methods. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-21T11:00:26.473997-05:
      DOI: 10.1002/2015JC011594
  • Wind relaxation and a coastal buoyant plume north of Pt. Conception, CA:
           Observations, simulations, and scalings
    • Authors: Sutara Suanda; Nirnimesh Kumar, Arthur J. Miller, Emanuele DiLorenzo, Kevin Haas, Donghua Cai, Christopher A. Edwards, Libe Washburn, Melanie Fewings, Rachel Torres, Falk Feddersen
      Abstract: In upwelling regions, wind relaxations lead to poleward propagating warm water plumes that are important to coastal ecosystems. The coastal ocean response to wind relaxation around Pt. Conception, CA is simulated with a Regional Ocean Model (ROMS) forced by realistic surface and lateral boundary conditions including tidal processes. The model reproduces well the statistics of observed subtidal water column temperature and velocity at both outer‐ and inner‐shelf mooring locations throughout the study. A poleward‐propagating plume of Southern California Bight water that increases shelf water temperatures by ≈ 5°C is also reproduced. Modeled plume propagation speed, spatial scales, and flow structure are consistent with a theoretical scaling for coastal buoyant plumes with both surface‐trapped and slope‐controlled dynamics. Plume momentum balances are distinct between the offshore (> 30‐m depth) region where the plume is surface‐trapped, and onshore of the 30‐m isobath (within 5 km from shore) where the plume water mass extends to the bottom and is slope‐controlled. In the onshore region, bottom stress is important in the alongshore momentum equation and generates vertical vorticity that is an order of magnitude larger than the vorticity in the plume core. Numerical experiments without tidal forcing show that modeled surface temperatures are biased 0.5°C high, potentially affecting plume propagation distance and persistence. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-20T03:45:32.764738-05:
      DOI: 10.1002/2016JC011919
  • Variability, trends, and predictability of seasonal sea ice retreat and
           advance in the Chukchi Sea
    • Authors: Mark C. Serreze; Alex D. Crawford, Julienne Stroeve, Andrew P. Barrett, Rebecca A. Woodgate
      Abstract: As assessed over the period 1979‐2014, the date that sea ice retreats to the shelf break (150m contour) of the Chukchi Sea has a linear trend of ‐0.7 days per year. The date of seasonal ice advance back to the shelf break has a steeper trend of about +1.5 days per year, together yielding an increase in the open water period of 80 days. Based on de‐trended time series, we ask how interannual variability in advance and retreat dates relate to various forcing parameters including radiation fluxes, temperature and wind (from numerical reanalyses), and the oceanic heat inflow through the Bering Strait (from in situ moorings). Of all variables considered, the retreat date is most strongly correlated (r∼0.8) with the April through June Bering Strait heat inflow. After testing a suite of statistical linear models using several potential predictors, the best model for predicting the date of retreat includes only the April through June Bering Strait heat inflow, which explains 68% of retreat date variance. The best model predicting the ice advance date includes the July through September inflow and the date of retreat, explaining 67% of advance date variance. We address these relationships by discussing heat balances within the Chukchi Sea, and the hypothesis of oceanic heat transport triggering ocean heat uptake and ice‐albedo feedback. Developing an operational prediction scheme for seasonal retreat and advance would require timely acquisition of Bering Strait heat inflow data. Predictability will likely always be limited by the chaotic nature of atmospheric circulation patterns. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-19T18:35:35.422629-05:
      DOI: 10.1002/2016JC011977
  • Remote sources for year‐to‐year changes in the seasonality of the
           Florida Current transport
    • Authors: Ricardo Domingues; Molly Baringer, Gustavo Goni
      Abstract: The seasonal variability of the Florida Current (FC) transport is often characterized by the presence of an average annual cycle (8% of the variance) of ∼3 Sv range peaking in boreal summer. However, the seasonality displayed by the FC transport in any individual year may have very distinct characteristics. In this study, the analysis focuses on seasonal changes (73—525 day frequency band) in the FC transport that are associated with a variable annual phase, which is defined as the transient seasonal component (FCt, 27% of the variance). It is shown that the FCt is largely modulated by westward propagating sea height anomaly (SHA) signals that are formed in the eastern North Atlantic 4 to 7 years earlier than observed at 27°N in the Florida Straits. These westward propagating SHA signals behave approximately like first baroclinic Rossby waves that can modulate changes in the FC seasonal variability upon arrival at the western boundary. The main finding from this study is that changes in coastal sea‐level between 25°N—42°N linked with westward propagating signals account for at least 50% of the FCt. The integrated changes in the coastal sea‐level between 25°N—42°N, in turn, drive adjustments in the geostrophic transport of the FC at 27°N. Results reported here provide an explanation for previously reported year‐to‐year changes in the FC seasonality, and suggest that large sea‐level variations along the coast of Florida may be partially predictable, given that these Rossby‐wave‐like signals propagate approximately at fixed rates in the open ocean along 27°N. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-19T18:35:31.731373-05:
      DOI: 10.1002/2016JC012070
  • Identification and classification of very‐low frequency waves on a
           coral reef flat
    • Authors: Matthijs Gawehn; Ap van Dongeren, Arnold van Rooijen, Curt Storlazzi, Olivia M. Cheriton, Ad Reniers
      Abstract: Very‐low frequency (VLF, 0.001‐0.005 Hz) waves are important drivers of flooding of low‐lying coral reef‐islands. In particular, VLF wave resonance is known to drive large wave runup and subsequent overwash. Using a five‐month dataset of water levels and waves collected along a cross‐reef transect on Roi‐Namur Island in the Republic of the Marshall Islands, the observed VLF motions were categorized into four different classes: (1) resonant, (2) (non‐resonant) standing, (3) progressive‐growing and (4) progressive‐dissipative waves. Each VLF class is set by the reef flat water depth and, in the case of resonance, the incident‐band offshore wave period. Using an improved method to identify VLF wave resonance, we find that VLF wave resonance caused prolonged (∼0.5 – 6.0 hr), large‐amplitude water surface oscillations at the inner reef flat ranging in wave height from 0.14 to 0.83 m. It was induced by relatively long‐period, grouped, incident‐band waves, and occurred under both storm and non‐storm conditions. Moreover, observed resonant VLF waves had non‐linear, bore‐like wave shapes, which likely have a larger impact on the shoreline than regular, sinusoidal waveforms. As an alternative technique to the commonly used Fast Fourier Transformation, we propose the Hilbert‐Huang Transformation that is more computationally expensive but can capture the wave shape more accurately. This research demonstrates that understanding VLF waves on reef flats is important for evaluating coastal flooding hazards. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-19T18:30:26.986267-05:
      DOI: 10.1002/2016JC011834
  • Glider observations of enhanced deep water upwelling at a shelf break
           canyon: A mechanism for cross‐slope carbon and nutrient exchange
    • Authors: M. Porter; M. E. Inall, J. Hopkins, M. R. Palmer, A. C. Dale, D. Aleynik, J. A. Barth, C. Mahaffey, D. A. Smeed
      Abstract: Using underwater gliders we have identified canyon driven upwelling across the Celtic Sea shelf‐break, in the vicinity of Whittard Canyon. The presence of this upwelling appears to be tied to the direction and strength of the local slope current, which is in itself highly variable. During typical summer time equatorward flow, an unbalanced pressure gradient force and the resulting disruption of geostrophic flow can lead to upwelling along the main axis of two small shelf break canyons. As the slope current reverts to poleward flow, the upwelling stops and the remnants of the upwelled features are mixed into the local shelf water or advected away from the region. The upwelled features are identified by the presence of sub‐pycnocline high salinity water on the shelf, and are upwelled from a depth of 300 m on the slope, thus providing a mechanism for the transport of nutrients across the shelf break onto the shelf. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-19T18:30:21.487541-05:
      DOI: 10.1002/2016JC012087
  • Surface shear stress dependence of gas transfer velocity parameterizations
           using DNS
    • Authors: S. T. Fredriksson; L. Arneborg, H. Nilsson, R. A. Handler
      Abstract: Air‐water gas‐exchange is studied in direct numerical simulations (DNS) of free‐surface flows driven by natural convection and weak winds. The wind is modeled as a constant surface‐shear‐stress and the gas‐transfer is modeled via a passive scalar. The simulations are characterized via a Richardson number Ri=Bν/u*4 where B, v, and u* are the buoyancy flux, kinematic viscosity, and friction velocity respectively. The simulations comprise 0 < Ri < ∞ ranging from convection‐dominated to shear‐dominated cases. The results are used to: (i) evaluate parameterizations of the air‐water gas‐exchange, (ii) determine, for a given buoyancy flux, the wind speed at which gas transfer becomes primarily shear driven, and (iii) find an expression for the gas‐transfer velocity for flows driven by both convection and shear. The evaluated gas transfer‐velocity parametrizations are based on either the rate of turbulent kinetic energy dissipation, the surface flow‐divergence, the surface heat‐flux, or the wind‐speed. The parametrizations using dissipation or divergence show an unfavorable Ri dependence for flows with combined forcing whereas the parametrization using heat‐flux only shows a limited Ri dependence. The two parametrizations using wind speed give reasonable estimates for the transfer‐velocity, depending however on the surface heat‐flux. The transition from convection‐ to shear‐dominated gas‐transfer‐velocity is shown to be at Ri ≈ 0.004. Furthermore, the gas‐transfer is shown to be well represented by two different approaches: (i) additive forcing expressed as kg,sum = AShear u* (Ri/Ric+1)1/4 Sc‐n where Ric = (AShear/ABuoy)4, and (ii) either buoyancy or shear dominated expressed as, kg = ABuoy (Bv)1/4Sc‐n, Ri>Ric or kg = Ashearu*Sc‐n, Ri
      PubDate: 2016-09-15T18:06:09.423857-05:
      DOI: 10.1002/2016JC011852
  • Trapping of the near‐inertial wave wakes of two consecutive
           hurricanes in the Loop Current
    • Authors: E. Pallàs‐Sanz; J. Candela, J. Sheinbaum, J. Ochoa, J. Jouanno
      Abstract: The near‐inertial trapping of the wave wakes of two consecutive hurricanes, Gustav and Ike (2008), at the base of the Loop Current is described using observations of a triangular mooring array. Hurricane Gustav translates over the Loop Current twice as fast and leads to a sharper, but equally strong, wind intensity peak than Hurricane Ike. Following the passage of Gustav, near‐inertial oscillations in the main thermocline have large horizontal (∼340±45 km) and vertical (∼850 m) scales. The wave kinetic energy propagates down with a vertical group velocity of several tens of meters per day and leads to a downward energy flux of [1.82‐7.10]×10−3 W m−2.Observations suggest that the dispersion of the wave wakes produced by the hurricanes is driven by Doppler shifting in the upper ∼600 m and the vertical‐varying vorticity inside the Loop Current. Near‐inertial kinetic energy is enhanced and near‐inertial oscillations are circularly polarized in a critical layer at the base of the Loop Current where the group velocity vector is nearly horizontal. The trapping and amplification of the near‐inertial wave wakes of two consecutive hurricanes is addressed using a primitive equation numerical model. Numerical results suggest an increase of the near‐inertial kinetic energy and vertical shear by a factor of ∼2 near the critical layer due to wave‐mean flow and wave‐wave interactions. A K‐Profile parameterization of these interactions results in banded regions of elevated turbulent kinetic energy dissipation rates of ε ϵ [0.5‐6.6]×10−6 W m−3 for critical Richardson number Ric = 1, depending on the stratification of the water column. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-15T18:00:56.412806-05:
      DOI: 10.1002/2015JC011592
  • Cross‐shelf water exchange in the East China Sea as estimated by
           satellite altimetry and in situ hydrographic measurement
    • Authors: Ruibin Ding; Daji Huang, Jiliang Xuan, Bernhard Mayer, Feng Zhou, Thomas Pohlmann
      Abstract: Combining satellite altimetry and in situ hydrographic measurement, we estimated the cross‐shelf transport (CST) and its spatial and temporal variations across 200 m isobath in the East China Sea (ECS) from 1993 to 2014. The vertically‐integrated CST can be dynamically divided into three parts: surface Ekman transport, geostrophic transport, and bottom Ekman transport. The results show that the 22‐year‐mean, sectionally‐integrated CST to be 1.7±2.0 Sv (positive in the on‐shelf direction), comprised of bottom and surface Ekman transports of 2.7±1.0 Sv and 0.6±0.6 Sv, respectively, that are partially offset by a geostrophic transport of ‐1.5±1.7 Sv. The sectionally‐integrated CST shows significantly high power at roughly annual period from 1999‐2001, with lower power at intra‐annual period. The time‐averaged, vertically‐integrated CST to the northeast of Taiwan is the main source of sectionally‐integrated CST. The vertically‐integrated CST also shows significant variations in the 6–15 month period band to the northeast of Taiwan as well. The temporal variations of the sectionally‐integrated and vertically‐integrated CST are both controlled primarily by geostrophic transport and modulated by bottom Ekman transport. In the upper 50 m, the geostrophic current to the northeast of Taiwan exhibits large mean and significant variability. The empirical orthogonal function analysis of vertical structure of geostrophic current shows two significant modes with strong annual signal. The first mode is associated with the migration of Kuroshio axis near Taiwan, while the second mode is associated with the variation of the meander of the Kuroshio to the northeast of Taiwan. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-15T08:35:25.891586-05:
      DOI: 10.1002/2016JC011972
  • Impacts of mesoscale activity on the water masses and circulation in the
           Coral Sea
    • Authors: L. Rousselet; A.M. Doglioli, C. Maes, B. Blanke, A. Petrenko
      Abstract: The climatological vision of the circulation within the Coral Sea is today well established with the westward circulation of two main jets, the North Caledonian Jet (NCJ) and the North Vanuatu Jet (NVJ) as a consequence of the separation of the South Equatorial Current (SEC) on the islands of New Caledonia, Vanuatu and Fiji. Each jet has its own dynamic and transports different water masses across the Coral Sea. The influence of mesoscale activity on mean flow and on water mass exchanges is not yet fully explored in this region of intense activity. Our study relies on the analysis of in situ, satellite and numerical data. Indeed we first use in situ data from the Bifurcation cruise and from an Argo float, jointly with satellite‐derived velocities, to study the eddy influence on the Coral Sea dynamics. We identify an anticyclonic eddy as participating in the transport of NVJ‐like water masses into the theoretical pathway of NCJ waters. This transfer from the NVJ to the NCJ is confirmed over the long‐term by a Lagrangian analysis. In particular, this numerical analysis shows that anticyclonic eddies can contribute up to 70% to 90% of the overall eddy transfer between those seemingly independent jets. Finally, transports calculated using S‐ADCP measurements (0‐500 m) show an eddy‐induced sensitivity that can reach up to 15 Sv, i.e, the order of the transport of the jets. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-15T08:30:53.907375-05:
      DOI: 10.1002/2016JC011861
  • Characterization and Assessment of the meteotsunami hazard in northern
           Lake Michigan
    • Authors: Álvaro Linares; Adam J. Bechle, Chin H. Wu
      Abstract: The meteotsunami hazard is assessed in northern Lake Michigan from both short‐term and long‐term records of water level, wind speed, and air pressure. Cross‐wavelet analysis reveals that meteotsunamis can be caused by atmospheric disturbances that are pressure dominated, wind dominated, or both pressure and wind forced. In total, air pressure and wind stress are found to contribute similarly to meteotsunami initiation in northern Lake Michigan. The pressure‐driven meteotsunamis tend to be associated with convective storms, whereas meteotsunamis that are mainly wind‐driven are associated more with cyclonic‐type storms. The atmospheric disturbances responsible for largest meteotsunamis in northern Lake Michigan are found to have a propagation speed close to 32 m/s and from the south to north direction. A heuristic approach is developed to estimate the maximum meteotsunami height from the atmospheric disturbance strength and velocity. Overall, the heuristic approach is shown to be an effective methodology to assess the meteotsunami hazard over a wide range of potential atmospheric disturbance conditions. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-10T10:30:25.686312-05:
      DOI: 10.1002/2016JC011979
  • Improving the simulation of landfast ice by combining tensile strength and
           a parameterization for grounded ridges
    • Authors: Jean‐François Lemieux; Frédéric Dupont, Philippe Blain, François Roy, Gregory C. Smith, Gregory M. Flato
      Abstract: In some coastal regions of the Arctic Ocean, grounded ice ridges contribute to stabilizing and maintaining a landfast ice cover. Recently, a grounding scheme representing this effect on sea ice dynamics was introduced and tested in a viscous‐plastic sea ice model. This grounding scheme, based on a basal stress parameterization, improves the simulation of landfast ice in many regions such as in the East Siberian Sea, the Laptev Sea and along the coast of Alaska. Nevertheless, in some regions such as the Kara Sea, the area of landfast ice is systematically underestimated. This indicates that another mechanism such as ice arching is at play for maintaining the ice cover fast. To address this problem, the combination of the basal stress parameterization and tensile strength is investigated using a 0.25° pan‐Arctic CICE‐NEMO configuration. Both uniaxial and isotropic tensile strengths notably improve the simulation of landfast ice in the Kara Sea but also in the Laptev Sea. However, the simulated landfast ice season for the Kara Sea is too short compared to observations. This is especially obvious for the onset of the landfast ice season which systematically occurs later in the model and with a slower build up. This suggests that improvements to the sea ice thermodynamics could reduce these discrepancies with the data. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-10T10:30:22.49546-05:0
      DOI: 10.1002/2016JC012006
  • Remote Forcing of Subsurface Currents and Temperatures near the Northern
           Limit of the California Current System
    • Authors: Zelalem Engida; Adam Monahan, Debby Ianson, Richard E. Thomson
      Abstract: Local and remote wind forcing of upwelling along continental shelves of coastal upwelling regions play key roles in driving biogeochemical fluxes, including vertical net fluxes of carbon and nutrients. These fluxes are responsible for high primary productivity, which in turn supports a lucrative fishery in these regions. However, the relative contributions of local versus remote wind forcing is not well quantified or understood. We present results of coherence analyses between currents at a single mooring site (48.5° N, 126° W) in the northern portion of the California Current System (CalCS) from 1989–2008 and coincident time series of North America Regional Reanalysis (NARR) 10 m wind stress within the CalCS (36–54° N, 120–132° W). The two‐decade long current records from the three shallowest depths (35, 100 and 175 m) show a remote response to winds from as far south as 36° N. In contrast, only temperatures at the deepest depth (400 m) show strong coherences with remote winds. Weaker local wind influence is observed in both the currents and 400 m temperatures but is mostly due to the large spatial coherence within the wind field itself. Lack of coherence between distal winds and the 400 m currents suggests that the temperature variations at that depth are driven by vertical motion resulting from poleward travelling coastal trapped waves (CTWs). Understanding the effects of remote forcing in coastal upwelling regions is necessary for determining the occurrence and timing of extreme conditions in coastal oceans, and their subsequent impact on marine ecosystems. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-10T10:25:30.534334-05:
      DOI: 10.1002/2016JC011880
  • Physical drivers of chlorophyll variability in the open South China Sea
    • Authors: Wen‐Zhou Zhang; Haili Wang, Fei Chai, Guoqiang Qiu
      Abstract: The variability of chlorophyll a concentration (Chl a) in the open South China Sea (SCS) was examined using observations from two Bio‐Argo floats. During the period of September 2014 to August 2015, there was a permanent subsurface Chl a maximum (SCM) in the depth range of 48 to 96 m in the central basin of the SCS. In the northern basin, the SCM disappeared in winter, replaced by enhanced surface layer phytoplankton with high Chl a. The values of the SCM were influenced by the vertical displacement of isotherms. Strong wind forcing and surface cooling were the main physical drivers of high surface Chl a in winter. In the north, stronger wind than in the center, lower sea surface temperature (SST) than in the center, and Kuroshio water intrusion were more favorable for the upward transport of nutrient‐rich deep water. A large amount of nitrate could be advected from the Taiwan Strait and shallow continental shelf to the northern basin in winter. A combination of strong wind mixing, surface cooling, Kuroshio water intrusion, and horizontal advection caused the winter surface phytoplankton bloom in the north. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-10T10:25:22.807672-05:
      DOI: 10.1002/2016JC011983
  • Observed subseasonal variability of heat flux and the SST response of the
           tropical Indian Ocean
    • Authors: Sindu Raj Parampil; G. N. Bharathraj, Matthew Harrison, Debasis Sengupta
      Abstract: We develop an experimental daily surface heat flux dataset based on satellite observations to study subseasonal variability (periods shorter than 90 days) in the tropical Indian Ocean. We use incoming shortwave and longwave radiation from the International Satellite Cloud Climatology Project, and sea surface temperature (SST) from microwave sensors, to estimate net radiative flux. Latent and sensible heat fluxes are estimated from scatterometer winds and near‐surface air temperature and specific humidity from Atmospheric Infrared Sounder (AIRS) observations calibrated to buoy data. Seasonal biases in net heat flux are generally within 10 Wm−2 of estimates from moorings, and the phases and amplitudes of subseasonal variability of heat fluxes are realistic. We find that the contribution of subseasonal changes in air‐sea humidity gradients to latent heat flux equals or exceeds the contribution of subseasonal changes in wind speed in all seasons. SST responds coherently to subseasonal oscillations of net heat flux associated with active and suppressed phases of atmospheric convection in the summer hemisphere. Thus subseasonal SST changes are mainly forced by heat flux in the northeast Indian Ocean in northern summer, and in the 15oS‐5oN latitude belt in southern summer. In the winter hemisphere, subseasonal SST changes are not a one‐dimensional response to heat flux, implying that they are mainly due to oceanic advection, entrainment or vertical mixing. The coherent evolution of subseasonal SST variability and surface heat flux suggests active coupling between SST and large‐scale, organized tropical convection in the summer season. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-09T10:15:53.136856-05:
      DOI: 10.1002/2016JC011948
  • Temporal variability in the Antarctic Polar Front (2002‐2014)
    • Authors: Natalie M. Freeman; Nicole S. Lovenduski, Peter R. Gent
      Abstract: We investigate intra‐annual to interannual variability in the Antarctic Polar Front (PF) using weekly PF realizations spanning 2002 to 2014 (found at While several PF studies have used gradient maxima in sea surface temperature (SST) or height to define its location, results from this study are based on a PF defined using SST measurements that avoid cloud contamination and the influence of steric sea level change. With a few regional exceptions, we find that the latitudinal position of the PF does not vary seasonally, yet its temperature exhibits a clear seasonal cycle. Consistent with previous studies, the position and intensity of the PF is largely influenced by bathymetry; generally, over steep topography we find that the front intensifies and interannual variability in its position is low. We also investigate drivers of PF variability in the context of large‐scale climate variability on various spatial and temporal scales, but find that the major modes of Southern Hemisphere climate variability explain only a tiny fraction of the interannual PF variance. Over the study time period, the PF intensifies at nearly all longitudes while exhibiting no discernible meridional displacement in its zonal mean path. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-08T03:55:33.75221-05:0
      DOI: 10.1002/2016JC012145
  • Observations of the vertical and temporal evolution of a Natal Pulse along
           the Eastern Agulhas Bank
    • Authors: Xavier Pivan; Marjolaine Krug, Steven Herbette
      Abstract: This study re‐investigates the work of Lutjeharms et al. [2001,2003] who documented the properties of a Natal Pulse using isopycnal Lagrangian floats. We combined Lagrangian analyses and Eulerian maps derived from objective analysis to better describe the evolution of a Natal Pulse along three density surfaces referred to as the surface (satellite‐observed), shallow (isopycnal‐1026.8 kg.m−3) and deep (isopycnal‐1027.2 kg.m−3) layer. Our observations show that this Natal Pulse extended to a depth of 1000m and was associated with cyclonic relative vorticity values of about 6.5 to 8.5x10−5.s−1 in the surface and shallow layer and 4x10−5.s−1 in the deep layer. This Natal Pulse contributed to cross‐shelf exchange through the offshore advection of Eastern Agulhas Bank water near the surface, onshore advection of South Indian Central Water and/or Indian Equatorial Water in the shallow layer and Antarctic Intermediate Water in the deep layer. Sea Surface Temperature maps showed that the downstream progression of the Natal Pulse along the 3000m isobath was related to a readjustment of its rotation axis. This readjustment advected Eastern Agulhas Bank water into the Natal Pulse eddy and triggered a SST cooling of about 3°C in the cyclonic area. The importance of a warm recirculating Agulhas plume originating from the Natal Pulse was highlighted. This warm water plume extended to a depth of 700m and was associated with onshore velocities exceeding those experienced within the Natal Pulse eddy by a factor of two. Our observations indicate that the June/July 1998 Natal Pulse and its associated plumes enhanced cross‐shelf exchanges. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-08T03:55:32.652903-05:
      DOI: 10.1002/2015JC011582
  • Bayesian hindcast of acoustic transmission loss in the western Pacific
    • Authors: Margaret Palmsten; J. Paquin Fabre
      Abstract: A Bayesian network is developed to demonstrate the feasibility of using environmental acoustic feature vectors (EAFVs) to predict underwater acoustic transmission loss (TL) versus range at two locations for a single acoustic source depth and frequency. Features for the networks are chosen based on a sensitivity analysis. The final network design resulted in a well‐trained network, with high skill, little gain error, and low bias. The capability presented here shows promise for expansion to a more generalized approach, which could be applied at varying locations, depths and frequencies to estimate acoustic performance over a highly variable oceanographic area in real‐time or near‐real‐time. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-08T03:55:30.22015-05:0
      DOI: 10.1002/2016JC011982
  • A tropical cyclone genesis potential index over the western North Pacific
           by using oceanic parameters
    • Authors: Min Zhang; Lei Zhou, Dake Chen, Chunzai Wang
      Abstract: This study attempts to create a tropical cyclone (TC) genesis potential index (GPI) by considering oceanic parameters and necessary atmospheric parameters. Based on the general understanding of the oceanic impacts on the TC genesis, many candidate factors are evaluated and discriminated, resulting in a new GPI index, which is referred to as GPIocean. GPIocean includes the parameters of (1) absolute vorticity at 1000 hPa, (2) net sea surface longwave radiation, (3) mean ocean temperature in the upper mixed layer, and (4) depth of the 26°C isotherm. GPIocean is comparable to existing GPIs in representing the TC genesis over the western North Pacific on seasonal and interannual variations. The same procedure can be applied to create a similar GPI for the other ocean basins. In the context of climate change, this new index is expected to be useful for evaluating the oceanic influences on TC genesis by using ocean reanalysis products and climate model outputs. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-07T04:23:36.076128-05:
      DOI: 10.1002/2016JC011851
  • Surface water subduction during a downwelling event in a
           semi‐enclosed bay
    • Authors: Barton E.D; Torres R, Figueiras F.G, Gilcoto M, Largier J.
      Abstract: The Ría de Vigo is a bay strongly influenced by upwelling‐downwelling cycles along the adjacent coast of NW Iberia. Moored and ship‐board observations during September 2006 showed that subduction, initially associated with an estuarine circulation, strengthened when a strong downwelling circulation, resulting from northward wind over the coastal ocean, was generated in the outer ría causing ambient waters to be advected outward in the lower layer. Incoming surface waters confined the estuarine circulation to the shallow interior and displaced isopleths downward through the water column at ∼10 m d−1. As the estuarine circulation retreated inward, strong flow convergence developed between middle and inner ria in the layer above 15 m, while divergence developed beneath. The convergence increased through the period of downwelling‐favorable wind at a rate consistent with the observed isopleth displacement velocities. The coefficient of turbulent diffusion Kt, from a microstructure profiler, indicated that mixing was strong in the estuarine circulation and subsequently in the downwelling zone, where localized instabilities and temperature‐salinity inversions were observed. During the downwelling, concentrations of phytoplankton, including potentially harmful species, increased, especially in the middle and inner ria, as a result of inward advection, subduction and the ability of the dinoflagellates to maintain their position in the water column by swimming. In the course of the 5 day event, the water mass of all but the innermost ría was flushed completely and replaced by waters originating in the coastally‐trapped poleward flow along the Atlantic coastline. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-06T10:20:30.21031-05:0
      DOI: 10.1002/2016JC011950
  • Contribution of Asian dust and volcanic material to the western Philippine
           Sea over the last 220 kyr as inferred from grain size and Sr‐Nd isotopes
    • Authors: Fuqing Jiang; Ye Zhou, Qingyun Nan, Yu Zhou, Xufeng Zheng, Tiegang Li, Anchun Li, Hongli Wang
      Abstract: Asian dust and volcanogenic materials are two major components in the northwestern Pacific. Quantitatively distinguishing them and estimating their mass accumulation rates (MARs) are very important for understanding regional and global climate change. Here, we present the grain‐size composition of detrital sediments and the radiogenic strontium (Sr) and neodymium (Nd) isotopic compositions of different grain‐size fractions of detrital sediments that were recovered from the western Philippine Sea. These new records show that the different grain‐size distributions can be associated with 1) Asian dust from the western and central Chinese deserts and Chinese loess and 2) volcanogenic materials that were derived from the Luzon Islands. The MARs of this Asian dust and volcanic materials are obtained by using Weibull‐function fitting. The MARs of Asian dust and volcanic materials are coupled with the glacial‐interglacial cycle; these values are found to have been higher and more variable during the glacial period than during the interglacial period. We argue that the strengthening aridity of the Asian continent, which is connected to solar insolation and ice volume variations from orbital eccentricity, constitutes an important mechanism that drives the high MARs of glacial dust in the western Philippine Sea. The internal positive feedback of dust may be another important mechanism. The significant increase in volcanic material during the glacial period was caused by sea level changes, which were driven by the ice volume and solar insolation at high latitudes, and by strengthened precipitation from the El Niño/Southern Oscillation (ENSO), which is driven by orbital eccentricity and precession cycles on the Luzon Islands. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-06T10:20:24.872305-05:
      DOI: 10.1002/2016JC012000
  • Estimation of Ocean Surface Currents from Maximum Cross Correlation
           applied to GOCI geostationary satellite remote sensing data over the
           Tsushima (Korea) Straits
    • Authors: M. A. Warren; G. D. Quartly, J. D. Shutler, P. I. Miller, Y. Yoshikawa
      Abstract: Attempts to automatically estimate surface current velocities from satellite‐derived thermal or visible imagery face the limitations of data occlusion due to cloud cover, the complex evolution of features and the degradation of their surface signature. The Geostationary Ocean Color Imager (GOCI) provides a chance to reappraise such techniques due to its multi‐year record of hourly high‐resolution visible spectrum data. Here we present the results of applying a Maximum Cross Correlation (MCC) technique to GOCI data. Using a combination of simulated and real data we derive suitable processing parameters and examine the robustness of different satellite products, those being water‐leaving radiance and chlorophyll concentration. These estimates of surface currents are evaluated using High Frequency (HF) radar systems located in the Tsushima (Korea) Strait. We show the performance of the MCC approach varies depending on the amount of missing data and the presence of strong optical contrasts. Using simulated data it was found that patchy cloud cover occupying 25% of the image pair reduces the number of vectors by 20% compared to using perfect images. Root mean square errors between the MCC and HF radar velocities are of the order of 20 cm s−1. Performance varies depending on the wavelength of the data with the blue‐green products out‐performing the red and near infra‐red products. Application of MCC to GOCI chlorophyll data results in similar performance to radiances in the blue‐green bands. The technique has been demonstrated using specific examples of an eddy feature and tidal induced features in the region. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-06T04:15:26.973047-05:
      DOI: 10.1002/2016JC011814
  • Assessing surface heat fluxes in atmospheric reanalyses with a decade of
           data from the NOAA Kuroshio Extension Observatory
    • Authors: Dongxiao Zhang; Meghan F. Cronin, Caihong Wen, Yan Xue, Arun Kumar, Dai McClurg
      Abstract: Previous studies have found large biases and uncertainties in the air‐sea fluxes from Numerical Weather Prediction model reanalyses, which must be identified and reduced in order to make progress on weather and climate predictions. Here, air‐sea heat fluxes from NOAA Kuroshio Extension Observatory (KEO) measurements are used to assess two new reanalyses, NCEP's Climate Forecast System Reanalysis (CFSR) and ECMWF Reanalysis‐Interim (ERA‐I), suggesting that these two new generation reanalyses have significantly improved. In both reanalyses, all four flux components (sensible and latent heat flux and net longwave and shortwave radiation) are highly correlated with observation, with the correlation of total net surface heat fluxes above 0.96. Although errors of the net surface heat flux have significantly reduced from previous reanalyses, the Root Mean Square Errors (RMSEs) and biases remain high especially for CFSR: the RMSEs of CFSR and ERA‐I are reduced by 25‐30% to 64 and 61 W/m2 respectively, while biases are reduced by 40‐60% to 28 and 20 W/m2. But CFSR overestimates the winter heat release by 90 W/m2. The main cause of biases is the latent heat flux, while RMS errors are primarily due to latent heat flux and shortwave radiation errors. Both reanalyses overestimate the wind speed associated with winter storms and underestimate specific humidity in summer. The ERA‐I latent heat flux, and its total net surface heat flux, are however closer to observation. It is the bulk algorithm in CFSR that is found to be mainly responsible for overestimates of winter heat release in CFSR. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-02T14:20:23.681054-05:
      DOI: 10.1002/2016JC011905
  • Seasonal predictability of sea surface temperature anomalies over the
           Kuroshio‐Oyashio Extension: Low in summer and high in winter
    • Authors: Yujie Wu; Wansuo Duan, Xinyao Rong
      Abstract: The seasonal predictability of sea surface temperature anomalies (SSTA) in the Kuroshio–Oyashio Extension (KOE) is explored by performing perfect model predictability experiments from the viewpoint of initial error growth in a global coupled model. It is found that prediction errors of KOE–SSTA always increase in the boreal summer and decrease in the boreal winter. This leads to smaller (larger) prediction errors and higher (lower) prediction skills in boreal winter (summer). This seasonal characteristic of the KOE–SSTA error growth implies a season‐dependent predictability that is lower in summer and higher in winter. The mechanism responsible for error growth associated with seasonal predictability is also explored. The error increase in summer and error decrease in winter in the KOE–SSTA are both largely attributed to the seasonal evolution of latent heat flux error and mean temperature advection by vertical current error in the KOE region, both of which are forced by the prediction error of one‐month leading zonal wind stress per unit mass for the mixed layer over the KOE region. The shallowest (deepest) mixed layer in summer (winter) amplifies (reduces) the forcing of zonal wind stress errors on the error growth of KOE–SSTA, thereby causing the seasonal evolution of prediction errors of KOE–SSTA and ultimately resulting in the season‐dependent predictability of the KOE–SSTA, i.e., low in summer and high in winter. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-02T14:05:36.503-05:00
      DOI: 10.1002/2016JC011887
  • A modulating effect of tropical instability wave (TIW)‐induced surface
           wind feedback in a hybrid coupled model of the tropical Pacific
    • Authors: Rong‐Hua Zhang
      Abstract: Tropical Instability Waves (TIWs) and the El Niño‐Southern Oscillation (ENSO) are two air‐sea coupling phenomena that are prominent in the tropical Pacific, occurring at vastly different space‐time scales. It has been challenging to adequately represent both of these processes within a large‐scale coupled climate model, which has led to a poor understanding of the interactions between TIW‐induced feedback and ENSO. In this study, a novel modeling system was developed that allows representation of TIW‐scale air‐sea coupling and its interaction with ENSO. Satellite data were first used to derive an empirical model for TIW‐induced sea surface wind stress perturbations (τTIW). The model was then embedded in a basin‐wide hybrid‐coupled model (HCM) of the tropical Pacific. Because τTIW were internally determined from TIW‐scale sea surface temperatures (SSTTIW) simulated in the ocean model, the wind‐SST coupling at TIW scales was interactively represented within the large‐scale coupled model. Because the τTIW–SSTTIW coupling part of the model can be turned on or off in the HCM simulations, the related TIW wind feedback effects can be isolated and examined in a straightforward way. Then, the TIW‐scale wind feedback effects on the large‐scale mean ocean state and interannual variability in the tropical Pacific were investigated based on this embedded system. The interactively represented TIW‐scale wind forcing exerted an asymmetric influence on SSTs in the HCM, characterized by a mean‐state cooling and by a positive feedback on interannual variability, acting to enhance ENSO amplitude. Roughly speaking, the feedback tends to increase interannual SST variability by approximately 9%. Additionally, there is a tendency for TIW wind to have an effect on the phase transition during ENSO evolution, with slightly shortened interannual oscillation periods. Additional sensitivity experiments were performed to elucidate the details of TIW wind effects on SST evolution during ENSO cycles. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-02T14:05:31.92588-05:0
      DOI: 10.1002/2015JC011567
  • Atmospheric forcing during active convection in the Labrador Sea and its
           impact on mixed‐layer depth
    • Authors: Lena M. Schulze; Robert S. Pickart, G.W.K. Moore
      Abstract: Hydrographic data from the Labrador Sea collected in February ‐ March 1997, together with atmospheric reanalysis fields, are used to explore relationships between the air‐sea fluxes and the observed mixed layer depths. The strongest winds and highest heat fluxes occurred in February, due to the nature and tracks of the storms. While greater numbers of storms occurred earlier and later in the winter, the storms in February followed a more organized track extending from the Gulf Stream region to the Irminger Sea where they slowed and deepened. The canonical low pressure system that drives convection is located east of the southern tip of Greenland, with strong westerly winds advecting cold air off the ice edge over the warm ocean. The deepest mixed layers were observed in the western interior basin, although the variability in mixed layer depth was greater in the eastern interior basin. The overall trend in mixed layer depth through the winter in both regions of the basin was consistent with that predicted by a 1‐D mixed layer model. We argue that the deeper mixed layers in the west were due to the enhanced heat fluxes on that side of the basin as opposed to oceanic preconditioning. This article is protected by copyright. All rights reserved.
      PubDate: 2016-09-01T10:05:21.616711-05:
      DOI: 10.1002/2015JC011607
  • A hybrid method to estimate suspended particle sizes from satellite
           measurements over Bohai Sea and Yellow Sea
    • Authors: Deyong Sun; Zhongfeng Qiu, Chuanmin Hu, Shengqiang Wang, Lin Wang, Lufei Zheng, Tian Peng, Yijun He
      Abstract: Particle size distribution (PSD), a measure of particle concentrations at different sizes, is of great importance to the understanding of many biogeochemical processes in coastal marine ecosystems. Here, a hybrid method, including analytical, semi‐analytical, and empirical steps, is developed to estimate PSD through the median diameter of suspended particles (Dv50). Four cruise surveys were conducted to measure optical scattering properties, particle concentrations, spectral reflectance, and particle size distributions (obtained with a LISST instrument covering a size range of 2.5‐500 μm) in coastal waters of Bohai Sea, Yellow Sea, and Jiangsu coastal region. Based on the Mie scattering theory, Dv50 is closely related to mass‐specific backscattering coefficient of suspended particles (bbp*), and their relationship is calibrated through a power model (R2=0.796, n=67, p
      PubDate: 2016-08-29T10:10:23.664014-05:
      DOI: 10.1002/2016JC011949
  • New insights on the upper layer circulation north of the Gulf of Guinea
    • Authors: Herbert G; Bourlès B, Penven P, Grelet J.
      Abstract: The oceanic circulation in the upper layers of the north of the Gulf of Guinea is analyzed, as inferred from in situ observations and numerical simulations. This particular region, in spite of the presence of a coastal upwelling and its impact on resources and regional climate, is still poorly documented. Cruises carried out in the framework of different international programs (e.g. EGEE/AMMA, PIRATA) allowed to show the existence of an eastward flowing undercurrent, found under the Guinea Current, named the Guinea UnderCurrent (GUC). Numerical results from high resolution simulation allowed the description of the seasonal variability of this current. It appears that the GUC is stronger in spring and reverses westward in August‐September. We also depict the fate and the sources of the GUC based on selected trajectories from numerical particle tracking. The simulated trajectories reveal: i) a preferred route of the GUC along 4°N from Cape Palmas to Cape Three Points and following the coast east of Cape Three Points; ii) strong recirculations in the most eastern part of the Gulf of Guinea and off Cape Palmas including warm and salty waters of the South Equatorial Current; iv) a weak inflow from northern latitudes through a subsurface current flowing southward along the West African coast. In addition, Lagrangian experiments show that the GUC is not an extension of the North Equatorial UnderCurrent and confirm that this current does not penetrate into the Gulf of Guinea. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-29T09:20:28.815618-05:
      DOI: 10.1002/2016JC011959
  • Diagnosing cross‐shelf transport along an ocean front: an observational
           case study in the Gulf of Lion
    • Authors: F. Nencioli; A. A. Petrenko, A. M. Doglioli
      Abstract: Exchanges between coastal regions and the open ocean are often associated with intermittent and localized processes such as eddies, fronts and filaments. Since these features are difficult to observe, their impact has been predominantly investigated using numerical models and remote sensing. In this study, satellite sea surface temperature maps, Lagrangian surface drifter trajectories, and ship‐based surveys of currents and hydrography from the Latex10 campaign are used to quantify cross‐shelf exchanges associated with a temperature front in the western Gulf of Lion. Satellite imagery and thermosalinograph sections provide the characterization of the various water masses associated with the front. Lagrangian drifter trajectories are used to identify the main transport structures and to quantify the velocity components associated with near‐inertial oscillations. These are removed from the instantaneous ADCP observations with which the cross‐shelf exchanges are then computed. The results indicate an average outflow of 0.074 ±0.013 Sv and an inflow of 0.021 ±0.006 Sv. Integrated over the two‐week lifetime of the front, such outflow induced a total export of ∼ 90 ± 14 km3 of water, indicating that 3 to 4 of such events are sufficient to completely renew the surface waters of the Gulf of Lion. The total import was ∼ 25 ± 7 km3, suggesting larger inflows at depth or in the eastern part of the gulf to maintain its volume balance. These in‐situ estimates represent a key term of comparison for the further development of numerical model‐ and satellite‐based studies of cross‐shelf exchanges associated with this type of processes. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-29T09:15:33.094553-05:
      DOI: 10.1002/2016JC011908
  • Seasonal evolution of the Yellow Sea Cold Water Mass and its interactions
           with ambient hydrodynamic system
    • Authors: Jianchao Li; Guangxue Li, Jishang Xu, Ping Dong, Lulu Qiao, Shidong Liu, Pingkuo Sun, Zhisong Fan
      Abstract: The Yellow Sea Cold Water Mass (YSCWM) is an important component of the hydrodynamic system in the South Yellow Sea (SYS). However, its intricate interactions with the ambient flows over long time scales are not fully understood. This paper presents the analysis of the dataset obtained from a seabed‐mounted Acoustic Doppler Current Profiler (ADCP) deployed for nearly one‐year in the western SYS. It allowed us to study the evolution of YSCWM, including the seasonal changes of tidal currents, near inertial oscillations (NIOs) and the wind‐driven currents due to typhoons and winter storms. Strong NIOs were found near the bottom of mixed layer and in the pycnocline with nearly opposite current directions, with maximum velocity of nearly 20cm·s−1 in summer. The YSCWM can also inhibit the direct downward energy transport in the water column due to typhoons. Conversely, the hydrodynamic system also feeds back to influence the change of YSCWM. A large current shear (S) of 20cm·s−1·m−1 is generated near the top of pycnocline. Generally the intensity and depth of the pycnocline determine S's magnitude and vertical location, respectively. Based on the monthly‐averaged density profile data, the Richardson number and wavelet analysis, the NIOs are considered to be capable of inducing predominant shear instability around the pycnocline. However the NIOs are not strong enough to influence the lower YSCWM. In addition, in autumn, each fortnightly spring tide corresponds with a bottom temperature increase of nearly 2°C, indicating that tidal currents are the leading hydrodynamic driving force to decline the YSCWM. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-29T09:15:27.859285-05:
      DOI: 10.1002/2016JC012186
  • Sea surface wind streaks in spaceborne synthetic aperture radar imagery
    • Authors: Yuan Zhao; Xiao‐Ming Li, Jin Sha
      Abstract: Wind streaks are often observed in Synthetic Aperture Radar (SAR) images. They are used to determine the sea surface wind direction for sea surface wind field retrievals. It is generally understood that visible wind streaks are caused by roll vortices in the marine atmospheric boundary layer. In this study, 227 X‐band spaceborne SAR TerraSAR‐X and TanDEM‐X images acquired from the three FiNO platforms in the North Sea and Baltic Sea were thoroughly analyzed for a comprehensive understanding of the manifestation of wind streaks in SAR images. Approximately 48.0% of the 227 SAR images displayed wind streaks, among which 67.3%, 20.0% and 12.7% occurred under unstable, neutral, stable atmospheric conditions, respectively. The proportions indicate that wind streaks are more likely to be generated from thermal convection. Further investigations suggest that the inflection point and the wind shear may be essential for the appearance of wind streaks in SAR images under stable atmospheric conditions. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-29T04:10:24.087185-05:
      DOI: 10.1002/2016JC012040
  • The phenology of Arctic Ocean Surface warming
    • Authors: Michael Steele; Suzanne Dickinson
      Abstract: In this work, we explore the seasonal relationships (i.e., the phenology) between sea ice retreat, sea surface temperature (SST), and atmospheric heat fluxes in the Pacific Sector of the Arctic Ocean, using satellite and reanalysis data. We find that where ice retreats early in most years, maximum summertime SSTs are usually warmer, relative to areas with later retreat. For any particular year, we find that anomalously early ice retreat generally leads to anomalously warm SSTs. However, this relationship is weak in the Chukchi Sea, where ocean advection plays a large role. It is also weak where retreat in a particular year happens earlier than usual, but still relatively late in the season, primarily because atmospheric heat fluxes are weak at that time. This result helps to explain the very different ocean warming responses found in two recent years with extreme ice retreat, 2007 and 2012. We also find that the timing of ice retreat impacts the date of maximum SST, owing to a change in the ocean surface buoyancy and momentum forcing that occurs in early August that we term the Late Summer Transition (LST). After the LST, enhanced mixing of the upper ocean leads to cooling of the ocean surface even while atmospheric heat fluxes are still weakly downward. Our results indicate that in the near‐term, earlier ice retreat is likely to cause enhanced ocean surface warming in much of the Arctic Ocean, although not where ice retreat still occurs late in the season. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-29T04:05:32.287449-05:
      DOI: 10.1002/2016JC012089
  • Experiments with mixing in stratified flow over a topographic ridge
    • Authors: Yvan Dossmann; Madelaine G. Rosevear, Ross W. Griffiths, Andrew McC. Hogg, Graham O. Hughes, Michael Copeland
      Abstract: The interaction of quasi‐steady abyssal ocean flow with submarine topography is expected to generate turbulent mixing in the ocean. This mixing may occur locally, close to topography, or via breaking quasi‐steady lee waves that can carry energy into the ocean interior. There is currently no theoretical, or empirically‐derived, prediction for the relative amounts of local and interior mixing. We report measurements of the mixing rate in laboratory experiments with a topographic ridge towed through a density stratification. The experiments span three parameter regimes including linear lee waves, nonlinear flow and an evanescent regime in which wave radiation is weak. Full field density measurements provide the depth‐dependence of energy loss to turbulent mixing, allowing separation of the local mixing in the turbulent wake and remote mixing by wave radiation. Remote mixing is significant only for a narrow band of forcing parameters where the flow speed is resonant with internal waves; in all other parameter regimes local mixing close to the topography is dominant. The results suggest that mixing by local nonlinear mechanisms close to abyssal ocean topography may be much greater than the remote mixing by quasi‐steady lee waves. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-25T17:45:48.081132-05:
      DOI: 10.1002/2016JC011990
  • Remote sensing of normalized diffuse attenuation coefficient of
           downwelling irradiance
    • Authors: Junfang Lin; Zhongping Lee, Mike Ondrusek, Keping Du
      Abstract: The diffuse attenuation of downwelling irradiance, Kd (m−1), is an important property related to light penetration and availability in aquatic ecosystems. The standard Kd(490) product (the diffuse attenuation coefficient at 490 nm) of the global oceans from satellite remote sensing has been produced with an empirical algorithm, which limits its reliability and applicability in coastal regions. More importantly, as an apparent optical property (AOP), Kd is a function of the angular distribution of the light field (e.g., solar zenith angle). The empirically derived product thus contains ambiguities when compared with in situ measurements as there is no specification regarding the corresponding solar zenith angle associated with this Kd(490) product. To overcome these shortcomings, we refined the Kd product with a product termed as the normalized diffuse attenuation coefficient (nKd, m−1), which is equivalent to the Kd in the absence of the atmosphere and with the sun at zenith. Models were developed to get nKd from both in situ measurements and ocean color remote sensing. Evaluations using field measurements indicated that the semi‐analytically derived nKd product will not only remove the ambiguities when comparing Kd values of different light fields, but will also improve the quality of such a product, therefore maximizing the value offered by satellite ocean color remote sensing. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-25T05:10:33.4159-05:00
      DOI: 10.1002/2016JC011895
  • Seaglider surveys at Ocean Station Papa: Circulation and water mass
           properties in a meander of the North Pacific current
    • Authors: Noel A. Pelland; Charles C. Eriksen, Meghan F. Cronin
      Abstract: A Seaglider autonomous underwater vehicle augmented the Ocean Station Papa (OSP; 50°N, 145°W) surface mooring, measuring spatial structure on scales relevant to the monthly evolution of the moored time series. During each of three missions from June 2008‐January 2010, a Seaglider made biweekly 50 km × 50 km surveys in a bowtie‐shaped survey track. Horizontal temperature and salinity gradients measured by these surveys were an order of magnitude stronger than climatological values and sometimes of opposite sign. Geostrophically‐inferred circulation was corroborated by moored acoustic Doppler current profiler measurements and AVISO satellite altimetry estimates of surface currents, confirming that glider surveys accurately resolved monthly‐scale mesoscale spatial structure. In contrast to climatological North Pacific Current circulation, upper ocean flow was modestly northward during the first half of the 18 month survey period, and weakly westward during its latter half, with Rossby number (0.01). This change in circulation coincided with a shift from cool and fresh to warm, saline, oxygen‐rich water in the upper‐ocean halocline, and an increase in vertical finestructure there and in the lower pycnocline. The anomalous flow and abrupt water mass transition were due to the slow growth of an anticyclonic meander within the North Pacific Current with radius comparable to the scale of the survey pattern, originating to the southeast of OSP. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-24T05:50:31.454779-05:
      DOI: 10.1002/2016JC011920
  • The effect of Kuroshio current on nitrate dynamics in the southern East
           China Sea revealed by nitrate isotopic composition
    • Authors: Wentao Wang; Zhiming Yu, Xiuxian Song, Zaixing Wu, Yongquan Yuan, Peng Zhou, Xihua Cao
      Abstract: In spring 2014 (May‒June), in the southern East China Sea (ECS) and east of Taiwan, nutrient and isotope samples were collected and analyzed. Also, dissolved oxygen (DO), chlorophyll‐a, and physical parameters were determined. The Kuroshio subsurface water intruded into the ECS and separated into two branches on the continental shelf: the nearshore Kuroshio branch current (NKBC) and the offshore Kuroshio branch current (OKBC). Nitrate concentration in the Kuroshio subsurface water slightly decreased east of Taiwan by assimilation, and was supplied by upwelling currents northeast of Taiwan. The variations of DO, nitrate and nitrogen isotopes in the bottom water showed that continuous nitrification occurred in the NKBC after intrusion into the ECS. This process might contribute to the hypoxia zone near the coast of Zhejiang Province, China. Our results also indicated that internal nitrogen cycles appeared in NKBC since the isotope fractionation ratio of oxygen and nitrogen (18ɛ:15ɛ) in NO3‐ was 1.40. The NO3‐ flux and budget were calculated in the NKBC via numerical simulations. It demonstrated that at least ∼0.52 kmol NO3‐·s−1 was produced by nitrification from DH9 to DH5 transect, and ∼0.11 kmol NO3‐·s−1 was consumed in the DH4 transect. Moreover, according to the Rayleigh model, primary production in most of southern ECS was supported by the intrusion of the Kuroshio subsurface water, causing 5‰ isotope fractionation. In some of nearshore stations which located in the northern investigated area, the assimilated nitrate was contributed from both the NKBC and coastal currents originated from the Changjiang diluted water. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-24T05:40:24.59285-05:0
      DOI: 10.1002/2016JC011882
  • Mesoscale modulation of air‐sea CO2 flux in Drake Passage
    • Authors: Hajoon Song; John Marshall, David R. Munro, Stephanie Dutkiewicz, Colm Sweeney, D. J. McGillicuddy, Ute Hausmann
      Abstract: We investigate the role of mesoscale eddies in modulating air‐sea CO2 flux and associated biogeochemical fields in Drake Passage using in situ observations and an eddy‐resolving numerical model. Both observations and model show a negative correlation between temperature and partial pressure of CO2 (pCO2) anomalies at the sea surface in austral summer, indicating that warm/cold anticyclonic/cyclonic eddies take up more/less CO2. In austral winter, in contrast, relationships are reversed: warm/cold anticyclonic/cyclonic eddies are characterized by a positive/negative pCO2 anomaly and more/less CO2 outgassing. It is argued that DIC‐driven effects on pCO2 are greater than temperature effects in austral summer, leading to a negative correlation. In austral winter, however, the reverse is true. An eddy‐centric analysis of the model solution reveals that nitrate and iron respond differently to the same vertical mixing: vertical mixing has a greater impact on iron because its normalized vertical gradient at the base of the surface mixed layer is an order of magnitude greater than that of nitrate. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-24T05:20:27.601083-05:
      DOI: 10.1002/2016JC011714
  • Western boundary currents and climate change
    • Authors: Richard Seager; Isla R. Simpson
      Abstract: A recent paper in Journal of Geophysical Research‐Oceans connects recent changes in atmospheric circulation to poleward movement and intensification of western boundary currents. Causes and character of past and future trends in surface wind stress and western boundary currents are discussed here. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-24T05:20:21.93621-05:0
      DOI: 10.1002/2016JC012156
  • Forcing of recent decadal variability in the Equatorial and North Indian
    • Authors: P. R. Thompson; C. G. Piecuch, M. A. Merrifield, J. P. McCreary, E. Firing
      Abstract: Recent decadal sea surface height (SSH) variability across the Equatorial and North Indian Ocean (ENIO, north of 5°S) is spatially coherent and related to a reversal in basin‐scale, upper‐ocean‐temperature trends. Analysis of ocean and forcing fields from a data‐assimilating ocean synthesis (ECCOv4) suggests that two equally‐important mechanisms of wind‐driven heat redistribution within the Indian Ocean account for a majority of the decadal variability. The first is the Cross‐Equatorial Cell (CEC) forced by zonal‐wind‐stress curl at the equator. The wind‐stress curl variability relates to the strength and position of the Mascarene High, which is influenced by the phase of the Indian Ocean Subtropical Dipole. The second mechanism is deep (700 m) upwelling related to zonal wind stress at the equator that causes deep, cross‐equatorial overturning due to the unique geometry of the basin. The CEC acts to cool the upper ocean throughout most of the first decade of satellite altimetry, while the deep upwelling delays and then amplifies the effect of the CEC on SSH. During the subsequent decade, reversals in the forcing anomalies drive warming of the upper ocean and increasing SSH, with the effect of the deep upwelling leading the CEC. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-24T03:56:09.328435-05:
      DOI: 10.1002/2016JC012132
  • Alongcoast structure and interannual variability of seasonal midshelf
           water properties and velocity in the Northern California Current System
    • Authors: B. Hickey; S. Geier, N. Kachel, S. Ramp, P. M. Kosro, T. Connolly
      Abstract: Moored sensors were maintained for ∼5 years on the northern California Current System (CCS) midshelf. The alongcoast sensor array spanned the area of influence of the plume from the Columbia River, several submarine canyons, as well as a coastal promontory where the equatorward coastal jet frequently separates from the shelf. Upwelling‐favorable wind stress magnitude decreases poleward by more than a factor of three over the latitudinal range and shelf width varies by a factor of two. In spite of the alongcoast structure in setting, both seasonal and interannual patterns in subsurface layer water properties were remarkably similar at all sites. Higher in the water column, freshwater forcing was substantial. Because of the near surface freshwater input, seasonal sea surface and subsurface temperatures were almost perfectly out of phase in the northernmost CCS (WA and OR), with a mid water column inversion in winter. Year to year differences in subsurface layer wintertime water properties were similar to spatial and temporal patterns of wind stress variability: little alongcoast structure except in salinity, but pronounced interannual differences. Summertime wind and property patterns were the opposite of those in winter: pronounced alongcoast wind stress structure, but little or no alongcoast or interannual variability in water property extremes, and only a weak relationship to local wind stress. Summertime interannual water property variability, including source waters, was shown to be more consistent with “remote forcing” via larger scale wind stress rather than with local wind stress, particularly in the northernmost CCS. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-24T03:56:02.562191-05:
      DOI: 10.1002/2015JC011424
  • The Atlantic Water boundary current in the Nansen Basin: Transport and
           mechanisms of lateral exchange
    • Authors: Kjetil Våge; Robert S. Pickart, Vladimir Pavlov, Peigen Lin, Daniel J. Torres, Randi Ingvaldsen, Arild Sundfjord, Andrey Proshutinsky
      Abstract: Data from a shipboard hydrographic survey near 30°E in the Nansen Basin of the Arctic Ocean are used to investigate the structure and transport of the Atlantic Water boundary current. Two high‐resolution synoptic crossings of the current indicate that it is roughly 30 km wide and weakly mid‐depth intensified. Using a previously‐determined definition of Atlantic Water, the transport of this water mass is calculated to be 1.6 ± 0.3 Sv, which is similar to the transport of Atlantic Water in the inner branch of the West Spitsbergen Current. At the time of the survey a small anti‐cyclonic eddy of Atlantic Water was situated just offshore of the boundary current. The data suggest that the feature was recently detached from the boundary current, and, due to compensating effects of temperature and salinity on the thermal wind shear, the maximum swirl speed was situated below the hydrographic property core. Two other similar features were detected within our study domain, suggesting that these eddies are common and represent an effective means of fluxing warm and salty water from the boundary current into the interior. An atmospheric low pressure system transiting south of our study area resulted in southeasterly winds prior to and during the field measurements. A comparison to hydrographic data from the Pacific Water boundary current in the Canada Basin under similar atmospheric forcing suggests that upwelling was taking place during the survey. This provides a second mechanism related to cross‐stream exchange of heat and salt in this region of the Nansen Basin. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-24T03:50:58.865812-05:
      DOI: 10.1002/2016JC011715
  • Annual cycle and destruction of Eighteen Degree Water
    • Authors: Sam Billheimer; Lynne D. Talley
      Abstract: Eighteen Degree Water (EDW), the subtropical mode water of the western North Atlantic, is a voluminous, weakly‐stratified upper ocean water mass that acts as a subsurface reservoir of heat, nutrients, and CO2. This thick layer persists throughout the year, but nearly half of its volume is dispersed or mixed away, diffusing its properties into the thermocline, from the time it outcrops in winter until it is renewed the following year. CTD observations from Argo profiling floats and acoustically‐tracked, isothermally‐bound profiling floats are used to quantify EDW destruction rates and investigate the relevant processes responsible for the large annual cycle of EDW. EDW destruction occurs primarily at the top of the EDW layer, with the highest EDW destruction rates occurring during early summer. Slower, steadier EDW destruction is observed in early winter. EDW destruction is dominated by 1‐D vertical diffusion, while mesoscale, along‐isopycnal stirring is also significant, explaining approximately 1/3 of the total annual EDW destruction. Destruction via along‐isopycnal processes is more prevalent near the Gulf Stream than in the southern Sargasso Sea, due to higher potential vorticity gradients and enhanced mesoscale activity. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-20T04:06:02.409243-05:
      DOI: 10.1002/2016JC011799
  • High export via small particles before the onset of the North Atlantic
           spring bloom
    • Authors: Giering S. L. C; R. Sanders, A. P. Martin, C. Lindemann, K.O. Möller, C. J. Daniels, D. J. Mayor, M. A. St. John
      Abstract: Sinking organic matter in the North Atlantic Ocean transfers 1‐3 Gt carbon year−1 from the surface ocean to the interior. The majority of this exported material is thought to be in form of large, rapidly sinking particles that aggregate during or after the spring phytoplankton bloom. However, recent work has suggested that intermittent water column stratification resulting in the termination of deep convection can isolate phytoplankton from the euphotic zone, leading to export of small particles. We present depth profiles of large (>0.1mm equivalent spherical diameter, ESD) and small (300m depth, leading to deep mixing of particles as deep as 600m. Subsequent re‐stratification could trap these particles at depth and lead to high particle fluxes at depth without the need for aggregation (‘mixed layer pump'). Overall we suggest that pre‐bloom fluxes to the mesopelagic are significant, and the role of small sinking particles requires careful consideration. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-19T09:45:29.206809-05:
      DOI: 10.1002/2016JC012048
  • Consequences of inhibition of mixed‐layer deepening by the West India
           Coastal Current for winter phytoplankton bloom in the northeastern Arabian
    • Authors: V. Vijith; P. N. Vinayachandran, V. Thushara, P. Amol, D. Shankar, A. C. Anil
      Abstract: The intense winter phytoplankton bloom during November – February in the northeastern Arabian Sea (NEAS) was thought, until recently, to be controlled only by a convective deepening of the mixed layer (ML) owing to cool and dry northeasterlies. But, a recent study has shown that the deepening of the ML in the southern NEAS is inhibited by the poleward advection of low‐salinity water from the south by the West India Coastal Current (WICC). Using an Ocean General Circulation Model coupled with an ecosystem model, we investigate the consequences of the inhibition of mixed‐layer deepening for winter phytoplankton bloom in the NEAS. We show that, during the winter monsoon, the shallow ML inhibits the entrainment of nutrients in the southern NEAS. Strong (weak) positive nitrate tendency in the northern (southern) NEAS seen in the model during the winter monsoon is maintained by strong (weak) entrainment. As a result, the chlorophyll integrated to 200 m depth from the surface is lower in the southern NEAS than in the northern NEAS. The inhibition of mixed‐layer deepening in the south affects the size‐based distribution of small and large phytoplankton, nutrient limitation terms and growth rate, and their elemental composition. The WICC, which inhibits the deepening of the ML and affects the winter bloom in the NEAS, is driven by coastal Kelvin waves generated by remote winds. This paper demonstrates a mechanism by which remotely forced coastal Kelvin waves impact the biology in the north Indian Ocean. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-19T09:35:30.038659-05:
      DOI: 10.1002/2016JC012004
  • Estimating dense water volume and its evolution for the year 2012‐2013
           in the North‐western Mediterranean Sea: An observing system simulation
           experiment approach
    • Authors: Robin Waldman; Samuel Somot, Marine Herrmann, Pierre Testor, Claude Estournel, Florence Sevault, Louis Prieur, Laurent Mortier, Laurent Coppola, Vincent Taillandier, Pascal Conan, Denis Dausse
      Abstract: The northwestern Mediterranean (NWMed) sea includes one of the best observed ocean deep convection sites in the World. An Observing System Simulation Experiment (OSSE) is developed to provide a methodology for estimating observing network errors. It is applied to quantify dense water volumes in the NWMed during 2012‐2013 with their observation error from MOOSE network.Results from the OSSE show low spatio‐temporal sampling errors, which confirms MOOSE network ability to measure dense waters. However, results are highly sensitive to instrumental stability.The dense water volume is then estimated in observations from four ship cruises between summers 2012 and 2013. A large seasonal cycle is found, maximal in spring 2013 and dominated by the area west of 6.5°E. The dense water volume (σ0>29.11kg/m3) is stable between summer 2012 (13.3±0.6 1013m3) and winter 2013 (13.7±1.3 1013m3). It increases dramatically in spring 2013 (17.7±0.9 1013m3) due to an intense convective event, and it finally decreases rapidly in summer 2013 (15.1±0.6 1013m3) due to restratification and spreading. We estimate an open‐sea dense water formation (DWF) rate of 1.4±0.3Sυ between summer 2012 and spring 2013 over the studied area, extrapolated to 2.3±0.5Sυ over the whole NWMed sea and for the optimal timing. This is to our knowledge the highest measured DWF rate, suggesting winter 2013 was exceptionally convective. The observed restratification rate between spring and summer 2013 is ‐0.8±0.4S4Sυ. This study provides robust quantifications of deep convection during an exceptional event that will allow to evaluate numerical simulations. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-19T09:35:26.150189-05:
      DOI: 10.1002/2016JC011694
  • An ensemble of ocean reanalyses for 1815–2013 with sparse
           observational input
    • Authors: Benjamin S. Giese; Howard F. Seidel, Gilbert P. Compo, Prashant D. Sardeshmukh
      Abstract: This paper describes a new 8‐member ensemble of oceanic reanalyses spanning nearly 200 years from 1815 to 2013 generated using the Simple Ocean Data Assimilation system with sparse observational input (SODAsi) to explore long‐term changes in the oceans. The 8 ensemble members assimilate surface temperature observations and use surface boundary conditions from an atmospheric reanalysis that is loosely coupled to the ocean reanalysis. Both surface and subsurface quantities, such as dynamic height and heat content, show a broad spectrum of variability. Surface temperature trends from 1815 to 2013 are positive in most regions, with some important exceptions; the central Tropical Pacific, around Antarctica, and in the Gulf Stream and Kuroshio extension regions all show cooling trends. A near‐global average shows warming of about 0.8°C over the full period, with most of the warming occurring after 1920. There is pronounced multi‐decadal variability in both the mid‐latitude and tropical oceans. In the North Atlantic Ocean, temperature variability is highly correlated with the meridional overturning streamfunction, with the largest correlation occurring when the streamfunction is advanced by 9 years. Trends of upper ocean heat content and dynamic height from the 1950s onward compare well with previously published values. Globally averaged heat content of the upper 700 m shows a nearly linear rise after the 1920s, requiring a net downward surface heat flux increase of 0.47 W m−2 into the ocean. This is close to published estimates of the increased flux required to explain the heat content increase from 1971 to 2010. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-18T06:20:49.310455-05:
      DOI: 10.1002/2016JC012079
  • Geochemical observations within the water column at the CO2‐rich
           hydrothermal systems Hatoma Knoll and Yonaguni Knoll IV, in the southern
           Okinawa Trough
    • Authors: Stine Kedzior; Antje Buß, Bernd Schneider, Jens Schneider von Deimling, Jürgen Sültenfuß, Maren Walter, Christian Mertens, Gregor Rehder
      Abstract: The Okinawa Trough is one of three known hydrothermal sites worldwide where liquid carbon dioxide is emitted from the seafloor into the water column. In March 2008 investigations were performed at two active areas, Yonaguni Knoll IV and Hatoma Knoll, in order to identify impacts of hydrothermal venting on the water column chemistry. Vertical profiles of pH and redox potential (Eh) were recorded and discrete water samples were taken for the analysis of total carbon dioxide (CT) and helium (3He, 4He). Anomalies with respect to reference stations (ΔCT, ΔpH) and 3He with respect to saturation with the atmosphere (3Heexcess) were used to characterize the impact of hydrothermal vents. These data indicate that the flux of CO2 into the water column is dominated by hot hydrothermal CO2‐rich vents located in close proximity to the liquid CO2 emission sites. Bubbles and droplets sampled at the cold gas outlets at Hatoma Knoll differed considerably from the water column regarding CO2/3He ratios, and thus, provide additional evidence that cold liquid phase CO2 is of minor importance for the total CO2 flux at both hydrothermal systems. Although hydrothermal vents at back‐arc basins are known to emit large amounts of acids other than CO2, the correlation between ΔpH and ΔCT at both research areas clearly suggests that the observed pH reduction is mainly caused by the addition of CO2. Deviating ΔCT/3He and ΔCT/ΔpH ratios and the prevailing water currents indicate a yet undiscovered vent site at the flank of a seamount in the northeast. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-18T06:16:35.563099-05:
      DOI: 10.1002/2016JC012003
  • Upstream control of the frontal jet regulating plankton production in the
           Alboran Sea (Western Mediterranean)
    • Authors: Temel Oguz; Baptiste Mourre, Joaquín Tintoré
      Abstract: Using a coupled physical‐biological model, we document that a ∼30 km wide meandering jet constitutes a major source of biological enrichment in the Alboran Sea (Western Mediterranean) even in the absence of wind forcing and tidal dynamics. The level of enrichment is shown to vary markedly during the year depending on the upstream characteristics of the jet as it exits from the Gibraltar Strait. When its intensity is sufficiently low and characterized by weaker cross‐frontal density gradients during winter‐spring, the jet is weakly nonlinear and may not fulfill the necessary conditions for frontogenesis. It then remains weakly productive. In the case of stronger jet intensity (>1.1 Sv) accompanied by stronger cross‐frontal density and velocity gradients within the Alboran Sea during summer‐autumn, the frontal jet becomes strongly nonlinear and ageostrophic with large cross‐frontal vorticity changes on the order of planetary vorticity. Under these conditions, upward vertical velocities in the range 10‐50 m d−1 supply nutrients into the euphotic layer more effectively and support high level frontogenesis‐induced phytoplankton production on the anticyclonic side of the main jet axis. The strong eddy pumping mechanism also provides a comparable level of plankton production within strongly nonlinear elongated cyclonic eddies along the outer periphery of the frontal jet. The plankton biomass is advected partially by the jet along its trajectory and dispersed within the basin by mesoscale eddies and meanders. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-18T06:16:23.855833-05:
      DOI: 10.1002/2016JC011667
  • How does Subantarctic Mode Water ventilate the Southern Hemisphere
    • Authors: Daniel C. Jones; Andrew J.S. Meijers, Emily Shuckburgh, Jean‐Baptiste Sallée, Peter Haynes, Ewa Karczewska, Matthew R. Mazloff
      Abstract: In several regions north of the Antarctic Circumpolar Current (ACC), deep wintertime convection refreshes pools of weakly stratified subsurface water collectively referred to as Subantarctic Mode Water (SAMW). SAMW ventilates the subtropical thermocline on decadal timescales, providing nutrients for low‐latitude productivity and potentially trapping anthropogenic carbon in the deep ocean interior for centuries. In this work, we investigate the spatial structure and timescales of mode water export and associated thermocline ventilation. We use passive tracers in an eddy‐permitting, observationally‐informed Southern Ocean model to identify the pathways followed by mode waters between their formation regions and the areas where they first enter the subtropics. We find that the pathways followed by the mode water tracers are largely set by the mean geostrophic circulation. Export from the Indian and Central Pacific mode water pools is primarily driven by large‐scale gyre circulation, whereas export from the Australian and Atlantic pools is heavily influenced by the ACC. Export from the Eastern Pacific mode water pool is driven by a combination of deep boundary currents and subtropical gyre circulation. More than 50% of each mode water tracer reaches the subtropical thermocline within 50 years, with significant variability between pools. The Eastern Pacific pathway is especially efficient, with roughly 80% entering the subtropical thermocline within 50 years. The time required for 50% of the mode water tracers to leave the Southern Ocean domain varies significantly between mode water pools, from 9 years for the Indian mode water pool to roughly 40 years for the Central Pacific mode water pool. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-18T06:16:17.051279-05:
      DOI: 10.1002/2016JC011680
  • Air‐sea interaction at the Southern Brazilian continental shelf: In
           situ observations
    • Authors: L. P. Pezzi; R. B. Souza, P. C. Farias, O. Acevedo, A. J. Miller
      Abstract: The influence of the cross‐shelf oceanographic front occurring between the Brazil Current (BC) and the Brazilian Coastal Current (BCC) on the local Marine Atmospheric Boundary Layer (MABL) is investigated here. This front is typical of wintertime in the Southern Brazilian Continental Shelf (SBCS) and this is the first time that its effects are investigated over the above MABL. Here we analyze variability, vertical structure and stability of MABL as well as heat fluxes at air‐sea interface, across five oceanographic transects in the SBCS made during a winter 2012 cruise. Local thermal gradients associated with mixing between distinct water masses, play an essential role on MABL modulation and stability. Although weaker when compared with other frontal regions, the cross‐shelf thermal gradients reproduce exactly what is expected for open ocean regions: Stronger (weaker) winds, lower (higher) sea level pressure and a more unstable (stable) MABL are found over the warm (cold) side of the oceanographic front between the BC (warm) and coastal (cold) waters. Our findings strongly support the coexistence of both known MABL modulation mechanisms: the static and hydrostatic MABL stability. This is the first time that these modulation mechanisms are documented for this region. Turbulent fluxes were found to be markedly dependent on the cross‐shelf SST gradients resulting in differences of up to 100 W.m−2 especially in the southernmost region where the gradients were more intense. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-18T06:15:59.672622-05:
      DOI: 10.1002/2016JC011774
  • Budget of organic carbon in the North‐Western Mediterranean Open Sea
           over the period 2004–2008 using 3‐D coupled physical‐biogeochemical
    • Authors: C. Ulses; P.‐A. Auger, K. Soetaert, P. Marsaleix, F. Diaz, L. Coppola, M.J. Herrmann, F. Kessouri, C. Estournel
      Abstract: A 3D hydrodynamic‐biogeochemical coupled model has been used to estimate a budget of organic carbon and its interannual variability over the 5‐year period 2004‐2008 in the North‐Western Mediterranean Open Sea (NWMOS). The comparison of its results with in situ and satellite observations reveals that the timing and the magnitude of the convection and bloom processes during the study period, marked by contrasted atmospheric conditions, are reasonably well reproduced by the model. Model outputs show that the amount of nutrients annually injected into the surface layer is clearly linked to the intensity of the events of winter convection. During cold winters, primary production is reduced by intense mixing events but then spectacularly increases when the water column restratifies. In contrast, during mild winters, the primary production progressively and continuously increases, sustained by moderate new production followed by regenerated production. Overall, interannual variability in the annual primary production is low. The export in sub‐surface and at mid‐depth is however affected by the intensity of the convection process, with annual values twice as high during cold winters than during mild winters. Finally, the estimation of a global budget of organic carbon reveals that the NWMOS acts as a sink for the shallower areas and as a source for the Algerian and Balearic sub‐basins. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-18T06:10:54.493874-05:
      DOI: 10.1002/2016JC011818
  • Estimation of melt pond fraction over high‐concentration Arctic sea ice
           using AMSR‐E passive microwave data
    • Authors: Yasuhiro Tanaka; Kazutaka Tateyama, Takao Kameda, Jennifer K. Hutchings
      Abstract: Melt pond fraction (MPF) on sea ice is an important factor for ice‐albedo feedback throughout the Arctic Ocean. We propose an algorithm to estimate MPF using satellite passive microwave data in this study. The brightness temperature (TB) data obtained from the Advanced Microwave Scanning Radiometer‐Earth observing system (AMSR‐E) were compared to the ship‐based MPF in the Beaufort Sea and Canadian Arctic Archipelago. The difference between the TB at horizontal and vertical polarizations of 6.9‐ and 89.0‐GHz (MP06H–89V), respectively, depend on the MPF. The correlation between MP06H–89V and ship‐based MPF was higher than that between ship‐based MPF and two individual channels (6.9‐ and 89.0‐GHz of horizontal and vertical polarizations, respectively). The MPF determined with the highest resolution channel, 89.0‐GHz (5 km × 5 km) provides spatial information with more detail than the 6.9‐GHz channel. The algorithm estimates the relative fraction of ice covered by water (1) over areas where sea ice concentration is higher than 95%, (2) during late summer, and (3) in areas with low atmospheric humidity. The MPF estimated from AMSR‐E data (AMSR‐E MPF) in early summer was underestimated at lower latitudes and overestimated at higher latitudes, compared to the MPF obtained from the Moderate Resolution Image Spectrometer (MODIS MPF). The differences between AMSR‐E MPF and MODIS MPF were less than 5% in most the regions and the periods. Our results suggest that the proposal algorithm serves as a basis for building time series of MPF in regions of consolidated ice pack. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-18T06:10:29.516362-05:
      DOI: 10.1002/2016JC011876
  • Evaluating the use of 1d transit time distributions to infer the mean
           state and variability of oceanic ventilation
    • Authors: Andrew E. Shao; Sabine Mecking, LuAnne Thompson, Rolf E. Sonnerup
      Abstract: An offline tracer transport model transport is used to simulate chlorofluorocarbon (CFCs), sulfur hexafluoride (SF6), oxygen, ideal age, and model transit time distributions (TTDs) to evaluate how well tracers can be used to constrain both the mean state and variability of oceanic ventilation. Using climatological transports, the two‐parameter 1d inverse Gaussian approximation of the model TTD is found to be an adequate representation of ventilation pathways within {the parts of the subtropical gyres with simple ventilation dynamics}, but a poor approximation for regions with large gradients in ideal age (i.e. near the base of the thermocline and the continental boundaries). TTDs inferred from CFC‐12 and SF6 using a Peclet number based lookup table approach yield poor representations of the model TTD with a consistent bias towards ventilation being strongly dominated by along‐isopycnal diffusion. In a run with variable circulation, ideal age is used to track changes in thermocline ventilation. Variability in both apparent oxygen utilization (AOU) and tracer‐inferred TTD mean ages inferred using CFC‐12 (assuming fixed Peclet number) and dual tracers (SF6 and CFC‐12) are well‐correlated to ideal age variability in most of the thermocline. Changes in AOU are correlated with ideal age variability in even more regions compared to the TTD ages both horizontally and vertically down to intermediate depths. Generally when changes in TTD mean age and AOU agreed in sign, correlations of both with ideal age changes were positive indicating the usefulness of tracers in diagnosing ventilation changes. This article is protected by copyright. All rights reserved.
      PubDate: 2016-08-06T03:14:14.535536-05:
      DOI: 10.1002/2016JC011900
  • Asymmetric oceanic response to a hurricane: Deepwater observations during
           Hurricane Isaac
    • Authors: Laura J. Spencer; Steven F. DiMarco, Zhankun Wang, Joseph J. Kuehl, David A. Brooks
      Abstract: The eye of Hurricane Isaac passed through the center of an array of six deepwater water‐column current meter moorings deployed in the northern Gulf of Mexico. The trajectory of the hurricane provided for a unique opportunity to quantify differences in the full water‐column oceanic response to a hurricane to the left and right of the hurricane trajectory. Prior to the storm passage, relative vorticity on the right side of the hurricane was strongly negative; while on the left, relative vorticity was positive. This resulted in an asymmetry in the near inertial frequencies oceanic response at depth and horizontally. A shift in the response to a slightly larger inertial frequencies ∼1.11f was observed and verified by theory. Additionally, the storm passage coincided with an asymmetric change in relative vorticity in the upper 1000 m, which persisted for ∼15 inertial periods. Vertical propagation of inertial energy was estimated at 29 m/day, while horizontal propagation at this frequency was approximately 5.7 km/day. Wavelet analysis showed two distinct sub‐inertial responses, one with a period of 2‐5 days and another with a period of 5‐12 days. Analysis of the sub‐inertial bands reveals that the spatial and temporal scales are shorter and less persistent than the near‐inertial variance. As the array is geographically located near the site of the Deepwater Horizon oil spill, the spatial and temporal scales of response have significant implications for the fate, transport, and distribution of hydrocarbons following a deepwater spill event. This article is protected by copyright. All rights reserved.
      PubDate: 2016-07-18T03:57:13.921395-05:
      DOI: 10.1002/2015JC011560
  • Issue Information
    • Pages: 6555 - 6556
      PubDate: 2016-10-20T02:19:30.43184-05:0
      DOI: 10.1002/jgrc.21409
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