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

Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 21, SJR: 2.156, h-index: 61)
Geophysical Research Letters     Full-text available via subscription   (Followers: 46, SJR: 2.668, h-index: 142)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 5, SJR: 2.4, h-index: 109)
J. of Advances in Modeling Earth Systems     Open Access   (Followers: 2, SJR: 0.126, h-index: 2)
J. of Geophysical Research : Atmospheres     Partially Free   (Followers: 21)
J. of Geophysical Research : Biogeosciences     Full-text available via subscription   (Followers: 7)
J. of Geophysical Research : Earth Surface     Partially Free   (Followers: 23)
J. of Geophysical Research : Oceans     Partially Free   (Followers: 16)
J. of Geophysical Research : Planets     Full-text available via subscription   (Followers: 13)
J. of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 23)
J. of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 15)
Paleoceanography     Full-text available via subscription   (Followers: 4, SJR: 2.16, h-index: 82)
Radio Science     Full-text available via subscription   (Followers: 3, SJR: 0.527, h-index: 47)
Reviews of Geophysics     Full-text available via subscription   (Followers: 19, SJR: 8.837, h-index: 87)
Space Weather     Full-text available via subscription   (Followers: 3, SJR: 0.496, h-index: 16)
Tectonics     Full-text available via subscription   (Followers: 7, SJR: 2.16, h-index: 79)
Water Resources Research     Full-text available via subscription   (Followers: 167, SJR: 1.769, h-index: 110)
Journal Cover Journal of Geophysical Research : Oceans
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     ISSN (Online) 2169-9291
     Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • Boundary mixing in Orkney Passage outflow
    • Authors: K. L. Polzin; A. C. Naveira Garabato, E. P. Abrahamsen, L. Jullion, M. P. Meredith
      Pages: n/a - n/a
      Abstract: One of the most remarkable features of contemporary oceanic climate change is the warming and contraction of Antarctic Bottom Water over much of global ocean abyss. These signatures represent changes in ventilation mediated by mixing and entrainment processes that may be location‐specific. Here we use available data to document, as best possible, those mixing processes as Weddell Sea Deep and Bottom Waters flow along the South Orkney Plateau, exit the Weddell Sea via Orkney Passage and fill the abyssal Scotia Sea. First, we find that an abrupt transition in topography upstream of Orkney Passage delimits the extent of the coldest waters along the Plateau's flanks and may indicate a region of especially intense mixing. Second, we revisit a control volume budget by Heywood et al. (Nature, 2002) for waters trapped within the Scotia Sea after entering through Orkney Passage. This budget requires extremely vigorous water mass transformations with a diapycnal transfer coefficient of 39(±10) × 10‐4 m2 s–1. Evidence for such intense diapycnal mixing is not found in the abyssal Scotia Sea interior and, while we do find large rates of diapycnal mixing in conjunction with a downwelling Ekman layer on the western side of Orkney Passage, it is insufficient to close the budget. This leads us to hypothesize that the Heywood budget is closed by a boundary mixing process in which the Ekman layer associated with the Weddell Sea Deep Water boundary current experiences relatively large‐vertical‐scale overturning associated with tidal forcing along the southern boundary of the Scotia Sea. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-21T17:01:09.952412-05:
      DOI: 10.1002/2014JC010099
       
  • Influence of summertime mesoscale convective systems on the heat balance
           and surface mixed‐layer dynamics of a large Amazonian hydroelectric
           reservoir
    • Authors: Marcelo P. Curtarelli; Igor Ogashawara, Carlos A. S. Araújo, Enner H. Alcântara, João A. Lorenzzetti, José L. Stech
      Pages: n/a - n/a
      Abstract: We evaluated the impacts of summertime mesoscale convective systems (MCS) on the heat balance and diel surface mixed layer (SML) dynamics of the Brazilian Amazon's Tucuruí Hydroelectric Reservoir (THR). We used a synergistic approach that combines in situ data, remote sensing data and three‐dimensional (3D) modeling to investigate the typical behavior of the components of the heat balance and the SML dynamics. During the study period (the austral summer of 2012‐2013), 22 days with MCS activity were identified. These events occurred approximately every 4 days, and they were most frequent during January (50% of the observations). An analysis of local meteorological data showed that when MCS occur, the environmental conditions at THR change significantly (p‐value < 0.01). The net longwave flux, which was the heat balance component most strongly impacted by MCS, increased more than 32% on days with MCS activity. The daily integrated heat balance became negative (‐54 W m‐2) on MCS days, while the balance was positive (19 W m‐2) on non MCS days. In response to the changes in the heat balance, the SML dynamics changed when a MCS was over the THR. The SML depth was typically 28% higher on the days with MCS (~1.6 m) compared with the days without MCS (~1.3 m). The results indicate that MCS are one of the main meteorological disturbances driving the heat balance and the mixing dynamics of Amazonian hydroelectric reservoirs during the summer. These events may have implications for the water quality and greenhouse gas emissions of Amazonian reservoirs. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-21T16:59:56.543432-05:
      DOI: 10.1002/2014JC010288
       
  • Estimating mean dynamic topography in boundary currents and the use of
           Argo trajectories
    • Authors: Melissa Bowen; Philip Sutton, Dean Roemmich
      Pages: n/a - n/a
      Abstract: A Mean Dynamic Topography (MDT) is required to estimate mean transport in the ocean, to combine with altimetry to derive instantaneous geostrophic surface velocities, and to estimate transport from shipboard hydrography. A number of MDTs are now available globally but differ most markedly in boundary currents and the Antarctic Circumpolar Current. We evaluate several MDTs in two boundary currents off New Zealand (in the subtropical western boundary current system east of the country and in the Subantarctic Front to the south) using satellite, hydrographic, and Argo observations near two altimeter tracks. Argo float trajectories are combined with estimates of shear to produce new MDTs along both altimeter tracks: sufficiently high numbers of Argo floats travel in both boundary currents to allow a useful estimate of the mean flow at 1000 m depth and conservation of potential vorticity is used to account for more realistic flow paths. In finding a MDT, we show the uncertainties in the estimates of velocity differences between 1000 m and the surface from density climatologies, while often not estimated, need to be considered. The MDT computed from the Argo trajectories is generally consistent with the CLS09 MDT [Rio et al., 2011] in both boundary currents and, in some locations, distinctly different from the MDT using a “level of no motion” assumption. The comparison suggests velocities from Argo trajectories can be usefully combined with other observations to improve estimates of flows and MDT in boundary currents. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-21T16:56:41.57145-05:0
      DOI: 10.1002/2014JC010281
       
  • Responses of the ocean planktonic ecosystem to finite‐amplitude
           perturbations
    • Authors: Qiang Wang; Mu Mu
      Pages: n/a - n/a
      Abstract: The responses of the ocean planktonic ecosystem to finite‐amplitude perturbations are investigated using an ocean planktonic ecosystem model. Through changing the higher predation rate on zooplankton, multiple equilibria of the model, namely “high‐nutrient” and “low‐nutrient” states, are obtained under certain parameter values. Based on these states, the perturbations with maximum nonlinear growth are determined using the conditional nonlinear optimal perturbation (CNOP) method. The linear and nonlinear evolutions of the CNOP perturbation are compared. The results show that the nonlinear evolution of the perturbation leads to predator–prey oscillations with larger amplitude than the linear evolution. Besides, after the perturbation amplitude exceeds a critical value, the nonlinear evolution of the perturbation will induce the linearly stable ecosystem state to lose the stability and become nonlinearly unstable. This implies that nonlinear processes have important impacts on the stability of the ecosystem. Specifically, we identify the nonlinear processes related to zooplankton grazing to impact the stability most for the high‐nutrient state, while for the low‐nutrient state the main nonlinear process affecting the stability is the uptake process. These results help to improve our understanding of the sensitivity of the oceanic ecosystem model to finite‐amplitude perturbations and the underlying nonlinear stability properties. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-21T16:53:18.074858-05:
      DOI: 10.1002/2014JC010339
       
  • Issue Information
    • Pages: i - vi
      PubDate: 2014-11-21T12:24:17.347831-05:
      DOI: 10.1002/jgrc.20355
       
  • Seasonal variation and biogeochemical cycling of dimethylsulfide (DMS) and
           dimethylsulfoniopropionate (DMSP) in the Yellow Sea and Bohai Sea
    • Authors: Gui‐Peng Yang; Yi‐Zhu Song, Hong‐Hai Zhang, Cheng‐Xuan Li, Guan‐Wei Wu
      Pages: n/a - n/a
      Abstract: The concentrations of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and chlorophyll a (Chl‐a) as well as the size distribution of particulate DMSP (DMSPp) were determined in the Yellow Sea (YS) and Bohai Sea (BS) during two cruises from 1 to 20 November, 2012 and from 21 June to 11 July, 2013. Besides, the biological production and consumption rates of DMS and the degradation rates of dissolved DMSP (DMSPd) were also measured. The concentrations of DMS and DMSP showed a significant seasonal variation with higher values in summer, which corresponded well with the seasonal change of Chl‐a in the study area. Both DMS and DMSPp concentrations were significantly correlated with Chl‐a levels, implying that phytoplankton biomass might play an important role in controlling the distributions of DMS and DMSP in the study area. The size‐fractionation research showed that nanophytoplankton (5‐20 µm) contributed to most of Chl‐a and DMSPp in autumn and summer. The average biological production and consumption rates of DMS during summer were 13.35 and 9.80 nmol L‐1 d‐1, respectively, which were much higher than those during autumn. The degradation rates of DMSPd during summer ranged from 7.10 to 21.70 nmol L‐1 d‐1, with an average of 14.71 nmol L‐1 d‐1, which was nearly equal to the average biological production rate (13.35 nmol L‐1 d‐1) of DMS. The average sea‐to‐air flux of DMS in the YS and BS were 12.06 and 20.81 µmol m‐2 d‐1 in autumn and in summer, respectively, which were much higher than the values reported in the ocean. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-20T02:08:45.710622-05:
      DOI: 10.1002/2014JC010373
       
  • The Seasonal evolution of sea ice floe size distribution
    • Authors: Donald K. Perovich; Kathleen F. Jones
      Pages: n/a - n/a
      Abstract: The Arctic sea ice cover undergoes large changes over an annual cycle. In winter and spring the ice cover consists of large, snow‐covered plate‐like ice floes, with very little open water. By the end of summer the snow cover is gone and the large floes have broken into a complex mosaic of smaller, rounded floes surrounded by a lace of open water. This evolution strongly affects the distribution and fate of the solar radiation deposited in the ice‐ocean system and consequently the heat budget of the ice cover. In particular, increased floe perimeter can result in enhanced lateral melting. We attempt to quantify the floe evolution process through the concept of a floe size distribution that is modified by lateral melting and floe breaking. A time series of aerial photographic surveys made during the SHEBA field experiment is analyzed to determine evolution of the floe size distribution from spring through summer. Based on earlier studies, we assume the floe size cumulative distribution could be represented by a power law D‐α where D is the floe diameter. The exponent α as well as the number density of floes Ntot are estimated from measurements of total ice area and perimeter. As summer progressed, there was an increase in α as the size distribution shifted towards smaller floes and the number of floes increased. Lateral melting causes the distribution to deviate from a power law for small floe sizes. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-20T02:05:29.482746-05:
      DOI: 10.1002/2014JC010136
       
  • Integrated modeling framework to quantify the coastal protection services
           supplied by vegetation
    • Authors: Greg Guannel; Peter Ruggiero, Joe Faries, Katie Arkema, Malin Pinsky, Guy Gelfenbaum, Anne Guerry, Choong‐Ki Kim
      Pages: n/a - n/a
      Abstract: Vegetation can protect communities by reducing nearshore wave height and altering sediment transport processes. However, quantitative approaches for evaluating the coastal protection services, or benefits, supplied by vegetation to people in a wide range of coastal environments are lacking. To begin to fill this knowledge gap, an integrated modeling approach is proposed for quantifying how vegetation modifies nearshore processes – including the attenuation of wave height, mean and total water level – and reduces shoreline erosion during storms. We apply the model to idealized seagrass‐sand and mangrove‐mud cases, illustrating its potential by quantifying how those habitats reduce water levels and sediment loss beyond what would be observed in the absence of vegetation. The integrated modeling approach provides an efficient way to quantify the coastal protection services supplied by vegetation and highlights specific research needs for improved representations of the ways in which vegetation modifies wave‐induced processes. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-14T18:35:35.32085-05:0
      DOI: 10.1002/2014JC009821
       
  • Accuracy and precision in the calculation of phenology metrics
    • Authors: Sofia A Ferreira; Andre W Visser, Brian R MacKenzie, Mark R Payne
      Pages: n/a - n/a
      Abstract: Phytoplankton phenology (the timing of seasonal events) is a commonly used indicator for evaluating responses of marine ecosystems to climate change. However, phenological metrics are vulnerable to observation‐ (bloom amplitude, missing data and observational noise) and analysis‐related (temporal resolution, pre‐processing technique and phenology metric) processes. Here, we consider the impact of these processes on the robustness of four phenology metrics (timing of maximum, 5% above median, maximum growth rate, and 15% of cumulative distribution). We apply a simulation testing approach, where a phenology metric is first determined from a noise‐ and gap‐free time series, and again once it has been modified. We show that precision is a greater concern than accuracy for many of these metrics, an important point that has been hereto overlooked in the literature. The variability in precision between phenology metrics is substantial, but it can be improved by the use of pre‐processing techniques (e.g. gap‐filling or smoothing). Furthermore, there are important differences in the inherent variability of the metrics, that may be crucial in the interpretation of studies based upon them. Of the considered metrics, the 15% of cumulative distribution metric best satisfies the precision criteria. However, the 5% above median metric is comparable in terms of precision and exhibits more inherent variability. We emphasise that the choice of phenology metric should be determined by the specific nature of the question being asked. We believe these findings to be useful to the current discussion on phenology metrics of phytoplankton dynamics. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-14T18:34:17.152246-05:
      DOI: 10.1002/2014JC010323
       
  • Southern Ocean wind‐driven entrainment enhances satellite
           chlorophyll‐a through the summer
    • Authors: Magdalena M. Carranza; Sarah T. Gille
      Pages: n/a - n/a
      Abstract: Despite being the largest High Nitrate Low Chlorophyll (HNLC) region, the Southern Ocean sustains phytoplankton blooms through the summer, when presumably there is sufficient light, but nutrients in the euphotic zone have been depleted. Physical processes that can potentially supply nutrients from subsurface waters to the euphotic zone, and promote phytoplankton growth in the summer, have not been fully explored at the large scale. By means of a correlation analysis, this study combines high resolution satellite observations of ocean color, winds and sea surface temperature (SST), surface heat fluxes from reanalysis and Argo mixed‐layer depth (MLD) estimates to explore the role of the atmospheric forcing (i.e. winds and surface heat fluxes) on upper ocean processes that may help sustain high satellite chlorophyl‐a (Chl‐a) through the summer. Two physical processes that can supply nutrients to the euphotic zone are: MLD deepening, caused by wind‐mixing and/or surface cooling, and Ekman pumping driven by the wind stress curl. We find that high winds correlate with high Chl‐a over broad open ocean areas, suggesting that transient MLD deepening through wind‐mixing (i.e. wind‐driven entrainment) helps sustain high Chl‐a. Wind‐driven entrainment plays a dominant role on timescales associated with atmospheric synoptic storms (i.e. 
      PubDate: 2014-11-14T18:32:37.639531-05:
      DOI: 10.1002/2014JC010203
       
  • Freshening in the South China Sea during 2012 revealed by Aquarius and in
           situ data
    • Authors: Lili Zeng; W. Timothy Liu, Huijie Xue, Peng Xiu, Dongxiao Wang
      Pages: n/a - n/a
      Abstract: Newly available sea surface salinity (SSS) data from the Aquarius together with in‐situ hydrographic data are used to explore the spatial and temporal characteristics of SSS in the South China Sea (SCS). Using in‐situ observations as the reference, an evaluation of daily Aquarius data indicates that there exists a negative bias of 0.45 psu for the version 3.0 dataset. The root‐mean‐square difference for daily Aquarius SSS is about 0.53 psu after correcting the systematic bias, and those for weekly and monthly Aquarius SSSs are 0.45 and 0.29 psu, respectively. Nevertheless, the Aquarius SSS shows a reliable freshening in the SCS in 2012, which is larger than the Aquarius uncertainty. The freshening of up to 0.4 psu in the upper‐ocean of the northern SCS was confirmed by in‐situ observations. This freshening in 2012 was caused by a combined effect of abundant local freshwater flux and limited Kuroshio intrusion. By comparing the Kuroshio intrusion in 2012 with that in 2011, we found the reduction as a relatively important cause for the freshening over the northern SCS. In contrast to the northern SCS, reduced river discharge in 2012 played the leading role to the saltier surface in the region near the Mekong River mouth with respect to 2011. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-14T18:32:28.43649-05:0
      DOI: 10.1002/2014JC010108
       
  • Intraseasonal variability of the subthermocline current east of Mindanao
    • Authors: Qingye Wang; Fangguo Zhai, Fujun Wang, Dunxin Hu
      Pages: n/a - n/a
      Abstract: The intraseasonal variability (ISV) of the subthermocline current east of Mindanao was characterized and shown to be caused by the activity of subthermocline eddies using mooring observations at 8°N, 127.03°E and a high‐resolution numerical model. The ISV of the observed current east of Mindanao is vertically coherent in the upper 940 m but is significantly intensified below the thermocline. The ISV amplitude (8 cm s‐1) of zonal subthermocline current is comparable with that (11 cm s‐1) of the meridional current, revealing the nature of active eddies. The ISV of the subthermocline current was caused by the subthermocline eddies from three different pathways. The subthermocline eddies propagating along approximately 10‐11°N contributed more to the ISV of the subthermocline current east of Mindanao than did those eddies propagating westward along 8°N or northwestward from the New Guinea coast. Subthermocline eddies mainly exist south of the bifurcation latitude of the North Equatorial Current in the western tropical Pacific, and their generation and propagation mechanisms are briefly discussed.
      PubDate: 2014-11-13T04:28:07.828136-05:
      DOI: 10.1002/2014JC010343
       
  • Long‐lived mesoscale eddies in the eastern Mediterranean Sea:
           Analysis of 20 years of AVISO geostrophic velocities
    • Authors: Nadia Mkhinini; Andre Louis Santi Coimbra, Alexandre Stegner, Thomas Arsouze, Isabelle Taupier‐Letage, Karine Béranger
      Pages: n/a - n/a
      Abstract: We analyzed 20 years of AVISO data set to detect and characterize long‐lived eddies, which stay coherent more than six months, in the Eastern Mediterranean Sea. In order to process the coarse gridded (1/8º) AVISO geostrophic velocity fields, we optimized a geometrical eddy detection algorithm. Our main contribution was to implement a new procedure based on the computation of the Local and Normalized Angular Momentum (LNAM) to identify the positions of the eddy centers and to follow their Lagrangian trajectories. We verify on two meso‐scale anticyclones, sampled during the EGYPT campaign in 2006, that our methodology provides a correct estimation of the eddy centers and their characteristic radius corresponding to the maximal tangential velocity. Our analysis reveals the dominance of anticyclones among the long‐lived eddies. This cyclone‐anticyclone asymmetry appears to be much more pronounced in Eastern Mediterranean Sea than in the global ocean. Then we focus our study on the formation areas of longlived eddies. We confirm that the generations of the Ierapetra and the Pelops anticyclones are recurrent and correlated to the Etesian wind‐forcing. We also provide some evidence that the smaller cyclonic eddies formed at the southwest of Crete may also be induced by the same wind forcing. On the other hand, the generation of long‐lived eddies along the Libyo‐Egyptian coast are not correlated to the local wind‐stress curl but surprinsingly, their initial formation points follow the Herodotus Trough bathymetry. Moreover, we identify a new formation area, not discussed before, along the curved shelf off Benghazi.
      PubDate: 2014-11-13T04:26:49.362932-05:
      DOI: 10.1002/2014JC010176
       
  • Drifter‐based estimate of the 5 year dispersal of
           Fukushima‐derived radionuclides
    • Authors: I. I. Rypina; S. R. Jayne, S. Yoshida, A. M. Macdonald, K. Buesseler
      Pages: n/a - n/a
      Abstract: Employing some 40 years of North Pacific drifter‐track observations from the Global Drifter Program database, statistics defining the horizontal spread of radionuclides from Fukushima nuclear power plant into the Pacific Ocean are investigated over a time‐scale of 5 years. A novel two‐iteration method is employed to make the best use of the available drifter data. Drifter‐based predictions of the temporal progression of the leading edge of the radionuclide distribution are compared to observed radionuclide concentrations from research surveys occupied in 2012 and 2013. Good agreement between the drifter‐based predictions and the observations is found.
      PubDate: 2014-11-13T04:05:33.737923-05:
      DOI: 10.1002/2014JC010306
       
  • The influence of salinity on tropical Atlantic instability waves
    • Authors: Tong Lee; Gary Lagerloef, Hsun‐Ying Kao, Michael J. McPhaden, Joshua Willis, Michelle M. Gierach
      Pages: n/a - n/a
      Abstract: Sea surface salinity (SSS) data derived from the Aquarius/SAC‐D satellite mission are analyzed along with other satellite and in‐situ data to assess Aquarius' capability to detect tropical instability waves (TIWs) and eddies in the tropical Atlantic Ocean and to investigate the influence that SSS has on the variability. Aquarius data show that the magnitude of SSS anomalies associated with the Atlantic TIWs is ±0.25 practical salinity unit, which is weaker than those in the Pacific by 50%. In the central equatorial Atlantic, SSS contribution to the mean meridional density gradient is similar to sea surface temperature (SST) contribution. Consequently, SSS is important to TIW‐related surface density anomalies and perturbation potential energy (PPE). In this region, SSS influences surface PPE significantly through the direct effect and the indirect effect associated with SSS‐SST co‐variability. Ignoring SSS effects would underestimate TIW‐related PPE by approximately three times in the surface layer. SSS also regulates the seasonality of the TIWs. The boreal‐spring peak of the PPE due to SSS leads that due to SST by about one month. Therefore, SSS not only affects the spatial structure, but the seasonal variability of the TIWs in the equatorial Atlantic. In the northeast Atlantic near the Amazon outflow and the North Brazil Current retroflection region and in the southeast Atlantic near the Congo River outflow, SSS accounts for 80‐90% of the contribution to mean meridional density gradient. Not accounting for SSS effect would underestimate surface PPE in these regions by a factor of 10 and 4, respectively.
      PubDate: 2014-11-13T03:59:35.573693-05:
      DOI: 10.1002/2014JC010100
       
  • Mode‐2 hydraulic control of flow over a small ridge on a continental
           shelf
    • Authors: M. C. Gregg; Jody M. Klymak
      Pages: n/a - n/a
      Abstract: Some of the most intense turbulence in the ocean occurs in hydraulic jumps formed in the lee of sills where flows are hydraulically controlled, usually by the first internal mode. Observations on the outer Texas‐Louisiana continental shelf reveal hydraulic control of internal mode‐2 lasting more than three hours over a 20‐meter‐high ridge on the 100‐meter‐deep continental shelf. When control began the base of the weakly stratified surface layer bulged upward and downward, a signature of mode‐2. As the westward flow producing control was lost, large‐amplitude disturbances, initially resembling a bore in the weakly stratified layer, began propagating eastward. Average dissipation rates inferred from density inversions over the ridge were and , one to two decades above local background. Corresponding diapycnal diffusivities, , were to . Short‐term mixing averages did not evolve systematically with hydraulic control, possibly owing to our inability to observe small overturns in strongly stratified water directly over the ridge. To test the feasibility of our interpretation of the observations, hydrostatic runs with a three‐dimensional MITgcm simulated mode‐2 control and intense mixing over the ridge below the interface. Details differed from observations, principally because we lacked three‐dimensional density fields to initialize the model which was forced with currents observed by a bottom‐mounted ADCP several kilometers east of the ridge. Consequently, the model did not capture all flow features around the bank. The principal conclusion is that hydraulic responses to higher modes can dominate flows around even modest bathymetric irregularities.
      PubDate: 2014-11-11T11:25:36.416152-05:
      DOI: 10.1002/2014JC010043
       
  • Multisensor observations of the Amazon‐Orinoco River plume
           interactions with hurricanes
    • Authors: Nicolas Reul; Yves Quilfen, Bertrand Chapron, Severine Fournier, Vladimir Kurdyavtsev, Roberto Sabia
      Pages: n/a - n/a
      Abstract: An analysis is presented for the spatial and intensity distributions of North Atlantic extreme atmospheric events crossing the buoyant Amazon‐Orinoco freshwater plume. The sea surface cooling amplitude in the wake of an ensemble of storm tracks travelling in that region is estimated from satellite products for the period 1998‐2012. For the most intense storms, cooling is systematically reduced by ~50% over the plume area compared to surroundings open ocean waters. Historical salinity and temperature observations from in situ profiles indicate that salt‐driven vertical stratification, enhanced oceanic heat content and barrier‐layer presence within the plume waters are likely key oceanic factors to explain these results. Satellite SMOS surface salinity data combined with in situ observations are further used to detail the oceanic response to Category 4 hurricane Igor in 2010. Argo and satellite measurements confirm the haline stratification impact on the cooling inhibition as the hurricane crossed the river plume. Over this region, the SSS mapping capability is further tested and demonstrated to monitor the horizontal distribution of the vertical stratification parameter. SMOS SSS data can thus be used to consistently anticipate the cooling inhibition in the wake of TCs travelling over the Amazon‐Orinoco plume region.
      PubDate: 2014-11-08T11:27:48.910934-05:
      DOI: 10.1002/2014JC010107
       
  • Unsteady stress partitioning and momentum transfer in the wave bottom
           boundary layer over movable rippled beds
    • Authors: S. Rodríguez‐Abudo; D. L. Foster
      Pages: n/a - n/a
      Abstract: Observations of the nearbed velocity field over a rippled sediment bed under asymmetric wave forcing conditions were collected using a submersible particle image velocimetry (PIV) system. To examine the role of bedform‐induced dynamics in the total momentum transfer, a double‐averaging technique was implemented on the two‐dimensional time‐dependent velocity field by means of the full momentum equation. This approach allows for direct determination of the bedform‐induced stresses, ie. stresses that arise due to the presence of bedforms, which are zero in flat bed conditions. This analysis suggests that bedform‐induced stresses are closely related to the presence of coherent motions and may be partitioned from the turbulent stresses. Inferences of stress provided by a bedload transport model suggest that total momentum transfer obtained from the double‐averaging technique is capable of reproducing bedform mobilization. Comparisons between the total momentum transfer and stress estimates obtained from local velocity profiles show significant variability across the ripple, and suggest that an array of sensors is necessary to reproduce bedform evolution. The imbalance of momentum obtained by resolving the different terms constituting the near‐bed momentum balance (i.e. acceleration deficit, stress gradient, and bedform‐induced skin friction) provides an estimate of the bedform‐induced pressure that is consistent with flow separation. This analysis reveals three regions in the flow: the free‐stream, where all terms are relatively balanced; the near‐bed, where momentum imbalance is significant during flow weakening; and below ripple crests, where bedform‐induced pressure is the leading order mechanism.
      PubDate: 2014-11-08T11:17:46.066485-05:
      DOI: 10.1002/2014JC010240
       
  • Mixed layer salinity budget in the tropical Pacific Ocean estimated by a
           global GCM
    • Authors: Shan Gao; Tangdong Qu, Xunwei Nie
      Pages: n/a - n/a
      Abstract: The mixed layer salinity (MLS) budget of the tropical Pacific is investigated using results from a model of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO). The results focusing on the western Pacific freshwater pool indicate that the long‐term averaged surface freshwater flux is well balanced by ocean dynamics, in which the subsurface processes account for the major part. The MLS budget shows significant seasonal and interannual variability, as a consequence of interplay among surface freshwater flux, advection, mixing, and vertical entrainment. On seasonal time scale, both the MLS and mixed layer depth are largely controlled by surface freshwater flux. The opposite phase between the subsurface processes and the barrier layer thickness confirms the important influence of the barrier layer on vertical mixing and entrainment from below. On interannual time scale, all the MLS budget terms show significant ENSO signal, which in turn is highly correlated with the salinity front and barrier layer thickness in the equatorial Pacific.
      PubDate: 2014-11-08T11:09:59.02301-05:0
      DOI: 10.1002/2014JC010336
       
  • Solar heating of the Arctic Ocean in the context of ice‐albedo
           feedback
    • Authors: Rachel T. Pinker; Xiaolei Niu, Yingtao Ma
      Pages: n/a - n/a
      Abstract: To study the relationship of solar heat input into the Arctic open water and the variations of sea ice extent, improved satellite based estimates of shortwave radiative (SWR) fluxes and most recent observations of ice extent are used. The SWR flux estimates are based on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and from the Advanced Very High Resolution Radiometer (AVHRR) for the period of 1984‐2009. Ice extent information at 25‐km resolution comes from Nimbus‐7 SMMR and DMSP SSM/I Passive Microwave Data as generated with the NASA Team algorithm developed by the Oceans and Ice Branch, Laboratory for Hydrospheric Processes, NASA Goddard Space Flight Center. The trends of the solar heat input into the ocean and the open water fraction for 1984‐2009 are found to be positive: 0.3%/year and 0.8%/year respectively at a 99% confidence level. There is an obvious transition region separating the 26 years into two periods: one with moderate change: 1984‐2002; one with an abrupt growth in both solar heat input and open water fraction: 2003‐2009. The impact of the observed changes on the reduction of winter ice growth in 2007 is estimated to be about 44 cm, and a delay in fall freeze‐up as about 10~36 days.
      PubDate: 2014-11-08T11:09:29.998514-05:
      DOI: 10.1002/2014JC010232
       
  • SST patterns and dynamics of the Southern Senegal‐Gambia upwelling
           center
    • Authors: S. Ndoye; X. Capet, P. Estrade, B. Sow, D. Dagorne, A. Lazar, A. Gaye, P. Brehmer
      Pages: n/a - n/a
      Abstract: The southern end of the Canary current system comprises of an original upwelling center that has so far received little attention, the Southern Senegal‐Gambia Upwelling Center (SSUC). We investigate its dynamical functioning by taking advantage of favorable conditions in terms of limited cloud coverage. Analyses and careful examinations of over 1500 satellite images of sea surface temperature scenes contextualized with respect to wind conditions confirm the regularity and stability of the SSUC dynamical functioning (as manifested by the recurrence and persistence of particular SST patterns). The analyses also reveal subtle aspects of its upwelling structure: shelf break cooling of surface waters consistent with internal tide breaking/mixing; complex interplay between local upwelling and the Mauritanian current off the Cape Verde headland; complexity of the inner‐shelf/mid shelf frontal transition. The amplitude of the diurnal cycle suggests that large uncertainties exist in the SSUC heat budget. The studies limitations underscore the need for continuous in situ measurement in the SSUC, particularly of winds.
      PubDate: 2014-11-08T11:09:26.706055-05:
      DOI: 10.1002/2014JC010242
       
  • Convective instability in sedimentation: 3‐D numerical study
    • Authors: Xiao Yu; Tian‐Jian Hsu, S. Balachandar
      Pages: n/a - n/a
      Abstract: To provide a probable explanation on the field observed rapid sedimentation process near river mouths, we investigate the convective sedimentation in stably stratified saltwater using 3D numerical simulations. Guided by the linear stability analysis (Yu et al. 2013, J. Geophys. Res. Oceans, 118, 256‐272), this study focuses on the nonlinear interactions of several mechanisms, which lead to various sediment finger patterns, and the effective settling velocity for sediment ranging from clay (single‐particle settling velocity V0 = 0.0036 and 0.0144 mm/s, or particle diameter d = 2 and 4 μ m) to silt (V0=0.36 mm/s, or d =20 μ m). For very fine sediment with V0=0.0036 mm/s, the convective instability is dominated by double diffusion, characterized by millimeter‐scale fingers. Gravitational settling slightly increases the growth rate; however, it has notable effect on the downward development of vertical mixing shortly after the sediment interface migrates below the salt interface. For sediment with V0 = 0.0144 mm/s, Rayleigh‐Taylor instabilities become dominant before double‐diffusive modes grow sufficiently large. Centimeter‐scale and highly asymmetric sediment fingers are obtained due to nonlinear interactions between different modes. For sediment with V0 = 0.36 mm/s, Rayleigh‐Taylor mechanism dominates and the resulting centimeter‐scale sediment fingers show a plume‐like structure. The flow pattern is similar to that without ambient salt stratification. Rapid sedimentation with effective settling velocity on the order of 1 cm/s is likely driven by convective sedimentation for sediment with V0 greater than 0.1 mm/s at concentration greater than 10 to 20 g/L.
      PubDate: 2014-11-08T11:09:22.108183-05:
      DOI: 10.1002/2014JC010123
       
  • The role of morphology and wave‐current interaction at tidal inlets:
           An idealized modeling analysis
    • Authors: Maitane Olabarrieta; W. Rockwell Geyer, Nirnimesh Kumar
      Pages: n/a - n/a
      Abstract: The outflowing currents from tidal inlets are influenced both by the morphology of the ebb‐tide shoal and interaction with incident surface gravity waves. Likewise, the propagation and breaking of incident waves are affected by the morphology and the strength and structure of the outflowing current. The 3D COAWST (Coupled Ocean‐Atmosphere‐Wave‐Sediment Transport) modeling system is applied to numerically analyze the interaction between currents, waves, and bathymetry in idealized inlet configurations. The bathymetry is found to be a dominant controlling variable. In the absence of an ebb shoal and with weak wave forcing, a narrow outflow jet extends seaward with little lateral spreading. The presence of an ebb‐tide shoal produces significant pressure gradients in the region of the outflow, resulting in enhanced lateral spreading of the jet. Incident waves cause lateral spreading and limit the seaward extent of the jet, due both to conversion of wave momentum flux and enhanced bottom friction. The interaction between the vorticity of the outflow jet and the wave stokes drift is also an important driving force for the lateral spreading of the plume. For weak outflows, the outflow jet is actually enhanced by strong waves when there is a channel across the bar, due to the “return current” effect. For both strong and weak outflows, waves increase the along‐shore transport in both directions from the inlet due to the wave‐induced set‐up over the ebb shoal. Wave‐breaking is more influenced by the topography of the ebb shoal than by wave‐current interaction, although strong outflows show intensified breaking at the head of the main channel.
      PubDate: 2014-11-08T11:09:12.981829-05:
      DOI: 10.1002/2014JC010191
       
  • Heat and salinity budgets at the Stratus mooring in the southeast Pacific
    • Authors: James Holte; Fiammetta Straneo, J. Thomas Farrar, Robert A. Weller
      Pages: n/a - n/a
      Abstract: The surface layer of the southeast Pacific Ocean (SEP) requires an input of cold, fresh water to balance heat gain and evaporation from air‐sea fluxes. Models typically fail to reproduce the cool sea surface temperatures (SST) of the SEP, limiting our ability to understand the variability of this climatically important region. We estimate the annual heat budget of the SEP for the period 2004 ‐ 2009, using data from the upper 250 m of the Stratus mooring, located at 85°W 20°S, and from Argo floats. The surface buoy measures meteorological conditions and air‐sea fluxes; the mooring line is heavily instrumented, measuring temperature, salinity, and velocity at more than 15 depth levels. We use a new method for estimating the advective component of the heat budget that combines Argo profiles and mooring velocity data, allowing us to calculate monthly profiles of heat advection. Averaged over the 6 year study period, we estimate a cooling advective heat flux of ‐41 ± 29 W m‐2, accomplished by a combination of the mean gyre circulation, Ekman transport, and eddies. This compensates for warming fluxes of 32 ± 4 W m‐2 due to air‐sea fluxes and 7 ± 9 W m‐2 due to vertical mixing and Ekman pumping. A salinity budget exhibits a similar balance, with advection of freshwater (‐60 psu m) replenishing the freshwater lost through evaporation (47 psu m) and Ekman pumping (14 psu m).
      PubDate: 2014-11-08T11:09:09.529159-05:
      DOI: 10.1002/2014JC010256
       
  • Origin of fine‐scale wind stress curl structures in the Benguela and
           Canary upwelling systems
    • Authors: F. Desbiolles; B. Blanke, A. Bentamy, N. Grima
      Pages: n/a - n/a
      Abstract: Numerous studies have shown the primary importance of wind stress curl in coastal upwelling dynamics. The main goal of this new analysis is to describe the QuikSCAT surface wind stress curl at various scales in the Benguela and Canary upwelling systems. The dominant spatial pattern is characterized by cyclonic curl near continental boundaries and anticyclonic curl offshore, in association with equatorward alongshore (upwelling favorable) wind stress. At a smaller scale, we demonstrate the sensitivity of the QuikSCAT wind stress curl to coastal processes related to sea surface temperature (SST) mesoscale fluctuations by presenting a linear relationship between the curl and crosswind SST gradients. Despite the spatial and temporal sensitivity of the underlying thermal coupling coefficient, a local analysis of the fraction of the curl ascribed to SST variability shows that SST is a main driver of the wind stress curl variability and magnitude over the upwelling extension zone (~100 to 300 km from the coast) in both the Canary and Benguela systems. Closer to the shore, the curl patterns derived from QuikSCAT observations are only loosely related to SST‐wind interactions. As a working hypothesis, they can also be associated with the coastline geometry and orographic effects that are likely to play an important role in local cooling processes.
      PubDate: 2014-11-06T18:20:52.661802-05:
      DOI: 10.1002/2014JC010015
       
  • Impact of eddies on surface chlorophyll in the South Indian Ocean
    • Authors: François Dufois; Nick J. Hardman‐Mountford, Jim Greenwood, Anthony J. Richardson, Ming Feng, Steven Herbette, Richard Matear
      Pages: n/a - n/a
      Abstract: A unique feature of the subtropical South Indian Ocean is the existence of anticyclonic eddies that have higher chlorophyll concentrations than cyclonic eddies. Off Western Australia, this anomalous behaviour is related to the seeding of anticyclonic eddies with shelf water enriched in phytoplankton biomass and nutrients. Further off‐shore, two mechanisms have been suggested to explain the eddy/chlorophyll relationship: (i) eddies originating from the Australian coast maintain their chlorophyll anomaly while propagating westward; and (ii) eddy‐induced Ekman upwelling (downwelling) enhances (dampens) nutrient supply in anticyclonic (cyclonic) eddies. Here we describe the relationship between eddies and surface chlorophyll within the South Indian Ocean, and discuss possible mechanisms to explain the anomalous behaviour in light of new analyses performed using satellite chlorophyll data. We show that anticyclonic eddies exhibit higher surface chlorophyll concentration than cyclonic eddies across the entire South Indian Ocean basin (from 20 to 28ºS), particularly in winter. Using Self Organizing Maps we analyse the chlorophyll patterns within anticyclonic eddies and cyclonic eddies and highlight their complexity. Our analysis suggests that multiple mechanisms may underlie the observed eddy/chlorophyll relationship. Based on Argo float data, we postulate the relationship may be partly related to seasonal adjustment of the mixed layer depth within eddies. Deeper mixing in anticyclonic eddies is expected to enhance nutrient supply to the mixed layer, while shallower mixing in cyclonic eddies is expected to reduce it. This could explain why the observed winter surface chlorophyll bloom is stronger in anticyclonic eddies than in cyclonic eddies.
      PubDate: 2014-11-06T18:16:16.109917-05:
      DOI: 10.1002/2014JC010164
       
  • On the physical and biogeochemical processes driving the
           high‐frequency variability of CO2 fugacity at 6°S, 10°W:
           Potential role of the internal waves
    • Authors: Gaëlle Parard; J. Boutin, Y. Cuypers, P. Bouruet‐Aubertot, G. Caniaux
      Pages: n/a - n/a
      Abstract: The availability of nutrients in the mixed layer is the main limitation to organic carbon biological production in the tropical regions. In this paper, we investigate the potential role of internal waves at promoting the development of biological activity on a PIRATA mooring at 6°S, 10°W. This mooring is located above the Mid‐Atlantic Ridge where we observe strong internal waves. Using a one dimensional physical and biogeochemical coupled model, we simulate dissolved inorganic carbon (DIC). Providing the influence of vertical advection and turbulent diapycnal diffusivity are accounted for, we find that this model provides a good fit with observed in‐situ CO2 fugacity (fCO2). Main effect of internal waves is to rapidly increase the DIC, thus the fCO2 and the nutrients in the mixed layer. The latter induce progressive development of biological activity leading to gradual DIC decrease. Our study highlights the importance of correctly taking into account the effect of internal waves in tropical regions.
      PubDate: 2014-11-06T03:43:05.678215-05:
      DOI: 10.1002/2014JC009965
       
  • Relationship between coral distributions and physical variables in Amitori
           Bay, Iriomote Island, Japan
    • Authors: Shinya Shimokawa; Tomokazu Murakami, Akiyuki Ukai, Hiroyoshi Kohno, Akira Mizutani, Kouta Nakase
      Pages: n/a - n/a
      Abstract: The relationship between coral distributions and physical variables was investigated in Amitori Bay, Iriomote Island, Japan. Field observations were conducted to obtain data on coral distributions, sea temperature, sea salinity, wind speed, and river flow rate. The observed data were then used in ocean and wave model numerical simulations and soil particle tracking analysis to obtain the spatial and temporal distributions of wave height and the numbers of soil particles. The main results of this study indicate that wave height and the number of soil particles have a significant correlation with coral distribution. Higher wave heights result in greater coverage of tabular coral and lower coverage of branching coral. A greater number of soil particles relates to lesser coverage of tabular coral. On the contrary, the number of soil particles is not correlated with branching coral coverage. The potential habitats for tabular corals largely depend on the species. Acropora hyacinthus is distributed in conditions with low numbers of soil particles, A. digitifera is distributed in conditions with low numbers of soil particles and high wave heights, and A. millepora is distributed in conditions with high numbers of soil particles and low wave heights. Averages of diversity index of the coral types at the mouth and inner parts of the bay are lower than average of the whole region, but average of diversity index at the intermediate part of the bay with the intermediate physical disturbances is higher than it, which seems to support the intermediate disturbance hypothesis.
      PubDate: 2014-11-05T01:41:43.056767-05:
      DOI: 10.1002/2014JC010307
       
  • Deep ocean water transport by acoustic‐gravity waves
    • Authors: U. Kadri
      Pages: n/a - n/a
      Abstract: Acoustic‐gravity waves are compression‐type waves propagating with amplitudes governed by the restoring force of gravity. They are generated, among others, by wind‐wave interactions, surface waves interactions, and submarine earthquakes. We show that acoustic‐gravity waves contribute to deep ocean currents and circulation; they cause chaotic flow trajectories of individual water parcels, which can be transported by a few centimetres per second.
      PubDate: 2014-11-04T07:46:26.848696-05:
      DOI: 10.1002/2014JC010234
       
  • Tidal and residual currents in the Qiongzhou Strait estimated from
           shipboard ADCP data using a modified tidal harmonic analysis method
    • Authors: Xiao‐Hua Zhu; Yun‐Long Ma, Xinyu Guo, Xiaopeng Fan, Yu Long, Yaochu Yuan, Ji‐Liang Xuan, Daji Huang
      Pages: n/a - n/a
      Abstract: In spring 2013, thirty‐three repeat shipboard Acoustic Doppler Current Profile (ADCP) surveys were conducted to measure the tidal current in the Qiongzhou Strait (QS). The major tidal currents and the residual current along a section across the QS were estimated using a modified tidal harmonic analysis method based on the inverse technique. A simple simulation and comparisons with previous observations demonstrated that the tidal currents estimated using the modified tidal harmonic analysis method are reasonable, and this method was able to control the magnitude and deviation of the estimation error. The direction of the major axis of tidal current ellipses is generally along the strait. Diurnal tidal constituents are dominant among the five tidal current constituents (K1, O1, M2, S2 and MSf). The ratio of the amplitudes of O1, K1, M2, S2 and MSf, averaged along the section across the QS is 1:0.79:0.42:0.27:0.29. The residual current along the entire section is all westward; the averaged velocity over the section is 6.0±2.1 cm s‐1; the associated volume transport through the section is ‐0.065±0.046 Sv (Sv=106×m3 s‐1), in which the second value denotes the uncertainty of first value. Dynamic analysis indicates that tidal current activity is more dominant than mean current and eddy activity, and tidal rectification and sea level difference between two entrances of the QS are important in maintaining the residual current through the strait.
      PubDate: 2014-11-04T07:46:15.306056-05:
      DOI: 10.1002/2014JC009855
       
  • Regional variations in the influence of mesoscale eddies on
           near‐surface chlorophyll
    • Authors: Peter Gaube; Dennis J. McGillicuddy, Dudley B. Chelton, Michael J. Behrenfeld, Peter G. Strutton
      Pages: n/a - n/a
      Abstract: Eddies can influence biogeochemical cycles through a variety of mechanisms, including the excitation of vertical velocities and the horizontal advection of nutrients and ecosystems, both around the eddy periphery by rotational currents and by the trapping of fluid and subsequent transport by the eddy. In this study, we present an analysis of the influence of mesoscale ocean eddies on near‐surface chlorophyll (CHL) estimated from satellite measurements of ocean color. The influences of horizontal advection, trapping, and upwelling/downwelling on CHL are analyzed in an eddy‐centric frame of reference by collocating satellite observations to eddy interiors, as defined by their sea surface height signatures. The influence of mesoscale eddies on CHL varies regionally. In most boundary current regions, cyclonic eddies exhibit positive CHL anomalies and anticyclonic eddies contain negative CHL anomalies. In the interior of the South Indian Ocean, however, the opposite occurs. The various mechanisms by which eddies can influence phytoplankton communities are summarized and regions where the observed CHL response to eddies is consistent with one or more of the mechanisms are discussed. This study does not attempt to link the observed regional variability definitively to any particular mechanism, but provides a global overview of how eddies influence CHL anomalies.
      PubDate: 2014-11-04T07:44:18.304894-05:
      DOI: 10.1002/2014JC010111
       
  • Estimating the global oceanic net freshwater flux from Argo and comparing
           it with satellite‐based freshwater flux products
    • Authors: Li Ren; Eric Hackert, Phillip Arkin, Antonio J. Busalacchi
      Pages: n/a - n/a
      Abstract: Following the idea that analysis of in‐situ information in the salt budget could be used as a surrogate for global “ocean rain gauge”, the annual mean oceanic net freshwater flux (E‐P) was estimated from the Argo profiles and the wind stress data on a global scale. The comparison between the independent E‐P estimation from Argo and the E‐P product sets, including the combination of precipitation from TRMM, GPCP, CMAP and evaporation from OAFlux, GSSTF3 and IFREMER and E‐P set from NEWS formed from satellite, generally show similar spatial patterns, particularly on the larg scale. However, there are differences among the different satellite‐based E‐P estimates and between satellite estimates and independent in‐situ estimates. Based on the pattern correlation and the RMSD, the evaporation and precipitation from OAFlux and TRMM agrees best with the E‐P estimated from the independent Argo‐based estimates.
      PubDate: 2014-11-04T07:43:54.979955-05:
      DOI: 10.1002/2013JC009620
       
  • Comparison analysis between Aquarius sea surface salinity and World Ocean
           Database in situ analyzed sea surface salinity
    • Authors: James Reagan; Tim Boyer, John Antonov, Melissa Zweng
      Pages: n/a - n/a
      Abstract: A new monthly sea surface salinity (SSS) product calculated from profile data within the World Ocean Database (WOD) is compared and contrasted with Aquarius SSS, both standard and Combined Active‐Passive (CAP) products, from September 2011 through September 2013. Aquarius exhibits similar biases as shown in previous comparison SSS studies, with negative biases in the tropics transitioning to positive biases in the higher latitudes when compared to WOD SSS. These biases are generally much weaker in CAP than the standard version, indicating that the biases are strongly related to the differences in algorithms used to retrieve satellite SSS. Non‐Argo data utilized in the study is shown to be of great use to validate Aquarius in regions with little to no Argo coverage and helps provide SSS measurements in regions where there are known errors in Aquarius retrievals. The annual cycle of WOD and Aquarius are found to be very similar, with Aquarius being generally more coherent and robust. All three products’ annual cycles compared favorably to the World Ocean Atlas 2013. The interannual changes in all three products generally corresponded well to one another and to changes in evaporation and precipitation (E‐P). Overall, Aquarius compares very well with in situ sea surface salinity fields under multiple comparison examinations; however, both products have their own strengths and weaknesses and a synthesis of the two should be used to study global scale SSS variability.
      PubDate: 2014-10-31T04:07:08.435271-05:
      DOI: 10.1002/2014JC009961
       
  • Barotropic and baroclinic contributions to along‐ and
           across‐stream transport in the Antarctic Circumpolar Current
    • Authors: B. Peña‐Molino; S. R. Rintoul, M. R. Mazloff
      Pages: n/a - n/a
      Abstract: The Southern Ocean's ability to store and transport heat and tracers as well as to dissipate momentum and energy are intimately related to the vertical structure of the Antarctic Circumpolar Current (ACC). Here the partition between barotropic and baroclinic flow in the time‐mean ACC is investigated in a Southern Ocean state estimate. The zonal geostrophic transport is predominantly baroclinic, with at most 25% of the transport at any longitude carried by the barotropic component. Following surface streamlines, changes in vertical shear and near‐bottom velocity are large, and result in changes in the local partition of barotropic/baroclinic vertically integrated transport from 10/90% in the center of the basins, to 50/50% near complex topography. The velocity at depth is not aligned with the surface velocity. This non‐equivalent barotropic flow supports significant cross‐stream transports. Barotropic and baroclinic mass transport across the ACC is, on average, in opposite directions, with the net barotropic cross‐stream transport being poleward and the net baroclinic equatorward. The sum partially cancels out, leaving a net geostrophic poleward transport across the different fronts between ‐5 and ‐20 Sv. Temperature is also transported across the fronts by the non‐equivalent barotropic part of the ACC, with maximum values across the northern ACC fronts equivalent to ‐0.2 PW. The sign and magnitude of these transports is not sensitive to the choice of stream‐coordinate. These cross‐stream volume and temperature transports are variable in space, and dependent on the interactions between deep flow and bathymetry, thus difficult to infer from surface and hydrographic observations alone.
      PubDate: 2014-10-31T03:48:56.744422-05:
      DOI: 10.1002/2014JC010020
       
  • Evaluating SODA for Indo‐Pacific Ocean decadal climate variability
           studies
    • Authors: J. Mauro Vargas‐Hernandez; Susan Wijffels, Gary Meyers, Neil J. Holbrook
      Pages: n/a - n/a
      Abstract: Estimates of changes in upper ocean temperature, heat content and sea level are dependent on the coverage of subsurface observations in space and time. Historically, these data are sparse, which has limited our understanding of ocean climate variability and change mechanisms. Ocean state estimates, which effectively represent a model synthesis and integration of the available observations, including internal observations in the ocean and surface forcing, help address the inhomogeneity of sparse observations in space and time. Here, we evaluate the representativeness of ocean state estimates from the Simple Ocean Data Assimilation Version 2.2.4 (SODA) data for studying Indo‐Pacific Ocean decadal temperature and sea level variability over the period 1950‐2007. The SODA data are evaluated against independent sea level anomalies from long‐record tide gauges at Midway Island and Fremantle, reconstructed sea surface height anomalies, and sea surface height anomalies from TOPEX/Poseidon satellite altimeter observations at the decadal time scale. This study demonstrates that SODA captures the characteristic Interdecadal Pacific Oscillation (IPO) over the upper 200 m, and accurately represents these decadal changes against the independent observations. The SODA‐product shows a meridional asymmetry of patterns that connect the western tropical Pacific and the Indian Ocean, apparently in relation to IPO changes. Regional sea level at the Midway Island and Fremantle tide‐gauges confirm this decadal connection and the relationship with the IPO. We concluded that SODA is potentially a useful tool to examine ocean decadal climate variability across the Indo‐Pacific Ocean.
      PubDate: 2014-10-31T03:34:49.75108-05:0
      DOI: 10.1002/2014JC010175
       
  • Lagrangian predictability characteristics of an Ocean Model
    • Authors: Guglielmo Lacorata; Luigi Palatella, Rosalia Santoleri
      Pages: n/a - n/a
      Abstract: The Mediterranean Forecasting System (MFS) Ocean Model, provided by INGV, has been chosen as case study to analyze Lagrangian trajectory predictability by means of a dynamical systems approach. To this regard, numerical trajectories are tested against a large amount of Mediterranean drifter data, used as sample of the actual tracer dynamics across the sea. The separation rate of a trajectory pair is measured by computing the Finite‐Scale Lyapunov Exponent (FSLE) of first and second kind. An additional kinematic Lagrangian model (KLM), suitably treated to avoid “sweeping”‐related problems, has been nested into the MFS in order to recover, in a statistical sense, the velocity field contributions to pair particle dispersion, at mesoscale level, smoothed out by finite resolution effects. Some of the results emerging from this work are: a) drifter pair dispersion displays Richardson's turbulent diffusion inside the [10‐100] km range, while numerical simulations of MFS alone (i.e. without subgrid model) indicate exponential separation; b) adding the subgrid model, model pair dispersion gets very close to observed data, indicating that KLM is effective in filling the energy “mesoscale gap” present in MFS velocity fields; c) there exists a threshold size beyond which pair dispersion becomes weakly sensitive to the difference between model and “real” dynamics; d) the whole methodology here presented can be used to quantify model errors and validate numerical current fields, as far as forecasts of Lagrangian dispersion are concerned.
      PubDate: 2014-10-31T03:33:33.795286-05:
      DOI: 10.1002/2014JC010313
       
  • A time‐series of incubation experiments to examine the production
           and loss of CH3I in surface seawater
    • Authors: Qiang Shi; Christa Marandino, Gert Petrick, Birgit Quack, Douglas Wallace
      Pages: n/a - n/a
      Abstract: In order to investigate production pathways of methyl iodide and controls on emissions from the surface ocean, a set of repeated in‐vitro incubation experiments were performed over an annual cycle in the context of a time‐series of in‐situ measurements in Kiel Fjord (54.3 N, 10.1E). The incubation experiments revealed a diurnal variation of methyl iodide in samples exposed to natural light, with maxima during day time and losses during night hours. The amplitude of the daily accumulation varied seasonally and was not affected by filtration (0.2µm), consistent with a photochemical pathway for CH3I production. The methyl iodide loss rate during night time correlate with the concentration accumulated during daytime suggesting a 1st order loss mechanism (R2=0.29, p
      PubDate: 2014-10-31T03:28:13.724562-05:
      DOI: 10.1002/2014JC010223
       
  • Evaluation of sea‐surface salinity observed by Aquarius
    • Authors: Hiroto Abe; Naoto Ebuchi
      Pages: n/a - n/a
      Abstract: Sea‐surface salinity (SSS) observed by Aquarius was compared with global observation from Argo floats and offshore moored buoys to evaluate the quality of satellite SSS data and to assess error structures. Aquarius products retrieved by different algorithms (Aquarius Official Release version 3.0 (V3.0), Combined Active‐Passive (CAP) algorithm version 3.0, Remote Sensing Systems testbed algorithm version 3) were compared. The Aquarius SSS was in good agreement with in situ salinity measurements for all three products. Root‐mean‐square (rms) differences of the salinity residual, with respect to Argo salinity, ranged from 0.41 to 0.52 psu. These three Aquarius products exhibit high SSS deviation from Argo salinity under lower sea‐surface temperature conditions (< 10 °C) due to lower sensitivity of microwave emissivity to SSS. The CAP product deviates under strong wind conditions (> 10 ms−1), probably due to model bias and uncertainty associated with sea‐surface roughness. Furthermore, significant SSS differences between ascending (south‐to‐north) and descending (north‐to‐south) paths were detected. The monthly‐averaged Aquarius SSS (1° × 1° grid) was also compared with outputs from the ocean data optimal interpolation (OI) system operated by the Japan Agency for Marine‐Earth Science Technology (JAMSTEC) and the ocean data assimilation system used by the Meteorological Research Institute, Japan Meteorological Agency (MRI/JMA). Negative bias, attributed to near‐surface salinity stratification by precipitation, was detected in tropical regions. For 40°S–40°N, rms difference, with respect to JAMSTEC OI, is 0.27 psu for the V3.0, while the CAP product rms difference is only 0.22 psu, which is close to the Aquarius mission goal.
      PubDate: 2014-10-31T03:28:00.537747-05:
      DOI: 10.1002/2014JC010094
       
  • The imprint of Southern Ocean overturning on seasonal water mass
           variability in Drake Passage
    • Authors: Dafydd Gwyn Evans; Jan D. Zika, Alberto C. Naveira Garabato, A. J. George Nurser
      Pages: n/a - n/a
      Abstract: Seasonal changes in water mass properties are discussed in thermohaline coordinates from a seasonal climatology and repeat hydrographic sections. The SR1b CTD transects along Drake Passage are used as a case study. The amount of water within temperature and salinity classes and changes therein are used to estimate dia‐thermal and dia‐haline transformations. These transformations are considered in combination with climatologies of surface buoyancy flux to determine the relative contributions of surface buoyancy fluxes and sub‐surface mixing to changes in the distribution of water in thermohaline coordinates. The framework developed provides unique insights into the thermohaline circulation of the water masses that are present within Drake Passage, including the erosion of Antarctic Winter Water (AAWW) during the summer months and the interaction between the Circumpolar Deep Waters (CDW) and Antarctic Intermediate Water (AAIW). The results presented are consistent with summertime wind‐driven inflation of the CDW layer and deflation of the AAIW layer, and with new AAIW produced in the winter as a mixture of CDW, remnant AAWW and surface waters. This analysis therefore highlights the role of surface buoyancy fluxes in the Southern Ocean overturning.
      PubDate: 2014-10-31T03:27:51.373817-05:
      DOI: 10.1002/2014JC010097
       
  • The ability of a barotropic model to simulate sea level extremes of
           meteorological origin in the Mediterranean Sea, including those caused by
           explosive cyclones
    • Authors: F. M. Calafat; E. Avgoustoglou, G. Jordà, H. Flocas, G. Zodiatis, M. N. Tsimplis, J. Kouroutzoglou
      Pages: n/a - n/a
      Abstract: Storm surges are responsible for great damage to coastal property and loss of life every year. Coastal management and adaptation practices are essential to reduce such damage. Numerical models provide a useful tool for informing these practices as they simulate sea level with high spatial resolution. Here we investigate the ability of a barotropic version of the HAMSOM model to simulate sea level extremes of meteorological origin in the Mediterranean Sea, including those caused by explosive cyclones. For this purpose, the output of the model is compared to hourly sea level observations from 6 tide gauge records (Valencia, Barcelona, Marseille, Civitavecchia, Trieste, and Antalya). It is found that the model underestimates the positive extremes significantly at all stations, in some cases by up to 65%. At Trieste, the model can also sometimes overestimate the extremes significantly. The differences between the model and the residuals are not constant for extremes of a given height, which limits the applicability of the numerical model for storm surge forecasting because calibration is difficult. The 50‐ and 10‐year return levels are reasonably well captured by the model at all stations except Barcelona and Marseille, where they are underestimated by over 30%. The number of exceedances of the 99.9th and 99.95% percentiles over a period of 25 years is severely underestimated by the model at all stations. The skill of the model for predicting the timing and value of the storm surges seems to be higher for the events associated with explosive cyclones at all stations.
      PubDate: 2014-10-31T03:13:19.427075-05:
      DOI: 10.1002/2014JC010360
       
  • Variability of zonal currents in the eastern equatorial Indian Ocean on
           seasonal to interannual time scales
    • Authors: Ebenezer S. Nyadjro; Michael J. McPhaden
      Pages: n/a - n/a
      Abstract: This study examines equatorial zonal current variations in the upper layers of eastern Indian Ocean in relation to variations in the Indian Ocean Dipole (IOD). The analysis utilizes data from the Research Moored Array for African‐Asian‐Australian Monsoon Analysis and Prediction (RAMA) and the European Centre for Medium‐Range Weather Forecasts ‐ Ocean Reanalysis System 4 (ECMWF‐ORAS4). Surface currents are characterized by semi‐annual eastward flowing Wyrtki jets along the equator in boreal spring and fall, forced by westerly monsoon transition winds. The fall jet intensifies during negative IOD (NIOD) events when westerlies are anomalously strong but significantly weakens during positive IOD (PIOD) events when westerlies are anomalously weak. As zonal wind stress weakens during PIOD events, sea surface height becomes unusually low in the eastern basin and high in the west, setting up an anomalous pressure force that drives increased eastward transport in the thermocline. Opposite tendencies are evident during NIOD events in response to intensified equatorial westerlies. Current transport adjustments to anomalous zonal wind forcing during IOD events extend into the following year, consistent with the cycling of equatorial wave energy around the basin. A surface layer mass budget calculation for the eastern sea surface temperature (SST) pole of the IOD indicates upwelling of ~2.9±0.7 Sv during normal periods, increasing by 40‐50% during PIOD events and reducing effectively to zero during NIOD events. IOD‐related variations in Wyrtki jet and thermocline transports are major influences on these upwelling rates and associated water mass transformations, which vary consistently with SST changes.
      PubDate: 2014-10-28T03:24:26.842397-05:
      DOI: 10.1002/2014JC010380
       
  • Investigation of rain effects on Aquarius sea surface salinity
           measurements
    • Authors: Andrea Santos‐Garcia; María Marta Jacob, W. Linwood Jones, William E. Asher, Yazan Hejazin, Hamideh Ebrahimi, Monica Rabolli
      Pages: n/a - n/a
      Abstract: The Aquarius/SAC‐D mission has been providing Sea Surface Salinity (SSS), globally over the ocean, for almost 3 years. As a member of the AQ/SAC‐D Cal/Val team, the Central Florida Remote Sensing Laboratory has analyzed these salinity retrievals in the presence of rain and has noted the strong correlation between the spatial patterns of reduced SSS and the spatial distribution of rainfall. It was determined that this is the result of a cause and effect relationship, as opposed to SSS measurement errors. Hence, it is important to understand these SSS changes due to seawater dilution by rain and the associated near‐surface salinity stratification. This paper addresses the effects of rainfall on the Aquarius (AQ) SSS retrieval using a macro‐scale Rain Impact Model (RIM) in the region of high convective rain over the Inter‐tropical Convergence Zone. This model, based on the superposition of a one‐dimension eddy diffusion (turbulent diffusion) model, relates sea surface salinity to depth, rain accumulation and time since rainfall. For aiding in the identification of instantaneous and prior rainfall accumulations, an AQ Rain Accumulation product was developed. This product, based on the NOAA CMORPH rain dataset, provides the rainfall history for 24 hours prior to the observation time, which is integrated over each AQ SSS measurement cell. In this paper results of the RIM validation are presented by comparing AQ measured and RIM simulated SSS for several months of 2012. Results show the high cross‐correlation for these comparisons and also with the corresponding SSS anomalies relative to HYCOM.
      PubDate: 2014-10-25T03:01:11.929923-05:
      DOI: 10.1002/2014JC010137
       
  • Tropical cyclone footprint in the ocean mixed layer observed by Argo in
           the northwest Pacific
    • Authors: HongLi Fu; Xidong Wang, Peter C. Chu, Xuefeng Zhang, Guijun Han, Wei Li
      Pages: n/a - n/a
      Abstract: This study systematically investigated the ocean mixed layer responses to tropical cyclone (TC) using available Argo profiles during the period of 1998‐2011 in the Northwest Pacific. Results reveal that isothermal layer (IL) deepening and isothermal layer (IL) cooling with evident rightward biases induced by strong TCs are clearer compared to the weak TCs. Likewise, the rightward biases of IL deepening and cooling induced by fast TCs are more obvious than that induced by slow TCs. The upwelling within TC's eye is much stronger for the strong (slow) TCs than weak (fast) TCs. For the strong and slow TCs, the TC‐induced rainfall reduces deepening of constant density layer [with its depth called the mixed layer depth (MLD)], and in turn increases the barrier layer thickness (BLT). The initial BL prior to TC can restrict IL cooling more markedly under the weak and fast TCs than under the strong and slow TCs. The inertial oscillation is stronger induced by the strong (fast) TCs than by the weak (slow) TCs. In addition, the most pronounced TC‐induced mixed layer deepening and IL cooling in July‐October climatology occur in the subtropical gyre of the Northwest Pacific with enhanced vertical diffusivity. The maximum increase of isothermal layer depth (ILD) and MLD is up to 5m, with IL cooling up to 0.4°C.
      PubDate: 2014-10-25T03:00:45.485957-05:
      DOI: 10.1002/2014JC010316
       
  • Observations of wave shear stress on a steep beach
    • Authors: G. W. Wilson; A. E. Hay, A. J. Bowen
      Pages: n/a - n/a
      Abstract: Observations are presented of the wave shear stress 〈u˜w˜〉 on a steeply sloping beach. Above the wave boundary layer (WBL), positive values of 〈u˜w˜〉 were observed, and are attributed to a combination of both wave shoaling due to the large‐scale bed slope, and dissipation due to wave breaking, in agreement with the wave theory of Zou et al. [2003]. Within the WBL, observed vertical profiles of 〈u˜w˜〉 were also in good agreement with theory, in cases where the wave height was small. As wave heights increased, however, the WBL profile of 〈u˜w˜〉 generally did not agree with theory. Near‐simultaneous rotary sonar observations of the bed suggest the disagreement with theory was due to the presence of orbital scale ripples, which the present theory does not accommodate.
      PubDate: 2014-10-25T02:42:36.001053-05:
      DOI: 10.1002/2014JC010193
       
  • Circulation and transports in the Newfoundland Basin, western subpolar
           North Atlantic
    • Authors: Christian Mertens; Monika Rhein, Maren Walter, Claus W. Böning, Erik Behrens, Dagmar Kieke, Reiner Steinfeldt, Uwe Stöber
      Pages: n/a - n/a
      Abstract: The southwestern part of the subpolar North Atlantic east of the Grand Banks of Newfoundland and Flemish Cap is a crucial area for the Atlantic Meridional Overturning Circulation. Here the exchange between subpolar and subtropical gyre takes place, southward flowing cold and fresh water is replaced by northward flowing warm and salty water within the North Atlantic Current (NAC). As part of a long‐term experiment, the circulation east of Flemish Cap has been studied by seven repeat hydrographic sections along 47°N (2003‐‐2011), a two‐year time series of current velocities at the continental slope (2009‐‐2011), 19 years of sea surface height, and 47 years of output from an eddy resolving ocean circulation model. The structure of the flow field in the measurements and the model shows a deep reaching NAC with adjacent recirculation and two distinct cores of southward flow in the Deep Western Boundary Current (DWBC): One core above the continental slope with maximum velocities at mid‐depth and the second farther east with bottom‐intensified velocities. The western core of the DWBC is rather stable, while the offshore core shows high temporal variability that in the model is correlated with the NAC strength. About 30 Sv of deep water flow southward below a density of σθ = 27.68kg‐3 in the DWBC. The NAC transports about 110 Sv northward, approximately 15 Sv originating from the DWBC, and 75 Sv recirculating locally east of the NAC, leaving 20 Sv to be supplied by the NAC from the south.
      PubDate: 2014-10-25T02:42:19.090311-05:
      DOI: 10.1002/2014JC010019
       
  • Mapping of sea surface nutrients in the North Pacific: Basin‐wide
           distribution and seasonal to interannual variability
    • Authors: Sayaka Yasunaka; Yukihiro Nojiri, Shin‐ichiro Nakaoka, Tsuneo Ono, Frank A. Whitney, Maciej Telszewski
      Pages: n/a - n/a
      Abstract: Monthly maps of sea surface nutrient (phosphate, nitrate and silicate) concentrations were produced for the North Pacific (10–60°N, 120°E–90°W) for the years 2001 to 2010 using a self‐organizing map trained with temperature, salinity, chlorophyll‐a concentration and mixed layer depth. Nutrient sampling was carried out mainly by ships of opportunity, providing good seasonal coverage of the surface ocean. Using the mapping results, we investigated the spatio‐temporal variability of surface North Pacific nutrient and dissolved inorganic carbon (DIC) distributions on seasonal and interannual time scales. Nutrient and DIC concentrations were high in the subarctic in winter and low in the subtropics. In the summer, substantial amount of nutrients remained unutilized in subarctic and the northern part of the subarctic‐subtropical boundary region while that was not the case in the southern part of the boundary region. In the subtropics, nutrients were almost entirely depleted throughout the year, while DIC concentrations showed a north‐south gradient and significant seasonal change. Nutrients and DIC show a large seasonal drawdown in the western subarctic region, while the drawdown in the eastern subarctic region was weaker, especially for silica. The subarctic‐subtropical boundary region also showed a large seasonal drawdown, which was most prominent for DIC and less obvious for nitrate and silicate. In the interannual time scale, the Pacific Decadal Oscillation was related to a seesaw pattern between the subarctic‐subtropical boundary region and the Alaskan Gyre through the changes in horizontal advection, vertical mixing and biological production.
      PubDate: 2014-10-24T20:40:39.872342-05:
      DOI: 10.1002/2014JC010318
       
  • Observations of the frontal region of a buoyant river plume using an
           autonomous underwater vehicle
    • Authors: Peter Rogowski; Eric Terrill, Jialin Chen
      Pages: n/a - n/a
      Abstract: To characterize the transitional region from the near‐field to far‐field of a river plume entering coastal waters we conducted four surveys using an autonomous underwater vehicle (AUV) to target the outflow of the New River Inlet, North Carolina, during maximum ebb tide. The utilization of a mobile sensor to synoptically observe current velocity data in tandem with natural river plume tracers (e.g. colored dissolved organic matter, salinity) was essential in understanding the mechanisms driving the observed circulation and mixing patterns within these waters. We find that this region is regularly impacted by two primary processes: (1) the interaction of an old dredged channel plume with the main discharge and (2) the recirculation of the discharge plume by an eddy that persistently forms between the old channel and main discharge location. Wind‐driven processes in the nearshore can enhance the interaction of these two plumes resulting in unstable regions where mixing of the merged plume with the receiving waters is accelerated. We also conduct comparisons between AUV velocity observations from two surveys and their corresponding velocity outputs from a parallelized quasi‐3D model. We conclude that the ability to observe the estuarine outflow transitional region at near‐synoptic temporal scales and resolutions discussed in this paper is key in providing the mechanisms driving local circulation which is essential for proper parameterization of high‐resolution numerical coastal models.
      PubDate: 2014-10-24T18:06:56.518096-05:
      DOI: 10.1002/2014JC010392
       
  • The North Atlantic subtropical surface salinity maximum as observed by
           Aquarius
    • Authors: Frederick M. Bingham; Julius Busecke, Arnold L. Gordon, Claudia F. Giulivi, Zhijin Li
      Pages: n/a - n/a
      Abstract: Aquarius satellite derived sea surface salinity (SSS) data from August 2011 through September 2013 reveals significant seasonal migration and freshening of the subtropical surface salinity maximum (SSS‐max) area in the North Atlantic, in good agreement with in situ observations, including those obtained as part of the SPURS (Salinity Processes in the Upper Ocean Regional Study) field experiment in 2012‐2013. The SSS‐max fluctuated in surface area ‐ as defined by the 37.4 surface isohaline ‐ during the course of the Aquarius time series by about 67%. The SSS‐max has a surprisingly large amount of non‐seasonal variability, including a general decrease in salinity throughout the eastern subtropical North Atlantic between 2011‐2012 and 2012‐2013 of about 0.1‐0.2. The documented seasonal variability is weakest in the maximum salinity area and increases towards the north and south respectively. This is consistent with the important role played by Ekman transport and regional excess of evaporation over precipitation in the formation of the SSS‐max.
      PubDate: 2014-10-24T18:03:47.134036-05:
      DOI: 10.1002/2014JC009825
       
  • Effects of ocean acidification on the biogenic composition of the
           sea‐surface microlayer: Results from a mesocosm study
    • Authors: Luisa Galgani; Christian Stolle, Sonja Endres, Kai G. Schulz, Anja Engel
      Pages: n/a - n/a
      Abstract: The sea‐surface microlayer (SML) is the ocean's uppermost boundary to the atmosphere and in control of climate relevant processes like gas exchange and emission of marine primary organic aerosols (POA). The SML represents a complex surface film including organic components like polysaccharides, proteins, and marine gel particles, and harbors diverse microbial communities. Despite the potential relevance of the SML in ocean‐atmosphere interactions still little is known about its structural characteristics and sensitivity to a changing environment such as increased oceanic uptake of anthropogenic CO2. Here, we report results of a large scale mesocosm study, indicating that ocean acidification can affect the abundance and activity of microorganisms during phytoplankton blooms, resulting in changes in composition and dynamics of organic matter in the SML. Our results reveal a potential coupling between anthropogenic CO2 emissions and the biogenic properties of the SML, pointing to a hitherto disregarded feedback process between ocean and atmosphere under climate change.
      PubDate: 2014-10-24T18:02:49.969586-05:
      DOI: 10.1002/2014JC010188
       
  • Turbidity maximum formation in a well‐mixed macrotidal estuary: The
           role of tidal pumping
    • Authors: Qian Yu; Yunwei Wang, Jianhua Gao, Shu Gao, Burg Flemming
      Pages: n/a - n/a
      Abstract: Traditionally, vertical circulation (induced by gravity circulation and tidal straining), tidal pumping, and resuspension are suggested as the major processes for the formation and maintenance of the estuarine turbidity maximum (ETM). Due to strong mixing, tidal pumping is considered as the dominating process in macro‐tidal estuaries. To analyze field observation data, the classical empirical decomposition method is commonly suggested, but the tidal pumping flux (TPF) based on this method may lead to erroneous conclusions about the mechanisms of ETM formation because the effects of advection induced by the horizontal SSC gradient and fine bed sediment supply are ignored. If these effects are included, the TPF clearly reproduces the convergence patterns and thus demonstrates its role in the formation of the ETM. By a simplified analytical solution, the TPF is the result of the competition between the downstream flux induced by the river current together with the lag in sediment response and the upstream flux induced by tidal asymmetry and the lag. Field observations in the well‐mixed macro‐tidal Yalu River estuary (located between China and North Korea were analyzed. Tidal pumping is identified as the dominant mechanism of its ETM formation, and the position of the ETM for different river discharges and sediment settling velocities can be predicted by the concept of tidal pumping by numerical and analytical procedures. The present study provides a typical example of how to evaluate the tidal pumping contributions on ETM formation using the combined information provided by field data, numerical modeling results and analytical solutions.
      PubDate: 2014-10-20T22:10:42.080373-05:
      DOI: 10.1002/2014JC010228
       
  • Mechanisms of Pacific Summer Water variability in the Arctic's central
           Canada Basin
    • Authors: M.‐L. Timmermans; A. Proshutinsky, E. Golubeva, J.M. Jackson, R. Krishfield, M. McCall, G. Platov, J. Toole, W. Williams
      Pages: n/a - n/a
      Abstract: Pacific Water flows northward through Bering Strait and penetrates the Arctic Ocean halocline throughout the Canadian Basin sector of the Arctic. In summer, Pacific Summer Water (PSW) is modified by surface buoyancy fluxes and mixing as it crosses the shallow Chukchi Sea before entering the deep ocean. Measurements from Ice‐Tethered Profilers, moorings and hydrographic surveys between 2003 and 2013 reveal spatial and temporal variability in the PSW component of the halocline in the Central Canada Basin with increasing trends in integrated heat and freshwater content, a consequence of PSW layer thickening as well as layer freshening and warming. It is shown here how properties in the Chukchi Sea in summer control the temperature‐salinity properties of PSW in the interior by subduction at isopycnals that outcrop in the Chukchi Sea. Results of an ocean model, forced by idealized winds, provide support to the mechanism of surface ocean Ekman transport convergence maintaining PSW ventilation of the halocline.
      PubDate: 2014-10-20T04:46:43.226752-05:
      DOI: 10.1002/2014JC010273
       
  • Exploiting satellite Earth observation to quantify current global oceanic
           DMS flux and its future climate sensitivity
    • Authors: P. E. Land; J. D. Shutler, T. G. Bell, M. Yang
      Pages: n/a - n/a
      Abstract: We used coincident Envisat RA2 and AATSR temperature and wind speed data from 2008/9 to calculate the global net sea‐air flux of dimethyl sulfide (DMS), which we estimate to be 19.6 Tg S a‐1. Our monthly flux calculations are compared to open ocean eddy correlation measurements of DMS flux from 10 recent cruises, with a root mean square difference of 3.1 μmol m‐2 day‐1. In a sensitivity analysis we varied temperature, salinity, surface wind speed and aqueous DMS concentration, using fixed global changes as well as CMIP5 model output. The range of DMS flux in future climate scenarios is discussed. The CMIP5 model predicts a reduction in surface wind speed and we estimate that this will decrease the global annual sea‐air flux of DMS by 22% over 25 years. Concurrent changes in temperature, salinity and DMS concentration increase the global flux by much smaller amounts. The net effect of all CMIP5 modelled 25‐year predictions was a 19% reduction in global DMS flux. 25‐year DMS concentration changes had significant regional effects, some positive (Southern Ocean, North Atlantic, Northwest Pacific) and some negative (isolated regions along the Equator and in the Indian Ocean). Using satellite‐detected coverage of coccolithophore blooms, our estimate of their contribution to North Atlantic DMS emissions suggests that the coccolithophores contribute only a small percentage of the North Atlantic annual flux estimate, but may be more important in the summertime and in the northeast Atlantic.
      PubDate: 2014-10-20T04:37:26.863615-05:
      DOI: 10.1002/2014JC010104
       
  • The salinity signature of the cross‐shelf exchanges in the
           southwestern Atlantic Ocean: Numerical simulations
    • Authors: Ricardo P. Matano; Vincent Combes, Alberto R. Piola, Raul Guerrero, Elbio D. Palma, P. Ted Strub, Corinne James, Harold Fenco, Yi Chao, Martin Saraceno
      Pages: n/a - n/a
      Abstract: A high‐resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA) the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high frequency component of the wind stress forcing controls the vertical structure of the plumes while the low‐frequency component of the wind stress forcing and the inter‐annual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross‐shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross‐shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf.
      PubDate: 2014-10-17T04:17:57.306452-05:
      DOI: 10.1002/2014JC010116
       
  • Summertime phytoplankton blooms and surface cooling in the western south
           equatorial Indian Ocean
    • Authors: Xiaomei Liao; Yan Du, Haigang Zhan, Ping Shi, Jia Wang
      Pages: n/a - n/a
      Abstract: Chlorophyll‐a (Chla) concentration derived from the Sea viewing Wide field of View sensor (SeaWiFS) data (January 1998‐December 2010) shows phytoplankton blooms in the western south equatorial Indian Ocean (WSEIO) during the summer monsoon. The mechanism that sustains the blooms is investigated with the high‐resolution Ocean General Circulation Model for the Earth Simulator (OFES) products. The summer blooms in the WSEIO are separated from the coast; they occur in June, reach their maximum in August, and decay in October. With summer monsoon onset, cross‐equatorial wind induces open‐ocean upwelling in the WSEIO, uplifting the nutricline. The mixed layer heat budget analysis reveals that both thermal forcing and ocean processes are important for the seasonal variations of SST, especially wind‐driven entrainment plays a significant role in cooling the WSEIO. These processes cause nutrient enrichment in the surface layer and trigger the phytoplankton blooms. As the summer monsoon develops, the strong wind deepens the mixed layer; the entrainment thus increases the nutrient supply and enhances the bloom. Horizontal advection associated with the Southern Gyre might also be an important process that sustains the bloom. This large clockwise gyre could advect nutrient‐rich water along its route, allowing Chla to bloom in a larger area.
      PubDate: 2014-10-17T04:03:53.263275-05:
      DOI: 10.1002/2014JC010195
       
  • SMOS sea surface salinity signals of tropical instability waves
    • Authors: Xiaobin Yin; Jacqueline Boutin, Gilles Reverdin, Tong Lee, Sabine Arnault, Nicolas Martin
      Pages: n/a - n/a
      Abstract: Sea Surface Salinity (SSS) measurements from the Soil Moisture and Ocean Salinity (SMOS) mission provide an unprecedented opportunity to observe the salinity structure of Tropical Instability Waves (TIWs) from space, especially during the intense 2010 La Niña condition. In the eastern equatorial Pacific Ocean, SMOS SSS signals correlate well and have similar amplitude to 1‐m salinity from the Tropical Atmosphere Ocean (TAO) array at 6 locations with strong TIW signals. At these locations, the linear negative relationships between SMOS SSS and OSTIA SST signals vary from ‐0.20 °C‐1 to ‐0.25 °C‐1, which are comparable to the ones obtained from TAO. From June to December 2010, the largest TIW signals and meridional gradients of both SSS and SST appear around 2°N west of 100°W. They shift southward and cross the equator at 90°W. In addition to the large negative correlation band around 2°N, a band of negative correlations between SSS and SST signals also exists around 8°N west of 110°W for the 33‐day signals. The peak amplitude of the 33‐day SMOS SSS signals west of 135°W is reduced by more than 40% with respect to values east of 135°W, while the reduction for SST is much lower (less than 20%). The amplitudes and longitudinal extents of TIW signals and the dominant westward propagation speed of 17‐day TIWs (as detected by SMOS and Aquarius) at the equator decrease from 2010 to 2013 associated with the transition from a strong La Niña to non La Niña conditions.
      PubDate: 2014-10-17T03:47:53.742659-05:
      DOI: 10.1002/2014JC009960
       
  • The salinity signature of the cross‐shelf exchanges in the
           southwestern Atlantic Ocean: Satellite observations
    • Authors: Raul A. Guerrero; Alberto R. Piola, Harold Fenco, Ricardo P. Matano, Vincent Combes, Yi Chao, Corinne James, Elbio D. Palma, Martin Saraceno, P. Ted Strub
      Pages: n/a - n/a
      Abstract: Satellite derived sea surface salinity (SSS) data from Aquarius and SMOS are used to study the shelf‐open ocean exchanges in the western South Atlantic near 35ºS. Away from the tropics these exchanges cause the largest SSS variability throughout the South Atlantic. The data reveal a well defined seasonal pattern of SSS during the analyzed period and of the location of the export of low salinity shelf waters. In spring and summer low salinity waters over the shelf expand offshore and are transferred to the open ocean primarily southeast of the river mouth (from 36 ºS to 37º30’S). In contrast, in fall and winter low salinity waters extend along a coastal plume and the export path to the open ocean distributes along the offshore edge of the plume. The strong seasonal SSS pattern is modulated by the seasonality of the along‐shelf component of the wind stress over the shelf. However, the combined analysis of SSS, satellite‐derived sea surface elevation and surface velocity data suggest that the precise location of the export of shelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluence and mesoscale eddies and meanders of the Brazil Current. The satellite data indicate that in summer, mixtures of low salinity shelf waters are swiftly driven towards the ocean interior along the axis of the Brazil/Malvinas Confluence. In winter, episodic wind reversals force the low salinity coastal plume offshore where they mix with tropical waters within the Brazil Current and create a warmer variety of low salinity waters in the open ocean.
      PubDate: 2014-10-17T03:45:52.932219-05:
      DOI: 10.1002/2014JC010113
       
  • Preliminary analysis of acceleration of sea level rise through the
           twentieth century using extended tide gauge data sets (August 2014)
    • Authors: Peter Hogarth
      Pages: n/a - n/a
      Abstract: This work explores the potential for extending tide gauge time series from the Permanent Service for Mean Sea Level (PSMSL) using historical documents, PSMSL ancillary data, and by developing additional composite time series using near neighbour tide gauges. The aim was to increase the number, completeness and geographical extent of records covering most or all of the 20th Century. The number of at least 75% complete century scale time series has been approximately doubled over the original PSMSL dataset. In total over 4800 station years have been added, with 294 of these added to 10 long Southern Hemisphere records. Individual century scale acceleration values derived from this new extended data set tend to converge on a value of 0.01 ± 0.008 mm/yr2. This result agrees closely with recent work and is statistically significant at the 1 sigma level. Possible causes of acceleration and errors are briefly discussed. Results confirm the importance of current data archaeology projects involving digitisation of the remaining archives of hard copy tide gauge data for sea level and climate studies.
      PubDate: 2014-10-16T03:41:51.932564-05:
      DOI: 10.1002/2014JC009976
       
  • The effect of water temperature on air entrainment, bubble plumes, and
           surface foam in a laboratory breaking‐wave analog
    • Authors: A. H. Callaghan; M. D. Stokes, G. B. Deane
      Pages: n/a - n/a
      Abstract: Air‐entraining breaking waves form oceanic whitecaps and play a key role in climate regulation through air‐sea bubble‐mediated gas transfer, and sea spray aerosol production. The effect of varying sea surface temperature on air entrainment, sub‐surface bubble plume dynamics, and surface foam evolution intrinsic to oceanic whitecaps has not been well studied. By using a breaking wave analogue in the laboratory over a range of water temperatures (Tw = 5 °C to Tw = 30 °C) and different source waters, we have examined changes in air entrainment, sub‐surface bubble plumes, and surface foam evolution over the course of a breaking event. For filtered seawater, air entrainment was estimated to increase by 6 % between Tw = 6 °C and Tw = 30 °C, driven by increases of about 43% in the measured surface roughness of the plunging water sheet. After active air entrainment, the rate of loss of air through bubble degassing was more rapid at colder water temperatures within the first 0.5 s of plume evolution. Thereafter, the trend reversed and bubbles degassed more quickly in warmer water. The largest observed temperature‐dependent differences in sub‐surface bubble distributions occurred at radii greater than about 700 μm. Temperature‐dependent trends observed in the sub‐surface bubble plume were mirrored in the temporal evolution of the surface whitecap foam area demonstrating the intrinsic link between surface whitecap foam and the sub‐surface bubble plume. Differences in foam and plume characteristics due to different water sources were greater than the temperature dependencies for the filtered seawater examined.
      PubDate: 2014-10-16T03:41:44.147171-05:
      DOI: 10.1002/2014JC010351
       
  • Impact of diurnal forcing on intraseasonal sea surface temperature
           oscillations in the Bay of Bengal
    • Authors: V. Thushara; P. N. Vinayachandran
      Pages: n/a - n/a
      Abstract: The diurnal cycle is an important mode of sea surface temperature (SST) variability in tropical oceans, influencing air‐sea interaction and climate variability. Upper ocean mixing mechanisms are significant at diurnal timescales controlling the intraseasonal variability (ISV) of SST. Sensitivity experiments using an Ocean General Circulation Model (OGCM) for the summer monsoon of the year 2007 show that incorporation of diurnal cycle in the model atmospheric forcings improves the SST simulation at both intraseasonal and shorter timescales in the Bay of Bengal (BoB). The increase in SST‐ISV amplitudes with diurnal forcing is ~0.05°C in the southern bay while it is ~0.02°C in the northern bay. Increased intraseasonal warming with diurnal forcing results from the increase in mixed layer heat gain from insolation, due to shoaling of the daytime mixed layer. Amplified intraseasonal cooling is dominantly controlled by the strengthening of sub‐surface processes owing to the nocturnal deepening of mixed layer. In the southern bay, intraseasonal variability is mainly determined by the diurnal cycle in insolation, while in the northern bay, diurnal cycle in insolation and winds have comparable contributions. Temperature inversions (TI) develop in the northern bay in the absence of diurnal variability in wind stress. In the northern bay, SST‐ISV amplification is not as large as that in the southern bay due to the weaker diurnal variability of mixed layer depth (MLD) limited by salinity stratification. Diurnal variability of model MLD is not sufficient to create large modifications in mixed layer heat budget and SST‐ISV in the northern bay.
      PubDate: 2014-10-15T03:05:34.369972-05:
      DOI: 10.1002/2013JC009746
       
  • The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE)
    • Authors: A. Ganachaud; S. Cravatte, A. Melet, A. Schiller, N. J. Holbrook, B. M. Sloyan, M. J. Widlansky, M. Bowen, J. Verron, P. Wiles, K. Ridgway, P. Sutton, J. Sprintall, C. Steinberg, G. Brassington, W. Cai, R. Davis, F. Gasparin, L. Gourdeau, T. Hasegawa, W. Kessler, C. Maes, K. Takahashi, K. J. Richards, U. Send
      Pages: n/a - n/a
      Abstract: The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) is an international research program under the auspices of CLIVAR. The key objectives are to understand the Southwest Pacific Ocean circulation and the South Pacific Convergence Zone (SPCZ) dynamics, as well as their influence on regional and basin‐scale climate patterns. South Pacific thermocline waters are transported in the westward flowing South Equatorial Current (SEC) toward Australia and Papua‐New Guinea. On its way, the SEC encounters the numerous islands and straits of the Southwest Pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes. The transit in the Coral, Solomon and Tasman Seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the El Niño‐Southern Oscillation, while the southward transports influence the climate and biodiversity in the Tasman Sea. After seven years of substantial in situ oceanic observational and modeling efforts, our understanding of the region has much improved. We have a refined description of the SPCZ behavior, boundary currents, pathways and water mass transformation, including the previously undocumented Solomon Sea. The transports are large and vary substantially in a counter‐intuitive way, with asymmetries and gating effects that depend on time scales. This paper provides a review of recent advancements, and discusses our current knowledge gaps and important emerging research directions.
      PubDate: 2014-10-14T12:01:59.029564-05:
      DOI: 10.1002/2013JC009678
       
  • Seasonality of biological feedbacks on sea surface temperature variations
           in the Arabian Sea: The role of mixing and upwelling
    • Authors: Jinfeng Ma; Hailong Liu, Pengfei Lin, Haigang Zhan
      Pages: n/a - n/a
      Abstract: The effects of biological heating on upper‐ocean temperature and circulation in the Arabian Sea are investigated using an ocean general circulation model. We find that the change of sea surface temperature (SST) is not only dependent on the variation of chlorophyll concentration, but also the dynamic processes, e.g., mixing and upwelling. Biological heating can warm the SST in the north Arabian Sea during spring and the central Arabian Sea during autumn when the mixed layer depth is shallow. However, the situation is quite different during winter and summer. Although the chlorophyll concentration is high in the north Arabian Sea during winter and in the western Arabian Sea during summer, the SSTs become significantly cool instead of warm. The heat budget analyses indicate that the cold SSTs result from both the strong convective mixing during the winter and the strong upwelling during the summer, which bring the cold water below the mixed layer to the surface.
      PubDate: 2014-10-10T04:16:41.458837-05:
      DOI: 10.1002/2014JC010186
       
  • Spatiotemporal chlorophyll‐a dynamics on the Louisiana continental
           shelf derived from a dual satellite imagery algorithm
    • Authors: Chengfeng Le; John C. Lehrter, Chuanmin Hu, Michael C. Murrell, Lin Qi
      Pages: n/a - n/a
      Abstract: A monthly time‐series of remotely sensed chlorophyll a (Chlars) over the Louisiana continental shelf (LCS) was developed and examined for its relationship to river discharge, nitrate concentration, total phosphorus concentration, photosynthetically available radiation (PAR), wind speed, and inter‐annual variation in hypoxic area size. A new algorithm for Chlars, tuned separately for clear and turbid waters, was developed using field‐observed chlorophyll a (Chlaobs) collected during 12 cruises from 2002‐2007. The new algorithm reproduced Chlaobs, with ~40% and ~60% uncertainties at satellite pixel level for clear offshore waters and turbid nearshore waters, respectively. The algorithm was then applied to SeaWiFS and MODIS images to calculate long‐term (1998‐2013) monthly mean Chlars estimates at 1 km resolution across the LCS. Correlation and multiple stepwise regression analyses were used to relate the Chlars estimates to key environmental drivers expected to influence phytoplankton variability. The Chlars time‐series covaried with river discharge and nutrient concentration, PAR, and wind speed, and there were spatial differences in how these environmental drivers influenced Chlars. The main axis of spatial variability occurred in a cross‐shelf direction with highest Chlars observed on the inner shelf. Both inner‐ (
      PubDate: 2014-10-10T03:58:57.378412-05:
      DOI: 10.1002/2014JC010084
       
  • Relative contributions of ocean mass and deep steric changes to sea level
           rise between 1993 and 2013
    • Authors: Sarah G. Purkey; Gregory C. Johnson, Don P. Chambers
      Pages: n/a - n/a
      Abstract: Regional and global trends of Sea Level Rise (SLR) owing to mass addition centered between 1996–2006 are assessed through a full‐depth SLR budget using full‐depth in‐situ ocean data and satellite altimetry. These rates are compared to regional and global trends in ocean mass addition estimated directly using data from the Gravity Recovery and Climate Experiment (GRACE) from 2003–2013. Despite the two independent methods covering different time periods with differing spatial and temporal resolution, they both capture the same large‐scale mass addition trend patterns including higher rates of mass addition in the North Pacific, South Atlantic, and the Indo‐Atlantic Sector of the Southern Ocean, and lower mass addition trends in the Indian, North Atlantic, South Pacific, and the Pacific Sector of the Southern Ocean. The global mean trend of ocean mass addition is 1.5 (±0.4) mm yr‐1 for 1996–2006 from the residual method and the same for 2003–2013 from the GRACE method. Furthermore, the residual method is used to evaluate the error introduced into the mass budget if the deep steric contributions below 700, 1000, 2000, 3000, and 4000 m are neglected, revealing errors of 65%, 38%, 13%, 8% and 4% respectively. The two methods no longer agree within error bars when only the steric contribution shallower than 1000 m is considered.
      PubDate: 2014-10-10T03:55:32.693136-05:
      DOI: 10.1002/2014JC010180
       
  • Coherent evidence from aquarius and argo for the existence of a shallow
           low‐salinity convergence zone beneath the Pacific ITCZ
    • Authors: Lisan Yu
      Pages: n/a - n/a
      Abstract: Aquarius observations featured a prominent zonal sea‐surface salinity (SSS) front that extended across the tropical Pacific between 2 – 10°N. By linking to Argo subsurface salinity observations and satellite‐derived surface forcing datasets, the study discovered that the SSS front was not a stand‐alone feature, but, in fact, the surface manifestation of a shallow low‐salinity convergence zone (LSCZ). A near‐surface salinity budget analysis was conducted, showing that the LSCZ was sourced from the rainfall in the Inter‐tropical convergence zone (ITCZ), but the mechanism of its generation and maintenance was dominated by the wind‐driven Ekman dynamics, not the surface freshwater flux. Three distinct features highlighted the relationship between the LSCZ and ITCZ. The first was that the seasonal movement of the LSCZ was characterized by a monotonic northward displacement starting from the near‐equatorial latitudes in boreal spring, which was different from the ITCZ that is known for its seasonal north‐south displacement. The second feature was that the lowest SSS waters were locked to the northern edge of the Ekman salt convergence throughout the year, but they showed no fixed relationship with the ITCZ rain band. The LSCZ and ITCZ collocated only during August‐October, the time that the ITCZ rain band coincided with the Ekman convergence zone. The third feature was the evidence of the collocation between the SSS front and the Ekman convergence zone, which not only established the Ekman convergence as the genesis of the LSCZ but also positioned the SST front as a surface manifestation of the LSCZ.
      PubDate: 2014-10-10T03:12:23.075232-05:
      DOI: 10.1002/2014JC010030
       
  • Seasonal variations of bio‐optical properties and their
           inter‐relationships observed by bio‐argo floats in the
           subpolar North Atlantic
    • Authors: Xiaogang Xing; Hervé Claustre, Julia Uitz, Alexandre Mignot, Antoine Poteau, Haili Wang
      Pages: n/a - n/a
      Abstract: Based on in situ datasets collected using two Bio‐Argo floats deployed in the sub‐polar North Atlantic from June, 2008 to May, 2010, the present study focuses on the seasonal variability of three bio‐optical properties, i.e. chlorophyll‐a concentration ([Chla]), particle backscattering coefficient at 532 nm (bbp(532)), and particle beam attenuation coefficient at 660 nm (cp(660)). In addition, the inter‐relationships among these properties are examined. Our results show that: 1) [Chla], bbp(532) and cp(660) are largely well‐coupled with each other in the upper layer, all being minimum in mid‐winter (January) and maximum in summer; 2) the backscattering coefficient presents an abrupt increase in late summer in the Icelandic Basin, likely due to a large contribution of coccolithophores following the diatom spring bloom; 3) the inter‐correlations between the three bio‐optical properties are basically consistent with previous studies; 4) seasonal variation in the of [Chla] to cp(660) ratio exhibits a clear light‐dependence, most likely due to the phytoplankton photoacclimation.
      PubDate: 2014-10-08T04:26:19.82501-05:0
      DOI: 10.1002/2014JC010189
       
  • Paper prepared for JGR Air‐sea exchange of methanol and acetone
           during HiWinGS—Estimation of air phase, water phase gas transfer
           velocities
    • Authors: Mingxi Yang; Byron W. Blomquist, Philip D. Nightingale
      Pages: n/a - n/a
      Abstract: The air‐sea fluxes of methanol and acetone were measured concurrently using a proton‐transfer‐reaction mass spectrometer (PTR‐MS) with the eddy covariance (EC) technique during the High Wind Gas Exchange Study (HiWinGS) in 2013. The seawater concentrations of these compounds were also measured twice daily with the same PTR‐MS coupled to a membrane inlet. Dissolved concentrations near the surface ranged from 7~28 nM for methanol and 3~9 nM for acetone. Both gases were consistently transported from the atmosphere to the ocean as a result of their low sea surface saturations. The largest influxes were observed in regions of high atmospheric concentrations and strong winds (up to 25 m s‐1). Comparison of the total air‐sea transfer velocity of these two gases (Ka), along with the in situ sensible heat transfer rate, allows us to constrain the individual gas transfer velocity in the air phase (ka) and water phase (kw). Among existing parameterizations, the scaling of ka from the COARE model is the most consistent with our observations. The kw we estimated is comparable to the tangential (shear‐driven) transfer velocity previously determined from measurements of dimethyl sulfide. Lastly, we estimate the wet deposition of methanol and acetone in our study region and evaluate the lifetimes of these compounds in the surface ocean and lower atmosphere with respect to total (dry plus wet) atmospheric deposition.
      PubDate: 2014-10-07T07:12:11.090916-05:
      DOI: 10.1002/2014JC010227
       
  • Near‐surface variability of temperature and salinity in the
           near‐tropical ocean: Observations from profiling floats
    • Authors: Jessica E. Anderson; Stephen C. Riser
      Pages: n/a - n/a
      Abstract: Upper ocean measurements of temperature and salinity obtained from profiling floats equipped with auxiliary Surface Temperature and Salinity sensors (STS) are presented. Using these instruments, high vertical resolution (10 cm) measurements in the near‐surface layer were acquired to within 20 cm of the sea surface, allowing for an examination of the ocean's near‐surface structure and variability not usually possible. We examine the data from sixty‐two Argo‐type floats equipped with STS units deployed in the Pacific, Atlantic, and Indian Oceans. The vertical variability of temperature and salinity in the near‐surface layer are characterized for each of these regions. While observations show the upper four meters of the ocean are well mixed most of the time, this homogeneity is interrupted by significant and often short‐lived warming/cooling and freshening events. In addition to the presence of barrier layers, a strong diurnal signal in temperature is observed, with salinity exhibiting somewhat weaker diurnal variations. The magnitude of the upper ocean diurnal cycle in temperature and salinity is largest in areas with light winds and heavy precipitation and was found to decay rapidly with depth (50% over the top two meters). Storm events, validated from meteorological data collected from nearby TAO moorings and the Tropical Rainfall Measuring Mission (TRMM) satellite, show downward mixing of rainfall‐derived fresh water to ten meters depth over only a few hours. Turner angle calculations show strong instability following these events.
      PubDate: 2014-10-06T22:51:57.842902-05:
      DOI: 10.1002/2014JC010112
       
  • Physical and biological controls on oxygen saturation variability in the
           upper Arctic Ocean
    • Authors: R. Eveleth; M.‐L. Timmermans, N. Cassar
      Pages: n/a - n/a
      Abstract: Employing continuous in situ measurements of dissolved O2/Ar and O2 in the Arctic Ocean, we investigate the mechanisms controlling the physical (abiotic) and biological oxygen saturation state variability in the surface ocean beneath sea ice. O2/Ar measurements were made underway using Equilibrator Inlet Mass Spectrometry (EIMS) during an icebreaker survey transiting the upper Arctic Ocean across the North Pole in late summer 2011. Using concurrently collected measurements of total oxygen we devolve biological oxygen saturation and physical oxygen (Ar) saturation signals at unprecedented horizontal resolution in the surface ocean. In the Nansen Basin Ar is undersaturated up to ‐7% while biological oxygen supersaturation peaks at 18.4%. We attribute this to ice melt, Atlantic Water influence and/or cooling. In the Canadian Basin, Ar is supersaturated up to 3%, likely because of Ar injection from freezing processes and long residence times of gas under ice cover. The overall Canadian Basin to Eurasian Basin gradient of Ar super‐ to under‐saturation may reflect net freezing in the Canadian basin and net melting in the Eurasian Basin over several seasons, either by Pacific to Atlantic sector ice transport or local changes over time. Ar saturation could thereby provide large scale high resolution estimates of current and future changes in these processes. O2/Ar supersaturation averages 4.9% with peaks up to 9.8% where first‐year ice and abundant melt ponds likely allow sufficient light for blooms in ice‐covered regions.
      PubDate: 2014-10-06T22:50:37.583714-05:
      DOI: 10.1002/2014JC009816
       
  • Interannual variability of the surface summertime eastward jet in the
           South China Sea
    • Authors: Yuanlong Li; Weiqing Han, John L. Wilkin, Weifeng G. Zhang, Hernan Arango, Javier Zavala‐Garay, Julia Levin, Frederic S. Castruccio
      Pages: n/a - n/a
      Abstract: The summertime eastward jet (SEJ) located around 12°N, 110°‐113°E, as the offshore extension of the Vietnam coastal current, is an important feature of the South China Sea (SCS) surface circulation in boreal summer. Analysis of satellite‐derived sea level and sea surface wind data during 1992‐2012 reveals pronounced interannual variations in its surface strength (SSEJ) and latitudinal position (YSEJ). In most of these years, the JAS (July, August, and September)‐mean SSEJ fluctuates between 0.17‐0.55 m s‐1, while YSEJ shifts between 10.7°‐14.3°N. These variations of the SEJ are predominantly contributed from the geostrophic current component that is linked to a meridional dipole pattern of sea level variations. This sea level dipole pattern is primarily induced by local wind changes within the SCS associated with the El Niño‐Southern Oscillation (ENSO). Enhanced (weakened) southwest monsoon at the developing (decaying) stage of an El Niño event causes a stronger (weaker) SEJ located south (north) of its mean position. Remote wind forcing from the tropical Pacific can also affect the sea level in the SCS via energy transmission through the Philippine archipelago, but its effect on the SEJ is small. The impact of the oceanic internal variability, such as eddy‐current interaction, is assessed using an ocean general circulation model (OGCM). Such impact can lead to considerable year‐to‐year changes of sea level and the SEJ, equivalent to ˜20% of the observed variation. This implies the complexity and prediction difficulty of the upper‐ocean circulation in this region.
      PubDate: 2014-10-06T22:48:02.393418-05:
      DOI: 10.1002/2014JC010206
       
  • Spectral form and source term balance of short gravity wind waves
    • Authors: Hitoshi Tamura; William M. Drennan, Erik Sahlée, Hans C. Graber
      Pages: n/a - n/a
      Abstract: We investigated the spectral structure and source term balance of short gravity waves, based on in situ observations of wavenumber spectra retrieved by air‐sea interaction spar (ASIS) buoys. The behaviors of wavenumber spectra up to 10 rad/m (the gravity wave regime) were analyzed for a wide range of wind and wave conditions. The observed wavenumber spectra showed the spectral power laws described by Toba [1973] and Phillips [1958] in addition to the characteristic nodal point at ˜10 rad/m where spectral energy becomes constant over the entire wind speed range. We also improved the third‐generation wave model using the nonlinear dissipation term. The wave model reproduced the spectral form in the higher wavenumber domain. In the equilibrium range, nonlinear transfer played a major role in maintaining equilibrium conditions. On the other hand, in the saturation range, which starts at the upper limit of the equilibrium range, the nonlinear transfer tended to be out of balance with other source terms, and the dissipation term was in balance with wind input.
      PubDate: 2014-10-06T22:39:48.04115-05:0
      DOI: 10.1002/2014JC009869
       
  • Mixed layer heat and salinity budgets during the onset of the 2011
           Atlantic cold tongue
    • Authors: Michael Schlundt; Peter Brandt, Marcus Dengler, Rebecca Hummels, Tim Fischer, Karl Bumke, Gerd Krahmann, Johannes Karstensen
      Pages: n/a - n/a
      Abstract: The mixed layer (ML) temperature and salinity changes in the central tropical Atlantic have been studied by a dedicated experiment (Cold Tongue Experiment (CTE)) carried out from May‐July 2011. The CTE was based on two successive research cruises, a glider swarm, and moored observations. The acquired in‐situ datasets together with satellite, reanalysis, and assimilation model data were used to evaluate box‐averaged ML heat and salinity budgets for two sub‐regions: 1) the western equatorial Atlantic Cold Tongue (ACT) (23°‐10°W) and 2) the region north of the ACT. The strong ML heat loss in the ACT region during the CTE was found to be the result of the balance of warming due to net surface heat flux and cooling due to zonal advection and diapycnal mixing. The northern region was characterized by weak cooling and the dominant balance of net surface heat flux and zonal advection. A strong salinity increase occurred at the equator, 10°W, just before the CTE. During the CTE, ML salinity in the ACT region slightly increased. Largest contributions to the ML salinity budget were zonal advection and the net surface freshwater flux. While essential for the ML heat budget in the ACT region, diapycnal mixing played only a minor role for the ML salinity budget. In the region north of the ACT, the ML freshened at the beginning of the CTE due to precipitation, followed by a weak salinity increase. Zonal advection changed sign contributing to ML freshening at the beginning of the CTE and salinity increase afterward.
      PubDate: 2014-10-06T03:49:07.7077-05:00
      DOI: 10.1002/2014JC010021
       
  • New total electron content retrieval improves SMOS sea surface salinity
    • Authors: Jean Luc Vergely; Philippe Waldteufel, Jacqueline Boutin, Xiaobin Yin, Paul Spurgeon, Steven Delwart
      Pages: n/a - n/a
      Abstract: The European Space Agency (ESA)‐led SMOS (Soil Moisture and Ocean Salinity) mission aims at monitoring both soil moisture (SM) and ocean surface salinity (OS) on a global scale. The SMOS instrument is a microwave interferometric radiometer which provides visibilities, from which brightness temperatures (TB) maps are reconstructed in the spacecraft’ antenna reference frame. In this study, we investigate how to improve the retrieval of salinity thanks to a better knowledge of the ionospheric Total Electron Content (TEC). We show how both the SMOS bias correction (the so‐called Ocean Target Transformation, OTT) and the half orbit TEC profile can be obtained from SMOS third Stokes parameter A3 using a location on the SMOS field of view (FOV) where the sensitivity of TB to TEC is highest. The resulting TEC global maps compare favorably with those built from the International Global navigation satellite system Service observations. TEC values obtained from A3 are next used to optimize the OTT estimation for every polarization, and proved to provide more stable values. Finally, improvements achieved in the salinity retrieved from SMOS data are reported.
      PubDate: 2014-10-06T03:45:54.561367-05:
      DOI: 10.1002/2014JC010150
       
  • Remote sensing of suspended particulate matter in turbid
           oyster‐farming ecosystems
    • Authors: Pierre Gernez; Laurent Barillé, Astrid Lerouxel, Constant Mazeran, Axel Lucas, David Doxaran
      Pages: n/a - n/a
      Abstract: High resolution satellite data of the Medium Resolution Imaging Spectrometer in full resolution mode (MERIS FR, pixel size is 300 m) were used to study the impact of suspended particulate matter (SPM) on oyster‐farming sites in a macrotidal bay of the French Atlantic coast where SPM concentration can exceed 100 g m‐3. Because MERIS standard SPM concentration retrieval saturates at about 50 g m‐3, we developed an alternative method for turbid nearshore waters. The method consists in the combination of the Semi‐Analytical Atmospheric and Bio‐Optical (SAABIO) atmospheric correction with a regional bio‐optical algorithm based on a linear relationship between SPM concentration and the reflectance band ratio at 865 and 560 nm. MERIS FR derived SPM concentrations were validated from 10 up to 300 g m‐3, and then merged with oyster ecophysiological responses to provide a spatial picture of the impact of SPM concentration on oyster‐farming sites. Our approach demonstrates the potential of high resolution satellite remote‐sensing for aquaculture management and shellfish‐farming ecosystems studies.
      PubDate: 2014-10-06T03:42:37.858664-05:
      DOI: 10.1002/2014JC010055
       
  • Structure of the turbidity field in the Guadalquivir estuary: Analysis of
           observations and a box model approach
    • Authors: M. Díez‐Minguito; A. Baquerizo, H.E. de Swart, M. A.Losada
      Pages: n/a - n/a
      Abstract: A study is presented on the transport of Suspended Particulate Matter (SPM) in the Guadalquivir estuary during low river flow conditions. Observations show that tidally‐induced SPM exceeds that associated with catchment‐derived inputs. The main mechanisms that contribute to longitudinal transport are identified and quantified by analyzing the tidally‐averaged and depth‐integrated SPM flux decomposition over time and space. The net transport is generally directed upstream, although differences in the direction between spring and neap tides are identified. The transport is largely controlled by the mean advection, the tidal pumping associated with the covariance between SPM concentration and current, and the tidal Stokes transport. The convergence of the transport associated to these mechanisms alone explains the presence of primary and secondary estuarine turbidity maxima. The tidal reflection at the upstream dam appears to play a significant role in their generation, as evidenced by the convergence zones of the M4 and M2 induced tidal pumping transports. The spatial structure of the transport motivates the development of a box model that describes the concentration of SPM and its exchange between different stretches along the estuary at subtidal time scales. The model is fed by the net SPM transport obtained from observations. Analysis of the morphodynamical state of the estuary using the box model indicates that erosion is dominant in the stretches close to the estuary mouth and that this sediment is transported upstream and deposited in the middle part of the estuary. This process is more influential during spring tides than during neap tides.
      PubDate: 2014-10-06T03:42:31.063957-05:
      DOI: 10.1002/2014JC010210
       
  • Estimates of horizontal fluxes of oxygen, heat, and salt in western Long
           Island Sound
    • Authors: Grant McCardell; James O'Donnell
      Pages: n/a - n/a
      Abstract: The dissolved oxygen (DO) concentration in the bottom waters of western Long Island Sound decreases to hypoxic levels between April and July. Since the rate of decline of DO is considerably less than measured respiration, there must be significant vertical transport of DO from oxygen richer waters near the surface and/or horizontal transport from the central Sound. Simple model budgets with either of these sources are able to provide predictions of the seasonal rate of decline that are consistent with the observed values. Although prior budget estimates indicated that vertical fluxes were a significant portion of the resupply of DO, these were not able to discount the possible importance of horizontal fluxes, nor have there been any measurements of horizontal fluxes in this region. We present an analysis of time‐series of moored conductivity, temperature, DO, and current observations in the hypoxic area of Long Island Sound during the summers of 2005 and 2006. We estimate the near bottom along‐channel flux divergences of salt, heat, and DO as 0.11±0.08 g kg−1 day−1, −5±6 W m−3 and 4±6 μM day−1, respectively. Since this horizontal DO transport is only 25% of the magnitude of the mean rate of respiration, we conclude that vertical transport by mixing forms the bulk of the physical resupply of DO to the hypoxic zone of the western Sound.
      PubDate: 2014-09-30T00:10:41.213788-05:
      DOI: 10.1002/2014JC009904
       
  • Variability in categories of Arctic sea ice in Fram Strait
    • Authors: E. Hansen; O‐C. Ekeberg, S. Gerland, O. Pavlova, G. Spreen, M. Tschudi
      Pages: n/a - n/a
      Abstract: An attempt to quantify the temporal variability in the volume composition of Arctic sea ice is presented. Categories of sea ice in the Transpolar Drift in Fram Strait are derived from monthly ice thickness distributions obtained by moored sonars (1990‐2011). The inflection points on each side of the old ice modal peak are used to separate modal ice from ice which is thinner and thicker than ice in the modal range. The volume composition is then quantified through the relative amount of ice belonging to each of the three categories thin, modal and thick ice in the monthly ice thickness distributions. The trend of thin ice was estimated to be negative at ‐9.2% per decade (relative to the long‐term mean), which was compensated for by increasing trends in modal and thick ice of 8.1% and 4.9% per decade, respectively. A 7‐8 year cycle is apparent in the thin and thick ice records, which may explain a loss of deformed ice since 2007. We also quantify how the categories contribute to the mean ice thickness over time. Thick (predominantly deformed) ice dominates the mean ice thickness, constituting on average 66% of the total mean. Following the loss of deformed ice since 2007, the contribution of thick ice to the mean decreased from 75% to 52% at the end of the record. Thin deformed ice did not contribute to this reduction; it was pressure ridges thicker than 5 m that were lost and hence caused the decrease in mean ice thickness.
      PubDate: 2014-09-30T00:09:23.481767-05:
      DOI: 10.1002/2014JC010048
       
  • An integrated database of ocean temperature and salinity observations
    • Authors: Christopher P. Atkinson; Nick A. Rayner, John J. Kennedy, Simon A. Good
      Pages: n/a - n/a
      Abstract: Observations made by surface‐based instruments and sub‐surface profiling instruments have, up to now, largely been treated separately, motivated by a focus on different aspects of the climate system. However, activities such as coupled climate reanalyses, long‐term forecasting, satellite validation and climate monitoring increasingly want observations from both sets of instruments. To address this we create an “Integrated” Ocean Database of global in situ temperature and salinity observations covering 1900‐2010, which we name HadIOD. The database merges data taken from the latest versions of the International Comprehensive Ocean‐Atmosphere Data Set (surface observations) and the Met Office Hadley Centre EN dataset (sub‐surface observations). Duplicates introduced by this process are flagged. In addition to the measurements and their basic metadata, each observation in the database is allocated a unique identifier, quality flags and, where possible, bias corrections and uncertainty estimates. A short investigation is presented demonstrating the use, and value, of some of the bias corrections and uncertainties in the database. Whilst this paper describes our initial attempt at building HadIOD, there is much that could be done to build on the foundations presented here. Some ideas for future development are discussed.
      PubDate: 2014-09-25T10:10:42.097246-05:
      DOI: 10.1002/2014JC010053
       
  • Ocean dynamics and tropical pacific climate change in ocean reanalyzes and
           coupled climate models
    • Authors: Chunxue Yang; Benjamin S. Giese, Lixin Wu
      Pages: n/a - n/a
      Abstract: The role of ocean dynamics in tropical Pacific climate change is studied using an ensemble run of Simple Ocean Data Assimilation – sparse input version 1 (SODA si.1) and the Coupled Model Intercomparison Project Phase 5 (CMIP5) historical runs. An eight‐member ensemble of ocean reanalyses (SODAsi.1) from 1871 to 2008 is produced by using forcing from eight ensemble members of an atmospheric reanalysis. The long‐term trends of tropical Pacific surface temperature, wind stress, subsurface temperature and strength of the sub‐tropical cells (STCs) are analyzed. The ensemble reanalysis shows that there is a slight cooling trend of surface and subsurface temperature in the central tropical Pacific due to enhanced tropical Pacific circulation. The STCs, which consist of equatorial upwelling, Ekman transport, extra‐tropical subduction and pycnocline transport from the sub‐tropical to the tropical region, strengthen from 1900 to 2008. When the STCs are accelerated, equatorial upwelling increases bringing cold water from the subsurface that cools the surface. An increasing trend in convergence transport is mainly from the Southern Hemisphere. In contrast with the reanalysis most of the CMIP5 models have warming trends at the surface and the transport of the STCs has a decreasing trend. The CMIP5 models also underestimate tropical Pacific Ocean circulation relative to the reanalysis that is mostly due to differences in wind forcing.
      PubDate: 2014-09-25T10:10:40.475108-05:
      DOI: 10.1002/2014JC009979
       
  • Detection time for global and regional sea level trends and accelerations
    • Authors: G. Jordà
      Pages: n/a - n/a
      Abstract: Many studies analyse trends on sea level data with the underlying purpose of finding indications of a long‐term change that could be interpreted as the signature of anthropogenic climate change. The identification of a long‐term trend is a signal‐to‐noise problem where the natural variability (the ‘noise’) can mask the long‐term trend (the ‘signal’). The signal‐to‐noise ratio depends on the magnitude of the long‐term trend, on the magnitude of the natural variability and on the length of the record, as the climate noise is larger when averaged over short timescales and becomes smaller over longer averaging periods. In this paper we evaluate the time required to detect centennial sea level linear trends and accelerations at global and regional scales. Using model results and tide gauge observations we find that the averaged detection time for a centennial linear trend is 87.9, 76.0, 59.3, 40.3 and 25.2 years for trends of 0.5, 1.0, 2.0, 5.0 and 10.0 mm/yr, respectively. However, in regions with large decadal variations like the Gulf Stream or the Circumpolar current these values can increase up to a 50%. The spatial pattern of the detection time for sea level accelerations is almost identical. The main difference is that the length of the records has to be about 40‐60 years longer to detect an acceleration than to detect a linear trend leading to an equivalent change after 100 years. Finally we have used a new sea level reconstruction which provides a more accurate representation of interannual variability for the last century in order to estimate the detection time for global mean sea level trends and accelerations. Our results suggest that the signature of natural variability in a 30 year global mean sea level record would be less than 1 mm/yr. Therefore, at least 2.2 mm/yr of the recent sea level trend estimated by altimetry cannot be attributed to natural multidecadal variability.
      PubDate: 2014-09-25T10:10:10.880156-05:
      DOI: 10.1002/2014JC010005
       
  • Subtidal variability in water levels inside a subtropical estuary
    • Authors: Krista Henrie; Arnoldo Valle‐Levinson
      Pages: n/a - n/a
      Abstract: Year‐long time series of water level are analyzed at 5 locations along the St. Johns River Estuary, Florida, to investigate propagation of subtidal pulses. Hilbert‐transformed Empirical Orthogonal Functions (HEOFs) are obtained after a dominant seasonal signal is extracted from the data. These functions provide information on spatial structure and propagation phase of subtidal water level pulses. The first HEOF mode explains 96% of the subtidal variability and features an unusual spatial structure: amplitude attenuation (averaging 1 mm/km) to 55 km upstream, slight amplification (0.16 mm/km) over the middle 70 km, and attenuation (2.3 mm/km) over the final 18 km of the estuary. The phase suggests a shift from progressive to quasi‐standing wave behavior at 55 km from the estuary mouth. Additionally, local minima in the phase suggest two sources of subtidal forcing: the coastal ocean and the upstream end. An analytical model describing the evolution of long waves through a channel with frictional damping is fit to the amplitude of HEOF mode 1. Solutions are obtained as a function of two parameters: the non‐dimensional length of the basin, κ, and the non‐dimensional frictional depth, δ. Values of κ between 0.55 and 0.67 and δ between 1.45 and 1.7 provide the best fit with the HEOF results (1% error or less). These values indicate a highly frictional environment in which the average subtidal wavelength is 10 times the basin length. Subtidal pulses in this estuary, therefore, behave as damped waves that can be represented with idealized models.
      PubDate: 2014-09-22T03:55:53.884782-05:
      DOI: 10.1002/2014JC009829
       
  • Comparison of Ellison and Thorpe scales from Eulerian ocean temperature
           observations
    • Authors: Andrea A. Cimatoribus; Hans van Haren, Louis Gostiaux
      Pages: n/a - n/a
      Abstract: Ocean turbulence dissipation rate is estimated either by means of microstructure shear measurements, or by adiabatically reordering vertical profiles of density. The latter technique leads to the estimate of the Thorpe scale, which in turn can be used to obtain average turbulence dissipation rate by comparing the Thorpe scale to the Ozmidov scale. In both cases, the turbulence dissipation rate can be estimated using single vertical profiles from shipborne instrumentation. We present here an alternative method to estimate the length scale of overturns by using the Ellison length scale. The Ellison scale is estimated from temperature variance just beyond the internal wave band, measured by moored instruments. We apply the method to high resolution temperature data from two moorings deployed at different locations around the Josephine seamount (North Eastern Atlantic Ocean), in a region of bottom‐intensified turbulence. The variance of the temperature time series just above the internal wave frequency band is well correlated with the Thorpe scale. The method is based on the time‐frequency decomposition of variance called “maximum overlap discrete wavelet transform”. The results show that the Ellison length scale can be a viable alternative to the Thorpe scale for indirectly estimating turbulence dissipation rate from moored instruments in the ocean if time resolution is sufficiently high. We suggest that fine structure contaminated temperature measurements can provide reliable information on turbulence intensity.
      PubDate: 2014-09-22T02:51:49.371644-05:
      DOI: 10.1002/2014JC010132
       
  • A weather‐type statistical downscaling framework for ocean wave
           climate
    • Authors: Paula Camus; Melisa Menéndez, Fernando J. Méndez, Cristina Izaguirre, Antonio Espejo, Verónica Cánovas, Jorge Pérez, Ana Rueda, Inigo J. Losada, Raúl Medina
      Pages: n/a - n/a
      Abstract: Wave climate characterization at different time scales (long‐term historical periods, seasonal prediction, future projections) is required for a broad number of marine activities. Wave reanalysis databases have become a valuable source of information covering time periods of decades. A weather‐type approach is proposed to statistically downscale multivariate wave climate over different time scales from the reanalysis long‐term period. The model calibration is performed using historical data of predictor (sea level pressure) and predictand (sea state parameters) from reanalysis databases. The storm activity responsible for the predominant swell composition of the local wave climate is included in the predictor definition. N‐days sea level pressure fields are used as predictor. K‐means algorithm with a post‐organization in a bidimensional lattice is used to obtain weather patterns. Multivariate hourly sea states are associated with each pattern. The model is applied at two locations on the east coast of the North Atlantic Ocean. The validation proves the model skill to reproduce the seasonal and interannual variability of monthly sea state parameters. Moreover, the projection of wave climate onto weather types provides a multivariate wave climate characterization with a physically interpretable linkage with atmospheric forcings. The statistical model is applied to reconstruct wave climate in the last twentieth century, to hindcast the last winter and to project wave climate under climate change scenarios. The statistical approach has been demonstrated to be a useful tool to analyze wave climate at different time scales.
      PubDate: 2014-09-22T02:47:45.571859-05:
      DOI: 10.1002/2014JC010141
       
  • Density stratification influences on generation of different modes
           internal solitary waves
    • Authors: Zhi‐Wu Chen; Jieshuo Xie, Dongxiao Wang, Jie‐Min Zhan, Jiexin Xu, Shuqun Cai
      Pages: n/a - n/a
      Abstract: An ideal tide‐topography interaction model is utilized for studying the influence of density stratification (pycnocline depth d, thickness δ, and the density difference Δρa across the pycnocline) on nonlinear disintegration of the first (mode‐1) and second (mode‐2) baroclinic mode internal tides into internal solitary waves (ISWs). The solution methods include weakly nonlinear analysis and fully nonlinear simulation. It is found that as d increases, even though the energy flux into mode‐1 internal tides is always larger than that into mode‐2 ones at generation, mode‐2 ISWs emerge and mode‐1 ISWs are suppressed. As δ increases, the total energy conversion and the fluxes into both mode‐1 and mode‐2 tides all increase first and then decrease. During propagation, a thick pycnocline is actually not favorable for the emergence of mode‐2 ISWs, and the simulated well‐developed mode‐2 ISWs for a pycnocline of intermediate thickness are due to the tide generation process. As Δρa increases, the total conversion and the fluxes into both mode‐1 and mode‐2 tides all increase almost linearly. Even though the flux into mode‐1 tides is always larger than that into mode‐2 ones at generation, mode‐1 tides cannot disintegrate but mode‐2 ISWs develop very well. During propagation, Δρa has no influence on the generation of ISWs. The present work systematically investigates the influence of density stratification on formation of ISWs by considering both internal tide generation and propagation processes.
      PubDate: 2014-09-22T02:47:16.97822-05:0
      DOI: 10.1002/2014JC010069
       
  • Potential drivers of sinking particle's size spectra and vertical flux of
           particulate organic carbon (POC): Turbulence, phytoplankton, and
           zooplankton
    • Authors: Ingrid Wiedmann; Marit Reigstad, Arild Sundfjord, Sünnje Basedow
      Pages: n/a - n/a
      Abstract: Phytoplankton spring blooms in temperate and high‐latitude shelf seas are commonly associated with an enhanced particulate organic carbon (POC) export of aggregates from the euphotic zone. In contrast, a post‐bloom situation is usually linked to a predominant POC retention, where small cells (
      PubDate: 2014-09-22T02:43:46.610116-05:
      DOI: 10.1002/2013JC009754
       
  • Confidence and sensitivity study of the OAFlux multisensor synthesis of
           the global ocean‐surface vector wind from 1987 onward
    • Authors: Lisan Yu; Xiangze Jin
      Pages: n/a - n/a
      Abstract: This study presents an uncertainty assessment of the high‐resolution global analysis of daily‐mean ocean‐surface vector winds (1987 onward) by the Objectively Analyzed air‐sea Fluxes (OAFlux) project. The time series was synthesized from multiple satellite sensors using a variational approach to find a best fit to input data in a weighted least‐squares cost function. This framework requires the a priori specification of the weights, or equivalently, the error covariances of input data, which are seldom known. Two issues are addressed. The first issue is the selection of the optimal weights used for the OAFlux synthesis. A set of weight‐varying experiments was conducted, from which the weights were selected by satisfying the condition that the chosen weights should make the best‐fit of the cost function be optimal with regard to both input satellite observations and the air‐sea buoy measurements at 126 locations. The buoy measurements were not part of the synthesis and served as an independent measure in the selection. The second issue is the quantification of the effect of the uncertainty in the resultant weight assignments on the synthesis. This was achieved by computing the ensemble statistics of weight perturbation experiments. The results show that high winds (>15 ms‐1) and rain conditions are the leading sources of uncertainty for the OAFlux vector wind analysis. High winds correlated with rain remain a major technical challenge for proper wind retrievals from satellites. Further improvement of the multi‐sensor synthesis in events of severe storms will rely on the future technical advancement in retrieval algorithms.
      PubDate: 2014-09-19T21:47:39.36176-05:0
      DOI: 10.1002/2014JC010194
       
  • Climatological monthly heat and freshwater flux estimates on a global
           scale from Argo
    • Authors: Donata Giglio; Dean Roemmich
      Pages: n/a - n/a
      Abstract: The global pattern of climatological monthly heat and freshwater fluxes at the ocean surface is estimated using Argo temperature and salinity profile data for the period 2004 to 2013. Temperature or salinity changes are calculated in a volume of water above an isopycnal that is below the mixed layer and not subject to mixed‐layer entrainment. Horizontal advection components from geostrophic velocity and from Ekman transport, based on wind stress, are also included. The climatological monthly heat or freshwater flux at the ocean surface is estimated as the sum of advective and time tendency contributions. The air‐sea flux estimates from Argo are described in global maps and basin‐wide integrals, in comparison to atmospheric reanalysis data and to air‐sea flux products based on observations. This ocean‐based estimate of surface fluxes is consistent with property variations in the subsurface ocean and indicates greater amplitude for the climatological monthly heat flux values in the subtropics compared to other products. Similarly, the combination of Argo freshwater flux and reanalysis evaporation, suggests greater amplitude for climatological monthly precipitation in the tropics.
      PubDate: 2014-09-19T05:12:45.396286-05:
      DOI: 10.1002/2014JC010083
       
  • Dust‐induced episodic phytoplankton blooms in the Arabian Sea during
           winter monsoon
    • Authors: Priyanka Banerjee; S. Prasanna Kumar
      Pages: n/a - n/a
      Abstract: Phytoplankton blooms mediated by the oceanic supply of nutrients is a well understood phenomenon in the Arabian Sea (AS), while the role of dust deposition in enhancing phytoplankton is less explored. In this paper we show that during winter monsoon the central Arabian Sea (CAS), away from the realm of active winter convection, supports episodic phytoplankton blooms. These blooms cannot be fully explained by the oceanic input of nutrients through processes such as advection and mixing in the upper ocean. Using satellite images we tracked about 45 dust storms over the AS during the winter monsoons of 2002‐2003 to 2010‐2011 of which only 8 were followed by chlorophyll enhancements. We used a regional climate model to get possible fluxes of dust and the amount of nutrients (nitrate, phosphate and iron) that can be derived from the dust depositions. Additionally, we used published in situ nutrients data in conjunction with carbon: nitrogen: phosphorus and iron: carbon molar ratios to compute the potential requirements of different nutrients for the 8 cases of chlorophyll enhancements. It is likely that the deepening of the mixed layer can incorporate nitrate and phosphate, but not enough iron from the subsurface waters leading to potential iron limitation. Although, all the phytoplankton blooms within CAS were observed following episodic dust events, only four blooms can be attributed to dust depositions. Our work shows that phytoplankton blooms fuelled by episodic dust storms are important in driving the inter‐annual variability in chlorophyll in a region away from active winter convection.
      PubDate: 2014-09-19T05:09:22.092955-05:
      DOI: 10.1002/2014JC010304
       
  • Mean sea level variability in the North Sea: Processes and implications
    • Authors: Sönke Dangendorf; Francisco M. Calafat, Arne Arns, Thomas Wahl, Ivan D. Haigh, Jürgen Jensen
      Pages: n/a - n/a
      Abstract: Mean sea level (MSL) variations across a range of timescales are examined for the North Sea under the consideration of different forcing factors since the late 19th century. We use multiple linear regression models, which are validated for the second half of the 20th century against the output of a tide+surge model, to determine the barotropic response of the ocean to fluctuations in atmospheric forcing. We find that local atmospheric forcing mainly initiates MSL variability on timescales up to a few years, with the inverted barometric effect dominating the variability along the UK and Norwegian coastlines and wind controlling the MSL variability in the south from Belgium up to Denmark. On decadal timescales, MSL variability mainly reflects steric changes, which are largely forced remotely. A spatial correlation analysis of altimetry observations and gridded steric heights suggests evidence for a coherent signal extending from the Norwegian shelf down to the Canary Islands. This fits with the theory of longshore wind forcing along the eastern boundary of the North Atlantic causing coastally trapped waves to propagate over thousands of kilometers along the continental slope. Implications of these findings are assessed with statistical Monte‐Carlo experiments. It is demonstrated that the removal of known variability increases the signal to noise ratio with the result that: (i) linear trends can be estimated more accurately; and (ii) possible accelerations (as expected e.g. due to anthropogenic climate change) can be detected much earlier. Such information is of crucial importance for anticipatory coastal management, engineering and planning.
      PubDate: 2014-09-19T05:08:15.632585-05:
      DOI: 10.1002/2014JC009901
       
  • Coastally trapped eddies in the north of the Gulf of Guinea
    • Authors: Sandrine Djakouré; Pierrick Penven, Bernard Bourlès, Jennifer Veitch, Vamara Koné
      Pages: n/a - n/a
      Abstract: Cyclonic eddies generated downstream of Cape Palmas and Cape Three points have been suggested to contribute to the coastal upwelling along the northern coast of the Gulf of Guinea. A numerical analysis using a high resolution model is used to investigate the mesoscale activity and the coastal upwelling generation processes. An eddy detection and tracking tool is applied to altimeter and model data, showing good agreement between these data sets. About 2 cyclonic eddies per year with an average radius of 60 km were identified downstream of both capes. These cyclonic eddies have an average lifetime of about 60 days during the major coastal upwelling period (boreal summer) and an eastward propagation. These cyclonic eddies are shallow, energetic (their relative vorticity can reach three times the earth's rotation) and dimensionless parameters show that they are in an eddy shedding regime. Mean flow interactions and barotropic instabilities associated with capes are their main generation processes. An idealized experiment is conducted in order to analyse the effect of capes on eddy generation and on coastal upwelling. It reveals that these cyclonic eddies generated downstream of capes are not the process responsible for this coastal upwelling. This experiment also suggests that the cyclonic eddies are the cause of the westward and coastal Guinea Counter Current that is associated with a transfer of energy from eddy kinetic to the mean flow.
      PubDate: 2014-09-19T05:04:25.010994-05:
      DOI: 10.1002/2014JC010243
       
  • A first estimation of SMOS‐based ocean surface T‐S diagrams
    • Authors: Roberto Sabia; Marlene Klockmann, Diego Fernández‐Prieto, Craig Donlon
      Pages: n/a - n/a
      Abstract: A first estimation of satellite‐based ocean surface T‐S diagrams is performed by using SMOS Sea Surface Salinity (SSS) and OSTIA Sea Surface Temperature (SST) and comparing them with in‐situ measurements interpolated fields obtained by the Argo‐buoys for the North Atlantic and over the entire year 2011. The key objectives at the base of this study are: 1) To demonstrate the feasibility of generating routinely satellite‐derived surface T‐S diagrams, obviating the lack of extensive sampling of the surface open ocean; 2) To display the T‐S diagrams variability and the distribution/dynamics of SSS, altogether with SST and the relative density with respect to in‐situ measurements, and 3) To assess the SMOS SSS data added value in detecting geophysical signals not sensed/resolved by the Argo measurements. To perform the latter analysis, the satellite‐Argo mismatches have been overlapped with geophysical parameters of precipitation rates, surface heat and freshwater fluxes and wind speed data. Ongoing and future efforts focus on enlarging the study area and the temporal frame of the analysis and aim at developing a method for the systematic identification of surface water masses formation areas by remotely‐sensed data.
      PubDate: 2014-09-19T04:59:30.519576-05:
      DOI: 10.1002/2014JC010120
       
  • Assimilating SMOS sea ice thickness into a coupled ice‐ocean model,
           using a local SEIK filter
    • Authors: Qinghua Yang; Svetlana N. Losa, Martin Losch, Xiangshan Tian‐Kunze, Lars Nerger, Jiping Liu, Lars Kaleschke, Zhanhai Zhang
      Pages: n/a - n/a
      Abstract: The impact of assimilating sea ice thickness data derived from ESA's Soil Moisture and Ocean Salinity (SMOS) satellite together with Special Sensor Microwave Imager/Sounder (SSMIS) sea ice concentration data of the National Snow and Ice Data Center (NSIDC) in a coupled sea ice‐ocean model is examined. A period of three months from November 1st, 2011 to January 31st, 2012 is selected to assess the forecast skill of the assimilation system. 24h‐forecasts and longer forecasts are based on the Massachusetts Institute of Technology general circulation model (MITgcm), and the assimilation is performed by a localized Singular Evolutive Interpolated Kalman (LSEIK) filter. For comparison, the assimilation is repeated only with the SSMIS sea ice concentrations. By running two different assimilation experiments, and comparing with the unassimilated model, independent satellite derived data, and in‐situ observation, it is shown that the SMOS ice thickness assimilation leads to improved thickness forecasts. With SMOS thickness data, the sea ice concentration forecasts also agree better with observations, although this improvement is smaller.
      PubDate: 2014-09-19T04:52:04.49611-05:0
      DOI: 10.1002/2014JC009963
       
  • Characteristics of surface signatures of Mediterranean water eddies
    • Authors: Bashmachnikov I; Carton X, Belonenko T.V.
      Pages: n/a - n/a
      Abstract: In this work we obtain new results on the manifestation of meddies (or of other deep eddies) at the sea‐surface, further developing the results by Bashmachnikov and Carton [2012]. The quasi‐geostrophic equations are used to describe a near‐axisymmetric vortex in the upper ocean, forced at its lower boundary by the isopycnal elevation of a moving meddy. The solution thus obtained provides a better approximation of the characteristics of meddy surface signals. The results show that in subtropics large meddies with dynamic radius Rm ≥ 30 km are always seen at the sea‐surface with AVISO altimetry, that medium‐size meddies with Rm = 20 km may be seen at the sea‐surface only if they are sufficiently shallow and strong, while small meddies with Rm = 10 km generally cannot be detected with the present accuracy of altimetry data. The intensity of meddy surface signals decreases to the south with the decrease of the f/N ratio. The seasonal variation in intensity of the surface signal for northern meddies (45° N) is on the order of 2‐3 cm, but for subtropical meddies (35° N) it can be on the order of 5‐10 cm. The radii of meddy surface signals range from 1 to 2 times the radii of the corresponding meddies. For most of the observed meddies the upper limit should be used. Numerical experiments show that surface signals of meddies translated with β‐ drift are efficiently dispersed by the radiation of Rossby waves. At the same time, for meddies translated by a background current, the surface signal does not show strong dissipation.
      PubDate: 2014-09-19T04:45:27.208541-05:
      DOI: 10.1002/2014JC010244
       
  • Influence of underwater barriers on the distribution of tsunami waves
    • Authors: V. Chugunov; S. Fomin, R. Shankar
      Pages: n/a - n/a
      Abstract: Solitary wave propagation over underwater shelves and bumps is examined using straightforward analytical methods. Explicit solutions for wave propagation are obtained. Using the nonlinear shallow‐water equations, it was found that propagation of small amplitude long waves can be well described by a linear approximation. The effects of topographical variety and proportion of underwater barriers (steps, bumps, multiple bumps) on the incident wave are demonstrated using linear wave theory. At a step, the incident wave is shown to be more strongly reflected for increased barrier size. The incident wave also transmits an amplified wave with smaller wavelength onto the obstacle. After propagating off of a bump, the wave experiences an amplitude decay. The decay rate is shown to be exponential with a variable number of bumps. Accounting for the presence of the small parameter, which represents the wave amplitude/water depth ratio, the non‐linear shallow water equations were solved by the method of asymptotic expansions. Using the method of renormalization, a uniformly valid solution was obtained accounting for nonlinear effects in the vicinity of the sharp depth change. Far‐field comparisons of the constructed solutions with the associated Riemann waves show good accuracy of the obtained solutions. Over an infinitely long shelf, the amplified transmitted wave breaks.
      PubDate: 2014-09-19T04:25:44.371039-05:
      DOI: 10.1002/2014JC010296
       
  • Global and regional sea level change during the 20th century
    • Authors: Manfred Wenzel; Jens Schröter
      Pages: n/a - n/a
      Abstract: Sea level variations prior to the launch of satellite altimeters are estimated by analysing historic tide gauge records. Recently, a number of groups have reconstructed sea level by applying EOF techniques to fill missing observations. We complement this study with alternative methods. In a first step gaps in 178 records of sea level change are filled using the pattern recognition capabilities of artificial neural networks. Afterwards satellite altimetry is used to extrapolate local sea level change to global fields. Patterns of sea level change are compared to prior studies. Global mean sea level change since 1900 is found to be 1.77 ± 0.38 mm year−1 on average. Local trends are essentially positive with the highest values found in the western tropical Pacific and in the Indian Ocean east of Madagascar where it reaches about +6 mm year−1. Regions with negative trends are spotty with a minimum value of about −2 mm year−1 south of the Aleutian Islands. Although the acceleration found for the global mean, +0.0042 ± 0.0092 mm year−2, is not significant, local values range from −0.1 mm year−2 in the central Indian Ocean to +0.1 mm year−2 in the western tropical Pacific and east of Japan. These extrema are associated with patterns of sea level change that differ significantly from the first half of the analyzed period (i.e. 1900 to 1950) to the second half (1950 to 2000). We take this as an indication of long period oceanic processes that are superimposed to the general sea level rise.
      PubDate: 2014-09-19T00:14:31.502269-05:
      DOI: 10.1002/2014JC009900
       
  • Mesoscale eddy variability in the southern extension of the East
           Madagascar Current: Seasonal cycle, energy conversion terms, and eddy mean
           properties
    • Authors: Issufo Halo; Pierrick Penven, Björn Backeberg, Isabelle Ansorge, Frank Shillington, Raymond Roman
      Pages: n/a - n/a
      Abstract: In this study we used more than seventeen years of satellite altimetry observations and output from an ocean model to investigate the mesoscale eddy variability and forcing mechanisms to the south of Madagascar. Analysis of energy conversion terms in the model has shown seasonality on eddy formation, both by barotropic and baroclinic instabilities: maximum in winter (JJA) and minimum in summer (DJF). The eddies were mainly formed in the upper ocean (0 ‐ 300 m) and at intermediate depths (800 ‐ 2000 m) by barotropic and baroclinic instabilities respectively. The former dominated in the southeastern margin of Madagascar, and the latter to the southwest, where the South East Madagascar Current (SEMC) separates from the continental shelf. Seasonality of the eddy formation appeared linked with the seasonal intensification of the SEMC. The energy conversion terms indicated that the eddies have a significant contribution to the large‐scale circulation, but not being persistent throughout the year, occurring mainly during the fall‐season (MAM). Eddy demography from altimetry and model provided information on eddy preferential sites for birth, annual occurrence (6 ‐ 13 per year), eddy mean diameter (124 ‐ 178 km), mean amplitude (9 ‐ 28 cm), life‐time (90 ‐ 183 days) and maximum traveling distances (325 ‐ 1052 km). Eddies formed to the southwest of Madagascar exhibited distinct characteristics from those formed in the southeast. Nevertheless, all eddies were highly nonlinear, suggesting that they are potential vectors of connectivity between Madagascar and Africa. This may have a significant impact on the ecology of this region.
      PubDate: 2014-09-18T23:59:42.138228-05:
      DOI: 10.1002/2014JC009820
       
  • Formation and distribution of sea ice in the Gulf of St. Lawrence: A
           process‐oriented study using a coupled ocean‐ice model
    • Authors: Jorge Urrego‐Blanco; Jinyu Sheng
      Pages: n/a - n/a
      Abstract: A coupled ocean‐ice model for the eastern Canadian shelf is used to examine main physical processes affecting sea ice conditions in the Gulf of St. Lawrence (GSL) and adjacent waters. The coupled model is based on NEMO and uses OPA9 as the ocean circulation component and the 2‐category dynamic‐thermodynamic LIM2 as the ice model. The coupled model is forced by atmospheric reanalysis fields produced by Large and Yeager [2004]. The model results are used to examine the roles of thermodynamics and dynamics on sea ice distributions and patterns of ice production and melting, and the influence of ice capping on the circulation in the study region. Analysis of model results indicates that local production of sea ice is important in shallower areas over the northern and western GSL. Equatorward advection of sea ice from the St. Lawrence Estuary is affected significantly by the Gaspé Current. An index is used to quantify the relative importance of thermodynamic and dynamics of sea ice in the GSL. It is found that both thermodynamics and dynamics are important over most of the GSL, except for waters around Anticosti Island, the southeastern Gulf, and the eastern Scotian Shelf, where dynamics (or sea ice movements) are the most important mechanism for the presence of sea ice. The study also demonstrates that ice capping significantly reduces the strength of the winter circulation in the GSL.
      PubDate: 2014-09-18T07:28:17.329459-05:
      DOI: 10.1002/2014JC010185
       
  • Local feedback mechanisms of the shallow water region around the Maritime
           Continent
    • Authors: Pengfei Xue; Elfatih A. B. Eltahir, Paola Malanotte‐Rizzoli, Jun Wei
      Pages: n/a - n/a
      Abstract: The focus of this study is the local‐scale air‐sea feedback mechanisms over the shallow shelf water region (water depth < 200m) of the Maritime Continent (MC). MC was selected as a pilot study site for its extensive shallow water coverage, geographic complexity and importance in the global climate system. To identify the local‐scale air‐sea feedback processes, we ran numerical experiments with perturbed surface layer water temperature using a coupled ocean‐atmosphere model and an uncoupled ocean model. By examining the responses of the coupled and uncoupled models to the water temperature perturbation, we identify that, at a local‐scale, a negative feedback process through the coupled dynamics that tends to restore the SST from its perturbation could dominate the shallow water region of the MC at a short time scale of several days. The energy budget shows that 38% of initial perturbation‐induced heat energy was adjusted through the air‐sea feedback mechanisms within 2 weeks, of which 58% is directly transferred into the atmosphere by the adjustment of latent heat flux due to the evaporative cooling mechanism. The increased inputs of heat and moisture into the lower atmosphere then modifies its thermal structure and increases the formation of low‐level clouds, which act as a shield preventing incoming solar radiation from reaching the sea surface, accounts for 38% of the total adjustment of surface heat fluxes, serving as the second mechanism for the negative feedback process. The adjustment of sensible heat flux and net long‐wave radiation play a secondary role. The response of the coupled system to the SST perturbation suggests a response time scale of the coupled feedback process of about 3‐5 days. The two‐way air‐sea feedback tightly links the surface heat fluxes, clouds and SST, and can play an important role in regulating the short‐term variability of the SST over the shallow shelf water regions.
      PubDate: 2014-09-18T05:20:59.142648-05:
      DOI: 10.1002/2013JC009700
       
  • Sea surface salinity variability in the East China Sea observed by the
           Aquarius instrument
    • Authors: Seung‐bum Kim; Jae Hak Lee, Paolo de Matthaeis, Simon Yueh, Chang‐Su Hong, Joon‐Ho Lee, Gary Lagerloef
      Pages: n/a - n/a
      Abstract: This study demonstrates that the spaceborne Aquarius instrument is able to monitor the sea surface salinity (SSS) variations in the East China Sea (ECS) with the spatial resolution of about 150 km at 7‐day interval, where routine observations are difficult. The two geophysical contaminants enter the sidelobes of the Aquarius antenna and bias the coastal SSS low: the emission from the land surface and the radiofrequency interference (RFI). Away from about one Aquarius pixel (150 km) from the coastline, the Aquarius SSS is fairly insensitive (less than about 0.2 psu) to the radiometric details of the method to correct for the land emission. The ascending orbits appear to be affected by unfiltered RFI much less than the descending tracks. The Aquarius SSS along the ascending tracks is low over the ECS by 0.40 to 0.93 psu (with respect to the in situ data during the two separate 7‐day periods) and is biased low by 0.41 to 1.07 psu (accuracy, or the time‐mean of difference from the regional model along three Aquarius tracks over a 18‐month period). The presence of the ascending and descending differences in the Aquarius SSS, and the spatially widespread bias suggest that the bias is attributed to the unfiltered RFI originating from strong point sources (rather than to the land contamination from weak distributed sources, or to other seasonally‐varying geophysical contaminants). Despite the bias, the Aquarius data describe well the temporal and spatial variability of the ECS SSS. The temporal trend and magnitude of salinity changes agree remarkably between Aquarius and a regional numerical model, during both the freshwater discharge season from the Yangtze river and the rest of the year. The precision of the Aquarius observation in the ECS is comparable with the Aquarius mission requirement (0.2 psu one‐sigma for a monthly average over the open ocean). The river discharge rate correlates with the Aquarius SSS with the coefficient of 0.71 on a seasonal scale with the discharge leading the SSS changes. The Aquarius SSS increases away from the coast, in response to the river outflow. The interannual changes in the Aquarius SSS capture the effect of the regional drought in summer 2013.
      PubDate: 2014-09-18T05:09:39.316904-05:
      DOI: 10.1002/2014JC009983
       
  • Laboratory study on coprecipitation of phosphate with ikaite in sea ice
    • Authors: Yu‐Bin Hu; Gerhard S. Dieckmann, Dieter A. Wolf‐Gladrow, Gernot Nehrke
      Pages: n/a - n/a
      Abstract: Ikaite (CaCO3·6H2O) has recently been discovered in sea ice, providing first direct evidence of CaCO3 precipitation in sea ice. However, the impact of ikaite precipitation on phosphate (PO4) concentration has not been considered so far. Experiments were set up at pH from 8.5 to 10.0, salinities from 0 to 105, temperatures from −4 to 0°C and PO4 concentrations from 5 to 50 µmol kg−1 in artificial sea ice brine so as to understand how ikaite precipitation affects the PO4 concentration in sea ice under different conditions. Our results show that PO4 is coprecipitated with ikaite under all experimental conditions. The amount of PO4 removed by ikaite precipitation increases with increasing pH. Changes in salinity (S ≥ 35) as well as temperature have little impact on PO4 removal by ikaite precipitation. The initial PO4 concentration affects the PO4 coprecipitation. These findings may shed some light on the observed variability of PO4 concentration in sea ice.
      PubDate: 2014-09-18T05:04:25.347027-05:
      DOI: 10.1002/2014JC010079
       
  • Enhanced sea‐air CO2 exchange influenced by a tropical depression in
           the South China Sea
    • Authors: Qingyang Sun; Danling Tang, Louis Legendre, Ping Shi
      Pages: n/a - n/a
      Abstract: Ship measurements made two days after the passage of a tropical depression (TD) in the South China Sea (SCS, April 2011) showed two contrasted responses of the partial pressure of CO2 at sea surface (pCO2,sw). In low sea‐surface salinity (SSS) waters, pCO2,sw was low (349 ± 7 µatm), and the area was a carbon sink (‐4.7 ± 1.8 mmol CO2 m‐2 d‐1), whereas in water with high SSS and chlorophyll a and low dissolved oxygen and sea surface temperature, pCO2,sw was higher than normal SCS water (376 ± 8 vs. 362 ± 4 µatm) and the area was a carbon source (1.2 ± 3.1 mmol CO2 m‐2 d‐1). Satellite data showed two large areas of low SSS before the TD, which were likely influenced by rainfall, and these areas were considered to have low pCO2,sw because of their low SSS. The high pCO2,sw after the TD is explained by the uplifting to the surface of deeper and CO2‐rich water, due to winds accompanied by the TD. The difference in sea‐air CO2 flux between the TD‐affected area and the lower‐SSS water was (1.99 + 4.70 = 6.7 mmol CO2 m‐2 d‐1), indicating a 100% change caused by the TD compared to the average seasonal value in spring in southern SCS (3.3 ± 0.3 mmol CO2 m‐2 d‐1). Undersaturation of CO2 prior to the TD due to dilution by freshwater and the pre‐existing cold eddy, and slow translation speed of the TD, are considered to be accounted for the CO2 flux change.
      PubDate: 2014-09-18T04:48:52.290777-05:
      DOI: 10.1002/2014JC010131
       
  • Storms modify baroclinic energy fluxes in a seasonally stratified shelf
           sea: Inertial‐tidal interaction
    • Authors: Joanne. E. Hopkins; Gordon R. Stephenson, J. Mattias Green, Mark E. Inall, Matthew R. Palmer
      Pages: n/a - n/a
      Abstract: Observations made near the Celtic Sea shelf edge are used to investigate the interaction between wind generated near‐inertial oscillations and the semi‐diurnal internal tide. Linear, baroclinic energy fluxes within the near‐inertial (f) and semi‐diurnal (M2) wave bands are calculated from measurements of velocity and density structure at two moorings located 40 km from the internal tidal generation zone. Over the two week deployment period the semi‐diurnal tide drove 28‐48 W m‐1 of energy directly on‐shelf. Little spring‐neap variability could be detected. Horizontal near‐inertial energy fluxes were an order of magnitude weaker, but non‐linear interaction between the vertical shear of inertial oscillations and the vertical velocity associated with the semi‐diurnal internal tide led to a 25‐43% increase in positive on‐shelf energy flux. The phase relationship between f and M2 determines whether this non‐linear interaction enhances or dampens the linear tidal component of the flux, and introduces a 2‐day counter clockwise beating to the energy transport. Two very clear contrasting regimes of (a) tidally and (b) inertially driven shear and energy flux are captured in the observations.
      PubDate: 2014-09-18T04:48:50.374667-05:
      DOI: 10.1002/2014JC010011
       
  • A numerical investigation of wave‐breaking‐induced turbulent
           coherent structure under a solitary wave
    • Authors: Zheyu Zhou; Jacob Sangermano, Tian‐Jian Hsu, Francis C. K. Ting
      Pages: n/a - n/a
      Abstract: To better understand the effect of wave‐breaking‐induced turbulence on the bed, we report a 3D Large‐Eddy Simulation (LES) study of a breaking solitary wave in spilling condition. Using a turbulence‐resolving approach, we study the generation and the fate of wave‐breaking‐induced turbulent coherent structures, commonly known as obliquely descending eddies (ODEs). Specifically, we focus on how these eddies may impinge onto bed. The numerical model is implemented using an open‐source CFD library of solvers, called OpenFOAM, where the incompressible 3D filtered Navier‐Stokes equations for the water and the air phases are solved with a finite volume scheme. The evolution of the water‐air interfaces are approximated with a volume of fluid method. Using the dynamic Smagorinsky closure, the numerical model has been validated with wave flume experiments of solitary wave breaking over a 1/50 sloping beach. Simulation results show that during the initial overturning of the breaking wave, 2D horizontal rollers are generated, accelerated and further evolve into a couple of 3D hairpin vortices. Some of these vortices are sufficiently intense to impinge onto the bed. These hairpin vortices possess counter‐rotating and downburst features, which are key characteristics of ODEs observed by earlier laboratory studies using Particle Image Velocimetry. Model results also suggest that those ODEs that impinge onto bed can induce strong near‐bed turbulence and bottom stress. The intensity and locations of these near‐bed turbulent events could not be parameterized by near‐surface (or depth integrated) turbulence unless in very shallow depth.
      PubDate: 2014-09-18T04:47:15.170217-05:
      DOI: 10.1002/2014JC009854
       
  • Energy transfer between wind waves and low‐frequency oscillations on
           a fringing reef, Ipan Guam
    • Authors: Anne‐Christine N. Péquignet; Janet M. Becker, Mark A. Merrifield
      Pages: n/a - n/a
      Abstract: Field observations from a Guam fringing reef are used to examine the cross‐reef energy exchange between high frequency sea and swell (SS) and low frequency infragravity (IG) and far infragravity (fIG) waves. Energetic SS waves (significant wave heights 2‐4 m) break at the outer reef, leading to weak (
      PubDate: 2014-09-15T21:57:36.268634-05:
      DOI: 10.1002/2014JC010179
       
  • Swell dissipation by induced atmospheric shear stress
    • Authors: Y. Perignon; F. Ardhuin, M. Cathelain, M. Robert
      Pages: n/a - n/a
      Abstract: Observations of swell dissipation across oceans reveal a significant loss of energy that can be the result of many of processes. Among these candidate mechanisms, this paper examines the properties of the viscous air‐sea boundary layer driven by swells in order to characterize the induced atmospheric flow regime and its associated viscous dissipation over swells. A series of 3D numerical experiments is carried out with a RANS model and appropriate turbulence closure. These experiments reveal a laminar to turbulent transition in the near free‐surface region for a common range of characteristic amplitudes and periods of swells under stationary conditions. At low Reynolds number, laminar conditions prevail and computed decay rates conform to the analytical formulation μv of the Stokes interfacial boundary layer for this problem. The turbulent regimes are characterized as well and the new decay rates follow a non‐dimensional relation μ=1.42μv(Re⁡1.5×105)0.41 above Re = 1.5 × 105 (e.g. amplitude larger than 1.1m for a 14s monochromatic wave period). Typical decay rates are up to 4 times above the laminar values, which is a factor 10 less than the largest rates estimated for oceanic conditions. A sensitivity analysis is finally conducted to evaluate the influence of the stationary hypothesis. It demonstrates a short setup‐length and low relative variations of the unsteady decay rates for laminar, transitioning and developed turbulent conditions, which confirms the evaluation of steady decay rates.
      PubDate: 2014-09-15T07:11:31.561552-05:
      DOI: 10.1002/2014JC009896
       
  • South Indian Countercurrent and associated fronts
    • Authors: Viviane V. Menezes; Helen E. Phillips, Andreas Schiller, Nathaniel L. Bindoff, Catia M. Domingues, Marcio L. Vianna
      Pages: n/a - n/a
      Abstract: A striking feature of the South Indian Ocean circulation is the presence of the eastward South Indian Countercurrent (SICC) that flows in a direction opposite to that predicted by the classical theories of wind‐driven circulation. Several authors suggest that the SICC resembles the subtropical countercurrents (STCCs) observed in other oceans, which are defined as narrow eastward jets on the equatorward side of subtropical gyres, where the depth‐integrated flow is westward. These jets are associated with subsurface thermal fronts at thermocline depths by the thermal wind relation. However, the subsurface thermal front associated with the SICC has not been described to date. Other studies conjecture an important role for salinity in controlling the SICC. In the present work, we analyse three Argo‐based atlases and data from six hydrographic cruises to investigate whether the SICC is accompanied by permanent thermal and density fronts including salinity effects. The seasonal cycle of these fronts in relation to the SICC strength are also investigated. We find that the SICC is better described as composed of three distinct jets, which we name the northern, central and southern SICC. We find that the southern SICC around 26° S has an associated thermal front at subsurface depths around 100‐200 m with salinity being of secondary importance. The southern branch strength is related to mode waters poleward of the front, similar to a STCC‐like current. However, the SICC multiple jet structure seems to be better described as resulting from PV staircases.
      PubDate: 2014-09-15T05:42:52.254511-05:
      DOI: 10.1002/2014JC010076
       
  • Impact of periodic intermediary flows on submarine melting of a Greenland
           glacier
    • Authors: R. Sciascia; C. Cenedese, D. Nicolì, P. Heimbach, F. Straneo
      Pages: n/a - n/a
      Abstract: The submarine melting of a vertical glacier front, induced by an intermediary circulation forced by periodic density variations at the mouth of a fjord, is investigated using a non–hydrostatic ocean general circulation model and idealized laboratory experiments. The idealized configurations broadly match that of Sermilik Fjord, southeast Greenland, a largely two‐layers system characterized by strong seasonal variability of subglacial discharge. Consistent with observations, the numerical results suggest that the intermediary circulation is an effective mechanism for the advection of shelf anomalies inside the fjord. In the numerical simulations, the advection mechanism is a density intrusion with a velocity which is an order of magnitude larger than the velocities associated with a glacier–driven circulation. In summer, submarine melting is mostly influenced by the discharge of surface runoff at the base of the glacier and the intermediary circulation induces small changes in submarine melting. In winter, on the other hand, submarine melting depends only on the water properties and velocity distribution at the glacier front. Hence, the properties of the waters advected by the intermediary circulation to the glacier front are found to be the primary control of the submarine melting. When the density of the intrusion is intermediate between those found in the fjord's two layers there is a significant reduction in submarine melting. On the other hand, when the density is close to that of the bottom layer, only a slight reduction in submarine melting is observed. The numerical results compare favorably to idealized laboratory experiments with a similar setup.
      PubDate: 2014-09-12T00:01:13.838272-05:
      DOI: 10.1002/2014JC009953
       
  • First “in situ” determination of gas transport coefficients
           (DO2, DAr, and DN2) from bulk gas concentration measurements (O2, N2, Ar)
           in natural sea ice
    • Authors: Odile Crabeck; B Delille, S Rysgaard, D.N. Thomas, N.X. Geilfus, B Else, J.L. Tison
      Pages: n/a - n/a
      Abstract: We report bulk gas concentrations of O2, N2 and Ar, as well as their transport coefficients, in natural landfast subarctic sea ice in southwest Greenland. The observed bulk ice gas composition was 27.5% O2, 71.4% N2 and 1.09% Ar. Most previous studies suggest that convective transport is the main driver of gas displacement in sea ice and have neglected diffusion processes. According to our data, brines were stratified within the ice, so that no convective transport could occur within the brine system. Therefore, diffusive transport was the main driver of gas migration. By analysing the temporal evolution of an internal gas peak within the ice, we deduced the bulk gas transport coefficients for oxygen (DO2), argon (DAr) and nitrogen (DN2). The values fit to the few existing estimates from experimental work, and are close to the diffusivity values in water (10‐5 cm2 s‐1). We suggest that gas bubbles escaping from the brine to the atmosphere ‐ as the ice gets more permeable during melt ‐ could be responsible for the previously reported high transport coefficients. These results underline that when there is no convective transport within the sea ice, the transport of gas by diffusion through the brines, either in the liquid or gaseous phases, is a major factor in controlling the ocean–atmosphere exchange.
      PubDate: 2014-09-10T01:58:08.847943-05:
      DOI: 10.1002/2014JC009849
       
  • Variability of Arctic sea ice topography and its impact on the atmospheric
           surface drag
    • Authors: G. Castellani; C. Lüpkes, R. Gerdes, S. Hendricks
      Pages: n/a - n/a
      Abstract: Over the polar oceans, near‐surface atmospheric transport of momentum is strongly influenced by sea‐ice surface topography. The latter is analyzed on the basis of laser altimeter data obtained during airborne campaigns between 1995 and 2011 over more than 10000 km of flight distance in different regions of the Arctic Ocean. Spectra of height and spacing between topographic features averaged over 10 km flight sections show that typical values are 0.45 m for the mean height and about 20 m for the mean spacing. Nevertheless the variability is high and the spatial variability is stronger than the temporal one. The total topography spectrum is divided into a range with small obstacles (between 0.2 m and 0.8 m height) and large obstacles (≥0.8 m). Results show that large pressure ridges represent the dominant topographic feature only along the coast of Greenland. In the Central Arctic the concentration of large ridges decreased over the years, accompanied by an increase of small obstacles concentration and this might be related to decreasing multi‐year ice. The application of a topography dependent parameterization of neutral atmospheric drag coefficients reflects the large variability in the sea ice topography and reveals characteristic differences between the regions. Based on the analysis of the two spectral ranges we find that the consideration of only large pressure ridges is not enough to characterize the roughness degree of an ice field, and the values of drag coefficients are in most regions strongly influenced by small obstacles.
      PubDate: 2014-09-10T01:49:56.147693-05:
      DOI: 10.1002/2013JC009712
       
  • Quantifying tidally driven benthic oxygen exchange across permeable
           sediments: An aquatic eddy correlation study
    • Authors: Daniel F. McGinnis; Stefan Sommer, Andreas Lorke, Ronnie N. Glud, Peter Linke
      Pages: n/a - n/a
      Abstract: Continental shelves are predominately (~70%) covered with permeable, sandy sediments. While identified as critical sites for intense oxygen, carbon and nutrient turnover, constituent exchange across permeable sediments remains poorly quantified. The central North Sea largely consists of permeable sediments and has been identified as increasingly at risk for developing hypoxia. Therefore, we investigate the benthic O2 exchange across the permeable North Sea sediments using a combination of in situ microprofiles, a benthic chamber and aquatic eddy correlation. Tidal bottom currents drive the variable sediment O2 penetration depth (from ~3 to 8 mm) and the concurrent turbulence‐driven 25‐fold variation in the benthic sediment O2 uptake. The O2 flux and variability were reproduced using a simple 1‐D model linking the benthic turbulence to the sediment porewater exchange. The high O2 flux variability results from deeper sediment O2 penetration depths and increased O2 storage during high velocities, which is then utilized during low flow periods. The study reveals that the benthic hydrodynamics, sediment permeability and porewater redox oscillations are all intimately linked and crucial parameters determining the oxygen availability in permeable sediments. These parameters must all be considered when evaluating mineralization pathways of organic matter and nutrients in permeable sediments.
      PubDate: 2014-09-09T19:25:33.632231-05:
      DOI: 10.1002/2014JC010303
       
  • Modulation of Rossby waves on the Pacific North Equatorial Current
           bifurcation associated with the 1976 climate regime shift
    • Authors: Li‐Chiao Wang; Chau‐Ron Wu, Bo Qiu
      Pages: n/a - n/a
      Abstract: Simulated current velocity and long‐term reanalysis wind data are used to investigate interannual variations in the bifurcation of the Pacific North Equatorial Current (NEC) after the 1976 climate regime shift. Wind stress curl anomaly (WSCA) in the region of 10°N–15°N and 160°E–170°E generates Rossby waves and affects the NEC bifurcation along the Philippine coast. From 1976 to 1992, following a regime shift to the positive Pacific Decadal Oscillation (PDO) phase, PDO and El Niño‐Southern Oscillation (ENSO) match each other in strength and have a neutralized effect on the WSCA. From 1993 to 2009, WSCA matches PDO well, and its correlation with ENSO is lower. Using a linear regression model, we show that the influence of PDO has nearly thirteen times weight over that of ENSO. Prior to the 1976 regime shift, WSCA is closely related to ENSO from 1961 to 1975, and it does not correlate significantly with PDO. Our analysis results show that Rossby waves are preferentially generated in either the negative PDO phase when the ENSO signal dominates, or in the positive PDO phase when the ENSO signal is overshadowed. In the phase when the positive PDO counteracts with the ENSO signal, neither ENSO nor PDO has a significant influence on Rossby wave generations through the WSCA.
      PubDate: 2014-09-05T04:20:49.538107-05:
      DOI: 10.1002/2014JC010233
       
  • Estimating dissolved organic carbon inventories in the East China Sea
           using remote sensing data
    • Authors: Qiong Liu; Delu Pan, Yan Bai, Kai Wu, Chen‐Tung Authur Chen, Zhiliang Liu, Lin Zhang
      Pages: n/a - n/a
      Abstract: The coastal ocean is characterized by a high dissolved organic carbon (DOC) concentration due to large terrestrial inputs and high primary production. Monitoring the dynamic variation of DOC inventories in coastal oceans provide more information on carbon flux, but is very challenging in practice. We propose a method of estimating DOC inventories in the East China Sea (ECS) by integrating the surface DOC distribution with a vertical model of the DOC profile via satellite data. Surface DOC concentration was retrieved from satellite‐derived chromophoric dissolved organic matter and chlorophyll concentration. Two vertical DOC profile models (uniform model and stratified model) were established based on water‐density profiles, and the usage of these two models was corresponded to water mass classification determined by a water mass index. The average bias of the satellite‐derived DOC inventory, in the euphotic layer was 23.8% in spring, 24.8% in autumn and 14.7% in winter, and in the water column was 15.6% in spring, 12.3% in autumn and 10.2% in winter. The total satellite‐derived DOC inventory integrated in the water column was about 31.84 Tg, 31.96 Tg, 28.59 Tg and 31.18 Tg in four seasons in the ECS (5.84×105 km2). Sensitivity analysis indicated that the remote‐sensing method of estimating DOC inventory is stable and reliable. The available of long‐term and large‐scale satellite‐derived DOC inventories in marginal sea would provide us basic information on carbon cycle, and the difference between the seasonal DOC inventories would help to understand the DOC export and relative biogeochemical processes in the ECS.
      PubDate: 2014-09-03T12:36:29.559443-05:
      DOI: 10.1002/2014JC009868
       
  • Annual sea‐air CO2 fluxes in the Bering Sea: Insights from new
           autumn and winter observations of a seasonally ice‐covered
           continental shelf
    • Authors: Jessica N. Cross; Jeremy T. Mathis, Karen E. Frey, Catherine E. Cosca, Seth L. Danielson, Nicholas R. Bates, Richard A. Feely, Taro Takahashi, Wiley Evans
      Pages: n/a - n/a
      Abstract: High‐resolution data collected from several programs has greatly increased the spatiotemporal resolution of pCO2 data in the Bering Sea, and provided the first autumn and winter observations. Using data from 2008 – 2012, monthly climatologies of sea‐air CO2 fluxes for the Bering Sea shelf area from April through December were calculated, and contributions of physical and biological processes to observed monthly sea‐air pCO2 gradients (ΔpCO2) were investigated. Net efflux of CO2 was observed during November, December, and April, despite the impact of sea surface cooling on ΔpCO2. Although the Bering Sea was believed to be a moderate to strong atmospheric CO2 sink, we found that autumn and winter CO2 effluxes balanced 65% of spring and summer CO2 uptake. Ice cover reduced sea‐air CO2 fluxes in December, April, and May. Our estimate for ice‐cover corrected fluxes suggests the mechanical inhibition of CO2 flux by sea‐ice cover has only a small impact on the annual scale (< 2%). An important data gap still exists for January through March, the period of peak ice cover and the highest expected retardation of the fluxes. By interpolating between December and April using assumptions of the described autumn and winter conditions, we estimate the Bering Sea shelf area is an annual CO2 sink of ~6.8 Tg C yr‐1. With changing climate, we expect warming sea surface temperatures, reduced ice cover, and greater wind speeds with enhanced gas exchange to decrease the size of this CO2 sink by augmenting conditions favorable for greater wintertime outgassing.
      PubDate: 2014-09-02T03:50:34.239473-05:
      DOI: 10.1002/2013JC009579
       
  • Geometry of tidal inlet systems: A key factor for the net sediment
           transport in tidal inlets
    • Authors: W. Ridderinkhof; H. E. de Swart, M. van der Vegt, N. C. Alebregtse, P. Hoekstra
      Pages: n/a - n/a
      Abstract: The net transport of sediment between the back‐barrier basin and the sea is an important process for determining the stability of tidal inlet systems. Earlier studies showed that in a short basin, tidal flats favor peak ebb‐currents stronger than peak flood currents, implying export of coarse sediment, while shallow basins favor stronger flood currents. The new elements considered in this study are 1) arbitrary basin lengths, 2) a narrow inlet that connects the basin to the sea, 3) an asymmetric tidal forcing, and 4) radiation damping. The objective is to gain fundamental insight in how the geometry of a tidal inlet system affects the net sand transport in a tidal inlet. For this purpose, a width‐ and depth averaged analytical model was constructed. It is found that the length of a back‐barrier basin controls the effect that nonlinear hydrodynamic processes have on the tidal asymmetry, and consequently controls whether the currents in the inlet are flood‐ or ebb‐dominant. Furthermore, the cross‐sectional area of the inlet controls the ratio between the net sediment transport that results from tidal asymmetry and that caused by the interaction of the principal tide with the residual current. Finally, it is shown that the effect of an asymmetric tidal forcing on the net sand transport depends on the length of the back‐barrier basin with respect to the tidal wavelength in that basin.
      PubDate: 2014-09-02T03:50:12.081442-05:
      DOI: 10.1002/2014JC010226
       
  • The central Pacific El Niño intraseasonal Kelvin wave
    • Authors: K. Mosquera‐Vásquez; B. Dewitte, Serena Illig
      Pages: n/a - n/a
      Abstract: In this study we document and interpret the characteristics of the Intraseasonal Kelvin wave (ISKw) in the Pacific over the 1989‐2011 period, based on observations, a linear model and the outputs of an Ocean General Circulation Model (OGCM). We focus on the wave activity during the Central Pacific (CP) El Niño events contrasting with the extraordinary El Niño of 1997/1998. We find that ISKw activity is enhanced in Austral Summer (Spring) in the central Pacific (west of ~120°W) during CP El Niño events. The linear model experiment indicates that the Austral Summer peak is wind‐forced while the Austral Spring peak is not and consequently results from non‐linear processes. In addition, a strong dissipation of the ISKws is observed east of 120°W which cannot be accounted for by a linear model using a Rayleigh friction. A vertical and horizontal mode decomposition of the OGCM simulation further confirms the sharp changes in characteristics of the ISKws as well as the reflection of the latter into first‐meridional Rossby wave at the longitude where the maximum zonal gradient of the thermocline is found (~ 120°W). Our analysis suggests that the confinement of CP El Niño warming in the central Pacific may result from the reinforcement of the zonal gradient in stratification associated with the La Niña‐like conditions since the late of the 1990s, leading to scattering of the energy of the ISKws in the eastern Pacific.
      PubDate: 2014-09-02T03:27:05.514268-05:
      DOI: 10.1002/2014JC010044
       
  • Meteotsunami‐tide interactions and high‐frequency sea level
           oscillations in the eastern Yellow Sea
    • Authors: Byoung‐Ju Choi; Chorong Hwang, Sang‐Ho Lee
      Pages: n/a - n/a
      Abstract: While an air pressure jump was moving southeastward over the shallow water region of the eastern Yellow Sea in March 2007, a long ocean wave (meteotsunami) was generated and amplified due to the Proudman resonance. The long wave arrived at the coast during high tide with wave amplitude of 1.4 m and seawater overflew seawalls and inundated the land. High‐frequency sea level oscillations continued for 8‐9 hours after the long wave hit a local coast. The Moon's age was 12 days, and the tidal range was about 4 m between neap and spring tides. Two‐dimensional numerical simulations were performed, to reproduce amplification of the long ocean wave in offshore and oscillations of sea level at the coast. Both tidal elevation and tidal currents were found to affect the growth of the long wave amplitude by the interactions between tides and the long wave. Long wave‐tides interactions are important processes for the accurate prediction of long wave arrival time and maximum height and for the reduction of coastal hazards in the macro‐tidal region. After the long wave hit the coast of remote regions, reflected waves propagated radially from remote regions to a local coast. The high‐frequency sea level oscillations at a local observation station continued, until all of the reflected waves at remote regions had passed by. It was concluded that high‐frequency oscillations of sea level are generated not only by local reflection of the long wave, but also by propagation of the reflected waves from remote regions.
      PubDate: 2014-09-02T03:21:22.846231-05:
      DOI: 10.1002/2013JC009788
       
  • The impact of the assimilation of Aquarius sea surface salinity data in
           the GEOS Ocean Data Assimilation System
    • Authors: G. Vernieres; R. Kovach, C. Keppenne, S. Akella, L. Brucker, E. Dinnat
      Pages: n/a - n/a
      Abstract: Ocean salinity and temperature differences drive thermohaline circulations. These properties also play a key role in the ocean‐atmosphere coupling. With the availability of L‐band space‐borne observations, it becomes possible to provide global scale sea surface salinity (SSS) distribution. This study analyzes globally the along‐track (Level 2) Aquarius SSS retrievals obtained using both passive and active L‐band observations. Aquarius along‐track retrieved SSS are assimilated into the ocean data assimilation component of Version 5 of the Goddard Earth Observing System (GEOS‐5) assimilation and forecast model. We present a methodology to correct the large biases and errors apparent in Version 2.0 of the Aquarius SSS retrieval algorithm and map the observed Aquarius SSS retrieval into the ocean model’s bulk salinity in the topmost layer. The impact of the assimilation of the corrected SSS on the salinity analysis is evaluated by comparisons with in‐situ salinity measurements from Argo. The results show a significant reduction of the global biases and RMS of observations‐minus‐forecast differences at in‐situ locations. The most striking results are found in the tropics and southern latitudes. Our results highlight the complementary role and problems that arise during the assimilation of salinity information from in‐situ (Argo) and space‐borne SSS retrievals.
      PubDate: 2014-08-30T11:44:40.548264-05:
      DOI: 10.1002/2014JC010006
       
  • Evaluation of directly wind‐coherent near‐inertial surface
           currents off Oregon using a statistical parameterization and analytical
           and numerical models
    • Authors: Sung Yong Kim; P. Michael Kosro, Alexander L. Kurapov
      Pages: n/a - n/a
      Abstract: Directly wind‐coherent near‐inertial surface currents off the Oregon coast are investigated with a statistical parameterization of observations and outputs of a regional numerical ocean model and three one‐dimensional analytical models including the slab layer, Ekman, and near‐surface averaged Ekman models. The transfer functions and response functions, statistically estimated from observed wind stress at NDBC buoys and surface currents derived from shoredbased high‐frequency radars, enable us to isolate the directly wind‐forced near‐inertial surface currents. Concurrent observations of the wind and currents are crucial to evaluate the directly wind‐forced currents. Thus, the wind stress and surface current fields obtained from a regional ocean model, which simulates variability of the wind and surface currents on scales comparable to those in observations, are analyzed with the same statistical parameterization to derive the point‐by‐point transfer functions and response functions. Model and data comparisons suggest that the regional ocean model describe near‐inertial variability of surface currents in quality and quantity correctly. The estimated response functions exhibit decay time scales in a range of 3 to 5 days, and about 40% of near‐inertial motions are explained by local wind stress. Among the one‐dimensional analytical models, the near‐surface averaged Ekman model explains the statistically derived wind‐current relationship better than other analytical models.
      PubDate: 2014-08-26T10:55:23.696434-05:
      DOI: 10.1002/2014JC010115
       
  • Water mass analysis of the Coral Sea through an Optimum Multiparameter
           method
    • Authors: Florent Gasparin; Christophe Maes, Joel Sudre, Veronique Garcon, Alexandre Ganachaud
      Pages: n/a - n/a
      Abstract: A water mass analysis of the Coral Sea thermocline waters provides a description of their distribution, pathways and mixture based on recent oceanographic cruises in this region of strong western boundary currents. The Optimum Multiparameter method is used to determine the relative contribution of core water masses based on their measured temperature, salinity and dissolved oxygen. The thermocline waters, carried by the broad South Equatorial Current (SEC), are essentially composed of four core water masses of different origins. Coming from the south, the South Pacic Tropical Water South (SPTWS, σ=25.3 kg.m−3) and the Western South Pa‐cic Central Water (WSPCW, σ=26.3 kg.m−3) enter the Coral Sea by the channel between the island of New Caledonia and the Vanuatu archipelago. Coming from the north, the South Pacic Tropical Water North (SPTWN, σ=24.5 kg.m−3) and the Pacic Equatorial Water (PEW, σ=26.3 kg.m−3) flow north of Vanuatu. The upper thermocline water that exits the Coral Sea equatorward, is mainly composed of SPTWN carried by the New Guinea Coastal Undercurrent. In contrast, upper thermocline waters exiting the Coral Sea poleward, in the East Australian Current, is dominated by SPTWS. The relative contributions are different in the lower thermocline where WSPCW dominates both western boundary currents. This refined description is consistent with the dynamics of the main currents, with a very strong depth dependence in the partitioning of incoming SEC waters.
      PubDate: 2014-08-19T03:41:16.580798-05:
      DOI: 10.1002/2014JC010246
       
  • SMOS salinity in the subtropical north Atlantic salinity maximum: 1.
           Comparison with Aquarius and in situ salinity
    • Authors: O. Hernandez; J. Boutin, N. Kolodziejczyk, G. Reverdin, N. Martin, F. Gaillard, N. Reul, J.L. Vergely
      Pages: n/a - n/a
      Abstract: Sea surface salinity (SSS) measured from space by the Soil Moisture and Ocean Salinity (SMOS) mission is validated in the subtropical North Atlantic Ocean. 39 transects of ships of opportunity equipped with thermosalinographs (TSG) crossed that region from 2010 to 2012, providing a large database of ground truth SSS. SMOS SSS is also compared to Aquarius SSS. Large seasonal biases remain in SMOS and Aquarius SSS. In order to look at the capability of satellite SSS to monitor spatial variability, especially at scales less than 300 km (not monitored with the Argo network), we first apply a monthly bias correction derived from satellite SSS and In Situ Analysis System (ISAS) SSS differences averaged over the studied region. Ship SSS averaged over 25 km is compared with satellite and ISAS SSS. Similar statistics are obtained for SMOS, Aquarius and ISAS products (root mean square error of about 0.15 and global correlation coefficient r of about 0.92). However, in the above statistics, SSS varies due to both large scale and mesoscale (here, for scales around 100 km) variability. In order to focus on mesoscale variability, we consider SSS anomalies with respect to a monthly climatology. SMOS SSS and Aquarius SSS anomalies are more significantly correlated (r > 0.5) to TSG SSS anomaly than ISAS. We show the effective gain of resolution and coverage provided by the satellite products over the interpolated in situ data. We also show the advantage of SMOS (r=0.57) over Aquarius (r=0.52) to reproduce SSS mesoscale features.
      PubDate: 2014-06-25T21:41:39.780213-05:
      DOI: 10.1002/2013JC009610
       
  • Intrusion of Rhone River diluted water into the Bay of Marseille:
           Generation processes and impacts on ecosystem functioning
    • Authors: Marion Fraysse; Ivane Pairaud, Oliver N. Ross, Vincent M. Faure, Christel Pinazo
      Pages: 6535 - 6556
      Abstract: The Rhone River provides the largest inputs of terrestrial freshwater and nutrients into the Mediterranean Sea. The Rhone River diluted water intrusions into the Bay of Marseille were investigated, examining their physical generation processes and associated biogeochemical impact by using in situ observations, remote sensing data, and a three‐dimensional physical/biogeochemical coupled model. During our study period from 2007 to 2011, Rhone River intrusions occurred on average 7.6 times per year and affected more frequently the northern part of the bay. A classification of intrusion events in three categories is proposed (short lived, big, and small) as a function of their duration and spatial extent. The intrusions appeared to be driven by: (i) wind forcing, (ii) the presence of a mesoscale eddy, (iii) the Rhone River discharge volume, and (iv) the variation in thermocline depth. Typically, a combination of these favorable factors was necessary to induce an intrusion. An intrusion strongly impacts the biogeochemical functioning of the Bay of Marseille by bringing large quantities of nutrients into the bay. Mass balances were computed allowing us to quantify this impact on the Bay of Marseille. The results show that the ecological impact depends very much on the type of intrusion, with big intrusions having the highest impact.
      PubDate: 2014-10-01T09:09:17.331363-05:
      DOI: 10.1002/2014JC010022
       
  • Polar Front around the Kerguelen Islands: An up‐to‐date
           determination and associated circulation of surface/subsurface waters
    • Authors: Young‐Hyang Park; Isabelle Durand, Elodie Kestenare, Gilles Rougier, Meng Zhou, Francesco d'Ovidio, Cédric Cotté, Jae‐Hak Lee
      Pages: 6575 - 6592
      Abstract: The circulation of iron‐rich shelf waters around the Kerguelen Islands plays a crucial role for a climatically important, annually recurrent phytoplankton spring bloom over the sluggish shelf region and its downstream plume area along the Antarctic circumpolar flow. However, there is a long‐standing confusion about the Polar Front (PF) in the Kerguelen region due to diverse suggestions in the literature for its geographical location with an extreme difference over 10° of latitude. Based on abundant historical hydrographic data, the in situ hydrographic and current measurements during the 2011 KEOPS2 cruise, satellite chlorophyll images, and altimetry‐derived surface velocity fields, we determine and validate an up‐to‐date location of the PF around the Kerguelen Islands. Artificial Lagrangian particle trajectories computed from altimetric velocity time series are analyzed for the possible pathways and sources of different surface/subsurface waters advected into the chlorophyll bloom area east off the islands studied during the KEOPS2 cruise. The PF location determined as the northernmost boundary of the Winter Water colder than 2°C, which is also associated with a band of strong currents, appears to be primarily controlled by topography. The PF rounds the Kerguelen Islands from the south to deflect northward along the eastern escarpment up to the northeastern corner of the Kerguelen Plateau before making its southward retroflection. It is shown that the major surface/subsurface waters found within the deep basin east of the Kerguelen Islands originate from the shelf around the Heard Island, rather than from the shallow shelf north of the Kerguelen Islands.
      PubDate: 2014-10-02T10:28:10.556415-05:
      DOI: 10.1002/2014JC010061
       
  • Distinguishing meanders of the Kuroshio using machine learning
    • Authors: David A. Plotkin; Jonathan Weare, Dorian S. Abbot
      Pages: 6593 - 6604
      Abstract: The Kuroshio south of Japan is often described as being bimodal, with abrupt transitions between a straight path state that stays near the coast (small meander) and a meandering state that deviates from the coast (large meander). Despite evidence of the existence of two or more states of the Kuroshio, previous data‐driven studies have shown only high variability of the current; they have not, however, demonstrated bimodality in the sense of two states of relatively high probability separated by a region of relatively low probability. We use singular value decomposition (SVD), a standard time series analysis method for characterizing variability, and diffusion maps and spectral clustering (DMSC), a machine learning algorithm that seeks multimodality, to investigate Kuroshio reanalysis output. By applying these methods to a time series of velocity fields, we find that (1) the Kuroshio is bimodal, with high inflow and low path variability in the small meander and low inflow and high path variability in the large meander, (2) the state of the system correlates highly with the location of the recirculation gyre south of Japan, and (3) the meanders are better characterized by path variability than by mean path. Because these results are consistent with satellite sea surface height data, they are not an artifact of the model used for reanalysis. Further, our results provide evidence for a previously proposed transition mechanism based on the strengthening, migration, and weakening of the recirculation gyre south of Japan and can therefore help direct future modeling studies.
      PubDate: 2014-10-02T13:34:07.570192-05:
      DOI: 10.1002/2014JC010128
       
 
 
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