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

Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 24, SJR: 2.56, h-index: 69)
Geophysical Research Letters     Full-text available via subscription   (Followers: 52, SJR: 3.493, h-index: 157)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 5, SJR: 3.239, h-index: 119)
J. of Advances in Modeling Earth Systems     Open Access   (Followers: 2, SJR: 1.944, h-index: 7)
J. of Geophysical Research : Atmospheres     Partially Free   (Followers: 22)
J. of Geophysical Research : Biogeosciences     Full-text available via subscription   (Followers: 6)
J. of Geophysical Research : Earth Surface     Partially Free   (Followers: 24)
J. of Geophysical Research : Oceans     Partially Free   (Followers: 15)
J. of Geophysical Research : Planets     Full-text available via subscription   (Followers: 13)
J. of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 26)
J. of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 15)
Paleoceanography     Full-text available via subscription   (Followers: 4, SJR: 3.22, h-index: 88)
Radio Science     Full-text available via subscription   (Followers: 3, SJR: 0.959, h-index: 51)
Reviews of Geophysics     Full-text available via subscription   (Followers: 20, SJR: 9.68, h-index: 94)
Space Weather     Full-text available via subscription   (Followers: 3, SJR: 1.319, h-index: 19)
Tectonics     Full-text available via subscription   (Followers: 9, SJR: 2.748, h-index: 85)
Water Resources Research     Full-text available via subscription   (Followers: 202, SJR: 2.189, h-index: 121)
Journal Cover   Journal of Geophysical Research : Oceans
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   Partially Free Journal Partially Free Journal
   ISSN (Online) 2169-9291
   Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • Ice thickness effects on Aquarius brightness temperatures over Antarctica
    • Authors: Miriam Pablos; María Piles, Verónica González‐Gambau, Adriano Camps, Mercè Vall‐llossera
      Pages: n/a - n/a
      Abstract: The Dome‐C region, in the East Antarctic Plateau, is regarded as an ideal natural laboratory for calibration/validation of space‐borne microwave radiometers. At L‐band, the thermal stability of this region has been confirmed by several experimental campaigns. However, its use as an independent external calibration target has recently been questioned due to some spatial inhomogeneities and seasonal effects revealed in the brightness temperatures (TB) acquired in this area. This paper shows the observed relationship, from exploratory research, between the Antarctic ice thickness spatial variations and the measured Aquarius TB changes. A three‐months no‐daylight period during the Austral winter has been analyzed. Four transects have been defined over East Antarctica covering areas with different ice thickness variations and ranges. The theoretical L‐band penetration depth has been estimated to understand the possible contributions to the measured signal. A good agreement has been observed between Aquarius TB and ice thickness variations over the whole Antarctica, with correlations of ∼0.6–0.7. The two variables show a linear trend with slopes of ∼8.3–9.5 K/km. No correlation has been observed with the subglacial bedrock. The maximum L‐band penetration depth has been estimated to be ∼1–1.5 km. Results are therefore consistent: the spatial variations found on Aquarius TB are not related to the emissivity of the bedrock, which lies deeper. This study provides evidence that new L‐band satellite observations could contribute to further our understanding of Antarctic geophysical processes. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-19T21:20:39.671117-05:
      DOI: 10.1002/2014JC010151
       
  • Whales and waves: Humpback whale foraging response and the shoaling of
           internal waves at Stellwagen Bank
    • Authors: Jesús Pineda; Victoria Starczak, José C.B. da Silva, Karl Helfrich, Michael Thompson, David Wiley
      Pages: n/a - n/a
      Abstract: We tested the hypothesis that humpback whales aggregate at the southern flank of Stellwagen Bank (SB) in response to internal waves (IWs) generated semi‐diurnally at Race Point (RP) channel because of the presence of their preferred prey, planktivorous fish, which in turn respond to zooplankton concentrated by the predictable IWs. Analysis of synthetic aperture radar (SAR) images indicates that RP IWs approach the southern flank of SB frequently (∼62% of the images). Published reports of whale sighting data and archived SAR images point to a coarse spatial coincidence between whales and Race Point IWs at SB's southern flank. The responses of whales to IWs were evaluated via sightings and behavior of humpback whales, and IWs were observed in situ by acoustic backscatter and temperature measurements. Modeling of IWs complemented the observations, and results indicate a change of ∼0.4m/s in current velocity, and ∼1.5 Pa in dynamic pressure near the bottom, which may be sufficient for bottom fish to detect the IWs. However, fish were rare in our acoustic observations, and fish response to the IWs could not be evaluated. RP IWs do not represent the leading edge of the internal tide, and they may have less mass‐transport potential than typical coastal IWs. There was large interannual variability in whale sightings at SB's southern flank, with decreases in both numbers of sightings and proportion of sightings where feeding was observed from 2008 to 2013. Coincidence of whales and IWs was inconsistent, and results do not support the hypothesis. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-18T10:47:18.811386-05:
      DOI: 10.1002/2014JC010564
       
  • Persistent organic pollutants in ocean sediments from the North Pacific to
           the Arctic Ocean
    • Authors: Yuxin Ma; Crispin J. Halsall, John D. Crosse, Carola Graf, Minghong Cai, Jianfeng He, Guoping Gao, Kevin Jones
      Pages: n/a - n/a
      Abstract: Concentrations of polychlorinated biphenyls (PCBs), organochlorine pesticides (OC pesticides) and polybrominated diphenyl ethers (PBDEs) are reported in surficial sediments sampled along cruise transects from the Bering Sea to the central Arctic Ocean. OCs and PCBs all had significantly higher concentrations in the relatively shallow water (500 m) of the Bering Sea and Arctic Ocean (e.g. Canada Basin ΣPCB 149±102 pg g−1 dw). Concentrations were similar to, or slightly lower than, studies from the 1990s, indicating a lack of a declining trend. PBDEs (excluding BDE‐209) displayed very low concentrations (e.g. range of median values, 3.5‐6.6 pg/g dw). In the shelf areas, the sediments comprised similar proportions of silt and clay, whereas the deep basin sediments were dominated by clay, with a lower total organic carbon (TOC) content. While significant positive correlations were observed between persistent organic pollutant (POP) concentrations and TOC (Pearson correlation, r=0.66‐0.75, p
      PubDate: 2015-03-18T08:15:38.604053-05:
      DOI: 10.1002/2014JC010651
       
  • Observation of the surface horizontal thermohaline variability at meso to
           submesoscales in the north‐eastern Subtropical Atlantic Ocean
    • Authors: Nicolas Kolodziejczyk; Gilles Reverdin, Jacqueline Boutin, Olga Hernandez
      Pages: n/a - n/a
      Abstract: The seasonal variability of the surface horizontal thermohaline structure is investigated in the north‐eastern Atlantic Surface Salinity Maximum (SSM) at length scales from five to hundreds of kilometers, i.e. at submeso‐ to meso‐scales. The near‐surface temperature and salinity data from merchant ship thermosalinograph (TSG) transects across the Atlantic are used to compute the horizontal temperature, salinity and density fluctuations, and the density ratio. During late winter in the north‐eastern SSM, thermohaline compensation is observed for wavelengths from 5 km to more than 200 km; in spite of large and sharp surface thermohaline fronts, a weak density surface horizontal gradient is observed. Temperature and salinity exhibit an energetic spectra in k−2 slope scale between 20‐100 km scale and a steeper slope at shorter wavelengths, while density spectra exhibit lower energy level with a clear k−3 slope below 20 km, consistent with interior quasi‐geostrophic turbulence. During summer in the north‐eastern SSM, salinity and temperature gradients are no longer compensated due to strong atmospheric heating of the upper ocean. In comparison with winter, the surface density spectrum is enhanced with a flatter slope between k−2‐k−1 between 5 and 20 km. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-18T04:54:41.155929-05:
      DOI: 10.1002/2014JC010455
       
  • Estimates of Lagrangian transport by surface gravity wave groups: The
           effects of finite depth and directionality
    • Authors: T.S. van den Bremer; P.H. Taylor
      Pages: n/a - n/a
      Abstract: Two physical phenomena drive the Lagrangian trajectories of neutrally buoyant particles underneath surface gravity wave groups: the Stokes drift results in a net displacement of particles in the direction of propagation of the group, whereas the Eulerian return flow transports such particles in the opposite direction. Generally, the Stokes drift is the larger of the two near the surface, whereas the effects of the return flow dominate at depth. A transition depth can be defined that separates the two regimes. Using a multiple‐scales expansion we provide leading‐order estimates of the forward transport, the backward transport and the transition depth for realistic sea states. We consider the effects of both finite depth and the directionally spread nature of the waves on our estimates. We show that from the perspective of the return flow, almost all seas are of finite depth. In fact, many seas can be shown to be “shallow” from the perspective of the return flow with little variation of this flow with depth. Furthermore, even small degrees of directional spreading can considerably reduce the magnitude of the return flow and its transport. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-18T03:06:51.466182-05:
      DOI: 10.1002/2015JC010712
       
  • Comparison of spaceborne measurements of sea surface salinity and colored
           detrital matter in the Amazon plume
    • Authors: S. Fournier; B. Chapron, J. Salisbury, D. Vandemark, N. Reul
      Pages: n/a - n/a
      Abstract: Large rivers are key hydrologic components in oceanography, particularly regarding air‐sea and land‐sea exchanges and biogeochemistry. We enter now in a new era of Sea Surface Salinity (SSS) observing system from Space with the recent launches of the ESA Soil Moisture and Ocean Salinity (SMOS) and the NASA Aquarius/Sac‐D missions. With these new sensors, we are now in an excellent position to revisit SSS and ocean color investigations in the tropical northwest Atlantic using multi‐year remote sensing time series and concurrent in situ observations. The Amazon is the world's largest river in terms of discharge. In its plume, SSS and upper water column optical properties such as the absorption coefficient of colored detrital matter (acdm) are strongly negatively correlated (
      PubDate: 2015-03-16T00:27:47.44327-05:0
      DOI: 10.1002/2014JC010109
       
  • Upwelling induced by the frictional stress curl and vertical squeezing of
           the vortex tube over a submerged valley in the East China Sea
    • Authors: Zhiqiang Liu; Jianping Gan
      Pages: n/a - n/a
      Abstract: We conducted a process‐oriented modeling study to investigate the characteristics and dynamics of the prominent upwelling over a vast submerged valley in the East China Sea (ECS). The valley is inversely funnel‐shaped with the west bank and the east bank oriented in the north‐south direction. A cross‐bank upward transport occurred along the west bank. It intensified northward and peaked around the head of the valley. An along‐bank southward pressure gradient force (PGF) formed the cross‐bank geostrophic transport for the upwelling over the valley. The PGF reached its maxima at the head of the valley. Our momentum and vorticity dynamic analyses revealed that a bottom stress curl mainly contributed the PGF along the west bank. At the same time, both the bottom stress curl and the nonlinear vorticity advection contributed to the PGF around the head. The bottom stress curl was due to the bottom shear vorticity of the coastal current and the curvature vorticity around the head. The nonlinear vorticity advection formed because of the vertical squeezing of vortex tube as the current flowed over the valley. The nonlinearity mainly affected the PGF around the head, whereas the bottom stress curl contributed to the PGF over the entire valley. The ratio of the nonlinear to frictional contributions to the PGF increased as the coastal current intensified. Our study demonstrates that the PGF that drives the upwelling over the valley is the combined result of the nonlinearity due to vertical squeezing of vortex tube and bottom frictional effects. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-16T00:27:25.020841-05:
      DOI: 10.1002/2015JC010715
       
  • Spatial and temporal variability of zooplankton off New Caledonia
           (Southwestern Pacific) from acoustics and net measurements
    • Authors: Houssem Smeti; Marc Pagano, Christophe Menkes, Florian de Boissieu, Anne Lebourges‐Dhaussy, Brian P. V. Hunt, Valerie Allain, Martine Rodier, Elodie Kestenare, Cherif Sammari
      Pages: n/a - n/a
      Abstract: Spatial and temporal distribution of zooplankton off New Caledonia in the eastern Coral Sea was studied during two multidisciplinary cruises in 2011, during the cool and the hot seasons. Acoustic measurements of zooplankton were made using a shipborne acoustic Doppler current profiler (S‐ADCP), a scientific echosounder and a Tracor acoustic profiling system (TAPS). Relative backscatter from ADCP was converted to biomass estimates using zooplankton weights from net‐samples collected during the cruises. Zooplankton biomass was estimated using four methods: weighing, digital imaging (ZooScan), ADCP and TAPS. Significant correlations were found between the different biomass estimators and between the backscatters of the ADCP and the echosounder. There was a consistent diel pattern in ADCP derived biomass and echosounder backscatter resulting from the diel vertical migration (DVM) of zooplankton. Higher DVM amplitudes were associated with higher abundance of small zooplankton and cold waters to the south of the study area, while lower DVM amplitudes in the north were associated with warmer waters and higher abundance of large organisms. Zooplankton was largely dominated by copepods (71‐73%) among which calanoids prevailed (40‐42%), with Paracalanus spp. as the dominant species (16‐17%). Overall, zooplankton exhibited low abundance and biomass (mean night dry biomass of 4.7 ± 2.2mg m3 during the cool season and 2.4 ± 0.4mg m3 during the hot season) but high richness and diversity (Shannon index ∼4). Substantially enhanced biomass and abundance appeared to be episodically associated with mesoscale features contributing to shape a rather patchy zooplankton distribution. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-13T23:41:17.248975-05:
      DOI: 10.1002/2014JC010441
       
  • Ocean variability east of Mindanao: Mooring observations at 7°N,
           revisited
    • Authors: Yuji Kashino; Iwao Ueki, Hedeharu Sasaki
      Pages: n/a - n/a
      Abstract: Two subsurface moorings were deployed east of Mindanao Island, the Philippines, at 7°01'N, 126°55'E and 7°01'N, 127°46'E, at the location of the inshore and offshore cores of the Mindanao Undercurrent (MUC) suggested by past studies, from September 2011 to October 2012 and March 2013. A steady northward undercurrent, the MUC, was not confirmed by these observations, not only at the location of its inshore core but also of the offshore core. The observed mean flow at the mooring sites seems to be part of an anti‐cyclonic eddy rather than the MUC. A Particle‐tracking experiment using a high‐resolution general circulation model output showed that the northward mean flow, called the MUC by past studies, was too weak to advect water to the north. The Mindanao Current during 2011–2012 was weaker than during 1999–2002 because the sea surface height in the Philippine Sea during 2011–2012 was lower than that during 1999–2002. Intraseasonal variability with periods of 50–100 days was observed at the mooring sites, comparable to previous observations during 1999–2002. Westward signal propagations were observed with periods and speeds of 50 days and 0.20m s−1 at 300m depth, and of 60–72 days and 0.11–0.14m s−1 at 960m depth. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-13T21:10:27.457726-05:
      DOI: 10.1002/2015JC010703
       
  • Interdecadal decrease of the Oyashio transport on the continental slope
           off the southeastern coast of Hokkaido, Japan
    • Authors: Hiroshi Kuroda; Taku Wagawa, Yugo Shimizu, Shin‐ichi Ito, Shigeho Kakehi, Takashi Okunishi, Sosuke Ohno, Akira Kusaka
      Pages: n/a - n/a
      Abstract: We investigated the interdecadal trend of Oyashio velocity and transport during 1993–2011 based mainly on linear trend analysis of altimetry and in situ temperature‐salinity data from a monitoring line (“A‐line”) off the southeastern Hokkaido coast. Significant trends of increasing sea level were detected on the continental slope, north of the Kuril‐Kamchatka Trench. Sea level anomaly data revealed a localized clockwise circulation centered near the trench, the suggestion being that the strength of the Oyashio on the slope and the offshore return flow had decreased. The Oyashio main stream seemed to have shifted from a nearshore to an offshore path. Steric heights estimated from the A‐line data exhibited an increasing trend north of the trench, where 50–80% of the increase was determined by halosteric components attributable to a trend of decreasing salinity in the subsurface. The trend of decreasing salinity was related to downward displacement of isohaline/isopycnal surfaces. The largest displacement was above the trench. Horizontal pressure gradients associated with southwestward flows on the slope were weakened. The Oyashio transport decreased by 8.9 Sv (106 m3 s−1) in 19 years. A mesoscale eddy analysis revealed that clockwise eddies appeared more frequently in recent years near the trench around the A‐line and could decrease the Oyashio transport. A baroclinic, long Rossby‐wave model also predicted that a large‐scale baroclinic response to the wind stress could weaken the Oyashio velocity in the upper layer. Dynamical linkage between the localized eddies and large‐scale response remains to be clarified in future work. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-13T10:49:40.330281-05:
      DOI: 10.1002/2014JC010402
       
  • Strengthening Kuroshio observed at its origin during November 2010 to
           October 2012
    • Authors: Zhaohui Chen; Lixin Wu, Bo Qiu, Lei Li, Dunxin Hu, Chengyan Liu, Fan Jia, Xi Liang
      Pages: n/a - n/a
      Abstract: Direct measurements of Kuroshio at its origin (18°N, east of the Luzon Island) are conducted from November 2010 to October 2012. It is found that the depth‐averaged Kuroshio between 200–700 m has increased over 15cm s−1 during the two‐year observational period and it is accompanied by the pronounced southward shift of the North Equatorial Current (NEC) bifurcation. Further analysis indicates that the Kuroshio's strengthening is confined to the upstream segment east of the Luzon Island while the Kuroshio decreased as it passed the Luzon Strait due to a dipole‐like sea surface height (SSH) trend between 15°N and 23°N. It is demonstrated that the two‐year strengthening of the Kuroshio, as well as the dipole‐like SSH trend can be adequately reproduced by a 1.5‐layer non‐linear reduced gravity model, suggesting an important role of upper ocean response to low‐frequency wind forcing in the western Pacific. Salinity at 500‐m depth is also found to increase during the concurrent 2 years. This subthermocline salinity increase is a combined outcome of vertical (basin‐scale isopycnal surface movement) and horizontal advections (i.e., strengthened Kuroshio) due to changes in the large‐scale wind‐driven ocean circulation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-13T10:27:03.128493-05:
      DOI: 10.1002/2014JC010590
       
  • Frontal structures associated with coastal upwelling and ice‐edge
           subduction events in southern Beaufort Sea during the Canadian Arctic
           Shelf Exchange Study
    • Authors: Caroline Sévigny; Yves Gratton, Peter S. Galbraith
      Pages: n/a - n/a
      Abstract: The near‐surface temperature structure in the southeastern Beaufort Sea is shown to have been largely dependent on frontal dynamics in spring 2004, which may be typical for the region. Easterly wind events generated coastal upwelling along the Cap Bathurst peninsula; a recurring event in that area. Further west, a large mesoscale anticyclone simultaneously developed and subsequently controlled the sea surface circulation in the central Amundsen Gulf. Sharp temperature and density fronts were created at the surface at both eastern and western ends of the domain. Sampling north of Cape Bathurst and Cape Parry showed evidence of frontal intensification. Frontal features were detected near the 50–200‐m isobaths, at the mouth of the gulf, where density‐compensated near‐surface intrusions driven by agesotrophic vertical circulation were identified. These warm water tongues intruded into the outcropping isopycnal layers, which dipped down between 5 and 25 m over the Mackenzie Shelf. They then crossed the density surfaces with an inverse slope consistent with N/f as predicted for quasi‐geostrophic flows. The front event ended prior to the breakup of the landfast‐ice bridge in late June with sea‐surface temperature undergoing quick and widespread changes throughout the Amundsen Gulf. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-13T10:12:33.273992-05:
      DOI: 10.1002/2014JC010641
       
  • Issue Information
    • Pages: i - vi
      PubDate: 2015-03-12T11:49:08.054615-05:
      DOI: 10.1002/jgrc.20858
       
  • Advection of North Atlantic deep water from the Labrador Sea to the
           Southern Hemisphere
    • Authors: Monika Rhein; Dagmar Kieke, Reiner Steinfeldt
      Pages: n/a - n/a
      Abstract: Recently formed Labrador Sea Water (LSW) and overflow water from Denmark Strait (DSOW) are main components of the Atlantic Meridional Overturning Circulation. Both exhibit a distinct chlorofluorocarbon (CFC) maximum. Here, we use 25 years of CFC observations in the Atlantic to study the main features of the circulation of LSW and DSOW. From the CFC data, the age and fraction of young deep water are inferred. Due to the superior spatial data resolution compared to former attempts, regional differences in the spreading velocity and pathways of young deep water become evident, dependent on the regional circulation. The observed distributions of young LSW and DSOW showed that the DWBC is the fastest pathway to reach the southern hemisphere. The downstream decrease of the fractions of young LSW in the DWBC is slower compared to model studies. From 47°N to 42°N, DWBC transports of young LSW and DSOW decrease by 44% and 49%, respectively. At 26°N, the DWBC transport of young water is still 39% of the LSW formation rate and 44% of the DSOW overflow transport. Interior pathways also exist, especially in the subpolar North Atlantic and in the transition zone between the subpolar and subtropical gyre. Compared to DSOW, the distributions indicate a higher tendency for LSW to follow additional interior pathways. North of 45°N the major part of LSW is younger than 20 years. The general weakening of new LSW formation since the 1990s worked towards a homogenization between the LSW in the western and the eastern subpolar North Atlantic. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-11T01:49:38.477365-05:
      DOI: 10.1002/2014JC010605
       
  • Seasonal variability of alongshore winds and sea surface temperature
           fronts in Eastern Boundary Current Systems
    • Authors: Yuntao Wang; Renato M. Castelao, Yeping Yuan
      Pages: n/a - n/a
      Abstract: Seven years of satellite observations (2003–2009) are used to describe variability in sea surface temperature (SST) fronts and in the alongshore component of ocean winds, and to investigate their relations in four Eastern Boundary Current Systems (EBCS). The general patterns of SST frontal activity are remarkably similar in all EBCS, with high frontal probabilities along the coast decreasing with distance from the coastline. Results from empirical orthogonal function decompositions reveal that the seasonal evolution of SST fronts and wind stress are significantly correlated, with intensified upwelling favorable winds associated with an increase in frontal probabilities. An offshore migration of the region of high frontal activity is observed during the period of upwelling favorable alongshore wind stress in EBCS. In all regions, the seasonal variability of frontal activity and wind stress is stronger at mid than at low latitudes. The width of the region of high frontal activity is relatively broader in the California and Benguela Current Systems, and narrower in the Canary and Humboldt Current Systems. The width of the band of high frontal activity may be influenced by multiple factors, including wind forcing, flow topography interactions and mesoscale dynamics. While seasonal variability in frontal activity in the California Current System acts to reinforce or weaken the average pattern, they are substantially different in the Canary Current System, where there is little overlap in the areas characterized by persistent and seasonally varying front activity. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-11T01:48:50.221928-05:
      DOI: 10.1002/2014JC010379
       
  • Local and remote wind stress forcing of the seasonal variability of the
           Atlantic Meridional Overturning Circulation (AMOC) transport at
           26.5°N
    • Authors: Jiayan Yang
      Pages: n/a - n/a
      Abstract: The transport of the Atlantic Meridional Overturning Circulation (AMOC) varies considerably on the seasonal time scale at 26.5˚N according to observations made at the RAPID‐MOCHA array. Previous studies indicate that the local wind stress at 26.5˚N, especially a large wind‐stress curl at the African coast, is the leading contributor to this seasonal variability. The purpose of the present study is to examine whether non‐local wind stress forcing, i.e., remote forcing from latitudes away from 26.5˚N, affects the seasonal AMOC variability at the RAPID‐MOCHA array. Our tool is a two‐layer and wind‐driven model with a realistic topography and an observation‐derived wind stress. The seasonal cycle of the modeled AMOC transport agrees well with RAPID‐MOCHA observations while the amplitude is in the lower end of the observational range. In contrast to previous studies, the seasonal AMOC variability at 26.5˚N is not primarily forced by the wind‐stress curl at the eastern boundary, but is a result of a basin‐wide adjustment of ocean circulation to seasonal changes in wind stress. Both the amplitude and phase of the seasonal cycle at 26.5˚N are strongly influenced by wind‐stress forcing from other latitudes, especially from the subpolar North Atlantic. The seasonal variability of the AMOC transport at 26.5˚N is due to the seasonal re‐distribution of the water‐mass volume and is driven by both local and remote wind stress. Barotropic processes make significant contributions to the seasonal AMOC variability through topography‐gyre interactions. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-11T01:40:20.201194-05:
      DOI: 10.1002/2014JC010317
       
  • A mechanistic semi‐analytical method for remotely sensing sea
           surface pCO2 in river‐dominated coastal oceans: A case study from
           the East China Sea
    • Authors: Yan Bai; Wei‐Jun Cai, Xianqiang He, Weidong Zhai, Delu Pan, Minhan Dai, Peisong Yu
      Pages: n/a - n/a
      Abstract: While satellite remote sensing has become a very useful tool contributing to assessments of sea surface partial pressure of carbon dioxide (pCO2) that subsequently allow quantification of air‐sea CO2 flux, the application of empirical approaches in coastal oceans has proven challenging owing to the interaction of multiple controlling factors. We propose a “mechanistic semi‐analytic algorithm” (MeSAA) to estimate sea surface pCO2 in river‐dominated coastal oceans using satellite data. Observed pCO2 can be analytically expressed as the sum of individual components controlled by major factors such as thermodynamics (or temperature), mixing, and biology. With marine carbonate system calculations, temperature and mixing effects can be predicted using thermodynamic principles and by assuming conservative two end‐member mixing of total dissolved inorganic carbon and total alkalinity (e.g. the Changjiang River and Kuroshio water in the East China Sea, ECS). Next, an integral expression for pCO2 drawdown due to biological effects can be parameterized using the chlorophyll a concentration (chla). We demonstrate the validity and applicability of the algorithm in the ECS during summertime. Sensitivity analysis shows that errors in empirical coefficients and three input satellite parameters (salinity, SST, chla) have limited influence on the algorithm, and satellite‐derived pCO2 is consistent with underway data, even though no in situ pCO2 data from the ECS shelves was used to train the algorithm. Our algorithm has more physical and biogeochemical mechanistic meaning than empirical methods, and should be applicable to other similar systems. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-02T14:16:29.790285-05:
      DOI: 10.1002/2014JC010632
       
  • Assessment of the upper‐ocean mixed layer parameterizations using a
           large eddy simulation model
    • Authors: Naoki Furuichi; Toshiyuki Hibiya
      Pages: n/a - n/a
      Abstract: A large eddy simulation (LES) of the upper ocean mixed layer processes in the winter northwestern Pacific is carried out and compared with concurrent microstructure measurements. We find that dissipation rates of turbulent kinetic energy (ε) and temperature variance from LES agree well with field observations in the areas where the Ozmidov length scale, calculated from the modeled ε and buoyancy frequency, exceeds the grid size of LES. It is also found that, even though the Ozmidov length scale is less than the grid size of LES, model estimates of the vertical turbulent heat flux near the base of the mixed layer are very similar to observed values, suggesting that this LES model reproduces the intensity of entrainment well. This enables us to use the results from LES to assess the turbulence closure models of Mellor and Yamada [1982, MY] and Nakanishi and Niino [2009, NN] for several forcing scenarios consisting of strong winds, surface heating, and surface cooling. It is found that NN performs better than MY in reproducing the results from LES for each forcing scenario, particularly when the turbulent length scale is adjusted to be more restricted by density stratification. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-02T14:16:19.774068-05:
      DOI: 10.1002/2014JC010665
       
  • Response of Arctic Ocean stratification to changing river runoff in a
           column model
    • Authors: Aleksi Nummelin; Camille Li, Lars H. Smedsrud
      Pages: n/a - n/a
      Abstract: A 1‐dimensional model of the atmosphere‐ice‐ocean column is used to study the effects of changing river runoff to the Arctic Ocean. River runoff is the largest contributor of freshwater to the Arctic and is expected to increase as the hydrological cycle accelerates due to global warming. The column model simulates the stratification of the Arctic Ocean reasonably well, capturing important features such as the fresh surface layer, the salty cold halocline, and the temperature maximum within the Atlantic Water layer. The model is run for 500 years with prescribed boundary conditions to reach steady‐state solutions. Increasing river runoff is found to strengthen the stratification and to produce a fresher and shallower surface mixed layer with warming (up to ∼1C for a doubling of present day runoff) in the Atlantic Water layer below. An important consequence is that the effect of the larger vertical temperature gradient is able to balance that of the stronger stratification and yield a close to constant vertical heat flux towards the surface. As a result the sea ice response is small, showing only slight increase (up to ∼15cm for a doubling of present day runoff) in annual mean ice thickness. Limitations of the study include the idealized nature of the column model and uncertainties in the background vertical mixing within the Arctic Ocean. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-02T14:15:32.858082-05:
      DOI: 10.1002/2014JC010571
       
  • Argo data assimilation and its effect on climate state estimation and
           forecasting in the western North Pacific using a coupled model
    • Authors: Shiro Nishikawa; Yoichi Ishikawa, Shuhei Masuda, Yoshihisa Hiyoshi, Yuji Sasaki, Hiromichi Igarashi
      Pages: n/a - n/a
      Abstract: In this study, we investigated the effects of ocean subsurface data (Argo data) on climate state estimation and forecasting, focusing on the reproduction of North Pacific subtropical mode water (STMW) using a four‐dimensional variational data assimilation system with a coupled model. We produced two reanalysis plus forecast datasets for the ocean and atmosphere in 2010 using a 3‐month assimilation period: the first including Argo data (Argo case) and the second did not include Argo data (control case). In the control case, the Kuroshio, Kuroshio Extension front, and recirculation gyres along the front were not adequately reproduced. Consequently, there were large biases in temperature and salinity in the western North Pacific. The assimilation of Argo data effectively corrected these biases and significantly improved reproduction of the Kuroshio fronts and recirculation gyres, resulting in a more realistic reproduction of the winter mixed layer and STMW. The correction of these biases is critical to the 1–3‐year predictions of the STMW core properties, and the assimilation of Argo data enables prediction of these properties for more than a year. We showed that assimilation of Argo data affects the surface atmospheric temperature above the STMW formation region. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-02T14:11:47.290814-05:
      DOI: 10.1002/2014JC010095
       
  • Recent accelerated warming of the continental shelf off New Jersey:
           Observations from the CMV Oleander XBT line
    • Authors: J. Forsyth; M. Andres, G.G. Gawarkiewicz
      Pages: n/a - n/a
      Abstract: Expendable bathythermographs (XBTs) have been launched along a repeat track from New Jersey to Bermuda from the CMV Oleander through the NOAA/NEFSC Ship of Opportunity Program about 14 times per year since 1977. The XBT temperatures on the Middle Atlantic Bight (MAB) shelf are binned with 10km horizontal and 5m vertical resolution to produce monthly, seasonally and annually‐averaged cross‐shelf temperature sections. The depth‐averaged shelf temperature, Ts, calculated from annually‐averaged sections that are spatially‐averaged across the shelf, increases at 0.026 ± 0.001 ˚C yr−1 from 1977‐2013, with the recent trend substantially larger than the overall 37‐year trend (0.11 ± 0.02 ˚C yr−1 since 2002). The Oleander temperature sections suggest that the recent acceleration in warming on the shelf is not confined to the surface, but occurs throughout the water column with some contribution from interactions between the shelf and the adjacent Slope Sea reflected in cross‐shelf motions of the shelfbreak front. The local warming on the shelf cannot explain the region's amplified rate of sea level rise relative to the global mean. Additionally, Ts exhibits significant interannual variability with the warmest anomalies increasing in intensity over the 37‐year record even as the cold anomalies remain relatively uniform throughout the record. Ts anomalies are not correlated with annually‐averaged coastal sea level anomalies at zero lag. However, positive correlation is found between 2‐year lagged Ts anomalies and coastal sea level anomalies, suggesting that the region's sea level anomalies may serve as a predictor of shelf temperature. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-02T14:11:36.77134-05:0
      DOI: 10.1002/2014JC010516
       
  • Bottom‐pressure signature of annual baroclinic Rossby waves in the
           northeast tropical Pacific Ocean
    • Authors: Christopher G. Piecuch
      Pages: n/a - n/a
      Abstract: The annual cycle in bottom pressure (pb) in the northeast tropical Pacific Ocean (NTPO) is studied. Focus is on a zonal section along 12∘N between 105–145∘W that is characterized by a strong annual cycle in sea level from satellite altimetry. Estimates of pb from the Gravity Recovery and Climate Experiment (GRACE), a state estimate produced by the Estimating the Circulation and Climate of the Ocean (ECCO) consortium, and a linear Rossby wave model (LRWM) are used. The GRACE NTPO pb annual cycle shows amplitudes as large as 1cm water equivalent. The GRACE data also evidence westward propagation that is consistent with the behavior of long mode‐1 Rossby waves at this latitude, with phase increasing from east to west at a rate of ∼0.34m s– 1. The ECCO and LRWM pb estimates corroborate the notion that GRACE reveals the pb signature of annual Rossby waves driven by interior wind stress curl and possibly damped by frictional processes. Results have implications for attempts to constrain global ocean mass using a single point mooring. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-02T14:11:04.102414-05:
      DOI: 10.1002/2014JC010667
       
  • Turbulent nitrate fluxes in the Lower St. Lawrence Estuary (Canada)
    • Authors: Frédéric Cyr; Daniel Bourgault, Peter S. Galbraith, Michel Gosselin
      Pages: n/a - n/a
      Abstract: Turbulent vertical nitrate fluxes were calculated using new turbulent microstructure observations in the Lower St. Lawrence Estuary (LSLE), Canada. Two stations were compared: the head of the Laurentian Channel (HLC), where intense mixing occurs on the shallow sill that marks the upstream limit of the LSLE, and another station located about 100 km downstream (St. 23), more representative of the LSLE mean mixing conditions. Mean turbulent diffusivities and nitrate fluxes at the base of the surface layer for both stations were respectively (with 95% confidence intervals): ,, , and . Observations suggest that the interplay between large isopleth heaving near the sill and strong turbulence is the key mechanism to sustain such high turbulent nitrate fluxes at the HLC (two to three orders of magnitude higher than those at Station 23). Calculations also suggest that nitrate fluxes at the HLC alone can sustain primary production rates of 3.4(0.6, 11) g Cm−2 mo−1 over the whole LSLE, approximately enough to account for a large part of the phytoplankton bloom and for most of the post‐bloom production. Surfacing nitrates are also believed to be consumed within the LSLE, not leaving much to be exported to the rest of the Gulf of St. Lawrence. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-26T10:46:32.186764-05:
      DOI: 10.1002/2014JC010272
       
  • Along‐isopycnal variability of spice in the North Pacific
    • Authors: Jody M. Klymak; William Crawford, Matthew H. Alford, Jennifer A. MacKinnon, Robert Pinkel
      Pages: n/a - n/a
      Abstract: Two hydrographic surveys in the Gulf of Alaska and the North Pacific subtropical gyre are presented. Both surveys are roughly perpendicular to lateral temperature gradients, and were collected in the summer when there was a shallow mixed layer and a seasonal thermocline. Isopycnal displacements and horizontal velocities are dominated by internal waves. Spice anomalies along isopycnals are examined to diagnose lateral stirring mechanisms. The spectra of spice anomaly gradients along near‐surface isopycnals roughly follow power laws of (variance spectra power laws of ), and in most cases the spectra become redder at depth. The near‐surface spectra are possibly consistent with the predictions of quasigeostrophic turbulence theory (when surface buoyancy effects are accounted for), but the spectra at depth are inconsistent with any quasi‐geostrophic theory. Probability distributions of spice gradients exhibit a large peak at low gradients and long tails for large gradients, symptomatic of fronts. Vertical coherence of the spice signal falls off with a decorrelation depth scale that has a maximum of about 80 m at 100‐ km wavelengths and depends on horizontal wavelength with a power law of approximately . Lateral decorrelation length scales are 20‐40 km, close to the baroclinic Rossby radius. Lateral stirring occurs over large scales, with average lateral displacements of about 200 km in the upper 75 m, decreasing to 100 km at greater depths. The depth variation of the statistics indicates that time history of tracer stirring on each isopycnal is important, or that there are unconsidered depth‐dependent stirring mechanisms. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-25T07:49:55.731256-05:
      DOI: 10.1002/2013JC009421
       
  • Characteristics of the meltwater field from a large Antarctic iceberg
           using δ18O
    • Authors: John J. Helly; Maria Vernet, Alison Murray, Gordon R. Stephenson
      Pages: n/a - n/a
      Abstract: Large tabular icebergs represent a disruptive influence on a stable water column when drifting in the open ocean. This is a study of one iceberg, C18A, encountered in the Powell Basin in the Weddell Sea in March, 2009, formed from iceberg C18 (76 × 7 km) originating from the Ross Ice Shelf in May, 2002. C18A was lunate in shape with longest dimensions of 31 km × 7 km × 184 m. The meltwater field from C18A was characterized using δ18O from water samples collected near C18A (Near‐field, 0.4‐2 km) and contrasted with a Far‐field comprised of samples from an Away site (19 km from C18A), a Control site (70 km away) and a region populated with small icebergs (Iceberg Alley, 175 km away). The in‐sample fractions of meteoric water were calculated relative δ18O in iceberg ice and Weddell Deep Water and converted to meteoric water height (m) and a percentage within 100 m depth‐bins. The the Near‐field and Far‐fielddifference from surface to 200 m was 0.51±0.28%. The concentration of meteoric water dropped to approximately half that value below 200 m, approximate keel depth of the iceberg, although detectable to 600 m. From surface to 600 m, the overall difference was statistically significant (P  
      PubDate: 2015-02-25T06:24:19.651993-05:
      DOI: 10.1002/2015JC010772
       
  • Intraseasonal sea surface salinity variability in the equatorial
           Indo‐Pacific Ocean induced by Madden‐Julian oscillations
    • Authors: Yuanlong Li; Weiqing Han, Tong Lee
      Pages: n/a - n/a
      Abstract: Intraseasonal sea surface salinity (SSS) variability in the equatorial Indo‐Pacific Ocean is investigated using the Aquarius/SAC‐D satellite measurements and Hybrid Coordinate Ocean Model (HYCOM). Large‐scale SSS variations at 20‐90 day timescales induced by Madden‐Julian oscillations (MJOs) are prominent in the central‐to‐eastern Indian Ocean (IO) and western Pacific Ocean (PO) with a standard deviation of ∼0.15 psu. The relationship between SSS anomaly and freshwater flux is nearly in phase in the central‐to‐eastern IO and out of phase in the western PO during a MJO cycle. A series of HYCOM experiments are performed to explore the causes for SSS variability. In most areas of the equatorial Indo‐Pacific Ocean, wind stress‐forced ocean dynamical processes act as the main driver of intraseasonal SSS, while precipitation plays a secondary role. In some areas of the western PO and western IO, however, precipitation effect is the leading contributor. In comparison, evaporation effect induced by radiation and wind speed changes is generally much smaller. Besides the external forcing by MJOs, ocean internal variability can also cause considerable intraseasonal SSS changes, explaining 10%‐20% of the total variance in some regions. Composite analysis for MJO events reveals that the effects of wind stress, precipitation, and evaporation vary at different phases of a MJO cycle. The MJO‐induced SSS signature is the result of complicated superimposition and interaction of these effects. The effect of wind stress also varies significantly from event to event. It affects SSS variability primarily through horizontal ocean current advection and to a lesser extent through vertical entrainment. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-25T06:07:09.427211-05:
      DOI: 10.1002/2014JC010647
       
  • Thermodynamic sea ice growth in the central Weddell Sea, observed in
           upward‐looking sonar data
    • Authors: A. Behrendt; W. Dierking, H. Witte
      Pages: n/a - n/a
      Abstract: Upward‐looking sonar (ULS) data were used to analyse thermodynamic sea ice growth. The study was carried out for an ocean region in the central Weddell Sea, for which data of sea ice thickness variability and of the oceanic heat flux through the ice are rare. In the study area the contribution of sea ice deformation to vertical ice growth is relatively small in some years. This provides the opportunity to simulate thermodynamic sea ice growth considering the influence of a snow cover and of the oceanic heat flux. To this end, a modified version of Stefan's Law was used. The resulting ice thickness variations were then compared with the ULS measurements. For the investigated cases, the best consistency between data and model results was obtained assuming a snow layer of less than 5cm thickness and average oceanic heat fluxes between 6 and 14 W m−2. It is demonstrated that in conjunction with ice drift data and analytical models for thermal sea ice growth, ULS ice thickness measurements are useful for studying the seasonal cycle of growth and decay, and for inferring the magnitude of the average oceanic heat flux under sea ice. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-25T03:47:43.076434-05:
      DOI: 10.1002/2014JC010408
       
  • Heat balances and thermally driven lagoon‐ocean exchangeson a
           tropical coral reef system (Moorea, French Polynesia)
    • Authors: Liv M. M. Herdman; James L. Hench, Stephen G. Monismith
      Pages: n/a - n/a
      Abstract: The role of surface and advective heat fluxes on buoyancy‐driven circulation was examined within a tropical coral reef system. Measurements of local meteorological conditions as well as water temperature and velocity were made at six lagoon locations for 2 months during the austral summer. We found that temperature rather than salinity dominated buoyancy in this system. The data were used to calculate diurnally phase‐averaged thermal balances. A one‐dimensional momentum balance developed for a portion of the lagoon indicates that the diurnal heating pattern and consistent spatial gradients in surface heat fluxes create a baroclinic pressure gradient that is dynamically important in driving the observed circulation. The baroclinic and barotropic pressure gradients make up 90% of the momentum budget in part of the system; thus, when the baroclinic pressure gradient decreases 20% during the day due to changes in temperature gradient, this substantially changes the circulation, with different flow patterns occurring during night and day. Thermal balances computed across the entire lagoon show that the spatial heating patterns and resulting buoyancy‐driven circulation are important in maintaining a persistent advective export of heat from the lagoon and for enhancing ocean‐lagoon exchange.
      PubDate: 2015-02-25T01:47:20.051917-05:
      DOI: 10.1002/2014JC010145
       
  • Anomalous chlorofluorocarbon uptake by mesoscale eddies in the Drake
           Passage region
    • Authors: Hajoon Song; John Marshall, Peter Gaube, Dennis J. McGillicuddy
      Pages: n/a - n/a
      Abstract: The role of mesoscale eddies in the uptake of anthropogenic chlorofluorocarbon‐11 (CFC‐11) gas is investigated with a 1/20° eddy‐resolving numerical ocean model of a region of the Southern Ocean. With a relatively fast air‐sea equilibrium time scale (about a month), the air‐sea CFC‐11 flux quickly responds to the changes in the mixed layer CFC‐11 partial pressure (pCFC‐11). At the mesoscale, significant correlations are observed between pCFC‐11 anomaly, anomalies in sea surface temperature (SST), net heat flux, and mixed layer depth. An eddy‐centric analysis of the simulated CFC‐11 field suggests that anticyclonic warm‐core eddies generate negative pCFC‐11 anomalies and cyclonic cold‐core eddies generate positive anomalies of pCFC‐11. Surface pCFC‐11 is modulated by mixed layer dynamics in addition to CFC‐11 air‐sea fluxes. A negative cross correlation between mixed layer depth and surface pCFC‐11 anomalies is linked to higher CFC‐11 uptake in anticyclones and lower CFC‐11 uptake in cyclones, especially in winter. An almost exact asymmetry in the air‐sea CFC‐11 flux between cyclones and anticyclones is found.
      PubDate: 2015-02-23T22:25:53.899918-05:
      DOI: 10.1002/2014JC010292
       
  • Modeling skin‐layer salinity with an extended surface‐salinity
           layer
    • Authors: Y. Tony Song; Tong Lee, Jae‐Hong Moon, Tangdong Qu, Simon Yueh
      Pages: n/a - n/a
      Abstract: Due to near‐surface salinity stratification, it is problematic to compare satellite‐measured surface salinity within the first few centimeters (skin‐layer) of the ocean with Argo‐measured top‐level salinity at about 5 m or with ocean models that do not resolve the skin layer. Although an instrument can be designed to measure the surface salinity, a global scale measurement is currently not available. A regional model can be configured to have a vertical grid in centimeters but it would be computationally prohibited on a global scale due to time step constraints. Here we propose an extended surface‐salinity layer (ESSL) within a global ocean circulation model to diagnose skin SSS without increasing the computational cost, while allowing comparable solutions with both satellite and Argo salinity at the respective depths. Using a quarter‐degree global ocean model, we show that the ESSL improves near‐surface salinity significantly in comparisons with the Aquarius SSS and Argo salinity at 5 and 10 m, respectively. Comparing with data‐assimilated HYCOM results reveal that the ESSL provides much stronger seasonal variability of SSS, similar to the Aquarius observations. We also demonstrate that the ESSL solution can be used to constrain the global mean SSS in Aquarius SSS retrieval.
      PubDate: 2015-02-23T03:47:16.025688-05:
      DOI: 10.1002/2014JC010346
       
  • Investigation of interbasin exchange and interannual variability in Lake
           Erie using an unstructured‐grid hydrodynamic model
    • Authors: Qianru Niu; Meng Xia, Edwards Rutherford, Doran Mason, Eric J. Anderson, David J. Schwab
      Pages: n/a - n/a
      Abstract: Inter‐basin exchange and interannual variability in Lake Erie's three basins are investigated with the help of a three‐dimensional unstructured‐grid based Finite Volume Coastal Ocean Model (FVCOM). Experiments were carried out to investigate the influence of grid resolutions and different sources of wind forcing on the lake dynamics. Based on the calibrated model, we investigated the sensitivity of lake dynamics to major external forcing, and seasonal climatological circulation patterns are presented and compared with the observational data and existing model results. It was found that water exchange between the western basin (WB) and the central basin (CB) was mainly driven by hydraulic and density‐driven flows, while density‐driven flows dominate the interaction between the CB and the eastern basin (EB). River‐induced hydraulic flows magnify the eastward water exchange and impede the westward one. Surface wind forcing shifts the pathway of hydraulic flows in the WB, determines the gyre pattern in the CB, contributes to thermal mixing, and magnifies inter‐basin water exchange during winter. Interannual variability is mainly driven by the differences in atmospheric forcing, and is most prominent in the CB. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-20T16:08:22.332516-05:
      DOI: 10.1002/2014JC010457
       
  • On the eastward shift of winter surface chlorophyll‐a bloom peak in
           the Bay of Bengal
    • Authors: M. V. Martin; C. Shaji
      Pages: n/a - n/a
      Abstract: Analysis of satellite‐derived surface layer phytoplankton chlorophyll‐a concentration (Chl‐a) in the Bay of Bengal revealed an eastward shift of peak of Chl‐a bloom during northeast monsoon period (November‐March) from western to the eastern Bay. The winter Chl‐a bloom in the western Bay is shorter duration (∼1‐2 months) while that in the eastern Bay is longer duration (∼3‐4 months). Unlike other oceans, the eastward bloom shift found in the Bay of Bengal is opposite to the direction of propagation of Rossby wave and seasonal mean zonal currents. During winter, sufficient light is available in the Bay of Bengal for phytoplankton growth. Herein, we studied the processes controlling the eastward winter bloom shift and the zonal depiction of bloom duration in the Bay of Bengal. There is no single dominant process that drives the eastward bloom shift everywhere in the Bay of Bengal. Rather, different physical processes operate in different regions. The physical mechanisms governing the eastward winter Chl‐a bloom shift reported here include open ocean Ekman pumping, coastal upwelling, upwelling driven by Rossby wave, wind induced vertical mixing, nutrients supply from river input, and westward advection through prevailing zonal currents. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-20T16:08:11.760274-05:
      DOI: 10.1002/2014JC010162
       
  • Shoreline variability from days to decades: Results of long‐term
           video imaging
    • Authors: C. Pianca; R. Holman, E. Siegle
      Pages: n/a - n/a
      Abstract: The present work characterizes the time‐space scales of variability and forcing dependencies of a unique 26‐year record of daily to hourly shoreline data from a steep beach at Duck, North Carolina. Shoreline positions over a 1500m alongshore span were estimated using a new algorithm called ASLIM based on fitting the band of high light intensity in time exposure images to a local Gaussian fit, with a subsequent Kalman filter to reduce noise and uncertainty. Our findings revealed that the shoreline change at long times scales dominates seasonal variability, despite that wave forcing had only 2\% variance at inter‐annual frequencies. The shoreline response presented 66\% of the variance at inter‐annual scales. These results were not expected since from wave forcing it would have expected that the shoreline response should similarly lack inter‐annual variability, but we found it to be dominated by this scale. The alongshore‐mean shoreline time series revealed no significant annual cycle. However, there are annual oscillations in the shoreline response that are coherent with wave forcing and deserves further explanations. The pier was found to have a significant influence on shoreline behavior since restricts the seasonal longshore transport between the sides, resulting in a seasonally‐reversing sediment accumulation. Thus, there is a significant annual peak in shoreline variability that is coherent with the annual forcing but becomes insignificant in the longshore‐average. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-20T16:05:30.520333-05:
      DOI: 10.1002/2014JC010329
       
  • A vertical gradient of nitrous oxide below the subsurface of the Canada
           Basin and its formation mechanisms
    • Authors: Liyang Zhan; Liqi Chen, Jiexia Zhang, Yuhong Li
      Pages: n/a - n/a
      Abstract: The ocean is regarded as a significant source of N2O, which is an ozone depleting greenhouse gas. However, the contribution of the Arctic Ocean to the global N2O budget is not yet known. Herein, the first observations of N2O concentrations in the Canada Basin (CB) and Greenland Sea Basin (GSB) are presented. A correlation between the historic atmospheric N2O record and N2O concentrations at the corresponding depth in the GSB suggests that the N2O distribution pattern is dominated by air‐sea exchanges and hydrographic processes in this region. The consistency between the observed N2O concentrations in the CB and calculated results based on the above correlation suggest that the N2O concentrations in the CB are most likely dominated by N2O dynamics and subsequent hydrographic processes in the sea adjacent to the GSB. The N2O concentration in the Canada Basin Intermediate Water (CBIW) reflects anthropogenic influences, whereas the N2O concentration in the Canada Basin Deep Water (CBDW) suggests that the CBDW may be a preindustrial “relict”. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-20T16:05:14.978946-05:
      DOI: 10.1002/2014JC010337
       
  • Spectral characterization of fine‐scale wind waves using shipboard
           optical polarimetry
    • Authors: Nathan J. M. Laxague; Brian K. Haus, Darek Bogucki, Tamay Özgökmen
      Pages: n/a - n/a
      Abstract: Fine‐scale sea surface waves are of profound importance to a number of air‐sea interaction processes. Due to a number of reasons, there exists a great degree of difficulty in obtaining quality in situ observations of these waves. This paper presents the application of a shipboard wave‐sensing method towards the following quantifications: regime‐specific contribution to sea surface slope and sensitivity to wind speed increases. Measurements were made via polarimetric camera, resolving waves with wavelengths ranging from 0.21 m to 0.003 m (30 rad/m 
      PubDate: 2015-02-20T03:54:30.756186-05:
      DOI: 10.1002/2014JC010403
       
  • Ocean salinity changes in the northwest Pacific subtropical gyre: The
           quasi‐decadal oscillation and the freshening trend
    • Authors: Feng Nan; Fei Yu, Huijie Xue, Ran Wang, Guangcheng Si
      Pages: n/a - n/a
      Abstract: Ocean salinity changes play an important role in modulating ocean and climate variability. Analyses of the repeating observations along PN, TK, and 137º E sections reveal that both surface and subsurface salinity in the Northwest Pacific Subtropical Gyre (NPSG) had clear quasi‐decadal oscillation (QDO) of ∼10‐year and a sustained freshening trend during 1987‐2012. Surface salinity in the NPSG troughed in 1989, 1999, and 2008, and peaked in 1993, and 2003. The peak‐to‐tough range of surface salinity oscillation can reach 0.3 psu. Meanwhile, surface salinity decreased about 0.10 psu from 1987 to 2012 with a freshening trend of ‐0.0042 psu yr−1. These surface salinity anomalies were subducted into the subsurface layer mainly in the ventilated zone along the Kuroshio Extension, and advected over the NPSG. The QDO of the subsurface salinity maximum (Smax) lagged that of the surface salinity by about 1∼2 years. Both the peak‐to‐tough range of the Smax oscillation (0.15 psu) and its freshening trend (‐0.0036 psu yr−1) are smaller than those of the surface salinity. Salinity changes in the NPSG likely began in the mid‐1970s associated with the North Pacific regime shift during 1976/77. Analyses of mixed layer salinity budget indicated that air‐sea freshwater flux change in the NPSG is the leading factor controlling the surface salinity anomalies, while change of large‐scale ocean circulation (Geostrophic advection) also plays a minor role. Salinity and air‐sea freshwater flux changes in the NPSG are all closely related to the Pacific Decadal Oscillation, indicating the large‐scale ocean‐atmosphere interaction. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-20T03:41:34.342954-05:
      DOI: 10.1002/2014JC010536
       
  • Short wind waves on the ocean: Wave number‐frequency spectra
    • Authors: William J. Plant
      Pages: n/a - n/a
      Abstract: Dominant surface waves on the ocean exhibit a dispersion relation that confines their energy to a curve in a wavenumber‐frequency spectrum. Short wind waves on the ocean, on the other hand, are advected by these dominant waves so that they do not exhibit a well defined dispersion relation over many realizations of the surface. Here we show that the short‐wave analog to the dispersion relation is a distributed spectrum in the wavenumber‐frequency plane that collapses to the standard dispersion relation in the absence of long waves. We compute probability distributions of short‐wave wavenumber given a [frequency, direction] pair and of short‐wave frequency given a [wavenumber, direction] pair. These two probability distributions must yield a single spectrum of surface displacements as a function of wavenumber and frequency, F(k,f). We show that the folded, azimuthally averaged version of this spectrum has a “butterfly” pattern in the wavenumber‐frequency plane if significant long waves are present. Integration of this spectrum over frequency yields the well‐known k−3 wavenumber spectrum. When integrated over wavenumber, the spectrum yields an f−4 form that agrees with measurement. We also show that a cut through the unfolded F(k,f) at constant k produces the well‐known form of moderate‐incidence‐angle Doppler spectra for electromagnetic scattering from the sea. This development points out the dependence of the short‐wave spectrum on the amplitude of the long waves. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-20T00:05:28.484172-05:
      DOI: 10.1002/2014JC010586
       
  • Summer upwelling and thermal fronts in the northwestern South China Sea:
           Observational analysis of two mesoscale mapping surveys
    • Authors: Zhiyou Jing; Yiquan Qi, Yan Du, Shuwen Zhang, Lingling Xie
      Pages: n/a - n/a
      Abstract: Persistent coastal upwelling and upwelling‐induced thermal fronts in the northwestern South China Sea are investigated using satellite measurements, two intensive mesoscale mapping surveys and three bottom‐mounted ADCPs. The results indicate that pronounced surface cooling and upwelling‐related fronts with a width of 20‐50 km occur around Hainan Island and persist through the summer upwelling season. Driven by the prevailing southwesterly monsoon, the subsurface cooling band is ~6°C colder than the water offshore of the East Coast, where the thermal gradients are generally more than 0.1°C/km. The cold and nutrient‐rich coastal water is identified to be derived primarily from the deep water of the outer shelf. At the same time, the spatial structure of the upwelling and thermal front, as well as the upwelling‐related coastal currents, are significantly regulated by wind forcing. A prominent lagged correlation between the moored temperature records and alongshore wind stress is detected in the East Coast. The correlation coefficient is ‐0.8 with the temperature lagging behind wind stress by 2.2 days, indicating that the cooling band off the East Coast is dominated mostly by the alongshore southwesterly monsoon during the upwelling season. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-19T10:47:56.138641-05:
      DOI: 10.1002/2014JC010601
       
  • On the coefficients of small eddy and surface divergence models for the
           air‐water gas transfer velocity
    • Authors: Binbin Wang; Qian Liao, Joseph H. Fillingham, Harvey A. Bootsma
      Pages: n/a - n/a
      Abstract: Recent studies suggested that under low to moderate wind conditions without bubble entraining wave breaking, the air‐water gas transfer velocity k+ can be mechanistically parameterized by the near‐surface turbulence, following the small eddy model (SEM). Field measurements have supported this model in a variety of environmental forcing systems. Alternatively, surface divergence model (SDM) has also been shown to predict the gas transfer velocity across the air‐water interface in laboratory settings. However, the empirically determined model coefficients (α in SEM and c1 in SDM) scattered over a wide range. Here we present the first field measurement of the near‐surface turbulence with a novel floating PIV system on Lake Michigan, which allows us to evaluate the SEM and SDM in situ in the natural environment. k+ was derived from the CO2 flux that was measured simultaneously with a floating gas chamber. Measured results indicate that α and c1 are not universal constants. Regression analysis showed that α ~ log(ε) while the near surface turbulence dissipation rate ε is approximately greater than 10–6 m2s–3 according to data measured for this study as well as from other published results measured in similar environments or in laboratory settings. It also showed that α scales linearly with the turbulent Reynolds number. Similarly, coefficient c1 in the SDM was found to linearly scale with the Reynolds number. These findings suggest that larger eddies are also important parameters, and the dissipation rate in the SEM or the surface divergence β’ in the SDM alone may not be adequate to determine k+ completely. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-19T10:47:12.311951-05:
      DOI: 10.1002/2014JC010253
       
  • Physical and biogeochemical mechanisms of internal carbon cycling in Lake
           Michigan
    • Authors: Darren J. Pilcher; Galen A. McKinley, Harvey A. Bootsma, Val Bennington
      Pages: n/a - n/a
      Abstract: The lakewide seasonal carbon cycle of Lake Michigan is poorly quantified and lacks the mechanistic links necessary to determine impacts upon it from eutrophication, invasive species, and climate change. A first step towards a full appreciation of Lake Michigan's carbon cycle is to quantify the dominant mechanisms of its internal carbon cycle. To achieve this, we use the MIT general circulation model configured to the bathymetry of Lake Michigan and coupled to an ecosystem model to simulate the seasonal cycle of productivity, temperature, circulation, and the partial pressure of CO2 in water (pCO2). This biogeochemistry is designed to be appropriate for the pre‐quagga mussel state of the lake. The primary mechanism behind the seasonal cycle of primary productivity is lake physics. The offshore spring phytoplankton bloom begins following a reduction in deep vertical mixing and ends with the depletion of nutrients via thermal stratification. The exception is the western shoreline, where summer winds drive coastal upwelling, providing hypolimnetic nutrients and generating significant productivity. Surface pCO2 is controlled by the net effect from temperature on solubility, and is modulated by biological uptake of dissolved inorganic carbon (DIC) and isothermal mixing of DIC‐rich water in winter. Temperature tends to have the greatest seasonal impact in nearshore regions, while local DIC has the greatest impact in offshore regions. Lakewide, the model suggests that carbon is absorbed from the atmosphere during the spring bloom and released to the atmosphere during winter mixing and when summer surface temperatures are at their maximum. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-18T11:28:17.460134-05:
      DOI: 10.1002/2014JC010594
       
  • Structure of turbulence and sediment stratification in
           wave‐supported mud layers
    • Authors: A. Hooshmand; A. R. Horner‐Devine, M. P. Lamb
      Pages: n/a - n/a
      Abstract: We present results from laboratory experiments in a wave flume with and without a sediment bed to investigate the turbulent structure and sediment dynamics of wave‐supported mud layers. The presence of sediment on the bed significantly alters the structure of the wave boundary layer relative to that observed in the absence of sediment, increasing the TKE by more than a factor of three at low wave orbital velocities and suppressing it at the highest velocities. The transition between the low and high velocity regimes occurs when Re∆ ≃ 450, where Re∆ is the Stokes Reynolds number. In the low velocity regime (Re∆ < 450) the flow is significantly influenced by the formation of ripples, which enhances the TKE and Reynolds stress, and increases the wave boundary layer thickness. In the high velocity regime (Re∆ > 450) the ripples are significantly smaller, the near‐bed sediment concentrations are significantly higher and density stratification due to sediment becomes important. In this regime the TKE and Reynolds stress are lower in the sediment bed runs than in comparable runs with no sediment. The regime transition at Re∆ = 450 appears to result from washout of the ripples and increased concentrations of fine sand suspended in the boundary layer, which increases the settling flux and the stratification near the bed. The increased stratification damps turbulence, especially near the top of the high concentration layer, reducing the layer thickness. We anticipate that these effects will influence the transport capacity of wave‐supported gravity currents on the continental shelf. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-18T11:27:54.955232-05:
      DOI: 10.1002/2014JC010231
       
  • Nutrient supply and biological response to wind‐induced mixing,
           
    • Authors: Shigeto Nishino; Yusuke Kawaguchi, Jun Inoue, Toru Hirawake, Amane Fujiwara, Ryosuke Futsuki, Jonaotraro Onodera, Michio Aoyama
      Pages: n/a - n/a
      Abstract: A fixed‐point observation station was set up in the northern Chukchi Sea during autumn 2013, and for about 2 weeks conductivity‐temperature‐depth (CTD)/water samplings (6‐hourly) and microstructure turbulence measurements (two to three times a day) were performed. This enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity. There have been no such fixed‐point observations in this region, where incoming low‐salinity water from the Pacific Ocean, river water, and sea‐ice meltwater promote a strong pycnocline (halocline) that stabilizes the water column. Previous studies have suggested that because of the strong pycnocline wind‐induced ocean mixing could not change the stratification to impact biological activity. However, the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind‐induced inertial motion and turbulent mixing caused by intense gale‐force winds (>10 m s‐1) did result in increases in upward nutrient fluxes, primary productivity, and phytoplankton biomass, particularly large phytoplankton such as diatoms. Convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there. For diatom production at the fixed‐point observation station, it was essential that silicate was supplied from a subsurface silicate maximum, a new feature that we identified during autumn in the northern Chukchi Sea. Water mass distributions obtained from wide‐area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the Canada Basin. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-18T11:22:47.687857-05:
      DOI: 10.1002/2014JC010407
       
  • Large icebergs characteristics from altimeter waveforms analysis
    • Authors: J. Tournadre; N. Bouhier, F. Girard‐Ardhuin, F. Remy
      Pages: n/a - n/a
      Abstract: Large uncertainties exist on the volume of ice transported by the Southern Ocean large icebergs, a key parameter for climate studies, because of the paucity of information, especially on iceberg thickness. Using icebergs tracks from the National Ice Center (NIC) and Brigham Young University (BYU) databases to select altimeter data over icebergs and a method of analysis of altimeter waveforms, a database of 5366 icebergs freeboard elevation, length and backscatter covering the 2002‐2012 period has been created. The database is analyzed in terms of distributions of freeboard, length and backscatter showing differences as a function of the iceberg's quadrant of origin. The database allows to analyze the temporal evolution of icebergs and to estimate a melt rate of 35 to 39 m/yr– 1 (neglecting the firn compaction). The total daily volume of ice, estimated by combining the NIC and altimeter sizes and the altimeter freeboards, regularly decreases from 2.2 104km3 in 2002 to 0.9 104km3 in 2012. During this decade, the total loss of ice (~ 1,800km3) is twice as large as than the input (~ 960km3) showing that the system is out of equilibrium after a very large input of ice between 1997 and 2002. Breaking into small icebergs represents 80% (~ 1,500km3) of the total ice loss while basal melting is only 18% (~ 320km3). Small icebergs are thus the major vector of freshwater input in the Southern Ocean. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-18T11:22:37.459056-05:
      DOI: 10.1002/2014JC010502
       
  • Eddy‐driven sediment transport in the Argentine Basin: Is the height
           of the Zapiola Rise hydrodynamically controlled?
    • Authors: Wilbert Weijer; Mathew E. Maltrud, William B. Homoky, Kurt L. Polzin, Leo R. M. Maas
      Pages: n/a - n/a
      Abstract: In this study we address the question whether eddy‐driven transports in the Argentine Basin can be held responsible for enhanced sediment accumulation over the Zapiola Rise, hence accounting for the existence and growth of this sediment drift. To address this question, we perform a 6‐year simulation with a strongly eddying ocean model. We release two passive tracers, with settling velocities that are consistent with silt and clay size particles. Our experiments show contrasting behavior between the silt fraction and the lighter clay. Due to its larger settling velocity, the silt fraction reaches a quasi‐steady state within a few years, with abyssal sedimentation rates that match net input. In contrast, clay settles only slowly, and its distribution is heavily stratified, being transported mainly along isopycnals. Yet, both size classes display a significant and persistent concentration minimum over the Zapiola Rise. We show that the Zapiola Anticyclone, a strong eddy‐driven vortex that circulates around the Zapiola Rise, is a barrier to sediment transport, and hence prevents significant accumulation of sediments on the Rise. We conclude that sediment transport by the turbulent circulation in the Argentine Basin alone cannot account for the preferred sediment accumulation over the Rise. We speculate that resuspension is a critical process in the formation and maintenance of the Zapiola Rise. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-18T11:22:01.540707-05:
      DOI: 10.1002/2014JC010573
       
  • Marine microbes rapidly adapt to consume ethane, propane, and butane
           within the dissolved hydrocarbon plume of a natural seep
    • Authors: Stephanie D. Mendes; Molly C. Redmond, Karl Voigritter, Christian Perez, Rachel Scarlett, David L. Valentine
      Pages: n/a - n/a
      Abstract: Simple hydrocarbon gases containing two to four carbons (ethane, propane, and butane) are among the most abundant compounds present in petroleum reservoirs, and are introduced into the ocean through natural seepage and industrial discharge. Yet little is known about the bacterial consumption of these compounds in ocean waters. To assess the timing by which microbes metabolize these gases, we conducted a 3‐phase study that tested and applied a radiotracer‐based method to quantify the oxidation rates of ethane, propane and butane in fresh seawater samples. Phase 1 involved the synthesis of tritiated ethane, propane, and butane using Grignard reagents and tritiated water. Phase 2 was a systematic assessment of experimental conditions, wherein the indigenous microbial community was found to rapidly oxidize ethane, propane, and butane. Phase 3 was the application of this tritium method near the Coal Oil Point seeps, offshore California. Spatial and temporal patterns of ethane, propane, and butane oxidation down current from the hydrocarbon seeps demonstrated that >99% of these gases are metabolized within 1.3 days following initial exposure. The oxidation of ethane outpaced oxidation of propane and butane with patterns indicating the microbial community responded to these gases by rapid adaptation or growth. Methane oxidation responded the slowest in plume waters. Estimates based on the observed metabolic rates and carbon mass balance suggest that ethane, propane, and butane consuming microorganisms may transiently account for a majority of the total microbial community in these impacted waters. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-18T11:16:13.489761-05:
      DOI: 10.1002/2014JC010362
       
  • The role of turbulent mixing in the modified Shelf Water overflows that
           produce Cape Darnley Bottom Water
    • Authors: Daisuke Hirano; Yujiro Kitade, Kay I. Ohshima, Yasushi Fukamachi
      Pages: n/a - n/a
      Abstract: The mixing process associated with modified Shelf Water (mSW) overflows that eventually mix to form Cape Darnley Bottom Water (CDBW) was investigated by hydrographic and microstructure observations off the Cape Darnley Polynya (CDP), East Antarctica, in January 2009. Closely spaced microstructure observations revealed that mSW properties varied considerably within a distance of ∼4 km across the shelf edge. Near the bottom, the rate of turbulent kinetic energy dissipation was enhanced to values greater than 10−7 W kg−1, and the vertical scale of the bottom boundary layer (BBL) was on the order of 10 m. The observed BBL around the shelf edge was characterized by strong vertical mixing with turbulent eddy diffusivities of ∼O(10−3−10−2) m2 s−1. A geostrophically balanced density current, which resulted from the presence of mSW over the continental shelf, is considered the primary energy source for the turbulent mixing in the BBL. This turbulent mixing transforms the overflowing mSW through mixing with ambient water masses, specifically with the overlying modified Circumpolar Deep Water. The BBL is also thought to partly contribute to the gradual descent of mSW down the continental slope through bottom Ekman transport. We conclude that turbulent mixing, primarily caused by a density current, plays an important role in CDBW formation, by modifying the mSW overflowing from the CDP.
      PubDate: 2015-02-17T06:17:40.333909-05:
      DOI: 10.1002/2014JC010059
       
  • Multiscale seismic reflectivity of shallow thermoclines
    • Authors: S. Ker; Y. Le Gonidec, L. Marié, Y. Thomas, D. Gibert
      Pages: n/a - n/a
      Abstract: Seismic Oceanography is coming of age as an established technique of observation of the thermohaline structure of the ocean. The present paper deals with the seismic reflectivity of the Armorican Shelf seasonal thermocline, west of France, based on two seismic experiments performed with a sparker source. The peak frequency was 500 Hz for the ASPEX experiment, where the thermocline was located at 27 m water depth, and reduced to 400 Hz associated to a higher source level for the IFOSISMO experiment, where the thermocline was 12 m deeper. Despite this settings, only the first experiment could clearly highlight the thermocline reflector, providing the first seismic observation of a shallow oceanic structure. To better understand the limitation of high‐resolution seismic devices in detecting weak oceanic features, we develop a wavelet‐based seismic analysis and consider, as a first approximation, a simple thermocline modelled by a Gauss Error function, allowing an analytical expression for the associated seismic reflectivity. We show that the acoustic impedance profile of the thermocline is mainly controlled by a sound velocity proportional to the temperature. We show that the seismic reflectivity is controlled by the reflection coefficient of the large‐scale structure of the thermocline and by an attenuation factor which depends on the ratio between the seismic wavelength and the characteristic size of the thermocline. Depending on this ratio, the strength of the thermocline‐related reflection may be too weak to be detected by seismic measurement. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-14T09:52:45.205229-05:
      DOI: 10.1002/2014JC010478
       
  • Role of particle stock and phytoplankton community structure in regulating
           particulate organic carbon export in a large marginal sea
    • Authors: Pinghe Cai; Daochen Zhao, Lei Wang, Bangqin Huang, Minhan Dai
      Pages: n/a - n/a
      Abstract: In this study, we utilize 234Th/238U disequilibrium to determine particulate organic carbon (POC) export from the euphotic zone in the South China Sea. Depth profiles of 234Th, total chlorophyll, pigments, and POC were collected during four cruises from August 2009 to May 2011, covering an entire seasonal cycle of spring, summer, autumn, and winter. The extensive data set that was acquired allows for an evaluation of the seasonal variability of upper ocean POC export and its controls in a large marginal sea. The results show that 234Th fluxes from the euphotic zone fall in the range of 528 − 1550, 340 − 2694, and 302–2647 dpm m−2 d−1 for the coastal, shelf, and basin regimes, respectively. In these regimes, POC/234Th ratios at the base of the euphotic zone fall in the range of 5.7‐58.2, 4.6‐44.0, and 2.5‐15.5 μmol dpm−1, respectively. Accordingly, for the coastal, shelf, and basin regimes, the mean POC export fluxes from the euphotic zone are 24.3, 18.3, and 6.3 mmolC m−2 d−1, respectively. Seasonal variations in POC export flux are remarkable in the study area, and POC export peaks were generally observed in autumn. We use a simple linear regression (LLS) method to examine the correlation of POC export vs. POC stock and vs. plankton community structure. We found a strong correlation (R2=0.73, p
      PubDate: 2015-02-14T09:24:29.148865-05:
      DOI: 10.1002/2014JC010432
       
  • On the transport modes of fine sediment in the wave boundary layer due to
           resuspension/deposition—A turbulence‐resolving numerical
           investigation
    • Authors: Zhen Cheng; Xiao Yu, Tian‐Jian Hsu, Celalettin E. Ozdemir, S. Balachandar
      Pages: n/a - n/a
      Abstract: Previous field observations revealed that the wave boundary layer is one of the main conduits delivering fine sediments from the nearshore to continental shelves. Recently, a series of turbulence‐resolving simulations further demonstrated the existence of a range of flow regimes due to different degrees of sediment‐induced density stratification controlled by the sediment availability. In this study, we investigate the scenario in which sediment availability is governed by the resuspension/deposition from/to the bed. Specifically, we focus on how the critical shear stress of erosion and the settling velocity, can determine the modes of transport. Simulations reveal that at a given wave intensity, which is associated with more energetic muddy shelves and a settling velocity of about 0.5 mm/s, three transport modes, ranging from the well‐mixed transport (mode I), two‐layer like transport with the formation of lutocline (mode II) and laminarized transport (mode III) are obtained as the critical shear stress of erosion reduces. Moreover, reductions in the settling velocity also yield similar transitions of transport modes. We also demonstrate that the onset of laminarization can be well‐explained by the reduction of wave‐averaged bottom stress to about 0.39 Pa due to attenuated turbulence by sediments. A 2D parametric map is proposed to characterize the transition from one transport mode to another as a function of the critical shear stress and the settling velocity at a fixed wave intensity. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-14T09:24:15.917949-05:
      DOI: 10.1002/2014JC010623
       
  • Invisible polynyas: Modulation of fast ice thickness by ocean heat flux on
           the Canadian polar shelf
    • Authors: Humfrey Melling; Christian Haas, Eric Brossier
      Pages: n/a - n/a
      Abstract: Although the Canadian polar shelf is dominated by thick fast ice in winter, areas of young ice or open water do recur annually at locations within and adjacent to the fast ice. These polynyas are detectable by eye and sustained by wind or tide‐driven ice divergence and ocean heat flux. Our ice‐thickness surveys by drilling and towed electromagnetic sounder reveal that visible polynyas comprise only a subset of thin‐ice coverage. Additional area in the coastal zone, in shallow channels and in fjords is covered by thin ice which is too thick to be discerned by eye. Our concurrent surveys by CTD reveal correlation between thin fast ice and above‐freezing seawater beneath it. We use winter time series of air and ocean temperatures and ice and snow thicknesses to calculate the ocean‐to‐ice heat flux as 15 and 22 W/m2 at locations with thin ice in Penny Strait and South Cape Fjord, respectively. Near‐surface seawater above freezing is not a sufficient condition for ocean heat to reach the ice; kinetic energy is needed to overcome density stratification. The ocean's isolation from wind under fast ice in winter leaves tides as the only source. Two tidal mechanisms driving ocean heat flux are discussed: diffusion via turbulence generated by shear at the under‐ice and benthic boundaries, and the internal hydraulics of flow over topography. The former appears dominant in channels and the coastal zone and the latter in some silled fjords where and when the layering of seawater density permits hydraulically critical flow.
      PubDate: 2015-02-12T11:23:57.905011-05:
      DOI: 10.1002/2014JC010404
       
  • Characteristics, generation and mass transport of nonlinear internal waves
           on the Washington continental shelf
    • Authors: Shuang Zhang; Matthew H. Alford, John B. Mickett
      Pages: n/a - n/a
      Abstract: As a step toward better understanding the generation of nonlinear internal waves (NLIWs) on continental shelves and the factors determining their morphology, amplitude and propagation, we analyze more than 1500 NLIWs detected on the Washington (WA) continental shelf using four summer/fall time series of temperature and velocity measurements from a surface mooring deployed in 100 m of water. Propagating onshore toward the northeast, these NLIWs take a variety of forms, including internal solitary waves, solitary wave trains and bores. Nearly all are mode‐1 depression waves that arrive semidiurnally along with the internal tide. The NLIW energy flux is correlated with the internal tide energy flux but not the local barotropic forcing, implying that the observed NLIWs arise primarily from shoaling remotely generated internal tides rather than local generation. Estimated onshore transport by the waves can equal or exceed offshore Ekman transport, suggesting the waves may play an important role in the mass balance on the continental shelf.
      PubDate: 2015-02-12T11:21:04.447456-05:
      DOI: 10.1002/2014JC010393
       
  • Spatial structure and temporal variability of the zonal flow in the Luzon
           Strait
    • Authors: Zhiwei Zhang; Wei Zhao, Jiwei Tian, Qingxuan Yang, Tangdong Qu
      Pages: n/a - n/a
      Abstract: One year long, full‐depth velocity measurements were used to examine the spatial structure and temporal variability of the zonal flow in the Luzon Strait (LSZF). The observation revealed a renewed mean flow structure: in the upper (2000 m) layers, the LSZF was mostly westward; in the intermediate layer (500–2000 m), it was dominated by an eastward flow in the south but a westward flow in the north. The volume transport across the observed section between 19.8°N and 21.2°N exhibited strong seasonal and intraseasonal variability. On the seasonal time scale, the upper‐layer transport showed a clear annual cycle, strongest in January and weakest in June; the intermediate‐layer transport also showed a semiannual cycle, attaining its peaks (troughs) in January and June (April and October). On the intraseasonal time scale, both the upper‐layer and intermediate‐layer transports showed significant energy peaks at about 60 and 10–30 days. Further analysis indicated that the ∼60 day variability might be attributed to the impinging mesoscale eddies from the Pacific, while the 10–30 day variability appeared to obtain its energy from local intraseasonal wind forcing and baroclinic instability of the background current. The 10–100 day upper‐layer and intermediate‐layer transport variabilities were highly anticorrelated, suggesting a baroclinic nature of the intraseasonal variabilities of the LSZF.
      PubDate: 2015-02-12T11:04:36.153048-05:
      DOI: 10.1002/2014JC010308
       
  • On the origin and propagation of Denmark Strait Overflow Water anomalies
           in the Irminger Basin
    • Authors: Kerstin Jochumsen; Manuela Köllner, Detlef Quadfasel, Stephen Dye, Bert Rudels, Hedinn Valdimarsson
      Pages: n/a - n/a
      Abstract: Denmark Strait Overflow Water (DSOW) supplies the densest contribution to North Atlantic Deep Water and is monitored at several locations in the subpolar North Atlantic. Hydrographic (temperature and salinity) and velocity time series from three multiple–mooring arrays at the Denmark Strait sill, at 180 km downstream (south of Dohrn Bank) and at a further 320 km downstream on the east Greenland continental slope near Tasiilaq (formerly Angmagssalik) were analyzed to quantify the variability and track anomalies in DSOW in the period 2007‐2012. No long term trends were detected in the time series, while variability on time scales from interannual to weekly was present at all moorings. The hydrographic time series from different moorings within each mooring array showed coherent signals, while the velocity fluctuations were only weakly correlated. Lagged correlations of anomalies between the arrays revealed a propagation from the sill of Denmark Strait to the Angmagssalik array in potential temperature with an average propagation time of 13 days, while the correlations in salinity were low. Entrainment of warm and saline Atlantic Water and fresher water from the East Greenland Current (via the East Greenland Spill Jet) can explain the whole range of hydrographic changes in the DSOW measured downstream of the sill. Changes in the entrained water masses and in the mixing ratio can thus strongly influence the salinity variability of DSOW. Fresh anomalies found in downstream measurements of DSOW within the Deep Western Boundary Current can therefore not be attributed to Arctic climate variability in a straightforward way. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-12T09:18:03.3247-05:00
      DOI: 10.1002/2014JC010397
       
  • An analysis of the evolution of Meddies in the North Atlantic using floats
           and multisensor satellite data
    • Authors: Young‐Heon Jo; Federico Ienna, Xiao‐Hai Yan
      Pages: n/a - n/a
      Abstract: Previous studies focusing on the remote detection of Mediterranean Eddies (Meddies) have reported that the isopycnal surface changes derived from satellite multi‐sensor measurements at the approximate depth of 400m can be used to sense the presence of underlying Meddies. While the isopycnal surface near that depth does indeed reveal the locations of Meddies, an analysis of isopycnal surface changes in response to the evolution of Meddies has yet to be made. Accordingly, this research focuses on analyzing the relationship between isopycnal surface changes and the evolution of Meddies. The vertical isopycnal surface variability of Meddies, which is directly related to contributions from rotational velocity, interior thermal variation, and vertical displacement of Meddies, is observed and studied using float observations from A Mediterranean Undercurrent Seeding Experiment (AMUSE). The contributions of each of the three aforementioned parameters are estimated, enabling us to understand their relative role in changing the isopycnal surface above Meddies. Furthermore, in order to further understand Meddies' evolution and their associated forcing, the dominant frequencies of their horizontal and vertical displacements, as well as the sea surface height variability above the Meddy, are analyzed using the Hilbert – Huang Transform. Finally, the horizontal and the vertical eddy viscosity dissipation of Meddies is computed and compared with a theoretical model. The empirical horizontal and the vertical eddy viscosities are found to be 7x106cm2sec−1 and 200cm2sec−1, respectively. This study will therefore contribute to understanding how the isopycnal surface is related to the presence of Meddies, what frequencies are dominate its variability, and the values of eddy viscosity which can be used for a numerical model. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-12T08:46:28.843521-05:
      DOI: 10.1002/2014JC010495
       
  • Spreading of Levantine Intermediate Waters by submesoscale coherent
           vortices in the northwestern Mediterranean Sea as observed with gliders
    • Authors: Anthony Bosse; Pierre Testor, Laurent Mortier, Louis Prieur, Vincent Taillandier, Fabrizio d'Ortenzio, Laurent Coppola
      Pages: n/a - n/a
      Abstract: Since 2007, gliders have been regularly deployed in the Northwestern Mediterranean Sea, a crucial region regarding the thermohaline circulation of the Mediterranean Sea. It revealed for the first time very warm (+0.4∘C) and saline (+0.1) submesoscale anticyclones at intermediate depth characterized by a small radius (∼5km), high Rossby (∼0.3) and Burger (∼0.7) numbers. They are likely order of 10 to be formed each year, have a life time order a year and certainly contribute significantly to the spreading of the Levantine Intermediate Waters (LIW) toward the whole sub‐basin, thus potentially impacting wintertime vertical mixing through hydrographical and dynamical preconditioning. They could be mainly formed by the combined action of turbulent mixing and flow detachment of the northward flow of LIW at the Northwestern headland of Sardinia. Upwelling conditions along the western coast of Sardinia associated with a southward geostrophic flow within the upper layers seem to play a key role in their formation process. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-12T05:38:17.134776-05:
      DOI: 10.1002/2014JC010263
       
  • Large variability of the Kuroshio at 23.75°N east of Taiwan
    • Authors: Sen Jan; Yiing Jang Yang, Joe Wang, Vigan Mensah, Tien‐Hsia Kuo, Ming‐Da Chiou, Ching‐Sheng Chern, Ming‐Huei Chang, Hwa Chien
      Pages: n/a - n/a
      Abstract: Synoptic features of the Kuroshio at 23.75°N were quantified using nine ship‐based surveys between September 2012 and September 2014. The new ship‐based data set provide an unprecedented view of the Kuroshio east of Taiwan and suggest tremendous variability in its velocity, hydrography, volume, heat, and salt transports, and water masses. The Kuroshio maximum velocity varied in 0.7–1.4 m s−1; the core current width, delineated with the limit v ≥ 0.2 m s−1, ranged from 85 to 135 km and the thickness varied from 400 to 600 m. A dual velocity maximum in the Kuroshio core current, though unexpected, was observed in 3 of 9 cruises. The Kuroshio core transport, integrated from the directly measured velocity, varied between 10.46 and 22.92 Sv (1 Sv=106 m3 s−1). The corresponding heat transport referenced to 0°C was 0.838–1.793 × 1015 W, and the salt transport was 345.0–775.9 ×106 kg s−1. The geostrophic transport estimated using the thermal wind relation with the observed hydrographic data and reference velocity at 900 m is comparable to the directly measured Kuroshio transport during most of the surveys, suggesting the directly measured velocity is mostly in geostrophic balance. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-12T05:08:09.676998-05:
      DOI: 10.1002/2014JC010614
       
  • Impact of submesoscale processes on dynamics of phytoplankton filaments
    • Authors: Igor Shulman; Bradley Penta, Jim Richman, Gregg Jacobs, Stephanie Anderson, Peter Sakalaukus
      Pages: n/a - n/a
      Abstract: In Monterey Bay, CA, during northwesterly, upwelling favorable winds, the development of a southward flowing cold jet along the entrance to the Bay is often observed. This dense cold jet separates warm waters of the anticyclonic circulation offshore from the water masses inside the Bay. Interactions between the cold jet and the offshore anticyclonic circulation generate ageostrophic secondary circulation (ASC) cells due to submesoscale processes as, for example, flow interaction with the development of surface frontogenesis and nonlinear Ekman pumping. Based on observations and modeling studies we evaluate the impact of these submesoscale processes on the formation of chlorophyll a filaments during late spring‐earlier summer and late summer time frames. We show that during the late summer time frame, ASC leads to the development of filaments with high values of chlorophyll a concentration along the edge of the cold jet–in contrast to the earlier summer time, when the ASC mixes phytoplankton much deeper to the area below of the euphotic depth, and chlorophyll a filaments are 3‐4 times weaker. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-12T04:28:14.461296-05:
      DOI: 10.1002/2014JC010326
       
  • Anomalous dispersion of sea ice in the Fram Strait region
    • Authors: A. Gabrielski; G. Badin, L. Kaleschke
      Pages: n/a - n/a
      Abstract: The single‐particle dispersion of sea ice in the Fram Strait region is investigated using ice drift buoys deployed from 2002 to 2009 within the Fram Strait Cyclones and the Arctic Climate System Study campaigns. A new method to estimate the direction of the mean flow, based on a satellite drift product, is introduced. As a result, the bias in the dispersion introduced by the mean flow is eliminated considering only the displacements of the buoys in the cross‐stream direction. Results show an absolute dispersion growing quadratically in time for the first 3 days and an anomalous dispersion regime exhibiting a strongly self‐similar scaling following a 5/4 power law for time scales larger than 6 days persisting over the whole time series of length 32 days. The non‐Gaussian distribution of the velocity fluctuations with a skewness of ‐0.15 and a kurtosis of 7.33 as well as the slope of the Lagrangian frequency spectrum between −2 and −1 are in agreement with the anomalous diffusion regime. Comparison with data from the International Arctic Buoy Program yields similar results with an anomalous dispersion starting after 10 days and persisting over the whole time series of length 50 days. The results suggest the presence of deformation and shear acting on the sea ice dispersion. The high correlation between the cross‐stream displacements and the cross‐stream wind velocities shows the important role of the wind as a source for the anomalous dispersion. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-10T06:22:17.931262-05:
      DOI: 10.1002/2014JC010359
       
  • Variability in the meteoric water, sea‐ice melt, and Pacific water
           contributions to the central Arctic Ocean, 2000–2014
    • Authors: Matthew B. Alkire; James Morison, Roger Andersen
      Pages: n/a - n/a
      Abstract: Fourteen years (2000‐2014) of bottle chemistry data collected during the North Pole Environmental Observatory were compiled to the examine variations in the composition of freshwater (meteoric water, net sea‐ice meltwater, and Pacific water) over the mixed layer of the Central Arctic Ocean. In addition to significant spatial and interannual variability, there was a general decrease in meteoric water (MW) fractions at the majority of stations re‐occupied over the duration of the program that was approximately balanced by a concomitant increase in freshwater from sea‐ice melt (SIM FW) between 2000 and 2012. Inventories (0‐120m) of MW and SIM FW computed using available data between 2005 and 2012 exhibited similar variations over the study area, allowing for first‐order estimates of the mean annual changes in MW (‐389 ± 194km3 yr−1) and SIM FW (292 ± 97km3 yr−1) for the Central Arctic region. These mean annual changes were attributed to the diversion of Siberian river runoff to the Beaufort Gyre and the overall reduction of sea ice volume across the Arctic, respectively. In addition to this lower frequency variability, spatial gradients and interannual variations in MW, SIM FW, and Pacific water contributions to specific locations were attributed to shifts in the Transpolar Drift that advects waters of eastern and western Arctic origin through the study area. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-10T05:18:43.323647-05:
      DOI: 10.1002/2014JC010023
       
  • Multiyear ice replenishment in the canadian arctic archipelago:
           1997–2013
    • Authors: Stephen E.L. Howell; Chris Derksen, Larissa Pizzolato, Michael Brady
      Pages: n/a - n/a
      Abstract: In the Canadian Arctic Archipelago (CAA), multi‐year ice (MYI) replenishment from first‐year ice aging (CAAMYI‐Oct‐1) and Arctic Ocean MYI exchange (CAAMYI‐exchange) contribute to the CAA's relatively heavy sea ice conditions at the end of the summer melt season. We estimate these components using RADARSAT and the Canadian Ice Service Digital Archive and explore processes responsible for interannual variability from 1997‐2013. CAAMYI‐Oct‐1 (52±36x103 km2) provides a larger contribution than CAAMYI‐exchange (13±11x103 km2). CAAMYI‐Oct‐1 represents ∼10% of the amount that occurs in the Arctic Ocean. CAAMYI‐exchange represents ∼50% of Nares Strait MYI export to Baffin Bay and ∼12% of Fram Strait MYI export to the Greenland Sea. CAAMYI‐Oct‐1 exhibits dependence on warmer (cooler) summers that increase (decrease) melt evident from strong relationships to surface air temperature (SAT), albedo and total absorbed solar radiation (Qtotal). CAAMYI‐exchange is influenced by summer sea level pressure (SLP) anomalies over the Beaufort Sea and Canadian Basin which shifts the primary source of CAAMYI‐exchange between less obstructed M'Clure Strait (low SLP anomalies) and the more obstructed Queen Elizabeth Islands (high SLP anomalies). Over the 17‐record, appreciable replenishment occurred for most years from 1997‐2004, reduced replenishment from 2005‐2012 and large replenishment in 2013. The reduced replenishment period was associated with positive SAT, negative albedo and positive Qtotal anomalies that facilitated more melt and less CAAMYI‐Oct‐1, together with high SLP anomalies that facilitated less CAAMYI‐exchange. Large replenishment in 2013 was primarily from CAAMYI‐Oct‐1 attributed to strongly negative SAT and Qtotal anomalies and strongly positive albedo that impeded melt. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-06T17:48:41.624611-05:
      DOI: 10.1002/2015JC010696
       
  • Modeled alongshore circulation and force balances onshore of a submarine
           canyon
    • Authors: Jeff E. Hansen; Britt Raubenheimer, Jeffrey H. List, Steve Elgar
      Pages: n/a - n/a
      Abstract: Alongshore force balances, including the role of nonlinear advection, in the shoaling and surf zones onshore of a submarine canyon are investigated using a numerical modeling system (Delft3D/SWAN). The model is calibrated with waves and alongshore flows recorded over a period of 1.5 months at 26 sites along the 1.0‐, 2.5‐, and 5.0‐m depth contours spanning about 2km of coast. Field‐observation‐based estimates of the alongshore pressure and radiation‐stress gradients are reproduced well by the model. Model simulations suggest that the alongshore momentum balance is between the sum of the pressure and radiation‐stress gradients and the sum of the nonlinear advective terms and bottom stress, with the remaining terms (e.g., wind stress and turbulent mixing) being negligible. The simulations also indicate that unexplained residuals in previous field‐based estimates of the momentum balance may be owing to the neglect of the nonlinear advective terms, which are similar in magnitude to the sum of the forcing (pressure and radiations stress gradients) and to the bottom stress. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-06T17:41:31.262621-05:
      DOI: 10.1002/2014JC010555
       
  • Seasonal evolution of an ice‐shelf influenced fast‐ice regime,
           derived from an autonomous thermistor chain
    • Authors: M. Hoppmann; M. Nicolaus, P. A. Hunkeler, P. Heil, L.K. Behrens, G. König‐Langlo, R. Gerdes
      Pages: n/a - n/a
      Abstract: Ice shelves strongly interact with coastal Antarctic sea ice and the associated ecosystem by creating conditions favourable to the formation of a sub‐ice platelet layer. The close investigation of this phenomenon and its seasonal evolution remain a challenge due to logistical constraints and a lack of suitable methodology. In this study, we characterize the seasonal cycle of Antarctic fast ice adjacent to the Ekström Ice Shelf in the eastern Weddell Sea. We used a thermistor chain with the additional ability to record the temperature response induced by cyclic heating of resistors embedded in the chain. Vertical sea‐ice temperature and heating profiles obtained daily between November 2012 and February 2014 were analyzed to determine sea‐ice and snow evolution, and to calculate the basal energy budget. The residual heat flux translated into an ice‐volume fraction in the platelet layer of 0.18 ± 0.09, which we reproduced by a independent model simulation and agrees with earlier results. Manual drillings revealed an average annual platelet‐layer thickness increase of at least 4m, and an annual maximum thickness of 10m beneath second‐year sea ice. The oceanic contribution dominated the total sea‐ice production during the study, effectively accounting for up to 70% of second‐year sea‐ice growth. In summer, an oceanic heat flux of 21 W m– 2 led to a partial thinning of the platelet layer. Our results further show that the active heating method, in contrast to the acoustic sounding approach, is well suited to derive the fast‐ice mass balance in regions influenced by ocean/ice‐shelf interaction, as it allows sub‐diurnal monitoring of the platelet‐layer thickness. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-06T17:31:35.237166-05:
      DOI: 10.1002/2014JC010327
       
  • Cross‐shelf exchange in the shelf of the East China Sea
    • Authors: Feng Zhou; Huijie Xue, Daji Huang, Jiliang Xuan, Xiaobo Ni, Peng Xiu, Qiang Hao
      Pages: n/a - n/a
      Abstract: A high‐resolution, 3‐dimensional primitive equation model is used to investigate the cross‐shelf exchange in the East China Sea (ECS). Favorable comparisons between field data and model simulations from both climatological run and hindcast run for 2006 indicate that the model has essential skills in capturing the key physics of the ECS. Temporal and spatial variations of the cross‐shelf exchanges are further analyzed. It was demonstrated from both observations and simulations that in 2006 high saline water could be delivered to the north of the Changjiang River mouth (near 32ºN) as a result of stronger than typical cross‐shelf exchanges at the shelf break and flows through the Taiwan Strait with an annual mean rate of 2.59 Sv and 1.83 Sv, respectively. A few new places at the shelf break were also identified where persistent and vigorous onshore or offshore exchanges occur throughout the year. Cross‐shelf exchange is largely determined by the along‐shelf geostrophic balance with weak seasonality, which is modulated in upper layers by northeasterly monsoon from early‐fall to late‐spring and at seabed by bottom friction during December − January, May and August − September. Nonlinear effect, with strong spatial variations and intra‐seasonal variability, is a secondary but persistent contributor to the net seaward transport, except for northeast of Taiwan where the nonlinear effect becomes significant but more varied. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-06T17:28:45.74817-05:0
      DOI: 10.1002/2014JC010567
       
  • Glider observations and modeling of sediment transport in Hurricane Sandy
    • Authors: Travis Miles; Greg Seroka, Josh Kohut, Oscar Schofield, Scott Glenn
      Pages: n/a - n/a
      Abstract: Regional sediment resuspension and transport are examined as Hurricane Sandy made landfall on the Mid Atlantic Bight (MAB) in October of 2012. A Teledyne‐Webb Slocum glider, equipped with a Nortek Aquadopp current profiler, was deployed on the continental shelf ahead of the storm, and is used to validate sediment transport routines coupled to the Regional Ocean Modeling System (ROMS). The glider was deployed on October 25th, 5 days before Sandy made landfall in southern New Jersey (NJ) and flew along the 40 meter isobath south of the Hudson Shelf Valley. We used optical and acoustic backscatter to compare with two modeled size classes along the glider track, 0.1 and 0.4mm sand respectively. Observations and modeling revealed full water column resuspension for both size classes for over 24 hours during peak waves and currents, with transport oriented along‐shelf toward the southwest. Regional model predictions showed over 3cm of sediment eroded on the northern portion of the NJ shelf where waves and currents were the highest. As the storm passed and winds reversed from onshore to offshore on the southern portion of the domain waves and subsequently orbital velocities necessary for resuspension were reduced leading to over 3cm of deposition across the entire shelf, just north of Delaware Bay. This study highlights the utility of gliders as a new asset in support of the development and verification of regional sediment resuspension and transport models, particularly during large tropical and extra‐tropical cyclones when in situ datasets are not readily available. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-06T17:28:32.946309-05:
      DOI: 10.1002/2014JC010474
       
  • Development of HF radar inversion algorithm for spectrum estimation (HIAS)
    • Authors: Yukiharu Hisaki
      Pages: n/a - n/a
      Abstract: A method for estimating ocean wave directional spectra using an HF (high‐frequency) ocean radar was developed. This method represents the development of work conducted in previous studies [Hisaki, 2005; 2006]. In the present method, ocean wave directional spectra are estimated on polar coordinates whose center is the radar position, while spectra are estimated on regular grids. This method can be applied to both single and multiple radar cases. The area for wave estimation is more flexible than that of the previous method. As the signal to noise (SN) ratios of Doppler spectra are critical for wave estimation, we develop a method to exclude low SN ratio Doppler spectra. The validity of the method is demonstrated by comparing results with in‐situ observed wave data that it would be impossible to estimate by the methods of other groups. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-06T17:28:26.126017-05:
      DOI: 10.1002/2014JC010548
       
  • A semianalytical ocean color inversion algorithm with explicit
           water‐column depth and substrate reflectance parameterization
    • Authors: Lachlan I.W. McKinna; Peter. R.C. Fearns, Scarla J. Weeks, P. Jeremy Werdell, Martina Reichstetter, Bryan A. Franz, Donald M. Shea, Gene C. Feldman
      Pages: n/a - n/a
      Abstract: A semi‐analytical ocean color inversion algorithm was developed for improving retrievals of inherent optical properties (IOPs) in optically shallow waters. In clear, geometrically shallow waters, light reflected off the seafloor can contribute to the water‐leaving radiance signal. This can have a confounding effect on ocean color algorithms developed for optically deep waters, leading to an overestimation of IOPs. The algorithm described here, the Shallow Water Inversion Model (SWIM), uses pre‐existing knowledge of bathymetry and benthic substrate brightness to account for optically shallow effects. SWIM was incorporated into the NASA Ocean Biology Processing Group's L2GEN code and tested in waters of the Great Barrier Reef, Australia, using the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua time‐series (2002 – 2013). SWIM‐derived values of the total non‐water absorption coefficient at 443nm, at(443), the particulate backscattering coefficient at 443nm, bbp(443), and the diffuse attenuation coefficient at 488nm, Kd(488), were compared with values derived using the Generalized Inherent Optical Properties algorithm (GIOP) and the Quasi‐Analytical Algorithm (QAA). The results indicated that in clear, optically shallow waters SWIM‐derived values of at(443), bbp(443), and Kd(443) were realistically lower than values derived using GIOP and QAA, in agreement with radiative transfer modelling. This signified that the benthic reflectance correction was performing as expected. However, in more optically complex waters, SWIM had difficulty converging to a solution, a likely consequence of internal IOP parameterizations. Whilst a comprehensive study of the SWIM algorithm's behavior was conducted, further work is needed to validate the algorithm using in situ data. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-06T17:26:19.580886-05:
      DOI: 10.1002/2014JC010224
       
  • Multidecadal variations of the surface Kuroshio between 1950s and 2000s
           and its impacts on surrounding waters
    • Authors: Yi‐Chia Hsin
      Pages: n/a - n/a
      Abstract: Based on the analyses of 59‐year (1950‐2008) surface geostrophic velocities, the multi‐decadal changes of Kuroshio from the eastern Luzon to the southern Japan are investigated. Result shows that the upstream Kuroshio from the east of Luzon to southern East China Sea suffers much more obvious multi‐decadal changes. Except for the decade of 1980, the Kuroshio east of Luzon possesses a multi‐decadal tendency opposite to that east of Taiwan. Besides 1980s, the multi‐decadal change of Kuroshio bordering Taiwan is mainly governed by the eddy activity off the eastern Taiwan, while the wind stress curl plays a major role in the Kuroshio in the east of Luzon and in the Luzon Strait. The wind‐stress‐induced Ekman transport plays a secondary role in regulating the Kuroshio east of Luzon. In addition, the multi‐decadal fluctuation of Kuroshio east of Luzon also modulates the westward intrusion in the Luzon Strait. Instead, the Ekman transport dominated the whole upstream Kuroshio area from the eastern Luzon to the vicinity of Taiwan during the exceptional decade of 1980. Associated changes of water properties in the northern South China Sea and southern East China Sea are also ascribed to the multi‐decadal changes of surface Kuroshio in the upstream area. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-06T17:26:07.543805-05:
      DOI: 10.1002/2014JC010582
       
  • Turbulence in the East China Sea: The summertime stratification
    • Authors: Iossif Lozovatsky; Jae‐Hak Lee, H.J.S. Fernando, Sok Kuh Kang, S.U.P. Jinadasa
      Pages: n/a - n/a
      Abstract: A series of 134 microstructure profiles were taken in the central East China Sea from a drifting ship, covering more than 12 miles over the sloping bottom. The water depth z varied in the range 52 ‐ 62m; the tidal elevation of semidiurnal component was ± 1m. Prior to the onset of 25‐hour drift, a hydrographic section consisting of 9 stations, 15 miles apart, was taken in the area. A shallow mixed surface layer (SL) underlain by a diurnal pycnocline (z 
      PubDate: 2015-02-06T17:25:53.906176-05:
      DOI: 10.1002/2014JC010596
       
  • Experimental study on plunging breaking waves in deep water
    • Authors: Ho‐Joon Lim; Kuang‐An Chang, Zhi‐Cheng Huang, Byoungjoon Na
      Pages: n/a - n/a
      Abstract: This study presents a unique data set that combines measurements of velocities and void fraction under an unsteady deep‐water plunging breaker in a laboratory. Flow properties in the aerated crest region of the breaking wave were measured using modified particle image velocimetry (PIV) and bubble image velocimetry (BIV). Results show that the maximum velocity in the plunging breaker reached 1.68C at the first impingement of the overturning water jet with C being the phase speed of the primary breaking wave, while the maximum velocity reached 2.14C at the beginning of the first splash‐up. A similarity profile of void fraction was found in the successive impinging and splash‐up rollers. In the highly foamy splashing roller, the increase of turbulent level and vorticity level were strongly correlated with the increase of void fraction when the range of void fraction was between 0 and 0.4 (from the trough level to approximately the center of the roller). The levels became constant when void fraction was greater than 0.5. The mass flux, momentum flux, kinetic energy, potential energy, and total energy were computed and compared with and without the void fraction being accounted for. The results show that all the mean and turbulence properties related to the air‐water mixture are considerably overestimated unless void fraction is considered. When including the density variation due to the air bubbles, the wave energy dissipated exponentially a short distance after breaking about 54% and 85% of the total energy dissipated within one and two wavelengths beyond the breaking wave impingement point, respectively. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-06T17:25:44.270641-05:
      DOI: 10.1002/2014JC010269
       
  • ENSO and the California Current coastal upwelling response
    • Authors: Michael G. Jacox; Jerome Fiechter, Andrew M. Moore, Christopher A. Edwards
      Pages: n/a - n/a
      Abstract: A 31‐year (1980‐2010) sequence of historical analyses of the California Current System (CCS) is used to describe the central CCS (35‐43˚N) coastal upwelling response to El Niño‐Southern Oscillation (ENSO) variability. The analysis period captures 10 El Niño and 10 La Niña events, including the extreme El Niños of 1982‐1983 and 1997‐1998. Data‐assimilative model runs and backward trajectory calculations of passive tracers are used to elucidate physical conditions and source water characteristics during the upwelling season of each year. In general, El Niño events produce anomalously weak upwelling and source waters that are unusually shallow, warm, and fresh, while La Niña conditions produce the opposite. Maximum vertical transport anomalies in the CCS occur ∼ 1 month after El Niño peaks in midwinter, and before the onset of the upwelling season. Source density anomalies peak later than transport anomalies and persist more strongly through the spring and summer, causing the former to impact the upwelling season more directly. As nitrate concentration covaries with density in the central CCS, El Niño may exert more influence over the nitrate concentration of upwelled waters than it does over vertical transport, although both factors are expected to reduce nitrate supply during El Niño events. Interannual comparison of individual diagnostics highlights their relative impacts during different ENSO events, as well as years deviating from the canonical response to ENSO variability. The net impact of ENSO on upwelling is explored through an “Upwelling Efficacy Index”, which may be a useful indicator of bottom‐up control on primary productivity. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-05T03:17:50.001093-05:
      DOI: 10.1002/2014JC010650
       
  • Evidence for multidecadal variability in U.S. extreme sea level records
    • Authors: Thomas Wahl; Don P. Chambers
      Pages: n/a - n/a
      Abstract: We analyze a set of 20 tide gauge records covering the contiguous United States (US) coastline and the period from 1929 to 2013 to identify long‐term trends and multi‐decadal variations in extreme sea levels (ESLs) relative to changes in mean sea level (MSL). Different data sampling and analysis techniques are applied to test the robustness of the results against the selected methodology. Significant but small long‐term trends in ESLs above/below MSL are found at individual sites along most coastline stretches, but are mostly confined to the southeast coast and the winter season when storm surges are primarily driven by extra‐tropical cyclones. We identify six regions with broadly coherent and considerable multi‐decadal ESL variations unrelated to MSL changes. Using a quasi‐non‐stationary extreme value analysis we show that the latter would have caused variations in design relevant return water levels (50 to 200 year return periods) ranging from ∼10cm to as much as 110cm across the six regions. The results raise questions as to the applicability of the “MSL offset method”, assuming that ESL changes are primarily driven by changes in MSL without allowing for distinct long‐term trends or low‐frequency variations. Identifying the coherent multi‐decadal ESL variability is crucial in order to understand the physical driving factors. Ultimately, this information must be included into coastal design and adaptation processes. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-03T23:01:31.625318-05:
      DOI: 10.1002/2014JC010443
       
  • Nodal variations and long‐term changes in the main tides on the
           coasts of China
    • Authors: Xiangbo Feng; Michael N. Tsimplis, Philip L. Woodworth
      Pages: n/a - n/a
      Abstract: The long‐term changes in the main tidal constituents (O1, K1, M2, N2 and S2) along the coasts of China and in adjacent seas are investigated based on 17 tide‐gauge records covering the period 1954‐2012. The observed 18.61‐year nodal modulations of the diurnal constituents O1 and K1 are in agreement with the equilibrium tidal theory, except in the South China Sea. The observed modulations of the M2 and N2 amplitudes are smaller than theoretically predicted at the northern stations and larger at the southern stations. The discrepancies between the theoretically predicted nodal variations and the observations are discussed. The 8.85‐year perigean cycle is identifiable in the N2 parameters at most stations, except those in the South China Sea. The radiational component of S2 contributes on average 16% of the observed S2 except in the Gulf of Tonkin, on the south coast, where it accounts for up to 65%. We confirmed the existence of nodal modulation in S2, which is stronger on the north coast. The semidiurnal tidal parameters show significant secular trends in the Bohai and Yellow Seas, on the north coast, and in the Taiwan Strait. The largest increase is found for M2 for which the amplitude increases by 4‐7 mm/yr in the Yellow Sea. The potential causes for the linear trends in tidal constants are discussed. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-03T22:16:24.03149-05:0
      DOI: 10.1002/2014JC010312
       
  • Effect of glacial drainage water on the CO2 system and ocean acidification
           state in an Arctic tidewater‐glacier fjord during two contrasting
           years
    • Authors: Agneta Fransson; Melissa Chierici, Daiki Nomura, Mats A. Granskog, Svein Kristiansen, Tõnu Martma, Gernot Nehrke
      Pages: n/a - n/a
      Abstract: In order to investigate the effect of glacial water on the CO2 system in the fjord, we studied the variability of the total alkalinity (AT), total dissolved inorganic carbon (CT), dissolved inorganic nutrients, oxygen isotopic ratio (δ18O), and freshwater fractions from the glacier front to the outer Tempelfjorden on Spitsbergen in winter 2012 (January, March and April) and 2013 (April) and summer/fall 2013 (September). The two contrasting years clearly showed that the influence of freshwater, mixing and haline convection affected the chemical and physical characteristics of the fjord. The seasonal variability showed the lowest calcium carbonate saturation state (Ω) and pH values in March 2012 coinciding with the highest freshwater fractions. The highest Ω and pH were found in September 2013, mostly due to CO2 uptake during primary production. Overall, we found that increased freshwater supply decreased Ω, pH and AT. On the other hand, we observed higher AT relative to salinity in the freshwater end‐member in the mild and rainy winter of 2012 (1142 µmol kg−1) compared to AT in 2013 (526 µmol kg−1). Observations of calcite and dolomite crystals in the glacial ice suggested supply of carbonate‐rich glacial drainage water to the fjord. This implies that winters with a large amount of glacial drainage water partly provide a lessening of further ocean acidification, which will also affect the air‐sea CO2 exchange. This article is protected by copyright. All rights reserved.
      PubDate: 2015-02-03T22:16:13.843762-05:
      DOI: 10.1002/2014JC010320
       
  • Mechanisms of surface wave energy dissipation over a
           high‐concentration sediment suspension
    • Authors: Peter Traykovski; John Trowbridge, Gail Kineke
      Pages: n/a - n/a
      Abstract: Field observations from the spring of 2008 on the Louisiana shelf were used to elucidate the mechanisms of wave energy dissipation over a muddy seafloor. After a period of high discharge from the Atchafalaya River, acoustic measurements showed the presence of 20‐cm thick mobile fluid‐mud layers during and after wave events. While total wave‐energy dissipation (D) was greatest during the high energy periods, these periods had relatively low normalized attenuation rates (к= Dissipation/Energy Flux). During declining wave energy conditions, as the fluid‐mud layer settled, the attenuation process became more efficient with high к and low D. The transition from high D and low к to high к and low D was caused by a transition from turbulent to laminar flow in the fluid‐mud layer as measured by a Pulse‐coherent Doppler profiler. Measurements of the oscillatory boundary layer velocity profile in the fluid‐mud layer during laminar flow reveal a very thick wave boundary layer with curvature filling the entire fluid‐mud layer, suggesting a kinematic viscosity two to three orders of magnitude greater than that of clear water. This high viscosity is also consistent with a high wave‐attenuation rates measured by across‐shelf energy flux differences. The transition to turbulence was forced by instabilities on the lutocline, with wavelengths consistent with the dispersion relation for this two‐layer system. The measurements also provide new insight into the dynamics of wave‐supported turbidity flows during the transition from a laminar to turbulent fluid‐mud layer. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-29T09:18:31.591463-05:
      DOI: 10.1002/2014JC010245
       
  • An interdecadal regime shift in rainfall predictability related to the
           Ningaloo Niño in the late 1990s
    • Authors: Takeshi Doi; Swadhin K. Behera, Toshio Yamagata
      Pages: n/a - n/a
      Abstract: The global warming and the Interdecadal Pacific Oscillation (IPO) started influencing the coastal ocean off Western Australia, leading to a dramatic change in the regional climate predictability.  The warmer ocean started driving rainfall variability regionally there after the late 1990s. Because of this, rainfall predictability near the coastal region of Western Australia on a seasonal time scale was drastically enhanced in the late 1990s; it is significantly predictable 5 months ahead after the late 1990s. The high prediction skill of the rainfall in recent decades is very encouraging and would help to develop of an early warning system of Ningaloo Niño/Niña events to mitigate possible societal as well as agricultural impacts in the granary of Western Australia. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-29T08:59:01.452872-05:
      DOI: 10.1002/2014JC010562
       
  • Anomalous eddy heat and freshwater transport in the Gulf of Alaska
    • Authors: John M. Lyman; Gregory C. Johnson
      Pages: n/a - n/a
      Abstract: Characteristics of eddies in the Gulf of Alaska are assessed from January 2003 through April 2012. Ensemble statistics for eddy subsurface water properties on isopycnals are computed using temperature and salinity profiles from Argo profiling floats located within eddies, which are identified in sea–surface height using objective techniques [Chelton et al., 2011]. Ninety cyclonic and 154 anticyclonic eddies are identified during this period. The anticyclonic eddies are strongly non‐linear and exhibit significant warm subsurface temperature anomalies and associated salty anomalies on isopycnals while no clear distinguishing subsurface anomalies on isopycnals are detected in association with the cyclonic eddies. Heat and freshwater fluxes for the eddies are estimated from integrations in depth coordinates. The anticyclonic eddies transport heat both westward off the continental shelf into the Subarctic Gyre and westward within the Alaskan Stream. However, they transport salt into the Subarctic Gyre and freshwater within the Alaskan Stream. In both pathways eddy heat and freshwater transport show possible year‐to‐year fluctuations, varying from 0 to 50.4 × 1018 J a−1 and ‐16.8 to +7.4 km3 a−1, respectively. The anticyclonic eddies are capped by relatively fresh water year‐round. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-29T08:18:26.948433-05:
      DOI: 10.1002/2014JC010252
       
  • Drivers of deep water renewal events observed over 13 years in the South
           Basin of Lake Baikal
    • Authors: Chrysanthi Tsimitri; Burkhardt Rockel, Alfred Wüest, Nikolay M. Budnev, Michael Sturm, Martin Schmid
      Pages: n/a - n/a
      Abstract: Lake Baikal, with a depth of 1637 m, is characterized by deep‐water intrusions that bridge the near‐surface layer to the hypolimnion. These episodic events transfer heat and oxygen over large vertical scales and maintain the permanent temperature stratified deep‐water status of the lake. Here we evaluate a series of intrusion events that reached the bottom of the lake in terms of the stratification and the wind conditions under which they occurred and provide a new insight into the triggering mechanisms. We make use of long‐term temperature and current meter data (2000 to 2013) recorded in the South Basin of the lake combined with wind data produced with a regional downscaling of the global NCEP‐RA1 reanalysis product. A total of 13 events were observed during which near‐surface cold water reached the bottom of the South Basin at 1350 m depth. We found that the triggering mechanism of the events is related to the time of the year that they take place. We categorized the events in three groups: (1) Winter events, observed shortly before the complete ice cover of the lake that are triggered by Ekman coastal downwelling, (2) under‐ice events, and (3) spring events, that show no correlation to the wind conditions and are possibly connected to the increased spring outflow of the Selenga River. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-29T07:57:58.932475-05:
      DOI: 10.1002/2014JC010449
       
  • Upper ocean flow statistics estimated from superresolved sea‐surface
           temperature images
    • Authors: Shane R. Keating; K. Shafer Smith
      Pages: n/a - n/a
      Abstract: Ocean turbulence on scales of 10‐50 km plays a key role in biogeochemical processes, frontal dynamics, and tracer transport in the upper ocean, but our understanding of these scales is limited because they are too small to be resolved using extant satellite altimetry products. By contrast, microwave imagery of the sea‐surface temperature field does resolve these scales and can be used to estimate the upper ocean flow field due to the strong correlation between the surface density field and the interior potential vorticity. However, because the surface density (or temperature) is a smoothed version of the geostrophic streamfunction, the resulting velocity field estimates are limited to scales of 100‐300 km in the first few hundred meters of the water column. A method is proposed for generating superresolved sea‐surface temperature images using direct low‐resolution (microwave) temperature observations in combination with an empirical parameterization for the unresolved scales modeled on statistical information from high‐resolution (infrared) imagery. Because the method relies only on the statistics of the small‐scale field, it is insensitive to data outages due to cloud cover that affect infrared observations. The method enhances the effective resolution of the temperature images by exploiting the effect of spatial aliasing and generates an optimal estimate of the small‐scale temperature field using standard Bayesian inference. The technique is tested in quasigeostrophic simulations driven by realistic climatological shear and stratification profiles for three contrasting regions at high, middle, and low latitudes. The resulting superresolved sea‐surface temperature images are then used to estimate the three‐dimensional velocity field in the upper ocean on scales of 10‐50km. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-29T07:21:34.836941-05:
      DOI: 10.1002/2014JC010357
       
  • Seasonal variation in the South China Sea deep circulation
    • Authors: Jian Lan; Yu Wang, Fengjuan Cui, Ningning Zhang
      Pages: n/a - n/a
      Abstract: The previous studies show that the SCS deep circulation is featured by a basin‐scale cyclonic gyre. On the basis of the Hybrid Coordinate Ocean Model (HYCOM) and the Simple Ocean Data Assimilation (SODA), this study attempts to examine its seasonal variability and to investigate the driving mechanism. During summer season, the basin‐scale cyclonic gyre is dominant and strong, corresponding to higher value of the deepwater overflow transport. During winter season, the basin‐scale cyclonic gyre can hardly be identified, corresponding to lower value of the deepwater overflow transport. The control run and the SODA show the similar results. Two sensitivity experiments are designed to investigate what could be possible responsible for the seasonal variation in the SCS deep circulation. The results reveal that the deepwater overflow through the Luzon Strait contributes to the seasonal variability of the SCS deep circulation, and the seasonal variation of the surface forcings have less influence on that. The mechanism is related to the potential vorticity flux by the deepwater overflow. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-29T06:19:40.373844-05:
      DOI: 10.1002/2014JC010413
       
  • Interannual Caribbean salinity in satellite data and model simulations
    • Authors: Semyon A. Grodsky; Benjamin K. Johnson, James A. Carton, Frank O. Bryan
      Pages: n/a - n/a
      Abstract: Aquarius sea surface salinity (SSS) reveals the presence of interannual variations in the Caribbean with about 0.5 psu change between salty and fresh events, which propagate westward across that basin at an average speed of 11cm/s and are preceded by corresponding SSS anomalies east of the Lesser Antilles. These upstream SSS anomalies are produced by interannual changes in the Amazon plume. Their presence is verified using in‐situ measurements from the Northwest Tropical Atlantic Station. In contrast to SSS, which displays westward propagation, SST changes almost immediately across the Caribbean, suggesting large‐scale atmospheric processes have a primary role in regulating interannual SST in contrast to SSS. A global 1/10° mesoscale ocean model is used to quantify possible origination mechanisms of the Caribbean salinity anomalies and their fate. Simulations confirm that they are produced by anomalous horizontal salt advection, which conveys these salinity anomalies from an area east of the Lesser Antilles across the Caribbean. Anomalous horizontal advection is dominated by mean currents acting on anomalous salinity. The model suggests that interannual Caribbean salinity anomalies eventually enter the Florida Current and reach the Gulf Stream 6 to 12 months after crossing the central Caribbean. Previous studies link the origin of salinity anomalies in the Amazon plume to variations in the annual freshwater discharge from the continent. In this model interannual discharge variations are absent while simulated SSS variability is in line with observations. This suggests that interannually forced ocean dynamics plays a key role in river plume variability and its spatial dispersion. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-29T05:36:10.136137-05:
      DOI: 10.1002/2014JC010625
       
  • Spatial variances of wind fields and their relation to second‐order
           structure functions and spectra
    • Authors: Jur Vogelzang; Gregory P. King, Ad Stoffelen
      Pages: n/a - n/a
      Abstract: Kinetic energy variance as a function of spatial scale for wind fields is commonly estimated either using second‐order structure functions (in the spatial domain) or by spectral analysis (in the frequency domain). Both techniques give an order‐of‐magnitude estimate. More accurate estimates are given by a statistic called spatial variance. Spatial variances have a clear interpretation and are tolerant for missing data. They can be related to second‐order structure functions, both for discrete and continuous data. Spatial variances can also be Fourier transformed to yield a relation with spectra. The flexibility of spatial variances is used to study various sampling strategies, and to compare them with second‐order structure functions and spectral variances. It is shown that the spectral sampling strategy is not seriously biased to calm conditions for scatterometer ocean surface vector winds. When the second‐order structure function behaves like rp, its ratio with the spatial variance equals (p+1)(p+2). Ocean surface winds in the tropics have p between 2/3 and 1, so one‐sixth to one‐fifth of the second‐order structure function value is a good proxy for the cumulative variance. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-29T04:38:13.763333-05:
      DOI: 10.1002/2014JC010239
       
  • Variability in diatom contributions to biomass, organic matter production,
           and export across a frontal gradient in the California Current Ecosystem
    • Authors: Jeffrey W. Krause; Mark A. Brzezinski, Ralf Goericke, Michael R. Landry, Mark D. Ohman, Michael R. Stukel, Andrew G. Taylor
      Pages: n/a - n/a
      Abstract: In the offshore waters of Southern California, sub‐mesoscale processes associated with fronts may stimulate phytoplankton blooms and lead to biomass shifts at multiple trophic levels. Here we report the results of a study on the cycling of biogenic silica (bSiO2) with estimates of the contributions of diatoms to primary and new production in water masses adjacent to (i.e. coastal or oceanic) and within an offshore front in the Southern California Current Ecosystem (CCE). The coastal and oceanic water were sampled in cyclonic and anticyclonic eddies, respectively, with the frontal water being an interaction region between the eddy types. Concentrations of bSiO2 varied by 25‐fold across the front, with concentrations in frontal waters 20–25% of those in coastal waters. Rates of biogenic silica production spanned an equally large range, with rates within the frontal region that were half those in the coastal regions. Contributions of diatoms to primary and new production were disproportionately higher than their contribution to autotrophic biomass in all areas, ranging from 5–8%, 19–30% and 32–43% for both processes in the oceanic, frontal and coastal waters, respectively. Across the frontal area, diatoms could account for
      PubDate: 2015-01-27T10:13:54.162384-05:
      DOI: 10.1002/2014JC010472
       
  • A model for partitioning the light absorption coefficient of natural
           waters into phytoplankton, nonalgal particulate, and colored dissolved
           organic components: A case study for the Chesapeake Bay
    • Authors: Guangming Zheng; Dariusz Stramski, Paul M. DiGiacomo
      Pages: n/a - n/a
      Abstract: We present a model, referred to as Generalized Stacked Constraints Model (G‐SCM), for partitioning the total light absorption coefficient of water (with pure‐water contribution subtracted), anw(λ), into phytoplankton, aph(λ), non‐algal particulate, ad(λ), and CDOM, ag(λ), components. The formulation of the model is based on the so‐called stacked‐constraints approach which utilizes a number of inequality constraints that must be satisfied simultaneously by the model outputs of component absorption coefficients. A major advancement is that G‐SCM provides a capability to separate the ad(λ) and ag(λ) coefficients from each other using only weakly restrictive assumptions about the component absorption coefficients. In contrast to the common assumption of exponential spectral shape of ad(λ) and ag(λ) in previous models, in our model these two coefficients are parameterized in terms of several distinct spectral shapes. These shapes are determined from field data collected in the Chesapeake Bay with an ultimate goal to adequately account for the actual variability in spectral shapes of ad(λ) and ag(λ) in the study area. Another advancement of this model lies in its capability to account for potentially non‐negligible magnitude of ad(λ) in the near‐infrared spectral region. Evaluation of model performance demonstrates good agreement with measurements in the Chesapeake Bay. For example, the median ratio of the model‐derived to measured ad(λ), ag(λ), and aph(λ) at 443 nm is 0.913, 1.064, and 1.056, respectively. Whereas our model in its present form can be a powerful tool for regional studies in the Chesapeake Bay, the overall approach is readily adaptable to other regions or bio‐optical water types. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-27T09:33:06.104342-05:
      DOI: 10.1002/2014JC010604
       
  • Remote versus local influence of ENSO on the California Current System
    • Authors: M. Frischknecht; M. Münnich, N. Gruber
      Pages: n/a - n/a
      Abstract: Much of the observed interannual variability in the physical and biogeochemical state of the California Current System (CalCS) is associated with El‐Niño‐Southern‐Oscillation. Yet it is unclear whether this is primarily a result of atmospheric teleconnections forcing the ocean locally through changes in wind and fluxes of heat and freshwater, or whether this is a consequence of oceanic interior processes that transport tropical variability through e.g., coastally trapped waves to the region. Here we investigate the relative contribution of these two mechanisms in the CalCS using a novel setup of the Regional Oceanic Modeling System coupled to a biogeochemical/ecological model. We conducted a hindcast simulation over the period 1979‐2013 and contrast the results with those from sensitivity simulations with climatological atmospheric boundary conditions either for the U.S. West Coast or the rest of the Pacific. We find that remote forcing dominates the variability of the physical state in the nearshore region of the CalCS, explaining up to 80% of monthly mean sea‐surface height and temperature variability. In contrast, local processes tend to drive variations in the biogeochemical/ecological state, particularly along central and northern California, explaining up to 50% of the observed surface variability. Most of the remote forcing is a consequence of coastally trapped waves that travel northward at speeds of approximately 230km day−1, and thereby alter sea‐level height, thermocline structure, and upwelling along California. Biogeochemically active tracers respond to this remote forcing as well, especially at depth, but are more strongly modulated by local atmospheric forcing, especially variations in upwelling‐favorable winds. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-27T08:56:46.09117-05:0
      DOI: 10.1002/2014JC010531
       
  • Seasonality of the transitional region of the California Current System
           off Baja California
    • Authors: Reginaldo Durazo
      Pages: n/a - n/a
      Abstract: Hydrographic data collected over the period 1997‐2013 are analyzed to investigate the seasonality of hydrographic features and associated geostrophic flows off the Baja California peninsula. The upper ocean in the region was found to be homogeneous in winter and spring but subdivided into two regions in the summer and autumn. In the first case, the system typically shows relatively low temperature and salinity waters, which give it a subarctic character. In the second, only the region north of Punta Eugenia (28° N) maintains subarctic characteristics, while the southern region receives an inflow of tropical and subtropical waters that results from the weakening of northwesterly winds, which allows the poleward advection of surface waters. Also during this period, a positive wind stress curl promotes the zonal advection of North Pacific's eastern edge waters into the coast and to the north as a surface coastal flow. Average seasonal patterns of geostrophic flow at 200 dbar revealed that the differentiation into provinces is also evident at that depth, with two clearly defined cyclonic structures in summer and autumn, both separated at the latitude of Punta Eugenia. The analyses conducted also showed a clear continuity of the California undercurrent along the shelf break, with more diffuse currents in the winter. Poleward flows were observed throughout the water column, especially in summer and autumn, although the origin of the surface flow does not necessarily involve a surfacing of the California Undercurrent. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-27T06:59:48.141271-05:
      DOI: 10.1002/2014JC010405
       
  • Numerical study of solute transport in shallow beach aquifers subjected to
           waves and tides
    • Authors: Xiaolong Geng; Michel C. Boufadel
      Pages: n/a - n/a
      Abstract: A numerical study was conducted to investigate the fate of solute in a laboratory beach in response to waves and tides. A new temporal upscaling approach labeled “net inflow” was introduced to address impacts of waves on solute transport within beaches. Numerical simulations using a computational fluid dynamic model were used as boundary conditions for the two‐dimensional variably saturated flow and solute transport model MARUN. The modeling approach was validated against experimental data of solute transport due to waves and tides. Exchange fluxes across the beach face and subsurface solute transport (e.g., trajectory, movement speed, and residence time) were quantified. Simulation results revealed that waves increased the exchange fluxes, and engendered a wider exchange flux zone along the beach surface. Compared to tide‐only forcing, waves superimposed on tide caused the plume to be deeper into the beach, and to migrate more seaward. The infiltration into the beach was found to be directly proportional to the general hydraulic gradient in the beach and inversely proportional to the matrix retention (or capillary) capacity. The simulations showed that a higher inland water table would attenuate wave‐caused seawater infiltration, which might impact beach geochemical processes (e.g., nutrient recycle and redox condition), especially at low tide zone. The concept of biochemical residence time maps (BRTM) was introduced to account for the net effect of limiting concentration of chemicals on biochemical reactions. It was found that waves shifted the BRTMs downward and seaward in the beach, and subsequently they engendered different biochemical conditions within the beach. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-27T06:37:08.161046-05:
      DOI: 10.1002/2014JC010539
       
  • Failure to bloom: Intense upwelling results in negligible phytoplankton
           response and prolonged CO2 outgassing over the Oregon shelf
    • Authors: Wiley Evans; Burke Hales, Peter G. Strutton, R. Kipp Shearman, John A. Barth
      Pages: n/a - n/a
      Abstract: During summer, upwelled water with elevated CO2 partial pressure (pCO2) and nutrients outcrops over the Oregon (OR) inner shelf. As this water transits across the shelf, high rates of primary production fueled by the upwelled nutrients results in net atmospheric CO2 drawdown. Upwelled source‐waters typically have pCO2 approaching 1000 μatm that is then reduced to ∼200 μatm. For almost the entire month of July 2008, strong and persistent upwelling brought cold (∼8 °C), saline (∼33.5), high‐pCO2 (>600 µatm) water to our midshelf buoy site, and high‐pCO2 water was broadly distributed over the shelf. Chlorophyll levels, as a proxy for phytoplankton biomass, were low (< 2mg m‐3) on the shelf during the period of most intense upwelling, and satellite data showed no evidence of a downstream phytoplankton bloom. A small chlorophyll increase to ∼4mg m‐3 was observed at our buoy site following a decrease in the strength of southward wind stress 10 days after upwelling initiated. Chlorophyll levels further increased to ∼10mg m‐3 only after a cease in upwelling. These higher levels were coincident with the appearance of water masses having temperature and salinity properties distinct from recently upwelled water. We suggest that rapid offshore transport and subsequent subduction before phytoplankton populations could respond is the most likely explanation for the persistent low chlorophyll and elevated surface‐water pCO2 throughout the July upwelling event. This mechanism likely dominates under conditions of strong and persistent upwelling‐favorable winds that coincide with close proximity of low‐density offshore waters, which may have implications for the biogeochemical functioning of this system under future climate scenarios. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-27T05:52:17.720265-05:
      DOI: 10.1002/2014JC010580
       
  • Peru‐Chile upwelling dynamics under climate change
    • Authors: Véra Oerder; Francois Colas, Vincent Echevin, Francis Codron, Jorge Tam, Ali Belmadani
      Pages: n/a - n/a
      Abstract: The consequences of global warming on the Peru‐Chile Current System (PCCS) ocean circulation are examined with a high‐resolution, eddy‐resolving regional oceanic model. We performed a dynamical downscaling of climate scenarios from the IPSL‐CM4 Coupled General Circulation Model (CGCM), corresponding to various levels of CO2 concentrations in the atmosphere. High‐resolution atmospheric forcing for the regional ocean model are obtained from the IPSL atmospheric model run on a stretched grid with increased horizontal resolution in the PCCS region. When comparing future scenarios to Pre‐Industrial (PI) conditions, the circulation along the Peru and Chile coasts is strongly modified by changes in surface winds and increased stratification caused by the regional warming. While the coastal poleward undercurrent is intensified, the surface equatorial coastal jet shoals and the nearshore mesoscale activity are reinforced. Reduction in alongshore wind stress and nearshore wind stress curl drive a year‐round reduction in upwelling intensity off Peru. Modifications in geostrophic circulation mitigate this upwelling decrease in late austral summer. The depth of the upwelling source waters becomes shallower in warmer conditions, which may have a major impact on the system's biological productivity. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-27T05:11:57.27011-05:0
      DOI: 10.1002/2014JC010299
       
  • The impact of mean state errors on equatorial Atlantic interannual
           variability in a climate model
    • Authors: Hui Ding; Noel Keenlyside, Mojib Latif, Wonsun Park, Sebastian Wahl
      Pages: n/a - n/a
      Abstract: Observations show that the Equatorial Atlantic Zonal Mode (ZM) obeys similar physics to the El Niño Southern Oscillation (ENSO): positive Bjerknes and delayed negative feedbacks. This implies the ZM may be predictable on seasonal timescales, but models demonstrate little prediction skill in this region. In this study using different configurations of the Kiel Climate Model (KCM) exhibiting different levels of systematic error, we show that a reasonable simulation of the ZM depends on realistic representation of the mean state, i.e., surface easterlies along the equator, upward sloping thermocline to the east, with an equatorial SST cold tongue in the east. We further attribute the differences in interannual variability among the simulations to the individual components of the positive Bjerknes and delayed negative feedbacks. Differences in the seasonality of the variability are similarly related to the impact of seasonal biases on the Bjerknes feedback. Our results suggest that model physics must be enhanced to enable skillful seasonal predictions in the Tropical Atlantic Sector, although some improvement with regard to the simulation of Equatorial Atlantic interannual variability may be achieved by momentum flux correction. This pertains especially to the seasonal phase locking of interannual SST variability. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-27T04:49:11.222553-05:
      DOI: 10.1002/2014JC010384
       
  • A semianalytical model for sheet flow layer thickness with application to
           the swash zone
    • Authors: Thijs Lanckriet; Jack A. Puleo
      Pages: n/a - n/a
      Abstract: A new semi‐analytical model for the time‐dependent thickness of the sheet flow layer that includes the effects of pressure gradients, bed slope, boundary layer growth, and bore turbulence is presented. The shear stress and boundary layer growth are computed using the boundary layer integral method. The model is expressed as two coupled ordinary differential equations that are solved numerically given a prescribed time series of free‐stream velocity, horizontal pressure gradient and bore turbulence, which together represent the hydrodynamic forcing. The model was validated against two datasets of sheet flow layer thickness collected in oscillatory flow tunnels and one dataset collected in the swash zone of a prototype‐scale laboratory experiment. In the oscillatory flow tunnel datasets, sheet flow is mostly generated by shear stress, with pressure gradients providing an important secondary forcing around flow reversal. In the swash zone, pressure gradients and shear stresses alone are not sufficient to generate the large sheet flow layer thickness observed at the initial stages of uprush. Bore turbulence is most likely the dominant generation mechanism for this intense sheet flow. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-27T03:35:01.688506-05:
      DOI: 10.1002/2014JC010378
       
  • Seasonal ice loss in the Beaufort Sea: Toward synchrony and prediction
    • Authors: Michael Steele; Suzanne Dickinson, Jinlun Zhang, Ron Lindsay
      Pages: n/a - n/a
      Abstract: The seasonal evolution of sea ice loss in the Beaufort Sea during 1979‐2012 is examined, focusing on differences between eastern and western sectors. Two stages in ice loss are identified: the Day of Opening (DOO) is defined as the spring decrease in ice concentration from its winter maximum below a value of 0.8 areal concentration; the Day of Retreat (DOR) is the summer decrease below 0.15 concentration. We consider three aspects of the subject, i.e. (i) the long‐term mean, (ii) long‐term linear trends, and (iii) interannual variability. We find that in the mean, DOO occurs earliest in the eastern Beaufort Sea (EBS) owing to easterly winds which act to thin the ice there, relative to the western Beaufort Sea (WBS) where ice has been generally thicker. There is no significant long‐term trend in EBS DOO, although WBS DOO is in fact trending toward earlier dates. This means that spatial differences in DOO across the Beaufort Sea have been shrinking over the past 33 years, i.e., these dates are becoming more synchronous, a situation which may impact human and marine mammal activity in the area. Retreat dates are also becoming more synchronous, although with no statistical significance over the studied time period. Finally, we find that in any given year, an increase in monthly mean easterly winds of ∼ 1m/s during spring is associated with earlier summer DOR of 6‐15 days, offering predictive capability with 2‐4 months lead time. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-27T03:34:50.375033-05:
      DOI: 10.1002/2014JC010247
       
  • Impact of improved light calculations on predicted phytoplankton growth
           and heating in an idealized upwelling‐downwelling channel geometry
    • Authors: Curtis D. Mobley; Fei Chai, Peng Xiu, Lydia K. Sundman
      Pages: n/a - n/a
      Abstract: Ocean ecosystem models require accurate calculations of both hydrodynamics and biology; those calculations in turn require accurate calculation of in‐water irradiance. Ecosystem models now achieve great accuracy in their hydrodynamical predictions, and the biological modules are becoming correspondingly sophisticated. The optical calculations are however often oversimplified, to the possible detriment of the physical and biological predictions. We used a recently developed, extremely fast radiative transfer code, EcoLight‐S, to study differences in ecosystem and thermal development in an idealized upwelling‐downwelling system when simple vs accurate irradiance calculations are used. The use of accurate irradiances gave up to 57% differences in chlorophyll concentrations after two weeks of simulated time, compared to predictions based on irradiances obtained using a simple exponential attenuation formula. Accurate irradiance calculations increased sea surface temperatures and decreased temperatures at depth, leading to increased stratification. Use of EcoLight‐S couples the physical and biological calculations so that biology feeds back to physics, and vice versa. EcoLight‐S outputs ancillary quantities such as remote sensing reflectance and in‐water spectral irradiance, which can be used to validate ecosystem predictions using remotely sensed ocean color imagery or optical measurements from buoys or gliders, without the need to convert such measurements to chlorophyll values. After optimization, the ecosystem model total run times with EcoLight‐S were less than 20% more than for the analytical irradiance models. We also found that the use of 24‐hour‐average irradiances gave factor‐of‐two differences in chlorophyll concentrations compared to the use of a diel irradiance pattern with the same 24‐hour average value. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-27T03:32:18.392567-05:
      DOI: 10.1002/2014JC010588
       
  • Modeling the impact of glacial runoff on fjord circulation and submarine
           melt rate using a new subgrid‐scale parameterization for glacial
           plumes
    • Authors: Tom Cowton; Donald Slater, Andrew Sole, Dan Goldberg, Peter Nienow
      Pages: n/a - n/a
      Abstract: The injection at depth of ice sheet runoff into fjords may be an important control on the frontal melt rate of tidewater glaciers. Here, we develop a new parameterization for ice marginal plumes within the Massachusetts Institute of Technology General Circulation Model (MITgcm), allowing three‐dimensional simulation of large (500km2) glacial fjords on annual (or longer) timescales. We find that for an idealized fjord (without shelf‐driven circulation), subglacial runoff produces a thin, strong and warm down‐fjord current in the upper part of the water column, balanced by a thick and slow up‐fjord current at greater depth. Although submarine melt rates increase with runoff due to higher melt rates where the plume is in contact with the ice front, we find that annual submarine melt rate across the ice front is relatively insensitive to variability in annual runoff. Better knowledge of the spatial distribution of runoff, controls on melt rate in those areas not directly in contact with plumes and feedback mechanisms linking submarine melting and iceberg calving are necessary to more fully understand the sensitivity of glacier mass balance to runoff‐driven fjord circulation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-22T09:02:24.362474-05:
      DOI: 10.1002/2014JC010324
       
  • A novel tracer technique to quantify the atmospheric flux of trace
           elements to remote ocean regions
    • Authors: David Kadko; William M. Landing, Rachel U. Shelley
      Pages: n/a - n/a
      Abstract: Atmospheric input into the global ocean constitutes an important budgetary component of numerous chemical species and plays a key role in controlling biogeochemical processes in the ocean. Assessment of this input is difficult however because measurements of deposition rates to the ocean, particularly in remote areas, are rare and susceptible to problems of temporal and spatial variability. While the collection and analysis of aerosol samples is somewhat routine, the chemical concentration data collected from ship board or land‐based aerosol samplers in and of themselves cannot yield the deposition flux of trace elements; a method is required to transform concentration measurements into flux. The ability to derive the atmospheric flux of 7Be from its ocean inventory provides a key linkage between the atmospheric concentration of chemical species and their deposition to the ocean. We have demonstrated that estimates of the atmospheric flux of trace elements (TEs) can be made by multiplying the ocean inventory of 7Be x [TE/7Be] ratio in bulk aerosols. Flux estimates for trace elements made by the 7Be ocean inventory method were comparable to fluxes derived from rain samples collected on the island of Bermuda. The situation at Bermuda allows such testing to be made, where ocean‐based methods can be calibrated by convenient land locations. Our results suggest that this method would be useful for remote areas where fixed sampling stations do not exist; that is, the majority of the global ocean. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-22T05:53:30.473059-05:
      DOI: 10.1002/2014JC010314
       
  • Analysis of ageostrophy in strong surface eddies in the Atlantic Ocean
    • Authors: E. M. Douglass; J. G. Richman
      Pages: n/a - n/a
      Abstract: Strongly nonlinear surface eddies are identified and analyzed in a general circulation model. Agulhas rings and Gulf Stream cold core eddies are examples of eddies that cannot be properly characterized using linear geostrophic dynamics. These eddies are compact, highly circular, persistent in time, and travel long distances while maintaining their characteristics. The nonlinear eddies can be identified by a large Rossby number and high circularity. The majority of the anomalous eddies are anticyclones. Calculation of the balance of forces on these eddies demonstrates that the centrifugal force associated with strong curvature is significant, and the force balance shifts from geostrophy towards a gradient wind balance. Using geostrophy instead of the gradient wind balance produces large errors in estimates of rotational velocity of these eddies. The gradient wind velocity can be calculated from geostrophic velocity and eddy radius. Comparison between the results demonstrates that even when only sea surface height and associated geostrophic velocities are available, strongly nonlinear eddies can be identified and properly characterized. This analysis is then applied to altimetric maps of sea surface height. Nonlinear eddies are present in the altimetric maps, but are less common and not as strongly nonlinear. This analysis demonstrates that by properly accounting for the dynamics of the eddy field, a more complete statistical description including nonlinear terms can be obtained from readily available observations. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-22T04:53:09.270766-05:
      DOI: 10.1002/2014JC010350
       
  • Seasonal and interannual variability of the West Greenland Current System
           in the Labrador Sea in 1993–2008
    • Authors: Tatiana Rykova; Fiammetta Straneo, Amy S. Bower
      Pages: n/a - n/a
      Abstract: The West Greenland Current system (WGCS) transports heat and freshwater into the Labrador Sea, influencing the formation of Labrador Sea Water, a key component of the Atlantic Meridional Overturning Circulation. Notwithstanding its importance, relatively little is known about the structure and transport of this current system and its seasonal and interannual variability. Here we use historical hydrographic data from 1992 to 2008, combined with AVISO satellite altimetry, to diagnose the mean properties as well as seasonal and interannual variability of the boundary current system. We find that while the surface, fresh, cold West Greenland Current is amplified in summer, the subsurface warm, salty Irminger Current has maximum transport in winter, when its waters are also warmer and saltier. Seasonal changes in the total transport are thus mostly due to changes in the baroclinic structure of the current. By contrast, we find a trend towards warmer/saltier waters and a slow down of the WGCS, within the period studied. The latter is attributed to changes in the barotropic component of the current. Superimposed on this trend, warm and salty anomalies transit through the system in 1997 and 2003 and are associated with a rapid increase in the transport of the boundary current due to changes in the baroclinic component. The boundary current changes precede similar changes in the interior with a one‐two year lag, indicating that anomalies advected into the region by the boundary current can play an important role in the modulation of convection in the Labrador Sea. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-22T04:32:05.982478-05:
      DOI: 10.1002/2014JC010386
       
  • Cross‐polarization geophysical model function for C‐band radar
           backscattering from the ocean surface and wind speed retrieval
    • Authors: Paul A. Hwang; Ad Stoffelen, Gerd‐Jan van Zadelhoff, William Perrie, Biao Zhang, Haiyan Li, Hui Shen
      Pages: n/a - n/a
      Abstract: The wind speed sensitivity of cross‐polarization (cross‐pol) radar backscattering cross section (VH) from the ocean surface increases toward high winds. The signal saturation problem of VH, if it exists, occurs at a much higher wind speed compared to the co‐polarization (co‐pol: VV or HH) sea returns. These properties make VH a better choice over VV or HH for monitoring severe weather. Combined with high spatial resolution of the synthetic aperture radar (SAR), the development of hurricane wind retrieval using VH is advancing rapidly. This paper describes a cross‐pol C‐band radar backscattering geophysical model function (GMF) with incidence angle dependence for the full wind speed range in the available datasets (up to 56m/s). The GMF is derived from RADARSAT‐2 (R2) dual‐polarization (dual‐pol) ScanSAR modes with 300 and 500km swaths. The proposed GMF is compared to other published algorithms. The result shows that the simulated VH cross section and the retrieved wind speed with the proposed GMF is in better agreement with measurements. With careful treatment of noise, the VH retrieved wind speeds may extend to mild or moderate conditions. The higher fraction of non‐Bragg contribution in VH can be exploited for analysis of surface wave breaking. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-22T04:22:43.51846-05:0
      DOI: 10.1002/2014JC010439
       
  • An analytical model for the description of the full polarimetric sea
           surface Doppler signature
    • Authors: Franco Fois; Peter Hoogeboom, Franҫois Le Chevalier, Ad Stoffelen
      Pages: n/a - n/a
      Abstract: This paper describes an analytical model of the full‐polarimetric sea surface scattering and Doppler signature. The model combines the Small‐Slope‐Approximation theory (at the 2nd order) with a weak non‐linear sea surface representation. Such a model is used to examine the variation of the Doppler central frequency/bandwidth and of the Normalized Radar Cross‐section as function of wind‐speed and direction. The results suggest that the model can be a valuable tool for the accurate observation of sea surface currents. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T17:13:49.704765-05:
      DOI: 10.1002/2014JC010589
       
  • Detecting the surface salinity signature of Gulf Stream cold‐core
           rings in Aquarius synergistic products
    • Authors: M. Umbert; S. Guimbard, G. Lagerloef, L. Thompson, M. Portabella, J. Ballabrera‐Poy, A. Turiel
      Pages: n/a - n/a
      Abstract: New sea surface salinity (SSS) observations derived from satellite remote sensing platforms provide a comprehensive view of salt exchanges across boundary currents such as the Gulf Stream. The high resolution (45km spatial resolution and three‐day repeat subcycle) of the Soil Moisture and Ocean Salinity (SMOS) observations allows detection (and tracking) of meander and ring structures of the Gulf Stream from SSS maps. These structures are however not resolved by the relatively lower resolution (100km and seven‐day repeat subcycle) of Aquarius observations. A recently developed fusion technique, based on singularity analysis technique, is applied in this study to reconstruct these mesoscale (from 100km and 3 days) features in Aquarius‐derived products. New quarter‐degree SSS maps are obtained by fusing Aquarius data with three different geophysical templates: sea surface height (SSH) from AVISO, SSS from SMOS, and sea surface temperature (SST) from AVHRR. The proposed method exploits the theoretical correspondence among the singularity exponents of different maps of ocean‐surface remotely sensed scalar fields. The analysis results over the year 2012 show that merging Aquarius with SSH data provides a series of negative salinity anomalies that better collocate with the position of the cyclonic eddies identified from sea level anomaly maps. This result is consistent with the hypothesis that this SLA derived cyclonic eddies in this area are indeed CCRs shed off the GS. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T17:13:36.525252-05:
      DOI: 10.1002/2014JC010466
       
  • An approach to estimate the freshwater contribution from glacial melt and
           precipitation in East Greenland shelf waters using colored dissolved
           organic matter (CDOM)
    • Authors: Colin A. Stedmon; Mats. A Granskog, Paul A. Dodd
      Pages: n/a - n/a
      Abstract: Changes in the supply and storage of freshwater in the Arctic Ocean and its subsequent export to the North Atlantic can potentially influence ocean circulation and climate. In order to understand how the Arctic freshwater budget is changing and the potential impacts, it is important to develop and refine empirical approaches for tracing freshwater contributions. This in turn can help develop and validate model simulations. Arctic rivers are an important source of freshwater and stable oxygen isotope measurements are used to separate contributions from meteoric water (river, glacial, and precipitation) and sea ice melt. We develop this approach further and investigate the use of an additional tracer, colored dissolved organic matter (CDOM), which is largely specific to freshwater originating from Arctic rivers. A robust relationship between the freshwater contribution from meteoric water and CDOM is derived from four years of measurements in Fram Strait (2009‐2012), combined with measurements from the East Greenland shelf and Dijmpha Sound (NE Greenland). Results confirm a high contribution of riverine CDOM in Arctic halocline waters with salinities > 31.5 and indicate the importance of shelf processes (riverine input and sea ice formation), while previously, these waters where thought to be derived from open sea processes (cooling and sea‐ice formation) in the northern Barents and Kara Seas. In Greenlandic coastal waters the meteoric water contribution is influenced by Greenland Ice Sheet meltwater and deviations from the CDOM ‐ meteoric water relationships found are applied to quantify meltwater contribution along the East Greenland shelf waters (0‐13%). This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T10:54:13.966479-05:
      DOI: 10.1002/2014JC010501
       
  • Interannual variability of the northwestern Iberia deep ocean: Response to
           large‐scale North Atlantic forcing
    • Authors: E. Prieto; C. González‐Pola, A. Lavín, N.P. Holliday
      Pages: n/a - n/a
      Abstract: The oceanic hydrography of the north‐easternmost region of the North Atlantic subtropical gyre has been monitored since 2003 by three sections extending between 100 to 200 nautical miles from the Spanish NW and N coast into the Atlantic and the Bay of Biscay. The sections were occupied twice a year from 2003 to 2010, annually after that, and measure the whole water column (>5000m). Correlation of series in the vertical and among sections, autocorrelation and estimates of the effect of the noise induced by the mesoscale field, all indicate that observed signatures are robust changes of water masses at the regional scale. The hydrographic timeseries are not characterized by smooth trends but instead by shifts that persist through consecutive cruises. The most notable features include a shift to more saline central waters around 2005 after which they remained stable, and a decrease in thermohaline properties of the Labrador Sea Water from autumn 2008 to 2010. Years with a strong winter North Atlantic Oscillation (NAO) index are characterized by shifts in thermohaline properties across most of the intermediate levels, with the most notable event being the warming and increasing salinity that followed the large NAO index drop of 2010. The observations are consistent with current understanding of the large‐scale functioning of the North Atlantic, which predicts a northeastwards expansion of subtropical temperate waters in the eastern boundary as a response to NAO forcing. The observed variability is discussed in relationship to large‐scale circulation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T10:36:57.571309-05:
      DOI: 10.1002/2014JC010436
       
  • Oceanic responses to Hurricane Igor over the Grand Banks: A modeling study
    • Authors: Zhimin Ma; Guoqi Han, Brad de Young
      Pages: n/a - n/a
      Abstract: A three‐dimensional (3‐D) baroclinic finite‐volume ocean model (FVCOM) was developed to examine the oceanic response to Hurricane Igor over the Grand Banks of Newfoundland. Hurricane Igor generated a storm surge of almost 1m at St. John's and about 0.8m at three nearby coastal tide gauge stations (Bonavista, Argentia and St. Lawrence). The surge magnitude from the 3‐D baroclinic model agrees approximately with tide‐gauge observations at all four stations, slightly better than that from an alternative 3‐D barotropic case. The sudden drop of sea surface temperature caused by the storm, approximately as observed by buoys, is well simulated by the baroclinic model with a k‐ε turbulence closure. A sensitivity simulation with the Mellor‐Yamada turbulence closure significantly underestimates sea surface cooling. It is shown that the sea surface cooling is mainly associated with turbulent mixing, and to a lesser degree with Ekman upwelling. The model solution shows that the largest surge occurred between Bonavista and St. John's. Further analysis suggests the generation of a free continental shelf wave after the storm made landfall, with the peak surge propagating from St. John's to St. Lawrence. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T10:12:58.90142-05:0
      DOI: 10.1002/2014JC010322
       
  • Hydro‐acoustic and tsunami waves generated by the 2012 Haida Gwaii
           earthquake: Modeling and in situ measurements
    • Authors: Ali Abdolali; Claudia Cecioni, Giorgio Bellotti, James T. Kirby
      Pages: n/a - n/a
      Abstract: Detection of low‐frequency hydro‐acoustic waves as precursor components of destructive tsunamis can enhance the promptness and the accuracy of Tsunami Early Warning Systems (TEWS). We reconstruct the hydro‐acoustic wave field generated by the 2012 Haida Gwaii tsunamigenic earthquake using a 2D horizontal numerical model based on the integration over the depth of the compressible fluid wave equation and considering a mild sloped rigid sea‐bed. Spectral analysis of the wave field obtained at different water depths and distances from the source revealed the frequency range of low‐frequency elastic oscillations of sea water. The resulting 2D numerical model gave us the opportunity to study the hydro‐acoustic wave propagation in a large‐scale domain with available computers and to support the idea of deep‐sea observatory and data interpretation. The model provides satisfactory results, compared with in situ measurements, in the reproduction of the long‐gravitational waves. Differences between numerical results and field data are probably due to lack of exact knowledge of sea bottom motion and to the rigid sea‐bed approximation, indicating the need for further study of poro‐elastic bottom effects. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T09:53:34.519912-05:
      DOI: 10.1002/2014JC010385
       
  • SMOS salinity in the subtropical North Atlantic salinity maximum: 2.
           Two‐dimensional horizontal thermohaline variability
    • Authors: Nicolas Kolodziejczyk; Olga Hernandez, Jacqueline Boutin, Gilles Reverdin
      Pages: n/a - n/a
      Abstract: The horizontal thermohaline seasonal variability of the surface ocean is investigated in the subtropical North Atlantic Surface Salinity Maximum (SSSmax) region. Satellite sea surface temperature and salinity are used, along with high‐resolution thermosalinograph data, and Argo interpolated products, to study the horizontal two‐dimensional field of density and thermohaline variability. During late winter, compensated temperature and salinity gradients at large and mesoscale are observed northeast of the SSSmax, in the Azores Front Current region. In spite of the large and sharp surface thermohaline fronts, satellite measurements reveal a rather weak surface horizontal density gradient. During summer, the front is dominated by salinity gradients. South of the SSSmax, at large scales, the density ratio is controlled by the salinity gradient and the horizontal density gradient is enhanced by a constructive contribution of opposite salinity and temperature gradients. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T09:26:27.33134-05:0
      DOI: 10.1002/2014JC010103
       
  • The carbon dioxide (CO2) system on the Mississippi River‐dominated
           continental shelf in the northern Gulf of Mexico: 1. Distribution and
           air‐sea CO2 flux
    • Authors: Wei‐Jen Huang; Wei‐Jun Cai, Yongchen Wang, Steven E. Lohrenz, Michael C. Murrell
      Pages: n/a - n/a
      Abstract: River‐dominated continental shelf environments are active sites of air‐sea CO2 exchange. We conducted 13 cruises in the northern Gulf of Mexico, a region strongly influenced by fresh water and nutrients delivered from the Mississippi and Atchafalaya River system. The sea surface partial pressure of carbon dioxide (pCO2) was measured, and the air‐sea CO2 flux was calculated. Results show that CO2 exchange exhibited a distinct seasonality: this study area was a net sink of atmospheric CO2 during spring and early summer, and it was neutral or a weak source of CO2 to the atmosphere during mid‐summer, fall, and winter. Along the salinity gradient, across the shelf, the sea surface shifted from a source of CO2 in low salinity zones (0≤S
      PubDate: 2015-01-21T08:57:33.024993-05:
      DOI: 10.1002/2014JC010498
       
  • Overturning circulation that ventilates the intermediate layer of the Sea
           of Okhotsk and the North Pacific: The role of salinity advection
    • Authors: Junji Matsuda; Humio Mitsudera, Tomohiro Nakamura, Yuichiro Sasajima, Hiroyasu Hasumi, Masaaki Wakatsuchi
      Pages: n/a - n/a
      Abstract: Dense Shelf Water (DSW) formation in the northwestern continental shelf of the Sea of Okhotsk is the beginning of the lower limb of the overturning circulation that ventilates the intermediate layer of the North Pacific Ocean. The upper limb consisting of surface currents in the Okhotsk Sea and the subarctic gyre has not been clarified. Using a high resolution North Pacific Ocean model with a curvilinear grid as fine as 3km × 3km in the Sea of Okhotsk, we succeeded in representing the three‐dimensional structure of the overturning circulation including the narrow boundary currents and flows through straits that constitute the upper limb, as well as the lower limb consisting of DSW formation and ventilation. In particular, pathways and timescales from the Bering Sea to the intermediate layer via the ventilation in the Sea of Okhotsk were examined in detail using tracer experiments. Further, we found that the overturning circulation that connects the surface and intermediate layer is sensitive to wind stress. In the case of strong winds, the coastal current under polynyas where DSW forms is intensified, and consequently diapycnal transport from the surface layer to the intermediate layer increases. Strong winds also induce a positive sea surface salinity anomaly in the subarctic region, causing a significant decrease in the density stratification and increase in the DSW salinity (i.e. density). These processes act together to produce intense overturning circulation and deep ventilation, which may subduct even to the bottom of the Sea of Okhotsk if the wind is strong. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T08:57:11.697553-05:
      DOI: 10.1002/2014JC009995
       
  • Potential impact of the colored Amazon and Orinoco plume on tropical
           cyclone intensity
    • Authors: C. Newinger; R. Toumi
      Pages: n/a - n/a
      Abstract: The Amazon and the Orinoco river plumes modulate ocean stratification and color in the tropical North Atlantic. This changes air‐sea interactions and may thus be important for tropical cyclones (TCs). Using a regional ocean model, we try to separate the potential impact of river freshwater and light absorption on ocean temperatures, stability, and TC intensity. While the freshwater plume stabilizes the water column, there is no significant change in sea surface temperatures. However, increased stability and temperature inversions may reduce surface cooling feedbacks. The cooling inhibition index (CI) is larger when the river freshwater plume is present. Ocean color in the river plume on the other hand, blocks the deeper ocean from sunlight, leading to moderate surface warming (+0.1oC) and substantial subsurface cooling (‐0.3oC 100m mean temperature). As a consequence cold water is more readily available to passing storms and the CI decreases by . Using simple, idealized relationships between expected surface cooling and TC intensity, we find that river‐induced stability enhances strong TCs by up to ‐5 to ‐12 hPa, while ocean color may reduce intensity by +8 hPa to +16 hPa. The net impact of the colored plume is negligible for weak storms and a slight intensity reduction for stronger cyclones. Within the Amazon and Orinoco plume, the river freshwater effect may thus be substantially reduced or even offset by light absorbing particles. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T07:58:53.96792-05:0
      DOI: 10.1002/2014JC010533
       
  • Phytoplankton phenology in the coastal upwelling region off
           central‐southern Chile (35°S‐–38°S):
           Time‐space variability, coupling to environmental factors, and
           sources of uncertainty in the estimates
    • Authors: Andrea Corredor‐Acosta; Carmen E. Morales, Samuel Hormazabal, Isabel Andrade, Marco A. Correa‐Ramirez
      Pages: n/a - n/a
      Abstract: The annual cycle and phenology of phytoplankton (satellite‐derived chlorophyll‐a, Chl‐a) in the coastal upwelling region off central‐southern Chile, their time‐space variation, and the extent of their coupling with those of wind‐driven upwelling (as Zonal Ekman Transport, ZET), Sea Surface Temperature (SST), and Photosynthetically Active Radiation (PAR), were analyzed using a ∼10 y satellite time series (2002‐2012). Wavelet analysis (WA) was applied to extract the dominant frequencies of variability and their recurrence, to derive the phenological indexes, and to assess the extent of the coupling between Chl‐a and environmental forcing in the annual frequency. Index estimates were obtained from minimum and maximum accumulated values in two different frequency bands, annual (WA‐ANF) and all except the synoptic (WA‐ALF). The annual frequency was dominant in all the variables, however, the annual cycle and phenology of Chl‐a displayed higher submeso‐ and mesoscale variability. The mean onset date of Chl‐a was similar to those of PAR and ZET with WA‐ALF and cross‐WA indicated that, for the most part, their annual cycles were coupled or coherent. Few interannual changes in Chl‐a phenology were detected, including a ∼1 month longer duration (WA‐ALF) during La Niña 2010‐2011. The mean anomalies in the magnitudes of Chl‐a and ZET during the upwelling season showed a slight but significant trend, negative for Chl‐a and positive for ZET, while SST remained relatively constant. This pattern was unexpected since three La Niña‐related conditions were identified during the 2007‐2012 period. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-19T08:46:54.185196-05:
      DOI: 10.1002/2014JC010330
       
  • The spatial‐temporal variability of air‐sea momentum fluxes
           observed at a tidal inlet
    • Authors: D.G. Ortiz‐Suslow; B.K. Haus, N.J. Williams, N.M. Laxague, A.J.H.M. Reniers, H.C. Graber
      Pages: n/a - n/a
      Abstract: Coastal waters are an aerodynamically unique environment that have been little explored from an air‐sea interaction point of view. Consequently, most studies must assume that open ocean derived parameterizations of the air‐sea momentum flux are representative of the near shore wind forcing. Observations made at the New River Inlet in North Carolina, during the Riverine and Estuarine Transport experiment (RIVET), were used to evaluate the suitability of wind speed dependent, wind stress parameterizations in coastal waters. As part of the field campaign, a small, agile research vessel was deployed to make high resolution wind velocity measurements in and around the tidal inlet. The eddy covariance method was employed to recover direct estimates of the 10m neutral atmospheric drag coefficient from the three dimensional winds. Observations of wind stress angle, near‐surface currents, and heat flux were used to analyze the cross‐shore variability of wind stress steering off the mean wind azimuth. In general, for on‐shore winds above 5m/s, the drag coefficient was observed to be two and a half times the predicted open ocean value. Significant wind stress steering is observed within 2km of the inlet mouth, which is observed to be correlated with the horizontal current shear. Other mechanisms such as the reduction in wave celerity or depth‐limited breaking could also play a role. It was determined that outside the influence of these typical coastal processes the open ocean parameterizations generally represent the wind stress field. The near shore stress variability has significant implications for observations and simulations of coastal transport, circulation, mixing, and general surf‐zone dynamics. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-19T04:22:12.706836-05:
      DOI: 10.1002/2014JC010412
       
  • Wave Breaking and Turbulence at a Tidal Inlet
    • Authors: Seth Zippel; Jim Thomson
      Pages: n/a - n/a
      Abstract: Field measurements collected with surface drifters at New River Inlet (NC, USA) are used to characterize wave breaking and turbulence in the presence of currents. Shoreward wave evolution is affected by currents, and breaking is observed in deeper water with opposing currents (ebb tides) relative to to following currents (flood tides). Wave dissipation models are evaluated with observed cross‐shore gradients in wave energy flux. Wave dissipation models that include the effects of currents are better correlated with the observations than the depth‐only models. Turbulent dissipation rates measured in the breaking regions are used to evaluate two existing scaling models for the vertical structure and magnitude of turbulent dissipation relative to wave dissipation. Although both describe the rapid decay of turbulence beneath the surface, exponential vertical scaling by water depth is superior to power law vertical scaling by wave height. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-14T09:22:51.485799-05:
      DOI: 10.1002/2014JC010025
       
  • Cyclonic entrainment of pre‐conditioned shelf waters into a frontal
           eddy
    • Authors: J.D. Everett; H. Macdonald, M.E. Baird, J. Humphries, M. Roughan, I. M. Suthers
      Pages: n/a - n/a
      Abstract: The volume transport of nutrient‐rich continental shelf water into a cyclonic frontal eddy (entrainment) was examined from satellite observations, a slocum glider and numerical simulation outputs. Within the frontal eddy, parcels of water with temperature/salinity signatures of the continental shelf (18‐19C and >35.5 respectively) were recorded. The distribution of patches of shelf water observed within the eddy were consistent with the spiral pattern shown within the numerical simulations. A numerical dye‐tracer experiment showed that the surface waters ( 50m depth) of the frontal eddy are almost entirely ( 95%) shelf waters. Particle tracking experiments showed that water was drawn into the eddy from over 4 degrees of latitude (30‐34.5S). Consistent with the glider observations, the modeled particles entrained into the eddy sunk relative to their initial position. Particles released south of 33S, where the waters are cooler and denser, sunk 30‐50m deeper than their release position. Distance to the shelf was a critical factor in determining the volume of shelf water entrained into the eddy. Entrainment reduced to 0.23 Sv when the eddy was furthest from the shelf, compared to 0.61 Sv when the eddy was within 10km of the shelf. From a biological perspective, quantifying the entrainment of shelf water into frontal eddies is important, as it is thought to play a significant role in providing an offshore nursery habitat for coastally‐spawned larval fish. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-14T08:57:57.475991-05:
      DOI: 10.1002/2014JC010301
       
  • Impacts of a mushy‐layer thermodynamic approach in global
           sea‐ice simulations using the CICE sea‐ice model
    • Authors: Adrian K. Turner; Elizabeth C. Hunke
      Pages: n/a - n/a
      Abstract: We perform global simulations of the Los Alamos sea‐ice model, CICE, with a new thermodynamics component that has a fully prognostic, variable bulk salinity vertical profile based on mushy layer physics. The processes of gravity drainage, melt‐water flushing and snow‐ice formation are parameterized to allow the bulk salinity to evolve with time. We analyze the seasonal and spatial variation of sea‐ice bulk salinity, area, volume and thickness and compare these quantities to simulations using the previous thermodynamic component. Adjusting one of the gravity drainage parameters, we find good agreement between simulation results and fieldwork ice‐core observations of sea‐ice bulk salinity. As expected, bulk salinity is highest during periods of ice growth and lowest after periods of ice melt. In the northern hemisphere the new thermodynamics component produces thicker ice than the previous thermodynamics component. Of the nine major differences between the two models, differences in how salinities are calculated and how melt‐pond flushing is parameterized are the principal causes of this thickness difference. Thickness differences are smaller in the southern hemisphere than in the northern hemisphere since a greater fraction of ice melts, and differences cannot accumulate year‐on‐year. Model differences in how ice thickness changes and snow‐ice formation are calculated are the most important causes of the different thickness between the two thermodynamic components in the southern hemisphere. The melt‐pond area and volume are found to be highly sensitive to a parameter choice controlling drainage through macroscopic holes in the ice, in both hemispheres. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-14T06:51:19.917722-05:
      DOI: 10.1002/2014JC010358
       
  • Salinity fronts in the tropical Pacific Ocean
    • Authors: Hsun‐Ying Kao; Gary S. E. Lagerloef
      Pages: n/a - n/a
      Abstract: This study delineates the salinity fronts (SF) across the tropical Pacific, and describes their variability and regional dynamical significance using Aquarius satellite observations. From the monthly maps of the SF, we find that the SF in the tropical Pacific are (1) usually observed around the boundaries of the fresh pool under the intertropical convergence zone (ITCZ), (2) stronger in boreal autumn than in other seasons and (3) usually stronger in the eastern Pacific than in the western Pacific. The relationship between the SF and the precipitation and the surface velocity are also discussed. We further present detailed analysis of the SF in three key tropical Pacific regions. Extending zonally around the ITCZ, where the temperature is nearly homogeneous, we find the strong SF of 1.2 psu from 7‐11°N to be the main contributor of the horizontal density difference of 0.8kg/m3. In the eastern Pacific, we observe a southward extension of the SF in the boreal spring that could be driven by both precipitation and horizontal advection. In the western Pacific, the importance of these newly resolved SF associated with the western Pacific warm/fresh pool and El Niño southern oscillations are also discussed in the context of prior literature. The main conclusions of this study are that (a) Aquarius satellite salinity measurements reveal the heretofore unknown proliferation, structure and variability of surface salinity fronts, and that (b) the fine‐scale structures of the SF in the tropical Pacific yield important new information on the regional air‐sea interaction and the upper ocean dynamics. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-14T06:21:18.60986-05:0
      DOI: 10.1002/2014JC010114
       
  • Landfast ice affects the stability of the Arctic halocline: Evidence from
           a numerical model
    • Authors: Polona Itkin; Martin Losch, Rüdiger Gerdes
      Pages: n/a - n/a
      Abstract: Landfast ice covers large surface areas of the winter Siberian Seas. The immobile landfast ice cover inhibits divergent and convergent motion, hence dynamical sea ice growth and re‐distribution, decouples winter river plumes in coastal seas from the atmosphere and positions polynyas at the landfast ice edge offshore. In spite of the potentially large effects, state‐of‐the‐art numerical models usually do not represent landfast ice in its correct extent. A simple parametrization of landfast ice based on bathymetry and internal sea ice strength is introduced and its effects on the simulated Arctic Ocean are demonstrated. The simulations suggest that the Siberian landfast ice impacts the Arctic halocline stability through enhanced brine production in polynyas located closer to the shelf break and by re‐directing river water to the Canadian Basin. These processes strengthen the halocline in the Canadian Basin, but erode its stability in the Makarov and Eurasian Basins. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-09T23:06:50.341598-05:
      DOI: 10.1002/2014JC010353
       
  • Tidal bore dynamics in funnel‐shaped estuaries
    • Authors: P. Bonneton; N. Bonneton, J‐P. Parisot, B. Castelle
      Pages: n/a - n/a
      Abstract: The formation and dynamics of tidal bores in funnel‐shaped estuaries is investigated from both a global tidal wave scaling analysis and new quantitative field observations. We show that tidal bore occurrence in convergent estuaries can be estimated from a dimensionless scaling parameter characterizing the relative intensity of nonlinear friction versus local inertia in the momentum equation. A detailed analysis of tidal bore formation and secondary wave structure is presented from a unique long term database (observations of more than 200 tides) acquired during 4 campaigns in the two main French tidal‐bore estuaries: the Seine and Gironde/Garonne estuaries. We describe the effect of freshwater discharge on the global tidal wave transformation at the estuarine scale and on local tidal bore occurrence in the upper estuary. Our field data suggest that the tidal bore intensity is mainly governed by the dimensionless tidal range, which characterizes the local tidal wave nonlinearity. We also show that the secondary wave field associated with tidal bore propagating in natural estuaries differs significantly from those associated to undular bores in rectangular channels. In particular, we observe an abrupt decrease of the whelp steepness when the Froude number goes below 1.1. This secondary field transition can explain why tidal bore occurrence in worldwide estuaries is certainly underestimated. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-09T23:06:42.00595-05:0
      DOI: 10.1002/2014JC010267
       
  • Analysis of riverine suspended particulate matter fluxes (Gulf of Lion,
           Mediterranean Sea) using a synergy of ocean color observations with a
           3‐D hydrodynamic sediment transport model
    • Authors: Vincent Le Fouest; Malik Chami, Romaric Verney
      Pages: n/a - n/a
      Abstract: The export of riverine suspended particulate matter (SPM) in the coastal ocean has major implications for the biogeochemical cycles. In the Mediterranean Sea (France), the Rhone River inputs of SPM into the Gulf of Lion (GoL) are highly variable in time, which severely impedes the assessment of SPM fluxes. The objectives of this study are i) to investigate the prediction of the land‐to‐ocean flux of SPM using the complementarity (i.e., synergy) between a hydrodynamic sediment transport model and satellite observations, and ii) to analyze the spatial distribution of the SPM export. An original approach that combines the MARS‐3D model with satellite ocean color data is proposed. Satellite derived SPM and light penetration depth are used to initialize MARS‐3D and to validate its predictions. A sensitivity analysis is performed to quantify the impact of riverine SPM size composition and settling rate on the horizontal export of SPM. The best agreement between the model and the satellite in terms of SPM spatial distribution and export is obtained for two conditions: (i) when the relative proportion of “heavy and fast” settling particles significantly increases relative to the “light and slow” ones, and ii) when the settling rate of heavy and light SPM increases by 5‐fold. The synergy between MARS‐3D and the satellite data improved the SPM flux predictions by 48% near the Rhone River mouth. Our results corroborate the importance of implementing satellite observations within initialization procedures of ocean models since data assimilation techniques may fail for river floods showing strong seasonal variability. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-09T23:06:16.990916-05:
      DOI: 10.1002/2014JC010098
       
  • Wind‐driven modifications to the residual circulation in an
           ebb‐tidal delta: Arcachon Lagoon, Southwestern France
    • Authors: Paulo Salles; Arnoldo Valle‐Levinson, Aldo Sottolichio, Nadia Senechal
      Pages: n/a - n/a
      Abstract: A combination of observations and analytical solutions were used to determine the modifications caused by wind forcing on the residual or non‐tidal circulation in an ebb‐tidal delta. Observations were obtained in the lower Arcachon Lagoon, southwestern France. The basic non‐tidal circulation was established with acoustic Doppler current profilers (ADCPs) that were i) moored in the delta's two deepest channels, and ii) towed along a cross‐lagoon transect. The bathymetry of the lower lagoon, or ebb‐tidal delta, featured two channels: North Pass (>9 m) and South Pass (>20 m). The basic non‐tidal circulation consisted of mostly inflow with weak surface outflow in the South Pass, and laterally sheared bidirectional flow, dominated by outflow, in the North Pass. Analytical solutions and comparison of observed dynamical terms suggested that, in addition to the conventionally accepted influence of tidal nonlinearities, density gradients contributed to the basic non‐tidal circulation in the lagoon. Observations also indicated that wind forcing altered the basic circulation by driving simultaneous upwind flows in both passes. This response was supported by an analytical solution to wind‐driven flows over the bathymetry of the transect sampled. The response to seaward winds was to enhance inflow in South Pass and reduce outflow in North Pass. Landward winds caused diminished inflow in South Pass and increased outflow in North Pass. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-08T04:14:06.634615-05:
      DOI: 10.1002/2014JC010311
       
  • The refreezing of melt ponds on Arctic sea ice
    • Authors: Daniela Flocco; Daniel L. Feltham, Eleanor Bailey, David Schroeder
      Pages: n/a - n/a
      Abstract: The presence of melt ponds on the surface of Arctic sea ice significantly reduces its albedo, inducing a positive feedback leading to sea ice thinning. While the role of melt ponds in enhancing the summer melt of sea ice is well known, their impact on supressing winter freezing of sea ice has, hitherto, received less attention. Melt ponds freeze by forming an ice lid at the upper surface which insulates them from the atmosphere and traps pond water between the underlying sea ice and the ice lid. The pond water is a store of latent heat, which is released during refreezing. Until a pond freezes completely there can be minimal ice growth at the base of the underlying sea ice. In this work, we present a model of the refreezing of a melt pond that includes the heat and salt balances in the ice lid, trapped pond, and underlying sea ice. The model uses a two‐stream radiation model to account for radiative scattering at phase boundaries. Simulations and related sensitivity studies suggest that trapped pond water may survive for over a month (Bogorodskiy et al. 2006). We focus on the role that pond salinity has on delaying the refreezing process and retarding basal sea ice growth. We estimate that for a typical sea ice pond coverage in autumn, excluding the impact of trapped ponds in models overestimates ice growth by up to 265 million km3, an overestimate of 26%. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-08T03:41:25.732424-05:
      DOI: 10.1002/2014JC010140
       
  • Spatial and temporal variability of freshwater discharge into the Gulf of
           Alaska
    • Authors: D.F. Hill; N. Bruhis, S.E. Calos, A. Arendt, J. Beamer
      Pages: n/a - n/a
      Abstract: A study of the freshwater discharge into the Gulf of Alaska (GOA) has been carried out. Using available streamgage data, regression equations were developed for monthly flows. These equations express discharge as a function of basin physical characteristics such as area, mean elevation, and land cover, and of basin meteorological characteristics such as temperature, precipitation, and accumulated water year precipitation. To provide the necessary input meteorological data, temperature and precipitation data for a 40 year hind‐cast period were developed on high‐spatial‐resolution grids using weather station data, PRISM climatologies, and statistical downscaling methods. Runoff predictions from the equations were found to agree well with observations. Once developed, the regression equations were applied to a network of delineated watersheds spanning the entire GOA drainage basin. The region was divided into a northern region, ranging from the Aleutian Chain to the Alaska / Canada border in the southeast panhandle, and a southern region, ranging from there to the Fraser River. The mean annual runoff volume into the northern GOA region was found to be 792±120 km3 yr– 1. A water balance using MODIS‐based evapotranspiration rates yielded seasonal storage volumes that were consistent with GRACE satellite‐based estimates. The GRACE data suggest that an additional 57±11 km3 yr–1 be added to the runoff from the northern region, due to glacier volume loss (GVL) in recent years. The ease of application of the derived regression equations provides an accessible tool for quantifying mean annual values, seasonal variation, and interannual variability of runoff in any ungaged basin of interest. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-08T03:02:29.488989-05:
      DOI: 10.1002/2014JC010395
       
  • Typhoon air‐sea drag coefficient in coastal regions
    • Authors: Zhong‐Kuo Zhao; Chun‐Xia Liu, Qi Li, Guang‐Feng Dai, Qing‐Tao Song, Wei‐Hua Lv
      Pages: n/a - n/a
      Abstract: The air‐sea drag during typhoon landfalls is investigated for a 10‐m wind speed as high as U10 ≈ 42 m s‐1, based on multi‐level wind measurements from a coastal tower located in the South China Sea. The drag coefficient (CD) plotted against the typhoon wind speed is similar to that of open ocean conditions; however, the CD curve shifts toward a regime of lower winds, and CD increases by a factor of approximately 0.5 relative to the open ocean. Our results indicate that the critical wind speed at which CD peaks is approximately 24 m s‐1, which is 5‐15 m s‐1 lower than that from deep water. Shoaling effects are invoked to explain the findings. Based on our results, the proposed CD formulation, which depends on both water depth and wind speed, is applied to a typhoon forecast model. The forecasts of typhoon track and surface wind speed are improved. Therefore, a water‐depth‐dependence formulation of CD may be particularly pertinent for parameterizing air‐sea momentum exchanges over shallow water. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T23:51:01.124671-05:
      DOI: 10.1002/2014JC010283
       
  • A dipole‐like SST trend in the Somalia region during the monsoon
           season
    • Authors: F. Santos; M. Gómez‐Gesteira, M. deCastro, J. M. Días
      Pages: n/a - n/a
      Abstract: SST trends measured in the Somalia region during the southwest monsoon season over the period 1982‐2013 have shown the existence of a warming‐cooling dipole. The positive spot, with a warming trend on the order of 0.37ºC dec‐1, is centered around 5.1 ºN – 50.3º E and the negative one, with a trend on the order of ‐0.43ºC dec‐1, around 11.1 ºN – 52.2º E. The migration of the Great Whirl (GW) over the last three decades at a speed of ‐0.3 deg dec‐1 in longitude and ‐0.6 deg dec‐1 in latitude was considered as the possible origin of the SST dipole. The displacement of the GW produces changes in the geostrophic currents which, in turn, generate changes in the amount of advected water from and to coast. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T15:57:23.377982-05:
      DOI: 10.1002/2014JC010319
       
  • Seasonal and interannual oxygen variability on the Washington and Oregon
           continental shelves
    • Authors: Siedlecki S.A; Banas N.S, Davis K.A, Giddings S, Hickey B.M, MacCready P, Connolly T, S. Geier
      Pages: n/a - n/a
      Abstract: The coastal waters of the northern portion of the California Current System experience a seasonal decline in oxygen concentrations and hypoxia over the summer upwelling season that results in negative impacts on habitat for many organisms. Using a regional model extending from 43° to 50°N, with an oxygen component developed in this study, drivers of seasonal and regional oxygen variability are identified. The model includes two pools of detritus, which was an essential addition in order to achieve good agreement with the observations. The model was validated using an extensive array of hydrographic and moored observations. The model captures the observed seasonal decline as well as spatial trends in bottom oxygen. Spatially, three regions of high respiration are identified as locations where hypoxia develops each modeled year. Two of the regions are previously identified re‐circulation regions. The third region is off of the Washington coast. Sediment oxygen demand causes the region on the Washington coast to be susceptible to hypoxia and is correlated to the broad area of shallow shelf (< 60 m) in the region. Respiration and circulation‐driven divergence contribute similar (60, 40%, respectively) amounts to the integrated oxygen budget on the Washington coast while respiration dominates the Oregon coast. Divergence, or circulation, contributes to the oxygen dynamics on the shelf in two ways: first, through the generation of retention features, and second, by determining variability. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-08T21:59:45.036318-05:
      DOI: 10.1002/2014JC010254
       
  • Quantifying the processes controlling intraseasonal mixed‐layer
           temperature variability in the Tropical Indian Ocean
    • Authors: D.J. Halkides; Duane E. Waliser, Tong Lee, Dimitris Menemenlis, Bin Guan
      Pages: n/a - n/a
      Abstract: Spatial and temporal variation of processes that determine ocean mixed‐layer (ML) temperature (MLT) variability on the timescale of the Madden‐Julian Oscillation (MJO) in the Tropical Indian Ocean (TIO) are examined in a heat‐conserving ocean state estimate for years 1993‐2011. We introduce a new metric for representing spatial variability of the relative importance of processes. In general, horizontal advection is most important at the Equator. Subsurface processes and surface heat flux are more important away from the Equator, with surface heat flux being the more dominant factor. Analyses at key sites are discussed in the context of local dynamics and literature. At 0°, 80.5°E, for MLT events > 2 standard deviations, ocean dynamics account for more than two thirds of the net tendency during cooling and warming phases. Zonal advection alone accounts for ~40% of the net tendency. Moderate events (1‐2 standard deviations) show more differences between events, and some are dominated by surface heat flux. At 8°S, 67°E in the Seychelles‐Chagos Thermocline Ridge (SCTR) area, surface heat flux accounts for ~70% of the tendency during strong cooling and warming phases; subsurface processes linked to ML depth (MLD) deepening (shoaling) during cooling (warming) account for ~30%. MLT is more sensitive to subsurface processes in the SCTR, due to the thin MLD, thin barrier layer and raised thermocline. Results for 8°S, 67°E support assertions by Vialard et al. [2008] not previously confirmed due to measurement error that prevented budget closure and the small number of events studied. The roles of MLD, barrier layer thickness and thermocline depth on different timescales are examined. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-29T03:39:55.568502-05:
      DOI: 10.1002/2014JC010139
       
 
 
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