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

Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 21, SJR: 2.156, h-index: 61)
Geophysical Research Letters     Full-text available via subscription   (Followers: 41, SJR: 2.668, h-index: 142)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 3, SJR: 2.4, h-index: 109)
J. of Advances in Modeling Earth Systems     Open Access   (Followers: 2, SJR: 0.126, h-index: 2)
J. of Geophysical Research : Atmospheres     Partially Free   (Followers: 18)
J. of Geophysical Research : Biogeosciences     Full-text available via subscription   (Followers: 5)
J. of Geophysical Research : Earth Surface     Partially Free   (Followers: 22)
J. of Geophysical Research : Oceans     Partially Free   (Followers: 14)
J. of Geophysical Research : Planets     Full-text available via subscription   (Followers: 12)
J. of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 21)
J. of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 13)
Paleoceanography     Full-text available via subscription   (Followers: 4, SJR: 2.16, h-index: 82)
Radio Science     Full-text available via subscription   (Followers: 2, SJR: 0.527, h-index: 47)
Reviews of Geophysics     Full-text available via subscription   (Followers: 17, SJR: 8.837, h-index: 87)
Space Weather     Full-text available via subscription   (Followers: 3, SJR: 0.496, h-index: 16)
Tectonics     Full-text available via subscription   (Followers: 7, SJR: 2.16, h-index: 79)
Water Resources Research     Full-text available via subscription   (Followers: 121, SJR: 1.769, h-index: 110)
Journal Cover Journal of Geophysical Research : Oceans
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     ISSN (Online) 2169-9291
     Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • Stable near‐surface ocean salinity stratifications due to
           evaporation observed during STRASSE
    • Authors: William E. Asher; Andrew T. Jessup, Dan Clark
      Pages: n/a - n/a
      Abstract: Under conditions with a large solar flux and low wind speed, a stably stratified warm layer forms at the ocean surface. Evaporation can then lead to an increase in salinity in the warm layer. A large temperature gradient will decrease density enough to counter the density increase caused by the salinity increase, forming a stable positive salinity anomaly at the surface. If these positive salinity anomalies are large in terms of the change in salinity from surface to the base of the gradient, if their areal coverage is a significant fraction of the satellite footprint, and if they persist long enough to be in the satellite field of view, they could be relevant for calibration and validation of L‐band microwave salinity measurements. A towed, surface‐following profiler was deployed from the N/O Thalassa during the Subtropical Atlantic Surface Salinity Experiment (STRASSE). The profiler measured temperature and conductivity in the surface ocean at depths of 10, 50, and 100 cm. The measurements show that positive salinity anomalies are common at the ocean surface for wind speeds less than 4 m s−1 when the average daily insolation is >300 W m−2 and the sea‐to‐air latent heat flux is greater than zero. A semiempirical model predicts the observed dependence of measured anomalies on environmental conditions. However, the model results and the field data suggest that these ocean surface salinity anomalies are not large enough in terms of the salinity difference to significantly affect microwave radiometric measurements of salinity.
      PubDate: 2014-05-30T10:50:22.007328-05:
      DOI: 10.1002/2014JC009808
       
  • Extreme cooling and dense water formation estimates in open and coastal
           regions of the Adriatic Sea during the winter of 2012
    • Authors: Ivica Janeković; Hrvoje Mihanović, Ivica Vilibić, Martina Tudor
      Pages: n/a - n/a
      Abstract: Generation of dense waters in the Adriatic Sea during an extreme cooling event in the winter of 2012, including its preconditioning and spreading phases, have been investigated using the one‐way coupled ROMS and the ALADIN/HR modeling system. Both climatological and real river fluxes are used in the simulations. Aside from the “convenient” dense water formation areas located at the northernmost Adriatic shelf, we found that a similar amount of dense water, with slightly lower density, was formed in the eastern and deeper Adriatic coastal area, which was subjected to extreme heat losses (up to 2000 W/m2) during peak cooling periods. This part of the Adriatic has been known for extreme cooling during wintertime bora outbreaks; nevertheless, no ocean model study has previously reproduced dense water formation in this area. The most likely reason for that was an overestimate of river discharges introduced to ocean models. From newly available data, we estimated that the contribution of eastern Adriatic rivers between the Neretva River and Rijeka Bay is more than six times lower than what has been previously documented. Transport of dense water toward the middle Adriatic had a peak value of about 0.6 Sv, while the speed of initial bottom density current surpassed 40–50 cm/s, which is several times faster than past events. Different pathways of the dense water toward the middle and south Adriatic depressions have also been documented. The contribution of the eastern coastal Adriatic area to the overall north Adriatic dense water formation has been quantified and discussed for average and low freshwater load conditions, indicating that this part of the Adriatic is a common place for dense water generation.
      PubDate: 2014-05-30T10:49:01.012439-05:
      DOI: 10.1002/2014JC009865
       
  • Modeling bed shear‐stress fluctuations in a shallow tidal channel
    • Authors: R. Mathis; I. Marusic, O. Cabrit, N. L. Jones, G. N. Ivey
      Pages: n/a - n/a
      Abstract: Recently, Mathis et al. (2013) developed a model for predicting the instantaneous fluctuations of the wall shear‐stress in turbulent boundary layers. This model is based on an inner‐outer scale interaction mechanism, incorporating superposition, and amplitude‐modulation effects, and the only input required for the model is a time series measurement of the streamwise velocity signal taken in the logarithmic region of the flow. The present study applies this new approach for the first time to environmental flows, for which the near‐bed information is typically inaccessible. The data used here are acoustic Doppler velocimeter time series measurements from a shallow tidal channel (Suisun Slough in North San Francisco Bay). We first extract segments of data sharing properties with canonical turbulent boundary layers. The wall (bed) shear‐stress model is then applied to these selected data. Statistical and spectral analysis demonstrates that the field data predictions are consistent with laboratory and DNS results. The model is also applied to the whole available data set to demonstrate, even for situations far from the canonical boundary layer case, its ability to preserve the overall Reynolds number trend. The predicted instantaneous bed stress is highly skewed and amplitude modulated with the variations in the large‐scale streamwise velocity. Finally, the model is compared to conventional methods employed to predict the bed shear‐stress. A large disparity is observed, but the present model is the only one able to predict both the correct spectral content and the probability density function.
      PubDate: 2014-05-30T10:40:20.230751-05:
      DOI: 10.1002/2013JC009718
       
  • Characteristics and dynamics of two major Greenland glacial fjords
    • Authors: David A. Sutherland; Fiammetta Straneo, Robert S. Pickart
      Pages: n/a - n/a
      Abstract: The circulation regimes of two major outlet glacial fjords in southeastern Greenland, Sermilik Fjord (SF) and Kangerdlugssuaq Fjord (KF), are investigated using data collected in summer 2009. The two fjords show similar flow patterns, with a time‐dependent, vertically sheared flow structure dominating over the background estuarine flow driven by buoyancy input. We show that this time‐dependent flow is consistent with circulation induced by density interface fluctuations at the fjord mouth, often referred to as intermediary circulation. One difference between the fjords is that the hydrographic and velocity structure below a surface modified layer is found to be three‐layer in KF in summer, compared to two‐layer in SF. Outside each fjord, large‐scale geostrophic currents dictate the stratification at the mouth, although the way in which these large‐scale flows impinge on each fjord is distinct. Combining the observations with estimates from existing theories, we find the magnitudes of the estuarine (Qe) and intermediary (Qi) circulation and show that Qi >> Qe, although along‐fjord winds can also be significant. We expect that the critical parameter determining Qi / Qe is the sill depth compared to the fjord depth, with shallower sills corresponding to weaker intermediary circulation. Finally, we discuss the implications of strong intermediary circulation on calculating heat transport to the glacier face and its potential feedbacks on the background circulation in these highly stratified estuaries.
      PubDate: 2014-05-29T10:27:47.923239-05:
      DOI: 10.1002/2013JC009786
       
  • Nitrous oxide cycling in the water column and sediments of the oxygen
           minimum zone, eastern subtropical North Pacific, Southern California, and
           Northern Mexico (23°N–34°N)
    • Authors: Amy Townsend‐Small; Maria G. Prokopenko, William M. Berelson
      Pages: n/a - n/a
      Abstract: Identifying sources and sinks of N2O can illuminate N cycling processes in marine systems, particularly where changes in dissolved O2 can lead to changes in N cycling pathways (i.e., nitrification versus denitrification). We measured N2O and NO3− concentration and their stable isotope ratios (δ15N and δ18O) in the water column and sediments of the oxygen minimum zone in the nearshore eastern subtropical North Pacific (23°N–34°N). Atmospheric efflux of N2O ranged from 2.2 to 17.9 μmol m−2 d−1 or about 2–20 times higher than in oxygenated regions of the North Pacific. Surface waters were a source of 15N‐depleted and 18O‐enriched N2O to the atmosphere, indicating a bacterial, not archaeal, nitrification N2O source. Stable isotopes indicated that nitrification in both surface and intermediate waters (∼0–200 m) was the major source of N2O in this study area, with denitrification acting as a small N2O sink in strongly O2‐depleted waters. Denitrification had a larger impact on observed patterns of N2O and NO3− concentrations and isotope ratios in the southern oxygen minimum zone. Sediments were generally neutral or a weak sink for N2O, with only one site (Soledad basin) showing a positive efflux of +3.5 ± 1.0 μmol N2O‐N m−2 d−1. Sediment fluxes of N2O at all sites were several orders of magnitude smaller than fluxes of dinitrogen, nitrate, and ammonium measured in previous studies and did not appear to impact water column N2O concentrations. N2O was less than 0.1% of the N2 efflux from sedimentary denitrification.
      PubDate: 2014-05-29T10:25:41.832341-05:
      DOI: 10.1002/2013JC009580
       
  • Recovery of temperature, salinity, and potential density from ocean
           reflectivity
    • Authors: Berta Biescas; Barry R. Ruddick, Mladen R. Nedimovic, Valentí Sallarès, Guillermo Bornstein, Jhon F. Mojica
      Pages: n/a - n/a
      Abstract: This work explores a method to recover temperature, salinity, and potential density of the ocean using acoustic reflectivity data and time and space coincident expendable bathythermographs (XBT). The acoustically derived (vertical frequency >10 Hz) and the XBT‐derived (vertical frequency
      PubDate: 2014-05-29T10:10:10.823383-05:
      DOI: 10.1002/2013JC009662
       
  • Observed upper ocean response to typhoon Megi (2010) in the Northern South
           China Sea
    • Authors: Shoude Guan; Wei Zhao, John Huthnance, Jiwei Tian, Jinhu Wang
      Pages: n/a - n/a
      Abstract: Typhoon Megi passed between two subsurface moorings in the northern South China Sea in October 2010 and the upper ocean thermal and dynamical response with strong internal tides present was examined in detail. The entire observed water column (60–360 m) was cooled due to strong Ekman‐pumped upwelling (up to 50 m in the thermocline) by Megi, with maximum cooling of 4.2°C occurring in thermocline. A relatively weak (maximum amplitude of 0.4 m s−1) and quickly damped (e‐folding time scale of 2 inertial periods) near‐inertial oscillation (NIO) was observed in the mixed layer. Power spectrum and wavelet analyses both indicated an energy peak appearing at exactly the sum frequency fD1 (with maximum amplitude up to 0.2 m s−1) of NIO (f) and diurnal tide (D1), indicating enhanced nonlinear wave‐wave interaction between f and D1 during and after typhoon. Numerical experiments suggested that energy transfer from NIO to fD1 via nonlinear interaction between f and D1 may have limited the growth and accelerated the damping of mixed layer NIO generated by Megi. The occurrence of fD1 had a high correlation with NIO; the vertical nonlinear momentum term, associated with the vertical shear of NIO and vertical velocity of D1 or vertical shear of D1 and vertical velocity of NIO, was more than 10 times larger than the horizontal terms and was responsible for forcing fD1. After Megi, surface‐layer diurnal energy was enhanced by up to 100%, attributed to the combined effect of the increased surface‐layer stratification and additional Megi‐forced diurnal current.
      PubDate: 2014-05-29T09:41:27.840518-05:
      DOI: 10.1002/2013JC009661
       
  • Evidence of inertially generated coastal‐trapped waves in the
           eastern tropical Pacific
    • Authors: X. Flores‐Vidal; R. Durazo, L. Zavala‐Sansón, P. Flament, C. Chavanne, F. J. Ocampo‐Torres, C. Reyes‐Hernández
      Pages: n/a - n/a
      Abstract: Observations of coastal‐trapped waves (CTW) are limited by instrumentation technologies and temporal and spatial resolutions; hence, their complete description is still limited. In the present work, we used measurements from high‐frequency radio scatterometers (HFR) to analyze the subinertial dynamics of the Gulf of Tehuantepec in the Mexican Pacific, a region strongly influenced by offshore gap winds. The data showed subinertial oscillations that may be explained by poleward propagating CTWs. The oscillations showed higher coherence (95% confidence) with gap winds in the Gulfs of Papagayo and Panama than with local winds. Vertical thermocline oscillations, measured with a moored thermistor‐chain, also showed subinertial oscillations coherent with Papagayo and Panama winds. The period of the observed oscillations was ∼4 days, which corresponds to the inertial period of the Gulf of Panama. This suggests that inertial oscillations generated by offshore wind outbursts over Panama may have traveled northward along the coastal shelf, and were detected as surface current pulses by the HFR installed approximately 2000 km further north in the Gulf of Tehuantepec. To further explore the presence of CTWs, the 4 day band‐pass filtered currents measured by the HFR were analyzed using empirical orthogonal functions. We found that the first mode behaved like a CTW confined to the shelf break. Additionally, the observed oscillations were compared with baroclinic and barotropic CTW models. The results support the notion that nearly inertial baroclinic CTWs are generated in the Gulfs of Panama and Papagayo and then propagate toward the Gulf of Tehuantepec.
      PubDate: 2014-05-29T09:24:39.739233-05:
      DOI: 10.1002/2013JC009118
       
  • Microwave backscattering from surf zone waves
    • Authors: Patricio A. Catalán; Merrick C. Haller, William J. Plant
      Pages: n/a - n/a
      Abstract: The microwave backscatter properties of surf zone waves are analyzed using field observations. By utilizing a preexisting, independent, water surface discrimination technique, the microwave returns were extracted along individual waveforms and the data from shoaling (steepening) waves, surf zone breaking waves, and remnant foam were separated and quantified. In addition, a wave tracking analysis technique allows the returns to be examined on a wave‐by‐wave basis as individual waves progress through the shoaling zone and break on a nearshore sand bar. Normalized radar cross sections (NRCS), polarization ratios, Doppler spectra, and scatterer velocities were collected using a dual‐polarized, X‐band radar operating at lower grazing angles than previously reported (1°–3.5°). The results indicate that the maximum NRCS levels are from the active breaking portions of the wave and were consistently about −20 dB, regardless of radar polarization, azimuth angle, wave height, or wind speed. In addition, breaking waves induce broadening of the Doppler spectra and mean scatterer velocities that correlate well with the carrier wave celerity. Analysis of the polarization ratios suggest that the active breaking portions of the wave are depolarized but that higher polarization ratios (>0 dB) are found on the leading edges shoreward of the active breaking portions of the waves, which indicates a clear distinction between two scattering regimes. These results are consistent with scattering from a very rough surface that is being mechanically generated by the breaking process, showing a good agreement with the expected grazing angle dependency of a Lambertian scatterer.
      PubDate: 2014-05-28T13:35:20.379053-05:
      DOI: 10.1002/2014JC009880
       
  • Dynamical mechanisms for asymmetric SSTA patterns associated with some
           Indian Ocean Dipoles
    • Authors: Shuangwen Sun; Yue Fang, Tana  , Baochao Liu
      Pages: n/a - n/a
      Abstract: Indian Ocean Dipole (IOD) can be divided into two types according to their SST anomaly (SSTA) patterns: the symmetric IODs and the asymmetric IODs. Dynamical mechanisms for the two types of IODs are investigated using an ocean general circulation model, and the numerical experiments indicate that the setup time of the equatorial easterly wind anomalies (EEWA) associated with IODs is crucially important for the symmetrical characteristics of the SSTA patterns. Early setup of the EEWA in spring can induce intense cooling in the east pole but weak warming in the west pole, making the two poles asymmetric. The intense cooling in the east pole is linked to the seasonal variations of thermocline depth, horizontal SST gradient, and unusually long duration of the EEWA, and the weak warming in the west pole is due to unusually cold zonal advection resulted from zonal SST gradient change. The numerical experiments demonstrate that the strength of the EEWA also plays an important role in the symmetrical characteristics of IODs. The SSTA in the two poles both intensify as the EEWA strength increases only when the EEWA speed is below a critical value. Above the critical value, the warming in the west pole starts to decrease while the cooling in the east pole still keeps increasing, leading to an asymmetric SSTA pattern. The mechanism behind this phenomenon is similar to the one in the situation when EEWA sets up earlier.
      PubDate: 2014-05-28T08:34:10.675824-05:
      DOI: 10.1002/2013JC009651
       
  • Flows in the Tasman Front south of Norfolk Island
    • Authors: Philip J. H. Sutton; Melissa Bowen
      Pages: n/a - n/a
      Abstract: The Tasman Front is a narrow band of eastward flowing subtropical water crossing the Tasman Sea from Australia to North Cape, New Zealand. It is the link between the two subtropical western boundary currents of the South Pacific, the East Australian Current (EAC) off eastern Australia, and the East Auckland Current (EAUC) off northeastern New Zealand. Here we report the first direct measurements of flow in the Tasman Front from a moored array deployed across gaps in the submarine ridges south of Norfolk Island and hydrographic and ADCP measurements during the deployment and recovery voyages. The mean flow through the array over July 2003 to August 2004 was found to be eastward only in the upper 800 m with a transport of ∼6 Sv. Below 800 m a weak westward mean flow (∼1.5 Sv) was measured, associated with Antarctic Intermediate Water (AAIW). Using sea surface height to account for additional transport south of the moored array results in a total mean eastward transport between Norfolk Island and North Cape, New Zealand of ∼8 Sv, varying between −4 and 18 Sv. The measurements show that the Tasman Front is much shallower than either the EAC or EAUC, both of which extend below 2000 m depth, has less transport than either the EAC or EAUC and has instances of flow reversal. Thus, the Tasman Front is a weaker connection between the EAC and EAUC than the paradigm of a contiguous South Pacific western boundary current system would suggest.
      PubDate: 2014-05-27T12:55:26.521837-05:
      DOI: 10.1002/2013JC009543
       
  • Surface and melt pond evolution on landfast first‐year sea ice in
           the Canadian Arctic Archipelago
    • Authors: Jack Landy; Jens Ehn, Megan Shields, David Barber
      Pages: n/a - n/a
      Abstract: The evolution of landfast sea ice melt pond coverage, surface topography, and mass balance was studied in the Canadian Arctic during May–June 2011 and 2012, using a terrestrial laser scanner, snow and sea ice sampling, and surface meteorological characterization. Initial melt pond formation was not limited to low‐lying areas, rather ponds formed at almost all premelt elevations. The subsequent evolution of melt pond coverage varied considerably between the 2 years owing to four principle, temporally variable factors. First, the range in premelt topographic relief was 0.5 m greater in 2011 (rougher surface) than in 2012 (smoother surface), such that a seasonal maximum pond coverage of 60% and maximum hydraulic head of 204 mm were reached in 2011, versus 78% and 138 mm in 2012. A change in the meltwater balance (production minus drainage) caused the ponds to spread or recede over an area that was almost 90% larger in 2012 than in 2011. Second, modification of the premelt topography was observed during mid‐June, due to preferential melting under certain drainage channels. Some of the lowest‐lying premelt areas were subsequently elevated above these deepening channels and unexpectedly became drained later in the season. Third, ice interior temperatures remained 1–2°C colder later into June in 2012 than in 2011, even though the ice was 0.35 m thinner at melt onset, thereby delaying permeability increases in the ice that would allow vertical meltwater drainage to the ocean. Finally, surface melt was estimated to account for approximately 62% of the net radiative flux to the sea ice cover during the melt season.
      PubDate: 2014-05-27T12:53:25.775011-05:
      DOI: 10.1002/2013JC009617
       
  • Precessional forced extratropical North Pacific mode and associated
           atmospheric dynamics
    • Authors: Yue Wang; Ping Zhao, ZhiMin Jian, Dong Xiao, JunMing Chen
      Pages: n/a - n/a
      Abstract: Using transient accelerated simulations of the Community Climate System Model version 3 and an Earth system Model of Intermediate Complexity as well as equilibrium experiments of the Community Earth System Model, we identified a response of the extratropical air‐ocean coupled system to the precessional insolation changes at orbital timescales and named this extratropical response pattern as the North Pacific mode (NPM). Corresponding to the increased/decreased boreal winter/summer insolation at 22ka (relative to 10‐8ka), the NPM is characterized by a western warm‐eastern cold seesaw pattern of sea surface temperature (SST) over the extratropical North Pacific from November to April, a weakened winter Aleutian low and an anomalous anticyclonic circulation throughout the troposphere. This feature forms a barotropic warm‐ridge response of tropospheric temperature and geopotential height to the precessional insolation. At the surface, rainfall increases over East Asia and the Northwest Pacific, which indicates a weakened East Asian winter monsoon, while drier conditions appear over the Northeast Pacific and the western coasts of North America. Associated with a negative phase of NPM is a weaker warming over the equatorial Pacific during winter. The increased winter insolation at precessional band not only induces the in‐phase SST warming over the Northwest Pacific and the tropical Pacific, but also explains those extratropical atmospheric changes associated with NPM. The latter might be associated with the warm SST‐induced tropospheric downstream ridge response through transient eddy activities. Besides the vital role of air‐ocean interactions, the decreased summer insolation is also essential to the zonal SST seesaw of NPM at precessional band.
      PubDate: 2014-05-27T06:25:18.770305-05:
      DOI: 10.1002/2013JC009765
       
  • Biological and physical processes influencing sea ice, under‐ice
           algae, and dimethylsulfoniopropionate during spring in the Canadian Arctic
           Archipelago
    • Authors: V. Galindo; M. Levasseur, C. J. Mundy, M. Gosselin, J.‐É. Tremblay, M. Scarratt, Y. Gratton, T. Papakiriakou, M. Poulin, M. Lizotte
      Pages: n/a - n/a
      Abstract: [1] This study presents temporal variations in concentrations of chlorophyll a (Chl a), particulate and dissolved dimethylsulfoniopropionate (DMSPp and DMSPd) in the sea ice and underlying water column in the Canadian Arctic Archipelago during the spring of 2010 and 2011. During both years, bottom‐ice Chl a, DMSPp and DMSPd concentrations were high (up to 1328 µg L-1, 15 000 nmol L-1, and 6000 nmol L-1, respectively) in May and decreased thereafter. The release of bottom ice algae and DMSPp in the water column was gradual in 2010 and rapid (8 days) in 2011. Bottom brine drainage during the pre‐snowmelt period in 2010 and a rapid loss of the snow cover in 2011 coinciding with rain events explain most of the difference between the two years. During both years, less than 13% of the DMSPd lost from the ice was detected in the water column, suggesting a rapid microbial consumption. An under‐ice diatom bloom developed in both years. In 2010, the bloom was dominated by centric diatoms while in 2011 pennates dominated, likely reflecting seeding by ice algae following the faster snow melt progression induced by rainfall events in 2011. Both under‐ice blooms were associated with high DMSPp concentrations (up to 185 nmol L-1), but pennate diatoms showed DMSPp/Chl a ratios twice higher than centrics. These results highlight the key role of snowmelt and precipitation on the temporal pattern of ice‐DMSP release to the water column and on the timing, taxonomic composition, and DMSP content of phytoplankton under‐ice blooms in the Arctic.
      PubDate: 2014-05-27T06:24:02.159445-05:
      DOI: 10.1002/2013JC009497
       
  • Seaglider observations of equatorial Indian Ocean Rossby waves associated
           with the Madden‐Julian Oscillation
    • Authors: Benjamin G. M. Webber; Adrian J. Matthews, Karen J. Heywood, Jan Kaiser, Sunke Schmidtko
      Pages: n/a - n/a
      Abstract: During the CINDY‐DYNAMO field campaign of September 2011 ‐ January 2012, a Seaglider was deployed at 80°E and completed 10 north‐south sections between 3 and 4°S, measuring temperature, salinity, dissolved oxygen concentration and chlorophyll fluorescence. These high‐resolution subsurface observations provide insight into equatorial ocean Rossby wave activity forced by three Madden‐Julian Oscillation (MJO) events during this time period. These Rossby waves generate variability in temperature O(1°C), salinity O(0.2 g kg‐1), density O(0.2 kg m‐3) and oxygen concentration O(10 µmol kg‐1), associated with 10 m vertical displacements of the thermocline. The variability extends down to 1000 m, the greatest depth of the Seaglider observations, highlighting the importance of surface forcing for the deep equatorial ocean. The temperature variability observed by the Seaglider is greater than that simulated in the ECCO‐JPL reanalysis, especially at depth. There is also marked variability in chlorophyll fluorescence at the surface and at the depth of the chlorophyll maximum. Upwelling from Rossby waves and local wind stress curl leads to an enhanced shoaling of the chlorophyll maximum by 10‐25 m in response to the increased availability of nutrients and light. This influence of the MJO on primary production via equatorial ocean Rossby waves has not previously been recognised.
      PubDate: 2014-05-26T04:27:03.501854-05:
      DOI: 10.1002/2013JC009657
       
  • From the subtropics to the equator in the Southwest Pacific: Continental
           material fluxes quantified using neodymium data along modeled thermocline
           water pathways
    • Authors: Mélanie Grenier; Catherine Jeandel, Sophie Cravatte
      Pages: n/a - n/a
      Abstract: The southwestern tropical Pacific, part of a major pathway for waters feeding the Equatorial Undercurrent, is a region of important geochemical enrichment through land‐ocean boundary exchange. Here we develop an original method based on the coupling between dynamical modeling and geochemical tracer data to identify regions of enrichment along the water pathways from the subtropics to the equator, and to allow a refined quantification of continental material fluxes. Neodymium data are interpreted with the help of modeled Lagrangian trajectories of an Ocean General Circulation Model. We reveal that upper and lower thermocline waters have different pathways together with different geochemical evolutions. The upper thermocline waters entering the Solomon Sea mainly originate from the central subtropical gyre, enter the Coral Sea in the North Vanuatu Jet and likely receive radiogenic neodymium from the basaltic island margins encountered along their route. The lower thermocline waters entering the Solomon Sea mainly originate from northeast of New Zealand and enter the Coral Sea in the North Caledonian Jet. Depletion of their neodymium content likely occurs when flowing along the Australian and Papua coasts. Downstream from the Solomon Sea, waters flowing along the Papua New Guinea margins near the Sepik river mouth become surprisingly depleted in their neodymium content in the upper thermocline while enriched in the lower thermocline. This coupled approach is proposed as strong support to interpret the origin of the equatorial Pacific natural fertilization through a better understanding of the circulation, important objectives of the international GEOTRACES and SPICE programs, respectively.
      PubDate: 2014-05-26T04:05:39.011215-05:
      DOI: 10.1002/2013JC009670
       
  • Interannual variations of Kuroshio transport in the East China Sea and its
           relation to the Pacific Decadal Oscillation and mesoscale eddies
    • Authors: Endro Soeyanto; Xinyu Guo, Jun Ono, Yasumasa Miyazawa
      Pages: n/a - n/a
      Abstract: Results of a data assimilative ocean model (JCOPE2) from 1993 to 2012 were used to examine the correlation between the Pacific Decadal Oscillation (PDO) index and interannual variations of the Kuroshio transport in the East China Sea (ECS) and the influences of mesoscale eddies on this correlation. In a period from 1993 to 2002, the Kuroshio transport estimated from the JCOPE2 reanalysis has a positive correlation with the PDO index. This well‐known correlation became weak or even disappeared when the analysis period was extended from 1993‐2002 to 1993‐2012. This occurs because the variation range of the PDO index became small during enhanced mesoscale eddy activity southeast of Taiwan in years after 2002. The eddies caused a larger variation in the Kuroshio transport in the years after 2002 than before 2002, and therefore changed the correlation between the PDO index and Kuroshio transport in the ECS. The influence of mesoscale eddies on the Kuroshio transport has strong regional dependence: the Kuroshio transport from the area east of Taiwan to the midway along the shelf break in the East China Sea depends mainly on eddies arriving from southeast of Taiwan, while transport from the midway along the shelf break to the Tokara Strait depends mainly on the eddies arriving from northeast of Okinawa Island. The combination of PDO‐related signals and eddy‐related signals determines the interannual variations of the Kuroshio transport in the ECS and sufficient attention must be paid to the spatial dependence of the Kuroshio transport in the ECS on eddies.
      PubDate: 2014-05-24T04:37:08.668037-05:
      DOI: 10.1002/2013JC009529
       
  • Linkage between the Pacific Decadal Oscillation and the low frequency
           variability of the Pacific Subtropical Cell
    • Authors: Lingya Hong; Liping Zhang, Zhaohui Chen, Lixin Wu
      Pages: n/a - n/a
      Abstract: The decadal variability of Pacific Subtropical Cell (STC) and its linkages with the Pacific Decadal Oscillation (PDO) are investigated in the present study based on a Simple Ocean Data Assimilation (SODA 2.2.4). It is found that, on decadal time scales, the western boundary and interior pycnocline transports are anticorrelated and the variation of the interior component is more significant, which is consistent with previous studies. The decadal variability of STC in the Northern Hemisphere is found to be strongly associated with PDO. Associated with a positive (negative) phase of PDO, the relaxation (acceleration) of the northeast trades slows down (spins up) the STC within a few years through baroclinic adjustment in conjunction with the subduction of the cold (warm) mixed layer anomalies in the extratropics. The cold (warm) water is then injected into the thermocline and advected further southwestward to the tropics along the isopycnal surfaces, leading to the slowdown (spin‐up) of STC due to zonal pressure gradient change at low latitude. Along with the STC weakening (strengthening), a significant warming (cold) anomaly appears in the tropics and it is advected to the mid‐latitude by the Kuroshio and North Pacific currents, thus feeding back to the atmosphere over the North Pacific. In contrast to the Northern Hemisphere, it is found the STC in the south only passively responds to the PDO. The mechanism found here highlights the role of the STC advection of extratropical anomalies to the tropics and horizontal gyre advection of the tropical anomalies to the extratropics in decadal variability of the STC and PDO.
      PubDate: 2014-05-24T04:37:06.521333-05:
      DOI: 10.1002/2013JC009650
       
  • Seismic observations from a Yakutat eddy in the northern Gulf of Alaska
    • Authors: Q. S. Tang; S. P. S. Gulick, L. T. Sun
      Pages: n/a - n/a
      Abstract: Recent works show that the seismic oceanography technique allows us to relate water column seismic reflections to oceanic finescale structures. In this study, finescale structures of a surface anticyclonic eddy have been unveiled by reprocessing two seismic transects acquired in the northern Gulf of Alaska using an 8‐km hydrophone streamer and 6600 cu in linear airgun array in September 2008. The eddy was a typical bowl‐like structure with around 55 km width and 700 m depth. It has two fringes around the eddy base and a spiral arm at the NE edge. The in situ sea surface temperature and salinity data from a shipboard thermosalinograph help to confirm our interpretations of a spiral arm shed from the warm eddy and the entrained cold water from elsewhere. Nearby the eddy and offshore the shelf‐break, there is a strong frontal feature, probably the Alaska Current. The eddy likely formed offshore Yakutat shelf and transported along the offshore shelf‐break by tracking the sea level anomalies. Its equivalent diameter of 65 km was measured using the along‐track altimeter and the seismic constraints. It was comparable with results from the representative conventional algorithms of eddy detection. Geostrophic velocities of the eddy were estimated from the dipping seismic reflections under the assumptions of approximate isopycnals and geostrophic balance. Measured water properties including sea surface temperature, salinity, and chlorophyll revealed that eddy translation transports coastal water to the pelagic regions. Structures synthesized from CTD profiles that sampled an earlier eddy suggest that thin striae around the base might be a common feature in Gulf of Alaska eddies.
      PubDate: 2014-05-24T04:21:50.176872-05:
      DOI: 10.1002/2014JC009938
       
  • Mindanao Current/Undercurrent measured by a subsurface mooring
    • Authors: Linlin Zhang; Dunxin Hu, Shijian Hu
      Pages: n/a - n/a
      Abstract: The mean structure and variability of the currents east of Mindanao are investigated through two‐year mooring observations at about 8ºN, 127º3'E from December 2010 to December 2012. The strong southward Mindanao Current (MC) exists in the upper 600 m with a maximum mean velocity of 73 cm/s and a standard deviation of 17 cm/s at 100 m. A northward mean flow is observed below 600 m to the depth deeper than 1000 m, which has been called the Mindanao Undercurrent (MUC) with a maximum mean velocity of about 10 cm/s at 950 m and a standard deviation of 19 cm/s. Further analysis with hydrographic data and an eddy‐resolving model outputs also suggests this northward mean current to be the MUC. Intraseasonal variability with a period of 60‐80 days is revealed through the whole water column from 200 m down to about 900 m. This intraseasonal variability appears to be closely related to subthermocline eddies, which translate westward and intensify near the Mindanao coast.
      PubDate: 2014-05-24T04:20:37.614635-05:
      DOI: 10.1002/2013JC009693
       
  • Improved mapping of sea ice production in the Arctic Ocean using
           AMSR‐E thin ice thickness algorithm
    • Authors: Katsushi Iwamoto; Kay I. Ohshima, Takeshi Tamura
      Pages: n/a - n/a
      Abstract: New and improved estimates of sea ice production in the Arctic Ocean are derived from AMSR‐E satellite and atmospheric reanalysis data for the period 2002–2011, at a spatial resolution of 6.25 km and using a newly‐developed fast‐ice mask. High ice production in the major coastal polynyas is well demonstrated. The total annual cumulative ice production in the major 10 polynya regions is about 1180 ±70km3. The interannual variability of the ice production for each polynya is presented during 2002–2011. No obvious relationship is noted between the ice production and the recent drastic reduction in the preceding summer Arctic sea ice extent. Most polynya regions exhibit maximum ice production in autumn (October – November), before areas offshore have been covered with consolidated pack ice. Sea ice production from October to November in the marginal ice zone of the Pacific Ocean sector is negatively correlated with summer ice extent there. The ice production from October to November of 2007 (a record minimum summer ice extent) was about twice as large as that in other years. The high ice production area shifted to higher latitudes i.e., towards the deep Canada Basin, due to the retreat of the summer ice edge. We speculate that the resultant increase in brine input could change the oceanic structure in the basin, specifically deepening the winter mixed layer.
      PubDate: 2014-05-23T23:50:57.633401-05:
      DOI: 10.1002/2013JC009749
       
  • Variation in the Kuroshio intrusion: Modeling and interpretation of
           observations collected around the Luzon Strait from July 2009 to March
           2011
    • Authors: Yaochu Yuan; Yu‐heng Tseng, Chenghao Yang, Guanghong Liao, Chun Hoe Chow, Zenghong Liu, Xiao‐Hua Zhu, Hong Chen
      Pages: n/a - n/a
      Abstract: This study analyzes the observed subtidal currents, 1/12˚ global HYCOM model results and the observed time series to interpret seasonal and interannual patterns in the behavior of the Kuroshio intrusion around the Luzon Strait (LS). The observations include current measurements conducted at mooring station N2 (20°40.441′ N, 120°38.324′ E) from July 7th, 2009 to March 31st, 2011, surface geostrophic currents derived from the merged absolute dynamic topography and the trajectory of an Argo float during the winter of 2010‐2011. Results from mooring station N2 confirmed the seasonal changes in the Kuroshio intrusion and the variation of the Kuroshio intrusion during El Niño event from July, 2009 to April, 2010 and La Niña even from June, 2010 to March, 2011. The strongest Kuroshio intrusion occurs in the winter, with successively weaker currents in spring, autumn and summer. Comparison of relative differences (Δmax(z)) in the maximum absolute value of monthly average zonal velocity components Umax (z) showed that the Kuroshio intrusion was stronger during the 2009‐2010 winter (El Niño) than the 2010‐2011 winter (La Niña). Furthermore, the relative differences (Δmax(z)) in deeper layers exceed those of the surface layer. Circulation patterns in surface geostrophic currents and the Argo float trajectory confirmed the results of mooring station N2. The Kuroshio intrusion velocity variation modeled using the 1/12˚ global HYCOM model resembled the observation on both seasonal to interannual scales. Modeled variation in the zonal mean velocity anomaly was also consistent with Niño3, Niño4 and North Equatorial Current (NEC) bifurcation latitude indices, indicating concurrent impacts of the ENSO influence. Monsoon winds strongly affect the seasonal variation while the weak upstream Kuroshio transport induced by El Niño, strongly affects the interannual variation, such as 2009‐2010 winter. In 2010‐2011 winter, the impact of winter monsoon forcing still exists in the LS. However, the stronger upstream Kuroshio transport during this period did not allow the Kuroshio to penetrate into the LS deeply. This explains why the 2009‐2010 winter Kuroshio intrusion (El Niño event) was stronger than that of the 2010‐2011 winter (La Niña event).
      PubDate: 2014-05-22T12:08:07.839022-05:
      DOI: 10.1002/2013JC009776
       
  • Connecting wind‐driven upwelling and offshore stratification to
           nearshore internal bores and oxygen variability
    • Authors: Ryan K. Walter; C. Brock Woodson, Paul R. Leary, Stephen G. Monismith
      Pages: n/a - n/a
      Abstract: This study utilizes field observations in southern Monterey Bay, CA to examine how regional scale upwelling and changing offshore (shelf) conditions influence nearshore internal bores. We show that the low‐frequency wind forcing (e.g., upwelling/relaxation time scales) modifies the offshore stratification and thermocline depth. This in turn alters the strength and structure of observed internal bores in the nearshore. An internal bore strength index is defined using the high‐pass filtered potential energy density anomaly in the nearshore. During weak upwelling favorable conditions and wind relaxations, the offshore thermocline deepens. In this case, both the amplitude of the offshore internal tide and the strength of the nearshore internal bores increase. In contrast, during strong upwelling conditions, the offshore thermocline shoals towards the surface, resulting in a decrease in the offshore internal tide amplitude. As a result, cold water accumulates in the nearshore (nearshore pooling), and the internal bore strength index decreases. Empirical orthogonal functions are utilized to support the claim that the bore events contribute to the majority of the variance in cross‐shelf exchange and transport in the nearshore. Observed individual bores can drive shock‐like drops in dissolved oxygen (DO) with rapid onset times, while extended upwelling periods with reduced bore activity produce longer duration, low DO events.
      PubDate: 2014-05-22T12:06:43.936813-05:
      DOI: 10.1002/2014JC009998
       
  • A modeling study of the processes of surface salinity seasonal cycle in
           the Bay of Bengal
    • Authors: V.P. Akhil; Fabien Durand, Matthieu Lengaigne, Jérôme Vialard, M.G. Keerthi, V.V. Gopalakrishna, Charles Deltel, Fabrice Papa, Clément de Boyer Montégut
      Pages: n/a - n/a
      Abstract: In response to the Indian Monsoon freshwater forcing, the Bay of Bengal exhibits a very strong seasonal cycle in sea surface salinity (SSS), especially near the mouths of the Ganges‐Brahmaputra and along the east coast of India. In this paper, we use an eddy‐permitting (~25 km resolution) regional ocean general circulation model simulation to quantify the processes responsible for this SSS seasonal cycle. Despite the absence of relaxation towards observations, the model reproduces the main features of the observed SSS seasonal cycle, with freshest water in the northeastern Bay, particularly during and after the monsoon. The model also displays an intense and shallow freshening signal in a narrow (~100 km wide) strip that hugs the east coast of India, from September to January, in good agreement with high‐resolution measurements along two ships of opportunity lines. The mixed layer salt budget confirms that the strong freshening in the northern Bay during the monsoon results from the Ganges‐Brahmaputra river discharge and from precipitation over the ocean. From September onward, the East India Coastal Current transports this freshwater southward along the east coast of India, reaching the southern tip of India in November. The surface freshening results in an enhanced vertical salinity gradient that increases salinity of the surface layer by vertical processes. Our results reveal that the erosion of the freshwater tongue along the east coast of India is not driven by northward horizontal advection, but by vertical processes that eventually overcome the freshening by southward advection and restore SSS to its pre‐monsoon values. The salinity‐stratified barrier layer hence only acts as a “barrier” for vertical heat fluxes, but is associated with intense vertical salt fluxes in the Bay of Bengal.
      PubDate: 2014-05-22T12:03:06.532129-05:
      DOI: 10.1002/2013JC009632
       
  • Upwelling influence on the number of extreme hot SST days along the Canary
           upwelling ecosystem
    • Authors: M. deCastro; M. Gómez‐Gesteira, X. Costoya, F. Santos
      Pages: n/a - n/a
      Abstract: Trends in the number of extreme hot days (days with SST anomalies higher than the 95% percentile) were analyzed along the Canary upwelling ecosystem (CUE) over the period 1982–2012 by means of SST data retrieved from NOAA OI1/4 Degree. The analysis will focus on the Atlantic Iberian sector and the Moroccan subregion where upwelling is seasonal (spring and summer) and permanent, respectively. Trends were analyzed both near coast and at the adjacent ocean where the increase in the number of extreme hot days is higher. Changes are clear at annual scale with an increment of 9.8 ± 0.3 (9.7 ± 0.1) days dec−1 near coast and 11.6 ± 0.2 (13.5 ± 0.1) days dec−1 at the ocean in the Atlantic Iberian sector (Moroccan subregion). The differences between near shore and ocean trends are especially patent for the months under intense upwelling conditions. During that upwelling season the highest differences in the excess of extreme hot days between coastal and ocean locations (Δn(# days dec−1)) occur at those regions where coastal upwelling increase is high. Actually, Δn and upwelling trends have shown to be significantly correlated in both areas, R = 0.88 (p 
      PubDate: 2014-05-22T10:12:58.314378-05:
      DOI: 10.1002/2013JC009745
       
  • Meridional overturning circulation in the South China Sea envisioned from
           the high‐resolution global reanalysis data GLBa0.08
    • Authors: Yeqiang Shu; Huijie Xue, Dongxiao Wang, Fei Chai, Qiang Xie, Jinglong Yao, Jingen Xiao
      Pages: n/a - n/a
      Abstract: The pattern of meridional overturning circulation (MOC) in the South China Sea (SCS) is studied using a numerical Lagrangian tracing method with the HYCOM+NCODA Global 1/12° Analysis (GLBa0.08) data. The SCS MOC has a “sandwich” structure, which consists of a layer of stronger clockwise circulation above 500 m depth, a counterclockwise layer in the mid layer between 500 and 1000 m depth, and a weaker clockwise layer below 1000 m. The deep (below 1000 m depth) clockwise layer is divided into three cells, namely, the deep southern MOC cell, DSMOC; the deep middle MOC cell, DMMOC; and the unclosed deep northern MOC cell, DNMOC. The inflow through the Luzon Strait is the main source for the SCS MOCs. The upper layer Luzon Strait inflow dominates the upper SCS MOC structure but has relatively less contribution to the DNMOC, whereas the deep layer Luzon Strait inflow mainly influences the DNMOC and it mostly rises near 18°N. The inflow through the Taiwan Strait mainly contributes to the upper layer MOC. Moreover, inflows from the Mindoro and Karimata straits contribute negatively to the upper MOC but play a significant role on the DSMOC. The backward integration of Lagrangian trajectories further validates that the SCS deep water comes not only from the deep inflow but also from the entrainment of the middle and upper layer inflow through the Luzon Strait. In the SCS basin, there are three northwest‐southeast tilted zones where tracers upwell, which correspond to the three deep MOC cells. One possible mechanism for these upwelling zones is the interaction between the continental slope‐trapped waves and the westward planetary Rossby waves.
      PubDate: 2014-05-22T10:11:46.912089-05:
      DOI: 10.1002/2013JC009583
       
  • The vertical structure of the circulation and dynamics in Hudson Shelf
           Valley
    • Authors: Steven J. Lentz; Bradford Butman, Courtney Harris
      Pages: n/a - n/a
      Abstract: Hudson Shelf Valley is a 20‐30 m deep, 5‐10 km wide v‐shaped submarine valley that extends across the Middle Atlantic Bight continental shelf. The valley provides a conduit for cross‐shelf exchange via along‐valley currents of 0.5 m s‐1 or more. Current profile, pressure, and density observations collected during the winter of 1999‐2000 are used to examine the vertical structure and dynamics of the flow. Near‐bottom along‐valley currents having times scales of a few days are driven by cross‐shelf pressure gradients set up by wind stresses, with eastward (westward) winds driving onshore (offshore) flow within the valley. The along‐valley momentum balance in the bottom boundary layer is predominantly between the pressure gradient and bottom stress because the valley bathymetry limits current veering. Above the bottom boundary layer the flow veers toward an along‐shelf (cross‐valley) orientation and a geostrophic balance with some contribution from the wind stress (surface Ekman layer). The vertical structure and strength of the along‐valley current depends on the magnitude and direction of the wind stress. During offshore flows driven by westward winds the near‐bottom stratification within the valley increases resulting in a thinner bottom boundary layer and weaker offshore currents. Conversely, during onshore flows driven by eastward winds the near‐bottom stratification decreases resulting in a thicker bottom boundary layer and stronger onshore currents. Consequently, for wind stress magnitudes exceeding 0.1 Nm‐2, onshore along‐valley transport associated with eastward wind stress exceeds the offshore transport associated with westward wind stress of the same magnitude.
      PubDate: 2014-05-22T04:19:48.675042-05:
      DOI: 10.1002/2014JC009883
       
  • Long‐term annual primary production in the Ulleung Basin as a
           biological hot spot in the East/Japan Sea
    • Authors: HuiTae Joo; Jung Woo Park, SeungHyun Son, Jae‐Hoon Noh, Jin‐Yong Jeong, Jung Hyun Kwak, Stephane Saux‐Picart, Jung Hwa Choi, Chang‐Keun Kang, Sang Heon Lee
      Pages: n/a - n/a
      Abstract: Although the Ulleung Basin is an important biological “hot spot” in East/Japan Sea (hereafter the East Sea), very limited knowledge for seasonal and annual variations in the primary productivity exists. In this study, a recent decadal trend of primary production in the Ulleung Basin was analyzed based on MODIS‐derived monthly primary production for a better annual production budget. Based on the MODIS‐derived primary production, the mean daily primary productivity was 766.8 mg C m−2 d−1 (SD = ±196.7 mg C m−2 d−1) and the annual primary productivity was 280.2 g C m−2 yr−1 (SD = ±14.9 g C m−2 yr−1) in the Ulleung Basin during the study period. The monthly contributions of primary production were not largely variable among different months, and a relatively small interannual production variability was also observed in the Ulleung Basin, which indicates that the Ulleung Basin is a sustaining biologically productive region called as “hot spot” in the East Sea. However, a significant recent decline in the annual primary production was observed in the Ulleung Basin after 2006. Although no strong possibilities were found in this study, the current warming sea surface temperature and a negative phase PDO index were suggested for the recent declining primary production. For a better understanding of subsequent effects on marine ecosystems, more intensive interdisciplinary field studies will be required in the Ulleung Basin.
      PubDate: 2014-05-21T13:32:01.538789-05:
      DOI: 10.1002/2014JC009862
       
  • Climate change projection in the Northwest Pacific marginal seas through
           dynamic downscaling
    • Authors: Gwang‐Ho Seo; Yang‐Ki Cho, Byoung‐Ju Choi, Kwang‐Yul Kim, Bong‐guk Kim, Yong‐jin Tak
      Pages: n/a - n/a
      Abstract: This study presents future climate change projections in the Northwest Pacific (NWP) marginal seas using dynamic downscaling from global climate models (GCMs). A regional climate model (RCM) for the Northwest Pacific Ocean was set up and integrated over the period from 2001 to 2100. The model used forcing fields from three different GCM simulations to downscale the effect of global climate change. MIROC, ECHAM, and HADCM were selected to provide climate change signals for the RCM. These signals were calculated from the GCMs using Cyclostationary Empirical Orthogonal Function analysis and added to the present lateral open boundary and the surface forcing. The RCM was validated by comparing hindcast result with the observation. It was able to project detailed regional climate change processes that GCMs were not able to resolve. A relatively large increases of water temperature were found in the marginal seas. However, only a marginal change was found along the Kuroshio path. Heat supply to the atmosphere decreases in most study areas due to a slower warming of the sea surface compared to the atmosphere. The RCM projection suggests that the temperature of the Yellow Sea Bottom Cold Water will gradually increase by 2100. Volume transports through major straits except the Taiwan Strait in the marginal seas are projected to increase slightly in future. Increased northeasterly wind stress in the East China Sea may also result in the transport change.
      PubDate: 2014-05-21T07:02:49.777515-05:
      DOI: 10.1002/2013JC009646
       
  • How well can we measure the ocean's mean dynamic topography from
           space?
    • Authors: R. J. Bingham; K. Haines, D. J. Lea
      Pages: n/a - n/a
      Abstract: Recent gravity missions have produced a dramatic improvement in our ability to measure the ocean's mean dynamic topography (MDT) from space. To fully exploit this oceanic observation, however, we must quantify its error. To establish a baseline, we first assess the error budget for an MDT calculated using a 3rd generation GOCE geoid and the CLS01 mean sea surface (MSS). With these products, we can resolve MDT spatial scales down to 250 km with an accuracy of 1.7 cm, with the MSS and geoid making similar contributions to the total error. For spatial scales within the range 133–250 km the error is 3.0 cm, with the geoid making the greatest contribution. For the smallest resolvable spatial scales (80–133 km) the total error is 16.4 cm, with geoid error accounting for almost all of this. Relative to this baseline, the most recent versions of the geoid and MSS fields reduce the long and short‐wavelength errors by 0.9 and 3.2 cm, respectively, but they have little impact in the medium‐wavelength band. The newer MSS is responsible for most of the long‐wavelength improvement, while for the short‐wavelength component it is the geoid. We find that while the formal geoid errors have reasonable global mean values they fail capture the regional variations in error magnitude, which depend on the steepness of the sea floor topography.
      PubDate: 2014-05-21T07:00:29.323757-05:
      DOI: 10.1002/2013JC009354
       
  • Wave‐driven along‐channel subtidal flows in a well‐mixed
           ocean inlet
    • Authors: Anna Wargula; Britt Raubenheimer, Steve Elgar
      Pages: n/a - n/a
      Abstract: Observations of waves, flows, and water levels collected for a month in and near a long, narrow, shallow (∼ 3000 m long, 1000 m wide, and 5 m deep), well‐mixed ocean inlet are used to evaluate the subtidal (periods > 30 h) along‐inlet momentum balance. Maximum tidal flows in the inlet were about 1.5 m/s and offshore significant wave heights ranged from about 0.5 to 2.5 m. The dominant terms in the local (across the km‐wide ebb shoal) along‐inlet momentum balance are the along‐inlet pressure gradient, the bottom stress, and the wave radiation‐stress gradient. Estimated nonlinear advective acceleration terms roughly balance in the channel. Onshore radiation‐stress gradients owing to breaking waves enhance the flood flows into the inlet, especially during storms.
      PubDate: 2014-05-20T15:45:37.623383-05:
      DOI: 10.1002/2014JC009839
       
  • Observations of surface waves interacting with ice using stereo imaging
    • Authors: Alexander J. Campbell; Adam J. Bechle, Chin H. Wu
      Pages: n/a - n/a
      Abstract: A powerful Automated Trinocular Stereo Imaging System (ATSIS) is used to remotely measure waves interacting with three distinct ice types: brash, frazil, and pancake. ATSIS is improved with a phase‐only correlation matching algorithm and parallel computation to provide high spatial and temporal resolution 3‐D profiles of the water/ice surface, from which the wavelength, frequency, and energy flux are calculated. Along‐shore spatial frequency distributions show that pancake and frazil ices differentially attenuate at a greater rate for higher frequency waves, causing a decrease in mean frequency. In contrast, wave propagation through brash ice causes a rapid increase in the dominant wave frequency, which may be caused by non‐linear energy transfer to higher frequencies due to collisions between the brash ice particles. Consistent to the results in frequency, the wavelengths in pancake and frazil ices increase but decrease in brash ice. The total wave energy fluxes decrease exponentially in both pancake and frazil ice, whereas the overall energy flux remain constant in the brash ice due to thin layer thickness. The spatial energy flux distributions also reveal that wave reflection occurs at the boundary of each ice layer, with reflection coefficient decaying exponentially away from the ice interface. Reflection is the strongest at the pancake/ice‐free and frazil/brash interfaces; and the weakest at the brash/ice‐free interface. These high resolution observations measured by ATSIS demonstrate the spatially variable nature of waves propagating through ice.
      PubDate: 2014-05-19T01:25:52.50953-05:0
      DOI: 10.1002/2014JC009894
       
  • Surface energy budget of landfast sea ice during the transitions from
           winter to snowmelt and melt pond onset: The importance of net longwave
           radiation and cyclone forcings
    • Authors: B.G.T. Else; T.N. Papakyriakou, R. Raddatz, R.J. Galley, C.J. Mundy, D. G. Barber, K. Swystun, S. Rysgaard
      Pages: n/a - n/a
      Abstract: Relatively few sea ice energy balance studies have successfully captured the transition season of warming, snowmelt, and melt pond formation. In this paper, we report a surface energy budget for landfast sea ice that captures this important period. The study was conducted in the Canadian Arctic Archipelago from 10 May – 20 June, 2010. Over the first 20 days of the study we found that short periods (1‐3 days) of increased net radiation associated with low longwave loss provided most of the energy required to warm the snowpack from winter conditions. An extended period of low longwave loss (5 days) combined with the seasonal increase in incoming shortwave radiation then triggered snowmelt onset. Melt progressed with a rapid reduction in albedo and attendant increases in shortwave energy absorption, resulting in melt pond formation 8 days later. The key role of longwave radiation in initiating melt onset supports past findings, and confirms the importance of clouds and water vapor associated with synoptic weather systems. However, we also observed a period of strong turbulent energy exchange associated with the passage of a cyclone. The cyclone event occurred shortly after melt pond formation, but it delivered enough energy to significantly hasten melt onset had it occurred earlier in the season. Changes in the frequency, duration, and timing of synoptic‐scale weather events that deliver clouds and/or strong turbulent heat fluxes may be important in explaining observed changes in sea ice melt onset timing.
      PubDate: 2014-05-17T03:53:33.081419-05:
      DOI: 10.1002/2013JC009672
       
  • Ocean eddy freshwater flux convergence into the North Atlantic subtropics
    • Authors: Arnold L. Gordon; Claudia F. Giulivi
      Pages: n/a - n/a
      Abstract: For a quasi‐steady state condition the water vapor flux from the ocean to atmosphere typical of the salty subtropics, must be compensated by ocean processes that transfer freshwater into the evaporative regime. Observations of the North Atlantic subtropical sea surface salinity maximum region frequently reveal the presence of eddies with distinct salinity/temperature signatures of up to 0.2 psu/1°C, with horizontal scales of up to 200 km. Using the surface layer salinity and meridional velocity from the Simple Ocean Data Assimilation (SODA) re‐analysis data we find that the eddy flux can accomplish 50% to 75% of the required freshwater convergence into the subtropical regime, the rest being delivered by Ekman transport convergence, and therefore represents a significant component of the marine hydrological cycle. Interannual fluctuations of the eddy freshwater flux are reflected in sea surface salinity variability.
      PubDate: 2014-05-17T03:53:24.153772-05:
      DOI: 10.1002/2013JC009596
       
  • Evolution of a supercooled Ice Shelf Water plume with an
           actively‐growing sub‐ice platelet matrix
    • Authors: Natalie J. Robinson; Michael J. M. Williams, Craig L. Stevens, Patricia J. Langhorne, Tim G. Haskell
      Pages: n/a - n/a
      Abstract: We use new observations in Western McMurdo Sound, combined with longitudinal hydrographic transects of the sound, to identify a northward‐flowing Ice Shelf Water (ISW) plume exiting the cavity of the McMurdo‐Ross Ice Shelf. We estimate the plume's net northward transport at 0.4 ± 0.1 Sv, carving out a corridor approximately 35 km wide aligned with the Victoria Land Coast. Basal topography of the McMurdo Ice Shelf is such that the plume is delivered to the surface without mixing with overlying warmer water, and is therefore able to remain below the surface freezing temperature at the point of observation beneath first‐year ice. Thus the upper ocean was supercooled, by up to 50 mK at the surface, due to pressure relief from recent rapid ascent of the steep basal slope. The 70 m thick supercooled layer supports the growth and maintenance of a thick, semi‐rigid and porous matrix of platelet ice, which is trapped by buoyancy at the ice‐ocean interface. Continued growth of individual platelets in supercooled water creates significant brine rejection at the top of the water column which resulted in convection over the upper 200 m thick, homogeneous layer. By examining the diffusive nature of the intermediate water between layers of ISW and High Salinity Shelf Water, we conclude that the ISW plume must have originated beneath the Ross Ice Shelf and demonstrate that it is likely to expand eastward across McMurdo Sound with the progression of winter.
      PubDate: 2014-05-17T03:53:21.027839-05:
      DOI: 10.1002/2013JC009399
       
  • Trends in Southern Hemisphere wind‐driven circulation in CMIP5
           models over the 21st century: Ozone recovery versus greenhouse forcing
    • Authors: Guojian Wang; Wenju Cai, Ariaan Purich
      Pages: n/a - n/a
      Abstract: During the late 20th century, Antarctic ozone depletion and increasing greenhouse gases (GHGs) conspired to generate conspicuous atmospheric circulation trends in the Southern Hemisphere (SH), contributing to a poleward intensification of the oceanic supergyre circulation. Forcing of Antarctic ozone depletion dominated the observed trends during the depletion period (1979–2005), but Antarctic ozone is projected to recover by the middle of the 21st century. The recovery provides a mechanism for offsetting the impact from increasing GHG emissions. To what extent will the recovery of ozone mitigate SH atmosphere and ocean circulation trends expected from increasing GHGs? We examine climate model output from the Representative Concentration Pathway 4.5 and 8.5 (RCP4.5 and RCP8.5, respectively) emission scenario experiments, submitted to the Coupled Model Intercomparison Project phase 5. Both scenarios are subject to the effect of ozone recovery. We show that during the recovery period (2006–2045), there is little poleward shift of the supergyre circulation under either RCP scenario in austral summer, due to the dominance of ozone recovery. Further, under RCP8.5 the trend in winter, a season in which ozone recovery has little impact, is greater (more poleward) than in summer, opposite to the seasonality of trends during the depletion period. Under RCP4.5, with the contribution from ozone recovery, the summer poleward shift is projected to stabilize into the postrecovery decades, whereas under RCP8.5, the summer poleward shift accelerates in the postrecovery period, presenting vastly different ocean circulation futures.
      PubDate: 2014-05-15T15:34:33.436908-05:
      DOI: 10.1002/2013JC009589
       
  • Observation of South Atlantic subtropical mode waters with Argo profiling
           float data
    • Authors: O. T. Sato; P. S. Polito
      Pages: n/a - n/a
      Abstract: South Atlantic subtropical mode water (SASTMW) is detected using temperature and salinity profiles obtained by Argo floats. Marked by low potential vorticity within its extent, mode waters are identified by homogeneous temperature and salinity values, both horizontally and vertically. Their presence is evident in three regions: the Brazil Current recirculation gyre on the western side of the basin, the eastern side of the basin, and along the southern edge of the gyre. Formation occurs between winter and mid‐spring in the regions of cumulative cooling of the ocean. We showed that Argo profilers do not preferentially sampled eddies. Yet, from the profiles that found SASTMW inside an eddy, 80% are anticyclonic. Furthermore, the mode water layer inside anticyclonic eddies is on average thicker than inside cyclonic eddies or anywhere else. We investigate the correlation between the presence of mode water with the eddy kinetic energy (EKE). The cross spectrum shows that the EKE and the layer thickness are out of phase in the annual period band. We addressed the role of negative surface heat fluxes during the SASTMW period of formation. Nearly all profiles that indicated mode water formation occurred at the time and within the region where the cumulative heat flux was negative.
      PubDate: 2014-05-14T15:55:45.225964-05:
      DOI: 10.1002/2013JC009438
       
  • Formation of homogeneous regions for regional frequency analysis of
           extreme significant wave heights
    • Authors: Jérôme Weiss; Pietro Bernardara, Michel Benoit
      Pages: n/a - n/a
      Abstract: Regional frequency analysis (RFA) can reduce uncertainties in the estimations of return levels, provided that homogeneous regions can be delineated. In the framework of extreme marine events, a physically based method to form homogeneous regions by identifying typical storms footprints is proposed. First, a spatiotemporal declustering procedure is employed to detect storms generating marine extremes. Second, the identification of the most typical storms footprints relies on a clustering algorithm based on a criterion of storm propagation. The resulting regions are readily explicable: sites from a given region are likely to be impacted by the same storms, and any storm impacting a region is likely to remain enclosed in this region. This procedure is fairly simple to implement, as the only information required is the time of occurrence of the observed extremes. An application to the estimation of extreme significant wave heights from the numerical sea‐state database ANEMOC‐2 is given. Six regions, both physically and statistically homogeneous, are delineated in the North‐East part of the Atlantic Ocean. It is shown that the identification of storms footprints allows the increase of the overall statistical homogeneity. Combined with RFA, the proposed method highlights regional differences in the spatial extent and intensity of storms.
      PubDate: 2014-05-14T15:26:38.433711-05:
      DOI: 10.1002/2013JC009668
       
  • Direct measurements of wind stress over the surf zone
    • Authors: Behnam Shabani; Peter Nielsen, Tom Baldock
      Pages: n/a - n/a
      Abstract: Field data of the wind stress over surf zone waves are presented from an open ocean beach on the East Australian Coast. Two ultrasonic anemometers were deployed at nominal heights of 5 and 10 m above the water surface in the intertidal and inner surf zones, with concurrent measurements of water levels and offshore wave parameters. Following a rigorous quality control procedure, the wind stress was determined by the eddy correlation technique. A constant stress layer was observed between 5 and 10 m elevation. Considering near‐neutral conditions only, the wind drag coefficients were found to systematically change with the wind angle of approach relative to the shoreline and are much smaller for longshore wind than during onshore wind. The concept of an apparent wave steepness changing with wind direction is suggested to explain this behavior. The drag coefficients over the surf zone during onshore wind and near‐neutral conditions were determined to be almost twice the values expected at the same wind speed and open ocean conditions. The observed Charnock coefficient was similarly an order of magnitude larger than open ocean values. A wave celerity of the order of that expected in the inner surf zone is required to explain the observed large roughness and drag coefficients using existing wave age‐dependent parameterizations. This suggests that the slower wave celerity in the surf zone is an important contributor to the increased wind stress, in addition to the sawtooth wave shape.
      PubDate: 2014-05-14T15:26:19.114725-05:
      DOI: 10.1002/2013JC009585
       
  • Physical and biological controls on DMS,P dynamics in ice
           shelf‐influenced fast ice during a winter‐spring and a
           spring‐summer transitions
    • Authors: Gauthier Carnat; Jiayun Zhou, Tim Papakyriakou, Bruno Delille, Thomas Goossens, Tim Haskell, Véronique Schoemann, François Fripiat, Janne‐Markus Rintala, Jean‐Louis Tison
      Pages: n/a - n/a
      Abstract: We report the seasonal and vertical variations of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) in fast ice at Cape Evans, McMurdo Sound (Antarctica) during the spring‐summer transition in 2011 and winter‐spring transition in 2012. We compare the variations of DMS,P observed to the seasonal evolution of the ice algal biomass and of the physical properties of the ice cover, with emphasis on the ice texture and brine dynamics. Isolated DMS and DMSP maxima were found during both seasonal episodes in interior ice and corresponded to the occurrence of platelet crystals in the ice texture. We show that platelet crystals formation corresponded in time and depth to the incorporation of dinoflagellates (strong DMSP producers) in the ice cover. We also show that platelet crystals could modify the environmental stresses on algal cells and perturb the vertical redistribution of DMS,P concentrations. We show that during the winter‐spring transition in 2012, the DMS,P profiles were strongly influenced by the development and decline of a diatom‐dominated bloom in the bottom ice, with DMSP variations remarkably following chl a variations. During the spring‐summer transition in 2011, the increase in brine volume fraction (influencing ice permeability) on warming was shown to trigger (1) an important release of DMS to the under‐ice water through brine convection and (2) a vertical redistribution of DMSP across the ice.
      PubDate: 2014-05-14T15:10:01.841911-05:
      DOI: 10.1002/2013JC009381
       
  • Issue Information
    • Pages: i - v
      PubDate: 2014-05-13T09:05:31.825284-05:
      DOI: 10.1002/jgrc.20349
       
  • Increasing carbon inventory of the intermediate layers of the Arctic Ocean
    • Authors: Ylva Ericson; Adam Ulfsbo, Steven vanHeuven, Gerhard Kattner, Leif G. Anderson
      Pages: n/a - n/a
      Abstract: Concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA), nutrients and oxygen in subsurface waters of the central Arctic Ocean have been investigated for conceivable time trends over the last two decades. Data from six cruises (1991‐2011) that cover the Nansen, Amundsen and Makarov Basins were included in this analysis. In waters deeper than 2000 m, no statistically significant trend could be observed for DIC, TA, phosphate or nitrate, but a small rate of increase in apparent oxygen utilization (AOU) was noticeable. For the individual stations, differences in concentration of each property were computed between the mean concentrations in the Arctic Atlantic Water (AAW) or the upper Polar Deep Water (uPDW), i.e. between about 150 and 1400 m depth, and in the deep water (assumed invariable over time). In these shallower water layers, we observe significant above‐zero time trends for DIC, in the range of 0.6 to 0.9 µmol kg‐1 yr‐1 (for AAW) and 0.4 to 0.6 µmol kg‐1 yr‐1 (for uPDW). No time trend in nutrients could be observed, indicating no change in the rate of organic matter mineralization within this depth range. Consequently, the buildup of DIC is attributed to increasing concentrations of anthropogenic carbon in the waters flowing into these depth layers of the Arctic Ocean. The resulting rate of increase of the column inventory of anthropogenic CO2 is estimated to be between 0.6 and 0.9 mol C m‐2 yr1, with distinct differences between basins.
      PubDate: 2014-03-20T05:22:35.457106-05:
      DOI: 10.1002/2013JC009514
       
  • Implications of fractured arctic perennial ice cover on thermodynamic and
           dynamic sea ice processes
    • Authors: Matthew G. Asplin; Randall Scharien, Brent Else, Stephen Howell, David G. Barber, Tim Papakyriakou, Simon Prinsenberg
      Pages: n/a - n/a
      Abstract: Decline of the Arctic summer minimum sea ice extent is characterized by large expanses of open water in the Siberian, Laptev, Chukchi and Beaufort Seas, and introduces large fetch distances in the Arctic Ocean. Long waves can propagate deep into the pack ice, thereby causing flexural swell and failure of the sea ice. This process shifts the floe size diameter distribution smaller, increases floe surface area, and thereby affects sea ice dynamic and thermodynamic processes. The results of Radarsat‐2 imagery analysis show that a flexural fracture event which occurred in the Beaufort Sea region on 06 September 2009 affected ~40,000 km2. Open water fractional area in the area affected initially decreased from 3.7% to 2.7%, but later increased to ~20% following wind‐forced divergence of the ice pack. Energy available for lateral melting was assessed by estimating the change in energy entrainment from longwave and shortwave radiation in the mixed‐layer of the ocean following flexural fracture. 11.54 MJ · m‐2 of additional energy for lateral melting of ice floes was identified in affected areas. The impact of this process in future Arctic sea ice melt seasons was assessed using estimations of earlier occurrences of fracture during the melt season, and is discussed in context with ocean heat fluxes, atmospheric mixing of the ocean mixed layer, and declining sea ice cover. We conclude that this process is an important positive feedback to Arctic sea ice loss, and timing of initiation is critical in how it affects sea ice thermodynamic and dynamic processes.
      PubDate: 2014-03-20T05:22:06.869805-05:
      DOI: 10.1002/2013JC009557
       
  • Dynamics of oxygen depletion in the nearshore of a coastal embayment of
           the southern Benguela upwelling system
    • Authors: Grant C. Pitcher; Trevor A. Probyn, Andre du Randt, Andrew. J. Lucas, Stewart Bernard, Haley Evers‐King, Tarron Lamont, Larry Hutchings
      Pages: n/a - n/a
      Abstract: Acquisition of high resolution time series of water column and bottom dissolved oxygen (DO) concentrations inform the dynamics of oxygen depletion in St Helena Bay in the southern Benguela upwelling system at several scales of variability. The bay is characterized by seasonally recurrent hypoxia (
      PubDate: 2014-03-20T05:20:03.487065-05:
      DOI: 10.1002/2013JC009443
       
  • Hindcasts of potential harmful algal bloom transport pathways on the
           Pacific Northwest coast
    • Authors: S.N Giddings; P MacCready, B.M Hickey, N.S Banas, K.A Davis, S.A Siedlecki, V.L Trainer, R.M Kudela, N.A Pelland, T.P Connolly
      Pages: n/a - n/a
      Abstract: Harmful algal blooms (HABs) pose a significant threat to human and marine organism health, and negatively impact coastal economies around the world. An improved understanding of HAB formation and transport is required to improve forecasting skill. A realistic numerical simulation of the US Pacific Northwest region is used to investigate transport pathways from known HAB formation hotspots, specifically for Pseudo‐nitzschia (Pn), to the coast. We show that transport pathways are seasonal, with transport to the Washington (WA) coast from a northern source (the Juan de Fuca Eddy) during the summer/fall upwelling season and from a southern source (Heceta Bank) during the winter/early spring due to the predominant wind driven currents. Interannual variability in transport from the northern source is related to the degree of wind intermittency with more transport during years with more frequent relaxation/downwelling events. The Columbia River plume acts to mitigate transport to the coast as the plume front blocks on‐shore transport. The plume's influence on along‐shore transport is variable although critical in aiding transport from the southern source to the WA coast via plume entrainment. Overall transport from our simulations captures most observed Pn HAB beach events from 2004‐2007 (characterized by Pseudo‐nitzschia cell abundance); however, numerous false positives occur. We show that incorporating phytoplankton biomass results from a coupled biogeochemical model reduces the number of false positives significantly and thus improves our Pn HAB predictions.
      PubDate: 2014-03-20T05:15:11.433027-05:
      DOI: 10.1002/2013JC009622
       
  • Seasonal overturning circulation in the Red Sea. 2: Winter circulation
    • Authors: Fengchao Yao; Ibrahim Hoteit, Larry J. Pratt, Amy S. Bower, Armin Köhl, Ganesh Gopalakrishnan, David Rivas
      Pages: n/a - n/a
      Abstract: The shallow winter overturning circulation in the Red Sea is studied using a 50‐year high‐resolution MITgcm (MIT general circulation model) simulation with realistic atmospheric forcing. The overturning circulation for a typical year, represented by 1980, and the climatological mean are analyzed using model output to delineate the three dimensional structure and to investigate the underlying dynamical mechanisms. The horizontal model circulation in the winter of 1980 is dominated by energetic eddies. The climatological model mean results suggest that the surface inflow intensifies in a western boundary current in the southern Red Sea that switches to an eastern boundary current north of 24 °N. The overturning is accomplished through a cyclonic recirculation and a cross‐basin overturning circulation in the northern Red Sea, with major sinking occurring along a narrow band of width about 20 km along the eastern boundary and weaker upwelling along the western boundary. The northward pressure gradient force, strong vertical mixing, and horizontal mixing near the boundary are the essential dynamical components in the model's winter overturning circulation. The simulated water exchange is not hydraulically controlled in the Strait of Bab el Mandeb; instead, the exchange is limited by bottom and lateral boundary friction and, to a lesser extent, by interfacial friction due to the vertical viscosity at the interface between the inflow and the outflow.
      PubDate: 2014-03-20T05:15:06.947652-05:
      DOI: 10.1002/2013JC009331
       
  • Observations and numerical modeling of the Pearl River plume in summer
           season
    • Authors: Jiayi Pan; Yanzhen Gu, Dongxiao Wang
      Pages: n/a - n/a
      Abstract: A cruise survey of the Pearl River plume during southeasterly and southwesterly winds, two typical wind patterns in summer in Guangdong coastal waters, is reported and the cruise data are analyzed to unveil the plume dynamics. The Kelvin number is derived from the in‐situ data, revealing that the Pearl River plume exhibits two different scales in response to the two kinds of the wind forcing. Numerical model simulations based on the regional oceanic modeling system (ROMS) with nesting‐domains are implemented to explore details of the plume dynamics, validated by cruise observations and tidal gauge sea level data. Modeling results suggest that there is a sub‐tidal, anti‐cyclonic recirculation bulge on the west side out of the estuary mouth under southeasterly winds, showing a re‐circulating plume in the near‐field. When the wind changes to the southwesterly, however, the re‐circulating plume vanishes. The distinct, supercritical tidal plume front occurs with southeasterly winds prevailing in spring tide due to the strong advection in the tidal plume. The tidal salt deficit flux can reach as high as 12.5% of the mean current flux, and illustrates the combined forcing of tide and wind.
      PubDate: 2014-03-18T14:03:24.590161-05:
      DOI: 10.1002/2013JC009042
       
  • Comparative hydrodynamics of 10 Mediterranean lagoons by means of
           numerical modeling
    • Authors: Georg Umgiesser; Christian Ferrarin, Andrea Cucco, Francesca De Pascalis, Debora Bellafiore, Michol Ghezzo, Marco Bajo
      Pages: n/a - n/a
      Abstract: A comparison study between ten Mediterranean lagoons has been carried out by means of the 3D numerical model SHYFEM. The investigated basins are the Venice and Marano‐Grado lagoons in the Northern Adriatic Sea, the Lesina and Varano lagoons in the Southern Adriatic Sea, the Taranto basin in the Ionian Sea, the Cabras Lagoon in Sardinia, the Ganzirri and Faro lagoons in Sicily, the Mar Menor in Spain and the Nador Lagoon in Morocco. This study has been focused on hydrodynamics in terms of exchange rates, transport time scale and mixing. Water exchange depends mainly on the inlet shape and tidal range, but also on the wind regimes in the case of multi‐inlet lagoons. Water renewal time, which is mostly determined by the exchange rate, is a powerful concept that allows lagoons to be characterized with a time scale. In the case of the studied lagoons the renewal time ranged from few days in the Marano‐Grado Lagoon up to one year in the case of the Mar Menor. The analysis of the renewal time frequency distribution allows identifying sub‐basins. The numerical study proved to be a useful tool for the inter‐comparison and classification of the lagoons. These environments range from a leaky type to a choked type of lagoons and give a representative picture of the lagoons situated around the Mediterranean basin. Mixing efficiency turns out to be a function of the morphological complexity, but also of the forcings acting on the system.
      PubDate: 2014-03-18T13:21:19.659207-05:
      DOI: 10.1002/2013JC009512
       
  • Wind‐forced interannual variability of the Atlantic meridional
           overturning circulation at 26.5°N
    • Authors: Jian Zhao; William Johns
      Pages: n/a - n/a
      Abstract: The observed Atlantic Meridional Overturning Circulation (AMOC) at 26.5°N shows interannual variability consisting of an increase from early 2004 to late 2005 and a following downtrend which reaches a minimum in the winter of 2009/2010. These interannual AMOC fluctuations are dominated by changes in the upper mid‐ocean geostrophic flow except during the winter of 2009/2010, when the anomalous wind‐driven Ekman transport also has a significant contribution. The physical mechanisms for the interannual changes of the AMOC are proposed and evaluated in a 2‐layer model. While the Ekman transport is linked to the North Atlantic Oscillation (NAO), the anomalous geostrophic transport involves the oceanic adjustment to surface wind forcing. In particular, the intensification and weakening of the southward interior geostrophic flow is modulated by the internal Rossby wave adjustment to the surface wind forcing. The Gulf Stream, on the other hand, is controlled by both topographic waves along the US coast and westward propagating planetary waves. Our study suggests that a large part of the observed AMOC interannual variability at 26.5°N can be explained by wind‐driven dynamics.
      PubDate: 2014-03-18T13:20:21.732104-05:
      DOI: 10.1002/2013JC009407
       
  • Exploring the mesoscale activity in the Solomon Sea: A complementary
           approach with a numerical model and altimetric data
    • Authors: L. Gourdeau; J. Verron, A. Melet, W. Kessler, F. Marin, B. Djath
      Pages: n/a - n/a
      Abstract: The Solomon Sea is an area of high level of eddy kinetic energy (EKE), and represents a transit area for the low latitude Western Boundary Currents (LLWBCs) connecting the subtropics to the equatorial Pacific and playing a major role in ENSO dynamics. This study aims at documenting the surface mesoscale activity in the Solomon Sea for the first time. Our analysis is based on the joint analysis of altimetric data and outputs from a 1/12° model simulation. The highest surface EKE is observed in the northern part of the basin and extends southward to the central basin. An eddy tracking algorithm is used to document the characteristics and trajectories of coherent mesoscale vortices. Cyclonic eddies, generated in the south basin, are advected to the north by the LLWBCs before merging with stationary mesoscale structures present in the mean circulation. Anticyclonic eddies are less numerous. They are generated in the southeastern basin, propagate westward, reach the LLWBCs and dissipate. The seasonal and interannual modulations of the mesoscale activity are well marked. At seasonal time scale, maximum (minimum) activity is in May‐June (September). At interannual time scale, the mesoscale activity is particularly enhanced during La Niña conditions. If instabilities of the regional circulations seem to explain the generation of mesoscale features, the modulation of the mesoscale activity seems to be rather related with the intrusion at Solomon Strait of the surface South Equatorial Current, rather than to the LLWBCs, by modulating the horizontal and vertical shears suitable for instabilities.
      PubDate: 2014-03-18T13:20:17.621218-05:
      DOI: 10.1002/2013JC009614
       
  • Seasonal overturning circulation in the Red Sea: 1. Model validation and
           summer circulation
    • Authors: Fengchao Yao; Ibrahim Hoteit, Larry J. Pratt, Amy S. Bower, Ping Zhai, Armin Köhl, Ganesh Gopalakrishnan
      Pages: n/a - n/a
      Abstract: The overturning circulation in the Red Sea exhibits a distinct seasonally reversing pattern and is studied using high‐resolution MITgcm (MIT general circulation model) simulations. In the first part of this study, the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results. The seasonal water exchange in the Strait of Bab el Mandeb is successfully simulated and the structures of the intruding subsurface Gulf of Aden intermediate water are in good agreement with summer observations in 2011. The model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the Gulf of Aden resulting from remote winds in the Arabian Sea and an upward surface slope from the Red Sea to the Gulf of Aden set up by local surface winds in the Red Sea. In addition during late summer, two processes associated respectively with latitudinally differential heating and increased salinity in the southern Red Sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation. Dynamically the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the Strait of Bab el Mandeb. Unlike some previous studies, the three‐layer summer exchange flows in the Strait of Bab el Mandeb do not appear to be hydraulically controlled.
      PubDate: 2014-03-17T04:14:27.055367-05:
      DOI: 10.1002/2013JC009004
       
  • Modulation of Kuroshio transport by mesoscale eddies at the Luzon Strait
           entrance
    • Authors: Ren‐Chieh Lien; Barry Ma, Yu‐Hsin Cheng, Chong‐Ru Ho, Bo Qiu, Craig M. Lee, Ming‐Huei Chang
      Pages: n/a - n/a
      Abstract: Measurements of Kuroshio Current velocity at the entrance to Luzon Strait along 18.75°N were made with an array of six moorings during June 2012–June 2013. Strong positive relative vorticity of the order of the planetary vorticity f was observed on the western flank of the Kuroshio in the upper 150 m. On the eastern flank, the negative vorticity observed was about an order of magnitude smaller than f. Kuroshio transport near its origin is computed from direct measurements for the first time. Kuroshio transport has an annual mean of 15 Sv with a standard deviation of 3 Sv. It is modulated strongly by impinging westward propagating eddies, which are identified by an improved eddy detection method and tracked back to the interior ocean. Eight Kuroshio transport anomalies > 5 Sv are identified; seven are explained by the westward propagating eddies. Cyclonic (anticyclonic) eddies decrease (increase) the zonal sea level anomaly (SLA) slope and reduce (enhance) Kuroshio transport. Large transport anomalies of >10 Sv within O(10 days) are associated with pairs of cyclonic and anticyclonic eddies. The observed Kuroshio transport was strongly correlated with the SLA slope (correlation = 0.9). Analysis of SLA slope data at the entrance to Luzon Strait over the period 1992–2013 reveals a seasonal cycle with a positive anomaly (i.e., an enhanced Kuroshio transport) in winter and spring and a negative anomaly in summer and fall. Eddy induced vorticity near the Kuroshio has a similar seasonal cycle, suggesting that seasonal variation of the Kuroshio transport near its origin is modulated by the seasonal variation of the impinging mesoscale eddies.
      PubDate: 2014-03-14T05:50:20.10389-05:0
      DOI: 10.1002/2013JC009548
       
  • Topographic scattering of the low mode internal tide in the deep ocean
    • Authors: Manikandan Mathur; Glenn S. Carter, Thomas Peacock
      Pages: n/a - n/a
      Abstract: We investigate the role of deep‐ocean topography in scattering energy from the large spatial scales of the low mode internal tide to the smaller spatial scales of higher modes. The complete Green function method, which is not subject to the restrictions of the WKB approximation, is used for the first time to study the two‐dimensional scattering of a mode‐1 internal tide incident on subcritical and supercritical topography of any form in arbitrary stratifications. For an isolated Gaussian ridge in a uniform stratification, large amplitude critical topography is the most efficient at mode‐1 scattering and small amplitude topography scatters with an efficiency on the order of 5‐10%. In a nonuniform stratification with a pycnocline, the results are qualitatively the same as for a constant stratification, albeit with the key features shifted to larger height ratios. Having validated these results by direct comparison with the results of nonlinear numerical simulations, and in the process demonstrated that WKB results are not appropriate for reasonable ocean predictions, we proceed to use the Green function approach to quantify the role of topographic scattering for the region of the Pacific ocean surrounding the Hawaiian Islands chain. To the south, the Line Islands ridge is found to scatter ~ 40% of a mode‐1 internal tide coming from the Hawaiian Ridge. To the north, realistic, small‐amplitude, rough topography scatters ~ 5‐10% of the energy out of mode‐1 for transects of length 1000‐3000km. A significant finding is that compared to large extents of small‐amplitude, rough topography a single large topographic feature along the path of a mode‐1 internal tide plays the dominant role in scattering the internal tide.
      PubDate: 2014-03-11T12:55:54.185158-05:
      DOI: 10.1002/2013JC009152
       
  • Cross‐shelf exchange in the northwestern Black Sea
    • Authors: Feng Zhou; Georgy Shapiro, Fred Wobus
      Pages: n/a - n/a
      Abstract: The transports of water, heat and salt between the northwestern shelf and deep interior of the Black Sea are investigated using a high‐resolution three‐dimensional primitive equation model. From April to August, 2005, both onshore and offshore cross‐shelf break transports in the top 20 m were 0.24 Sv on average, which is equivalent to the replacement of 60% of the volume of surface shelf waters (0 – 20 m) per month. Two main exchange mechanisms are studied: Ekman transport, and transport by mesoscale eddies and associated meanders of the Rim Current. The Ekman drift causes nearly uniform onshore or offshore flow over a large section of the shelf break, but it is confined to the upper layers. In contrast, eddies and meanders penetrate deep down to the bottom, but they are restricted laterally. During the strong wind events of April 15 – 22 and July 1 – 4, some 0.66×1012 and 0.44×1012 m3 of water were removed from the northwestern shelf respectively. In comparison, the single long‐lived Sevastopol Eddy generated a much larger offshore transfer of 2.84×1012 m3 over the period April 23 to June 30, which is equivalent to 102% of the volume of northwestern shelf waters. Over the study period, salt exchanges increased the average density of the shelf waters by 0.67 kg m‐3 and reduced the density contrast between the shelf and deep sea, while lateral heat exchanges reduced the density of the shelf waters by 0.16 kg m‐3 and sharpened the shelf break front.
      PubDate: 2014-03-11T12:39:52.162389-05:
      DOI: 10.1002/2013JC009484
       
  • Bayesian near‐field tsunami forecasting with uncertainty estimates
    • Authors: Daisuke Tatsumi; Catherine A. Calder, Takashi Tomita
      Pages: 2201 - 2211
      Abstract: Tsunami waveforms can be observed at offshore locations such as sea‐bottom pressure gauges or GPS‐mounted buoys. Recent work has focused on using these observations to make near‐field tsunami forecasts in real time. However, existing forecasting methods are limited in that they do not provide uncertainty estimates. This study develops a near‐field tsunami forecasting method with uncertainty estimates. The method embeds a conditional autoregressive model in a hierarchical Bayesian inverse model. Since we sample from the posterior distribution of interest using a Markov Chain Monte Carlo algorithm, not only the mean but also the variance for forecasts can be readily obtained. The proposed method is validated through simulation‐based experiments for four historical earthquakes in the Nankai Trough, Japan.
      PubDate: 2014-04-04T09:55:17.345657-05:
      DOI: 10.1002/2013JC009334
       
  • Study of the phytoplankton plume dynamics off the Crozet Islands (Southern
           Ocean): A geochemical‐physical coupled approach
    • Authors: Virginie Sanial; Pieter van Beek, Bruno Lansard, Francesco d'Ovidio, Elodie Kestenare, Marc Souhaut, Meng Zhou, Stéphane Blain
      Pages: 2227 - 2237
      Abstract: The Crozet Archipelago, in the Indian sector of the Southern Ocean, constitutes one of the few physical barriers to the Antarctic Circumpolar Current. Interaction of the currents with the sediments deposited on the margins of these islands contributes to the supply of chemical elements—including iron and other micro‐nutrients—to offshore high‐nutrient, low‐chlorophyll (HNLC) waters. This natural fertilization sustains a phytoplankton bloom that was studied in the framework of the KEOPS‐2 project. In this work, we investigated the time scales of the surface water transport between the Crozet Island shelves and the offshore waters, a transport that contributes iron to the phytoplankton bloom. We report shelf‐water contact ages determined using geochemical tracers (radium isotopes) and physical data based on in situ drifter data and outputs of a model based on altimetric Lagrangian surface currents. The apparent ages of surface waters determined using the three independent methods are in relatively good agreement with each other. Our results provide constraints on the time scales of the transport between the shelf and offshore waters near the Crozet Islands and highlight the key role played by horizontal transport in natural iron fertilization and in defining the extension of the chlorophyll plume in this HNLC region of the Southern Ocean.
      PubDate: 2014-04-10T08:20:43.598008-05:
      DOI: 10.1002/2013JC009305
       
  • The influence of an Antarctic glacier tongue on near‐field ocean
           circulation and mixing
    • Authors: C. L. Stevens; M. G. McPhee, A. L. Forrest, G. H. Leonard, T. Stanton, T. G. Haskell
      Pages: 2344 - 2362
      Abstract: In situ measurements of flow and stratification in the vicinity of the Erebus Glacier Tongue, a 12 km long floating Antarctic glacier, show the significant influence of the glacier. Three ADCPs (75, 300, and 600 kHz) were deployed close (
      PubDate: 2014-04-14T10:55:25.14293-05:0
      DOI: 10.1002/2013JC009070
       
  • Application of the implicit particle filter to a model of nearshore
           circulation
    • Authors: R. N. Miller; L. L. Ehret
      Pages: 2363 - 2385
      Abstract: The implicit particle filter is applied to a stochastically forced shallow water model of nearshore flow, and found to produce reliable state estimates with tens of particles. The state vector of this model consists of a height anomaly and two horizontal velocity components at each point on a 128 × 98 regular rectangular grid, making for a state dimension O(104). The particle filter was applied to the model with two parameter choices representing two distinct dynamical regimes, and performed well in both. Demands on computing resources were manageable. Simulations with as many as a hundred particles ran overnight on a modestly configured workstation. In this case of observations defined by a linear function of the state vector, taken every time step of the numerical model, the implicit particle filter is equivalent to the optimal importance filter, i.e., at each step any given particle is drawn from the density of the system conditioned jointly upon observations and the state of that particle at the previous time. Even in this ideal case, the sample occasionally collapses to a single particle, and resampling is necessary. In those cases, the sample rapidly reinflates, and the analysis never loses track. In both dynamical regimes, the ensembles of particles deviated significantly from normality.
      PubDate: 2014-04-14T10:53:17.852216-05:
      DOI: 10.1002/2013JC009440
       
  • Mixing dynamics at the confluence of two large rivers undergoing weak
           density variations
    • Authors: Cintia L. Ramón; Joan Armengol, Josep Dolz, Jordi Prats, Francisco J. Rueda
      Pages: 2386 - 2402
      Abstract: Simulations of tracer experiments conducted with a three‐dimensional primitive‐equation hydrodynamic and transport model are used to understand the processes controlling the rate of mixing between two rivers (Ebro and Segre), with distinct physical and chemical properties, at their confluence, upstream of a meandering reservoir (Ribarroja reservoir). Mixing rates downstream of the confluence are subject to hourly scale oscillations, driven partly by changes in inflow densities and also as a result of turbulent eddies that develop within the shear layer between the confluent rivers and near a dead zone located downstream of the confluence. Even though density contrasts are low—at most O(10−1) kg m−3 difference among sources—and almost negligible from a dynamic point of view—compared with inertial forces—they are important for mixing. Mixing rates between the confluent streams under weakly buoyant conditions can be of up to 40% larger than those occurring under neutrally buoyant conditions. The buoyancy effects on mixing rates are interpreted as the result of changes in the contact area available for mixing (distortion of the mixing layer). For strong density contrasts, though, when the contact area between the streams becomes nearly horizontal, larger density differences between streams will lead to weaker mixing rates, as a result of the stabilizing effect of vertical density gradients.
      PubDate: 2014-04-14T12:59:39.050808-05:
      DOI: 10.1002/2013JC009488
       
  • Geometric and oceanographic controls on melting beneath Pine Island
           Glacier
    • Authors: J. De Rydt; P. R. Holland, P. Dutrieux, A. Jenkins
      Pages: 2420 - 2438
      Abstract: Observations beneath the floating section of Pine Island Glacier have revealed the presence of a subglacial ridge which rises up to 300 m above the surrounding bathymetry. This topographic feature probably served as a steady grounding line position until sometime before the 1970s, when an ongoing phase of rapid grounding line retreat was initiated. As a result, a large ocean cavity has formed behind the ridge, strongly controlling the ocean circulation beneath the ice shelf and modulating the ocean water properties that cause ice melting in the vicinity of the grounding line. In order to understand how melt rates have changed during the various phases of cavity formation, we use a high‐resolution ocean model to simulate the cavity circulation for a series of synthetic geometries. We show that the height of the ridge and the gap between the ridge and ice shelf strongly control the inflow of warm bottom waters into the cavity, and hence the melt rates. Model results suggest a rapid geometrically controlled increase of meltwater production at the onset of ice thinning, but a weak sensitivity to geometry once the gap between the ridge and ice shelf has passed a threshold value of about 200 m. This provides evidence for a new, coupled, ice‐ocean feedback acting to enhance the initial retreat of an ice stream from a bedrock high. The present gap is over 200 m, and our results suggest that observed variability in melt rates is now controlled by other factors, such as the depth of the thermocline.
      PubDate: 2014-04-15T10:00:30.249568-05:
      DOI: 10.1002/2013JC009513
       
  • Wind‐induced interannual variability of sea level slope,
           along‐shelf flow, and surface salinity on the Northwest Atlantic
           shelf
    • Authors: Yun Li; Rubao Ji, Paula S. Fratantoni, Changsheng Chen, Jonathan A. Hare, Cabell S. Davis, Robert C. Beardsley
      Pages: 2462 - 2479
      Abstract: In this study, we examine the importance of regional wind forcing in modulating advective processes and hydrographic properties along the Northwest Atlantic shelf, with a focus on the Nova Scotian Shelf (NSS)‐Gulf of Maine (GoM) region. Long‐term observational data of alongshore wind stress, sea level slope, and along‐shelf flow are analyzed to quantify the relationship between wind forcing and hydrodynamic responses on interannual time scales. Additionally, a simplified momentum balance model is used to examine the underlying mechanisms. Our results show significant correlation among the observed interannual variability of sea level slope, along‐shelf flow, and alongshore wind stress in the NSS‐GoM region. A mechanism is suggested to elucidate the role of wind in modulating the sea level slope and along‐shelf flow: stronger southwesterly (northeastward) winds tend to weaken the prevailing southwestward flow over the shelf, building sea level in the upstream Newfoundland Shelf region, whereas weaker southwesterly winds allow stronger southwestward flow to develop, raising sea level in the GoM region. The wind‐induced flow variability can influence the transport of low‐salinity water from the Gulf of St. Lawrence to the GoM, explaining interannual variations in surface salinity distributions within the region. Hence, our results offer a viable mechanism, besides the freshening of remote upstream sources, to explain interannual patterns of freshening in the GoM.
      PubDate: 2014-04-16T12:52:41.989916-05:
      DOI: 10.1002/2013JC009385
       
  • River flow and ocean temperatures: The Congo River
    • Authors: R. H. White; R. Toumi
      Pages: 2501 - 2517
      Abstract: Using a regional ocean model, the impacts of the Congo River on ocean temperatures, mixed layer depths (MLDs), and barrier layers are studied. A sensitivity simulation with no Congo flow shows that the river shallows the mixed layer by up to 7 m and creates barrier layers up to 6 m thick and temperature inversions of up to 0.5 K. Contrary to previous modeling studies, but in agreement with observational analysis, simulation results show no substantial SST signal from the Congo River in the eastern Atlantic. A cooling signal,
      PubDate: 2014-04-17T09:47:40.754714-05:
      DOI: 10.1002/2014JC009836
       
  • Zooplankton community structure and dynamics in the Arctic Canada Basin
           during a period of intense environmental change (2004–2009)
    • Authors: Brian P. V. Hunt; R. John Nelson, Bill Williams, Fiona A. McLaughlin, Kelly V. Young, Kristina A. Brown, Svein Vagle, Eddy C. Carmack
      Pages: 2518 - 2538
      Abstract: Mesozooplankton were sampled in the Canada Basin in the summers of 2004, 2006, 2007, 2008, and fall 2009. Six taxa (Calanus hyperboreus, Calanus glacialis, Oithona similis, Limacina helicina, Microcalanus pygmaeus, and Pseudocalanus spp.) accounted for 77–91% of the abundance in all years, and 70–80% of biomass in 2004–2008. The biomass of C. hyperboreus and C. glacialis was reduced in 2009, likely due to seasonal migration below the sampling depth. Mean abundance was consistent across surveys while biomass increased from 18.92 to 32.56 mg dry weight m−3 between 2004 and 2008. Multivariate analysis identified a clear separation between shelf and deep basin (>1000 m) assemblages. Within the deep basin abundance and biomass were higher in the west, associated with a higher chlorophyll maximum. In 2007 and 2008 considerable heterogeneity developed in the assemblage structure, associated with variability in the contribution of the short‐lived (
      PubDate: 2014-04-22T09:58:10.837458-05:
      DOI: 10.1002/2013JC009156
       
  • Cross‐shelf seawater exchange controls the distribution of
           temperature, salinity, and neritic carbonate sediments in the Great
           Australian Bight
    • Authors: John F. Middleton; Noel P. James, Charles James, Yvonne Bone
      Pages: 2539 - 2549
      Abstract: The seasonally averaged wind stress of the Great Australian Bight (GAB) during the austral winter is directed to the east along the shelf and results in downwelling that extends to depths of 250 m. This downwelling is enhanced in the eastern GAB through the outflow of cold saline water formed in the broad shallow regions of the GAB and gulfs. During the austral summer, the averaged wind stress field of the GAB is anticyclonic with upwelling favorable winds along much of the coastline. In general however, significant slope upwelling is only observed in the eastern and western GAB where the shelf is narrow. Upwelling there provides nutrients to support the planktic and pelagic communities and the observed distribution of benthic invertebrate communities that lead to the formation of neritic carbonate sediments. At the shelf break of the central GAB where the shelf is very wide, the observed cross‐shelf distributions of temperature, salinity, and sediments indicate that downwelling occurs year round. The implied lack of nutrients is argued to explain the smaller communities of invertebrates found at the shelf edge (100–250 m) in these areas. A previous numerical study is cited to show that summer downwelling very likely results from a convergence of the deep ocean and poleward Sverdrup transports. The unique aspect of this integrated oceanographic‐sedimentological investigation is to tie outcomes of that numerical study with extant observations and benthic habitat to provide a consistent picture of how cross‐shelf exchange regulates water properties and benthos in the GAB.
      PubDate: 2014-04-22T10:35:18.339268-05:
      DOI: 10.1002/2013JC009420
       
  • Relative contributions of local wind and topography to the coastal
           upwelling intensity in the northern South China Sea
    • Authors: Dongxiao Wang; Yeqiang Shu, Huijie Xue, Jianyu Hu, Ju Chen, Wei Zhuang, TingTing Zu, Jindian Xu
      Pages: 2550 - 2567
      Abstract: Topographically induced upwelling caused by the interaction between large‐scale currents and topography was observed during four cruises in the northern South China Sea (NSCS) when the upwelling favorable wind retreated. Using a high‐resolution version of the Princeton Ocean Model, we investigate relative contributions of local wind and topography to the upwelling intensity in the NSCS. The results show that the topographically induced upwelling is sensitive to alongshore large‐scale currents, which have an important contribution to the upwelling intensity. The topographically induced upwelling is comparable with the wind‐driven upwelling at surface and has a stronger contribution to the upwelling intensity than the local wind does at bottom in the near‐shore shelf region. The widened shelf to the southwest of Shanwei and west of the Taiwan Banks intensifies the bottom friction, especially off Shantou, which is a key factor for topographically induced upwelling in terms of bottom Ekman transport and Ekman pumping. The local upwelling favorable wind enhances the bottom friction as well as net onshore transport along the 50 m isobath, whereas it has less influence along the 30 m isobath. This implies the local wind is more important in upwelling intensity in the offshore region than in the nearshore region. The contribution of local upwelling favorable wind on upwelling intensity is comparable with that of topography along the 50 m isobath. The effects of local upwelling favorable wind on upwelling intensity are twofold: on one hand, the wind transports surface warm water offshore, and as a compensation of mass the bottom current transports cold water onshore; on the other hand, the wind enhances the coastal current, and the bottom friction in turn increases the topographically induced upwelling intensity.
      PubDate: 2014-04-22T09:57:53.56524-05:0
      DOI: 10.1002/2013JC009172
       
  • Evaluating CMIP5 simulations of mixed layer depth during summer
    • Authors: Chuan Jiang Huang; Fangli Qiao, Dejun Dai
      Pages: 2568 - 2582
      Abstract: The ability of CMIP5 models in simulating surface mixed layer depth (MLD) during summer is assessed using 45 climate models. Their ocean models differ greatly in terms of vertical mixing parameterizations and model configurations. In some models, effects of surface waves, Langmuir circulations, submesoscale eddies, as well as additional wind mixing are included to improve upper‐ocean simulation. Similar to findings by previous studies, the summer MLDs are significantly underestimated in most of the models. Compared with the observation, only five of these models have deeper summer MLDs in the Southern Ocean, eight models have deeper summer MLDs in the central North Atlantic Ocean, and nine models have deeper summer MLDs in the central North Pacific Ocean. This underestimation of MLD is not caused by sea surface forcing, because most of the models tend to overestimate the surface wind stress, while they underestimate the net surface heat flux. Therefore, insufficient vertical mixing in the upper ocean may still be one of the potential reasons for this systematic underestimation of MLD in the climate models.
      PubDate: 2014-04-22T09:58:03.556984-05:
      DOI: 10.1002/2013JC009535
       
  • Three way validation of MODIS and AMSR‐E sea surface temperatures
    • Authors: Chelle L. Gentemann
      Pages: 2583 - 2598
      Abstract: The estimation of retrieval uncertainty and stability are essential for the accurate interpretation of data in scientific research, use in analyses, or numerical models. The primary uncertainty sources of satellite SST retrievals are due to errors in spacecraft navigation, sensor calibration, sensor noise, retrieval algorithms, and incomplete identification of corrupted retrievals. In this study, comparisons to in situ data are utilized to investigate retrieval accuracies of microwave (MW) SSTs from the Advanced Microwave Scanning Radiometer—Earth Observing System (AMSR‐E) and infrared (IR) SSTs from the Moderate Resolution Imaging Spectroradiometer (MODIS). The highest quality MODIS data were averaged to 25 km for comparison. The in situ SSTs are used to determine dependencies on environmental parameters, evaluate the identification of erroneous retrievals, and examine biases and standard deviations (STD) for each of the satellite SST data sets. Errors were identified in both the MW and IR SST data sets: (1) at low atmospheric water vapor a posthoc correction added to AMSR‐E was incorrectly applied and (2) there is significant cloud contamination of nighttime MODIS retrievals at SST
      PubDate: 2014-04-22T11:39:32.760618-05:
      DOI: 10.1002/2013JC009716
       
  • Local shear and mass transfer on individual coral colonies: Computations
           in unidirectional and wave‐driven flows
    • Authors: Sandy Chang; Gianluca Iaccarino, Frank Ham, Chris Elkins, Stephen Monismith
      Pages: 2599 - 2619
      Abstract: Flows through single coral colonies were simulated with an implementation of the Immersed Boundary (IB) method in Large‐Eddy Simulation (LES). The method was first validated with magnetic velocimetry experiments, which demonstrated that computational results were within approximately 7% of flow measurements. The algorithm was then applied to simulate unidirectional and wave‐driven flow conditions through two morphologically distinct coral colonies that naturally grow in very different hydrodynamic environments, with detailed analysis on spatial hydrodynamic and mass transfer variability. When the hydrodynamics of each coral's native environment was simulated, the dynamics in the interior of both branching species appeared to converge, in spite of vast differences between the hydrodynamic conditions and morphologies. A correlation between local surface shear and mass transfer was derived from simulated data. The results suggest that the corals grew in such a way that mass transfer characteristics are similar despite of vast differences in their physical shapes and hydrodynamic conditions.
      PubDate: 2014-04-22T11:44:58.9457-05:00
      DOI: 10.1002/2013JC009751
       
  • The critical role of stratification in submarine channels: Implications
           for channelization and long runout of flows
    • Authors: R. M. Dorrell; S. E. Darby, J. Peakall, E. J. Sumner, D. R. Parsons, R. B. Wynn
      Pages: 2620 - 2641
      Abstract: Channelized submarine gravity currents travel remarkable distances, transporting sediment to the distal reaches of submarine fans. However, the mechanisms by which flows can be sustained over these distances remain enigmatic. In this paper we consider two shallow water models the first assumes the flow is unstratified whilst the second uses empirical models to describe vertical stratification, which effects depth averaged mass and momentum transfer. The importance of stratification is elucidated through comparison of modeled flow dynamics. It is found that the vertically stratified model shows the best fit to field data from a channelized field‐scale gravity current in the Black Sea. Moreover, the stratified flow is confined by the channel to a much greater degree than the flow in the unstratified model. However, both models fail to accurately represent flow dynamics in the distal end of the system, suggesting current empirical stratification models require improvement to accurately describe field‐scale gravity currents. It also highlights the limitations of weakly stratified small‐scale experiments in describing field‐scale processes. The results suggest that in real‐world systems stratification is likely to enable maintenance of velocity and discharge within the channel, thus facilitating sediment suspension over distances of hundreds of kilometers on low seafloor gradients. This explains how flows can travel remarkable distances and transport their sediment to the distal parts of submarine fans.
      PubDate: 2014-04-22T11:22:42.158128-05:
      DOI: 10.1002/2014JC009807
       
  • Sea surface temperature and salinity seasonal changes in the western
           Solomon and Bismarck Seas
    • Authors: Thierry Delcroix; Marie‐Hélène Radenac, Sophie Cravatte, Gaël Alory, Lionel Gourdeau, Fabien Léger, Awnesh Singh, David Varillon
      Pages: 2642 - 2657
      Abstract: We analyze mean and seasonal change of Sea Surface Temperature (SST) and Salinity (SSS) in the Solomon and Bismarck Seas, using 1977–2009 in situ data collected from Voluntary Observing Ships. Covariability of these two variables with surface wind, altimeter‐derived and model‐derived horizontal currents, precipitation, and Sepik River discharge are examined. SST and SSS show large annual oscillations in the Solomon Sea, with the coldest and saltiest waters occurring in July/August mainly due to horizontal advection. In contrast, they show large semiannual oscillations in the Bismarck Sea. There, the coldest and saltiest waters happen in January/February, when the northwest monsoon winds drive coastal upwelling, and in July/August, when the New Guinea Coastal Current advects cold and high‐salinity waters from the Solomon Sea through Vitiaz Strait. The low SSS values observed in April/May, stuck between the January/February and July/August SSS maxima, are further enhanced by the Sepik River discharge annual maximum. A high‐resolution model strengthens the conclusions we derive from observations. The impacts of ENSO on SST and SSS are also discussed with, for instance, saltier‐than‐average and fresher‐than‐average waters during the 2002–2003 El Niño and 2007–2008 La Niña, respectively.
      PubDate: 2014-04-25T10:17:34.900418-05:
      DOI: 10.1002/2013JC009733
       
  • Meridional volume transport in the South Pacific: Mean and
           SAM‐related variability
    • Authors: N. V. Zilberman; D. H. Roemmich, S. T. Gille
      Pages: 2658 - 2678
      Abstract: The large increase in upper‐ocean sampling during the past decade enables improved estimation of the mean meridional volume transport in the midlatitude South Pacific, and hence of the climatically important Meridional Overturning Circulation. Transport is computed using Argo float profile data for geostrophic shear and trajectory data for reference velocities at 1000 m. For the period 2004–2012, the mean geostrophic transport across 32°S is 20.6 ± 6.0 Sv in the top 2000 m of the ocean. From west to east, this includes the southward East Australian Current (23.3 ± 2.9 Sv), its northward recirculation (16.3 ± 3.6 Sv), the broad interior northward flow (18.4 ± 4.1 Sv), and the net northward flow (9.2 ± 2.2 Sv) in opposing currents in the eastern Pacific. The basin‐integrated geostrophic transport includes 7.3 ± 0.9 Sv of surface and thermocline waters, 4.9 ± 1.0 Sv of Subantarctic Mode Water, and 4.9 ± 1.4 Sv of Antarctic Intermediate Water. Interannual variability in volume transport across 32°S in the South Pacific shows a Southern Annual Mode signature characterized by an increase during the positive phase of the Southern Annular Mode and a decrease during the negative phase. Maximum amplitudes in geostrophic transport anomalies, seen in the East Australian Current and East Australian Current recirculation, are consistent with wind stress curl anomalies near the western boundary.
      PubDate: 2014-04-25T10:31:27.106039-05:
      DOI: 10.1002/2013JC009688
       
  • Refugium for surface life on Snowball Earth in a nearly enclosed sea?
           A numerical solution for sea‐glacier invasion through a narrow
           strait
    • Authors: Adam J. Campbell; Edwin D. Waddington, Stephen G. Warren
      Pages: 2679 - 2690
      Abstract: Where photosynthetic eukaryotic organisms survived during the Snowball Earth events of the Neoproterozoic remains unclear. Our previous research tested whether a narrow arm of the ocean, similar to the modern Red Sea, could have been a refugium for photosynthetic eukaryotes during the Snowball Earth. Using an analytical ice‐flow model, we demonstrated that a limited range of climate conditions could restrict sea‐glacier flow sufficiently to allow an arm of the sea to remain partially free from sea‐glacier penetration, a necessary condition for it to act as a refugium. Here we expand on the previous study, using a numerical ice‐flow model, with the ability to capture additional physics, to calculate sea‐glacier penetration, and to explore the effect of a channel with a narrow entrance. The climatic conditions are made self‐consistent by linking sublimation rate to surface temperature. As expected, the narrow entrance allows parts of the nearly enclosed sea to remain safe from sea‐glacier penetration for a wider range of climate conditions.
      PubDate: 2014-04-25T10:28:24.514646-05:
      DOI: 10.1002/2013JC009703
       
  • The assimilation of satellite‐derived data into a
           one‐dimensional lower trophic level marine ecosystem model
    • Authors: Yongjin Xiao; Marjorie A. M. Friedrichs
      Pages: 2691 - 2712
      Abstract: Lower trophic level marine ecosystem models are highly dependent on the parameter values given to key rate processes, however many of these are either unknown or difficult to measure. One solution to this problem is to apply data assimilation techniques that optimize key parameter values, however in many cases in situ ecosystem data are unavailable on the temporal and spatial scales of interest. Although multiple types of satellite‐derived data are now available with high temporal and spatial resolution, the relative advantages of assimilating different satellite data types are not well known. Here these issues are examined by implementing a lower trophic level model in a one‐dimensional data assimilative (variational adjoint) model testbed. A combination of experiments assimilating synthetic and actual satellite‐derived data, including total chlorophyll, size‐fractionated chlorophyll and particulate organic carbon (POC), reveal that this is an effective tool for improving simulated surface and subsurface distributions both for assimilated and unassimilated variables. Model‐data misfits were lowest when parameters were optimized individually at specific sites; however, this resulted in unrealistic overtuned parameter values that deteriorated model skill at times and depths when data were not available for assimilation, highlighting the importance of assimilating data from multiple sites simultaneously. Finally, when chlorophyll data were assimilated without POC, POC simulations still improved, however the reverse was not true. For this two‐phytoplankton size class model, optimal results were obtained when satellite‐derived size‐differentiated chlorophyll and POC were both assimilated simultaneously.
      PubDate: 2014-04-28T09:38:49.58411-05:0
      DOI: 10.1002/2013JC009433
       
  • Summer circulation and exchange in the Saginaw Bay‐Lake Huron system
    • Authors: Tuan D. Nguyen; Pramod Thupaki, Eric J. Anderson, Mantha S. Phanikumar
      Pages: 2713 - 2734
      Abstract: We use a three‐dimensional, unstructured grid hydrodynamic model to examine circulation and exchange in the Saginaw Bay‐Lake Huron system during the summer months for three consecutive years (2009–2011). The model was tested against ADCP observations of currents, data from a Lagrangian drifter experiment in the Saginaw Bay, and temperature data from the National Data Buoy Center stations. Mean circulation was predominantly cyclonic in the main basin of Lake Huron with current speeds in the surface layer being highest in August. Circulation in the Saginaw Bay was characterized by the presence of an anticyclonic gyre at the mouth of the outer bay and two recirculating cells within the inner bay. New estimates are provided for the mean flushing times (computed as the volume of the bay divided by the rate of inflow) and residence times (computed as e‐folding flushing times based on dye concentration modeling treating the bay as a continuously stirred tank reactor) for Saginaw Bay. The average flushing time (over the 3 months of summer and for all 3 years) was 23.0 days for the inner bay and 9.9 days for the entire bay. The mean e‐folding flushing time was 62 days (2 months) for the inner bay and 115 days (3.7 months) for the entire bay for the summer conditions examined in this work. To characterize the behavior of river plumes in the inner Saginaw Bay, trajectory data from GPS‐enabled Lagrangian drifters were used to compute the absolute diffusivity values in the alongshore and cross‐shore directions.
      PubDate: 2014-04-29T09:45:59.046046-05:
      DOI: 10.1002/2014JC009828
       
 
 
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