for Journals by Title or ISSN
for Articles by Keywords
help

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

Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 21, SJR: 2.156, h-index: 61)
Geophysical Research Letters     Full-text available via subscription   (Followers: 46, SJR: 2.668, h-index: 142)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 5, SJR: 2.4, h-index: 109)
J. of Advances in Modeling Earth Systems     Open Access   (Followers: 2, SJR: 0.126, h-index: 2)
J. of Geophysical Research : Atmospheres     Partially Free   (Followers: 21)
J. of Geophysical Research : Biogeosciences     Full-text available via subscription   (Followers: 6)
J. of Geophysical Research : Earth Surface     Partially Free   (Followers: 22)
J. of Geophysical Research : Oceans     Partially Free   (Followers: 16)
J. of Geophysical Research : Planets     Full-text available via subscription   (Followers: 13)
J. of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 23)
J. of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 15)
Paleoceanography     Full-text available via subscription   (Followers: 4, SJR: 2.16, h-index: 82)
Radio Science     Full-text available via subscription   (Followers: 3, SJR: 0.527, h-index: 47)
Reviews of Geophysics     Full-text available via subscription   (Followers: 19, SJR: 8.837, h-index: 87)
Space Weather     Full-text available via subscription   (Followers: 3, SJR: 0.496, h-index: 16)
Tectonics     Full-text available via subscription   (Followers: 7, SJR: 2.16, h-index: 79)
Water Resources Research     Full-text available via subscription   (Followers: 156, SJR: 1.769, h-index: 110)
Journal Cover Journal of Geophysical Research : Oceans
   Journal TOC RSS feeds Export to Zotero [18 followers]  Follow    
   Partially Free Journal Partially Free Journal
     ISSN (Online) 2169-9291
     Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • Turbidity maximum formation in a well‐mixed macrotidal estuary: The
           role of tidal pumping
    • Authors: Qian Yu; Yunwei Wang, Jianhua Gao, Shu Gao, Burg Flemming
      Pages: n/a - n/a
      Abstract: Traditionally, vertical circulation (induced by gravity circulation and tidal straining), tidal pumping, and resuspension are suggested as the major processes for the formation and maintenance of the estuarine turbidity maximum (ETM). Due to strong mixing, tidal pumping is considered as the dominating process in macro‐tidal estuaries. To analyze field observation data, the classical empirical decomposition method is commonly suggested, but the tidal pumping flux (TPF) based on this method may lead to erroneous conclusions about the mechanisms of ETM formation because the effects of advection induced by the horizontal SSC gradient and fine bed sediment supply are ignored. If these effects are included, the TPF clearly reproduces the convergence patterns and thus demonstrates its role in the formation of the ETM. By a simplified analytical solution, the TPF is the result of the competition between the downstream flux induced by the river current together with the lag in sediment response and the upstream flux induced by tidal asymmetry and the lag. Field observations in the well‐mixed macro‐tidal Yalu River estuary (located between China and North Korea were analyzed. Tidal pumping is identified as the dominant mechanism of its ETM formation, and the position of the ETM for different river discharges and sediment settling velocities can be predicted by the concept of tidal pumping by numerical and analytical procedures. The present study provides a typical example of how to evaluate the tidal pumping contributions on ETM formation using the combined information provided by field data, numerical modeling results and analytical solutions.
      PubDate: 2014-10-20T22:10:42.080373-05:
      DOI: 10.1002/2014JC010228
       
  • Mechanisms of Pacific Summer Water variability in the Arctic's central
           Canada Basin
    • Authors: M.‐L. Timmermans; A. Proshutinsky, E. Golubeva, J.M. Jackson, R. Krishfield, M. McCall, G. Platov, J. Toole, W. Williams
      Pages: n/a - n/a
      Abstract: Pacific Water flows northward through Bering Strait and penetrates the Arctic Ocean halocline throughout the Canadian Basin sector of the Arctic. In summer, Pacific Summer Water (PSW) is modified by surface buoyancy fluxes and mixing as it crosses the shallow Chukchi Sea before entering the deep ocean. Measurements from Ice‐Tethered Profilers, moorings and hydrographic surveys between 2003 and 2013 reveal spatial and temporal variability in the PSW component of the halocline in the Central Canada Basin with increasing trends in integrated heat and freshwater content, a consequence of PSW layer thickening as well as layer freshening and warming. It is shown here how properties in the Chukchi Sea in summer control the temperature‐salinity properties of PSW in the interior by subduction at isopycnals that outcrop in the Chukchi Sea. Results of an ocean model, forced by idealized winds, provide support to the mechanism of surface ocean Ekman transport convergence maintaining PSW ventilation of the halocline.
      PubDate: 2014-10-20T04:46:43.226752-05:
      DOI: 10.1002/2014JC010273
       
  • Exploiting satellite Earth observation to quantify current global oceanic
           DMS flux and its future climate sensitivity
    • Authors: P. E. Land; J. D. Shutler, T. G. Bell, M. Yang
      Pages: n/a - n/a
      Abstract: We used coincident Envisat RA2 and AATSR temperature and wind speed data from 2008/9 to calculate the global net sea‐air flux of dimethyl sulfide (DMS), which we estimate to be 19.6 Tg S a‐1. Our monthly flux calculations are compared to open ocean eddy correlation measurements of DMS flux from 10 recent cruises, with a root mean square difference of 3.1 μmol m‐2 day‐1. In a sensitivity analysis we varied temperature, salinity, surface wind speed and aqueous DMS concentration, using fixed global changes as well as CMIP5 model output. The range of DMS flux in future climate scenarios is discussed. The CMIP5 model predicts a reduction in surface wind speed and we estimate that this will decrease the global annual sea‐air flux of DMS by 22% over 25 years. Concurrent changes in temperature, salinity and DMS concentration increase the global flux by much smaller amounts. The net effect of all CMIP5 modelled 25‐year predictions was a 19% reduction in global DMS flux. 25‐year DMS concentration changes had significant regional effects, some positive (Southern Ocean, North Atlantic, Northwest Pacific) and some negative (isolated regions along the Equator and in the Indian Ocean). Using satellite‐detected coverage of coccolithophore blooms, our estimate of their contribution to North Atlantic DMS emissions suggests that the coccolithophores contribute only a small percentage of the North Atlantic annual flux estimate, but may be more important in the summertime and in the northeast Atlantic.
      PubDate: 2014-10-20T04:37:26.863615-05:
      DOI: 10.1002/2014JC010104
       
  • The salinity signature of the cross‐shelf exchanges in the
           southwestern Atlantic Ocean: Numerical simulations
    • Authors: Ricardo P. Matano; Vincent Combes, Alberto R. Piola, Raul Guerrero, Elbio D. Palma, P. Ted Strub, Corinne James, Harold Fenco, Yi Chao, Martin Saraceno
      Pages: n/a - n/a
      Abstract: A high‐resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA) the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high frequency component of the wind stress forcing controls the vertical structure of the plumes while the low‐frequency component of the wind stress forcing and the inter‐annual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross‐shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross‐shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf.
      PubDate: 2014-10-17T04:17:57.306452-05:
      DOI: 10.1002/2014JC010116
       
  • Summertime phytoplankton blooms and surface cooling in the western south
           equatorial Indian Ocean
    • Authors: Xiaomei Liao; Yan Du, Haigang Zhan, Ping Shi, Jia Wang
      Pages: n/a - n/a
      Abstract: Chlorophyll‐a (Chla) concentration derived from the Sea viewing Wide field of View sensor (SeaWiFS) data (January 1998‐December 2010) shows phytoplankton blooms in the western south equatorial Indian Ocean (WSEIO) during the summer monsoon. The mechanism that sustains the blooms is investigated with the high‐resolution Ocean General Circulation Model for the Earth Simulator (OFES) products. The summer blooms in the WSEIO are separated from the coast; they occur in June, reach their maximum in August, and decay in October. With summer monsoon onset, cross‐equatorial wind induces open‐ocean upwelling in the WSEIO, uplifting the nutricline. The mixed layer heat budget analysis reveals that both thermal forcing and ocean processes are important for the seasonal variations of SST, especially wind‐driven entrainment plays a significant role in cooling the WSEIO. These processes cause nutrient enrichment in the surface layer and trigger the phytoplankton blooms. As the summer monsoon develops, the strong wind deepens the mixed layer; the entrainment thus increases the nutrient supply and enhances the bloom. Horizontal advection associated with the Southern Gyre might also be an important process that sustains the bloom. This large clockwise gyre could advect nutrient‐rich water along its route, allowing Chla to bloom in a larger area.
      PubDate: 2014-10-17T04:03:53.263275-05:
      DOI: 10.1002/2014JC010195
       
  • SMOS sea surface salinity signals of tropical instability waves
    • Authors: Xiaobin Yin; Jacqueline Boutin, Gilles Reverdin, Tong Lee, Sabine Arnault, Nicolas Martin
      Pages: n/a - n/a
      Abstract: Sea Surface Salinity (SSS) measurements from the Soil Moisture and Ocean Salinity (SMOS) mission provide an unprecedented opportunity to observe the salinity structure of Tropical Instability Waves (TIWs) from space, especially during the intense 2010 La Niña condition. In the eastern equatorial Pacific Ocean, SMOS SSS signals correlate well and have similar amplitude to 1‐m salinity from the Tropical Atmosphere Ocean (TAO) array at 6 locations with strong TIW signals. At these locations, the linear negative relationships between SMOS SSS and OSTIA SST signals vary from ‐0.20 °C‐1 to ‐0.25 °C‐1, which are comparable to the ones obtained from TAO. From June to December 2010, the largest TIW signals and meridional gradients of both SSS and SST appear around 2°N west of 100°W. They shift southward and cross the equator at 90°W. In addition to the large negative correlation band around 2°N, a band of negative correlations between SSS and SST signals also exists around 8°N west of 110°W for the 33‐day signals. The peak amplitude of the 33‐day SMOS SSS signals west of 135°W is reduced by more than 40% with respect to values east of 135°W, while the reduction for SST is much lower (less than 20%). The amplitudes and longitudinal extents of TIW signals and the dominant westward propagation speed of 17‐day TIWs (as detected by SMOS and Aquarius) at the equator decrease from 2010 to 2013 associated with the transition from a strong La Niña to non La Niña conditions.
      PubDate: 2014-10-17T03:47:53.742659-05:
      DOI: 10.1002/2014JC009960
       
  • The salinity signature of the cross‐shelf exchanges in the
           southwestern Atlantic Ocean: Satellite observations
    • Authors: Raul A. Guerrero; Alberto R. Piola, Harold Fenco, Ricardo P. Matano, Vincent Combes, Yi Chao, Corinne James, Elbio D. Palma, Martin Saraceno, P. Ted Strub
      Pages: n/a - n/a
      Abstract: Satellite derived sea surface salinity (SSS) data from Aquarius and SMOS are used to study the shelf‐open ocean exchanges in the western South Atlantic near 35ºS. Away from the tropics these exchanges cause the largest SSS variability throughout the South Atlantic. The data reveal a well defined seasonal pattern of SSS during the analyzed period and of the location of the export of low salinity shelf waters. In spring and summer low salinity waters over the shelf expand offshore and are transferred to the open ocean primarily southeast of the river mouth (from 36 ºS to 37º30’S). In contrast, in fall and winter low salinity waters extend along a coastal plume and the export path to the open ocean distributes along the offshore edge of the plume. The strong seasonal SSS pattern is modulated by the seasonality of the along‐shelf component of the wind stress over the shelf. However, the combined analysis of SSS, satellite‐derived sea surface elevation and surface velocity data suggest that the precise location of the export of shelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluence and mesoscale eddies and meanders of the Brazil Current. The satellite data indicate that in summer, mixtures of low salinity shelf waters are swiftly driven towards the ocean interior along the axis of the Brazil/Malvinas Confluence. In winter, episodic wind reversals force the low salinity coastal plume offshore where they mix with tropical waters within the Brazil Current and create a warmer variety of low salinity waters in the open ocean.
      PubDate: 2014-10-17T03:45:52.932219-05:
      DOI: 10.1002/2014JC010113
       
  • Preliminary analysis of acceleration of sea level rise through the
           twentieth century using extended tide gauge data sets (August 2014)
    • Authors: Peter Hogarth
      Pages: n/a - n/a
      Abstract: This work explores the potential for extending tide gauge time series from the Permanent Service for Mean Sea Level (PSMSL) using historical documents, PSMSL ancillary data, and by developing additional composite time series using near neighbour tide gauges. The aim was to increase the number, completeness and geographical extent of records covering most or all of the 20th Century. The number of at least 75% complete century scale time series has been approximately doubled over the original PSMSL dataset. In total over 4800 station years have been added, with 294 of these added to 10 long Southern Hemisphere records. Individual century scale acceleration values derived from this new extended data set tend to converge on a value of 0.01 ± 0.008 mm/yr2. This result agrees closely with recent work and is statistically significant at the 1 sigma level. Possible causes of acceleration and errors are briefly discussed. Results confirm the importance of current data archaeology projects involving digitisation of the remaining archives of hard copy tide gauge data for sea level and climate studies.
      PubDate: 2014-10-16T03:41:51.932564-05:
      DOI: 10.1002/2014JC009976
       
  • The effect of water temperature on air entrainment, bubble plumes, and
           surface foam in a laboratory breaking‐wave analog
    • Authors: A. H. Callaghan; M. D. Stokes, G. B. Deane
      Pages: n/a - n/a
      Abstract: Air‐entraining breaking waves form oceanic whitecaps and play a key role in climate regulation through air‐sea bubble‐mediated gas transfer, and sea spray aerosol production. The effect of varying sea surface temperature on air entrainment, sub‐surface bubble plume dynamics, and surface foam evolution intrinsic to oceanic whitecaps has not been well studied. By using a breaking wave analogue in the laboratory over a range of water temperatures (Tw = 5 °C to Tw = 30 °C) and different source waters, we have examined changes in air entrainment, sub‐surface bubble plumes, and surface foam evolution over the course of a breaking event. For filtered seawater, air entrainment was estimated to increase by 6 % between Tw = 6 °C and Tw = 30 °C, driven by increases of about 43% in the measured surface roughness of the plunging water sheet. After active air entrainment, the rate of loss of air through bubble degassing was more rapid at colder water temperatures within the first 0.5 s of plume evolution. Thereafter, the trend reversed and bubbles degassed more quickly in warmer water. The largest observed temperature‐dependent differences in sub‐surface bubble distributions occurred at radii greater than about 700 μm. Temperature‐dependent trends observed in the sub‐surface bubble plume were mirrored in the temporal evolution of the surface whitecap foam area demonstrating the intrinsic link between surface whitecap foam and the sub‐surface bubble plume. Differences in foam and plume characteristics due to different water sources were greater than the temperature dependencies for the filtered seawater examined.
      PubDate: 2014-10-16T03:41:44.147171-05:
      DOI: 10.1002/2014JC010351
       
  • Impact of diurnal forcing on intraseasonal sea surface temperature
           oscillations in the Bay of Bengal
    • Authors: V. Thushara; P. N. Vinayachandran
      Pages: n/a - n/a
      Abstract: The diurnal cycle is an important mode of sea surface temperature (SST) variability in tropical oceans, influencing air‐sea interaction and climate variability. Upper ocean mixing mechanisms are significant at diurnal timescales controlling the intraseasonal variability (ISV) of SST. Sensitivity experiments using an Ocean General Circulation Model (OGCM) for the summer monsoon of the year 2007 show that incorporation of diurnal cycle in the model atmospheric forcings improves the SST simulation at both intraseasonal and shorter timescales in the Bay of Bengal (BoB). The increase in SST‐ISV amplitudes with diurnal forcing is ~0.05°C in the southern bay while it is ~0.02°C in the northern bay. Increased intraseasonal warming with diurnal forcing results from the increase in mixed layer heat gain from insolation, due to shoaling of the daytime mixed layer. Amplified intraseasonal cooling is dominantly controlled by the strengthening of sub‐surface processes owing to the nocturnal deepening of mixed layer. In the southern bay, intraseasonal variability is mainly determined by the diurnal cycle in insolation, while in the northern bay, diurnal cycle in insolation and winds have comparable contributions. Temperature inversions (TI) develop in the northern bay in the absence of diurnal variability in wind stress. In the northern bay, SST‐ISV amplification is not as large as that in the southern bay due to the weaker diurnal variability of mixed layer depth (MLD) limited by salinity stratification. Diurnal variability of model MLD is not sufficient to create large modifications in mixed layer heat budget and SST‐ISV in the northern bay.
      PubDate: 2014-10-15T03:05:34.369972-05:
      DOI: 10.1002/2013JC009746
       
  • Issue Information
    • Pages: i - vi
      PubDate: 2014-10-14T15:26:31.918264-05:
      DOI: 10.1002/jgrc.20354
       
  • The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE)
    • Authors: A. Ganachaud; S. Cravatte, A. Melet, A. Schiller, N. J. Holbrook, B. M. Sloyan, M. J. Widlansky, M. Bowen, J. Verron, P. Wiles, K. Ridgway, P. Sutton, J. Sprintall, C. Steinberg, G. Brassington, W. Cai, R. Davis, F. Gasparin, L. Gourdeau, T. Hasegawa, W. Kessler, C. Maes, K. Takahashi, K. J. Richards, U. Send
      Pages: n/a - n/a
      Abstract: The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) is an international research program under the auspices of CLIVAR. The key objectives are to understand the Southwest Pacific Ocean circulation and the South Pacific Convergence Zone (SPCZ) dynamics, as well as their influence on regional and basin‐scale climate patterns. South Pacific thermocline waters are transported in the westward flowing South Equatorial Current (SEC) toward Australia and Papua‐New Guinea. On its way, the SEC encounters the numerous islands and straits of the Southwest Pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes. The transit in the Coral, Solomon and Tasman Seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the El Niño‐Southern Oscillation, while the southward transports influence the climate and biodiversity in the Tasman Sea. After seven years of substantial in situ oceanic observational and modeling efforts, our understanding of the region has much improved. We have a refined description of the SPCZ behavior, boundary currents, pathways and water mass transformation, including the previously undocumented Solomon Sea. The transports are large and vary substantially in a counter‐intuitive way, with asymmetries and gating effects that depend on time scales. This paper provides a review of recent advancements, and discusses our current knowledge gaps and important emerging research directions.
      PubDate: 2014-10-14T12:01:59.029564-05:
      DOI: 10.1002/2013JC009678
       
  • Seasonality of biological feedbacks on sea surface temperature variations
           in the Arabian Sea: The role of mixing and upwelling
    • Authors: Jinfeng Ma; Hailong Liu, Pengfei Lin, Haigang Zhan
      Pages: n/a - n/a
      Abstract: The effects of biological heating on upper‐ocean temperature and circulation in the Arabian Sea are investigated using an ocean general circulation model. We find that the change of sea surface temperature (SST) is not only dependent on the variation of chlorophyll concentration, but also the dynamic processes, e.g., mixing and upwelling. Biological heating can warm the SST in the north Arabian Sea during spring and the central Arabian Sea during autumn when the mixed layer depth is shallow. However, the situation is quite different during winter and summer. Although the chlorophyll concentration is high in the north Arabian Sea during winter and in the western Arabian Sea during summer, the SSTs become significantly cool instead of warm. The heat budget analyses indicate that the cold SSTs result from both the strong convective mixing during the winter and the strong upwelling during the summer, which bring the cold water below the mixed layer to the surface.
      PubDate: 2014-10-10T04:16:41.458837-05:
      DOI: 10.1002/2014JC010186
       
  • Spatiotemporal chlorophyll‐a dynamics on the Louisiana continental
           shelf derived from a dual satellite imagery algorithm
    • Authors: Chengfeng Le; John C. Lehrter, Chuanmin Hu, Michael C. Murrell, Lin Qi
      Pages: n/a - n/a
      Abstract: A monthly time‐series of remotely sensed chlorophyll a (Chlars) over the Louisiana continental shelf (LCS) was developed and examined for its relationship to river discharge, nitrate concentration, total phosphorus concentration, photosynthetically available radiation (PAR), wind speed, and inter‐annual variation in hypoxic area size. A new algorithm for Chlars, tuned separately for clear and turbid waters, was developed using field‐observed chlorophyll a (Chlaobs) collected during 12 cruises from 2002‐2007. The new algorithm reproduced Chlaobs, with ~40% and ~60% uncertainties at satellite pixel level for clear offshore waters and turbid nearshore waters, respectively. The algorithm was then applied to SeaWiFS and MODIS images to calculate long‐term (1998‐2013) monthly mean Chlars estimates at 1 km resolution across the LCS. Correlation and multiple stepwise regression analyses were used to relate the Chlars estimates to key environmental drivers expected to influence phytoplankton variability. The Chlars time‐series covaried with river discharge and nutrient concentration, PAR, and wind speed, and there were spatial differences in how these environmental drivers influenced Chlars. The main axis of spatial variability occurred in a cross‐shelf direction with highest Chlars observed on the inner shelf. Both inner‐ (
      PubDate: 2014-10-10T03:58:57.378412-05:
      DOI: 10.1002/2014JC010084
       
  • Relative contributions of ocean mass and deep steric changes to sea level
           rise between 1993 and 2013
    • Authors: Sarah G. Purkey; Gregory C. Johnson, Don P. Chambers
      Pages: n/a - n/a
      Abstract: Regional and global trends of Sea Level Rise (SLR) owing to mass addition centered between 1996–2006 are assessed through a full‐depth SLR budget using full‐depth in‐situ ocean data and satellite altimetry. These rates are compared to regional and global trends in ocean mass addition estimated directly using data from the Gravity Recovery and Climate Experiment (GRACE) from 2003–2013. Despite the two independent methods covering different time periods with differing spatial and temporal resolution, they both capture the same large‐scale mass addition trend patterns including higher rates of mass addition in the North Pacific, South Atlantic, and the Indo‐Atlantic Sector of the Southern Ocean, and lower mass addition trends in the Indian, North Atlantic, South Pacific, and the Pacific Sector of the Southern Ocean. The global mean trend of ocean mass addition is 1.5 (±0.4) mm yr‐1 for 1996–2006 from the residual method and the same for 2003–2013 from the GRACE method. Furthermore, the residual method is used to evaluate the error introduced into the mass budget if the deep steric contributions below 700, 1000, 2000, 3000, and 4000 m are neglected, revealing errors of 65%, 38%, 13%, 8% and 4% respectively. The two methods no longer agree within error bars when only the steric contribution shallower than 1000 m is considered.
      PubDate: 2014-10-10T03:55:32.693136-05:
      DOI: 10.1002/2014JC010180
       
  • Coherent evidence from aquarius and argo for the existence of a shallow
           low‐salinity convergence zone beneath the Pacific ITCZ
    • Authors: Lisan Yu
      Pages: n/a - n/a
      Abstract: Aquarius observations featured a prominent zonal sea‐surface salinity (SSS) front that extended across the tropical Pacific between 2 – 10°N. By linking to Argo subsurface salinity observations and satellite‐derived surface forcing datasets, the study discovered that the SSS front was not a stand‐alone feature, but, in fact, the surface manifestation of a shallow low‐salinity convergence zone (LSCZ). A near‐surface salinity budget analysis was conducted, showing that the LSCZ was sourced from the rainfall in the Inter‐tropical convergence zone (ITCZ), but the mechanism of its generation and maintenance was dominated by the wind‐driven Ekman dynamics, not the surface freshwater flux. Three distinct features highlighted the relationship between the LSCZ and ITCZ. The first was that the seasonal movement of the LSCZ was characterized by a monotonic northward displacement starting from the near‐equatorial latitudes in boreal spring, which was different from the ITCZ that is known for its seasonal north‐south displacement. The second feature was that the lowest SSS waters were locked to the northern edge of the Ekman salt convergence throughout the year, but they showed no fixed relationship with the ITCZ rain band. The LSCZ and ITCZ collocated only during August‐October, the time that the ITCZ rain band coincided with the Ekman convergence zone. The third feature was the evidence of the collocation between the SSS front and the Ekman convergence zone, which not only established the Ekman convergence as the genesis of the LSCZ but also positioned the SST front as a surface manifestation of the LSCZ.
      PubDate: 2014-10-10T03:12:23.075232-05:
      DOI: 10.1002/2014JC010030
       
  • Seasonal variations of bio‐optical properties and their
           inter‐relationships observed by bio‐argo floats in the
           subpolar North Atlantic
    • Authors: Xiaogang Xing; Hervé Claustre, Julia Uitz, Alexandre Mignot, Antoine Poteau, Haili Wang
      Pages: n/a - n/a
      Abstract: Based on in situ datasets collected using two Bio‐Argo floats deployed in the sub‐polar North Atlantic from June, 2008 to May, 2010, the present study focuses on the seasonal variability of three bio‐optical properties, i.e. chlorophyll‐a concentration ([Chla]), particle backscattering coefficient at 532 nm (bbp(532)), and particle beam attenuation coefficient at 660 nm (cp(660)). In addition, the inter‐relationships among these properties are examined. Our results show that: 1) [Chla], bbp(532) and cp(660) are largely well‐coupled with each other in the upper layer, all being minimum in mid‐winter (January) and maximum in summer; 2) the backscattering coefficient presents an abrupt increase in late summer in the Icelandic Basin, likely due to a large contribution of coccolithophores following the diatom spring bloom; 3) the inter‐correlations between the three bio‐optical properties are basically consistent with previous studies; 4) seasonal variation in the of [Chla] to cp(660) ratio exhibits a clear light‐dependence, most likely due to the phytoplankton photoacclimation.
      PubDate: 2014-10-08T04:26:19.82501-05:0
      DOI: 10.1002/2014JC010189
       
  • Paper prepared for JGR Air‐sea exchange of methanol and acetone
           during HiWinGS—Estimation of air phase, water phase gas transfer
           velocities
    • Authors: Mingxi Yang; Byron W. Blomquist, Philip D. Nightingale
      Pages: n/a - n/a
      Abstract: The air‐sea fluxes of methanol and acetone were measured concurrently using a proton‐transfer‐reaction mass spectrometer (PTR‐MS) with the eddy covariance (EC) technique during the High Wind Gas Exchange Study (HiWinGS) in 2013. The seawater concentrations of these compounds were also measured twice daily with the same PTR‐MS coupled to a membrane inlet. Dissolved concentrations near the surface ranged from 7~28 nM for methanol and 3~9 nM for acetone. Both gases were consistently transported from the atmosphere to the ocean as a result of their low sea surface saturations. The largest influxes were observed in regions of high atmospheric concentrations and strong winds (up to 25 m s‐1). Comparison of the total air‐sea transfer velocity of these two gases (Ka), along with the in situ sensible heat transfer rate, allows us to constrain the individual gas transfer velocity in the air phase (ka) and water phase (kw). Among existing parameterizations, the scaling of ka from the COARE model is the most consistent with our observations. The kw we estimated is comparable to the tangential (shear‐driven) transfer velocity previously determined from measurements of dimethyl sulfide. Lastly, we estimate the wet deposition of methanol and acetone in our study region and evaluate the lifetimes of these compounds in the surface ocean and lower atmosphere with respect to total (dry plus wet) atmospheric deposition.
      PubDate: 2014-10-07T07:12:11.090916-05:
      DOI: 10.1002/2014JC010227
       
  • Near‐surface variability of temperature and salinity in the
           near‐tropical ocean: Observations from profiling floats
    • Authors: Jessica E. Anderson; Stephen C. Riser
      Pages: n/a - n/a
      Abstract: Upper ocean measurements of temperature and salinity obtained from profiling floats equipped with auxiliary Surface Temperature and Salinity sensors (STS) are presented. Using these instruments, high vertical resolution (10 cm) measurements in the near‐surface layer were acquired to within 20 cm of the sea surface, allowing for an examination of the ocean's near‐surface structure and variability not usually possible. We examine the data from sixty‐two Argo‐type floats equipped with STS units deployed in the Pacific, Atlantic, and Indian Oceans. The vertical variability of temperature and salinity in the near‐surface layer are characterized for each of these regions. While observations show the upper four meters of the ocean are well mixed most of the time, this homogeneity is interrupted by significant and often short‐lived warming/cooling and freshening events. In addition to the presence of barrier layers, a strong diurnal signal in temperature is observed, with salinity exhibiting somewhat weaker diurnal variations. The magnitude of the upper ocean diurnal cycle in temperature and salinity is largest in areas with light winds and heavy precipitation and was found to decay rapidly with depth (50% over the top two meters). Storm events, validated from meteorological data collected from nearby TAO moorings and the Tropical Rainfall Measuring Mission (TRMM) satellite, show downward mixing of rainfall‐derived fresh water to ten meters depth over only a few hours. Turner angle calculations show strong instability following these events.
      PubDate: 2014-10-06T22:51:57.842902-05:
      DOI: 10.1002/2014JC010112
       
  • Physical and biological controls on oxygen saturation variability in the
           upper Arctic Ocean
    • Authors: R. Eveleth; M.‐L. Timmermans, N. Cassar
      Pages: n/a - n/a
      Abstract: Employing continuous in situ measurements of dissolved O2/Ar and O2 in the Arctic Ocean, we investigate the mechanisms controlling the physical (abiotic) and biological oxygen saturation state variability in the surface ocean beneath sea ice. O2/Ar measurements were made underway using Equilibrator Inlet Mass Spectrometry (EIMS) during an icebreaker survey transiting the upper Arctic Ocean across the North Pole in late summer 2011. Using concurrently collected measurements of total oxygen we devolve biological oxygen saturation and physical oxygen (Ar) saturation signals at unprecedented horizontal resolution in the surface ocean. In the Nansen Basin Ar is undersaturated up to ‐7% while biological oxygen supersaturation peaks at 18.4%. We attribute this to ice melt, Atlantic Water influence and/or cooling. In the Canadian Basin, Ar is supersaturated up to 3%, likely because of Ar injection from freezing processes and long residence times of gas under ice cover. The overall Canadian Basin to Eurasian Basin gradient of Ar super‐ to under‐saturation may reflect net freezing in the Canadian basin and net melting in the Eurasian Basin over several seasons, either by Pacific to Atlantic sector ice transport or local changes over time. Ar saturation could thereby provide large scale high resolution estimates of current and future changes in these processes. O2/Ar supersaturation averages 4.9% with peaks up to 9.8% where first‐year ice and abundant melt ponds likely allow sufficient light for blooms in ice‐covered regions.
      PubDate: 2014-10-06T22:50:37.583714-05:
      DOI: 10.1002/2014JC009816
       
  • Interannual variability of the surface summertime eastward jet in the
           South China Sea
    • Authors: Yuanlong Li; Weiqing Han, John L. Wilkin, Weifeng G. Zhang, Hernan Arango, Javier Zavala‐Garay, Julia Levin, Frederic S. Castruccio
      Pages: n/a - n/a
      Abstract: The summertime eastward jet (SEJ) located around 12°N, 110°‐113°E, as the offshore extension of the Vietnam coastal current, is an important feature of the South China Sea (SCS) surface circulation in boreal summer. Analysis of satellite‐derived sea level and sea surface wind data during 1992‐2012 reveals pronounced interannual variations in its surface strength (SSEJ) and latitudinal position (YSEJ). In most of these years, the JAS (July, August, and September)‐mean SSEJ fluctuates between 0.17‐0.55 m s‐1, while YSEJ shifts between 10.7°‐14.3°N. These variations of the SEJ are predominantly contributed from the geostrophic current component that is linked to a meridional dipole pattern of sea level variations. This sea level dipole pattern is primarily induced by local wind changes within the SCS associated with the El Niño‐Southern Oscillation (ENSO). Enhanced (weakened) southwest monsoon at the developing (decaying) stage of an El Niño event causes a stronger (weaker) SEJ located south (north) of its mean position. Remote wind forcing from the tropical Pacific can also affect the sea level in the SCS via energy transmission through the Philippine archipelago, but its effect on the SEJ is small. The impact of the oceanic internal variability, such as eddy‐current interaction, is assessed using an ocean general circulation model (OGCM). Such impact can lead to considerable year‐to‐year changes of sea level and the SEJ, equivalent to ˜20% of the observed variation. This implies the complexity and prediction difficulty of the upper‐ocean circulation in this region.
      PubDate: 2014-10-06T22:48:02.393418-05:
      DOI: 10.1002/2014JC010206
       
  • Spectral form and source term balance of short gravity wind waves
    • Authors: Hitoshi Tamura; William M. Drennan, Erik Sahlée, Hans C. Graber
      Pages: n/a - n/a
      Abstract: We investigated the spectral structure and source term balance of short gravity waves, based on in situ observations of wavenumber spectra retrieved by air‐sea interaction spar (ASIS) buoys. The behaviors of wavenumber spectra up to 10 rad/m (the gravity wave regime) were analyzed for a wide range of wind and wave conditions. The observed wavenumber spectra showed the spectral power laws described by Toba [1973] and Phillips [1958] in addition to the characteristic nodal point at ˜10 rad/m where spectral energy becomes constant over the entire wind speed range. We also improved the third‐generation wave model using the nonlinear dissipation term. The wave model reproduced the spectral form in the higher wavenumber domain. In the equilibrium range, nonlinear transfer played a major role in maintaining equilibrium conditions. On the other hand, in the saturation range, which starts at the upper limit of the equilibrium range, the nonlinear transfer tended to be out of balance with other source terms, and the dissipation term was in balance with wind input.
      PubDate: 2014-10-06T22:39:48.04115-05:0
      DOI: 10.1002/2014JC009869
       
  • Mixed layer heat and salinity budgets during the onset of the 2011
           Atlantic cold tongue
    • Authors: Michael Schlundt; Peter Brandt, Marcus Dengler, Rebecca Hummels, Tim Fischer, Karl Bumke, Gerd Krahmann, Johannes Karstensen
      Pages: n/a - n/a
      Abstract: The mixed layer (ML) temperature and salinity changes in the central tropical Atlantic have been studied by a dedicated experiment (Cold Tongue Experiment (CTE)) carried out from May‐July 2011. The CTE was based on two successive research cruises, a glider swarm, and moored observations. The acquired in‐situ datasets together with satellite, reanalysis, and assimilation model data were used to evaluate box‐averaged ML heat and salinity budgets for two sub‐regions: 1) the western equatorial Atlantic Cold Tongue (ACT) (23°‐10°W) and 2) the region north of the ACT. The strong ML heat loss in the ACT region during the CTE was found to be the result of the balance of warming due to net surface heat flux and cooling due to zonal advection and diapycnal mixing. The northern region was characterized by weak cooling and the dominant balance of net surface heat flux and zonal advection. A strong salinity increase occurred at the equator, 10°W, just before the CTE. During the CTE, ML salinity in the ACT region slightly increased. Largest contributions to the ML salinity budget were zonal advection and the net surface freshwater flux. While essential for the ML heat budget in the ACT region, diapycnal mixing played only a minor role for the ML salinity budget. In the region north of the ACT, the ML freshened at the beginning of the CTE due to precipitation, followed by a weak salinity increase. Zonal advection changed sign contributing to ML freshening at the beginning of the CTE and salinity increase afterward.
      PubDate: 2014-10-06T03:49:07.7077-05:00
      DOI: 10.1002/2014JC010021
       
  • New total electron content retrieval improves SMOS sea surface salinity
    • Authors: Jean Luc Vergely; Philippe Waldteufel, Jacqueline Boutin, Xiaobin Yin, Paul Spurgeon, Steven Delwart
      Pages: n/a - n/a
      Abstract: The European Space Agency (ESA)‐led SMOS (Soil Moisture and Ocean Salinity) mission aims at monitoring both soil moisture (SM) and ocean surface salinity (OS) on a global scale. The SMOS instrument is a microwave interferometric radiometer which provides visibilities, from which brightness temperatures (TB) maps are reconstructed in the spacecraft’ antenna reference frame. In this study, we investigate how to improve the retrieval of salinity thanks to a better knowledge of the ionospheric Total Electron Content (TEC). We show how both the SMOS bias correction (the so‐called Ocean Target Transformation, OTT) and the half orbit TEC profile can be obtained from SMOS third Stokes parameter A3 using a location on the SMOS field of view (FOV) where the sensitivity of TB to TEC is highest. The resulting TEC global maps compare favorably with those built from the International Global navigation satellite system Service observations. TEC values obtained from A3 are next used to optimize the OTT estimation for every polarization, and proved to provide more stable values. Finally, improvements achieved in the salinity retrieved from SMOS data are reported.
      PubDate: 2014-10-06T03:45:54.561367-05:
      DOI: 10.1002/2014JC010150
       
  • Remote sensing of suspended particulate matter in turbid
           oyster‐farming ecosystems
    • Authors: Pierre Gernez; Laurent Barillé, Astrid Lerouxel, Constant Mazeran, Axel Lucas, David Doxaran
      Pages: n/a - n/a
      Abstract: High resolution satellite data of the Medium Resolution Imaging Spectrometer in full resolution mode (MERIS FR, pixel size is 300 m) were used to study the impact of suspended particulate matter (SPM) on oyster‐farming sites in a macrotidal bay of the French Atlantic coast where SPM concentration can exceed 100 g m‐3. Because MERIS standard SPM concentration retrieval saturates at about 50 g m‐3, we developed an alternative method for turbid nearshore waters. The method consists in the combination of the Semi‐Analytical Atmospheric and Bio‐Optical (SAABIO) atmospheric correction with a regional bio‐optical algorithm based on a linear relationship between SPM concentration and the reflectance band ratio at 865 and 560 nm. MERIS FR derived SPM concentrations were validated from 10 up to 300 g m‐3, and then merged with oyster ecophysiological responses to provide a spatial picture of the impact of SPM concentration on oyster‐farming sites. Our approach demonstrates the potential of high resolution satellite remote‐sensing for aquaculture management and shellfish‐farming ecosystems studies.
      PubDate: 2014-10-06T03:42:37.858664-05:
      DOI: 10.1002/2014JC010055
       
  • Structure of the turbidity field in the Guadalquivir estuary: Analysis of
           observations and a box model approach
    • Authors: M. Díez‐Minguito; A. Baquerizo, H.E. de Swart, M. A.Losada
      Pages: n/a - n/a
      Abstract: A study is presented on the transport of Suspended Particulate Matter (SPM) in the Guadalquivir estuary during low river flow conditions. Observations show that tidally‐induced SPM exceeds that associated with catchment‐derived inputs. The main mechanisms that contribute to longitudinal transport are identified and quantified by analyzing the tidally‐averaged and depth‐integrated SPM flux decomposition over time and space. The net transport is generally directed upstream, although differences in the direction between spring and neap tides are identified. The transport is largely controlled by the mean advection, the tidal pumping associated with the covariance between SPM concentration and current, and the tidal Stokes transport. The convergence of the transport associated to these mechanisms alone explains the presence of primary and secondary estuarine turbidity maxima. The tidal reflection at the upstream dam appears to play a significant role in their generation, as evidenced by the convergence zones of the M4 and M2 induced tidal pumping transports. The spatial structure of the transport motivates the development of a box model that describes the concentration of SPM and its exchange between different stretches along the estuary at subtidal time scales. The model is fed by the net SPM transport obtained from observations. Analysis of the morphodynamical state of the estuary using the box model indicates that erosion is dominant in the stretches close to the estuary mouth and that this sediment is transported upstream and deposited in the middle part of the estuary. This process is more influential during spring tides than during neap tides.
      PubDate: 2014-10-06T03:42:31.063957-05:
      DOI: 10.1002/2014JC010210
       
  • Estimates of horizontal fluxes of oxygen, heat, and salt in western Long
           Island Sound
    • Authors: Grant McCardell; James O'Donnell
      Pages: n/a - n/a
      Abstract: The dissolved oxygen (DO) concentration in the bottom waters of western Long Island Sound decreases to hypoxic levels between April and July. Since the rate of decline of DO is considerably less than measured respiration, there must be significant vertical transport of DO from oxygen richer waters near the surface and/or horizontal transport from the central Sound. Simple model budgets with either of these sources are able to provide predictions of the seasonal rate of decline that are consistent with the observed values. Although prior budget estimates indicated that vertical fluxes were a significant portion of the resupply of DO, these were not able to discount the possible importance of horizontal fluxes, nor have there been any measurements of horizontal fluxes in this region. We present an analysis of time‐series of moored conductivity, temperature, DO, and current observations in the hypoxic area of Long Island Sound during the summers of 2005 and 2006. We estimate the near bottom along‐channel flux divergences of salt, heat, and DO as 0.11±0.08 g kg−1 day−1, −5±6 W m−3 and 4±6 μM day−1, respectively. Since this horizontal DO transport is only 25% of the magnitude of the mean rate of respiration, we conclude that vertical transport by mixing forms the bulk of the physical resupply of DO to the hypoxic zone of the western Sound.
      PubDate: 2014-09-30T00:10:41.213788-05:
      DOI: 10.1002/2014JC009904
       
  • Variability in categories of Arctic sea ice in Fram Strait
    • Authors: E. Hansen; O‐C. Ekeberg, S. Gerland, O. Pavlova, G. Spreen, M. Tschudi
      Pages: n/a - n/a
      Abstract: An attempt to quantify the temporal variability in the volume composition of Arctic sea ice is presented. Categories of sea ice in the Transpolar Drift in Fram Strait are derived from monthly ice thickness distributions obtained by moored sonars (1990‐2011). The inflection points on each side of the old ice modal peak are used to separate modal ice from ice which is thinner and thicker than ice in the modal range. The volume composition is then quantified through the relative amount of ice belonging to each of the three categories thin, modal and thick ice in the monthly ice thickness distributions. The trend of thin ice was estimated to be negative at ‐9.2% per decade (relative to the long‐term mean), which was compensated for by increasing trends in modal and thick ice of 8.1% and 4.9% per decade, respectively. A 7‐8 year cycle is apparent in the thin and thick ice records, which may explain a loss of deformed ice since 2007. We also quantify how the categories contribute to the mean ice thickness over time. Thick (predominantly deformed) ice dominates the mean ice thickness, constituting on average 66% of the total mean. Following the loss of deformed ice since 2007, the contribution of thick ice to the mean decreased from 75% to 52% at the end of the record. Thin deformed ice did not contribute to this reduction; it was pressure ridges thicker than 5 m that were lost and hence caused the decrease in mean ice thickness.
      PubDate: 2014-09-30T00:09:23.481767-05:
      DOI: 10.1002/2014JC010048
       
  • An integrated database of ocean temperature and salinity observations
    • Authors: Christopher P. Atkinson; Nick A. Rayner, John J. Kennedy, Simon A. Good
      Pages: n/a - n/a
      Abstract: Observations made by surface‐based instruments and sub‐surface profiling instruments have, up to now, largely been treated separately, motivated by a focus on different aspects of the climate system. However, activities such as coupled climate reanalyses, long‐term forecasting, satellite validation and climate monitoring increasingly want observations from both sets of instruments. To address this we create an “Integrated” Ocean Database of global in situ temperature and salinity observations covering 1900‐2010, which we name HadIOD. The database merges data taken from the latest versions of the International Comprehensive Ocean‐Atmosphere Data Set (surface observations) and the Met Office Hadley Centre EN dataset (sub‐surface observations). Duplicates introduced by this process are flagged. In addition to the measurements and their basic metadata, each observation in the database is allocated a unique identifier, quality flags and, where possible, bias corrections and uncertainty estimates. A short investigation is presented demonstrating the use, and value, of some of the bias corrections and uncertainties in the database. Whilst this paper describes our initial attempt at building HadIOD, there is much that could be done to build on the foundations presented here. Some ideas for future development are discussed.
      PubDate: 2014-09-25T10:10:42.097246-05:
      DOI: 10.1002/2014JC010053
       
  • Ocean dynamics and tropical pacific climate change in ocean reanalyzes and
           coupled climate models
    • Authors: Chunxue Yang; Benjamin S. Giese, Lixin Wu
      Pages: n/a - n/a
      Abstract: The role of ocean dynamics in tropical Pacific climate change is studied using an ensemble run of Simple Ocean Data Assimilation – sparse input version 1 (SODA si.1) and the Coupled Model Intercomparison Project Phase 5 (CMIP5) historical runs. An eight‐member ensemble of ocean reanalyses (SODAsi.1) from 1871 to 2008 is produced by using forcing from eight ensemble members of an atmospheric reanalysis. The long‐term trends of tropical Pacific surface temperature, wind stress, subsurface temperature and strength of the sub‐tropical cells (STCs) are analyzed. The ensemble reanalysis shows that there is a slight cooling trend of surface and subsurface temperature in the central tropical Pacific due to enhanced tropical Pacific circulation. The STCs, which consist of equatorial upwelling, Ekman transport, extra‐tropical subduction and pycnocline transport from the sub‐tropical to the tropical region, strengthen from 1900 to 2008. When the STCs are accelerated, equatorial upwelling increases bringing cold water from the subsurface that cools the surface. An increasing trend in convergence transport is mainly from the Southern Hemisphere. In contrast with the reanalysis most of the CMIP5 models have warming trends at the surface and the transport of the STCs has a decreasing trend. The CMIP5 models also underestimate tropical Pacific Ocean circulation relative to the reanalysis that is mostly due to differences in wind forcing.
      PubDate: 2014-09-25T10:10:40.475108-05:
      DOI: 10.1002/2014JC009979
       
  • Detection time for global and regional sea level trends and accelerations
    • Authors: G. Jordà
      Pages: n/a - n/a
      Abstract: Many studies analyse trends on sea level data with the underlying purpose of finding indications of a long‐term change that could be interpreted as the signature of anthropogenic climate change. The identification of a long‐term trend is a signal‐to‐noise problem where the natural variability (the ‘noise’) can mask the long‐term trend (the ‘signal’). The signal‐to‐noise ratio depends on the magnitude of the long‐term trend, on the magnitude of the natural variability and on the length of the record, as the climate noise is larger when averaged over short timescales and becomes smaller over longer averaging periods. In this paper we evaluate the time required to detect centennial sea level linear trends and accelerations at global and regional scales. Using model results and tide gauge observations we find that the averaged detection time for a centennial linear trend is 87.9, 76.0, 59.3, 40.3 and 25.2 years for trends of 0.5, 1.0, 2.0, 5.0 and 10.0 mm/yr, respectively. However, in regions with large decadal variations like the Gulf Stream or the Circumpolar current these values can increase up to a 50%. The spatial pattern of the detection time for sea level accelerations is almost identical. The main difference is that the length of the records has to be about 40‐60 years longer to detect an acceleration than to detect a linear trend leading to an equivalent change after 100 years. Finally we have used a new sea level reconstruction which provides a more accurate representation of interannual variability for the last century in order to estimate the detection time for global mean sea level trends and accelerations. Our results suggest that the signature of natural variability in a 30 year global mean sea level record would be less than 1 mm/yr. Therefore, at least 2.2 mm/yr of the recent sea level trend estimated by altimetry cannot be attributed to natural multidecadal variability.
      PubDate: 2014-09-25T10:10:10.880156-05:
      DOI: 10.1002/2014JC010005
       
  • Subtidal variability in water levels inside a subtropical estuary
    • Authors: Krista Henrie; Arnoldo Valle‐Levinson
      Pages: n/a - n/a
      Abstract: Year‐long time series of water level are analyzed at 5 locations along the St. Johns River Estuary, Florida, to investigate propagation of subtidal pulses. Hilbert‐transformed Empirical Orthogonal Functions (HEOFs) are obtained after a dominant seasonal signal is extracted from the data. These functions provide information on spatial structure and propagation phase of subtidal water level pulses. The first HEOF mode explains 96% of the subtidal variability and features an unusual spatial structure: amplitude attenuation (averaging 1 mm/km) to 55 km upstream, slight amplification (0.16 mm/km) over the middle 70 km, and attenuation (2.3 mm/km) over the final 18 km of the estuary. The phase suggests a shift from progressive to quasi‐standing wave behavior at 55 km from the estuary mouth. Additionally, local minima in the phase suggest two sources of subtidal forcing: the coastal ocean and the upstream end. An analytical model describing the evolution of long waves through a channel with frictional damping is fit to the amplitude of HEOF mode 1. Solutions are obtained as a function of two parameters: the non‐dimensional length of the basin, κ, and the non‐dimensional frictional depth, δ. Values of κ between 0.55 and 0.67 and δ between 1.45 and 1.7 provide the best fit with the HEOF results (1% error or less). These values indicate a highly frictional environment in which the average subtidal wavelength is 10 times the basin length. Subtidal pulses in this estuary, therefore, behave as damped waves that can be represented with idealized models.
      PubDate: 2014-09-22T03:55:53.884782-05:
      DOI: 10.1002/2014JC009829
       
  • Comparison of Ellison and Thorpe scales from Eulerian ocean temperature
           observations
    • Authors: Andrea A. Cimatoribus; Hans van Haren, Louis Gostiaux
      Pages: n/a - n/a
      Abstract: Ocean turbulence dissipation rate is estimated either by means of microstructure shear measurements, or by adiabatically reordering vertical profiles of density. The latter technique leads to the estimate of the Thorpe scale, which in turn can be used to obtain average turbulence dissipation rate by comparing the Thorpe scale to the Ozmidov scale. In both cases, the turbulence dissipation rate can be estimated using single vertical profiles from shipborne instrumentation. We present here an alternative method to estimate the length scale of overturns by using the Ellison length scale. The Ellison scale is estimated from temperature variance just beyond the internal wave band, measured by moored instruments. We apply the method to high resolution temperature data from two moorings deployed at different locations around the Josephine seamount (North Eastern Atlantic Ocean), in a region of bottom‐intensified turbulence. The variance of the temperature time series just above the internal wave frequency band is well correlated with the Thorpe scale. The method is based on the time‐frequency decomposition of variance called “maximum overlap discrete wavelet transform”. The results show that the Ellison length scale can be a viable alternative to the Thorpe scale for indirectly estimating turbulence dissipation rate from moored instruments in the ocean if time resolution is sufficiently high. We suggest that fine structure contaminated temperature measurements can provide reliable information on turbulence intensity.
      PubDate: 2014-09-22T02:51:49.371644-05:
      DOI: 10.1002/2014JC010132
       
  • A weather‐type statistical downscaling framework for ocean wave
           climate
    • Authors: Paula Camus; Melisa Menéndez, Fernando J. Méndez, Cristina Izaguirre, Antonio Espejo, Verónica Cánovas, Jorge Pérez, Ana Rueda, Inigo J. Losada, Raúl Medina
      Pages: n/a - n/a
      Abstract: Wave climate characterization at different time scales (long‐term historical periods, seasonal prediction, future projections) is required for a broad number of marine activities. Wave reanalysis databases have become a valuable source of information covering time periods of decades. A weather‐type approach is proposed to statistically downscale multivariate wave climate over different time scales from the reanalysis long‐term period. The model calibration is performed using historical data of predictor (sea level pressure) and predictand (sea state parameters) from reanalysis databases. The storm activity responsible for the predominant swell composition of the local wave climate is included in the predictor definition. N‐days sea level pressure fields are used as predictor. K‐means algorithm with a post‐organization in a bidimensional lattice is used to obtain weather patterns. Multivariate hourly sea states are associated with each pattern. The model is applied at two locations on the east coast of the North Atlantic Ocean. The validation proves the model skill to reproduce the seasonal and interannual variability of monthly sea state parameters. Moreover, the projection of wave climate onto weather types provides a multivariate wave climate characterization with a physically interpretable linkage with atmospheric forcings. The statistical model is applied to reconstruct wave climate in the last twentieth century, to hindcast the last winter and to project wave climate under climate change scenarios. The statistical approach has been demonstrated to be a useful tool to analyze wave climate at different time scales.
      PubDate: 2014-09-22T02:47:45.571859-05:
      DOI: 10.1002/2014JC010141
       
  • Density stratification influences on generation of different modes
           internal solitary waves
    • Authors: Zhi‐Wu Chen; Jieshuo Xie, Dongxiao Wang, Jie‐Min Zhan, Jiexin Xu, Shuqun Cai
      Pages: n/a - n/a
      Abstract: An ideal tide‐topography interaction model is utilized for studying the influence of density stratification (pycnocline depth d, thickness δ, and the density difference Δρa across the pycnocline) on nonlinear disintegration of the first (mode‐1) and second (mode‐2) baroclinic mode internal tides into internal solitary waves (ISWs). The solution methods include weakly nonlinear analysis and fully nonlinear simulation. It is found that as d increases, even though the energy flux into mode‐1 internal tides is always larger than that into mode‐2 ones at generation, mode‐2 ISWs emerge and mode‐1 ISWs are suppressed. As δ increases, the total energy conversion and the fluxes into both mode‐1 and mode‐2 tides all increase first and then decrease. During propagation, a thick pycnocline is actually not favorable for the emergence of mode‐2 ISWs, and the simulated well‐developed mode‐2 ISWs for a pycnocline of intermediate thickness are due to the tide generation process. As Δρa increases, the total conversion and the fluxes into both mode‐1 and mode‐2 tides all increase almost linearly. Even though the flux into mode‐1 tides is always larger than that into mode‐2 ones at generation, mode‐1 tides cannot disintegrate but mode‐2 ISWs develop very well. During propagation, Δρa has no influence on the generation of ISWs. The present work systematically investigates the influence of density stratification on formation of ISWs by considering both internal tide generation and propagation processes.
      PubDate: 2014-09-22T02:47:16.97822-05:0
      DOI: 10.1002/2014JC010069
       
  • Potential drivers of sinking particle's size spectra and vertical flux of
           particulate organic carbon (POC): Turbulence, phytoplankton, and
           zooplankton
    • Authors: Ingrid Wiedmann; Marit Reigstad, Arild Sundfjord, Sünnje Basedow
      Pages: n/a - n/a
      Abstract: Phytoplankton spring blooms in temperate and high‐latitude shelf seas are commonly associated with an enhanced particulate organic carbon (POC) export of aggregates from the euphotic zone. In contrast, a post‐bloom situation is usually linked to a predominant POC retention, where small cells (
      PubDate: 2014-09-22T02:43:46.610116-05:
      DOI: 10.1002/2013JC009754
       
  • Confidence and sensitivity study of the OAFlux multisensor synthesis of
           the global ocean‐surface vector wind from 1987 onward
    • Authors: Lisan Yu; Xiangze Jin
      Pages: n/a - n/a
      Abstract: This study presents an uncertainty assessment of the high‐resolution global analysis of daily‐mean ocean‐surface vector winds (1987 onward) by the Objectively Analyzed air‐sea Fluxes (OAFlux) project. The time series was synthesized from multiple satellite sensors using a variational approach to find a best fit to input data in a weighted least‐squares cost function. This framework requires the a priori specification of the weights, or equivalently, the error covariances of input data, which are seldom known. Two issues are addressed. The first issue is the selection of the optimal weights used for the OAFlux synthesis. A set of weight‐varying experiments was conducted, from which the weights were selected by satisfying the condition that the chosen weights should make the best‐fit of the cost function be optimal with regard to both input satellite observations and the air‐sea buoy measurements at 126 locations. The buoy measurements were not part of the synthesis and served as an independent measure in the selection. The second issue is the quantification of the effect of the uncertainty in the resultant weight assignments on the synthesis. This was achieved by computing the ensemble statistics of weight perturbation experiments. The results show that high winds (>15 ms‐1) and rain conditions are the leading sources of uncertainty for the OAFlux vector wind analysis. High winds correlated with rain remain a major technical challenge for proper wind retrievals from satellites. Further improvement of the multi‐sensor synthesis in events of severe storms will rely on the future technical advancement in retrieval algorithms.
      PubDate: 2014-09-19T21:47:39.36176-05:0
      DOI: 10.1002/2014JC010194
       
  • Climatological monthly heat and freshwater flux estimates on a global
           scale from Argo
    • Authors: Donata Giglio; Dean Roemmich
      Pages: n/a - n/a
      Abstract: The global pattern of climatological monthly heat and freshwater fluxes at the ocean surface is estimated using Argo temperature and salinity profile data for the period 2004 to 2013. Temperature or salinity changes are calculated in a volume of water above an isopycnal that is below the mixed layer and not subject to mixed‐layer entrainment. Horizontal advection components from geostrophic velocity and from Ekman transport, based on wind stress, are also included. The climatological monthly heat or freshwater flux at the ocean surface is estimated as the sum of advective and time tendency contributions. The air‐sea flux estimates from Argo are described in global maps and basin‐wide integrals, in comparison to atmospheric reanalysis data and to air‐sea flux products based on observations. This ocean‐based estimate of surface fluxes is consistent with property variations in the subsurface ocean and indicates greater amplitude for the climatological monthly heat flux values in the subtropics compared to other products. Similarly, the combination of Argo freshwater flux and reanalysis evaporation, suggests greater amplitude for climatological monthly precipitation in the tropics.
      PubDate: 2014-09-19T05:12:45.396286-05:
      DOI: 10.1002/2014JC010083
       
  • Dust‐induced episodic phytoplankton blooms in the Arabian Sea during
           winter monsoon
    • Authors: Priyanka Banerjee; S. Prasanna Kumar
      Pages: n/a - n/a
      Abstract: Phytoplankton blooms mediated by the oceanic supply of nutrients is a well understood phenomenon in the Arabian Sea (AS), while the role of dust deposition in enhancing phytoplankton is less explored. In this paper we show that during winter monsoon the central Arabian Sea (CAS), away from the realm of active winter convection, supports episodic phytoplankton blooms. These blooms cannot be fully explained by the oceanic input of nutrients through processes such as advection and mixing in the upper ocean. Using satellite images we tracked about 45 dust storms over the AS during the winter monsoons of 2002‐2003 to 2010‐2011 of which only 8 were followed by chlorophyll enhancements. We used a regional climate model to get possible fluxes of dust and the amount of nutrients (nitrate, phosphate and iron) that can be derived from the dust depositions. Additionally, we used published in situ nutrients data in conjunction with carbon: nitrogen: phosphorus and iron: carbon molar ratios to compute the potential requirements of different nutrients for the 8 cases of chlorophyll enhancements. It is likely that the deepening of the mixed layer can incorporate nitrate and phosphate, but not enough iron from the subsurface waters leading to potential iron limitation. Although, all the phytoplankton blooms within CAS were observed following episodic dust events, only four blooms can be attributed to dust depositions. Our work shows that phytoplankton blooms fuelled by episodic dust storms are important in driving the inter‐annual variability in chlorophyll in a region away from active winter convection.
      PubDate: 2014-09-19T05:09:22.092955-05:
      DOI: 10.1002/2014JC010304
       
  • Mean sea level variability in the North Sea: Processes and implications
    • Authors: Sönke Dangendorf; Francisco M. Calafat, Arne Arns, Thomas Wahl, Ivan D. Haigh, Jürgen Jensen
      Pages: n/a - n/a
      Abstract: Mean sea level (MSL) variations across a range of timescales are examined for the North Sea under the consideration of different forcing factors since the late 19th century. We use multiple linear regression models, which are validated for the second half of the 20th century against the output of a tide+surge model, to determine the barotropic response of the ocean to fluctuations in atmospheric forcing. We find that local atmospheric forcing mainly initiates MSL variability on timescales up to a few years, with the inverted barometric effect dominating the variability along the UK and Norwegian coastlines and wind controlling the MSL variability in the south from Belgium up to Denmark. On decadal timescales, MSL variability mainly reflects steric changes, which are largely forced remotely. A spatial correlation analysis of altimetry observations and gridded steric heights suggests evidence for a coherent signal extending from the Norwegian shelf down to the Canary Islands. This fits with the theory of longshore wind forcing along the eastern boundary of the North Atlantic causing coastally trapped waves to propagate over thousands of kilometers along the continental slope. Implications of these findings are assessed with statistical Monte‐Carlo experiments. It is demonstrated that the removal of known variability increases the signal to noise ratio with the result that: (i) linear trends can be estimated more accurately; and (ii) possible accelerations (as expected e.g. due to anthropogenic climate change) can be detected much earlier. Such information is of crucial importance for anticipatory coastal management, engineering and planning.
      PubDate: 2014-09-19T05:08:15.632585-05:
      DOI: 10.1002/2014JC009901
       
  • Coastally trapped eddies in the north of the Gulf of Guinea
    • Authors: Sandrine Djakouré; Pierrick Penven, Bernard Bourlès, Jennifer Veitch, Vamara Koné
      Pages: n/a - n/a
      Abstract: Cyclonic eddies generated downstream of Cape Palmas and Cape Three points have been suggested to contribute to the coastal upwelling along the northern coast of the Gulf of Guinea. A numerical analysis using a high resolution model is used to investigate the mesoscale activity and the coastal upwelling generation processes. An eddy detection and tracking tool is applied to altimeter and model data, showing good agreement between these data sets. About 2 cyclonic eddies per year with an average radius of 60 km were identified downstream of both capes. These cyclonic eddies have an average lifetime of about 60 days during the major coastal upwelling period (boreal summer) and an eastward propagation. These cyclonic eddies are shallow, energetic (their relative vorticity can reach three times the earth's rotation) and dimensionless parameters show that they are in an eddy shedding regime. Mean flow interactions and barotropic instabilities associated with capes are their main generation processes. An idealized experiment is conducted in order to analyse the effect of capes on eddy generation and on coastal upwelling. It reveals that these cyclonic eddies generated downstream of capes are not the process responsible for this coastal upwelling. This experiment also suggests that the cyclonic eddies are the cause of the westward and coastal Guinea Counter Current that is associated with a transfer of energy from eddy kinetic to the mean flow.
      PubDate: 2014-09-19T05:04:25.010994-05:
      DOI: 10.1002/2014JC010243
       
  • A first estimation of SMOS‐based ocean surface T‐S diagrams
    • Authors: Roberto Sabia; Marlene Klockmann, Diego Fernández‐Prieto, Craig Donlon
      Pages: n/a - n/a
      Abstract: A first estimation of satellite‐based ocean surface T‐S diagrams is performed by using SMOS Sea Surface Salinity (SSS) and OSTIA Sea Surface Temperature (SST) and comparing them with in‐situ measurements interpolated fields obtained by the Argo‐buoys for the North Atlantic and over the entire year 2011. The key objectives at the base of this study are: 1) To demonstrate the feasibility of generating routinely satellite‐derived surface T‐S diagrams, obviating the lack of extensive sampling of the surface open ocean; 2) To display the T‐S diagrams variability and the distribution/dynamics of SSS, altogether with SST and the relative density with respect to in‐situ measurements, and 3) To assess the SMOS SSS data added value in detecting geophysical signals not sensed/resolved by the Argo measurements. To perform the latter analysis, the satellite‐Argo mismatches have been overlapped with geophysical parameters of precipitation rates, surface heat and freshwater fluxes and wind speed data. Ongoing and future efforts focus on enlarging the study area and the temporal frame of the analysis and aim at developing a method for the systematic identification of surface water masses formation areas by remotely‐sensed data.
      PubDate: 2014-09-19T04:59:30.519576-05:
      DOI: 10.1002/2014JC010120
       
  • Assimilating SMOS sea ice thickness into a coupled ice‐ocean model,
           using a local SEIK filter
    • Authors: Qinghua Yang; Svetlana N. Losa, Martin Losch, Xiangshan Tian‐Kunze, Lars Nerger, Jiping Liu, Lars Kaleschke, Zhanhai Zhang
      Pages: n/a - n/a
      Abstract: The impact of assimilating sea ice thickness data derived from ESA's Soil Moisture and Ocean Salinity (SMOS) satellite together with Special Sensor Microwave Imager/Sounder (SSMIS) sea ice concentration data of the National Snow and Ice Data Center (NSIDC) in a coupled sea ice‐ocean model is examined. A period of three months from November 1st, 2011 to January 31st, 2012 is selected to assess the forecast skill of the assimilation system. 24h‐forecasts and longer forecasts are based on the Massachusetts Institute of Technology general circulation model (MITgcm), and the assimilation is performed by a localized Singular Evolutive Interpolated Kalman (LSEIK) filter. For comparison, the assimilation is repeated only with the SSMIS sea ice concentrations. By running two different assimilation experiments, and comparing with the unassimilated model, independent satellite derived data, and in‐situ observation, it is shown that the SMOS ice thickness assimilation leads to improved thickness forecasts. With SMOS thickness data, the sea ice concentration forecasts also agree better with observations, although this improvement is smaller.
      PubDate: 2014-09-19T04:52:04.49611-05:0
      DOI: 10.1002/2014JC009963
       
  • Characteristics of surface signatures of Mediterranean water eddies
    • Authors: Bashmachnikov I; Carton X, Belonenko T.V.
      Pages: n/a - n/a
      Abstract: In this work we obtain new results on the manifestation of meddies (or of other deep eddies) at the sea‐surface, further developing the results by Bashmachnikov and Carton [2012]. The quasi‐geostrophic equations are used to describe a near‐axisymmetric vortex in the upper ocean, forced at its lower boundary by the isopycnal elevation of a moving meddy. The solution thus obtained provides a better approximation of the characteristics of meddy surface signals. The results show that in subtropics large meddies with dynamic radius Rm ≥ 30 km are always seen at the sea‐surface with AVISO altimetry, that medium‐size meddies with Rm = 20 km may be seen at the sea‐surface only if they are sufficiently shallow and strong, while small meddies with Rm = 10 km generally cannot be detected with the present accuracy of altimetry data. The intensity of meddy surface signals decreases to the south with the decrease of the f/N ratio. The seasonal variation in intensity of the surface signal for northern meddies (45° N) is on the order of 2‐3 cm, but for subtropical meddies (35° N) it can be on the order of 5‐10 cm. The radii of meddy surface signals range from 1 to 2 times the radii of the corresponding meddies. For most of the observed meddies the upper limit should be used. Numerical experiments show that surface signals of meddies translated with β‐ drift are efficiently dispersed by the radiation of Rossby waves. At the same time, for meddies translated by a background current, the surface signal does not show strong dissipation.
      PubDate: 2014-09-19T04:45:27.208541-05:
      DOI: 10.1002/2014JC010244
       
  • Influence of underwater barriers on the distribution of tsunami waves
    • Authors: V. Chugunov; S. Fomin, R. Shankar
      Pages: n/a - n/a
      Abstract: Solitary wave propagation over underwater shelves and bumps is examined using straightforward analytical methods. Explicit solutions for wave propagation are obtained. Using the nonlinear shallow‐water equations, it was found that propagation of small amplitude long waves can be well described by a linear approximation. The effects of topographical variety and proportion of underwater barriers (steps, bumps, multiple bumps) on the incident wave are demonstrated using linear wave theory. At a step, the incident wave is shown to be more strongly reflected for increased barrier size. The incident wave also transmits an amplified wave with smaller wavelength onto the obstacle. After propagating off of a bump, the wave experiences an amplitude decay. The decay rate is shown to be exponential with a variable number of bumps. Accounting for the presence of the small parameter, which represents the wave amplitude/water depth ratio, the non‐linear shallow water equations were solved by the method of asymptotic expansions. Using the method of renormalization, a uniformly valid solution was obtained accounting for nonlinear effects in the vicinity of the sharp depth change. Far‐field comparisons of the constructed solutions with the associated Riemann waves show good accuracy of the obtained solutions. Over an infinitely long shelf, the amplified transmitted wave breaks.
      PubDate: 2014-09-19T04:25:44.371039-05:
      DOI: 10.1002/2014JC010296
       
  • Global and regional sea level change during the 20th century
    • Authors: Manfred Wenzel; Jens Schröter
      Pages: n/a - n/a
      Abstract: Sea level variations prior to the launch of satellite altimeters are estimated by analysing historic tide gauge records. Recently, a number of groups have reconstructed sea level by applying EOF techniques to fill missing observations. We complement this study with alternative methods. In a first step gaps in 178 records of sea level change are filled using the pattern recognition capabilities of artificial neural networks. Afterwards satellite altimetry is used to extrapolate local sea level change to global fields. Patterns of sea level change are compared to prior studies. Global mean sea level change since 1900 is found to be 1.77 ± 0.38 mm year−1 on average. Local trends are essentially positive with the highest values found in the western tropical Pacific and in the Indian Ocean east of Madagascar where it reaches about +6 mm year−1. Regions with negative trends are spotty with a minimum value of about −2 mm year−1 south of the Aleutian Islands. Although the acceleration found for the global mean, +0.0042 ± 0.0092 mm year−2, is not significant, local values range from −0.1 mm year−2 in the central Indian Ocean to +0.1 mm year−2 in the western tropical Pacific and east of Japan. These extrema are associated with patterns of sea level change that differ significantly from the first half of the analyzed period (i.e. 1900 to 1950) to the second half (1950 to 2000). We take this as an indication of long period oceanic processes that are superimposed to the general sea level rise.
      PubDate: 2014-09-19T00:14:31.502269-05:
      DOI: 10.1002/2014JC009900
       
  • Mesoscale eddy variability in the southern extension of the East
           Madagascar Current: Seasonal cycle, energy conversion terms, and eddy mean
           properties
    • Authors: Issufo Halo; Pierrick Penven, Björn Backeberg, Isabelle Ansorge, Frank Shillington, Raymond Roman
      Pages: n/a - n/a
      Abstract: In this study we used more than seventeen years of satellite altimetry observations and output from an ocean model to investigate the mesoscale eddy variability and forcing mechanisms to the south of Madagascar. Analysis of energy conversion terms in the model has shown seasonality on eddy formation, both by barotropic and baroclinic instabilities: maximum in winter (JJA) and minimum in summer (DJF). The eddies were mainly formed in the upper ocean (0 ‐ 300 m) and at intermediate depths (800 ‐ 2000 m) by barotropic and baroclinic instabilities respectively. The former dominated in the southeastern margin of Madagascar, and the latter to the southwest, where the South East Madagascar Current (SEMC) separates from the continental shelf. Seasonality of the eddy formation appeared linked with the seasonal intensification of the SEMC. The energy conversion terms indicated that the eddies have a significant contribution to the large‐scale circulation, but not being persistent throughout the year, occurring mainly during the fall‐season (MAM). Eddy demography from altimetry and model provided information on eddy preferential sites for birth, annual occurrence (6 ‐ 13 per year), eddy mean diameter (124 ‐ 178 km), mean amplitude (9 ‐ 28 cm), life‐time (90 ‐ 183 days) and maximum traveling distances (325 ‐ 1052 km). Eddies formed to the southwest of Madagascar exhibited distinct characteristics from those formed in the southeast. Nevertheless, all eddies were highly nonlinear, suggesting that they are potential vectors of connectivity between Madagascar and Africa. This may have a significant impact on the ecology of this region.
      PubDate: 2014-09-18T23:59:42.138228-05:
      DOI: 10.1002/2014JC009820
       
  • Formation and distribution of sea ice in the Gulf of St. Lawrence: A
           process‐oriented study using a coupled ocean‐ice model
    • Authors: Jorge Urrego‐Blanco; Jinyu Sheng
      Pages: n/a - n/a
      Abstract: A coupled ocean‐ice model for the eastern Canadian shelf is used to examine main physical processes affecting sea ice conditions in the Gulf of St. Lawrence (GSL) and adjacent waters. The coupled model is based on NEMO and uses OPA9 as the ocean circulation component and the 2‐category dynamic‐thermodynamic LIM2 as the ice model. The coupled model is forced by atmospheric reanalysis fields produced by Large and Yeager [2004]. The model results are used to examine the roles of thermodynamics and dynamics on sea ice distributions and patterns of ice production and melting, and the influence of ice capping on the circulation in the study region. Analysis of model results indicates that local production of sea ice is important in shallower areas over the northern and western GSL. Equatorward advection of sea ice from the St. Lawrence Estuary is affected significantly by the Gaspé Current. An index is used to quantify the relative importance of thermodynamic and dynamics of sea ice in the GSL. It is found that both thermodynamics and dynamics are important over most of the GSL, except for waters around Anticosti Island, the southeastern Gulf, and the eastern Scotian Shelf, where dynamics (or sea ice movements) are the most important mechanism for the presence of sea ice. The study also demonstrates that ice capping significantly reduces the strength of the winter circulation in the GSL.
      PubDate: 2014-09-18T07:28:17.329459-05:
      DOI: 10.1002/2014JC010185
       
  • Local feedback mechanisms of the shallow water region around the Maritime
           Continent
    • Authors: Pengfei Xue; Elfatih A. B. Eltahir, Paola Malanotte‐Rizzoli, Jun Wei
      Pages: n/a - n/a
      Abstract: The focus of this study is the local‐scale air‐sea feedback mechanisms over the shallow shelf water region (water depth < 200m) of the Maritime Continent (MC). MC was selected as a pilot study site for its extensive shallow water coverage, geographic complexity and importance in the global climate system. To identify the local‐scale air‐sea feedback processes, we ran numerical experiments with perturbed surface layer water temperature using a coupled ocean‐atmosphere model and an uncoupled ocean model. By examining the responses of the coupled and uncoupled models to the water temperature perturbation, we identify that, at a local‐scale, a negative feedback process through the coupled dynamics that tends to restore the SST from its perturbation could dominate the shallow water region of the MC at a short time scale of several days. The energy budget shows that 38% of initial perturbation‐induced heat energy was adjusted through the air‐sea feedback mechanisms within 2 weeks, of which 58% is directly transferred into the atmosphere by the adjustment of latent heat flux due to the evaporative cooling mechanism. The increased inputs of heat and moisture into the lower atmosphere then modifies its thermal structure and increases the formation of low‐level clouds, which act as a shield preventing incoming solar radiation from reaching the sea surface, accounts for 38% of the total adjustment of surface heat fluxes, serving as the second mechanism for the negative feedback process. The adjustment of sensible heat flux and net long‐wave radiation play a secondary role. The response of the coupled system to the SST perturbation suggests a response time scale of the coupled feedback process of about 3‐5 days. The two‐way air‐sea feedback tightly links the surface heat fluxes, clouds and SST, and can play an important role in regulating the short‐term variability of the SST over the shallow shelf water regions.
      PubDate: 2014-09-18T05:20:59.142648-05:
      DOI: 10.1002/2013JC009700
       
  • Sea surface salinity variability in the East China Sea observed by the
           Aquarius instrument
    • Authors: Seung‐bum Kim; Jae Hak Lee, Paolo de Matthaeis, Simon Yueh, Chang‐Su Hong, Joon‐Ho Lee, Gary Lagerloef
      Pages: n/a - n/a
      Abstract: This study demonstrates that the spaceborne Aquarius instrument is able to monitor the sea surface salinity (SSS) variations in the East China Sea (ECS) with the spatial resolution of about 150 km at 7‐day interval, where routine observations are difficult. The two geophysical contaminants enter the sidelobes of the Aquarius antenna and bias the coastal SSS low: the emission from the land surface and the radiofrequency interference (RFI). Away from about one Aquarius pixel (150 km) from the coastline, the Aquarius SSS is fairly insensitive (less than about 0.2 psu) to the radiometric details of the method to correct for the land emission. The ascending orbits appear to be affected by unfiltered RFI much less than the descending tracks. The Aquarius SSS along the ascending tracks is low over the ECS by 0.40 to 0.93 psu (with respect to the in situ data during the two separate 7‐day periods) and is biased low by 0.41 to 1.07 psu (accuracy, or the time‐mean of difference from the regional model along three Aquarius tracks over a 18‐month period). The presence of the ascending and descending differences in the Aquarius SSS, and the spatially widespread bias suggest that the bias is attributed to the unfiltered RFI originating from strong point sources (rather than to the land contamination from weak distributed sources, or to other seasonally‐varying geophysical contaminants). Despite the bias, the Aquarius data describe well the temporal and spatial variability of the ECS SSS. The temporal trend and magnitude of salinity changes agree remarkably between Aquarius and a regional numerical model, during both the freshwater discharge season from the Yangtze river and the rest of the year. The precision of the Aquarius observation in the ECS is comparable with the Aquarius mission requirement (0.2 psu one‐sigma for a monthly average over the open ocean). The river discharge rate correlates with the Aquarius SSS with the coefficient of 0.71 on a seasonal scale with the discharge leading the SSS changes. The Aquarius SSS increases away from the coast, in response to the river outflow. The interannual changes in the Aquarius SSS capture the effect of the regional drought in summer 2013.
      PubDate: 2014-09-18T05:09:39.316904-05:
      DOI: 10.1002/2014JC009983
       
  • Laboratory study on coprecipitation of phosphate with ikaite in sea ice
    • Authors: Yu‐Bin Hu; Gerhard S. Dieckmann, Dieter A. Wolf‐Gladrow, Gernot Nehrke
      Pages: n/a - n/a
      Abstract: Ikaite (CaCO3·6H2O) has recently been discovered in sea ice, providing first direct evidence of CaCO3 precipitation in sea ice. However, the impact of ikaite precipitation on phosphate (PO4) concentration has not been considered so far. Experiments were set up at pH from 8.5 to 10.0, salinities from 0 to 105, temperatures from −4 to 0°C and PO4 concentrations from 5 to 50 µmol kg−1 in artificial sea ice brine so as to understand how ikaite precipitation affects the PO4 concentration in sea ice under different conditions. Our results show that PO4 is coprecipitated with ikaite under all experimental conditions. The amount of PO4 removed by ikaite precipitation increases with increasing pH. Changes in salinity (S ≥ 35) as well as temperature have little impact on PO4 removal by ikaite precipitation. The initial PO4 concentration affects the PO4 coprecipitation. These findings may shed some light on the observed variability of PO4 concentration in sea ice.
      PubDate: 2014-09-18T05:04:25.347027-05:
      DOI: 10.1002/2014JC010079
       
  • Enhanced sea‐air CO2 exchange influenced by a tropical depression in
           the South China Sea
    • Authors: Qingyang Sun; Danling Tang, Louis Legendre, Ping Shi
      Pages: n/a - n/a
      Abstract: Ship measurements made two days after the passage of a tropical depression (TD) in the South China Sea (SCS, April 2011) showed two contrasted responses of the partial pressure of CO2 at sea surface (pCO2,sw). In low sea‐surface salinity (SSS) waters, pCO2,sw was low (349 ± 7 µatm), and the area was a carbon sink (‐4.7 ± 1.8 mmol CO2 m‐2 d‐1), whereas in water with high SSS and chlorophyll a and low dissolved oxygen and sea surface temperature, pCO2,sw was higher than normal SCS water (376 ± 8 vs. 362 ± 4 µatm) and the area was a carbon source (1.2 ± 3.1 mmol CO2 m‐2 d‐1). Satellite data showed two large areas of low SSS before the TD, which were likely influenced by rainfall, and these areas were considered to have low pCO2,sw because of their low SSS. The high pCO2,sw after the TD is explained by the uplifting to the surface of deeper and CO2‐rich water, due to winds accompanied by the TD. The difference in sea‐air CO2 flux between the TD‐affected area and the lower‐SSS water was (1.99 + 4.70 = 6.7 mmol CO2 m‐2 d‐1), indicating a 100% change caused by the TD compared to the average seasonal value in spring in southern SCS (3.3 ± 0.3 mmol CO2 m‐2 d‐1). Undersaturation of CO2 prior to the TD due to dilution by freshwater and the pre‐existing cold eddy, and slow translation speed of the TD, are considered to be accounted for the CO2 flux change.
      PubDate: 2014-09-18T04:48:52.290777-05:
      DOI: 10.1002/2014JC010131
       
  • Storms modify baroclinic energy fluxes in a seasonally stratified shelf
           sea: Inertial‐tidal interaction
    • Authors: Joanne. E. Hopkins; Gordon R. Stephenson, J. Mattias Green, Mark E. Inall, Matthew R. Palmer
      Pages: n/a - n/a
      Abstract: Observations made near the Celtic Sea shelf edge are used to investigate the interaction between wind generated near‐inertial oscillations and the semi‐diurnal internal tide. Linear, baroclinic energy fluxes within the near‐inertial (f) and semi‐diurnal (M2) wave bands are calculated from measurements of velocity and density structure at two moorings located 40 km from the internal tidal generation zone. Over the two week deployment period the semi‐diurnal tide drove 28‐48 W m‐1 of energy directly on‐shelf. Little spring‐neap variability could be detected. Horizontal near‐inertial energy fluxes were an order of magnitude weaker, but non‐linear interaction between the vertical shear of inertial oscillations and the vertical velocity associated with the semi‐diurnal internal tide led to a 25‐43% increase in positive on‐shelf energy flux. The phase relationship between f and M2 determines whether this non‐linear interaction enhances or dampens the linear tidal component of the flux, and introduces a 2‐day counter clockwise beating to the energy transport. Two very clear contrasting regimes of (a) tidally and (b) inertially driven shear and energy flux are captured in the observations.
      PubDate: 2014-09-18T04:48:50.374667-05:
      DOI: 10.1002/2014JC010011
       
  • A numerical investigation of wave‐breaking‐induced turbulent
           coherent structure under a solitary wave
    • Authors: Zheyu Zhou; Jacob Sangermano, Tian‐Jian Hsu, Francis C. K. Ting
      Pages: n/a - n/a
      Abstract: To better understand the effect of wave‐breaking‐induced turbulence on the bed, we report a 3D Large‐Eddy Simulation (LES) study of a breaking solitary wave in spilling condition. Using a turbulence‐resolving approach, we study the generation and the fate of wave‐breaking‐induced turbulent coherent structures, commonly known as obliquely descending eddies (ODEs). Specifically, we focus on how these eddies may impinge onto bed. The numerical model is implemented using an open‐source CFD library of solvers, called OpenFOAM, where the incompressible 3D filtered Navier‐Stokes equations for the water and the air phases are solved with a finite volume scheme. The evolution of the water‐air interfaces are approximated with a volume of fluid method. Using the dynamic Smagorinsky closure, the numerical model has been validated with wave flume experiments of solitary wave breaking over a 1/50 sloping beach. Simulation results show that during the initial overturning of the breaking wave, 2D horizontal rollers are generated, accelerated and further evolve into a couple of 3D hairpin vortices. Some of these vortices are sufficiently intense to impinge onto the bed. These hairpin vortices possess counter‐rotating and downburst features, which are key characteristics of ODEs observed by earlier laboratory studies using Particle Image Velocimetry. Model results also suggest that those ODEs that impinge onto bed can induce strong near‐bed turbulence and bottom stress. The intensity and locations of these near‐bed turbulent events could not be parameterized by near‐surface (or depth integrated) turbulence unless in very shallow depth.
      PubDate: 2014-09-18T04:47:15.170217-05:
      DOI: 10.1002/2014JC009854
       
  • Energy transfer between wind waves and low‐frequency oscillations on
           a fringing reef, Ipan Guam
    • Authors: Anne‐Christine N. Péquignet; Janet M. Becker, Mark A. Merrifield
      Pages: n/a - n/a
      Abstract: Field observations from a Guam fringing reef are used to examine the cross‐reef energy exchange between high frequency sea and swell (SS) and low frequency infragravity (IG) and far infragravity (fIG) waves. Energetic SS waves (significant wave heights 2‐4 m) break at the outer reef, leading to weak (
      PubDate: 2014-09-15T21:57:36.268634-05:
      DOI: 10.1002/2014JC010179
       
  • Swell dissipation by induced atmospheric shear stress
    • Authors: Y. Perignon; F. Ardhuin, M. Cathelain, M. Robert
      Pages: n/a - n/a
      Abstract: Observations of swell dissipation across oceans reveal a significant loss of energy that can be the result of many of processes. Among these candidate mechanisms, this paper examines the properties of the viscous air‐sea boundary layer driven by swells in order to characterize the induced atmospheric flow regime and its associated viscous dissipation over swells. A series of 3D numerical experiments is carried out with a RANS model and appropriate turbulence closure. These experiments reveal a laminar to turbulent transition in the near free‐surface region for a common range of characteristic amplitudes and periods of swells under stationary conditions. At low Reynolds number, laminar conditions prevail and computed decay rates conform to the analytical formulation μv of the Stokes interfacial boundary layer for this problem. The turbulent regimes are characterized as well and the new decay rates follow a non‐dimensional relation μ=1.42μv(Re⁡1.5×105)0.41 above Re = 1.5 × 105 (e.g. amplitude larger than 1.1m for a 14s monochromatic wave period). Typical decay rates are up to 4 times above the laminar values, which is a factor 10 less than the largest rates estimated for oceanic conditions. A sensitivity analysis is finally conducted to evaluate the influence of the stationary hypothesis. It demonstrates a short setup‐length and low relative variations of the unsteady decay rates for laminar, transitioning and developed turbulent conditions, which confirms the evaluation of steady decay rates.
      PubDate: 2014-09-15T07:11:31.561552-05:
      DOI: 10.1002/2014JC009896
       
  • South Indian Countercurrent and associated fronts
    • Authors: Viviane V. Menezes; Helen E. Phillips, Andreas Schiller, Nathaniel L. Bindoff, Catia M. Domingues, Marcio L. Vianna
      Pages: n/a - n/a
      Abstract: A striking feature of the South Indian Ocean circulation is the presence of the eastward South Indian Countercurrent (SICC) that flows in a direction opposite to that predicted by the classical theories of wind‐driven circulation. Several authors suggest that the SICC resembles the subtropical countercurrents (STCCs) observed in other oceans, which are defined as narrow eastward jets on the equatorward side of subtropical gyres, where the depth‐integrated flow is westward. These jets are associated with subsurface thermal fronts at thermocline depths by the thermal wind relation. However, the subsurface thermal front associated with the SICC has not been described to date. Other studies conjecture an important role for salinity in controlling the SICC. In the present work, we analyse three Argo‐based atlases and data from six hydrographic cruises to investigate whether the SICC is accompanied by permanent thermal and density fronts including salinity effects. The seasonal cycle of these fronts in relation to the SICC strength are also investigated. We find that the SICC is better described as composed of three distinct jets, which we name the northern, central and southern SICC. We find that the southern SICC around 26° S has an associated thermal front at subsurface depths around 100‐200 m with salinity being of secondary importance. The southern branch strength is related to mode waters poleward of the front, similar to a STCC‐like current. However, the SICC multiple jet structure seems to be better described as resulting from PV staircases.
      PubDate: 2014-09-15T05:42:52.254511-05:
      DOI: 10.1002/2014JC010076
       
  • Impact of periodic intermediary flows on submarine melting of a Greenland
           glacier
    • Authors: R. Sciascia; C. Cenedese, D. Nicolì, P. Heimbach, F. Straneo
      Pages: n/a - n/a
      Abstract: The submarine melting of a vertical glacier front, induced by an intermediary circulation forced by periodic density variations at the mouth of a fjord, is investigated using a non–hydrostatic ocean general circulation model and idealized laboratory experiments. The idealized configurations broadly match that of Sermilik Fjord, southeast Greenland, a largely two‐layers system characterized by strong seasonal variability of subglacial discharge. Consistent with observations, the numerical results suggest that the intermediary circulation is an effective mechanism for the advection of shelf anomalies inside the fjord. In the numerical simulations, the advection mechanism is a density intrusion with a velocity which is an order of magnitude larger than the velocities associated with a glacier–driven circulation. In summer, submarine melting is mostly influenced by the discharge of surface runoff at the base of the glacier and the intermediary circulation induces small changes in submarine melting. In winter, on the other hand, submarine melting depends only on the water properties and velocity distribution at the glacier front. Hence, the properties of the waters advected by the intermediary circulation to the glacier front are found to be the primary control of the submarine melting. When the density of the intrusion is intermediate between those found in the fjord's two layers there is a significant reduction in submarine melting. On the other hand, when the density is close to that of the bottom layer, only a slight reduction in submarine melting is observed. The numerical results compare favorably to idealized laboratory experiments with a similar setup.
      PubDate: 2014-09-12T00:01:13.838272-05:
      DOI: 10.1002/2014JC009953
       
  • First “in situ” determination of gas transport coefficients
           (DO2, DAr, and DN2) from bulk gas concentration measurements (O2, N2, Ar)
           in natural sea ice
    • Authors: Odile Crabeck; B Delille, S Rysgaard, D.N. Thomas, N.X. Geilfus, B Else, J.L. Tison
      Pages: n/a - n/a
      Abstract: We report bulk gas concentrations of O2, N2 and Ar, as well as their transport coefficients, in natural landfast subarctic sea ice in southwest Greenland. The observed bulk ice gas composition was 27.5% O2, 71.4% N2 and 1.09% Ar. Most previous studies suggest that convective transport is the main driver of gas displacement in sea ice and have neglected diffusion processes. According to our data, brines were stratified within the ice, so that no convective transport could occur within the brine system. Therefore, diffusive transport was the main driver of gas migration. By analysing the temporal evolution of an internal gas peak within the ice, we deduced the bulk gas transport coefficients for oxygen (DO2), argon (DAr) and nitrogen (DN2). The values fit to the few existing estimates from experimental work, and are close to the diffusivity values in water (10‐5 cm2 s‐1). We suggest that gas bubbles escaping from the brine to the atmosphere ‐ as the ice gets more permeable during melt ‐ could be responsible for the previously reported high transport coefficients. These results underline that when there is no convective transport within the sea ice, the transport of gas by diffusion through the brines, either in the liquid or gaseous phases, is a major factor in controlling the ocean–atmosphere exchange.
      PubDate: 2014-09-10T01:58:08.847943-05:
      DOI: 10.1002/2014JC009849
       
  • Distinguishing meanders of the Kuroshio using machine learning
    • Authors: David A. Plotkin; Jonathan Weare, Dorian S. Abbot
      Pages: n/a - n/a
      Abstract: The Kuroshio south of Japan is often described as being bimodal, with abrupt transitions between a straight path state that stays near the coast (small meander) and a meandering state the deviates from the coast (large meander). Despite evidence of the existence of two or more states of the Kuroshio, previous data‐driven studies have shown only high variability of the current; they have not, however, demonstrated bimodality in the sense of two states of relatively high probability separated by a region of relatively low probability. We use singular value decomposition (SVD), a standard time series analysis method for characterizing variability, and diffusion maps and spectral clustering (DMSC), a machine learning algorithm that seeks multimodality, to investigate Kuroshio reanalysis output. By applying these methods to a time series of velocity fields, we find that 1) the Kuroshio is bimodal, with high inflow and low path variability in the small meander and low inflow and high path variability in the large meander, 2) the state of the system correlates highly with the location of the recirculation gyre south of Japan, and 3) the meanders are better characterized by path variability than by mean path. Because these results are consistent with satellite sea surface height data, they are not an artifact of the model used for reanalysis. Further, our results provide evidence for a previously proposed transition mechanism based on the strengthening, migration, and weakening of the recirculation gyre south of Japan and can therefore help direct future modeling studies.
      PubDate: 2014-09-10T01:51:57.218342-05:
      DOI: 10.1002/2014JC010128
       
  • Variability of Arctic sea ice topography and its impact on the atmospheric
           surface drag
    • Authors: G. Castellani; C. Lüpkes, R. Gerdes, S. Hendricks
      Pages: n/a - n/a
      Abstract: Over the polar oceans, near‐surface atmospheric transport of momentum is strongly influenced by sea‐ice surface topography. The latter is analyzed on the basis of laser altimeter data obtained during airborne campaigns between 1995 and 2011 over more than 10000 km of flight distance in different regions of the Arctic Ocean. Spectra of height and spacing between topographic features averaged over 10 km flight sections show that typical values are 0.45 m for the mean height and about 20 m for the mean spacing. Nevertheless the variability is high and the spatial variability is stronger than the temporal one. The total topography spectrum is divided into a range with small obstacles (between 0.2 m and 0.8 m height) and large obstacles (≥0.8 m). Results show that large pressure ridges represent the dominant topographic feature only along the coast of Greenland. In the Central Arctic the concentration of large ridges decreased over the years, accompanied by an increase of small obstacles concentration and this might be related to decreasing multi‐year ice. The application of a topography dependent parameterization of neutral atmospheric drag coefficients reflects the large variability in the sea ice topography and reveals characteristic differences between the regions. Based on the analysis of the two spectral ranges we find that the consideration of only large pressure ridges is not enough to characterize the roughness degree of an ice field, and the values of drag coefficients are in most regions strongly influenced by small obstacles.
      PubDate: 2014-09-10T01:49:56.147693-05:
      DOI: 10.1002/2013JC009712
       
  • Mesoscale dynamics in the Arabian Sea and a focus on the Great Whirl life
           cycle: A numerical investigation using ROMS
    • Authors: C. Vic; G. Roullet, X. Carton, X. Capet
      Pages: n/a - n/a
      Abstract: The Great Whirl (GW) is a persistent anticyclonic mesoscale eddy that is observed seasonally in the Arabian Sea during a period embedding the three months of the southwest monsoon (June‐July‐August) at a quasi‐steady location. Its dynamics remain unclear despite it being one of the largest coherent vortices in the world ocean. Realistic regional numerical experiments using ROMS are performed to investigate the life cyle of the GW, which is not well resolved by sparse available in situ measurements in the region. Using a set of sensitivity experiments and an accurate temporal characterization of the eddy properties (including position, radius, depth and vorticity) we (i) confirm the role of basin‐scale downwelling Rossby waves in the GW generation (ii) clarify the role of the monsoonal strong anticyclonic wind in its maintenance and barotropization (iii) suggest a connection between basin‐scale Rossby wave dynamics and GW collapse.
      PubDate: 2014-09-09T23:51:31.112037-05:
      DOI: 10.1002/2014JC009857
       
  • Quantifying tidally driven benthic oxygen exchange across permeable
           sediments: An aquatic eddy correlation study
    • Authors: Daniel F. McGinnis; Stefan Sommer, Andreas Lorke, Ronnie N. Glud, Peter Linke
      Pages: n/a - n/a
      Abstract: Continental shelves are predominately (~70%) covered with permeable, sandy sediments. While identified as critical sites for intense oxygen, carbon and nutrient turnover, constituent exchange across permeable sediments remains poorly quantified. The central North Sea largely consists of permeable sediments and has been identified as increasingly at risk for developing hypoxia. Therefore, we investigate the benthic O2 exchange across the permeable North Sea sediments using a combination of in situ microprofiles, a benthic chamber and aquatic eddy correlation. Tidal bottom currents drive the variable sediment O2 penetration depth (from ~3 to 8 mm) and the concurrent turbulence‐driven 25‐fold variation in the benthic sediment O2 uptake. The O2 flux and variability were reproduced using a simple 1‐D model linking the benthic turbulence to the sediment porewater exchange. The high O2 flux variability results from deeper sediment O2 penetration depths and increased O2 storage during high velocities, which is then utilized during low flow periods. The study reveals that the benthic hydrodynamics, sediment permeability and porewater redox oscillations are all intimately linked and crucial parameters determining the oxygen availability in permeable sediments. These parameters must all be considered when evaluating mineralization pathways of organic matter and nutrients in permeable sediments.
      PubDate: 2014-09-09T19:25:33.632231-05:
      DOI: 10.1002/2014JC010303
       
  • Intrusion of Rhone River diluted water into the Bay of Marseille:
           Generation processes and impacts on ecosystem functioning
    • Authors: Marion Fraysse; Ivane Pairaud, Oliver N. Ross, Vincent M. Faure, Christel Pinazo
      Pages: n/a - n/a
      Abstract: The Rhone River provides the largest inputs of terrestrial freshwater and nutrients into the Mediterranean Sea. The Rhone River diluted water intrusions into the Bay of Marseille were investigated, examining their physical generation processes and associated biogeochemical impact by using in situ observations, remote sensing data, and a three‐dimensional physical/biogeochemical coupled model. During our study period from 2007 to 2011, Rhone River intrusions occurred on average 7.6 times per year and affected more frequently the northern part of the bay. A classification of intrusion events in three categories is proposed (short‐lived, big and small) as a function of their duration and spatial extent. The intrusions appeared to be driven by: (i) wind forcing, (ii) the presence of a mesoscale eddy, (iii) the Rhone River discharge volume, and (iv) the variation in thermocline depth. Typically, a combination of these favorable factors was necessary to induce an intrusion. An intrusion strongly impacts the biogeochemical functioning of the Bay of Marseille by bringing large quantities of nutrients into the bay. Mass balances were computed allowing us to quantify this impact on the Bay of Marseille. The results show that the ecological impact depends very much on the type of intrusion, with big intrusions having the highest impact.
      PubDate: 2014-09-05T04:21:53.953366-05:
      DOI: 10.1002/2014JC010022
       
  • Modulation of Rossby waves on the Pacific North Equatorial Current
           bifurcation associated with the 1976 climate regime shift
    • Authors: Li‐Chiao Wang; Chau‐Ron Wu, Bo Qiu
      Pages: n/a - n/a
      Abstract: Simulated current velocity and long‐term reanalysis wind data are used to investigate interannual variations in the bifurcation of the Pacific North Equatorial Current (NEC) after the 1976 climate regime shift. Wind stress curl anomaly (WSCA) in the region of 10°N–15°N and 160°E–170°E generates Rossby waves and affects the NEC bifurcation along the Philippine coast. From 1976 to 1992, following a regime shift to the positive Pacific Decadal Oscillation (PDO) phase, PDO and El Niño‐Southern Oscillation (ENSO) match each other in strength and have a neutralized effect on the WSCA. From 1993 to 2009, WSCA matches PDO well, and its correlation with ENSO is lower. Using a linear regression model, we show that the influence of PDO has nearly thirteen times weight over that of ENSO. Prior to the 1976 regime shift, WSCA is closely related to ENSO from 1961 to 1975, and it does not correlate significantly with PDO. Our analysis results show that Rossby waves are preferentially generated in either the negative PDO phase when the ENSO signal dominates, or in the positive PDO phase when the ENSO signal is overshadowed. In the phase when the positive PDO counteracts with the ENSO signal, neither ENSO nor PDO has a significant influence on Rossby wave generations through the WSCA.
      PubDate: 2014-09-05T04:20:49.538107-05:
      DOI: 10.1002/2014JC010233
       
  • Heat fluxes across the Antarctic Circumpolar Current in Drake Passage:
           Mean flow and eddy contributions
    • Authors: Ramiro Ferrari; Christine Provost, Young‐Hyang Park, Nathalie Sennéchael, Zoé Koenig, Hela Sekma, Gilles Garric, Romain Bourdallé‐Badie
      Pages: n/a - n/a
      Abstract: In contrast to a long‐standing belief, observations in the Antarctic Circumpolar Current (ACC) show that mean velocity vectors rotate with depth, thus suggesting a possible importance of the time‐mean flow for the local poleward heat transport. The respective contributions of the eddy and mean flows to the heat flux across the ACC in Drake Passage (DP) are investigated using recently acquired and historical time series of velocity and temperature from a total of 24 current meter moorings and outputs of a high‐resolution (1/12 degree) model with realistic topography. Only 11 out of the 24 depth‐integrated eddy heat flux estimates are found to be significant, and they are poleward. Model depth‐integrated eddy heat fluxes have similar signs and amplitudes as the in situ estimates at the mooring sites. They are mostly poleward or non‐significant, with amplitude decreasing to the south. The cross‐stream temperature fluxes caused by the mean flow at the moorings have a sign that varies with location and corresponds to the opposite of the vertical velocity estimates. The depth‐integrated temperature fluxes due to the mean flow in the model exhibit small spatial scales and are of opposite sign to the bottom vertical velocities. This suggests that the rotation of the mean velocity vectors with depth is mainly due to bottom topography. The rough hilly topography in DP likely promotes the small‐scale vertical velocities and temperature fluxes. Eddy heat fluxes and cross‐stream temperature fluxes are integrated over mass balanced regions defined by the model transport streamlines. The contribution of the mean flow to the ocean heat fluxes across the Southern ACC Front in DP (covering about 4 % of the circumpolar longitudes) is about four times as large as the eddy heat flux contribution and the sum of the two represent on the order of 10% of the heat loss to the atmosphere south of 60°S.
      PubDate: 2014-09-05T03:38:20.554388-05:
      DOI: 10.1002/2014JC010201
       
  • Observations on stratified flow over a bank at low Froude numbers
    • Authors: Ewa Jarosz; Hemantha W. Wijesekera, William J. Teague, Diane B. Fribance, Mark A. Moline
      Pages: n/a - n/a
      Abstract: In June 2011, a nine‐day oceanographic survey was conducted over the East Flower Garden Bank, a coral reef, located on the outer shelf in the northwestern Gulf of Mexico. Current, temperature, conductivity, and microstructure measurements were collected to characterize flow evolution, turbulence, and mixing over the bank. During the experiment, the flow was highly stratified, subcritical (Froude number below 0.4), hydrostatic, and nonlinear with rotational effects being important. Observations showed that flow structure, turbulence, and mixing were highly dependent on the direction and strength of the current; thus, they varied spatially and temporarily. Responses resulting from interactions between the free‐stream flow and the obstacle were significantly different on the upstream and downstream sides of the bank. Blocking and diverging of the flow just below the bank height was observed on the upstream side. On the downstream side, a wake with imbedded vortices developed. Moreover, turbulence was amplified over the bank top and on its downstream side. Turbulent dissipation rates were as high as 10‐6 W kg‐1 and resulted in measured rates of energy dissipation and mixing by turbulence per unit width as high as 40 W m‐1. Mixing on the downstream side was elevated with eddy diffusivities reaching 10‐3 m2 s‐1, well above a typical value of 10‐5 m2 s‐1 commonly found in the ocean thermocline and over shelves with flat topography. On the upstream side, estimated eddy diffusivities were close to that for the ocean thermocline, i.e., they were generally less than 0.5·10‐4 m2 s‐1.
      PubDate: 2014-09-05T03:37:59.808359-05:
      DOI: 10.1002/2014JC009934
       
  • Net community production and export from seaglider measurements in the
           North Atlantic after the spring bloom
    • Authors: Matthew B. Alkire; Craig Lee, Eric D’Asaro, Mary Jane Perry, Nathan Briggs, Ivona Cetinić, Amanda Gray
      Pages: n/a - n/a
      Abstract: Mean rates of net community production (NCP) and particulate organic carbon (POC) export were estimated from sensor measurements of dissolved oxygen (O2), chlorophyll fluorescence (chl F), and particulate backscatter (bbp700) collected from three Seagliders that surveyed a 20 x 20 km area in the North Atlantic subsequent to a large diatom bloom. Since the Seagliders sampled geographically fixed patterns, care was taken in the calculation of all terms applicable to the Eulerian reference frame, including local rate of change, vertical mixing, air‐sea exchange, and horizontal advection. Although similar studies of NCP in the open ocean have generally assumed advection to be insignificant we have found that this term cannot be ignored when dealing with temporal scales of ≤ 1 month and/or spatial scales ≤ 20 km. The overlapping sampling pattern of the Seagliders was sufficiently rapid such that 4‐5 day timescales observed in the O2 and POC data were adequately resolved and variations were not a consequence of aliasing spatial variability. During the study period, ratios of chlorophyll fluorescence‐to‐particulate backscatter (chl:bbp700) were lower than values encountered during the spring diatom bloom, suggesting the phytoplankton community was predominantly composed of smaller cells (pico‐ and nanoplankton) and/or coccolithophorids. Coupled budgets of oxygen and POC indicated a net community production of 1.0 mol C m‐2 and carbon export of 0.6 mol C m‐2, respectively over a period of 23 days. Thus, the production and export of carbon that occurred over the month‐long experiment period was comparable to that encountered during the spring bloom.
      PubDate: 2014-09-04T07:36:41.236157-05:
      DOI: 10.1002/2014JC010105
       
  • Estimating dissolved organic carbon inventories in the East China Sea
           using remote sensing data
    • Authors: Qiong Liu; Delu Pan, Yan Bai, Kai Wu, Chen‐Tung Authur Chen, Zhiliang Liu, Lin Zhang
      Pages: n/a - n/a
      Abstract: The coastal ocean is characterized by a high dissolved organic carbon (DOC) concentration due to large terrestrial inputs and high primary production. Monitoring the dynamic variation of DOC inventories in coastal oceans provide more information on carbon flux, but is very challenging in practice. We propose a method of estimating DOC inventories in the East China Sea (ECS) by integrating the surface DOC distribution with a vertical model of the DOC profile via satellite data. Surface DOC concentration was retrieved from satellite‐derived chromophoric dissolved organic matter and chlorophyll concentration. Two vertical DOC profile models (uniform model and stratified model) were established based on water‐density profiles, and the usage of these two models was corresponded to water mass classification determined by a water mass index. The average bias of the satellite‐derived DOC inventory, in the euphotic layer was 23.8% in spring, 24.8% in autumn and 14.7% in winter, and in the water column was 15.6% in spring, 12.3% in autumn and 10.2% in winter. The total satellite‐derived DOC inventory integrated in the water column was about 31.84 Tg, 31.96 Tg, 28.59 Tg and 31.18 Tg in four seasons in the ECS (5.84×105 km2). Sensitivity analysis indicated that the remote‐sensing method of estimating DOC inventory is stable and reliable. The available of long‐term and large‐scale satellite‐derived DOC inventories in marginal sea would provide us basic information on carbon cycle, and the difference between the seasonal DOC inventories would help to understand the DOC export and relative biogeochemical processes in the ECS.
      PubDate: 2014-09-03T12:36:29.559443-05:
      DOI: 10.1002/2014JC009868
       
  • Vertical structure of eddies and Rossby waves and their effect on the
           Atlantic meridional overturning circulation at 26.5°N
    • Authors: L. Clément; E. Frajka‐Williams, Z. B. Szuts, S. A. Cunningham
      Pages: n/a - n/a
      Abstract: The meridional overturning circulation (MOC) at 26.5°N in the Atlantic has a standard deviation of 4.9 Sv and contains large fluctuations at subannual periods. The geostrophic component of the MOC is believed to be influenced on subannual timescales by eddies and Rossby waves. To quantify this effect, the vertical structure and surface characteristics of westward propagating signals are studied using altimetric data and full‐depth mooring measurements from the RAPID array at 26.5°N. Westward propagating features are observed in the western North Atlantic in both datasets and have periods of 80‐250 days in the first baroclinic mode. These features are still observed by the RAPID moorings 20 km offshore of the western boundary. The western boundary also exhibits deep variability characterized by enhanced energy in higher baroclinic modes. The effect of eddies and Rossby waves on the geostrophic transport is quantified by representing their vertical structure with the first baroclinic mode. In total, 42% of the variance of the transbasin thermocline transport inferred from geostrophic calculations at 26.5°N can be attributed to first mode variability, which is associated with eddies and Rossby waves at periods of 80‐250 days. The standard deviation of the transbasin thermocline transport due to eddies and Rossby waves is estimated to be 2.6 Sv.
      PubDate: 2014-09-03T03:09:55.031686-05:
      DOI: 10.1002/2014JC010146
       
  • Differential distribution of diatoms and dinoflagellates in a cyclonic
           eddy confined in the Bay of La Paz, Gulf of California
    • Authors: Erik Coria‐Monter; María Adela Monreal‐Gómez, David Alberto Salas‐de‐León, Javier Aldeco‐Ramírez, Martín Merino‐Ibarra
      Pages: n/a - n/a
      Abstract: The differential distribution of diatoms and dinoflagellates in the Bay of La Paz, Gulf of California, Mexico, was analyzed in summer of 2009, when a cyclonic eddy confined in the bay dominated the circulation. An uplift of the nutricline in the eddy drove high concentrations of nutrients to the euphotic layer. A differential phytoplankton distribution was observed to be associated with the eddy: there was an abundance of dinoflagellates close to the center of the cyclonic eddy, whereas diatoms were more abundant at the periphery. A significant inverse correlation (R=‐0.62, p
      PubDate: 2014-09-02T03:50:54.679207-05:
      DOI: 10.1002/2014JC009916
       
  • Diurnal cross‐shore thermal exchange on a tropical fore reef
    • Authors: L. Molina; G. Pawlak, J. R. Wells, S. G. Monismith, M. A. Merrifield
      Pages: n/a - n/a
      Abstract: Observations of the velocity structure at the Kilo Nalu Observatory on the south shore of Oahu, Hawaii show that thermally driven baroclinic exchange is a dominant mechanism for cross‐shore transport for this tropical forereef environment. Estimates of the exchange and net volume fluxes are comparable and show that the average residence time for the zone shoreward of the 12 m isobath is generally much less than one day. Although cross‐shore wind stress influences the diurnal cross‐shore exchange, surface heat flux is identified as the primary forcing mechanism from the phase relationships and from analysis of momentum and buoyancy balances for the record‐averaged diurnal structure. Dynamic flow regimes are characterized based on a two‐dimensional theoretical framework and the observations of the thermal structure at Kilo Nalu are shown to be in the unsteady temperature regime. Diurnal phasing and the cross‐shore momentum balance suggest that turbulent stress divergence is an important driver of the baroclinic exchange. While the thermally driven exchange has a robust diurnal profile in the long‐term, there is high temporal variability on shorter timescales. Ensemble averaged diurnal profiles indicate that the exchange is strongly modulated by surface heat flux, wind speed/direction and along‐shore velocity direction. The latter highlights the role of along‐shore variability in the thermally driven exchange. Analysis of the thermal balance in the nearshore region indicates that the cross‐shore exchange accounts for roughly 38 of the advective heat transport on a daily basis.
      PubDate: 2014-09-02T03:50:44.508846-05:
      DOI: 10.1002/2013JC009621
       
  • Annual sea‐air CO2 fluxes in the Bering Sea: Insights from new
           autumn and winter observations of a seasonally ice‐covered
           continental shelf
    • Authors: Jessica N. Cross; Jeremy T. Mathis, Karen E. Frey, Catherine E. Cosca, Seth L. Danielson, Nicholas R. Bates, Richard A. Feely, Taro Takahashi, Wiley Evans
      Pages: n/a - n/a
      Abstract: High‐resolution data collected from several programs has greatly increased the spatiotemporal resolution of pCO2 data in the Bering Sea, and provided the first autumn and winter observations. Using data from 2008 – 2012, monthly climatologies of sea‐air CO2 fluxes for the Bering Sea shelf area from April through December were calculated, and contributions of physical and biological processes to observed monthly sea‐air pCO2 gradients (ΔpCO2) were investigated. Net efflux of CO2 was observed during November, December, and April, despite the impact of sea surface cooling on ΔpCO2. Although the Bering Sea was believed to be a moderate to strong atmospheric CO2 sink, we found that autumn and winter CO2 effluxes balanced 65% of spring and summer CO2 uptake. Ice cover reduced sea‐air CO2 fluxes in December, April, and May. Our estimate for ice‐cover corrected fluxes suggests the mechanical inhibition of CO2 flux by sea‐ice cover has only a small impact on the annual scale (< 2%). An important data gap still exists for January through March, the period of peak ice cover and the highest expected retardation of the fluxes. By interpolating between December and April using assumptions of the described autumn and winter conditions, we estimate the Bering Sea shelf area is an annual CO2 sink of ~6.8 Tg C yr‐1. With changing climate, we expect warming sea surface temperatures, reduced ice cover, and greater wind speeds with enhanced gas exchange to decrease the size of this CO2 sink by augmenting conditions favorable for greater wintertime outgassing.
      PubDate: 2014-09-02T03:50:34.239473-05:
      DOI: 10.1002/2013JC009579
       
  • Geometry of tidal inlet systems: A key factor for the net sediment
           transport in tidal inlets
    • Authors: W. Ridderinkhof; H. E. de Swart, M. van der Vegt, N. C. Alebregtse, P. Hoekstra
      Pages: n/a - n/a
      Abstract: The net transport of sediment between the back‐barrier basin and the sea is an important process for determining the stability of tidal inlet systems. Earlier studies showed that in a short basin, tidal flats favor peak ebb‐currents stronger than peak flood currents, implying export of coarse sediment, while shallow basins favor stronger flood currents. The new elements considered in this study are 1) arbitrary basin lengths, 2) a narrow inlet that connects the basin to the sea, 3) an asymmetric tidal forcing, and 4) radiation damping. The objective is to gain fundamental insight in how the geometry of a tidal inlet system affects the net sand transport in a tidal inlet. For this purpose, a width‐ and depth averaged analytical model was constructed. It is found that the length of a back‐barrier basin controls the effect that nonlinear hydrodynamic processes have on the tidal asymmetry, and consequently controls whether the currents in the inlet are flood‐ or ebb‐dominant. Furthermore, the cross‐sectional area of the inlet controls the ratio between the net sediment transport that results from tidal asymmetry and that caused by the interaction of the principal tide with the residual current. Finally, it is shown that the effect of an asymmetric tidal forcing on the net sand transport depends on the length of the back‐barrier basin with respect to the tidal wavelength in that basin.
      PubDate: 2014-09-02T03:50:12.081442-05:
      DOI: 10.1002/2014JC010226
       
  • The central Pacific El Niño intraseasonal Kelvin wave
    • Authors: K. Mosquera‐Vásquez; B. Dewitte, Serena Illig
      Pages: n/a - n/a
      Abstract: In this study we document and interpret the characteristics of the Intraseasonal Kelvin wave (ISKw) in the Pacific over the 1989‐2011 period, based on observations, a linear model and the outputs of an Ocean General Circulation Model (OGCM). We focus on the wave activity during the Central Pacific (CP) El Niño events contrasting with the extraordinary El Niño of 1997/1998. We find that ISKw activity is enhanced in Austral Summer (Spring) in the central Pacific (west of ~120°W) during CP El Niño events. The linear model experiment indicates that the Austral Summer peak is wind‐forced while the Austral Spring peak is not and consequently results from non‐linear processes. In addition, a strong dissipation of the ISKws is observed east of 120°W which cannot be accounted for by a linear model using a Rayleigh friction. A vertical and horizontal mode decomposition of the OGCM simulation further confirms the sharp changes in characteristics of the ISKws as well as the reflection of the latter into first‐meridional Rossby wave at the longitude where the maximum zonal gradient of the thermocline is found (~ 120°W). Our analysis suggests that the confinement of CP El Niño warming in the central Pacific may result from the reinforcement of the zonal gradient in stratification associated with the La Niña‐like conditions since the late of the 1990s, leading to scattering of the energy of the ISKws in the eastern Pacific.
      PubDate: 2014-09-02T03:27:05.514268-05:
      DOI: 10.1002/2014JC010044
       
  • Seasonal variability of primary production and phytoplankton biomass in
           the western Pacific subarctic gyre: Control by light availability within
           the mixed layer
    • Authors: Kazuhiko Matsumoto; Makio C. Honda, Kosei Sasaoka, Masahide Wakita, Hajime Kawakami, Shuichi Watanabe
      Pages: n/a - n/a
      Abstract: A distinct seasonal variation of primary production was revealed from shipboard observations conducted from 2005 to 2013 at time‐series station K2 in the western Pacific subarctic gyre (WSG). The mean depth‐integrated primary production was highest (569 ± 162 mg C m–2 d–1) in summer and lowest (101 ± 16 mg C m–2 d–1) in winter. Strong winter mixing enriched the mixed layer (ML) with nutrients that were not fully consumed during the remainder of the year, the result being that the WSG was a high‐nutrient, low‐chlorophyll (HNLC) region. The deep ML reduced primary production by reducing light availability in winter, whereas primary production was enhanced by strong light availability in the shallower ML as summer progressed. However, primary production was often attenuated by a reduction of light availability attributable to dense sea fog in summer. We found a significant relationship between primary production and light availability in this HNLC region. However, chlorophyll a was less variable seasonally than primary production. The highest depth‐integrated chlorophyll a was observed in summer (54.6 ± 13.4 mg m–2), but chlorophyll a remained high in winter (45.3 ± 7.7 mg m–2). Reduced light availability depressed primary production, but a reduction of the chlorophyll a concentration was prevented by a relaxation of grazing in the deep ML during winter. We found that light availability exerted an important control on the seasonal variability of primary production and phytoplankton biomass in the WSG.
      PubDate: 2014-09-02T03:26:09.433622-05:
      DOI: 10.1002/2014JC009982
       
  • Meteotsunami‐tide interactions and high‐frequency sea level
           oscillations in the eastern Yellow Sea
    • Authors: Byoung‐Ju Choi; Chorong Hwang, Sang‐Ho Lee
      Pages: n/a - n/a
      Abstract: While an air pressure jump was moving southeastward over the shallow water region of the eastern Yellow Sea in March 2007, a long ocean wave (meteotsunami) was generated and amplified due to the Proudman resonance. The long wave arrived at the coast during high tide with wave amplitude of 1.4 m and seawater overflew seawalls and inundated the land. High‐frequency sea level oscillations continued for 8‐9 hours after the long wave hit a local coast. The Moon's age was 12 days, and the tidal range was about 4 m between neap and spring tides. Two‐dimensional numerical simulations were performed, to reproduce amplification of the long ocean wave in offshore and oscillations of sea level at the coast. Both tidal elevation and tidal currents were found to affect the growth of the long wave amplitude by the interactions between tides and the long wave. Long wave‐tides interactions are important processes for the accurate prediction of long wave arrival time and maximum height and for the reduction of coastal hazards in the macro‐tidal region. After the long wave hit the coast of remote regions, reflected waves propagated radially from remote regions to a local coast. The high‐frequency sea level oscillations at a local observation station continued, until all of the reflected waves at remote regions had passed by. It was concluded that high‐frequency oscillations of sea level are generated not only by local reflection of the long wave, but also by propagation of the reflected waves from remote regions.
      PubDate: 2014-09-02T03:21:22.846231-05:
      DOI: 10.1002/2013JC009788
       
  • The impact of the assimilation of Aquarius sea surface salinity data in
           the GEOS Ocean Data Assimilation System
    • Authors: G. Vernieres; R. Kovach, C. Keppenne, S. Akella, L. Brucker, E. Dinnat
      Pages: n/a - n/a
      Abstract: Ocean salinity and temperature differences drive thermohaline circulations. These properties also play a key role in the ocean‐atmosphere coupling. With the availability of L‐band space‐borne observations, it becomes possible to provide global scale sea surface salinity (SSS) distribution. This study analyzes globally the along‐track (Level 2) Aquarius SSS retrievals obtained using both passive and active L‐band observations. Aquarius along‐track retrieved SSS are assimilated into the ocean data assimilation component of Version 5 of the Goddard Earth Observing System (GEOS‐5) assimilation and forecast model. We present a methodology to correct the large biases and errors apparent in Version 2.0 of the Aquarius SSS retrieval algorithm and map the observed Aquarius SSS retrieval into the ocean model’s bulk salinity in the topmost layer. The impact of the assimilation of the corrected SSS on the salinity analysis is evaluated by comparisons with in‐situ salinity measurements from Argo. The results show a significant reduction of the global biases and RMS of observations‐minus‐forecast differences at in‐situ locations. The most striking results are found in the tropics and southern latitudes. Our results highlight the complementary role and problems that arise during the assimilation of salinity information from in‐situ (Argo) and space‐borne SSS retrievals.
      PubDate: 2014-08-30T11:44:40.548264-05:
      DOI: 10.1002/2014JC010006
       
  • Polar Front around the Kerguelen Islands: An up‐to‐date
           determination and associated circulation of surface/subsurface waters
    • Authors: Young‐Hyang Park; Isabelle Durand, Elodie Kestenare, Gilles Rougier, Meng Zhou, Francesco d’Ovidio, Cédric Cotté, Jae‐Hak Lee
      Pages: n/a - n/a
      Abstract: The circulation of iron‐rich shelf waters around the Kerguelen Islands plays a crucial role for a climatically important, annually‐recurrent phytoplankton spring bloom over the sluggish shelf region and its downstream plume area along the Antarctic circumpolar flow. However, there is a long‐standing confusion about the Polar Front (PF) in the Kerguelen region due to diverse suggestions in the literature for its geographical location with an extreme difference over 10° of latitude. Based on abundant historical hydrographic data, the in situ hydrographic and current measurements during the 2011 KEOPS2 cruise, satellite chlorophyll images, and altimetry‐derived surface velocity fields, we determine and validate an up‐to‐date location of the PF around the Kerguelen Islands. Artificial Lagrangian particle trajectories computed from altimetric velocity time series are analysed for the possible pathways and sources of different surface/subsurface waters advected into the chlorophyll bloom area east off the islands studied during the KEOPS2 cruise. The PF location determined as the northernmost boundary of the Winter Water colder than 2°C, which is also associated with a band of strong currents, appears to be primarily controlled by topography. The PF rounds the Kerguelen Islands from the south to deflect northward along the eastern escarpment up to the northeastern corner of the Kerguelen Plateau before making its southward retroflection. It is shown that the major surface/subsurface waters found within the deep basin east of the Kerguelen Islands originate from the shelf around the Heard Island, rather than from the shallow shelf north of the Kerguelen Islands.
      PubDate: 2014-08-30T11:20:29.471501-05:
      DOI: 10.1002/2014JC010061
       
  • On the temporal memory of coastal upwelling off NW Africa
    • Authors: Aïssa Benazzouz; Josep L. Pelegrí, Herve Demarcq, Francisco Machín, Evan Mason, Abdellatif Orbi, Jesus Peña‐Izquierdo, Mordane Soumia
      Pages: n/a - n/a
      Abstract: We use a combination of satellite, in situ and numerical data to provide a comprehensive view of the seasonal coastal upwelling cycle off NW Africa in terms of both wind forcing and sea surface temperature (SST) response. Wind forcing is expressed in terms of both instantaneous (local) and time‐integrated (non‐local) indices, and the ocean response is expressed as the SST difference between coastal and offshore waters. The classical local index, the cross‐shore Ekman transport, reproduces reasonably well the time‐latitude distribution of SST differences but with significant time lags at latitudes higher than Cape Blanc. Two non‐local indices are examined. One of them, a cumulative index calculated as the backward averaged Ekman transport that provides the highest correlation with SST differences, reproduces well the timing of the SST differences at all latitudes (except near Cape Blanc). The corresponding time lags are close to zero south of Cape Blanc and range between two and four months at latitudes between Cape Blanc and the southern Gulf of Cadiz. The results are interpreted based on calculations of spatial and temporal auto‐ and cross‐correlations for wind forcing and SST differences. At temporal scales of 2‐3 weeks the along‐shore advection of along‐shore momentum compensates for interfacial friction, allowing the upwelling jet and associated frontal system to remain active. We conclude that the coastal jet plays a key role in maintaining the structure of coastal upwelling, even at times of relaxed winds, by introducing a seasonal memory to the system in accordance with the atmospheric‐forcing annual cycle.
      PubDate: 2014-08-30T11:17:16.417032-05:
      DOI: 10.1002/2013JC009559
       
  • Interannual variability of wintertime temperature on the inner continental
           shelf of the Middle Atlantic Bight
    • Authors: Thomas P. Connolly; Steven J. Lentz
      Pages: n/a - n/a
      Abstract: The shallow depth of the inner continental shelf allows for rapid adjustment of the ocean to air‐sea exchange of heat and momentum compared with offshore locations. Observations during 2001‐2013 are used to evaluate the contributions of air‐sea heat flux and oceanic advection to interannual variability of inner‐shelf temperature in the Middle Atlantic Bight. Wintertime processes are important for interpreting regional interannual variability at nearshore locations since winter anomalies account for 69–77% of the variance of the annual anomalies and are correlated over broad alongshelf scales, from New England to North Carolina. At the Martha's Vineyard Coastal Observatory on the 12‐m isobath, a heat budget is used to test the hypothesis that interannual differences in winter temperatures are due solely to air‐sea heat flux. Bimonthly averages of air‐sea heat flux are correlated with temporal changes in temperature, but overestimate the observed wintertime cooling. Velocity and satellite‐derived temperature data show that interannual variability in wintertime surface cooling is partially compensated for by alongshore advection of warmer water from the west at this particular location. It is also shown that surface heat flux is a strong function of air‐sea temperature difference. Because of this coupling between ocean and air temperatures in shallow water, along‐shelf advection can significantly modify the surface heat flux at seasonal and interannual time scales. While alongshelf advection at relatively small (˜100‐km) scales can be an important component of the heat budget over the inner shelf, interannual temperature variability is still largely determined by adjustment to large‐scale air‐temperature anomalies.
      PubDate: 2014-08-30T04:28:38.691208-05:
      DOI: 10.1002/2014JC010153
       
  • Seasonal salinity stratifications in the near‐surface layer from
           Aquarius, Argo, and an ocean model: Focusing on the tropical
           Atlantic/Indian Oceans
    • Authors: Jae‐Hong Moon; Y. Tony Song
      Pages: n/a - n/a
      Abstract: A newly available sea surface salinity (SSS) measurement from Aquarius/SAC‐D satellite reveals strong seasonal variability in the tropical Atlantic and Indian Oceans. The seasonal SSS variability at skin layer differs/agrees regionally in their amplitude from/with Argo‐measured salinity at 5 m depth and model salinity at the top layer, indicating various characteristics of near‐surface salinity stratifications. By comparing the three different salinity products, we have examined the near‐surface salinity stratifications with emphasis on the dynamical processes that differ from one region to another. Our analysis shows that for the western part of tropical Atlantic and southern tropical Indian, a large amount of river runoff and/or surface freshwater significantly stratifies the surface layer above 5m depth, resulting in the differences among the Aquarius, Argo and model. Differently for the southern Arabian Sea, the surface water can be mixed down to the depth of 5 m due to seasonally reversing currents driven by monsoons, resulting in an agreement among the datasets. The comparison suggests that dynamical differences can lead to different vertical salinity stratifications locally, which explain the differences between the Aquarius observations in the first cm of the sea surface, the Argo measurements at the 5m depth, and model’s representation of the surface‐layer averaged salinity.
      PubDate: 2014-08-26T11:12:06.537099-05:
      DOI: 10.1002/2014JC009969
       
  • ENSO‐driven interhemispheric Pacific mass transports
    • Authors: Shayne McGregor; Paul Spence, Franziska U. Schwarzkopf, Matthew H. England, Agus Santoso, William S. Kessler, Axel Timmermann, Claus W. Böning
      Pages: n/a - n/a
      Abstract: Previous studies have shown that ENSO’s anomalous equatorial winds, including the observed southward shift of zonal winds that occurs around the event peak, can be reconstructed with the first two Empirical Orthogonal Functions (EOFs) of equatorial region wind stresses. Using a high resolution Ocean General Circulation Model we investigate the effect of these two EOFs on changes in warm water volume (WWV), interhemispheric mass transports and Indonesian Throughflow (ITF). Wind stress anomalies associated with the first EOF produce changes in WWV that are dynamically consistent with the conceptual recharge oscillator paradigm. The ITF is found to heavily damp these WWV changes, reducing their variance by half. Wind stress anomalies associated with the second EOF, which depicts the southward wind shift, are responsible for WWV changes that are of comparable magnitude to those driven by the first mode. The southward wind shift is also responsible for the majority of the observed interhemispheric upper ocean mass exchanges. These winds transfer mass between the Northern and the Southern Hemisphere during El Niño events. Whilst water is transferred in the opposite direction during La Niña events, the magnitude of this exchange is roughly half of that seen during El Niño events. Thus, the discharging of WWV during El Niño events is meridionally asymmetric, while the WWV recharging during a La Niña event is largely symmetric. The inclusion of the southward wind shift is also shown to allow ENSO to exchange mass with much higher latitudes than that allowed by the first EOF alone.
      PubDate: 2014-08-26T11:12:00.726183-05:
      DOI: 10.1002/2014JC010286
       
  • Summertime Changjiang River plume variation during 1998–2010
    • Authors: Yan Bai; Xianqiang He, Delu Pan, Chen‐Tung Arthur Chen, Yan Kang, Xiaoyan Chen, Wei‐Jun Cai
      Pages: n/a - n/a
      Abstract: Using an improved satellite‐derived salinity algorithm in the East China Sea (ECS), we presented and examined a general view on summertime Changjiang River plume variation during 1998–2010. Three types of plume shapes were identified: 1) the commonly known northeastward transportation, 2) a case in which most of the plume water crossed the Cheju Strait into the Tsushima‐Korea Straits with only a small fraction staying on the shelf of the ECS, and 3) a rare case in which the plume front moved southeastward. Satellite time‐series data suggested that, during the peak river discharge time in July with favorable southwest monsoon, the plume area was highly correlated with the river discharge of the same month. Interestingly, the plume area in August was also dominated by the discharge in July. In August, as the direct effect of freshwater discharge weakening, the plume area also became positively correlated with wind speed in the 45o and 60odirection, suggesting that the plume extension was more influenced by the southwesterly wind during periods of smaller discharge. Furthermore, a few special cases with unique plume extensions were found under extreme weather conditions. Finally, we found no significant long‐term trend of plume area change over 1998–2010 in summertime and concluded that the interannual variation was probably regulated by natural variation rather than anthropogenic effects, such as construction of the Three Gorges Dam. This study will have implications for biogeochemical and modeling studies in large river plume areas.
      PubDate: 2014-08-26T11:08:08.287214-05:
      DOI: 10.1002/2014JC009866
       
  • Evaluation of directly wind‐coherent near‐inertial surface
           currents off Oregon using a statistical parameterization and analytical
           and numerical models
    • Authors: Sung Yong Kim; P. Michael Kosro, Alexander L. Kurapov
      Pages: n/a - n/a
      Abstract: Directly wind‐coherent near‐inertial surface currents off the Oregon coast are investigated with a statistical parameterization of observations and outputs of a regional numerical ocean model and three one‐dimensional analytical models including the slab layer, Ekman, and near‐surface averaged Ekman models. The transfer functions and response functions, statistically estimated from observed wind stress at NDBC buoys and surface currents derived from shoredbased high‐frequency radars, enable us to isolate the directly wind‐forced near‐inertial surface currents. Concurrent observations of the wind and currents are crucial to evaluate the directly wind‐forced currents. Thus, the wind stress and surface current fields obtained from a regional ocean model, which simulates variability of the wind and surface currents on scales comparable to those in observations, are analyzed with the same statistical parameterization to derive the point‐by‐point transfer functions and response functions. Model and data comparisons suggest that the regional ocean model describe near‐inertial variability of surface currents in quality and quantity correctly. The estimated response functions exhibit decay time scales in a range of 3 to 5 days, and about 40% of near‐inertial motions are explained by local wind stress. Among the one‐dimensional analytical models, the near‐surface averaged Ekman model explains the statistically derived wind‐current relationship better than other analytical models.
      PubDate: 2014-08-26T10:55:23.696434-05:
      DOI: 10.1002/2014JC010115
       
  • Distribution of vertical velocity inferred from secondary flow in a curved
           tidal channel
    • Authors: P. Russell; R. Vennell
      Pages: n/a - n/a
      Abstract: High resolution observations from the curved tidal channel of the Otago Harbour show secondary flows up to 20 % of the primary flow and vertical velocity inferred from secondary flow up to 1% of the primary flow. This vertical velocity is inferred on a much finer scale than previous works. The spatial pattern of this vertical velocity is upwards on the inside and downwards on the outside of the bend, consistent with previous laboratory flume measurements. Linear regression, rp = 0.95, shows the cross‐channel distribution of the observed secondary flow can be resolved from the horizontal ADCP measurements well enough to be consistent with the cross‐channel distribution of secondary flow derived from the observed primary flow using the model of Kalkwijk and Booij [1986]. Linear regression, rp = 0.80, shows the vertical velocity inferred from observed secondary flow is consistent with vertical velocity derived from the observed primary flow using the model of Kalkwijk and Booij [1986]. This also shows the cross‐channel distribution of the observed secondary flow is resolved well enough from the horizontal ADCP measurements to be able to infer the vertical velocity from mass continuity. The required horizontal resolution is made possible by Radial Basis Function (RBF) smoothing and spatial interpolation that allows for continuity of the spatial derivatives. Modeling trajectories using channel dimensions and velocity field values equivalent to the observations show that 3‐dimensional secondary circulation forms a loose helical flow pattern.
      PubDate: 2014-08-26T10:53:10.901529-05:
      DOI: 10.1002/2014JC010003
       
  • Direct velocity observations of volume flux between Iceland and the
           Shetland Islands
    • Authors: Katelin H. Childers; Charles N. Flagg, Thomas Rossby
      Pages: n/a - n/a
      Abstract: Atlantic Waters flowing northward into the Nordic Seas are important for their role as an early indicator of changes to deepwater formation. As such this requires a fundamental understanding of the pathways and volume fluxes through the primary passageways from the Atlantic into the Nordic Seas. A mean annual volume transport of 6.1±0.3 Sv was observed flowing in above the σt =27.8 isopycnal (a proxy for the lower limit of Atlantic Water depth), through the Faroe Shetland Channel (FSC) and over the Iceland Faroes Ridge (IFR) from March 2008 through June 2012, using repeat velocity sections obtained from a vessel mounted Acoustic Doppler Current Profiler (ADCP). A new vessel route has expanded the spatial coverage of FSC observations and reveals a difference in average inflow transport, which most likely results from an interannual variation in the total transport through the FSC, which in turn is tied to a weakening of the southerly flow over the western slope of the channel. This interannual variability has increased the mean transport through the FSC from 0.9 Sv observed over the first two years of this program by Rossby and Flagg [2012] to a 4.5 year mean of 1.7±0.2 Sv, which emphasizes the importance of knowing the flow along the Faroese shelf. Interannual fluctuations in transport observed over the IFR are related to the width of the inflow over the Faroese half of the ridge.
      PubDate: 2014-08-25T10:12:37.453855-05:
      DOI: 10.1002/2014JC009946
       
  • Storm tracks in the Southern Hemisphere subtropical oceans
    • Authors: T. J. O’Kane; R. J. Matear, M. A. Chamberlain, E. C. J. Oliver, N. J. Holbrook
      Pages: n/a - n/a
      Abstract: Ocean storm tracks have previously been associated with the mid‐latitude western boundary currents (WBCs) and the Antarctic Circumpolar Current (ACC). Here we identify and examine large‐scale baroclinically unstable waves occurring within waveguides associated with potential density gradients in the subtropical regions of the Southern Hemisphere (SH) oceans where the trade winds and westerlies meet and at depths associated with mode water formation. In contrast to the Northern Hemisphere subtropics, the SH pathways are more extensive allowing large scale coherent disturbances to communicate information westward from the mid‐latitudes to the subtropics (South Pacific Ocean) and from the subtropics to the tropics (Indian Ocean). Particular consideration is given to the subtropical South Pacific Ocean as this is a region where resonant interactions between large‐scale Rossby waves and significant topographic features have been reported to occur. Using an ocean general circulation model and a simple potential energy transfer diagnostic we identify the relevant nonlinearly modified structures comparing their propagation characteristics to planetary Rossby waves calculated using a shallow water model. Although at first appearance baroclinic disturbances resemble planetary Rossby waves, we show they are inherently nonlinear, multi‐scale and are amplified where topography occurs. The location of the disturbances coincides with regions of high variability in sea surface height observed in satellite altimetry and their speeds closely match the large‐scale coherent westward propagating structures described in the observational literature. Our study provides evidence that, in addition to the mid‐latitude WBCs and the ACC, significant ocean storm tracks are also manifest in the SH subtropics.
      PubDate: 2014-08-23T04:43:21.763814-05:
      DOI: 10.1002/2014JC009990
       
  • Interannual variability of the eastward current in the western South China
           Sea associated with the summer Asian monsoon
    • Authors: Changlin Chen; Guihua Wang
      Pages: n/a - n/a
      Abstract: The interannual variability of the eastward current in the western South China Sea (SCS) during the summer of 1993‐2012 is examined with satellite altimeter data and Regional Ocean Modeling System (ROMS) model output. It is found that the meridional location of the eastward current displays apparent interannual variability. The core of the eastward currentshifts between 10.7°N and 17.6°N with a standard deviation of 1.6°. Results from Sverdrup theory and ROMS experiments demonstrate a close dynamic linkage between the north‐south migration of the eastward current and the SCS summer monsoon anomaly on the interannual time scale. When the summer monsoon has southwesterly (northeasterly) anomaly, the eastward current moves southward (northward). With the southward (northward) shift of the eastward current, the summer cold filament in the SCS moves southward (northward) as well.
      PubDate: 2014-08-23T04:40:28.57138-05:0
      DOI: 10.1002/2014JC010309
       
  • The diurnal salinity cycle in the tropics
    • Authors: Kyla Drushka; Sarah T. Gille, Janet Sprintall
      Pages: n/a - n/a
      Abstract: Observations from 35 tropical moorings are used to characterize the diurnal cycle in salinity at 1‐m depth. The amplitude of diurnal salinity anomalies is up to 0.01 psu and more typically ~0.005 psu. Diurnal variations in precipitation and vertical entrainment appear to be the dominant drivers of diurnal salinity variability, with evaporation also contributing. Areas where these processes are strong are expected to have relatively strong salinity cycles: the eastern Atlantic and Pacific equatorial regions, the southwestern Bay of Bengal, the Amazon outflow region, and the Indo‐Pacific warm pool. We hypothesize that salinity anomalies resulting from precipitation and evaporation are initially trapped very near the surface and may not be observed at the 1‐m instrument depths until they are mixed downward. As a result, the pattern of diurnal salinity variations is not only dependent on the strength of the forcing terms, but also on the phasing of winds and convective overturning. A comparison of mixed‐layer depth computed with hourly and with daily‐averaged salinity reveals that diurnal salinity variability can have a significant effect on upper‐ocean stratification, suggesting that representing diurnal salinity variability could potentially improve air‐sea interaction in climate models. Comparisons between salinity observations from moorings and from the Aquarius satellite (level 2 version 2.5.1 data) reveal that the typical difference between ascending‐node and descending‐node Aquarius salinity is an order of magnitude greater than the observed diurnal salinity anomalies at 1‐m depth.
      PubDate: 2014-08-23T04:38:16.525451-05:
      DOI: 10.1002/2014JC009924
       
  • The emission and scattering of L‐band microwave radiation from rough
           ocean surfaces and wind speed measurements from the Aquarius sensor
    • Authors: Thomas Meissner; Frank J. Wentz, Lucrezia Ricciardulli
      Pages: n/a - n/a
      Abstract: In order to achieve the required accuracy in sea surface salinity (SSS) measurements from L‐band radiometers such as the Aquarius/SAC‐D or SMOS (Soil Moisture and Ocean Salinity) mission, it is crucial to accurately correct the radiation that is emitted from the ocean surface for roughness effects. We derive a geophysical model function (GMF) for the emission and backscatter of L‐band microwave radiation from rough ocean surfaces. The analysis is based on radiometer brightness temperature and scatterometer backscatter observations both taken on board Aquarius. The data are temporally and spatially collocated with wind speeds from WindSat and F17 SSMIS (Special Sensor Microwave Imager Sounder) and wind directions from NCEP (National Center for Environmental Prediction) GDAS (Global Data Assimilation System). This GMF is the basis for retrieval of ocean surface wind speed combining L‐band H‐pol radiometer and HH‐pol scatterometer observations. The accuracy of theses combined passive/active L‐band wind speeds matches those of many other satellite microwave sensors. The L‐band GMF together with the combined passive/active L‐band wind speeds are utilized in the Aquarius SSS retrieval algorithm for the surface roughness correction. We demonstrate that using these L‐band wind speeds instead of NCEP wind speeds leads to a significant improvement in the SSS accuracy. Further improvements in the roughness correction algorithm can be obtained by adding VV‐pol scatterometer measurements and wave height (WH) data into the GMF.
      PubDate: 2014-08-23T04:05:33.650966-05:
      DOI: 10.1002/2014JC009837
       
  • Effect of mesoscale eddies and streamers on sardine spawning habitat and
           recruitment success off southern and central California
    • Authors: Karen Nieto; Sam McClatchie, Edward D. Weber, Cleridy E. Lennert‐Cody
      Pages: n/a - n/a
      Abstract: We quantified the effect of mesoscale eddies and streamers on the spatial distribution of Pacific sardine spawning habitat using a merged altimetry dataset and a statistical spawning habitat model. The distribution of eggs could be predicted using sea‐surface temperature, chlorophyll concentration, and eddy kinetic energy (EKE) similarly to previous studies. Eddies alone did not have a significant additional or emergent effect on the probability of capturing eggs beyond these predictors. Rather, mesoscale features (eddies and streamers) entrained water with the appropriate conditions in terms of temperature, chlorophyll, and EKE. These dynamic features moved appropriate spawning habitat for sardine offshore to areas where appropriate habitat otherwise would not exist. Using centroids of predicted sardine habitat, we showed that sardine recruitment success was inversely correlated with distance from shore of predicted sardine habitat centroids. This indicates that offshore transport has a negative effect on sardine recruitment, despite expanding favorable spawning habitat further offshore.
      PubDate: 2014-08-22T04:19:02.575041-05:
      DOI: 10.1002/2014JC010251
       
  • Quad‐polarization SAR features of ocean currents
    • Authors: V. Kudryavtsev; I. Kozlov, B. Chapron, J. A. Johannessen
      Pages: n/a - n/a
      Abstract: A methodology is demonstrated to exploit the polarization sensitivity of high‐resolution radar measurements to interpret and quantify upper ocean dynamics. This study particularly illustrates the potential of quad‐polarization synthetic aperture radar (SAR) measurements. The analysis relies on essential characteristics of the electromagnetic scattering mechanisms and hydrodynamical principles. As the relaxation scale of centimeter‐scale ocean surface scatters is typically small, radar signal anomalies associated with surface manifestations of the upper ocean dynamics on spatial scales exceeding 100 m are mostly dominated by non‐resonant and non‐polarized scatters. These “scalar” contributions can thus efficiently trace local breaking and near‐breaking areas, caused by surface current variations. Using dual co‐polarized measurements, the polarized Bragg‐type radar scattering is isolated by considering the difference (PD) between vertically and horizontally polarized radar signals. The non‐polarized (NP) contribution associated with wave breaking is then deduced, using the measured polarization ratio (PR) between polarized signals. Considering SAR scenes depicting various surface manifestations of the upper ocean dynamics (internal waves, meso‐scale surface current features, SST front), the proposed methodology and set of decompositions (PD, PR, NP) efficiently enable the discrimination between surface manifestation of upper ocean dynamics and wind field variability. Applied to quad‐polarized SAR images, such decompositions further provide unique opportunities to more directly assess the cross‐polarized (CP for HV or VH) signal sensitivity to surface roughness changes. As demonstrated, such an analysis unambiguously demonstrates and quantitatively evaluates the relative impact of breakers on cross‐polarized signals under low to moderate wind conditions.
      PubDate: 2014-08-21T04:03:42.140894-05:
      DOI: 10.1002/2014JC010173
       
  • Winter sea ice melting in the Atlantic Water subduction area, Svalbard
           Norway
    • Authors: V. Tverberg; O. A. N⊘st, C. Lydersen, K. M. Kovacs
      Pages: n/a - n/a
      Abstract: Herein we study a small area along the shelf west of Spitsbergen, near Prins Karls Forland, where warm, saline Atlantic Water of the West Spitsbergen Current currently first encounters sea ice. This sea ice is drifting in a coastal current that carries Arctic Water originating from the Barents Sea northward over the shelf. Our aim was to investigate whether melting of sea ice by Atlantic Water in this area might be a significant factor that could contribute to the formation of a cold halocline layer that isolates the sea ice from further melting from below. Observations of temperature and salinity profiles were collected during two winters, via CTD‐SRDL instruments deployed on harbor seals (Phoca vitulina), and fed into a heat and freshwater budget box model in order to quantify the importance of melting relative to other processes that could transform the shelf water mass during winter. Cross frontal exchange of Atlantic Water from the West Spitsbergen Current, driven by buoyancy forcing rather than Ekman upwelling, was determined to be the source of the heat that melted drift ice on the shelf. Some local sea ice formation did take place, but its importance in the total heat and freshwater budgets appeared to be minor. The data suggest that the production of a cold halocline layer was preceded by southerly winds and rapid drift ice melting.
      PubDate: 2014-08-21T03:54:07.624775-05:
      DOI: 10.1002/2014JC010013
       
  • Hydrography and circulation in the Filchner Depression, Weddell Sea,
           Antarctica
    • Authors: E. Darelius; K. Makinson, K. Daae, I. Fer, P. R. Holland, K. W. Nicholls
      Pages: n/a - n/a
      Abstract: Cold and dense Ice Shelf Water (ISW) emerging from the Filchner‐Ronne Ice Shelf cavity in the southwestern Weddell Sea flows northward through the Filchner Depression to eventually descend the continental slope and contribute to the formation of bottom water. New ship‐born observations of hydrography and currents from Filchner Depression in January 2013 suggest that the northward flow of ISW takes place in a mid‐depth jet along the eastern flank of the depression, thus questioning the traditional view with outflow along the western flank. This interpretation of the data is supported by results from a regional numerical model, which shows that ISW flowing northward along the eastern coast of Berkner Island turns eastward and crosses the depression to its eastern side upon reaching the Filchner ice front. The ice front represents a sudden change in the thickness of the water column and thus a potential vorticity barrier. Transport estimates of northward ISW flux based on observations ranges from 0.2‐1.0 Sv.
      PubDate: 2014-08-20T04:27:38.782472-05:
      DOI: 10.1002/2014JC010225
       
  • Water mass analysis of the Coral Sea through an Optimum Multiparameter
           method
    • Authors: Florent Gasparin; Christophe Maes, Joel Sudre, Veronique Garcon, Alexandre Ganachaud
      Pages: n/a - n/a
      Abstract: A water mass analysis of the Coral Sea thermocline waters provides a description of their distribution, pathways and mixture based on recent oceanographic cruises in this region of strong western boundary currents. The Optimum Multiparameter method is used to determine the relative contribution of core water masses based on their measured temperature, salinity and dissolved oxygen. The thermocline waters, carried by the broad South Equatorial Current (SEC), are essentially composed of four core water masses of different origins. Coming from the south, the South Pacic Tropical Water South (SPTWS, σ=25.3 kg.m−3) and the Western South Pa‐cic Central Water (WSPCW, σ=26.3 kg.m−3) enter the Coral Sea by the channel between the island of New Caledonia and the Vanuatu archipelago. Coming from the north, the South Pacic Tropical Water North (SPTWN, σ=24.5 kg.m−3) and the Pacic Equatorial Water (PEW, σ=26.3 kg.m−3) flow north of Vanuatu. The upper thermocline water that exits the Coral Sea equatorward, is mainly composed of SPTWN carried by the New Guinea Coastal Undercurrent. In contrast, upper thermocline waters exiting the Coral Sea poleward, in the East Australian Current, is dominated by SPTWS. The relative contributions are different in the lower thermocline where WSPCW dominates both western boundary currents. This refined description is consistent with the dynamics of the main currents, with a very strong depth dependence in the partitioning of incoming SEC waters.
      PubDate: 2014-08-19T03:41:16.580798-05:
      DOI: 10.1002/2014JC010246
       
  • Seasonal surface layer dynamics and sensitivity to runoff in a high Arctic
           fjord (Young Sound/Tyrolerfjord, 74°N)
    • Authors: Jørgen Bendtsen; John Mortensen, Søren Rysgaard
      Pages: n/a - n/a
      Abstract: Runoff from the Greenland Ice Sheet, local glaciers and snow melt along the northeastern Greenland coastline has a significant impact on coastal water masses flowing south towards Denmark Strait. Very few direct measurements of runoff currently exist in this large area and the water masses near the coast are also difficult to measure due to the presence of icebergs and sea ice. Measurements from the Zackenberg Research station, located in Young Sound/Tyrolerfjord in northeast Greenland (74° N), provide some of the few observations of hydrographic, hydrologic and atmospheric parameters from this remote area. Here we analyze measurements from the fjord and also measurements in the ambient water masses which are found in the outer fjord and between the fjord and the East Greenland Current and validate and apply a numerical model of the fjord. A model sensitivity study allows us to constrain runoff estimates for the area.We also show that a total runoff between 0.9 ‐ 1.4 km3 in 2006 is in accordance with observed surface salinities and calculated freshwater content in the fjord. This indicates that earlier reported runoff to the area is significantly underestimated and that melt from glaciers and the Greenland Ice Sheet in this region may be up to 50% larger than the current estimate. Model simulations indicate the presence of a cold low‐saline coastal water mass formed by runoff from fjords north of the Young Sound/Tyrolerfjord system. Simulations of passive and age tracers show that residence time of river water during the summer period is about one month in the inner part of the fjord.
      PubDate: 2014-08-19T03:37:54.431675-05:
      DOI: 10.1002/2014JC010077
       
  • Southern Ocean CO2 sink: The contribution of the sea ice
    • Authors: Bruno Delille; Martin Vancoppenolle, Nicolas‐Xavier Geilfus, Bronte Tilbrook, Delphine Lannuzel, Véronique Schoemann, Sylvie Becquevort, Gauthier Carnat, Daniel Delille, Christiane Lancelot, Lei Chou, Gerhard S. Dieckmann, Jean‐Louis Tison
      Pages: n/a - n/a
      Abstract: We report first direct measurements of the partial pressure of CO2 (pCO2) within Antarctic pack sea ice brines and related CO2 fluxes across the air‐ice interface. From late winter to summer, brines encased in the ice change from a CO2 large over‐saturation, relative to the atmosphere, to a marked under‐saturation while the underlying oceanic waters remains slightly oversaturated. The decrease from winter to summer of pCO2 in the brines is driven by dilution with melting ice, dissolution of carbonate crystals and net primary production. As the ice warms, its permeability increases, allowing CO2 transfer at the air‐sea ice interface. The sea ice changes from a transient source to a sink for atmospheric CO2. We upscale these observations to the whole Antarctic sea ice cover using the NEMO‐LIM3 large‐scale sea ice‐ocean, and provide first estimates of spring and summer CO2 uptake from the atmosphere by Antarctic sea ice. Over the spring‐summer period, the Antarctic sea ice cover is a net sink of atmospheric CO2 of 0.029 PgC, about 58% of the estimated annual uptake from the Southern Ocean. Sea ice then contributes significantly to the sink of CO2 of the Southern Ocean.
      PubDate: 2014-08-19T03:26:32.244071-05:
      DOI: 10.1002/2014JC009941
       
  • Drivers of variability in Arctic sea‐ice drift speed
    • Authors: Einar Olason; Dirk Notz
      Pages: n/a - n/a
      Abstract: We explore the main drivers of seasonal and long‐term variations in basin‐scale Arctic sea‐ice drift speed. To do so, we examine the relationship between the observed time‐varying area‐mean ice drift‐speed in the central Arctic and observed thickness and concentration as well as surface wind‐stress. Drift speeds are calculated from the positions of drifting buoys, thickness is based on submarine observations, concentration on satellite observations and the wind stress comes from a global reanalysis. We find that seasonal changes in drift speed are correlated primarily with changes in concentration when concentration is low and with changes in thickness otherwise. The correlation between drift speed and concentration occurs because changing concentration changes how readily the ice responds to the synoptic‐scale forcing of the atmosphere. Drift speed is correlated with neither concentration nor thickness in April and May. We show this behaviour to be correlated with a decrease in the localisation of deformation. This indicates that the increase in drift speed is caused by newly formed fractures not refreezing, leading to an overall reduced ice‐cover strength without a detectable change in ice concentration. We show that a strong long‐term trend exists in months of relatively low ice concentration. Using our analysis of the seasonal cycle we show that the trend in concentration drives a significant portion of the drift‐speed trend, possibly reinforced by a trend in cyclone activity. Hence, the trend in drift‐speed in this period is primarily caused by increased synoptic‐scale movement of the ice pack.
      PubDate: 2014-08-19T03:17:12.3387-05:00
      DOI: 10.1002/2014JC009897
       
  • Simulating extreme total water levels using a time‐dependent,
           extreme value approach
    • Authors: Katherine A. Serafin; Peter Ruggiero
      Pages: n/a - n/a
      Abstract: Coastal flood hazard zones and the design of coastal defenses are often devised using the maximum recorded water level or a ‘design' event such as the 100‐year return‐level, usually projected from observed extremes. Despite technological advances driving more consistent instrumental records of waves and water levels, the observational record may be short, punctuated with intermittent gaps, and vary in quality. These issues in the record often preclude accurate and robust estimates of extreme return‐level events. Here we present a total water level full simulation model (TWL‐FSM) that simulates the various components of TWLs (waves, tides, and non‐tidal residuals) in a Monte Carlo sense, taking into account conditional dependencies that exist between the various components. Extreme events are modeled using non‐stationary extreme value distributions that include seasonality and climate variability. The resulting synthetic TWLs allow for empirical extraction of return level events and the ability to more robustly estimate and assess present‐day flood and erosion hazards. The approach is demonstrated along a northern Oregon, USA littoral cell but is applicable to beaches anywhere wave and water level records or hindcasts are available. Simulations result in extreme 100‐year TWL return‐levels as much as 1 m higher than those extrapolated from the “observational” record. At the Oregon site, this would result in 30% more coastal flooding than the “observational” 100‐year TWL return‐level projections. More robust estimates of extreme TWLs and tighter confidence bounds on return level events can aid coastal engineers, managers, and emergency planners in evaluating exposure to hazards.
      PubDate: 2014-08-19T03:10:22.928777-05:
      DOI: 10.1002/2014JC010093
       
  • Low calcium carbonate saturation state in an Arctic inland sea having
           large and varying fluvial inputs: The Hudson Bay system
    • Authors: Kumiko Azetsu‐Scott; Michel Starr, Zhi‐Ping Mei, Mats Granskog
      Pages: n/a - n/a
      Abstract: The Hudson Bay system (HBS) is a shallow inland sea in the Arctic, composed of Hudson Strait, Foxe Basin/Channel, James Bay and Hudson Bay. Dissolved inorganic carbon (DIC) and total alkalinity (TA) measurements were used to investigate the state of ocean acidification, specifically calcium carbonate saturation states (Ω) and pH. The freshwater sources were identified from the relationship between oxygen isotope composition (δ18O) and salinity to understand the role of freshwater in ocean acidification. The saturation state of seawater with respect to calcium carbonate (Ω) in surface water (2300 µmol/kg) were observed in the depths of central Hudson Bay with a pHtotal of 7.49 and Ωarg of 0.37. Over 67% and 22% of the bottom water of Hudson Bay was undersaturated with respect to aragonite and calcite respectively, despite Hudson Bay being very shallow (less than 250m deep). The aragonite saturation horizon in the central Hudson Bay was around 50m.
      PubDate: 2014-08-14T03:23:18.857362-05:
      DOI: 10.1002/2014JC009948
       
  • Scaling and stochastic cascade properties of NEMO oceanic simulations and
           their potential value for GCM evaluation and downscaling
    • Authors: Sébastien Verrier; Michel Crépon, Sylvie Thiria
      Pages: n/a - n/a
      Abstract: Spectral scaling properties have already been evidenced on oceanic numerical simulations and have been subject to several interpretations. They can be used to evaluate classical turbulence theories that predict scaling with specific exponents and to evaluate the quality of GCM outputs from a statistical and multiscale point of view. However, a more complete framework based on multifractal cascades is able to generalize the classical but restrictive second‐order spectral framework to other moment orders, providing an accurate description of probability distributions of the fields at multiple scales. The predictions of this formalism still needed systematic verification in oceanic GCM while they have been confirmed recently for their atmospheric counterparts by several papers. The present paper is devoted to a systematic analysis of several oceanic fields produced by the NEMO oceanic GCM. Attention is focused to regional, idealized configurations that permit to evaluate the NEMO engine core from a scaling point of view regardless of limitations involved by land masks. Based on classical multifractal analysis tools, multifractal properties were evidenced for several oceanic state variables (sea surface temperature and salinity, velocity components…). While first order structure functions estimated a different non‐conservativity parameter H in two scaling ranges, the multi‐order statistics of turbulent fluxes were scaling over almost the whole available scaling range. This multifractal scaling was then parameterized with the help of the Universal Multifractal framework, providing parameters that are coherent with existing empirical literature. Finally, we argue that the knowledge of these properties may be useful for oceanographers. The framework seems very well suited for the statistical evaluation of OGCM outputs. Moreover, it also provides practical solutions to simulate sub‐pixel variability stochastically for GCM downscaling purposes. As an independent perspective, the existence of multifractal properties in oceanic flows seems also interesting for investigating scale‐dependencies in remote‐sensing inversion algorithms.
      PubDate: 2014-08-14T02:57:58.50133-05:0
      DOI: 10.1002/2014JC009811
       
  • Temporal and spatial variability of tidal‐fluvial dynamics in the
           St. Lawrence fluvial estuary: An application of nonstationary tidal
           harmonic analysis
    • Authors: Pascal Matte; Yves Secretan, Jean Morin
      Pages: n/a - n/a
      Abstract: Predicting tides in upstream reaches of rivers is a challenge, because tides are highly nonlinear and nonstationary, and accurate short‐time predictions of river flow are hard to obtain. In the St. Lawrence fluvial estuary, tide forecasts are produced using a one‐dimensional model (ONE‐D), forced downstream with harmonic constituents and upstream with daily discharges using 30‐day flow forecasts from Lake Ontario and the Ottawa River. Although this operational forecast system serves its purpose of predicting water levels, information about nonstationary tidal‐fluvial processes that can be gained from it is limited, particularly the temporal changes in mean water level and tidal properties (i.e. constituent amplitudes and phases), which are function of river flow and ocean tidal range. In this paper, a harmonic model adapted to nonstationary tides, NS_TIDE, was applied to the St. Lawrence fluvial estuary, where the time‐varying external forcing is directly built into the tidal basis functions. Model coefficients from 13 analysis stations were spatially interpolated to allow tide predictions at arbitrary locations as well as to provide insights into the spatiotemporal evolution of tides. Model hindcasts showed substantial improvements compared to classical harmonic analyses at upstream stations. The model was further validated by comparison with ONE‐D predictions at a total of 32 stations. The slightly lower accuracy obtained with NS_TIDE is compensated by model simplicity, efficiency and capacity to represent stage and tidal variations in a very compact way, and thus represents a new means for understanding tidal rivers.
      PubDate: 2014-08-14T02:52:13.611913-05:
      DOI: 10.1002/2014JC009791
       
  • Formation of fine sediment deposit from a flash flood river in the
           Mediterranean Sea
    • Authors: Manel Grifoll; Vicenç Gracia, Alfredo Aretxabaleta, Jorge Guillén, Manuel Espino, John C. Warner
      Pages: n/a - n/a
      Abstract: We identify the mechanisms controlling fine deposits on the inner‐shelf in front of the Besòs River, in the northwestern Mediterranean Sea. This river is characterized by a flash flood regime discharging large amounts of water (more than twenty times the mean water discharge) and sediment in very short periods lasting from hours to few days. Numerical model output was compared with bottom sediment observations and used to characterize the multiple spatial and temporal scales involved in offshore sediment deposit formation. A high‐resolution (50 m grid size) coupled hydrodynamic‐wave‐sediment transport model was applied to the initial stages of the sediment dispersal after a storm‐related flood event. After the flood, sediment accumulation was predominantly confined to an area near the coastline as a result of preferential deposition during the final stage of the storm. Subsequent reworking occurred due to wave‐induced bottom shear stress that resuspended fine materials, with seaward flow exporting them towards the mid‐shelf. Wave characteristics, sediment availability and shelf circulation determined the transport after the reworking, and the final sediment deposition location. One‐year simulations of the regional area revealed a prevalent southwestward average flow with increased intensity downstream. The circulation pattern was consistent with the observed fine‐deposit depocenter being shifted southwards from the river mouth. At the southern edge, bathymetry controlled the fine deposition by inducing near‐bottom flow convergence enhancing bottom shear stress. According to the short term and long term analyses a seasonal pattern in the fine deposit formation is expected.
      PubDate: 2014-08-14T02:40:25.707666-05:
      DOI: 10.1002/2014JC010187
       
  • Wind‐modulated buoyancy circulation over the Texas‐Louisiana
           shelf
    • Authors: Zhaoru Zhang; Robert Hetland, Xiaoqian Zhang
      Pages: n/a - n/a
      Abstract: This numerical investigation examines buoyancy‐driven circulation on the Texas‐Louisiana shelf modulated by seasonal winds. In wintertime, with downcoast (in the direction of Kelvin wave propagation) wind forcing, the Mississippi‐Atchafalaya River plume exhibits a bottom‐advected pattern. The plume is fairly wide and the horizontal density gradients span almost across the entire shelf inshore of 50m. Within the plume, vertical shear of alongshore flow is in thermal wind balance with the cross‐shore density gradient, and the shear causes a slight reversal of alongshore flow near the bottom. An alongshore flow estimated by the thermal wind relation, along with an assumption of zero bottom velocity, generally well agrees with the actual flow near the surface in regions deeper than 20 m. In spring and summer, the thermal‐wind‐balance‐derived flow deviates from the actual alongshore flow, and an Ekman flow driven by strong onshore wind makes the major contribution to the deviation. Besides, the summertime upcoast wind component transforms the plume to a surface‐advected state, resulting in reduced cross‐shore density gradients and increasing the relative importance of wind‐driven, barotropic alongshore flow, which contributes to the remaining deviation.
      PubDate: 2014-08-14T02:38:49.412571-05:
      DOI: 10.1002/2013JC009763
       
  • Pathways of basal meltwater from Antarctic ice shelves: A model study
    • Authors: Kazuya Kusahara; Hiroyasu Hasumi
      Pages: n/a - n/a
      Abstract: We investigate spreading pathways of basal meltwater released from all Antarctic ice shelves using a circumpolar coupled ice shelf‐sea ice‐ocean model that reproduces major features of the Southern Ocean circulation, including the Antarctic Circumpolar Current (ACC). Several independent virtual tracers are used to identify detailed pathways of basal meltwaters. The spreading pathways of the meltwater tracers depend on formation sites because the meltwaters are transported by local ambient ocean circulation. Meltwaters from ice shelves in the Weddell and Amundsen—Bellingshausen Seas in surface/subsurface layers are effectively advected to lower latitudes with the ACC. Although a large portion of the basal meltwaters is present in surface and subsurface layers, a part of the basal meltwaters penetrates into the bottom layer through active dense water formation along the Antarctic coastal margins. The signals at the seafloor extend along the topography, showing a horizontal distribution similar to the observed spreading of Antarctic Bottom Water. Meltwaters originating from ice shelves in the Weddell and Ross Seas and in the Indian sector significantly contribute to the bottom signals. A series of numerical experiments in which thermodynamic interaction between the ice shelf and ocean is neglected regionally demonstrates that the basal meltwater of each ice shelf impacts sea ice and/or ocean thermohaline circulation in the Southern Ocean.
      PubDate: 2014-08-12T02:39:34.773313-05:
      DOI: 10.1002/2014JC009915
       
  • Interannual variability of the Kuroshio onshore intrusion along the East
           China Sea shelf break: Effect of the Kuroshio volume transport
    • Authors: Chuanyu Liu; Fan Wang, Xinping Chen, Jin‐Song von Storch
      Pages: n/a - n/a
      Abstract: The interannual variability of the Kuroshio onshore intrusion (KOI) across the East China Sea (ECS) shelf break and its response to the ECS Kuroshio volume transport (KVT) during 1993~2010 are studied based on a high resolution, real time and global ocean general circulation model. Since variability of KVT is mainly determined in the interior Pacific, it is rather a remote than a local factor for the local ECS KOI. On interannual time scales, KVT affects KOI not only in the net volume transport across the entire shelf break but also in the spatial pattern along the shelf break. When KVT increases, the intrusion decreases (increases) upstream (downstream) of the major intrusion region northeast of Taiwan, the retreating increases (decreases) upstream (downstream) of the main veering region southwest of Kyushu. These patterns are caused by cyclonic eddies induced by the seaward deflection of the Kuroshio axis from the shelf break, which ultimately results from the KVT increase. A diagnostic mechanism of KOI ~ M sin(θ) h–1 is proposed, where h is the bottom depth, θ is the angle between isobaths and the vertically averaged current, and M is the absolute volume transport at the shelf break. θ is large in the major intrusion/retreating regions and stable on interannual time scales while M changes with opposite signs between upstream and downstream of the major intrusion/retreating regions. The mechanism explains well the relation of local KVT and the spatial pattern of KOI along the shelf break, in both the mean state and the interannual variations.
      PubDate: 2014-08-08T11:59:35.237931-05:
      DOI: 10.1002/2013JC009653
       
  • Layered mixing on the New England Shelf in summer
    • Authors: Jianing Wang; Blair J. W. Greenan, Youyu Lu, Neil S. Oakey, William J. Shaw
      Pages: n/a - n/a
      Abstract: The layered structure of stratification and mixing on the New England Shelf (NES) in summer is examined by analyzing a comprehensive set of observations of hydrography, currents and turbulence. A clear distinction in mixing characteristics between the mid‐column water (consisting of sub‐surface stratification, mid‐depth weak stratification and lower‐layer stratification) and a well‐mixed bottom boundary layer (BBL) is revealed. The combination of subtidal Ekman onshore bottom transport and cross‐shore density gradient created a lower‐layer stratification that inhibited the upward extension of the BBL turbulence. The BBL mixing was related to strong shear generated by bottom stress, and the magnitude and periodic variation of BBL mixing was determined by both the tidal and subtidal flows. Mixing in the mid‐column water occurred under stably‐stratified conditions and showed correspondence with the occurrence of near‐inertial and semi‐diurnal internal waves. Positive correlations between buoyancy frequency squared (N2) and shear variance (S2), S2 and dissipation rate (ε), N2 and ε are established in the mid‐column, but not in the BBL. The mid‐column ε was reasonably described by a slightly modified MacKinnon‐Gregg (MG) model.
      PubDate: 2014-08-07T04:37:56.573516-05:
      DOI: 10.1002/2014JC009947
       
  • Validation of Aquarius sea surface salinity with in situ measurements from
           Argo floats and moored buoys
    • Authors: Wenqing Tang; Simon H. Yueh, Alexander G. Fore, Akiko Hayashi
      Pages: n/a - n/a
      Abstract: We validate sea surface salinity (SSS) retrieved from Aquarius instrument on SAC‐D satellite with in situ measurements by Argo floats and moored buoy arrays. We assess the error structure of three Aquarius SSS products: the standard product processed by Aquarius Data Processing System (ADPS) and two datasets produced at the Jet Propulsion Laboratory (JPL): the Combined Active‐Passive algorithm with and without rain correction, CAP and CAP_RC respectively. We examine the effect of various filters to prevent unreliable point retrievals from entering Level‐3 averaging, such as land or ice contamination, radio‐frequency‐interference (RFI), and cold water. Our analyses show that Aquarius SSS agrees well with Argo in a monthly average sense between 40°S and 40°N except in the Eastern Pacific Fresh Pool and Amazon River outflow. Buoy data within these regions show excellent agreement with Aquarius but have discrepancies with the Argo gridded products. Possible reasons include strong near surface stratification and sampling problems in Argo in regions with significant western boundary currents. We observe large root‐mean‐square (RMS) difference and systematic negative bias between ADPS and Argo in the tropical Indian Ocean and along the Southern Pacific Convergence Zone. Excluding these regions removes the suspicious seasonal peak in the monthly RMS difference between the Aquarius SSS products and Argo. Between 40°S and 40°N, the RMS difference for CAP is less than 0.22 PSU for all 28 months, CAP_RC has essentially met the monthly 0.2 PSU accuracy requirement, while that for ADPS fluctuates between 0.22 and 0.3 PSU.
      PubDate: 2014-08-02T00:49:13.424573-05:
      DOI: 10.1002/2014JC010101
       
  • Decadal trends in global pelagic ocean chlorophyll: A new assessment
           integrating multiple satellites, in situ data, and models
    • Authors: Watson W. Gregg; Cécile S. Rousseaux
      Pages: n/a - n/a
      Abstract: Quantifying change in ocean biology using satellites is a major scientific objective. We document trends globally for the period 1998‐2012 by integrating three diverse methodologies: ocean color data from multiple satellites, bias correction methods based on in situ data, and data assimilation to provide a consistent and complete global representation free of sampling biases. The results indicated no significant trend in global pelagic ocean chlorophyll over the 15 year data record. These results were consistent with previous findings that were based on the first 6 years and first 10 years of the SeaWiFS mission. However, all of the Northern Hemisphere basins (north of 10o latitude), as well as the Equatorial Indian basin, exhibited significant declines in chlorophyll. Trend maps showed the local trends and their change in percent per year. These trend maps were compared with several other previous efforts using only a single sensor (SeaWiFS) and more limited time series, showing remarkable consistency. These results suggested the present effort provides a path forward to quantifying global ocean trends using multiple satellite missions, which is essential if we are to understand the state, variability, and possible changes in the global oceans over longer time scales.
      PubDate: 2014-07-31T04:03:08.962624-05:
      DOI: 10.1002/2014JC010158
       
  • Is weaker Arctic sea ice changing the Atlantic water circulation?
    • Authors: Polona Itkin; Michael Karcher, Rüdiger Gerdes
      Pages: n/a - n/a
      Abstract: With a numerical model we test the sensitivity of the Arctic Ocean circulation at mid‐depth (212‐1200 m) to the change in the sea ice rheology parameter P* that controls the sea ice compressive strength. We show that the reduction of the sea ice strength via P* within commonly used envelope reduces the sea ice extent and consequently enhances the ocean surface heat loss in the marginal ice zone. This leads to cooling of the Atlantic water inflow into the Arctic Ocean. As a result Eurasian Basin and Amerasian Basin temperatures are in average cooled by 0.1 °C and 0.05 °C, respectively. An increased sea ice drift speed in the central Arctic leads to an enhanced circulation of the anticyclonic Beaufort Gyre of the Amerasian Basin, which in turn weakens the cyclonic Atlantic water circulation below and enhances the recirculation of the Atlantic water in the Eurasian Basin. Consequently the balance of the volume fluxes through the Arctic gateways changes. Fram Strait net outflow increases by 0.46 Sv, Barents Sea Opening net inflow increases by 0.19 Sv and Davis Strait net outflow decreases by 0.28 Sv. This can spread the effects of the sea ice strength change beyond the limits of the Arctic Ocean and into the deep water convection zones in the North Atlantic. These substantial effects should be considered also in the model optimization efforts where P* is commonly used as one of the tuning parameters to achieve better sea ice simulations, whereas the effects on the ocean circulation are rarely taken into account.
      PubDate: 2014-07-25T23:32:34.515752-05:
      DOI: 10.1002/2013JC009633
       
  • Role of the western tropical Pacific in the North Pacific regime shift in
           the winter of 1998/1999
    • Authors: Hyun‐Su Jo; Sang‐Wook Yeh, Ben P. Kirtman
      Pages: n/a - n/a
      Abstract: In this study we examine the role of the western tropical Pacific in the North Pacific regime shift during the winter (December‐January‐February) of 1998/99. The North Pacific regime shift in the winter of 1998/99 is characterized by a dipole‐like structure along 40°N where significant warming is prominent in the western and central North Pacific. This shift might have been associated with an abrupt warming in the western tropical Pacific after 1998/99, in the North Equatorial Current (NEC) bifurcation region (8°N‐18°N, 125°E‐160°E) in particular. The NEC bifurcation region experiences a regime shift from cooling to warming during the 1998/99. Consequently, the Kuroshio current, which originates in the NEC bifurcation region, could transport the anomalous warm water into the North Pacific. In addition, a sudden shift in the NEC bifurcation latitude to the south also contributes to the 1998/99 regime shift in the North Pacific. We suggest a possible mechanism that could have caused the regime shift in the NEC bifurcation region during the 1998/99. An abrupt deepening of the thermocline depth in the NEC bifurcation region from 1997/98 to 1998/99, which is associated with the biggest El Niño in 1997/98 and a subsequent La Niña event in 1998/99, plays a role in initiating the shift in the NEC bifurcation region. Subsequently, the frequent occurrence of the La Niña events after 1998/99 plays a role in maintaining the regime shift toward warming by sustaining a deepening of the thermocline depth.
      PubDate: 2014-07-25T23:18:28.213633-05:
      DOI: 10.1002/2013JC009527
       
  • Coherent sea level variability on the North Atlantic western boundary
    • Authors: P. R. Thompson; G. T. Mitchum
      Pages: n/a - n/a
      Abstract: Interannual to decadal sea level variability on the North Atlantic western boundary is surprisingly coherent over substantial distances stretching from the Caribbean to Nova Scotia. The physical mechanisms responsible for this basin‐scale, low‐frequency coherence are explored in a diagnosis of simulated ocean fields from GECCO, which reproduces the observations to good approximation. Coastal sea level variability on the western boundary is known to be influenced by meridional divergence in the boundary current resulting in a geostrophic tilting of the sea surface. This mechanism is found to be of leading order along some stretches of the boundary, but it does not account for the coherence spanning the western North Atlantic. Instead, the coherence along the entire boundary is accounted for by vertical divergence resulting in the uniform rise and fall of the sea surface west of the 295°E meridian. The vertical divergence is found to be due to net vertically integrated zonal transport across this meridian resulting from meridional variation in the Sverdrup transport over the basin interior.
      PubDate: 2014-07-25T05:04:30.969259-05:
      DOI: 10.1002/2014JC009999
       
  • Investigation of the causes of historical changes in the subsurface
           salinity minimum of the South Atlantic
    • Authors: Marlos Goes; Ilana Wainer, Natalia Signorelli
      Pages: n/a - n/a
      Abstract: In this study we investigate the sub‐surface salinity changes on decadal timescales across the Subtropical South Atlantic Ocean using two ocean reanalysis products, the latest version of the Simple Ocean Data Assimilation and the Estimating the Circulation and Climate of the Ocean, Phase II, as well as with additional climate model experiments. Results show that there is a recent significant salinity increase at the core of the salinity minimum at intermediate levels. The main underlying mechanism for this sub‐surface salinity increase is the lateral advective (gyre) changes due to the Southern Annular mode variability, which conditions an increased contribution from the Indian Ocean high salinity waters into the Atlantic. The global warming signal has a secondary but complementary contribution. Latitudinal differences at intermediate depth in response to large‐scale forcing are in part caused by local variation of westward propagation features, and by compensating contributions of salinity and temperature to density changes.
      PubDate: 2014-07-24T04:37:41.348152-05:
      DOI: 10.1002/2014JC009812
       
  • Impact of climate change on the Northwestern Mediterranean Sea pelagic
           planktonic ecosystem and associated carbon cycle
    • Authors: Marine Herrmann; Claude Estournel, Fanny Adloff, Frédéric Diaz
      Pages: n/a - n/a
      Abstract: The Northwestern Mediterranean Sea (NWMS) is biologically one of the most productive Mediterranean regions. NWMS pelagic planktonic ecosystem is strongly influenced by hydrodynamics, in particular by deep convection, that could significantly weaken under the influence of climate change. Here we investigate the response of this ecosystem and associated carbon cycle to the long‐term evolution of oceanic and atmospheric circulations. For that we developed a tridimensional coupled physical‐biogeochemical model and performed two groups of annual simulations under the climate conditions of respectively the XXth and the end of XXIst century. Our results suggest that the evolution of oceanic and atmospheric circulations does not modify the NWMS pelagic planktonic ecosystem and associated carbon cycle at a first order. However differences mainly induced by the deep convection weakening and the surface warming are obtained at a second order. The spring bloom occurs one month earlier. Resulting from the decrease in nutrients availability, the bottom up control of phytoplankton development and bacteria growth by the nitrogen and phosphorus availability strengthens and the microbial loop intensifies as the small‐sized plankton biomass increases. Carbon net fixation and deep export do not change significantly. The choice of the biogeochemical initial and boundary conditions does not change the representation of the ecosystem seasonal cycle, but the associated uncertainty range can be one order of magnitude larger than the predicted interannual and long term variabilities. The uncertainty range of long‐term trends associated to the physical forcing (hydrological, atmospheric, hydrodynamical and socio‐economic) is much smaller (
      PubDate: 2014-07-21T22:56:50.233667-05:
      DOI: 10.1002/2014JC010016
       
  • Multiscale dynamical analysis of a high resolution numerical model
           simulation of the Solomon Sea circulation
    • Authors: Bughsin' Djath; Jacques Verron, Angelique Melet, Lionel Gourdeau, Bernard Barnier, Jean‐Marc Molines
      Pages: n/a - n/a
      Abstract: A high 1/36° resolution numerical model is used to study the ocean circulation in the Solomon Sea. An evaluation of the model with (the few) available observation shows that the 1/36° resolution model realistically simulates the Solomon Sea circulations. The model notably reproduces the high levels of mesoscale eddy activity observed in the Solomon Sea. With regard to previous simulations at 1/12° resolution, the average eddy kinetic energy levels are increased by up to ~30‐40% in the present 1/36° simulation, and the enhancement extends at depth. At the surface, the eddy kinetic energy level is maximum in March‐April‐May and is minimum in December‐January‐February. The high subsurface variability is related to the variability of the western boundary current (New Guinea Coastal Undercurrent). Moreover, the emergence of submesoscales is clearly apparent in the present simulations. A spectral analysis is conducted in order to evidence and characterize the modeled submesoscale dynamics and to provide a spectral view of scales interactions. The corresponding spectral slopes show a strong consistency with the Surface Quasigeostrophic turbulence theory.
      PubDate: 2014-07-17T04:09:28.480867-05:
      DOI: 10.1002/2013JC009695
       
  • Impact of an extreme flood event on optical and biogeochemical properties
           in a sub‐tropical coastal peri‐urban embayment (Eastern
           Australia)
    • Authors: Kadija Oubelkheir; Phillip W. Ford, Lesley A. Clementson, Nagur Cherukuru, Gary Fry, Andrew D.L. Steven
      Pages: n/a - n/a
      Abstract: Major floods impacted the city of Brisbane, eastern Australia, in January 2011, delivering large amounts of dissolved and particulate materials and nutrients into the adjacent coastal embayment, Moreton Bay. The resulting spatially‐resolved changes in biogeochemical and optical properties in Moreton Bay were examined 1, 2, 6, 19 and 49 weeks after the main freshwater discharge. One week post‐flood, total suspended matter (TSM) and chlorophyll a (TChla) concentrations varied over one order of magnitude throughout Moreton Bay, the particle scattering coefficient at 555 nm varied by a factor of 20, and the total absorption coefficient and coloured dissolved organic matter (CDOM) absorption coefficient at 440 nm varied by a factor of 5. The largest changes in biogeochemical and optical properties observed during our study were from one to two weeks after the floods: near the Brisbane River mouth, TSM decreased by a factor of 3, CDOM by a factor of 2, while TChla increased by a factor of 3. Within a year, optical and biogeochemical properties recovered to levels similar to non‐flood conditions. The strong changes in the characteristics of the particulate and dissolved material following the flood event and subsequent biological and photochemical processes led to a large spatial and temporal variability in the relative contribution of different constituents to the total absorption coefficient at 440 nm, the particle single scattering albedo, and the specific inherent optical properties. This work has significant implications for the accuracy of standard ocean colour remote sensing algorithms in coastal waters during flood events.
      PubDate: 2014-07-14T19:23:20.886476-05:
      DOI: 10.1002/2014JC010205
       
  • Modeling the winter‐spring transition of first‐year ice in the
           western Weddell Sea
    • Authors: N. Jeffery; E. C. Hunke
      Pages: n/a - n/a
      Abstract: A new halodynamic scheme is coupled with the Los Alamos sea ice model to simulate western Weddell Sea ice during the winter‐spring transition. One‐dimensional temperature and salinity profiles are consistent with the warming and melt stages exhibited in first‐year ice cores from the 2004 Ice Station POLarstern (ISPOL) expedition. Results are highly sensitive to snowfall. Simulations which use reanalysis precipitation data do not retain a snow cover beyond mid‐December, and the warming transition occurs too rapidly. Model performance is greatly improved by prescribing a snowfall rate based on reported snow thicknesses. During ice growth prior to ISPOL, simulations indicate a period of thick snow and upper ice salinity enrichment. Gravity drainage model parameters impact the simulation immediately, while effects from the flushing parameter (snow porosity at the ice top) appear as the freeboard becomes negative. Simulations using a snow porosity of 0.3, consistent with that of wet snow, agree with salinity observations. The model does not include lateral sources of sea‐water flooding, but vertical transport processes account for the high upper‐ice salinities observed in ice cores at the start of the expedition. As the ice warms, a fresh upperice layer forms, and the high salinity layer migrates downwards. This pattern is consistent with the early spring development stages of high‐porosity layers observed in Antarctic sea ice that are associated with rich biological production. Future extensions of the model may be valuable in Antarctic icebiogeochemical applications.
      PubDate: 2014-07-11T03:08:03.088371-05:
      DOI: 10.1002/2013JC009634
       
  • An in situ‐satellite blended analysis of global sea surface salinity
    • Authors: P. Xie; T. Boyer, E. Bayler, Y. Xue, D. Byrne, J. Reagan, R. Locarnini, F. Sun, R. Joyce, A. Kumar
      Pages: n/a - n/a
      Abstract: Ablended monthly sea‐surface salinity (SSS) analysis, called the NOAA “Blended Analysis of Surface Salinity” (BASS), is constructed for the four year period from 2010 to 2013. Three data sets are employed as inputs to the blended analysis: in situ SSS measurements aggregated and quality controlled by NOAA/NODC, and passive microwave (PMW) retrievals from both the National Aeronautics and Space Administration's (NASA) Aquarius/SAC‐D and the European Space Agency's (ESA) Soil Moisture – Ocean Salinity (SMOS) satellites. The blended analysis comprises two steps. First, the biases in the satellite retrievals are removed through probability distribution function (PDF) matching against temporally‐spatially co‐located in situ measurements. The blended analysis is then achieved through optimal interpolation (OI), where the analysis for the previous time step is used as the first guess while the in situ measurements and bias‐corrected satellite retrievals are employed as the observations to update the first guess. Cross‐validations illustrate improved quality of the blended analysis, with reduction in bias and random errors over most of the global oceans as compared to the individual inputs. Large uncertainty, however, remains in high‐latitude oceans and coastal regions where the in situ networks are sparse and current‐generation satellite retrievals have limitations. Our blended SSS analysis shows good agreements with the NODC in situ ‐ based analysis over most of the tropical and sub‐tropical oceans, but large differences are observed for high‐latitude oceans and along coasts. In the tropical oceans, the BASS is shown to have coherent variability with precipitation and evaporation associated with the evolution of the El Niño – Southern Oscillation (ENSO).
      PubDate: 2014-07-11T00:14:08.446024-05:
      DOI: 10.1002/2014JC010046
       
  • Effects of mangroves and tidal flats on suspended‐sediment dynamics:
           Observational and numerical study of Darwin Harbour, Australia
    • Authors: Li Li; Xiao Hua Wang, Fernando Andutta, David Williams
      Pages: n/a - n/a
      Abstract: The suspended‐sediment dynamics in Darwin Harbour, Australia were investigated using field measurements and numerical modeling. The model suspended‐sediment concentration (SSC) agreed well with observation; the root‐mean‐square error was less than 0.02kgm‐3 and the anomaly‐correlation‐coefficient greater than 0.6. Model results indicate that the tide is the dominant forcing for suspended‐sediment transport: total sediment transport was seaward in the channel and landward at the East and Middle Arm entrances, dominated by the Eulerian residual current. Further numerical experiments indicate that mangroves and tidal flats play key roles in redistributing suspended sediment and affecting total sediment transport by modulating the tides and the tidal asymmetry. In Darwin Harbour, if these areas were reclaimed, there would be a significant transport of sediment into the inner harbor. However, the water in East Arm would be less turbid, with about 70% lower bottom SSC during spring tides. The landward sediment flux at its entrance would decrease by 99%, because of reduced currents in the Arm due to a weakened tidal choking effect. Tidal pumping would then dominate sediment transport in the channel and at the entrances of East and Middle Arms. Dredging for the East Arm Wharf affected the SSC upstream in East Arm. According to the model, material from dredging disposed of at a location outside the harbor will be transported back into the outer harbor, generating higher SSC values there. Although this study is site‐specific, the findings may be applicable to suspended‐sediment dynamics in other harbors and estuaries with extensive tidal flats and mangroves.
      PubDate: 2014-06-26T14:18:20.614901-05:
      DOI: 10.1002/2014JC009987
       
  • SMOS salinity in the subtropical north Atlantic salinity maximum: 1.
           Comparison with Aquarius and in situ salinity
    • Authors: O. Hernandez; J. Boutin, N. Kolodziejczyk, G. Reverdin, N. Martin, F. Gaillard, N. Reul, J.L. Vergely
      Pages: n/a - n/a
      Abstract: Sea surface salinity (SSS) measured from space by the Soil Moisture and Ocean Salinity (SMOS) mission is validated in the subtropical North Atlantic Ocean. 39 transects of ships of opportunity equipped with thermosalinographs (TSG) crossed that region from 2010 to 2012, providing a large database of ground truth SSS. SMOS SSS is also compared to Aquarius SSS. Large seasonal biases remain in SMOS and Aquarius SSS. In order to look at the capability of satellite SSS to monitor spatial variability, especially at scales less than 300 km (not monitored with the Argo network), we first apply a monthly bias correction derived from satellite SSS and In Situ Analysis System (ISAS) SSS differences averaged over the studied region. Ship SSS averaged over 25 km is compared with satellite and ISAS SSS. Similar statistics are obtained for SMOS, Aquarius and ISAS products (root mean square error of about 0.15 and global correlation coefficient r of about 0.92). However, in the above statistics, SSS varies due to both large scale and mesoscale (here, for scales around 100 km) variability. In order to focus on mesoscale variability, we consider SSS anomalies with respect to a monthly climatology. SMOS SSS and Aquarius SSS anomalies are more significantly correlated (r > 0.5) to TSG SSS anomaly than ISAS. We show the effective gain of resolution and coverage provided by the satellite products over the interpolated in situ data. We also show the advantage of SMOS (r=0.57) over Aquarius (r=0.52) to reproduce SSS mesoscale features.
      PubDate: 2014-06-25T21:41:39.780213-05:
      DOI: 10.1002/2013JC009610
       
  • Data assimilative modeling investigation of Gulf Stream Warm Core Ring
           interaction with continental shelf and slope circulation
    • Authors: Ke Chen; Ruoying He, Brian S. Powell, Glen G. Gawarkiewicz, Andrew M. Moore, Hernan G. Arango
      Pages: n/a - n/a
      Abstract: A data assimilative ocean circulation model is used to hindcast the interaction between a large Gulf Stream Warm Core Ring (WCR) with the Mid‐Atlantic Bight (MAB) shelf and slope circulation. Using the recently developed Incremental Strong constraint 4D Variational (I4D‐Var) data assimilation algorithm, the model assimilates mapped satellite sea surface height (SSH), sea surface temperature (SST), in situ temperature and salinity profiles measured by expendable bathythermograph, Argo floats, shipboard CTD casts, and glider transects. Model validations against independent hydrographic data show 60% and 57% error reductions in temperature and salinity, respectively. The WCR significantly changed MAB continental slope and shelf circulation. The mean cross‐shelf transport induced by the WCR is estimated to be 0.28 Sv offshore, balancing the mean along‐shelf transport by the shelfbreak jet. Large heat/salt fluxes with peak values of ‐8900 Watt m‐2/‐4×10‐4 Kg m‐2 s‐1 are found when the WCR was impinging upon the shelf break. Vorticity analysis reveals the nonlinear advection term, as well as the residual of joint effect of baroclinicity and bottom relief (JEBAR) and advection of potential vorticity (APV) play important roles in controlling the variability of the eddy vorticity.
      PubDate: 2014-06-14T03:39:41.892753-05:
      DOI: 10.1002/2014JC009898
       
  • Effects of super typhoons on cyclonic ocean eddies in the western North
           Pacific: A satellite data‐based evaluation between 2000 and 2008
    • Authors: Liang Sun; Ying‐Xin Li, Yuan‐Jian Yang, Qiaoyan Wu, Xue‐Tao Chen, Qiu‐Yang Li, Yu‐Bin Li, Tao Xian
      Pages: 5585 - 5598
      Abstract: A composite time series of the merged satellite altimeters sea surface height anomaly (SSHA) data and satellite‐observed sea surface temperature (SST) data were used to identify eddies in the Western North Pacific Ocean (WNPO), where there were numbers of intense typhoons. This study systematically investigated 15 super typhoons during the period of 2000‐2008 in the WNPO to study their impacts on the pre‐typhoon ocean features, e.g., the cyclonic ocean eddy (COE) feature (closed contours of SSHA < −6 cm) and neutral condition (SSHA between −6 and 6 cm). Two new COEs are generated by two super typhoons, and 18 pre‐existing COEs are intensified by 13 super typhoons. 5 of the 13 super typhoons each influenced two pre‐exisiting COEs. Although the typhoon‐induced maximum cooling centers had a right bias along the tracks due to wind conditions, pre‐existing COEs also play a significant role in determining the strength and location of large SST cooling. Three possible factors (maximum wind speed, typhoon translation speed and the typhoon forcing time, Tf) are employed to explain the interactions. Above all, the changes of the COE geometric and physical parameters (e.g., effective radius, area, SST, SSHA, and eddy kinetic energy) were mostly related to the typhoon forcing time, Tf. This is because Tf is a parameter that is a combination of the typhoon's translation speed, intensity and size. Although the typhoons may significantly impact COEs, such samples were not commonly observed. Thus, the impact of typhoon on the strength of COEs is generally inefficient.
      PubDate: 2014-09-02T09:33:11.385844-05:
      DOI: 10.1002/2013JC009575
       
  • A physically based parameterization of gravity drainage for sea‐ice
           modeling
    • Authors: David W. Rees Jones; M. Grae Worster
      Pages: 5599 - 5621
      Abstract: We incorporate a physically derived parameterization of gravity drainage, in terms of a convective upwelling velocity, into a one‐dimensional, thermodynamic sea‐ice model of the kind currently used in coupled climate models. Our parameterization uses a local Rayleigh number to represent the important feedback between ice salinity, porosity, permeability, and desalination rate. It allows us to determine salt fluxes from sea ice and the corresponding evolution of the bulk salinity of the ice, in contrast to older, established models that prescribe the ice salinity. This improves the predictive power of climate models in terms of buoyancy fluxes to the polar oceans, and also the thermal properties of sea ice, which depend on its salinity. We analyze the behavior of existing fixed‐salinity models, elucidate the physics by which changing salinity affects ice growth and compare against our dynamic‐salinity model, both in terms of laboratory experiments and also deep‐ocean calculations. These comparisons explain why the direct effect of ice salinity on growth is relatively small (though not always negligible, and sometimes different from previous studies), and also highlight substantial differences in the qualitative pattern and quantitative magnitude of salt fluxes into the polar oceans. Our study is particularly relevant to growing first‐year ice, when gravity drainage is the dominant mechanism by which ice desalinates. We expect that our dynamic model, which respects the underlying physics of brine drainage, should be more robust to changes in polar climate and more responsive to rapid changes in oceanic and atmospheric forcing.
      PubDate: 2014-09-02T09:14:47.69508-05:0
      DOI: 10.1002/2013JC009296
       
  • Ocean response to volcanic eruptions in Coupled Model Intercomparison
           Project 5 simulations
    • Authors: Yanni Ding; James A. Carton, Gennady A. Chepurin, Georgiy Stenchikov, Alan Robock, Lori T. Sentman, John P. Krasting
      Pages: 5622 - 5637
      Abstract: We examine the oceanic impact of large tropical volcanic eruptions as they appear in ensembles of historical simulations from eight Coupled Model Intercomparison Project Phase 5 models. These models show a response that includes lowering of global average sea surface temperature by 0.1–0.3 K, comparable to the observations. They show enhancement of Arctic ice cover in the years following major volcanic eruptions, with long‐lived temperature anomalies extending to the middepth and deep ocean on decadal to centennial timescales. Regional ocean responses vary, although there is some consistent hemispheric asymmetry associated with the hemisphere in which the eruption occurs. Temperature decreases and salinity increases contribute to an increase in the density of surface water and an enhancement in the overturning circulation of the North Atlantic Ocean following these eruptions. The strength of this overturning increase varies considerably from model to model and is correlated with the background variability of overturning in each model. Any cause/effect relationship between eruptions and the phase of El Niño is weak.
      PubDate: 2014-09-02T09:16:11.891771-05:
      DOI: 10.1002/2013JC009780
       
  • Spring carbonate chemistry dynamics of surface waters in the northern East
           China Sea: Water mixing, biological uptake of CO2, and chemical buffering
           capacity
    • Authors: Wei‐Dong Zhai; Jian‐Fang Chen, Hai‐Yan Jin, Hong‐Liang Li, Jin‐Wen Liu, Xian‐Qiang He, Yan Bai
      Pages: 5638 - 5653
      Abstract: We investigated sea surface total alkalinity (TAlk), dissolved inorganic carbon (DIC), dissolved oxygen (DO), and satellite‐derived chlorophyll‐a in the connection between the Yellow Sea and the East China Sea (ECS) during April to early May 2007. In spring, Changjiang dilution water (CDW), ECS offshore water, and together with Yellow Sea water (YSW) occupied the northern ECS. Using 16 day composite satellite‐derived chlorophyll‐a images, several algal blooms were identified in the CDW and ECS offshore water. Correspondingly, biological DIC drawdown of 73 ± 20 μmol kg−1, oversaturated DO of 10–110 μmol O2 kg−1, and low fugacity of CO2 of 181–304 μatm were revealed in these two waters. YSW also showed CO2 uptake in spring, due to the very low temperature. However, its intrusion virtually counteracted CO2 uptake in the northern ECS. In the CDW and the ECS offshore water, Revelle factor was 9.3–11.7 and 8.9–10.6, respectively, while relatively high Revelle factor values of 11.4–13.0 were revealed in YSW. In the ECS offshore water, the observed relationship between DIC drawdown and oversaturated DO departed from the Redfield ratio, indicating an effect of chemical buffering capacity on the carbonate system during air‐sea reequilibration. Given the fact that the chemical buffering capacity slows down the air‐sea reequilibration of CO2, the early spring DIC drawdown may have durative effects on the sea surface carbonate system until early summer. Although our study is subject to limited temporal and spatial coverage of sampling, these insights are fundamental to understanding sea surface carbonate chemistry dynamics in this important ocean margin.
      PubDate: 2014-09-02T09:14:59.993569-05:
      DOI: 10.1002/2014JC009856
       
 
 
JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327
 
About JournalTOCs
API
Help
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-2014