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

Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 21, SJR: 2.156, h-index: 61)
Geophysical Research Letters     Full-text available via subscription   (Followers: 48, SJR: 2.668, h-index: 142)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 5, SJR: 2.4, h-index: 109)
J. of Advances in Modeling Earth Systems     Open Access   (Followers: 2, SJR: 0.126, h-index: 2)
J. of Geophysical Research : Atmospheres     Partially Free   (Followers: 21)
J. of Geophysical Research : Biogeosciences     Full-text available via subscription   (Followers: 7)
J. of Geophysical Research : Earth Surface     Partially Free   (Followers: 24)
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: 16)
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: 176, SJR: 1.769, h-index: 110)
Journal Cover Journal of Geophysical Research : Oceans
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     ISSN (Online) 2169-9291
     Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • Changes in the mesoscale variability and in extreme sea levels over two
           decades as observed by satellite altimetry
    • Authors: Philip L. Woodworth; Melisa Menéndez
      Pages: n/a - n/a
      Abstract: A data set of precise radar altimeter sea surface heights obtained from the same 10‐day repeat ground track has been analysed to determine the magnitude of change in the ocean ‘mesoscale’ variability over two decades. Trends in the standard deviation of sea surface height variability each year are found to be small (typically ~0.5 percent/yr) throughout the global ocean. Trends in positive and negative extreme sea level in each region are in general found to be similar to those of mean sea level, with some small regional exceptions. Generalised Extreme Value Distribution (GEVD) analysis also demonstrates that spatial variations in the statistics of extreme positive sea levels are determined largely by the corresponding spatial variations in mean sea level changes, and are related to regional modes of the climate system such as the El Niño – Southern Oscillation. Trends in the standard deviation of along‐track sea level gradient variability are found to be close to zero on a global basis, with regional exceptions. Altogether our findings suggest an ocean mesoscale variability that displays little change when considered over an extended period of two decades, but that is superimposed on a spatially and temporally varying signal of mean sea level change. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-18T16:29:05.478045-05:
      DOI: 10.1002/2014JC010363
       
  • Monitoring the spreading of the Amazon freshwater plume by MODIS, SMOS,
           Aquarius, and TOPAZ
    • Authors: Anton Korosov; Francois Counillon, Johnny A. Johannessen
      Pages: n/a - n/a
      Abstract: A synergistic tool for studying the Amazon River Plume dynamics based on a novel algorithm for deriving sea surface salinity (SSS) from MODIS reflectance data together with SSS data from the SMOS and Aquarius satellites and the TOPAZ data assimilation system is proposed. The new algorithm is based on a neural network to relate spectral remote sensing reflectance measured by MODIS with SSS measured by SMOS in the Amazon river plume. The algorithm is validated against independent in‐situ data and is found to be valid in the range of SSS from 29 to 35 psu, for the period of highest rates of Amazon River discharge with RMSE=0.79 psu and r2=0.84. Monthly SSS fields were reconstructed from the MODIS data for late summers from 2002 to 2012 at a 10 km resolution and compared to surface currents and SSS derived from the TOPAZ reanalysis system. The two datasets reveal striking agreement, suggesting that the TOPAZ system could be used for a detailed study of the Amazon River plume dynamics. Both the position and speed of the North Brazilian Current as well as the spreading of the Amazon River plume are monitored. In particular a recurrent mechanism was observed for the spreading of the rivers plumes, notably that the fresh water is usually advected towards the Caribbean Sea by the North Brazilian Current but get diverted into the tropical Atlantic when North Brazilian Current rings are shed. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-18T16:20:17.428491-05:
      DOI: 10.1002/2014JC010155
       
  • Climate change impacts on wave and surge processes in a Pacific Northwest
           (USA) estuary
    • Authors: T.K. Cheng; D.F. Hill, J. Beamer, G. García‐Medina
      Pages: n/a - n/a
      Abstract: Total water levels (TWLs) within estuaries are influenced by tides, wind, offshore waves and streamflow, all of which are uniquely affected by climate change. The magnitude of TWL associated with various return periods is relevant to understanding how the hydrodynamics of a bay or estuary may evolve under distinct climate scenarios. A methodology for assessing the hydrodynamic response of a small estuary under major boundary condition perturbations is presented in this study. The coupled Advanced Circulation (ADCIRC) and Simulating Waves Nearshore (SWAN) model was used to simulate wave and water elevation conditions within Tillamook Bay, OR (USA) for two long‐term scenarios; 1979‐1998 and 2041‐2060. The model output provided multi‐decadal time series of TWLs for statistical analysis. Regional climate data from the North American Regional Climate Change Assessment Program (NARCCAP) were used to drive streamflow modeling (MicroMet/SnowModel/HydroFlow) and meteorological forcing within ADCIRC‐SWAN. WAVEWATCH III, which was forced with global climate data from the Community Climate Science Model (ccsm; a contributing model to NARCCAP), was used to produce open boundary wave forcing. Latitudinal and seasonal gradients were found in TWLs associated with varying return periods for both the hindcast and forecast. Changes in TWLs from hindcast to forecast included the sea level rise component and were also modulated by changes in boundary conditions. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-18T16:20:02.704851-05:
      DOI: 10.1002/2014JC010268
       
  • Wind forcing controls on river plume spreading on a tropical continental
           shelf
    • Authors: A. Tarya; M. van der Vegt, A.J.F. Hoitink
      Pages: n/a - n/a
      Abstract: The Berau Continental Shelf is located close to the Equator in the Indonesian Archipelago, hosting a complex of coral reefs along its oceanic edge. The Berau coral reefs have a very high biodiversity, but the area is under serious risk due to river‐derived nutrients and sediments. The region is characterized by weak winds, moderate tides and almost absent Coriolis forcing. Existing knowledge about river plume behaviour in tropical environments is limited. The aim of this paper is to investigate the influence of the subtle physical forcing on the dynamics of the Berau river plume. A three‐dimensional model (ECOMSED) was calibrated with observational data. The model was forced by freshwater input from the Berau river distributaries, tides at the open boundaries and measured hourly wind. The model reproduces the freshwater dynamics on the shelf adequately and highlights that the river plume spreads symmetrically for river forcing only. Tides cause vertical mixing and suppress the cross‐shelf spreading of the river plume. However, the spreading of the river plume over the shelf is mainly controlled by the weak monsoonal winds, resulting in a seasonal development. During the Southeast Monsoon, the southerly winds push the plume northeastward and cause a stratified water column in the northern part of the continental shelf. Northerly winds during the Northwest Monsoon disperse the plume to the south, promoting a vertically well‐mixed water column. The results can be used to predict the possible impact of land‐use changes in the steadily developing Berau region on coral reef health. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-16T15:28:22.691686-05:
      DOI: 10.1002/2014JC010456
       
  • Field Observations of Wave‐Driven Circulation over Spur and Groove
           Formations on a Coral Reef
    • Authors: Justin S. Rogers; Stephen G. Monismith, Robert B. Dunbar, David Koweek
      Pages: n/a - n/a
      Abstract: Spur and groove (SAG) formations are found on the forereefs of many coral reefs worldwide. Modeling results have shown that SAG formations together with shoaling waves induce a nearshore Lagrangian circulation pattern of counter‐rotating circulation cells, but these have never been observed in the field. We present results from two separate field studies of SAG formations on Palmyra Atoll which show their effect on waves to be small, but reveal a persistent order 1 cm/s depth‐averaged Lagrangian offshore flow over the spur and onshore flow over the grooves. This circulation was stronger for larger, directly‐incident waves and low alongshore flow conditions, consistent with predictions from modeling. Favorable forcing conditions must be maintained on the order of one hour to accelerate and develop the SAG circulation cells. The primary cross‐ and alongshore depth‐averaged momentum balances were between the pressure gradient, radiation stress gradient and nonlinear convective terms, and the bottom drag was similar to values found on other reefs. The vertical structure of these circulation cells was previously unknown and the results show a complex horizontal offshore Lagrangian flow over the spurs near the surface driven by alongshore variability in radiation stress gradients. Vertical flow was downward over the spur and upward over the groove, likely driven by alongshore differences in bottom stress and not by vortex forcing. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-16T15:23:37.044777-05:
      DOI: 10.1002/2014JC010464
       
  • Impact of measurement uncertainties on determination of
           chlorophyll‐specific absorption coefficient for marine phytoplankton
           
    • Authors: David McKee; Rüdiger Röttgers, Griet Neukermans, Violeta Sanjuan Calzado, Charles Trees, Marina Ampolo‐Rella, Claire Neil, Alex Cunningham
      Pages: n/a - n/a
      Abstract: Understanding variability in the chlorophyll‐specific absorption of marine phytoplankton, aph*Chl (λ), is essential for primary production modelling, calculation of underwater light field characteristics, and development of algorithms for remote sensing of chlorophyll concentrations. Previous field and laboratory studies have demonstrated significant apparent variability in aph*Chl (λ) for natural samples and algal cultures. However, the potential impact of measurement uncertainties on derived values of aph*Chl (λ) has received insufficient study. This study presents an analysis of measurement uncertainties for a data set collected in the Ligurian Sea in Spring and assesses the impact on estimates of aph*Chl (λ). It is found that a large proportion of apparent variability in this set of aph*Chl (λ) can be attributed to measurement errors. Application of the same analysis to the global NOMAD data set suggests that a significant fraction of variability in aph*Chl (λ) may also be due to measurement errors. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-16T15:23:17.948473-05:
      DOI: 10.1002/2014JC009909
       
  • Energy and heat fluxes due to vertically‐propagating Yanai waves
           observed in the equatorial Indian ocean
    • Authors: W.D. Smyth; T.S. Durland, J.N. Moum
      Pages: n/a - n/a
      Abstract: Shipboard current measurements in the equatorial Indian Ocean in October and November of 2011 revealed oscillations in the meridional velocity with amplitude ~ 0.10m/s. These were clearest in a layer extending from ~300 to 600 m depth and had periods near 3 weeks. Phase propagation was upward. Measurements from two sequential time series at the equator, four meridional transects and one zonal transect are used to identify the oscillation as a Yanai wave packet and to establish its dominant frequency and vertical wavelength. The Doppler shift is accounted for, so that measured wave properties are translated into the reference frame of the mean zonal flow. We take advantage of the fact that, in the depth range where the wave signal was clearest, the time‐averaged current and buoyancy frequency were nearly uniform with depth, allowing application of the classical theoretical representation of vertically propagating plane waves. Using the theory, we estimate wave properties that are not directly measured, such as the group velocity and the zonal wavelength and phase speed. The theory predicts a vertical energy flux that is comparable to that carried by midlatitude near‐inertial waves. We also quantify the wave‐driven meridional heat flux and the Stokes drift. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-16T15:10:40.419464-05:
      DOI: 10.1002/2014JC010152
       
  • An optimal XBT‐based monitoring system for the South Atlantic
           Meridional Overturning Circulation at 34°S
    • Authors: Marlos Goes; Gustavo Goni, Shenfu Dong
      Pages: n/a - n/a
      Abstract: The South Atlantic is an important pathway for the inter‐basin exchanges of heat and freshwater with strong influence on the global meridional overturning stability and variability. Along the 34°S parallel, a quarterly, high resolution XBT transect (AX18) samples the temperature structure in the upper ocean. The AX18 transect has been shown to be a useful component of a meridional overturning monitoring system of the region. However, a feasible, cost‐effective design for an XBT‐based system has not yet been developed. Here we use a high‐resolution ocean assimilation product to simulate an XBT‐based observational system across the South Atlantic. The sensitivity of the meridional heat transport, meridional overturning circulation, and geostrophic velocities to key observational and methodological assumptions is studied. Key assumptions taken into account are horizontal and temporal sampling of the transect, salinity and deep temperature inference, as well as the level of reference for geostrophic velocities. With the current sampling strategy, the largest errors in the meridional overturning and heat transport estimations are the reference (barotropic) velocity and the western boundary resolution. We show how altimetry can be used along with hydrography to resolve the barotropic component of the flow. We use the results obtained by the state estimation under observational assumptions to make recommendations for potential improvements in the AX18 transect implementation. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-16T15:08:26.191144-05:
      DOI: 10.1002/2014JC010202
       
  • Issue Information
    • Pages: i - vi
      PubDate: 2014-12-10T08:49:36.251254-05:
      DOI: 10.1002/jgrc.20356
       
  • Forced and intrinsic variability in the response to increased wind stress
           of an idealized Southern Ocean
    • Authors: Chris Wilson; Christopher W. Hughes, Jeffrey R. Blundell
      Pages: n/a - n/a
      Abstract: We use ensemble runs of a three‐layer, quasigeostrophic idealized Southern Ocean model to explore the roles of forced and intrinsic variability in response to a linear increase of wind stress imposed over a 30‐year period. We find no increase of eastward circumpolar volume transport in response to the increased wind stress. A large part of the resulting time series can be explained by a response in which the eddy kinetic energy is linearly proportional to the wind stress with a possible time lag, but no statistically significant lag is found. However, this simple relationship is not the whole story: several intrinsic timescales also influence the response. We find an e‐folding timescale for growth of small perturbations of 1‐2 weeks. The energy budget for intrinsic variability at periods shorter than a year is dominated by exchange between kinetic and potential energy. At longer timescales, we find an intrinsic mode with period in the region of 15 years, which is dominated by changes in potential energy and frictional dissipation in a manner consistent with that seen by Hogg and Blundell [2006]. A similar mode influences the response to changing wind stress. This influence, robust to perturbations, is different from the supposed linear relationship between wind stress and eddy kinetic energy, and persists for 5‐10 years in this model, suggestive of a forced oscillatory mode with period of around 15 years. If present in the real ocean, such a mode would imply a degree of predictability of Southern Ocean dynamics on multi‐year timescales. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-09T04:28:32.807942-05:
      DOI: 10.1002/2014JC010315
       
  • Spatiotemporal characteristics of seasonal to multidecadal variability of
           pCO2 and air‐sea CO2 fluxes in the equatorial Pacific Ocean
    • Authors: Vinu K. Valsala; Mathew Koll Roxy, Karumuri Ashok, Raghu Murtugudde
      Pages: n/a - n/a
      Abstract: Seasonal, interannual and multi‐decadal variability of seawater pCO2 and air‐sea CO2 fluxes in the equatorial Pacific Ocean for the past 45 years (1961 to 2005) are examined using a suite of experiments performed with an offline biogeochemical model driven by re‐analysis ocean products. The processes we focus on are: (a) the evolution of seasonal cycle of pCO2 and air‐sea CO2 fluxes during the dominant interannual mode in the equatorial Pacific, i.e., the El Niño‐Southern Oscillation (ENSO), (b) its spatio‐temporal characteristics, (c) the combined and individual effects of wind and ocean dynamics on pCO2 and CO2 flux variability and their relation to canonical (eastern Pacific) and central Pacific (Modoki) ENSOs and (d) the multi‐decadal variability of carbon dynamics in the equatorial Pacific and its association with the Pacific Decadal Oscillations (PDO). The simulated mean and seasonal cycle of pCO2 and CO2 fluxes are comparable with the observational estimates and with other model results. A new analysis methodology based on the traditional Empirical Orthogonal Functions (EOF) applied over a time‐time domain is employed to elucidate the dominant mode of interannual variability of pCO2 and air‐sea CO2 fluxes at each longitude in the equatorial Pacific. The results show that the dominant interannual variability of CO2 fluxes in the equatorial Pacific (averaged over 50N‐100S) co‐evolves with that of ENSO. Generally a reduced CO2 source in the central‐to‐eastern equatorial Pacific evident during June‐July of the El Niño year (Year:0) peaks through September of Year:0 to February of Year:+1 and recovers to a normal source thereafter. In the region between 1600W‐1100W, the canonical El Niño controls the dominant variability of CO2 fluxes (mean and RMS of anomaly from 1961 to 2005 is 0.43±0.12 PgC yr‐1). However, in the western (1600E‐1600W) and far eastern (1100W‐900W) equatorial Pacific, CO2 flux variability is dominantly influenced by the El Niño‐Modoki (0.3±0.06 and 0.11±0.04 PgC yr‐1, respectively). On the other hand, the interannual variability of pCO2 is correlated with the canonical El Niño mostly to the east of 1400W and with El Niño‐Modoki to the west of 1400W. De‐coupling of CO2 flux and pCO2 variability at various locations in the equatorial Pacific is attributable to the differences in the combined and individual effects of ocean dynamics and winds associated with these two types of ENSO. A multi‐decadal variability in the equatorial Pacific sea‐air CO2 fluxes and pCO2 exhibits a positive phase during the 1960s, a negative phase during the 1980s, and then positive again by the 2000s. Within the ocean, the dissolved inorganic carbon (DIC) anomalies are traceable to the northern Pacific via thermocline pathways at decadal timescales. The multi‐decadal variability of equatorial Pacific CO2 fluxes and pCO2 are determined by the phases of the PDO and the corresponding scale of the El Niño‐Modoki variability, whereas canonical El Niño's contribution is to mainly determine the variability at interannual timescales. This study segregates the impacts of different types of ENSOs on the equatorial Pacific carbon cycle and sets the framework for analysing its spatio‐temporal variability under global warming. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-09T04:28:25.061879-05:
      DOI: 10.1002/2014JC010212
       
  • On the subsurface countercurrents in the Philippine Sea
    • Authors: Fan Wang; Nan Zang, Yuanlong Li, Dunxin Hu
      Pages: n/a - n/a
      Abstract: The subsurface countercurrents in the Philippine Sea and their roles in water mass transportation have been reported in previous studies. Their existence is still controversial, and the underlying dynamics remains unclear. This study investigates the climatological structures and relationships of three subsurface countercurrents, namely the Mindanao Undercurrent (MUC), the Luzon Undercurrent (LUC) and the North Equatorial Undercurrent (NEUC), using recently available hydrographic and satellite altimeter data. The three subsurface currents below and opposite to the surface currents are confirmed by multi‐sections analysis. The MUC, as traced at zonal sections between 6.5‐10.5°N, shows two northward velocity cores, both with maximum speed larger than 10cm.s−1. The LUC exhibits an obscure core with southward velocity larger than 2cm.s−1 under the Kuroshio at 18°N and 16.25°N sections. The eastward flowing NEUC also has two separated cores at 128.2°E and 130°E sections with velocity larger than 1cm.s−1. Analyses of θ‐S relationship suggest that the southern part of NEUC is fed by the MUC with the South Pacific water and South/North Pacific water mixture, while the northern NEUC is likely a destiny of the North Pacific water carried by the LUC. Tightly associated with the opposite horizontal gradients between sea surface height (SSH) and the depth of thermocline (DTC), the subsurface countercurrents exist in connected zones where the baroclinic adjustment below the thermocline overcomes the barotropic forcing at the sea surface, which indicates the dynamical linkages among the three subsurface countercurrents. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-09T04:26:15.419206-05:
      DOI: 10.1002/2013JC009690
       
  • Second‐order structure function analysis of scatterometer winds over
           the tropical Pacific
    • Authors: Gregory P. King; Jur Vogelzang, Ad Stoffelen
      Pages: n/a - n/a
      Abstract: Kolmogorov second‐order structure functions are used to quantify and compare the small‐scale information contained in near‐surface ocean wind products derived from measurements by ASCAT on MetOp‐A and SeaWinds on QuikSCAT. Two ASCAT and three SeaWinds products are compared in nine regions (classified as rainy or dry) in the tropical Pacific between 10°S and 10°N and 140° and 260°E for the period November 2008 ‐ October 2009. Monthly and regionally averaged longitudinal and transverse structure functions are calculated using along‐track samples. To ease the analysis, the following quantities were estimated for the scale range 50 – 300km and used to intercompare the wind products: (i) structure function slopes, (ii) turbulent kinetic energies (TKE), and (iii) vorticity‐to‐divergence ratios. All wind products are in good qualitative agreement, but also have important differences. Structure function slopes and TKE differ per wind product, but also show a common variation over time and space. Independent of wind product, longitudinal slopes decrease when sea surface temperature exceeds the threshold for onset of deep convection (about 28 °C). In rainy areas and in dry regions during rainy periods, ASCAT has larger divergent TKE than SeaWinds, while SeaWinds has larger vortical TKE than ASCAT. Differences between SeaWinds and ASCAT vortical TKE and vorticity‐to‐divergence ratios for the convectively active months of each region are large. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-09T04:23:16.082857-05:
      DOI: 10.1002/2014JC009992
       
  • Seasonal and interannual oxygen variability on the Washington and Oregon
           continental shelves
    • Authors: Siedlecki S.A; Banas N.S, Davis K.A, Giddings S, Hickey B.M, MacCready P, Connolly T, S. Geier
      Pages: n/a - n/a
      Abstract: The coastal waters of the northern portion of the California Current System experience a seasonal decline in oxygen concentrations and hypoxia over the summer upwelling season that results in negative impacts on habitat for many organisms. Using a regional model extending from 43° to 50°N, with an oxygen component developed in this study, drivers of seasonal and regional oxygen variability are identified. The model includes two pools of detritus, which was an essential addition in order to achieve good agreement with the observations. The model was validated using an extensive array of hydrographic and moored observations. The model captures the observed seasonal decline as well as spatial trends in bottom oxygen. Spatially, three regions of high respiration are identified as locations where hypoxia develops each modeled year. Two of the regions are previously identified re‐circulation regions. The third region is off of the Washington coast. Sediment oxygen demand causes the region on the Washington coast to be susceptible to hypoxia and is correlated to the broad area of shallow shelf (< 60 m) in the region. Respiration and circulation‐driven divergence contribute similar (60, 40%, respectively) amounts to the integrated oxygen budget on the Washington coast while respiration dominates the Oregon coast. Divergence, or circulation, contributes to the oxygen dynamics on the shelf in two ways: first, through the generation of retention features, and second, by determining variability. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-08T21:59:45.036318-05:
      DOI: 10.1002/2014JC010254
       
  • Adaptive observation in the South China Sea using CNOP approach based on a
           3‐D ocean circulation model and its adjoint model
    • Authors: Yineng Li; Shiqiu Peng, Duanling Liu
      Pages: n/a - n/a
      Abstract: This study investigates the effect of adaptive (or targeted) observation on improving the mid‐range (30 days) forecast skill of ocean state of the South China Sea (SCS). A region associated with the South China Sea Western Boundary Current (SCSWBC) is chosen as the “target” of the adaptive observation. The Conditional Nonlinear Optimal Perturbation (CNOP) approach is applied to a 3‐dimensional ocean model and its adjoint model for determining the sensitive region. Results show that the initial errors in the sensitive region determined by the CNOP approach have significant impacts on the forecast of ocean state in the target region; thus, reducing these initial errors through adaptive observation can lead to a better 30‐day prediction of ocean state in the target region. Our results suggest that implementing adaptive observation is an effective and cost‐saving way to improve an ocean model's forecast skill over the SCS. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-08T11:13:33.092864-05:
      DOI: 10.1002/2014JC010220
       
  • Moored observations of synoptic and seasonal variability in the East
           Greenland Coastal Current
    • Authors: B. E. Harden; F. Straneo, D. A. Sutherland
      Pages: n/a - n/a
      Abstract: We present a year‐round assessment of the hydrographic variability within the East Greenland Coastal Current on the Greenland shelf from five synoptic crossings and four years of moored hydrographic data. From the five synoptic sections the current is observed as a robust, surface intensified flow with a total volume transport of 0.66 ± 0.18 Sv and a freshwater transport of 42 ± 12 mSv. The moorings showed heretofore unobserved variability in the abundance of Polar and Atlantic water masses in the current on synoptic scales. This is exhibited as large vertical displacement of isotherms (often greater than 100 m). Seasonally, the current is hemmed into the coast during the fall by a full depth Atlantic Water layer that has penetrated onto the inner shelf. The Polar Water layer in the current then thickens through the winter and spring seasons increasing the freshwater content in the current; the timing implies that this is probably driven by the seasonally varying export of freshwater from the Arctic and not the local runoff from Greenland. The measured synoptic variability is enhanced during the winter and spring period due to a lower halocline and a concurrent enhancement in the along‐coast wind speed. The local winds force much of the high‐frequency variability in a manner consistent with downwelling, but variability distinct from downwelling is also visible. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-08T05:00:08.749295-05:
      DOI: 10.1002/2014JC010134
       
  • Multimodel simulations of Arctic Ocean sea surface height variability in
           the period 1970–2009
    • Authors: Nikolay V. Koldunov; Nuno Serra, Armin Köhl, Detlef Stammer, Olivier Henry, Anny Cazenave, Pierre Prandi, Per Knudsen, Ole Baltazar Andersen, Yongqi Gao, Johnny Johannessen
      Pages: n/a - n/a
      Abstract: The performance of several numerical ocean models is assessed with respect to their simulation of sea surface height (SSH) in the Arctic Ocean, and the main patterns of SSH variability and their causes over the past 40 years (1970‐2009) are analyzed. In comparison to observations, all tested models broadly reproduce the mean SSH in the Arctic and reveal a good correlation with both tide gauge data and SSH anomalies derived from satellite observations. Although the models do not represent the positive Arctic SSH trend observed over the last two decades, their interannual‐to‐decadal SSH variability is in reasonable agreement with available measurements. Focusing on results from one of the models for a detailed analysis it is shown that the decadal‐scale SSH variability over shelf areas and deep parts of the Arctic Ocean have pronounced differences that are determined mostly by salinity variations. A further analysis of the three time periods 1987‐1992, 1993‐2002 and 2003‐2009, corresponding to the transition times between cyclonic and anticyclonic regimes of the atmospheric circulation over the Arctic, revealed an unusual increase of SSH in the Amerasian basin during 2003‐2009. Results from this model support the recent finding that the increase is caused mainly by changes in freshwater content brought about by the freshwater export through the Canadian Arctic Archiplago and increased Ekman pumping in the Amerasian basin and partly by lateral freshwater transport changes, leading to a re‐distribution of low‐salinity shelf water. Overall we show that present day models can be used for investigating the reasons for low‐frequency SSH variability in the region. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-08T05:00:00.186117-05:
      DOI: 10.1002/2014JC010170
       
  • Thermal variations in the South China Sea associated with the eastern and
           central Pacific El Niño events and their mechanisms
    • Authors: Qin‐Yan Liu; Dongxiao Wang, Xin Wang, Yeqiang Shu, Qiang Xie, Ju Chen
      Pages: n/a - n/a
      Abstract: In this study, we investigate the interannual variability of the sea surface temperature (SST) in the South China Sea (SCS) associated with two types of El Niño, namely, the eastern Pacific (EP) El Niño and the central Pacific (CP) El Niño. First, double warm peaks can occur during both types of El Niño events in the SCS. However, the strong warm basin mode can only develop in the EP El Niño, while the warm semi‐basin mode exists during the CP El Niño. Associated with an anomalous positive (negative) net surface heat flux in the EP (CP) El Niño, along with a shallower thermocline with weaker (stronger) northeasterly wind anomalies, the SST anomalies become warmer (cooler) in the developing autumn. Over the background of cooling SST in autumn of CP El Niño, therefore, only a weak warming can occur in the subsequent years, which is limited in the western boundary area under the forcing of warm ocean advection. Second, the SST oscillation periods are different in these two types of El Niño. The SST evolution in the EP El Niño is negative‐positive with a quasi‐biennial oscillation, but that in the CP El Niño is positive‐negative‐positive‐negative with an annual oscillation. It seems that the double cooling in the CP El Niño is phase‐locked to the late autumn season. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-08T04:08:43.394953-05:
      DOI: 10.1002/2014JC010429
       
  • A neural network‐based four‐band model for estimating the
           total absorption coefficients from the global oceanic and coastal waters
    • Authors: Jun Chen; Tingwei Cui, Wenting Quan
      Pages: n/a - n/a
      Abstract: In this study, a neural network‐based four‐band model (NNFM) for the global oceanic and coastal waters has been developed in order to retrieve the total absorption coefficients a(λ). The applicability of the quasi‐analytical algorithm (QAA) and NNFM models is evaluated by five independent datasets. Based on the comparison of a(λ) predicted by these two models with the field measurements taken from the global oceanic and coastal waters, it was found that both the QAA and NNFM models had good performances in deriving a(λ), but that the NNFM model works better than the QAA model. The results of the QAA model‐derived a(λ), especially in highly turbid waters with strong backscattering properties of optical activity, was found to be lower than the field measurements. The QAA and NNFM models‐derived a(λ) could be obtained from the MODIS data after atmospheric corrections. When compared with the field measurements, the NNFM model decreased by a 0.86 to 24.15% uncertainty (root mean square relative error) of the estimation from the QAA model in deriving a(λ) from the Bohai, Yellow, and East China seas. Finally, the NNFM model was applied to map the global climatological seasonal mean a(443) for the time range of July, 2002 to May, 2014. As expected, the a(443) value around the coastal regions was always larger than the open ocean around the equator. Viewed on a global scale, the oceans at a high latitude exhibited higher a(443) values than those at a low latitude. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-08T03:23:51.698254-05:
      DOI: 10.1002/2014JC010461
       
  • Quantifying the processes controlling intraseasonal mixed‐layer
           temperature variability in the Tropical Indian Ocean
    • Authors: D.J. Halkides; Duane E. Waliser, Tong Lee, Dimitris Menemenlis, Bin Guan
      Pages: n/a - n/a
      Abstract: Spatial and temporal variation of processes that determine ocean mixed‐layer (ML) temperature (MLT) variability on the timescale of the Madden‐Julian Oscillation (MJO) in the Tropical Indian Ocean (TIO) are examined in a heat‐conserving ocean state estimate for years 1993‐2011. We introduce a new metric for representing spatial variability of the relative importance of processes. In general, horizontal advection is most important at the Equator. Subsurface processes and surface heat flux are more important away from the Equator, with surface heat flux being the more dominant factor. Analyses at key sites are discussed in the context of local dynamics and literature. At 0°, 80.5°E, for MLT events > 2 standard deviations, ocean dynamics account for more than two thirds of the net tendency during cooling and warming phases. Zonal advection alone accounts for ~40% of the net tendency. Moderate events (1‐2 standard deviations) show more differences between events, and some are dominated by surface heat flux. At 8°S, 67°E in the Seychelles‐Chagos Thermocline Ridge (SCTR) area, surface heat flux accounts for ~70% of the tendency during strong cooling and warming phases; subsurface processes linked to ML depth (MLD) deepening (shoaling) during cooling (warming) account for ~30%. MLT is more sensitive to subsurface processes in the SCTR, due to the thin MLD, thin barrier layer and raised thermocline. Results for 8°S, 67°E support assertions by Vialard et al. [2008] not previously confirmed due to measurement error that prevented budget closure and the small number of events studied. The roles of MLD, barrier layer thickness and thermocline depth on different timescales are examined. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-29T03:39:55.568502-05:
      DOI: 10.1002/2014JC010139
       
  • The “winter predictability barrier” for IOD events and its
           error growth dynamics: Results from a fully coupled GCM
    • Authors: Rong Feng; Wansuo Duan, Mu Mu
      Pages: n/a - n/a
      Abstract: Within the Geophysical Fluid Dynamics Laboratory Climate Model version 2p1 (GFDL CM2p1) coupled model, we find that the winter predictability barrier (WPB) exists in both the growing and decaying phases of positive Indian Ocean dipole (IOD) events, due to the effects of initial errors. The physical mechanism of the WPB, in which the initial errors show a significant seasonal‐dependent evolution with the fastest error growth in winter, is explored from the dynamical and thermodynamical viewpoints. In terms of dynamics, in the growing phase of pure positive IOD events, the vertical temperature advection associated with the reference state IOD events plays a dominant role in advancing the fastest error growth in winter; in terms of thermodynamics, the latent heat flux error and the shortwave radiation error lead to the fastest error growth in winter and favor the occurrence of the WPB. In the decaying phase of pure positive IOD events, the occurrence of the WPB is mainly due to the latent heat flux error since the dynamics play an insignificant role in advancing the fast error growth in winter. For positive IOD events accompanied by El Niño–Southern Oscillation (ENSO), the physical mechanism of the WPB is similar to that for pure positive IOD events in both the growing and decaying phases, except that the shortwave radiation error has a different effect on the error growth in winter, which may be closely related to the perturbed atmospheric circulation in the tropical Indian Ocean associated with ENSO. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-29T03:35:54.510975-05:
      DOI: 10.1002/2014JC010473
       
  • Detecting and understanding the accelerated sea level rise along the east
           coast of U.S. during recent decades
    • Authors: J. S. Kenigson; W. Han
      Pages: n/a - n/a
      Abstract: A “hotspot” of accelerated sea level rise has recently been detected between Cape Hatteras and Cape Cod. The acceleration in the long‐term trend, however, is difficult to isolate from transient acceleration due to variability, particularly the ~60‐year cycle associated with the Atlantic Multidecadal Oscillation (AMO). The Empirical Mode Decomposition (EMD) and Ensemble EMD (EEMD) methods have been used to isolate oscillations and provide robust acceleration estimates for the trend. Yet the reliability of these methods in detecting accelerated sea level rise, particularly given the limited lengths of tide gauge records, has not been fully tested. Here, the EMD and EEMD methods are applied to both tide gauge observations and synthetic sea level time series constructed as a sum of oscillations extracted from tide gauge records and trends with prescribed acceleration rates. The successively truncated synthetic and observed data are analyzed with (E)EMD, and estimates of the acceleration error based on the record length are produced. Generally, EEMD provides more stable acceleration estimates than EMD, and the error decreases as the record length increases, although not monotonically. Records exceeding two multidecadal oscillation periods in length provide superior estimates over shorter records. In addition, the AMO may have contributed significantly to the rapid acceleration detected in the hotspot during recent decades. These findings have important implications for improved detection of regional sea level acceleration in a warming climate. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-29T03:35:52.917115-05:
      DOI: 10.1002/2014JC010305
       
  • Assessing ecosystem response to phosphorus and nitrogen limitation in the
           Pearl River plume using the Regional Ocean Modeling System (ROMS)
    • Authors: Jianping Gan; Zhongming Lu, Anson Cheung, Minhan Dai, Linlin Liang, Paul J. Harrison, Xiaozheng Zhao
      Pages: n/a - n/a
      Abstract: The effect of phosphorus limitation on the Pearl River plume ecosystem, where large gradients in both nitrogen (N) and phosphorus (P) concentrations exist, is investigated in this process‐oriented study by coupling the Regional Ocean Modeling System (ROMS) model with a new nitrogen, phosphorus, phytoplankton, zooplankton, and detritus (NPPZD) ecosystem model. The results of the N‐based only model of Gan et al. [2010] were compared with those of the new NP‐based model for the plume. The inclusion of P‐limitation noticeably reduces the total phytoplankton production in the plume in the P‐limited near and mid field regions of the plume. However, the nitrate in the plume extends farther downstream and forms a broad area of phytoplankton bloom in the N‐limited far field. Moreover, it changes the photosynthetically active radiation and strengthens the subsurface chlorophyll maximum in the near and mid fields, but weakens it in the far field. A high N:P ratio of ~120 in the near field decreases quickly to a low N:P ratio of
      PubDate: 2014-11-28T08:04:55.708693-05:
      DOI: 10.1002/2014JC009951
       
  • Retrieving density and velocity fields of the ocean's interior from
           surface data
    • Authors: Lei Liu; Shiqiu Peng, Jinbo Wang, Rui Xin Huang
      Pages: n/a - n/a
      Abstract: Using the “interior + surface quasigeostrophic” (isQG) method, the density and horizontal velocity fields of the ocean's interior can be retrieved from surface data. This method was applied to the Simple Ocean Data Assimilation (SODA) and the Hybrid Coordinate Ocean Model (HYCOM)/Navy Coupled Ocean Data Assimilation (NCODA) reanalysis datasets. The input surface data include sea surface height (SSH), sea surface temperature (SST), sea surface salinity (SSS), and a region‐averaged stratification. The retrieved subsurface fields are compared with reanalysis data for three tested regions, and the results indicate that the isQG method is robust. The isQG method is particularly successful in the energetic regions like the Gulf Stream region with weak stratification, and the Kuroshio region with strong correlation between sea surface density (SSD) and SSH. It also works, though less satisfactorily, in the Agulhas leakage region. The performance of the isQG method in retrieving subsurface fields varies with season, and peaks in winter when the mixed layer is deeper and stratification is weaker. In addition, higher‐resolution data may facilitate the isQG method to achieve a more successful reconstruction for the velocity retrieval. Our results suggested that the isQG method can be used to reconstruct the ocean interior from the satellite‐derived SSH, SST and SSS data in the near future. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-28T07:59:41.678496-05:
      DOI: 10.1002/2014JC010221
       
  • A subtropical North Atlantic regional atmospheric moisture budget
    • Authors: Joseph M. D'Addezio; Frederick M. Bingham
      Pages: n/a - n/a
      Abstract: The synergistic effects of evaporation (E), precipitation (P), and Ekman transport make the SPURS (Salinity Processes in the Upper Ocean Regional Study) region in the subtropical North Atlantic (15‐30°N, 30‐45°W) the natural location for the world's highest open ocean SSS maximum. Using the MERRA and ERA‐Interim atmospheric reanalyses, we reproduce the mean hydrologic state of the atmosphere over the SPURS region since 1979 and roughly deduce the change in salinity across the meridional domain due solely to interactions between E‐P and Ekman transport. Our findings suggest a region that is highly evaporative at a mean rate of 4.87 mm/day with a standard deviation of 1.2 mm/day and little seasonality. Precipitation is much more variable with an annual fall maximum around 3 mm/day but only a mean rate of 1.37 mm/day with a standard deviation of 1.46 mm/day. The resulting E‐P variable has a mean rate of 3.50 mm/day with a standard deviation of 1.92 mm/day and matches well with the moisture flux divergence term although the former is typically larger by a small margin. Strong prevailing easterly trade winds generate northward Ekman transports that advect water toward the salinity maximum around 25°N. A short calculation shows that atmospheric moisture dynamics could potentially account for about 1/3 of the change in salinity between 15°N and 25°N giving an estimate of the role that surface freshwater flux plays in the maintenance of the salinity maximum. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-28T07:59:16.934157-05:
      DOI: 10.1002/2014JC010300
       
  • Antarctic bottom water temperature changes in the western South Atlantic
           from 1989‐2014
    • Authors: Gregory C. Johnson; Kristene E. McTaggart, Rik Wanninkhof
      Pages: n/a - n/a
      Abstract: Warming of abyssal waters in recent decades contributes to global heat uptake and sea level rise. Repeat oceanographic section data in the western South Atlantic taken mostly in 1989 (1995 across the Scotia Sea), 2005, and 2014 are used to quantify warming in abyssal waters that spread northward through the region from their Antarctic origins in the Weddell Sea. While much of the Scotia Sea warmed between 1995 and 2005, only the southernmost portion, on the north side of the Weddell Gyre, continued to warm between 2005 and 2014. The abyssal Argentine Basin also warmed between 1989 and 2005, but again only the southernmost portion continued to warm between 2005 and 2014, suggesting a slowdown in the inflow of the coldest, densest Antarctic Bottom Waters into the western South Atlantic between 1989 and 2014. In contrast, the abyssal waters of the Brazil Basin warmed both between 1989 and 2005 and between 2005 and 2014, at a rate of about 2 mºC yr‐1. This warming is also assessed in terms of the rates of change of heights above the bottom for deep isotherms in each deep basin studied. These results, together with findings from previous studies, suggest the deep warming signal observed in the Weddell Sea after the mid‐1970s Weddell Polynya was followed by abyssal warming in the Argentine Basin from the late 1970s through about 2005, then warming in the deep Vema Channel from about 1992 through at least 2010, and warming in the Brazil Basin from 1989 to 2014. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-27T02:34:27.103652-05:
      DOI: 10.1002/2014JC010367
       
  • River runoff effect on the suspended sediment property in the upper
           Chesapeake Bay using MODIS observations and ROMS simulations
    • Authors: Xiaoming Liu; Menghua Wang
      Pages: n/a - n/a
      Abstract: Ocean color data derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the satellite Aqua from 2002–2012 and simulations from the Regional Ocean Modeling System (ROMS) are used to study the impact of the Susquehanna River discharge on the total suspended sediment (TSS) concentration in the upper Chesapeake Bay. Since the water in the upper Chesapeake Bay is highly turbid, the shortwave infrared (SWIR)‐based atmospheric correction algorithm is used for deriving the normalized water‐leaving radiance nLw(λ) spectra from MODIS‐Aqua measurements. nLw(λ) spectra are further processed into the diffuse attenuation coefficient at the wavelength of 490 nm Kd(490) and TSS. MODIS‐Aqua‐derived monthly TSS concentration in the upper Chesapeake Bay and in situ Susquehanna River discharge data show similar patterns in seasonal variations. The TSS monthly temporal variation in the upper Chesapeake Bay is also found in phase with the monthly averaged river discharge data. Since the Susquehanna River discharge is mainly dominated by a few high discharge events due to winter‐spring freshets or tropical storms in each year, the impact of these high discharge events on the upper Chesapeake Bay TSS is investigated. Both MODIS‐measured daily TSS images and sediment data derived from ROMS simulations show that the Susquehanna River discharge is the dominant factor for the variations of TSS concentration in the upper Chesapeake Bay. Although the high river discharge event usually lasts for only a few days, its induced high TSS concentration in the upper Chesapeake Bay can sustain for ~10–20 days. The elongated TSS rebounding stage is attributed to horizontal advection of slowly settling fine sediment from the Susquehanna River. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-27T02:22:43.673483-05:
      DOI: 10.1002/2014JC010081
       
  • Characterizing the eddy field in the Arctic Ocean halocline
    • Authors: Mengnan Zhao; Mary‐Louise Timmermans, Sylvia Cole, Richard Krishfield, Andrey Proshutinsky, John Toole
      Pages: n/a - n/a
      Abstract: Ice‐Tethered Profilers (ITP), deployed in the Arctic Ocean between 2004 and 2013, have provided detailed temperature and salinity measurements of an assortment of halocline eddies. A total of 127 mesoscale eddies have been detected, 95% of which were anticyclones, the majority of which had anomalously cold cores. These cold‐core anticyclonic eddies were observed in the Beaufort Gyre region (Canadian water eddies) and the vicinity of the Transpolar Drift Stream (Eurasian water eddies). An Arctic‐wide calculation of the first baroclinic Rossby deformation radius Rd has been made using ITP data coupled with climatology; Rd ~ 13 km in the Canadian water and ~ 8 km in the Eurasian water. The observed eddies are found to have scales comparable to Rd. Halocline eddies are in cyclogeostrophic balance and can be described by a Rankine Vortex with maximum azimuthal speeds between 0.05 and 0.4 m/s. The relationship between radius and thickness for the eddies is consistent with adjustment to the ambient stratification. Eddies may be divided into four groups, each characterized by distinct core depths and core temperature and salinity properties, suggesting multiple source regions and enabling speculation of varying formation mechanisms. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-27T02:14:53.169603-05:
      DOI: 10.1002/2014JC010488
       
  • Stratified turbulence in the nearshore coastal ocean: Dynamics and
           evolution in the presence of internal bores
    • Authors: Ryan K. Walter; Michael E. Squibb, C. Brock Woodson, Jeffrey R. Koseff, Stephen G. Monismith
      Pages: n/a - n/a
      Abstract: High‐frequency measurements of stratified turbulence throughout the water column were collected over a two‐week period in the nearshore environment of southern Monterey Bay, CA using a cabled observatory system and an underwater turbulence flux tower. The tower contained a vertical array of acoustic Doppler velocimeters and fast‐response conductivity‐temperature sensors, providing a nearly continuous data set of turbulent velocity and density fluctuations and a unique look into the stratified turbulence field. The evolution of various turbulence quantities and direct measurements of the vertical turbulent diffusivity are examined in the presence of nearshore internal bores, both in the near‐bed region and in the stratified interior. We show that individual bores can drive substantial changes in local turbulence and mixing dynamics, with considerable differences between the leading and trailing edges of the bores. Using direct observations of the flux Richardson number, our measurements confirm previous observations that show the highest mixing efficiencies (Γ) occurring in regions of buoyancy‐controlled turbulence. Parameterizations of the flux Richardson number as a function of the turbulence activity number are also presented. Finally, we demonstrate that the commonly used assumption of a constant mixing efficiency (Γ = 0.2) for calculating turbulent diffusivities leads to significant overestimates compared to diffusivity values calculated using the directly measured mixing efficiency. Implications of the results are discussed. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-27T02:11:27.666885-05:
      DOI: 10.1002/2014JC010396
       
  • Extension of an Ice Shelf Water plume model beneath sea ice with
           application in McMurdo Sound, Antarctica
    • Authors: K. G. Hughes; P. J. Langhorne, G. H. Leonard, C. L. Stevens
      Pages: n/a - n/a
      Abstract: A one‐dimensional, frazilladen plume model predicts the properties of Ice Shelf Water (ISW) as it evolves beneath sea ice beyond the ice shelf edge. An idealized background ocean circulation, which moves parallel to the plume, imitates forcings other than the plume's own buoyancy. The size distribution and concentration of the plume's suspended frazil ice crystals are affected by the background circulation velocity, the rootmeansquare tidal velocity, the drag coefficient, and the efficiency of secondary nucleation. Consequently, these variables are the key physical controls on the survival of supercooled water with distance from the ice shelf, which is predicted using several realistic parameter choices. Starting at 65m thick, the in situ supercooled layer thins to 11 ± 5m and 4±3m at distances of 50 km and 100 km, respectively. We apply the extended model in McMurdo Sound, Antarctica, along the expected path of the coldest water. Three latewinter oceanographic stations along this path, in conjunction with historical data, provide initial conditions and evaluation of the simulations. Near the ice shelf in the western Sound, the water column consisted entirely of ISW, and the subice platelet layer thickness exceeded 5m with platelet crystals dominating the sea ice structure suggesting that ISW persisted throughout winter. Presuming a constant ISW flux, the model predicts that the plume increases thermodynamic growth of sea ice by approximately 0.1myr‐1 (~5% of the average growth rate) even as far as 100 km beyond the ice shelf edge. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-27T02:11:20.231223-05:
      DOI: 10.1002/2013JC009411
       
  • Assessment of radar‐derived snow depth over Arctic sea ice
    • Authors: Thomas Newman; Sinead L. Farrell, Jacqueline Richter‐Menge, Laurence N. Connor, Nathan T. Kurtz, Bruce C. Elder, David McAdoo
      Pages: n/a - n/a
      Abstract: Knowledge of contemporaneous snow depth on Arctic sea ice is important both to constrain the regional climatology and to improve the accuracy of satellite altimeter estimates of sea ice thickness. We assess new data available from the NASA Operation IceBridge snow radar instrument and derive snow depth estimates across the western Arctic ice pack using a novel methodology based on wavelet techniques that define the primary reflecting surfaces within the snow pack. We assign uncertainty to the snow depth estimates based upon both the radar system parameters and sea ice topographic variability. The accuracy of the airborne snow depth estimates are examined via comparison with coincident measurements gathered in situ across a range of ice types in the Beaufort Sea. We discuss the effect of surface morphology on the derivation, and consequently the accuracy, of airborne snow depth estimates. We find that snow depths derived from the airborne snow radar using the wavelet‐based technique are accurate to 1 cm over level ice. Over rougher surfaces including multiyear and ridged ice, the radar system is impacted by ice surface morphology. Across basin scales we find the snow‐radar‐derived snow depth on first‐year ice is at least ˜60% of the value reported in the snow climatology for the Beaufort Sea, Canada Basin and parts of the central Arctic, since these regions were previously dominated by multiyear ice during the measurement period of the climatology. Snow on multiyear ice is more consistent with the climatology. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-25T09:01:17.044156-05:
      DOI: 10.1002/2014JC010284
       
  • Mean sea level variability along the northeast American Atlantic coast,
           and the roles of the wind and the overturning circulation
    • Authors: Philip L. Woodworth; Miguel Á. Morales Maqueda, Vassil M. Roussenov, Richard G. Williams, Chris W. Hughes
      Pages: n/a - n/a
      Abstract: The variability in mean sea level (MSL) during 1950‐2009 along the northeast American Atlantic coast north of Cape Hatteras has been studied, using data from tide gauges and satellite altimetry and information from the Liverpool/Hadley Centre (LHC) ocean model, thereby providing new insights into the spatial and temporal scales of the variability. Although a relationship between sea level and the overturning circulation can be identified (an increase of approximately 1.5 cm in MSL for a decrease of 1 Sv in overturning transport), it is the effect of the near‐shore wind forcing on the shelf that is found to dominate the interannual sea level variability. In particular, winds are found to be capable of producing low‐frequency changes in MSL (‘accelerations') in a narrow coastal band, comparable to those observed by the tide gauges. Evidence is presented supporting the idea of a ‘common mode' of spatially‐coherent low‐frequency MSL variability, both to the north and south of Cape Hatteras and throughout the northwest Atlantic, which is associated with large spatial‐scale density changes from year to year. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-24T04:24:37.152666-05:
      DOI: 10.1002/2014JC010520
       
  • Comment on “Buoyancy frequency profiles and internal semidiurnal
           tide turning depths in the oceans” by King et al.
    • Authors: Trevor J. McDougall; Paul M. Barker
      Pages: n/a - n/a
      Abstract: The assertion by King et al. (2012) that the CSIRO SeaWater library of oceanographic computer software implements an incorrect definition of the buoyancy frequency N is demonstrated to be false. We examine why King et al. (2012) found significantly different values of the buoyancy frequency in the deep ocean when using the CSIRO software compared with using the TEOS‐10 software, and we conclude that this is due to the variable composition of seawater, as encapsulated in the difference between Absolute Salinity and Reference Salinity. Also, any pre‐processing of data such vertical averaging or smoothing, should be performed on the conservative variables Conservative Temperature and Absolute Salinity rather than on in situ temperature or on any type of density since these variables are not conservative. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-24T04:18:00.184193-05:
      DOI: 10.1002/2014JC010066
       
  • Enhancement in vertical fluxes at a front by mesoscale‐submesoscale
           coupling
    • Authors: Sanjiv Ramachandran; Amit Tandon, Amala Mahadevan
      Pages: n/a - n/a
      Abstract: Oceanic frontal instabilities are of importance for the vertical exchange of properties in the ocean. Submesoscale, O(1) Rossby number, dynamics are particularly relevant for inducing the vertical (and lateral) flux of buoyancy and tracers in the mixed layer, but how these couple with the stratified pycnocline is less clear. Observations show surface fronts often persist beneath the mixed layer. Here, we use idealized, three‐dimensional model simulations to show how surface fronts that extend deeper into the pycnocline invoke enhanced vertical fluxes through the coupling of submesoscale and mesoscale instabilities. We contrast simulations in which the front is restricted to the mixed layer with those in which it extends deeper. For the deeper fronts, we examine the effect of density stratification on the vertical coupling. Our results show deep fronts can dynamically couple the mixed layer and pycnocline on time scales that increase with the peak stratification beneath the mixed layer. Eddies in the interior generate skew fluxes of buoyancy and tracer oriented along isopycnals, thus providing an adiabatic pathway for the interior to interact with the mixed layer at fronts. The vertical enhancement of tracer fluxes through the meso‐submeso‐scale coupling described here is thus relevant to the vertical supply of nutrients for phytoplankton in the ocean. A further implication for wind‐forced fronts is that the vertical structure of the streamfunction characterizing the exchange between the interior and the mixed layer exhibits significant qualitative differences compared to a linear combination of existing parameterizations of submesoscale eddies in the mixed layer and mesoscale eddies in the interior. The discrepancies are most severe within the mixed layer suggesting a potential role for Ekman‐layer dynamics absent in existing submesoscale parameterizations. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-24T04:09:16.301625-05:
      DOI: 10.1002/2014JC010211
       
  • Reply to comment by McDougall and Barker on “Buoyancy frequency
           profiles and internal semidiurnal tide turning depths in the oceans”
           
    • Authors: Theo Gerkema; Harry L. Swinney, M. Stone, M. Marder
      Pages: n/a - n/a
      Abstract: The Comment concerns a remark in Section 2.2 of King et al. (J. Geophys. Res., 2012), where we stated that the script sw_bfrq.m for computing N2, the square of the buoyancy frequency, is incorrect. We were mistaken and regret our error. We here clarify the intent of that Section. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-24T04:04:21.861087-05:
      DOI: 10.1002/2014JC010222
       
  • Estuary‐enhanced upwelling of marine nutrients fuels coastal
           productivity in the U.S. Pacific Northwest
    • Authors: Kristen A. Davis; Neil S. Banas, Sarah N. Giddings, Samantha A. Siedlecki, Parker MacCready, Evelyn J Lessard, Raphael M Kudela, Barbara M. Hickey
      Pages: n/a - n/a
      Abstract: The Pacific Northwest (PNW) shelf is the most biologically productive region in the California Current System. A coupled physical‐biogeochemical model is used to investigate the influence of freshwater inputs on the productivity of PNW shelf waters using realistic hindcasts and model experiments that omit outflow from the Columbia River and Strait of Juan de Fuca (outlet for the Salish Sea estuary). Outflow from the Strait represents a critical source of nitrogen to the PNW shelf‐accounting for almost half of the primary productivity on the Vancouver Island shelf, a third of productivity on the Washington shelf, and a fifth of productivity on the Oregon shelf during the upwelling season. The Columbia River has regional effects on the redistribution of phytoplankton, but does not affect PNW productivity as strongly as does the Salish Sea. A regional nutrient budget shows that nitrogen exiting the Strait is almost entirely (98%) of ocean‐origin ‐ upwelled into the Strait at depth, mixed into surface waters by tidal mixing, and returned to the coastal ocean. From the standpoint of nitrogen availability in the coastal euphotic zone, the estuarine circulation driven by freshwater inputs to the Salish Sea is more important than the supply of terrigenous nitrogen by rivers. Nitrogen‐rich surface waters exiting the Strait follow two primary pathways—to the northwest in the Vancouver Island Coastal Current and southward toward the Washington and Oregon shelves. Nitrogen flux from the Juan de Fuca Strait and Eddy Region to these shelves is comparable to flux from local wind‐driven upwelling. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-22T03:36:21.296937-05:
      DOI: 10.1002/2014JC010248
       
  • Preferential burial of permafrost‐derived organic carbon in
           Siberian‐Arctic shelf waters
    • Authors: Jorien E. Vonk; Igor P. Semiletov, Oleg V. Dudarev, Timothy I. Eglinton, August Andersson, Natalia Shakhova, Alexander Charkin, Birgit Heim, Örjan Gustafsson
      Pages: n/a - n/a
      Abstract: The rapidly changing East Siberian Arctic Shelf (ESAS) receives large amounts of terrestrial organic carbon (OC) from coastal erosion and Russian‐Arctic rivers. Climate warming increases thawing of coastal Ice Complex Deposits (ICD) and can change both the amount of released OC, as well as its propensity to be converted to greenhouse gases (fueling further global warming) or to be buried in coastal sediments. This study aimed to unravel the susceptibility to degradation, and transport and dispersal patterns of OC delivered to the ESAS. Bulk and molecular radiocarbon analyses on surface particulate matter (PM), sinking PM and underlying surface sediments illustrate the active release of old OC from coastal permafrost. Molecular tracers for recalcitrant soil OC showed ages of 3.4‐13 14C‐ky in surface PM and 5.5‐18 14C‐ky in surface sediments. The age difference of these markers between surface PM and surface sediments is larger (i) in regions with low OC accumulation rates, suggesting a weaker exchange between water column and sediments, and (ii) with increasing distance from the Lena River, suggesting preferential settling of fluvially‐derived old OC nearshore. A dual‐carbon end‐member mixing model showed that (i) contemporary terrestrial OC is dispersed mainly by horizontal transport while being subject to active degradation, (ii) marine OC is most affected by vertical transport and also actively degraded in the water column, and (iii) OC from ICD settles rapidly and dominates surface sediments. Preferential burial of ICD‐OC released into ESAS coastal waters might therefore lower the suggested carbon cycle climate feedback from thawing ICD permafrost. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-21T22:36:47.252084-05:
      DOI: 10.1002/2014JC010261
       
  • Boundary mixing in Orkney Passage outflow
    • Authors: K. L. Polzin; A. C. Naveira Garabato, E. P. Abrahamsen, L. Jullion, M. P. Meredith
      Pages: n/a - n/a
      Abstract: One of the most remarkable features of contemporary oceanic climate change is the warming and contraction of Antarctic Bottom Water over much of global ocean abyss. These signatures represent changes in ventilation mediated by mixing and entrainment processes that may be location‐specific. Here we use available data to document, as best possible, those mixing processes as Weddell Sea Deep and Bottom Waters flow along the South Orkney Plateau, exit the Weddell Sea via Orkney Passage and fill the abyssal Scotia Sea. First, we find that an abrupt transition in topography upstream of Orkney Passage delimits the extent of the coldest waters along the Plateau's flanks and may indicate a region of especially intense mixing. Second, we revisit a control volume budget by Heywood et al. (Nature, 2002) for waters trapped within the Scotia Sea after entering through Orkney Passage. This budget requires extremely vigorous water mass transformations with a diapycnal transfer coefficient of 39(±10) × 10‐4 m2 s–1. Evidence for such intense diapycnal mixing is not found in the abyssal Scotia Sea interior and, while we do find large rates of diapycnal mixing in conjunction with a downwelling Ekman layer on the western side of Orkney Passage, it is insufficient to close the budget. This leads us to hypothesize that the Heywood budget is closed by a boundary mixing process in which the Ekman layer associated with the Weddell Sea Deep Water boundary current experiences relatively large‐vertical‐scale overturning associated with tidal forcing along the southern boundary of the Scotia Sea. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-21T17:01:09.952412-05:
      DOI: 10.1002/2014JC010099
       
  • Influence of summertime mesoscale convective systems on the heat balance
           and surface mixed‐layer dynamics of a large Amazonian hydroelectric
           reservoir
    • Authors: Marcelo P. Curtarelli; Igor Ogashawara, Carlos A. S. Araújo, Enner H. Alcântara, João A. Lorenzzetti, José L. Stech
      Pages: n/a - n/a
      Abstract: We evaluated the impacts of summertime mesoscale convective systems (MCS) on the heat balance and diel surface mixed layer (SML) dynamics of the Brazilian Amazon's Tucuruí Hydroelectric Reservoir (THR). We used a synergistic approach that combines in situ data, remote sensing data and three‐dimensional (3D) modeling to investigate the typical behavior of the components of the heat balance and the SML dynamics. During the study period (the austral summer of 2012‐2013), 22 days with MCS activity were identified. These events occurred approximately every 4 days, and they were most frequent during January (50% of the observations). An analysis of local meteorological data showed that when MCS occur, the environmental conditions at THR change significantly (p‐value < 0.01). The net longwave flux, which was the heat balance component most strongly impacted by MCS, increased more than 32% on days with MCS activity. The daily integrated heat balance became negative (‐54 W m‐2) on MCS days, while the balance was positive (19 W m‐2) on non MCS days. In response to the changes in the heat balance, the SML dynamics changed when a MCS was over the THR. The SML depth was typically 28% higher on the days with MCS (~1.6 m) compared with the days without MCS (~1.3 m). The results indicate that MCS are one of the main meteorological disturbances driving the heat balance and the mixing dynamics of Amazonian hydroelectric reservoirs during the summer. These events may have implications for the water quality and greenhouse gas emissions of Amazonian reservoirs. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-21T16:59:56.543432-05:
      DOI: 10.1002/2014JC010288
       
  • Estimating mean dynamic topography in boundary currents and the use of
           Argo trajectories
    • Authors: Melissa Bowen; Philip Sutton, Dean Roemmich
      Pages: n/a - n/a
      Abstract: A Mean Dynamic Topography (MDT) is required to estimate mean transport in the ocean, to combine with altimetry to derive instantaneous geostrophic surface velocities, and to estimate transport from shipboard hydrography. A number of MDTs are now available globally but differ most markedly in boundary currents and the Antarctic Circumpolar Current. We evaluate several MDTs in two boundary currents off New Zealand (in the subtropical western boundary current system east of the country and in the Subantarctic Front to the south) using satellite, hydrographic, and Argo observations near two altimeter tracks. Argo float trajectories are combined with estimates of shear to produce new MDTs along both altimeter tracks: sufficiently high numbers of Argo floats travel in both boundary currents to allow a useful estimate of the mean flow at 1000 m depth and conservation of potential vorticity is used to account for more realistic flow paths. In finding a MDT, we show the uncertainties in the estimates of velocity differences between 1000 m and the surface from density climatologies, while often not estimated, need to be considered. The MDT computed from the Argo trajectories is generally consistent with the CLS09 MDT [Rio et al., 2011] in both boundary currents and, in some locations, distinctly different from the MDT using a “level of no motion” assumption. The comparison suggests velocities from Argo trajectories can be usefully combined with other observations to improve estimates of flows and MDT in boundary currents. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-21T16:56:41.57145-05:0
      DOI: 10.1002/2014JC010281
       
  • Responses of the ocean planktonic ecosystem to finite‐amplitude
           perturbations
    • Authors: Qiang Wang; Mu Mu
      Pages: n/a - n/a
      Abstract: The responses of the ocean planktonic ecosystem to finite‐amplitude perturbations are investigated using an ocean planktonic ecosystem model. Through changing the higher predation rate on zooplankton, multiple equilibria of the model, namely “high‐nutrient” and “low‐nutrient” states, are obtained under certain parameter values. Based on these states, the perturbations with maximum nonlinear growth are determined using the conditional nonlinear optimal perturbation (CNOP) method. The linear and nonlinear evolutions of the CNOP perturbation are compared. The results show that the nonlinear evolution of the perturbation leads to predator–prey oscillations with larger amplitude than the linear evolution. Besides, after the perturbation amplitude exceeds a critical value, the nonlinear evolution of the perturbation will induce the linearly stable ecosystem state to lose the stability and become nonlinearly unstable. This implies that nonlinear processes have important impacts on the stability of the ecosystem. Specifically, we identify the nonlinear processes related to zooplankton grazing to impact the stability most for the high‐nutrient state, while for the low‐nutrient state the main nonlinear process affecting the stability is the uptake process. These results help to improve our understanding of the sensitivity of the oceanic ecosystem model to finite‐amplitude perturbations and the underlying nonlinear stability properties. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-21T16:53:18.074858-05:
      DOI: 10.1002/2014JC010339
       
  • Seasonal variation and biogeochemical cycling of dimethylsulfide (DMS) and
           dimethylsulfoniopropionate (DMSP) in the Yellow Sea and Bohai Sea
    • Authors: Gui‐Peng Yang; Yi‐Zhu Song, Hong‐Hai Zhang, Cheng‐Xuan Li, Guan‐Wei Wu
      Pages: n/a - n/a
      Abstract: The concentrations of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and chlorophyll a (Chl‐a) as well as the size distribution of particulate DMSP (DMSPp) were determined in the Yellow Sea (YS) and Bohai Sea (BS) during two cruises from 1 to 20 November, 2012 and from 21 June to 11 July, 2013. Besides, the biological production and consumption rates of DMS and the degradation rates of dissolved DMSP (DMSPd) were also measured. The concentrations of DMS and DMSP showed a significant seasonal variation with higher values in summer, which corresponded well with the seasonal change of Chl‐a in the study area. Both DMS and DMSPp concentrations were significantly correlated with Chl‐a levels, implying that phytoplankton biomass might play an important role in controlling the distributions of DMS and DMSP in the study area. The size‐fractionation research showed that nanophytoplankton (5‐20 µm) contributed to most of Chl‐a and DMSPp in autumn and summer. The average biological production and consumption rates of DMS during summer were 13.35 and 9.80 nmol L‐1 d‐1, respectively, which were much higher than those during autumn. The degradation rates of DMSPd during summer ranged from 7.10 to 21.70 nmol L‐1 d‐1, with an average of 14.71 nmol L‐1 d‐1, which was nearly equal to the average biological production rate (13.35 nmol L‐1 d‐1) of DMS. The average sea‐to‐air flux of DMS in the YS and BS were 12.06 and 20.81 µmol m‐2 d‐1 in autumn and in summer, respectively, which were much higher than the values reported in the ocean. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-20T02:08:45.710622-05:
      DOI: 10.1002/2014JC010373
       
  • The Seasonal evolution of sea ice floe size distribution
    • Authors: Donald K. Perovich; Kathleen F. Jones
      Pages: n/a - n/a
      Abstract: The Arctic sea ice cover undergoes large changes over an annual cycle. In winter and spring the ice cover consists of large, snow‐covered plate‐like ice floes, with very little open water. By the end of summer the snow cover is gone and the large floes have broken into a complex mosaic of smaller, rounded floes surrounded by a lace of open water. This evolution strongly affects the distribution and fate of the solar radiation deposited in the ice‐ocean system and consequently the heat budget of the ice cover. In particular, increased floe perimeter can result in enhanced lateral melting. We attempt to quantify the floe evolution process through the concept of a floe size distribution that is modified by lateral melting and floe breaking. A time series of aerial photographic surveys made during the SHEBA field experiment is analyzed to determine evolution of the floe size distribution from spring through summer. Based on earlier studies, we assume the floe size cumulative distribution could be represented by a power law D‐α where D is the floe diameter. The exponent α as well as the number density of floes Ntot are estimated from measurements of total ice area and perimeter. As summer progressed, there was an increase in α as the size distribution shifted towards smaller floes and the number of floes increased. Lateral melting causes the distribution to deviate from a power law for small floe sizes. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-20T02:05:29.482746-05:
      DOI: 10.1002/2014JC010136
       
  • Integrated modeling framework to quantify the coastal protection services
           supplied by vegetation
    • Authors: Greg Guannel; Peter Ruggiero, Joe Faries, Katie Arkema, Malin Pinsky, Guy Gelfenbaum, Anne Guerry, Choong‐Ki Kim
      Pages: n/a - n/a
      Abstract: Vegetation can protect communities by reducing nearshore wave height and altering sediment transport processes. However, quantitative approaches for evaluating the coastal protection services, or benefits, supplied by vegetation to people in a wide range of coastal environments are lacking. To begin to fill this knowledge gap, an integrated modeling approach is proposed for quantifying how vegetation modifies nearshore processes – including the attenuation of wave height, mean and total water level – and reduces shoreline erosion during storms. We apply the model to idealized seagrass‐sand and mangrove‐mud cases, illustrating its potential by quantifying how those habitats reduce water levels and sediment loss beyond what would be observed in the absence of vegetation. The integrated modeling approach provides an efficient way to quantify the coastal protection services supplied by vegetation and highlights specific research needs for improved representations of the ways in which vegetation modifies wave‐induced processes. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-14T18:35:35.32085-05:0
      DOI: 10.1002/2014JC009821
       
  • Accuracy and precision in the calculation of phenology metrics
    • Authors: Sofia A Ferreira; Andre W Visser, Brian R MacKenzie, Mark R Payne
      Pages: n/a - n/a
      Abstract: Phytoplankton phenology (the timing of seasonal events) is a commonly used indicator for evaluating responses of marine ecosystems to climate change. However, phenological metrics are vulnerable to observation‐ (bloom amplitude, missing data and observational noise) and analysis‐related (temporal resolution, pre‐processing technique and phenology metric) processes. Here, we consider the impact of these processes on the robustness of four phenology metrics (timing of maximum, 5% above median, maximum growth rate, and 15% of cumulative distribution). We apply a simulation testing approach, where a phenology metric is first determined from a noise‐ and gap‐free time series, and again once it has been modified. We show that precision is a greater concern than accuracy for many of these metrics, an important point that has been hereto overlooked in the literature. The variability in precision between phenology metrics is substantial, but it can be improved by the use of pre‐processing techniques (e.g. gap‐filling or smoothing). Furthermore, there are important differences in the inherent variability of the metrics, that may be crucial in the interpretation of studies based upon them. Of the considered metrics, the 15% of cumulative distribution metric best satisfies the precision criteria. However, the 5% above median metric is comparable in terms of precision and exhibits more inherent variability. We emphasise that the choice of phenology metric should be determined by the specific nature of the question being asked. We believe these findings to be useful to the current discussion on phenology metrics of phytoplankton dynamics. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-14T18:34:17.152246-05:
      DOI: 10.1002/2014JC010323
       
  • Southern Ocean wind‐driven entrainment enhances satellite
           chlorophyll‐a through the summer
    • Authors: Magdalena M. Carranza; Sarah T. Gille
      Pages: n/a - n/a
      Abstract: Despite being the largest High Nitrate Low Chlorophyll (HNLC) region, the Southern Ocean sustains phytoplankton blooms through the summer, when presumably there is sufficient light, but nutrients in the euphotic zone have been depleted. Physical processes that can potentially supply nutrients from subsurface waters to the euphotic zone, and promote phytoplankton growth in the summer, have not been fully explored at the large scale. By means of a correlation analysis, this study combines high resolution satellite observations of ocean color, winds and sea surface temperature (SST), surface heat fluxes from reanalysis and Argo mixed‐layer depth (MLD) estimates to explore the role of the atmospheric forcing (i.e. winds and surface heat fluxes) on upper ocean processes that may help sustain high satellite chlorophyl‐a (Chl‐a) through the summer. Two physical processes that can supply nutrients to the euphotic zone are: MLD deepening, caused by wind‐mixing and/or surface cooling, and Ekman pumping driven by the wind stress curl. We find that high winds correlate with high Chl‐a over broad open ocean areas, suggesting that transient MLD deepening through wind‐mixing (i.e. wind‐driven entrainment) helps sustain high Chl‐a. Wind‐driven entrainment plays a dominant role on timescales associated with atmospheric synoptic storms (i.e. 
      PubDate: 2014-11-14T18:32:37.639531-05:
      DOI: 10.1002/2014JC010203
       
  • Freshening in the South China Sea during 2012 revealed by Aquarius and in
           situ data
    • Authors: Lili Zeng; W. Timothy Liu, Huijie Xue, Peng Xiu, Dongxiao Wang
      Pages: n/a - n/a
      Abstract: Newly available sea surface salinity (SSS) data from the Aquarius together with in‐situ hydrographic data are used to explore the spatial and temporal characteristics of SSS in the South China Sea (SCS). Using in‐situ observations as the reference, an evaluation of daily Aquarius data indicates that there exists a negative bias of 0.45 psu for the version 3.0 dataset. The root‐mean‐square difference for daily Aquarius SSS is about 0.53 psu after correcting the systematic bias, and those for weekly and monthly Aquarius SSSs are 0.45 and 0.29 psu, respectively. Nevertheless, the Aquarius SSS shows a reliable freshening in the SCS in 2012, which is larger than the Aquarius uncertainty. The freshening of up to 0.4 psu in the upper‐ocean of the northern SCS was confirmed by in‐situ observations. This freshening in 2012 was caused by a combined effect of abundant local freshwater flux and limited Kuroshio intrusion. By comparing the Kuroshio intrusion in 2012 with that in 2011, we found the reduction as a relatively important cause for the freshening over the northern SCS. In contrast to the northern SCS, reduced river discharge in 2012 played the leading role to the saltier surface in the region near the Mekong River mouth with respect to 2011. This article is protected by copyright. All rights reserved.
      PubDate: 2014-11-14T18:32:28.43649-05:0
      DOI: 10.1002/2014JC010108
       
  • Intraseasonal variability of the subthermocline current east of Mindanao
    • Authors: Qingye Wang; Fangguo Zhai, Fujun Wang, Dunxin Hu
      Pages: n/a - n/a
      Abstract: The intraseasonal variability (ISV) of the subthermocline current east of Mindanao was characterized and shown to be caused by the activity of subthermocline eddies using mooring observations at 8°N, 127.03°E and a high‐resolution numerical model. The ISV of the observed current east of Mindanao is vertically coherent in the upper 940 m but is significantly intensified below the thermocline. The ISV amplitude (8 cm s‐1) of zonal subthermocline current is comparable with that (11 cm s‐1) of the meridional current, revealing the nature of active eddies. The ISV of the subthermocline current was caused by the subthermocline eddies from three different pathways. The subthermocline eddies propagating along approximately 10‐11°N contributed more to the ISV of the subthermocline current east of Mindanao than did those eddies propagating westward along 8°N or northwestward from the New Guinea coast. Subthermocline eddies mainly exist south of the bifurcation latitude of the North Equatorial Current in the western tropical Pacific, and their generation and propagation mechanisms are briefly discussed.
      PubDate: 2014-11-13T04:28:07.828136-05:
      DOI: 10.1002/2014JC010343
       
  • Long‐lived mesoscale eddies in the eastern Mediterranean Sea:
           Analysis of 20 years of AVISO geostrophic velocities
    • Authors: Nadia Mkhinini; Andre Louis Santi Coimbra, Alexandre Stegner, Thomas Arsouze, Isabelle Taupier‐Letage, Karine Béranger
      Pages: n/a - n/a
      Abstract: We analyzed 20 years of AVISO data set to detect and characterize long‐lived eddies, which stay coherent more than six months, in the Eastern Mediterranean Sea. In order to process the coarse gridded (1/8º) AVISO geostrophic velocity fields, we optimized a geometrical eddy detection algorithm. Our main contribution was to implement a new procedure based on the computation of the Local and Normalized Angular Momentum (LNAM) to identify the positions of the eddy centers and to follow their Lagrangian trajectories. We verify on two meso‐scale anticyclones, sampled during the EGYPT campaign in 2006, that our methodology provides a correct estimation of the eddy centers and their characteristic radius corresponding to the maximal tangential velocity. Our analysis reveals the dominance of anticyclones among the long‐lived eddies. This cyclone‐anticyclone asymmetry appears to be much more pronounced in Eastern Mediterranean Sea than in the global ocean. Then we focus our study on the formation areas of longlived eddies. We confirm that the generations of the Ierapetra and the Pelops anticyclones are recurrent and correlated to the Etesian wind‐forcing. We also provide some evidence that the smaller cyclonic eddies formed at the southwest of Crete may also be induced by the same wind forcing. On the other hand, the generation of long‐lived eddies along the Libyo‐Egyptian coast are not correlated to the local wind‐stress curl but surprinsingly, their initial formation points follow the Herodotus Trough bathymetry. Moreover, we identify a new formation area, not discussed before, along the curved shelf off Benghazi.
      PubDate: 2014-11-13T04:26:49.362932-05:
      DOI: 10.1002/2014JC010176
       
  • Drifter‐based estimate of the 5 year dispersal of
           Fukushima‐derived radionuclides
    • Authors: I. I. Rypina; S. R. Jayne, S. Yoshida, A. M. Macdonald, K. Buesseler
      Pages: n/a - n/a
      Abstract: Employing some 40 years of North Pacific drifter‐track observations from the Global Drifter Program database, statistics defining the horizontal spread of radionuclides from Fukushima nuclear power plant into the Pacific Ocean are investigated over a time‐scale of 5 years. A novel two‐iteration method is employed to make the best use of the available drifter data. Drifter‐based predictions of the temporal progression of the leading edge of the radionuclide distribution are compared to observed radionuclide concentrations from research surveys occupied in 2012 and 2013. Good agreement between the drifter‐based predictions and the observations is found.
      PubDate: 2014-11-13T04:05:33.737923-05:
      DOI: 10.1002/2014JC010306
       
  • The influence of salinity on tropical Atlantic instability waves
    • Authors: Tong Lee; Gary Lagerloef, Hsun‐Ying Kao, Michael J. McPhaden, Joshua Willis, Michelle M. Gierach
      Pages: n/a - n/a
      Abstract: Sea surface salinity (SSS) data derived from the Aquarius/SAC‐D satellite mission are analyzed along with other satellite and in‐situ data to assess Aquarius' capability to detect tropical instability waves (TIWs) and eddies in the tropical Atlantic Ocean and to investigate the influence that SSS has on the variability. Aquarius data show that the magnitude of SSS anomalies associated with the Atlantic TIWs is ±0.25 practical salinity unit, which is weaker than those in the Pacific by 50%. In the central equatorial Atlantic, SSS contribution to the mean meridional density gradient is similar to sea surface temperature (SST) contribution. Consequently, SSS is important to TIW‐related surface density anomalies and perturbation potential energy (PPE). In this region, SSS influences surface PPE significantly through the direct effect and the indirect effect associated with SSS‐SST co‐variability. Ignoring SSS effects would underestimate TIW‐related PPE by approximately three times in the surface layer. SSS also regulates the seasonality of the TIWs. The boreal‐spring peak of the PPE due to SSS leads that due to SST by about one month. Therefore, SSS not only affects the spatial structure, but the seasonal variability of the TIWs in the equatorial Atlantic. In the northeast Atlantic near the Amazon outflow and the North Brazil Current retroflection region and in the southeast Atlantic near the Congo River outflow, SSS accounts for 80‐90% of the contribution to mean meridional density gradient. Not accounting for SSS effect would underestimate surface PPE in these regions by a factor of 10 and 4, respectively.
      PubDate: 2014-11-13T03:59:35.573693-05:
      DOI: 10.1002/2014JC010100
       
  • Mode‐2 hydraulic control of flow over a small ridge on a continental
           shelf
    • Authors: M. C. Gregg; Jody M. Klymak
      Pages: n/a - n/a
      Abstract: Some of the most intense turbulence in the ocean occurs in hydraulic jumps formed in the lee of sills where flows are hydraulically controlled, usually by the first internal mode. Observations on the outer Texas‐Louisiana continental shelf reveal hydraulic control of internal mode‐2 lasting more than three hours over a 20‐meter‐high ridge on the 100‐meter‐deep continental shelf. When control began the base of the weakly stratified surface layer bulged upward and downward, a signature of mode‐2. As the westward flow producing control was lost, large‐amplitude disturbances, initially resembling a bore in the weakly stratified layer, began propagating eastward. Average dissipation rates inferred from density inversions over the ridge were and , one to two decades above local background. Corresponding diapycnal diffusivities, , were to . Short‐term mixing averages did not evolve systematically with hydraulic control, possibly owing to our inability to observe small overturns in strongly stratified water directly over the ridge. To test the feasibility of our interpretation of the observations, hydrostatic runs with a three‐dimensional MITgcm simulated mode‐2 control and intense mixing over the ridge below the interface. Details differed from observations, principally because we lacked three‐dimensional density fields to initialize the model which was forced with currents observed by a bottom‐mounted ADCP several kilometers east of the ridge. Consequently, the model did not capture all flow features around the bank. The principal conclusion is that hydraulic responses to higher modes can dominate flows around even modest bathymetric irregularities.
      PubDate: 2014-11-11T11:25:36.416152-05:
      DOI: 10.1002/2014JC010043
       
  • Multisensor observations of the Amazon‐Orinoco River plume
           interactions with hurricanes
    • Authors: Nicolas Reul; Yves Quilfen, Bertrand Chapron, Severine Fournier, Vladimir Kurdyavtsev, Roberto Sabia
      Pages: n/a - n/a
      Abstract: An analysis is presented for the spatial and intensity distributions of North Atlantic extreme atmospheric events crossing the buoyant Amazon‐Orinoco freshwater plume. The sea surface cooling amplitude in the wake of an ensemble of storm tracks travelling in that region is estimated from satellite products for the period 1998‐2012. For the most intense storms, cooling is systematically reduced by ~50% over the plume area compared to surroundings open ocean waters. Historical salinity and temperature observations from in situ profiles indicate that salt‐driven vertical stratification, enhanced oceanic heat content and barrier‐layer presence within the plume waters are likely key oceanic factors to explain these results. Satellite SMOS surface salinity data combined with in situ observations are further used to detail the oceanic response to Category 4 hurricane Igor in 2010. Argo and satellite measurements confirm the haline stratification impact on the cooling inhibition as the hurricane crossed the river plume. Over this region, the SSS mapping capability is further tested and demonstrated to monitor the horizontal distribution of the vertical stratification parameter. SMOS SSS data can thus be used to consistently anticipate the cooling inhibition in the wake of TCs travelling over the Amazon‐Orinoco plume region.
      PubDate: 2014-11-08T11:27:48.910934-05:
      DOI: 10.1002/2014JC010107
       
  • Unsteady stress partitioning and momentum transfer in the wave bottom
           boundary layer over movable rippled beds
    • Authors: S. Rodríguez‐Abudo; D. L. Foster
      Pages: n/a - n/a
      Abstract: Observations of the nearbed velocity field over a rippled sediment bed under asymmetric wave forcing conditions were collected using a submersible particle image velocimetry (PIV) system. To examine the role of bedform‐induced dynamics in the total momentum transfer, a double‐averaging technique was implemented on the two‐dimensional time‐dependent velocity field by means of the full momentum equation. This approach allows for direct determination of the bedform‐induced stresses, ie. stresses that arise due to the presence of bedforms, which are zero in flat bed conditions. This analysis suggests that bedform‐induced stresses are closely related to the presence of coherent motions and may be partitioned from the turbulent stresses. Inferences of stress provided by a bedload transport model suggest that total momentum transfer obtained from the double‐averaging technique is capable of reproducing bedform mobilization. Comparisons between the total momentum transfer and stress estimates obtained from local velocity profiles show significant variability across the ripple, and suggest that an array of sensors is necessary to reproduce bedform evolution. The imbalance of momentum obtained by resolving the different terms constituting the near‐bed momentum balance (i.e. acceleration deficit, stress gradient, and bedform‐induced skin friction) provides an estimate of the bedform‐induced pressure that is consistent with flow separation. This analysis reveals three regions in the flow: the free‐stream, where all terms are relatively balanced; the near‐bed, where momentum imbalance is significant during flow weakening; and below ripple crests, where bedform‐induced pressure is the leading order mechanism.
      PubDate: 2014-11-08T11:17:46.066485-05:
      DOI: 10.1002/2014JC010240
       
  • Mixed layer salinity budget in the tropical Pacific Ocean estimated by a
           global GCM
    • Authors: Shan Gao; Tangdong Qu, Xunwei Nie
      Pages: n/a - n/a
      Abstract: The mixed layer salinity (MLS) budget of the tropical Pacific is investigated using results from a model of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO). The results focusing on the western Pacific freshwater pool indicate that the long‐term averaged surface freshwater flux is well balanced by ocean dynamics, in which the subsurface processes account for the major part. The MLS budget shows significant seasonal and interannual variability, as a consequence of interplay among surface freshwater flux, advection, mixing, and vertical entrainment. On seasonal time scale, both the MLS and mixed layer depth are largely controlled by surface freshwater flux. The opposite phase between the subsurface processes and the barrier layer thickness confirms the important influence of the barrier layer on vertical mixing and entrainment from below. On interannual time scale, all the MLS budget terms show significant ENSO signal, which in turn is highly correlated with the salinity front and barrier layer thickness in the equatorial Pacific.
      PubDate: 2014-11-08T11:09:59.02301-05:0
      DOI: 10.1002/2014JC010336
       
  • Solar heating of the Arctic Ocean in the context of ice‐albedo
           feedback
    • Authors: Rachel T. Pinker; Xiaolei Niu, Yingtao Ma
      Pages: n/a - n/a
      Abstract: To study the relationship of solar heat input into the Arctic open water and the variations of sea ice extent, improved satellite based estimates of shortwave radiative (SWR) fluxes and most recent observations of ice extent are used. The SWR flux estimates are based on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and from the Advanced Very High Resolution Radiometer (AVHRR) for the period of 1984‐2009. Ice extent information at 25‐km resolution comes from Nimbus‐7 SMMR and DMSP SSM/I Passive Microwave Data as generated with the NASA Team algorithm developed by the Oceans and Ice Branch, Laboratory for Hydrospheric Processes, NASA Goddard Space Flight Center. The trends of the solar heat input into the ocean and the open water fraction for 1984‐2009 are found to be positive: 0.3%/year and 0.8%/year respectively at a 99% confidence level. There is an obvious transition region separating the 26 years into two periods: one with moderate change: 1984‐2002; one with an abrupt growth in both solar heat input and open water fraction: 2003‐2009. The impact of the observed changes on the reduction of winter ice growth in 2007 is estimated to be about 44 cm, and a delay in fall freeze‐up as about 10~36 days.
      PubDate: 2014-11-08T11:09:29.998514-05:
      DOI: 10.1002/2014JC010232
       
  • SST patterns and dynamics of the Southern Senegal‐Gambia upwelling
           center
    • Authors: S. Ndoye; X. Capet, P. Estrade, B. Sow, D. Dagorne, A. Lazar, A. Gaye, P. Brehmer
      Pages: n/a - n/a
      Abstract: The southern end of the Canary current system comprises of an original upwelling center that has so far received little attention, the Southern Senegal‐Gambia Upwelling Center (SSUC). We investigate its dynamical functioning by taking advantage of favorable conditions in terms of limited cloud coverage. Analyses and careful examinations of over 1500 satellite images of sea surface temperature scenes contextualized with respect to wind conditions confirm the regularity and stability of the SSUC dynamical functioning (as manifested by the recurrence and persistence of particular SST patterns). The analyses also reveal subtle aspects of its upwelling structure: shelf break cooling of surface waters consistent with internal tide breaking/mixing; complex interplay between local upwelling and the Mauritanian current off the Cape Verde headland; complexity of the inner‐shelf/mid shelf frontal transition. The amplitude of the diurnal cycle suggests that large uncertainties exist in the SSUC heat budget. The studies limitations underscore the need for continuous in situ measurement in the SSUC, particularly of winds.
      PubDate: 2014-11-08T11:09:26.706055-05:
      DOI: 10.1002/2014JC010242
       
  • Convective instability in sedimentation: 3‐D numerical study
    • Authors: Xiao Yu; Tian‐Jian Hsu, S. Balachandar
      Pages: n/a - n/a
      Abstract: To provide a probable explanation on the field observed rapid sedimentation process near river mouths, we investigate the convective sedimentation in stably stratified saltwater using 3D numerical simulations. Guided by the linear stability analysis (Yu et al. 2013, J. Geophys. Res. Oceans, 118, 256‐272), this study focuses on the nonlinear interactions of several mechanisms, which lead to various sediment finger patterns, and the effective settling velocity for sediment ranging from clay (single‐particle settling velocity V0 = 0.0036 and 0.0144 mm/s, or particle diameter d = 2 and 4 μ m) to silt (V0=0.36 mm/s, or d =20 μ m). For very fine sediment with V0=0.0036 mm/s, the convective instability is dominated by double diffusion, characterized by millimeter‐scale fingers. Gravitational settling slightly increases the growth rate; however, it has notable effect on the downward development of vertical mixing shortly after the sediment interface migrates below the salt interface. For sediment with V0 = 0.0144 mm/s, Rayleigh‐Taylor instabilities become dominant before double‐diffusive modes grow sufficiently large. Centimeter‐scale and highly asymmetric sediment fingers are obtained due to nonlinear interactions between different modes. For sediment with V0 = 0.36 mm/s, Rayleigh‐Taylor mechanism dominates and the resulting centimeter‐scale sediment fingers show a plume‐like structure. The flow pattern is similar to that without ambient salt stratification. Rapid sedimentation with effective settling velocity on the order of 1 cm/s is likely driven by convective sedimentation for sediment with V0 greater than 0.1 mm/s at concentration greater than 10 to 20 g/L.
      PubDate: 2014-11-08T11:09:22.108183-05:
      DOI: 10.1002/2014JC010123
       
  • The role of morphology and wave‐current interaction at tidal inlets:
           An idealized modeling analysis
    • Authors: Maitane Olabarrieta; W. Rockwell Geyer, Nirnimesh Kumar
      Pages: n/a - n/a
      Abstract: The outflowing currents from tidal inlets are influenced both by the morphology of the ebb‐tide shoal and interaction with incident surface gravity waves. Likewise, the propagation and breaking of incident waves are affected by the morphology and the strength and structure of the outflowing current. The 3D COAWST (Coupled Ocean‐Atmosphere‐Wave‐Sediment Transport) modeling system is applied to numerically analyze the interaction between currents, waves, and bathymetry in idealized inlet configurations. The bathymetry is found to be a dominant controlling variable. In the absence of an ebb shoal and with weak wave forcing, a narrow outflow jet extends seaward with little lateral spreading. The presence of an ebb‐tide shoal produces significant pressure gradients in the region of the outflow, resulting in enhanced lateral spreading of the jet. Incident waves cause lateral spreading and limit the seaward extent of the jet, due both to conversion of wave momentum flux and enhanced bottom friction. The interaction between the vorticity of the outflow jet and the wave stokes drift is also an important driving force for the lateral spreading of the plume. For weak outflows, the outflow jet is actually enhanced by strong waves when there is a channel across the bar, due to the “return current” effect. For both strong and weak outflows, waves increase the along‐shore transport in both directions from the inlet due to the wave‐induced set‐up over the ebb shoal. Wave‐breaking is more influenced by the topography of the ebb shoal than by wave‐current interaction, although strong outflows show intensified breaking at the head of the main channel.
      PubDate: 2014-11-08T11:09:12.981829-05:
      DOI: 10.1002/2014JC010191
       
  • Heat and salinity budgets at the Stratus mooring in the southeast Pacific
    • Authors: James Holte; Fiammetta Straneo, J. Thomas Farrar, Robert A. Weller
      Pages: n/a - n/a
      Abstract: The surface layer of the southeast Pacific Ocean (SEP) requires an input of cold, fresh water to balance heat gain and evaporation from air‐sea fluxes. Models typically fail to reproduce the cool sea surface temperatures (SST) of the SEP, limiting our ability to understand the variability of this climatically important region. We estimate the annual heat budget of the SEP for the period 2004 ‐ 2009, using data from the upper 250 m of the Stratus mooring, located at 85°W 20°S, and from Argo floats. The surface buoy measures meteorological conditions and air‐sea fluxes; the mooring line is heavily instrumented, measuring temperature, salinity, and velocity at more than 15 depth levels. We use a new method for estimating the advective component of the heat budget that combines Argo profiles and mooring velocity data, allowing us to calculate monthly profiles of heat advection. Averaged over the 6 year study period, we estimate a cooling advective heat flux of ‐41 ± 29 W m‐2, accomplished by a combination of the mean gyre circulation, Ekman transport, and eddies. This compensates for warming fluxes of 32 ± 4 W m‐2 due to air‐sea fluxes and 7 ± 9 W m‐2 due to vertical mixing and Ekman pumping. A salinity budget exhibits a similar balance, with advection of freshwater (‐60 psu m) replenishing the freshwater lost through evaporation (47 psu m) and Ekman pumping (14 psu m).
      PubDate: 2014-11-08T11:09:09.529159-05:
      DOI: 10.1002/2014JC010256
       
  • Origin of fine‐scale wind stress curl structures in the Benguela and
           Canary upwelling systems
    • Authors: F. Desbiolles; B. Blanke, A. Bentamy, N. Grima
      Pages: n/a - n/a
      Abstract: Numerous studies have shown the primary importance of wind stress curl in coastal upwelling dynamics. The main goal of this new analysis is to describe the QuikSCAT surface wind stress curl at various scales in the Benguela and Canary upwelling systems. The dominant spatial pattern is characterized by cyclonic curl near continental boundaries and anticyclonic curl offshore, in association with equatorward alongshore (upwelling favorable) wind stress. At a smaller scale, we demonstrate the sensitivity of the QuikSCAT wind stress curl to coastal processes related to sea surface temperature (SST) mesoscale fluctuations by presenting a linear relationship between the curl and crosswind SST gradients. Despite the spatial and temporal sensitivity of the underlying thermal coupling coefficient, a local analysis of the fraction of the curl ascribed to SST variability shows that SST is a main driver of the wind stress curl variability and magnitude over the upwelling extension zone (~100 to 300 km from the coast) in both the Canary and Benguela systems. Closer to the shore, the curl patterns derived from QuikSCAT observations are only loosely related to SST‐wind interactions. As a working hypothesis, they can also be associated with the coastline geometry and orographic effects that are likely to play an important role in local cooling processes.
      PubDate: 2014-11-06T18:20:52.661802-05:
      DOI: 10.1002/2014JC010015
       
  • Impact of eddies on surface chlorophyll in the South Indian Ocean
    • Authors: François Dufois; Nick J. Hardman‐Mountford, Jim Greenwood, Anthony J. Richardson, Ming Feng, Steven Herbette, Richard Matear
      Pages: n/a - n/a
      Abstract: A unique feature of the subtropical South Indian Ocean is the existence of anticyclonic eddies that have higher chlorophyll concentrations than cyclonic eddies. Off Western Australia, this anomalous behaviour is related to the seeding of anticyclonic eddies with shelf water enriched in phytoplankton biomass and nutrients. Further off‐shore, two mechanisms have been suggested to explain the eddy/chlorophyll relationship: (i) eddies originating from the Australian coast maintain their chlorophyll anomaly while propagating westward; and (ii) eddy‐induced Ekman upwelling (downwelling) enhances (dampens) nutrient supply in anticyclonic (cyclonic) eddies. Here we describe the relationship between eddies and surface chlorophyll within the South Indian Ocean, and discuss possible mechanisms to explain the anomalous behaviour in light of new analyses performed using satellite chlorophyll data. We show that anticyclonic eddies exhibit higher surface chlorophyll concentration than cyclonic eddies across the entire South Indian Ocean basin (from 20 to 28ºS), particularly in winter. Using Self Organizing Maps we analyse the chlorophyll patterns within anticyclonic eddies and cyclonic eddies and highlight their complexity. Our analysis suggests that multiple mechanisms may underlie the observed eddy/chlorophyll relationship. Based on Argo float data, we postulate the relationship may be partly related to seasonal adjustment of the mixed layer depth within eddies. Deeper mixing in anticyclonic eddies is expected to enhance nutrient supply to the mixed layer, while shallower mixing in cyclonic eddies is expected to reduce it. This could explain why the observed winter surface chlorophyll bloom is stronger in anticyclonic eddies than in cyclonic eddies.
      PubDate: 2014-11-06T18:16:16.109917-05:
      DOI: 10.1002/2014JC010164
       
  • On the physical and biogeochemical processes driving the
           high‐frequency variability of CO2 fugacity at 6°S, 10°W:
           Potential role of the internal waves
    • Authors: Gaëlle Parard; J. Boutin, Y. Cuypers, P. Bouruet‐Aubertot, G. Caniaux
      Pages: n/a - n/a
      Abstract: The availability of nutrients in the mixed layer is the main limitation to organic carbon biological production in the tropical regions. In this paper, we investigate the potential role of internal waves at promoting the development of biological activity on a PIRATA mooring at 6°S, 10°W. This mooring is located above the Mid‐Atlantic Ridge where we observe strong internal waves. Using a one dimensional physical and biogeochemical coupled model, we simulate dissolved inorganic carbon (DIC). Providing the influence of vertical advection and turbulent diapycnal diffusivity are accounted for, we find that this model provides a good fit with observed in‐situ CO2 fugacity (fCO2). Main effect of internal waves is to rapidly increase the DIC, thus the fCO2 and the nutrients in the mixed layer. The latter induce progressive development of biological activity leading to gradual DIC decrease. Our study highlights the importance of correctly taking into account the effect of internal waves in tropical regions.
      PubDate: 2014-11-06T03:43:05.678215-05:
      DOI: 10.1002/2014JC009965
       
  • Relationship between coral distributions and physical variables in Amitori
           Bay, Iriomote Island, Japan
    • Authors: Shinya Shimokawa; Tomokazu Murakami, Akiyuki Ukai, Hiroyoshi Kohno, Akira Mizutani, Kouta Nakase
      Pages: n/a - n/a
      Abstract: The relationship between coral distributions and physical variables was investigated in Amitori Bay, Iriomote Island, Japan. Field observations were conducted to obtain data on coral distributions, sea temperature, sea salinity, wind speed, and river flow rate. The observed data were then used in ocean and wave model numerical simulations and soil particle tracking analysis to obtain the spatial and temporal distributions of wave height and the numbers of soil particles. The main results of this study indicate that wave height and the number of soil particles have a significant correlation with coral distribution. Higher wave heights result in greater coverage of tabular coral and lower coverage of branching coral. A greater number of soil particles relates to lesser coverage of tabular coral. On the contrary, the number of soil particles is not correlated with branching coral coverage. The potential habitats for tabular corals largely depend on the species. Acropora hyacinthus is distributed in conditions with low numbers of soil particles, A. digitifera is distributed in conditions with low numbers of soil particles and high wave heights, and A. millepora is distributed in conditions with high numbers of soil particles and low wave heights. Averages of diversity index of the coral types at the mouth and inner parts of the bay are lower than average of the whole region, but average of diversity index at the intermediate part of the bay with the intermediate physical disturbances is higher than it, which seems to support the intermediate disturbance hypothesis.
      PubDate: 2014-11-05T01:41:43.056767-05:
      DOI: 10.1002/2014JC010307
       
  • Deep ocean water transport by acoustic‐gravity waves
    • Authors: U. Kadri
      Pages: n/a - n/a
      Abstract: Acoustic‐gravity waves are compression‐type waves propagating with amplitudes governed by the restoring force of gravity. They are generated, among others, by wind‐wave interactions, surface waves interactions, and submarine earthquakes. We show that acoustic‐gravity waves contribute to deep ocean currents and circulation; they cause chaotic flow trajectories of individual water parcels, which can be transported by a few centimetres per second.
      PubDate: 2014-11-04T07:46:26.848696-05:
      DOI: 10.1002/2014JC010234
       
  • Tidal and residual currents in the Qiongzhou Strait estimated from
           shipboard ADCP data using a modified tidal harmonic analysis method
    • Authors: Xiao‐Hua Zhu; Yun‐Long Ma, Xinyu Guo, Xiaopeng Fan, Yu Long, Yaochu Yuan, Ji‐Liang Xuan, Daji Huang
      Pages: n/a - n/a
      Abstract: In spring 2013, thirty‐three repeat shipboard Acoustic Doppler Current Profile (ADCP) surveys were conducted to measure the tidal current in the Qiongzhou Strait (QS). The major tidal currents and the residual current along a section across the QS were estimated using a modified tidal harmonic analysis method based on the inverse technique. A simple simulation and comparisons with previous observations demonstrated that the tidal currents estimated using the modified tidal harmonic analysis method are reasonable, and this method was able to control the magnitude and deviation of the estimation error. The direction of the major axis of tidal current ellipses is generally along the strait. Diurnal tidal constituents are dominant among the five tidal current constituents (K1, O1, M2, S2 and MSf). The ratio of the amplitudes of O1, K1, M2, S2 and MSf, averaged along the section across the QS is 1:0.79:0.42:0.27:0.29. The residual current along the entire section is all westward; the averaged velocity over the section is 6.0±2.1 cm s‐1; the associated volume transport through the section is ‐0.065±0.046 Sv (Sv=106×m3 s‐1), in which the second value denotes the uncertainty of first value. Dynamic analysis indicates that tidal current activity is more dominant than mean current and eddy activity, and tidal rectification and sea level difference between two entrances of the QS are important in maintaining the residual current through the strait.
      PubDate: 2014-11-04T07:46:15.306056-05:
      DOI: 10.1002/2014JC009855
       
  • Regional variations in the influence of mesoscale eddies on
           near‐surface chlorophyll
    • Authors: Peter Gaube; Dennis J. McGillicuddy, Dudley B. Chelton, Michael J. Behrenfeld, Peter G. Strutton
      Pages: n/a - n/a
      Abstract: Eddies can influence biogeochemical cycles through a variety of mechanisms, including the excitation of vertical velocities and the horizontal advection of nutrients and ecosystems, both around the eddy periphery by rotational currents and by the trapping of fluid and subsequent transport by the eddy. In this study, we present an analysis of the influence of mesoscale ocean eddies on near‐surface chlorophyll (CHL) estimated from satellite measurements of ocean color. The influences of horizontal advection, trapping, and upwelling/downwelling on CHL are analyzed in an eddy‐centric frame of reference by collocating satellite observations to eddy interiors, as defined by their sea surface height signatures. The influence of mesoscale eddies on CHL varies regionally. In most boundary current regions, cyclonic eddies exhibit positive CHL anomalies and anticyclonic eddies contain negative CHL anomalies. In the interior of the South Indian Ocean, however, the opposite occurs. The various mechanisms by which eddies can influence phytoplankton communities are summarized and regions where the observed CHL response to eddies is consistent with one or more of the mechanisms are discussed. This study does not attempt to link the observed regional variability definitively to any particular mechanism, but provides a global overview of how eddies influence CHL anomalies.
      PubDate: 2014-11-04T07:44:18.304894-05:
      DOI: 10.1002/2014JC010111
       
  • Estimating the global oceanic net freshwater flux from Argo and comparing
           it with satellite‐based freshwater flux products
    • Authors: Li Ren; Eric Hackert, Phillip Arkin, Antonio J. Busalacchi
      Pages: n/a - n/a
      Abstract: Following the idea that analysis of in‐situ information in the salt budget could be used as a surrogate for global “ocean rain gauge”, the annual mean oceanic net freshwater flux (E‐P) was estimated from the Argo profiles and the wind stress data on a global scale. The comparison between the independent E‐P estimation from Argo and the E‐P product sets, including the combination of precipitation from TRMM, GPCP, CMAP and evaporation from OAFlux, GSSTF3 and IFREMER and E‐P set from NEWS formed from satellite, generally show similar spatial patterns, particularly on the larg scale. However, there are differences among the different satellite‐based E‐P estimates and between satellite estimates and independent in‐situ estimates. Based on the pattern correlation and the RMSD, the evaporation and precipitation from OAFlux and TRMM agrees best with the E‐P estimated from the independent Argo‐based estimates.
      PubDate: 2014-11-04T07:43:54.979955-05:
      DOI: 10.1002/2013JC009620
       
  • Comparison analysis between Aquarius sea surface salinity and World Ocean
           Database in situ analyzed sea surface salinity
    • Authors: James Reagan; Tim Boyer, John Antonov, Melissa Zweng
      Pages: n/a - n/a
      Abstract: A new monthly sea surface salinity (SSS) product calculated from profile data within the World Ocean Database (WOD) is compared and contrasted with Aquarius SSS, both standard and Combined Active‐Passive (CAP) products, from September 2011 through September 2013. Aquarius exhibits similar biases as shown in previous comparison SSS studies, with negative biases in the tropics transitioning to positive biases in the higher latitudes when compared to WOD SSS. These biases are generally much weaker in CAP than the standard version, indicating that the biases are strongly related to the differences in algorithms used to retrieve satellite SSS. Non‐Argo data utilized in the study is shown to be of great use to validate Aquarius in regions with little to no Argo coverage and helps provide SSS measurements in regions where there are known errors in Aquarius retrievals. The annual cycle of WOD and Aquarius are found to be very similar, with Aquarius being generally more coherent and robust. All three products’ annual cycles compared favorably to the World Ocean Atlas 2013. The interannual changes in all three products generally corresponded well to one another and to changes in evaporation and precipitation (E‐P). Overall, Aquarius compares very well with in situ sea surface salinity fields under multiple comparison examinations; however, both products have their own strengths and weaknesses and a synthesis of the two should be used to study global scale SSS variability.
      PubDate: 2014-10-31T04:07:08.435271-05:
      DOI: 10.1002/2014JC009961
       
  • Barotropic and baroclinic contributions to along‐ and
           across‐stream transport in the Antarctic Circumpolar Current
    • Authors: B. Peña‐Molino; S. R. Rintoul, M. R. Mazloff
      Pages: n/a - n/a
      Abstract: The Southern Ocean's ability to store and transport heat and tracers as well as to dissipate momentum and energy are intimately related to the vertical structure of the Antarctic Circumpolar Current (ACC). Here the partition between barotropic and baroclinic flow in the time‐mean ACC is investigated in a Southern Ocean state estimate. The zonal geostrophic transport is predominantly baroclinic, with at most 25% of the transport at any longitude carried by the barotropic component. Following surface streamlines, changes in vertical shear and near‐bottom velocity are large, and result in changes in the local partition of barotropic/baroclinic vertically integrated transport from 10/90% in the center of the basins, to 50/50% near complex topography. The velocity at depth is not aligned with the surface velocity. This non‐equivalent barotropic flow supports significant cross‐stream transports. Barotropic and baroclinic mass transport across the ACC is, on average, in opposite directions, with the net barotropic cross‐stream transport being poleward and the net baroclinic equatorward. The sum partially cancels out, leaving a net geostrophic poleward transport across the different fronts between ‐5 and ‐20 Sv. Temperature is also transported across the fronts by the non‐equivalent barotropic part of the ACC, with maximum values across the northern ACC fronts equivalent to ‐0.2 PW. The sign and magnitude of these transports is not sensitive to the choice of stream‐coordinate. These cross‐stream volume and temperature transports are variable in space, and dependent on the interactions between deep flow and bathymetry, thus difficult to infer from surface and hydrographic observations alone.
      PubDate: 2014-10-31T03:48:56.744422-05:
      DOI: 10.1002/2014JC010020
       
  • Evaluating SODA for Indo‐Pacific Ocean decadal climate variability
           studies
    • Authors: J. Mauro Vargas‐Hernandez; Susan Wijffels, Gary Meyers, Neil J. Holbrook
      Pages: n/a - n/a
      Abstract: Estimates of changes in upper ocean temperature, heat content and sea level are dependent on the coverage of subsurface observations in space and time. Historically, these data are sparse, which has limited our understanding of ocean climate variability and change mechanisms. Ocean state estimates, which effectively represent a model synthesis and integration of the available observations, including internal observations in the ocean and surface forcing, help address the inhomogeneity of sparse observations in space and time. Here, we evaluate the representativeness of ocean state estimates from the Simple Ocean Data Assimilation Version 2.2.4 (SODA) data for studying Indo‐Pacific Ocean decadal temperature and sea level variability over the period 1950‐2007. The SODA data are evaluated against independent sea level anomalies from long‐record tide gauges at Midway Island and Fremantle, reconstructed sea surface height anomalies, and sea surface height anomalies from TOPEX/Poseidon satellite altimeter observations at the decadal time scale. This study demonstrates that SODA captures the characteristic Interdecadal Pacific Oscillation (IPO) over the upper 200 m, and accurately represents these decadal changes against the independent observations. The SODA‐product shows a meridional asymmetry of patterns that connect the western tropical Pacific and the Indian Ocean, apparently in relation to IPO changes. Regional sea level at the Midway Island and Fremantle tide‐gauges confirm this decadal connection and the relationship with the IPO. We concluded that SODA is potentially a useful tool to examine ocean decadal climate variability across the Indo‐Pacific Ocean.
      PubDate: 2014-10-31T03:34:49.75108-05:0
      DOI: 10.1002/2014JC010175
       
  • Lagrangian predictability characteristics of an Ocean Model
    • Authors: Guglielmo Lacorata; Luigi Palatella, Rosalia Santoleri
      Pages: n/a - n/a
      Abstract: The Mediterranean Forecasting System (MFS) Ocean Model, provided by INGV, has been chosen as case study to analyze Lagrangian trajectory predictability by means of a dynamical systems approach. To this regard, numerical trajectories are tested against a large amount of Mediterranean drifter data, used as sample of the actual tracer dynamics across the sea. The separation rate of a trajectory pair is measured by computing the Finite‐Scale Lyapunov Exponent (FSLE) of first and second kind. An additional kinematic Lagrangian model (KLM), suitably treated to avoid “sweeping”‐related problems, has been nested into the MFS in order to recover, in a statistical sense, the velocity field contributions to pair particle dispersion, at mesoscale level, smoothed out by finite resolution effects. Some of the results emerging from this work are: a) drifter pair dispersion displays Richardson's turbulent diffusion inside the [10‐100] km range, while numerical simulations of MFS alone (i.e. without subgrid model) indicate exponential separation; b) adding the subgrid model, model pair dispersion gets very close to observed data, indicating that KLM is effective in filling the energy “mesoscale gap” present in MFS velocity fields; c) there exists a threshold size beyond which pair dispersion becomes weakly sensitive to the difference between model and “real” dynamics; d) the whole methodology here presented can be used to quantify model errors and validate numerical current fields, as far as forecasts of Lagrangian dispersion are concerned.
      PubDate: 2014-10-31T03:33:33.795286-05:
      DOI: 10.1002/2014JC010313
       
  • A time‐series of incubation experiments to examine the production
           and loss of CH3I in surface seawater
    • Authors: Qiang Shi; Christa Marandino, Gert Petrick, Birgit Quack, Douglas Wallace
      Pages: n/a - n/a
      Abstract: In order to investigate production pathways of methyl iodide and controls on emissions from the surface ocean, a set of repeated in‐vitro incubation experiments were performed over an annual cycle in the context of a time‐series of in‐situ measurements in Kiel Fjord (54.3 N, 10.1E). The incubation experiments revealed a diurnal variation of methyl iodide in samples exposed to natural light, with maxima during day time and losses during night hours. The amplitude of the daily accumulation varied seasonally and was not affected by filtration (0.2µm), consistent with a photochemical pathway for CH3I production. The methyl iodide loss rate during night time correlate with the concentration accumulated during daytime suggesting a 1st order loss mechanism (R2=0.29, p
      PubDate: 2014-10-31T03:28:13.724562-05:
      DOI: 10.1002/2014JC010223
       
  • Evaluation of sea‐surface salinity observed by Aquarius
    • Authors: Hiroto Abe; Naoto Ebuchi
      Pages: n/a - n/a
      Abstract: Sea‐surface salinity (SSS) observed by Aquarius was compared with global observation from Argo floats and offshore moored buoys to evaluate the quality of satellite SSS data and to assess error structures. Aquarius products retrieved by different algorithms (Aquarius Official Release version 3.0 (V3.0), Combined Active‐Passive (CAP) algorithm version 3.0, Remote Sensing Systems testbed algorithm version 3) were compared. The Aquarius SSS was in good agreement with in situ salinity measurements for all three products. Root‐mean‐square (rms) differences of the salinity residual, with respect to Argo salinity, ranged from 0.41 to 0.52 psu. These three Aquarius products exhibit high SSS deviation from Argo salinity under lower sea‐surface temperature conditions (< 10 °C) due to lower sensitivity of microwave emissivity to SSS. The CAP product deviates under strong wind conditions (> 10 ms−1), probably due to model bias and uncertainty associated with sea‐surface roughness. Furthermore, significant SSS differences between ascending (south‐to‐north) and descending (north‐to‐south) paths were detected. The monthly‐averaged Aquarius SSS (1° × 1° grid) was also compared with outputs from the ocean data optimal interpolation (OI) system operated by the Japan Agency for Marine‐Earth Science Technology (JAMSTEC) and the ocean data assimilation system used by the Meteorological Research Institute, Japan Meteorological Agency (MRI/JMA). Negative bias, attributed to near‐surface salinity stratification by precipitation, was detected in tropical regions. For 40°S–40°N, rms difference, with respect to JAMSTEC OI, is 0.27 psu for the V3.0, while the CAP product rms difference is only 0.22 psu, which is close to the Aquarius mission goal.
      PubDate: 2014-10-31T03:28:00.537747-05:
      DOI: 10.1002/2014JC010094
       
  • The imprint of Southern Ocean overturning on seasonal water mass
           variability in Drake Passage
    • Authors: Dafydd Gwyn Evans; Jan D. Zika, Alberto C. Naveira Garabato, A. J. George Nurser
      Pages: n/a - n/a
      Abstract: Seasonal changes in water mass properties are discussed in thermohaline coordinates from a seasonal climatology and repeat hydrographic sections. The SR1b CTD transects along Drake Passage are used as a case study. The amount of water within temperature and salinity classes and changes therein are used to estimate dia‐thermal and dia‐haline transformations. These transformations are considered in combination with climatologies of surface buoyancy flux to determine the relative contributions of surface buoyancy fluxes and sub‐surface mixing to changes in the distribution of water in thermohaline coordinates. The framework developed provides unique insights into the thermohaline circulation of the water masses that are present within Drake Passage, including the erosion of Antarctic Winter Water (AAWW) during the summer months and the interaction between the Circumpolar Deep Waters (CDW) and Antarctic Intermediate Water (AAIW). The results presented are consistent with summertime wind‐driven inflation of the CDW layer and deflation of the AAIW layer, and with new AAIW produced in the winter as a mixture of CDW, remnant AAWW and surface waters. This analysis therefore highlights the role of surface buoyancy fluxes in the Southern Ocean overturning.
      PubDate: 2014-10-31T03:27:51.373817-05:
      DOI: 10.1002/2014JC010097
       
  • The ability of a barotropic model to simulate sea level extremes of
           meteorological origin in the Mediterranean Sea, including those caused by
           explosive cyclones
    • Authors: F. M. Calafat; E. Avgoustoglou, G. Jordà, H. Flocas, G. Zodiatis, M. N. Tsimplis, J. Kouroutzoglou
      Pages: n/a - n/a
      Abstract: Storm surges are responsible for great damage to coastal property and loss of life every year. Coastal management and adaptation practices are essential to reduce such damage. Numerical models provide a useful tool for informing these practices as they simulate sea level with high spatial resolution. Here we investigate the ability of a barotropic version of the HAMSOM model to simulate sea level extremes of meteorological origin in the Mediterranean Sea, including those caused by explosive cyclones. For this purpose, the output of the model is compared to hourly sea level observations from 6 tide gauge records (Valencia, Barcelona, Marseille, Civitavecchia, Trieste, and Antalya). It is found that the model underestimates the positive extremes significantly at all stations, in some cases by up to 65%. At Trieste, the model can also sometimes overestimate the extremes significantly. The differences between the model and the residuals are not constant for extremes of a given height, which limits the applicability of the numerical model for storm surge forecasting because calibration is difficult. The 50‐ and 10‐year return levels are reasonably well captured by the model at all stations except Barcelona and Marseille, where they are underestimated by over 30%. The number of exceedances of the 99.9th and 99.95% percentiles over a period of 25 years is severely underestimated by the model at all stations. The skill of the model for predicting the timing and value of the storm surges seems to be higher for the events associated with explosive cyclones at all stations.
      PubDate: 2014-10-31T03:13:19.427075-05:
      DOI: 10.1002/2014JC010360
       
  • Variability of zonal currents in the eastern equatorial Indian Ocean on
           seasonal to interannual time scales
    • Authors: Ebenezer S. Nyadjro; Michael J. McPhaden
      Pages: n/a - n/a
      Abstract: This study examines equatorial zonal current variations in the upper layers of eastern Indian Ocean in relation to variations in the Indian Ocean Dipole (IOD). The analysis utilizes data from the Research Moored Array for African‐Asian‐Australian Monsoon Analysis and Prediction (RAMA) and the European Centre for Medium‐Range Weather Forecasts ‐ Ocean Reanalysis System 4 (ECMWF‐ORAS4). Surface currents are characterized by semi‐annual eastward flowing Wyrtki jets along the equator in boreal spring and fall, forced by westerly monsoon transition winds. The fall jet intensifies during negative IOD (NIOD) events when westerlies are anomalously strong but significantly weakens during positive IOD (PIOD) events when westerlies are anomalously weak. As zonal wind stress weakens during PIOD events, sea surface height becomes unusually low in the eastern basin and high in the west, setting up an anomalous pressure force that drives increased eastward transport in the thermocline. Opposite tendencies are evident during NIOD events in response to intensified equatorial westerlies. Current transport adjustments to anomalous zonal wind forcing during IOD events extend into the following year, consistent with the cycling of equatorial wave energy around the basin. A surface layer mass budget calculation for the eastern sea surface temperature (SST) pole of the IOD indicates upwelling of ~2.9±0.7 Sv during normal periods, increasing by 40‐50% during PIOD events and reducing effectively to zero during NIOD events. IOD‐related variations in Wyrtki jet and thermocline transports are major influences on these upwelling rates and associated water mass transformations, which vary consistently with SST changes.
      PubDate: 2014-10-28T03:24:26.842397-05:
      DOI: 10.1002/2014JC010380
       
  • Investigation of rain effects on Aquarius sea surface salinity
           measurements
    • Authors: Andrea Santos‐Garcia; María Marta Jacob, W. Linwood Jones, William E. Asher, Yazan Hejazin, Hamideh Ebrahimi, Monica Rabolli
      Pages: n/a - n/a
      Abstract: The Aquarius/SAC‐D mission has been providing Sea Surface Salinity (SSS), globally over the ocean, for almost 3 years. As a member of the AQ/SAC‐D Cal/Val team, the Central Florida Remote Sensing Laboratory has analyzed these salinity retrievals in the presence of rain and has noted the strong correlation between the spatial patterns of reduced SSS and the spatial distribution of rainfall. It was determined that this is the result of a cause and effect relationship, as opposed to SSS measurement errors. Hence, it is important to understand these SSS changes due to seawater dilution by rain and the associated near‐surface salinity stratification. This paper addresses the effects of rainfall on the Aquarius (AQ) SSS retrieval using a macro‐scale Rain Impact Model (RIM) in the region of high convective rain over the Inter‐tropical Convergence Zone. This model, based on the superposition of a one‐dimension eddy diffusion (turbulent diffusion) model, relates sea surface salinity to depth, rain accumulation and time since rainfall. For aiding in the identification of instantaneous and prior rainfall accumulations, an AQ Rain Accumulation product was developed. This product, based on the NOAA CMORPH rain dataset, provides the rainfall history for 24 hours prior to the observation time, which is integrated over each AQ SSS measurement cell. In this paper results of the RIM validation are presented by comparing AQ measured and RIM simulated SSS for several months of 2012. Results show the high cross‐correlation for these comparisons and also with the corresponding SSS anomalies relative to HYCOM.
      PubDate: 2014-10-25T03:01:11.929923-05:
      DOI: 10.1002/2014JC010137
       
  • Tropical cyclone footprint in the ocean mixed layer observed by Argo in
           the northwest Pacific
    • Authors: HongLi Fu; Xidong Wang, Peter C. Chu, Xuefeng Zhang, Guijun Han, Wei Li
      Pages: n/a - n/a
      Abstract: This study systematically investigated the ocean mixed layer responses to tropical cyclone (TC) using available Argo profiles during the period of 1998‐2011 in the Northwest Pacific. Results reveal that isothermal layer (IL) deepening and isothermal layer (IL) cooling with evident rightward biases induced by strong TCs are clearer compared to the weak TCs. Likewise, the rightward biases of IL deepening and cooling induced by fast TCs are more obvious than that induced by slow TCs. The upwelling within TC's eye is much stronger for the strong (slow) TCs than weak (fast) TCs. For the strong and slow TCs, the TC‐induced rainfall reduces deepening of constant density layer [with its depth called the mixed layer depth (MLD)], and in turn increases the barrier layer thickness (BLT). The initial BL prior to TC can restrict IL cooling more markedly under the weak and fast TCs than under the strong and slow TCs. The inertial oscillation is stronger induced by the strong (fast) TCs than by the weak (slow) TCs. In addition, the most pronounced TC‐induced mixed layer deepening and IL cooling in July‐October climatology occur in the subtropical gyre of the Northwest Pacific with enhanced vertical diffusivity. The maximum increase of isothermal layer depth (ILD) and MLD is up to 5m, with IL cooling up to 0.4°C.
      PubDate: 2014-10-25T03:00:45.485957-05:
      DOI: 10.1002/2014JC010316
       
  • Observations of wave shear stress on a steep beach
    • Authors: G. W. Wilson; A. E. Hay, A. J. Bowen
      Pages: n/a - n/a
      Abstract: Observations are presented of the wave shear stress 〈u˜w˜〉 on a steeply sloping beach. Above the wave boundary layer (WBL), positive values of 〈u˜w˜〉 were observed, and are attributed to a combination of both wave shoaling due to the large‐scale bed slope, and dissipation due to wave breaking, in agreement with the wave theory of Zou et al. [2003]. Within the WBL, observed vertical profiles of 〈u˜w˜〉 were also in good agreement with theory, in cases where the wave height was small. As wave heights increased, however, the WBL profile of 〈u˜w˜〉 generally did not agree with theory. Near‐simultaneous rotary sonar observations of the bed suggest the disagreement with theory was due to the presence of orbital scale ripples, which the present theory does not accommodate.
      PubDate: 2014-10-25T02:42:36.001053-05:
      DOI: 10.1002/2014JC010193
       
  • Circulation and transports in the Newfoundland Basin, western subpolar
           North Atlantic
    • Authors: Christian Mertens; Monika Rhein, Maren Walter, Claus W. Böning, Erik Behrens, Dagmar Kieke, Reiner Steinfeldt, Uwe Stöber
      Pages: n/a - n/a
      Abstract: The southwestern part of the subpolar North Atlantic east of the Grand Banks of Newfoundland and Flemish Cap is a crucial area for the Atlantic Meridional Overturning Circulation. Here the exchange between subpolar and subtropical gyre takes place, southward flowing cold and fresh water is replaced by northward flowing warm and salty water within the North Atlantic Current (NAC). As part of a long‐term experiment, the circulation east of Flemish Cap has been studied by seven repeat hydrographic sections along 47°N (2003‐‐2011), a two‐year time series of current velocities at the continental slope (2009‐‐2011), 19 years of sea surface height, and 47 years of output from an eddy resolving ocean circulation model. The structure of the flow field in the measurements and the model shows a deep reaching NAC with adjacent recirculation and two distinct cores of southward flow in the Deep Western Boundary Current (DWBC): One core above the continental slope with maximum velocities at mid‐depth and the second farther east with bottom‐intensified velocities. The western core of the DWBC is rather stable, while the offshore core shows high temporal variability that in the model is correlated with the NAC strength. About 30 Sv of deep water flow southward below a density of σθ = 27.68kg‐3 in the DWBC. The NAC transports about 110 Sv northward, approximately 15 Sv originating from the DWBC, and 75 Sv recirculating locally east of the NAC, leaving 20 Sv to be supplied by the NAC from the south.
      PubDate: 2014-10-25T02:42:19.090311-05:
      DOI: 10.1002/2014JC010019
       
  • Mapping of sea surface nutrients in the North Pacific: Basin‐wide
           distribution and seasonal to interannual variability
    • Authors: Sayaka Yasunaka; Yukihiro Nojiri, Shin‐ichiro Nakaoka, Tsuneo Ono, Frank A. Whitney, Maciej Telszewski
      Pages: n/a - n/a
      Abstract: Monthly maps of sea surface nutrient (phosphate, nitrate and silicate) concentrations were produced for the North Pacific (10–60°N, 120°E–90°W) for the years 2001 to 2010 using a self‐organizing map trained with temperature, salinity, chlorophyll‐a concentration and mixed layer depth. Nutrient sampling was carried out mainly by ships of opportunity, providing good seasonal coverage of the surface ocean. Using the mapping results, we investigated the spatio‐temporal variability of surface North Pacific nutrient and dissolved inorganic carbon (DIC) distributions on seasonal and interannual time scales. Nutrient and DIC concentrations were high in the subarctic in winter and low in the subtropics. In the summer, substantial amount of nutrients remained unutilized in subarctic and the northern part of the subarctic‐subtropical boundary region while that was not the case in the southern part of the boundary region. In the subtropics, nutrients were almost entirely depleted throughout the year, while DIC concentrations showed a north‐south gradient and significant seasonal change. Nutrients and DIC show a large seasonal drawdown in the western subarctic region, while the drawdown in the eastern subarctic region was weaker, especially for silica. The subarctic‐subtropical boundary region also showed a large seasonal drawdown, which was most prominent for DIC and less obvious for nitrate and silicate. In the interannual time scale, the Pacific Decadal Oscillation was related to a seesaw pattern between the subarctic‐subtropical boundary region and the Alaskan Gyre through the changes in horizontal advection, vertical mixing and biological production.
      PubDate: 2014-10-24T20:40:39.872342-05:
      DOI: 10.1002/2014JC010318
       
  • Observations of the frontal region of a buoyant river plume using an
           autonomous underwater vehicle
    • Authors: Peter Rogowski; Eric Terrill, Jialin Chen
      Pages: n/a - n/a
      Abstract: To characterize the transitional region from the near‐field to far‐field of a river plume entering coastal waters we conducted four surveys using an autonomous underwater vehicle (AUV) to target the outflow of the New River Inlet, North Carolina, during maximum ebb tide. The utilization of a mobile sensor to synoptically observe current velocity data in tandem with natural river plume tracers (e.g. colored dissolved organic matter, salinity) was essential in understanding the mechanisms driving the observed circulation and mixing patterns within these waters. We find that this region is regularly impacted by two primary processes: (1) the interaction of an old dredged channel plume with the main discharge and (2) the recirculation of the discharge plume by an eddy that persistently forms between the old channel and main discharge location. Wind‐driven processes in the nearshore can enhance the interaction of these two plumes resulting in unstable regions where mixing of the merged plume with the receiving waters is accelerated. We also conduct comparisons between AUV velocity observations from two surveys and their corresponding velocity outputs from a parallelized quasi‐3D model. We conclude that the ability to observe the estuarine outflow transitional region at near‐synoptic temporal scales and resolutions discussed in this paper is key in providing the mechanisms driving local circulation which is essential for proper parameterization of high‐resolution numerical coastal models.
      PubDate: 2014-10-24T18:06:56.518096-05:
      DOI: 10.1002/2014JC010392
       
  • The North Atlantic subtropical surface salinity maximum as observed by
           Aquarius
    • Authors: Frederick M. Bingham; Julius Busecke, Arnold L. Gordon, Claudia F. Giulivi, Zhijin Li
      Pages: n/a - n/a
      Abstract: Aquarius satellite derived sea surface salinity (SSS) data from August 2011 through September 2013 reveals significant seasonal migration and freshening of the subtropical surface salinity maximum (SSS‐max) area in the North Atlantic, in good agreement with in situ observations, including those obtained as part of the SPURS (Salinity Processes in the Upper Ocean Regional Study) field experiment in 2012‐2013. The SSS‐max fluctuated in surface area ‐ as defined by the 37.4 surface isohaline ‐ during the course of the Aquarius time series by about 67%. The SSS‐max has a surprisingly large amount of non‐seasonal variability, including a general decrease in salinity throughout the eastern subtropical North Atlantic between 2011‐2012 and 2012‐2013 of about 0.1‐0.2. The documented seasonal variability is weakest in the maximum salinity area and increases towards the north and south respectively. This is consistent with the important role played by Ekman transport and regional excess of evaporation over precipitation in the formation of the SSS‐max.
      PubDate: 2014-10-24T18:03:47.134036-05:
      DOI: 10.1002/2014JC009825
       
  • Effects of ocean acidification on the biogenic composition of the
           sea‐surface microlayer: Results from a mesocosm study
    • Authors: Luisa Galgani; Christian Stolle, Sonja Endres, Kai G. Schulz, Anja Engel
      Pages: n/a - n/a
      Abstract: The sea‐surface microlayer (SML) is the ocean's uppermost boundary to the atmosphere and in control of climate relevant processes like gas exchange and emission of marine primary organic aerosols (POA). The SML represents a complex surface film including organic components like polysaccharides, proteins, and marine gel particles, and harbors diverse microbial communities. Despite the potential relevance of the SML in ocean‐atmosphere interactions still little is known about its structural characteristics and sensitivity to a changing environment such as increased oceanic uptake of anthropogenic CO2. Here, we report results of a large scale mesocosm study, indicating that ocean acidification can affect the abundance and activity of microorganisms during phytoplankton blooms, resulting in changes in composition and dynamics of organic matter in the SML. Our results reveal a potential coupling between anthropogenic CO2 emissions and the biogenic properties of the SML, pointing to a hitherto disregarded feedback process between ocean and atmosphere under climate change.
      PubDate: 2014-10-24T18:02:49.969586-05:
      DOI: 10.1002/2014JC010188
       
  • Turbidity maximum formation in a well‐mixed macrotidal estuary: The
           role of tidal pumping
    • Authors: Qian Yu; Yunwei Wang, Jianhua Gao, Shu Gao, Burg Flemming
      Pages: n/a - n/a
      Abstract: Traditionally, vertical circulation (induced by gravity circulation and tidal straining), tidal pumping, and resuspension are suggested as the major processes for the formation and maintenance of the estuarine turbidity maximum (ETM). Due to strong mixing, tidal pumping is considered as the dominating process in macro‐tidal estuaries. To analyze field observation data, the classical empirical decomposition method is commonly suggested, but the tidal pumping flux (TPF) based on this method may lead to erroneous conclusions about the mechanisms of ETM formation because the effects of advection induced by the horizontal SSC gradient and fine bed sediment supply are ignored. If these effects are included, the TPF clearly reproduces the convergence patterns and thus demonstrates its role in the formation of the ETM. By a simplified analytical solution, the TPF is the result of the competition between the downstream flux induced by the river current together with the lag in sediment response and the upstream flux induced by tidal asymmetry and the lag. Field observations in the well‐mixed macro‐tidal Yalu River estuary (located between China and North Korea were analyzed. Tidal pumping is identified as the dominant mechanism of its ETM formation, and the position of the ETM for different river discharges and sediment settling velocities can be predicted by the concept of tidal pumping by numerical and analytical procedures. The present study provides a typical example of how to evaluate the tidal pumping contributions on ETM formation using the combined information provided by field data, numerical modeling results and analytical solutions.
      PubDate: 2014-10-20T22:10:42.080373-05:
      DOI: 10.1002/2014JC010228
       
  • Mechanisms of Pacific Summer Water variability in the Arctic's central
           Canada Basin
    • Authors: M.‐L. Timmermans; A. Proshutinsky, E. Golubeva, J.M. Jackson, R. Krishfield, M. McCall, G. Platov, J. Toole, W. Williams
      Pages: n/a - n/a
      Abstract: Pacific Water flows northward through Bering Strait and penetrates the Arctic Ocean halocline throughout the Canadian Basin sector of the Arctic. In summer, Pacific Summer Water (PSW) is modified by surface buoyancy fluxes and mixing as it crosses the shallow Chukchi Sea before entering the deep ocean. Measurements from Ice‐Tethered Profilers, moorings and hydrographic surveys between 2003 and 2013 reveal spatial and temporal variability in the PSW component of the halocline in the Central Canada Basin with increasing trends in integrated heat and freshwater content, a consequence of PSW layer thickening as well as layer freshening and warming. It is shown here how properties in the Chukchi Sea in summer control the temperature‐salinity properties of PSW in the interior by subduction at isopycnals that outcrop in the Chukchi Sea. Results of an ocean model, forced by idealized winds, provide support to the mechanism of surface ocean Ekman transport convergence maintaining PSW ventilation of the halocline.
      PubDate: 2014-10-20T04:46:43.226752-05:
      DOI: 10.1002/2014JC010273
       
  • Exploiting satellite Earth observation to quantify current global oceanic
           DMS flux and its future climate sensitivity
    • Authors: P. E. Land; J. D. Shutler, T. G. Bell, M. Yang
      Pages: n/a - n/a
      Abstract: We used coincident Envisat RA2 and AATSR temperature and wind speed data from 2008/9 to calculate the global net sea‐air flux of dimethyl sulfide (DMS), which we estimate to be 19.6 Tg S a‐1. Our monthly flux calculations are compared to open ocean eddy correlation measurements of DMS flux from 10 recent cruises, with a root mean square difference of 3.1 μmol m‐2 day‐1. In a sensitivity analysis we varied temperature, salinity, surface wind speed and aqueous DMS concentration, using fixed global changes as well as CMIP5 model output. The range of DMS flux in future climate scenarios is discussed. The CMIP5 model predicts a reduction in surface wind speed and we estimate that this will decrease the global annual sea‐air flux of DMS by 22% over 25 years. Concurrent changes in temperature, salinity and DMS concentration increase the global flux by much smaller amounts. The net effect of all CMIP5 modelled 25‐year predictions was a 19% reduction in global DMS flux. 25‐year DMS concentration changes had significant regional effects, some positive (Southern Ocean, North Atlantic, Northwest Pacific) and some negative (isolated regions along the Equator and in the Indian Ocean). Using satellite‐detected coverage of coccolithophore blooms, our estimate of their contribution to North Atlantic DMS emissions suggests that the coccolithophores contribute only a small percentage of the North Atlantic annual flux estimate, but may be more important in the summertime and in the northeast Atlantic.
      PubDate: 2014-10-20T04:37:26.863615-05:
      DOI: 10.1002/2014JC010104
       
  • The salinity signature of the cross‐shelf exchanges in the
           southwestern Atlantic Ocean: Numerical simulations
    • Authors: Ricardo P. Matano; Vincent Combes, Alberto R. Piola, Raul Guerrero, Elbio D. Palma, P. Ted Strub, Corinne James, Harold Fenco, Yi Chao, Martin Saraceno
      Pages: n/a - n/a
      Abstract: A high‐resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA) the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high frequency component of the wind stress forcing controls the vertical structure of the plumes while the low‐frequency component of the wind stress forcing and the inter‐annual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross‐shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross‐shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf.
      PubDate: 2014-10-17T04:17:57.306452-05:
      DOI: 10.1002/2014JC010116
       
  • Summertime phytoplankton blooms and surface cooling in the western south
           equatorial Indian Ocean
    • Authors: Xiaomei Liao; Yan Du, Haigang Zhan, Ping Shi, Jia Wang
      Pages: n/a - n/a
      Abstract: Chlorophyll‐a (Chla) concentration derived from the Sea viewing Wide field of View sensor (SeaWiFS) data (January 1998‐December 2010) shows phytoplankton blooms in the western south equatorial Indian Ocean (WSEIO) during the summer monsoon. The mechanism that sustains the blooms is investigated with the high‐resolution Ocean General Circulation Model for the Earth Simulator (OFES) products. The summer blooms in the WSEIO are separated from the coast; they occur in June, reach their maximum in August, and decay in October. With summer monsoon onset, cross‐equatorial wind induces open‐ocean upwelling in the WSEIO, uplifting the nutricline. The mixed layer heat budget analysis reveals that both thermal forcing and ocean processes are important for the seasonal variations of SST, especially wind‐driven entrainment plays a significant role in cooling the WSEIO. These processes cause nutrient enrichment in the surface layer and trigger the phytoplankton blooms. As the summer monsoon develops, the strong wind deepens the mixed layer; the entrainment thus increases the nutrient supply and enhances the bloom. Horizontal advection associated with the Southern Gyre might also be an important process that sustains the bloom. This large clockwise gyre could advect nutrient‐rich water along its route, allowing Chla to bloom in a larger area.
      PubDate: 2014-10-17T04:03:53.263275-05:
      DOI: 10.1002/2014JC010195
       
  • SMOS sea surface salinity signals of tropical instability waves
    • Authors: Xiaobin Yin; Jacqueline Boutin, Gilles Reverdin, Tong Lee, Sabine Arnault, Nicolas Martin
      Pages: n/a - n/a
      Abstract: Sea Surface Salinity (SSS) measurements from the Soil Moisture and Ocean Salinity (SMOS) mission provide an unprecedented opportunity to observe the salinity structure of Tropical Instability Waves (TIWs) from space, especially during the intense 2010 La Niña condition. In the eastern equatorial Pacific Ocean, SMOS SSS signals correlate well and have similar amplitude to 1‐m salinity from the Tropical Atmosphere Ocean (TAO) array at 6 locations with strong TIW signals. At these locations, the linear negative relationships between SMOS SSS and OSTIA SST signals vary from ‐0.20 °C‐1 to ‐0.25 °C‐1, which are comparable to the ones obtained from TAO. From June to December 2010, the largest TIW signals and meridional gradients of both SSS and SST appear around 2°N west of 100°W. They shift southward and cross the equator at 90°W. In addition to the large negative correlation band around 2°N, a band of negative correlations between SSS and SST signals also exists around 8°N west of 110°W for the 33‐day signals. The peak amplitude of the 33‐day SMOS SSS signals west of 135°W is reduced by more than 40% with respect to values east of 135°W, while the reduction for SST is much lower (less than 20%). The amplitudes and longitudinal extents of TIW signals and the dominant westward propagation speed of 17‐day TIWs (as detected by SMOS and Aquarius) at the equator decrease from 2010 to 2013 associated with the transition from a strong La Niña to non La Niña conditions.
      PubDate: 2014-10-17T03:47:53.742659-05:
      DOI: 10.1002/2014JC009960
       
  • The salinity signature of the cross‐shelf exchanges in the
           southwestern Atlantic Ocean: Satellite observations
    • Authors: Raul A. Guerrero; Alberto R. Piola, Harold Fenco, Ricardo P. Matano, Vincent Combes, Yi Chao, Corinne James, Elbio D. Palma, Martin Saraceno, P. Ted Strub
      Pages: n/a - n/a
      Abstract: Satellite derived sea surface salinity (SSS) data from Aquarius and SMOS are used to study the shelf‐open ocean exchanges in the western South Atlantic near 35ºS. Away from the tropics these exchanges cause the largest SSS variability throughout the South Atlantic. The data reveal a well defined seasonal pattern of SSS during the analyzed period and of the location of the export of low salinity shelf waters. In spring and summer low salinity waters over the shelf expand offshore and are transferred to the open ocean primarily southeast of the river mouth (from 36 ºS to 37º30’S). In contrast, in fall and winter low salinity waters extend along a coastal plume and the export path to the open ocean distributes along the offshore edge of the plume. The strong seasonal SSS pattern is modulated by the seasonality of the along‐shelf component of the wind stress over the shelf. However, the combined analysis of SSS, satellite‐derived sea surface elevation and surface velocity data suggest that the precise location of the export of shelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluence and mesoscale eddies and meanders of the Brazil Current. The satellite data indicate that in summer, mixtures of low salinity shelf waters are swiftly driven towards the ocean interior along the axis of the Brazil/Malvinas Confluence. In winter, episodic wind reversals force the low salinity coastal plume offshore where they mix with tropical waters within the Brazil Current and create a warmer variety of low salinity waters in the open ocean.
      PubDate: 2014-10-17T03:45:52.932219-05:
      DOI: 10.1002/2014JC010113
       
  • Preliminary analysis of acceleration of sea level rise through the
           twentieth century using extended tide gauge data sets (August 2014)
    • Authors: Peter Hogarth
      Pages: n/a - n/a
      Abstract: This work explores the potential for extending tide gauge time series from the Permanent Service for Mean Sea Level (PSMSL) using historical documents, PSMSL ancillary data, and by developing additional composite time series using near neighbour tide gauges. The aim was to increase the number, completeness and geographical extent of records covering most or all of the 20th Century. The number of at least 75% complete century scale time series has been approximately doubled over the original PSMSL dataset. In total over 4800 station years have been added, with 294 of these added to 10 long Southern Hemisphere records. Individual century scale acceleration values derived from this new extended data set tend to converge on a value of 0.01 ± 0.008 mm/yr2. This result agrees closely with recent work and is statistically significant at the 1 sigma level. Possible causes of acceleration and errors are briefly discussed. Results confirm the importance of current data archaeology projects involving digitisation of the remaining archives of hard copy tide gauge data for sea level and climate studies.
      PubDate: 2014-10-16T03:41:51.932564-05:
      DOI: 10.1002/2014JC009976
       
  • The effect of water temperature on air entrainment, bubble plumes, and
           surface foam in a laboratory breaking‐wave analog
    • Authors: A. H. Callaghan; M. D. Stokes, G. B. Deane
      Pages: n/a - n/a
      Abstract: Air‐entraining breaking waves form oceanic whitecaps and play a key role in climate regulation through air‐sea bubble‐mediated gas transfer, and sea spray aerosol production. The effect of varying sea surface temperature on air entrainment, sub‐surface bubble plume dynamics, and surface foam evolution intrinsic to oceanic whitecaps has not been well studied. By using a breaking wave analogue in the laboratory over a range of water temperatures (Tw = 5 °C to Tw = 30 °C) and different source waters, we have examined changes in air entrainment, sub‐surface bubble plumes, and surface foam evolution over the course of a breaking event. For filtered seawater, air entrainment was estimated to increase by 6 % between Tw = 6 °C and Tw = 30 °C, driven by increases of about 43% in the measured surface roughness of the plunging water sheet. After active air entrainment, the rate of loss of air through bubble degassing was more rapid at colder water temperatures within the first 0.5 s of plume evolution. Thereafter, the trend reversed and bubbles degassed more quickly in warmer water. The largest observed temperature‐dependent differences in sub‐surface bubble distributions occurred at radii greater than about 700 μm. Temperature‐dependent trends observed in the sub‐surface bubble plume were mirrored in the temporal evolution of the surface whitecap foam area demonstrating the intrinsic link between surface whitecap foam and the sub‐surface bubble plume. Differences in foam and plume characteristics due to different water sources were greater than the temperature dependencies for the filtered seawater examined.
      PubDate: 2014-10-16T03:41:44.147171-05:
      DOI: 10.1002/2014JC010351
       
  • Impact of diurnal forcing on intraseasonal sea surface temperature
           oscillations in the Bay of Bengal
    • Authors: V. Thushara; P. N. Vinayachandran
      Pages: n/a - n/a
      Abstract: The diurnal cycle is an important mode of sea surface temperature (SST) variability in tropical oceans, influencing air‐sea interaction and climate variability. Upper ocean mixing mechanisms are significant at diurnal timescales controlling the intraseasonal variability (ISV) of SST. Sensitivity experiments using an Ocean General Circulation Model (OGCM) for the summer monsoon of the year 2007 show that incorporation of diurnal cycle in the model atmospheric forcings improves the SST simulation at both intraseasonal and shorter timescales in the Bay of Bengal (BoB). The increase in SST‐ISV amplitudes with diurnal forcing is ~0.05°C in the southern bay while it is ~0.02°C in the northern bay. Increased intraseasonal warming with diurnal forcing results from the increase in mixed layer heat gain from insolation, due to shoaling of the daytime mixed layer. Amplified intraseasonal cooling is dominantly controlled by the strengthening of sub‐surface processes owing to the nocturnal deepening of mixed layer. In the southern bay, intraseasonal variability is mainly determined by the diurnal cycle in insolation, while in the northern bay, diurnal cycle in insolation and winds have comparable contributions. Temperature inversions (TI) develop in the northern bay in the absence of diurnal variability in wind stress. In the northern bay, SST‐ISV amplification is not as large as that in the southern bay due to the weaker diurnal variability of mixed layer depth (MLD) limited by salinity stratification. Diurnal variability of model MLD is not sufficient to create large modifications in mixed layer heat budget and SST‐ISV in the northern bay.
      PubDate: 2014-10-15T03:05:34.369972-05:
      DOI: 10.1002/2013JC009746
       
  • The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE)
    • Authors: A. Ganachaud; S. Cravatte, A. Melet, A. Schiller, N. J. Holbrook, B. M. Sloyan, M. J. Widlansky, M. Bowen, J. Verron, P. Wiles, K. Ridgway, P. Sutton, J. Sprintall, C. Steinberg, G. Brassington, W. Cai, R. Davis, F. Gasparin, L. Gourdeau, T. Hasegawa, W. Kessler, C. Maes, K. Takahashi, K. J. Richards, U. Send
      Pages: n/a - n/a
      Abstract: The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) is an international research program under the auspices of CLIVAR. The key objectives are to understand the Southwest Pacific Ocean circulation and the South Pacific Convergence Zone (SPCZ) dynamics, as well as their influence on regional and basin‐scale climate patterns. South Pacific thermocline waters are transported in the westward flowing South Equatorial Current (SEC) toward Australia and Papua‐New Guinea. On its way, the SEC encounters the numerous islands and straits of the Southwest Pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes. The transit in the Coral, Solomon and Tasman Seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the El Niño‐Southern Oscillation, while the southward transports influence the climate and biodiversity in the Tasman Sea. After seven years of substantial in situ oceanic observational and modeling efforts, our understanding of the region has much improved. We have a refined description of the SPCZ behavior, boundary currents, pathways and water mass transformation, including the previously undocumented Solomon Sea. The transports are large and vary substantially in a counter‐intuitive way, with asymmetries and gating effects that depend on time scales. This paper provides a review of recent advancements, and discusses our current knowledge gaps and important emerging research directions.
      PubDate: 2014-10-14T12:01:59.029564-05:
      DOI: 10.1002/2013JC009678
       
  • Seasonality of biological feedbacks on sea surface temperature variations
           in the Arabian Sea: The role of mixing and upwelling
    • Authors: Jinfeng Ma; Hailong Liu, Pengfei Lin, Haigang Zhan
      Pages: n/a - n/a
      Abstract: The effects of biological heating on upper‐ocean temperature and circulation in the Arabian Sea are investigated using an ocean general circulation model. We find that the change of sea surface temperature (SST) is not only dependent on the variation of chlorophyll concentration, but also the dynamic processes, e.g., mixing and upwelling. Biological heating can warm the SST in the north Arabian Sea during spring and the central Arabian Sea during autumn when the mixed layer depth is shallow. However, the situation is quite different during winter and summer. Although the chlorophyll concentration is high in the north Arabian Sea during winter and in the western Arabian Sea during summer, the SSTs become significantly cool instead of warm. The heat budget analyses indicate that the cold SSTs result from both the strong convective mixing during the winter and the strong upwelling during the summer, which bring the cold water below the mixed layer to the surface.
      PubDate: 2014-10-10T04:16:41.458837-05:
      DOI: 10.1002/2014JC010186
       
  • Spatiotemporal chlorophyll‐a dynamics on the Louisiana continental
           shelf derived from a dual satellite imagery algorithm
    • Authors: Chengfeng Le; John C. Lehrter, Chuanmin Hu, Michael C. Murrell, Lin Qi
      Pages: n/a - n/a
      Abstract: A monthly time‐series of remotely sensed chlorophyll a (Chlars) over the Louisiana continental shelf (LCS) was developed and examined for its relationship to river discharge, nitrate concentration, total phosphorus concentration, photosynthetically available radiation (PAR), wind speed, and inter‐annual variation in hypoxic area size. A new algorithm for Chlars, tuned separately for clear and turbid waters, was developed using field‐observed chlorophyll a (Chlaobs) collected during 12 cruises from 2002‐2007. The new algorithm reproduced Chlaobs, with ~40% and ~60% uncertainties at satellite pixel level for clear offshore waters and turbid nearshore waters, respectively. The algorithm was then applied to SeaWiFS and MODIS images to calculate long‐term (1998‐2013) monthly mean Chlars estimates at 1 km resolution across the LCS. Correlation and multiple stepwise regression analyses were used to relate the Chlars estimates to key environmental drivers expected to influence phytoplankton variability. The Chlars time‐series covaried with river discharge and nutrient concentration, PAR, and wind speed, and there were spatial differences in how these environmental drivers influenced Chlars. The main axis of spatial variability occurred in a cross‐shelf direction with highest Chlars observed on the inner shelf. Both inner‐ (
      PubDate: 2014-10-10T03:58:57.378412-05:
      DOI: 10.1002/2014JC010084
       
  • Relative contributions of ocean mass and deep steric changes to sea level
           rise between 1993 and 2013
    • Authors: Sarah G. Purkey; Gregory C. Johnson, Don P. Chambers
      Pages: n/a - n/a
      Abstract: Regional and global trends of Sea Level Rise (SLR) owing to mass addition centered between 1996–2006 are assessed through a full‐depth SLR budget using full‐depth in‐situ ocean data and satellite altimetry. These rates are compared to regional and global trends in ocean mass addition estimated directly using data from the Gravity Recovery and Climate Experiment (GRACE) from 2003–2013. Despite the two independent methods covering different time periods with differing spatial and temporal resolution, they both capture the same large‐scale mass addition trend patterns including higher rates of mass addition in the North Pacific, South Atlantic, and the Indo‐Atlantic Sector of the Southern Ocean, and lower mass addition trends in the Indian, North Atlantic, South Pacific, and the Pacific Sector of the Southern Ocean. The global mean trend of ocean mass addition is 1.5 (±0.4) mm yr‐1 for 1996–2006 from the residual method and the same for 2003–2013 from the GRACE method. Furthermore, the residual method is used to evaluate the error introduced into the mass budget if the deep steric contributions below 700, 1000, 2000, 3000, and 4000 m are neglected, revealing errors of 65%, 38%, 13%, 8% and 4% respectively. The two methods no longer agree within error bars when only the steric contribution shallower than 1000 m is considered.
      PubDate: 2014-10-10T03:55:32.693136-05:
      DOI: 10.1002/2014JC010180
       
  • Coherent evidence from aquarius and argo for the existence of a shallow
           low‐salinity convergence zone beneath the Pacific ITCZ
    • Authors: Lisan Yu
      Pages: n/a - n/a
      Abstract: Aquarius observations featured a prominent zonal sea‐surface salinity (SSS) front that extended across the tropical Pacific between 2 – 10°N. By linking to Argo subsurface salinity observations and satellite‐derived surface forcing datasets, the study discovered that the SSS front was not a stand‐alone feature, but, in fact, the surface manifestation of a shallow low‐salinity convergence zone (LSCZ). A near‐surface salinity budget analysis was conducted, showing that the LSCZ was sourced from the rainfall in the Inter‐tropical convergence zone (ITCZ), but the mechanism of its generation and maintenance was dominated by the wind‐driven Ekman dynamics, not the surface freshwater flux. Three distinct features highlighted the relationship between the LSCZ and ITCZ. The first was that the seasonal movement of the LSCZ was characterized by a monotonic northward displacement starting from the near‐equatorial latitudes in boreal spring, which was different from the ITCZ that is known for its seasonal north‐south displacement. The second feature was that the lowest SSS waters were locked to the northern edge of the Ekman salt convergence throughout the year, but they showed no fixed relationship with the ITCZ rain band. The LSCZ and ITCZ collocated only during August‐October, the time that the ITCZ rain band coincided with the Ekman convergence zone. The third feature was the evidence of the collocation between the SSS front and the Ekman convergence zone, which not only established the Ekman convergence as the genesis of the LSCZ but also positioned the SST front as a surface manifestation of the LSCZ.
      PubDate: 2014-10-10T03:12:23.075232-05:
      DOI: 10.1002/2014JC010030
       
  • 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
       
  • 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
       
  • 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
       
  • 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
       
  • 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
       
  • 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
       
 
 
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