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

Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 22, SJR: 2.156, h-index: 61)
Geophysical Research Letters     Full-text available via subscription   (Followers: 50, 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: 22)
J. of Geophysical Research : Biogeosciences     Full-text available via subscription   (Followers: 6)
J. of Geophysical Research : Earth Surface     Partially Free   (Followers: 23)
J. of Geophysical Research : Oceans     Partially Free   (Followers: 15)
J. of Geophysical Research : Planets     Full-text available via subscription   (Followers: 13)
J. of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 22)
J. of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 15)
Paleoceanography     Full-text available via subscription   (Followers: 4, SJR: 2.16, h-index: 82)
Radio Science     Full-text available via subscription   (Followers: 3, SJR: 0.527, h-index: 47)
Reviews of Geophysics     Full-text available via subscription   (Followers: 19, SJR: 8.837, h-index: 87)
Space Weather     Full-text available via subscription   (Followers: 3, SJR: 0.496, h-index: 16)
Tectonics     Full-text available via subscription   (Followers: 7, SJR: 2.16, h-index: 79)
Water Resources Research     Full-text available via subscription   (Followers: 192, 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]
  • Modeling the impact of glacial runoff on fjord circulation and submarine
           melt rate using a new subgrid‐scale parameterization for glacial
           plumes
    • Authors: Tom Cowton; Donald Slater, Andrew Sole, Dan Goldberg, Peter Nienow
      Pages: n/a - n/a
      Abstract: The injection at depth of ice sheet runoff into fjords may be an important control on the frontal melt rate of tidewater glaciers. Here, we develop a new parameterization for ice marginal plumes within the Massachusetts Institute of Technology General Circulation Model (MITgcm), allowing three‐dimensional simulation of large (500km2) glacial fjords on annual (or longer) timescales. We find that for an idealized fjord (without shelf‐driven circulation), subglacial runoff produces a thin, strong and warm down‐fjord current in the upper part of the water column, balanced by a thick and slow up‐fjord current at greater depth. Although submarine melt rates increase with runoff due to higher melt rates where the plume is in contact with the ice front, we find that annual submarine melt rate across the ice front is relatively insensitive to variability in annual runoff. Better knowledge of the spatial distribution of runoff, controls on melt rate in those areas not directly in contact with plumes and feedback mechanisms linking submarine melting and iceberg calving are necessary to more fully understand the sensitivity of glacier mass balance to runoff‐driven fjord circulation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-22T09:02:24.362474-05:
      DOI: 10.1002/2014JC010324
       
  • A novel tracer technique to quantify the atmospheric flux of trace
           elements to remote ocean regions
    • Authors: David Kadko; William M. Landing, Rachel U. Shelley
      Pages: n/a - n/a
      Abstract: Atmospheric input into the global ocean constitutes an important budgetary component of numerous chemical species and plays a key role in controlling biogeochemical processes in the ocean. Assessment of this input is difficult however because measurements of deposition rates to the ocean, particularly in remote areas, are rare and susceptible to problems of temporal and spatial variability. While the collection and analysis of aerosol samples is somewhat routine, the chemical concentration data collected from ship board or land‐based aerosol samplers in and of themselves cannot yield the deposition flux of trace elements; a method is required to transform concentration measurements into flux. The ability to derive the atmospheric flux of 7Be from its ocean inventory provides a key linkage between the atmospheric concentration of chemical species and their deposition to the ocean. We have demonstrated that estimates of the atmospheric flux of trace elements (TEs) can be made by multiplying the ocean inventory of 7Be x [TE/7Be] ratio in bulk aerosols. Flux estimates for trace elements made by the 7Be ocean inventory method were comparable to fluxes derived from rain samples collected on the island of Bermuda. The situation at Bermuda allows such testing to be made, where ocean‐based methods can be calibrated by convenient land locations. Our results suggest that this method would be useful for remote areas where fixed sampling stations do not exist; that is, the majority of the global ocean. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-22T05:53:30.473059-05:
      DOI: 10.1002/2014JC010314
       
  • Analysis of ageostrophy in strong surface eddies in the Atlantic Ocean
    • Authors: E. M. Douglass; J. G. Richman
      Pages: n/a - n/a
      Abstract: Strongly nonlinear surface eddies are identified and analyzed in a general circulation model. Agulhas rings and Gulf Stream cold core eddies are examples of eddies that cannot be properly characterized using linear geostrophic dynamics. These eddies are compact, highly circular, persistent in time, and travel long distances while maintaining their characteristics. The nonlinear eddies can be identified by a large Rossby number and high circularity. The majority of the anomalous eddies are anticyclones. Calculation of the balance of forces on these eddies demonstrates that the centrifugal force associated with strong curvature is significant, and the force balance shifts from geostrophy towards a gradient wind balance. Using geostrophy instead of the gradient wind balance produces large errors in estimates of rotational velocity of these eddies. The gradient wind velocity can be calculated from geostrophic velocity and eddy radius. Comparison between the results demonstrates that even when only sea surface height and associated geostrophic velocities are available, strongly nonlinear eddies can be identified and properly characterized. This analysis is then applied to altimetric maps of sea surface height. Nonlinear eddies are present in the altimetric maps, but are less common and not as strongly nonlinear. This analysis demonstrates that by properly accounting for the dynamics of the eddy field, a more complete statistical description including nonlinear terms can be obtained from readily available observations. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-22T04:53:09.270766-05:
      DOI: 10.1002/2014JC010350
       
  • Seasonal and interannual variability of the West Greenland Current System
           in the Labrador Sea in 1993–2008
    • Authors: Tatiana Rykova; Fiammetta Straneo, Amy S. Bower
      Pages: n/a - n/a
      Abstract: The West Greenland Current system (WGCS) transports heat and freshwater into the Labrador Sea, influencing the formation of Labrador Sea Water, a key component of the Atlantic Meridional Overturning Circulation. Notwithstanding its importance, relatively little is known about the structure and transport of this current system and its seasonal and interannual variability. Here we use historical hydrographic data from 1992 to 2008, combined with AVISO satellite altimetry, to diagnose the mean properties as well as seasonal and interannual variability of the boundary current system. We find that while the surface, fresh, cold West Greenland Current is amplified in summer, the subsurface warm, salty Irminger Current has maximum transport in winter, when its waters are also warmer and saltier. Seasonal changes in the total transport are thus mostly due to changes in the baroclinic structure of the current. By contrast, we find a trend towards warmer/saltier waters and a slow down of the WGCS, within the period studied. The latter is attributed to changes in the barotropic component of the current. Superimposed on this trend, warm and salty anomalies transit through the system in 1997 and 2003 and are associated with a rapid increase in the transport of the boundary current due to changes in the baroclinic component. The boundary current changes precede similar changes in the interior with a one‐two year lag, indicating that anomalies advected into the region by the boundary current can play an important role in the modulation of convection in the Labrador Sea. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-22T04:32:05.982478-05:
      DOI: 10.1002/2014JC010386
       
  • Cross‐polarization geophysical model function for C‐band radar
           backscattering from the ocean surface and wind speed retrieval
    • Authors: Paul A. Hwang; Ad Stoffelen, Gerd‐Jan van Zadelhoff, William Perrie, Biao Zhang, Haiyan Li, Hui Shen
      Pages: n/a - n/a
      Abstract: The wind speed sensitivity of cross‐polarization (cross‐pol) radar backscattering cross section (VH) from the ocean surface increases toward high winds. The signal saturation problem of VH, if it exists, occurs at a much higher wind speed compared to the co‐polarization (co‐pol: VV or HH) sea returns. These properties make VH a better choice over VV or HH for monitoring severe weather. Combined with high spatial resolution of the synthetic aperture radar (SAR), the development of hurricane wind retrieval using VH is advancing rapidly. This paper describes a cross‐pol C‐band radar backscattering geophysical model function (GMF) with incidence angle dependence for the full wind speed range in the available datasets (up to 56m/s). The GMF is derived from RADARSAT‐2 (R2) dual‐polarization (dual‐pol) ScanSAR modes with 300 and 500km swaths. The proposed GMF is compared to other published algorithms. The result shows that the simulated VH cross section and the retrieved wind speed with the proposed GMF is in better agreement with measurements. With careful treatment of noise, the VH retrieved wind speeds may extend to mild or moderate conditions. The higher fraction of non‐Bragg contribution in VH can be exploited for analysis of surface wave breaking. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-22T04:22:43.51846-05:0
      DOI: 10.1002/2014JC010439
       
  • An analytical model for the description of the full polarimetric sea
           surface Doppler signature
    • Authors: Franco Fois; Peter Hoogeboom, Franҫois Le Chevalier, Ad Stoffelen
      Pages: n/a - n/a
      Abstract: This paper describes an analytical model of the full‐polarimetric sea surface scattering and Doppler signature. The model combines the Small‐Slope‐Approximation theory (at the 2nd order) with a weak non‐linear sea surface representation. Such a model is used to examine the variation of the Doppler central frequency/bandwidth and of the Normalized Radar Cross‐section as function of wind‐speed and direction. The results suggest that the model can be a valuable tool for the accurate observation of sea surface currents. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T17:13:49.704765-05:
      DOI: 10.1002/2014JC010589
       
  • Detecting the surface salinity signature of Gulf Stream cold‐core
           rings in Aquarius synergistic products
    • Authors: M. Umbert; S. Guimbard, G. Lagerloef, L. Thompson, M. Portabella, J. Ballabrera‐Poy, A. Turiel
      Pages: n/a - n/a
      Abstract: New sea surface salinity (SSS) observations derived from satellite remote sensing platforms provide a comprehensive view of salt exchanges across boundary currents such as the Gulf Stream. The high resolution (45km spatial resolution and three‐day repeat subcycle) of the Soil Moisture and Ocean Salinity (SMOS) observations allows detection (and tracking) of meander and ring structures of the Gulf Stream from SSS maps. These structures are however not resolved by the relatively lower resolution (100km and seven‐day repeat subcycle) of Aquarius observations. A recently developed fusion technique, based on singularity analysis technique, is applied in this study to reconstruct these mesoscale (from 100km and 3 days) features in Aquarius‐derived products. New quarter‐degree SSS maps are obtained by fusing Aquarius data with three different geophysical templates: sea surface height (SSH) from AVISO, SSS from SMOS, and sea surface temperature (SST) from AVHRR. The proposed method exploits the theoretical correspondence among the singularity exponents of different maps of ocean‐surface remotely sensed scalar fields. The analysis results over the year 2012 show that merging Aquarius with SSH data provides a series of negative salinity anomalies that better collocate with the position of the cyclonic eddies identified from sea level anomaly maps. This result is consistent with the hypothesis that this SLA derived cyclonic eddies in this area are indeed CCRs shed off the GS. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T17:13:36.525252-05:
      DOI: 10.1002/2014JC010466
       
  • An approach to estimate the freshwater contribution from glacial melt and
           precipitation in East Greenland shelf waters using colored dissolved
           organic matter (CDOM)
    • Authors: Colin A. Stedmon; Mats. A Granskog, Paul A. Dodd
      Pages: n/a - n/a
      Abstract: Changes in the supply and storage of freshwater in the Arctic Ocean and its subsequent export to the North Atlantic can potentially influence ocean circulation and climate. In order to understand how the Arctic freshwater budget is changing and the potential impacts, it is important to develop and refine empirical approaches for tracing freshwater contributions. This in turn can help develop and validate model simulations. Arctic rivers are an important source of freshwater and stable oxygen isotope measurements are used to separate contributions from meteoric water (river, glacial, and precipitation) and sea ice melt. We develop this approach further and investigate the use of an additional tracer, colored dissolved organic matter (CDOM), which is largely specific to freshwater originating from Arctic rivers. A robust relationship between the freshwater contribution from meteoric water and CDOM is derived from four years of measurements in Fram Strait (2009‐2012), combined with measurements from the East Greenland shelf and Dijmpha Sound (NE Greenland). Results confirm a high contribution of riverine CDOM in Arctic halocline waters with salinities > 31.5 and indicate the importance of shelf processes (riverine input and sea ice formation), while previously, these waters where thought to be derived from open sea processes (cooling and sea‐ice formation) in the northern Barents and Kara Seas. In Greenlandic coastal waters the meteoric water contribution is influenced by Greenland Ice Sheet meltwater and deviations from the CDOM ‐ meteoric water relationships found are applied to quantify meltwater contribution along the East Greenland shelf waters (0‐13%). This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T10:54:13.966479-05:
      DOI: 10.1002/2014JC010501
       
  • Interannual variability of the northwestern Iberia deep ocean: Response to
           large‐scale North Atlantic forcing
    • Authors: E. Prieto; C. González‐Pola, A. Lavín, N.P. Holliday
      Pages: n/a - n/a
      Abstract: The oceanic hydrography of the north‐easternmost region of the North Atlantic subtropical gyre has been monitored since 2003 by three sections extending between 100 to 200 nautical miles from the Spanish NW and N coast into the Atlantic and the Bay of Biscay. The sections were occupied twice a year from 2003 to 2010, annually after that, and measure the whole water column (>5000m). Correlation of series in the vertical and among sections, autocorrelation and estimates of the effect of the noise induced by the mesoscale field, all indicate that observed signatures are robust changes of water masses at the regional scale. The hydrographic timeseries are not characterized by smooth trends but instead by shifts that persist through consecutive cruises. The most notable features include a shift to more saline central waters around 2005 after which they remained stable, and a decrease in thermohaline properties of the Labrador Sea Water from autumn 2008 to 2010. Years with a strong winter North Atlantic Oscillation (NAO) index are characterized by shifts in thermohaline properties across most of the intermediate levels, with the most notable event being the warming and increasing salinity that followed the large NAO index drop of 2010. The observations are consistent with current understanding of the large‐scale functioning of the North Atlantic, which predicts a northeastwards expansion of subtropical temperate waters in the eastern boundary as a response to NAO forcing. The observed variability is discussed in relationship to large‐scale circulation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T10:36:57.571309-05:
      DOI: 10.1002/2014JC010436
       
  • Oceanic responses to Hurricane Igor over the Grand Banks: A modeling study
    • Authors: Zhimin Ma; Guoqi Han, Brad de Young
      Pages: n/a - n/a
      Abstract: A three‐dimensional (3‐D) baroclinic finite‐volume ocean model (FVCOM) was developed to examine the oceanic response to Hurricane Igor over the Grand Banks of Newfoundland. Hurricane Igor generated a storm surge of almost 1m at St. John's and about 0.8m at three nearby coastal tide gauge stations (Bonavista, Argentia and St. Lawrence). The surge magnitude from the 3‐D baroclinic model agrees approximately with tide‐gauge observations at all four stations, slightly better than that from an alternative 3‐D barotropic case. The sudden drop of sea surface temperature caused by the storm, approximately as observed by buoys, is well simulated by the baroclinic model with a k‐ε turbulence closure. A sensitivity simulation with the Mellor‐Yamada turbulence closure significantly underestimates sea surface cooling. It is shown that the sea surface cooling is mainly associated with turbulent mixing, and to a lesser degree with Ekman upwelling. The model solution shows that the largest surge occurred between Bonavista and St. John's. Further analysis suggests the generation of a free continental shelf wave after the storm made landfall, with the peak surge propagating from St. John's to St. Lawrence. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T10:12:58.90142-05:0
      DOI: 10.1002/2014JC010322
       
  • Hydro‐acoustic and tsunami waves generated by the 2012 Haida Gwaii
           earthquake: Modeling and in situ measurements
    • Authors: Ali Abdolali; Claudia Cecioni, Giorgio Bellotti, James T. Kirby
      Pages: n/a - n/a
      Abstract: Detection of low‐frequency hydro‐acoustic waves as precursor components of destructive tsunamis can enhance the promptness and the accuracy of Tsunami Early Warning Systems (TEWS). We reconstruct the hydro‐acoustic wave field generated by the 2012 Haida Gwaii tsunamigenic earthquake using a 2D horizontal numerical model based on the integration over the depth of the compressible fluid wave equation and considering a mild sloped rigid sea‐bed. Spectral analysis of the wave field obtained at different water depths and distances from the source revealed the frequency range of low‐frequency elastic oscillations of sea water. The resulting 2D numerical model gave us the opportunity to study the hydro‐acoustic wave propagation in a large‐scale domain with available computers and to support the idea of deep‐sea observatory and data interpretation. The model provides satisfactory results, compared with in situ measurements, in the reproduction of the long‐gravitational waves. Differences between numerical results and field data are probably due to lack of exact knowledge of sea bottom motion and to the rigid sea‐bed approximation, indicating the need for further study of poro‐elastic bottom effects. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T09:53:34.519912-05:
      DOI: 10.1002/2014JC010385
       
  • SMOS salinity in the subtropical North Atlantic salinity maximum: 2.
           Two‐dimensional horizontal thermohaline variability
    • Authors: Nicolas Kolodziejczyk; Olga Hernandez, Jacqueline Boutin, Gilles Reverdin
      Pages: n/a - n/a
      Abstract: The horizontal thermohaline seasonal variability of the surface ocean is investigated in the subtropical North Atlantic Surface Salinity Maximum (SSSmax) region. Satellite sea surface temperature and salinity are used, along with high‐resolution thermosalinograph data, and Argo interpolated products, to study the horizontal two‐dimensional field of density and thermohaline variability. During late winter, compensated temperature and salinity gradients at large and mesoscale are observed northeast of the SSSmax, in the Azores Front Current region. In spite of the large and sharp surface thermohaline fronts, satellite measurements reveal a rather weak surface horizontal density gradient. During summer, the front is dominated by salinity gradients. South of the SSSmax, at large scales, the density ratio is controlled by the salinity gradient and the horizontal density gradient is enhanced by a constructive contribution of opposite salinity and temperature gradients. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T09:26:27.33134-05:0
      DOI: 10.1002/2014JC010103
       
  • The carbon dioxide (CO2) system on the Mississippi River‐dominated
           continental shelf in the northern Gulf of Mexico: 1. Distribution and
           air‐sea CO2 flux
    • Authors: Wei‐Jen Huang; Wei‐Jun Cai, Yongchen Wang, Steven E. Lohrenz, Michael C. Murrell
      Pages: n/a - n/a
      Abstract: River‐dominated continental shelf environments are active sites of air‐sea CO2 exchange. We conducted 13 cruises in the northern Gulf of Mexico, a region strongly influenced by fresh water and nutrients delivered from the Mississippi and Atchafalaya River system. The sea surface partial pressure of carbon dioxide (pCO2) was measured, and the air‐sea CO2 flux was calculated. Results show that CO2 exchange exhibited a distinct seasonality: this study area was a net sink of atmospheric CO2 during spring and early summer, and it was neutral or a weak source of CO2 to the atmosphere during mid‐summer, fall, and winter. Along the salinity gradient, across the shelf, the sea surface shifted from a source of CO2 in low salinity zones (0≤S
      PubDate: 2015-01-21T08:57:33.024993-05:
      DOI: 10.1002/2014JC010498
       
  • Overturning circulation that ventilates the intermediate layer of the Sea
           of Okhotsk and the North Pacific: The role of salinity advection
    • Authors: Junji Matsuda; Humio Mitsudera, Tomohiro Nakamura, Yuichiro Sasajima, Hiroyasu Hasumi, Masaaki Wakatsuchi
      Pages: n/a - n/a
      Abstract: Dense Shelf Water (DSW) formation in the northwestern continental shelf of the Sea of Okhotsk is the beginning of the lower limb of the overturning circulation that ventilates the intermediate layer of the North Pacific Ocean. The upper limb consisting of surface currents in the Okhotsk Sea and the subarctic gyre has not been clarified. Using a high resolution North Pacific Ocean model with a curvilinear grid as fine as 3km × 3km in the Sea of Okhotsk, we succeeded in representing the three‐dimensional structure of the overturning circulation including the narrow boundary currents and flows through straits that constitute the upper limb, as well as the lower limb consisting of DSW formation and ventilation. In particular, pathways and timescales from the Bering Sea to the intermediate layer via the ventilation in the Sea of Okhotsk were examined in detail using tracer experiments. Further, we found that the overturning circulation that connects the surface and intermediate layer is sensitive to wind stress. In the case of strong winds, the coastal current under polynyas where DSW forms is intensified, and consequently diapycnal transport from the surface layer to the intermediate layer increases. Strong winds also induce a positive sea surface salinity anomaly in the subarctic region, causing a significant decrease in the density stratification and increase in the DSW salinity (i.e. density). These processes act together to produce intense overturning circulation and deep ventilation, which may subduct even to the bottom of the Sea of Okhotsk if the wind is strong. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T08:57:11.697553-05:
      DOI: 10.1002/2014JC009995
       
  • Potential impact of the colored Amazon and Orinoco plume on tropical
           cyclone intensity
    • Authors: C. Newinger; R. Toumi
      Pages: n/a - n/a
      Abstract: The Amazon and the Orinoco river plumes modulate ocean stratification and color in the tropical North Atlantic. This changes air‐sea interactions and may thus be important for tropical cyclones (TCs). Using a regional ocean model, we try to separate the potential impact of river freshwater and light absorption on ocean temperatures, stability, and TC intensity. While the freshwater plume stabilizes the water column, there is no significant change in sea surface temperatures. However, increased stability and temperature inversions may reduce surface cooling feedbacks. The cooling inhibition index (CI) is larger when the river freshwater plume is present. Ocean color in the river plume on the other hand, blocks the deeper ocean from sunlight, leading to moderate surface warming (+0.1oC) and substantial subsurface cooling (‐0.3oC 100m mean temperature). As a consequence cold water is more readily available to passing storms and the CI decreases by . Using simple, idealized relationships between expected surface cooling and TC intensity, we find that river‐induced stability enhances strong TCs by up to ‐5 to ‐12 hPa, while ocean color may reduce intensity by +8 hPa to +16 hPa. The net impact of the colored plume is negligible for weak storms and a slight intensity reduction for stronger cyclones. Within the Amazon and Orinoco plume, the river freshwater effect may thus be substantially reduced or even offset by light absorbing particles. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-21T07:58:53.96792-05:0
      DOI: 10.1002/2014JC010533
       
  • Issue Information
    • Pages: i - v
      PubDate: 2015-01-20T00:16:34.482851-05:
      DOI: 10.1002/jgrc.20357
       
  • Phytoplankton phenology in the coastal upwelling region off
           central‐southern Chile (35°S‐–38°S):
           Time‐space variability, coupling to environmental factors, and
           sources of uncertainty in the estimates
    • Authors: Andrea Corredor‐Acosta; Carmen E. Morales, Samuel Hormazabal, Isabel Andrade, Marco A. Correa‐Ramirez
      Pages: n/a - n/a
      Abstract: The annual cycle and phenology of phytoplankton (satellite‐derived chlorophyll‐a, Chl‐a) in the coastal upwelling region off central‐southern Chile, their time‐space variation, and the extent of their coupling with those of wind‐driven upwelling (as Zonal Ekman Transport, ZET), Sea Surface Temperature (SST), and Photosynthetically Active Radiation (PAR), were analyzed using a ∼10 y satellite time series (2002‐2012). Wavelet analysis (WA) was applied to extract the dominant frequencies of variability and their recurrence, to derive the phenological indexes, and to assess the extent of the coupling between Chl‐a and environmental forcing in the annual frequency. Index estimates were obtained from minimum and maximum accumulated values in two different frequency bands, annual (WA‐ANF) and all except the synoptic (WA‐ALF). The annual frequency was dominant in all the variables, however, the annual cycle and phenology of Chl‐a displayed higher submeso‐ and mesoscale variability. The mean onset date of Chl‐a was similar to those of PAR and ZET with WA‐ALF and cross‐WA indicated that, for the most part, their annual cycles were coupled or coherent. Few interannual changes in Chl‐a phenology were detected, including a ∼1 month longer duration (WA‐ALF) during La Niña 2010‐2011. The mean anomalies in the magnitudes of Chl‐a and ZET during the upwelling season showed a slight but significant trend, negative for Chl‐a and positive for ZET, while SST remained relatively constant. This pattern was unexpected since three La Niña‐related conditions were identified during the 2007‐2012 period. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-19T08:46:54.185196-05:
      DOI: 10.1002/2014JC010330
       
  • The spatial‐temporal variability of air‐sea momentum fluxes
           observed at a tidal inlet
    • Authors: D.G. Ortiz‐Suslow; B.K. Haus, N.J. Williams, N.M. Laxague, A.J.H.M. Reniers, H.C. Graber
      Pages: n/a - n/a
      Abstract: Coastal waters are an aerodynamically unique environment that have been little explored from an air‐sea interaction point of view. Consequently, most studies must assume that open ocean derived parameterizations of the air‐sea momentum flux are representative of the near shore wind forcing. Observations made at the New River Inlet in North Carolina, during the Riverine and Estuarine Transport experiment (RIVET), were used to evaluate the suitability of wind speed dependent, wind stress parameterizations in coastal waters. As part of the field campaign, a small, agile research vessel was deployed to make high resolution wind velocity measurements in and around the tidal inlet. The eddy covariance method was employed to recover direct estimates of the 10m neutral atmospheric drag coefficient from the three dimensional winds. Observations of wind stress angle, near‐surface currents, and heat flux were used to analyze the cross‐shore variability of wind stress steering off the mean wind azimuth. In general, for on‐shore winds above 5m/s, the drag coefficient was observed to be two and a half times the predicted open ocean value. Significant wind stress steering is observed within 2km of the inlet mouth, which is observed to be correlated with the horizontal current shear. Other mechanisms such as the reduction in wave celerity or depth‐limited breaking could also play a role. It was determined that outside the influence of these typical coastal processes the open ocean parameterizations generally represent the wind stress field. The near shore stress variability has significant implications for observations and simulations of coastal transport, circulation, mixing, and general surf‐zone dynamics. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-19T04:22:12.706836-05:
      DOI: 10.1002/2014JC010412
       
  • Wave Breaking and Turbulence at a Tidal Inlet
    • Authors: Seth Zippel; Jim Thomson
      Pages: n/a - n/a
      Abstract: Field measurements collected with surface drifters at New River Inlet (NC, USA) are used to characterize wave breaking and turbulence in the presence of currents. Shoreward wave evolution is affected by currents, and breaking is observed in deeper water with opposing currents (ebb tides) relative to to following currents (flood tides). Wave dissipation models are evaluated with observed cross‐shore gradients in wave energy flux. Wave dissipation models that include the effects of currents are better correlated with the observations than the depth‐only models. Turbulent dissipation rates measured in the breaking regions are used to evaluate two existing scaling models for the vertical structure and magnitude of turbulent dissipation relative to wave dissipation. Although both describe the rapid decay of turbulence beneath the surface, exponential vertical scaling by water depth is superior to power law vertical scaling by wave height. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-14T09:22:51.485799-05:
      DOI: 10.1002/2014JC010025
       
  • Cyclonic entrainment of pre‐conditioned shelf waters into a frontal
           eddy
    • Authors: J.D. Everett; H. Macdonald, M.E. Baird, J. Humphries, M. Roughan, I. M. Suthers
      Pages: n/a - n/a
      Abstract: The volume transport of nutrient‐rich continental shelf water into a cyclonic frontal eddy (entrainment) was examined from satellite observations, a slocum glider and numerical simulation outputs. Within the frontal eddy, parcels of water with temperature/salinity signatures of the continental shelf (18‐19C and >35.5 respectively) were recorded. The distribution of patches of shelf water observed within the eddy were consistent with the spiral pattern shown within the numerical simulations. A numerical dye‐tracer experiment showed that the surface waters ( 50m depth) of the frontal eddy are almost entirely ( 95%) shelf waters. Particle tracking experiments showed that water was drawn into the eddy from over 4 degrees of latitude (30‐34.5S). Consistent with the glider observations, the modeled particles entrained into the eddy sunk relative to their initial position. Particles released south of 33S, where the waters are cooler and denser, sunk 30‐50m deeper than their release position. Distance to the shelf was a critical factor in determining the volume of shelf water entrained into the eddy. Entrainment reduced to 0.23 Sv when the eddy was furthest from the shelf, compared to 0.61 Sv when the eddy was within 10km of the shelf. From a biological perspective, quantifying the entrainment of shelf water into frontal eddies is important, as it is thought to play a significant role in providing an offshore nursery habitat for coastally‐spawned larval fish. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-14T08:57:57.475991-05:
      DOI: 10.1002/2014JC010301
       
  • Impacts of a mushy‐layer thermodynamic approach in global
           sea‐ice simulations using the CICE sea‐ice model
    • Authors: Adrian K. Turner; Elizabeth C. Hunke
      Pages: n/a - n/a
      Abstract: We perform global simulations of the Los Alamos sea‐ice model, CICE, with a new thermodynamics component that has a fully prognostic, variable bulk salinity vertical profile based on mushy layer physics. The processes of gravity drainage, melt‐water flushing and snow‐ice formation are parameterized to allow the bulk salinity to evolve with time. We analyze the seasonal and spatial variation of sea‐ice bulk salinity, area, volume and thickness and compare these quantities to simulations using the previous thermodynamic component. Adjusting one of the gravity drainage parameters, we find good agreement between simulation results and fieldwork ice‐core observations of sea‐ice bulk salinity. As expected, bulk salinity is highest during periods of ice growth and lowest after periods of ice melt. In the northern hemisphere the new thermodynamics component produces thicker ice than the previous thermodynamics component. Of the nine major differences between the two models, differences in how salinities are calculated and how melt‐pond flushing is parameterized are the principal causes of this thickness difference. Thickness differences are smaller in the southern hemisphere than in the northern hemisphere since a greater fraction of ice melts, and differences cannot accumulate year‐on‐year. Model differences in how ice thickness changes and snow‐ice formation are calculated are the most important causes of the different thickness between the two thermodynamic components in the southern hemisphere. The melt‐pond area and volume are found to be highly sensitive to a parameter choice controlling drainage through macroscopic holes in the ice, in both hemispheres. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-14T06:51:19.917722-05:
      DOI: 10.1002/2014JC010358
       
  • Salinity fronts in the tropical Pacific Ocean
    • Authors: Hsun‐Ying Kao; Gary S. E. Lagerloef
      Pages: n/a - n/a
      Abstract: This study delineates the salinity fronts (SF) across the tropical Pacific, and describes their variability and regional dynamical significance using Aquarius satellite observations. From the monthly maps of the SF, we find that the SF in the tropical Pacific are (1) usually observed around the boundaries of the fresh pool under the intertropical convergence zone (ITCZ), (2) stronger in boreal autumn than in other seasons and (3) usually stronger in the eastern Pacific than in the western Pacific. The relationship between the SF and the precipitation and the surface velocity are also discussed. We further present detailed analysis of the SF in three key tropical Pacific regions. Extending zonally around the ITCZ, where the temperature is nearly homogeneous, we find the strong SF of 1.2 psu from 7‐11°N to be the main contributor of the horizontal density difference of 0.8kg/m3. In the eastern Pacific, we observe a southward extension of the SF in the boreal spring that could be driven by both precipitation and horizontal advection. In the western Pacific, the importance of these newly resolved SF associated with the western Pacific warm/fresh pool and El Niño southern oscillations are also discussed in the context of prior literature. The main conclusions of this study are that (a) Aquarius satellite salinity measurements reveal the heretofore unknown proliferation, structure and variability of surface salinity fronts, and that (b) the fine‐scale structures of the SF in the tropical Pacific yield important new information on the regional air‐sea interaction and the upper ocean dynamics. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-14T06:21:18.60986-05:0
      DOI: 10.1002/2014JC010114
       
  • Circulation, retention, and mixing of waters within the
           Weddell‐Scotia Confluence, Southern Ocean: The role of stratified
           Taylor columns
    • Authors: Michael P. Meredith; Andrew S. Meijers, Alberto C. Naveira Garabato, Peter J. Brown, Hugh J. Venables, E. Povl Abrahamsen, Loïc Jullion, Marie‐José Messias
      Pages: n/a - n/a
      Abstract: The waters of the Weddell‐Scotia Confluence (WSC) lie above the rugged topography of the South Scotia Ridge in the Southern Ocean. Meridional exchanges across the WSC transfer water and tracers between the Antarctic Circumpolar Current (ACC) to the north and the subpolar Weddell Gyre to the south. Here, we examine the role of topographic interactions in mediating these exchanges, and in modifying the waters transferred. A case study is presented using data from a free‐drifting, intermediate‐depth float, which circulated anticyclonically over Discovery Bank on the South Scotia Ridge for close to four years. Dimensional analysis indicates that the local conditions are conducive to the formation of Taylor columns. Contemporaneous ship‐derived transient tracer data enable estimation of the rate of isopycnal mixing associated with this column, with values of O(1000m2/s) obtained. Although necessarily coarse, this is of the same order as the rate of isopycnal mixing induced by transient mesoscale eddies within the ACC. A picture emerges of the Taylor column acting as a slow, steady blender, retaining the waters in the vicinity of the WSC for lengthy periods during which they can be subject to significant modification. A full regional float dataset, bathymetric data and a Southern Ocean state estimate are used to identify other potential sites for Taylor column formation. We find that they are likely to be sufficiently widespread to exert a significant influence on water mass modification and meridional fluxes across the southern edge of the ACC in this sector of the Southern Ocean. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-13T23:51:24.838381-05:
      DOI: 10.1002/2014JC010462
       
  • Landfast ice affects the stability of the Arctic halocline: Evidence from
           a numerical model
    • Authors: Polona Itkin; Martin Losch, Rüdiger Gerdes
      Pages: n/a - n/a
      Abstract: Landfast ice covers large surface areas of the winter Siberian Seas. The immobile landfast ice cover inhibits divergent and convergent motion, hence dynamical sea ice growth and re‐distribution, decouples winter river plumes in coastal seas from the atmosphere and positions polynyas at the landfast ice edge offshore. In spite of the potentially large effects, state‐of‐the‐art numerical models usually do not represent landfast ice in its correct extent. A simple parametrization of landfast ice based on bathymetry and internal sea ice strength is introduced and its effects on the simulated Arctic Ocean are demonstrated. The simulations suggest that the Siberian landfast ice impacts the Arctic halocline stability through enhanced brine production in polynyas located closer to the shelf break and by re‐directing river water to the Canadian Basin. These processes strengthen the halocline in the Canadian Basin, but erode its stability in the Makarov and Eurasian Basins. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-09T23:06:50.341598-05:
      DOI: 10.1002/2014JC010353
       
  • Tidal bore dynamics in funnel‐shaped estuaries
    • Authors: P. Bonneton; N. Bonneton, J‐P. Parisot, B. Castelle
      Pages: n/a - n/a
      Abstract: The formation and dynamics of tidal bores in funnel‐shaped estuaries is investigated from both a global tidal wave scaling analysis and new quantitative field observations. We show that tidal bore occurrence in convergent estuaries can be estimated from a dimensionless scaling parameter characterizing the relative intensity of nonlinear friction versus local inertia in the momentum equation. A detailed analysis of tidal bore formation and secondary wave structure is presented from a unique long term database (observations of more than 200 tides) acquired during 4 campaigns in the two main French tidal‐bore estuaries: the Seine and Gironde/Garonne estuaries. We describe the effect of freshwater discharge on the global tidal wave transformation at the estuarine scale and on local tidal bore occurrence in the upper estuary. Our field data suggest that the tidal bore intensity is mainly governed by the dimensionless tidal range, which characterizes the local tidal wave nonlinearity. We also show that the secondary wave field associated with tidal bore propagating in natural estuaries differs significantly from those associated to undular bores in rectangular channels. In particular, we observe an abrupt decrease of the whelp steepness when the Froude number goes below 1.1. This secondary field transition can explain why tidal bore occurrence in worldwide estuaries is certainly underestimated. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-09T23:06:42.00595-05:0
      DOI: 10.1002/2014JC010267
       
  • Analysis of riverine suspended particulate matter fluxes (Gulf of Lion,
           Mediterranean Sea) using a synergy of ocean color observations with a
           3‐D hydrodynamic sediment transport model
    • Authors: Vincent Le Fouest; Malik Chami, Romaric Verney
      Pages: n/a - n/a
      Abstract: The export of riverine suspended particulate matter (SPM) in the coastal ocean has major implications for the biogeochemical cycles. In the Mediterranean Sea (France), the Rhone River inputs of SPM into the Gulf of Lion (GoL) are highly variable in time, which severely impedes the assessment of SPM fluxes. The objectives of this study are i) to investigate the prediction of the land‐to‐ocean flux of SPM using the complementarity (i.e., synergy) between a hydrodynamic sediment transport model and satellite observations, and ii) to analyze the spatial distribution of the SPM export. An original approach that combines the MARS‐3D model with satellite ocean color data is proposed. Satellite derived SPM and light penetration depth are used to initialize MARS‐3D and to validate its predictions. A sensitivity analysis is performed to quantify the impact of riverine SPM size composition and settling rate on the horizontal export of SPM. The best agreement between the model and the satellite in terms of SPM spatial distribution and export is obtained for two conditions: (i) when the relative proportion of “heavy and fast” settling particles significantly increases relative to the “light and slow” ones, and ii) when the settling rate of heavy and light SPM increases by 5‐fold. The synergy between MARS‐3D and the satellite data improved the SPM flux predictions by 48% near the Rhone River mouth. Our results corroborate the importance of implementing satellite observations within initialization procedures of ocean models since data assimilation techniques may fail for river floods showing strong seasonal variability. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-09T23:06:16.990916-05:
      DOI: 10.1002/2014JC010098
       
  • Wind‐driven modifications to the residual circulation in an
           ebb‐tidal delta: Arcachon Lagoon, Southwestern France
    • Authors: Paulo Salles; Arnoldo Valle‐Levinson, Aldo Sottolichio, Nadia Senechal
      Pages: n/a - n/a
      Abstract: A combination of observations and analytical solutions were used to determine the modifications caused by wind forcing on the residual or non‐tidal circulation in an ebb‐tidal delta. Observations were obtained in the lower Arcachon Lagoon, southwestern France. The basic non‐tidal circulation was established with acoustic Doppler current profilers (ADCPs) that were i) moored in the delta's two deepest channels, and ii) towed along a cross‐lagoon transect. The bathymetry of the lower lagoon, or ebb‐tidal delta, featured two channels: North Pass (>9 m) and South Pass (>20 m). The basic non‐tidal circulation consisted of mostly inflow with weak surface outflow in the South Pass, and laterally sheared bidirectional flow, dominated by outflow, in the North Pass. Analytical solutions and comparison of observed dynamical terms suggested that, in addition to the conventionally accepted influence of tidal nonlinearities, density gradients contributed to the basic non‐tidal circulation in the lagoon. Observations also indicated that wind forcing altered the basic circulation by driving simultaneous upwind flows in both passes. This response was supported by an analytical solution to wind‐driven flows over the bathymetry of the transect sampled. The response to seaward winds was to enhance inflow in South Pass and reduce outflow in North Pass. Landward winds caused diminished inflow in South Pass and increased outflow in North Pass. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-08T04:14:06.634615-05:
      DOI: 10.1002/2014JC010311
       
  • Characterizing horizontal variability and energy spectra in the Arctic
           Ocean halocline
    • Authors: Charlotte L. J. Marcinko; Adrian P. Martin, John T. Allen
      Pages: n/a - n/a
      Abstract: Energy transfer from the atmosphere into the upper Arctic Ocean is expected to become more efficient as summer sea‐ice coverage decreases and multiyear ice thins due to recent atmospheric warming. However, relatively little is known about how energy is transferred within the ocean by turbulent processes from large to small scales in the presence of ice and how these pathways might change in future. This study characterises horizontal variability in several regions of the Eurasian Arctic Ocean under differing sea‐ice conditions. Historic along track CTD data collected by a Royal Navy submarine during summer 1996 allows a unique examination of horizontal variability and associated wavenumber spectra within the Arctic Ocean halocline. Spectral analysis indicates that potential energy variance under perennial sea‐ice in the Amundsen Basin is O(100) less than within the Marginal Ice Zone (MIZ) of Fram Strait. Spectra from all regions show a transition in scaling at wavelengths of approximately 5 to 7 km. At scales greater than the transition wavelength to 50 km, energy spectra are consistent with a k‐3 scaling (where k is wavenumber) and interior quasi‐geostrophic dynamics. The scaling of spectra at these scales is extremely similar between regions suggesting similar dynamics and energy exchange pathways. The k‐3 scaling is steeper than typically found in regions of mid latitude open ocean. At scales below the transition wavelength to 300 m, spectra are close to a k‐5/3 scaling or flatter, indicating a change in dynamics, which is potentially due to internal waves dominating variability at small scales. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-08T03:56:07.12919-05:0
      DOI: 10.1002/2014JC010381
       
  • The refreezing of melt ponds on Arctic sea ice
    • Authors: Daniela Flocco; Daniel L. Feltham, Eleanor Bailey, David Schroeder
      Pages: n/a - n/a
      Abstract: The presence of melt ponds on the surface of Arctic sea ice significantly reduces its albedo, inducing a positive feedback leading to sea ice thinning. While the role of melt ponds in enhancing the summer melt of sea ice is well known, their impact on supressing winter freezing of sea ice has, hitherto, received less attention. Melt ponds freeze by forming an ice lid at the upper surface which insulates them from the atmosphere and traps pond water between the underlying sea ice and the ice lid. The pond water is a store of latent heat, which is released during refreezing. Until a pond freezes completely there can be minimal ice growth at the base of the underlying sea ice. In this work, we present a model of the refreezing of a melt pond that includes the heat and salt balances in the ice lid, trapped pond, and underlying sea ice. The model uses a two‐stream radiation model to account for radiative scattering at phase boundaries. Simulations and related sensitivity studies suggest that trapped pond water may survive for over a month (Bogorodskiy et al. 2006). We focus on the role that pond salinity has on delaying the refreezing process and retarding basal sea ice growth. We estimate that for a typical sea ice pond coverage in autumn, excluding the impact of trapped ponds in models overestimates ice growth by up to 265 million km3, an overestimate of 26%. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-08T03:41:25.732424-05:
      DOI: 10.1002/2014JC010140
       
  • Spatial and temporal variability of freshwater discharge into the Gulf of
           Alaska
    • Authors: D.F. Hill; N. Bruhis, S.E. Calos, A. Arendt, J. Beamer
      Pages: n/a - n/a
      Abstract: A study of the freshwater discharge into the Gulf of Alaska (GOA) has been carried out. Using available streamgage data, regression equations were developed for monthly flows. These equations express discharge as a function of basin physical characteristics such as area, mean elevation, and land cover, and of basin meteorological characteristics such as temperature, precipitation, and accumulated water year precipitation. To provide the necessary input meteorological data, temperature and precipitation data for a 40 year hind‐cast period were developed on high‐spatial‐resolution grids using weather station data, PRISM climatologies, and statistical downscaling methods. Runoff predictions from the equations were found to agree well with observations. Once developed, the regression equations were applied to a network of delineated watersheds spanning the entire GOA drainage basin. The region was divided into a northern region, ranging from the Aleutian Chain to the Alaska / Canada border in the southeast panhandle, and a southern region, ranging from there to the Fraser River. The mean annual runoff volume into the northern GOA region was found to be 792±120 km3 yr– 1. A water balance using MODIS‐based evapotranspiration rates yielded seasonal storage volumes that were consistent with GRACE satellite‐based estimates. The GRACE data suggest that an additional 57±11 km3 yr–1 be added to the runoff from the northern region, due to glacier volume loss (GVL) in recent years. The ease of application of the derived regression equations provides an accessible tool for quantifying mean annual values, seasonal variation, and interannual variability of runoff in any ungaged basin of interest. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-08T03:02:29.488989-05:
      DOI: 10.1002/2014JC010395
       
  • Modeling skin‐layer salinity with an extended surface‐salinity
           layer
    • Authors: Y. Tony Song; Tong Lee, Jae‐Hong Moon, Tangdong Qu, Simon Yueh
      Pages: n/a - n/a
      Abstract: Due to near‐surface salinity stratification, it is problematic to compare satellite‐measured surface salinity within the first few centimeters (skin‐layer) of the ocean with Argo‐measured top‐level salinity at about 5 m, or with ocean models that do not resolve the skin layer. Although an instrument can be designed to measure the surface salinity, a global scale measurement is currently not available. A regional model can be configured to have a vertical grid in centimeters, but it would be computationally prohibited on a global scale due to time step constraints. Here, we propose an extended surface‐salinity layer (ESSL) within a global ocean circulation model to diagnose skin SSS without increasing the computational cost, while allowing comparable solutions with both satellite and Argo salinity at the respective depths. Using a quarter‐degree global ocean model, we show that the ESSL improves near‐surface salinity significantly in comparisons with the Aquarius SSS and Argo salinity at 5 m and 10 m, respectively. Comparing with data‐assimilated HYCOM results reveals that the ESSL provides much stronger seasonal variability of SSS, similar to the Aquarius observations. We also demonstrate that the ESSL solution can be used to constrain the global mean SSS in Aquarius SSS retrieval. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-08T02:39:26.526629-05:
      DOI: 10.1002/2014JC010346
       
  • Anomalous chlorofluorocarbon uptake by mesoscale eddies in the Drake
           Passage region
    • Authors: Hajoon Song; John Marshall, Peter Gaube, Dennis J. McGillicuddy
      Pages: n/a - n/a
      Abstract: The role of mesoscale eddies in the uptake of anthropogenic chlorofluorocarbon‐11 (CFC‐11) gas is investigated with a 1/20th degree eddy‐resolving numerical ocean model of a region of the Southern Ocean. With a relatively fast air‐sea equilibrium time scale (about a month), the air‐sea CFC‐11 flux quickly responds to the changes in the mixed layer CFC‐11 partial pressure (pCFC‐11). At the mesoscale, significant correlations are observed between pCFC‐11 anomaly, anomalies in sea surface temperature (SST), net heat flux, and mixed layer depth. An eddy‐centric analysis of the simulated CFC‐11 field suggests that anticyclonic warm‐core eddies generate negative pCFC‐11 anomalies and cyclonic cold‐core eddies generate positive anomalies of pCFC‐11. Surface pCFC‐11 is modulated by mixed layer dynamics in addition to CFC‐11 air‐sea fluxes. A negative cross correlation between mixed layer depth and surface pCFC‐11 anomalies is linked to higher CFC‐11 uptake in anticyclones and lower CFC‐11 uptake in cyclones, especially in winter. An almost exact asymmetry in the air‐sea CFC‐11 flux between cyclones and anticyclones is found. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-08T02:17:24.349716-05:
      DOI: 10.1002/2014JC010292
       
  • Typhoon air‐sea drag coefficient in coastal regions
    • Authors: Zhong‐Kuo Zhao; Chun‐Xia Liu, Qi Li, Guang‐Feng Dai, Qing‐Tao Song, Wei‐Hua Lv
      Pages: n/a - n/a
      Abstract: The air‐sea drag during typhoon landfalls is investigated for a 10‐m wind speed as high as U10 ≈ 42 m s‐1, based on multi‐level wind measurements from a coastal tower located in the South China Sea. The drag coefficient (CD) plotted against the typhoon wind speed is similar to that of open ocean conditions; however, the CD curve shifts toward a regime of lower winds, and CD increases by a factor of approximately 0.5 relative to the open ocean. Our results indicate that the critical wind speed at which CD peaks is approximately 24 m s‐1, which is 5‐15 m s‐1 lower than that from deep water. Shoaling effects are invoked to explain the findings. Based on our results, the proposed CD formulation, which depends on both water depth and wind speed, is applied to a typhoon forecast model. The forecasts of typhoon track and surface wind speed are improved. Therefore, a water‐depth‐dependence formulation of CD may be particularly pertinent for parameterizing air‐sea momentum exchanges over shallow water. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T23:51:01.124671-05:
      DOI: 10.1002/2014JC010283
       
  • Characteristics, generation, and mass transport of nonlinear internal
           waves on the Washington continental shelf
    • Authors: Shuang Zhang; Matthew H. Alford, John B. Mickett
      Pages: n/a - n/a
      Abstract: As a step toward better understanding the generation of nonlinear internal waves (NLIWs) on continental shelves and the factors determining their morphology, amplitude and propagation, we analyze more than 1500 NLIWs detected on the Washington (WA) continental shelf using four summer/fall time series of temperature and velocity measurements from a surface mooring deployed at a depth of 100 m. Propagating onshore towards the northeast, these NLIWs take a variety of forms, including internal solitary waves, solitary wave trains and bores. Nearly all are mode‐1 depression waves that arrive semi‐diurnally along with the internal tide. The NLIW energy flux is correlated with the internal tide energy flux but not the local barotropic forcing, implying that the observed NLIWs arise primarily from shoaling remotely generated internal tides rather than local generation. Estimated onshore transport by the waves can equal or exceed offshore Ekman transport, suggesting the waves may play an important role in the mass balance on the continental shelf. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T16:19:36.033363-05:
      DOI: 10.1002/2014JC010393
       
  • A dipole‐like SST trend in the Somalia region during the monsoon
           season
    • Authors: F. Santos; M. Gómez‐Gesteira, M. deCastro, J. M. Días
      Pages: n/a - n/a
      Abstract: SST trends measured in the Somalia region during the southwest monsoon season over the period 1982‐2013 have shown the existence of a warming‐cooling dipole. The positive spot, with a warming trend on the order of 0.37ºC dec‐1, is centered around 5.1 ºN – 50.3º E and the negative one, with a trend on the order of ‐0.43ºC dec‐1, around 11.1 ºN – 52.2º E. The migration of the Great Whirl (GW) over the last three decades at a speed of ‐0.3 deg dec‐1 in longitude and ‐0.6 deg dec‐1 in latitude was considered as the possible origin of the SST dipole. The displacement of the GW produces changes in the geostrophic currents which, in turn, generate changes in the amount of advected water from and to coast. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T15:57:23.377982-05:
      DOI: 10.1002/2014JC010319
       
  • An objective algorithm for estimating maximum oceanic mixed layer depth
           
    • Authors: Ge Chen; Fangjie Yu
      Pages: n/a - n/a
      Abstract: In this study, we propose a new algorithm for estimating the annual maximum mixed layer depth (M2LD) analogous to a full range of local “ventilation” depth, and corresponding to the deepest surface to which atmospheric influence can be “felt”. Two “seasonality indices” are defined respectively for temperature and salinity through Fourier analysis of their time series using Argo data, on the basis of which a significant local minimum of the index corresponding to a maximum penetration depth can be identified. A final M2LD is then determined by maximizing the thermal and haline effects. Unlike most of the previous schemes which use arbitrary thresholds or subjective criteria, the new algorithm is objective, robust, and property adaptive provided a significant periodic geophysical forcing such as annual cycle is available. The validity of our methodology is confirmed by the spatial correlation of the tropical dominance of saline effect (mainly related to rainfall cycle) and the extratropical dominance of thermal effect (mainly related to solar cycle). It is also recognized that the M2LD distribution is characterized by the coexistence of basin‐scale zonal structures and eddy‐scale local patches. In addition to the fundamental buoyancy forcing caused mainly by latitude‐dependent solar radiation, the impressive two‐scale pattern is found to be primarily attributable to 1) large‐wave climate due to extreme winds (large‐scale); and 2) systematic eddy shedding as a result of persistent winds (meso‐scale). Moreover, a general geographical consistency and a good quantitative agreement are found between the new algorithm and those published in the literature. However, a major discrepancy in our result is the existence of a constantly deeper M2LD band compared to other results in the midlatitude oceans of both hemispheres. Given the better correspondence of our M2LDs with the depth of the oxygen saturation limit, it is argued that there might be a systematic underestimation with existing criteria in these regions. Our results demonstrate that the M2LD may serve as an integrated proxy for studying the coherent multidisciplinary variabilities of the coupled ocean‐atmosphere system. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T15:37:33.171805-05:
      DOI: 10.1002/2014JC010383
       
  • Occurrence of large temperature inversion in the thermohaline frontal zone
           at the Yellow Sea entrance in winter and its relation to advection
    • Authors: Heung‐Jae Lie; Cheol‐Ho Cho, Kyung Tae Jung
      Pages: n/a - n/a
      Abstract: Temperature inversion (higher temperature at a deeper depth) in winter and its relation to advection were investigated by analyzing both conductivity‐temperature‐depth data in the southern Yellow Sea (YS) and northwestern East China Sea during the winter of 2002–2003 and time series data of temperature, salinity, and currents at a buoy station at the YS entrance. Significant temperature inversions occur predominantly along the thermohaline front at the YS entrance where the Cheju Warm Current water (CWCW) and the cold coastal waters meet. In February 2003, on the northern frontal zone along 34° N where isotherms and isohalines declined downwards to the north, particularly large inversions with temperature differences of larger than 2.0 °C were observed to occur more in troughs than in the crests of the wave‐like frontal meander where the cold Korean coastal water (KCW) advances farther southward. The inversion persisted until mid‐April at the buoy station in the frontal zone, and both temperature and salinity showed simultaneous variations in the same manner. During episodic occurrences of large inversions, temperature and salinity decreased sharply in the upper layer, but increased concurrently in the lower layer. These episodic inversions were found to be closely related to the westward advection of the KCW in the upper layer and the northward advection of the CWCW in the lower layer. It is considered that these advections may play an important role in maintaining baroclinicity in the northern frontal zone, which is responsible for driving the westward transversal flow across the YS entrance. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T15:16:11.154602-05:
      DOI: 10.1002/2014JC010653
       
  • Spatial structure and temporal variability of the zonal flow in the Luzon
           Strait
    • Authors: Zhiwei Zhang; Wei Zhao, Jiwei Tian, Qingxuan Yang, Tangdong Qu
      Pages: n/a - n/a
      Abstract: One‐year long, full‐depth velocity measurements were used to examine the spatial structure and temporal variability of the zonal flow in the Luzon Strait (LSZF). The observation revealed a renewed mean flow structure: in the upper (< 500 m) and deep (>2000 m) layers, the LSZF was mostly westward; in the intermediate layer (500–2000 m), it was dominated by an eastward flow in the south but a westward flow in the north. The volume transport across the observed section between 19.8° N and 21.2° N exhibited strong seasonal and intra‐seasonal variability. On the seasonal time scale, the upper‐layer transport showed a clear annual cycle, strongest in January and weakest in June; the intermediate‐layer transport also showed a semiannual cycle, attaining its peaks (troughs) in January and June (April and October). On the intra‐seasonal time scale, both the upper‐layer and intermediate‐layer transports showed significant energy peaks at about 60 and 10–30 days. Further analysis indicated that the ~60 day variability might be attributed to the impinging mesoscale eddies from the Pacific, while the 10–30 day variability appeared to obtain its energy from local intra‐seasonal wind forcing and baroclinic instability of the background current. The 10–100 day upper‐layer and intermediate‐layer transport variabilities were highly anti‐correlated, suggesting a baroclinic nature of the intra‐seasonal variabilities of the LSZF. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T15:05:34.160414-05:
      DOI: 10.1002/2014JC010308
       
  • Heat balances and thermally driven lagoon‐ocean exchanges on a
           tropical coral reef system (Moorea, French Polynesia)
    • Authors: Liv M. M. Herdman; James L. Hench, Stephen G. Monismith
      Pages: n/a - n/a
      Abstract: The role of surface and advective heat‐fluxes on buoyancy driven circulation was examined within a tropical coral reef system. Measurements of local meteorological conditions as well as water temperature and velocity were made at six lagoon locations for two months during the austral summer. We found that temperature rather than salinity dominated buoyancy in this system. The data were used to calculate diurnally phase‐averaged thermal balances. A one‐dimensional momentum balance developed for a portion of the lagoon indicates that the diurnal heating pattern and consistent spatial gradients in surface heat fluxes creates a baroclinic pressure gradient that is dynamically important in driving the observed circulation. The baroclinic and barotropic pressure gradients make up 90% of the momentum budget in part of the system, thus, when the baroclinic pressure gradient decreases 20% during the day due to changes in temperature gradient this substantially changes the circulation, with different flow patterns occurring during night and day. Thermal balances computed across the entire lagoon show that the spatial heating patterns and resulting buoyancy driven circulation are important in maintaining a persistent advective export of heat from the lagoon, and for enhancing ocean‐lagoon exchange. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T14:39:43.959376-05:
      DOI: 10.1002/2014JC010145
       
  • Invisible polynyas: Modulation of fast ice thickness by ocean heat flux on
           the Canadian polar shelf
    • Authors: Humfrey Melling; Christian Haas, Eric Brossier
      Pages: n/a - n/a
      Abstract: Although the Canadian polar shelf is dominated by thick fast ice in winter, areas of young ice or open water do recur annually at locations within and adjacent to the fast ice. These polynyas are detectable by eye and sustained by wind or tide‐driven ice divergence and ocean heat flux. Our ice‐thickness surveys by drilling and towed electromagnetic sounder reveal that visible polynyas comprise only a subset of thin‐ice coverage. Additional area in the coastal zone, in shallow channels and in fjords is covered by thin ice which is too thick to be discerned by eye. Our concurrent surveys by CTD reveal correlation between thin fast ice and above‐freezing seawater beneath it. We use winter time series of air and ocean temperatures and ice and snow thicknesses to calculate the ocean‐to‐ice heat flux as 15 and 22 W/m2 at locations with thin ice in Penny Strait and South Cape Fjord respectively. Near‐surface seawater above freezing is not a sufficient condition for ocean heat to reach the ice; kinetic energy is needed to overcome density stratification. The ocean's isolation from wind under fast ice in winter leaves tides as the only source. Two tidal mechanisms driving ocean heat flux are discussed: diffusion via turbulence generated by shear at the under‐ice and benthic boundaries, and the internal hydraulics of flow over topography. The former appears dominant in channels and the coastal zone and the latter in some silled fjords where and when the layering of seawater density permits hydraulically critical flow. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-07T04:28:21.17691-05:0
      DOI: 10.1002/2014JC010404
       
  • Retrieving the vertical distribution of chlorophyll a concentration and
           phytoplankton community composition from in situ fluorescence profiles: A
           method based on a neural network with potential for global‐scale
           applications
    • Authors: R. Sauzède; H. Claustre, C. Jamet, J. Uitz, J. Ras, A. Mignot, F. D'Ortenzio
      Pages: n/a - n/a
      Abstract: A neural network‐based method is developed to assess the vertical distribution of (1) chlorophyll a concentration ([Chl]) and (2) phytoplankton community size indices (i.e. microphytoplankton, nanophytoplankton and picophytoplankton) from in situ vertical profiles of chlorophyll fluorescence. This method (FLAVOR for Fluorescence to Algal communities Vertical distribution in the Oceanic Realm) uses as input only the shape of the fluorescence profile associated with its acquisition date and geo‐location. The neural network is trained and validated using a large database including 896 concomitant in situ vertical profiles of High‐Performance Liquid Chromatography (HPLC) pigments and fluorescence. These profiles were collected during 22 oceanographic cruises representative of the global ocean in terms of trophic and oceanographic conditions, making our method applicable to most oceanic waters. FLAVOR is validated with respect to the retrieval of both [Chl] and phytoplankton size indices using an independent in situ dataset and appears to be relatively robust spatially and temporally. To illustrate the potential of the method, we applied it to in situ measurements of the BATS (Bermuda Atlantic Time‐Series Study) site and produce monthly climatologies of [Chl] and associated phytoplankton size indices. The resulting climatologies appear very promising compared to climatologies based on available in situ HPLC data. With the increasing availability of spatially and temporally well‐resolved datasets of chlorophyll fluorescence, one possible global‐scale application of FLAVOR could be to develop 3D and even 4D climatologies of [Chl] and associated composition of phytoplankton communities. The Matlab and R codes of the proposed algorithm are provided as auxiliary material. This article is protected by copyright. All rights reserved.
      PubDate: 2015-01-05T10:00:36.29473-05:0
      DOI: 10.1002/2014JC010355
       
  • Drivers of inorganic carbon dynamics in first‐year sea ice: A model
           study
    • Authors: Sébastien Moreau; Martin Vancoppenolle, Bruno Delille, Jean‐Louis Tison, Jiayun Zhou, Marie Kotovitch, David N. Thomas, Nicolas‐Xavier Geilfus, Hugues Goosse
      Pages: n/a - n/a
      Abstract: Sea ice is an active source or a sink for carbon dioxide (CO2), although to what extent is not clear. Here, we analyze CO2 dynamics within sea ice using a one‐dimensional halo‐thermodynamic sea ice model including gas physics and carbon biogeochemistry. The ice‐ocean fluxes, and vertical transport, of total dissolved inorganic carbon (DIC) and total alkalinity (TA) are represented using fluid transport equations. Carbonate chemistry, the consumption and release of CO2 by primary production and respiration, the precipitation and dissolution of ikaite (CaCO3•6H2O) and ice‐air CO2 fluxes, are also included. The model is evaluated using observations from a 6‐month field study at Point Barrow, Alaska and an ice‐tank experiment. At Barrow, results show that the DIC budget is mainly driven by physical processes, wheras brine‐air CO2 fluxes, ikaite formation, and net primary production, are secondary factors. In terms of ice‐atmosphere CO2 exchanges, sea ice is a net CO2 source and sink in winter and summer, respectively. The formulation of the ice‐atmosphere CO2 flux impacts the simulated near‐surface CO2 partial pressure (pCO2), but not the DIC budget. Because the simulated ice‐atmosphere CO2 fluxes are limited by DIC stocks, and therefore < 2 mmol m‐2 day‐1, we argue that the observed much larger CO2 fluxes from eddy covariance retrievals cannot be explained by a sea ice direct source and must involve other processes or other sources of CO2. Finally, the simulations suggest that near surface TA/DIC ratios of ~2, sometimes used as an indicator of calcification, would rather suggest outgassing. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-30T15:06:45.274697-05:
      DOI: 10.1002/2014JC010388
       
  • A new algorithm to retrieve chromophoric dissolved organic matter (CDOM)
           absorption spectra in the UV from ocean color
    • Authors: Fang Cao; William L. Miller
      Pages: n/a - n/a
      Abstract: Accurate estimation of the absorption coefficient (ag) for chromophoric dissolved organic matter (CDOM) over ultraviolet (UV) and short visible radiation wavelengths (with λ = 275‐450 nm) is crucial to provide a robust assessment of the biogeochemical significance of UV in the global ocean. Using a training data set spanning a variety of water types from the clearest open ocean to dynamic inshore waters, a novel algorithm to accurately resolve CDOM absorption spectra from ocean color is presented. Employing a suite of multivariate statistical approaches (principal component analysis, cluster analysis, and multiple linear regression), this new algorithm was developed with matched field data for CDOM spectra and remote sensing reflectance (Rrs) at Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) bands. Freed from any presupposition about CDOM spectral shape or conventional spectral extrapolations from visible data, our algorithm allows direct retrieval of a fully resolved CDOM absorption spectrum over UV wavelengths from visible Rrs, and further enables a global scale view of the dynamics of CDOM over different water types. Accuracy of ag retrieval is good, with a mean absolute percent difference for ag in the UV of ~25%. With fully resolved spectra, maps of calculated CDOM spectral slopes (S275‐295, S350‐400) and slope ratios (SR) are presented with the potential to provide new information about the chemical composition (e.g., molecular weight, aromaticity), sources, transformation, and cycling pathways of CDOM on global as well as regional scales. The new algorithm will contribute to improved accuracy for photochemical and photobiological rate calculations from ocean color. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-30T15:06:34.219853-05:
      DOI: 10.1002/2014JC010241
       
  • Dynamics of the surface layer diurnal cycle in the equatorial Atlantic
           Ocean (0°W, 23°W)
    • Authors: Jacob O. Wenegrat; Michael J. McPhaden
      Pages: n/a - n/a
      Abstract: A 15 year time series (1999‐2014) from the 0°, 23°W Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) mooring, which includes an 8‐month record (10/2008‐6/2009) of high‐resolution near‐surface velocity data, is used to analyze the diurnal variability of sea surface temperature, shear, and stratification in the central equatorial Atlantic. The ocean diurnal cycle exhibits pronounced seasonality that is linked to seasonal variations in the wind field. In boreal summer and fall steady trade winds and clear skies dominate, with limited diurnal variability in sea surface temperature. Diurnal shear layers, with reduced Richardson numbers, are regularly observed descending into the marginally unstable equatorial undercurrent below the mixed layer, conditions favorable for the generation of deep‐cycle turbulence. In contrast, in boreal winter and spring winds are lighter and more variable, mixed layers are shallow, and diurnal variability of sea surface temperature is large. During these conditions diurnal shear layers are less prominent, and the stability of the undercurrent increases, suggesting seasonal covariance between diurnal near‐surface shear and deep‐cycle turbulence. Modulation of the ocean diurnal cycle by tropical instability waves is also identified. This work provides the first observational assessment of the diurnal cycle of near surface shear, stratification, and marginal instability in the equatorial Atlantic, confirming previous modeling results, and offering a complementary perspective on similar work in the equatorial Pacific. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-30T15:06:24.335944-05:
      DOI: 10.1002/2014JC010504
       
  • Winter bloom and associated upwelling northwest of the Luzon Island: A
           coupled physical‐biological modeling approach
    • Authors: Wenfang Lu; Xiao‐Hai Yan, Yuwu Jiang
      Pages: n/a - n/a
      Abstract: For this paper, a coupled physical‐biological model was developed in order to study the mechanisms of the winter bloom in the Luzon Strait (referred as LZB). Based on a simulation for January, 2010, the results showed that the model was capable of reproducing the key features of the LZB, such as the location, inverted‐V shape, twin‐core structure and bloom intensity. The simulation showed that the LZB occurred during the relaxation period of intensified northeasterly winds, when the deepened mixed layer started to shoal. Nutrient diagnostics showed that vertical mixing was responsible for the nutrient supply to the upper ~40 m layer, while subsurface upwelling supplied nutrients to the region below the mixed layer. Hydrodynamic diagnostics showed that the advection of relative vorticity (RV) primarily contributed to the subsurface upwelling. The RV advection was resulted from an offshore jet, which was associated with a northeasterly wind, flowed across the ambient RV field. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-30T14:57:54.843486-05:
      DOI: 10.1002/2014JC010218
       
  • Mesoscale eddies case study at Xisha waters in the South China Sea in
           2009/2010
    • Authors: Qiang Wang; Lili Zeng, Weidong Zhou, Qiang Xie, Shuqun Cai, Dongxiao Wang
      Pages: n/a - n/a
      Abstract: Analyzing the observed currents at Xisha (110.3899oE, 17.1038oN) during May 2009 to May 2010, it is found that the kinetic energy has significant mesoscale variability, and each peak responds to large positive/negative ocean surface current curl caused by mesoscale eddies. Compared the kinetic energy with the wind stress work and the pressure work, it is also found that the barotropic pressure work which is mainly contributed by the sea surface height (SSH) corresponding to the mesoscale eddies behaves like the kinetic energy. The contribution of the mesoscale eddies to the kinetic energy can be up to 90 percent sometimes and reach deep level every time. Using the satellite altimeter data, the paths of mesoscale eddies contributing to the kinetic energy variability are traced back. In the winter half of the year, the mesoscale eddies propagating along the northern South China Sea shelf or across the basin from the west of the Philippines towards Xisha arrive at Xisha, influencing the kinetic energy. In the summer half of the year, the mesoscale eddies are mainly from the south, which were shed from the Vietnam coast current. And the cause for eddy shedding may be related to the relaxation of the Ekman transport anomalies. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-30T14:57:47.25167-05:0
      DOI: 10.1002/2014JC009814
       
  • Decadal variations in trace metal concentrations on a coral reef: Evidence
           from a 159 year record of Mn, Cu, and V in a Porites coral from the
           northern South China Sea
    • Authors: Xuefei Chen; Gangjian Wei, Wenfeng Deng, Ying Liu, Yali Sun, Ti Zeng, Luhua Xie
      Pages: n/a - n/a
      Abstract: Geochemical cycles of trace metals are important influences on the composition and function of the marine ecosystem. Although spatial distributions of most trace metals have now been determined in at least some parts of the oceans, temporal variations have barely been studied on account of data limitations. In this paper, we report on a 159‐year record of trace metal concentrations from a Porites coral from the northern South China Sea (SCS), and discuss how oceanic and climatic processes control variations in Mn, Cu, and V concentrations in this region. Our results show that trace metal concentrations in the coral skeleton demonstrate decadal to interdecadal fluctuations, and that their variations are controlled by different mechanisms. The input of Mn to reef water is partly controlled by the Pacific Decadal Oscillation (PDO), which controls precipitation and river runoff. Surface‐water concentrations of the nutrient‐like element Cu are controlled by summer upwelling to the east of Hainan Island. The concentrations of V show complex inter‐relationships, and are linked to riverine input prior to the 1990 and to upwelling after the 1990. Our results imply that in the northern SCS, ocean‐atmosphere climate fluctuations, such as the PDO and the East Asian Summer Monsoon (EASM), are important factors that influence long‐term variability of Mn, Cu, and V concentrations in seawater, by controlling precipitation‐related river runoff and the strength of upwelling systems. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-30T14:51:50.471107-05:
      DOI: 10.1002/2014JC010390
       
  • Natural variability of CO2 and O2 fluxes: What can we learn from
           centuries‐long climate models simulations?
    • Authors: L. Resplandy; R. Séférian, L. Bopp
      Pages: n/a - n/a
      Abstract: Ocean carbon uptake and oxygen content estimates over the past decades suggest that the anthropogenic carbon sink has changed and that the oxygen concentration in the ocean interior has decreased. Although these detected changes appear consistent with those expected from anthropogenic forced climate change, large uncertainties remain in the contribution of natural variability. Using century‐long simulations (500‐1000 years) of unforced natural variability from 6 Earth System Models (ESMs), we examine the internally‐driven natural variability of carbon and oxygen fluxes from interannual to multi‐decadal time scales. The intensity of natural variability differs between the ESMs, in particular decadal variability locally accounts for 10 to 50% of the total variance. Although the variability is higher in all regions with strong climate modes (North Atlantic, North Pacific, etc.), we find that only the Southern Ocean and the tropical Pacific significantly modulate the global fluxes. On (multi‐)decadal timescales, deep convective events along the Antarctic shelf drive the global fluxes variability by transporting deep carbon‐rich/oxygen‐depleted waters to the surface and by reducing the sea‐ice coverage. On interannual timescales, the global flux is modulated by 1) variations of the upwelling of circumpolar deep waters associated with the Southern Annular Mode in the subpolar Southern Ocean and 2) variations of the equatorial/costal upwelling combined with changes in the solubility‐driven fluxes in response to El Niño Southern Oscillation (ENSO) in the tropical Pacific. We discuss the challenges of measuring and detecting long‐term trends from a few decade‐long records influenced by internal variability. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-23T16:49:56.244385-05:
      DOI: 10.1002/2014JC010463
       
  • The role of turbulent mixing in the modified Shelf Water overflows that
           produce Cape Darnley Bottom Water
    • Authors: Daisuke Hirano; Yujiro Kitade, Kay I. Ohshima, Yasushi Fukamachi
      Pages: n/a - n/a
      Abstract: The mixing process associated with modified Shelf Water (mSW) overflows that eventually mix to form Cape Darnley Bottom Water (CDBW) was investigated by hydrographic and microstructure observations off the Cape Darnley Polynya (CDP), East Antarctica, in January 2009. Closely spaced microstructure observations revealed that mSW properties varied considerably within a distance of ~4 km across the shelf edge. Near the bottom, the rate of turbulent kinetic energy dissipation was enhanced to values greater than 10–7 W kg–1, and the vertical scale of the bottom boundary layer (BBL) was on the order of 10 m. The observed BBL around the shelf edge was characterized by strong vertical mixing with turbulent eddy diffusivities of ~О (10–3–10–2) m2 s–1. A geostrophically balanced density current, which resulted from the presence of mSW over the continental shelf, is considered the primary energy source for the turbulent mixing in the BBL. This turbulent mixing transforms the overflowing mSW through mixing with ambient water masses, specifically with the overlying modified Circumpolar Deep Water. The BBL is also thought to partly contribute to the gradual descent of mSW down the continental slope through bottom Ekman transport. We conclude that turbulent mixing, primarily caused by a density current, plays an important role in CDBW formation, by modifying the mSW overflowing from the CDP. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-23T16:47:17.225642-05:
      DOI: 10.1002/2014JC010059
       
  • Upscale and downscale energy transfer over the tropical Pacific revealed
           by scatterometer winds
    • Authors: Gregory P. King; Jur Vogelzang, Ad Stoffelen
      Pages: n/a - n/a
      Abstract: The direction of the energy cascade in the mesoscales of atmospheric turbulence is investigated using near‐surface winds over the tropical Pacific measured by satellite scatterometers SeaWinds (QuikSCAT) and ASCAT (MetOp‐A). The tropical Pacific was subdivided into nine regions, classified as rainy or dry. Longitudinal third‐order along‐track structure functions DLLLa and skewness SLa were calculated as a function of separation r for each region and month during the period November 2008 – October 2009. We find that the results support both downscale and upscale interpretations, depending on region and month. The results indicate that normally energy cascades downscale, but cascades upscale over the cold tongue in the cold season and over the west Pacific in summer months. An explanation is offered based on the heating or cooling of the air by the underlying sea surface temperature. It is also found that the signature of intermittent small‐scale (< 100 km) events could be identified in graphs of SLa, implying that this diagnostic may be useful in studies of tropical disturbances. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-23T16:47:09.819785-05:
      DOI: 10.1002/2014JC009993
       
  • Recent trends in the Southern Ocean eddy field
    • Authors: Andrew McC. Hogg; Michael P. Meredith, Don P. Chambers, E. Povl Abrahamsen, Chris W. Hughes, Adele K. Morrison
      Pages: n/a - n/a
      Abstract: Eddies in the Southern Ocean act to moderate the response of the Antarctic Circumpolar Current (ACC) to changes in forcing. An updated analysis of the Southern Ocean satellite altimetry record indicates an increase in eddy kinetic energy (EKE) in recent decades, contemporaneous with a probable decrease in ACC transport. The EKE trend is largest in the Pacific (14.9 ± 4.1 cm2 s‐2 per decade) and Indian (18.3 ± 5.1 cm2 s‐2 per decade) sectors of the Southern Ocean. We test the hypothesis that variations in wind stress can account for the observed EKE trends using perturbation experiments conducted with idealised high‐resolution ocean models. The decadal increase in EKE is most likely due to continuing increases in the wind stress over the Southern Ocean, albeit with considerable interannual variability superposed. ACC transport correlates well with wind stress on these interannual timescales, but is weakly affected by wind forcing at longer periods. The increasing intensity of the Southern Ocean eddy field has implications for overturning circulation, carbon cycling and climate. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-23T16:46:59.349512-05:
      DOI: 10.1002/2014JC010470
       
  • Quality assessment of spaceborne sea surface salinity observations over
           the northern North Atlantic
    • Authors: Julia Köhler; Meike Sena Martins, Nuno Serra, Detlef Stammer
      Pages: n/a - n/a
      Abstract: Space‐borne sea surface salinity (SSS) measurements provided by the European Space Agency's (ESA) “Soil Moisture and Ocean Salinity” (SMOS) and the National Aeronautical Space Agency's (NASA) “Aquarius/SAC‐D” missions, covering the period from May 2012 to April 2013, are compared against in situ salinity measurements obtained in the northern North Atlantic between 20° N and 80° N. In cold water, SMOS SSS fields show a temperature‐dependent negative SSS bias of up to ‐2 g/kg for temperatures < 5 °C. Removing this bias significantly reduces the differences to independent ship‐based thermosalinograph data but potentially corrects simultaneously also other effects not related to temperature, such as land contamination or Radio Frequency Interference (RFI). The resulting time‐mean bias, averaged over the study area, amounts to 0.1 g/kg. A respective correction applied previously by the Jet Propulsion Laboratory to the Aquarius data is shown here to have successfully removed an SST‐related bias in our study area. For both missions, resulting spatial structures of SSS variability agree very well with those available from an eddy‐resolving numerical simulation and from Argo data and, additionally they also show substantial salinity changes on monthly and seasonal time scales. Some fraction of the root‐mean‐square difference between in situ, and SMOS and Aquarius data (approximately 0.9 g/kg) can be attributed to short‐time scale ocean processes, notably at the Greenland shelf, and could represent associated sampling errors there. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-23T16:31:51.41331-05:0
      DOI: 10.1002/2014JC010067
       
  • Numerical analysis of stratification and destratification processes in a
           tidally energetic inlet with an ebb tidal delta
    • Authors: Kaveh Purkiani; Johannes Becherer, Götz Flöser, Ulf Gräwe, Volker Mohrholz, Henk M. Schuttelaars, Hans Burchard
      Pages: n/a - n/a
      Abstract: Stratification and de‐stratification processes in a tidally energetic, weakly stratified inlet in the Wadden Sea (south eastern North Sea) are investigated in this modeling study. Observations of current velocity and vertical density structure show strain‐induced periodic stratification for the southern shoal of the tidal channel. In contrast to this, in the nearby central region of the channel increased stratification is already observed directly after full flood. To investigate the processes leading to this different behavior, a nested model system using the GETM is set up and successfully validated against field data. The simulated density development along a cross‐section that includes both stations shows that cross‐channel stratification is strongly increasing during flood, such that available potential energy is released in the deeper part of the channel during flood. An analysis of the potential energy anomaly budget confirms that the early onset of vertical stratification during flood at the deeper station is mainly controlled by the stratifying cross‐channel straining of the density field. In contrast to this, in the shallow parts of the channel, the relatively weak cross‐channel straining is balanced by along‐channel straining and vertical mixing in the shallow part of the channel. An idealized analytical model confirms the following hypothesis: The laterally convergent flood current advecting laterally stratified water masses from the shallow and wide ebb tidal delta to the deep and narrow tidal channel has the tendency to substantially increase cross‐channel density gradients in the tidal channel. This process leads to stratification during flood. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-23T14:43:21.691185-05:
      DOI: 10.1002/2014JC010325
       
  • Evolution of summer Arctic sea ice albedo in CCSM4 simulations: Episodic
           summer snowfall and frozen summers
    • Authors: Bonnie Light; Suzanne Dickinson, Donald K. Perovich, Marika M. Holland
      Pages: n/a - n/a
      Abstract: The albedo of Arctic sea ice is calculated from summertime output of 20th century Community Climate System Model v.4 (CCSM4) simulations. This is compared with an empirical record based on generalized observations of the summer albedo progression along with melt onset dates determined from remote sensing. Only the contributions to albedo from ice, snow, and ponds are analyzed; fractional ice area is not considered in this assessment. Key factors dictating summer albedo evolution are the timing and extent of ponding and accumulation of snow. The CCSM4 summer sea ice albedo decline was found, on average, to be less pronounced than either the empirical record or the CLARA‐SAL satellite record. The modeled ice albedo does not go as low as the empirical record, nor does the low summer albedo last as long. In the model, certain summers were found to retain snow on sea ice, thus inhibiting ice surface melt and the formation or retention of melt ponds. These “frozen” summers were generally not the summers with the largest spring snow accumulation, but were instead summers that received at least trace snowfall in June or July. When these frozen summers are omitted from the comparison, the model and empirical records are in much better agreement. This suggests that the representation of summer Arctic snowfall events and/or their influence on the sea ice conditions are not well represented in CCSM4 integrations, providing a target for future model development work. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-23T14:34:25.214683-05:
      DOI: 10.1002/2014JC010149
       
  • Lagrangian measurements of incipient motion in oscillatory flows
    • Authors: Donya Frank; Diane Foster, In Mei Sou, Joseph Calantoni, Pai Chou
      Pages: n/a - n/a
      Abstract: Incipient motion of coarse gravel‐sized sediment was investigated under a range of oscillatory flows. This article examines the relative significance of shear stresses and pressure gradients in triggering motion, which was directly measured with electronic Smart Sediment Grains (SSGs). The data suggest that incipient motion was induced by the pressure gradients in flows with large accelerations; by the shear stresses in flows with low accelerations and greater shear; and by the combined effects in intermediate flows. A modified incipient motion criterion was evaluated accounting for the combined effects of the shear stresses and pressure gradients, which may be more widely applicable in the marine environment. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-23T14:33:59.727986-05:
      DOI: 10.1002/2014JC010183
       
  • Decadal variability of the Pacific Subtropical Cells and its relevance to
           the sea surface height in the western tropical Pacific during recent
           decades
    • Authors: G. Yamanaka; H. Tsujino, H. Nakano, M. Hirabara
      Pages: n/a - n/a
      Abstract: Decadal variability of the Pacific Subtropical Cells (STCs) and associated sea surface height (SSH) in the western tropical Pacific during recent decades are examined by using an historical OGCM simulation. The model represents decadal variations of the STCs concurrent with tropical Pacific thermal anomalies: the eastern tropical Pacific is warmer when the STCs are weaker and cooler when they are stronger. The spatial patterns of the SSH in the western tropical Pacific show different features, depending on events associated with decadal variability. During the warm phase (1977‐1987), the SSH anomalies exhibit deviations from a meridionally symmetric distribution, with weakly positive (strongly negative) anomalies in the western tropical North (South) Pacific. Analysis of the heat budget in the upper tropical Pacific indicates that the termination of the warm phase around 1985 results from a poleward heat transport anomaly that is induced by a horizontal gyre associated with the SSH anomalies. During the cold phase (1996‐2006), in contrast, the SSH anomalies are nearly meridionally symmetric, with positive anomalies in both hemispheres. Enhanced easterly wind anomalies contribute to the development of the cold phase after the late 1990s. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-23T14:27:30.553598-05:
      DOI: 10.1002/2014JC010190
       
  • Decoupling the influence of biological and physical processes on the
           dissolved oxygen in the Chesapeake Bay
    • Authors: Jiabi Du; Jian Shen
      Pages: n/a - n/a
      Abstract: It is instructive and essential to decouple the effects of biological and physical processes on the dissolved oxygen condition, in order to understand their contribution to the interannual variability of hypoxia in Chesapeake Bay since the 1980s. A conceptual bottom DO budget model is applied, using the vertical exchange timescale (VET) to quantify the physical condition and net oxygen consumption rate to quantify biological activities. By combining observed DO data and modeled VET values along the mainstem of Chesapeake Bay, the monthly net bottom DO consumption rate was estimated for 1985‐2012. The DO budget model results show that the interannual variations of physical conditions accounts for 88.8% of the interannual variations of observed DO. The high similarity between the VET spatial pattern and the observed DO suggests that physical processes play a key role in regulating the DO condition. Model results also show that long‐term VET has a slight increase in summer, but no statistically significant trend is found. Correlations among southerly wind strength, North Atlantic Oscillation index, and VET demonstrate that the physical condition in the Chesapeake Bay is highly controlled by the large‐scale climate variation. The relationship is most significant during the summer, when the southerly wind dominates throughout the Chesapeake Bay. The seasonal pattern of the averaged net bottom DO consumption rate (B'20) along the main channel coincides with that of the chlorophyll‐a concentration. A significant correlation between nutrient loading and B'20 suggests that the biological processes in April‐May are most sensitive to the nutrient loading. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-23T14:27:11.803127-05:
      DOI: 10.1002/2014JC010422
       
  • Temporal variations in air‐sea CO2 exchange near large kelp beds
           near San Diego, California
    • Authors: Hiroki Ikawa; Walter C. Oechel
      Pages: n/a - n/a
      Abstract: This study presents nearly continuous air‐sea CO2 flux for seven years using the eddy covariance method for nearshore water near San Diego, California, as well as identifying environmental processes that appear to control temporal variations in air‐sea CO2 flux at different time scales using time‐series decomposition. Monthly variations in CO2 uptake are shown to be positively influenced by photosynthetically active photon flux density (PPFD) and negatively related to wind speeds. In contrast to the monthly scale, wind speeds often influenced CO2 uptake positively on an hourly scale. Inter‐annual variations in CO2 flux were not correlated with any independent variables, but did reflect surface area of the adjacent kelp bed in the following year. Different environmental influences on CO2 flux at different temporal scales suggest the importance of long‐term flux monitoring for accurately identifying important environmental processes for the coastal carbon cycle. Overall, the study area was a strong CO2 sink into the sea (CO2 flux of ca. ‐260 g C m‐2 yr‐1). If all coastal areas inhabited by macrophytes had a similar CO2 uptake rate, the net CO2 uptake from these areas alone would roughly equal the net CO2 sink estimated for the entire global coastal ocean to date. A similar‐strength CO2 flux, ranging between ‐0.09 to ‐0.01 g C m‐2 hr‐1, was also observed over another kelp bed from a pilot study of boat‐based eddy covariance measurements. This article is protected by copyright. All rights reserved.
      PubDate: 2014-12-19T20:36:20.017672-05:
      DOI: 10.1002/2014JC010229
       
  • 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
       
  • 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
       
  • 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
       
  • 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
       
  • 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
       
  • 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
       
  • 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
       
  • 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
       
  • 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
       
  • 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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