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Geophysical Research Letters     Full-text available via subscription   (Followers: 128, SJR: 3.323, h-index: 185)
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Paleoceanography     Full-text available via subscription   (Followers: 5, SJR: 3.067, h-index: 100)
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Journal Cover Journal of Geophysical Research : Oceans
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  • Probability Distribution of Turbulent Kinetic Energy Dissipation Rate in
           Ocean: Observations and Approximations
    • Authors: I. Lozovatsky; H.J.S. Fernando, J. Planella-Morato, Z. Liu, J.-H. Lee, S.U.P. Jinadasa
      Abstract: The probability distribution of kinetic energy dissipation rate in stratified ocean usually deviates from the classic lognormal distribution that has been formulated for and often observed in unstratified homogeneous layers of atmospheric and oceanic turbulence. Our measurements of vertical profiles of small-scale shear, collected in the East China Sea, northern Bay of Bengal, to the south and east of Sri Lanka, and in the Gulf Stream region show that the probability distributions of the dissipation rate in the pycnoclines (r ∼ 1.4 m is the averaging scale) can be successfully modeled by the Burr (type XII) probability distribution. In weakly stratified boundary layers, lognormal distribution of is preferable, although the Burr is an acceptable alternative. The skewness Skɛ and the kurtosis Kɛ of the dissipation rate appear to be well correlated in a wide range of Skɛ and Kɛ variability.
      PubDate: 2017-09-17T14:53:45.487025-05:
      DOI: 10.1002/2017JC013076
  • Seismic Oceanography in the Tyrrhenian Sea – Thermohaline Staircases,
           Eddies and Internal Waves
    • Authors: G.G. Buffett; G. Krahmann, D. Klaeschen, K. Schroeder, V. Sallarès, C. Papenberg, C. Ranero, N. Zitellini
      Abstract: We use seismic oceanography to document and analyze oceanic thermohaline finestructure across the Tyrrhenian Sea. Multichannel seismic (MCS) reflection data were acquired during the MEDiterranean OCcidental survey in April-May 2010. We deployed along-track expendable bathythermograph probes simultaneous with MCS acquisition. At nearby locations we gathered conductivity-temperature-depth data. An autonomous glider survey added in-situ measurements of oceanic properties. The seismic reflectivity clearly delineates thermohaline finestructure in the upper 2,000 m of the water column, indicating the interfaces between Atlantic Water/Winter Intermediate Water, Levantine Intermediate Water, and Tyrrhenian Deep Water. We observe the Northern Tyrrhenian Anticyclone, a near-surface meso-scale eddy, plus laterally and vertically extensive thermohaline staircases. Using MCS we are able to fully image the anticyclone to a depth of 800 m and to confirm the horizontal continuity of the thermohaline staircases of more than 200 km. The staircases show the clearest step-like gradients in the center of the basin while they become more diffuse towards the periphery and bottom, where impedance gradients become too small to be detected by MCS. We quantify the internal wave field and find it to be weak in the region of the eddy and in the center of the staircases, while it is stronger near the coastlines. Our results indicate this is because of the influence of the boundary currents, which disrupt the formation of staircases by preventing diffusive convection. In the interior of the basin the staircases are clearer and the internal wave field weaker, suggesting that other mixing processes such as double-diffusion prevail.
      PubDate: 2017-09-17T14:53:41.85555-05:0
      DOI: 10.1002/2017JC012726
  • CO2-Induced Ocean Warming of the Antarctic Continental Shelf in an Eddying
           Global Climate Model
    • Authors: Paul B. Goddard; Carolina O. Dufour, Jianjun Yin, Stephen M. Griffies, Michael Winton
      Abstract: Ocean warming near the Antarctic ice shelves has critical implications for future ice sheet mass loss and global sea level rise. A global climate model with an eddying ocean is used to quantify the mechanisms contributing to ocean warming on the Antarctic continental shelf in an idealized 2xCO2 experiment. The results indicate that relatively large warm anomalies occur both in the upper 100 m and at depths above the shelf floor, which are controlled by different mechanisms. The near-surface ocean warming is primarily a response to enhanced onshore advective heat transport across the shelf break. The deep shelf warming is initiated by onshore intrusions of relatively warm Circumpolar Deep Water (CDW), in density classes that access the shelf, as well as the reduction of the vertical mixing of heat. CO2-induced shelf freshening influences both warming mechanisms. The shelf freshening slows vertical mixing by limiting gravitational instabilities and the upward diffusion of heat associated with CDW, resulting in the build-up of heat at depth. Meanwhile, freshening near the shelf break enhances the lateral density gradient of the Antarctic Slope Front (ASF) and disconnect isopycnals between the shelf and CDW, making cross-ASF heat exchange more difficult. However, at several locations along the ASF, the cross-ASF heat transport is less inhibited and heat can move onshore. Once onshore, lateral and vertical heat advection work to disperse the heat anomalies across the shelf region. Understanding the inhomogeneous Antarctic shelf warming will lead to better projections of future ice sheet mass loss.
      PubDate: 2017-09-17T14:50:46.827575-05:
      DOI: 10.1002/2017JC012849
  • Effects of the Relaxation of Upwelling-Favorable Winds on the Diurnal and
           Semidiurnal Water Temperature Fluctuations in the Santa Barbara Channel,
    • Authors: María F. Aristizábal; Melanie R. Fewings, Libe Washburn
      Abstract: In the Santa Barbara Channel, California, and around the Northern Channel Islands, water temperature fluctuations in the diurnal and semidiurnal frequency bands are intermittent, with amplitudes that vary on time scales of days to weeks. The cause of this intermittency is not well understood.We studied the effects of the barotropic tide, vertical stratification, propagation of coastal trapped waves, regional wind relaxations, and diurnal-band winds on the intermittency of the temperature fluctuations during 1992–2015. We used temperature data from 43 moorings in 10-200 m water depth and wind data from two buoys and one land station.Subtidal-frequency changes in vertical stratification explain 20–40% of the intermittency in diurnal and semidiurnal temperature fluctuations at time scales of days to weeks. Along the mainland north of Point Conception and at the Northern Channel Islands, the relaxation of upwelling-favorable winds substantially increases vertical stratification, accounting for up to 55% of the subtidal-frequency variability in stratification. As a result of the enhanced stratification, wind relaxations enhance the diurnal and semidiurnal temperature fluctuations at those sites, even though the diurnal-band wind forcing decreases during wind relaxation. A linear model where the background stratification is advected vertically explains a substantial fraction of the temperature fluctuations at most sites. The increase of vertical stratification and subsequent increase in diurnal and semidiurnal temperature fluctuations during wind relaxation is a mechanism that can supply nutrients to the euphotic zone and kelp forests in the Channel in summer when upwelling is weak.
      PubDate: 2017-09-17T14:50:38.779862-05:
      DOI: 10.1002/2017JC013199
  • Impact of the Mesoscale Dynamics on Ocean Deep Convection: The 2012-2013
           Case Study in the Northwestern Mediterranean Sea
    • Authors: Robin Waldman; Marine Herrmann, Samuel Somot, Thomas Arsouze, Rachid Benshila, Anthony Bosse, Jerome Chanut, Herve Giordani, Florence Sevault, Pierre Testor
      Abstract: Winter 2012-2013 was a particularly intense and well-observed Dense Water Formation (DWF) event in the Northwestern Mediterranean Sea. In this study, we investigate the impact of the mesoscale dynamics on DWF. We perform two perturbed initial state simulation ensembles from summer 2012 to 2013, respectively mesoscale-permitting and mesoscale-resolving, with the AGRIF refinement tool in the Mediterranean configuration NEMOMED12.The mean impact of the mesoscale on DWF occurs mainly through the high-resolution physics and not the high-resolution bathymetry. This impact is shown to be modest: the mesoscale doesn't modify the chronology of the deep convective winter nor the volume of dense waters formed. It however impacts the location of the mixed patch by reducing its extent to the west of the North Balearic Front and by increasing it along the Northern Current, in better agreement with observations. The maximum mixed patch volume is significantly reduced from 5.7 ± 0.2 to 4.2 ± 0.6 1013m3. Finally, the spring restratification volume is more realistic and enhanced from 1.4 ± 0.2 to 1.8 ± 0.2 1013m3 by the mesoscale.We also address the mesoscale impact on the ocean intrinsic variability by performing perturbed initial state ensemble simulations. The mesoscale enhances the intrinsic variability of the deep convection geography, with most of the mixed patch area impacted by intrinsic variability. The DWF volume has a low intrinsic variability but it is increased by 2-3 times with the mesoscale. We relate it to a dramatic increase of the Gulf of Lions eddy kinetic energy from 5.0 ± 0.6 to 17.3 ± 1.5cm2/s2, in remarkable agreement with observations.
      PubDate: 2017-09-17T14:50:31.520503-05:
      DOI: 10.1002/2016JC012587
  • Fingerprints of Sea-Level Rise on Changing Tides in the Chesapeake and
           Delaware Bays
    • Authors: Andrew C. Ross; Raymond G. Najjar, Ming Li, Serena Blyth Lee, Fan Zhang, Wei Liu
      Abstract: Secular tidal trends are present in many tide gauge records, but their causes are often unclear. This study examines trends in tides over the last century in the Chesapeake and Delaware Bays. Statistical models show negative M2 amplitude trends at the mouths of both bays, while some upstream locations have insignificant or positive trends. To determine whether sea-level rise is responsible for these trends, we include a term for mean sea level in the statistical models and compare the results with predictions from numerical and analytical models. The observed and predicted sensitivities of M2 amplitude and phase to mean sea level are similar, although the numerical model amplitude is less sensitive to sea level. The sensitivity occurs as a result of strengthening and shifting of the amphidromic system in the Chesapeake Bay and decreasing frictional effects and increasing convergence in the Delaware Bay. After accounting for the effect of sea level, significant negative background M2 and S2 amplitude trends are present; these trends may be related to other factors such as dredging, tide gauge errors, or river discharge. Projected changes in tidal amplitudes due to sea-level rise over the twenty-first century are substantial in some areas, but depend significantly on modeling assumptions.
      PubDate: 2017-09-17T14:50:26.116881-05:
      DOI: 10.1002/2017JC012887
  • Inconsistent subsurface and deeper ocean warming signals during recent
           global warming and hiatus
    • Authors: Hua Su; Xiangbai Wu, Wenfang Lu, Weiwei Zhang, Xiao-Hai Yan
      Abstract: Ocean heat content (OHC) evolutions calculated from the datasets (WOA, MyOcean, ORAS4, and SODA) was examined at different depth ranges in this study. According to the OHC changes, the subsurface and deeper ocean (SDO, 300-2000 m) heat content rapidly increased over the world's ocean basins during 1998-2013, indicating significant warming in the SDO during the recent global surface warming hiatus. Almost all the ocean basins warmed up, but with various contributions to the global SDO warming tied to the recent hiatus. The role of the Indian Ocean is particularly important as it has accounted for about 30% of global SDO heat uptake during the hiatus. The combined use of multiple datasets can reveal inconsistencies in SDO warming analysis results, and improve our understanding of the role of the SDO in the recent hiatus. The heat uptake in global SDO during the hiatus was about 2.37, 5.44, 3.75, and 2.44*1022 joules with trends of 0.40, 0.70, 0.77, and 0.48 W m−2 according to WOA, MyOcean, ORAS4, and SODA respectively, presenting obviously inconsistent SDO warming signals. MyOcean shows OHC overestimates in different ocean basins, while ORAS4 presents more reliable SDO OHC analysis. In general, the global SDO has sequestered a significant amount of heat – about 3.50*1022 joules with trends of 0.59 W m−2 on average among the four datasets – during the recent hiatus, demonstrating widespread and significant warming signals in the global SDO. There remain substantial uncertainties and discrepancies, however (especially in the PO and SO), in the available SDO warming information due to insufficient subsurface observation coverage and variations in the dataset generation techniques used among different researchers.
      PubDate: 2017-09-17T14:50:21.191054-05:
      DOI: 10.1002/2016JC012481
  • The 2004 Sumatra Tsunami in the Southeastern Pacific Ocean: New Global
           Insight From Observations and Modeling
    • Authors: A.B. Rabinovich; V.V. Titov, C.W. Moore, M.C. Eblé
      Abstract: The 2004 Sumatra tsunami was an unprecedented global disaster measured throughout the world oceans. The present study focused on a region of the southeastern Pacific Ocean where the ‘westward' circumferentially propagating tsunami branch converged with the ‘eastward' branch, based on data from fortuitously placed Chilean DART 32401 and tide gauges along the coast of South America. By comparison of the tsunami and background spectra, we suppressed the influence of topography and reconstructed coastal ‘spectral ratios' that were in close agreement with a ratio at DART 32401 and spectral ratios in other oceans. Findings indicate that even remote tsunami records carry spectral source signatures (‘birth-marks'). The 2004 tsunami waves were found to occupy the broad frequency band of 0.25-10 cph with the prominent ratio peak at period of 40 min related to the southern fast-slip source domain. This rupture “hot-spot” of ∼350-km was responsible for the global impact of the 2004 tsunami. Data from DART 32401 provided validation of model results: the simulated maximum tsunami wave height of 2.25 cm was a conservative approximation to the measured height of 2.05 cm; the computed tsunami travel time of 25h 35min to DART 32401, although 20 min earlier than the actual travel time, provided a favorable result in comparison with 24h 25min estimated from classical kinematic theory. The numerical simulations consistently reproduced the wave height changes observed along the coast of South America, including local amplification of tsunami waves at the northern stations of Arica (72 cm) and Callao (67 cm).
      PubDate: 2017-09-14T15:12:04.33762-05:0
      DOI: 10.1002/2017JC013078
  • Mapping of a Typhoon-Driven Coastal Upwelling by Assimilating Coastal
           Acoustic Tomography Data
    • Authors: Minmo Chen; Arata Kaneko, Ju Lin, Chuanzheng Zhang
      Abstract: A typhoon-driven upwelling event was observed with coastal acoustic tomography in Hiroshima Bay during September 2013. The tomography data were used to obtain state estimates from an ocean model, employing the ensemble Kalman filter (EnKF) for data assimilation. Hiroshima Bay was represented as a two-layer system with a fresh, near-surface layer overlaying a more saline, lower layer. Wind from the typhoon forced the surface layer southward, thus drawing the lower layer northward and causing upwelling. After the upwelling, these currents reversed for a period. During the upwelling, the total volume transports for the upper and lower layers were well balanced, showing continuity of the two layers. However, the total upper-layer volume transported northward during the reverse-flow period was significantly smaller than the total upper-layer volume transported southward during the upwelling, and significantly larger than the total lower-layer volume transported southward during the reverse-flow period. The downstream reductions of transported volume indicated mixing fractions of 24-30%, with water mixing at the interface of the upper and lower layers. Errors in state estimates were less than the changes in current and salinity associated with the upwelling.
      PubDate: 2017-09-14T15:11:54.653457-05:
      DOI: 10.1002/2017JC012812
  • Preparing for the Future Nankai Trough Tsunami: A Data Assimilation and
           Inversion Analysis From Various Observational Systems
    • Authors: I. E. Mulia; D. Inazu, T. Waseda, A. R. Gusman
      Abstract: The future Nankai Trough tsunami is one of the imminent threats to the Japanese coastal communities that could potentially cause a catastrophic event. As a part of the countermeasure efforts for such an occurrence, this study analyzes the efficacy of combining tsunami data assimilation (DA) and waveform inversion (WI). The DA is used to continuously refine a wave field model whereas the WI is used to estimate the tsunami source. We consider a future scenario of the Nankai Trough tsunami recorded at various observational systems, including ocean bottom pressure (OBP) gauges, global positioning system (GPS) buoys, and ship height positioning data. Since most of the OBP gauges are located inside the source region, the recorded tsunami signals exhibit significant offsets from surface measurements due to coseismic seafloor deformation effects. Such biased data are not applicable to the standard DA, but can be taken into account in the WI. On the other hand, the use of WI for the ship data may not be practical because a considerably large precomputed tsunami database is needed to cope with the spontaneous ship locations. The DA is more suitable for such an observational system as it can be executed sequentially in time and does not require precomputed scenarios. Therefore, the combined approach of DA and WI allows us to concurrently make use of all observational resources. Additionally, we introduce a bias correction scheme for the OBP data to improve the accuracy, and an adaptive thinning of observations to determine the efficient number of observations.
      PubDate: 2017-09-14T15:11:51.485222-05:
      DOI: 10.1002/2017JC012695
  • Diurnal Critical Latitude and the Latitude Dependence of Internal Tides,
           Internal Waves and Mixing Based on Barcoo Seamount
    • Authors: Robin Robertson; Jihai Dong, Paul Hartlipp
      Abstract: Vertical mixing is a key issue in ocean circulation modeling today. Mixing, particularly tidal mixing, is poorly represented in ocean and climate models, which generally ignore critical latitude effects. Critical latitude is the latitude where the inertial frequency equals the tidal frequency and differs for each tidal constituent. Critical latitudes strongly influence generation and propagation of internal tides. Using a model, latitude effects on tidal interactions with a seamount were examined by varying the latitude from 20°-38°, through the range of the diurnal critical latitudes. The diurnal critical latitudes were found to strongly influence propagation of the diurnal internal tides, the magnitude of the semidiurnal tides, the energy in the harmonic and higher frequencies, the barotropic mean flow, and the diffusivities. The strongest effects occurred between the K1 and O1 critical latitudes. Here, the semidiurnal tides, harmonics and high frequencies were enhanced, barotropic mean velocities weakened, energy at the harmonics and higher frequencies increased, and diffusivities increased. Spectral techniques indicate that most of these impacts are the result of non-linear wave-wave interactions and resonant phenomena with the prominent mechanism harmonic transfers. There was no evidence of parametric subharmonic instabilities. The semidiurnal tides indicated a resonant response at 20oS, which is near the latitude for the combined M2 and K1 tidal period, ∼19oS.
      PubDate: 2017-09-14T15:11:46.920357-05:
      DOI: 10.1002/2016JC012591
  • Erosion and Accretion on a Mudflat: The Importance of Very Shallow-Water
    • Authors: Benwei Shi; James R. Cooper, Paula D. Pratolongo, Shu Gao, T. J. Bouma, Gaocong Li, Chunyan Li, S.L. Yang, YaPing Wang
      Abstract: Understanding erosion and accretion dynamics during an entire tidal cycle is important for assessing their impacts on the habitats of biological communities and the long-term morphological evolution of intertidal mudflats. However, previous studies often omitted erosion and accretion during very shallow-water stages (VSWS, water depths 0.2 m (i.e., probe submerged) are considered. These findings suggest that the magnitude of bed-level changes during VSWS should not be neglected when modeling morphodynamic processes. Our results are useful in understanding the mechanisms of micro-topography formation and destruction that often occur at VSWS, and also improve our understanding and modeling ability of coastal morphological changes.
      PubDate: 2017-09-14T15:11:14.379536-05:
      DOI: 10.1002/2016JC012316
  • Unexpected Covariant Behavior of the Aegean and Ionian Seas in the Period
           1987-2008 by Means of a Nondimensional Sea Surface Height Index
    • Authors: M. Reale; S. Salon, A. Crise, R. Farneti, R. Mosetti, G. Sannino
      Abstract: In this work we use a set of recent multi-year simulations to develop a simplified sea surface height index (SSH). The index characterizes the dynamics of Ionian upper layer circulation and its links with sea surface height and salinity in the Southern Adriatic and Aegean Seas during the period 1987-2008. The analysis highlights a covariant behavior between Ionian Sea and Aegean Sea associated with a mutual zonal exchange of water masses with different salinity characteristics. Our analysis confirms that the variability observed in the period 1987-2008 in the upper layer circulation of the Ionian was driven by the salinity variability in the Southern Adriatic and Aegean Sea. This study supports and reinforces the hypothesis that two observed BiOS-like reversals reflect the existence of multiple equilibrium states in the Mediterranean Thermohaline circulation in the Eastern Mediterranean and that a complete characterization of observed variability needs to take into account a fully coupled Adriatic-Ionian-Aegean System.
      PubDate: 2017-09-14T15:10:54.236009-05:
      DOI: 10.1002/2017JC012983
  • Size Distribution and Dispersion of Droplets Generated by Impingement of
           Breaking Waves on Oil Slicks
    • Authors: C. Li; J. Miller, J. Wang, S. S. Koley, J. Katz
      Abstract: This laboratory experimental study investigates the temporal evolution of the size distribution of subsurface oil droplets generated as breaking waves entrain oil slicks. The measurements are performed for varying wave energy, as well as large variations in oil viscosity and oil-water interfacial tension, the latter achieved by premixing the oil with dispersant. In situ measurements using digital inline holography at two magnifications is applied for measuring the droplet sizes, and Particle Image Velocimetry (PIV) for determining the temporal evolution of turbulence after wave breaking. All early (2-10s) size distributions have two distinct size ranges with different slopes. For low dispersant to oil ratios (DOR), the transition between them could be predicted based on a turbulent Weber (We) number in the 2-4 range, suggesting that turbulence plays an important role. For smaller droplets, all the number size distributions have power of about -2.1, and for larger droplets, the power decreases well below -3. The measured steepening of the size distribution over time is predicted by a simple model involving buoyant rise and turbulence dispersion. Conversely, for DOR 1:100 and 1:25 oils, the diameter of slope transition decreases from ∼1mm to 46µm and 14µm respectively, much faster than the We-based prediction, and the size distribution steepens with increasing DOR. Furthermore, the concentration of micron-sized droplets of DOR 1:25 oil increase for the first ten minutes after entrainment. These phenomena are presumably caused by the observed formation and breakup oil micro-threads associated with tip streaming.
      PubDate: 2017-09-14T15:10:48.849115-05:
      DOI: 10.1002/2017JC013193
  • Air-Sea CO2 Exchange in the Ross Sea, Antarctica
    • Authors: Hans B. DeJong; Robert B. Dunbar
      Abstract: Although the Ross Sea is one of the most productive regions in Antarctica, it is not clear to what extent this region is an atmospheric CO2 sink. We calculate instantaneous CO2 flux rates with in situ pCO2 and wind speed data from 20 cruises in the Ross Sea. In addition, we estimate annual CO2 fluxes into the Ross Sea with nutrient budgets from a late summer cruise. We find that the Ross Sea is a lesser atmospheric CO2 sink (-7.5±0.5 Tg C yr−1, -1.3±0.1 mol C m−2 yr−1) than previously reported (-13 Tg C yr−1, -1.7 to -4.2 mol C m−2 yr−1). One exception is Terra Nova Bay (TNB) in the western Ross Sea, with CO2 flux rates (-4.8±0.3 mol C m−2, January-March) that are 3-4 times greater than the Ross Sea mean. The majority of the CO2 flux into TNB occurs during the late summer with instantaneous CO2 flux rates up to -246 mmol C m−2 d−1. These extraordinary CO2 flux rates are caused by the unique coupling of strong katabatic winds and low surface pCO2 values. Although strong katabatic winds deepen the mixed layer and entrain CO2 rich water from below, late season net community productivity maintains low surface water pCO2 levels. While TNB only covers ∼1% (3600 km2) of the Ross Sea continental shelf, extraordinary air-to-sea CO2 fluxes during the late summer may be regular features in many of the major sea ice production polynyas (148,000 km2 combined), including Antarctic Bottom Water formation regions.
      PubDate: 2017-09-14T15:10:40.305185-05:
      DOI: 10.1002/2017JC012853
  • The Dynamics of Cuba Anticyclones (CubANs) and Interaction With the Loop
           Current/Florida Current System
    • Authors: Vassiliki Kourafalou; Yannis Androulidakis, Matthieu Le Hénaff, HeeSook Kang
      Abstract: Mesoscale anticyclonic eddies along the northern Cuban coast (CubANs) have been identified in the Straits of Florida, associated with the northward shift of the Florida Current (FC) and the anticyclonic curvature of the Loop Current (LC) at the western entrance of the Straits. The dynamics of CubAN eddies and their interaction with the LC/FC system are described for the first time using satellite, drifter and buoy data and a high resolution model. It is shown that the evolution of CubANs to the south of the FC front complements the evolution of cyclonic eddies to the north of the FC, advancing previous studies on synergy between FC meandering and eddy activity. Two types of CubAN eddies are characterized: a) a main anticyclonic cell (type “A”) within the core of the LC during retracted phase conditions, associated with the process of LC Eddy (LCE) shedding from an extended LC, and b) an individual, distinct anticyclonic eddy that is released from the main LC core and is advected eastward, along the northern Cuban coast (type “B”). There are also mixed cases, when the process of LCE shedding has started, so a type “A” CubAN is being formed, in the presence of one or more eastward progressing type “B” eddies. CubAN evolution is associated with an increased mixed layer and weaker stratification of the upper ocean along the eddy's track. The cyclonic activity along the Cuban coast and wind-induced upwelling events also contribute to the evolution and fate of the CubAN eddies.
      PubDate: 2017-09-14T15:10:34.540315-05:
      DOI: 10.1002/2017JC012928
  • Internal Solitary Wave Reflection Near Dongsha Atoll, the South China Sea
    • Authors: Xiaolin Bai; Xiaofeng Li, Kevin G. Lamb, Jianyu Hu
      Abstract: Internal solitary wave (ISW) reflection is rarely observed in satellite images, even in the South China Sea (SCS), where the strongest and most energetic ISWs in the world have been observed. Compared to the large number of satellite images showing shoaling ISW in the SCS, fewer than ten satellite images have been reported showing ISW reflection. In this study, we collect recent satellite images and implement a numerical model to analyze ISW reflection near Dongsha Atoll, in the SCS. Satellite observations show that the reflection appears to be associated with the large-amplitude ISWs generated by strong tidal currents in Luzon Strait. Numerical simulations show that ISWs break when reaching the sloping bottom. Part of ISW energy is reflected by mode-1 waves and their trailing mode-2 waves. The mode-1 waves have two types: long inertial-gravity waves and breaking ISW-induced short waves. They propagate quickly but induce weak vertical velocity and surface imprints. Mode-2 waves induce strong vertical velocity, showing visible signature in satellites. Horizontal distribution of the energy indicates that a maximum energy of about 2% of the incident energy is contained in a single reflected wave. This could explain why the reflected waves are rarely observed, because reflected waves must be sufficiently large to be detected in satellite images. Although individual wave's energy is small, in total up to 20% of the incident wave is reflected by the groups of mode-1 and mode-2 waves. This suggests that ISW reflection has a significant impact on energy distribution over the continental slopes.
      PubDate: 2017-09-14T15:10:31.695111-05:
      DOI: 10.1002/2017JC012880
  • Spatio-temporal variations of mesoscale eddies in the Sulu Sea
    • Authors: Yinghui He; Ming Feng, Jieshuo Xie, Junliang Liu, Zhiwu Chen, Jiexin Xu, Wendong Fang, Shuqun Cai
      Abstract: Mesoscale eddies have been observed in the Sulu Sea, but their characteristics have not been well described. This study investigates the eddy population in the Sulu Sea using 22 years of satellite altimeter data with high spatiotemporal resolution. On average, there are approximately 1.6 eddies observed in the Sulu Sea each day and 1.8 eddy tracks generated each month. Two of the main eddy genesis regions are west of Negros Island and the Zamboanga Peninsula. The mean radius, lifespan and propagation speed of the eddies are 76.6 km, 32 days and 4.5 cm/s, respectively. The eddy radius and amplitude are generally large in the central Sulu Sea but small on its margin. The mean eddy kinetic energy and vorticity generally monotonically decrease from south to north, consistent with the distributions of background current kinetic energy. Over the seasonal cycle, there are more cyclonic eddies during boreal winter, and they tend to have a larger amplitude and radius than the other 3 seasons, while there are more anti-cyclonic eddies during boreal summer, and they tend to have a larger amplitude and radius than the other 3 seasons. The instability of the mean current and the island gap wind jets are the two key eddy genesis mechanisms in the Sulu Sea.
      PubDate: 2017-09-11T12:16:04.498208-05:
      DOI: 10.1002/2017JC013153
  • Estimation of melt pond fractions on first year sea ice using compact
           polarization SAR
    • Authors: Haiyan Li; Will Perrie, Qun Li, Yijun Hou
      Abstract: Melt ponds are a common feature on Arctic sea ice. They are linked to the sea ice surface albedo and transmittance of energy to the ocean from the atmosphere and thus constitute an important process to parameterize in Arctic climate models and simulations. This paper presents a first attempt to retrieve the melt pond fraction from hybrid-polarized compact polarization (CP) SAR imagery, which has wider swath and shorter revisit time than the quad-polarization systems, e.g. from RADARSAT-2 (RS-2). The co-polarization (co-pol) ratio has been verified to provide estimates of melt pond fractions. However, it is a challenge to link CP parameters and the co-pol ratio. The theoretical possibility is presented, for making this linkage with the CP parameter C22/C11 (the ratio between the elements of the coherence matrix of CP SAR) for melt pond detection and monitoring with the tilted-Bragg scattering model for the ocean surface. The empirical transformed formulation, denoted as the ‘compact polarization and quad-pol' (‘CPQP') model, is proposed, based on 2062 RS-2 quad-pol SAR images, collocated with in situ measurements. We compared the retrieved melt pond fraction with CP parameters simulated from quad-pol SAR data with results retrieved from the co-pol ratio from quad-pol SAR observations acquired during the Arctic-Ice (Arctic-Ice Covered Ecosystem in a Rapidly Changing Environment) field project. The results are shown to be comparable for observed melt pond measurements in spatial and temporal distributions. Thus, the utility of CP mode SAR for melt pond fraction estimation on first year level ice is presented.
      PubDate: 2017-09-11T12:15:27.626346-05:
      DOI: 10.1002/2017JC013248
  • Acidification mediated by a river plume and coastal upwelling on a
           fringing reef at the east coast of Hainan Island, Northern South China Sea
    • Authors: Xu Dong; Haining Huang, Nan Zheng, Aijun Pan, Sumin Wang, Cheng Huo, Kaiwen Zhou, Hui Lin, Weidong Ji
      Abstract: We investigated the dynamics of carbonate system which was greatly modulated by a river plume and coastal upwelling in July 2014 and July 2015 at the east coast of Hainan Island where a fringing reef distributes inshore. By using a three end-member mixing model, we semi-quantitatively estimated the removal of dissolved inorganic carbon (DIC) mediated by biological production in the river plume and upwelled water to be 13±17 μmol kg−1 and 15±16 μmol kg−1, respectively. The enhanced organic production was mainly responsible for these DIC consumptions in both two regimes, however, nearly a half of DIC removal was attributed to biocalcification in the plume system while it was negligible in the upwelling system. Furthermore, the modeled results over reefs revealed that river plume and coastal upwelling were two major threats of acidification to coral communities at the east coast of Hainan Island during cruises. In comparison, the biological contribution to acidification was limited for balancing between organic production and biocalcification during July 2014 cruise whereas the acidification was greatly intensified by organic degradation during July 2015 cruise. It was verified that naturally local acidification (physical and biological processes) played a major role in great pH decreases on a short-term scale, leading to coastal waters more vulnerable to anthropogenic “ocean acidification” (uptake of atmospheric CO2) by reducing buffering capacity of waters. Finally, effects of acidification associated with other local threats on a fringing reef was further depicted with a conceptual model.
      PubDate: 2017-09-08T14:15:40.477212-05:
      DOI: 10.1002/2017JC013228
  • On the dynamics of the Sri Lanka Dome in the Bay of Bengal
    • Authors: Jessica M. Burns; Bulusu Subrahmanyam, V. S. N. Murty
      Abstract: East of Sri Lanka, in the Northern Indian Ocean, a cold dome, known as the Sri Lanka Dome (SLD), develops during southwest monsoon season (June-September). The SLD first forms around May, matures in July and decays around September, in association with the strong cyclonic wind stress curl. In this study, the structure and dynamics of SLD in response to the climatic events such as the Indian Ocean Dipole (IOD) are examined. Our results reveal that these climatic events modulated the subsurface temperature variability in the thermocline at ∼100 m depth, whose signature was also evident in the satellite derived Sea Surface Height (SSH) anomaly in the SLD region. We find that the mechanisms for the formation of SLD are consistent with previous research, and there is year-to-year variability in the SLD dynamics. This study also reveals that the atmospheric parameters including vertical wind shear and mid-tropospheric relative humidity are high over the SLD region and adjacent southern Bay of Bengal and show an upward (increasing) trend over the decades. This has impacted the atmospheric parameters over the northern Bay of Bengal over the decades and as a consequence the total number of monsoon depressions (June-September) decreased over the decades from 1980 to 2015, as reported by the India Meteorological Department, New Delhi. Thus the new insight emerged from this study is the variability in the cyclogenesis and the occurrence of total number of monsoon depressions over northern Bay of Bengal over the decades are much related to the SLD dynamics.
      PubDate: 2017-09-08T14:00:26.159195-05:
      DOI: 10.1002/2017JC012986
  • Climatology and Decadal Variations in Multicore Structure of the North
           Pacific Subtropical Mode Water
    • Authors: Cong Liu; Shang-Ping Xie, Peiliang Li, Lixiao Xu, Wendian Gao
      Abstract: The pycnostad of the North Pacific subtropical mode water (STMW) often displays multiple vertical minima in the potential vorticity profile. Argo profile data from 2004 to 2015 are used to investigate inter-annual to decadal variations of the multicore structure. Climatologically, about 24% pycostads of STMW have multicore structure, and most of them distribute in the region west of 150°E. STMW cores are classified into three sub-modes—the cold, middle and warm ones with potential temperatures of 16.0°∼17 °C, 17°∼18 °C and 18°∼19.5 °C, respectively. The Kuroshio Extension (KE) varies between stable and unstable states. The unstable KE with large meanders increases the subsurface stratification and shoals the winter mixed layer east of 150°E with warmer temperatures. There, the dominant STMW type varies from the cold single type in stable KE years (making up 72% of the profiles with STMW) to the middle single one (53%) in unstable years. The variation of the dominant STMW type in the region east of 150°E subsequently affects the multicore structure of STMW west of 150°E. In a broad region between 130°E and 180°E, profiles with STMW are fewer in unstable years but the proportion of multicore profiles increases among STMW profiles. This might be due to the split recirculation gyre with a chaotic KE.
      PubDate: 2017-09-08T13:51:13.646264-05:
      DOI: 10.1002/2017JC013071
  • Satellite observed salinity distributions at high latitudes in the
           Northern Hemisphere: A Comparison of four products
    • Authors: Cynthia Garcia-Eidell; Josefino C. Comiso, Emmanuel Dinnat, Ludovic Brucker
      Abstract: Global surface ocean salinity measurements have been available since the launch of SMOS in 2009 and coverage was further enhanced with the launch of Aquarius in 2011. In the polar regions where spatial and temporal changes in sea surface salinity (SSS) are deemed important, the data has not been as robustly validated because of the paucity of in situ measurements. This study presents a comparison of four SSS products in the ice-free Arctic region, three using Aquarius data and one using SMOS data. The accuracy of each product is assessed through comparative analysis with ship and other in situ measurements. Results indicate RMS errors ranging between 0.33 and 0.89 psu. Overall, the four products show generally good consistency in spatial distribution with the Atlantic side being more saline than the Pacific side. A good agreement between the ship and satellite measurements were also observed in the low salinity regions in the Arctic Ocean, where SSS in situ measurements are usually sparse, at the end of summer melt seasons. Some discrepancies including biases of about 1 psu between the products in spatial and temporal distribution are observed. These are due in part to differences in retrieval techniques, geophysical filtering, and sea ice and land masks. The monthly SSS retrievals in the Arctic from 2011 to 2015 showed variations (within ∼1 psu) consistent with effects of sea ice seasonal cycles. This study indicates that spaceborne observations capture the seasonality and interannual variability of SSS in the Arctic with reasonably good accuracy.
      PubDate: 2017-09-08T13:10:46.811984-05:
      DOI: 10.1002/2017JC013184
  • Effects of topography and Earth's rotation on the oblique interaction of
           internal solitary-like waves in the Andaman Sea
    • Authors: Kenji Shimizu; Keisuke Nakayama
      Abstract: High-resolution three-dimensional MITgcm simulations and an extended Miles theory are used to investigate the oblique interaction of internal solitary-like waves (ISWs) in the Andaman Sea. Oblique solitary-wave interaction is well-studied in various fields of physics; however, this process in the ocean has seldom been investigated, despite the observations of its surface signature by remote sensing and potential 4-fold increase of ISW amplitude by the development of a (Mach) stem. This study confirms the development of stem-like ISWs under realistic oceanic conditions. The modeled interaction is found to be approximately consistent with the Miles theory extended to unequal incident-wave amplitudes and small-but-finite incident angles. Although topography does not appear to affect the process in the deep part of the Andaman Sea, substantial topographic amplitude variation along the wave trough needs to be adjusted before comparisons with the theory. Earth's rotation has a small effect on ISW propagation due to the low latitude (≈9°N), but it does slow down the growth of stem-like ISWs. Potential observation of the process by the next-generation wide-swath satellite altimeter is discussed.
      PubDate: 2017-08-30T12:30:41.252892-05:
      DOI: 10.1002/2017JC012888
  • Spectral decomposition of internal gravity wave sea surface height in
           global models
    • Authors: Anna C. Savage; Brian K. Arbic, Matthew H. Alford, Joseph K. Ansong, J.Thomas Farrar, Dimitris Menemenlis, Amanda K. O'Rourke, James G. Richman, Jay F. Shriver, Gunnar Voet, Alan J. Wallcraft, Luis Zamudio
      Abstract: Two global ocean models ranging in horizontal resolution from 1/12° to 1/48° are used to study the space- and time-scales of sea surface height (SSH) signals associated with internal gravity waves (IGWs). Frequency-horizontal wavenumber SSH spectral densities are computed over seven regions of the world ocean from three simulations of the HYbrid Coordinate Ocean Model (HYCOM) and two simulations of the Massachusetts Institute of Technology general circulation model (MITgcm). High-wavenumber, high-frequency SSH variance follows the predicted IGW linear dispersion curves. The realism of high-frequency motions (>0.87cpd) in the models is tested through comparison of the frequency spectral density of dynamic height variance computed from the highest resolution runs of each model (1/25° HYCOM and 1/48° MITgcm) with dynamic height variance frequency spectral density computed from 9 in-situ profiling instruments. These high-frequency motions are of particular interest because of their contributions to the small-scale SSH variability that will be observed on a global scale in the upcoming Surface Water and Ocean Topography (SWOT) satellite altimetry mission. The variance at supertidal frequencies can be comparable to the tidal and low-frequency variance for high-wavenumbers (length scales smaller than ∼50km), especially in the higher resolution simulations. In the highest resolution simulations, the high-frequency variance can be greater than the low-frequency variance at these scales.
      PubDate: 2017-08-30T12:30:37.79542-05:0
      DOI: 10.1002/2017JC013009
  • Modeling Arctic sea-ice algae: Physical drivers of spatial distribution
           and algae phenology
    • Authors: Giulia Castellani; Martin Losch, Benjamin A. Lange, Hauke Flores
      Abstract: Algae growing in sea ice represent a source of carbon for sympagic and pelagic ecosystems, and contribute to the biological carbon pump. The biophysical habitat of sea ice on large scales and the physical drivers of algae phenology are key to understanding Arctic ecosystem dynamics and for predicting its response to ongoing Arctic climate change. In addition, quantifying potential feedback mechanisms between algae and physical processes is particularly important during a time of great change. These mechanisms include a shading effect due to the presence of algae, and increased basal ice melt. The present study shows pan-Arctic results obtained from a new Sea Ice Model for Bottom Algae (SIMBA) coupled with a 3D sea-ice–ocean model. The model is evaluated with data collected during a ship-based campaign to the Eastern Central Arctic in summer 2012. The algal bloom is triggered by light, and shows a latitudinal dependency. Snow and ice also play a key role in ice algal growth. Simulations show that after the spring bloom, algae are nutrient-limited before the end of summer and finally they leave the ice habitat during ice melt. The spatial distribution of ice algae at the end of summer agrees with available observations, and it emphasizes the importance of thicker sea-ice regions for hosting biomass. Particular attention is given to the distinction between level ice and ridged ice. Ridge-associated algae are strongly light-limited, but they can thrive towards the end of summer, and represent an additional carbon source during the transition into polar night.
      PubDate: 2017-08-30T12:30:32.289063-05:
      DOI: 10.1002/2017JC012828
  • Moored observations of the Deep Western Boundary Current in the NW
           Atlantic: 2004-2014
    • Authors: John M. Toole; Magdalena Andres, Isabela A. Le Bras, Terrence M. Joyce, Michael S. McCartney
      Abstract: A moored array spanning the continental slope southeast of Cape Cod sampled the equatorward-flowing Deep Western Boundary Current (DWBC) for a 10-year period: May 2004 - May 2014. Daily profiles of subinertial velocity, temperature, salinity and neutral density are constructed for each mooring site and cross-line DWBC transport time series are derived for specified water mass layers. Time-averaged transports based on daily estimates of the flow and density fields in stream coordinates are contrasted with those derived from the Eulerian-mean flow field, modes of DWBC transport variability are investigated through compositing, and comparisons are made to transport estimates for other latitudes. Integrating the daily velocity estimates over the neutral density range of 27.8 - 28.125 kg/m3 (encompassing Labrador Sea and Overflow Water layers), a mean equatorward DWBC transport of 22.8 x 106 m3/s ± 1.9 x 106 m3/s is obtained. Notably, a statistically-significant trend of decreasing equatorward transport is observed in several of the DWBC components as well as the current as a whole. The largest linear change (a 4% decrease per year) is seen in the layer of Labrador Sea Water that was renewed by deep convection in the early 1990s whose transport fell from 9.0 x 106 m3/s at the beginning of the field program to 5.8 x 106 m3/s at its end. The corresponding linear fit to the combined Labrador Sea and Overflow Water DWBC transport decreases from 26.4 x 106 m3/s to 19.1 x 106 m3/s. In contrast, no long-term trend is observed in upper-ocean Slope Water transport. These trends are discussed in the context of decadal observations of the North Atlantic circulation, and subpolar air-sea interaction/water mass transformation.
      PubDate: 2017-08-30T12:30:25.776048-05:
      DOI: 10.1002/2017JC012984
  • On the secular changes in the tidal constituents in San Francisco Bay
    • Authors: Isaac Rodríguez-Padilla; Modesto Ortiz
      Abstract: Secular changes up to 7% in amplitude, as well as phase advances of 13 minutes of time per century in the diurnal and semidiurnal tidal constituents have been found in previous investigations on the sea level record of San Francisco Bay, California. A numerical hydrodynamic model for barotropic tide is used to explore local causes that may contribute to the secular changes found in the tidal constituents. The results indicate that the morphological evolution of the seabed in the region of the ebb-tidal delta a major factor that contribute to explain the secular changes observed in the tidal constituents in San Francisco Bay, besides of minor contributions from river flow changes and sea-level rise.
      PubDate: 2017-08-30T12:30:23.164262-05:
      DOI: 10.1002/2016JC011770
  • Eddy heat flux across the Antarctic Circumpolar Current estimated from sea
           surface height standard deviation
    • Authors: Annie Foppert; Kathleen A. Donohue, D. Randolph Watts, Karen L. Tracey
      Abstract: Eddy heat flux (EHF) is a predominant mechanism for heat transport across the zonally unbounded mean flow of the Antarctic Circumpolar Current (ACC). Observations of dynamically relevant, divergent, 4 year mean EHF in Drake Passage from the cDrake project, as well as previous studies of atmospheric and oceanic storm tracks, motivates the use of sea surface height (SSH) standard deviation, H*, as a proxy for depth-integrated, downgradient, time-mean EHF ([EHF¯]) in the ACC. Statistics from the Southern Ocean State Estimate corroborate this choice and validate throughout the ACC the spatial agreement between H* and [EHF¯] seen locally in Drake Passage. Eight regions of elevated [EHF¯] are identified from nearly 23.5 years of satellite altimetry data. Elevated cross-front exchange usually does not span the full latitudinal width of the ACC in each region, implying a hand-off of heat between ACC fronts and frontal zones as they encounter the different [EHF¯] hot spots along their circumpolar path. Integrated along circumpolar streamlines, defined by mean SSH contours, there is a convergence of ∮[EHF¯] in the ACC: 1.06 PW enters from the north and 0.02 PW exits to the south. Temporal trends in low-frequency [EHF] are calculated in a running-mean sense using H* from overlapping 4 year subsets of SSH. Significant increases in downgradient [EHF] magnitude have occurred since 1993 at Kerguelen Plateau, Southeast Indian Ridge, and the Brazil-Malvinas Confluence, whereas the other five [EHF¯] hot spots have insignificant trends of varying sign.
      PubDate: 2017-08-30T06:40:59.828025-05:
      DOI: 10.1002/2017JC012837
  • Slow acidification of the winter mixed layer in the subarctic western
           North Pacific
    • Authors: Masahide Wakita; Akira Nagano, Tetsuichi Fujiki, Shuichi Watanabe
      Abstract: We used carbon dioxide (CO2) system data collected during 1999–2015 to investigate ocean acidification at time series sites in the western subarctic region of the North Pacific Ocean. The annual mean pH at station K2 decreased at a rate of 0.0025 ± 0.0010 year−1 mostly in response to oceanic uptake of anthropogenic CO2. The Revelle factor increased rapidly (0.046 ± 0.022 year−1), an indication that the buffering capacity of this region of the ocean has declined faster than at other time series sites. In the western subarctic region, the pH during the winter decline at a slower rate of 0.0008 ± 0.0004 year−1. This was attributed to a reduced rate of increase of dissolved inorganic carbon (DIC) and an increase of total alkalinity (TA). The reduction of DIC increase was caused by the decline of surface water density associated with the pycnocline depression and the reduction of vertical diffusion flux from the upper pycnocline. These physical changes were probably caused by northward shrinkage of the western subarctic gyre and global warming. Meanwhile, the contribution of the density decline to the TA increase is canceled out by that of the reduced vertical diffusive flux. We speculated that the winter TA increase is caused mainly by the accumulation of TA due to the weakened calcification by organisms during the winter.
      PubDate: 2017-08-30T06:35:30.986382-05:
      DOI: 10.1002/2017JC013002
  • Coral record of variability in the upstream Kuroshio Current during
    • Authors: Xiaohua Li; Yi Liu, Yi-Chia Hsin, Weiguo Liu, Zhengguo Shi, Hong-Wei Chiang, Chuan-Chou Shen
      Abstract: The Kuroshio Current (KC), one of the most important western boundary currents in the North Pacific Ocean, strongly affects regional hydroclimate in East Asia and upper ocean thermal structure. Limited by few on-site observations, the responses of the KC to regional and remote climate forcings are still poorly understood. Here we use monthly coral δ18O data to reconstruct a KC transport record with annual to interannual resolution for the interval 1953–2004. The field site is located in southern Taiwan on the western flank of the upstream KC. Increased (reduced) KC transport would generate strong (weak) upwelling, resulting in relatively high (low) local coral δ18O. The upstream KC transport and downstream transport, off Tatsukushi Bay, Japan, covary on interannual and decadal time scales. This suggests common forcings, such as meridional drift of the North Equatorial Current bifurcation, or zonal climatic oscillations in the Pacific. The intensities of KC transport off southeastern and northeastern Taiwan are in phase before 1990 and antiphase after 1990. This difference may be due to a poleward shift of the subtropical western boundary current as a response to global warming.
      PubDate: 2017-08-30T06:30:42.715453-05:
      DOI: 10.1002/2017JC012944
  • Propagation of the subsurface freshening water and its major source in the
           northwestern Pacific
    • Authors: Youfang Yan; Dazhi Xu, Kai Yu, Yiquan Qi
      Abstract: Previous studies of the exchanges of the subtropical-tropical salinity in the North Pacific are still not conclusive. Some studies suggest that surface salinity anomalies formed in the northeastern subtropics can subduct and penetrate to the subsurface of the northwestern Pacific, whereas others demonstrate that subsurface salinity anomalies in the northwestern Pacific cannot be traced back to those of the eastern subtropics. This study examined the variability of subsurface salinity in the northwestern Pacific, with focus on its propagation characteristic and forcing mechanism in its outcrop region. It is found that salinity anomalies on 24.5–25.4 kg m−3 isopycnals exhibited a pronounced freshening trend in the northwestern Pacific during 2003–2012. This freshening can be traced back to the surface salinity anomalies in the outcrop zone of the northwestern subtropical gyre, rather than that of northeastern subtropics. The representative transit time from its outcrop region to the eastern Luzon Strait is about 1–3 years. The surface salinity anomalies in the outcrop zone are mainly controlled by air-sea freshwater flux change, although the contribution of horizontal advection is also important, in particular for year-to-year variation. Compared to the air-sea freshwater flux and horizontal advection, the contribution of mixed-layer depth to the surface salinity anomalies is smaller and can be neglected in the outcrop zone of the northwestern Pacific.
      PubDate: 2017-08-29T07:36:59.722899-05:
      DOI: 10.1002/2017JC013033
  • Transfer and dissipation of energy during wave group propagation on a
           gentle beach slope
    • Authors: Enrique M. Padilla; José M. Alsina
      Abstract: The propagation of bichromatic wave groups over a constant 1:100 beach slope and the influence of the group modulation is presented. The modulation is controlled by varying the group frequency, fg, which is shown to remarkably affect the energy transfer to high and low frequency components. The growth of the high frequency (hf) wave skewness increases when fg decreases. This is explained by nonlinear coupling between the primary frequencies, which results in a larger growth of hf components as fg decreases, causing the hf waves to break earlier. Due to high spatial resolution, wave tracking has provided an accurate measurement of the varying breakpoint. These breaking locations are very well described (R2>0.91) by the wave-height to effective-depth ratio (γ). However, for any given Iribarren number, this γ is shown to increase with fg. Therefore, a modified Iribarren number is proposed to include the grouping structure, leading to a considerable improvement in reproducing the measured γ-values. Within the surf zone, the behavior of the Incident Long Wave also depends on the group modulation. For low fg conditions, the lf wave decays only slightly by transferring energy back to the hf wave components. However, for high fg wave conditions, strong dissipation of low frequency (lf) components occurs close to the shoreline associated with lf wave breaking. This mechanism is explained by the growth of the lf wave height, induced partly by the self-self interaction of fg, and partly by the nonlinear coupling between the primary frequencies and fg.
      PubDate: 2017-08-28T02:25:43.551619-05:
      DOI: 10.1002/2017JC012703
  • Numerical simulations of rotating bubble plumes in stratified environments
    • Authors: Alexandre Fabregat Tomàs; Andrew C. Poje, Tamay M. Özgökmen, William K. Dewar
      Abstract: The effects of system rotation on the turbulent dynamics of bubble plumes evolving in stratified environments are numerically investigated by considering variations in both the system rotation rate and the gas-phase slip velocity. The turbulent dispersion of a passive scalar injected at the source of a buoyant plume is strongly altered by the rotation of the system and the nature of the buoyancy at the source. When the plume is driven by the density defect associated with the presence of slipping gas bubbles, the location of the main lateral intrusion decreases with respect to the single-phase case with identical inlet volume, momentum, and buoyancy fluxes. Enhanced downdrafts of carrier phase fluid result in increased turbulent mixing and short-circuiting of detraining plume water that elevate near-field effluent concentrations. Similarly, rotation fundamentally alters dynamic balances within the plume leading to the encroachment of the trapping height on the source and an increase in turbulent dispersion in the near field. System rotation, even at modest Rossby numbers, produces a sustained, robust, anticyclonic precession of the plume core. The effects of rotation and the presence of bubbles are cumulative. The vertical encroachment of the primary intrusion and the overall dispersion of effluent are greatest at smallest Rossby numbers and largest slip velocities. The main characteristic feature in rotating single-phase plumes, namely the robust anticyclonic precession, persists in bubble plumes. Analysis of the momentum budgets reveal that the mechanism responsible for the organized precession, i.e., the establishment of an unstable vertical hydrostatic equilibrium related to radial cyclostrophic balance, does not differ from the single-phase case.
      PubDate: 2017-08-28T02:20:38.37946-05:0
      DOI: 10.1002/2017JC013110
  • The Lofoten Basin eddy: Three years of evolution as observed by Seagliders
    • Authors: Lu-Sha Yu; Anthony Bosse, Ilker Fer, Kjell A. Orvik, Erik M. Bruvik, Idar Hessevik, Karsten Kvalsund
      Abstract: The Lofoten Basin in the Norwegian Sea is an area where the warm Atlantic Water is subject to the greatest heat losses anywhere in the Nordic Seas. A long-lived, deep, anticyclonic eddy is located in the central part of the basin (the Lofoten Basin Eddy, LBE). Here we use observations from Seagliders, collected between July 2012 and July 2015, to describe LBE in unprecedented detail. The missions were designed to sample LBE repeatedly, allowing for multiple realizations of radial sections across the eddy. LBE has a mean radius of 18 ± 4 km and propagates cyclonically with a mean speed of approximately 3–4 cm s−1. The anticyclonic azimuthal peak velocity varies between 0.5 and 0.7 m s−1, located between 700 and 900 m depth. The average contribution of geostrophy in the cyclogeostrophic balance is 44%. The relative vorticity of the core is close to the local Coriolis parameter. The evolution of core water properties shows substantial interannual variability, influenced by surface buoyancy flux and advection of anomalous low-salinity near-surface waters that may affect the vertical extent of winter convection. A comparison of the eddy properties to those inferred from automated tracking of satellite altimeter observations shows that the location of eddy center is successfully detected to within one half eddy radius, but vorticity is underestimated and the radius overestimated, each approximately by a factor of 2, because of excessive smoothing relative to the small eddy radius.
      PubDate: 2017-08-28T02:16:10.29233-05:0
      DOI: 10.1002/2017JC012982
  • The origins of the anomalous warming in the California coastal ocean and
           San Francisco Bay during 2014-2016
    • Authors: Yi Chao; John D. Farrara, Eric Bjorkstedt, Fei Chai, Francisco Chavez, Daniel L. Rudnick, Wendy Enright, Jennifer L. Fisher, William T. Peterson, Gregory F. Welch, Curtiss O. Davis, Richard C. Dugdale, Frances P. Wilkerson, Hongchun Zhang, Yinglong Zhang, Eli Ateljevich
      Abstract: During 2014 exceptionally warm water temperatures developed across a wide area off the California coast and within San Francisco Bay (SFB) and persisted into 2016. Observations and numerical model output are used to document this warming and determine its origins. The coastal warming was mostly confined to the upper 100 meters of the ocean and was manifested strongly in the two leading modes of upper ocean (0-100 m) temperature variability in the extra-tropical eastern Pacific. Observations suggest that the coastal warming in 2014 propagated into nearshore regions from the west while later indicating a warming influence that propagated from south to north into the region associated with the 2015-16 El Niño event. An analysis of the upper ocean (0-100 m) heat budget in a Regional Ocean Modeling System simulation confirmed this scenario. The results from a set of sensitivity runs with the model in which the lateral boundary conditions varied supported the conclusions drawn from the heat budget analysis. Concerning the warming in the SFB, an examination of the observations and the heat budget in an unstructured-grid numerical model simulation suggested that the warming during the second half of 2014 and early 2016 originated in the adjacent California coastal ocean and propagated through the Golden Gate into the Bay. The finding that the coastal and Bay warming are due to the relatively slow propagation of signals from remote sources raises the possibility that such warming events may be predictable many months or even several seasons in advance.
      PubDate: 2017-08-25T13:37:59.172569-05:
      DOI: 10.1002/2017JC013120
  • Late-summer biogeochemistry in the Mertz Polynya: East Antarctica
    • Authors: E. H. Shadwick; B. Tilbrook, K. I. Currie
      Abstract: A marked reconfiguration of the Mertz Polynya following the 2010 calving of the Mertz Glacier Tongue has been associated with a decrease in the size and activity of the polynya. We report observations of the oceanic carbonate (CO2) system in late summer 2013, the third post-calving summer season. Estimates of seasonal net community production (NCP) based on inorganic carbon deficits and the oxygen-argon ratio indicate that the waters on the shelf to the east of Commonwealth Bay (adjacent to the Mertz Glacier) remain productive compared to pre-calving conditions. The input of residual or excess alkalinity from melting ice is found to contribute to the seasonal enhancement of carbonate saturation state and pH in shelf waters. Mean rates of NCP in 2012-2013 are more than twice as large as those observed in the pre-calving summers of 2001 and 2008 and suggest that the new (post-calving) configuration of the polynya favours enhanced net community production and a stronger surface ocean sink for atmospheric CO2 due at least in part to the the redistribution of sea-ice and associated changes in summer surface stratification.
      PubDate: 2017-08-25T13:37:53.653519-05:
      DOI: 10.1002/2017JC013015
  • The role of wave-current interaction in Lake Erie's seasonal and episodic
    • Authors: Qianru Niu; Meng Xia
      Abstract: Although the significance of surface gravity waves has been consistently emphasized in previous limnetic studies, the roles of wave-current interactions in lake dynamics are not sufficiently understood due to the lack of high-resolution wave information. With a two-way coupled hydrodynamic and wave model system, this study investigated how the Lake Erie dynamics are impacted by the wave-induced surface and radiation stresses on the seasonal-mean and episodic scales. The results showed that the surface radiation stress was the same as or an order of magnitude larger than the wave-induced surface stress in the nearshore area (< 5 km offshore), while the latter prevailed in the offshore areas. By enhancing air-lake momentum and heat transfers, the wave-enhanced surface stress improved the model's skill in simulating hydrodynamics in the Central and Eastern Basins, and it was of greater importance (at least an order of magnitude larger) in modifying surges, offshore currents and thermal structures compared to those of the radiation stress. Nevertheless, the radiation stress played key roles in wave-induced nearshore currents, especially in the shallow Western Basin. Their significances reached O (0.01 to 0.1 m/s) on the seasonal and episodic scales, respectively, and could have similar importance in other shallow water environments.
      PubDate: 2017-08-25T13:37:40.037628-05:
      DOI: 10.1002/2017JC012934
  • Tidal and residual currents across the northern Ryukyu Island chain
           observed by ferryboat ADCP
    • Authors: Zhao-Jun Liu; Hirohiko Nakamura, Xiao-Hua Zhu, Ayako Nishina, Menghong Dong
      Abstract: Ferryboat Acoustic Doppler Current Profiler (ADCP) data from 2003 to 2012 are used to estimate the tidal and residual currents across the northern Ryukyu Island chain (RIC) between the islands of Okinawa and Amamioshima. In this region, the M2 tide current is the strongest tidal component, and the K1 tide current is the strongest diurnal tidal component. The corresponding maximum amplitudes are 40 and 34 cm s−1, respectively. After removal of the tidal currents, the mean volume transport, 1.5 ± 2.7 Sv, flows into the East China Sea (ECS) from the western North Pacific through four channels in this area. In an empirical orthogonal function (EOF) analysis performed to clarify the temporal and spatial variability of currents through the four channels, the first two EOF modes account for 71% and 18% of the total variance, respectively. The EOF1 mode shows a clear bottom-intensified mode through the deep channel, which is likely to be formed by the propagation of bottom-trapped long topographic Rossby wave caused by the impingement of westward propagating mesoscale eddies upon the eastern slope of the northern RIC. The EOF2 mode has significant seasonal variability and may be driven by the wind stress prevailing over the Kuroshio flow region around the northern RIC in October to November. This study provides observational evidence of the water exchanges across the northern RIC, which is essential for constructing a circulation scheme in the North Pacific subtropical western boundary region.
      PubDate: 2017-08-25T13:37:29.990654-05:
      DOI: 10.1002/2017JC012876
  • Three-dimensional tidal flow in a fjord-like basin with converging width:
           An analytical model
    • Authors: Lauren Ross; Huib de Swart, Erik Ensing, Arnoldo Valle-Levinson
      Abstract: A three-dimensional analytical model was used to understand tidal dynamics in deep and narrow (fjord-like) basins. This model allows the width of the basin to decay exponentially with along-channel distance from the mouth. Both the length scale of exponential convergence, Lb*, and the friction parameter, Aν* (vertical eddy viscosity), were the free parameters. Model results show amplification of the tidal amplitude toward the head of the basin. Amplification depends on the narrowing rate of the funnel-like width of the channel and on friction. Cross-channel variations in along-channel tidal ow are also sensitive to the friction parameter. A typical along-channel tidal ow distribution was found across the channel when the vertical eddy viscosity was characteristic of a basin with strong friction, or the Stokes number was larger than 0.1 (St > 0:1). Maximum along-channel tidal velocities (ranging from 0:25 to 0:5 m s−1 depending on width convergence strength) were located in the center of the basin and at the surface. Decreasing values of the Stokes number, St 
      PubDate: 2017-08-25T13:37:22.647655-05:
      DOI: 10.1002/2017JC012820
  • Mechanisms underlying recent decadal changes in subpolar North Atlantic
           Ocean heat content
    • Authors: Christopher G. Piecuch; Rui M. Ponte, Christopher M. Little, Martha W. Buckley, Ichiro Fukumori
      Abstract: The subpolar North Atlantic (SPNA) is subject to strong decadal variability, with implications for surface climate and its predictability. In 2004–2005, SPNA decadal upper-ocean and sea-surface temperature trends reversed from warming during 1994–2004 to cooling over 2005–2015. This recent decadal trend reversal in SPNA ocean heat content (OHC) is studied using a physically consistent, observationally constrained global ocean state estimate covering 1992–2015. The estimate's physical consistency facilitates quantitative causal attribution of ocean variations. Closed heat budget diagnostics reveal that the SPNA OHC trend reversal is the result of heat advection by midlatitude ocean circulation. Kinematic decompositions reveal that changes in the deep and intermediate vertical overturning circulation cannot account for the trend reversal, but rather ocean heat transports by horizontal gyre circulations render the primary contributions. The shift in horizontal gyre advection reflects anomalous circulation acting on the mean temperature gradients. Maximum covariance analysis (MCA) reveals strong covariation between the anomalous horizontal gyre circulation and variations in the local wind stress curl, suggestive of a Sverdrup response. Results have implications for decadal predictability.
      PubDate: 2017-08-25T13:37:11.655975-05:
      DOI: 10.1002/2017JC012845
  • Tsunami and shelf resonance on the Northern Chile Coast
    • Authors: Pablo Cortés; Patricio A. Catalán, Rafael Aránguiz, Giorgio Bellotti
      Abstract: This work presents the analysis of long waves resonance in two of the main cities along the northern coast of Chile, Arica and Iquique, where a large tsunamigenic potential remains despite recent earthquakes. By combining a modal analysis solving the equation of free surface oscillations, with the analysis of background spectra derived from in situ measurements, the spatial and temporal structures of the modes are recovered. Comparison with spectra from three tsunamis of different characteristics shows that the modes found have been excited by past events. Moreover, the two locations show different response patterns. Arica is more sensitive to the characteristics of the tsunami source, whereas Iquique shows a smaller dependency and similar response for different tsunami events. Results are further compared with other methodologies with good agreement. These findings are relevant in characterizing the tsunami hazard in the area, and the methodology can be further extended to other regions along the Chilean coast.
      PubDate: 2017-08-25T13:36:59.104883-05:
      DOI: 10.1002/2017JC012922
  • The warmer the ocean surface, the shallower the mixed layer: How much of
           this is true'
    • Authors: R. Somavilla; C. González-Pola, J. Fernandez
      Abstract: Ocean surface warming is commonly associated with a more stratified, less productive, and less oxygenated ocean. Such assertion is mainly based on consistent projections of increased near-surface stratification and shallower mixed layers under global warming scenarios. However, while the observed sea surface temperature (SST) is rising at mid-latitudes, the concurrent ocean record shows that stratification is not unequivocally increasing nor is MLD shoaling. We find that while SST increases at three study areas at mid-latitudes, stratification both increases and decreases, and MLD deepens with enhanced deepening of winter MLDs at rates over 10m decade−1. These results rely on the estimation of several MLD and stratification indexes of different complexity on hydrographic profiles from long term hydrographic time-series, ocean reanalysis and Argo floats. Combining this information with estimated MLDs from buoyancy fluxes and the enhanced deepening/attenuation of the winter MLD trends due to changes in the Ekman pumping, MLD variability reveals itself as a subtle interplay between circulation and atmospheric forcing at mid-latitudes. Besides, it is highlighted that the density difference between the surface and 200 m, the most widely used stratification index, should not be expected to reliably inform about changes in the vertical extent of mixing.
      PubDate: 2017-08-25T13:36:50.356715-05:
      DOI: 10.1002/2017JC013125
  • Pathways and supply of dissolved iron in the Amundsen Sea (Antarctica)
    • Authors: P. St-Laurent; P.L. Yager, R.M. Sherrell, S.E. Stammerjohn, M.S. Dinniman
      Abstract: Numerous coastal polynyas fringe the Antarctic continent and strongly influence the productivity of Antarctic shelf systems. Of the 46 Antarctic coastal polynyas documented in a recent study, the Amundsen Sea Polynya (ASP) stands out as having the highest net primary production per unit area. Incubation experiments suggest that this productivity is partly controlled by the availability of dissolved iron (dFe). As a first step toward understanding the iron supply of the ASP, we introduce four plausible sources of dFe and simulate their steady spatial distribution using conservative numerical tracers. The modeled distributions replicate important features from observations including dFe maxima at the bottom of deep troughs and enhanced concentrations near the ice shelf fronts. A perturbation experiment with an idealized drawdown mimicking summertime biological uptake and subsequent resupply suggests that glacial meltwater and sediment-derived dFe are the main contributors to the pre-bloom dFe inventory in the top 100m of the ASP. The sediment-derived dFe depends strongly on the buoyancy-driven overturning circulation associated with the melting ice shelves (the ‘meltwater pump') to add dFe to the upper 300m of the water column. The results support the view that ice shelf melting plays an important direct and indirect role in the dFe supply and delivery to polynyas such as the ASP.
      PubDate: 2017-08-25T13:36:28.518044-05:
      DOI: 10.1002/2017JC013162
  • Thermohaline staircases in the Amundsen Basin: Possible disruption by
           shear and mixing
    • Authors: John D. Guthrie; Ilker Fer, James H. Morison
      Abstract: As part of the 2013 and 2014 North Pole Environmental Observatories (NPEO) in the Amundsen Basin of the Arctic Ocean, two similar temperature microstructure experiments were performed with different results. In 2013, vertical fluxes were through a thermohaline staircase, and in 2014 the thermohaline staircase was largely absent. Here we investigate the reasons for this difference. The 2013 data set was characterized by an extensive thermohaline staircase, indicative of the diffusive convective type of double diffusion (DC), from 120-250 m depths. The staircase was absent above 200 m in 2014, even though analysis of density ratio, Rρ, still shows high susceptibility to DDC. In the depth range of interest, survey averaged Rρ = 3.8 in 2013 and Rρ = 3.6 in 2014, indicating that the temperature-salinity structure in the pycnocline was not the cause of the lack of a staircase in 2014. We propose that exceptionally weak turbulent mixing, even for the typically quiescent Arctic Ocean, allowed formation of the staircase in 2013. Average thermal diffusivity, KT, between 50 – 120 m is elevated in 2014, 2 x 10−5 m2s−1, compared to 2013, 1 x 10−6 m2s−1. However, vertical Atlantic Water (AW) DC heat fluxes in 2013 are remarkably consistent with turbulent heat fluxes in 2014. Similar data sets collected in 2007 and 2008 both resemble 2014, showing consistently higher mixing values compared to 2013. The suppression of turbulence during NPEO 2013 resulted from increased near-surface stratification, possibly caused by a different large-scale circulation pattern that year.
      PubDate: 2017-08-25T13:31:16.285431-05:
      DOI: 10.1002/2017JC012993
  • Lateral variability of subtidal flow at the mid-reaches of a macrotidal
    • Authors: Lauren Ross; Arnoldo Valle-Levinson, Aldo Sottolichio, Nicolas Huybrechts
      Abstract: Transverse variations of tidal and subtidal ow were investi-gated in a macrotidal and convergent estuary. This was accomplished by combining data analysis of current velocities and water density with numericalmodeling at the mid-reaches of the Gironde Estuary (France). Nonlinear mech-anisms responsible for overtide generation and hence subtidal ows were foundto vary across the estuary and from neap to spring tides. Subtidal ows weredriven by a combination of internal asymmetry, tidal advective accelerations, nonlinear effects of water level variations, quadratic friction and river discharge. The quarter-diurnal overtide band (D4) in ow was generated by in-ternal asymmetry and tidal advective accelerations during neap tide. Theratio of quarter-diurnal to squared semidiurnal bands (D4/D22) was largest(>0.3) in sections of the channel showing subtidal outow. River dischargeincreased from neap to spring tides causing a subsequent increase of sea-ward subtidal currents. During spring tide D4 was generated by tidal advec-tive accelerations and quadratic friction combined with river discharge, ratherthan by internal asymmetry. The sixth-diurnal overtide (D6) in the ow wascomparable to D4 for both neap and spring tides. Largest D6/D23 ratios werefound in the shallowest cross-channel locations during both neap and springtides.
      PubDate: 2017-08-25T13:31:12.755533-05:
      DOI: 10.1002/2016JC012504
  • The influence of variable slope-water characteristics on dissolved oxygen
           levels in the northern California Current System
    • Authors: Scott M. Durski; John A. Barth, James C. McWilliams, Hartmut Frenzel, Curtis Deutsch
      Abstract: Observations have suggested a trend of decreasing dissolved oxygen (DO) and increasing spiciness in summertime mid-depth slope waters and bottom shelf waters along the United States west coast over the past 50 years, but they have also demonstrated a large amount of interannual and decadal variability. Shelf bottom water and slope water properties can be influenced by both local and remote effects, including changes in circulation or changes in the characteristics of the source waters supplying the region. A regional-scale, coupled physical biogeochemical model has been developed to simulate seasonal-to-decadal scale variability along the US west coast to discern the physical dynamics behind these spatial and temporal patterns. A simulation run from 1981 through 2006 with forcing that incorporates the larger scale interannual trends reproduces the development of low DO late in the upwelling season, the considerable interannual variability and the reported tendency towards a shoaling, more spicy and oxygen-depleted, northern California Undercurrent (CU). Whereas the trend in spiciness in the model results from increased influence of equatorial relative to subarctic source waters, the decreases in DO are found to additionally be a consequence of local biogeochemical processes. In order to better understand the interannual variability, years of the simulation were classified into four groups based on intensity of upwelling forcing and undercurrent strength. Slope water characteristics, shelf-slope exchange, and slope-basin exchange were compared across the four cases. Years with both strong upwelling and a strong undercurrent generated the most negative anomalies in slope-water DO late in the upwelling season.
      PubDate: 2017-08-25T13:31:01.991174-05:
      DOI: 10.1002/2017JC013089
  • Characterization of the structure and cross-shore transport properties of
           a coastal upwelling filament using three-dimensional finite–size
           Lyapunov exponents
    • Authors: João H. Bettencourt; Vincent Rossi, Emilio Hernández-García, Martinho Marta-Almeida, Cristóbal López
      Abstract: The three dimensional structure, dynamics and dispersion characteristics of a simulated upwelling filament in the Iberian upwelling system are analyzed using Lagrangian tools. We used a realistic regional simulation of the western Iberian shelf which is concomitant with an in-situ oceanographic campaign that surveyed the area. We compute 3d fields of finite–size Lyapunov exponents (FSLE) from 3d velocity fields and extract the field's ridges to study the spatial distribution and temporal evolution of the Lagrangian Coherent Structures (LCSs) evolving around the filament. We find that the most intense curtain-like LCSs delimit the boundaries of the whole filamentary structure whose general properties match well the observations. The filament interior is characterized by small dispersion of fluid elements. Furthermore, we identify a weak LCS separating the filament into a warmer vein and a colder filament associated with the interaction of a mesoscale eddy with the upwelling front. The cold upwelled water parcels move along the filament conserving their density. The filament itself is characterized by small dispersion of fluid elements in its interior. The comparison of LCSs with potential temperature and salinity gradient fields shows that the outer limits of the filament coincide with regions of large hydrographic gradients, similar to those observed, explaining the isolation of the interior of the filament with the surrounding waters. We conclude that the Lagrangian analysis used in this work is useful in explaining the dynamics of cross-shore exchanges of materials between coastal regions and the open ocean due to mesoscale processes.
      PubDate: 2017-08-25T13:30:51.311667-05:
      DOI: 10.1002/2017JC012700
  • Phytoplankton light absorption and the package effect in relation to
           photosynthetic and photoprotective pigments in the northern tip of
           Antarctic Peninsula
    • Authors: Amabile Ferreira; Áurea M. Ciotti, Carlos Rafael B. Mendes, Julia Uitz, Annick Bricaud
      Abstract: This study investigates the variability in the spectral absorption of phytoplankton in Antarctic waters. A large in situ dataset comprising phytoplankton pigments and hyperspectral absorption was measured in the northern tip of Antarctic Peninsula during 2013 and 2014 summers at several depths. A proxy of package effect was estimated from the phytoplankton absorption spectra, independently of chlorophyll-a. Variations in the concentration of photosynthetic and photoprotective pigments were discernible by changes in this metric but not in a*ph(λ). The fucoxanthin to chlorophyll-a ratio correlated positively to package effect due to an increase in cell size of phytoplankton (diatoms) and increasing fucoxanthin content per cell to maximize light-harvesting in depth. The package effect was found to covary inversely with photoprotective pigments relative to chlorophyll-a, partially due to their contribution to enhance absorption in the blue part of the spectrum. Using a cluster analysis (k-means algorithm) on the phytoplankton absorption spectra, we illustrate the capacity to identify a regular increase in the degree of package effect. This approach can be useful to classify the phytoplankton assemblages in Antarctic waters according to different degrees of pigment packaging, each one related to a specific pigment composition. Our results demonstrate the potential for this classification at different temporal and spatial scales from ocean color satellite data. This should improve our understanding of deviations in global bio-optical algorithms when applied to the Southern Ocean.
      PubDate: 2017-08-25T13:30:47.223097-05:
      DOI: 10.1002/2017JC012964
  • Variability of the Subtropical Mode Water in the Southwest Pacific
    • Authors: Denise Fernandez; Philip Sutton, Melissa Bowen
      Abstract: The variability of Subtropical Mode Water (STMW) in the Southwest Pacific is investigated using a 28-year-long time series (1986 to 2014) of high-resolution expendable bathythermograph data north of New Zealand (PX06) and a shorter time series, the Roemmich-Gilson monthly Argo optimal interpolation for the 2004-2014 period. The variability in STMW inventories is compared to the variability in air-sea heat fluxes, mixed layer depths and transport of the East Auckland Current (EAUC) to assess both the atmospheric and oceanic roles influencing the formation and decay of STMW. The STMW north of New Zealand has a short lifespan with little persistence of the water mass from one year to the next one. Deeper mixed layers and negative anomalies in surface heat fluxes are correlated with increased formation of STMW. The heat content of the STMW layer is anticorrelated with inventories, particularly during the El Niño years. This suggests that large volumes of STMW are coincident with cooler conditions in the prior winter and less oceanic heat storage. There is significant seasonal and interannual variability in STMW inventories, however there are no trends in STMW properties, including its core layer temperature over the last decade. The variability of the winter EAUC transport is highly correlated with the STMW inventories and thermocline depth in the following spring, suggesting ocean dynamics deepen the thermocline and precondition for deeper mixed layers.
      PubDate: 2017-08-25T13:30:43.802087-05:
      DOI: 10.1002/2017JC013011
  • The pelagic ecosystem in the northern California Current off Oregon during
           the 2014-2016 warm anomalies within the context of the past 20 years
    • Authors: William T. Peterson; Jennifer L. Fisher, P. Ted Strub, Xiuning Du, Craig Risien, Jay Peterson, C. Tracy Shaw
      Abstract: A warm anomaly in the upper ocean, colloquially named “the Blob”, appeared in the Gulf of Alaska during the calm winter of 2013-2014, spread across the northern North Pacific (NP) Ocean and shifted eastward and onto the Oregon shelf. At least 14 species of copepods occurred which had never been observed in shelf/slope waters off Oregon, some of which are known to have NP Gyre affinities, indicating that the source waters of the coastal “Blob” were likely of both offshore (from the west) and subtropical/tropical origin. The anomalously warm conditions were reduced during strong upwelling in spring 2015 but returned when upwelling weakened in July 2015 and transitioned to downwelling in fall 2015. The extended period of warm conditions resulted in prolonged effects on the ecosystem off central Oregon, lasting at least through 2016. Impacts to the lower trophic levels were unprecedented and include a novel plankton community composition resulting from increased copepod, diatom and dinoflagellate species richness and increased abundance of dinoflagellates. Additionally, the multi-year warm anomalies were associated with reduced biomass of copepods and euphausiids, high abundance of larvaceans and doliolids (indictors of oligotrophic ocean conditions), and a toxic diatom bloom (Pseudo-nitzschia) throughout the California Current in 2015, thereby changing the composition of the food web that is relied upon by many commercially and ecologically important species.
      PubDate: 2017-08-25T13:30:41.263614-05:
      DOI: 10.1002/2017JC012952
  • Fine-scale variability of isopycnal salinity in the California Current
    • Authors: Sachihiko Itoh; Daniel L. Rudnick
      Abstract: This paper examines the finescale structure and seasonal fluctuations of the isopycnal salinity of the California Current System from 2007 to 2013 using temperature and salinity profiles obtained from a series of underwater glider surveys. The seasonal mean distributions of the spectral power of the isopycnal salinity gradient averaged over submesoscale (12–30 km) and mesoscale (30–60 km) ranges along three survey lines off Monterey Bay, Point Conception, and Dana Point were obtained from 298 transects. The mesoscale and submesoscale variance increased as coastal upwelling caused the isopycnal salinity gradient to steepen. Areas of elevated variance were clearly observed around the salinity front during the summer then spread offshore through the fall and winter. The high finescale variances were observed typically above 25.8 kg m−3 and decreased with depth to a minimum at around 26.3 kg m−3. The mean spectral slope of the isopycnal salinity gradient with respect to wavenumber was 0.19 ± 0.27 over the horizontal scale of 12–60 km, and 31% to 35% of the spectra had significantly positive slopes. In contrast, the spectral slope over 12–30 km was mostly flat, with mean values of −0.025 ± 0.32. An increase in submesoscale variability accompanying the steepening of the spectral slope was often observed in inshore areas; e.g., off Monterey Bay in winter, where a sharp front developed between the California Current and the California Under Current, and the lower layers of the Southern California Bight, where vigorous interaction between a synoptic current and bottom topography is to be expected.
      PubDate: 2017-08-25T13:30:30.634842-05:
      DOI: 10.1002/2017JC013080
  • Seasonal fluctuations of ichthyoplankton assemblage in the northeastern
           South China Sea influenced by the Kuroshio intrusion
    • Authors: D. Huang; X. Zhang, Z. Jiang, J. Zhang, I. Arbi, X. Jiang, X. Huang, W. Zhang
      Abstract: The distribution and assemblage of ichthyoplankton related to local hydrographic features, especially intrusion of the Kuroshio Current (KC) and Guangdong Coastal Current (GCC) in the northeastern South China Sea (NESCS) were investigated in this study. A total of 193 species of ichthyoplankton belonging to 141 genera and 66 families were recognized in summer 2015 and late-winter 2016. The ichthyoplankton assemblage was identified with distinct seasonal differences, and the differences were responded well with the oceanography conditions. In summer, the assemblages were identified into offshore and inshore groups, as controlled by the South China Sea Warm Current (SCSWC) in off-shelf, upwelling and the diluted water from the Pearl River in inshore. In winter, three groups were divided, representing the southwestern inshore, intrusion of the KC in the eastern offshore and the GCC in the northern inshore area, respectively. Furthermore, Sigmops gracilis and Vinciguerria sp.3 were probably brought into the NESCS by intrusion of the KC from the eastern Luzon Strait. In addition, high ichthyoplankton abundance was found in high chlorophyll a located in upwelling areas in the northern coastal area in summer and in the southwestern Taiwan Bank in winter, respectively. The nutrition outcropped by the upwelling together, and those brought from the Pearl River probably supported high food availability of the ichthyoplankton in the northern coast of the NESCS.
      PubDate: 2017-08-25T13:30:24.025498-05:
      DOI: 10.1002/2017JC012906
  • Seismic estimates of turbulent diffusivity and evidence of nonlinear
           internal wave forcing by geometric resonance in the South China Sea
    • Authors: W.F.J. Fortin; W.S. Holbrook, R.W. Schmitt
      Abstract: The Luzon Passage generates some of the largest amplitude internal waves in the global ocean as the result of coupling between strong tides, strong stratification, and topography. These internal waves propagate into the South China Sea (SCS) and develop into soliton-like internal wave pulses that are observed by moored instruments and satellite backscatter data. Despite the observation of these waves, little is known of the mechanisms related to their evolution into nonlinear wave pulses. Using seismic data, we find evidence that the geometry of bathymetric conditions between the Heng-Chun and Lan-Yu ridges drive nonlinear internal wave pulse generation. We produce three seismic images and associated maps of turbulent diffusivity to investigate structure around the two ridges and into the SCS. We do not observe large amplitude soliton-like internal waves between the ridges, but do observe one outside the ridges, a finding in accord with the interpretation that wave pulses form due to geometrical resonance. Additionally, we find no evidence for lee wave activity above the ridges in either the seismic images or associated turbulence maps, suggesting an unlikelihood of hydraulic jump driven generation around the ridges. Our results show increased levels of turbulent diffusivity (1) in deep water below 1000m, (2) associated with internal tide pulses, and (3) near the steep slopes of the Heng-Chun and Lan-Yu ridges as explored in this paper.
      PubDate: 2017-08-25T13:30:19.881429-05:
      DOI: 10.1002/2017JC012690
  • Turbulent mixing within the Kuroshio in the Tokara Strait
    • Authors: Eisuke Tsutsumi; Takeshi Matsuno, Ren-Chieh Lien, Hirohiko Nakamura, Tomoharu Senjyu, Xinyu Guo
      Abstract: Turbulent mixing and background current were observed using a microstructure profiler and acoustic Doppler current profilers in the Tokara Strait, where many seamounts and small islands exist within the route of the Kuroshio in the East China Sea. Vertical structure and water properties of the Kuroshio were greatly modified downstream from shallow seamounts. In the lee of a seamount crest at 200 -m depth, the modification made the flow tend to shear instability, and the vertical eddy diffusivity is enhanced by nearly 100 times that of the upstream site, to Kρ ∼ O(10−3)–O(10−2) m2 s−1. A one-dimensional diffusion model using the observed eddy diffusivity reproduced the observed downstream evolution of the temperature-salinity profile. However, the estimated diffusion time-scale is at least 10 times longer than the observed advection time-scale. This suggests that the eddy diffusivity reaches to O(10−1) m2 s−1 in the vicinity of the seamount. At a site away from the abrupt topography, eddy diffusivity was also elevated to O(10−3) m2 s−1, and was associated with shear instability presumably induced by the Kuroshio shear and near-inertial internal-wave shear. Our study suggests that a better prediction of current, water-mass properties, and nutrients within the Kuroshio requires accurate understanding and parameterization of flow-topography interaction such as internal hydraulics, the associated internal-wave processes, and turbulent mixing processes.
      PubDate: 2017-08-25T11:57:41.94591-05:0
      DOI: 10.1002/2017JC013049
  • A data assimilating model for estimating Southern Ocean biogeochemistry
    • Authors: A. Verdy; M.R. Mazloff
      Abstract: A biogeochemical Southern Ocean state estimate (B-SOSE) is introduced that includes carbon and oxygen fields as well as nutrient cycles. The state estimate is constrained with observations while maintaining closed budgets and obeying dynamical and thermodynamic balances. Observations from profiling floats, shipboard data, underway measurements, and satellites are used for assimilation. The years 2008–2012 are chosen due to the relative abundance of oxygen observations from Argo floats during this time. The skill of the state estimate at fitting the data is assessed. The agreement is best for fields that are constrained with the most observations, such as surface pCO2 in Drake Passage (44% of the variance captured) and oxygen profiles (over 60% of the variance captured at 200 m and 1000 m). The validity of adjoint method optimization for coupled physical-biogeochemical state estimation is demonstrated with a series of gradient check experiments. The method is shown to be mature and ready to synthesize in situ biogeochemical observations as they become more available. Documenting the B-SOSE configuration and diagnosing the strengths and weaknesses of the solution informs usage of this product as both a climate baseline and as a way to test hypotheses. Transport of Intermediate Waters across 32°S supplies significant amounts of nitrate to the Atlantic Ocean (5.57±2.94 Tmol yr-1) and Indian Ocean (5.09±3.06 Tmol yr-1), but much less nitrate reaches the Pacific Ocean (1.78±1.91 Tmol yr-1). Estimates of air-sea carbon dioxide fluxes south of 50°S suggest a mean uptake of 0.18 Pg C/yr for the time period analyzed.
      PubDate: 2017-08-15T02:12:16.88532-05:0
      DOI: 10.1002/2016JC012650
  • Space and time variability of the Southern Ocean carbon budget
    • Authors: Isabella Rosso; Matthew R. Mazloff, Ariane Verdy, Lynne D. Talley
      Abstract: The upper ocean dissolved inorganic carbon (DIC) concentration is regulated by advective and diffusive transport divergence, biological processes, freshwater and air-sea CO2 fluxes. The relative importance of these mechanisms in the Southern Ocean is uncertain, as year-round observations in this area have been limited. We use a novel physical-biogeochemical state estimate of the Southern Ocean to construct a closed DIC budget of the top 650 m and investigate the spatial and temporal variability of the different components of the carbon system.The dominant mechanisms of variability in upper ocean DIC depend on location and time and space scales considered. Advective transport is the most influential mechanism and governs the local DIC budget across the 10 day to 5-year timescales analyzed. Diffusive effects are nearly negligible. The large-scale transport structure is primarily set by up- and downwelling, though both the lateral ageostrophic and geostrophic transports are significant. In the Antarctic Circumpolar Current, the carbon budget components are also influenced by the presence of topography and biological hot spots. In the subtropics, evaporation and air-sea CO2 flux primarily balances the sink due to biological production and advective transport. Finally, in the subpolar region sea ice processes, which change the seawater volume and thus the DIC concentration, compensate the large impact of the advective transport and modulate the timing of biological activity and air-sea CO2 flux.
      PubDate: 2017-08-11T12:27:33.772047-05:
      DOI: 10.1002/2016JC012646
  • Characterising the chaotic nature of ocean ventilation
    • Authors: Graeme A. MacGilchrist; David P. Marshall, Helen L. Johnson, Camille Lique, Matthew Thomas
      Abstract: Ventilation of the upper ocean plays an important role in climate variability on interannual to decadal timescales by influencing the exchange of heat and carbon dioxide between the atmosphere and ocean. The turbulent nature of ocean circulation, manifest in a vigorous mesoscale eddy field, means that pathways of ventilation, once thought to be quasi-laminar, are in fact highly chaotic. We characterise the chaotic nature of ventilation pathways according to a nondimensional ‘filamentation number', which estimates the reduction in filament width of a ventilated fluid parcel due to mesoscale strain. In the subtropical North Atlantic of an eddy-permitting ocean model, the filamentation number is large everywhere across three upper ocean density surfaces — implying highly chaotic ventilation pathways — and increases with depth. By mapping surface ocean properties onto these density surfaces, we directly resolve the highly filamented structure and confirm that the filamentation number captures its spatial variability. These results have implications for the spreading of atmospherically-derived tracers into the ocean interior.
      PubDate: 2017-08-11T12:27:14.989634-05:
      DOI: 10.1002/2017JC012875
  • Characteristics and evolution of an Agulhas Ring
    • Authors: M. Casanova-Masjoan; J. L. Pelegrí, P. Sangrà, A. Martínez, D. Grisolía-Santos, M. D. Pérez-Hernández, A. Hernández-Guerra
      Abstract: A South Atlantic ring is studied through remote sensing altimetry, hydrographic stations and drifters' trajectories. The ring's core was characterized by warmer and saltier Indian Ocean waters. At the time of the cruise the ring's signature extended out 110 km and down to 2000 m, and its core absolute dynamic topography (ADT) exceeded the surrounding Atlantic Ocean waters in 0.4 m. The geostrophic velocities were anticyclonic with maximum velocities about 35 cm s−1 at 100 m and reaching negligible values near 4500 m. The rotational transport inside the ring was 33 Sv in the thermocline and intermediate layers. The drifters' data distinguishes a 30-km core revolving as a solid body with periodicity near 5 days and a transitional band that revolves with constant tangential velocity, resembling a Rankine vortex. The ADT data identifies the ring's track, showing that it was shed by the Agulhas Current retroflection in November 2009 and propagated northwest rapidly during the first two months (mean speed ca. 10 cm s−1) but slowed down substantially (3-4 cm s−1) between March and July 2010, when it was last detected. The altimetry data also outlines the evolution of the ring's core ADT, radius, vorticity and, through a simple calibration with the cruise data, rotational transport. In particular, the ring surface and mean vorticity decay with time scales of 373 and 230 days, respectively, indicating that most of the property anomalies contained by the ring are diffused out to the subtropical gyre before it reaches the western boundary current system.
      PubDate: 2017-08-11T12:27:03.280732-05:
      DOI: 10.1002/2017JC012969
  • Observing System Simulation Experiments for an array of autonomous
           biogeochemical profiling floats in the Southern Ocean
    • Authors: Igor Kamenkovich; Angelique Haza, Alison R. Gray, Carolina O. Dufour, Zulema Garraffo
      Abstract: This study uses Observing System Simulation Experiments (OSSEs) to examine the reconstruction of biogeochemical variables in the Southern Ocean from an array of autonomous profiling floats. In these OSSEs, designed to be relevant to the Southern Ocean Carbon and Climate Observation and Modeling (SOCCOM) project, the simulated floats move with oceanic currents and sample dissolved oxygen and inorganic carbon. The annual mean and seasonal cycle of these fields are then reconstructed and compared to the original model fields. The reconstruction skill is quantified with the reconstruction error (RErr), defined as the difference between the reconstructed and actual model fields, weighted by a local measure of the spatio-temporal variability. The square of the RErr is small (< 0.5) for 150 floats in most of the domain, which is interpreted to mean that the reconstruction skill is high. An idealized analytical study demonstrates that the RErr depends on the magnitude of the seasonal cycle, spatial gradients, speed of float movement, amplitude of mesoscale variability and number of floats. These factors explain a large part of the spatial variability in the RErr and can be used to predict the reconstruction skill of the SOCCOM array. Furthermore, our results demonstrate that an array size of 150 floats is a reasonable choice for reconstruction of surface properties and annual-mean 2000 m inventories, with the exception of the seasonal cycle in parts of the Indo-Atlantic, and that doubling this number to 300 results in a very modest increase in the reconstruction skill for dissolved oxygen.
      PubDate: 2017-08-11T12:26:56.258436-05:
      DOI: 10.1002/2017JC012819
  • Spatiotemporal changes in extreme sea levels along the coasts of the North
           Atlantic and the Gulf of Mexico
    • Authors: Marta Marcos; Philip L. Woodworth
      Abstract: Extreme sea levels along the densely monitored coasts of the North Atlantic Ocean and the Gulf of Mexico have been investigated using high frequency tide gauge measurements in the GESLA-2 data set ( Our results, based on non-tidal residuals and skew surges in records since 1960, confirm that mean sea level (MSL) is a major, but not a unique, driver of extremes. Regionally-coherent linear trends and correlations with large scale climate patterns are found in extreme events, even after the removal of MSL. A similar conclusion, that MSL is a major but not the only driver of extremes, comes from a small number of long records starting in the mid-19th century. The records show slight increases in the intensity of extreme episodes at centennial time scales, together with multi-decadal variability unrelated to MSL. Objective statistical criteria have been used to investigate whether extreme sea level distributions are stationary or not, resulting in non-stationarity being favoured in many records, with or without accounting for changes in MSL. Extremes have been found to favour a non-Gumbel behaviour at many locations, with implications for the accuracy of return levels for coastal engineering.
      PubDate: 2017-08-11T12:26:53.64096-05:0
      DOI: 10.1002/2017JC013065
  • ENSO impact on surface radiative fluxes as observed from space
    • Authors: R. T. Pinker; S. A. Grodsky, B. Zhang, A. Busalacchi, W. Chen
      Abstract: We investigate the impact of El Niño - Southern Oscillation (ENSO) on surface radiative fluxes over the tropical Pacific using satellite observations and fluxes derived from selected atmospheric re-analyses. Agreement between the two in this region is important because re-analysis information is frequently used to assess surface energy budget sensitivity to ENSO. We found that during the traditional ENSO, the maximum variance of anomalous incoming solar radiation is located just west of the dateline and coincides with the area of largest anomalous SST gradient. It can reach up to ∼60 W/m2 and lags behind the Niño3 index by about a month, suggesting a response to anomalous SST gradient. The magnitude of longwave anomaly is only half that large, and varies in phase with the SST anomaly. Similar anomalies were derived from outputs: from the European Centre for Medium-Weather Forecasts Reanalysis Interim (ERA-I), from the Modern Era Retrospective Analysis version 2 (MERRA-2), from the NCEP/NCAR Re-analysis 1 (R1), and from the Japanese JRA55 re-analysis. Among the four re-analyses used, results from ERA-I are the closest to observations. We have also investigated the surface wind divergence/convergence and found that the main factor limiting eastward excursions of convection is the surface wind convergence. Due to the wind divergence pattern normally present over the eastern cold tongue, anomalous convection extends into the eastern equatorial Pacific only during the strongest warm events. Our analysis also considers the El Niño Modoki events, for which the radiation flux patterns are shifted westward following the SST pattern.
      PubDate: 2017-08-11T12:26:46.522423-05:
      DOI: 10.1002/2017JC012900
  • Assimilation of coastal acoustic tomography data using an unstructured
    • Authors: Ze-Nan Zhu; Xiao-Hua Zhu, Xinyu Guo, Xiaopeng Fan, Chuanzheng Zhang
      Abstract: For the first time, we present the application of an unstructured triangular grid to the Finite-Volume Community Ocean Model using the ensemble Kalman filter scheme, to assimilate coastal acoustic tomography (CAT) data. The fine horizontal and vertical current field structures around the island inside the observation region were both reproduced well. The assimilated depth-averaged velocities had better agreement with the independent acoustic Doppler current profiler (ADCP) data than the velocities obtained by inversion and simulation. The root mean square difference (RMSD) between depth-averaged current velocities obtained by data assimilation and those obtained by ADCPs was 0.07 m s−1, which was less than the corresponding difference obtained by inversion and simulation (0.12 m s−1 and 0.17 m s−1, respectively). The assimilated vertical layer velocities also exhibited better agreement with ADCP than the velocities obtained by simulation. RMSDs between assimilated and ADCP data in vertical layers ranged from 0.02 to 0.14 m s−1, while RMSDs between simulation and ADCP data ranged from 0.08 to 0.27 m s−1. These results indicate that assimilation had the highest accuracy. Sensitivity experiments involving the elimination of sound transmission lines showed that missing data had less impact on assimilation than on inversion. Sensitivity experiments involving the elimination of CAT stations showed that the assimilation with four CAT stations was the relatively economical and reasonable procedure in this experiment. These results indicate that, compared with inversion and simulation, data assimilation of CAT data with an unstructured triangular grid is more effective in reconstructing the current field.
      PubDate: 2017-08-11T12:26:43.623956-05:
      DOI: 10.1002/2017JC012715
  • Variability and wind forcing of ocean temperature and thermal fronts in
           the slope water region of the Northwest Atlantic
    • Authors: Ingrid Peterson; Blair Greenan, Denis Gilbert, Dave Hebert
      Abstract: Subsurface temperatures in the Slope Water region of the Northwest Atlantic from Argo profiling floats and on the adjacent continental shelf from ship-based measurements are compared with the latitudinal position of the Shelf-Slope Front (SSF) and the Gulf Stream North Wall (GSNW). The Slope Water and shelf temperature anomalies at 200 m depth are in agreement for the period, 2002-2015. For the period 1978-2015, shelf temperatures are significantly correlated with the SSF position, and to a lesser extent with the GSNW position. Annual SSF position anomalies near the Grand Banks at 50-55°W lead anomalies to the west at 65-75°W by 1-2 years. Wind stress curl is compared with the annual change in the SSF and GSNW latitudinal positions, rather than with the positions directly. Changes in the mean position of the SSF are related to the wind stress curl pattern in the mid-Atlantic, with an 8-month lag. It is suggested that a wind pattern favoring a southward shift of the SSF is associated with a southward shift of the zero-curl line near 40°W, resulting in an expanded subpolar gyre and enhanced flow of Labrador Current Water westward from the Tail of the Grand Banks. However changes in the GSNW position are related to an NAO-like wind stress curl pattern in the eastern Atlantic in the winter-spring period, in agreement with other studies. High sea surface temperatures in the Gulf of Maine and on the Scotian Shelf in recent years can be largely attributed to positive local onshore wind anomalies.
      PubDate: 2017-08-11T12:26:36.570759-05:
      DOI: 10.1002/2017JC012788
  • Iceland-Scotland Overflow Water transport variability through the
           Charlie-Gibbs Fracture Zone and the impact of the North Atlantic Current
    • Authors: Amy Bower; Heather Furey
      Abstract: The Charlie-Gibbs Fracture Zone (CGFZ), a deep and wide gap in the Mid-Atlantic Ridge near 52°N, is a gateway between the eastern and western subpolar regions for the Atlantic Meridional Overturning Circulation (AMOC). In 2010-2012, an eight-mooring array of current meters and temperature/salinity sensors was installed across the CGFZ between 500 m and the sea floor to measure the mean transport of westward-flowing Iceland-Scotland Overflow Water (ISOW), and investigate the impact of the eastward-flowing North Atlantic Current (NAC) on ISOW transport variability. The 22-month record mean ISOW transport through the CGFZ, -1.7 ± 0.5 Sv (95% confidence interval), is 30% lower than the previously published estimate based on 13 months of current-only measurements, -2.4 Sv ± 1.2 Sv [Saunders, 1994]. The latter mean estimate may have been biased high due to the lack of continuous salinity measurements, although the two estimates are not statistically different due to strong mesoscale variability in both data sets. Empirical Orthogonal Function analysis and maps of satellite-derived absolute dynamic topography show that weak westward ISOW transport events and eastward reversals, are caused by northward meanders of the NAC, with its deep-reaching eastward velocities. These results add to growing evidence that a significant fraction of ISOW exits the Iceland Basin by routes other than the CGFZ.
      PubDate: 2017-08-05T10:20:26.00191-05:0
      DOI: 10.1002/2017JC012698
  • Deriving colored dissolved organic matter absorption coefficient from
           ocean color with a neural quasi-analytical algorithm
    • Authors: Jun Chen; Xianqiang He, Bin Zhou, Delu Pan
      Abstract: The objective of this study is to develop an approach to estimate the gelbstoff absorption coefficient (ag) from remote sensing reflectance (Rrs). This approach includes two components: the inherent optical properties are semi-analytically derived from the Rrs by a neural quasi-analytical algorithm (NQAA), and then the derivations are semi-analytically extended to ag estimations using a band difference approach. This method is then evaluated with the various type of ocean color data including synthetic, field measured, and satellite-observed data. The results show that the method can produce an excellent quantitative agreement between the estimated and known ag in ocean waters with a wide range of optical properties, while significantly reducing the effects of residual error in SeaWiFS Rrs, primarily from the imperfect atmospheric correction algorithm on the retrieval of ag in the clear open oceans. Furthermore, with the application of this new algorithm, the SeaWiFS ag products exhibit more spatially and temporally uniform results than the band ratio approach-based ag retrieval algorithm. These results indicate that the new algorithm is an encouraging approach to process ocean color images for ag retrieval, although a greater number of independent tests with in situ and satellite data are required to further validate and improve this approach.
      PubDate: 2017-08-03T07:46:08.680167-05:
      DOI: 10.1002/2017JC013115
  • Upper ocean cooling and air-sea fluxes under typhoons: A case study
    • Authors: Henry Potter; William M. Drennan, Hans C. Graber
      Abstract: Direct observations of ocean temperatures and air-sea energy exchange underneath three typhoons and a tropical storm encountered in the Philippine Sea during the 2010 Pacific typhoon season are examined. Data are reported from two buoys at 180 km apart with ocean temperatures recorded to 150 m and wind speeds up to 26 m s−1. A detailed examination of the cold wakes is used to determine the mechanisms though which the ocean cools. The result show that net cooling varied between storms by two orders of magnitude, accounting for between 9 and 1000 MJ m−2 of heat loss, and were a result of entrainment, advection, and surface fluxes. In some cases a marked temperature increase below the mixed layer occurred due to entrainment of warm water across the thermocline. Mixed layer temperatures decreases ranged from 0.35 to 1.6°C and found to be well predicted by typhoon translation speed and wind speed. Of the mixed layer heat loss, 12 to 47% could be attributed to enthalpy fluxes, the upper range of which is much greater than previous reports and related to storm intensity. Results are discussed in terms of their relevance to tropical cyclone and climate modeling.
      PubDate: 2017-08-03T07:40:32.953782-05:
      DOI: 10.1002/2017JC012954
  • Nitrogen enrichment and speciation in a coral reef lagoon driven by
           groundwater inputs of bird guano
    • Authors: Ashly McMahon; Isaac R. Santos
      Abstract: While the influence of river inputs on coral reef biogeochemistry has been investigated, there is limited information on nutrient fluxes related to submarine groundwater discharge (SGD). Here, we investigate whether significant saline groundwater-derived nutrient inputs from bird guano drive coral reef photosynthesis and calcification off Heron Island (Great Barrier Reef, Australia). We used multiple experimental approaches including groundwater sampling, beach face transects, and detailed time series observations to assess the dynamics and speciation of groundwater nutrients as they travel across the island and discharge into the coral reef lagoon. Nitrogen speciation shifted from nitrate-dominated groundwater (>90% of total dissolved nitrogen) to a coral reef lagoon dominated by dissolved organic nitrogen (DON; ∼86%). There was a minimum input of nitrate of 2.1 mmol m−2 d−1 into the lagoon from tidally-driven submarine groundwater discharge estimated from a radon mass balance model. An independent approach based on the enrichment of dissolved nutrients during isolation at low tide implied nitrate fluxes of 5.4 mmol m−2 d−1. A correlation was observed between nitrate and daytime net ecosystem production and calcification. We suggest that groundwater nutrients derived from bird guano may offer a significant addition to oligotrophic coral reef lagoons and drive ecosystem productivity and the coastal carbon cycle near Heron Island. The large input of groundwater nutrients in Heron Island may serve as a natural ecological analogue to other coral reefs subject to large nutrient inputs from anthropogenic sources.
      PubDate: 2017-08-03T07:40:26.710949-05:
      DOI: 10.1002/2017JC012929
  • Dissolved Scandium, Yttrium, and Lanthanum in the Surface Waters of the
           North Atlantic: Potential use an indicator of scavenging intensity
    • Authors: C.P. Till; R.U. Shelley, W.M. Landing, K.W. Bruland
      Abstract: Recent work has begun to elucidate the biogeochemical cycling of scandium (Sc) in the open ocean, but so far no surface distribution data has been reported of dissolved Sc, and no basin-scale surface distributions have been reported of yttrium (Y) or lanthanum (La). This work presents basin-wide surface Sc, Y and La data in a section across the North Atlantic subtropical gyre (2011 GEOTRACES GA03) and investigates the potential utility of these distributions. This work uses dissolved and aerosol concentration data for La and Sc to estimate their surface ocean residence times in both the center of the oligotrophic gyre and near the African coastline. This work additionally shows that the surface distribution of Sc in the North Atlantic correlates with the shape of the gyre as inferred by isotherm depth, with lower Sc concentrations at the gyre boundaries. This pattern suggests that Sc could be drawn down by the elevated particle flux at the gyre boundaries. In this case, Sc removal could be used as an indicator of scavenging intensity. In order to account for variable input of Sc to the surface ocean, we propose normalizing the Sc distribution to that of Y or La, which are much less particle reactive and are input via dust to the surface North Atlantic in constant ratios with Sc. Such normalization improves the correlation with isotherm depth. We propose that the variations in dissolved Y/Sc and La/Sc ratios may be due to preferential Sc scavenging, and could therefore indicate scavenging intensity.
      PubDate: 2017-07-27T10:30:45.82785-05:0
      DOI: 10.1002/2017JC012696
  • Structure, characteristics and simulation of monsoon low-pressure systems
           in CFSv2 coupled model
    • Authors: Ankur Srivastava; Suryachandra A. Rao, D. Nagarjuna Rao, Gibies George, Maheswar Pradhan
      Abstract: Indian Summer Monsoon (ISM) synoptic scale systems (low-pressure systems, LPS) are known to produce increased rainfall over central India (CI). Fidelity of the Climate Forecast System version 2 (CFSv2) at simulating the LPS and their characteristics is evaluated in this study using a feature tracking algorithm. The model is able to reproduce the clustering of LPS by monsoon intra-seasonal oscillations and the associated precipitation over eastern-central India. It is found that mean biases in circulation and moisture stem from cold sea surface temperature (SST) bias in the model which results in weak LPS linked rainfall events over central India. Two sensitivity experiments were carried out to study the effect of coupled dynamics of tropical basins on LPS. Suppression of active dynamics of the tropical Indian Ocean in CFSv2 causes a reduction in cold SST bias and enhanced cyclogenesis in the northern Bay of Bengal. The reduced low-level anti-cyclonic bias and enhanced moisture availability result in a better simulation of LPS structure, and associated precipitation over CI. Suppression of active ocean dynamics in tropical Pacific Ocean causes a perennial El-Niño type bias which restricts LPS propagation over the Indian landmass, possibly due to time-mean subsidence induced by remote El-Niño forcing. Sensitivity experiments indicate the need for improvements in the representation of tropical Indian Ocean coupled dynamics as well as convective parameterization schemes in the model for subsequent improvements in the simulation of ISM at various time scales.
      PubDate: 2017-07-27T10:30:38.037838-05:
      DOI: 10.1002/2016JC012322
  • Annual nitrate drawdown observed by SOCCOM profiling floats and the
           relationship to annual net community production
    • Authors: Kenneth S. Johnson; Joshua N. Plant, John P. Dunne, Lynne D. Talley, Jorge L. Sarmiento
      Abstract: Annual nitrate cycles have been measured throughout the pelagic waters of the Southern Ocean, including regions with seasonal ice cover and southern hemisphere subtropical zones. Vertically resolved nitrate measurements were made using in situ ultraviolet spectrophotometer (ISUS) and submersible ultraviolet nitrate analyzer (SUNA) optical nitrate sensors deployed on profiling floats. Thirty-one floats returned forty complete annual cycles. The mean nitrate profile from the month with the highest winter nitrate minus the mean profile from the month with the lowest nitrate yields the annual nitrate drawdown. This quantity was integrated to 200 m depth and converted to carbon using the Redfield Ratio to estimate Annual Net Community Production (ANCP) throughout the Southern Ocean south of 30° S. A well-defined, zonal mean distribution is found with highest values (3 to 4 mol C m−2 y−1) from 40 to 50° S. Lowest values are found in the subtropics and in the seasonal ice zone. The area weighted mean was 2.9 mol C m−2 y−1 for all regions south of 40° S. Cumulative ANCP south of 50° S is 1.3 Pg C y−1. This represents about 13% of global ANCP in about 14% of the global ocean area.
      PubDate: 2017-07-26T11:40:05.535305-05:
      DOI: 10.1002/2017JC012839
  • Trophic pathways of phytoplankton size classes through the zooplankton
           food-web over the spring transition period in the north-west Mediterranean
    • Authors: Brian P. V. Hunt; François Carlotti, Katty Donoso, Marc Pagano, Fabrizio D'Ortenzio, Vincent Taillandier, Pascal Conan
      Abstract: Knowledge of the relative contributions of phytoplankton size classes to zooplankton biomass is necessary to understand food-web functioning and response to climate change. During the DEep Water formation EXperiment (DEWEX), conducted in the north-west Mediterranean Sea in winter (February) and spring (April) of 2013, we investigated phytoplankton-zooplankton trophic links in contrasting oligotrophic and eutrophic conditions. Size fractionated particulate matter (pico, nano and micro POM) and zooplankton (64 to > 4000 μm) composition and carbon and nitrogen stable isotope ratios were measured inside and outside of the nutrient rich deep convection zone in the central Liguro-Provencal basin. In winter, phytoplankton biomass was low (0.28 mg.m−3) and evenly spread among pico, nano and micro phytoplankton. Using an isotope mixing model we estimated average contributions to zooplankton biomass by pico, nano and micro POM of 28, 59 and 15% respectively. In spring, the nutrient poor region outside of the convection zone had low phytoplankton biomass (0.58 mg.m−3) and was dominated by pico/nano phytoplankton. Estimated average contributions to zooplankton biomass by pico, nano and micro POM were 64, 28 and 10% respectively, although the model did not differentiate well between pico and nano POM in this region. In the deep convection zone, spring phytoplankton biomass was high (1.34 mg.m−3) and dominated by micro/nano phytoplankton. Estimated average contributions to zooplankton biomass by pico, nano and micro POM were 42, 42 and 20% respectively, indicating that a large part of the microphytoplankton biomass may have remained ungrazed.
      PubDate: 2017-07-26T10:30:40.700023-05:
      DOI: 10.1002/2016JC012658
  • Heartbeat of the Southern Oscillation explains ENSO climatic resonances
    • Authors: John T Bruun; J. Icarus Allen, Timothy J Smyth
      Abstract: The El Niño–Southern Oscillation (ENSO) non-linear oscillator phenomenon has a far reaching influence on the climate and human activities. The upto 10 year quasi-period cycle of the El Niño and subsequent La Niña is known to be dominated in the tropics by non-linear physical interaction of wind with the equatorial wave-guide in the Pacific. Long term cyclic phenomena do not feature in the current theory of the ENSO process. We update the theory by assessing low (> 10 years) and high (< 10 years) frequency coupling using evidence across tropical, extratropical and Pacific basin scales. We analyse observations and model simulations with a highly accurate method called Dominant Frequency State Analysis (DFSA) to provide evidence of stable ENSO features. The observational datasets of the Southern Oscillation Index (SOI), North Pacific Index Anomaly and ENSO Sea Surface Temperature Anomaly, as well as a theoretical model all confirm the existence of long and short term climatic cycles of the ENSO process with resonance frequencies of {2.5, 3.8, 5, 12 to 14, 61 to 75, 180} years. This fundamental result shows long and short term signal coupling with mode locking across the dominant ENSO dynamics. These dominant oscillation frequency dynamics, defined as ENSO frequency states, contain a stable attractor with three frequencies in resonance allowing us to coin the term Heartbeat of the Southern Oscillation due to its characteristic shape. We predict future ENSO states based on a stable hysteresis scenario of short and long term ENSO oscillations over the next century.
      PubDate: 2017-07-26T10:30:34.275381-05:
      DOI: 10.1002/2017JC012892
  • Coastal ocean circulation during Hurricane Sandy
    • Authors: Travis Miles; Greg Seroka, Scott Glenn
      Abstract: Hurricane Sandy (2012) was the second costliest tropical cyclone to impact the United States and resulted in numerous lives lost due to its high winds and catastrophic storm surges. Despite its impacts little research has been performed on the circulation on the continental shelf as Sandy made landfall. In this study integrated ocean observing assets and regional ocean modeling were used to investigate the coastal ocean response to Sandy's large wind field. Sandy's unique cross-shelf storm track, large size, and slow speed resulted in along-shelf wind stress over the coastal ocean for nearly 48 hours before the eye made landfall in southern New Jersey. Over the first inertial period (∼18 hours) this along-shelf wind stress drove onshore flow in the surface of the stratified continental shelf and initiated a two-layer downwelling circulation. During the remaining storm forcing period a bottom Ekman layer developed and the bottom Cold Pool was rapidly advected offshore ∼70 kilometers. This offshore advection removed the bottom Cold Pool from the majority of the shallow continental shelf and limited ahead-of-eye-center sea surface temperature (SST) cooling, which has been observed in previous storms on the MAB such as Hurricane Irene (2011). This cross-shelf advective process has not been observed previously on continental shelves during tropical cyclones and highlights the need for combined ocean observing systems and regional modeling in order to further understand the range of coastal ocean responses to tropical cyclones.
      PubDate: 2017-07-26T10:21:02.109276-05:
      DOI: 10.1002/2017JC013031
  • Distributions, sources and transformations of dissolved and particulate
           iron on the Ross Sea continental shelf during summer
    • Authors: Chris M. Marsay; Pamela M. Barrett, Dennis J. McGillicuddy, Peter N. Sedwick
      Abstract: We report water column dissolved iron (dFe) and particulate iron (pFe) concentrations from fifty stations sampled across the Ross Sea during austral summer (January-February) of 2012. Concentrations of dFe and pFe were measured in each of the major Ross Sea water masses, including the Ice Shelf Water and off-shelf Circumpolar Deep Water. Despite significant lateral variations in hydrography, macronutrient depletion and primary productivity across several different regions on the continental shelf, dFe concentrations were consistently low (
      PubDate: 2017-07-26T10:20:53.71886-05:0
      DOI: 10.1002/2017JC013068
  • Predicting the consequence of natural and chemical dispersion for oil
           slick size over time
    • Authors: Marieke Zeinstra-Helfrich; Wierd Koops, Albertinka J. Murk
      Abstract: Application of dispersants aims to enhance the natural dispersion process in order to reduce the size of the slick and the amount of oil at the surface. This study presents an approach for modelling the development of the surface oil slick as a function of the wind speed, oil viscosity and dispersant application. We modelled the oil slick mass distribution across a transect through the slick over time taking into account the continuous entrainment of oil, resurfacing process of the different oil droplet size classes and horizontal transport. Outcomes show distinctively different oil slick features, depending on how favorable conditions are for dispersion. A large comet shaped slick is formed in the case of sub-optimal dispersion. Optimal dispersion yields a small surface oil slick, with a large mass of oil suspended. The benefit of dispersants is limited to in conditions with sub-optimal natural dispersion, with the exception of extremely unfavorable conditions in which the slick size would be increased.The oil slick length, fraction of oil still floating, lifetime of the slick and wind drift are highly influenced by wind speed and related mixing conditions, and to a lesser extent by oil properties. In the newly defined ‘Dispersability Factor' (DF) the oil slick properties and environmental conditions can be combined into one value that correlates with the simulation outcomes and therefore can be used as an indicator of favorability of natural dispersion and likelihood of added value of chemical dispersion.
      PubDate: 2017-07-26T10:20:26.873245-05:
      DOI: 10.1002/2017JC012789
  • Physical and biological characteristics of the winter-summer transition in
           the Central Red Sea
    • Authors: Nikolaos D. Zarokanellos; Vassilis P. Papadopoulos, Sarantis S. Sofianos, Burton H. Jones
      Abstract: The Central Red Sea (CRS) lies between two distinct hydrographic and atmospheric regimes. In the southern Red Sea, seasonal monsoon reversal regulates the exchange of water between the Red Sea and the Indian Ocean. In the northern Red Sea intermediate and occasionally deep water are formed during winter to sustain the basin's overturning circulation. Highly variable mesoscale eddies and the northward flowing eastern boundary current (EBC) determine the physical and biogeochemical characteristics of the CRS. Ship-based and glider observations in the CRS between March and June 2013 capture key features of the transition from winter to summer and depict the impact of the eddy activity on the EBC flow. Less saline and relatively warmer water of Indian Ocean origin reaches the CRS via the EBC. Initially, an anticyclonic eddy with diameter of 140km penetrating to 150m depth with maximum velocities up to 30-35 cm s−1 prevails in the CRS. This anticyclonic eddy appears to block or at least redirect the northward flow of the EBC. Dissipation of the eddy permits the near-coastal, northward flow of the EBC and gives place to a smaller cyclonic eddy with a diameter of about 50km penetrating to 200m depth. By the end of May, as the northerly winds become stronger and persistent throughout the basin, characteristic of the summer southwest monsoon wind regime, the EBC and its associated lower salinity water became less evident, replaced by the saltier surface water that characterizes the onset of the summer stratification in the CRS.
      PubDate: 2017-07-24T17:08:24.952901-05:
      DOI: 10.1002/2017JC012882
  • Deep-water dynamics and mixing processes during a major inflow event in
           the central Baltic Sea
    • Authors: Peter L. Holtermann; Ralf Prien, Michael Naumann, Volker Mohrholz, Lars Umlauf
      Abstract: Intrusions of large amounts of dense and oxygen-rich waters during so-called Major Baltic Inflows (MBIs) form an essential component of the Baltic Sea overturning circulation and deep-water ventilation. Despite their importance, however, detailed observations of the processes occuring in the central basins during an MBI are virtually lacking. Here, data from a long-term deployment of an autonomous profiling platform located in the center of one of the main basins are presented, providing the first direct and detailed view of the deep-water modifications and dynamics induced by one of the largest MBIs ever recorded (MBI 2014/2015). Approximately 21 Gmol of oxygen were imported during three distinct inflow phases with an unexpectedly large contribution of oxic intrusions at intermediate depth. Oxygen consumption rates during the stagnation period immediately following the inflow phase was found to be 87 g m−2 yr−1 with a dominant contribution of sedimentary oxygen demand. The most energetic deep-water processes (topographic and near-inertial waves) were only marginally affected by the inflow; however, sub-inertial energy levels associated with intrusions and eddies were strongly enhanced. Turbulence microstructure data revealed that the deep interior regions remain essentially non-turbulent even during the energetic conditions of an MBI, emphasizing the importance of boundary mixing. Warm intrusions frequently showed a temperature fine-structure with vertical scales of the order of 0.1∼m, without any signs of active turbulence. At the upper flanks of these intrusions double-diffusive staircases were often found to develop, suggesting an important alternative mixing process during inflow conditions.
      PubDate: 2017-07-24T17:07:44.268661-05:
      DOI: 10.1002/2017JC013050
  • The role of wind gusts in upper ocean diurnal variability
    • Authors: Donata Giglio; Sarah T. Gille, Aneesh C. Subramanian, San Nugyen
      Abstract: Upper ocean processes play a key role in air-sea coupling, with variability on both short and long timescales. The diurnal cycle associated with diurnal solar insolation and night-time cooling, may act, along with stochastic wind variability, on upper ocean temperatures and stratification resulting in a diurnal warm layer and a nonlinear rectified effect on longer timescales. This study describes diurnal changes in upper ocean temperature for a location in the equatorial Indian Ocean, using observations from the Dynamics of the Madden-Julian Oscillation field campaign, a high vertical resolution 1-D process model, and a diurnal cycling scheme [Large and Caron, 2015]. Solar forcing is the main driver of diurnal variability in upper ocean temperature and stratification. Yet, except during nighttime convection, winds with variability on the order of hours (here referred to as “wind gusts”) regulate how fast surface water is mixed to greater depths when daily mean winds are weak. Wind gusts are much stronger than diurnal winds. Even using stochastic wind gusts but no diurnal winds as input in a 1-D process model yields an estimate of diurnal temperature that compares well with observations.A new version of the Large and Caron [2015] scheme (LC2015) provides an estimate of upper ocean diurnal temperature that is consistent with observations. LC2015 has the advantage of being suitable for implementation in a climate model, with the goal to improve SST estimates, hence the simulated heat flux at the air-sea interface. Yet LC2015 is not very sensitive to the inclusion or omission of the high-frequency component of the wind.
      PubDate: 2017-07-24T17:07:33.301736-05:
      DOI: 10.1002/2017JC012794
  • Testing Munk's hypothesis for submesoscale eddy generation using
           observations in the North Atlantic
    • Authors: Christian E. Buckingham; Zammath Khaleel, Ayah Lazar, Adrian P. Martin, John T. Allen, Alberto C. Naveira Garabato, Andrew F. Thompson, Clément Vic
      Abstract: A high-resolution satellite image that reveals a train of coherent, submesoscale (6-km) vortices along the edge of an ocean front is examined in concert with hydrographic measurements in an effort to understand formation mechanisms of the submesoscale eddies. The infrared satellite image consists of ocean surface temperatures at ∼390-m resolution over the mid-latitude North Atlantic (48.69°N, 16.19°W). Concomitant altimetric observations coupled with regular spacing of the eddies suggests the eddies result from mesoscale stirring, filamentation and subsequent frontal instability. While horizontal shear or barotropic instability (BTI) is one mechanism for generating such eddies (Munk's hypothesis), we conclude from linear theory coupled with the in situ data that mixed layer or submesoscale baroclinic instability (BCI) is a more plausible explanation for the observed submesoscale vortices. Here, we assume that the frontal disturbance remains in its linear growth stage and is accurately described by linear dynamics. This result likely has greater applicability to the open ocean–i.e., regions where the gradient Rossby number is reduced relative to its value along coasts and within strong current systems. Given that such waters comprise an appreciable percentage of the ocean surface and that energy and buoyancy fluxes differ under BTI and BCI, this result has wider implications for open-ocean energy/buoyancy budgets and parameterizations within ocean general circulation models. In summary, this work provides rare observational evidence of submesoscale eddy generation by BCI in the open ocean.
      PubDate: 2017-07-24T15:40:27.521455-05:
      DOI: 10.1002/2017JC012910
  • Subglacial discharge-driven renewal of tidewater glacier fjords
    • Authors: Dustin Carroll; David A. Sutherland, Emily L. Shroyer, Jonathan D. Nash, Ginny A. Catania, Leigh A. Stearns
      Abstract: The classic model of fjord renewal is complicated by tidewater glacier fjords, where submarine melt and subglacial discharge provide substantial buoyancy forcing at depth. Here we use a suite of idealized, high-resolution numerical ocean simulations to investigate how fjord circulation driven by subglacial plumes, tides, and wind stress depends on fjord width, grounding line depth, and sill height. We find that the depth of the grounding line compared to the sill is a primary control on plume-driven renewal of basin waters. In wide fjords the plume exhibits strong lateral recirculation, increasing the dilution and residence time of glacially-modified waters. Rapid drawdown of basin waters by the subglacial plume in narrow fjords allows for shelf waters to cascade deep into the basin; wide fjords result in a thin, boundary current of shelf waters that flow toward the terminus slightly below sill depth. Wind forcing amplifies the plume-driven exchange flow; however, wind-induced vertical mixing is limited to near-surface waters. Tidal mixing over the sill increases in-fjord transport of deep shelf waters and erodes basin stratification above the sill depth. These results underscore the first-order importances of fjord-glacier geometry in controlling circulation in tidewater glacier fjords and, thus, ocean heat transport to the ice.
      PubDate: 2017-07-24T15:39:22.002367-05:
      DOI: 10.1002/2017JC012962
  • Effect of potential vorticity flux on the circulation in the South China
    • Authors: Yaohua Zhu; Junchuan Sun, Yonggang Wang, Zexun Wei, Dezhou Yang, Tangdong Qu
      Abstract: This study analyzes temperature and salinity products from the U.S. Navy Generalized Digital Environment Model. To avoid the fictitious assumption of no-motion reference level, a P-vector inverse method is employed to derive geostrophic velocity. Line integral of geostrophic velocity shows evidence for the existence of a sandwiched circulation in the South China Sea (SCS), i.e., cyclonic circulation in the subsurface and deep layers and anticyclonic in the intermediate layer. To reveal the factors responsible for the sandwiched circulation, we derive the potential vorticity equation based on a four-and-a-half-layer quasi-geostrophic model and apply theoretical potential vorticity constraint to density layers. The result shows that the sandwiched circulation is largely induced by planetary potential vorticity flux through lateral boundaries, mainly the Luzon Strait. This dynamical mechanism lies in the fact that the net potential vorticity inflow in the subsurface and deep layers leads to a positive layer-average vorticity in the SCS basin, yielding vortex stretching and a cyclonic basin-wide circulation. On the contrary, the net potential vorticity outflow in the intermediate layer induces a negative layer-average vorticity, generating an anticyclonic basin-wide circulation in the SCS. Furthermore, by illustrating different consequence from depth/density layers, we clarify that density layers are essential for applying theoretical potential vorticity constraint to the isolated deep SCS basin.
      PubDate: 2017-07-24T15:38:06.146781-05:
      DOI: 10.1002/2016JC012375
  • Seawater-groundwater mixing in and fluxes from coastal sediment overlying
           discrete fresh seepage zones: A modeling study
    • Authors: Peter B. Zamora; M. Bayani Cardenas, Ronald Lloren, Fernando P. Siringan
      Abstract: Submarine fresh groundwater discharging from discrete zones such as conduits overlain by thick sediment remains poorly documented and understood despite common anecdotal accounts of it. We analyzed this phenomenon by a suite of variable-density, variably-saturated groundwater flow simulations guided by field studies. The field observations included point flux and salinity measurements using seepage meters spread across the intertidal and the subtidal zones. The discretely measured seepage fluxes in the subtidal region were as high and the salinity was as fresh as those from the intertidal zone. Both fluxes and salinities varied with tides. Two-dimensional simulations of the idealized beach-ocean vertical section with discrete freshwater springs at the base showed the development of seawater recirculation cells along the edge of freshwater discharge plumes emanating from the outlets, causing mixing. Brackish water discharges at the sediment-water interface above where the plume mixes with the recirculating seawater. Sensitivity analyses showed that stronger terrestrial fresh groundwater flow increases the freshwater plume size but does not affect the mixing zone width. Tidal oscillations and a dynamic fresh groundwater flow widened the mixing zones and increased porewater flux across the sediment-water interface. Sediment thickness had a minor effect on the width of both the freshwater plume and its surrounding mixing zone. The subtidal freshwater plume and mixing zone likely represent a unique but potentially ubiquitous setting which hosts dramatic ecological and chemical gradients. Their local biogeochemical niche and coastal scale ecosystem impacts will need to be considered in investigations of coastlines.
      PubDate: 2017-07-24T15:38:02.45886-05:0
      DOI: 10.1002/2017JC012769
  • Bridging the gap between cyclone wind and wave by C-band SAR measurements
    • Authors: Weizeng Shao; Xiaofeng Li, Paul Hwang, Biao Zhang, Xiaofeng Yang
      Abstract: Active microwave remote sensing of hurricane-strength wind is a challenging task due to the saturation of col-polarization backscattering signal under such condition. Here, we take advantage of the fact that wind-sea wave growth does not saturate at high wind and the intrinsic relationship among wind-wave triplets (sea surface wind speed, significant wave height, and peak wave period) within a tropical storm to derive the wind speed. Three Sentinel-1 (S-1) and nine RADARSAT-2 (R-2) C-band synthetic aperture radar (SAR) images acquired between 20 and 40 m/s winds are collected in this study. The S-1 and R-2 SAR-derived winds are compared with those measured by coincident National Oceanic and Atmospheric Administration Stepped-Frequency Microwave Radiometer (SFMR) and simulated by Symmetric Hurricane Estimates for Wind (SHEW) model. Validations against SFMR winds for S-1 show Root Mean Square Error (RMSE) of 1.7 m/s with a 0.2 m/s bias at the left-side of cyclone centers and RMSE of 2.9 m/s RMSE with a 0.56 bias at the back-side of cyclone centers. R-2 SAR-derived winds against SHEW model results show a RMSE of 2.4 m/s with a 0.3 m/s bias and 2.6 m/s with a 0.35 m/s bias at the right-side and the left-side of cyclone centers, while the RMSE is 3.9 m/s with a 0.1 m/s bias at the back-side of cyclone centers. The wave-information-based wind retrieval method works well at the left-side and right-side, but less accurately at the back-side of a tropical storm when wind-wave and swell are mixed.
      PubDate: 2017-07-24T15:37:23.095462-05:
      DOI: 10.1002/2017JC012908
  • Exploring the “solid turbulence” of sea ice dynamics down to
           unprecedented small scales
    • Authors: Jérôme Weiss
      Abstract: Sea ice decline is an essential player, as well as an emblematic signature, of global warming. Besides sea surface temperature rising, sea ice drift and deformation play a major role on the observed negative mass balance, thus calling for a deeper understanding of sea ice mechanics. Over the last decades, drifters and satellite data allowed a detailed characterization of sea ice dynamics, however limited by relatively coarse space (∼10 km) and time (∼ day) resolutions. A new work [Oikkonen et al., 2017] allows bridging the gap between these large scales and fundamental ice physics and mechanics.
      PubDate: 2017-07-24T15:37:16.605473-05:
      DOI: 10.1002/2017JC013236
  • Circulation in the northwest Laptev Sea in the eastern Arctic Ocean:
           Crossroads between Siberian river water, Atlantic water and polynya-formed
           dense water
    • Authors: Markus A. Janout; Jens Hölemann, Leonid Timokhov, Oliver Gutjahr, Günther Heinemann
      Abstract: This paper investigates new observations from the poorly understood region between the Kara and Laptev Seas in the Eastern Arctic Ocean. We discuss relevant circulation features including riverine freshwater, Atlantic-derived water, and polynya-formed dense water, emphasize Vilkitsky Strait (VS) as an important Kara Sea gateway, and analyze the role of the adjacent ∼250 km-long submarine Vilkitsky Trough (VT) for the Arctic boundary current. Expeditions in 2013 and 2014 operated closely-spaced hydrographic transects and one year-long oceanographic mooring near VT's southern slope, and found persistent annually averaged flow of 0.2 m s−1 toward the Nansen Basin. The flow is nearly barotropic from winter through early summer and becomes surface-intensified with maximum velocities of 0.35 m s−1 from August-October. Thermal wind shear is maximal above the southern flank at ∼30 m depth, in agreement with basinward flow above VT's southern slope. The sub-surface features a steep front separating warm (-0.5°C) Atlantic-derived waters in central VT from cold (
      PubDate: 2017-07-22T11:11:02.269431-05:
      DOI: 10.1002/2017JC013159
  • Dynamical ocean response to projected changes of the global water cycle
    • Authors: Xin Liu; Armin Köhl, Detlef Stammer
      Abstract: Over the next century substantial changes will occur in the ocean as a consequence of an accelerated global hydrological cycle and the associated net surface freshwater flux change is projected to result from global warming. This paper is concerned with the dynamical response to the associated surface volume flux anomalies. Based on ocean model runs driven by RCP8.5 surface freshwater flux anomalies over the period 2081-2100 relative to 1986-2005, we show that the adjustment of the circulation involves a barotropic circulation response as predicted from the Goldsbrough-Stommel theory. The corresponding barotropic circulation intensifies by approximately 20% with a stronger intensification of about 50% in the Southern Ocean, comparing to the present-day Goldsbrough-Stommel Circulation. The barotropic circulation anomaly induced by intensified freshwater flux reaches to 0.6 Sv in the Antarctic Circumpolar Current region. The adjustment also involves changes in the meridional overturning circulation mirroring the basin-wide averages of changes in the convergence and divergence of the mass transport driven by the surface volume flux. The subsequent pathways of fresh water match with the spreading of volume flux in the shallow cells but diverge substantially with depth. Associated with changes of the flow field are the changes in meridional heat and freshwater transports. Changes in the circulation also lead to a redistribution of temperature and salinity from which a significant contribution result in form of regional steric sea level changes. These changes are of the order of 0.5 cm and can be largely attributed to the displacement of the isopycnals.
      PubDate: 2017-07-22T11:10:58.879149-05:
      DOI: 10.1002/2017JC013061
  • Seasonal dynamics of particulate organic matter and its response to
           flooding in the Pearl River Estuary, China, revealed by stable isotope
           (δ13C and δ15N) analyses
    • Authors: Feng Ye; Wei Guo, Zhen Shi, Guodong Jia, Gangjian Wei
      Abstract: Nine cruises were conducted on a seasonal basis from 2013 to 2015 to investigate the spatial distribution and seasonal variability of δ13C and δ15N in particulate organic matter (POM), and its response to flooding in the Pearl River Estuary (PRE), south China. Our study reveals highly variable isotope ratios between seasons in this subtropical estuary, following seasonal climatic and hydrological cycles. Wet seasons had more isotopically depleted δ13C values, indicating the dominance of terrestrial and freshwater algae POM, whereas the contribution from marine phytoplankton (16%–59%) was higher during the dry seasons. In contrast, δ15N exhibited a sharp increase (up to 17.6‰) at low salinities (0–5) during high flow seasons. This was consistent with high NO3− concentrations, reflecting phytoplankton and bacteria assimilation of δ15N enriched-NO3− as well as notable isotope fractionation during microbial mineralization. There was little annual variability in δ13C over the two-year period; however, particulate nitrogen (PN) exhibited lower concentrations but more enriched isotope values in 2015 than in 2014. This can be best explained by temperature-modulated biological processing of particulate organic nitrogen, partially due to different biogeochemical responses during normal (2014) and strong El Niño (2015) years. After flooding in June 2015, terrestrial organic matter and freshwater phytoplankton were the major components of POM within the estuary and shelf areas, whereas marine phytoplankton was the dominant component in the adjacent coastal waters with mid-salinities (10 
      PubDate: 2017-07-22T11:10:55.941124-05:
      DOI: 10.1002/2017JC012931
  • Changes in water properties and flow regime on the continental shelf off
           the Adélie/George V Land coast, East Antarctica, after glacier tongue
    • Authors: S. Aoki; R. Kobayashi, S. R. Rintoul, T. Tamura, K. Kusahara
      Abstract: Oceanic changes before and after the relocation of iceberg B9B and calving of the Mertz Glacier Tongue (MGT) in February 2010 are examined on the continental shelf off the Adélie Land/George V Land coast, East Antarctica. Summer hydrographic observations, including stable oxygen isotope ratio (δ18O), in 2001/08 and 2011/15 and results of a numerical model are used. Along the western flank of the MGT, temperature decreased between 2001 and 2015 for most of the water column in the Adélie Depression. δ18O generally decreased, especially at the MGT draft depths on the northern side. West of the MGT, temperature, salinity, and δ18O decreased in the intermediate layer. East of the MGT, in contrast, temperature increased between 2001 and 2011 at intermediate depths, salinity increased in the intermediate and deep layers, and δ18O slightly decreased in the deep layer but did not change much around 300 dbar. The numerical experiment exhibits a change in ocean circulation, revealing an increase in modified Circumpolar Deep Water (mCDW) inflow in the east and a decrease in the west. The contrasting changes in mCDW intrusion are consistent between the observations and numerical model, and are indicative of the effect of removal of the ice barriers. The contrast is overlain by overall decreases in salinity and δ18O, which suggests an increase in the continental meltwater fraction of 5–20% and might reveal a wide-ranging influence from West Antarctica. The oxygen isotope ratio is, hence, effective in monitoring the increase in continental melt over the Antarctic shelf.
      PubDate: 2017-07-22T11:10:41.175728-05:
      DOI: 10.1002/2017JC012925
  • Runup of granular landslide generated tsunamis on planar coasts and
           conical islands
    • Authors: Brian C. McFall; Hermann M. Fritz
      Abstract: Large-scale physical model experiments of tsunamis generated by granular landslides and volcanic flank collapses are conducted to study the wave runup on both the hill slope laterally adjacent to the landslide and an opposing hill slope. A pneumatic landslide tsunami generator was deployed on planar and convex conical hill slopes to simulate deformable landslides with various geometries and kinematics. On the landslide hill slope, maximum runup and rundown were observed in the landslide impact region followed by adjacent second maxima after the lateral waves were fully formed. The runup and rundown decayed asymptotically from the second maxima. In the conical island scenario, a localized runup amplification was measured on the lee side of the island. Outside the landslide impact region, the effects of the landslide granulometry on the lateral wave runup are minimal. The lateral wave runup on the planar hill slope was generally larger than on the convex conical hill slope outside the landslide impact region. The convex conical hill slope traps less lateral wave energy. The zeroth mode of the edge wave dispersion relation matched the first and second lateral waves on the planar hill slope and the first wave on the convex conical hill slope. Predictive equations for the laterally propagating wave characteristics are derived and a method to predict the runup on an opposing hill slope is presented. The predictive wave and runup equations are benchmarked against the 2007 landslide generated tsunami in Chehalis Lake, British Columbia, Canada.
      PubDate: 2017-07-21T11:43:29.533925-05:
      DOI: 10.1002/2017JC012832
  • Observation of oxygen ventilation into deep waters through targeted
           deployment of multiple Argo-O2 floats in the north-western Mediterranean
           Sea in 2013
    • Authors: L. Coppola; L. Prieur, I. Taupier-Letage, C. Estournel, P. Testor, D. Lefevre, S. Belamari, S. LeReste, V. Taillandier
      Abstract: During the winter 2013, an intense observation and monitoring was performed in the north-western Mediterranean Sea to study deep water formation process that drives thermohaline circulation and biogeochemical processes (HYMEX SOP2 and DEWEX projects). To observe intensively and continuously the impact of deep convection on oxygen (O2) ventilation, an observation strategy was based on the enhancement of the Argo-O2 floats to monitor the offshore dense water formation area (DWF) in the Gulf of Lion prior to and at the end of the convective period (December 2012 to April 2013). The intense O2 measurements performed through shipborne CTD casts and Argo-O2 floats deployment revealed an O2 inventory rapidly impacted by mixed layer (ML) deepening on the month scale. The open-sea convection in winter 2013 ventilated the deep waters from mid-February to the end of May 2013. The newly ventilated dense water volume, based on an Apparent Oxygen Utilization (AOU) threshold, was estimated to be about 1.5 1013 m3 during the DWF episode, increasing the deep O2 concentrations from 196 to 205 µmol kg−1 in the north-western basin.
      PubDate: 2017-07-18T11:05:39.275542-05:
      DOI: 10.1002/2016JC012594
  • Seasonal cycle of hydrography on the Eastern Shelf of the Filchner Trough,
           Weddell Sea, Antarctica
    • Authors: S. Ryan; T. Hattermann, E. Darelius, M. Schröder
      Abstract: New two-year long records from three moorings, located at 76°S along the eastern flank and shelf of the Filchner Trough, give insight in the seasonal cycle of hydrography to a region where Modified Warm Deep Water (MWDW) enters the southern Weddell Sea continental shelf, possibly reaching the Filchner Ronne Ice Shelf, the biggest ice shelf (by volume) in Antarctica. A persistent northward flow of Ice Shelf Water (ISW) is found along the slope of the trough at 600 m depth, while the data on the shelf indicate a seasonal cycle, characterized by four phases. A distinct warm inflow period (separated in two phases), with maximum temperatures of −1°C, appears to be related to the seasonal heaving of the Antarctic Slope Front thermocline along the continental shelf break further north and a seasonal extension of the ISW layer onto the Eastern Shelf. The density gradients between the ISW in the trough and the MWDW on the adjacent shelf drive the southward flow during these phases. A flow reversal is found in winter, ceasing the southward flow along the eastern flank of the trough. Weaker density gradients between the trough and the shelf during winter allow a westward flow, partly driven by a N-S density gradient, existing across the Eastern Shelf during this time. From spring through to summer the ISW layer in the trough extends onto the eastern shelf where it occupies the bottom layer at our moorings and it is associated with northward flow.
      PubDate: 2017-07-15T03:20:47.385037-05:
      DOI: 10.1002/2017JC012916
  • Understanding the spatial variation of sea level rise in the North Sea
           using satellite altimetry
    • Authors: Paul Sterlini; Dewi Le Bars, Hylke de Vries, Nina Ridder
      Abstract: This paper examines the spatial variation of sea surface height trends in the North Sea Basin as seen by satellite altimetry and assesses its underlying causes. Changes in the potential temperature and salinity of the North Sea are transposed into corresponding changes in sea surface height and regional anomalies of linear sea level trend calculated. The same is carried out for the meteorological processes which act on the sea surface. The steric and meteorological regional sea level rise anomalies are summed with those from contributions from land ice and compared against the values seen by satellite altimetry over the period 1993 - 2014. Results show that there is good agreement between the observations and the reconstruction. The local meteorological contribution appears to be most important in describing regional variation in linear sea level rise and is reinforced with a local halosteric contribution which shows a similar spatial pattern.
      PubDate: 2017-07-15T03:20:31.042185-05:
      DOI: 10.1002/2017JC012907
  • Modulation of frontogenetic plankton production along a meandering jet by
           zonal wind forcing: An application to the Alboran Sea
    • Authors: Temel Oguz; Baptiste Mourre, Joaquin Tintore
      Abstract: We present a coupled physical-biological modeling study to elucidate the changes in ageostrophic frontal dynamics and the frontogenetic plankton production characteristics of a meandering jet under the impacts of successive westerly/easterly wind events combined with seasonal variations in the upstream transport and buoyancy flux characteristics of the jet, using a case study for the Alboran Sea (Western Mediterranean). Their nonlinear coupling is shown to result in different forms of physical and biological characteristics of the background jet structure that follows a meandering path around two anticyclonic gyres in the western and eastern basins and a cyclonic eddy in between. The westerly, downfront wind events broaden the jet, and result in stronger cross-frontal density contrast and intensify ageostrophic cross-frontal secondary circulation. Thus, they improve the frontogenetic plankton production with respect to the no-wind case. They also support higher production along the northern coast in response to wind-induced coastal upwelling and spreading of resulting nutrient-rich, productive water by mesoscale stirring. These features weaken gradually as the jet transport reduces. In contrast, stronger and longer-lasting easterlies during the reduced jet transport phase weaken the currents and frontal density structure, change the circular Western Alboran Gyre to an elongated form, and shift the main axis of the jet towards the southern basin. Then, frontogenesis fails to contribute to phytoplankton production that becomes limited to the eddy pumping within cyclones. Apart from the frontogenetic production, eddy pumping, mesoscale stirring, and diapycnal mixing of nutrients support intermittent and localized phytoplankton patches over the basin.
      PubDate: 2017-07-13T03:59:40.489082-05:
      DOI: 10.1002/2017JC012866
  • Interannual variability of the evaporation duct over the South China Sea
           and its relations with regional evaporation
    • Authors: Kunde Yang; Qi Zhang, Yang Shi
      Abstract: The interannual variability of the evaporation duct over the South China Sea is investigated during the boreal winter and summer seasons using datasets from the National Centers for Environment Prediction Climate Forecast System Reanalysis. During winter, the distribution is characterized by a tripole-like structure, whereas in summer the pattern exhibits a west–east contrast. Special attention is paid to the links of the evaporation duct with the regional evaporation by analyzing the leading empirical orthogonal functions of both elements. Both the structural similarity in spatial patterns and the significant correlation in the principal components imply the inherent relevance between evaporation duct and evaporation. During both the winter and summer seasons, the empirical orthogonal function principal component 1 of the evaporation duct and evaporation are linked significantly with the regional atmospheric dynamics, the primary factor dominating the whole South China Sea. The partial correlation analysis reveals that, similar to the evaporation process, surface wind is a more important factor affecting evaporation duct than sea surface temperature. The results also indicate that the influence of surface wind and SST not only has an obvious seasonal dependence, but also displays a prominent south-north contrast.
      PubDate: 2017-07-13T03:59:08.182064-05:
      DOI: 10.1002/2017JC012683
  • Trends and interannual variability of mass and steric sea level in the
           Tropical Asian Seas
    • Authors: Marcel Kleinherenbrink; Riccardo Riva, Thomas Frederikse, Mark Merrifield, Yoshihide Wada
      Abstract: The mass and steric components of sea level changes have been separated in the Tropical Asian Seas (TAS) using a statistically optimal combination of Jason satellite altimetry, GRACE satellite gravimetry and ocean reanalyses. Using observational uncertainties, statistically optimally weighted time series for both components have been obtained in four regions within the TAS over the period January 2005 - December 2012.The mass and steric sea level variability is regressed with the first two principal components (PC1&2) of Pacific equatorial wind stress and the Dipole Mode Index (DMI). Sea level in the the South China Sea is not affected by any of the indices. Steric variability in the TAS is largest in the deep Banda and Celebes seas and is affected by both PCs and the DMI. Mass variability is largest on the continental shelves, which is primarily controlled by PC1. We argue that a water flux from the Western Tropical Pacific Ocean is the cause for mass variability in the TAS.The steric trends are about 2 mm yr−1 larger than the mass trends in the TAS. A signifcant part of the mass trend can be explained by the aforementioned indices and the nodal cycle. Trends obtained from fingerprints of mass redistribution are statistically equal to mass trends after subtracting the nodal cycle and the indices.Ultimately, the effect of omitting the TAS in global sea level budgets is estimated to be 0.3 mm yr−1.
      PubDate: 2017-07-13T03:57:34.308972-05:
      DOI: 10.1002/2017JC012792
  • Variability and trends in the Arctic Sea ice cover: Results from different
    • Authors: Josefino C. Comiso; Walter N. Meier, Robert Gersten
      Abstract: Variability and trend studies of sea ice in the Arctic have been conducted using products derived from the same raw passive microwave data but by different groups using different algorithms. This study provides consistency assessment of four of the leading products namely: Goddard Bootstrap (SB2), Goddard NASA Team (NT1), EUMETSAT Ocean and Sea Ice Satellite Application Facility (OSI-SAF 1.2) and Hadley HadISST 2.2 data in evaluating variability and trends in the Arctic sea ice cover. All four provide generally similar ice patterns but significant disagreements in ice concentration distributions especially in the marginal ice zone and adjacent regions in winter and meltponded areas in summer. The discrepancies are primarily due to different ways the four techniques accounts for occurrences of new ice and meltponding. However, results show that the different products generally provide consistent and similar representation of the state of the Arctic sea ice cover. Hadley and NT1 data usually provide the highest and lowest monthly ice extents, respectively. The Hadley data also show the lowest trends in ice extent and ice area at -3.88%/decade and -4.37%/decade, respectively, compared to an average of -4.36%/decade and -4.57%/decade for all four. Trend maps also show similar spatial distribution for all four with the largest negative trends occurring at the Kara/Barents Sea and Beaufort Sea regions, where sea ice has been retreating the fastest. The good agreement of the trends especially with updated data provides strong confidence in the quantification of the rate of decline in the Arctic sea ice cover.
      PubDate: 2017-07-13T03:51:04.011607-05:
      DOI: 10.1002/2017JC012768
  • Using remote sensing to detect the polarized sunglint reflected from oil
           slicks beyond the critical angle
    • Authors: Yingcheng Lu; Yang Zhou, Yongxue Liu, Zhihua Mao, Weixian Qian, Mengqiu Wang, Minwei Zhang, Jiang Xu, Shaojie Sun, Peijun Du
      Abstract: The critical angle at which the brightness of oil slicks and oil-free seawater is reversed occurs under sunglint and is often shown as an area of uncertainty due to different roughness and surface Fresnel reflection parameters. Consequently, differentiating oil slicks from the seawater in these areas using optical sensors is a challenge. Polarized optical remote sensing techniques provide complementary information for intensity imagery with different physical properties and, thus, possess the ability to resolve this difficult problem. In the polarized reflectance model, the degree of linear polarization (DOLP) of sunglint depends on accurately knowing the Stokes parameter for the reflected light, and varies with the refractive index of the surface layer and the viewing angles. For the polarized detection of oil slicks, the highest sensitivity of the DOLP to the refractive index is located within the specular reflection direction where the sum of the solar and sensor zenith angles is 82.6°. The modeled results clearly indicate that the DOLP of oil slicks is weaker in comparison with oil-free seawater under sunglint. Using measurements from the space-borne Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar (PARASOL) over the Deepwater Horizon oil spill in the Gulf of Mexico, we illustrate that the PARASOL-derived DOLP difference between the oil spill and seawater is obvious and is in accordance with the modeled results. These preliminary results suggest that the potential of multi-angle measurement and feasibility of deriving refractive index of ocean surface from space-borne sensors need further researches.
      PubDate: 2017-07-13T03:50:35.378746-05:
      DOI: 10.1002/2017JC012793
  • Assessing variability in the size and strength of the North Atlantic
           subpolar gyre
    • Authors: Nicholas P. Foukal; M. Susan Lozier
      Abstract: Recent studies on the size and strength of the North Atlantic subpolar gyre (SPG) offer contrasting assessments of the gyre's temporal variability: studies that use empirical orthogonal function (EOF) analyses of satellite sea-surface height (SSH) report a rapid decline in SPG size and strength since 1992 (∼20% per decade), while concurrent in situ observations report either no trend or a slight decline. Here we investigate this discrepancy by analyzing the size and strength of the SPG with satellite SSH from 1993 to 2015 with two separate methods: indirectly via EOF analysis and more directly through measurements of the gyre center and boundary. We define the boundary of the gyre as the largest closed contour of SSH, the center as the minimum SSH, and the strength as the difference between the SSH at the boundary and the center. We identify a linear decline over the study period in the SPG strength (5.1% per decade), but find no statistically significant trend in the SPG area. The trend in the gyre strength is weaker than the EOF-based trend and is most likely below the level of detection of the in situ measurements. We conclude that the variability previously identified as a sharp decline in SPG circulation can be more appropriately attributed to basin-wide sea level rise during the satellite altimetry period. In addition, we find that the properties of the eastern SPG do not co-vary with the SPG size, suggesting that SPG dynamics do not control the strength of the inter-gyre throughput.
      PubDate: 2017-07-11T10:56:20.040974-05:
      DOI: 10.1002/2017JC012798
  • Impacts of preexisting ocean cyclonic circulation on sea surface
           Chlorophyll-a concentration off northeastern Taiwan following episodic
           typhoon passages
    • Authors: Fang-Hua Xu; Yao Yuan, Leo Oey, Yanluan Lin
      Abstract: Off northeastern Taiwan, enhancement of sea surface chlorophyll-a (Chl-a) concentration is frequently found after typhoon passages. From 1998 to 2013, forty-six typhoon events are analyzed to examine the variations in Chl-a concentration from satellite ocean color data. On average, Chl-a concentration increased by 38% after a typhoon passage. Noticeably, four remarkable Chl-a increases after typhoons coincide with pre-existing oceanic cyclones in the study area. The Chl-a increase is significantly anti-correlated (p
      PubDate: 2017-07-08T03:10:31.275942-05:
      DOI: 10.1002/2016JC012625
  • Revisiting Ocean Color algorithms for chlorophyll a and particulate
           organic carbon in the Southern Ocean using biogeochemical floats
    • Authors: Nils Haëntjens; Emmanuel Boss, Lynne D. Talley
      Abstract: The Southern Ocean (SO) ecosystem plays a key role in the carbon cycle by sinking a major part (43%) of the ocean uptake of anthropogenic CO2, and being an important source of nutrients for primary producers. However, undersampling of SO biogeochemical properties limits our understanding of the mechanisms taking place in this remote area. The Southern Ocean Carbon and Climate Observions and Modeling project (SOCCOM) has been deploying a large number of autonomous biogeochemical floats to study the SO (as of December 2016, 74 floats out of 200 have been deployed). SOCCOM floats measurements can be used to extend remote sensing chlorophyll a (chla) and particulate organic carbon (POC) products under the clouds or during the polar night as well as adding the depth dimension to the satellite-based view of the SO.Chlorophyll a concentrations measured by fluorometers embedded on the floats and POC concentrations derived from backscattering coefficients were calibrated with samples collected during the floats' deployment cruise. Float chla and POC were compared with products derived from observations of MODIS and VIIRS sensors.We find the Ocean Color Index (OCI) global algorithm to agree well with the matchups (within 9%, on average, for the Visible Infrared Imaging Radioneter Suite (VIIRS) and 12%, on average, for the Moderate Resolution Imaging Spectroradiometer Aqua(MODIS)). SO specific algorithms estimating chla are offset by ∼45% south of the Sea Ice Extent Front (∼ 60°S). In addition, POC estimates based on floats agree well with NASA's POC algorithm.
      PubDate: 2017-07-05T12:45:20.454629-05:
      DOI: 10.1002/2017JC012844
  • The evolution of scaling laws in the sea ice floe size distribution
    • Authors: Christopher Horvat; Eli Tziperman
      Abstract: The sub-gridscale floe size and thickness distribution (FSTD) is an emerging climate variable, playing a leading-order role in the coupling between sea ice, the ocean, and the atmosphere. The FSTD, however, is difficult to measure given the vast range of horizontal scales of individual floes, leading to the common use of power-law scaling to describe it. The evolution of a coupled mixed-layer-FSTD model of a typical marginal ice zone is explicitly simulated here, to develop a deeper understanding of how processes active at the floe scale may or may not lead to scaling laws in the floe size distribution. The time evolution of mean quantities obtained from the FSTD (sea ice concentration, mean thickness, volume) is complex even in simple scenarios, suggesting that these quantities, which affect climate feedbacks, should be carefully calculated in climate models. The emergence of FSTDs with multiple separate power-law regimes, as seen in observations, is found to be due to the combination of multiple scale-selective processes. Limitations in assuming a power-law FSTD are carefully analyzed, applying methods used in observations to FSTD model output. Two important sources of error are identified that may lead to model biases: one when observing an insufficiently small range of floe sizes, and one from the fact that floe-scale processes often do not produce power-law behavior. These two sources of error may easily lead to biases in mean quantities derived from the FSTD of greater than 100%, and therefore biases in modeled sea ice evolution.
      PubDate: 2017-07-05T08:26:41.477368-05:
      DOI: 10.1002/2016JC012573
  • Biogeochemical sensor performance in the SOCCOM profiling float array
    • Authors: Kenneth S. Johnson; Joshua N. Plant, Luke J. Coletti, Hans W. Jannasch, Carole M. Sakamoto, Stephen C. Riser, Dana D. Swift, Nancy L. Williams, Emmanuel Boss, Nils Haëntjens, Lynne D. Talley, Jorge L. Sarmiento
      Abstract: The Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) program has begun deploying a large array of biogeochemical sensors on profiling floats in the Southern Ocean. As of February 2016, 86 floats have been deployed. Here the focus is on 56 floats with quality controlled and adjusted data that have been in the water at least 6 months. The floats carry oxygen, nitrate, pH, chlorophyll fluorescence, and optical backscatter sensors. The raw data generated by these sensors can suffer from inaccurate initial calibrations and from sensor drift over time. Procedures to correct the data are defined. The initial accuracy of the adjusted concentrations is assessed by comparing the corrected data to laboratory measurements made on samples collected by a hydrographic cast with a rosette sampler at the float deployment station. The long-term accuracy of the corrected data is compared to the GLODAPv2 data set whenever a float made a profile within 20 km of a GLODAPv2 station. Based on these assessments, the fleet average oxygen data are accurate to 1±1%, nitrate to within 0.5±0.5 µmol kg−1, and pH to 0.005±0.01, where the error limit is 1 standard deviation of the fleet data. The bio-optical measurements of chlorophyll fluorescence and optical backscatter are used to estimate chlorophyll a and particulate organic carbon concentration. The particulate organic carbon concentrations inferred from optical backscatter appear accurate to with 35 mg C m−3 or 20%, whichever is larger. Factors affecting the accuracy of the estimated chlorophyll a concentrations are evaluated.
      PubDate: 2017-07-05T08:26:33.469098-05:
      DOI: 10.1002/2017JC012838
  • Air-sea interaction regimes in the sub-Antarctic Southern Ocean and
           Antarctic marginal ice zone revealed by icebreaker measurements
    • Authors: Lisan Yu; Xiangze Jin, Eric Schulz, Simon A. Josey
      Abstract: This study analyzed shipboard air-sea measurements acquired by the icebreaker Aurora Australis during its off-winter operation in December 2010 – May 2012. Mean conditions over 7 months (October-April) were compiled from a total of 22 ship tracks. The icebreaker traversed the water between Hobart, Tasmania and the Antarctic continent, providing valuable in situ insight into two dynamically important, yet poorly sampled, regimes: the sub-Antarctic Southern Ocean and the Antarctic marginal ice zone (MIZ) in the Indian Ocean sector. The transition from the open water to the ice-covered surface creates sharp changes in albedo, surface roughness, and air temperature, leading to consequential effects on air-sea variables and fluxes. Major effort was made to estimate the air-sea fluxes in the MIZ using the bulk flux algorithms that are tuned specifically for the sea-ice effects, while computing the fluxes over the sub-Antarctic section using the COARE3.0 algorithm. The study evidenced strong sea-ice modulations on winds, with the southerly airflow showing deceleration (convergence) in the MIZ and acceleration (divergence) when moving away from the MIZ. Marked seasonal variations in heat exchanges between the atmosphere and the ice margin were noted. The monotonic increase in turbulent latent and sensible heat fluxes after summer turned the MIZ quickly into a heat loss regime, while at the same time the sub-Antarctic surface water continued to receive heat from the atmosphere. The drastic increase in turbulent heat loss in the MIZ contrasted sharply to the non-significant and seasonally invariant turbulent heat loss over the sub-Antarctic open water.
      PubDate: 2017-07-05T08:26:18.2386-05:00
      DOI: 10.1002/2016JC012281
  • A reflecting, steepening, and breaking internal tide in a submarine canyon
    • Authors: M. S. Alberty; S. Billheimer, M. M. Hamann, C. Y. Ou, V. Tamsitt, A. J. Lucas, M. H. Alford
      Abstract: Submarine canyons are common features of the coastal ocean. Although they are known to be hotspots of turbulence that enhance diapycnal transport in their stratified waters, the dynamics of canyon mixing processes are poorly understood. Most studies of internal wave dynamics within canyons have focused on a handful of canyons with along-axis slopes less steep than semidiurnal (D2) internal wave characteristics (subcritical). Here, we present the first tidally-resolving observations within a canyon with a steeply sloping axis (supercritical). A process study consisting of two 24-hour shipboard stations and a profiling mooring was conducted in the La Jolla Canyon off the coast of La Jolla, CA. Baroclinic energy flux is oriented up-canyon and decreases from 182 ± 18 W m−1 at the canyon mouth to 46 ± 5 W m−1 near the head. The ratio of horizontal kinetic energy to available potential energy and the observed group speed of each mode are lower than expected for freely propagating D2 internal waves at each station, indicating partial reflection. Harmonic analysis reveals that variance is dominated by the D2 tide. Moving up-canyon, the relative importance of D2 decreases and its higher harmonics are needed to account for a majority of the observed variance, indicating steepening. Steep internal tides cause large isopycnal displacements (∼50 m in 100m water depth) and high strain events. These events coincide with enhanced O(10−7 -10−5 m2 s−3) dissipation of turbulent kinetic energy at mid-depths.
      PubDate: 2017-06-09T11:10:20.824706-05:
      DOI: 10.1002/2016JC012583
  • Episodic surface intrusions in the Yellow Sea during relaxation of
           northerly winds
    • Authors: Zifeng Hu; Dong-Ping Wang, Xianqiang He, Mingting Li, Jun Wei, Delu Pan, Yan Bai
      Abstract: The surface currents over the Yellow and East China Seas are mapped from the Geostationary Ocean Color Imager (GOCI). Based on a composite of six intrusion events in January–April, the strong northward surface current in the Yellow Sea is shown to be concentrated along the deep trough, accompanied by a broad northward surface current over the East China Sea. From the corresponding surface winds, the episodic northward surface flow bursts appear to be associated with abrupt changes from the strong northerly winds to weak southerly winds during cold front passages. A three-dimensional model driven with observed surface winds is used to simulate the observed shelf-wide response to northerly winds. There is an outstanding agreement between the simulated and observed surface currents. The surface intrusion in the Yellow Sea is shown to be driven primarily by a barotropic longitudinal surface slope, while the strong northward current in the East China Sea is associated with a coastal trapped wave. Moreover, the surface intrusion is associated with a large volume transport, suggesting that the transient intrusions could be important in the northward heat transport. The unprecedented capability of GOCI satellite in providing a regional circulation pattern, in conjunction with complementary model simulations, could contribute greatly to understanding of the dynamics of the Yellow and East China Seas.
      PubDate: 2017-06-09T11:05:47.895589-05:
      DOI: 10.1002/2017JC012830
  • Impact of Sea Spray on the Yellow and East China Seas Thermal Structure
           during the passage of Typhoon Rammasun (2002)
    • Authors: Lianxin Zhang; Xuefeng Zhang, P. C. Chu, Changlong Guan, Hongli Fu, Guofang Chao, Guijun Han, Wei Li
      Abstract: Strong winds lead to large amounts of sea spray in the lowest part of the atmospheric boundary layer. The spray droplets affect the air-sea heat fluxes due to their evaporation and the momentum due to the change of sea surface, and in turn change the upper ocean thermal structure. In this study, impact of sea spray on upper ocean temperatures in the Yellow and East China Seas (YES) during typhoon Rammasun's passage is investigated using the POMgcs ocean model with a sea spray parameterization scheme, in which the sea spray-induced heat fluxes are based on an improved Fairall's sea spray heat fluxes algorithm, and the sea spray-induced momentum fluxes are derived from an improved COARE version 2.6 bulk model.The distribution of the sea spray mediated turbulent fluxes was primarily located at Rammasun eye-wall region, in accord with the maximal wind speeds regions. When Rammasun enters the Yellow sea, the sea spray mediated latent (sensible) heat flux maximum is enhanced by 26% (13.5%) compared to that of the interfacial latent (sensible) heat flux. The maximum of the total air-sea momentum fluxes is enhanced by 43% compared to the counterpart of the interfacial momentum flux. Furthermore, the sea spray plays a key role in enhancing the intensity of the typhoon-induced “cold suction” and “heat pump” processes. When the effect of sea spray is considered, the maximum of the sea surface cooling in the right side of Rammasun's track is increased by 0.5°C, which is closer to the available satellite observations.
      PubDate: 2017-06-09T06:48:46.329082-05:
      DOI: 10.1002/2016JC012592
  • Warm layer and cool skin corrections for bulk water temperature
           measurements for air-sea interaction Studies
    • Authors: Denny P. Alappattu; Qing Wang, Ryan Yamaguchi, Richard J. Lind, Mike Reynolds, Adam J. Christman
      Abstract: The sea surface temperature (SST) relevant to air-sea interaction studies is the temperature immediately adjacent to the air, referred to as skin SST. Generally, SST measurements from ships and buoys are taken at depths varies from several centimeters to five meters below the surface. These measurements, known as bulk SST, can differ from skin SST up to O(1°C).Shipboard bulk and skin SST measurements were made during the Coupled Air-Sea Processes and Electromagnetic ducting Research east coast field campaign (CASPER-East). An Infrared SST Autonomous Radiometer (ISAR) recorded skin SST, while R/V Sharp's Surface Mapping System (SMS) provided bulk SST from one-meter water depth. Since the ISAR is sensitive to sea spray and rain, missing skin SST data occurred in these conditions. However, SMS measurement is less affected by adverse weather and provided continuous bulk SST measurements. It is desirable to correct the bulk SST to obtain a good representation of the skin SST, which is the objective of this research.Bulk-skin SST difference has been examined with respect to meteorological factors associated with cool skin and diurnal warm layers. Strong influences of wind speed, diurnal effects and net longwave radiation flux on temperature difference are noticed. A three-step scheme is established to correct for wind effect, diurnal variability and then for dependency on net longwave radiation flux. Scheme is tested and compared to existing correction schemes. This method is able to effectively compensate for multiple factors acting to modify bulk SST measurements over the range of conditions experienced during CASPER-East.
      PubDate: 2017-05-24T07:20:29.369419-05:
      DOI: 10.1002/2017JC012688
  • Modeling postconvective submesoscale coherent vortices in the northwestern
           Mediterranean Sea
    • Authors: P. Damien; A. Bosse, P. Testor, P. Marsaleix, C. Estournel
      Abstract: For the first time, the formation of Submesoscale Coherent Vortices (SCVs) during intermediate and deep convection events is documented in a realistic high resolution (1 km) numerical simulation of the oceanic circulation in the northwestern Mediterranean Sea. Winter intermediate and deep convection leads to the formation of anticyclonic and cyclonic eddies with lifetimes exceeding one year. By focusing on three typical eddies, the main characteristics of such vortices are discussed. The anticyclonic eddies are typical of SCVs observed in deep convection areas so far. They are characterized by a small radius (∼ 6.5 km) and orbital peak velocities of about 7 cm/s located at great depth (∼ 1500 m) or intermediate depth (∼ 500 m). The cyclonic vortices show very similar characteristics, such as a high Rossby number (∼ 0.4), but with surface-intensified structures. The long lifetimes of both anticyclonic and cyclonic eddies reflect very slow diffusive processes between their core and their surroundings and a strong resistance to external perturbations. These long-lived eddies are found to participate in the spreading of a significant portion (from 15 to 35%) of the convected waters in the Gulf of Lions and contribute to the ventilation of the deep basin.
      PubDate: 2017-03-31T13:51:16.311955-05:
      DOI: 10.1002/2016JC012114
  • Physical and biogeochemical controls of the phytoplankton blooms in
           North-Western Mediterranean Sea: A multiplatform approach over a complete
           annual cycle (2012–2013 DEWEX experiment)
    • Authors: Nicolas Mayot; Fabrizio D'Ortenzio, Vincent Taillandier, Louis Prieur, Orens Pasqueron de Fommervault, Hervé Claustre, Anthony Bosse, Pierre Testor, Pascal Conan
      Abstract: The North Western Mediterranean Sea exhibits recurrent and significant autumnal and spring phytoplankton blooms. The existence of these two blooms coincide with typical temperate dynamics. To determine the potential control of physical and biogeochemical factors on these phytoplankton blooms, data from a multiplatform approach (combining ships, Argo and BGC-Argo floats, and bio-optical gliders) were analyzed in association with satellite observations in 2012-2013. The satellite framework allowed a simultaneous analysis over the whole annual cycle of in situ observations of mixed layer depth, photosynthetical available radiation, particle backscattering, nutrients (nitrate and silicate) and chlorophyll-a concentrations. During the year 2012-2013, satellite ocean color observations, confirmed by in situ data, have revealed the existence of two areas (or bioregions) with comparable autumnal blooms but contrasting spring blooms. In both bioregions, the ratio of the euphotic zone (defined as the isolume 0.415 mol photons m−2 d−1, Z0.415) and the MLD identified the initiation of the autumnal bloom, as well as the maximal annual increase in [Chl-a] in spring. In fact, the autumnal phytoplankton bloom might be initiated by mixing of the summer shallowing deep chlorophyll maximum, while the spring restratification (when Z0.415/MLD ratio became > 1) might induce surface phytoplankton production that largely overcomes the losses. Finally, winter deep convection events that took place in one of the bioregions induced higher net accumulation rate of phytoplankton in spring associated with a diatom-dominated phytoplankton community principally. We suggest that very deep winter MLD lead to an increase in surface silicates availability, which favored the development of diatoms.
      PubDate: 2017-03-31T13:50:32.70281-05:0
      DOI: 10.1002/2016JC012052
  • Influence of the phytoplankton community structure on the spring and
           annual primary production in the North-Western Mediterranean Sea
    • Authors: Nicolas Mayot; Fabrizio D'Ortenzio, Julia Uitz, Bernard Gentili, Joséphine Ras, Vincenzo Vellucci, Melek Golbol, David Antoine, Hervé Claustre
      Abstract: Satellite ocean color observations revealed that unusually deep convection events in 2005, 2006, 2010 and 2013 led to an increased phytoplankton biomass during the spring bloom over a large area of the North-Western Mediterranean Sea (NWM). Here we investigate the effects of these events on the seasonal phytoplankton community structure, we quantify their influence on primary production, and we discuss the potential biogeochemical impact. For this purpose, we compiled in situ phytoplankton pigment data from five ship surveys performed in the NWM and from monthly cruises at a fixed station in the Ligurian Sea. We derived primary production rates from a light-photosynthesis model applied to these in situ data. Our results confirm that the maximum phytoplankton biomass during the spring bloom is larger in years associated with intense deep convection events (+ 51%). During these enhanced spring blooms, the contribution of diatoms to total phytoplankton biomass increased (+ 33%), as well as the primary production rate (+ 115%). The occurrence of a highly productive bloom is also related to an increase in the phytoplankton bloom area (+ 155%), and in the relative contribution of diatoms to primary production (+ 63%). Therefore, assuming that deep convection in the NWM could be significantly weakened by future climate changes, substantial decreases in the spring production of organic carbon and of its export to deep waters can be expected. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-17T19:15:43.10201-05:0
      DOI: 10.1002/2016JC012668
  • Observations of flooding and snow-ice formation in a thinner Arctic sea
           ice regime during the N-ICE2015 campaign: Influence of basal ice melt and
    • Authors: Christine Provost; Nathalie Sennéchael, Jonas Miguet, Polona Itkin, Anja Rösel, Zoé Koenig, Nicolas Villacieros-Robineau, Mats A. Granskog
      Abstract: Seven ice mass balance instruments deployed near 83°N on different first-year and second-year ice floes, representing variable snow and ice conditions, documented the evolution of snow and ice conditions in the Arctic Ocean north of Svalbard in Jan-Mar 2015. Frequent profiles of temperature and thermal diffusivity proxy were recorded to distinguish changes in snow depth and ice thickness with 2 cm vertical resolution. Four instruments documented flooding and snow-ice formation. Flooding was clearly detectable in the simultaneous changes in thermal diffusivity proxy, increased temperature and heat propagation through the underlying ice. Slush then progressively transformed into snow-ice. Flooding resulted from two different processes; i) after storm-induced break-up of snow-loaded floes and ii) after loss of buoyancy due to basal ice melt. In the case of break-up, when the ice was cold and not permeable, rapid flooding, probably due to lateral intrusion of seawater, led to slush and snow-ice layers at the ocean freezing temperature (-1.88°C). After the storm the instruments documented basal sea-ice melt over warm Atlantic waters and ocean-to-ice heat flux peaked at up to 400 Wm−2. The warm ice was then permeable and flooding was more gradual probably involving vertical intrusion of brines and led to colder slush and snow-ice (-3°C). The N-ICE2015 campaign provided the first documentation of significant flooding and snow-ice formation in the Arctic ice pack as the slush partially refroze. Snow-ice formation may become a more-frequently observed process in a thinner-ice Arctic. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-14T03:35:35.750566-05:
      DOI: 10.1002/2016JC012011
  • Issue Information
    • Pages: 6067 - 6070
      PubDate: 2017-09-15T04:47:03.536026-05:
      DOI: 10.1002/jgrc.21931
  • Air-sea fluxes for Hurricane Patricia (2015): Comparison with supertyphoon
           Haiyan (2013) and under different ENSO conditions
    • Authors: Hsiao-Ching Huang; Julien Boucharel, I.-I. Lin, Fei-Fei Jin, Chun-Chi Lien, Iam-Fei Pun
      Pages: 6076 - 6089
      Abstract: Hurricane Patricia formed on 20 October 2015 in the Eastern Pacific and, in less than 3 days, rapidly intensified from a Tropical Storm to a record-breaking hurricane with maximum sustained winds measured around 185 knots. It is almost 15 knots higher than 2013's supertyphoon Haiyan (the previous strongest tropical cyclone (TC) ever observed). This research focuses on analyzing the air-sea enthalpy flux conditions that contributed to Hurricane Patricia's rapid intensification, and comparing them to supertyphoon Haiyan's. Despite a stronger cooling effect, a higher enthalpy flux supply is found during Patricia, in particular due to warmer pre-TC sea surface temperature conditions. This resulted in larger temperature and humidity differences at the air-sea interface, contributing to larger air-sea enthalpy heat fluxes available for Patricia's growth (24% more than for Haiyan). In addition, air-sea fluxes simulations were performed for Hurricane Patricia under different climate conditions to assess specifically the impact of local and large-scale conditions on storm intensification associated with six different phases and types of El Niño Southern Oscillation (ENSO) and long-term climatological summer condition. We found that the Eastern Pacific El Niño developing and decaying summers, and the Central Pacific El Niño developing summer are the three most favorable ENSO conditions for storm intensification. This still represents a 37% smaller flux supply than in October 2015, suggesting that Patricia extraordinary growth is not achievable under any of these typical ENSO conditions but rather the result of the exceptional environmental conditions associated with the buildup of the strongest El Niño ever recorded.
      PubDate: 2017-08-01T04:12:14.127579-05:
      DOI: 10.1002/2017JC012741
  • Development of upwelling on pathway and freshwater transport of Pearl
           River plume in northeastern South China Sea
    • Authors: Zhaoyun Chen; Yuwu Jiang, James T. Liu, Wenping Gong
      Pages: 6090 - 6109
      Abstract: In situ observations, satellite images, and numerical modeling results have shown that the Pearl River plume axis extends alongshore and passes through two separate upwelling regions—one off the Guangdong and Fujian coasts (the Yuedong upwelling) and the other in the Taiwan Bank during the initial and medium stages of the Yuedong upwelling, while it is directed offshore when the Yuedong upwelling is strong. Model experiments are conducted to examine the effects of wind strength and baroclinicity on the upwelling and the corresponding pathway and freshwater transport of the Pearl River plume. The baroclinic effect is important to intensifying the horizontal velocity at the upwelling front and freshwater transport in the northeastern South China Sea. The freshwater transport flux is further decomposed into advection, vertical shear, and tidal pumping components, and advection is the dominant contributor. As the Yuedong upwelling develops, the zone with a relatively high-pressure gradient moves offshore due to offshore Ekman transport and the shift in the upwelling front, which is responsible for the offshore transport of the river plume. When the river plume is transported to the outer-shelf, sometimes it can be further entrained into eddies, allowing its export to the open sea.
      PubDate: 2017-08-01T04:11:40.671088-05:
      DOI: 10.1002/2016JC012411
  • On the imprint of surfactant-driven stabilization of laboratory breaking
           wave foam with comparison to oceanic whitecaps
    • Authors: A. H. Callaghan; G. B. Deane, M. D. Stokes
      Pages: 6110 - 6128
      Abstract: Surfactants are ubiquitous in the global oceans: they help form the materially-distinct sea surface microlayer (SML) across which global ocean-atmosphere exchanges take place, and they reside on the surfaces of bubbles and whitecap foam cells prolonging their lifetime thus altering ocean albedo. Despite their importance, the occurrence, spatial distribution, and composition of surfactants within the upper ocean and the SML remains under-characterized during conditions of vigorous wave breaking when in-situ sampling methods are difficult to implement. Additionally, no quantitative framework exists to evaluate the importance of surfactant activity on ocean whitecap foam coverage estimates. Here we use individual laboratory breaking waves generated in filtered seawater and seawater with added soluble surfactant to identify the imprint of surfactant activity in whitecap foam evolution. The data show a distinct surfactant imprint in the decay phase of foam evolution. The area-time-integral of foam evolution is used to develop a time-varying stabilization function, ϕ(t) and a stabilization factor, Θ, which can be used to identify and quantify the extent of this surfactant imprint for individual breaking waves. The approach is then applied to wind-driven oceanic whitecaps, and the laboratory and ocean Θ distributions overlap. It is proposed that whitecap foam evolution may be used to determine the occurrence and extent of oceanic surfactant activity to complement traditional in-situ techniques and extend measurement capabilities to more severe sea states occurring at wind speeds in excess of about 10 m/s. The analysis procedure also provides a framework to assess surfactant-driven variability within and between whitecap coverage data sets.
      PubDate: 2017-08-01T04:07:59.165354-05:
      DOI: 10.1002/2017JC012809
  • Energetics of eddy-mean flow interactions in the Brazil current between
           20°S and 36°S
    • Authors: F. C. Magalhães; J. L. L. Azevedo, L. R. Oliveira
      Pages: 6129 - 6146
      Abstract: The energetics of eddy-mean flow interactions in the Brazil Current (BC) between 20°S and 36°S are investigated in 19 transects perpendicular to the 200 m isobath. Ten years (2000–2009) of output data from the Hybrid Coordinate Ocean Model (HYCOM) NCODA reanalysis, with a spatial resolution of 1/12.5° and 5 day averages, are used. The mean kinetic energy (MKE) and eddy kinetic energy (EKE) fields presented the same subsurface spatial pattern but with reduced values. The EKE increases southward, with high values along the BC path and the offshore portion of the jet. The values of the barotropic conversion term (BTC) are highest in the surface layers and decreased with depth, whereas the values of the baroclinic conversion term (BCC) and the vertical eddy heat flux (VEHF) are highest in the subsurface. Despite the vertical thickening of the BC, the highest energy conversion rates are confined to the upper 700 m of the water column. The energetic analysis showed that the current features mixed instability processes. The vertical weighted mean of the BTC and BCC presented an oscillatory pattern related to the bathymetry. The eddy field accelerates the time-mean flow upstream and downstream of bathymetric features and drains energy from the time-mean flow over the features. The BC is baroclinically unstable south of 28°S, and the highest energy conversion rates occur in Cabo de São Tomé, Cabo Frio, and the Cone do Rio Grande.
      PubDate: 2017-08-01T04:02:26.387913-05:
      DOI: 10.1002/2016JC012609
  • Behavior of flexural gravity waves on ice shelves: Application to the Ross
           Ice Shelf
    • Authors: O. V. Sergienko
      Pages: 6147 - 6164
      Abstract: Ocean waves continuously impact floating ice shelves and affect their stress regime. Low-frequency, long-period (75–400 s), ocean waves are able to reach ice-shelf cavities from distant sources and excite flexural gravity waves that represent coupled motion in the water of the cavity and the ice covering above. Analytic treatment of simplified geometric configuration and three-dimensional numerical simulations of these flexural gravity waves applied to the Ross Ice Shelf show that propagation and ice-shelf flexural stresses are strongly controlled by the geometry of the system, bathymetry of the ice-shelf cavity, and ice-shelf cavity thickness. The derived dispersion relationships, group and phase velocities of these waves can be used to infer poorly constrained characteristics of ice shelves from field observations. The results of numerical simulations show that the flexural gravity waves propagate as beams. The orientation of these beams is determined by the direction of the open ocean waves incident on the ice-shelf front. The higher frequency ocean waves cause larger flexural stresses, while lower frequency waves can propagate farther away from the ice-shelf front and cause flexural stresses in the vicinity of the grounding line.
      PubDate: 2017-08-01T03:55:07.68974-05:0
      DOI: 10.1002/2017JC012947
  • Temporal evolution of near-surface chlorophyll over cyclonic eddy
           lifecycles in the southeastern Pacific
    • Authors: Jie Huang; Fanghua Xu, Kuanbo Zhou, Peng Xiu, Yanluan Lin
      Pages: 6165 - 6179
      Abstract: Temporal evolution of near-surface chlorophyll (CHL) associated with mesoscale eddies over entire eddy lifespan is complicated. Based on satellite measurements and a reanalysis data set, we identify and quantify major temporal and spatial CHL responses in cyclonic eddies in the southeastern Pacific, and explore the associated mechanisms. Only few temporal CHL variations can be directly linked to the four primary mechanisms: “eddy pumping,” “eddy trapping,” “eddy stirring,” and “eddy-induced Ekman pumping.” About 80% of the temporal CHL variations are too complex to be explained by a single mechanism. Five characteristic CHL responses, including classic dipoles (CD), positive-dominant dipoles (PD), negative-dominant dipoles (ND), positive monopoles (PM), and negative monopoles (NM) are identified using the self-organizing map (SOM). CD, a dominant response induced primarily by “eddy stirring,” has a continued increasing of frequency of occurrence with time, although its contribution to the total CHL variability remains low. As the secondary prominent response, NM has two peaks of frequency of occurrence at eddy formation and maturation stages, mainly accounted by “eddy trapping” after eddy breakup and “eddy-induced Ekman pumping,” respectively. The sum of frequency of occurrence of PD and PM are comparable to that of NM. The initial positive CHL at eddy formation stage is associated with “eddy trapping.” The significant positive CHL increase from the eddy intensification to early decay stage is mainly attributed to “eddy pumping.” Although the frequency of occurrence of ND is the smallest, its contribution to negative CHL anomalies is unnegligible.
      PubDate: 2017-08-01T04:01:37.123678-05:
      DOI: 10.1002/2017JC012915
  • Amundsen and Bellingshausen Seas simulation with optimized ocean, sea ice,
           and thermodynamic ice shelf model parameters
    • Authors: Y. Nakayama; D. Menemenlis, M. Schodlok, E. Rignot
      Pages: 6180 - 6195
      Abstract: Recent studies suggest that the thickness of Winter Water (WW), that is, water with potential temperature below ∼−1°C located below Antarctic Surface Water and above Circumpolar Deep Water (CDW) is critical in determining the ice shelf melt rate, especially for the Pine Island Glacier (PIG). Existing model studies, however, misrepresent WW thickness and properties in the Amundsen Sea (AS). Here, we adjust a small number of model parameters in a regional Amundsen and Bellingshausen Seas configuration of the Massachusetts Institute of Technology general circulation model in order to reproduce properties and thickness of WW and CDW close to observations, with significant improvement for WW compared to previous studies. The cost, which is defined as weighted model-data difference squared, is reduced by 23%. Although a previous modeling study points out that the local surface heat loss upstream from Pine Island Polynya could be the reason for the observed 2012 PIG melt decline and WW thickening, they did not show WW freshening, which was observed at the same time. Model sensitivity experiments for surface heat loss, PIG melt rate, and precipitation fail to replicate WW freshening concurrent with PIG melt decline, implying that these processes cannot fully explain the observed PIG melt decrease.
      PubDate: 2017-08-03T00:31:17.502704-05:
      DOI: 10.1002/2016JC012538
  • A submesoscale coherent vortex in the Ligurian Sea: From dynamical
           barriers to biological implications
    • Authors: Anthony Bosse; Pierre Testor, Nicolas Mayot, Louis Prieur, Fabrizio D'Ortenzio, Laurent Mortier, Hervé Le Goff, Claire Gourcuff, Laurent Coppola, Héloïse Lavigne, Patrick Raimbault
      Pages: 6196 - 6217
      Abstract: In June 2013, a glider equipped with oxygen and fluorescence sensors has been used to extensively sample an anticyclonic Submesoscale Coherent Vortex (SCV) in the Ligurian Sea (NW Mediterranean Sea). Those measurements are complemented by full-depth CTD casts (T, S, and oxygen) and water samples documenting nutrients and phytoplankton pigments within the SCV and outside. The SCV has a very homogeneous core of oxygenated waters between 300 and 1200 m formed 4.5 months earlier during the winter deep convection event. It has a strong dynamical signature with peak velocities at 700 m depth of 13.9 cm s−1 in cyclogeostrophic balance. The eddy has a small radius of 6.2 km corresponding to high Rossby number of −0.45. The vorticity at the eddy center reaches −0.8f. Cross-stream isopycnic diffusion of tracers between the eddy core and the surroundings is found to be very limited due to dynamical barriers set by the SCV associated with a diffusivity coefficient of about 0.2 m2 s−1. The deep core is nutrients-depleted with concentrations of nitrate, phosphate, and silicate, 13–18% lower than the rich surrounding waters. However, the nutriclines are shifted of about 20–50 m toward the surface thus increasing the nutrients availability for phytoplankton. Chlorophyll-a concentrations at the deep chlorophyll maximum are subsequently about twice bigger as compared to outside. Pigments further reveal the predominance of nanophytoplankton inside the eddy and an enhancement of the primary productivity. This study demonstrates the important impact of postconvective SCVs on nutrients distribution and phytoplankton community, as well as on the subsequent primary production and carbon sequestration.
      PubDate: 2017-08-03T00:30:59.749628-05:
      DOI: 10.1002/2016JC012634
  • Winter to summer oceanographic observations in the Arctic Ocean north of
    • Authors: Amelie Meyer; Arild Sundfjord, Ilker Fer, Christine Provost, Nicolas Villacieros Robineau, Zoe Koenig, Ingrid H. Onarheim, Lars H. Smedsrud, Pedro Duarte, Paul A. Dodd, Robert M. Graham, Sunke Schmidtko, Hanna M. Kauko
      Pages: 6218 - 6237
      Abstract: Oceanographic observations from the Eurasian Basin north of Svalbard collected between January and June 2015 from the N-ICE2015 drifting expedition are presented. The unique winter observations are a key contribution to existing climatologies of the Arctic Ocean, and show a ∼100 m deep winter mixed layer likely due to high sea ice growth rates in local leads. Current observations for the upper ∼200 m show mostly a barotropic flow, enhanced over the shallow Yermak Plateau. The two branches of inflowing Atlantic Water are partly captured, confirming that the outer Yermak Branch follows the perimeter of the plateau, and the inner Svalbard Branch the coast. Atlantic Water observed to be warmer and shallower than in the climatology, is found directly below the mixed layer down to 800 m depth, and is warmest along the slope, while its properties inside the basin are quite homogeneous. From late May onwards, the drift was continually close to the ice edge and a thinner surface mixed layer and shallower Atlantic Water coincided with significant sea ice melt being observed.
      PubDate: 2017-08-04T08:05:58.613009-05:
      DOI: 10.1002/2016JC012391
  • Dense shelf water spreading from Antarctic coastal polynyas to the deep
           Southern Ocean: A regional circumpolar model study
    • Authors: Kazuya Kusahara; Guy D. Williams, Takeshi Tamura, Robert Massom, Hiroyasu Hasumi
      Pages: 6238 - 6253
      Abstract: The spreading of dense shelf water (DSW) from Antarctic coastal margins to lower latitudes plays a vital role in the ocean thermohaline circulation and the global climate system. Through enhanced localized sea ice production in Antarctic coastal polynyas, cold and saline DSW is formed over the continental shelf regions as a precursor to Antarctic Bottom Water (AABW). However, the detailed fate of coastal DSW over the Southern Ocean is still unclear. Here we conduct extensive passive tracer experiments using a circumpolar ocean-sea ice-ice shelf model to investigate pathways of the regional polynya-based DSW from the Antarctic margins to the deep Southern Ocean basins. In the numerical experiments, the Antarctic coastal margin is divided into nine regions, and a passive tracer is released from each region at the same rate as the local sea ice production. The modeled spatial distribution of the total concentration of the nine tracers is consistent with the observed AABW distribution and clearly demonstrates nine routes of the DSW over the Southern Ocean along its bottom topography. Furthermore, the model shows that while ∼50% of the total tracer is distributed northward from the continental shelf to the deep ocean, ∼7% is transported poleward beneath ice shelf cavities. The comprehensive tracer experiments allow us to estimate the contribution of local DSW to the total concentration along each of the pathways.
      PubDate: 2017-08-04T08:07:54.802418-05:
      DOI: 10.1002/2017JC012911
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