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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C02008, doi:10.1029/2011JC007589.
    Description: Upper ocean thermohaline structure in the California Current System is investigated using sustained observations from autonomous underwater gliders and a numerical state estimate. Both observations and the state estimate show layers distinguished by the temperature and salinity variability along isopycnals (i.e., spice variance). Mesoscale and submesoscale spice variance is largest in the remnant mixed layer, decreases to a minimum below the pycnocline near 26.3 kg m−3, and then increases again near 26.6 kg m−3. Layers of high (low) meso- and submesoscale spice variance are found on isopycnals where large-scale spice gradients are large (small), consistent with stirring of large-scale gradients to produce smaller scale thermohaline structure. Passive tracer adjoint calculations in the state estimate are used to investigate possible mechanisms for the formation of the layers of spice variance. Layers of high spice variance are found to have distinct origins and to be associated with named water masses; high spice variance water in the remnant mixed layer has northerly origin and is identified as Pacific Subarctic water, while the water in the deeper high spice variance layer has southerly origin and is identified as Equatorial Pacific water. The layer of low spice variance near 26.3 kg m−3 lies between the named water masses and does not have a clear origin. Both effective horizontal diffusivity, κh, and effective diapycnal diffusivity, κv, are elevated relative to the diffusion coefficients set in the numerical simulation, but changes in κh and κv with depth are not sufficient to explain the observed layering of thermohaline structure.
    Description: We gratefully acknowledge funding from the Gordon and Betty Moore Foundation, the Coastal Ocean Currents Monitoring Project (COCMP), and NOAA. R. E. Todd was partially supported by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution, with funding provided by the Cooperative Institute for the North Atlantic Region.
    Description: 2012-08-03
    Keywords: California Current System ; Adjoint model ; Glider ; Passive tracer ; Spice ; Thermohaline structure
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 47(10), (2020): e2020GL087215, doi:10.1029/2020GL087215.
    Description: Cross‐equator transects occupied by an underwater glider and a research vessel in the western Indian Ocean captured the evolution of equatorial circulation during onset of the boreal summer monsoon in 2018. At the end of the winter monsoon in March, surface currents were westward, while the equatorial undercurrent carried salty Arabian Sea High‐Salinity Water eastward. As winds transitioned from westward to eastward during April, an eastward near‐surface Wyrtki Jet developed, while the equatorial undercurrent weakened, vanishing by May. A first‐mode baroclinic Kelvin wave propagated through the survey region after westward winds relaxed. However, the vertical structure of the evolving circulation was inconsistent with the first baroclinic mode, suggesting the influence of higher modes in setting observed vertical structure. The strong equatorial undercurrent at the end of the winter monsoon allowed high‐salinity waters from the western equatorial Indian Ocean to reach the southern Bay of Bengal in summer 2018.
    Description: This work was supported by the Office of Naval Research as part of the NASCar DRI under Grant N000141512632 and as part of the MISO‐BOB DRI under Grant N000141712968.
    Keywords: Monsoon ; Indian Ocean ; Equatorial ; Underwater glider ; Equatorial undercurrent
    Repository Name: Woods Hole Open Access Server
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  • 4
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(2), (2021): e2020GL090287, https://doi.org/10.1029/2020GL090287.
    Description: Salt marsh survival with sea‐level rise (SLR) increasingly relies on soil organic carbon (SOC) accumulation and preservation. Using a novel combination of geochemical approaches, we characterized fine SOC (≤1 mm) supporting marsh elevation maintenance. Overlaying thermal reactivity, source (δ13C), and age (F14C) information demonstrates several processes contributing to soil development: marsh grass production, redeposition of eroded material, and microbial reworking. Redeposition of old carbon, likely from creekbanks, represented ∼9%–17% of shallow SOC (≤26 cm). Soils stored marsh grass‐derived compounds with a range of reactivities that were reworked over centuries‐to‐millennia. Decomposition decreases SOC thermal reactivity throughout the soil column while the decades‐long disturbance of ponding accelerated this shift in surface horizons. Empirically derived estimates of SOC turnover based on geochemical composition spanned a wide range (640–9,951 years) and have the potential to inform predictions of marsh ecosystem evolution.
    Description: This work was supported by NSF (OCE1233678) and NOAA (NA14OAR4170104 and NA14NOS4190145) grants to ACS, USGS Coastal & Marine Geology Program, and PIE‐LTER (NSF OCE1238212 and OCE1637630).
    Description: 2021-06-11
    Keywords: Carbon isotopes ; Decomposition ; Organic matter composition ; Salt marsh ; Soil organic carbon
    Repository Name: Woods Hole Open Access Server
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  • 5
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125, (2020): e2020JC016609, doi:10.1029/2020JC016609.
    Description: The Equatorial Undercurrent (EUC) is a vital component of the coupled ocean‐atmosphere system in the tropical Pacific. The details of its termination near the Galápagos Islands in the eastern Pacific have an outsized importance to regional circulation and ecosystems. Subject to diverse physical processes, the EUC is also a rigorous benchmark for global climate models (GCMs). Simulations of the EUC in three generations of GCMs are evaluated relative to recent underwater glider observations along 93°W. Simulations of the EUC have improved, but a slow bias of ~36% remains in the eastern Pacific, along with a dependence on resolution. Additionally, the westward surface current is too slow, and stratification is too strong (weak) by ~50% above (within) the EUC. These biases have implications for mixing in the equatorial cold tongue. Downstream lies the Galápagos, now resolved to varying degrees by GCMs. Properly representing the Galápagos is necessary to avoid new biases as the EUC improves.
    Description: We gratefully acknowledge support from the National Science Foundation (OCE‐1232971 and OCE‐1233282) and the Global Ocean Monitoring and Observing program (formerly the Ocean Observing and Monitoring Division) of the National Oceanographic and Atmospheric Administration (NA13OAR4830216).
    Description: 2021-04-22
    Keywords: equatorial Pacific Ocean ; Equatorial Undercurrent ; global climate models ; underwater gliders
    Repository Name: Woods Hole Open Access Server
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  • 6
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(5), (2019):2704-2714, doi:10.1029/2019GL081919.
    Description: Seismic images and glider sections of the Gulf Stream front along the U.S. eastern seaboard capture deep, lens‐shaped submesoscale features. These features have radii of 5–20 km, thicknesses of 150–300 m, and are located at depths greater than 500 m. These are typical signatures of anticyclonic submesoscale coherent vortices. A submesoscale‐resolving realistic simulation, which reproduces submesoscale coherent vortices with the same characteristics, is used to analyze their generation mechanism. Submesoscale coherent vortices are primarily generated where the Gulf Stream meets the Charleston Bump, a deep topographic feature, due to the frictional effects and intense mixing in the wake of the topography. These submesoscale coherent vortices can transport waters from the Charleston Bump's thick bottom mixed layer over long distances and spread them within the subtropical gyre. Their net effect on heat and salt distribution remains to be quantified.
    Description: J. G. gratefully acknowledges support from the French government, managed by the French National Agency for Research (ANR), through programs ISblue (ANR‐17‐EURE‐0015) and LabexMER (ANR‐10‐LABX‐19) and from LEFE/IMAGO through the project AO2017‐994457‐RADII. Simulations were performed using HPC resources from GENCI‐TGCC (grant 2017‐A0010107638). Simulations output is available upon request. Seismic data were processed using the Echos software package by Paradigm, Matlab, and Generic Mapping Tools. The Eastern North America Margin Community Seismic Experiment was funded by the National Science Foundation under grant OCE‐1347498 and UNOLS; cruise data are freely available via the Marine Geoscience Data System Academic Seismic Portal at Lamont‐Doherty Earth Observatory (http://www.marine-geo.org/portals/seismic/). Spray glider observations in the Gulf Stream are available from http://spraydata.ucsd.edu and should be cited using the following DOI (10.21238/S8SPRAY2675; Todd & Owens, 2016). Spray glider operations were funded by the National Science Foundation (OCE‐1633911) and the Office of Naval Research (N000141713040).
    Description: 2019-08-27
    Keywords: Submesoscale coherent vortices ; Glider ; Seismic observations ; Gulf Stream ; Topographic interactions ; Charleston Bump
    Repository Name: Woods Hole Open Access Server
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  • 7
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 125(4), (2020): e2019JC016006, doi:10.1029/2019JC016006.
    Description: Equatorward flow of Middle Atlantic Bight (MAB) shelf waters meets poleward flowing South Atlantic Bight shelf waters over the continental shelf near Cape Hatteras, NC, leading to net export of shelf waters into the deep ocean. This export occurs in close proximity to the Gulf Stream, which separates from the continental margin near Cape Hatteras. Observations from sustained underwater glider surveys of the outer continental shelf and slope north of Cape Hatteras from spring 2017 to spring 2019 are used to examine the mean and variability of MAB shelf water export in the region. The 0.3 Sv (1 Sv = 106 m3 s−1) time‐mean export of MAB shelf water south of 37°N was dominated by discrete export events; 50% of export occurred during the 17% of the time during which transport was more than 1 standard deviation above the mean. These events typically occurred in late spring and summer of both years when equatorward flow into the region peaked. Export of MAB shelf water was correlated with equatorward flow into the region, which was itself correlated with the density gradient across the continental shelf break. Observations during specific time periods that capture extrema in MAB shelf water export are examined to highlight the variability in shelf‐deep ocean exchange scenarios in the Hatteras region. These include near‐surface export driven by hurricanes, subsurface export below the northern edge of the Gulf Stream, and a multi‐month near‐cessation of export.
    Description: Patrick Deane at WHOI and the Instrument Development Group at the Scripps Institution of Oceanography were key to the success of the Spray glider operations. Mike Muglia, Trip Taylor, and Nick DeSimone at the East Carolina University Coastal Studies Institute (CSI) provided support for glider deployments and recoveries. WHOI Summer Student Fellow Devon Gaynes assisted with analysis related to 2017 hurricanes. Spray glider observations used here are available from http://spraydata.ucsd.edu and should be cited using the following DOIs: 10.21238/S8SPRAY2675 (Todd & Owens, 2016) and 10.21238/S8SPRAY0880 (Todd, 2020). Buoy winds are available from the National Data Buoy Center (https://www.ndbc.noaa.gov). SST imagery was obtained from the Mid‐Atlantic Regional Association Coastal Ocean Observing System (MARACOOS) THREDDS server (http://tds.maracoos.org/thredds/ARCHIVE-SST.html). Automated Tropical Cyclone Forecast System data are available online (https://ftp.nhc.noaa.gov/atcf/). PEACH was funded by the National Science Foundation (OCE‐1558521). Colormaps are from Thyng et al. (2016).
    Description: 2020-09-17
    Keywords: Cape Hatteras ; Shelf-deep ocean exchange ; Underwater glider
    Repository Name: Woods Hole Open Access Server
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  • 8
    Publication Date: 2020-08-04
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
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  • 9
    Publication Date: 2017-06-26
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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