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  • 1
    Publication Date: 2017-10-24
    Description: This study examines the role of processes transporting tracers across the Polar Front (PF) in the depth interval between the surface and major topographic sills, which this study refers to as the “PF core.” A preindustrial control simulation of an eddying climate model coupled to a biogeochemical model [GFDL Climate Model, version 2.6 (CM2.6)– simplified version of the Biogeochemistry with Light Iron Nutrients and Gas (miniBLING) 0.1° ocean model] is used to investigate the transport of heat, carbon, oxygen, and phosphate across the PF core, with a particular focus on the role of mesoscale eddies. The authors find that the total transport across the PF core results from a ubiquitous Ekman transport that drives the upwelled tracers to the north and a localized opposing eddy transport that induces tracer leakages to the south at major topographic obstacles. In the Ekman layer, the southward eddy transport only partially compensates the northward Ekman transport, while below the Ekman layer, the southward eddy transport dominates the total transport but remains much smaller in magnitude than the near-surface northward transport. Most of the southward branch of the total transport is achieved below the PF core, mainly through geostrophic currents. This study finds that the eddy-diffusive transport reinforces the southward eddy-advective transport for carbon and heat, and opposes it for oxygen and phosphate. Eddy-advective transport is likely to be the leading-order component of eddy-induced transport for all four tracers. However, eddy-diffusive transport may provide a significant contribution to the southward eddy heat transport due to strong along-isopycnal temperature gradients.
    Type: Article , PeerReviewed
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  • 2
    Publication Date: 2018-02-02
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 8 (2017): 172, doi:10.1038/s41467-017-00197-0.
    Description: Upwelling of global deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. However, the exact pathways and role of topography in Southern Ocean upwelling remain largely unknown. Here we show detailed upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution models. The analysis reveals that the northern-sourced deep waters enter the Antarctic Circumpolar Current via southward flow along the boundaries of the three ocean basins, before spiraling southeastward and upward through the Antarctic Circumpolar Current. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the Antarctic Circumpolar Current, with a spatially nonuniform distribution. The timescale for half of the deep water to upwell from 30° S to the mixed layer is ~60–90 years.
    Description: V.T., L.D.T., and M.R.M. were supported by NSF OCE-1357072. A.K.M., H.F.D., and W.W. were supported by the RGCM program of the US Department of Energy under Contract DE-SC0012457. J.L.S. acknowledges NSF’s Southern Ocean Carbon and Climate Observations and Modeling project under NSF PLR-1425989, which partially supported L.D.T. and M.R.M. as well. C.O.D was supported by the National Aeronautics and Space Administration (NASA) under Award NNX14AL40G and by the Princeton Environmental Institute Grand Challenge initiative. A.R.G. was supported by a Climate and Global Change Postdoctoral Fellowship from the National Oceanic and Atmospheric Administration (NOAA). S.M.G. acknowledges the ongoing support of NOAA/GFDL for high-end ocean and climate-modeling activities. J.W. acknowledges support from NSF OCE-1234473.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
    Publication Date: 2018-02-05
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 9 (2018): 209, doi:10.1038/s41467-017-02105-y.
    Description: Correction to: Nature Communications 8:172 https://doi.org/10.1038/s41467-017-00197-0; Article published online: 2 August 2017
    Repository Name: Woods Hole Open Access Server
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  • 4
    Publication Date: 2016-09-26
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 41 (2014): 8438–8444, doi:10.1002/2014GL061574.
    Description: Along the continental margins, rivers and submarine groundwater supply nutrients, trace elements, and radionuclides to the coastal ocean, supporting coastal ecosystems and, increasingly, causing harmful algal blooms and eutrophication. While the global magnitude of gauged riverine water discharge is well known, the magnitude of submarine groundwater discharge (SGD) is poorly constrained. Using an inverse model combined with a global compilation of 228Ra observations, we show that the SGD integrated over the Atlantic and Indo-Pacific Oceans between 60°S and 70°N is (12 ± 3) × 1013 m3 yr−1, which is 3 to 4 times greater than the freshwater fluxes into the oceans by rivers. Unlike the rivers, where more than half of the total flux is discharged into the Atlantic, about 70% of SGD flows into the Indo-Pacific Oceans. We suggest that SGD is the dominant pathway for dissolved terrestrial materials to the global ocean, and this necessitates revisions for the budgets of chemical elements including carbon.
    Description: This work was supported by the Ministry of Oceans and Fisheries, Korea, through the Korea Institute of Marine Science and Technology (KIMST) (20120176) and National Research Foundation (NRF) of Korea (2013R1A2A1A05004343 and 2013R1A1A1058203). Charette and Moore's contributions were supported by the US National Science Foundation through the GEOTRACES project.
    Keywords: Submarine groundwater discharge ; Radium ; Inverse modeling ; Land-ocean interaction ; Brackish groundwater ; Coastal flux
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
    Publication Date: 2018-07-31
    Description: Author Posting. © American Geophysical Union, 2018. 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 45 (2018): 891–898, doi:10.1002/2017GL076045.
    Description: In this paper we study upwelling pathways and timescales of Circumpolar Deep Water (CDW) in a hierarchy of models using a Lagrangian particle tracking method. Lagrangian timescales of CDW upwelling decrease from 87 years to 31 years to 17 years as the ocean resolution is refined from 1° to 0.25° to 0.1°. We attribute some of the differences in timescale to the strength of the eddy fields, as demonstrated by temporally degrading high-resolution model velocity fields. Consistent with the timescale dependence, we find that an average Lagrangian particle completes 3.2 circumpolar loops in the 1° model in comparison to 0.9 loops in the 0.1° model. These differences suggest that advective timescales and thus interbasin merging of upwelling CDW may be overestimated by coarse-resolution models, potentially affecting the skill of centennial scale climate change projections.
    Description: Department of Energy's RGCM Grant Number: DE-SC0012457; Southern Ocean Carbon and Climate Observation and Modeling Grant Number: PLR-1425989; Climate and Global Change Postdoctoral Fellowship from the National Oceanic and Atmospheric Administration; Australian Research Council DECRA Fellowship Grant Number: DE170100184
    Description: 2018-07-31
    Keywords: Meridional overturning circulation ; Southern Ocean ; Circumpolar Deep Water ; Upwelling ; Eddy parameterization ; Ocean modeling
    Repository Name: Woods Hole Open Access Server
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  • 6
    Publication Date: 2018-05-07
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Remote Sensing of Environment 135 (2013): 77-91, doi:10.1016/j.rse.2013.03.025.
    Description: Photosynthetic production of organic matter by microscopic oceanic phytoplankton fuels ocean ecosystems and contributes roughly half of the Earth's net primary production. For 13 years, the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) mission provided the first consistent, synoptic observations of global ocean ecosystems. Changes in the surface chlorophyll concentration, the primary biological property retrieved from SeaWiFS, have traditionally been used as a metric for phytoplankton abundance and its distribution largely reflects patterns in vertical nutrient transport. On regional to global scales, chlorophyll concentrations covary with sea surface temperature (SST) because SST changes reflect light and nutrient conditions. However, the ocean may be too complex to be well characterized using a single index such as the chlorophyll concentration. A semi-analytical bio-optical algorithm is used to help interpret regional to global SeaWiFS chlorophyll observations from using three independent, well-validated ocean color data products; the chlorophyll a concentration, absorption by CDM and particulate backscattering. First, we show that observed long-term, global-scale trends in standard chlorophyll retrievals are likely compromised by coincident changes in CDM. Second, we partition the chlorophyll signal into a component due to phytoplankton biomass changes and a component caused by physiological adjustments in intracellular chlorophyll concentrations to changes in mixed layer light levels. We show that biomass changes dominate chlorophyll signals for the high latitude seas and where persistent vertical upwelling is known to occur, while physiological processes dominate chlorophyll variability over much of the tropical and subtropical oceans. The SeaWiFS data set demonstrates complexity in the interpretation of changes in regional to global phytoplankton distributions and illustrates limitations for the assessment of phytoplankton dynamics using chlorophyll retrievals alone.
    Description: The authors would like to acknowledge the NASA Ocean Biology and Biogeochemistry program for its long-term support of satellite ocean color research and the Orbital Sciences Corporation and GeoEye who were responsible for the launch, satellite integration and on-orbit management the SeaWiFS mission.
    Keywords: Ocean color ; SeaWiFS ; Phytoplankton ; Colored dissolved organic matter ; Decadal trends
    Repository Name: Woods Hole Open Access Server
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  • 7
    Publication Date: 2019-09-23
    Description: The ocean is estimated to contribute up to ~20% of global fluxes of atmospheric nitrous oxide (N2O), an important greenhouse gas and ozone depletion agent. Marine oxygen minimum zones contribute disproportionately to this flux. To further understand the partition of nitrification and denitrification and their environmental controls on marine N2O fluxes, we report new relationships between oxygen concentration and rates of N2O production from nitrification and denitrification directly measured with 15N tracers in the Eastern Tropical Pacific. Highest N2O production rates occurred near the oxic‐anoxic interface, where there is strong potential for N2O efflux to the atmosphere. The dominant N2O source in oxygen minimum zones was nitrate reduction, the rates of which were 1 to 2 orders of magnitude higher than those of ammonium oxidation. The presence of oxygen significantly inhibited the production of N2O from both nitrification and denitrification. These experimental data provide new constraints to a multicomponent global ocean biogeochemical model, which yielded annual oceanic N2O efflux of 1.7–4.4 Tg‐N (median 2.8 Tg‐N, 1 Tg = 1012 g), with denitrification contributing 20% to the oceanic flux. Thus, denitrification should be viewed as a net N2O production pathway in the marine environment.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 8
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    AGU (American Geological Union) | Wiley
    In:  Global Biogeochemical Cycles, 33 (8). pp. 942-956.
    Publication Date: 2019-11-15
    Description: We use observations from novel biogeochemical profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling program to estimate annual net community production (ANCP; associated with carbon export) from the seasonal drawdown of mesopelagic oxygen and surface nitrate in the Southern Ocean. Our estimates agree with previous observations in showing an increase in ANCP in the vicinity of the polar front (∼3 mol C m−2 y−1), compared to lower rates in the subtropical zone (≤ 1 mol C m−2 y−1) and the seasonal ice zone (〈2 mol C m−2 y−1). Paradoxically, the increase in ANCP south of the subtropical front is associated with elevated surface nitrate and silicate concentrations, but decreasing surface iron. We hypothesize that iron limitation promotes silicification in diatoms, which is evidenced by the low silicate to nitrate ratio of surface waters around the Antarctic polar front. High diatom silicification increases the ballasting effect of particulate organic carbon and overall ANCP in this region. A model-based assessment of our methods shows a good agreement between ANCP estimates based on oxygen and nitrate drawdown and the modeled downward organic carbon flux at 100 m. This agreement supports the presumption that net biological consumption is the dominant process affecting the drawdown of these chemical tracers and that, given sufficient data, ANCP can be inferred from observations of oxygen and/or nitrate drawdown in the Southern Ocean.
    Keywords: Course of study: MSc Biological Oceanography
    Type: Article , PeerReviewed
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  • 9
    Publication Date: 2015-12-01
    Print ISSN: 0012-821X
    Electronic ISSN: 1385-013X
    Topics: Geosciences , Physics
    Published by Elsevier
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  • 10
    Publication Date: 2018-12-01
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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