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Eddy transport as a key component of the Antarctic overturning circulation

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Abstract

The exchange of water masses across the Antarctic continental shelf break regulates the export of dense shelf waters to depth as well as the transport of warm, mid-depth waters towards ice shelves and glacial grounding lines1. The penetration of the warmer mid-depth waters past the shelf break has been implicated in the pronounced loss of ice shelf mass over much of west Antarctica2,3,4. In high-resolution, regional circulation models, the Antarctic shelf break hosts an energetic mesoscale eddy field5,6, but observations that capture this mesoscale variability have been limited. Here we show, using hydrographic data collected from ocean gliders, that eddy-induced transport is a primary contributor to mass and property fluxes across the slope. Measurements along ten cross-shelf hydrographic sections show a complex velocity structure and a stratification consistent with an onshore eddy mass flux. We show that the eddy transport and the surface wind-driven transport make comparable contributions to the total overturning circulation. Eddy-induced transport is concentrated in the warm, intermediate layers away from frictional boundaries. We conclude that understanding mesoscale dynamics will be critical for constraining circumpolar heat fluxes and future rates of retreat of Antarctic ice shelves.

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Figure 1: Overview of the study region.
Figure 2: Cross-slope PV characteristics.
Figure 3: Summary of cross-slope exchange.

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Acknowledgements

The authors thank the officers and crew of the RRS James Clark Ross for help in deploying and recovering the gliders. A.F.T. was financially supported by NSF award OPP-1246460. S.S. and K.J.H. were financially supported by the NERC Antarctic Funding Initiative research grant GENTOO NE/H01439X/1. A.L.S. was supported by the President’s and Director’s Fund program at Caltech.

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Authors and Affiliations

  1. Environmental Science and Engineering, California Institute of Technology, MC 131-24, 1200 East California Boulevard, Pasadena, California 91125, USA

    Andrew F. Thompson & Andrew L. Stewart

  2. School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK

    Karen J. Heywood & Sunke Schmidtko

  3. GEOMAR, Helmholtz Center for Ocean Research, Düsternbrooker Weg 20, D-24105 Kiel, Germany

    Sunke Schmidtko

  4. Los Angeles Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California 90095, USA

    Andrew L. Stewart

Authors
  1. Andrew F. Thompson
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  2. Karen J. Heywood
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  3. Sunke Schmidtko
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  4. Andrew L. Stewart
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Contributions

K.J.H. and A.F.T. conceived and designed the field program; A.F.T., K.J.H. and S.S. collected the data; S.S. processed the data; A.F.T. and S.S. analysed the data; A.F.T., K.J.H., S.S. and A.L.S. co-wrote the paper.

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Correspondence to Andrew F. Thompson.

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The authors declare no competing financial interests.

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Thompson, A., Heywood, K., Schmidtko, S. et al. Eddy transport as a key component of the Antarctic overturning circulation. Nature Geosci 7, 879–884 (2014). https://doi.org/10.1038/ngeo2289

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