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Minimal change in Antarctic Circumpolar Current flow speed between the last glacial and Holocene

Nature Geoscience volume 7, pages 113–116 (2014)Cite this article

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Abstract

The Antarctic Circumpolar Current is key to the mixing and ventilation of the world’s oceans1,2,3,4,5. This current flows from west to east between about 45° and 70° S (refs 1, 2, 3) connecting the Atlantic, Pacific and Indian oceans, and is driven by westerly winds and buoyancy forcing. High levels of productivity in the current regulate atmospheric CO2 concentrations6. Reconstructions of the current during the last glacial period suggest that flow speeds were faster7 or similar8 to present, and it is uncertain whether the strength and position of the westerly winds changed9,10,11. Here we reconstruct Antarctic Circumpolar Current bottom speeds through the constricting Drake Passage and Scotia Sea during the Last Glacial Maximum and Holocene based on the mean grain size of sortable silt from a suite of sediment cores. We find essentially no change in bottom flow speeds through the region, and, given that the momentum imparted by winds, and modulated by sea-ice cover, is balanced by the interaction of these flows with the seabed, this argues against substantial changes in wind stress. However, glacial flow speeds in the sea-ice zone12 south of 56° S were significantly slower than present, whereas flow in the north was faster, but not significantly so. We suggest that slower flow over the rough topography south of 56° S may have reduced diapycnal mixing in this region during the last glacial period, possibly reducing the diapycnal contribution to the Southern Ocean overturning circulation.

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Figure 1: Scotia Sea core locations.
Figure 2: Average particle size.

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Acknowledgements

This work was financially supported by the award of an Emeritus Fellowship to I.N.M. by the Leverhulme Foundation. We are grateful to R. Pugh for his Coulter counter measurements on core PC287 and C. Pudsey for providing some of the magnetic susceptibility data on the BAS cores. We are grateful for discussions with A. Watson, H. Bryden, A. de Boer and A. Naveira-Garabato.

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Authors and Affiliations

  1. Department of Earth Sciences, Godwin Laboratory for Palaeoclimate Research, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK

    I. N. McCave & S. J. Crowhurst

  2. Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Am Alten Hafen 26, Bremerhaven D-27568, Germany

    G. Kuhn

  3. British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK

    C-D. Hillenbrand & M. P. Meredith

  4. Scottish Association for Marine Science, Oban PA37 1QA, UK

    M. P. Meredith

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  1. I. N. McCave
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  4. C-D. Hillenbrand
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  5. M. P. Meredith
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Contributions

The study was conceived by I.N.M. who performed the age modelling, made some of the size measurements and wrote the paper. S.J.C. prepared samples and made some of the size measurements. G.K. (who had support from the ESF HOLOCLIP project) and C-D.H. provided some prepared samples and ancillary core data that enabled age modelling, and provided critical input on regional oceanography and sedimentation. M.P.M. provided input and writing on the physical oceanographic interpretation of the sediment records. All authors contributed to the final version.

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Correspondence to I. N. McCave.

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McCave, I., Crowhurst, S., Kuhn, G. et al. Minimal change in Antarctic Circumpolar Current flow speed between the last glacial and Holocene. Nature Geosci 7, 113–116 (2014). https://doi.org/10.1038/ngeo2037

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