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A seasonal cycle in the export of bottom water from the Weddell Sea

Nature Geoscience volume 3, pages 551–556 (2010)Cite this article

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Abstract

Dense water formed over the Antarctic continental shelf rapidly descends into the deep ocean where it spreads throughout the global ocean as Antarctic Bottom Water1,2. The coldest and most voluminous component of this water mass is Weddell Sea bottom water1,3,4,5,6,7. Here we present observations over eight years of the temperature and salinity stratification in the lowermost ocean southeast of the South Orkney Islands, marking the export of Weddell Sea bottom water. We observe a pronounced seasonal cycle in bottom temperatures, with a cold pulse in May/June and a warm one in October/November, but the timing of these phases varies each year. We detect the coldest bottom water in 1999 and 2002, whereas there was no cold phase in 2000. On the basis of current velocities and water mass characteristics, we infer that the pulses originate from the southwest Weddell Sea. We propose that the seasonal fluctuations of Weddell Sea bottom-water properties are governed by the seasonal cycle of the winds over the western margin of the Weddell Sea. Interannual fluctuations are linked to the variability of the wind-driven Weddell Sea gyre and hence to large-scale climate phenomena such as the Southern Annular Mode and El Niño/Southern Oscillation.

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Figure 1: Weddell Sea moorings.
Figure 2: Eight-year time series at mooring M2 and M3.
Figure 3: Bottom θ °C and salinity relationship at M2 and M3.
Figure 4: Weddell Sea wind and climate indices.

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Acknowledgements

This research was financially supported under the Cooperative Institute for Climate Applications Research award number NA08OAR4320754 from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. The statements, findings, conclusions and recommendations are those of the author(s) and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration or the Department of Commerce. Lamont Doherty Contribution number 7369.

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Authors and Affiliations

  1. Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, New York 10964-8000, USA

    Arnold L. Gordon, Bruce Huber & Darren McKee

  2. Leibniz-Institut fuer Meereswissenschaften (IFM-GEOMAR), Duesternbrooker Weg 20 D-24105 Kiel, Germany

    Martin Visbeck

Authors
  1. Arnold L. Gordon
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  2. Bruce Huber
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  3. Darren McKee
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  4. Martin Visbeck
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Contributions

A.L.G. led the data analysis and leads the data collection programme. B.H. supervised the collection and processing of the data reported, and prepared the Methods section. D.M. investigated the relation of the Weddell Sea wind. M.V. contributed to the SAM discussion and was instrumental in the initiation of the Weddell time series.

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Correspondence to Arnold L. Gordon.

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Gordon, A., Huber, B., McKee, D. et al. A seasonal cycle in the export of bottom water from the Weddell Sea. Nature Geosci 3, 551–556 (2010). https://doi.org/10.1038/ngeo916

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