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Abrupt changes in Antarctic Intermediate Water circulation over the past 25,000 years

Nature Geoscience volume 1, pages 870874 (2008) | Download Citation

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Abstract

The circulation of Antarctic Intermediate Water is thought to make an important contribution to the global ocean–climate system, but the details of this interaction are not fully understood. Furthermore, the behaviour of Antarctic Intermediate Water under glacial and interglacial conditions is not well constrained. Here we present a 25,000-year-long record of neodymium isotopic variations—a tracer of water-mass mixing—from the middle depths of the tropical Atlantic Ocean. Our data reveal abruptly enhanced northward advection of Antarctic Intermediate Water during periods of reduced North Atlantic overturning circulation during the last deglaciation. These events coincide with an increase in the formation of Antarctic Intermediate Water and warming in the southwest Pacific Ocean, which suggests a tight link with Southern Hemisphere climate. In contrast, the initial incursion of southern source water into the North Atlantic 19,000 years ago coincided with weak Antarctic Intermediate Water formation in the Pacific and reduced overturning in the North Atlantic. We conclude that reduced competition at intermediate water depth at this time allowed expansion of Antarctic Intermediate Water into the North Atlantic. This early incursion of Antarctic Intermediate Water may have contributed to freshening of the North Atlantic, perhaps spurring the subsequent collapse of North Atlantic deep convection.

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Acknowledgements

We thank R. Zahn (Universitat Autonoma de Barcelona, Spain) and D. Oppo (Woods Hole Oceanographic Institution, USA) for providing core material, S. Gitt (UNC Chapel Hill) for laboratory assistance and R. Mortlock (LDEO) for running the stable isotope mass spectrometer. K.P. thanks T. van de Flierdt, D. Zylberberg and Y. Cai for introducing her to laboratory procedures and methods. This study was supported by a Lamont Postdoctoral Fellowship to K.P., and grants from the US National Science Foundation and National Oceanographic and Atmospheric Administration. The data will be made available on the NOAA Paleoclimatology website (www.ngdc.noaa.gov/paleo/data.html). This is LDEO contribution no. 7214.

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Affiliations

  1. Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA

    • Katharina Pahnke
    • , Steven L. Goldstein
    •  & Sidney R. Hemming
  2. Department of Earth and Environmental Sciences, Columbia University, New York 10027, USA

    • Steven L. Goldstein
    •  & Sidney R. Hemming

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Contributions

Samples were processed and analysed by K.P. All authors contributed to the discussion and interpretation of the results.

Corresponding author

Correspondence to Katharina Pahnke.

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https://doi.org/10.1038/ngeo360

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