Article | Published:

Strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation

Naturevolume 430pages851856 (2004) | Download Citation



The climate of the last glacial period was extremely variable, characterized by abrupt warming events in the Northern Hemisphere, accompanied by slower temperature changes in Antarctica and variations of global sea level. It is generally accepted that this millennial-scale climate variability was caused by abrupt changes in the ocean thermohaline circulation. Here we use a coupled ocean–atmosphere–sea ice model to show that freshwater discharge into the North Atlantic Ocean, in addition to a reduction of the thermohaline circulation, has a direct effect on Southern Ocean temperature. The related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical North Atlantic caused by a fast wave-adjustment process. We present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of Greenland and Antarctic temperature changes, the slow changes in Antarctic temperature and its similarity to sea level, as well as a possible time lag of sea level with respect to Antarctic temperature during Marine Isotope Stage 3.

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We are grateful to the model developers and KNMI for making ECBILT-CLIO available to the scientific community, to F. Justino and U. Krebs for setting-up the glacial version of the model, and to N. Shackleton for discussions. This work was supported by the Swiss National Science Foundation, the Swiss Federal Office of Science and Education through the EC project POP and the University of Bern. A.T. was supported by the Deutsche Forschungsgemeinschaft through a Collaborative Research Project.

Author information


  1. Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, CH-3012, Bern, Switzerland

    • R. Knutti
    • , J. Flückiger
    •  & T. F. Stocker
  2. IFM-GEOMAR, Leibniz-Institut für Meereswissenschaften, Düsternbrooker Weg 20, D-24105, Kiel, Germany

    • A. Timmermann


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Competing interests

The authors declare that they have no competing financial interests.

Corresponding author

Correspondence to R. Knutti.

Supplementary information

  1. Supplementary Figure 1

    Sensitivity of the CGAOM to glacial boundary conditions. (PDF 90 kb)

  2. Supplementary Figure 1 Legend

    Sensitivity of the CGAOM to glacial boundary conditions. (DOC 24 kb)

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