A Tropical Mechanism for Northern Hemisphere Deglaciation


  Keith B. Rodgers, Gerrit Lohmann, Stephan Lorenz, Ralph Schneider, and Gideon M. Henderson


  Geochemistry, Geophysics, Geosystems (G3) 4(5), 1046, doi: 10.1029/2003GC0000508, 2003



  We investigate the role of the tropics in the melting and reforming of the Laurentide ice sheet on glacial timescales using an atmospheric general circulation model. It is found that warming of tropical sea surface temperatures (SST) from glacial boundary conditions, as observed at the end of glacial periods [Bard et al., 1997 (Somali Basin records); Lea et al., 2000; N?rnberg et al., 2000; Seltzer et al., 2002], causes a large increase in summer temperatures centered over the ice-sheet-forming regions of Canada. This high latitude response to tropical change is due to relatively small changes in the circulation of the extratropical atmosphere which lead to changes in the vertical profiles of temperature and moisture in the extratropical atmosphere. These changes via an atmospheric bridge between the tropics and extratropics represent a mechanism for deglaciations which is consistent with timing constraints. In contrast, a cold perturbation to tropical SST for interglacial boundary conditions results in very little change in circulation and almost no cooling over the Canadian region. This implies that tropical SSTs could play a more important role in melting ice sheets in the northern hemisphere than in reforming them, possibly providing a mechanism which could help to explain the relative rapidity of deglaciation.



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  Keith B. Rodgers

LSCE-UMR CEA-CNRS 1572, CE Saclay L'Orme de Merisiers Bat. 709, 91191 Gif sur Yvette Cedex, France

correspondence to Keith Rodgers rodgers@lodyc.jussieu.fr


  Gerrit Lohmann

Hamburg University, Department of Meteorology, Bundesstrasse 55, 20146 Hamburg, Germany

Bremen University, Geoscience Department, P.O. 330 440, 28334 Bremen, Germany


  Stephan Lorenz

Max Planck Institute for Meteorology, Bundesstrasse 55, 20146 Hamburg, Germany


  Ralph Schneider

Bremen University, Geoscience Department, P.O. 330 440, 28334 Bremen, Germany


  Gideon M. Henderson

Earth Sciences Department, University of Oxford, Oxford OX1 EPR, UK