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Science 17 July 2009:
Vol. 325. no. 5938, pp. 310 - 314
DOI: 10.1126/science.1171041
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Reports

Transient Simulation of Last Deglaciation with a New Mechanism for Bølling-Allerød Warming

Z. Liu,1,2,3,* B. L. Otto-Bliesner,4 F. He,3 E. C. Brady,4 R. Tomas,4 P. U. Clark,5 A. E. Carlson,6 J. Lynch-Stieglitz,7 W. Curry,8 E. Brook,5 D. Erickson,9 R. Jacob,10 J. Kutzbach,3 J. Cheng1,3

We conducted the first synchronously coupled atmosphere-ocean general circulation model simulation from the Last Glacial Maximum to the Bølling-Allerød (BA) warming. Our model reproduces several major features of the deglacial climate evolution, suggesting a good agreement in climate sensitivity between the model and observations. In particular, our model simulates the abrupt BA warming as a transient response of the Atlantic meridional overturning circulation (AMOC) to a sudden termination of freshwater discharge to the North Atlantic before the BA. In contrast to previous mechanisms that invoke AMOC multiple equilibrium and Southern Hemisphere climate forcing, we propose that the BA transition is caused by the superposition of climatic responses to the transient CO2 forcing, the AMOC recovery from Heinrich Event 1, and an AMOC overshoot.

1 Key Laboratory of Meteorological Disaster, Nanjing University of Information Science and Technology, Nanjing, 210044, China.
2 State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, 710075, China.
3 Center for Climatic Research and Department of Atmospheric and Oceanic Sciences, University of Wisconsin, Madison, WI 53706, USA.
4 Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO 80307–3000, USA.
5 Department of Geosciences, Oregon State University, Corvallis, OR 97331, USA.
6 Department of Geology and Geophysics and Center for Climatic Research, University of Wisconsin, Madison, WI 53706, USA.
7 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA.
8 Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
9 Oak Ridge National Laboratory, Oak Ridge, TN 37831–6016, USA.
10 Mathematics and Computer Science Division, Argonne National Laboratory, Argonne, IL 60439–4843, USA.

* To whom correspondence should be addressed. E-mail: zliu3{at}wisc.edu

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