Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
Clim. Past, 3, 97-107, 2007
http://www.clim-past.net/3/97/2007/
doi:10.5194/cp-3-97-2007
© Author(s) 2007. This work is licensed under the
Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.
 
07 Feb 2007
Low-frequency oscillations of the Atlantic Ocean meridional overturning circulation in a coupled climate model
M. Schulz1,2, M. Prange1,2, and A. Klocker1,* 1Department of Geosciences, University of Bremen, Germany
2DFG Research Center "Ocean Margins", University of Bremen, Germany
*now at: CSIRO Marine and Atmospheric Research, Hobart, Australia
Abstract. Using a 3-dimensional climate model of intermediate complexity we show that the overturning circulation of the Atlantic Ocean can vary at multicentennial-to-millennial timescales for modern boundary conditions. A continuous freshwater perturbation in the Labrador Sea pushes the overturning circulation of the Atlantic Ocean into a bi-stable regime, characterized by phases of active and inactive deep-water formation in the Labrador Sea. In contrast, deep-water formation in the Nordic Seas is active during all phases of the oscillations. The actual timing of the transitions between the two circulation states occurs randomly. The oscillations constitute a 3-dimensional phenomenon and have to be distinguished from low-frequency oscillations seen previously in 2-dimensional models of the ocean. A conceptual model provides further insight into the essential dynamics underlying the oscillations of the large-scale ocean circulation. The model experiments indicate that the coupled climate system can exhibit unforced climate variability at multicentennial-to-millennial timescales that may be of relevance for Holocene climate variations.

Citation: Schulz, M., Prange, M., and Klocker, A.: Low-frequency oscillations of the Atlantic Ocean meridional overturning circulation in a coupled climate model, Clim. Past, 3, 97-107, doi:10.5194/cp-3-97-2007, 2007.
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