Articles | Volume 3, issue 1
Clim. Past, 3, 97–107, 2007
https://doi.org/10.5194/cp-3-97-2007

Special issue: Paleoclimate, environmental sustainability and our future

Clim. Past, 3, 97–107, 2007
https://doi.org/10.5194/cp-3-97-2007

  07 Feb 2007

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,* M. Schulz et al.
  • 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.