under a Creative Commons License. Climate of the Past Low-frequency oscillations of the Atlantic Ocean meridional overturning circulation in a coupled climate model

• Main Authors: M. Schulz, M. Prange, A. Klocker
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Labrador Sea; Nordic Seas
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.382.9365; http://hal.archives-ouvertes.fr/docs/00/29/80/67/PDF/cp-3-97-2007.pdf

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 deepwater 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. 1