Low-frequency oscillations of the Atlantic Ocean meridional overturning circulation in a coupled climate model

M Schulz (1, 2) , M. Prange (1, 2) , A. Klocker (1)

1 Department of Geosciences
2 DFG Research Center "Ocean Margins"

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 present-day boundary conditions. A weak and continuous freshwater input into 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 and future climate variations.

Domaines: Interfaces continentales, environnement; Sciences de la Terre

M Schulz, M. Prange, A. Klocker. Low-frequency oscillations of the Atlantic Ocean meridional overturning circulation in a coupled climate model. Climate of the Past Discussions, 2006, 2 (5), pp.801-830. ⟨hal-00298149⟩