Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation

• Published in: Nature
• Main Authors: Biastoch, Arne, Böning, Claus W., Lutjeharms, J. R. E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Publishing Group 2008
• Subjects: Arctic; Labrador Sea; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/8189/; https://oceanrep.geomar.de/id/eprint/8189/1/nature07426.pdf; https://doi.org/10.1038/nature07426

Predicting the evolution of climate over decadal timescales requires a quantitative understanding of the dynamics that govern the meridional overturning circulation (MOC)1. Comprehensive ocean measurement programmes aiming to monitor MOC variations have been established in the subtropical North Atlantic2, 3 (RAPID, at latitude 26.5° N, and MOVE, at latitude 16° N) and show strong variability on intraseasonal to interannual timescales. Observational evidence of longer-term changes in MOC transport remains scarce, owing to infrequent sampling of transoceanic sections over past decades4, 5. Inferences based on long-term sea surface temperature records, however, supported by model simulations, suggest a variability with an amplitude of plusminus1.5–3 Sv (1 Sv = 106 m3 s-1) on decadal timescales in the subtropics6. Such variability has been attributed to variations of deep water formation in the sub-arctic Atlantic, particularly the renewal rate of Labrador Sea Water7. Here we present results from a model simulation that suggest an additional influence on decadal MOC variability having a Southern Hemisphere origin: dynamic signals originating in the Agulhas leakage region at the southern tip of Africa. These contribute a MOC signal in the tropical and subtropical North Atlantic that is of the same order of magnitude as the northern source. A complete rationalization of observed MOC changes therefore also requires consideration of signals arriving from the south.