Decadal Variations of the Atlantic Meridional Overturning Circulation

Thursday, 18 December 2014: 9:45 AM
Martin Visbeck, Jürgen Fischer, Johannes Karstensen and Rainer Zantopp, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
The Atlantic Meridional Overturning Circulation (AMOC) is a major component of the Earth’s climate system and a number of modelling and observational studies have proposed a declining AMOC in response to the expected global warming for the 21st century. Here we present 15 year-long time series of shallow and deep AMOC fingerprints in the North Atlantic. We find coherent decadal transport fluctuations in the range of 5•106 m3s-1, accounting for a significant fraction of the overall AMOC variability. At the exit of Labrador Sea, the fluctuations are confined to the deepest layers and explain 70% of the variance of transport fluctuations longer than 90 days. In the two upper layer time series, in the Gulf Stream region, and in the eastern part of the subpolar gyre, about 20% of the variances are associated with the decadal AMOC fluctuation. Wind stress curl fluctuations in the northern part of the subpolar gyre appear to be in phase with the transport fluctuation and suggest atmospheric forcing of the basin-scale decadal variability. Implications for the AMOC variability on these time scales and AMOC observing system requirements to detect long-term trends are discussed.