| 英文摘要: | The Atlantic overturning circulation plays a key role in large-scale climate but how it varies is not well known. Now a study proposes that the weakening it may have experienced in the late 1970s is unprecedented over the last millennium. The Atlantic Ocean is the stage for one of the greatest oceanographic characters: the Atlantic Meridional Overturning Circulation (AMOC). This large-scale oceanic circulation links the surface and deep ocean through convection processes occurring in the North Atlantic. It brings warm waters from the tropics to the North Atlantic, where they cool, sink and return southwards at depth1. The associated net transport of heat plays a pivotal role in the climate of the regions bordering the Atlantic. For example, decadal variability of this circulation is believed to influence changes in Atlantic hurricane activity2 or frequency of droughts in the Sahel, in Africa3. Nevertheless, past changes in the AMOC are still not well understood due to the very short period of available reconstructions. A few estimates for the last 50 years propose that a substantial weakening of the AMOC has occurred in the 1970s4, followed by a recovery in the 1990s5. Writing in Nature Climate Change, Stefan Rahmstorf and colleagues6 report that the AMOC minimum in the late 1970s may have been the lowest over the last millennium.
FERRON / IFREMER / OVIDE
Iceberg in the North Atlantic. According to Rahmstorf et al.6, the melting of the Greenland ice sheet over the twentieth century may have lead to an exceptional weakening of the oceanic circulation in the North Atlantic in the 1970s. This photo was taken off the tip of Greenland, during an OVIDE oceanographic cruise in 2010.
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Affiliations
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Didier Swingedouw is at the Environnements et Paléoenvironnements Océaniques et Continentaux CNRS Laboratory, University of Bordeaux, Allée Geoffroy Saint-Hilaire, 33615 Pessac, France
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