Freshwater flux forcing of decadal and interdecadal oceanic variability

THE ocean's thermohaline circulation, driven by fluxes of freshwater and heat through the ocean's surface, is important in the transport of heat from low to high latitudes. Changes in the intensity of this circulation, and hence the poleward heat transport, would have a significant effect on global climate. Numerous observations of the air–sea–ice climate system in and around the North Atlantic show significant variability on decadal and inter-decadal timescales1–11; these timescales suggest that the source of the variability lies in the ocean itself. Here we present the results of three numerical experiments which show the importance of freshwater flux forcing (the difference between precipitation and evaporation, or 'P–E') in exciting decadal and interdecadal oceanic variability. If a sufficiently strong local minimum exists in this P–E forcing field (as is observed over the Greenland Sea), self-sustained oscillations of the ocean circulation may be excited. We propose that such variability may be important in interpreting observations of decadal/interdecadal variability in the air‐sea–ice climate system.

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