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Assessing Meridional Transports in the North Atlantic Ocean
Artists concept of OSTM/Jason-2 over a cloud covered Earth.
Authors:
Kathryn Kelly
(University of Washington)

Co-Investigator(s):
LuAnne Thompson
(University of Washington)

Abstract:

The conceptual model of the ocean heat conveyor has warm water flowing poleward primarily through the Gulf Stream (GS) and the North Atlantic Current (NAC) as the upper limb of the Atlantic Meridional Overturning Circulation (AMOC). This paradigm has been challenged by recent observations showing little coherence along the boundary currents and little cross-gyre exchange between the subtropical and subpolar gyres of the North Atlantic. For the AMOC to cause observed decadal anomalies of heat and freshwater, there must be a robust mechanism to move water properties poleward between ocean gyres that responds coherently to forcing. However, our previous research shows that upper ocean transport anomalies in the subpolar/subtropical boundary, the NAC, do not correspond to anomalies in GS transport. Instead, anomalies are generated when the GS sends more flow either into the NAC or back into the subtropical gyre, with the pathway switching on interannual time scales. The dependence of the NAC anomalies on this switching, rather than on GS anomalies, suggests that monitoring the Florida Current may be inadequate to characterize the AMOC. Estimates of cross-gyre exchange inferred from observations are much smaller than the overturning transport in climate models, because both surface drifters and subsurface floats tend to remain in the gyre in which they were deployed. However, the exchange could be accomplished by meridional excursions of the gyre boundary (NAC) itself, as seen in recent observations. A combination of high-resolution ocean modeling and analysis of altimetry and related observations is underway, focusing on the impact on property transports of the switching of transport between gyres and of excursions of the gyre boundary, and whether these changes are forced by winds. A detailed examination of this critical region will aid in the design of an AMOC observing system, in response to the Ocean Research Priorities Plan



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