Volume, Heat, and Freshwater Divergences in the Subpolar North Atlantic Suggest the Nordic Seas as Key to the State of the Meridional Overturning Circulation

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The meridional overturning circulation (MOC) decreases rapidly in subpolar and Nordic regions where the warm upper layer loses its buoyancy due to intense heat loss, sinks, and flows south. The major volume loss of the upper limb of the MOC, ~9.6 Sv out of 18.4 ± 3.4 Sv, occurs as subduction across the Iceland Basin and Irminger Sea while the major heat loss, 273 TW out of 395 ± 74 TW is associated with the MOC branch that continues into the Nordic Seas where North Atlantic deep overflow water is produced. The 122 ± 79 TW heat flux convergence in the subpolar gyre appears to be significantly larger than various estimates of heat loss to the atmosphere. Much of the 0.09 ± 0.02 Sv freshwater divergence is presumably balanced by runoff from the Greenland shelf. These estimates suggest that the Nordic Seas, not the Labrador Sea, are key to the state of the MOC.

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Geophysical Research Letters