Temporal variation of the intensity of the thermohaline circulation in the North Atlantic Ocean from the 4XC, 2XC, and S integrations of a coupled, global atmosphere-ocean model including sea ice. Here the intensity is defined as the maximum value of the streamfunction representing the meridional circulation in the North Atlantic Ocean.
Units are Sverdrups.
Diagnostic analysis of the model results shows that the weakening of the thermohaline circulation results mainly from the capping of the oceans by relatively low-density water in high latitudes, attributable to the enhanced poleward transport of water vapor, especially in the Arctic Ocean where the intense halocline prevents mixing between the surface and deeper layers.