Pathways of Atlantic Subpolar Heat Uptake

The rate and depth of ocean heat uptake affects the rate of global warming due to radiative forcing. Observations and climate model simulations show that heat penetration rates and depths are especially great in the Atlantic Ocean. We observe the pathways of heat and a heat-like tracer into the subpolar ocean in an abrupt-warming ocean general circulation model experiment. The tracer fills the entire subpolar region to a depth of about 250 m in the first few years of the experiment. Deeper penetration appears to occur first in much smaller regions associated with deep winter convection. In the model the deepest convection regions occur near the Greenland-Iceland-Scotland Ridge. At depths such as 500 m and 1000 m, tracer spreads out in a counterclockwise direction around the subpolar North Atlantic, apparently carried by the currents of the subpolar gyre. This indicates that the rate of heat uptake is influenced by both the depth of winter convection and the circulation speed in the gyre. Despite homogenization of tracer within the convective region, annual average tracer maintains a strong vertical gradient over several decades, apparently due to the circulation and the seasonality of convection.