Ice Pumping: Influence of Ice Thickness Gradients on the Arctic Ocean Circulation

Abstract

Surface currents beneath sea ice are influenced by ice thickness in much the same way bottom currents are influenced by bathymetry. Despite the gentle slope of the ice cover—only a few meters over thousands of kilometers—surface currents on the order of a few centimeters per second generate vertical velocities of a few meters per year, which are the same order of magnitude as the surface Ekman pumping. We dub this vertical velocity “ice pumping.” Using theory and numerical modeling, we show that this ice pumping exerts a first-order control on both the structure and intensity of the large-scale Arctic Ocean circulation. We find that the dominant effect is the generation of a basin-scale anticyclonic circulation anomaly, forced by the interaction of the Transpolar Drift Current with the overlying sea ice that grows thicker toward Greenland. The most notable consequence is a shift of the Transpolar Drift Current itself toward the Eurasian coast and a modulation of the intensity of the large-scale circulation. Ice pumping should therefore be considered alongside Ekman pumping, mesoscale eddies, and the ice–ocean governor as a fundamental constraint on Arctic circulation and is likely to be important in other scenarios, such as underneath ice shelves and on ice-covered exoplanets.