Rigid topographic control of currents in the Nordic Seas

Neutrally buoyant floats, deployed across the northern slope of the Iceland-Faroe Ridge at 800m depth, reveal tight topographic control of their movement: a cluster of 22 floats drifts southeast to the Faroe-Shetland Channel where it bifurcates such that floats deployed over the upper slope turn south and eventually exit the Norwegian Sea through the Faroe Bank Channel, and floats over the deeper slope turn north in the Norwegian Sea. A subset of the latter group moves quickly north along the western slope of the Voring Plateau and divides with most of the floats turning east into the Lofoten Basin and the remainder circulating cyclonically around the Norwegian Basin. This study establishes that i) the Faroe Bank Channel overflow waters must come from along the slope north of the Faroes, not the interior of the Norwegian Sea, and ii) exchange of intermediate waters between basins takes place along topographically controlled routes.