How the Yermak Pass Branch Regulates Atlantic Water Inflow to the Arctic Ocean

The Yermak Plateau is a topographic obstacle which warm water in the West Spitsbergen Current (Atlantic Water) must pass in order to enter the Arctic Ocean. The main route for Atlantic Water to cross the Yermak Plateau is the Yermak Pass Branch, a winter-intensified pathway characterized by pulse-like high-transport events. Here we use an eddy-resolving sea ice and ocean model to investigate oceanographic conditions that promote flow over the Yermak Plateau. Yermak Pass Branch pulses were associated with a warmer, faster West Spitsbergen Current; these conditions created a region of high offshore Ertel potential vorticity upstream of the plateau. As potential vorticity was low in the current itself, this region of high offshore potential vorticity acted as a barrier that guided flow onto the plateau. During times of enhanced recirculation in Fram Strait, this offshore potential vorticity barrier was weaker, likely allowing the current to deflect away from the continental slope. Through this potential vorticity mechanism, the upstream hydrography of the West Spitsbergen Current can determine how much Atlantic Water crosses the plateau, implying that less dense West Spitsbergen Current core water promotes more inflow into the Arctic Ocean and less recirculation in Fram Strait.