How the Yermak Pass Branch Regulates Atlantic Water Inflow to the Arctic Ocean. Issue 1 (14th January 2019)

• Record Type: Journal Article
• Authors: Crews, L.; Sundfjord, A.; Hattermann, T.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 1(2019)
• Page Start: 267
• Page End: 280
• Publication Date: 2019-01-14
• Subjects: Yermak Pass Branch -- Fram Strait -- West Spitsbergen Current -- Potential vorticity -- Arctic Inflow -- Arctic Heat Budget; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2018JC014476
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: 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. Plain Language Summary: We used an ocean and sea ice model to study a current (the West Spitsbergen Current) which carries relatively warm water to the Arctic Ocean. In a key gateway region called Fram Strait, just before the current enters the Arctic Ocean, some of the water takes a shortcut and returns south along Greenland. The rest flows over a shallower area called the Yermak Plateau. Our goal was to learn what pushed pulses of wintertime flow through one pathway or the other. We found that flow was routed into the Arctic Ocean when the current was warmer and faster. This is because the current must conserve a quantity called potential vorticity, and when the current was warmer and faster, the potential vorticity alongside the current increased. This potential vorticity "wall" guided the flow to enter the Arctic Ocean. This means that if the temperature of the current flowing toward the Arctic Ocean increases, the amount of warm water that actually enters the Arctic Ocean could also increase. Key Points: The Yermak Pass Branch is the main route through which Atlantic Water in the West Spitsbergen Current enters the Arctic Ocean The winter increase in WSC transport is divided between the YPB (dominant earlier in winter) and Fram Strait recirculation (later) A less dense WSC strengthens a potential vorticity barrier that guides flow into the Yermak Pass Branch