Seasonal cyclonic eddy in Amundsen Sea Polynya, Antarctica

Abstract

Amundsen Sea recently attracted particular interest, because it is most rapidly warming in the Western Antarctic (WA). Many studies reported that the relatively warm circumpolar deep water (CDW) and seasonal variation of its intrusion to the Amundsen Sea are associated with the regional warming. However, few studies examined why the intrusion varies seasonally. The strong seasonal cyclonic eddy in Amundsen Sea Polynya was found from the shipborne measurements LADCP data during 2010/2011 and 2011/2012 IBRV Araon expeditions. Also this ocean surface circulation was reconfirmed by the OSCAR (Ocean Surface Current Analysis) calculated from quasi-linear and steady flow momentum equations using sea surface height, wind and temperature obtained from satellites. A polynya larger than 200 km in diameters tends to be formed by the effect of wind and ocean currents in front of DIS (Dotson Ice Shelf) during austral summer season. It is found that the strong upwelling was induced by latitudinal variations of westward wind velocities and sea ice concentration on the northern boundary of the Polynya. Such upwelling generates the cyclonic eddy that maximum current speed is larger than 10 cm s-1. However, as the Polynya was almost closed during austral winter, upwelling was reduced compared to that during the summer season and the cyclonic eddy disappeared in front of DIS. Additionally, the influence of seasonal variation in the strong ocean surface circulation on oceanic heat transport to ice shelves will be discussed.