Thermal structure of the coastal polynya off Syowa Station, Antarctica

Abstract

Open water areas between fast-ice and pack-ice zones are frequently observed off Lutzow-Holm Bay, Antarctica. In such open waters, called polynyas or leads, which are exposed to the cold air, new sea ice can form with a high growth rate. So the open polynya releases large quantities of heat to the atmosphere and excludes high-salinity brine to the ocean. In 1990-1992 the 31st and 32nd Japanese Antarctic Research Expeditions conducted oceanographic observations in Lutzow-Holm Bay to reveal the atmosphere-sea ice-ocean interaction. Thirty AXBT's (aircraft-deployed expendable bathythermograph) were cast to examine the thermal structure in the polynya "Otone Suiro". Based on the AXBT data the depths of the winter convective-mixed layer were estimated. The thickness of the mixed layer near the freezing point (-1.9∿-1.8℃) reached to 350∿450m. These mixed layers were clearly thick as compared with those in the offshore pack-ice region. Furthermore the mixed layer has a tendency to deepen in winter.