A significant late-season change in the regional sea ice regime in the vicinity of the Mertz Glacier Polynya, East Antarctica

Satellite, modelled wind-field, wave-field and automatic weather station data are used to examine a significant late-season change in the behaviour of Antarctic sea ice in the region 110-180°E in 1999. This change had a profound effect on the Mertz Glacier Polynya (a major site of cold high-density water formation contributing to Antarctic Bottom Water production). Prior to early October, prevailing ice drift within the near-coastal East Wind Drift was from the E/SE. After this, an abrupt reversal in the regional ice drift regime to a net westerly-south-westerly pattern occurred in response to a change in synoptic wind patterns. This shift halted the supply of thick vast ice floes from the E, dispersing a compact "stream" of thick floes to the N and removing its effect as a zonal barrier. Swell penetration may have played a significant initial roˆle by "loosening" the pack in the vicinity of 120-130°E. The overall effect was to create a more divergent, diffuse ice cover around the polynya, enlarging its area. By "flushing out" the polynya, the observed events accelerated the austral spring-summer meltback of the seasonal sea-ice zone in the region