Occurrence of an unusual extensive ice-free feature within the pack ice of the central Weddell Sea, Antarctica

Abstract

We investigate an unusual extensive ice-free feature (EIF) within the pack ice that developed in the central Weddell Sea in December 1980 on the edge of the multi-year sea ice off the east coast of the Antarctic Peninsula. The EIF was first apparent on satellite imagery on 8 December 1980 and expanded until it reached its largest areal extent of ~5.4 × 105km2 on 26 December. The combined influences of near-record strength (~ 15 ms−1) cold winds from the Antarctic continent (transporting sea ice northward and creating an area of thin ice), increased shortwave radiation and net heat flux into the ocean, passage of deep polar storms, and the upwelling of high saline warm water led to the opening of this unique EIF. It is still the largest ice-free feature within the pack ice resembling a polynya observed in the central Weddell Sea during the satellite era, contributing significantly to the 1981 Weddell Sea sea ice extent minimum of 0.793 × 106km2, the lowest on record. The development mechanism of this EIF was different from the 1970’s Weddell open ocean polynya which occurred within the winter sea ice cover through enhanced ocean convection.