COSMONAUT POLYNYA IN THE SOUTHERN-OCEAN - STRUCTURE AND VARIABILITY

Along the far eastern margin of the Weddell Gyre is a persistent featu re in the middle of the ice pack which we previously reported and call ed the Cosmonaut polynya. A study of polynya occurrences from 1973 to 1993 reveals that since 1986 the polynya has become more active with a n average size of about 7.2 x 10(4) km(2) and an average location at 5 2 degrees E and 65 degrees S. Satellite observations indicate that the polynya has recurred several times during winter in recent years with intervals ranging from a few days to a few weeks. The centroid of the polynya varies only slightly with each formation during the year and from one year to another, suggesting a controlling influence of the oc ean and bottom topography that may be initially induced by wind. The d aily time series indicates two primary modes of formation: one that is initiated in the early winter during a storm at a site usually preced ed by an embayment of the ice edge and another that occurs during midw inter often preceded by a coastal polynya event adjacent to Cape Ann. The Cosmonaut polynya region is characterized in this study by compres sion of the westward flowing coastal current and the eastward flowing southern edge of the Antarctic Circumpolar Current. Following the prin ciple of conservation of potential vorticity, vertical stretching of t he water column would ensue, enhancing upwelling. Such a process accel erates the injection of relatively warm salty deep water into the surf ace layer, inhibiting sea ice growth and causing the polynya formation . This theory appears to explain the general behavior of the polynya i n terms of frequency, duration, size, and location.