The calving event of the Drygalski Ice Tongue of February 2005

摘要

The Drygalski Ice Tongue (DIT) is the seaward extension of David Glacier, the largest outlet glacier in Victoria Land, east Antarctica. DIT marks the southern border of Terra Nova Bay and plays a decisive role in the development of Terra Nova Bay polynya. A sketch map of the area around Terra Nova Bay is shown in figure 1. DIT is a major 'landmark' in any (cloud-free) satellite image of the Ross Sea, allowing an immediate recognition of the area of Terra Nova Bay. As measured from an Advanced Synthetic Aperture Radar (ASAR) wide swath (WS) image of Terra Nova Bay of January 2005, the DIT was 96 km long and its width was 22.5 km at 50 km from the coast and 14.1 km across at the snout; these three figures compare with those of a US Geological Survey (USGS) map of 1956 which were 110, 22 and 13km, respectively (Frezzotti and Mabin 1994). The evolution of DIT in the twentieth century was studied by Frezzotti and Mabin (1994) who showed that DIT experienced two major calving events, both of the order of 40 km in length, with a time interval of about 50 years: the first one at the beginning of the century, the second one between the end of 1956 and December 1957, most probably in June 1957. In the recent years we have been following sea-ice conditions at Terra Nova Bay in the framework of a European Space Agency (ESA) project on the use of near real time (NRT) ASAR images to assist ship-routing in Antarctica. From a pair of ASAR WS images of Terra Nova Bay, the first of 15 January (see figure 2(a)) and the second of 19 March 2005 (see figure 2(b)) we noticed how DIT had undergone a moderate calving event during this two month interval. From the quick-look collection of ASAR images in the ESA catalogue, we can state that the calving event occurred in the second half of February 2005.