ICEBERG OBSERVATIONS AND ESTIMATION OF SUBMARINE RIDGES IN THE WESTERN WEDDELL-SEA

A number of small patches of relatively high temperatures and low refl ectances were observed in the western and south-western Weddell Sea be tween October 1991 and February 1994 by aid of Advanced Very High Reso lution Radiometer (AVHRR) images. From ERS-1 Synthetic Aperture Radar (SAR) data acquired during the same period these patches could be iden tified as high backscatter areas in the lee of small icebergs. Most of the icebergs were grounded for the entire period of observation. Nort h of the icebergs a number of extended bands (> 100 km) of high backsc atter and low reflectance were detected in most of the images. These b ands demonstrate the effect of the icebergs as fixed barriers on the d rifting ice cover creating a perturbation in the lee of the barriers. The combination of SAR data, AVHRR data and the Argos tracked buoys sh ows a very homogenous behaviour of the ice cover on the continental sh elf with strong tidal component and low large scale shear activities. From the analysis of the shadows created by the tabular icebergs a rou gh estimation of the heights of the icebergs and the corresponding dra ughts could be made, which were then used for an estimation of the sub marine topography responsible for the grounding of the icebergs. These indirect measurements are the first ones made on the continental shel f off the Antarctic Peninsula. They indicate a submarine ridge of abou t 150 to 300 m water depth nearly perpendicular to the coastline at ab out 70 degrees 45'S between 56 degrees 30'W and 58 degrees 30'W.