Sea ice and snow thickness and physical properties of an ice floe in the western Weddell Sea and their changes during spring warming

Helicopter-borne and ground-based electromagnetic (EM) ice thickness and ruler-stick snow thickness measurements as well as ice-core analyses of ice temperature, salinity and texture were performed over a 5-week observation period between November 27, 2004, and January 2, 2005, on an ice floe in the western Weddell Sea at approximately 67 degrees S, 55 degrees W. The study was part of the Ice Station Polarstern (ISPOL) expedition of German research icebreaker RN. Polarstern, investigating changes of physical, biological, and biogeochemical properties during the spring warming as a function of atmospheric and oceanic boundary conditions. The ice floe was composed of fragments of thin and thick first-year ice and thick second-year ice, with modal total thicknesses of 1.2-1.3, 2.1, and 2.4-2.9m, respectively. This included modal snow thicknesses of 0.2-0.5 m on first-year ice and 0.75 m on second-year ice. During the observation period, snow thickness decreased by less than 0.2 m. There was hardly any ice thinning. Warming of snow and ice between 0.1 and 1.9 degrees C resulted in decreased ice salinity and increased brine volume. Direct current (DC) geoelectric and electromagnetic (EM) induction depth sounding were performed to study changes of electrical ice conductivity as a result of the observed ice warming. Bulk ice conductivity increased from to 37 to 97mS/m. Analysis of conductivity anisotropy showed that the horizontal ice conductivity changed from 9 to 70mS/m. These conductivity changes have only negligible effects on the thickness retrieval from EM measurements. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.