-1- Cruise Report Winter Weddell Outflow Study (WWOS) – ANT XXIII/7 4. Regional variability of sea ice properties and thickness in the northwestern Weddell Sea obtained by in-situ and satellite measurements C. Haas, A. Friedrich, Z. Li, M. Nicolaus, A. Pfaffling, T. Toyota The western Weddell Sea is one of only a few regions of the southern Ocean covered by perennial sea ice. As such, it is of particular importance for atmosphere-ice-ocean processes and in particular for the oceanic freshwater balance. Therefore, the main objectives of the sea ice geophysical program were: 1. Quantification of the regional variability of first- and second year sea ice and snow thickness in the north-western Weddell Sea, and observations of their interannual variability in comparison with earlier measurements of other researchers, obtained by drilling and upward-looking-sonar. In particular, we aimed at continuing observations performed during ISPOL (Ant 22/2) in December 2005. 2. Validation of satellite measurements of radar backscatter and surface temperature of different ice types and polynya processes by means of coincident real-time Envisat-SAR and NOAA-AVHRR imagery received on board, and in-situ measurements of ice and snow thickness and other physical properties. With an improved understanding of satellite signatures, the results of our in-situ measurements can be spatially extrapolated and extended to longer time periods. 3. Investigation of physical and biological ice properties and processes and the fate of perennial ice after surviving one summer melt season. From earlier Polarstern cruises including ISPOL it is clear that the ice undergoes significant changes during the summer season. Ant 23/7 offered the opportunity to study the fate of this ice during the following winter, in particular the properties of remnant metamorphous snow, superimposed ice, and refrozen gap layers. To address those objectives, measurements have been carried out on the ice, from the ship, and by helicopter, including: • Ice coring and analyses of ice temperature, salinity and texture profiles, and snow-pit measurements of snow properties during ice stations. Additionally, ice and snow thickness profiles were measured by means of electromagnetic (EM), ground-penetrating radar (GPR), and drill-hole profiling. • Ship-based visual and photo observations of general ice conditions, and continuous EM, GPR, and video measurements of ice and snow thickness. • Helicopter-borne EM ice thickness and GPR snow thickness surveys, laser profiling of surface roughness and ridge distribution, and video-recordings of floe size distributions. In total, measurements have been performed on 40 days when the ship was travelling through ice. The map in Figure 4.1 shows the locations of all 27 ice stations and helicopter EM flight tracks