Winter sea-ice thicknesses in the Weddell Sea and their variability over the past 24 years

The sea-ice thickness distribution is one of the most important sea-ice properties, but also one of the less frequently observed ones so far. Satellite retrievals of Antarctic sea-ice thickness are currently limited to laser and radar altimetry observations of snow freeboard with large uncertainties, and electromagnetic measurements have been obtained only sporadically. For the investigation of the variability and changes in the sea-ice thickness distribution over the last decades, data are mainly available from very basic methods such as drilling or ship-based observations following the Antarctic Sea Ice Processes and Climate (ASPeCt) protocol. Thereby it is an advantage that those data also include information on the snow-depth and partly on the sea-ice freeboard distribution, which are as sparse as information on the sea-ice thickness distribution, in particular during winter conditions. The most recent data based on those methods were obtained during austral winter 2013, when various sea-ice parameters were measured in the Weddell Sea as part of the Antarctic Winter Ecosystem Climate Study (AWECS). Here, we present first results of the sea-ice thickness, freeboard and snow-depth distribution obtained by drill-hole measurements from this expedition. The new data set is compared with results from three previous winter campaigns done in 1989, 1992 and 2006 in the Weddell Sea in order to determine the long-term variability of sea-ice thickness, snow depth and freeboard. A challenge in comparing all those data is that measurement sites are based only on individual floes, which are expected to be representative for an entire region. In addition, sampling rates differ between the considered field experiments. Therefore, drill-hole thicknesses are cross-correlated with ground-based EM-measurements in order to identify for the newest data set, how representative the chosen study areas have been for the respective sea-ice floes and which consequences different measurement spacing has for the comparison of data from different years