Organic sulphur compounds have received much attention due to their potential role in climate control. Sea ice constitutes an important pool of organic sulphur compounds. The most important sulphur compounds are: dimethylsulphoniopropionate (DMSP), dimethylsulphide (DMS) and dimethylsulphoxide (DMSO). DMSP is produced by algae, DMS is one of the cleavage products of DMSP and DMSO is a (photo-)oxidation product of DMS. DMS is a semivolatile compound that is studied intensively because its atmospheric oxidation products are involved in the formation of condensation nuclei and clouds. Model studies indicate that, especially over large areas of the Southern Hemisphere, DMS may affect climate. Estimations on Antarctic DMS production are based on a very limited number of data. The marginal ice zone has been depicted as the main source area for high DMS emissions during the period of ice melt. There are, however, very limited data available on the distribution, pool sizes and dynamics of DMS and related compounds in sea ice itself. Sea ice is an extreme habitat. Notwithstanding the very low temperatures, high salinities and low light conditions, high algal biomasses are found between snow and ice, in confined layers within the ice and at the bottom. These distinct habitats comprise different communities. It is hypothesized that DMS, DMSP and DMSO are major compounds to survive the harsh environment in sea ice, as they may play a role in cryoprotection, osmoprotection and scavenging of radical oxygen species. We will present data from two cruises into Weddell Sea ice with R/V Polarstern (ANTXXII-2 and ANTXXIII-7). Physicochemical parameters, algal marker pigments and S-compounds were analysed in high-resolution sea-ice profiles. The dynamics within the sea-ice sulphur pool during melting experiments were followed through the addition of stable isotopes of DMS and DMSP. Various uptake and conversion pathways could be detected, indicating a dynamic system. In wintertime, the sulphur pool in sea ice exceeds the total water column burden many times. During ice melt, the release of S-compounds to the water can largely explain the build-up of concentrations in the water column, indicating the importance of sea ice as source for DMS(O/P) in the marginal ice zone.