Methanesulfonic acid (MSA) is an atmospheric oxidation product of dimethyl sulfide, produced by marine biota. MSA preserved in a Svalbard glacier between 1920 and 1996 is compared with the sea surface temperature (SST) and sea-ice extent of the surrounding ocean over the same period. On decadal timescales high MSA concentrations are found to be associated with warm SST and reduced sea-ice extent. MSA appears to be influenced by climatic changes related to variations in the import of warm Atlantic Water to the Barents Sea. Atlantic Water plays an important role in the Arctic climate system, therefore MSA concentrations may indirectly reflect larger-scale changes in the region and may be useful as a proxy for past climate.