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Five species of guide fossils from the Holocene warm period in Svalbard are considered: Mytilus edulis, Madia/us modiolus, Arctica islandica, Littorina littorea and Zirphaea crispata. These arc now extinct in Svalbard; Zirphaea crispata, especially, requires considerable higher water temperatures than occur there today. Known radiocarbon dates on Mytilus, Modiolus and Zirphata arc given. Thirty-four dates on Mytilus edulis show that it lived in Svalbard from before 9500 BP to about 3500 BP, and probably again around 1000 BP. Five dates on Modiolus and Zirphaea indicate a climatic optimum in Svalbard from about 8700 BP to 7700 BP. The most favourable places then had conditions similar to the northeastern coast of Finnmark, northernmost Norway, today. Mytilus edu/is is considered a good climate indicator, and a future warming of the marine climate in Svalbard could be indicated by its eventual re-immigration into the area.

Most scientists have concluded previously that the west coast of Spitsbergen, Svalbard, remained ice-free during the late Weichselian, between 25,000 and 10,000 yr B.P. We conclude that the glaciation was more extensive. Terraces that were postulated to have been ice-free are covered by a thin, late Weichselian till. Sudden drop in the marine limit and basal radiocarbon dates of raised glaciomarine sediments demonstrates that the glaciers in the main fjords, Isfjorden and Van Mijenfjorden, terminated west (outside) of the fjord mouths. Basal radiocarbon dates from glaciomarine clay above till in cores from the continental shelf west of Spitsbergen yielded ages of about 12,500 yr B.P., from which we conclude that the ice extended to the shelf edge. Based on the extent of amino acid diagenesis in radiocarbon-dated molluscs, the duration of the maximum extension of the late Weichselian glaciation was short, certainly less than 10,000 years. During the ice-free period preceding that glaciation, at least back to 40,000 yr B.P., the glaciers on Svalbard were not significantly larger than at present, as shown by marine deposits close to the glacier snouts. Many radiocarbon dates place deglaciation of the outer coast at about 12,500 yr B.P. At about 10,000 yr B.P., the rest of the archipelago rapidly became ice-free.

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