FOSSIL MAMMALS AS CLIMATE PROXIES IN SOUTHEAST ALASKA

Late Quaternary climate change in Southeast Alaska involved the advance and retreat of glaciers, radical changes in plant communities, and the colonization of islands by mammals and birds. Cave faunas from several islands have helped to unravel these complex changes. On Your Knees Cave on Prince of Wales Island is the only known site in the region with a record of the Last Glacial Maximum.

The presence of sea ice is indicated from 24,150 to 13,690 years B.P. by the presence of Phoca hispida based on 26 radiocarbon dates. The Last Glacial Maximum is also marked by the temporary disappearance of Ursus americanus, U. arctos, and Rangifer tarandus, and by an increase in Phenacomys intermedius and Lemmus trimucronatus relative to Microtus longicaudus and Marmota caligata. This indicates coastal tundra conditions. Alopex lagopus and Vulpes vulpes appear to be the main bone accumulators at On Your Knees Cave during this period. Other pinnipeds and sea birds have also been dated to the Last Glacial Maximum. A date gap from 17,130 to 14,520 years B.P. and the loss of all rodents from Prince of Wales Island suggest that Prince of Wales Island was overrun by glaciers at that time.

The early postglacial period is marked by the loss of P. hispida and the reappearance of U. arctos, U. americanus, and R. tarandus on Prince of Wales Island. The gradual development of the modern coastal rainforest resulted in the gradual loss of R. tarandus, A. lagopus, V. vulpes, and U. arctos and by the appearance of Odocoileus hemionus, Canis lupus, M. longicaudus, Peromyscus keeni, Glaucomys sabrinus, Lontra canadensis, and several other mustelids.

Large land mammals, as well as marine mammals and birds, appear to have colonized the islands of Southeast Alaska as soon as suitable habitat became available. Small terrestrial mammals had much greater difficulty reaching the islands from the mainland because of glacier and ocean barriers. Even today several species of rodents and lagomorphs inhabit the coastal mainland but none of the southern islands.