Using modern zoogeographic data and inferred temperature ranges for Champlain Sea ostracode species, bottom water paleotemperatures were estimated for three phases of deposition of this inland sea. The temporal distribution of these and other environmentally diagnostic species in Champlain Sea deposits reveals a significant local climatic change in the Champlain Valley from frigid/subfrigid to cold-temperate marine conditions about 11 000 to 10 600 yr BP. Oceanographic changes in the Champlain Sea are correlated with major deglaciation events recorded in the North Atlantic.-from Author