Climatic optimum during the Holocene and the distribution of warm-water mollusks in the Sea of Japan

The geographical distribution of warm-water mollusks has been analyzed and the paleobiogeographical significance of the climatic optimum during the Holocene in the formation of the shallow-water malacofauna in the Sea of Japan has been assessed. The shift of the southern boundary of the Pacific boreal region was 700–800 km to the north compared to its present-day position (based on bivalve mollusks). On the continental coast of the Sea of Japan this boundary is observed in Peter the Great Bay (∼43°N) and on the Japanese side it seems to be at the central part of Hokkaido. It can be concluded that a temperature increase of the surface water mass of 0.1–0.2°C can cause a shift of about 100 km of the northern boundary of the area of warm-water mollusks.