Latest Quaternary oceanographic changes in the Okhotsk Sea based on diatom records

Abstract The Okhotsk Sea is a locus of the North Pacific Intermediate Water formation today. The formation of the Okhotsk Intermediate Water is linked with seasonal sea-ice cover. Diatom records from the Okhotsk Sea show the following. (1) During the last glacial maximum (between 21,000 yr B.P. and 18,000 yr B.P.), sea ice covered the western side of the sea throughout the whole year, but the eastern part was open. This permitted more efficient heat exchange with the atmosphere than waters and hence ventilation of the glacial Okhotsk Sea waters which in turn caused a greater extent of Intermediate Water formation through the Bussol' Strait. (2) The perennial sea-ice cover extended northward, and sea ice was present throughout the whole year over a great part of the sea except for the eastern part between 18,000 yr B.P. and 17,000 yr B.P. (3) The ice-free area extended greatly to the south during the interval between 17,000 yr B.P. and 11,000 yr B.P. (4) There was no perennial ice cover over the whole sea, and the ice-free area that appeared as the seasonal ice area began to extend to the western part between 11,000 yr B.P. and 8,000 yr B.P. (5) After 8000 yr B.P. the ice-free waters contracted to the present extent.