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Abstract: Sea-ice diatom taxa (Fragilariopsis cylindrus and Fragilariopsis oceanica) and their relative abundance in the Okhotsk Sea were used to reconstruct the history of sea-ice distribution and atmospheric pressure patterns since the Last Glacial Maximum (LGM). The temporal state of sea-ice distribution and atmospheric pressure patterns since the LGM can be divided into three modes: northern Aleutian Low mode, southern Aleutian Low mode, and strong Siberian High mode. The Southern Aleutian Low mode was dominant before 15ka and after 6.5ka, respectively, showing expanded sea-ice distribution into the central and southern Okhotsk Sea. During the deglaciation period (15ka to 10ka), sea-ice retreated from the southern Okhotsk Sea because of the pronounced westerly winds under the strong Siberian High mode. However, sea-ice distribution expanded in the northern Okhotsk Sea, which favors the development of extensive polynyas on the northern continental shelf. Occurrences of northern Aleutian Low mode were frequent between 10 and 6.5ka, while sea-ice distribution expanded into the eastern Okhotsk Sea. Formation of the Okhotsk Sea Intermediate Water, inferred from radiolarian species Cycladophora davisiana, intensified under both northern Aleutian Low mode and strong Siberian High mode. [Copyright &y& Elsevier]

Abstract: A 58-m-long sediment core IMAGES MD01-2412 was recovered in the southwestern part of the Okhotsk Sea for high resolution paleocenography. An age model of the core was obtained by accelerator mass spectrometry (AMS) 14C dating of planktonic foraminifer shells, oxygen–isotope stratigraphy of benthic foraminifer calcite, and tephrochronology, resulting in a core-bottom age of 115 kyr. Sea-ice expansion in the Okhotsk Sea was reconstructed by ice-rafted debris (IRD) based on measurement of dropstone, coarse fraction, sand fractions of terrigenous particles, and the magnetic properties. The SW Okhotsk Sea has not had perennial but seasonal sea-ice conditions during the 115 kyr. Seasonal sea ice fluctuated with large amplitudes on millennial scale during the glacials (Marine isotope stage: MIS 2, 3, and 4) and varied relatively little during the Holocene (MIS 1) and the last interglacial (MIS 5). Enhanced polar atmospheric circulation during the glacial resulted in strong wind fields over the Okhotsk Sea and accelerated the large sea-ice expansion during the glacials (MIS 2, 3, and 4). During the interglacials (MIS 1 and 5), sea ice also expanded by small amplitudes. During these periods, decrease of the Amur River discharge would be one of the possible factors for sea-ice expansion. The two main factors of polar atmospheric circulation and Amur River discharge would be responsible for sea-ice expansion during 120 kyr. [Copyright &y& Elsevier]