Okhotsk Sea ice coverage and Kamchatka glaciation over the last 350 ka — Evidence from ice-rafted debris and planktonic δ18O

Abstract

High-resolution records of ice-rafted debris (IRD) and oxygen isotope records spanning an E–W-trending transect across the Okhotsk Sea unravel the marine and terrestrial cryogenic history of NE-Siberia over the last 350 kyr. IRD, predominantly dispersed basin-wide by sea-ice, shows lowest fluxes during interglacial periods implying a reduced and seasonal sea-ice coverage. Highest IRD accumulation rates are observed during glacial and deglacial periods with a more extended, but highly dynamic ice cover. Although being rather synchronous, IRD fluxes are on average higher in the western Okhotsk Sea than in the eastern part, pointing to a persistent but mobile, particle-supplying sea-ice cover even during full glacial conditions, presumably less dense in the eastern parts. MIS 6 is exceptional in this respect: Asynchronous fluxes of IRD, which vary spatially, reflect rapid paleoclimatic and paleo-glaciomarine changes. IRD accumulation rates were by factor 2–3 higher during MIS 6 as compared to the last glacial maximum, and the IRD depositional center shifted from the western Okhotsk Sea (early MIS 6) toward Kamchatka (late MIS 6), synchronous to a distinct change in the IRD mineral composition. Both, the characteristic composition of late MIS 6 IRD originating from the Sredinny Mountain Range of Kamchatka and their significantly enhanced accumulation rates refer to intensified iceberg dispersal across the eastern part of the Okhotsk Sea at ~138 ka, ~135 ka, ~129 ka, and ~128 ka BP. This scenario affords the presence of extended mountain glaciers protruding down to sea level on the western side of Kamchatka. Anomalously light planktonic stable oxygen isotopes during MIS 6.3, Termination II and MIS 5.5–5.4 suggest significant freshwater supply related to the westward drainage of Kamchatka glaciers. The intensified Kamchatka glaciation observed during late MIS 6 was repeated during MIS 3. Iceberg discharges into the eastern Okhotsk Sea are observed at ~60 ka, ~51 ka, ~42 ka, ~38 ka, ~36 ka, and ~31 ka, and may partly correspond to N-Atlantic Heinrich Events.