ABSTRACT

A sediment core collected from the Sea of Okhotsk, a marginal sea of the western North Pacific, has been analyzed for alkenones to reconstruct changes in the sea surface temperatures (SST) over the last 15 kyrs. A comparison of the core-top U₃₇^K' value with the modern surface temperatures indicates that alkenones are produced at present in summer-fall season, a production seasonality probably identical to the one prevailing in the past, as suggested by evidences of enhanced sea ice cover and subsequent limitation of the phytoplankton growth period to summer-fall at the glacial/deglacial transition. The alkenone downcore profile indicated that summer SST at the early deglaciation period (15 kyrs BP) were around 5°C lower than today (ca. 11°C). A rapid SST increase (more than 3°C) was found to occur from 13.7 to 11.6 kyrs BP, following the melting water pulse event (MWP-1A). This warming was assumed to be the consequence of a radical change in the atmospheric/oceanic circulations which induced an enhanced heat transport from the sub-tropical to the northern North Pacific. A significant surface water cooling was evidenced from 11 to 8 kyrs BP, possibly caused by the supply of cold Siberian permafrost melt-water to the Okhotsk Sea through the Amur River.