Variation of alkenone sea surface temperature in the Sea of Okhotsk over the last 85 kyrs

Abstract

Sea-surface temperatures (SSTs) in the Sea of Okhotsk were reconstructed based on alkenone unsaturation indices in two sediment cores. Alkenone-SSTs were found to range from 3 to 9 °C over the last 85 kyr with higher SST values in warm periods: Holocene and the oxygen isotope stage (OIS) 5a. In the last glacial periods (OIS 4 and 3), average alkenone SST was estimated to be 4 °C, which was 4 °C lower than the Holocene on average. However, alkenone SSTs around the last glacial maximum (LGM) are as high as those of the Holocene. The variation patterns of U 37 K′ in the Okhotsk Sea were found to be similar to those reported in the Sea of Japan [Org. Chem. 32 (2001) 57] over the last 30 kyr, although the SSTs were lower in the Sea of Okhotsk. The higher U 37 K′ values around the LGM may be a rather common phenomenon in semi-closed marginal seas such as the Japan Sea and the Okhotsk Sea, which are both adjacent to the northwestern Pacific. Such an anomaly in the LGM may have been caused by either a seasonal shift of coccolith blooming or a contribution from a different strain or species that produces alkenones.