Sea surface temperature and salinity changes near the Soya Strait during the last 19 ka

Past sea surface temperature (SST) and salinity (SSS) changes in the northeastern East Sea/Japan Sea since 19 cal ka BP have been reconstructed by using an alkenone unsaturation index and the oxygen isotope ratio of planktonic foraminifera Neogloboquadrina pachyderma(s) in Core MR0604-PC03B. Coretop alkenone temperature and calcification temperature correspond to the temperature of seawater in summer and spring at the depth of 10–30 m, respectively. Based on the records from this core and previous studies, spatio-temporal changes in alkenone temperature of the East Sea/Japan Sea have been reconstructed to investigate changes of surface circulations and the subpolar front (SPF) position. During the transitional period from the glacial to the Holocene, the SST was lower (about 2–3 °C) than that of today and the SSS dramatically increased at that time in the entire East Sea/Japan Sea but it was still lower than that of today. However, the northern SSS was higher than that of the southern part. The source of the cold and saline seawater could have been the Oyashio Current (OY, inflow from the north), not the Tsushima Warm Current (TWC, inflow from the south). Probably, sea level rose rapidly at that time. There might be no strong development of the SPF during the transitional period due to the restricted inflow of the TWC. During the early Holocene, the SST and SSS of the East Sea/Japan Sea increased compared to the transitional period due to increased seawater exchange through straits. The SPF was tilted orienting from southwest to northeast because the inflow of the TWC was not fully developed due to lower sea level. Subsequently, the surface condition of the East Sea/Japan Sea was similar to that of today at 6 cal ka BP. The Forerunner of Soya Warm Water (FSWW) that flowed out through the Soya Strait in early spring did not affect the formation of the Okhotsk Sea Intermediate Water and the North Pacific Intermediate Water during the glacial and interglacial periods.