Surface water changes recorded in Late Quaternary marine sediments of the Ulleung Basin, East Sea (Japan Sea)

In order to reconstruct past sea surface temperature (SST) and salinity (SSS) in the East Sea (Japan Sea), this study investigated the oxygen isotopic composition of the planktonic foraminifer Globigerina bulloides, and the degree of unsaturation of alkenones in bulk sediments of core TY99PC18 recovered from the southeastern part of the Ulleung Basin, East Sea. Between 11 and 15 cal kyr BP, the surface waters were 2–4 °C cooler than today. The surface salinity was 12‰ lower during 14–15 cal kyr BP than today, then increased after 14 cal kyr BP, but remained lower during 11–14 cal kyr BP than present values. Between 14 and 15 cal kyr BP, the northern East China Sea surface waters were likely to be greatly diluted by fresh water discharge from land, and coastal waters would have flowed into the East Sea through the Korea Strait. During 11–14 cal kyr BP, the southern input waters most likely changed from fresh water-influenced coastal water to open ocean water. The increased salinity probably enhanced active deep water convection at that time. During 7–11 cal kyr BP, the surface waters were warmer (∼ 1 °C) and more saline (1–3‰) than today, indicating that the warm and saline Kuroshio Current became stronger, and that one of its branches flowed into the East Sea during this time interval. The cold (∼ 2 °C) and less saline waters (∼ 1‰) at 3–6 cal kyr BP may indicate a suppression of the Kuroshio Current. The SST and SSS values are close to the present values at about 3 cal kyr BP, suggesting that the physiological conditions of the East Sea approached that of the present at this time.