Temperature and salinity changes in the permanent thermocline as recorded byGloborotalia inflata: implications for intermediate water changes in the Northern South China Sea since 20 ka BP

Intermediate circulation is one of the crucial controls of thermohaline changes in seawater. Due to the lack of data for some of the more significant indicators, there has been little research into past intermediate waters in the South China Sea (SCS). In particular, little is known of the thermohaline properties of intermediate water. Here, we present paired Mg/Ca and δ18O data for the planktonic foraminifera Globorotalia inflata from Core GHE27L in the northern SCS that provide records of temperature and residual δ18Oseawater(δ18Osw) values(δ18Oresidual is taken as a proxy of salinity) for permanent thermocline waters. We used these data to tentatively investigate changes in the intermediate water of the SCS since the Last Glacial Maximum (LGM). Our results showed that Globorotalia inflata in the SCS grew principally within the 200-400 m water depth interval over the past 20 ka. Thermohaline changes in the permanent thermocline are quite remarkable, and are characterized by the warm and fresh waters of the LGM, changing to warm and saline waters between 17.7 and 13.6 ka BP. In general, waters during the 13.6-8.3 ka BP period were characterized by high temperatures and salinity, with obvious millennial-scale fluctuations, after which, during the Holocene,they became cold and fresh. This suggests that the temperature and salinity of the permanent thermocline water in the SCS were mainly impacted by North Pacific Intermediate Water (NPIW) during the Last Glacial Maximum (20-17.7 ka BP) in the northern SCS, but that subsequently the influence of Antarctica Intermediate Water (AAIW) strengthened during the last deglaciation and Pre-Boreal (PB) period (17.7-8.3 ka BP). After this period, NPIW was the principal control, but with obvious fluctuations.