Geochemical record of foraminifera and its reflection on climate change in the central South China Sea since Holocene

Foraminifera form their crust by absorption or capture of calcium or silica from the seawater they live in. As the results, the geochemical features of the crust are the efficient indicators of palaeoclimate, palaeooceanography and palaeoenvironments during their life. In the year of 2017, columnar samples of a pushcore were collected by the “Jiaolong” submersible precisely at the foot of the Zhenbei seamount near the Huangyan Island in the Middle of South China Sea. The Mg/Ca ratios and the carbon and oxygen isotope compositions of the planktonic foraminifera Globigerinoides ruber and Globeriginoides sacculifer shells were measured to trace the history of sea surface temperatures (SST) and influence parameters. The results show that the SST in the sea area varied from 24.4 to 29.3 ℃ since 12.6 ka with an average of 26.2 ℃. Some cold events can be the obviously identified, which could be correlated with the events of Younger Dryas and Holocene East Asian summer monsoon. These events may be controlled by the ENSO activities and the shift of the mean location of ITCZ, and even influenced by the North Atlantic ice rafting events. In addition, we found that during the period of Holocene the fractionation of Δ¹³C_{G.sacculifer-G.ruber} between the carbon isotope compositions of G.sacculifer and G.ruber may also be constrained by SST since the Δ¹³C_{G.sacculifer-G.ruber} values was negatively biased when SST decreased and vice versa.