Sea surface temperature and salinity variations from the end of Last Glacial Maximum (LGM) to the Holocene in the northern South China Sea

Paleoclimatic and palaeoceanographic studies in land and sea, especially monsoon and sea surface conditions in the past, help to better understand the internal feedback processes within the climate system. However, asynchronisms were observed between records from land and sea at the warming transition from the end of the Last Glacial Maximum (LGM) to the Holocene, raising debating of primary forcing of paleoclimatically variations. In this work, a sediment core ZSQD2, from the northern South China Sea (SCS), spanning the end of the LGM to the mid-Holocene, was utilized to evaluate variations of sea surface temperature and salinity, and then analyze the correspond pattern to the Asian Monsoon system, based on measured Mg/Ca ratio and isotopic compositions (δ¹⁸O and δ¹³C) of planktonic foraminifera Globigerinoides ruber sensu stricto (s.s.). These records show that the warming started from ~16 ka, which agrees well with the East Asian Summer Monsoon (EASM) records, revealing the synchronism in variations between the northern SCS sea surface conditions and the palaeoclimate of China Mainland, at the beginning of warming transition from the end of LGM. Mirrored SST and SSS variations were in step with stalagmite δ¹⁸O signals, also unveiling a close relationship between sea surface water condition in the northern SCS and the EASM intensity. On millennial timescales, asynchronism between the China Mainland palaleoclimatic changes and seawater conditions of the northern SCS is displayed by declined SST and heavier δ¹³CG.ᵣᵤbₑᵣ during ~15–13.5 and ~ 11.5–9.5 ka, when the EASM enhanced and SSS declined. This is resulted from strengthened the EASM driven upwelling cooled down the surface water and enhanced nutrient supply in the northern SCS, combined increasing cold and fresh water input from the Pearl River.