Planktic foraminiferal δ18O values indicate precipitation variability in the southeastern South China Sea over the last 175 ka BP

The South China Sea (SCS) is an important research area of the tropical water cycle and an important pathway by which the Asian monsoon transports water vapor and heat from the tropical ocean to the Asian continent, yet its response to low-latitude tropical processes is poorly resolved. Here, we report high-resolution records of the oxygen isotopes (delta O-18) of planktic Globigerinoides ruber and Globorotalia menardii at different depths and Mg/Ca ratios from a core in the southeastern SCS over the last 175 ka BP to discuss the variability of sea surface temperature (SST) and salinity (SSS) patterns, which can provide insights into understanding SCS hydroclimate dynamics. The records show that SST was characterized by glacial-interglacial cycles largely controlled by ice volume and orbital insolation-driven changes in monsoon circulation. Several short high-frequency intervals of high SST in the glacial periods and low SST in the stadial periods corresponded to variations involving enhanced winter or summer monsoons. The variation in delta O-18 is obviously influenced by monsoon-driven SSS. Although the delta O-18 values in different areas of the SCS were similar, the comparison shows that the delta O-18 values in the study area were lower than those in the northern SCS but higher than those in the southern SCS, appearing to reveal the tropical water cycle process of evaporation, transmission and rainfall in the SCS. The negative deviation in delta O-18 peaks indicated heavy precipitation in the southeastern SCS caused by an enhanced convection intensity and strengthened summer monsoons. A valuable set of surface and subsurface Delta delta O-18(G.r-G.m) (Delta delta O-18(G. ruber) - Delta delta O-18(G. menardii)) records proved that more negative 8 18 0 shifts must be closely related to the surface seawater environment. However, negative shifts in delta O-18 were controlled by different mechanisms during the glacial and interglacial periods. In the interglacial periods, the northward shift of the intertropical convergence zone (ITCZ) and summer solar insolation played a key role in precipitation, whereas in the glacial periods, El Nino events and differences in the thermal properties between the sea and land dominated. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The research provides insights into the hydroclimate dynamics of the South China Sea through high-resolution records of the past 175 ka BP. The study reveals the variability of sea surface temperature and salinity patterns, as well as the influence of monsoon-driven processes on oxygen isotopes in the region. The findings suggest a connection between heavy precipitation in the southeastern South China Sea and enhanced convection intensity and strengthened summer monsoons.