Global sea level and monsoon effects on terrigenous input and temperature in the north-western South China Sea during the last glacial

Abstract

On glacial/interglacial timescales, sedimentation in shallow, near-coastal environments is mainly a function of climate, tectonics and global sea level changes, the latter two regulating changes in morphology and sedimentation space accommodation. Climatic fluctuations affect parameters of the ocean currents and primary production, as well as sediment inputs from terrestrial sources regulated by precipitation, weathering and runoff. Deciphering changes in the interplay of these different variables with time is primordial for environmental reconstruction. Here, the paleoenvironmental evolution of the north-western South China Sea (southwest of Hainan Island) has been investigated for the period 80–50 kyr BP, i.e. between Marine Stage Isotope (MIS) 5a and early MIS 3, which includes the formation of the Hainan paleo-delta. A combination of records based on bulk sediment parameters, molecular organic proxies and oxygen stable isotopes of benthic foraminifera suggests that terrigenous input was mainly controlled by changes in global sea level and summer monsoon intensity, and likely influenced primary production. Global sea level fluctuations probably triggered local changes in sea surface temperature and air temperature on the adjacent land through changes in the advection of water masses from the northern Pacific and periodic closing/opening of the Taiwan and Qiongzhou straits. Combining proxies based on both terrestrial and marine organic matter within the same sedimentary archive allows understanding the influence of both the global sea level and the East Asian Monsoon on the evolution of the sedimentary environment of the north-western South China Sea during the last glacial period.