Orbital forcing on paleo-productivity in the northern South China sea during the late Pleistocene

Abstract

Unraveling marine productivity and its driving forces is crucial for understanding the ocean carbon cycle. In this study, we present data on the relative abundance of planktonic foraminifer Globigerina bulloides, the ratio of mixed-layer species to thermocline species, the thermal gradient of upper water column, δ¹⁸O_residual, TOC content, and TOC/TN ratio in the northern South China Sea over the past 350 kyr. These proxies provide insights into the variations and forces on marine paleo-productivity. Our results show distinct glacial-interglacial cyclicity superimposed with precession-driven variability in the paleo-productivity record. On a glacial-interglacial timescale, enhanced paleo-productivity coincided with increased terrestrial nutrient matter input during glacial sea-level lowstands and strong mixing of the upper water column caused by the intensified glacial East Asian winter monsoon. On a precession timescale, greater East Asian summer monsoon intensity, coupled with the relatively unstable upper water column due to increased surface water salinity during insolation maxima, promoted strong mixing of the upper water column, thereby enhancing paleo-productivity. Furthermore, paleo-productivity may be constrained by low insolation and a relatively stable upper water column during periods of intensified East Asian winter monsoon on a precession timescale. We propose that terrestrial nutrient matter input and upper water mixing caused by the East Asian monsoon play a crucial role in paleo-productivity changes in the northern SCS on glacial-interglacial and precession timescales, respectively.