Planktonic Foraminifera Reveal Late Pleistocene Paleo-Productivity Changes in the Northern South China Sea

The ocean productivity plays a crucial role in the ocean carbon cycle by influencing atmospheric CO₂ levels. Although upper water column mixing associated with East Asian monsoon and terrestrial weathering input are the primary sources of surface water nutrients in the northern South China Sea (SCS), their contributions to paleo-productivity changes in the northern SCS during the late Pleistocene remains contentious. This study reconstructs paleo-productivity, East Asian monsoon dynamics, and terrestrial nutrient matter inputs over the past 350kyr, using multiple proxies, including the relative abundance of planktonic foraminifer Globigerina bulloides, sediment TOC content, TOC/TN ratio, the ratio of mixed-layer species to thermocline species, the thermal gradient of the upper water column and δ¹⁸O_residual from International Ocean Discovery Program (IODP) Site U1505. The results reveal a distinct glacial-interglacial cyclicity with higher paleo-productivity attributed to increased terrestrial nutrient inputs and intensified East Asian winter monsoon during glacial lowstands. Furthermore, paleo-productivity exhibits a pronounced ~23 kyr cyclicity and is coupled with enhanced East Asian summer monsoon intensity during periods of low-latitude insolation maximum, suggesting a precession forcing on paleo-productivity via East Asian summer monsoon intensity and insolation maximum.