Glacial-interglacial shifts in dominant climate forcing over the last 33 ka in the northern South China Sea

Abstract. The northern South China Sea (SCS) is a critical region for understanding East Asian Monsoon dynamics. However, integrated, multi-proxy records elucidating long-term climatic and vegetation changes in this region remain fragmented, with a notable scarcity of coherent land-ocean interaction data during the Last Glacial Maximum (LGM). This gap has impeded progress in elucidating the mechanisms underpinning monsoon variability and in rigorously evaluating the performance of palaeoclimate models. To address this, we conducted a multi-proxy analysis combining palynological, organic- and inorganic-geochemical methods on a marine sediment core from the northern SCS to reconstruct environmental and oceanic dynamics at millennial-scale resolution that spans the last 33 ka. Our results reveal a clear contrast between glacial and interglacial regimes. The glacial period, especially the LGM, was characterized by higher sedimentation rates, elevated marine primary productivity, cooler and drier conditions, herb-dominated vegetation, and intensified fire activity. This regime was dominantly forced by low sea level and glacial aridity, which together promoted open terrestrial vegetation and enhanced nutrient input to the ocean. The deglaciation was characterized by pronounced warming, reduced productivity, increased moisture availability, a shift to pine-dominated vegetation, and reduced fire activity. A key finding is the ocean warming which began around 1.3 ka earlier than major terrestrial changes, indicating that tropical ocean-atmosphere interactions initiated the deglacial transition. The overall findings highlight a fundamental transition in climatic controls, from a glacial regime dominated by sea-level-driven shelf exposure and arid climate to an interglacial regime governed by tropical ocean-atmosphere dynamics. This study underscores the sensitivity of the northern SCS to both high- and low-latitude forcing and the value of integrated land-sea proxies in deciphering complex climate interactions.