High‐Resolution Diatom Record of Kuroshio Intrusion and East Asian Monsoon Variability in the Northern South China Sea Over the Past 40 kyr

Abstract The South China Sea (SCS), one of the largest semi‐enclosed marginal seas in the western Pacific, is strongly influenced by the East Asian monsoon and the Kuroshio intrusion (KI). A high‐resolution diatom record from the northern SCS reveals orbital‐scale variability since the Late Pleistocene. KI intensified during late Marine Isotope Stage 3 (MIS 3) (40–29 cal kyr BP), the last deglaciation (19–11.5 cal kyr BP), and the mid‐late Holocene (after 9 cal kyr BP), but weakened during early MIS 2 (29–19 cal kyr BP) and the early Holocene (11.5–9 cal kyr BP). These fluctuations are closely linked to El Niño‐Southern Oscillation (ENSO)‐like climate conditions, with El Niño‐like phases promoting stronger KI and La Niña‐like conditions suppressing its intensity. During the Last Glacial Maximum (LGM, 22.4–19 cal kyr BP), anomalous wind‐stress‐curl patterns counteracted ENSO forcing, weakening the KI despite a strengthened North Equatorial Current. Variations in coastal diatoms abundance reflect East Asian summer monsoon (EASM)–driven sea surface salinity (SSS) changes, with maxima during humid intervals (late MIS 3 and early Holocene) and lower values during arid stages (LGM and Younger Dryas). A significant finding is the abrupt increase in abundance of the neritic diatom species Paralia sulcata at approximately 11 cal kyr BP, which we interpret as marking either a rapid sea level rise or the opening of the Taiwan Strait. Overall, ENSO primarily modulated KI strength while the monsoon governed SSS, highlighting SCS sensitivity to tropical Pacific forcing and offering a framework for past and future ocean–atmosphere interactions.