Variable Kuroshio Current intrusion into the northern South China Sea over the last 7.3 kyr

Abstract

The branch intrusion of the Kuroshio Current (KC) into the northern South China Sea (SCS) has a significant effect on temperature, salinity, circulation, and eddy generation. However, the study of Holocene hydrological changes and the historical influence of the KC in this region is limited. Here, we report high-resolution sea surface temperature (SST) and δ18Osw (as a proxy for sea surface salinity, SSS) records based on paired Mg/Ca ratios and δ18O analyses of the planktonic foraminifera Globigerinoides ruber combined the Pulleniatina obliquiloculata and G. sacculifer/G. ruber ratios from core 05E306 (22°0.06′ N, 118°59.64′ E; water depth = 1440 m) in the northern SCS. By comparing these data with records from cores located within and outside of the main KC flow pathway, we evaluate the spatiotemporal evolution of the KC in this region over the last 7.3 kyr. The strongest influence was observed from 6.1 to 5.3 ka, recorded as an abrupt increase in SST and SSS with remarkably increased P. obliquiloculata abundance (37.4%) and G. sacculifer/G. ruber ratios (3.18). During the following period, 5–2.5 ka, SST decreased by 0.4–1.1 °C with an associated decrease in δ18Osw, indicating a weakened KC. After 2.5 ka, the influence of the KC on the northern SCS strengthened; however, the high SST record still exhibits a spatial constraint in the longitude distribution of the KC during this period of strongest intrusion. Moreover, the abundance of planktonic foraminifera in the study area more strongly correlates with SSS than SST. The δ18Osw records in core 05E306 show a freshening trend after 5.7 ka, which is inconsistent with the declining East Asian Summer Monsoon precipitation record but consistent with the Holocene freshening trend recorded in the Western Pacific. This suggests that hydrological variability of the northern SCS is mainly influenced by the Western Pacific Ocean.