Paleoceanographic changes in the East China Sea during the last ～400 kyr reconstructed using planktic foraminifera

摘要

East China Sea (ECS) is greatly influenced by East Asian Summer Monsoon (EASM), precipitation discharge and differential inflow of the warm and saline Kuroshio Current (KC). Any change in surface water conditions either due to variations in ocean currents or discharge from terrestrial rivers have pronounced effects on the population abundance of planktic foraminifera; therefore, planktic foraminifera happen to be a valuable proxy to decipher paleoceanographic changes in the ECS. To understand the influence of KC and EASM at ECS, paleoceanographic changes are reconstructed for the last 400 kyr using planktic foraminiferal population abundances and Mg/Ca ratio derived Sea Surface Temperature (SST) from IODP site U1429. Nine different species/species associations of planktic foraminifera are found to be significant at this site. Q-mode factor analysis of these abundant species helped to retain four factors explaining similar to 91% of the data variance suggesting four different conditions prevailing at ECS over the last 400 kyr. The species association of factor 1 reflects cold surface water conditions in the ECS, factor 2 suggests the influence of the coastal water, factor 3 can be linked with the upwelling of lower thermocline water, and factor 4 is strongly associated with the strength of the KC. This study suggests that KC and EASM were stronger during the interglacial periods. The proxy that responds to KC strength (Globogerinoides ruber) and calculated Mg/Ca SST shows the presence of 23 kyr precession and 100 kyr eccentricity cycles modulated by the differential inflow of KC due to global and local factors. The comparison of SST of the western Pacific with SST of the ECS shows that KC actively transports heat to ECS from the equatorial western Pacific warm pool.