Variations in temperature and salinity of the surface water above the middle Okinawa Trough during the past 37 kyr

Abstract

East China Sea (ECS) is an important climate modulator of East Asia. In the last glacial period, the global sea level, the path and strength of the Kuroshio Current experienced great changes; combined with the variable volume of fresh run-off input, they made the hydrographic situation in the ECS quite different from nowadays. Based on high-resolution alkenone-sea surface temperature (SST) and oxygen isotope composition of planktonic foraminifera Globigerinoides sacculifer we reconstructed paleo-sea surface salinity (SSS) of a long piston core DGKS9604 retrieved from the middle Okinawa Trough of the eastern ECS. The δ 18O and SST records display significant variations with global ice volume. Synchrony of the millennial-scale climate events like YD and Heinrich events of core DGKS9604 to the ice core from the northern high latitudes, and the synchroneity of deglacial warming with the Bølling–Allerød warming suggests a strong coupling of the SST variations in the marginal Pacific Ocean to the climate of the North Atlantic, most likely through the Asian monsoon atmospheric circulation. The ECS documents lowest SST (22 °C) at ~ 26 cal kyr BP and ~ 3 °C SST difference between the full glaciation (26 to 19 cal kyr BP) and mid-to-late Holocene (6 cal kyr BP–present). The overall long-term hydrographic variations in the middle Okinawa Trough are controlled by temporal and spatial variations in: (i) the intensity and position of the Kuroshio Current, (ii) intensity of the Asian summer monsoon and (iii) sea-level fluctuations coupled with ECS topography. Saline surface water dominated over the middle Okinawa Trough during early pre-glaciation (37 to 31 cal kyr BP), last deglaciation (19 to 11.6 cal kyr BP), and mid-to-late Holocene (6 cal kyr BP–present), whilst freshened surface water prevailed during the late pre-glaciation (31 to 26 cal kyr BP), full glaciation (26 to 19 cal kyr BP) and early Holocene (11.6 to 6 cal kyr BP).