264 / 2022-03-31 16:52:59

Alkenone-derived SST and implication for upwelling changes off the eastern Hainan Island over the last 4500 years

alkenone, Hainan Island, SST, upwelling, monsoon

The sea surface temperature (SST) off the eastern Hainan Island in the South China Sea is significantly influenced by the upwelling effect during summer monsoon season. But how the temperature in upwelling zone respond to monsoon changes at centennial to millennial-scale are less clear. Here we report a 4500-years SST record based on long-chain alkenones of a gravity sediment core retrieved off the eastern Hainan Island. The SST increased ~1 °C from 4500 to 1800 years BP, then experienced a relative cooler period during 600-1200 AD and warmer period during 1200-1550AD, showing oppsite pattern to the so-called Medieval Warm Period (WMP) and Little Ice Age (LIA) in Northern Hemisphere temperature. The SST gennerally decreased ~1 °C after 1250 AD, almost in anti-phase with the SST changes in non-upwelling zone in the northern SCS. Within chronological uncertainty, the variation of SST off eastern Hainan Island overall show anti-phase with the summer monsoon indicated by stalagmite isotope in the Dongge Cave. It suggest the increase of SST may relate to the weakening of summer monsoon from 4500 to 1800 years BP, while decreased SST from 1250 AD might reflect a stronger summer monsoon under global warming background since the LIA. This may help to assess how summer monsoon and monsoon-induced upwelling would respond to the global warming in future.