Coral Sr/Ca-derived seasonal sea surface temperature variations in the Qiongdong upwelling area of the northern South China Sea during the Medieval Climate Anomaly

Abstract

Geological records of seasonal sea surface temperature (SST) records are useful for better understanding the past dynamics of coastal upwelling, and for inferring future scenarios. By using Sr/Ca records obtained from Porites lutea corals in the Qiongdong upwelling (QDU) area of the northern South China Sea (SCS), seasonal SST variations were reconstructed for the 1129–1263 CE interval of the Medieval Climate Anomaly (MCA). On an annual scale, summer SST is negatively correlated with the intensity of the East Asian Summer Monsoon (EASM), indicating a dominant role of the EASM on summer SST in the QDU area. The lack of correlation between winter SST and the East Asian Winter Monsoon (EAWM) may result from the dating errors of the climate archives and the low temporal resolution of EAWM records. Winter SST and summer SST played similarly affected the SST seasonality during the MCA. On the centennial scale, the differences in the averages of summer SST and winter SST in the QDU area between the MCA and the Current Warm Period were attributed to the different EASM and EAWM intensities. The consistent variations between the summer QDU and the winter Sumatra-Java upwelling during both climate intervals may imply that the SST variabilities in these two coastal upwelling systems responded to cross-equatorial winds originating from the Indian Ocean.