Sea surface temperature seasonality in northern South China Sea during the middle Holocene derived from high resolution Sr/Ca ratios of Tridacna shells

Seasonal climate variability is an important component of the climate system, and has a significant impact on ecosystems and social systems. However, the temporal resolution of most proxy-based paleoclimate records is limiting to fully understand the past seasonal changes. Here we used high-precision monthly resolution Sr/Ca records of three Tridacna squamosa from northern SCS to reconstruct the SST seasonality during three-time windows of the middle Holocene. The results suggested that the SST seasonality in northern SCS during the middle Holocene (3.21 ± 0.98℃) was smaller than that for recent decades (1994-2004 AD, 4.32 ± 0.59℃). The analysis of modern instrumental data showed that the SST seasonality in northern SCS was dominated by the winter SST, which was deeply influenced by the intensity of EAWM. Strong EAWM usually resulted in cooler winter SST and a larger SST seasonality in northern SCS. The reconstructed Holocene EAWM records showed that the EAWM strengthened from the middle to late Holocene, which could be demonstrated by our reconstruction of a smaller SST seasonality during the middle Holocene in northern SCS. This study highlighted that the Sr/Ca ratios of Tridacna shells can be used as a potential high-resolution indicator of past seasonal climate changes.