Sr/Ca differences within and among three Tridacnidae species from the South China Sea: Implication for paleoclimate reconstruction

- The Sr/Ca ratios of eight Tridacnidae specimens of three different species were analyzed.
- Interspecies differences were observed in mean Sr/Ca values.
- Within-species differences were insignificant in this study.
- The Sr/Ca ratios in the inner layer of T. gigas and T. derasa have good potentials to be SST proxies.

In this study, eight Tridacnidae specimens of three different species (Tridacna gigas, Tridacna derasa and Hippopus hippopus) were collected from Xisha Islands of South China Sea. The Sr/Ca ratio, which has been widely used as sea surface temperature (SST) proxy in coral samples, was determined on these specimens using ICP-OES to examine their potential for paleoclimate reconstruction. While within-species differences were found to be insignificant, the mean Sr/Ca ratios of the three species (2.24 ± 0.1, 1.77 ± 0.1 and 1.91 ± 0.14 mmol/mol for modern T. gigas, T. derasa and H. hippopus specimens, respectively) are statistically different. Species identification, therefore, is necessary before using Tridacnidae Sr/Ca ratios as paleoclimate recorders. While the relationship between local SST and Sr/Ca ratios of H. hippopus was unclear, the Sr/Ca profiles of modern T. gigas and T. derasa specimens are significantly correlated to local SST, implying that they can be used as SST proxies. The range of Sr/Ca ratios measured in this study is comparable to the Tridacnidae Sr/Ca measurements obtained in previous studies from other areas, but there are also substantial differences in detail, indicating that calibration for regional differences is also needed before paleoclimate reconstruction is attempted. In addition, although the mean Sr/Ca values of T. gigas, T. derasa and coral samples in Xisha Islands were significantly different, their Sr/Ca-SST calibration slopes were comparable, pointing to a similar thermodynamic fractionation and highlighting the potential of the combination of Tridacnidae and coral samples for paleo-SST seasonality reconstruction.