古环境研究室知识库

High-resolution delta O-18 and Sr/Ca ratio profiles of a modern (live-caught) and a fossil (dead-collected) giant bivalve shell (Tridacna gigas) from northern South China Sea were analyzed. The high-resolution delta O-18 profiles, as documented in most of previous studies, showed pronounced seasonal cycles and recorded the combined influence of seawater delta O-18 and sea surface temperature. The Sr/Ca ratio profiles derived from ICP-OES had well-defined annual cycles and significant and negative correlation with sea surface temperature, while the Sr/Ca profiles derived from LA-ICP-MS did not reveal clear annual cycles. This difference was likely caused by the organics contents in T. gigas shells, which had a chemical composition different than CaCO3 crystals and a heterogeneous distribution across the shell, the sampling methods, and the experimental errors. Two calibration equations between Sr/Ca ratios, determined by ICP-OES, of modern T. gigas shell and instrumental SST were calculated based on all monthly and extremum SST data, and the equation from extremum data produced better SST predictions. These results suggested that the high-resolution ICP-OES derived Sr/Ca ratios of T. gigas in the South China Sea had the potential of providing a good proxy of historical SST.