Oxygen isotope temperature calibrations for modern Tridacna shells in western Pacific
The oxygen isotope ratio of carbonate in Tridacna shell (δ18Oshell) is assumed to be precipitated in isotopic equilibrium with surrounding seawater and thus reflects a combination of the Sea surface temperature (SST) and the δ18O of seawater (δ18OSW). Accordingly, Tridacna δ18Oshell has been widely used for high-resolution paleoclimate reconstructions. However, the influences of interspecific differences, spatial heterogeneity, as well as the “growth effect” on the δ18Oshell-SST relationship, have not been fully tested. Here, we present a monthly resolved δ18Oshell record of a Tridacna squamosa specimen from Yagong Island, South China sea (SCS). Our results suggested that the monthly resolved δ18Oshell from northern SCS was dominated by the seasonal SST variations, which was highly correlated with measured SST after excluding the influence of δ18OSW. Then, the SST = f(δ18Oshell-δ18OSW) equations of all published monthly δ18Oshell records of modern Tridacna from the Indo-Pacific were collected. The resulting investigation revealed that similar SST = f(δ18Oshell-δ18OSW) equations for each shell, indicating the minor influences of spatial heterogeneity and interspecific differences. The average equation for Tridacna (Tridacna gigas, Tridacna derasa, Tridacna squamosa, Tridacna maxima and Hippopus hippopus) was SST = − 3.56 ± 1.26 (δ18Oshell-δ18Osw) + 22.44 ± 2.77 (− 0.28 ± 0.08 ‰°C−1, VPDB) (2σ), which was close to the equations set up for other mollusks (without Tridacna) and inorganic aragonite. Finally, although the growth rates varied greatly among Tridacna specimens and within different growth stages of each specimen, we did not find a significant influence of the growth rates on SST = f(δ18Oshell − δ18OSW) equations, indicating that the “growth effect” might have at best a slight impact on the δ18Oshell of Tridacna.
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National Natural Science Foundation of China