A high-resolution δ18O record of modern Tridacna gigas bivalve and its paleoenvironmental implications

Abstract

The lack of monthly-resolved paleoenvironmental records beyond the instrumental era hinders our full understanding of global climate dynamics. Tridacna gigas shells have a large potential to quantitatively document the variability of the ocean surface environment on time scales from daily to interannual in the past, while the applicability of the geochemical proxies of Tridacna gigas needs to be quantitively investigated. Here we establish a chronology for a Tridacna gigas shell from the southern South China Sea (SCS) by identifying daily growth laminae using a laser scanning confocal microscope (LSCM). Our high-resolution Tridacna gigas shell δ18Oshell record throughout 1989–2013 shows a high correlation with changes in local precipitation and the index of El Niño-Southern Oscillations (ENSO) on the interannual time scale. Together with observed sea surface temperature (SST), we calculated seawater δ18O (δ18Osw) and derived sea surface salinity (SSS) change in the southern SCS based on the Tridacna gigas shell δ18O record. Our salinity-budget calculation results suggest that the SSS variability in the southern SCS is predominantly affected by the vertical mixing and sea surface freshwater flux. Our study reveals that the Tridacna gigas shell is an ideal archive for high-resolution and quantitative paleoenvironmental reconstructions in tropical ocean regions, thus providing a new window to explore paleoenvironmental changes on annual and interannual time scales.