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

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 δ18O shell 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 (δ18O sw) 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. • A method to analyze the growth chronology of Tridacna gigas bivalve shell was developed. • A δ18O record of Tridacna gigas shell between 1989 and 2013 was generated. • The δ18O record indicates the variability of precipitation and ENSO. • A sea surface salinity (SSS) record between 1989 and 2013 was reconstructed. • SSS in the southern South China Sea is dominated by vertical mixing and freshwater flux. [ABSTRACT FROM AUTHOR]