A daily-weekly-resolved δ18O record derived from a modern giant clam shell in the northern South China Sea: Implications for paleoclimate and paleoweather reconstruction

The aragonite shells of giant clam (Tridacna spp.) with clear daily growth bands have been demonstrated to be an ideal paleoweather archive. However, the current paleoweather proxies of Tridacna spp. are still limited in variety and require further expansion. δ18O, one of the most commonly used geochemical proxies in paleoclimate research, has been widely used for monthly paleoclimate reconstruction in Tridacna spp., which usually reflects sea surface temperature (SST) and seawater δ18O. However, its implication in paleoweather reconstruction is seldomly discussed due to the limitation of data resolution. Here, the daily to weekly resolved Tridacna δ18O profiles from northern South China Sea (SCS) were analyzed using secondary ion mass spectrometer (SIMS). The results show that the daily to weekly resolved δ18O profiles have distinct seasonal cycles, but the derived SST seasonality cannot rule out the possibility of influence from high-frequency fluctuations. More importantly, the daily to weekly resolved δ18O profiles show significant intraseasonal oscillation (ISO). Together with the contemporaneous instrumental data, it is suggested that the ultrahigh resolution Tridacna δ18O has the potential to record the ISO via hydrological and thermal processes.