Seasonal to interannual variations of daily growth rate of Tridacna shell from Palau Island, western Pacific, and their paleoclimatic implication

Seasonal-interannual climate change is an important component of Earth’s climate system and has a significant impact on ecosystems and social systems. However, the scarcity of modern observational data limits our understanding of the seasonal-interannual climates in long-term timescales. The natural archives can provide information on climate change before the industrial period, but most of their temporal resolution is too low to capture the seasonal-interannual climate signals. Tridacna spp. is the largest marine bivalve, and its shell has the potential to trace climatic/environmental changes on a daily to interannual scale. In this study, we have investigated the daily growth pattern of modern Tridacna gigas shell (PL-1) from Palau based on laser scanning confocal microscopy images. The results showed that the growth pattern of PL-1 was affected by OLR primarily on the seasonal timescale. On the interannual timescale, the growth rate of the shell was modulated by ENSO through the changing OLR, SLH, and upwelling, which affect the effective solar radiation and nutrients accepted by Tridacna. The growth rate of Tridacna PL-1 is accelerated during the ENSO positive phase, and vice versa. This study indicates that the daily growth rate of Tridacna shells in equatorial regions may have the potential to reconstruct seasonal-interannual climate/environment variations.