Tridacna spp. usually have annual and even daily growth bands, and thus provide great potential to be the high resolution recorders of past climate and environmental changes of the ocean. However, current studies mainly focus on the geochemical records of Tridacna shells, the environmental and climatic implications of long time sequenced daily growth increments are relatively unexplored. In this study, based on the confocal microscopic line-scanning imaging, a 23.7-year long (from 5 June 1989 to 21 February 2013) daily growth rate (DGR) record of Tridacna gigas shell MD3 from southern South China Sea was established and its climatic implication was investigated. On seasonal scale, significant positive correlation was found between the DGR and sea surface temperature (SST). The main growing season of T. gigas MD3 was from March to August, when sufficient sunlight and warmer SST prevailed. While high rainfall (low sunlight) from September to December and low SST from December to March hindered the growth of the shell in autumn and winter. On an inter-annual scale, the DGR of the shell varied periodically on timescales of 2-3 years and 4-5 years, which possibly represented the impacts of the Tropospheric Biennial Oscillation and El Niño-Southern Oscillation activities respectively. Our result suggested that the daily growth lines of T. gigas can establish an extraordinarily high-resolution chronology and have high potential to explore daily to inter-annual paleoenvironmental changes in tropical ocean. Compared with the paleoclimate reconstructions of geochemical approaches, this method has the advantages of low cost and short experimental time.
 

Tridacna shell; daily growth rate; seasonal growth; inter-annual oscillation; South China Sea