Frequency of enhanced food availability controlled the growth of bamboo corals in the Northwestern South China Sea

Abstract

Cold-water bamboo corals are promising high-resolution archives of paleoceanography and cold-water coral (CWC) development research. Nevertheless, obtaining accurate, high-resolution chronology of these corals are still challenging. In this study, organic nodes of the bamboo corals in the northwest South China Sea (SCS) were used for growth ring imaging, and counting, as well as radiocarbon analysis to establish the high-resolution coral chronology. Our results show that the ratios between the growth ring numbers and coral ages are ~8 (~6) for specimen at ~700 m before (after) 1997 AD, and ~2 for specimen at ~1400 m during the whole life-span. These ratios are two times the frequency of the enhanced particulate organic carbon (POC) flux that determines the frequency of enhanced food availability to the corals, at the corresponding water depths. In analogue to the modern suitable habitat of the thriving CWCs, the growth ring formation of bamboo corals is most likely controlled by the frequency of the enhanced POC flux. Furthermore, the coral chronology and annual to seasonal radial growth rate (RGR) were obtained based on growth ring counting and summarizing the widths of the growth rings, respectively. Correlation between the coral RGRs and the climatic parameters, i.e., the Pacific Decadal Oscillation, the ENSO and the East Asian Monsoons (EAMs) are consistent with the relationship between these climatic parameters. These results further confirm the validity of age model of bamboo corals based on the concentric ring counting.