A Pilot Study On Zinc Isotopic Compositions In Shallow-Water Coral Skeletons

The trace metal element zinc (Zn) participates in coral metabolic processes and therefore accumulates in their skeletons. These metabolic processes are largely controlled by the changes of environment in which they live, so Zn isotopic compositions (delta Zn-66) in coral skeletons may possibly serve as potential tracers for climate and environmental changes. In this study, we first reported the delta Zn-66 in shallow-water coral skeletons by investigating with monthly resolution delta Zn-66 values in the skeleton of a modern Porites coral 10AR2 from the Great Barrier Reef of Australia, and the bulk skeletal delta Zn-66 values of several coral species from the Luhuitou Reef of Hainan Island in the northern South China Sea. Correlations between delta Zn-66 and other climate and environmental proxies (Sr/Ca, delta O-18, and delta C-13) and instrumental environmental variables (sea surface temperature, river runoff, and chlorophyll a) are poor, suggesting that the effects of external environmental changes on monthly variations in delta Zn-66 in coral skeletons are not significant. However, significant interspecific differences in the skeletal delta Zn-66 of corals growing under identical external environments may suggest the occurrence of biologically controlled delta Zn-66 fractionation during coral skeletons formation. In addition, the monthly delta Zn-66 in the 10AR2 coral skeleton roughly decreases with increasing temperature, which is in agreement with the recent finding that delta Zn-66 in coral tissues and zooxanthellae increases with increasing temperature and can serve as a proxy for thermal stress in corals. We thus suggest that the complicated coral internal biological processes hinder the use of skeletal delta Zn-66 as a climate and environmental proxy.