ABSTRACT                            

Zinc (Zn), an essential trace nutrient in marine ecosystems, exhibits a nutrient-type vertical distribution. Increasing anthropogenic inputs have significantly modified the Zn fluxes in coastal surface waters, disrupting the natural biogeochemical cycling of Zn. Although the spatial distributions of Zn in seawater and sediments have been extensively investigated, the lack of long-term, high-resolution records restricts our understanding of the behavior of Zn in marine systems. Here, we present annually resolved Zn/Ca ratios obtained from a continuously growing Porites lutea coral in Xiaodonghai Bay, Sanya, northern South China Sea, to reconstruct the variability of surface seawater Zn from 1870 to 2006. Our results suggest that the trends of surface seawater Zn are influenced by submarine groundwater discharge, and the extreme values are mainly related to local military activities and infrastructure construction. This study offers novel perspectives on the Zn biogeochemistry in coastal seawater and emphasizes the key role of terrestrial input in coastal Zn budgets.