Isotope Compositions of Century‐Long Corals Reveal Significant Dissolved Cu, Zn Fluxes From Human‐Accelerated Weathering Into the Ocean

Abstract

Earth is thought to have entered a new geological epoch, the Anthropocene, as humans have become the dominant force in contemporary environmental changes (Waters et al., 2016). In particular, huge amounts of toxic chemicals from industry, agriculture and urbanization have been widely and rapidly introduced into the ocean since the 1950s (Steffen et al., 2015). Among these chemicals, pollution of heavy metals (e.g., Pb, Cd, Cr, Cu, Hg, and Zn) have attracted great attention because they are persistent and biologically active, and readily assimilated by marine biota and by humans (Kalisinska, 2019). Shallow-water corals are widely distributed in the subtropical and tropical ocean and ambient seawater can be transported to the calcifying site where the marine metals substitute for Ca in the coral skeleton during skeletal calcification (Gaetani & Cohen, 2006). Thus, the seasonally and annually banded corals are unique archives of trace metals' chemistry in the marine environment, providing centennial-scale records at high (annual-seasonal) resolution (Saha et al., 2016;Sun et al., 2016;Weerabaddana et al., 2021). These records are valuable for our understanding of human impacts on the natural cycles of metals and for assessing global efforts to reduce anthropogenic metal emissions.However, metal concentrations in corals alone cannot provide direct provide diagnostic information on historical sources or migration processes of heavy metals. The heavy metal sources are diverse and their migration processes are complex. In addition to direct anthropogenic inputs from metal mining, smelting, domestic and industrial sewage (Araújo et al., 2019;Liao et al., 2021), natural rock weathering and soil erosion can also introduce large amounts of heavy metals to the surface ocean (Chester & Jickells, 2012). Several studies have successfully used