Pervasive contamination of the remote open ocean with anthropogenic zinc

Abstract Anthropogenic emissions may drive the isotopically light zinc that pervades the low-latitude upper ocean, but major gaps in our understanding of oceanic zinc cycling have hindered the unequivocal detection of an anthropogenic fingerprint. Here, we address this issue using the geochemistry of marine particles from the remote South Pacific Ocean (GEOTRACES cruise GP21). The isotope composition of zinc in marine particles resembles that of locally collected atmospheric aerosols and is predominantly lighter than dissolved zinc, inconsistent with the view that heavy zinc isotopes are preferentially removed via scavenging. Coupled with established pollution tracers (lead isotopes) and elemental mixing models, we show that the marine particulate zinc pool is overwhelmingly dominated by aerosol-derived anthropogenic inputs, with minimal natural controls. Atmospheric deposition of anthropogenic zinc likely drives the isotopically light signature of the oligotrophic upper ocean, offering insights into modern marine zinc cycling and further illustrating the extent of the human footprint on the most remote oceanic regions.