Anthropogenic emissions of volatile Cd detected in western tropical North Atlantic surface seawater

Abstract

The Cd concentrations and isotope compositions of open ocean surface waters are generally thought to be governed by internal cycling, and particularly by the balance between upwelling of more Cd-rich deeper water masses and Cd uptake by phytoplankton. Here we present a new dataset of coupled Cd isotope compositions and concentrations for seawater depth profiles sampled in the western tropical Atlantic Ocean during Leg 2 of the GEOTRACES GA02 section. A box model for the Cd source and sink fluxes of the oligotrophic surface waters of the study area shows that the observed light Cd isotope compositions and low Cd concentrations are a consequence of biological Cd uptake and atmospheric deposition of isotopically light anthropogenic Cd. Aerosols enriched in anthropogenic Cd thereby contributed at least 19%, and possibly more than 45%, to the dissolved surface water Cd inventory during the sampling period. This reveals that anthropogenic emissions of volatile Cd can have a key impact on the distribution of Cd in open ocean surface waters