Distribution and Biogeochemical Cycling of Dissolved Copper in the Indian Ocean

Abstract The present study illustrates the distribution of dissolved copper (dCu)—an essential micronutrient for marine phytoplankton—across the Indian Ocean. Our research covers the Arabian Sea, the Bay of Bengal (BoB), the Eastern Equatorial Indian Ocean (EIO), the Southern Sector of the Indian Ocean (SIO) up to 30°S, and the Central Indian Ocean Basin (CIOB) along the GEOTRACES transects GI09 and GI10. Coastal waters of the Northern Indian Ocean exhibit elevated dCu levels, attributed to diverse sources such as riverine input, atmospheric dust, shelf release, and submarine groundwater discharge (SGD). Unlike certain other trace metals, hydrothermal vents are not a significant source of dCu in this region. However, the Java‐Sumatra subduction zone and porewaters from polymetallic nodule‐rich sediments in the CIOB contribute dCu to deeper waters. The dCu vertical profile reveals a linear increase with depth, driven by reversible scavenging processes and/or benthic flux. This distinguishes dCu from Cadmium (Cd), which follows a typical nutrient‐type distribution. Anthropogenic activities, including industrialization, have introduced excess dCu into coastal regions, impacting phytoplankton communities. Notably, the recent prevalence of anthropogenic dust in the BoB may be heightening dCu concentrations to levels that pose toxicity risks, thereby influencing primary productivity and ecosystem community dynamics. Ultimately, this study highlights how external inputs and natural or anthropogenic processes govern dCu distribution. It underscores the need for future research into the resulting impacts on marine ecosystem composition and global biogeochemical cycles.