Delivery of anthropogenically-sourced trace metals to the surface ocean in the eastern North Atlantic: A16N

Trace metals in the surface ocean can function as essential micronutrients that regulate the productivity of phytoplankton, and hence the uptake of carbon dioxide by the oceans (e.g. Fe, Zn), or as potential toxins to marine organisms (e.g. Pb, Cu). Many biologically important trace metals are abundant in emissions from coal and oil combustion. To assess the impact of trace metals from atmospheric pollution on the open ocean, particulate samples from the upper 1000m of the Atlantic Ocean were collected between 62ºN and 5ºS during the CLIVAR/CO2 Repeat Hydrography section A16N from June to August 2003. Samples were analyzed by energy-dispersive X-ray fluorescence for Al, Si, P, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Sr, As, and Pb. Surface-ocean particles were enriched in Cr, Ni, Cu, Zn and Pb compared to average crustal composition. Trace metals enrichment displayed similar latitudinal trends as atmospheric aerosol V:Ti ratios, suggesting deposition of atmospheric pollution products was the primary source of excess trace metals in the surface ocean. Robust anthropogenic sources for Cr, Ni, Cu, Zn and Pb were apparent at most locations between 62ºN and 5ºS. Lithogenic sources dominated only within a region between 10 and 20ºN where surface waters were heavily impacted by the delivery of desert dust from the African continent. Enrichment in anthropogenically-sourced trace metals was correlated with increased aerosol-Fe solubility. Surface-ocean distributions of particulate Cu indicate that aerosol-Cu delivery to the North Atlantic and the spatial extent of Cu toxicity on phytoplankton may be underestimated by current models.