Contribution of Anthropogenic and Lithogenic Aerosol Fe in the East China Sea

Aerosol deposition is one of the major processes providing bioavailable Fe to the surface ocean. However, the quantification of aerosol Fe flux in the surface ocean is highly challenging operationally. In this study, we measured both Fe isotopic composition and specific elemental ratios in 5 size-fraction aerosols collected over the East China Sea (ECS) to quantify the relative contribution of lithogenic and anthropogenic aerosol Fe. Both the isotopic and elemental ratios indicate that anthropogenic aerosol Fe mainly originates from high-temperature combustion activities with the end member of the δ⁵⁶Fe to be −4.5‰. We found that the Cd/Ti ratio is a much more reliable proxy to quantify the contribution of anthropogenic aerosol Fe in coarse aerosols than δ⁵⁶Fe in the ECS. Attributed to extremely high deposition velocities and high total Fe concentrations for large size aerosols, lithogenic aerosols are still the dominant dissolved aerosol Fe source in the ECS.