Contribution of metal production to bioaccessible Fe deposition into Southern Indian Ocean

Atmospheric iron (Fe) from anthropogenic, lithogenic, and pyrogenic sources contributes to ocean fertilization, climate change, and human health risk. However, significant uncertainties remain in the source apportionment, due to a lack of source-specific evaluation of Fe-laden aerosols. Here, the large uncertainties in the model estimates are investigated using different Fe emissions from metal production.  The anthropogenic and lithogenic factors are evaluated by using high-time-resolution measurements of Fe-laden species in fine particulate matter at Fukue observational site in downstream region of East Asian outflow. The better agreement in anthropogenic factor of aerosol Fe concentrations with the field data is obtained with the low estimate of smelting Fe emission. Our simulation with the low estimate of smelting Fe emission confirms that anthropogenic aerosols play dominant roles in bioaccessible Fe deposition to the northwestern Pacific, compared to lithogenic sources. Aerosol Fe co-emitted with sulfur dioxide from metal production predominantly contributes to atmospheric bioaccessible Fe input to the Southern Indian Ocean. Our simulation with different estimates of smelting Fe emission reveals that accurate representation of aerosol Fe from metal production is a key to reduce large uncertainties in bioaccessible Fe deposition to the Southern Ocean.