Conway and co-authors (2019, see reference below) present the first evidence that anthropogenic iron (Fe) from combustion sources is visible at the basin scale, using iron isotopic composition (δ56Fe) analysis of the soluble aerosol phases collected during GEOTRACES cruise GA03 in the North Atlantic Ocean. Off Sahara, soluble aerosol samples have near-crustal δ56Fe whereas those from near North America and Europe display δ56Fe values as light as −1.6‰. Coupled to aerosol deposition modeling these results reveal that soluble anthropogenic aerosol Fe flux to the global surface oceans is highly likely to be underestimated.
Figure. Tracing anthropogenic iron with iron isotopes (adapted from Conway et al., 2019). Panels a and b show that aerosols collected from near the Sahara have low solubility, a near-crustal iron isotope composition (beige circle) and a near-crustal Pb/Al composition (beige diamond). In contrast, those collected from near North America or Western Europe have very soluble iron, very light iron isotopes and are very enriched in Pb, indicating pollution from humans. When sampling points are overlain on output from dust modelling, it can be seen that the light iron isotopes correspond to where fossil fuel iron is expected to be important, and the crustal iron isotopes correspond to where natural dust iron is most important (panel c).
Conway, T. M., Hamilton, D. S., Shelley, R. U., Aguilar-Islas, A. M., Landing, W. M., Mahowald, N. M., & John, S. G. (2019). Tracing and constraining anthropogenic aerosol iron fluxes to the North Atlantic Ocean using iron isotopes. Nature Communications, 10(1), 2628. DOI: https://doi.org/10.1038/s41467-019-10457-w