Evaluation of aerosol iron solubility over Australian coastal regions based on inverse modeling: implications of bushfires on bioaccessible iron concentrations in the Southern Hemisphere

• Published in: Progress in Earth and Planetary Science
• Main Authors: Ito, A, Perron, MMG, Proemse, BC, Strzelec, M, Gault-Ringold, M, Boyd, PW, Bowie, AR
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer 2020
• Subjects: Earth Sciences; Oceanography; Chemical oceanography; Southern Ocean
• Online Access: https://doi.org/10.1186/s40645-020-00357-9; http://ecite.utas.edu.au/150208

Mineral dust is the major source of external micro-nutrients such as iron (Fe) to the open ocean. However, large uncertainties in model estimates of Fe emissions and aerosol-bearing Fe solubility (i.e., the ratio of labile Fe (L Fe ) to total Fe (T Fe )) in the Southern Hemisphere (SH) hampered accurate estimates of atmospheric delivery of bioavailable Fe to the Southern Ocean. This study applied an inverse modeling technique to a global aerosol chemistry transport model (IMPACT) in order to optimize predictions of mineral aerosol Fe concentrations based on recent observational data over Australian coastal regions (110E160E and 10S41S). The optimized (a posteriori) model did not only better capture aerosol T Fe concentrations downwind from Australian dust outbreak but also successfully reproduced enhanced Fe solubility (7.8 8.4%) and resulted in much better agreement of L Fe concentrations with the field measurements (1.4 1.5 vs. 1.4 2.3 ng Fe m 3 ). The a posteriori model estimates suggested that bushfires contributed a large fraction of L Fe concentrations in aerosols, although substantial contribution from missing sources (e.g., coal mining activities, volcanic eruption, and secondary formation) was still inferred. These findings may have important implications for the projection of future micro-nutrient supply to the oceans as increasing frequency and intensity of open biomass burning are projected in the SH.