[MIS06-02] Implications of overestimates in mineral dust emissions from Australia on labile iron concentrations in aerosols
Keywords:Mineral dust, Bushfires in Australia, climate change
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 dust emissions and aerosol-bearing Fe solubility (i.e., the ratio of labile Fe (LFe) to total Fe (TFe)) 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 (110ºE–160ºE and 10ºS–41ºS).
The atmospheric model considered the deposition of both lithogenic and pyrogenic Fe-containing aerosols and their chemical transformation due to reactions with gaseous species. Sensitivity simulations are carried out before (a priori) and after (a posteriori) model optimizations.
The optimal (a posteriori) model successfully estimated TFe concentrations in aerosols sampled over the 70ºE–150 ºE and 10ºS–70ºS oceanic sector of the SH. As a consequence, the a posteriori model reproduced enhanced Fe solubility associated with better agreement of LFe concentrations with the field measurements. The a posteriori model estimates suggested that bushfires contributed a large fraction of LFe 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 micronutrient supply to the oceans as increasing frequency and intensity of open biomass burning are projected in the SH.
The atmospheric model considered the deposition of both lithogenic and pyrogenic Fe-containing aerosols and their chemical transformation due to reactions with gaseous species. Sensitivity simulations are carried out before (a priori) and after (a posteriori) model optimizations.
The optimal (a posteriori) model successfully estimated TFe concentrations in aerosols sampled over the 70ºE–150 ºE and 10ºS–70ºS oceanic sector of the SH. As a consequence, the a posteriori model reproduced enhanced Fe solubility associated with better agreement of LFe concentrations with the field measurements. The a posteriori model estimates suggested that bushfires contributed a large fraction of LFe 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 micronutrient supply to the oceans as increasing frequency and intensity of open biomass burning are projected in the SH.