Do dust emissions from sparsely vegetated regions dominate atmospheric iron supply to the Southern Ocean?

Atmospheric deposition of dust aerosols is a significant source of exogenous iron (Fe) in marine ecosystems and is critical in setting primary marine productivity during summer. This dust-borne input of Fe is particularly important to the Southern Ocean, which is arguably the most biogeochemically important ocean because of its large spatial extent and its considerable influence on the global carbon cycle. However, there is large uncertainty in estimates of dust emissions in the Southern Hemisphere and thus of the deposition of Fe-containing aerosols onto oceans. Here we hypothesize that sparsely vegetated surfaces in arid and semiarid regions are important sources of Fe-containing aerosols to the Southern Ocean. We test this hypothesis using an improved dust emission scheme in conjunction with satellite products of vegetation cover and soil moisture in an atmospheric chemistry transport model. Our improved model shows a twofold increase of Fe input into the Southern Ocean in austral summer with respect to spring and estimates that the Fe input is more than double that simulated using a conventional dust emission scheme in summer. Our model results suggest that dust emissions from open shrublands contribute over 90% of total Fe deposition into the Southern Ocean. These findings have important implications for the projection of the Southern Ocean's carbon uptake. Plain Language Summary Atmospheric deposition of dust aerosols is a significant source of exogenous iron (Fe) in marine ecosystems and is critical in setting primary marine productivity during summer. This dust-borne input of Fe is particularly important to the Southern Ocean, which is arguably the most biogeochemically important ocean because of its large spatial extent and its considerable influence on the global carbon cycle. However, there is large uncertainty in estimates of dust emissions in the Southern Hemisphere and thus of the deposition of Fe-containing aerosols onto oceans. Here we hypothesize that sparsely vegetated surfaces in arid and semiarid regions are important sources of Fe-containing aerosols to the Southern Ocean. We found that open shrubland could be a key contributor to atmospheric soluble Fe input to the Southern Ocean, especially in austral summer. These findings have important implications for the projection of the Southern Ocean's carbon uptake.