The Effect of Atmospheric Acid Processing on the Global Deposition of Bioavailable Phosphorus From Dust

The role of dust as a source of bioavailable phosphorus (Bio‐P) is quantified using a new parameterization for apatite dissolution in combination with global soil data maps and a global aerosol transport model. Mineral dust provides 31.2 Gg‐P/year of Bio‐P to the oceans, with 14.3 Gg‐P/year from labile P present in the dust, and an additional 16.9 Gg‐P/year from acid dissolution of apatite in the atmosphere, representing an increase of 120%. The North Atlantic, northwest Pacific, and Mediterranean Sea are identified as important sites of Bio‐P deposition from mineral dust. The acid dissolution process increases the fraction of total‐P that is bioavailable from ~10% globally from the labile pool to 18% in the Atlantic Ocean, 42% in the Pacific Ocean, and 20% in the Indian Ocean, with an ocean global mean value of 22%. Strong seasonal variations, especially in the North Pacific, northwest Atlantic, and Indian Ocean, are driven by large‐scale meteorology and pollution sources from industrial and biomass‐burning regions. Globally constant values of total‐P content and bioavailable fraction used previously do not capture the simulated variability. We find particular sensitivity to the representation of particle‐to‐particle variability of apatite, which supplies Bio‐P through acid‐dissolution, and calcium carbonate, which helps to buffer the dissolution process. A modest 10% external mixing results in an increase of Bio‐P deposition by 18%. The total Bio‐P calculated here (31.2 Gg‐P/year) represents a minimum compared to previous estimates due to the relatively low total‐P in the global soil map used. Plain Language Summary Phosphorus (P) is an essential requirement for life. Natural sources of P on land are from rock weathering and fertilizers. By contrast over the open ocean, the major source of P is from falling dust. However, less than 10% of the P in dust is automatically available to phytoplankton for growth, a percentage we call bioavailable‐P. Therefore, changes to the supply of bioavailable‐P to oceans can have considerable impacts on marine ecosystems and the global carbon cycle. Previous work shows acid processes in the atmosphere can convert nonbioavailable minerals to bioavailable‐P. In our previous study we found a simple relationship between acid in the atmosphere and bioavailable‐P formed. Here we use this new relationship, together with global soil data maps on the amount and type of P in dust and a global aerosol transport model, which predicts