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

Abstract

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.

Phosphorus solubility in aerosol particles related to particle sources and atmospheric acidification in Asian continental outflow

“…He et al (2011) studied the atmospheric dry and wet deposition of P in Singapore and reported that DIP comprised 38 % of TP in aerosols. In the dust samples of this study, however, the P solubility was approximately 8 %, which was close to the value of 10 % measured in dust aerosols collected at the Mediterranean coast (Carbo et al, 2005;Herut et al, 2002;Nenes et al, 2011) but was considerably lower than the value of 20 % measured in Asian dust at the coastal site of the East China Sea and in African dust in the western subtropical North Atlantic (Guo et al, 2014;Zamora et al, 2013). There are few available data for P solubility in the marine atmosphere (Hsu et al, 2014;Baker et al, 2006a, b), and the limited data show that the solubility of P in marine aerosols is generally higher than that in coastal aerosols ( Table 1).…”

“…Aerosol P from anthropogenic sources usually has a higher solubility than that from mineral sources. The reason is that anthropogenic P tends to associate loosely with particulates, dissolve more readily than mineral P and, consequently, interact easily with acid gases to produce more bioavailable P (Herut et al, 2002;Baker et al, 2006a, b;Anderson et al, 2010;Hsu et al, 2014;Herbert et al, 2018). Our results indicate that the P solubility was approximately 35 % in the aerosols when the fraction of anthropogenic P in the TP was more than 70 %.…”

“…In the South China Sea, P solubility in aerosols related to biomass combustion is around 50 ± 14 % (Hsu et al, 2014). These results imply that an increase in the relative amounts of aerosols from anthropogenic sources might lead to the increase in bioavailable P. In addition, atmospheric acidic processes associated with anthropogenic pollutants may transform unreactive P to bioavailable P. Recent model studies predict that the acid dissolution process increases the fraction of bioavailable P from ∼ 10 % globally at labile pools to 42 % in the Pacific Ocean, with the mean value of 22% in the global marine atmosphere (Herbert et al, 2018). Myriokefalitakis et al (2016) estimated that acid-driven solubilization flux of P from mineral dust contributed about one-third to the global TDP atmospheric source.…”

“…P solubility in aerosols from different sources varies greatly and is generally low in particles from mineral sources and high in particles from anthropogenic sources. In the Mediterranean atmosphere, P solubility ranges from 2 % to 20 % with an average of 10 % in aerosols affected by Saharan dust, whereas P solubility ranges from 30 % to 79 % with an average of 50 % in aerosols with anthropogenic sources (Herut et al, 2002). Similar results were also observed in the Atlantic atmosphere, where the P solubility in aerosols affected by Saharan dust is approximately 8 % and can be up to 87 % in aerosols originating from terrestrial air masses in South America (Baker et al, 2006a, b).…”

Radium Tracing Cross‐Shelf Fluxes of Nutrients in the Northwest Pacific Ocean

“…The atmospheric depositional flux of DIN is from Vet et al (). The atmospheric depositional flux of P to the North Pacific is the total phosphorus flux (Herbert et al, ). The fluxes from the subsurface layer by water mixing in the North Pacific Ocean gyre are from Letscher et al ().…”