Bioavailable atmospheric phosphorous supply to the global ocean: a 3-D global modelling study (original) (raw)

The atmospheric cycle of phosphorus (P) is here parameterized in a global 3-D chemistry-transport model, taking into account primary emissions of total P (TP) and dissolved P (DP) associated with mineral dust, combustion particles of natural and anthropogenic sources, bioaerosols, sea-spray and volcanic aerosols. Global TP emissions are calculated to amount roughly 1.33 Tg-P yr-1 with mineral sources (about 1.10 Tg-P yr-1) contributing more than 80% to these emissions. Additionally, under acidic atmospheric conditions, for the present study we take into account the P mobilization from 20 mineral dust, that is calculated to contribute about one third (0.14 Tg-P yr-1) to the global DP atmospheric source. The calculated global annual DP deposition flux equals to 0.43 Tg-P yr-1 (about 40% enters the ocean), and shows a strong spatial and temporal variability. Considering that all bioaerosol P is bioavailable (BP) and accounting for all other sources of DP, a flux of 0.16 Tg-P yr-1 BP to the ocean is derived. Present day simulations of atmospheric P aerosol concentrations and deposition fluxes are satisfactory compared with available observations, indicating however a 50% uncertainty of current 25 knowledge on primary and secondary sources of P that drive its atmospheric cycle. Sensitivity simulations using preindustrial (year 1850) and future (2100) anthropogenic and biomass burning emission scenarios, showed a present-day increase of 75% in the dissolution flux of P present in dust aerosol compared to the 1850 dissolution flux due to increasing atmospheric acidity over the last 150 years. Future reductions in air pollutants, due to the implementation of air-quality regulations, are expected to decrease P mobilization flux by about 30% for the year 2100 compared to the present-day. A 30 striking result is that more than 50% of the BP deposition flux to the ocean originates from biological particle and this contribution is found to maximize in summer when atmospheric deposition impact on the marine ecosystem is the highest due to ocean stratification. These findings reveal the largely unknown but important role of terrestrial bioaerosols as suppliers of bioavailable P to the oceanwith very important implications for past and future responses of ecosystems to global change. Therefore, our study provides new insights to the atmospheric P cycle by demonstrating that bioaerosols are 35 as important carriers of bioavailable P as dust aerosol, that was up to now considered as the only large source of DP external to the open ocean.