Aerosol trace element concentrations and fractional solubility in the North Pacific Ocean: US GEOTRACES GP-15 Pacific Meridional Transect

Aerosol transport and deposition is an important pathway for bioactive trace elements to move from the continents to the open ocean. In the case of the biolimiting micronutrient iron, atmospheric deposition of soluble aerosols can stimulate primary production. The North Pacific Ocean receives aerosol inputs from Asia and North America which can include lithogenic, anthropogenic, and pyrogenic sources. The 2018 US GEOTRACES Pacific Meridional Transect traveled from Alaska to Tahiti and provided a platform for the collection of bulk aerosols in the marine boundary layer. The chemical composition has been analyzed (by quadrupole ICP-MS after strong acid digestion) with a focus on bioactive trace elements. Aerosol concentrations show a distinct gradient from the relatively dusty north to the more pristine southern end of the transect. Aerosol fractional solubility of aerosol iron, as well as other trace elements, was measured in three leach solutions: i.) ultrapure deionized water; ii.) filtered surface seawater; iii.) acetic acid with hydroxylamine hydrochloride. The results provide a range of potential fractional solubility which may represent processes observed in precipitation as well as potential dissolution during passage through a zooplankton gut or inside a fecal pellet. Coupled with an estimate of deposition velocity, concentration data can be used to estimate an atmospheric deposition flux to the surface ocean. The resulting dataset will benefit models of aerosol deposition and help to constrain estimates of aerosol iron fractional solubility.