Geochemical characteristics and potential biogeochemical effect of water-soluble ions in atmospheric aerosols over the western boundary regions of Pacific Ocean

Abstract

Atmospheric aerosol samples over the western boundary regions of Pacific Ocean were collected during August 2014–October 2014 and November 2015–February 2016 on R/V Ke Xue, and concentrations of major water-soluble ions, NO3−, NO2−, NH4+, PO43−, SO42−, MSA−, Cl−, and Na+, were determined to study their seasonal distributions, sources and biogeochemical effect. The results showed that the average concentrations of NO3−, Cl− and Na+ were higher in winter, while the other ions had higher concentrations in summer. Most water-soluble ions presented obvious high-value centers in nearshore, indicating the significant influence of terrestrial input. Terrestrial input and marine emission were two major factors causing variation in concentrations of water-soluble ions, although their relative contributions were different in summer and winter. The average MSA/nss-SO42− ratios in summer and in winter were 1.60% and 2.10%, respectively, based on which the contributions of anthropogenic sources to the total SO42− were calculated to be 45.7% and 30.1% in summer and winter, respectively. Yet the contribution of biogenic sources to the total SO42−, which was 14.9% in summer and 14.4% in winter, showed no seasonal change. Apart from air masses from Asian continent, air masses from Japan as well as from Indonesia were also important terrestrial sources of aerosol ions according to air mass backward trajectories analysis. Based on the distribution patterns of aerosol ions, the studied area was divided into Southeast China coastal sea area and Western Pacific open sea area, and the dry deposition fluxes of DIN for these two areas were 6166 μg m−2 day−1 and 574 μg m−2 day−1, which could support 5.6–19.4% and ~13.8% of the new production in the East China Sea and the Western Pacific, respectively. Therefore, atmospheric aerosols as an important medium for transporting nutrients to the study area should attract much attention.