Bioactive Trace Elements' Composition and Their Fractional Solubility in Aerosols from the Arabian Sea during the Southwest Monsoon

Abstract

Atmospheric dust deposition supplies a significant amount of macro- and micronutrients to surface ocean water, thus playing a vital role in modulating phytoplankton growth.In this context, we measured soluble and total bioactive trace elements (TEs; Fe, Mn, and Cu) along with eolian dust concentration in aerosol samples collected over a wide area of the Arabian Sea during the southwest monsoon (SWM) month of two consecutive years (2017 and 2018).Our objective in this study is to assess the spatial variability of TEs and quantify their fluxes over the Arabian Sea.Relatively higher mineral dust concentrations were observed during the campaign period compared to earlier studies over the Arabian Sea.A large spatial variability in total Fe (91-2830 ng m-3) and soluble Fe (0.3-32.7 ng m-3) concentrations was observed in contrast to Mn and Cu.However, the operational fractional solubility (defined as the fraction of soluble metal leached using ultrapure deionized water out of the total metal) is relatively low (less than 3.6%) for Fe as compared to Mn (range: 6-87%) and Cu (4-79%).Higher enrichment factors were observed for Mn (range: 1-37) and Cu (range: 6-96), particularly in the northern sector, suggesting the partial contribution of TEs from the anthropogenic emissions that is further corroborated by air-mass back trajectory analyses.An inverse hyperbolic relationship between fractional solubility and total metal concentration is observed for Fe (similar to previous observations); however, no such association is found in case of Mn and Cu.The dry deposition fluxes of Fe, Mn, and Cu to surface water of the Arabian Sea were estimated as 757, 38.8, and 1.4 �g m-2 day-1, respectively.These fluxes are on the higher side compared to those reported from other oceanic regions of the globe.