Assessment of aeolian dust concentration, elemental composition, and their wet and dry deposition fluxes over the Northeast Arabian Sea

Abstract

ABSTRACT Atmospheric aerosol over the Arabian Sea is significantly impacted by the long-range transported mineral dust from the surrounding continents. This transported mineral dust is hypothesized and tested during several studies to see the impacts on the surface ocean biogeochemical processes and subsequently to the Carbon cycle. It is, thus important to quantify dust contributions and their fluxes to the Arabian Sea. Here we assess temporal variability of dust concentration, their elemental characteristics as well as quantify their dry and wet deposition fluxes over the North-eastern Arabian Sea. The dust concentrations were found to vary from 59 to 132 µg m−3 which accounts for 50% to 90% of total mass during dusty days. However, its contribution during pre and post dust storms ranges between 6% and 60%. Relatively higher dust dry deposition flux of 28 ± 7 mg m−2 day−1 (range: 20–44) is estimated for dusty days compared to pre and post dusty days (range: 0.4–22 mg m−2 day−1). In contrast to dry deposition fluxes, significantly higher fluxes are estimated from wet deposition, averaging around 240 ± 220 mg m−2 day−1. These values are five times higher than those reported from cruise samples collected over the Arabian Sea. The contribution of dust to aerosol mass is further ascertained using elemental composition, wherein a significant correlation was observed between Fe and Al (r2 = 0.77) for samples collected during the dusty period, highlighting their similar crustal sources. Our estimation of dust flux over this region has implications for the supply of nutrients associated with natural dust to the surface water of the Arabian Sea. Implications: The Arabian Sea, one of the productive oceanic regions among the global oceans, has been identified as a perennial source of atmospheric CO2. This basin is heavily impacted by atmospheric dust deposition/inputs owing to its geographical location being surrounded by arid and semi-arid regions. It has been hypothesized that aeolian dust plays a significant role in modulating surface water biogeochemical processes including primary productivity, in the Arabian Sea. Furthermore, modelling studies have highlighted on the role of dust (containing Fe) in fueling and enhancing primary productivity in the Arabian Sea. However, quantification of dust deposition fluxes (wet and dry) on seasonal time scale is missing in the literature. This paper aims to partially fulfil this research gap by providing a long-term data of wet and dry deposition fluxes over the northeastern Arabian Sea. We have also discussed their seasonal variability and factors affecting this flux. Thus, this study will be valuable contribution to the aeolian research community and have significant implication toward the role of aeolian deposition to the surface water biogeochemical processes in the Arabian Sea.