Concentrations, Solubility, and Deposition Fluxes of Aerosol Trace Elements in the Central Arctic During Winter and Spring: Results From the MOSAiC Expedition

Abstract Atmospheric deposition is an important pathway for delivering micronutrient and pollutant trace elements (TEs) to the surface ocean. In the central Arctic, much of this supply takes place onto sea ice during winter, before eventual delivery to the ocean during summertime melt. However, the seasonality of aerosol TE loading, solubility, and deposition flux are poorly studied over the Arctic Ocean, due to the difficulties of wintertime sampling. As part of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, aerosols collected during winter and spring (December–May) were analyzed for soluble, labile, and total TE concentrations. Despite low dust loading, mineral aerosol accounted for most of the variation in total Fe, Al, Ti, V, Mn, and Th concentrations. In contrast, soluble TE concentrations were more closely linked to non‐sea‐salt sulfate, and Fe solubility was significantly higher during Arctic winter (median = 6.5%) than spring (1.9%), suggesting an influence from Arctic haze. Beryllium‐7 data were used to calculate an average bulk deposition velocity of 613 ± 153 m d −1 over most of the study period, which was applied to calculate seasonal deposition fluxes of total, labile, and soluble TEs to the central Arctic. Total TE fluxes (173 ± 145 nmol m −2 d −1 for Fe) agreed within a factor of two or three with earlier summertime estimates, with generally higher wintertime concentrations offset by a lower deposition velocity. Cumulative seasonal deposition of total, labile, and soluble Fe to the central Arctic Ocean was calculated at 25 ± 21, 5 ± 3, and 2 ± 2 μmol m −2 , respectively.