Atmosphere–ocean exchange of heavy metals and polycyclic aromatic hydrocarbons in the Russian Arctic Ocean

Abstract

Heavy metals and polycyclic aromatic hydrocarbons (PAHs) can greatly influence biotic activities and organic sources in the ocean. However, fluxes of these compounds as well as their fate, transport, and net input to the Arctic Ocean have not been thoroughly assessed. During April–November of the 2016 “Russian High-Latitude Expedition”, 51 air (gases, aerosols, and wet deposition) and water samples were collected from the Russian Arctic within the Barents Sea, the Kara Sea, the Laptev Sea, and the East Siberian Sea. Here, we report on the Russian Arctic assessment of the occurrence of 35 PAHs and 9 metals (Pb, Cd, Cu, Co, Zn, Fe, Mn, Ni, and Hg) in dry and wet deposition as well as the atmosphere–ocean fluxes of 35 PAHs and Hg0. We observed that Hg was mainly in the gas phase and that Pb was most abundant in the gas phase compared with the aerosol and dissolved water phases. Mn, Fe, Pb, and Zn showed higher levels than the other metals in the three phases. The concentrations of PAHs in aerosols and the dissolved water phase were approximately 1 order of magnitude higher than those in the gas phase. The abundances of higher molecular weight PAHs were highest in the aerosols. Higher levels of both heavy metals and PAHs were observed in the Barents Sea, the Kara Sea, and the East Siberian Sea, which were close to areas with urban and industrial sites. Diagnostic ratios of phenanthrene/anthracene to fluoranthene/pyrene showed a pyrogenic source for the aerosols and gases, whereas the patterns for the dissolved water phase were indicative of both petrogenic and pyrogenic sources; pyrogenic sources were most prevalent in the Kara Sea and the Laptev Sea. These differences between air and seawater reflect the different sources of PAHs through atmospheric transport, which included anthropogenic sources for gases and aerosols and mixtures of anthropogenic and biogenic sources along the continent in the Russian Arctic. The average dry deposition of ∑9 metals and ∑35 PAHs was 1749 and 1108 ng m−2 d−1, respectively. The average wet deposition of ∑9 metals and ∑35 PAHs was 33.29 and 221.31 µg m−2 d−1, respectively. For the atmosphere–sea exchange, the monthly atmospheric input of ∑35 PAHs was estimated at 1040 t. The monthly atmospheric Hg input was approximately 530 t. These additional inputs of hazardous compounds may be disturbing the biochemical cycles in the Arctic Ocean.