Atmospheric distribution, source apportionment, and sea-air fluxes of gaseous elemental mercury over the Barents, Kara, Laptev and East Siberian Seas.

Abstract

Mercury is a persistent global pollutant, and the Arctic remains a region of special concern due to rapid warming and complex mercury cycling. This study presents continuous measurements of atmospheric gaseous elemental mercury (GEM) during a cruise from the Kara Sea to the East Siberian Sea (September-October 2024). GEM concentrations ranged from 0.73 to 1.32 ng m-3 (mean 0.97 ng m-3), below the Northern Hemisphere background, but consistent with the global trend of decreasing atmospheric GEM concentrations. The Kara Sea exhibited a slightly elevated mean GEM concentration (1.00 ng m-3) compared to the other seas. Backward trajectory and concentration-weighted trajectory analyses identified three major potential source regions: the central Arctic Ocean (suggesting re-emission from ice-free waters); the West Siberian Plain (industrial cities including Surgut and Novosibirsk); and northern Europe and the Baltic region (long-range transport). Preliminary sea-air GEM evasion flux measurements over active methane seeps reached 3.5 ng m-2 h-1, substantially above regional background. Control experiments showed that ship thruster operation artificially enhanced measured fluxes by a factor of 1.3-1.7. While these results suggest that methane seep areas may warrant further investigation as potential sites of enhanced GEM evasion, the present measurements should be considered exploratory. The possibility of thruster-induced artifacts and the absence of direct geochemical characterization at the seep sites preclude definitive attribution. The findings are consistent with the Arctic Ocean playing a role as an active secondary mercury source and underscore the need for flux studies accounting for hydrodynamic artifacts.