Mercury Export Flux in the Arctic Ocean Estimated from 234Th/238U Disequilibria

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High mercury (Hg) levels have been observed for arctic biota, despite limited local sources of anthropogenic Hg in the Arctic. Scavenging of Hg exerts an important control on the residence time of Hg in surface waters. The downward Hg export flux and Hg burial rates in bottom sediments are not well-constrained as a result of the lack of particulate Hg (Hgp) observations in the Arctic Ocean. Here, we estimated downward Hg export flux based on Hg concentrations in suspended particulate matter (SPM) and using the radionuclide pair 234Th/238U, coupled to Hgp/234Th ratios in particles. Using new observations made during the German GEOTRACES TransArcII (GN04) and the U.S. Arctic GEOTRACES (GN01) cruises in August–October 2015, we estimated the Hgp export flux in the central Arctic Ocean and the outer shelf. We find that 81 ± 58 Mg year–1 Hgp is exported from the upper 100 m, of which 16 ± 10 Mg year–1 is ultimately buried in marine sediments. An extrapolation to the entire Arctic Ocean, including the inner shelf, results in 156 Mg year–1Hgp export from the surface ocean and 28 Mg year–1 Hg burial rate. Our study shows that the Hgp export flux could be higher than previously thought, and this should be taken into consideration for future arctic Hg budget estimations.

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DOI 10.1021/acsearthspacechem.0c00055

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Tesán Onrubia, J. A. , Petrova, M. V. , Puigcorbé, V. , Black, E. E. , Valk, O. , Dufour, A. , Hamelin, B. , Buesseler, K. O. , Masqué, P. , Le Moigne, F. c. A. C. , Sonke, J. E. , Rutgers v. d. Loeff, M. and Heimbürger-Boavida, L. E. (2020): Mercury Export Flux in the Arctic Ocean Estimated from 234Th/238U Disequilibria , ACS Earth and Space Chemistry, 4 (5), pp. 795-801 . doi: 10.1021/acsearthspacechem.0c00055

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