Work

Atmospherically deposited elemental mercury drives evasion of mercury from the ocean and freshwaters

Year: 2025

Type: article

Abstract: ABSTRACT The sources and mechanisms driving fluxes of dissolved gaseous mercury (DGM) in aquatic ecosystems represent a critical yet poorly constrained component of the global mercury (Hg) cycle. Current models assume that DGM is primarily formed through the reduction of HgII in water, largely supplied by atmospheric HgII deposition. Here we quantify the Δ200Hg signatures of DGM across marine (median: 0.02‰) and freshwater (0.02‰) ecosystems, intermediate between water dissolved HgII and atmospheric Hg0. This indicates that DGM in natural waters is not derived solely from HgII reduction as previous assumed but also from atmospheric input of Hg0 during air-sea gas exchange. A Δ200Hg-based mixing model reveals that ∼40% and 54% of DGM in seawater and freshwater, respectively, is derived directly from atmospheric Hg0 input. Combining these findings with an existing oceanic Hg budget, we show that re-emission of previously deposited atmospheric Hg0 accounts for ∼70% of gross oceanic Hg0 evasion. Consequently, we demonstrate that existing models have systematically underestimated gross atmospheric Hg0 deposition while overestimating net oceanic Hg0 emissions.

Source: National Science Review

DOI: 10.1093/nsr/nwaf590