Atmospheric source of mercury to the ocean constrained by isotopic model

Mercury is a potent neurotoxin that poses significant health risks to humans, primarily through seafood consumption. Atmospheric deposition is the largest source of oceanic mercury, in either oxidized (HgII) or elemental (Hg0) form. Understanding the relative contributions of atmospheric HgII and Hg0 to the ocean is essential for accurately assessing global mercury budgets. Earlier even mercury isotope (Delta 200Hg) analyses suggested equivalent HgII/Hg0 contributions but neglected spatial variations in atmospheric Delta 200Hg signatures. Here, we developed a 3D atmospheric model incorporating mercury chemistry and isotopic fractionation to address this limitation. Our simulations reveal distinct atmospheric Delta 200Hg patterns and quantify their deposition to the ocean. Constrained by observed Delta 200Hg data in the ocean, we propose an updated deposition ratio of atmospheric HgII to Hg0 to the ocean, which may exceed 2:1, higher than the previously reported 1:1. Our findings are crucial for assessing atmospheric mercury dispersal and predicting the recovery of marine ecosystems.