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 (Hg) or elemental (Hg) form. Understanding the relative contributions of atmospheric Hg and Hg to the ocean is essential for accurately assessing global mercury budgets. Earlier even mercury isotope (ΔHg) analyses suggested equivalent Hg/Hg contributions but neglected spatial variations in atmospheric ΔHg signatures. Here, we developed a 3D atmospheric model incorporating mercury chemistry and isotopic fractionation to address this limitation. Our simulations reveal distinct atmospheric ΔHg patterns and quantify their deposition to the ocean. Constrained by observed ΔHg data in the ocean, we propose an updated deposition ratio of atmospheric Hg to Hg 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.