Abstract
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(II)) or elemental (Hg(0)) form. Understanding the relative contributions of atmospheric Hg(II) and Hg(0) to the ocean is essential for accurately assessing global mercury budgets. Earlier even mercury isotope (Δ(200)Hg) analyses suggested equivalent Hg(II)/Hg(0) contributions but neglected spatial variations in atmospheric Δ(200)Hg signatures. Here, we developed a 3D atmospheric model incorporating mercury chemistry and isotopic fractionation to address this limitation. Our simulations reveal distinct atmospheric Δ(200)Hg patterns and quantify their deposition to the ocean. Constrained by observed Δ(200)Hg data in the ocean, we propose an updated deposition ratio of atmospheric Hg(II) to Hg(0) 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.