Seasonal Variability in Marine Atmospheric Mercury Isotope Signatures and Environmental Drivers

Atmospheric deposition is the dominant source of mercury
(Hg) to
the ocean, shaping its transport, transformation, and potential exposure
to global populations. Mercury isotopes offer a powerful tool for
evaluating these processes; however, the isotopic composition of atmospheric
Hg over the ocean remains poorly understood. This study applies a
three-dimensional isotopic model to investigate the mass-independent
fractionation (MIF, represented by Δ199Hg and Δ200Hg) signatures in atmospheric Hg within the marine boundary
layer. The model reveals marked spatial and seasonal variations in
Δ199Hg and Δ200Hg of oxidized Hg
species. These variations are driven by sea salt aerosol debromination,
influenced by environmental factors such as solar radiation, sea surface
temperature, and wind speed, which modulate Hg redox chemistry and
deposition processes. Simulations indicate that seasonal changes in
atmospheric MIF signatures substantially influence the isotopic composition
of Hg deposited to the ocean, particularly through dry and wet deposition
of oxidized Hg species. These findings underscore the importance of
accounting for spatial and temporal variability in atmospheric end-members
when tracing marine Hg sources and interpreting sedimentary Hg isotope
records under a changing climate.