Seasonal Variability in Marine Atmospheric Mercury Isotope Signatures and Environmental Drivers

Area of Science:

• Environmental Chemistry
• Atmospheric Science
• Oceanography

Background:

• Atmospheric deposition is the primary source of mercury (Hg) to marine environments.
• Understanding the isotopic composition of atmospheric Hg over oceans is crucial for tracing Hg sources and transformations.
• Mercury isotopes provide insights into Hg transport, transformation, and exposure pathways.

Purpose of the Study:

• To investigate the mass-independent fractionation (MIF) signatures (Δ¹⁹⁹Hg and Δ²⁰⁰Hg) in atmospheric Hg within the marine boundary layer.
• To understand the drivers of spatial and seasonal variations in atmospheric Hg isotopes over the ocean.
• To assess the influence of atmospheric Hg isotope signatures on marine Hg deposition.

Main Methods:

• Application of a three-dimensional isotopic model for atmospheric Hg.
• Simulation of Hg redox chemistry and deposition processes.
• Analysis of environmental factors influencing Hg isotopic fractionation, including solar radiation, sea surface temperature, and wind speed.

Main Results:

• The model identified significant spatial and seasonal variations in Δ¹⁹⁹Hg and Δ²⁰⁰Hg of oxidized Hg species in the marine boundary layer.
• Sea salt aerosol debromination was identified as a key process driving these isotopic variations.
• Environmental factors modulate Hg redox chemistry and deposition, influencing isotopic signatures.

Conclusions:

• Seasonal variations in atmospheric MIF signatures significantly impact the isotopic composition of Hg deposited to the ocean.
• Dry and wet deposition of oxidized Hg species are key pathways for this influence.
• Accounting for spatio-temporal variability in atmospheric Hg end-members is essential for marine Hg source tracing and interpreting sedimentary records, especially under climate change.