Modeling the Mercury Cycle in the Sea Ice Environment: A Buffer between the Polar Atmosphere and Ocean

Thisstudy presents a comprehensive simulation of Hg cyclingacross the ocean-sea ice-atmosphere interface, whichoffers an insightful framework for understanding the behavior of Hgin the polar cryosphere. The seasonal cycling of mercury (Hg) in thepolar sea ice environment, encompassing both sea ice and the overlyingsnow, is depicted in a graphic. The illustration highlights that thenet atmospheric Hg is primarily absorbed by snow, which in turn becomesan important source of Hg deposition to the underlying sea ice duringwarm seasons. Furthermore, first-year sea ice functions as a bufferfor atmospheric Hg. During the ice growth season, Hg is graduallyincorporated into the ice, only to cascade into the underlying oceanin warm seasons. Seaice (including overlying snow) is a dynamic interface betweenthe atmosphere and the ocean, influencing the mercury (Hg) cyclingin polar oceans. However, a large-scale and process-based model forthe Hg cycle in the sea ice environment is lacking, hampering ourunderstanding of regional Hg budget and critical processes. Here,we develop a comprehensive model for the Hg cycle at the ocean-seaice-atmosphere interface with constraints from observationalpolar cryospheric data. We find that seasonal patterns of averagetotal Hg (THg) in snow are governed by snow thermodynamics and deposition,peaking in springtime (Arctic: 5.9 ng/L; Antarctic: 5.3 ng/L) andminimizing during ice formation (Arctic: 1.0 ng/L, Antarctic: 0.5ng/L). Arctic and Antarctic sea ice exhibited THg concentration peaksin summer (0.25 ng/L) and spring (0.28 ng/L), respectively, governedby different snow Hg transmission pathways. Antarctic snow-ice formationfacilitates Hg transfer to sea ice during spring, while in the Arctic,snow Hg is primarily moved through snowmelt. Overall, first-year seaice acts as a buffer, receiving atmospheric Hg during ice growth andreleasing it to the ocean in summer, influencing polar atmosphericand seawater Hg concentrations. Our model can assess climate changeeffects on polar Hg cycles and evaluate the Minamata Convention'seffectiveness for Arctic populations.

Automated summary

This study provides a comprehensive simulation of mercury (Hg) cycling in the polar cryosphere, offering insights into its behavior across the ocean-sea ice-atmosphere interface. The study highlights the seasonal cycling of Hg in the polar sea ice environment, with snow acting as an important source of Hg deposition to the underlying sea ice. The model developed in this study can evaluate the impact of climate change on polar Hg cycles and the effectiveness of the Minamata Convention for Arctic populations.