Sea ice (including overlying snow) is a dynamic interface between the atmosphere and the ocean, and is crucial for the mercury (Hg) cycle in polar oceans. However, large-scale and process-based numerical models for Hg in the sea ice environment remain scarce, impeding our comprehension of regional and global Hg cycling. To bridge this gap, we developed a comprehensive simulation of the Hg cycling across the ocean-sea ice-atmosphere interface based on available polar cryospheric Hg data. Our findings revealed that the seasonal patterns of average snow content of total Hg (THg) are predominantly governed by the thermodynamic variation of snow and deposition, culminating in a springtime peak (6.3 and 5.2 ng/L for Arctic and Antarctic snow, respectively) and a nadir during ice formation (1.2 and 0.5 ng/L, respectively). Conversely, average THg concentrations in Arctic and Antarctic sea ice peak in summer (0.23 ng/L) and spring (0.28 ng/L), respectively, due to the snow Hg transmission. This hemispheric discrepancy arises from heavy snowfall in the Southern Ocean, causing frequent snow flooding, while the Arctic experiences less of this process. Overall, first-year sea ice acts as a buffer that receives atmospheric Hg during the ice growth season, and subsequently collapses in the succeeding summer, leading to a cascading of retained Hg to the underlying ocean. This implies a potential impact on the seasonal variation of polar atmospheric and seawater Hg concentrations. Our model contributes to assess climate change effects on polar Hg cycles and aids in evaluating the Minamata Convention's effectiveness for Arctic populations.

Mercury, Sea Ice, Snow, polar oceans, MITgcm