| Summary: | Recent studies suggest an active role of sea ice as a source or sink for climatically significant gases such as CO2 and DMS. However, the dynamics of such biogeochemically active gases within sea ice are still not well understood. Modeling can help to understand and upscale the physical and biogeochemical processes that affect gas diffusion, production, consumption and transport within sea ice and through the brine network. Argon (Ar), which is a biogeochemically inert gas, can be used, as a first step, to constrain the physical processes that determine gas dynamics within sea ice. To accomplish this goal, in this study, we aim at constraining the dynamics of Ar within sea ice using observation data and a one-dimensional halo-thermodynamic sea ice model, including gas physics. The incorporation and transport of dissolved Ar within sea ice, as well as its rejection via gas-enriched brine drainage to the ocean, are modeled following fluid transport equations through sea ice. In addition, gas bubbles nucleate within sea ice when Ar concentration is above saturation. The uplift of gas bubbles due to buoyancy is allowed when the brine volume fraction is above a prescribed threshold. Ice-atmosphere Ar fluxes are formulated as a function of wind speed, the differential partial pressure of Ar between sea ice brine and the atmosphere, the sea ice brine aspect ratio and the presence or absence of snow. Two simulations corresponding to two case studies were run, the first one covering the seasonal growth of first-year ice at Point Barrow, Alaska, and the second corresponding to the growth and melt of artificial sea ice in an ice-tank experiment (INTERICE IV). Modeled snow depth and ice thickness, ice temperature and bulk salinity realistically reproduce the observations. Basal entrapment and vertical transport due to brine motion enable a qualitatively sound representation of the vertical profile of Ar. Sensitivity analyses suggest that bubble nucleation should account for more than half of the observed Ar concentrations. ...
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