Modelling argon dynamics in first-year sea ice

Abstract: Focusing on physical processes, we aim at constraining the
dynamics of argon (Ar), a biogeochemically inert gas, within first year
sea ice, using observation data and a one-dimensional halo-thermodynamic
sea ice model, including parameterization of gas physics. The
incorporation and transport of dissolved Ar within sea ice and its
rejection via gas-enriched brine drainage to the ocean, are modeled
following fluid transport equations through sea ice. Gas bubbles nucleate
within sea ice when Ar is above saturation and when the total partial
pressure of all three major atmospheric gases (N2, O2 and Ar) is above
the brine hydrostatic pressure. The uplift of gas bubbles due to buoyancy
is allowed when the brine network is connected with a brine volume above
a given threshold. Ice-atmosphere Ar fluxes are formulated as a diffusive
process proportional to the differential partial pressure of Ar between
brine inclusions and the atmosphere. Two simulations corresponding to two
case studies that took place at Point Barrow (Alaska, 2009) and during an
ice-tank experiment (INTERICE IV, Hamburg, Germany, 2009) are presented.
Basal entrapment and vertical transport due to brine motion enable a
qualitatively sound representation of the vertical profile of the total
Ar (i.e. the Ar dissolved in brine inclusions and contained in gas
bubbles; TAr). Sensitivity analyses suggest that gas bubble nucleation
and rise are of most importance to describe gas dynamics within sea ice.
Ice-atmosphere Ar fluxes and the associated parameters do not drastically
change the simulated TAr. Ar dynamics are dominated by uptake, transport
by brine dynamics and bubble nucleation in winter and early spring; and
by an intense and rapid release of gas bubbles to the atmosphere in
spring. Important physical processes driving gas dynamics in sea ice are
identified, pointing to the need for further field and experimental
studies.