Simulation of gas diffusion through inhomogeneous layered snow and firn

Diffusion of gases through snow and firn is important for air-snow transfer in temperate regions and decoding ice core climate records from the polar regions. The diffusion process depends on a number of factors, including temperature and chemical concentration gradients, layering and pore structure of the snow and firn, and fractionation of gases. Assessing the potential impact of layering on of gases through the firn column over time is crucial for understanding the natural archive of past atmospheric composition. Existing 1-D firn air models include gravitational settling and thermal diffusion in order to explain seasonal anomalies found in firn-air measurements but have not considered the possibility of inhomogeneous firn structure and layering effects in time-varying simulations. This work presents development, testing, and use of a multidimensional numerical diffusion model for investigating impacts of spatial heterogeneity of firn layering over time, in addition to thermal and gravitational effects on gas diffusion in firn. The model is verified using existing data. Results of numerical experiments are presented that show impacts of varying the spatial structure of firn on the magnitude of the impact on gas profiles in firn. Comparison of numerical results with published firn air field studies will be discussed.