Layering Effects on Gas Diffusivity of Firn

The gas diffusivity of layered snow and firn is important to air snow transfer, ice core interpretation, and a host of other applications. It directly depends on the size, connectivity and tortuosity of the porous space that lies between the snow grains. In firn, the gas diffusivity may vary significantly even in adjacent layers, due in part to differences in weather conditions during the original depositional events, and also due to differences in metamorphic and compressional processes that affect the evolution of the porous space. In order to understand the total effective diffusivity profile of layered firn, we test the hypothesis that the firn may be treated as a composite porous media using resistance theory, where the resistance to gaseous transfer is inversely related to the different layer diffusivities arranged in series. The diffusivity of multiple homogeneous single firn layers, and also combinations of the individual layers together, have been measured in a cold room lab on samples of near-surface firn taken from Summit Station, Greenland in July 2016, and from deeper firn samples from other sites. Results aim to help inform differences between model and measured diffusivity profiles of firn.