Permeability of H2 in ice Ih

Reconstructions of paleoatmospheric H2 using polar firn air and ice cores would lead to a better understanding of the H2 biogeochemical cycle and how it is influenced by climate change and human activity. H2 is a small, highly diffusive molecule, and its mobility in the ice matrix must be accounted for when intepreting polar firn air and ice core measurements. Previous work on the mobility of H2 in ice has focused on warm (272-273 K), high pressure systems that are not directly comparable to conditions in polar ice sheets. In this study, the permeability, diffusivity, and solubility of H2 are determined experimentally in ice Ih at temperatures relevant to polar ice sheets (199-253 K).

The data are reported as the optimized diffusivity (m2 s-1), solubility (mol m-3 Pa-1), and permeability (mol m-1 s-1 Pa-1) for each of 17 experiments using two different samples of ice. Optimized values are reported with their ±1σ uncertainties. The temperature (K) for each experiment is also reported. 

Methods
This study was carried out using a “block degassing” method. This involves exposing a block of ice to a pure H2 atmosphere for several hours, then replacing the H2 with air and

monitoring the H2 outgassing as a function of time. The measurements were analyzed using 3-dimensional finite difference diffusion model of the block of ice. The model diffusivity and solubility were varied across a wide range of possible values. Reported diffusivities and solubilities are the values which minimized the sum of the squared residuals between modeled and measured rates of H2 outgassing. For more detailed methods, see Patterson & Saltzman (2021).