Diffusivity and Solubility of H2 in Ice Ih: Implications for the Behavior of H2 in Polar Ice

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. 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 experimental data are used in conjunction with simplified diffusion models to assess the implications for: (a) Diffusion of H2 from pressurized closed bubbles to open pores in polar firn, (b) diffusive smoothing of H2 gradients in the ice sheet, and (c) post‐coring diffusive losses of H2 from ice core samples. The results indicate that diffusive equilibrium between open and closed pores is likely achieved in the firn lock‐in zone. Diffusive smoothing of atmospheric variations is significant and should be accounted for in atmospheric reconstructions on millennial time scales. Diffusive losses from a bubbly ice sample are sufficiently slow that samples may be meaningfully analyzed for H2 after storage on the order of a year. These results suggest that the mobility of H2 in ice should not preclude the reconstruction of paleoatmospheric H2 from firn air and ice cores. Plain Language Summary Documenting the variations in atmospheric H2 is useful for understanding how H2 cycles through the Earth system. The polar ice sheets contain an archive of ancient air that could be used to reconstruct the history of atmospheric H2. Because of its small size, H2 is more mobile in ice than other trace gases such as methane or carbon dioxide. In this work, we experimentally determine the rate of permeation of H2 in ice and use the results to assess how the mobility of H2 in polar ice affects the incorporation of atmospheric H2 into the ice archive and the interpretation of ice core measurements. Key Points The diffusivity and solubility of H2 in ice Ih were measured at temperatures relevant to polar ice sheets (199–253 K) The implications of these measurements for the interpretation of firn air and ice core measurements of H2 are assessed and discussed