Effects of Climate Changes on Firn Properties and Gas Transport in Firn

Abstract:

Knowledge of the physics of firn-density evolution and gas transport in firn has several important applications in glaciology, including (1) correcting for firn air content when estimating ice-sheet mass-balance changes from satellite altimetry and (2) determining the ice-age/gas-age difference for paleoclimate interpretations of ice-core records. The firn-physics group at the University of Washington is developing modular and open-source community models describing evolution of firn density, temperature, diffusivity, and other structural properties affecting gas transport. A novel aspect is that the gas model can be coupled to the density model, allowing bubble-close-off depth, lock-in depth, depth-integrated porosity, and effective diffusivity to evolve in the gas-transport model. This feature allows us to investigate changes in firn physical properties and the evolving impacts of those changes on gas diffusion, thermal and gravitational fractionation, and the mixing ratio of gasses in bubbles trapped in firn during climate change events. Here, we use ice-core derived and synthetic climate data to show the scope of these impacts for gradual and abrupt climate changes.