Spatial Distribution of Firn Close-Off Depth, Delta Age, and Depth-Integrated Porosity in the Greenland Ice Sheet

Abstract:

Ice cores in dry snow zones can provide a unique record of Earth’s past climate history and atmospheric composition for up to 800,000 years. However, in order to interpret ice-core data accurately, scientists must understand the entire firnification process. In addition, satellite-based measurements of ice-sheet elevation changes must be accompanied by estimates of the air content, or depth-integrated porosity of the firn, in order to infer rates of mass gain or loss. The firn physics group at University of Washington is developing an open source Community Firn Model to simulate firn densification and gas-transport processes. We have calculated the spatial distribution of depth and age of the firn at pore close-off, as well as the depth-integrated porosity, using gridded mean-annual temperature over Greenland over a 173 year period together with gridded snow accumulation-rate data (Box). Our results can contribute to a better understanding of past climate changes, and knowing the close-off depth and age will provide guidelines for future core sites for investigation of pre-industrial levels of trace gases. Knowing the depth-integrated porosity will allow more accurate mass-loss estimates, and to future sea-level predictions.