Antarctic firn compaction rates from repeat-track airborne radar data: II. Firn model evaluation

The thickness and density of the Antarctic firn layer vary considerably in time and space, thereby contributing to ice-sheet volume and mass changes. Distinguishing between these mass and volume changes is important for ice-sheet mass-balance studies. Evolution of firn layer depth and density is often modeled, because direct measurements are scarce. Here we directly compare modeled firn compaction rates with observed rates obtained from repeat-track airborne radar data over a 2 year interval (2009-11) in West Antarctica. Spatially, the observed compaction rates exhibit significant variability, but when averaged to scales comparable to the model resolution (20-50 km), the measurements and model results qualitatively agree. A colder and drier period preceding the 2009 survey led to lower compaction rates during the 2009-10 interval, when compared to 2010-11, which is partly captured by the firn model. Spatially, higher compaction rates are observed and modeled in warmer regions with higher accumulation.