Meltwater Percolation's Impact on Firn Densification

The impact of meltwater on the compaction of snow and firn is becoming increasingly important as surface melt increases across the Greenland Ice Sheet. However, our understanding of the effect meltwater infiltration has on firn densification is limited, complicating ice sheet mass estimates and sea level rise predictions. We hypothesize that meltwater infiltration alters firn densification regimes to the point where models developed for the dry snow zone are ineffective. This study evaluates the Herron and Langway (H&L) firn densification model by comparing model outputs to in situ measurements from multiple sites on the Greenland Ice Sheet, with a focus on the dry snow zone (little to no melt) and the percolation zone (consistent melt). Percolation zone data were analyzed with and without ice content to assess meltwater’s impact on densification. Characteristics of infiltration-based ice and its influence on the firn column were investigated. We recalculated the average density of infiltration-based ice to be 818 ± 110 based on 401 measurements, updating the previous calculation of 843 ± 46 (Harper et al., 2012). A linear correlation was found between ice content and cumulative water equivalent, indicating that cores with more ice content have greater bulk density. The Herron and Langway model performed better in the dry snow zone than in the percolation zone. At low-ice sites, combining data from multiple cores improved model performance, whereas at high-ice sites, analyzing only the firn fraction produced better results. Increased variability of density at high-ice sites suggests that meltwater infiltration introduces densification complexities beyond increased bulk density. These findings highlight the need for densification models that account for meltwater processes to improve volume-based estimates of Greenland’s contribution to sea level rise.