The FirnCover Project – Real-time Monitoring of Greenland’s Firn Compaction in a Changing Climate

Abstract:

An unavoidable source of uncertainty in altimetry-based mass balance assessments of ice sheets is the conversion from volume change into mass change. A primary component of this volume change is firn compaction, or the rate at which snow compresses into glacial ice. Firn densification models simulate this process, but model outputs vary widely, and Greenland’s rapidly changing climate challenges many of the steady-state assumptions held in most of these models. Contemporary measurements of firn compaction rates are extremely sparse across Greenland in both time and space and are nonexistent in many large regions. Here we present initial results from Greenland’s Firn Compaction Verification and Reconnaissance (FirnCover) Project, a network of real-time strain gauges at over thirty boreholes that continuously monitor compaction rates at eight locations in Greenland’s accumulation zones, ranging from areas of heavy percolation to dry snow. Initial results from these stations indicate a strong seasonality in compaction, especially in regions where heavy melt and refreezing release latent heat into the firn column, a process that will intensify as melt increases across Greenland. We also discuss the substantial challenge of measuring firn compaction in regions of heterogeneous percolation, and other challenges encountered when validating firn models and monitoring contemporary mass changes of the Greenland ice sheet.