A Unique Opportunity for In-Situ Measurement of Seasonally-Varying Firn Densification at Summit, Greenland

This is a collaborative proposal by Principal Investigators at the University of Washington and the Desert Research Institute. They will make detailed measurements of the temporal and spatial variations of firn compaction to advance knowledge and understanding of ice deformation and across different fields, including remote sensing, snow morphology, and paleoclimatology. They will make detailed measurements through two winter and three summer seasons at Summit Greenland using the concept of Borehole Optical Stratigraphy, which will use a borehole camera to record details of the wall. These details can be tracked over time to determine vertical motion and strain, which in the shallow depth is dominated by firn compaction. Quantitative understanding of firn compaction is important for remote-sensing mass-balance studies, which seek to measure and interpret the changing height of the ice sheet; the surface can rise due to snow accumulation, and fall due to ice flow and increased densification rates. Quantitative knowledge of all three processes is essential. Evidence suggests that the rate of densification undergoes a seasonal cycle, related to the seasonal cycle of temperature. When interpreting ice core trapped-gas data for paleoclimate, it is important to know at what point the gas was actually trapped in the ice. The pores do not close off until deep in the firn, leading to a difference between the age of the ice and the age of the trapped gas. If summer high temperatures have more impact on compaction than mean annual temperatures, the gas-age/ice-age offset might be incorrectly calculated. Greater understanding of firn densification physics will help the interpretation of these records.

This data covers accumulation rates occurring between 1980-2008, and the data were collected between 2004-2008.