Assessment of Basal Melt of Petermann Gletscher in Northwestern Greenland

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0135450SteffanThe research is a collaborative effort between the University of Colorado, Boulder, the British Antarctic Survey, Cambridge, and the Jet Propulsion Laboratory. The Office of Polar Programs (OPP) at National Science Foundation and the National Aeronautical and Space Administration (NASA) will support the project. The Greenland Ice Sheet is thinning rapidly along its outlet glaciers and is contributing an estimated 0.13 mm/yr global sea level rise. Signs of its warming have been documented, including rising air temperature in its central part and retreating sea ice in its surrounding ocean. Extensive floating ice tongues in the northwest sector are ice undergoing massive rates of ablation from the surrounding warm ocean waters and are presently in a state of fragile equilibrium, but this ablation rate has never been measured. The Petermann Gletscher is the largest and most influential outlet glacier in northern Greenland, draining an area of 71,580 km2, with a discharge of 12 cubic km of ice per year. Remote sensing results suggest that its ice discharge exceeds that required to maintain the ice sheet interior in a state of mass equilibrium by 63%, and its grounding line is retreating at an anticipated rate at nearly one meter per year. Its floating ice tongue is only a few meters above sea level at the ice front, so it is highly vulnerable to ice thinning. If confirmed by in-situ observations and if this trend continues for several decades, the rate of thinning would be sufficient to threaten the stability and survival of the ice tongue. The Principal Investigators propose to do a detailed analysis of the glacier floating ice tongue in front of Petermann Gletscher that integrates key field observations with remote sensing data. The field program is designed to obtain the in-situ observations to confirm, validate, and calibrate the remote sensing estimates of basal melting, derive reliable estimates of surface melt from an energy balance model, observe changes in ice volume with precision, and understand the contribution of ice dynamics, surface melt and bottom melt to volume changes of floating ice. The experiment is will take place at the most crucial part of the glacier, the grounding line. Bottom melt rates are estimated to reach 25 m/yr near the grounding zone from remote sensing data, and 75% of the ice that crosses melts in contact with warm ocean waters in the first 20% area of floating ice. Basal melting will be measured in-situ over several time intervals using a novel phase-sensitive radar sounding system developed and tested by the British Antarctic Survey. At the surface, the energy budget of the ice will be characterized using a network of automated micrometeorological stations, and the results will be employed to determine how well surface melt can be predicted from an energy balance model and how much it changes with time. Remote sensing data that include strain rates from interferometric synthetic-aperture radar (InSAR), elevation changes from airborne laser altimetry, and ice thickness from airborne ice-radar sounding, will be employed to yield spatial estimates of basal melting to be compared with in-situ data. InSAR and Global Positioning Systems will be used to detect changes in flow rate with time. The results will provide invaluable insights into dynamics and climatic processes of northern Greenland glaciers.