EFFECTS OF HETEROGENEITY IN SUBSURFACE PROPERTIES ON FUTURE THINNING OF PETERMANN GLACIER, N. GREENLAND

Model projections of future glacier mass change are sensitive to the physical properties of ice and rock that govern the glacial stress balance. One property of particular interest is the ice fluidity. Without a way to uniquely infer ice fluidity and bed friction simultaneously, models often assume that fluidity varies only with temperature, and use this value to invert for basal friction during model spin-up. But remote sensing studies of Petermann Glacier, a marine-terminating outlet glacier in Northwest Greenland, have found widespread radar reflection anomalies in the deep ice that may indicate variability that is not temperature controlled. The origin and composition of these anomalies have been widely debated, but modern radar data show that the basal ice at Petermann Glacier and the top surfaces of many of these anomalies are debris rich ice, rather than pure, meteoric ice, with the most extreme examples of debris more than 1000 m above the bed. In this work, we investigate how the spatial pattern of debris rich ice may affect the response of Petermann Glacier to climate forcing. Using Icepack, a numerical glacial flow model, this study reproduces the dynamics of Petermann Glacier with and without the observed material anomalies present. We show the effects of heterogeneity in the fluidity field on the spatial pattern of interior thinning at Petermann. This output can be compared against future observations of surface height change and acceleration to test our hypothesis of mechanical differences associated with observed englacial structures. This work highlights the importance of ice properties beyond just temperature, and the power of geophysical data to inform ice-flow model initialization and improve mass change projections.