The Greenland Ice Sheet in Three Dimensions

Tuesday, 16 December 2014: 4:30 PM
Joseph A MacGregor1, Mark A Fahnestock2, Ginny A Catania3, John Drysdale Paden4, Sivaprasad Gogineni4, Mathieu Morlighem5, William T Colgan6, Jilu Li4, David E Stillman7, Robert E Grimm8, Gary D Clow9, Stewart Keith Young3, Alexandria N. Mabrey3, Susan C Rybarski3, Benjamin M Wagman10 and Kelly Rodriguez4, (1)Univ of TX-Inst for Geophysics, Austin, TX, United States, (2)University of Alaska Fairbanks, Fairbanks, AK, United States, (3)University of Texas at Austin, Austin, TX, United States, (4)University of Kansas, Lawrence, KS, United States, (5)University of California Irvine, Irvine, CA, United States, (6)Geological Survey of Denmark and Greenland, Copenhagen, Denmark, (7)Southwest Research Institute Boulder, Boulder, CO, United States, (8)Southwest Research Institute Boulder, Broomfield, CO, United States, (9)INSTAAR, Boulder, CO, United States, (10)The Univ. of Texas at Austin, Austin, TX, United States
We have produced a dated radiostratigraphy for the whole of the Greenland Ice Sheet (GrIS) from two decades of airborne radar-sounding surveys performed by The University of Kansas. This radiostratigraphy reveals a wealth of new information regarding this ice sheet’s three-dimensional structure and history. South of Jakobshavn Isbræ, most of the ice sheet is Holocene-aged. Eemian ice is mostly confined to central northern Greenland. Disrupted radiostratigraphy is often located near the onset of the largest outlet glaciers, suggesting a strong coupling between the initiation of faster ice flow and anomalous basal processes in the ice-sheet interior. Ice-flow modeling constrained by this radiostratigraphy reveals that the Holocene-averaged pattern of surface accumulation is similar to the modern pattern, but that Holocene surface-accumulation rates were substantially higher than present rates in the interior. The pattern of predicted basal melt is strongly modulated by surface accumulation, further suggesting that geothermal flux beneath the GrIS is low except in the vicinity of the Northeast Greenland Ice Stream. This observation also raises the possibility that the position of the GrIS’s central ice divide is coupled to local basal conditions, including spatially varying subglacial geology and geothermal flux. The Holocene-averaged flow of the GrIS was significantly faster than at present, implying that the ice-sheet interior is presently dynamically thickening, likely due to the viscosity contrast between Holocene and Last Glacial Period ice. Englacial dielectric attenuation, inferred from the echo intensity of mapped reflections, is related to borehole-measured temperature and constrains depth-averaged englacial temperature across the GrIS. This ice-sheet-wide radiostratigraphy and its related inferences are new and powerful constraints on the dynamics of the GrIS, and they should be used to evaluate and improve the next generation of ice-sheet models.