The Coupled Dynamics of the Ice-Lithosphere System: Sediments and Hydrology

The Earth's ice sheets, oceans and lithosphere are inherently a coupled system. Integrated analysis of geophysics enables us to decipher the ice sheet processes and their lithospheric drivers. The decades of experience since the major 1970's NSF/SPRI/TUD Antarctic mapping program in the LC-130 have highlighted repeatedly the power of the integrated approach. The geology of the ice sheet bed influences the friction, hydrological routing and geothermal heat flux at the base of the ice and these parameters provide essential boundary conditions for glaciological modeling. With knowledge of the bed topography from radar surveys, gravity and magnetics can be used to constrain the lithology of the underlying bedrock. The identification of sedimentary basins along the onset regions of the fast flowing Antarctic Ice Streams and beneath the Jakobshaven outlet glacier in Greenland highlight the role sediments play in ice dynamics. Airborne gravity, magnetics, ice penetrating radar and laser have facilitated the identification of these basins. Surface seismic experiments have confirmed the presence of sedimentary basin along these fast flowing regions. Subglacial hydrology is also closely linked to the underlying lithosphere. One strong control on the source of basal water in the interior will be the geothermal heat flux. Regions of elevated heat flux have been linked to basal melt both in Greenland and West Antarctica. The flowpaths are strongly controlled by the subglacial topography as illustrated in the water networks in the Gamburtsev Mountains. Similarly the distribution of basal freeze-on is linked to either isostatically or tectonically controlled topography. Freeze-on removes water from the water networks, producing new basal ice. Beneath Dome A, East Antarctica, the tectonically formed mountains ridges serve as the sites of basal freeze-on. In Greenland, basal freeze-on is distributed along isostatically back tilted bed topography. In both cases the ice sheet drives the water up the topography until basal freeze-on occurs. From melt to freeze-on, the properties of the underlying lithosphere are key controls to the subglacial hydrologic cycle. A number of key challenges remain for understanding the coupled ice-lithosphere system including integrated radar and magnetics analysis to constrain basal heat flow and radar.