Airborne geophysical investigations of conditions at the bed of fast-flowing outlet glaciers of large Canadian Arctic ice caps

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Recent work has shown that the single largest unknown in assessing the contribution of mountain glaciers and ice caps tocontemporary global sea-level rise is the rate of mass loss by iceberg calving from large Arctic ice caps (Radic and Hock,2011, Nature Geoscience). The largest ice caps in the Arctic, and indeed the largest ice masses outside the Antarctic andGreenland ice sheets, are those of the Canadian Arctic islands. Importantly, new findings indicate that, for 2004-2009, asharp increase in the rate of mass loss also makes the Canadian Arctic Archipelago the single largest contributor to globalsea-level rise outside Greenland and Antarctica (Gardner et al., 2011, Nature). Each of these large Canadian ice caps isdivided into a series of drainage basins that flow into fjords via narrow, heavily crevassed fast-flowing outlet glaciers whichdissect the islands' fringing mountains. A major question for scientists and policymakers is, therefore, how these ice capswill continue to react to the temperature rises that are predicted for the 21st century, noting that Atmospheric GeneralCirculation Models predict that temperature rise will be significantly greater in the Arctic than at lower latitudes. Numericalmodelling of large ice masses is constrained, however, by a lack of knowledge of the geometry and nature of the bed ofthese outlet glaciers. We will acquire geophysical data from ice-cap outlet glaciers draining the large ice caps on Ellesmereand Devon islands in the Canadian Arctic using an airborne ice-penetrating radar, laser altimeter, gravimeter,magnetometer and GPS instruments. We will focus on three key areas of each drainage basin: the heavily crevassed fastflowingoutlet glaciers themselves, an upper transition zone between the ice-cap interior and the narrow outlet glaciers; andthe grounding zone marking the transition to floating ice tongues at the head of some Canadian High-Arctic fjords. Our scientific objectives are: (a) to determine ice-surface and subglacial-bed elevation; (b) to characterize the substrate, inparticular whether it is bedrock or deformable sediment; (c) to establish the distribution of subglacial melting; (d) to revealbasal character changes at the transition zones between inland ice, outlet glaciers and the grounding zone; (e) to providenew estimates of outlet glacier calving fluxes and their variability on up to decadal timescales. This information, integratedwith satellite datasets on outlet-glacier surface motion and our earlier observations of the regional-scale geometry of theseice caps, will provide fundamental boundary conditions for the numerical modelling of these ice caps and, thus, how theymay respond to atmospheric and ocean warming over the coming decades, with implications for sea-level rise.