Subglacial Controls on the Short Term Dynamics at the Margins of the Greenland Ice Sheet: Seismic experiments

Though near balance in the 1970s and 1980s, the Greenland ice sheet has been losing mass at an accelerated rate, currently contributing 0.46mm per year to global sea level rise. The mass loss has been spreading from the southern regions of the ice sheet to the northwest and is currently equally divided between dynamic discharge into the ocean and negative surface balance. The increased surface melt has raised concerns that ice flow may accelerate in response to water-enhanced basal motion. In such a scenario increases in surface melt and mass transport to lower and warmer altitudes would enter into a feedback loop accelerating the mass loss and possibly initiate ice sheet disintegration. To assess the likelihood of such a scenario imperatively requires an understanding and parameterization of the subglacial drainage system, as it controls the relationship between changes in surface runoff and changes in basal motion.

The subglacial drainage system beneath slow flowing parts of the Greenland ice sheet is investigated using innovative seismic techniques and recent advances in glacier seismology. Our study will focus on the capacity of the subglacial drainage system to adapt to changes in water input. This will elucidate how water input affects basal motion. Our project includes the deployment of a high-density seismic network in Greenland's ablation zone and an artificial supraglacial lake drainage into a borehole constituting a sudden perturbation to the subglacial drainage system. Our seismic analysis will consist of performing a seismic noise tomography and determining icequake source mechanisms. This will provide valuable information about englacial water flow, basal and englacial shear motion in response to the lake drainage and changes in englacial water storage in response to basal water pressure fluctuations.

This project is a compliment to the funded SNF proposal “Subglacial Controls on the Short Term dynamics at the Margin of the Greenland Ice Sheet”. This SNF project includes hot water drilling and borehole geophysical measurements such as englacial deformation and basal water pressure. These measurements will be highly valuable to the interpretation of the seismic results. The seismic data acquisition and analysis we will be achieved in collaboration with the Swiss Seismological Service (SED), which will provide seismic instrumentation and technical support to the project.

Collaboration:

Dr. Stephan Husen (Swiss Seismological Service SED, ETH Zurich)

Dr. John Clinton (Swiss Seismological Service SED, ETH Zurich)