Subglacial Hydrology

Each summer, surface ablation on top of ice sheets generates a large amount of meltwater. This surface water can infiltrate the ice sheet through fractures and moulins. In Greenland, studies have shown that almost 90% of the surface meltwater ended up at the ice sheet bed into the subglacial hydrologic system. Once there, the movement of subglacial water can accelerate glacier velocity by temporarily lubricate the ice-bed interface. However, precisely how the glacier's velocity responds to this "meltwater lubrication" effect varies from glacier to glacier and from one year to another. The lack of proper constrain on the meltwater impact on ice motion currently hinders our efforts in predicting how the Greenland Ice Sheet and the future of Antarctica ice sheet will respond to a warming climate.

We believe that the morphology of the subglacial hydrologic system and how meltwater is connected from the surface to the ice-sheet bed are two critical parameters that determine how individual glacier responds to meltwater. Our research uses NASA airborne ice-penetrating radar sounding and field measurements to study subglacial hydrology and meltwater interactions in Greenland and West Antarctica. We develop new signal processing techniques to analyze, calibrate, and model radar basal power returns. We then use this radar power information to tell us how much water is at the base of the ice sheet, how it is changing over time with climate, and the importance of subglacial hydrology in controlling the ice sheet vulnerability to surface melting in the future.

Collaborators: John Paden (CReSIS), Riley Culberg (Stanford), Stephen Livingstone (U of Sheffield)

Selected Publications

  • Bowling, J.S., Livingstone, S. J., Sole, A. J., & Chu, W. Distribution and dynamics of Greenland subglacial lakes. Nature Communications, 10, 2810.
  • Chu, W., Schroeder, D. M., Seroussi, H., Creyts, T. T., Palmer S. J., & Bell, R. E. Extensive winter subglacial water storage beneath the Greenland Ice Sheet. Geophysical Research Letters, 43(24), 12484-12492.
  • Livingstone S.J., Chu, W., Ely, J. C. & Kingslake, J. Paleofluvial and subglacial channel networks beneath Humboldt Glacier, Greenland. Geology, 45(6), 551-554

Basal Thermal Regime

On multiannual to centennial timescale, meltwater flow at the ice-sheet bed can impact the ice sheet basal thermal condition. Thawing and freezing of basal ice at the ice-sheet bed can cause glaciers to slow down. Basal freeze-on could also heat, soften, deform near-basal ice through latent-heat release. In dramatic cases, rerouting of subglacial meltwater has been hypothesized to cause one of the West Antarctica ice streams to shut down several centuries ago.

This interaction of meltwater and ice sheet thermal conditions makes it very challenging to assess the long-term impact of meltwater on ice-sheet stability. In addition, changes in basal temperature related to melting and refreezing at the ice sheet bed also muddle the ice-penetrating radar signals by influencing attenuation losses. Some of these thermal changes can be easily misinterpreted as hydrological signals.

Our research group dedicates effort to designing new geophysical methodology to overcome these challenges. These efforts include combining numerical ice-sheet thermomechanical models with radar observations and using models to inform data and vice versa. We also work with other geophysicists in EAS to develop joint-inversion methods of radar-sounding, electromagnetics, resistivity, fiber optics, and seismic techniques to enable more robust separation of signals related to changes in hydrology, temperatures, and ice sheet roughness.

Collaborators: Helene Seroussi (Dartmouth), Eliza Dawson (Stanford), Riley Culberg (Stanford)

Selected Publications

  • Chu, W., Schroeder, D.M., Seroussi, H., Creyts, T.T. & Bell, R.E. Complex basal thermal transition near the onset of Petermann Glacier, Greenland. Journal of Geophysical Research: Earth Surface. 544(7), 985-995
  • Bell R.E., Tinto, T., Das, I., Wolovick, M., Chu, W., Creyts, T. T., Frearson, N., Abdi, A., Paden, J. D., Deformation, warming and softening of Greenland’s ice by refreezing meltwater. Nature Geoscience. 7(7), 497–502. doi:10.1038/ngeo2179