Letter | Published:

Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet

Nature volume 514, pages 8083 (02 October 2014) | Download Citation

Abstract

Seasonal acceleration of the Greenland Ice Sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed1,2 via crevasses and moulins (vertical conduits connecting supraglacial water to the bed of the ice sheet). As the melt season progresses, the subglacial hydrologic system drains supraglacial meltwater more efficiently1,2,3,4, decreasing basal water pressure4 and moderating the ice velocity response to surface melting1,2. However, limited direct observations of subglacial water pressure4,5,6,7 mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood. Here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby (0.3–2 kilometres away) boreholes, indicating that moulins connect to an efficient, channelized component of the subglacial hydrologic system, which exerts the primary control on diurnal and multi-day changes in ice velocity. Our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the Paakitsoq region of western Greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin-connected channels to convey supraglacial melt. Instead, these observations suggest that decreasing late-season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system. Understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt-season dynamics affect ice velocity beyond the conclusion of the melt season8,9,10.

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Acknowledgements

This project was supported by United States National Science Foundation grants OPP-0908156, OPP-0909454 and ANT-0424589 (to CReSIS), Swiss National Science Foundation grant 200021_127197, and National Geographic Society grant 9067-12. L.C.A. was also supported by UTIG Ewing-Worzel and Gale White Graduate Student Fellowships. M.J.H. was also supported by NASA Cryospheric Sciences and Climate Modeling Programs within the US Department of Energy, Office of Science. J.D.G. was also supported by an NSF Postdoctoral Fellowship (EAR-0946767). Logistical support was provided by CH2MHill Polar Services. The GPS base station and several on-ice GPS units were provided by the UNAVCO facility with support from the NSF and NASA under cooperative agreement EAR-0735156. The University of Minnesota Polar Geospatial Center, funded under NSF OPP collaborative agreement ANT-1043681, provided WorldView imagery. We thank K. M. Schild, J. A. MacGregor, J. D. Nowinski, B. F. Morriss and others for assistance in the field.

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Affiliations

  1. Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas 78758, USA

    • Lauren C. Andrews
    • , Ginny A. Catania
    •  & Jason D. Gulley
  2. Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas 78712, USA

    • Lauren C. Andrews
    •  & Ginny A. Catania
  3. Fluid Dynamics and Solid Mechanics Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

    • Matthew J. Hoffman
  4. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

    • Matthew J. Hoffman
    •  & Thomas A. Neumann
  5. Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, Michigan 49931, USA

    • Jason D. Gulley
  6. Glaciology and Geomorphodynamics Group, Physical Geography Division, Department of Geography, University of Zürich, 8057 Zürich, Switzerland

    • Martin P. Lüthi
  7. Laboratory of Hydraulics, Hydrology and Glaciology, Swiss Federal Institute of Technology (ETH) Zürich, 8093 Zürich, Switzerland

    • Martin P. Lüthi
    •  & Claudia Ryser
  8. Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA

    • Robert L. Hawley

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Contributions

G.A.C., J.D.G., M.P.L., R.L.H. and T.A.N. designed this study. L.C.A., R.L.H., M.J.H., M.P.L., C.R. and J.D.G. performed the fieldwork. L.C.A. analysed the results and wrote the manuscript. All authors discussed the results and edited the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Lauren C. Andrews.

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https://doi.org/10.1038/nature13796

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