Evolution of the subglacial drainage system beneath the Greenland Ice Sheet revealed by tracers

Journal name:
Nature Geoscience
Volume:
6,
Pages:
195–198
Year published:
DOI:
doi:10.1038/ngeo1737
Received
Accepted
Published online

Predictions of the Greenland Ice Sheet’s response to climate change are limited in part by uncertainty in the coupling between meltwater lubrication of the ice-sheet bed and ice flow1, 2, 3. This uncertainty arises largely from a lack of direct measurements of water flow characteristics at the bed of the ice sheet. Previous work has been restricted to indirect observations based on seasonal and spatial variations in surface ice velocities4, 5, 6, 7 and on meltwater flux8. Here, we employ rhodamine and sulphur hexafluoride tracers, injected into the drainage system over three melt seasons, to observe subglacial drainage properties and evolution beneath the Greenland Ice Sheet, up to 57km from the margin. Tracer results indicate evolution from a slow, inefficient drainage system to a fast, efficient channelized drainage system over the course of the melt season. Further inland, evolution to efficient drainage occurs later and more slowly. An efficient routing of water was established up to 41km or more from the margin, where the ice is approximately 1km thick. Overall, our findings support previous interpretations of drainage system characteristics, thereby validating the use of surface observations as a means of investigating basal processes.

At a glance

Figures

  1. Field site and example traces.
    Figure 1: Field site and example traces.

    a, MODIS (Moderate Resolution Imaging Spectroradiometer) image showing locations of moulins used for tracing, and the estimated boundary of the Leverett catchment (pink) calculated from a surface DEM (ref. 7). Insets: example dye and SF6 traces at each site. Note the coherent dye and SF6 returns from moulin L14 and a retarded SF6 return from moulins L1 and L7. Tracer concentrations have been scaled to give unity area under the peaks, apart from the trace from L57 where the end of the SF6 peak was not captured.

  2. Drainage system characteristics revealed by tracing.
    Figure 2: Drainage system characteristics revealed by tracing.

    a, Evolution of tracer velocity with time. Cumulative discharge (ΣQ) is used to measure time because of variation in melt season onset and intensity between years (see Supplementary Fig. S3.1). The regression curve for maximum velocity (v05; Supplementary Section S2.3) from moulin L7 is v05=Aln(ΣQ)+B. b, Evolution of SF6 traces at moulin L41 in 2011. c, Variation in SF6 retardation R50 (Supplementary Section S2.4) with distance up-glacier from the terminus. The time taken for an empty channel to shrink to 1/10 of its original radius is also indicated (Supplementary Section S4).

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Author information

Affiliations

  1. Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK

    • D. M. Chandler,
    • J. L. Wadham,
    • G. P. Lis,
    • J. Telling &
    • E. B. Bagshaw
  2. Department of Geography, School of Geosciences, University of Edinburgh, Edinburgh EH8 9XP, UK

    • T. Cowton,
    • I. Bartholomew &
    • P. Nienow
  3. Department of Geography, University of Sheffield, Sheffield S10 2TN, UK

    • A. Sole
  4. Department of Geography and the Environment, School of Geoscience, University of Aberdeen, Aberdeen AB24 3UF, UK

    • D. Mair
  5. School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK

    • S. Vinen
  6. Institute of Geography and Earth Science, University of Aberystwyth, Aberystwyth SY23 3DB, UK

    • A. Hubbard

Contributions

D.M.C. designed the tracer experiments in the field and conducted tracer data analysis, developed the model of drainage evolution and co-wrote the manuscript. J.L.W. led the project, designed the tracer experiments in the field and conducted tracer data analysis, and co-wrote the manuscript with D.M.C. G.P.L., S.V. and J.T. were responsible for SF6 analysis by gas chromatography and method development. P.N., D.M.C., A.S., T.C. and I.B. contributed discharge and dye tracing data, and input to writing of the manuscript. E.B.B. contributed to field logistics and input to writing of the manuscript. A.H. was responsible for in-field support of the campaign, provided ice thickness data and input to writing of manuscript.

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The authors declare no competing financial interests.

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