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

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Abstract

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 57 km 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 41 km or more from the margin, where the ice is approximately 1 km 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.

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Figure 1: Field site and example traces.
Figure 2: Drainage system characteristics revealed by tracing.

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Acknowledgements

This work was supported by the Leverhulme Trust (Phillip Leverhulme Prize to J.L.W.), UK NERC grant NE/H023879/1 to J.L.W., NERC NE/F021380/1 grant to P.N., NERC grant NE/G005796/1 to A.H, financial support from the Greenland Analogue Project and SKB/Positiva to A.H., and Moss Scholarships to T.C. and I.B. We thank the Atmospheric Chemistry Research Group at the University of Bristol who aided with SF6 analysis in the early stages of the project. We acknowledge the use of ice thickness data collected by the NASA IceBridge project. We thank Hozelock for supplying hoses, and are grateful to the many field assistants who have contributed to the collection of field data.

Author information

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.

Correspondence to J. L. Wadham.

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Chandler, D., Wadham, J., Lis, G. et al. Evolution of the subglacial drainage system beneath the Greenland Ice Sheet revealed by tracers. Nature Geosci 6, 195–198 (2013) doi:10.1038/ngeo1737

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