Abstract
Greenland Ice Sheet mass loss is impacting connected terrestrial and marine hydrologic systems with global consequences. Groundwater is a key component of water cycling in the Arctic, underlying the 1.7e6 km2 ice sheet and forming offshore freshwater reserves. However, despite its vast extent, the response of Greenland’s groundwater to ongoing ice sheet change is unknown. Here we present in-situ observations of deep groundwater conditions under the Greenland Ice Sheet, obtained in a 651-metre-long proglacial bedrock borehole angled under the ice sheet margin. We find that Greenland’s groundwater system responds rapidly and sensitively to relatively minor ice sheet forcing. Hydraulic head clearly varies over multi-annual, seasonal and diurnal timescales, which we interpret as a response to fluid pressure forcing at the ice/bed interface associated with changes in overlying ice loading and ice sheet hydrology. We find a systematic decline in hydraulic head over the eight-year observational period is linked primarily to ice sheet mass loss. Ongoing and future ice thinning will probably reduce groundwater discharge rates, with potential impacts to submarine freshwater discharge, freshwater delivery to fjords and biogeochemical fluxes in the Arctic.
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Data availability
Bedrock temperature (https://doi.org/10.1594/PANGAEA.928163) and groundwater head (https://doi.org/10.1594/PANGAEA.928193) data are both freely available without restrictions. Ice-sheet runoff data are archived by the Programme for Monitoring of the Greenland Ice Sheet (http://www.promice.org/PromiceDataPortal/), with identifiers: https://doi.org/10.22008/FK2/GUW0Y8. Ice-sheet basal water-pressure data have been previously published (https://doi.org/10.1002/2016JF003819), as have GPS data (https://doi.org/10.1126/sciadv.aaw5406).
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Acknowledgements
This work has been supported by the Greenland Analogue Project (GAP), the Catchment transport and Cryo-hydrology Network (CatchNet), Svensk Kärnbränslehantering AB (SKB) and National Science Foundation Office of Polar Programs–Arctic Natural Sciences award #0909495. T.M. is additionally supported by NSF-EPSCoR award 1929068 and Montana NASA EPSCoR award G185-19-W5586. K. Hansson, J. Sundberg (Geosigma) and L. Andersson (SKB) are acknowledged for field and borehole instrument support. J. Moore, B. Woessner, S. Berglund and J. Liakka are thanked for valuable comments on an early manuscript draft. B. Kurylyk and G. Clarke are thanked for detailed comments that resulted in improvements to the manuscript.
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The study was conceived by L.C.L., J.-O.N., J.-O.S., T.R. and A.K. L.C.L., T.R. and A.K. led the bedrock borehole drilling and data collection. T.M., J.H. and N.H. completed ice-sheet borehole drilling and data collection and D.v.A. collected AWS data. J.S. completed the DEM analysis. L.C.L., T.M. and J.H. wrote the manuscript. All authors contributed to data interpretation and manuscript edits.
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Peer review information Primary handling editor: Tom Richardson. Nature Geoscience thanks Barret Kurylyk, Garry Clarke and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Extended data
Extended Data Fig. 1 Annual groundwater head and ice sheet runoff over eight years.
a-h, Annual groundwater head in Up (blue) and Low (pink), and corresponding calculated runoff integrated over the Isunnguata Sermia catchment (gray, Supplementary Methods). Vertical lines show the transition to increasing groundwater head in spring (yellow), annual maximum head (red), and minimum head (purple) in Up (solid) and Low (dashed) sections. Years without transition lines for Low section either indicate identical timing to Up, or are obscured by pumping.
Extended Data Fig. 2 Proglacial and subglacial hydraulic head over study area.
a, Plan view of computed hydraulic head. Solid black line indicates ice sheet margin and gray dashed line (A-A’) shows location of the glacier cross section in b. Colormap shows calculated hydraulic head in meters equivalent (Supplementary Discussion). Solid and dashed magenta lines delineate the 490 m head contour and uncertainty, respectively. This contour is presented to illustrate locations of head conditions similar to measured heads in Low. White solid and dashed lines indicate the bed elevation and uncertainty, respectively, corresponding to the elevation of the packer separating the Low section from the remainder of the borehole. b, Ice surface and bed topography (black) along S-N cross section intersecting bedrock borehole location. Bed topography uncertainty is shown in shaded gray. Hydraulic head and corresponding uncertainty in magenta and shaded magenta, respectively. Borehole is shown in red, with lower packer as red dot.
Supplementary information
Supplementary Information
Supplementary methods, discussion and Fig. 1.
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Liljedahl, L.C., Meierbachtol, T., Harper, J. et al. Rapid and sensitive response of Greenland’s groundwater system to ice sheet change. Nat. Geosci. 14, 751–755 (2021). https://doi.org/10.1038/s41561-021-00813-1
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DOI: https://doi.org/10.1038/s41561-021-00813-1
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