Extensive liquid meltwater storage in firn within the Greenland ice sheet

Journal name:
Nature Geoscience
Volume:
7,
Pages:
95–98
Year published:
DOI:
doi:10.1038/ngeo2043
Received
Accepted
Published online

Mass loss from the Greenland ice sheet contributes significantly to present sea level rise1. High meltwater runoff is responsible for half of Greenland’s mass loss2. Surface melt has been spreading and intensifying in Greenland, with the highest ever surface area melt and runoff recorded in 20123. However, how surface melt water reaches the ocean, and how fast it does so, is poorly understood. Firn—partially compacted snow from previous years—potentially has the capacity to store significant amounts of melt water in liquid or frozen form4, and thus delay its contribution to sea level. Here we present direct observations from ground and airborne radar, as well as ice cores, of liquid water within firn in the southern Greenland ice sheet. We find a substantial amount of water in this firn aquifer that persists throughout the winter, when snow accumulation and melt rates are high. This represents a previously unknown storage mode for water within the ice sheet. We estimate, using a regional climate model, aquifer area at about 70,000km2 and the depth to the top of the water table as 5–50m. The perennial firn aquifer could be important for estimates of ice sheet mass and energy budget.

At a glance

Figures

  1. Perennial firn aquifer (PFA) locations on the Greenland ice sheet detected by radar and firn cores in April 2011.
    Figure 1: Perennial firn aquifer (PFA) locations on the Greenland ice sheet detected by radar and firn cores in April 2011.

    NASA’s OIB airborne accumulation radar flight lines are grey and locations of detected PFA are magenta dots. The red line represents the ACT 2011 with PFA firn-core locations and names (blue diamonds) and dry firn-core locations (red diamonds). The green line corresponds to the ACT 2010 that found no PFA evidence from firn cores (green diamonds). The ice sheet margin is blue and the black segment on the ACT-11 line (inset) matches the GPR echogram (Fig. 2).

  2. Profile of the top of the PFA from GPR along the ACT-11 traverse including PFA firn-core locations (ACT11-A and ACT11-A2).
    Figure 2: Profile of the top of the PFA from GPR along the ACT-11 traverse including PFA firn-core locations (ACT11-A and ACT11-A2).

    a, Surface elevation profile from simultaneously acquired GPS and topographically corrected GPR PFA top horizon. This indicates that the depth to the top of the firn aquifer is influenced by the local topographic slope. b, GPR echogram with the top of the firn aquifer as the bright contiguous horizon cutting the numerous internal firn reflecting horizons. The location of the GPR profile is shown in Fig. 1.

  3. Annual snow accumulation (1958-2008) from regional climate model with output calibrated by ice core values (colour).
    Figure 3: Annual snow accumulation (1958–2008) from regional climate model with output calibrated by ice core values10 (colour).

    Terrain elevation23 contours are white. NASA OIB flight lines are grey. The ACT-11 traverse is red. Locations of radar-retrieved firn aquifer positions from the OIB accumulation radar are illustrated as black dots.

  4. Modelled liquid water content (LWC) in the firn and detected PFA from airborne radar.
    Figure 4: Modelled liquid water content (LWC) in the firn and detected PFA from airborne radar.

    The simulation of liquid water content (LWC) is from RACMO2/GR for April 2011 (colour). OIB flight lines (grey), ACT-11 traverse (red) and locations of PFA from OIB radar (black dots) are all data acquired in April 2011. The LWC is integrated for the entire firn column from the surface down to approximately 20m, varying with location (see Methods for details).

References

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Author information

Affiliations

  1. Department of Geography, University of Utah, Salt Lake City, Utah 84112, USA

    • Richard R. Forster,
    • Clément Miège &
    • Evan W. Burgess
  2. Geological Survey of Denmark and Greenland (GEUS), Copenhagen DK-1350, Denmark

    • Jason E. Box
  3. Byrd Polar Research Center, The Ohio State University, Columbus, Ohio 43210, USA

    • Jason E. Box
  4. Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht 3508 TA, The Netherlands

    • Michiel R. van den Broeke,
    • Jan H. van Angelen &
    • Jan T. M. Lenaerts
  5. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

    • Lora S. Koenig
  6. Center for Remote Sensing of the Ice Sheets, University of Kansas, Lawrence, Kansas 66045, USA

    • John Paden,
    • Cameron Lewis,
    • S. Prasad Gogineni &
    • Carl Leuschen
  7. Desert Research Institute, University of Nevada, Reno, Nevada 89512, USA

    • Joseph R. McConnell

Contributions

R.R.F. and J.E.B conceived the idea of the analysis. M.R.v.d.B., J.H.v.A. and J.T.M.L. conducted the modelling. C.M. processed and analysed the GPR data. E.W.B and C.M. collected the field data. L.S.K., J.P. and S.P.G. assisted with airborne radar data processing and identification of melt features. C.L., S.P.G. and C.L. developed the airborne radar and assisted in its interpretation. J.R.M. dated and analysed the firn cores. R.R.F. analysed the airborne radar. R.R.F., J.E.B. and M.R.v.d.B. wrote the manuscript. All authors commented on the data and the manuscript.

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The authors declare no competing financial interests.

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