Supraglacial Lake Formation and What it Means for Greenland s Future

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1 Supraglacial Lake Formation and What it Means for Greenland s Future GreenPeace Ulyana Nadia Horodyskyj GEOG 5271

2 questions of interest How, when and where do these lakes form in Greenland? How do these lakes evolve over time? What is the future of these lakes as climate warms? How do they compare with dirty ice Himalayan lakes? H. Patton

3 how, when and where Lakes form on the surface of the ice sheet, usually near ice margins. What causes them? Topography and surface melt. Net shortwave radiation largely controls the ablation rate on the ice sheet (Greuell and Knap 2000).

4 how, when and where Lakes also depend on: latitude, elevation and time Lower latitudes and elevations result in a longer and more intense summer melting season (McMillan et al., 2007) Lakes are typically found below 1500 meters. Melting begins in June, lowering albedo, causing a positive feedback. H. Patton

5 mapping of lake locations West Greenland ice sheet margin (Thomsen, 1986) Lakes seem to be found in the same locations during different years (Thomsen and others, 1988). MODIS image, Scott Polar Research Institute, University of Cambridge

6 attempts to model lake evolution Modelling the evolution of supraglacial lakes on the West Greenland ice-sheet margin M. Luthje, L.T. Pedersen, N. Reeh and W. Greuell, 2006 Use of a 1-D model to determine surface ablation for bare ice vs. beneath supraglacial lakes (1999; 2001) Includes conductive heat transport through ice; turbulent heat transfer through lake water, surface boundary conditions between ice and atmosphere. Use of results to further model horizontal and vertical evolution of lakes. Final comparison with satellite images.

7 West Greenland This MODIS image taken on 26 August 2000 shows most of Greenland, with a resolution of (a) 1000 and (b) 250m. (a) The arrows mark the positions of the field camp occupied in August 2003 and the climate station. (b) The area investigated for aerial coverage of supraglacial lakes. Luthje et al Fig. 1. MODIS image taken on 26 August 2000 showing most of

8 Major Findings: modeling, cont d Surface ablation beneath lake was enhanced by 110% in 1999 and 170% in 2001 compared with ablation for bare ice. Despite higher melt rates (on bare ice) in 1999 than 2001, lake area was only 7% larger in Compared with satellite data, model-calculated area coverage still 3-4x too large. H. Patton

9 what happened? Resolution of the applied ice-surface DEM as too low; drainage through moulins was not accounted for in model. Moulins, from field data, can nearly halve the area covered by the lakes. Moulin: vertical to nearly vertical well-like shaft that transports water from the surface down to depth.face H. Patton

10 future predictions (according to Luthje et al.) Supraglacial lakes are known to form in depressions on the ice surface. Need drastic change in topography to grow large lakes Satellite analysis: less than 1% of ablation region in SW Greenland has lakes. So, despite enhanced melt rates, extra surface ablation is minimal. H. Patton

11 future predictions (according to Luthje et al.) HOWEVER, in a warmer climate, surface melting tends to occur higher up on the ice sheet. Small surface slopes will favor formation of large supraglacial lakes. Thus, enhanced surface melting due to these lakes is an important feedback mechanism. H. Patton

12 how lakes evolve They typically drain through crevasses later in the summer (by July, (MacMillan et al. 2007)). Importance? Can deliver meltwater to the bed of the ice sheet. There may be a link between surface melt and ice dynamics. H. Patton

13 lake impact on glacial dynamics Fracture propagation to the Base of the Greenland Ice Sheet During Supraglacial Lake Drainage S.B. Das, I. Joughin, M.D. Behn, I.M. Howat, M.A. King, D. Lizarralde, M.P. Bhatia, 2008 Observed rapid (< 2 hour) drainage of large supraglacial lake down 980 meters through to the bed of the Greenland ice sheet. Initiated by water-driven fracture propagation evolving into moulin flow. H. Patton

14 the field study Drainage coincided with: Increased seismicity Ice sheet uplift Horizontal displacement Das et al., 2008

15 himalayan supraglacial lakes Unlike Greenland s ephemeral lakes, Himalayan lakes have been present since the 1950s. Unlike on Greenland, they form at high elevation. They, too, drain subglacially, but at a slower rate. They, too, change the dynamics of the glacial ice. They are starting to evolve into large proglacial lakes, which can lead to large flood events. H. Patton

16 himalayan lakes Ngozumpa Glacier, Nepalese Himalaya --> Debris-covered glacier --> Supraglacial lakes along mid-ablation zone Terminus proglacial lake

17 himalayan lakes Supraglacial lake area, 2008

19 why the lakes matter As the climate warms, this can lead to earlier, expanded, and elevated surface lake formation. Subglacial connections may occur earlier in melt season, possibly over a larger area. Result: increase in subglacial meltwater --> change in ice sheet dynamics H. Patton

20 References Das, S.B., Joughin, I., Behn, M.D., Howat, I.M., King, M.A., Lizarralde, D. and M.P. Bhatia, 2008, Fracture Propagation to the Base of the Greenland Ice Sheet During Supraglacial Lake Drainage, Science, v. 320, Greuell, W. and W.H. Knap, 2000, Remote sensing of the albedo and detection of the slush line on the Greenland ice sheet, J. Geophys. Res., 105(D12), Luthje, M., Pedersen, L.T., Reeh, N. and W. Greuell, 2006, Modelling the evolution of supraglacial lakes on the West Greenland ice-sheet margin, Journal of Glaciology, v. 52, no. 179, MacMillan, M., Nienow, P., Shepherd, A., Benham, T. and A. Sole, 2007, Seasonal evolution of supra-glacial lakes on the Greenland Ice Sheet, Earth and Planetary Science Letters, 262, Thomsen, H.H., 1986, Photogrammetric and satellite mapping of the margin of the inland ice, West Greenland, Ann. Glaciol., 8, Thomsen, H.H., Thorning, L., and R.J. Braithwaite, 1988, Glacier-hydrological conditions on the Inland Ice north-east of Jacobshavn/Ilulissat, West Greenland. Gronl. Geol. Unders. Rapp. 138.

Modelling meltwater delivery to the ice-bed interface through fractures at the margin of the Greenland Ice Sheet

$Modelling meltwater delivery to the ice-bed interface through fractures at the margin of the Greenland Ice Sheet$ Modelling meltwater delivery to the ice-bed interface through fractures at the margin of the Greenland Ice Sheet Caroline Clason, Douglas Mair & Peter Nienow CESM Land Ice Working Group Meeting, January