Recharge of a subglacial lake by surface meltwater in northeast Greenland

In a warming climate, surface meltwater production on large ice sheets is expected to increase. If this water is delivered to the ice sheet base it may have important consequences for ice dynamics. For example, basal water distributed in a diffuse network can decrease basal friction and accelerate ice flow, whereas channelized basal water can move quickly to the ice margin, where it can alter fjord circulation and submarine melt rates. Less certain is whether surface meltwater can be trapped and stored in subglacial lakes beneath large ice sheets. Here we show that a subglacial lake in Greenland drained quickly, as seen in the collapse of the ice surface, and then refilled from surface meltwater input. We use digital elevation models from stereo satellite imagery and airborne measurements to resolve elevation changes during the evolution of the surface and basal hydrologic systems at the Flade Isblink ice cap in northeast Greenland. During the autumn of 2011, a collapse basin about 70 metres deep and about 0.4 cubic kilometres in volume formed near the southern summit of the ice cap as a subglacial lake drained into a nearby fjord. Over the next two years, rapid uplift of the floor of the basin (which is approximately 8.4 square kilometres in area) occurred as surface meltwater flowed into crevasses around the basin margin and refilled the subglacial lake. Our observations show that surface meltwater can be trapped and stored at the bed of an ice sheet. Sensible and latent heat released by this trapped meltwater could soften nearby colder basal ice and alter downstream ice dynamics. Heat transport associated with meltwater trapped in subglacial lakes should be considered when predicting how ice sheet behaviour will change in a warming climate.

[1]  Robin E. Bell,et al.  Identification and control of subglacial water networks under Dome A, Antarctica , 2013 .

[2]  B. Denby,et al.  Spatially integrated geodetic glacier mass balance and its uncertainty based on geostatistical analysis: application to the western Svartisen ice cap, Norway , 2009, Journal of Glaciology.

[3]  M. Broxton,et al.  Ames Stereo Pipeline, NASA's Open Source Automated Stereogrammetry Software , 2010 .

[4]  F. Pattyn,et al.  Ice-flow sensitivity to boundary processes: a coupled model study in the Vostok Subglacial Lake area, Antarctica , 2012, Annals of Glaciology.

[5]  H. Björnsson,et al.  The response of a glacier to a surface disturbance: a case study on Vatnajökull ice cap, Iceland , 2000, Annals of Glaciology.

[6]  Konrad Steffen,et al.  Surface Melt-Induced Acceleration of Greenland Ice-Sheet Flow , 2002, Science.

[7]  Ian M. Howat,et al.  A new bed elevation dataset for Greenland , 2012 .

[8]  Ian Joughin,et al.  Seasonal Speedup Along the Western Flank of the Greenland Ice Sheet , 2008, Science.

[9]  Leigh A. Stearns,et al.  Increased flow speed on a large East Antarctic outlet glacier caused by subglacial floods , 2008 .

[10]  J. Box,et al.  Evidence of meltwater retention within the Greenland ice sheet , 2012 .

[11]  Z. Martinec,et al.  Effects of uncertainties in the geothermal heat flux distribution on the Greenland Ice Sheet: An assessment of existing heat flow models , 2012 .

[12]  A. Shepherd,et al.  InSAR observations of ice elevation and velocity fluctuations at the Flade Isblink ice cap, eastern North Greenland , 2010 .

[13]  Helen Amanda Fricker,et al.  An Active Subglacial Water System in West Antarctica Mapped from Space , 2007, Science.

[14]  Jamin S. Greenbaum,et al.  Greenland subglacial lakes detected by radar , 2013 .

[15]  John Woodward,et al.  Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets , 2013 .

[16]  Mats Nilsson,et al.  Energy exchange and water budget partitioning in a boreal minerogenic mire , 2013 .

[17]  N. Glasser,et al.  Calculating basal temperatures in ice sheets: an Excel spreadsheet method , 2002 .

[18]  C. Schoof.  Ice-sheet acceleration driven by melt supply variability , 2010, Nature.

[19]  Robert N. Swift,et al.  Aircraft laser altimetry measurement of elevation changes of the greenland ice sheet: technique and accuracy assessment , 2002 .

[20]  Ian Joughin,et al.  Ice-Sheet Response to Oceanic Forcing , 2012, Science.

[21]  Harihar Rajaram,et al.  Evaluation of cryo‐hydrologic warming as an explanation for increased ice velocities in the wet snow zone, Sermeq Avannarleq, West Greenland , 2013 .

[22]  T. Murray,et al.  Ocean regulation hypothesis for glacier dynamics in southeast Greenland and implications for ice sheet mass changes , 2010 .

[23]  Duncan J. Wingham,et al.  On the recent elevation changes at the Flade Isblink Ice Cap, northern Greenland , 2011 .

[24]  R. L. Shreve.  Movement of water in glaciers , 1972 .

[25]  B. Smith,et al.  Rates of southeast Greenland ice volume loss from combined ICESat and ASTER observations , 2008 .

[26]  H. Carlson,et al.  Convection surrounding mesoscale ionospheric flow channels , 2011 .

[27]  Ian Joughin,et al.  Fracture Propagation to the Base of the Greenland Ice Sheet During Supraglacial Lake Drainage , 2008, Science.

[28]  J. D. Gulley,et al.  Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet , 2014, Nature.

[29]  Matt A. King,et al.  Short‐term variability in Greenland Ice Sheet motion forced by time‐varying meltwater drainage: Implications for the relationship between subglacial drainage system behavior and ice velocity , 2012 .

[30]  John Paden,et al.  Deformation, warming and softening of Greenland’s ice by refreezing meltwater , 2014 .

[31]  P. Głowacki,et al.  The effect of discrete recharge by moulins and heterogeneity in flow-path efficiency at glacier beds on subglacial hydrology , 2012, Journal of Glaciology.

[32]  B. Smith,et al.  An inventory of active subglacial lakes in Antarctica detected by ICESat (2003–2008) , 2009, Journal of Glaciology.

[33]  Robin E. Bell,et al.  The role of subglacial water in ice-sheet mass balance , 2008 .

[34]  R. Bindschadler,et al.  Combined measurements of subglacial water pressure and surface velocity of Findelengletscher, Switzerland: conclusions about drainage system and sliding mechanism , 1986 .