A preliminary investigation of the influence of basal and surface topography on supraglacial lake distribution near Jakobshavn Isbrae, western Greenland

Lampkin, D. J.; VanderBerg, J.

doi:10.1002/hyp.8170

Cited by 60 publications

(63 citation statements)

References 61 publications

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“…We characterized the impact, I , of SGLs on melting by percentage additional melt with respect to bare ice. We calculate I by assuming that the melt rate (↵) beneath SGLs is twice that of the surrounding ice and using equation (2). Total lake area (A lakes ) is estimated for the entire ice sheet by multiplying lake density modelled in the study region by the total lake-covered area (including that which lies below 1,100 m a.s.l.)…”

Section: Simulation Of Sglsmentioning

confidence: 99%

Supraglacial lakes on the Greenland ice sheet advance inland under warming climate

et al. 2014

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Supraglacial lakes (SGLs) form annually on the Greenland ice sheet 1,2 and, when they drain, their discharge enhances ice-sheet flow 3 by lubricating the base 4 and potentially by warming the ice 5 . Today, SGLs tend to form within the ablation zone, where enhanced lubrication is o set by e cient subglacial drainage 6,7 . However, it is not clear what impact a warming climate will have on this arrangement. Here, we use an SGL initiation and growth 8 model to show that lakes form at higher altitudes as temperatures rise, consistent with satellite observations 9 . Our simulations show that in southwest Greenland, SGLs spread 103 and 110 km further inland by the year 2060 under moderate (RCP 4.5) and extreme (RCP 8.5) climate change scenarios, respectively, leading to an estimated 48-53% increase in the area over which they are distributed across the ice sheet as a whole. Up to half of these new lakes may be large enough to drain, potentially delivering water and heat to the ice-sheet base in regions where subglacial drainage is ine cient. In such places, ice flow responds positively to increases in surface water delivered to the bed through enhanced basal lubrication 4,10,11 and warming of the ice 5 , and so the inland advance of SGLs should be considered in projections of ice-sheet change.The volume of water stored in SGLs on the surface of the Greenland ice sheet is determined by the presence of depressions in the local terrain 2 , by the amount of runo 8 (melt water plus rain minus refreezing in the snowpack) and by lake drainage 3 . It is estimated that 13% of Greenland's SGLs drain on timescales of the order of a few hours 12 , often by the creation of moulins as waterfilled fractures propagate through the full thickness of the ice sheet (termed hydro-fracture) 13 . SGLs act as a source of en-and subglacial water when they drain and afterwards, the moulin acts as a conduit allowing runo to pass between the ice-sheet surface and base 1,3 . Satellite and ground-based observations show a correlation between the degree of runo and the rate of ice motion 4,6,7 ; however, there are known spatial and temporal variations in the magnitude and sign of this relationship. For example, near the ice-sheet margin, lower annual ice speeds have been recorded in years of high melting 6,7 but further inland-at higher elevations-the reverse seems to be the case 4,11 . This dichotomy can be attributed to an abundance of melt water at the margin, enabling the evolution of e cient subglacial drainage early in the melt season 6,10 , and thicker ice and less water farther inland hindering the development of an e cient evacuation system 14,15 . In addition to their impact on basal sliding, draining SGLs, and moulins that persist post-drainage, can exert a local warming as relatively warm water passes through the colder

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Section: Simulation Of Sglsmentioning

confidence: 99%

Supraglacial lakes on the Greenland ice sheet advance inland under warming climate

et al. 2014

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“…Cloud-free images from seven imaging systems are used to quantify the hydrologic state of each water-filled crevasses system. The presence of ponded water is easily identified in imagery acquired over the visible part of the electromagnetic spectrum resulting from the propensity for water to absorb incoming solar radiation more effectively than the surrounding ice and firn 5 (Lampkin and VanderBerg, 2011). Data from Landsat-7 ETM+, Landsat-8 OLI, Quickbird-2, Worldview-1/2, EO-1 ALI, SPOT-5, ASTER, and Google Earth are used in this analysis to offset the relative performance limitations inherent to the use of data from a single system.…”

Section: Satellite Imagerymentioning

confidence: 99%

Spatial and temporal variability of water-filled crevasse hydrologic states along the shear margins of Jakobshavn Isbrae, Greenland

Joseph

Lampkin

2017

Preprint

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The impact of melt water injection into ice streams over the Greenland Ice Sheet is not well understood. Water-filled crevasses along the shear margins of Jakobshavn Isbrae are known to fill and drain, resulting in weakening of the shear margins due to reduced basal friction. Seasonal variability in the hydrologic dynamics of these features has not been 10 quantified. In this work, we characterize the spatial and temporal variability in the hydrological state (filled or drained) of these water-filled crevasse systems. A fusion of multi-sensor optical satellite imagery was used to examine hydrologic states from 2000 to 2015. The monthly distribution of crevasse systems observed as water filled is unimodal with peak number of filled days during the month of July at 329 days, while May has the least at 15. Over the study period the occurrence of drainage within a given season increases. Inter-seasonal drain frequencies over these systems ranged from 0 to 5. The 15 frequency of multi-drainage events are correlated with warmer seasons and large strain rates. Over the study period, summer temperatures averaged from -1 and 2 ⁰C and tensile strain rates have increased to as high as ~ 1.2 s -1 . Intermittent melt water input during hydrofracture drainage responsible for transporting surface water to the bed is largely facilitated by high local tensile stresses. Drainage due to fracture propagation may be increasingly modulated by ocean-induced calving dynamics for the lower elevation ponds. Water-filled crevasses could expand in extent and volume as temperatures increase resulting in 20 regional amplification of ice mass flux into the ice stream system. Motivation and Prior WorkThe Greenland Ice Sheet (GrIS) has experienced considerable mass loss over the last few decades (Krabill et al., 2004;Joughin et al., 2004;Alley et al., 2005aAlley et al., , 2005bLuthcke et al., 2006;Hanna et al., 2008) resulting in negative mass balance and substantive contribution to sea level rise (Rignot et al., 2008;van den Broeke et al., 2009; Shepherd et al., 2012). 25Commensurate with these changes has been the documented impact of surface meltwater on ice sheet velocity during the summer within the ablation zone (Zwally et al., 2002;Joughin et al., 2008; van de Wal et al., 2008;Shepherd et al., 2009;Bartholomew et al., 2010;Sundal et al., 2011;Palmer et al., 2011;Hoffman et al., 2011), via supraglacial lakes, channels, The Cryosphere Discuss., doi:10.5194/tc-2017Discuss., doi:10.5194/tc- -86, 2017 Manuscript under review for journal The Cryosphere Discussion started: 24 May 2017 c Author(s) 2017. CC-BY 3.0 License. 2and moulins largely beyond regions of fast flow (Echelmeyer et. al., 1991;Box and Ski, 2007; McMillan et al., 2007;Sneed and Hamilton, 2007;Das et al., 2008, Sundal et al, 2009Lampkin, 2011;Selmes et al., 2011; Tedesco and Steiner, 2011;Howat et al., 2013; Koenig et al., 2015). The presence of ponded water within regions of fast flow has received little attention. Lampkin et al. (2013) evaluated the spatial and tempora...

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“…The position of lakes from year to year is fixed by the bedrock topography [Box and Ski, 2007;Fitzpatrick et al, 2014], with the majority of supraglacial lakes forming in the middle to upper ablation zone in regions of lower surface slope with few surface-tobed meltwater pathways [Lampkin and VanderBerg, 2011;Sergienko, 2013]. Regions of high surface slopes and crevasses in the lower ablation zone prevent supraglacial lake formation, as meltwater can drain to the bed or off of the ice sheet without ponding [Sneed and Hamilton, 2007].…”

Section: Rapid Supraglacial Lake Drainagesmentioning

confidence: 99%

“…As new lakes form at higher elevations in a warming climate [Sundal et al, 2009;Howat et al, 2013;Fitzpatrick et al, 2014;Parizek and Alley, 2004;Leeson et al, 2015] they will encounter longer wavelength surface topography [Joughin et al, 2013;Sergienko, 2013;Lampkin and VanderBerg, 2011], resulting in greater distances between compressive lake basins and extensional crevasse-forming regions. Thus, lake water must be routed greater distances in surface streams down the ice sheet before encountering crevasses where through-ice drainage conduits can be established, minimizing local stress transients and potentially obstructing in situ rapid drainage of high elevation lakes and the formation of new surface-to-bed hydro-fractures beneath lake basins [Poinar et al, 2015].…”

Section: Main Textmentioning

confidence: 99%

“…If clustered lake drainage are the result of tensile stress transients at the ice sheet surface instigated by a neighboring lake drainage, we may also be able to constrain a critical radius over which a supraglacial lake drainage can trigger its neighbor. This critical radius could then be used to make a prediction of the drainage characteristics of future lakes forming at higher elevations [Parizek and Alley, 2004;Howat et al, 2013;Leeson et al, 2015] over longer-wavelength surface topography [Lampkin and VanderBerg, 2011;Joughin et al, 2013;Sergienko, 2013;Poinar et al, 2015].…”

Section: Future Directions Towards Synthesismentioning

confidence: 99%

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Influence of meltwater on Greenland Ice Sheet dynamics

Stevens¹

2017

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Seasonal fluxes of meltwater control ice-flow processes across the Greenland Ice Sheet ablation zone and subglacial discharge at marine-terminating outlet glaciers. With the increase in annual ice sheet meltwater production observed over recent decades and predicted into future decades, understanding mechanisms driving the hourly to decadal impact of meltwater on ice flow is critical for predicting Greenland Ice Sheet dynamic mass loss. This thesis investigates a wide range of meltwater-driven processes using empirical and theoretical methods for a region of the western margin of the Greenland Ice Sheet. I begin with an examination of the seasonal and annual ice flow record for the region using in situ observations of ice flow from a network of Global Positioning System (GPS) stations. Annual velocities decrease over the seven-year time-series at a rate consistent with the negative trend in annual velocities observed in neighboring regions. Using observations from the same GPS network, I next determine the trigger mechanism for rapid drainage of a supraglacial lake. In three consecutive years, I find precursory basal slip and uplift in the lake basin generates tensile stresses that promote hydrofracture beneath the lake. As these precursors are likely associated with the introduction of meltwater to the bed through neighboring moulin systems, our results imply that lakes may be less able to drain in the less crevassed, interior regions of the ice sheet. Expanding spatial scales to the full ablation zone, I then use a numerical model of subglacial hydrology to test whether model-derived effective pressures exhibit the theorized inverse relationship with melt-season ice sheet surface velocities. Finally, I pair near-ice fjord hydrographic observations with modeled and observed subglacial discharge for the Saqqardliup sermia-Sarqardleq Fjord system. I find evidence of two types of glacially modified waters whose distinct properties and locations in the fjord align with subglacial discharge from two prominent subcatchments beneath Saqqardliup sermia. Continued observational and theoretical work reaching across discipline boundaries is required to further narrow our gap in understanding the forcing mechanisms and magnitude of Greenland Ice Sheet dynamic mass loss.

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A preliminary investigation of the influence of basal and surface topography on supraglacial lake distribution near Jakobshavn Isbrae, western Greenland

Cited by 60 publications

References 61 publications

Supraglacial lakes on the Greenland ice sheet advance inland under warming climate

Supraglacial lakes on the Greenland ice sheet advance inland under warming climate

Spatial and temporal variability of water-filled crevasse hydrologic states along the shear margins of Jakobshavn Isbrae, Greenland

Influence of meltwater on Greenland Ice Sheet dynamics

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