Winter motion mediates dynamic response of the Greenland Ice Sheet to warmer summers

Sole, Andrew; Nienow, Peter; Bartholomew, I. D.; Mair, D.; Cowton, Tom; Tedstone, Andrew; King, Matt

doi:10.1002/grl.50764

Cited by 154 publications

(274 citation statements)

References 23 publications

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“…For that to occur requires the maintenance of hydraulically inefficient subglacial drainage and thus a positive relationship between meltwater input and ice motion [61,66]. In contrast, the weight of evidence suggests a seasonal increase in drainage efficiency beneath the GrIS [62,64] with no net acceleration on annual timescales [84,87]. Furthermore if meltwater does continue to access the bed at increasingly high elevations (which may not be possible [52]), it will likely only be able to do so through the rapid drainage of large supraglacial lakes.…”

Section: Discussion Regarding Future Prioritiesmentioning

confidence: 99%

“…Any rapid changes in meltwater flux into the drainage system caused either by lake drainage events [8,81], sudden increases in surface melt rate [84], or rainfall [85] may overpressurise the system and cause ice acceleration even when the drainage system is already efficient [63]. At the cessation of summer surface melting, the ice sheet slows to an annual minimum [8,86,87] prior to a steady increase in motion overwinter, the latter presumably the result of basal melt repressurising the distributed subglacial drainage system in the absence of efficient channels that have been closed by ice deformation.…”

Section: The Greenland Ice Sheet's Dynamic Response To Meltwater Inputsmentioning

confidence: 99%

“…If so, this could lead to a positive feedback between warming and ice loss, due to the more rapid transfer of ice to lower, and thus warmer, elevations [8]. While increased surface melt can lead to higher average ice motion during some or all of the melt season, as the drainage system is repeatedly forced to accommodate greater volumes of meltwater [8,86,87], numerous studies have shown that increased melt does not enhance ice motion on annual timescales [79, 87, 88•, 89-91]. This is due to both the seasonal evolution in the efficiency of the subglacial drainage system which ensures that ice motion does not scale with melt [61], and potentially of greater importance, the role of water pressure in the more extensive distributed component of the subglacial drainage system •] observed a 12% decrease in mean annual ice velocity across an 8000 km 2 land-terminating area of the ice sheet, extending to~1200 m elevation, at the same time as melt rates increased by~50%.…”

Section: The Greenland Ice Sheet's Dynamic Response To Meltwater Inputsmentioning

confidence: 99%

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Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Nienow

Sole

Slater

et al. 2017

Curr Clim Change Rep

100

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Purpose of the Review This review discusses the role that meltwater plays within the Greenland ice sheet system. The ice sheet's hydrology is important because it affects mass balance through its impact on meltwater runoff processes and ice dynamics. The review considers recent advances in our understanding of the storage and routing of water through the supraglacial, englacial, and subglacial components of the system and their implications for the ice sheet. Recent Findings There have been dramatic increases in surface meltwater generation and runoff since the early 1990s, both due to increased air temperatures and decreasing surface albedo. Processes in the subglacial drainage system have similarities to valley glaciers and in a warming climate, the efficiency of meltwater routing to the ice sheet margin is likely to increase. The behaviour of the subglacial drainage system appears to limit the impact of increased surface melt on annual rates of ice motion, in sections of the ice sheet that terminate on land, while the large volumes of meltwater routed subglacially deliver significant volumes of sediment and nutrients to downstream ecosystems. Summary Considerable advances have been made recently in our understanding of Greenland ice sheet hydrology and its wider influences. Nevertheless, critical gaps persist both in our understanding of hydrology-dynamics coupling, notably at tidewater glaciers, and in runoff processes which ensure that projecting Greenland's future mass balance remains challenging.

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Section: Discussion Regarding Future Prioritiesmentioning

confidence: 99%

Section: The Greenland Ice Sheet's Dynamic Response To Meltwater Inputsmentioning

confidence: 99%

Section: The Greenland Ice Sheet's Dynamic Response To Meltwater Inputsmentioning

confidence: 99%

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Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Nienow

Sole

Slater

et al. 2017

Curr Clim Change Rep

100

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“…However, studies since the AR5 support the conclusion that enhanced basal lubrication makes an insignificant contribution to the likely range of sea level rise over the twenty-first century. Some studies suggested that this occurs through the subglacial drainage system becoming more efficient with increased discharge, thus reducing basal sliding [99,100]. Mayaud et al [101] forced a subglacial hydrological model of the western ice sheet margin in the Paakitsoq region with surface runoff that was derived from climate model output for the RCP2.6, 4.5, and 8.5 scenarios.…”

Section: Greenland Ice Sheetmentioning

confidence: 99%

Recent Progress in Understanding and Projecting Regional and Global Mean Sea Level Change

Clark

Church

Gregory

et al. 2015

Curr Clim Change Rep

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Considerable progress has been made in understanding the present and future regional and global sea level in the 2 years since the publication of the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change. Here, we evaluate how the new results affect the AR5's assessment of (i) historical sea level rise, including attribution of that rise and implications for the sea level budget, (ii) projections of the components and of total global mean sea level (GMSL), and (iii) projections of regional variability and emergence of the anthropogenic signal. In each of these cases, new work largely provides additional evidence in support of the AR5 assessment, providing greater confidence in those findings. Recent analyses confirm the twentieth century sea level rise, with some analyses showing a slightly smaller rate before 1990 and some a slightly larger value than reported in the AR5. There is now more evidence of an acceleration in the rate of rise. Ongoing ocean heat uptake and associated thermal expansion have continued since 2000, and are consistent with ocean thermal expansion reported in the AR5. A significant amount of heat is being stored deeper in the water column, with a larger rate of heat uptake since 2000 compared to the previous decades and with the largest storage in the Southern Ocean. The first formal detection studies for ocean thermal expansion and glacier mass loss since the AR5 have confirmed the AR5 finding of a significant anthropogenic contribution to sea level rise over the last 50 years. New projections of glacier loss from two regions suggest smaller contributions to GMSL rise from these regions than in studies assessed by the AR5; additional regional studies are required to further assess whether there are broader implications of these results. Mass loss from the Greenland Ice Sheet, primarily as a result of increased surface melting, and from the Antarctic Ice Sheet, primarily as a result of increased ice discharge, has accelerated. The largest estimates of acceleration in mass loss from the two ice sheets for 2003-2013 equal or exceed the acceleration of GMSL rise calculated from the satellite altimeter sea level record over the longer period of 1993-2014. However, when increased mass gain in land water storage and parts of East Antarctica, and decreased mass loss from glaciers in Alaska and some other regions are taken into account, the net acceleration in the ocean mass gain is consistent with the satellite altimeter record. New studies suggest that a marine ice sheet instability (MISI) may have been initiated in parts of the West Antarctic Ice Sheet (WAIS), but that it will affect only a limited number of ice streams in the twenty-first century. New projections of mass loss from the Greenland and Antarctic Ice Sheets by 2100, including a contribution from parts of WAIS undergoing unstable retreat, suggest a contribution that falls largely within the likely range (i.e., two thirds probability) of the AR5. These new results increase confidence in the AR5 likel...

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“…Extending the results of our model, we estimate that 48-53% more of the ice sheet will be similarly a ected. Ice in these inland areas has been shown to exhibit a positive dynamical response to increased runo 11 , in contrast to that at lower elevations, where the e ects of enhanced basal ice lubrication are o set by e cient subglacial drainage 6 .…”

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confidence: 98%

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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Winter motion mediates dynamic response of the Greenland Ice Sheet to warmer summers

Cited by 154 publications

References 23 publications

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Recent Progress in Understanding and Projecting Regional and Global Mean Sea Level Change

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

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