Cascading lake drainage on the Greenland Ice Sheet triggered by tensile shock and fracture

Christoffersen, Poul; Bougamont, Marion; Hubbard, Alun; Doyle, Samuel; Grigsby, S.; Pettersson, Rickard

doi:10.1038/s41467-018-03420-8

Cited by 62 publications

(100 citation statements)

References 59 publications

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“…The longitudinal coupling effect observed here may be part of a catchment‐wide phenomenon that is governed by melt‐induced perturbations from surface water forming and reaching the bed, which propagate upglacier through the course of the summer melt season. A detailed numerical analysis of the longitudinal coupling effect by Christoffersen et al () supports the vertical thickening observed throughout the ice column starting in July at S30. Here widespread melt occurring at the surface lubricates the bed at S30, encouraging faster velocities, while ice flow at lower elevations becomes markedly slower in response to the formation of an efficient basal drainage system from large, continued meltwater influx into the subglacial environment.…”

Section: Discussionmentioning

confidence: 65%

“…The lower degree of viscosity attributed to Wisconsin ice facilitates enhanced deformation, in contrast to the Holocene ice residing above this layer. The latter, being more viscous and cold, may thus act as a stiff beam, which accommodates the far‐field transfer of stresses via longitudinal coupling (Christoffersen et al, ). The latter plays a crucial role in the force balance of the ice sheet in summer but may also be important in winter and spring, when a significant increase in the water pressure inside small basal cavities reduces the basal traction, resulting in faster glacier motion.…”

Section: Discussionmentioning

confidence: 99%

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Physical Conditions of Fast Glacier Flow: 3. Seasonally‐Evolving Ice Deformation on Store Glacier, West Greenland

et al. 2019

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Temporal variations in ice sheet flow directly impact the internal structure within ice sheets through englacial deformation. Large‐scale changes in the vertical stratigraphy within ice sheets have been previously conducted on centennial to millennial timescales; however, intra‐annual changes in the morphology of internal layers have yet to be explored. Over a period of 2 years, we use autonomous phase‐sensitive radio‐echo sounding to track the daily displacement of internal layers on Store Glacier, West Greenland, to millimeter accuracy. At a site located ∼30 km from the calving terminus, where the ice is ∼600 m thick and flows at ∼700 m/a, we measure distinct seasonal variations in vertical velocities and vertical strain rates over a 2‐year period. Prior to the melt season (March–June), we observe increasingly nonlinear englacial deformation with negative vertical strain rates (i.e., strain thinning) in the upper half of the ice column of approximately −0.03 a−1, whereas the ice below thickens under vertical strain reaching up to +0.16 a−1. Early in the melt season (June–July), vertical thinning gradually ceases as the glacier increasingly thickens. During late summer to midwinter (August–February), vertical thickening occurs linearly throughout the entire ice column, with strain rates averaging 0.016 a−1. We show that these complex variations are unrelated to topographic setting and localized basal slip and hypothesize that this seasonality is driven by far‐field perturbations in the glacier's force balance, in this case generated by variations in basal hydrology near the glacier's terminus and propagated tens of kilometers upstream through transient basal lubrication longitudinal coupling.

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Section: Discussionmentioning

confidence: 65%

Section: Discussionmentioning

confidence: 99%

Physical Conditions of Fast Glacier Flow: 3. Seasonally‐Evolving Ice Deformation on Store Glacier, West Greenland

et al. 2019

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“…High discharge into moulins from supraglacial streams (Smith et al, ) are particularly important in the LG catchment at lower elevations (Clason et al, ). Above 1,000 m, supraglacial lake drainage events become increasingly important (Clason et al, ), and Q rates can change rapidly when supraglacial lakes drain from the ablation zone during the outburst period (i.e., outburst events) (Bartholomew et al, ; Christoffersen et al, ). These drainage events are characterized by rapid changes in SPM concentrations and SpC (Bartholomew et al, ), as stored waters at the bed are evacuated by incoming supraglacial water (Hatton et al, ), and thus may coincide with compositional changes in DOM in subglacial outflow.…”

Section: Discussionmentioning

confidence: 99%

Glacier Outflow Dissolved Organic Matter as a Window Into Seasonally Changing Carbon Sources: Leverett Glacier, Greenland

et al. 2020

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The Greenland Ice Sheet is losing mass at a remarkable rate as a result of climatic warming.This mass loss coincides with the export of dissolved organic matter (DOM) in glacial meltwaters. However, little is known about how the source and composition of exported DOM changes over the melt season, which is key for understanding its fate in downstream ecosystems. Over the 2015 ablation season, we sampled the outflow of Leverett Glacier, a large land-terminating glacier of the Greenland Ice Sheet. Dissolved organic carbon (DOC) concentrations and DOM fluorescence were analyzed to assess the evolution of DOM sources over the course of the melt season. DOC concentrations and red-shifted fluorescence were highly associated (R 2 > 0.95) and suggest terrestrial inputs from overridden soils dominated DOM early season inputs before progressive dilution with increasing discharge. During the outburst period, supraglacial drainage events disrupted the subglacial drainage system and introduced dominant protein-like fluorescence signatures not observed in basal flow. These results suggest that subglacial hydrology and changing water sources influence exported DOC concentration and DOM composition, and these sources were differentiated using fluorescence characteristics. Red-shifted fluorescence components were robust proxies for DOC concentration. Finally, the majority of DOM flux, which occurs during the outburst and postoutburst periods, was characterized by protein-like fluorescence from supraglacial and potentially subglacial microbial sources. As protein-like fluorescence is linked to the bioavailability of DOM, the observed changes likely reflect seasonal variations in the impact of glacial inputs on secondary production in downstream ecosystems due to shifting hydrologic regimes.

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“…• High-elevation firn-aquifer water drainage drives evolution of the subglacial hydrologic system >30 km inland, potentially affecting outlet glacier speed • Persistent input of water from firn aquifers can maintain subglacial channels outside the melt season and across years • The timing and duration of firn-aquifer water delivery to the bed is an important but underconstrained variable in ice sheet hydrology Firn aquifers currently occupy areas low in the accumulation zone around much of the Greenland Ice Sheet (Miège et al, 2016), with inland expansion anticipated in future warm climates . If new surface-to-bed connections are made at inland locations, the subsequent evolution of the subglacial hydrologic system may alter ice dynamics (e.g., Bartholomew et al, 2011b;Christoffersen et al, 2018;Clason et al, 2015;Doyle et al, 2014;Poinar et al, 2015). Here, we implement a modeling study whereby a series of idealized scenarios drain surface water to the bed at low-elevation locations and at higher elevations through the downstream end of a firn aquifer.…”

Section: 1029/2019gl082786mentioning

confidence: 99%

Long‐Term Support of an Active Subglacial Hydrologic System in Southeast Greenland by Firn Aquifers

Poinar

Dow

Andrews

2019

Geophysical Research Letters

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The state of the subglacial hydrologic system, which can modify ice motion, is sensitive to the volume and rate of meltwater reaching it. Bare‐ice regions rapidly transport meltwater to the bed via moulins, while in certain accumulation zone regions, meltwater first flows through firn aquifers, which can introduce a substantial delay. We use a subglacial hydrological model forced with idealized meltwater input scenarios to test the effect of this delay on subglacial hydrology. We find that addition of firn‐aquifer water to the subglacial system elevates the inland subglacial water pressure while reducing water pressure and enhancing subglacial channelization near the terminus. This effect dampens seasonal variations in subglacial water pressure and may explain regionally anomalous ice velocity patterns observed in Southeast Greenland. As surface melt rates increase and firn aquifers expand inland, it is crucial to understand how inland drainage of meltwater affects the evolution of the subglacial hydrologic system.

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Cascading lake drainage on the Greenland Ice Sheet triggered by tensile shock and fracture

Cited by 62 publications

References 59 publications

Physical Conditions of Fast Glacier Flow: 3. Seasonally‐Evolving Ice Deformation on Store Glacier, West Greenland

Physical Conditions of Fast Glacier Flow: 3. Seasonally‐Evolving Ice Deformation on Store Glacier, West Greenland

Glacier Outflow Dissolved Organic Matter as a Window Into Seasonally Changing Carbon Sources: Leverett Glacier, Greenland

Long‐Term Support of an Active Subglacial Hydrologic System in Southeast Greenland by Firn Aquifers

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