Heat sources within the Greenland Ice Sheet: dissipation, temperate paleo-firn and cryo-hydrologic warming

Lüthi, Martin P.; Ryser, Claudia; Andrews, Lauren C.; Catania, G. A.; Funk, Martin; Hawley, R. L.; Hoffman, Matthew J.; Neumann, T.

doi:10.5194/tc-9-245-2015

Cited by 61 publications

(98 citation statements)

References 34 publications

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“…Increased flow velocity and strain rates cause more heat to be generated englacially bringing cold ice near the bed to the melting temperature as noted in earlier modeling studies (Pohjola and Hedfors, 2003;Lüthi et al, 2015) and in conceptual models (Krabbendam, 2016). This strain heating effect is shown in Fig.…”

Section: Basal Conditionsmentioning

confidence: 49%

Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum

Cohen¹,

Gillet-Chaulet²,

Haeberli³

et al. 2017

Preprint

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Abstract. At the Last Glacial Maximum (LGM), the Rhine glacier in the Swiss Alps covered an area of about 16,000 km 2 .As part of an integrative study about the safety of repositories for radioactive waste under ice age conditions in Switzerland, we modeled the Rhine glacier using a fully-coupled, three-dimensional, transient, thermo-mechanical Stokes flow model down to a horizontal resolution of about 500 m. The accumulation and ablation gradients that roughly reproduced the geomorphic reconstructions of glacial extent and ice thickness suggested extremely cold (T July ∼ 0 • C at the glacier terminus) and dry (∼ 10 5 to 20% of today's precipitation) climatic conditions. Forcing the numerical simulations with warmer and wetter conditions that better matched LGM climate proxy records yielded a glacier on average 500 to 700 m thicker than geomorphic reconstructions.Mass balance gradients also controlled ice velocities, fluxes, and sliding speeds. These gradients, however, had only a small effect on basal conditions. All simulations indicated that basal ice reached the pressure melting point over much of the Rhine and Linth piedmont lobes, and also in the glacial valleys that fed these lobes. Only the outer margin of the lobes, bedrock highs ). In the lobes, despite low surface slopes and low basal shear stresses, sliding dictated main fluxes of ice which closely followed bedrock topography: ice was channeled in between bedrock highs along troughs, some of which coincided with glacially eroded overdeepenings. These sliding conditions may have favored glacial erosion by abrasion and quarrying. 20Our results confirmed general earlier findings but provided more insights into the detailed flow and basal conditions of the Rhine glacier at the LGM. Our model results suggested that the trimline could have been buried by a significant thickness of cold ice. These findings have significant implications for interpreting trimlines in the Alps and for our understanding of ice-climate interactions.

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Section: Basal Conditionsmentioning

confidence: 49%

Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum

Cohen¹,

Gillet-Chaulet²,

Haeberli³

et al. 2017

Preprint

View full text Add to dashboard Cite

show abstract

“…The temperate basal ice layer is thickest in the Rhine valley below the Sargans diffluence, probably because of flow constriction associated with the valley width and due to higher viscous strain heating there. Increased flow velocity and strain rates cause more heat to be generated englacially, bringing cold ice near the bed to the melting temperature as noted in earlier modeling studies (Pohjola and Hedfors, 2003;Lüthi et al, 2015) and in conceptual models (Krabbendam, 2016). This strain heating effect is shown in Fig.…”

Section: Basal Conditionsmentioning

confidence: 58%

Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum

et al. 2018

View full text Add to dashboard Cite

Abstract. At the Last Glacial Maximum (LGM), the Rhine glacier in the Swiss Alps covered an area of about 16 000 km 2 . As part of an integrative study about the safety of repositories for radioactive waste under ice age conditions in Switzerland, we modeled the Rhine glacier using a thermodynamically coupled three-dimensional, transient Stokes flow and heat transport model down to a horizontal resolution of about 500 m. The accumulation and ablation gradients that roughly reproduced the geomorphic reconstructions of glacial extent and ice thickness suggested extremely cold (T July ∼ 0 • C at the glacier terminus) and dry (∼ 10 % to 20 % of today's precipitation) climatic conditions. Forcing the numerical simulations with warmer and wetter conditions that better matched LGM climate proxy records yielded a glacier on average 500 to 700 m thicker than geomorphic reconstructions. Mass balance gradients also controlled ice velocities, fluxes, and sliding speeds. These gradients, however, had only a small effect on basal conditions. All simulations indicated that basal ice reached the pressure melting point over much of the Rhine and Linth piedmont lobes, and also in the glacial valleys that fed these lobes. Only the outer margin of the lobes, bedrock highs beneath the lobes, and Alpine valleys at high elevations in the accumulation zone remained cold based. The Rhine glacier was thus polythermal. Sliding speed estimated with a linear sliding rule ranged from 20 to 100 m a −1 in the lobes and 50 to 250 m a −1 in Alpine valleys. Velocity ratios (sliding to surface speeds) were > 80 % in lobes and ∼ 60 % in valleys. Basal shear stress was very low in the lobes (0.03-0.1 MPa) and much higher in Alpine valleys (> 0.2 MPa). In these valleys, viscous strain heating was a dominant source of heat, particularly when shear rates in the ice increased due to flow constrictions, confluences, or flow past large bedrock obstacles, contributing locally up to several watts per square meter but on average 0.03 to 0.2 W m −2 . Basal friction acted as a heat source at the bed of about 0.02 W m −2 , 4 to 6 times less than the geothermal heat flow which is locally high (up to 0.12 W m −2 ). In the lobes, despite low surface slopes and low basal shear stresses, sliding dictated main fluxes of ice, which closely followed bedrock topography: ice was channeled in between bedrock highs along troughs, some of which coincided with glacially eroded overdeepenings. These sliding conditions may have favored glacial erosion by abrasion and quarrying. Our results confirmed general earlier findings but provided more insights into the detailed flow and basal conditions of the Rhine glacier at the LGM. Our model results suggested that the trimline could have been buried by a significant thickness of cold ice. These findings have significant implications for interpreting trimlines in the Alps and for our understanding of ice-climate interactions.

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“…The increased meltwater being generated at the ice sheet surface and draining subsequently into the ice has the potential to warm the ice that is in close proximity to water flowing through or filling moulins and crevasses [122] and being routed at the ice bed interface. It is unclear whether this increased meltwater will result in a significant rise in ice temperatures and thus deformation and flow rates [123], or will instead be of negligible importance to longer term ice dynamics [124].…”

Section: Cryo-hydrologic Warmingmentioning

confidence: 99%

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

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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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Heat sources within the Greenland Ice Sheet: dissipation, temperate paleo-firn and cryo-hydrologic warming

Cited by 61 publications

References 34 publications

Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum

Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum

Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum

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

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