Seasonal Surface-Velocity Variations on a Sub-Polar Glacier in West Greenland

Andreasen, Jørn-Ole

doi:10.1017/s0022143000006651

Cited by 20 publications

(5 citation statements)

References 13 publications

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“…Our study has also shown that the presence of a large region of cold basal ice in the lower tongue acts as an important sticky spot, and has a damming effect which results in high subglacial water pressures upglacier of the dam, and thus high velocities here. Similar, tentative conclusions were reached on the polythermal Kitdlerssuaq Glacier, West Greenland, where summer velocity increases in the upper ablation area were attributed to high basal water pressures caused by the backing-up of meltwater at the bed, due to inefficient drainage in the ablation area (Andreasen, 1985). Work on John Evans Glacier also highlights the importance of the thermal dam on the flow of basal water in controlling surface velocity patterns on polythermal glaciers (Copland and others, 2003).…”

Section: Discussionmentioning

confidence: 62%

“…The few studies that have been undertaken suggest that seasonal and intra-seasonal surface velocity variations occur, although the precise mechanisms responsible are not known (e.g. Iken, 1974;Andreasen, 1985;Rabus and Echelmeyer, 1997;Copland and others, 2003). At John Evans Glacier, Ellesmere Island, Canada, seasonal surface velocity variations are due to surface water reaching the glacier bed in summer, and intra-seasonal variations reflect short-term variations in surface water inputs to the subglacial drainage system (Copland and others, 2003).…”

Section: Introductionmentioning

confidence: 99%

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Spatial and temporal variations in surface velocity and basal drag across the tongue of the polythermal glacier midre Lovénbreen, Svalbard

Rippin¹,

Willis²,

Arnold³

et al. 2005

J. Glaciol.

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We present results of a detailed investigation of surface motion across the tongue of a polythermal glacier, midre Lovénbreen, Svalbard, during the 1999 summer. Surface velocities in the warm-based upper tongue increased during periods of enhanced surface melting and rainfall events, and force-balance analysis indicates that these velocity variations were locally forced, probably by fluctuations in subglacial water pressure. Surface speed-ups were also observed on the cold-based lower tongue (which acted as a sticky spot, through which there was minimal subglacial drainage for most of the summer), but these were largely non-locally forced by longitudinal coupling to the faster-moving ice up-glacier. On one occasion, however, a large, rapid input of surface water to the glacier reduced the basal drag beneath the cold-based lower tongue, presumably due to hydraulic jacking. This resulted in locally forced enhanced surface velocities across the entire tongue, accompanied by a breaching of the lower tongue and an outburst of subglacially stored water.

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Section: Discussionmentioning

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Spatial and temporal variations in surface velocity and basal drag across the tongue of the polythermal glacier midre Lovénbreen, Svalbard

Rippin¹,

Willis²,

Arnold³

et al. 2005

J. Glaciol.

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“…For example, Andreasen (1985) observed seasonal velocity fluctuations at Kitdlerssuaq Glacier, West Greenland, and Zwally and others (2002) observed similar variations on the Greenland ice sheet at a location where cold ice was 41200 m thick. Iken (1974) found a strong relationship between short-term summer velocity increases and water pressures in nearby moulins at White Glacier, Axel Heiberg Island, Canada.…”

Section: Introductionmentioning

confidence: 76%

The distribution of basal motion beneath a High Arctic polythermal glacier

Copland¹,

Sharp²,

Nienow

et al. 2003

J. Glaciol.

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The longitudinal pattern of surface velocity of a large, predominantly cold, polythermal glacier (John Evans Glacier, Ellesmere Island, Canada) was measured over summer and winter periods. In the accumulation and upper ablation areas, where ice is predominantly cold-based, summer velocities were slightly higher than overwinter velocities. Predicted velocities due to ice deformation alone in these areas closely matched these observations in the winter, with limited basal motion likely in the summer. In the lower ablation area, where ice is likely warm-based, measured summer velocities were up to double overwinter velocities. Predicted ice deformation could not account for all of these measured velocities in either summer or winter. This suggests that basal motion occurs throughout the year over at least part of the lower ablation area. This finding is supported by radio-echo sounding, subglacial drainage reconstructions and analyses of early-summer meltwater chemistry, which suggest that subglacial water is present throughout the year in this region. In summer, basal motion may account for up to 75% of the total surface velocity throughout the lower ablation area. The inferred rate of basal motion increases sharply directly below a set of moulins by which most surface meltwater reaches the glacier bed.

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“…Subglacial discharge is confined near the bottom of the glacier where the input of freshwater is likely to have the largest impact on the fjord dynamics. It is also consistent with the notion that the bulk of the seasonal surface runoff is discharged at the base of the glacier through a series of drainage channels [ Andreasen , ; Zwally et al ., ; Das et al ., ; Catania et al ., ].…”

Section: Model Setupmentioning

confidence: 99%

Seasonal variability of submarine melt rate and circulation in an East Greenland fjord

et al. 2013

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[1] The circulation in a glacial fjord driven by a large tidewater glacier is investigated using a nonhydrostatic ocean general circulation model with a melt rate parameterization at the vertical glacier front. The model configuration and water properties are based on data collected in Sermilik Fjord near Helheim Glacier, a major Greenland outlet glacier. The approximately two-layer stratification of the fjord's ambient waters causes the meltwater plume at the glacier front to drive a "double cell" circulation with two distinct outflows, one at the free surface and one at the layers' interface. In summer, the discharge of surface runoff at the base of the glacier (subglacial discharge) causes the circulation to be much more vigorous and associated with a larger melt rate than in winter. The simulated "double cell" circulation is consistent, in both seasons, with observations from Sermilik Fjord. Seasonal differences are also present in the vertical structure of the melt rate, which is maximum at the base of the glacier in summer and at the layers' interface in winter. Simulated submarine melt rates are strongly sensitive to the amount of subglacial discharge, to changes in water temperature, and to the height of the layers. They are also consistent with those inferred from simplified one-dimensional models based on the theory of buoyant plumes. Our results also indicate that to correctly represent the dynamics of the meltwater plume, care must be taken in the choice of viscosity and diffusivity values in the model. Citation: Sciascia, R., F. Straneo, C. Cenedese, and P. Heimbach (2013), Seasonal variability of submarine melt rate and circulation in an East Greenland fjord,

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Seasonal Surface-Velocity Variations on a Sub-Polar Glacier in West Greenland

Cited by 20 publications

References 13 publications

Spatial and temporal variations in surface velocity and basal drag across the tongue of the polythermal glacier midre Lovénbreen, Svalbard

Spatial and temporal variations in surface velocity and basal drag across the tongue of the polythermal glacier midre Lovénbreen, Svalbard

The distribution of basal motion beneath a High Arctic polythermal glacier

Seasonal variability of submarine melt rate and circulation in an East Greenland fjord

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