scholarly journals Variability in ice motion and dynamic discharge from Devon Ice Cap, Nunavut, Canada

2017 ◽  
Vol 63 (239) ◽  
pp. 436-449 ◽  
Author(s):  
WESLEY VAN WYCHEN ◽  
JAMIE DAVIS ◽  
LUKE COPLAND ◽  
DAVID O. BURGESS ◽  
LAURENCE GRAY ◽  
...  
Keyword(s):  
Feature Tracking ◽  
Ice Thickness ◽  
Tidewater Glaciers ◽  
Bed Topography ◽  
Ice Cap ◽  
The North ◽  
Landsat 7 ◽  
Devon Ice Cap ◽  
Dynamic Discharge ◽  
Observation Period

ABSTRACTFeature tracking of approximately annually separated Landsat-7 ETM+ imagery acquired from 1999 to 2010 and speckle tracking of 24-day separated RADARSAT-2 imagery acquired from 2009 to 2015 reveal that motion of the major tidewater glaciers of Devon Ice Cap is more variable than previously described. The flow of almost half (six of 14) of the outlet glaciers slowed over the observation period, while that of the terminus regions of three of 14 of the glaciers sped up in the most recent years of observation. The North Croker Bay Glacier of southern Devon Ice Cap showed the greatest variability in motion, oscillating between multi-year (three or more) periods of slower and faster flow and exhibited a pattern of velocity variability that is different from that of the rest of the ice cap's outlet glaciers. Comparisons between areas of dynamic variability and glacier bed topography indicate that velocity variability is largely restricted to regions where the glacier bed is grounded below sea level. Derived velocities are combined with measurements of ice thickness at the fronts of tidewater glacier to determine a mean annual (2009; 2011–15) dynamic ice discharge of 0.41 ± 0.11 Gt a−1for Devon Ice Cap. The Belcher Glacier is becoming a larger source of mass loss via ice discharge.

scholarly journals A 40 Year Record in an Ice Core from the Dunde Ice Cap, China (Abstract)

1988 ◽  
Vol 10 ◽  
pp. 221 ◽  
Author(s):  
Wu Xiaoling ◽  
Lonnie G. Thompson
Keyword(s):  
Oxygen Isotope ◽  
Ice Core ◽  
Field Work ◽  
Tibet Plateau ◽  
Ice Thickness ◽  
Ice Cap ◽  
Pulse Radar ◽  
The North ◽  
Isotope Profile ◽  
Isotope Content

A cooperative glacio-climatological ice-core drilling and analysis program, administered by LIGC and BPRC, has been carried out since 1984. The major objective of this study is to extract from the Dunde ice cap records of the general environmental conditions, which include drought, volcanic activity, moisture sources, glacier net balance and possibly temperature over the last 3000 years. In 1984 a group of 18 Chinese scientists and an American scientist spent 6 weeks on the Dunde ice cap. The central objective of their research was to evaluate the potential of the ice cap to yield a lengthy ice-core climate record. Results of the 1984 field work and 1985 laboratory analysis are submitted here. The Dunde ice cap (38°96′N, 96°24.5′E) is located in the north-eastern section of the Tibet plateau, China. Its length is 10.9 km; the width varies from 2.5 to 7.5 km. The total area of the ice cap is 57 km2. A 16 m core was drilled at the first site, located on a flat part of the ice cap, 5150 m a.s.l. A 10.2 m ice core was drilled at the ice cap summit (5300 m). A series of shallow cores and 2 m pits were excavated at each of the two sites and in the lower section of the ice cap. A mono-pulse radar unit was used to determine ice thickness. The ice thickness ranged between 94 and 167 m, with an average thickness of 140 m. Using a thermistor cable, minimum temperatures of −9.1° and −9.5 °C were measured in the 16 m hole and 10.2 m hole respectively. Microparticle analysis of the ice core from the Dunde ice cap revealed a very high dust content, on average 16 × 105 particles (≥0.63 to ≤16 μ in diameter) per ml of sample, i.e. 3−4 times higher than the microparticle content in the Quelccaya ice cap, Peru, and 100 times higher than in the core from Byrd Station, Antarctica. Oxygen-isotope content ranged between −12 and −14 per mil. Initially it was anticipated that the oxygen-isotope content would produce a more negative value in the Dunde ice cap. More work is required to explain the mechanism controlling δ18o variation in the ice core from the Dunde ice cap. The microparticles, oxygen-isotope content, conductivity, and tritium measurements, together with stratigraphy, temperature and density, are presented in the figures. The 40 year net-balance record reconstructed from the ice-core and oxygen-isotope profile is in good agreement with data from precipitation and major temperature trends obtained for the last 30 years from Delingha meteorological station, which is located 160 km south-east of the ice cap.

scholarly journals Helicopter-borne radio-echo sounding of Svartisen, Norway

1993 ◽  
Vol 17 ◽  
pp. 23-26 ◽  
Author(s):  
Michael Kennett ◽  
Tron Laumann ◽  
Cecilie Lund
Keyword(s):  
Low Frequency ◽  
Ice Thickness ◽  
Digital Receiver ◽  
Outlet Glacier ◽  
Northern Norway ◽  
Bed Topography ◽  
Ice Cap ◽  
Radio Echo Sounding ◽  
Depth Sounding ◽  
Ice Radar

A helicopter-mounted low frequency ice-radar has been developed for the depth sounding of temperate glaciers. The radar consists of standard transmitter and digital receiver equipment. The long antennae are supported on a special aluminium and fibreglass construction which hangs 20 m below the helicopter. The radar has been used on Engabreen, an outlet glacier of the Svartisen Ice Cap in northern Norway, where ice thicknesses of up to 350 m were obtained. The results have been used to construct a map of bed topography of the lower part of Engabreen. This map is largely consistent with ice thickness data obtained by drilling.

scholarly journals Equilibrium-Line Altitudes, Mass Balance, and July Freezing-Level Heights in the Canadian High Arctic

1975 ◽  
Vol 14 (71) ◽  
pp. 267-274 ◽  
Author(s):  
R. S. Bradley
Keyword(s):  
Mass Balance ◽  
High Arctic ◽  
Equilibrium Line ◽  
Canadian High Arctic ◽  
North West ◽  
Freezing Level ◽  
Ice Cap ◽  
The North ◽  
Devon Ice Cap ◽  
Axel Heiberg Island

Equilibrium-line altitudes on the White Glacier, Axel Heiberg Island, and the north-west sector of the Devon Ice Cap are shown to be closely related to mean July freezing-level heights at nearby upper-air weather stations. An inverse relationship between July freezing-level heights and mass balance on the Devon Ice Cap is also shown. Reasons for such correlations are suggested and some limitations of the relationship are outlined. Recent lowering of the freezing level in July is discussed in relation to the theoretical “steady-state” equilibrium-line altitudes in the Canadian high Arctic. It is suggested that positive mass-balance years have predominated over a large part of northern Ellesmere Island and north-central Axel Heiberg Island since 1963, and some glaciological evidence supporting this hypothesis is given.

scholarly journals Equilibrium-Line Altitudes, Mass Balance, and July Freezing-Level Heights in the Canadian High Arctic

1975 ◽  
Vol 14 (71) ◽  
pp. 267-274 ◽  
Author(s):  
R. S. Bradley
Keyword(s):  
Mass Balance ◽  
High Arctic ◽  
Equilibrium Line ◽  
Canadian High Arctic ◽  
North West ◽  
Freezing Level ◽  
Ice Cap ◽  
The North ◽  
Devon Ice Cap ◽  
Axel Heiberg Island

AbstractEquilibrium-line altitudes on the White Glacier, Axel Heiberg Island, and the north-west sector of the Devon Ice Cap are shown to be closely related to mean July freezing-level heights at nearby upper-air weather stations. An inverse relationship between July freezing-level heights and mass balance on the Devon Ice Cap is also shown. Reasons for such correlations are suggested and some limitations of the relationship are outlined. Recent lowering of the freezing level in July is discussed in relation to the theoretical “steady-state” equilibrium-line altitudes in the Canadian high Arctic. It is suggested that positive mass-balance years have predominated over a large part of northern Ellesmere Island and north-central Axel Heiberg Island since 1963, and some glaciological evidence supporting this hypothesis is given.

scholarly journals Linking surface hydrology to flow regimes and patterns of velocity variability on Devon Ice Cap, Nunavut

2015 ◽  
Vol 61 (226) ◽  
pp. 387-399 ◽  
Author(s):  
Faye R. Wyatt ◽  
Martin J. Sharp
Keyword(s):  
Drainage System ◽  
System Structure ◽  
Surface Velocity ◽  
Point Distribution ◽  
Drainage Systems ◽  
Ice Cap ◽  
Basal Sliding ◽  
Landsat 7 ◽  
Devon Ice Cap ◽  
Glacier Flow

AbstractSupraglacial meltwater reaching a glacier bed can increase ice surface velocities via hydraulic jacking and enhanced basal sliding. However, the relationships between the structure of supraglacial drainage systems, sink-point distributions, glacier flow processes and the magnitude of interannual velocity variability are poorly understood. To explore the hypothesis that spatial variations in the rate and mechanisms of glacier flow are linked to variations in supraglacial drainage system structure and sink-point distribution across an ice cap, we mapped supraglacial drainage systems on Devon Ice Cap from Landsat-7 ETM+ imagery. Spatial patterns of surface velocity and interannual velocity variability were determined using gradient correlation applied to Landsat-7 ETM+ images. Velocity variability is greater in areas close to sink-point locations, presumably because hydrologically forced basal sliding and/or bed deformation are enhanced in such areas. The distribution and characteristics of supraglacial drainage systems may play an important role in determining the distribution of regions of basal sliding, highlighting the need for knowledge of the supraglacial drainage system structure and sink-point distribution to inform efforts to model the dynamic response of Arctic ice caps to future climate warming.

scholarly journals Measurements of ice thickness on glaciers at Isortuarssûp tasia, southern West Greenland and Pâkitsoq, central West Greenland

1989 ◽  
Vol 145 ◽  
pp. 59-63
Author(s):  
L Thorning ◽  
E Hansen
Keyword(s):  
Short Distance ◽  
Ice Thickness ◽  
West Greenland ◽  
Ice Cap ◽  
North East ◽  
The North ◽  
Electromagnetic Resonance ◽  
Area North ◽  
Inland Ice ◽  
Ice Radar

Two separate geophysical projects were carried out in 1988 as part of glacier-hydrological investigations of the margin of the Inland Ice. We made a reconnaissance electromagnetic resonance survey over the ice margin adjacent to Sermilik and Isortuarssup tasia, south-east of Nuuk/Godthåb and measured ice thickness along some lines in the area of Qamanârssûp serrnia, Kangiata nunâta sermia and Kangaussarssup sermia a short distance to the north, as well as a few profiles over a local ice cap just east of Isortuarssup tasia. In the Pâkitsoq area, north east of Ilulissat/Jakobshavn, we finished the mono-pulse ice radar work started last year (Thorning & Hansen, 1988a).

scholarly journals Helicopter-borne radio-echo sounding of Svartisen, Norway

1993 ◽  
Vol 17 ◽  
pp. 23-26 ◽  
Author(s):  
Michael Kennett ◽  
Tron Laumann ◽  
Cecilie Lund
Keyword(s):  
Low Frequency ◽  
Ice Thickness ◽  
Digital Receiver ◽  
Outlet Glacier ◽  
Northern Norway ◽  
Bed Topography ◽  
Ice Cap ◽  
Radio Echo Sounding ◽  
Depth Sounding ◽  
Ice Radar

A helicopter-mounted low frequency ice-radar has been developed for the depth sounding of temperate glaciers. The radar consists of standard transmitter and digital receiver equipment. The long antennae are supported on a special aluminium and fibreglass construction which hangs 20 m below the helicopter. The radar has been used on Engabreen, an outlet glacier of the Svartisen Ice Cap in northern Norway, where ice thicknesses of up to 350 m were obtained. The results have been used to construct a map of bed topography of the lower part of Engabreen. This map is largely consistent with ice thickness data obtained by drilling.

scholarly journals A 40 Year Record in an Ice Core from the Dunde Ice Cap, China (Abstract)

1988 ◽  
Vol 10 ◽  
pp. 221-221
Author(s):  
Wu Xiaoling ◽  
Lonnie G. Thompson
Keyword(s):  
Oxygen Isotope ◽  
Ice Core ◽  
Field Work ◽  
Tibet Plateau ◽  
Ice Thickness ◽  
Ice Cap ◽  
Pulse Radar ◽  
The North ◽  
Isotope Profile ◽  
Isotope Content

A cooperative glacio-climatological ice-core drilling and analysis program, administered by LIGC and BPRC, has been carried out since 1984. The major objective of this study is to extract from the Dunde ice cap records of the general environmental conditions, which include drought, volcanic activity, moisture sources, glacier net balance and possibly temperature over the last 3000 years.In 1984 a group of 18 Chinese scientists and an American scientist spent 6 weeks on the Dunde ice cap. The central objective of their research was to evaluate the potential of the ice cap to yield a lengthy ice-core climate record. Results of the 1984 field work and 1985 laboratory analysis are submitted here.The Dunde ice cap (38°96′N, 96°24.5′E) is located in the north-eastern section of the Tibet plateau, China. Its length is 10.9 km; the width varies from 2.5 to 7.5 km. The total area of the ice cap is 57 km2. A 16 m core was drilled at the first site, located on a flat part of the ice cap, 5150 m a.s.l. A 10.2 m ice core was drilled at the ice cap summit (5300 m). A series of shallow cores and 2 m pits were excavated at each of the two sites and in the lower section of the ice cap.A mono-pulse radar unit was used to determine ice thickness. The ice thickness ranged between 94 and 167 m, with an average thickness of 140 m. Using a thermistor cable, minimum temperatures of −9.1° and −9.5 °C were measured in the 16 m hole and 10.2 m hole respectively.Microparticle analysis of the ice core from the Dunde ice cap revealed a very high dust content, on average 16 × 105 particles (≥0.63 to ≤16 μ in diameter) per ml of sample, i.e. 3−4 times higher than the microparticle content in the Quelccaya ice cap, Peru, and 100 times higher than in the core from Byrd Station, Antarctica. Oxygen-isotope content ranged between −12 and −14 per mil. Initially it was anticipated that the oxygen-isotope content would produce a more negative value in the Dunde ice cap. More work is required to explain the mechanism controlling δ18o variation in the ice core from the Dunde ice cap.The microparticles, oxygen-isotope content, conductivity, and tritium measurements, together with stratigraphy, temperature and density, are presented in the figures. The 40 year net-balance record reconstructed from the ice-core and oxygen-isotope profile is in good agreement with data from precipitation and major temperature trends obtained for the last 30 years from Delingha meteorological station, which is located 160 km south-east of the ice cap.

scholarly journals Interferometric discrimination of cross-track bed clutter in ice-penetrating radar sounding data

2020 ◽  
Vol 61 (81) ◽  
pp. 68-73 ◽  
Author(s):  
Kirk M. Scanlan ◽  
Anja Rutishauser ◽  
Duncan A. Young ◽  
Donald D. Blankenship
Keyword(s):  
Center Frequency ◽  
Adjacent Area ◽  
Bed Topography ◽  
Ice Cap ◽  
Digital Elevation ◽  
Interferometric Phase ◽  
Devon Ice Cap ◽  
Track Surface ◽  
Cross Track ◽  
Climate Studies

AbstractThe interpretations of relevant interfaces (i.e. the surface and bed) in radar sounding datasets over glaciers and ice sheets are primary boundary conditions in a variety of climate studies and particularly subglacial water routing models. It is therefore necessary to ensure these interpretations are consistent and not affected by cross-track clutter. For the surface interface, interferometry and a family of methods relying on digital elevation models have been used to successfully discriminate cross-track surface clutter. Here we present how interferometry can be applied to the problem of basal clutter from cross-track bed topography. Our approach is based on a comparison of the differential phases of ambiguous reflectors that may represent bed clutter and the differential phase of a reflector in an adjacent area that appears unaffected by basal clutter. The reflector yielding the smallest interferometric phase difference relative to the unambiguous bed reflector is considered to represent its consistent continuation. We successfully demonstrate our approach using 60 MHz center frequency MARFA data collected over Devon Ice Cap in the Canadian Arctic. Finally, we investigate the effects of clutter-affected and interferometry-corrected bed interpretations on ice layer thickness estimates, basal hydraulic head gradients and the potential extent of inferred subglacial water bodies.

scholarly journals Revisiting Austfonna, Svalbard with potential field methods – A new characterization of the bed topography and its physical properties

2019 ◽  
Author(s):  
Marie-Andrée Dumais ◽  
Marco Brönner
Keyword(s):  
Physical Properties ◽  
Potential Field ◽  
Gravity Data ◽  
Magnetic Data ◽  
Gravity Modeling ◽  
Airborne Gravity ◽  
Ice Thickness ◽  
Field Methods ◽  
Bed Topography ◽  
Ice Cap

Abstract. With hundreds of meters of ice, the bedrock underlying Austfonna, the largest ice cap on Svalbard, is hardly characterized in terms of topography and physical properties. Ground penetrating radar (GPR) measurements supply ice thickness estimation but the data quality is temperature-dependent, comprising uncertainties. To remedy this, we include airborne gravity measurements. With a significant density contrast between ice and bedrock, sub-glacial bed topography is effectively derived from gravity modeling. While the ice thickness model relies primarily on the gravity data, integrating airborne magnetic data provides an extra insight of the basement distribution. This contributes to refine the range of density expected under the ice and improve the sub-ice model. From this study, a prominent magmatic N-S oriented intrusion and the presence of carbonates are assessed. The results reveal the complexity of the sub-surface lithology characterized with different basement affinities. With the geophysical parameters of the bedrock determined, a new bed topography is extracted, adjusted for the potential field interpretation. When the results are compared to bed elevation maps previously produced by radio echo-sounding (RES) and GPR data, the discrepancies are pronounced where the RES and GPR data are scarce. Hence, areas with limited coverage are addressed with the potential field interpretation, increasing the accuracy of the overall bed topography. In addition, the methodology improves the understanding of the geology, assigns physical properties to the basements, and reveals the presence of softer bed, carbonates and magmatic intrusions under Austfonna which influence the basal sliding rates and surges.

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