scholarly journals Mapping thermal and hydrological conditions beneath a polythermal glacier with radio-echo sounding

2001 ◽  
Vol 47 (157) ◽  
pp. 232-242 ◽  
Author(s):  
Luke Copland ◽  
Martin Sharp
Keyword(s):  
Thermal Structure ◽  
Basal Layer ◽  
Equipotential Surface ◽  
High Arctic ◽  
Hydrological Conditions ◽  
Glacier Terminus ◽  
Radio Echo Sounding ◽  
Pressure Melting ◽  
Polythermal Glacier ◽  
Echo Sounding

AbstractSpatial patterns in residual bed reflection power (BRPr), derived from ground-based radio-echo sounding, were mapped and interpreted in terms of the thermal and hydrological conditions at the base of a high-Arctic polythermal glacier (John Evans Glacier, Ellesmere Island, Canada). BRPr is the residual from a statistical relationship between measured bed reflection power and ice thickness that describes the rate of dielectric loss with depth in the glacier. We identified three types of thermal structure: (a) Positive BRPr and an internal reflecting horizon occur over the glacier terminus. The reflecting horizon is interpreted as the boundary between warm and cold ice, and suggests the presence of a warm basal layer. (b) Positive BRPr occurs without an internal reflector in the upper part of the ablation zone. This suggests that ice is at the pressure-melting point only at the bed. (c) Negative BRPr without an internal reflector occurs in all other regions, suggesting cold ice at the bed. Where BRPr is positive, its pattern is similar to the pattern of subglacial water flow predicted from the form of the subglacial hydraulic equipotential surface. This suggests that hydrological conditions at the glacier bed are a major control on BRPr, probably because the dielectric contrast between ice and water is higher than that between ice and other subglacial materials.

scholarly journals The distribution of basal motion beneath a High Arctic polythermal glacier

2003 ◽  
Vol 49 (166) ◽  
pp. 407-414 ◽  
Author(s):  
Luke Copland ◽  
Martin J. Sharp ◽  
Peter Nienow ◽  
Robert G. Bingham
Keyword(s):  
High Arctic ◽  
Early Summer ◽  
Ellesmere Island ◽  
Surface Velocity ◽  
Ablation Area ◽  
Radio Echo Sounding ◽  
Longitudinal Pattern ◽  
Polythermal Glacier ◽  
Meltwater Chemistry ◽  
Echo Sounding

AbstractThe 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.

scholarly journals Factors influencing the basal temperatures of a High Arctic polythermal glacier

2009 ◽  
Vol 50 (52) ◽  
pp. 9-16 ◽  
Author(s):  
Trudy Wohlleben ◽  
Martin Sharp ◽  
Andrew Bush
Keyword(s):  
Thermal Characteristics ◽  
High Arctic ◽  
Ice Thickness ◽  
Temperature Model ◽  
Canadian High Arctic ◽  
Basal Ice ◽  
Air Temperatures ◽  
Modelling Studies ◽  
Pressure Melting ◽  
Polythermal Glacier

AbstractA number of glaciers in the Canadian High Arctic are composed primarily of cold ice, but the ice at or near their beds reaches the pressure-melting point (PMP) in the ablation zone. Past modelling studies have suggested that the basal temperatures of some of these glaciers reach the PMP where they should not, indicating that they are not in thermal equilibrium with present-day surface air temperatures. To investigate the possible reasons for thermal disequilibria in such glaciers, a two-dimensional ice temperature model was used to simulate the inferred thermal characteristics of John Evans Glacier, Ellesmere Island. Results indicate that while surface refreezing and historical ice-thickness changes have had a warming effect upon basal ice temperatures, supraglacial meltwater reaching the glacier bed provides the single most critical heat source for explaining the apparent thermal disequilibrium between present-day inferred ice–bed temperatures and those modelled under present-day boundary conditions.

scholarly journals Enhancement of glacial solute fluxes in the proglacial zone of a polythermal glacier

2001 ◽  
Vol 47 (158) ◽  
pp. 378-386 ◽  
Author(s):  
J. L Wadham ◽  
R. J. Cooper ◽  
M. Tranter ◽  
R. Hodgkins
Keyword(s):  
Active Layer ◽  
Chemical Weathering ◽  
High Arctic ◽  
Weathering Rate ◽  
Glacier Terminus ◽  
Solute Fluxes ◽  
Solute Acquisition ◽  
Polythermal Glacier ◽  
Arctic Glacier ◽  
Chemical Weathering Rate

AbstractAnnual proglacial solute fluxes and chemical weathering rates at a polythermal high-Arctic glacier are presented. Bulk meltwater chemistry and discharge were monitored continuously at gauging stations located at the eastern and western margins of the glacier terminus and at “the Outlet”, 2.5 km downstream where meltwaters discharge into the fjord. Fluxes of non-snowpack HCO3−, SO42−, Ca2+ and Mg2+ increase by 30–47% between the glacier terminus and the Outlet, indicating that meltwaters are able to access and chemically weather efflorescent sulphates, carbonates and sulphides in the proglacial zone. Smaller increases in the fluxes of non-snowpack-derived Na+, K+ and Si indicate that proglacial chemical weathering of silicates is less significant. En3hanced solute fluxes in the proglacial zone are mainly due to the chemical weathering of active-layer sediments. The PCO2 of active-layer ground-waters is above atmospheric pressure. This implies that solute acquisition in the active layer involves no drawdown of CO2. The annual proglacial chemical weathering rate in 1999 is calculated to be 2600 meqΣ+ m−2. This exceeds the chemical weathering rate for the glaciated part of the catchment (790 meqΣ+ m−2) by a factor of 3.3. Hence, the proglacial zone at Finster-walderbreen is identified as an area of high geochemical reactivity and a source of CO2.

scholarly journals Radio Echo-Sounding of Spitsbergen Glaciers: Problems in the Interpretation of Layer and Bottom Returns

1984 ◽  
Vol 30 (104) ◽  
pp. 16-21 ◽  
Author(s):  
J. A. Dowdeswell ◽  
D.J. Drewry ◽  
O. Liestøl ◽  
O. Orheim
Keyword(s):  
Melting Point ◽  
Water Content ◽  
Ice Thickness ◽  
Drill Core ◽  
Ice Cap ◽  
Radio Echo Sounding ◽  
Pressure Melting ◽  
Radio Frequencies ◽  
Similar Depth ◽  
Echo Sounding

AbstractAirborne radio echo-sounding of Spitsbergen glaciers during 1980 used 60 MHz SPR1 Mk IV equipment. On several glaciers results showed unambiguous bottom returns at depths 2–3 times those reported in previous Soviet echo-sounding at 440 and 620 MHz. Comparison of 60 MHZ records and independent gravity-surveyed ice thickness for two glaciers agreed to within 10%, whereas Soviet ice thicknesses were only 30–60% of gravity depths. Soviet bed echoes often coincided closely with an internal reflecting horizon recorded by the SPRI Mk IV system, and it is shown that Soviet U.H.F. equipment failed to penetrate to the true glacier bed on a number of ice masses (e.g. Finsterwalderbreen, Kongsvegen, Negribreen). This was probably due to increased absorption and scattering at higher radio frequencies, related to the inhomogeneous nature of Spitsbergen glaciers, which are often at or near the pressure-melting point. Both 60 MHz and U.H.F. equipment seldom recorded bed echoes in ice-cap accumulation areas (e.g. Isachsenfonna), where firn soaking during summer and 10 m temperatures of zero degrees have been observed. An isolated internal reflecting horizon was recorded on many glaciers. It is unlikely to be a moraine layer, but may be related to ice with a water content of 1–2% observed at a similar depth (115 m) in a drill core from Fridtjovbreen.

scholarly journals Hydrothermal structure of a polythermal glacier in Spitsbergen by measurements and numerical modeling

2016 ◽  
Vol 56 (2) ◽  
pp. 149-160 ◽  
Author(s):  
A. V. Sosnovsky ◽  
Yu. Ya. Macheret ◽  
A. F. Glazovsky ◽  
I. I. Lavrentiev
Keyword(s):  
Numerical Modeling ◽  
Snow Cover ◽  
Air Temperature ◽  
Lower Layer ◽  
Glacier Surface ◽  
Ablation Area ◽  
Radio Echo Sounding ◽  
Polythermal Glacier ◽  
Cover Thickness ◽  
Echo Sounding

Thickness of the upper cold ice layer in the ablation area of the polythermal glacier Grønfjordbreen (Spitsbergen) was estimated by means of numerical modeling. The results were compared with data of radio-echo sounding of the same glacier obtained in 1979 and 2012. Numerical experiments with changing water content in the lower layer of temperate ice and surface snow cover thickness made possible to compare calculated and modeled cold ice thicknesses and to estimate their changes for 33‑year period caused by regional climate change. According to data of radio-echo sounding, thickness of the cold ice layer decreased, on average, by 34 m. Numerical modeling shown similar results: the cold ice layer became thinner by 31 m and 39 m at altitudes 100–300 a.s.l. under the snow cover thickness of 1 m and 2 m. We explain this by rising of annual mean air temperature by 0,6 °С as compared to data of the nearest meteorological station Barentsburg in the same period. We believe that changes in cold ice layer thickness in polythermal glaciers can be used for estimation of changes in such regional climatic parameter as mean air temperature at different altitudes of the glacier surface in the ablation area.

scholarly journals Drainage system and thermal structure of a High Arctic polythermal glacier: Waldemarbreen, western Svalbard

2021 ◽  
pp. 1-14
Author(s):  
Jānis Karušs ◽  
Kristaps Lamsters ◽  
Ireneusz Sobota ◽  
Jurijs Ješkins ◽  
Pēteris Džeriņš ◽  
...  
Keyword(s):  
Thermal Structure ◽  
Drainage System ◽  
Radar Data ◽  
High Arctic ◽  
Ice Age ◽  
Water Drainage ◽  
Near Surface ◽  
Thermal Change ◽  
Polythermal Glacier ◽  
Surface Ice

Abstract Understanding glacier drainage system behaviour and its response to increased meltwater production faces several challenges in the High Arctic because many glaciers are transitioning from polythermal to almost entirely cold thermal structures. We, therefore, used ground-penetrating radar data to investigate the thermal structure and drainage system of Waldemarbreen in Svalbard: a small High Arctic glacier believed to be undergoing thermal change. We found that Waldemarbreen retains up to 80 m of temperate ice in its upper reaches, but this thickness most likely is a relict from the Little Ice Age when greater ice volumes were insulated from winter cooling and caused greater driving stresses. Since then, negative mass balance and firn loss have prevented latent heat release and allowed near-surface ice temperatures to cool in winter, thus reducing the thickness of the temperate ice. Numerous reflectors that can be traced up-glacier are interpreted as englacial channels formed by hydrofracturing in the crevassed upper region of the glacier. The alternative cut and closure mechanism of conduit initiation only forms conduits in parts of the lower ablation area. Consequently, Waldemarbreen provides evidence that hydrofracturing at higher elevations can play a major role in englacial water drainage through cold ice.

scholarly journals Comparison of radio-echo sounding (30–1000 MHz) and high-resolution borehole-temperature measurements at Finsterwalderbreen, southern Spitsbergen, Svalbard

1997 ◽  
Vol 24 ◽  
pp. 262-267 ◽  
Author(s):  
R. S. Ødegård ◽  
J. O. Hagen ◽  
S. -E. Hamranw
Keyword(s):  
High Resolution ◽  
Thermal Structure ◽  
Temperature Measurements ◽  
Relative Amplitude ◽  
Ice Flow ◽  
Radio Echo Sounding ◽  
Glacier Ice ◽  
Pressure Melting ◽  
Reflected Signal ◽  
Borehole Temperature

Radio-echo soundings in four different frequency bands ranging from 30 to 1000 MHz were compared with temperature measurements in boreholes in the accumulation area and ablation area of Finsterwalderbreen (77°26′ N, 15°15′ E), southern Spitsbergen. Finsterwalderbreen is a polythermal surge-type glacier in the quiescent phase after its last surge around AD 1900. The objective of the study was to investigate the relation between internal echos and the glacier ice temperature to map the overall thermal structure of the glacier. The thermal structure is important for ice flow velocities and hydrology of glaciers, and it also affects their ability to surge. At the borehole site in the accumulation area (three boreholes within a range of 60 m), a change in the relative amplitude of the reflected signal is detected in the 320–370 and 600–650 MHz bands at 52–55 m depth. The high-resolution temperature measurements with 2 m intervals show that the transition zone between cold and temperate ice corresponds to the change in the relative amplitude on the 320–370 and 600–650 MHz bandwidth data. The overall thermal structure of the glacier was mapped based on the radar sounding. The radar results show (a) that the glacier is at the pressure-melting point over most of its bed except within 500–700 m of the terminus, and (b) that there is an upper cold ice layer of variable thickness (25–170 m) underlain by temperate ice. This thermal structure is confirmed by the thermistor-instrumented access holes to the bed in both the accumulation and ablation zones of the glacier. The variations in the thermal structure in lower parts of the accumulation area are explained by superimposed ice and ice layers that cause variations in the downward heat transfer by refreezing of meltwater.

scholarly journals Thermal structure and drainage system of a small valley glacier (Tellbreen, Svalbard), investigated by Ground Penetrating Radar

2010 ◽  
Vol 4 (4) ◽  
pp. 2169-2199
Author(s):  
K. Bælum ◽  
D. I. Benn
Keyword(s):  
Ground Penetrating Radar ◽  
Thermal Structure ◽  
Drainage System ◽  
High Arctic ◽  
Differential Gps ◽  
Glacier Surface ◽  
Drainage Channels ◽  
Polythermal Glacier ◽  
Ground Penetrating ◽  
Subglacial Drainage

Abstract. Proglacial icings accumulate in front of many High Arctic glaciers during the winter months, as water escapes from englacial or subglacial storage. Such icings have been interpreted as evidence for warm-based subglacial conditions, but several are now known to occur in front of cold-based glaciers. In this study, we investigate the drainage system of Tellbreen, a 3.5 km long cold-based polythermal glacier in central Spitsbergen, where a large proglacial icing develops each winter, to determine the location and geometry of storage elements. DEMs of the glacier surface and bed were constructed using maps, differential GPS and GPR. Patterns of surface lowering indicate that the glacier has a long-term mass balance of −0.6 ± 0.2 m/year. Englacial and subglacial drainage channels were mapped using Ground penetrating radar (GPR), showing that Tellbreen has a diverse drainage system that is capable of storing, transporting and releasing water year round. In the upper part of the glacier, drainage is mainly via supraglacial channels. These transition downglacier into shallow englacial "cut and closure" channels, formed by the incision and closure of supraglacial channels. Below thin ice near the terminus, these channels reach the bed and contain stored water throughout the winter months. Even though the bed is below pressure-melting point, Tellbreen has a surface-fed, channelized subglacial drainage system, which allows significant storage and delayed discharge.

scholarly journals Comparison of measurements from different radio-echo sounding systems and synchronization with the ice core at Dome C, Antarctica

2017 ◽  
Vol 11 (1) ◽  
pp. 653-668 ◽  
Author(s):  
Anna Winter ◽  
Daniel Steinhage ◽  
Emily J. Arnold ◽  
Donald D. Blankenship ◽  
Marie G. P. Cavitte ◽  
...  
Keyword(s):  
Ice Core ◽  
Basal Layer ◽  
Radar Data ◽  
Sensitivity Study ◽  
Data Set ◽  
Range Resolution ◽  
Radio Echo Sounding ◽  
Conductivity Profile ◽  
The Individual ◽  
Echo Sounding

Abstract. We present a compilation of radio-echo sounding (RES) measurements of five radar systems (AWI, BAS, CReSIS, INGV and UTIG) around the EPICA Dome C (EDC) drill site, East Antarctica. The aim of our study is to investigate the differences of the various systems in their resolution of internal reflection horizons (IRHs) and bed topography, penetration depth and capacity of imaging the basal layer. We address the questions of the compatibility of existing radar data for common interpretation and the suitability of the individual systems for reconnaissance surveys. We find that the most distinct IRHs and IRH patterns can be identified and transferred between most data sets. Considerable differences between the RES systems exist in range resolution and depiction of the bottom-most region. Considering both aspects, which we judge as crucial factors in the search for old ice, the CReSIS and the UTIG systems are the most suitable ones. In addition to the RES data set comparison we calculate a synthetic radar trace from EDC density and conductivity profiles. We identify 10 common IRHs in the measured RES data and the synthetic trace. We then conduct a sensitivity study for which we remove certain peaks from the input conductivity profile. As a result the respective reflections disappear from the modeled radar trace. In this way, we establish a depth conversion of the measured travel times of the IRHs. Furthermore, we use these sensitivity studies to investigate the cause of observed reflections. The identified IRHs are assigned ages from the EDC's timescale. Due to the isochronous character of these conductivity-caused IRHs, they are a means to extend the Dome C age structure by tracing the IRHs along the RES profiles.

scholarly journals Radio Echo-Sounding of Spitsbergen Glaciers: Problems in the Interpretation of Layer and Bottom Returns

1984 ◽  
Vol 30 (104) ◽  
pp. 16-21 ◽  
Author(s):  
J. A. Dowdeswell ◽  
D.J. Drewry ◽  
O. Liestøl ◽  
O. Orheim
Keyword(s):  
Melting Point ◽  
Water Content ◽  
Ice Thickness ◽  
Drill Core ◽  
Ice Cap ◽  
Radio Echo Sounding ◽  
Pressure Melting ◽  
Radio Frequencies ◽  
Similar Depth ◽  
Echo Sounding

AbstractAirborne radio echo-sounding of Spitsbergen glaciers during 1980 used 60 MHz SPR1 Mk IV equipment. On several glaciers results showed unambiguous bottom returns at depths 2–3 times those reported in previous Soviet echo-sounding at 440 and 620 MHz. Comparison of 60 MHZ records and independent gravity-surveyed ice thickness for two glaciers agreed to within 10%, whereas Soviet ice thicknesses were only 30–60% of gravity depths. Soviet bed echoes often coincided closely with an internal reflecting horizon recorded by the SPRI Mk IV system, and it is shown that Soviet U.H.F. equipment failed to penetrate to the true glacier bed on a number of ice masses (e.g. Finsterwalderbreen, Kongsvegen, Negribreen). This was probably due to increased absorption and scattering at higher radio frequencies, related to the inhomogeneous nature of Spitsbergen glaciers, which are often at or near the pressure-melting point. Both 60 MHz and U.H.F. equipment seldom recorded bed echoes in ice-cap accumulation areas (e.g. Isachsenfonna), where firn soaking during summer and 10 m temperatures of zero degrees have been observed. An isolated internal reflecting horizon was recorded on many glaciers. It is unlikely to be a moraine layer, but may be related to ice with a water content of 1–2% observed at a similar depth (115 m) in a drill core from Fridtjovbreen.

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