scholarly journals Electrical Resistivity Profiles and Temperatures in the Ross Ice Shelf

1976 ◽  
Vol 16 (74) ◽  
pp. 307-308
Author(s):  
C.R. Bentley
Keyword(s):  
Electrical Resistivity ◽  
Computer Program ◽  
Depth Profile ◽  
Apparent Resistivity ◽  
Ice Shelf ◽  
Resistivity Measurements ◽  
Ross Ice Shelf ◽  
Field Season ◽  
A Site ◽  
Temperature Depth

AbstractDuring the 1973-74 Antarctic field season, two electrical resistivity profiles were completed along directions perpendicular to each other at a site in the south-easternpart of the Ross Ice Shelf. These profiles differ from each other only at short electrode spacings (less than 10 m) indicating no measurable horizontal anisotropy below the uppermost firn zone. The shape of the apparent resistivity curves is similar to that found by Hochstein on the Ross Ice Shelf near Roosevelt Island, but is displaced toward lower resistivities despite the colder 10 m temperature (—29°C instead of —26°C) at the more southerly site. Some factor other than temperature must therefore be effective in determining the overall magnitude of the resistivities in the shelf, although the variation with depth can still be expected to be primarily a temperature phenomenon.A computer program has been written to calculate apparent resistivities based on Crary’s analysis of temperatures in an ice shelf. Results are not yet available; when completed they should indicate the sensitivity of the resistivity measurements to differences in the temperature- depth profile, and hence their usefulness in estimating bottom melt/freeze rates.

scholarly journals Electrical Resistivity Profiles and Temperatures in the Ross Ice Shelf

1976 ◽  
Vol 16 (74) ◽  
pp. 307-308
Author(s):  
C.R. Bentley
Keyword(s):  
Electrical Resistivity ◽  
Computer Program ◽  
Depth Profile ◽  
Apparent Resistivity ◽  
Ice Shelf ◽  
Resistivity Measurements ◽  
Ross Ice Shelf ◽  
Field Season ◽  
A Site ◽  
Temperature Depth

Abstract During the 1973-74 Antarctic field season, two electrical resistivity profiles were completed along directions perpendicular to each other at a site in the south-easternpart of the Ross Ice Shelf. These profiles differ from each other only at short electrode spacings (less than 10 m) indicating no measurable horizontal anisotropy below the uppermost firn zone. The shape of the apparent resistivity curves is similar to that found by Hochstein on the Ross Ice Shelf near Roosevelt Island, but is displaced toward lower resistivities despite the colder 10 m temperature (—29°C instead of —26°C) at the more southerly site. Some factor other than temperature must therefore be effective in determining the overall magnitude of the resistivities in the shelf, although the variation with depth can still be expected to be primarily a temperature phenomenon. A computer program has been written to calculate apparent resistivities based on Crary’s analysis of temperatures in an ice shelf. Results are not yet available; when completed they should indicate the sensitivity of the resistivity measurements to differences in the temperature- depth profile, and hence their usefulness in estimating bottom melt/freeze rates.

scholarly journals Temperature investigation and modeling on the Filchner-Ronne Ice Shelf, Antarctica

1994 ◽  
Vol 20 ◽  
pp. 377-385 ◽  
Author(s):  
K. Grosfeld ◽  
F. Thyssen
Keyword(s):  
Depth Profile ◽  
Basal Layer ◽  
Melting Rate ◽  
Ice Shelf ◽  
Depth Profiles ◽  
Steady State Temperature ◽  
Antarctic Expedition ◽  
Field Season ◽  
Basal Melting ◽  
Temperature Depth

During the German Antarctic Expedition field season 1989–90. hotwater drilling was undertaken on the Filchner-Ronne Ice Shelf (FRIS) at 77° S 52°c W to investigate the temperature-depth profile and the bottom-melting rate, which arc significant parameters for mass- and energy-balance studies of the ice shelf. Remeasurements of installed chains in 1991-92 yie1ded reliable results.Taking glaciological, geodetic and geophysical data on a flowline through the central part of FRIS. we developed a two-dimensional thermal model to reconstruct the measurernents from a steady-state temperature depth profile about 550 km upstream on Möllereisstrom. Considering mass and energy conservation, a basal layer of 350 m of marine ice was calculated with thermal properties, depending on salinity and temperature. In areas with strong basal freezing, almost isothermal depth profiles in the marine ice layer are derived. Further downstream, in areas of basal melting, a nearly cubic temperarure-depth profile is observed.

scholarly journals Electrical Resistivity Measurements On The Ross Ice Shelf

1977 ◽  
Vol 18 (78) ◽  
pp. 15-35 ◽  
Author(s):  
Charles R. Bentley
Keyword(s):  
Activation Energy ◽  
Electrical Resistivity ◽  
Seismic Velocity ◽  
Sea Water ◽  
Field Measurements ◽  
Ice Shelf ◽  
Glacial Ice ◽  
Resistivity Measurements ◽  
Ross Ice Shelf ◽  
The North

AbstractElectrical resistivity measurements were made along two perpendicular profiles on the Ross Ice Shelf, Antarctica, in 1973–74. Apparent resistivities are generally well determined at electrode separations from 10 m out to 600 m, where the effect of the highly conducting sea-water beneath the shelf becomes strongly fell. Schlumberger and equatorial-dipole data are in excellent agreement on each profile; apparent resistivities on the two profiles, however, differ by about 12% at separations greater than about 30 m. This apparent anisotropy is attributed to a presumed inhomogeneity at a few tens of meters depth, rather than to true anisotropy in the bulk resistivity.A computer program has been developed to calculate apparent resistivities on an ice shelf in which the density and temperature, and thus the resistivity, vary continuously with depth. Temperatures have been calculated according to the analysis of Crary (1961 [b]) for a steady-state ice shelf; densities have been calculated from seismic velocity data. Several different models of the dependence of resistivity on density have been tested—one appears to fit the observations very closely, but it must be accepted only with great caution because the assumptions on which it is based are violated in the ice shelf.The activation energy and the rate of bottom melting or freezing upon which the temperature-depth variations depend have been treated as variable parameters in the modeling. The most satisfactory model corresponds to a melt/freeze rate close to zero, and an activation energy, 0.25 eV (24 kJ mol−1), in agreement with laboratory measurements on Antarctic ice samples, although less than that suggested by previous field measurements. However, since the actual temperatures in the ice shelf are unknown, models that combine a substantial melt rate with a higher activation energy, or a substantial freeze rate with a lower activation energy, cannot be ruled out at present. Future measurements in places where the temperature profile is known should resolve this uncertainty.The actual resistivity in the solid ice at a depth of about 100 m (temperature about —23°C), lies within ±10% of 70000 Ω m, thus once again confirming the very low resistivities typical of polar glacial ice. The resistivity is, in fact, only about half that found near Roosevelt Island to the north and “Byrd” station to the east. That difference is believed to be real, but its cause is not known and probably will not be known until the basic cause for the generally low resistivity of polar ice is better understood.

scholarly journals Temperature investigation and modeling on the Filchner-Ronne Ice Shelf, Antarctica

1994 ◽  
Vol 20 ◽  
pp. 377-385
Author(s):  
K. Grosfeld ◽  
F. Thyssen
Keyword(s):  
Depth Profile ◽  
Basal Layer ◽  
Melting Rate ◽  
Ice Shelf ◽  
Depth Profiles ◽  
Steady State Temperature ◽  
Antarctic Expedition ◽  
Field Season ◽  
Basal Melting ◽  
Temperature Depth

During the German Antarctic Expedition field season 1989–90. hotwater drilling was undertaken on the Filchner-Ronne Ice Shelf (FRIS) at 77° S 52°c W to investigate the temperature-depth profile and the bottom-melting rate, which arc significant parameters for mass- and energy-balance studies of the ice shelf. Remeasurements of installed chains in 1991-92 yie1ded reliable results. Taking glaciological, geodetic and geophysical data on a flowline through the central part of FRIS. we developed a two-dimensional thermal model to reconstruct the measurernents from a steady-state temperature depth profile about 550 km upstream on Möllereisstrom. Considering mass and energy conservation, a basal layer of 350 m of marine ice was calculated with thermal properties, depending on salinity and temperature. In areas with strong basal freezing, almost isothermal depth profiles in the marine ice layer are derived. Further downstream, in areas of basal melting, a nearly cubic temperarure-depth profile is observed.

scholarly journals Investigation of Bottom Mass-Balance Rates by Electrical Resistivity Soundings on the Ross Ice Shelf, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 331-343 ◽  
Author(s):  
Sion Shabtaie ◽  
Charles R. Bentley
Keyword(s):  
Activation Energy ◽  
Electrical Resistivity ◽  
Steady State ◽  
Mass Balance ◽  
Apparent Resistivity ◽  
Ice Thickness ◽  
Seasonal Temperature ◽  
Ice Shelf ◽  
Near Surface ◽  
Ross Ice Shelf

AbstractElectrical resistivity sounding, using the four-electrode Schlumberger array, has been carried out at 11 locations on the Ross Ice Shelf. The apparent resistivity curves generally show four characteristic zones. The first, at distances from 1 to 10 m, reflects the near-surface zone of seasonal temperature changes and inhomogeneities. The second zone, from 10 m to 100 m, reflects primarily the increasing density with depth in the upper 50 m of the ice shelf, modified, in some locations, by temperature variations. The third zone, from 100 m to a distance roughly equal to the ice thickness, is affected principally by the temperature gradient in the solid ice. In the fourth zone, at distances greater than approximately twice the ice thickness, the apparent resistivity usually decreases rapidly with distance, owing to the highly conductive sea-water beneath the ice shelf. At some stations associated with ice streams and outlet glaciers, however, an increase at large spacings indicates much more resistive basal ice.Using data from seven locations on the grid eastern half of the shelf that do not show obvious evidence of a basal resistive zone, including temperatures to 100 m at two of the sites, the mass-balance rate at the bottom of the ice is estimated to be within a few tenths of a meter per year of zero at distances between 90 and 530 km from the ice front, assuming steady-state condition over most of the ice shelf. However, the assumption of steady-state is questionable at locations close to outlet glaciers, and must be treated with great caution. The temperature measurements at the two sites, along with previously observed temperatures at the RISP drill site, make it possible to estimate the activation energy in the solid ice. The models fitted to the observed values suggest an “apparent” activation energy in the solid ice closer to 0.15 eV (14 kJ mol−1) than to 0.25 eV (24 kJ mol−1). This difference is believed to be due to a decrease in the ionic impurity content with increasing depth in the ice by a factor of two or more.

scholarly journals Electrical Resistivity Measurements On The Ross Ice Shelf

1977 ◽  
Vol 18 (78) ◽  
pp. 15-35 ◽  
Author(s):  
Charles R. Bentley
Keyword(s):  
Activation Energy ◽  
Electrical Resistivity ◽  
Seismic Velocity ◽  
Sea Water ◽  
Field Measurements ◽  
Ice Shelf ◽  
Glacial Ice ◽  
Resistivity Measurements ◽  
Ross Ice Shelf ◽  
The North

AbstractElectrical resistivity measurements were made along two perpendicular profiles on the Ross Ice Shelf, Antarctica, in 1973–74. Apparent resistivities are generally well determined at electrode separations from 10 m out to 600 m, where the effect of the highly conducting sea-water beneath the shelf becomes strongly fell. Schlumberger and equatorial-dipole data are in excellent agreement on each profile; apparent resistivities on the two profiles, however, differ by about 12% at separations greater than about 30 m. This apparent anisotropy is attributed to a presumed inhomogeneity at a few tens of meters depth, rather than to true anisotropy in the bulk resistivity.A computer program has been developed to calculate apparent resistivities on an ice shelf in which the density and temperature, and thus the resistivity, vary continuously with depth. Temperatures have been calculated according to the analysis of Crary (1961 [b]) for a steady-state ice shelf; densities have been calculated from seismic velocity data. Several different models of the dependence of resistivity on density have been tested—one appears to fit the observations very closely, but it must be accepted only with great caution because the assumptions on which it is based are violated in the ice shelf.The activation energy and the rate of bottom melting or freezing upon which the temperature-depth variations depend have been treated as variable parameters in the modeling. The most satisfactory model corresponds to a melt/freeze rate close to zero, and an activation energy, 0.25 eV (24 kJ mol−1), in agreement with laboratory measurements on Antarctic ice samples, although less than that suggested by previous field measurements. However, since the actual temperatures in the ice shelf are unknown, models that combine a substantial melt rate with a higher activation energy, or a substantial freeze rate with a lower activation energy, cannot be ruled out at present. Future measurements in places where the temperature profile is known should resolve this uncertainty.The actual resistivity in the solid ice at a depth of about 100 m (temperature about —23°C), lies within ±10% of 70000 Ω m, thus once again confirming the very low resistivities typical of polar glacial ice. The resistivity is, in fact, only about half that found near Roosevelt Island to the north and “Byrd” station to the east. That difference is believed to be real, but its cause is not known and probably will not be known until the basic cause for the generally low resistivity of polar ice is better understood.

scholarly journals Investigation of Bottom Mass-Balance Rates by Electrical Resistivity Soundings on the Ross Ice Shelf, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 331-343 ◽  
Author(s):  
Sion Shabtaie ◽  
Charles R. Bentley
Keyword(s):  
Activation Energy ◽  
Electrical Resistivity ◽  
Steady State ◽  
Mass Balance ◽  
Apparent Resistivity ◽  
Ice Thickness ◽  
Seasonal Temperature ◽  
Ice Shelf ◽  
Near Surface ◽  
Ross Ice Shelf

AbstractElectrical resistivity sounding, using the four-electrode Schlumberger array, has been carried out at 11 locations on the Ross Ice Shelf. The apparent resistivity curves generally show four characteristic zones. The first, at distances from 1 to 10 m, reflects the near-surface zone of seasonal temperature changes and inhomogeneities. The second zone, from 10 m to 100 m, reflects primarily the increasing density with depth in the upper 50 m of the ice shelf, modified, in some locations, by temperature variations. The third zone, from 100 m to a distance roughly equal to the ice thickness, is affected principally by the temperature gradient in the solid ice. In the fourth zone, at distances greater than approximately twice the ice thickness, the apparent resistivity usually decreases rapidly with distance, owing to the highly conductive sea-water beneath the ice shelf. At some stations associated with ice streams and outlet glaciers, however, an increase at large spacings indicates much more resistive basal ice.Using data from seven locations on the grid eastern half of the shelf that do not show obvious evidence of a basal resistive zone, including temperatures to 100 m at two of the sites, the mass-balance rate at the bottom of the ice is estimated to be within a few tenths of a meter per year of zero at distances between 90 and 530 km from the ice front, assuming steady-state condition over most of the ice shelf. However, the assumption of steady-state is questionable at locations close to outlet glaciers, and must be treated with great caution. The temperature measurements at the two sites, along with previously observed temperatures at the RISP drill site, make it possible to estimate the activation energy in the solid ice. The models fitted to the observed values suggest an “apparent” activation energy in the solid ice closer to 0.15 eV (14 kJ mol−1) than to 0.25 eV (24 kJ mol−1). This difference is believed to be due to a decrease in the ionic impurity content with increasing depth in the ice by a factor of two or more.

scholarly journals In Situ Measurements of the Activation Energy for D.C. Conduction in Polar Ice

1978 ◽  
Vol 21 (85) ◽  
pp. 698-699
Author(s):  
Charles R. Bentley
Keyword(s):  
Activation Energy ◽  
Apparent Resistivity ◽  
Personal Communication ◽  
Depth Range ◽  
Polar Ice ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
True Value ◽  
Basal Melting ◽  
Ice Water

Abstract During the 1976-77 Antarctic field season, electrical resistivity profiling was carried out in the south-eastern quadrant of the Ross Ice Shelf. Drilling to a depth slightly greater than 300 m at the same site, where the total ice thickness is 425 m, permitted tem-perature determinations (personal communication from B. L. Hanson and J. H. Rand) that can be extrapolated to the ice-water boundary. Numerical modelling of the apparent resistivity, allowing for a continuous variation of temperature and density, and hence con-ductivity, with depth, was done in the same manner as has been described previously (Bentley, 1977). Temperatures calculated by assuming no basal melting or freezing show excellent agreement with those measured. Two models of apparent resistivity, taking the activation energy in the solid ice to be 0.15 eV and 0.25 eV, respectively, bracket the observed data, with the points tending to favor the lower value. This is in satisfactory agreement with (although perhaps slightly lower than) other measurements on polar ice. Assuming that the same temperature model applies at the site of the earlier measurements (Bentley, 1977), only 30 km away and approximately "up-stream", leads to apparent resistivity models, with activation energies of 0.15 eV and 0.25 eV, that again bracket the observations. The effect of other possible causes for the change of conductivity with depth besides temperature, such as varying grain size, crystal orientation, CO2 content, etc., is unknown but believed to be small because of the similar history of all the ice in the relevant depth range, about 100-350 In, over which the conductivity increases by a factor of 2. The conductivity in the ice at 100 m depth (temperature —23°C) at both sites is within ± 10% of 1.4 × 10-5 Ω-1. We conclude that an activation energy of 0.20 ± 0.05 eV not only can be used for modelling, but also closely represents the true value for ice-shelf ice.

scholarly journals The BAS ice-shelf hot-water drill: design, methods and tools

2014 ◽  
Vol 55 (68) ◽  
pp. 44-52 ◽  
Author(s):  
Keith Makinson ◽  
Paul G.D. Anker
Keyword(s):  
Modular Design ◽  
Sea Water ◽  
Sediment Cores ◽  
Hot Water ◽  
Ice Shelf ◽  
Water Conductivity ◽  
Ice Shelves ◽  
Field Season ◽  
Temperature Depth

AbstractThe 2011/12 Antarctic field season saw the first use of a new British Antarctic Survey (BAS) ice-shelf hot-water drill system on the Larsen C and George VI ice shelves. Delivering 90 L min−1 at 80°C, a total of five holes >30 cm in diameter at three locations were successfully drilled through almost 400 m of ice to provide access to the underlying ocean, including the first access beneath the Larsen C ice shelf. These access holes enabled the deployment of instruments to measure sea-water conductivity, temperature, depth and microstructure, the collection of water samples and up to 2.9 m long sediment cores, before long-term oceanographic moorings were deployed. The simple modular design allowed for Twin Otter aircraft deployment, rapid assembly and commissioning of the system, which proved highly reliable with minimal supervision. A number of novel solutions to various operational sub-ice-shelf profiling and mooring deployment issues were successfully employed through the hot-water drilled access holes to aid the positioning, recovery and deployment of instruments. With future activities now focusing on the Filchner–Ronne Ice Shelf, the drill has been upgraded from its current 500 m capability to 1000 m with additional drill hose and further generator, pumping and heating modules.

scholarly journals Electrical Resistivity Of George VI Ice Shelf, Antarctic Peninsula

1982 ◽  
Vol 3 ◽  
pp. 279-283 ◽  
Author(s):  
John M. Reynolds
Keyword(s):  
Apparent Resistivity ◽  
Sea Water ◽  
Free Water ◽  
Melting Rate ◽  
Small Range ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Melt Water ◽  
Electrical Sounding ◽  
Basal Melting

A georesistivity survey was made on part of George VI Ice Shelf (71°55'S, 67°20'W). The principal objectives were to determine the electrical structure of the 1ce shelf, in particular how refrozen melt water differs in electrical behaviour from dry firn, and to Investigate the environment beneath the ice shelf.Apparent resistivity profiles using a Schlumberger electrode configuration have been interpreted using Ghosh's convolution method for vertical electrical sounding (VES), adapted for use where extreme resistivity contrasts are present.Warm, wet surface conditions tend to reduce the gross resistivity of shallow permeable layers. The electrical results indicate that the refrozen free water has affected the resistivity only indirectly; the mean density of firn is raised to about 0.915 Mg m−3within the uppermost 10 m of the ice shelf at which point the resistivity is comparable to that of Ice of the same density but formed by compaction of firn. The apparent resistivities in the top 100 m reflect the variation of density with depth; a small range of resistivities implies that the range of density 1s narrow and that densification is affected by the percolation and refreezing of melt water.The bulk of the ice behaves as if resistivity either Is independent of temperature or has only a slight dependence (activation energy ~0.15 eV) with a basal melting rate in excess of 1 to 2 m a−1. The principal resistivities determined for two sites on George VI Ice Shelf were within 10% of those at station BC on the Ross Ice Shelf, allowing for differences in temperature. This Indicates that polar ice, I.e. non-temperate ice, has a very narrow range of resistivity. The apparent resistivity profiles are consistent with there being sea-water of oceanic salinity under the Ice shelf.

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