bluuebunny/crossref_metadata_2025_split huggingface dataset:
In Situ Measurements of the Activation Energy for D.C. Conduction in Polar Ice
Authors: Bentley Charles R. 
Published: September 2017

AbstractDuring 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.
Comparison of Electromagnetic and Seismic-Gravity Ice Thickness Measurements in East Antarctica
Authors: Drewry David J. 
Published: September 2017

AbstractThe errors involved in ice thickness determinations in Antarctica by seismic reflection shooting, gravity observations and radio-echo sounding are briefly discussed. Relative accuracies of 3%, 7-10% and 1.5% have been suggested. Double checks of ice depths from radar sounding in east Antarctica indicate an internal consistency of measurement for this technique of <1%. Comparison of carefully executed seismic shooting and routine radio-echo sounding results against absolute ice thickness values from two deep core drilling sites show no significant differences between these two remote methods (i.e. both are better than 1.5%).Over 60 comparisons are examined between radar ice thicknesses and over-snow measurements obtained on eight independent traverses in east Antarctica. Three traverses exhibit consistently unacceptable results-U.S. Victoria Land Traverse II (southern leg), Commonwealth Transanlarctic Expedition and the U.S.S.R. Vostok to South Pole Traverse—which probably result from misinterpretation of “noisy” seismograms. The remaining comparisons indicate mean differences, including some navigational uncertainty, of ≈3%, <8% and 5% between radio-echo and (1) seismic, (2) gravity, and (3) gravity tied to seismic determinations, respectively.
Temperature Measurement of Ice and Water Surfaces in the North Water Area Using an Airborne Radiation Thermometer
Authors: Müller F. , Blatter H. , Kappenberger G. 
Published: September 2017

AbstractIce and water surface temperatures were measured with an airborne radiation thermometer PRT-5 over the North Water polynya during three missions between late winter and early summer 1974. Error corrections, problems of data analyses and mapping are discussed. Attempts are made to relate the main types of sea ice to temperature ranges, which then are used in conjunction with satellite pictures to produce surface temperature maps.
Characterization of Cold-Regions Terrain Using Airborne Laser Profilometry
Authors: Hibler W. D. 
Published: September 2017

AbstractThis paper provides a review of the characteristics of airborne laser profilometry and its application to quantitative characterization of cold-regions terrain. The limitations of profilometry due to the profiler instrumental characteristics and instability of the aircraft platform (resulting from variations in aircraft altitude and attitude) are discussed. For typical aircraft speeds of the order of 100 m/s these limitations restrict the accurately measured roughness content to the approximate wavelength range 2 m to 300 m. Digital filtering and hardware techniques for removing the aircraft motion, and hence extending the long wavelength validity of the profile, are discussed.Regarding terrain characterization, particular attention is given to Arctic, sea ice. Ridge height and spacing distribution models for sea ice in conjunction with digitally processed laser profiles allow efficient characterization of sea-ice ridging using only a few parameters. In particular, a single ridging intensity parameter has been found to allow reasonable estimation of the number of ridges encountered at any height level along a straight-line path. Examination of spectral characteristics of first-year and multi-year ice suggest that laser profiles may be used to identify the ice type of floes and ridges. Comparisons of laser data and submarine sonar data are made which suggest that ratios of c. 6.5: 1 can be used to estimate ridge keel depths from laser data. Use of laser profilometry to characterize tundra and indirectly 10 measure variation in snow depth is briefly discussed.
Antarctic Sea-Ice Variations from Satellite Sensing in Relation to Climate
Authors: Budd W. F. 
Published: September 2017

AbstractAn analysis of records of annual mean temperatures around Antarctica shows large-scale anomalies of thousands of kilometers extent with typical variations of a deg from one year to another From 1967 on, composite satellite photographs are available which show considerable variation in the sea-ice extent in different years up to about 5º of latitude. These largest differences seem to persist over entire seasons. In general there seems to be considerable association between the region around the Antarctic with the coldest temperatures and the regions of greatest sea-ice extent. An analysis of long-term records at a single location near the edge of the Antarctic sea ice indicates a strong correlation between variations in the annual mean temperature and the duration of the sea ice, such that a change of 1 deg in the annual mean temperature corresponds to about 70 d variation in the duration of the sea ice. A relation is obtained between variations of annual mean temperature and the mean extent of the sea ice, viz. a 1 deg change corresponds to approximately 2.5º latitude variation in the maximum sea-ice extent. The magnitude of the variations in the sea-ice extent observed from the satellite data in comparison with the large-scale temperature anomalies is compatible with the above relations, although some rotational shifts appear to take place.
Glaciological Studies in Iceland with Erts-I Imagery
Authors: Williams Richard S. , Bödvarsson Ágúst , Rist Sigurjón , Sæmundsson Kristján , Thorarinsson Sigurdur 
Published: September 2017

Under a long-term, bi-national, multi-disciplinary research project between the U.S. Geological Survey and various Icelandic scientific organizations, MSS imagery from the ERTS-I satellite is being used to study the varied dynamic environmental phenomena of Iceland, including its glaciers and ice caps. Initial analysis of the ERTS-I imagery has shown the importance of the repetitive imagery to:
Record relatively short-term glaciological changes. According to measurements made on two ERTS-I images, taken 11 months apart, an outlet glacier in the north-east part of Vatnajökull, had surged 1.8 km. A combination of field observations and analysis of ERTS imagery shows a total surge in excess of 3 km which probably took place in a few months, perhaps in as little as a few weeks. Contorted moraines on another of Vatnajökull’s outlet glaciers, Skeiðararjökull, on the south-east coast, show a movement of 600 m in an 11 month period even though the snout of the glacier remained in essentially the same position.Several glacier-margin lakes have been observed to change in size during the year (1972-73), particularly Grjœnalón, which continued to enlarge in area each time it was imaged until its size diminished markedly after a jökulhlaup partially emptied the lake in August 1973. Seasonal changes in the size of sediment plumes along the coast, where glacial rivers debouch their sediment-laden water into the ocean, can also be observed in a time-lapse manner.Furnish the data necessary to revise certain glaciological features on maps, and to produce ortho-image maps of ice caps directly from ERTS imagery, at least to map scales of 1: 250 000. Sufficient ERTS-I imagery of Iceland from the late summer and early fall of 1973 now exists to map accurately, from a planimetric standpoint, 90% of that area of Iceland covered by glacial ice (previously estimated to be 11.5% of total area of Iceland). Optimum imagery (minimum snow cover, maximum exposure of glacial ice) has been obtained of Vatnajökull, Langjrikull, Hofsjökull, Myrdalsjökull, and Eyjafjallajökull or five (including the four biggest) of the seven largest ice caps in Iceland and five of the smaller (less than 50 km2) ice caps as well. On 19 August 1973 Hofsjökull had an area of 915 km- on ERTS imagery. Its area has usually been cited as 996 km2. On a 1945 Danish Geodetic Institute map (1: 500 000) the area is 981 km2; U.S. Army maps (1 : 250 000, 1969) show an area of 943 km2.Map subglacial volcanic and structural features. Within or at the margins of the ice caps and outlet glaciers, a number of new glaciological, structural, and volcanic features can be mapped from ERTS-I imagery, particularly at low solar illumination angles (<10°) including several probable subglacial central volcanoes, calderas, and tectonic lineaments. Some of the effects of jökulhlaups can be mapped, including subsidence cauldrons resulting from subglacial volcanic or intense geothermal activity.
Polarization Changes of Radio Signals in Vertical Radio-Echo Sounding of Glaciers
Authors: Bogorodskiy V. V. , Trepov G. V. , Fedorov B. A. 
Published: September 2017

An electromagnetic linearly-polarized signal transmitted through the glacier in a vertical direction, reflected from the bedrock, and received with a receiving antenna, is found to be changed into one either partially or elliptically polarized. The polarization changes are believed to be due mainly to the crystal structure of the glacier and anisotropy caused by the pressure of the upper layers.An analysis of the polarization diagrams obtained is up to the present the main method used for studies of the reflected signal polarization. Evidently using a simple dipole a partially-polarized signal is not distinguishable from one that is elliptically polarized, nor is a nonpolarized signal distinguished from circularly polarized. However, the data recently obtained are of great importance, particularly from studies of glacier crystal structure made in deep core drilling.Possible reasons for the polarization changes of the signal have been analysed. Results of the analyses of the polarization diagrams obtained both at individual points and along extended traverses are discussed. It has been found that the signal reflected from a considerable ice thickness is polarized in such a way that the parallel orientation of the receiving and transmitting dipoles can be disregarded. En route recordings of the signal fluctuations obtained by parallel and orthogonally polarized dipoles are shown. The results of polarization studies are important for practical purposes. For example, bedrock relief sounding carried out with crossed dipoles makes it possible to get rid of interference signals occurring due to scattering from inhomogeneous structures of the upper part of the glacier.
Interpretation of Radio-Echo Sounding Data on a Temperate Mountain Glacier from its Surface
Authors: Luchininov V. S. , Macheret Yu. Ya. 
Published: September 2017

Temperate mountain glaciers have specific peculiarities which make the interpretation of radio-echo sounding data much more difficult than for polar ice sheets. On the A or Z indicators one can observe a plurality of pulses differing in shape, amplitude, and range. Often a gap is observed on the film. The problem is to select the pulses from the bed or internal reflecting horizon and to reconstruct the subglacial relief or internal interface.During preliminary processing, the radio-coordinates of all marks on a type A radiogram are written into a table. Then non-informative marks are eliminated and informative marks are situated on a continuous line or trace.We put into practice three methods of interpretation: (1) an envelope method, (2) Harrison’s transformation method, (3) approximation of segments of a trace by straight lines. Harrison’s transformation method is the most general one; the others are useful for the presentation of results in a graphical form. The suggested methods are used for the interpretation of the data from a transverse profile of the valley glacier Lednik Bezengiy, Caucasus, 1970-71. Radar RW-10 with a carrier frequency of 440 MHz and overall receiver sensitivity relative to the transmitter pulse power 130 dB was used. It was revealed that the transparency of the glacier changes from year to year. The maximum ice thickness measured was 33°±15 m. Some extended interfaces in the body of the glacier were discovered. One of them, 80 m deep, coincides with seismic contrast interface and with the 0° C isotherm. Radio-echo sounding data are in agreement with gravity measurements on the same profile.
Triaxial experiments on iceberg and glacier ice
Authors: Gagnon R. E. , Gammon P. H. 
Published: September 2017

AbstractTriaxial experiments, at confining pressures in the range 0–13.79 MPa, have been performed on glacial ice collected from four icebergs and one glacier. Tests were conducted at strain rates in the range of 5 × 10−5 to 5 × 10−5s−1 and at four temperatures in the range of −1° to −16°C. Depending on test conditions, the ice failed by one of four possible modes ductile deformation, due to extensive non-interacting microcracks; fracture along a shear plane followed by continuous or stick-slip sliding; large-scale brittle fracture; and combined ductile and shear-plane fracture and slip The strength Increased with decreasing temperature, increasing strain rate up to 5 × 10−3s−1 and increasing confining pressure at the lower temperatures. The strength at 5 × 10−2s−1 was lower than at 5 × 10−3s−1 probably because extension and interaction of microcracks is enhanced at the higher rate. For higher confining pressures at −1°C, the strength decreased due to freezing-point depression. The ice from the different sources exhibited different mean uniaxial compressive strengths. The mean number of air bubbles per unit volume correlated with the mean uniaxial compressive strengths and this may be the dominant factor distinguishing the strengths of the various ice types.
Bubbly-ice densification in ice sheets: II. Applications
Authors: Lipenkov Vladimir Ya. , Salamatin Andrey N. , Duval Paul 
Published: September 2017

AbstractA mathematical model for simulating the densification of bubbly glacier ice is used to interpret the following experimental data from the Vostok (central Antarctica) ice core: two ice-porosity profiles obtained by independent methods and a bubble-pressure profile obtained by direct measurements of air pressure within individual bubbles. The rheological properties of pure polycrystalline ice are deduced from the solution of the inverse problem. The model and the inferred ice-flow law are then validated, using porosity profiles from seven other ice cores drilled in Antarctica and Greenland, in the temperature range from -55° to -20° C. The following expression is adopted for the constitutive law:where ė and τ are the effective strain rate and stress, respectively, α is the creep exponent taken as 3.5, Rs is the gas constant and T(Ts) is the temperature (standard temperature). The numerical values obtained for the “linear” and “non-linear” viscosities are: μ1 = 2.9 ± 1.3 M Pa year and μ2 = 0.051 ± 0.019 M Paα year, and the apparent activation energy Q is confirmed to be 60 k J mole−1. The corresponding flow law is in good agreement with results of both mechanical tests and independent estimations based on the analysis of different natural phenomena associated with glacier-ice deformation. When the model is constrained by the porosity and bubble-pressure profiles from Vostok, the mean air content in Holocene ice is inferred to be about 0.088 cm3g−1. The corresponding mean air pressure in bubbles at the end of pore closure is about 0.083 M Pa, whereas the atmospheric pressure at this depth level would be 0.063 M Pa. The influence of the climatic change on the ice-porosity profile is discussed. It resulted in an increased air content in ice at Vostok during the Last Glacial Maximum: 0.096 cm3 g−1.
Pore-water controlled grain fracturing as an indicator for subglacial shearing in tills
Authors: Hiemstra John F. , Van Der Meer Jaap J. M. 
Published: September 2017

AbstractGenetic classification of glacial deposits still proves to be highly controversial. In many cases, it remains unclear whether a particular sediment has been sub-glacially deformed. In the present paper it is suggested that micromorphological research is helpful where current techniques fail to lead to unambiguous interpretations. It is argued that the occurrence of fractured grains in glacial sediments is indicative of subglacial shearing and that such grains may be used as diagnostic evidence of glaciotectonism. Deformational mechanisms associated with the fracturing process are outlined and explained, using a series of thin sections from Wijnjewoude, The Netherlands.
Glacial regime of the highest Tien Shan mountain, Pobeda-Khan Tengry massif
Authors: Aizen Vladimir B. , Aizen Elena M. , Dozier Jeff , Melack John M. , Sexton David D. , Nesterov Victor N. 
Published: September 2017

AbstractMajor processes controlling the existence of a large sub-continental glacier system were identified on the basis of glaciological, meteorological and isotopic analyses using expeditionary and long-term data. Observations were made on the southern Inylchek glacier located in the Pobeda-Khan Tengry massif, the largest sub-continental glacier system on the northern periphery of central Asia. More than 1200 glaciers with a total area of about 4320 km2 comprise the massif. Melt is for the most part caused by radiation and is most intensive during periods of anticyclonic weather with fohn development. The proportion of solar radiation input in relation to heat balance is more than 90%. Evaporation and condensation are negligible during most times and comprise 7% of heat expenditure. Accumulation was associated with cold cyclonic weather. Four ice-formation zones were identified, the upper boundary of liquid runoff is at 5200 m and the recryslallization zone is above 5900 m. The calculated net glacier mass is negative, −318 kg m−2 a−1, and indicates the degradation of modern Pobeda-Khan Tengry glaciers.
Snow accumulation and ice flow at Dôme du Goûter (4300 m), Mont Blanc, French Alps
Authors: Vincent C. , Vallon M. , Pinglot J. F. , Funk M. , Reynaud L. 
Published: September 2017

AbstractGlaciological experiments have been carried out at Dôme du Goûter (4300 m a.s.l.), Mont Blanc, in order to understand the flow of firn/ice in this high-altitude Alpine glacierized area. Accumulation measurements from stakes show a very strong spatial variability and an unusual feature of mass-balance fluctuations for the Alps, i.e. the snow accumulation does not show any seasonal patterns. Measured vertical velocities which should match with long-term mean mass balance are consistent with observed accumulations. Therefore, the measurement of vertical velocities seems a good way of quickly obtaining reliable mean accumulation values for several decades in such a region.A simple flow model can be used to determine the main flowlines of the glacier and to propose snow/ice age of core samples from the two boreholes drilled down tο the bedrock in June 1994. These results coincide with radioactivity measurements made to identify the well-known radioactive snow layers of 1963 and 1986. We can hope to obtain ice samples 55–60 years old about 20 or 30 m above the bedrock (110 m deep). Below, the deformation of the ice layers is loo great to be dated accurately.
Changes in glaciers in Hidden Valley, Mukut Himal, Nepal Himalayas, from 1974 to 1994
Authors: Fujita Koji , Nakawo Masayoshi , Fujii Yoshiyuki , Paudyal Prem 
Published: September 2017

AbstractGlaciological investigations were carried out in 1994 on the glaciers in Hidden Valley, Mukut Himal, Nepal Himalayas, in order to make a comparison with observations made in 1974. Most of the glaciers were found to have retreated by 30–60 m in terminus elevation over the 20 years between the two studies. Rikha Samba Glacier, the longest glacier in the valley, has retreated by about 200m. The areal average of the amount of surface lowering and the volume loss of the glacier was estimated to be 12.6 m ice equivalent and 13% of the total mass, respectively. The annual mass balance of −0.35 m a−1 water equivalent was obtained as an average for 20 years, which is one of the largest negative values amongst small glaciers of the world.
Borehole temperatures at the Colle Gnifetti core-drilling site (Monte Rosa, Swiss Alps)
Authors: Haeberli Wilfried , Funk Martin 
Published: September 2017

AbstractMeasured englacial temperatures at the Colle Gnifetti core-drilling site are presented and compared with model calculations concerning possible effects of 20th century warming. The firn/ice saddle at the 124 m deep saddle borehole is cold throughout with a mean annual surface temperature near –14°C and a basal temperature slightly below –12°C. Influence of refreezing meltwater is weak and limited to near-surface formation of ice layers (recrystallization-infiltration). Temperature gradients in the saddle borehole are positive and increase from 0.015° to 0.019°C m−1 between 30 m depth and bedrock, corresponding to a mean vertical heat flow of around 50mWm−2. The observed temperature profile is close to steady-state conditions. It can well be reproduced with time-dependent model calculations using mean annual air temperatures from the nearby weather station of Grand St. Bernard within the main chain of the Swiss Alps, but it significantly deviates from similar calculations based on Säntis data, reflecting developments of air temperatures on the northern slope of the Alps. 20th century warming of cold Alpine firn seems to be much less pronounced than in polar areas, where strong heat-flow anomalies are commonly observed.