bluuebunny/crossref_metadata_2025 huggingface dataset:
Borehole water-level variations and the structure of the subglacial hydrological system of Haut Glacier d’Arolla, Valais, Switzerland
Authors: Hubbard B. P. , Sharp M. J. , Willis I. C. , Nielsen M. K. , Smart C. C.
Published: September 2017

Late-summer subglacial water pressures have been measured in a dense array of boreholes in the ablation area of Haut Glacier d’Arolla, Switzerland. Interpolated surfaces of minimum diurnal water pressure and diurnal water-pressure variation suggest the presence of a subglacial channel within a more widespread, distributed drainage system. The channel flows along the centre of a variable pressure axis (VPA), some tens of metres wide, that is characterized by low minimum diurnal water pressures (frequently atmospheric) and high diurnal water-pressure variations. These characteristics are transitional over a lateral distance of c. 70 m to higher and more stable subglacial water pressures in the adjacent distributed system. Water-pressure variations recorded in boreholes located close to the centre of the VPA reflect the delivery of surface-derived meltwater to the glacier bed and result in a diurnally reversing, transverse hydraulic gradient that drives water out from the channel into the distributed system during the afternoon and back to the channel overnight. Subglacial observations suggest that such flow occurs through a vertically confined sediment layer. Borehole turbidity records indicate that the resulting diurnal water flows are responsible for the mobilization and transport of fine debris in suspension. Analysis of the propagation velocity and amplitude attenuation cf the diurnal pressure waves suggests that the hydraulic conductivity of the sediment layer decreases exponentially with distance from the channel, falling from c. 10−4 m s−1 at the channel boundary to c. 10−7 m s−1 70 m away. These apparent hydraulic conductivities are consistent with Darcian flow through clean sand and typical glacial till, respectively.

We suggest that fine material is systematically flushed from basal sediments located adjacent to large, melt-season drainage channels beneath warm-based glaciers. This process may have important implications for patterns of glacier erosion, hydro-chemistry and dynamics.
Mapping tide-water glacier dynamics in East Greenland using Landsat data
Authors: Dwyer John L.
Published: September 2017

Landsat multispectral scanner and thematic mapper images were co-registered For the Kangerdlugssuaq Fjord region in East Greenland and were used to map glacier drainage-basin areas, changes in the positions of tide-water glacier termini and to estimate surface velocities of the larger tide-water glaciers. Statistics were compiled to document distance and area changes to glacier termini. The methodologies developed in this study are broadly applicable to the investigation of tide-water glaciers in other areas. The number of images available for consecutive years and the accuracy with which images are co-registered are key factors that influence the degree to which regional glacier dynamics can be characterized using remotely sensed data.

Three domains of glacier state were interpreted: net increase in terminus area in the southern part of the study area, net loss of terminus area for glaciers in upper Kangerdlugssuaq Fjord and a slight loss of glacier terminus area northward from Ryberg Fjord. Local increases in the concentrations of drifting icebergs in the fjords coincide with the observed extension of glacier termini positions Ice-surface velocity estimates were derived for several glaciers using automated image cross-correlation techniques The velocity determined for Kangerdlugssuaq Gletscher is approximately 5.0 km a−1and that for Kong Christian IV Gletscher is 0.9 km a−1. The continuous presence of icebergs and brash ice in front of these glaciers indicates sustained rates of ice-front calving.
An investigation of the deforming layer/debris-rich basal-ice continuum, illustrated from three Alaskan glaciers
Authors: Hart Jane K.
Published: September 2017

Three small Alaskan glaciers with different bed conditions were studied: Exit Glacier had a thin deforming layer and produced subglacial and proglacial glaciotectonic land forms; Childs Glacier also had a thin deforming layer but the upper part was frozen to the ice; Matanuska Glacier had no deforming layer but had subglacial debris-rich ice. Since it has been shown that sediment at the base can account for the majority of ice movement, it is suggested that there is a deforming bed/debris-rich continuum whereby similar processes occur throughout the different subglacial environments. These include: similar longitudinal deformation patterns (compression at the margin, extension and simple shear up-glacier); similar vertical deformation patterns, increase in deformation (and fabric strength) upwards through the sequence (leading to the attenuation of stratified ice into dispersed ice); and similar and interrelated incorporation processes. The major differences were that the processes occurred at a much faster rate within the deforming layer and that probably only the deforming layer will be recorded in the geological record.
On the strain-rate sensitivity of columnar ice
Authors: Manley M. E. , Schulson E. M.
Published: September 2017

A power law relation between stress and strain rate of the form was used to describe the response to strain rate of S1 ice loaded across the columns at –10° C. The rate exponent, n, decreased with increasing strain from about 4.6 at an observed peak on the load displacement curve to approximately 2.6 at a shortening of 2%. Analysis of these results and of the results of other authors on different forms of ice deformed at the same temperature suggests that the power law exponent, n is proportional to Fc/Fg The parameter Fc/Fg is the far-field basal dislocation climb force divided by the glide force.
The marginal shear stress of Ice Stream B, West Antarctica
Authors: Jackson Miriam , Kamb Barclay
Published: September 2017

To ascertain whether the velocity of Ice Stream B, West Antarctica, may be controlled by the stresses in its marginal shear zones (the “Snake” and the “Dragon”), we undertook a determination of the marginal shear stress in the Dragon near Camp Up B by using ice itself as a stress meter. The observed marginal shear strain rate of 0.14 a−1is used to calculate the marginal shear stress from the flow law of ice determined by creep tests on ice cores from a depth of 300 m in the Dragon, obtained by using a hot-water ice-coring drill. The test-specimen orientation relative to the stress axes in the tests is chosen on the basis ofc-axis fabrics so that the test applies horizontal shear across vertical planes parallel to the margin. The resulting marginal shear stress is (2.2 ± 0.3) × 105Pa. This implies that 63–100% of the ice stream’s support against gravitational loading comes from the margins and only 37–0% from the base, so that the margins play an important role in controlling the ice-stream motion. The marginal shear-stress value is twice that given by the ice-stream model of Echelmeyer and others (1994) and the corresponding strain-rate enhancement factors differ greatly (E≈ 1–2 vs 10–12.5). This large discrepancy could be explained by recrystallization of the ice during or shortly after coring. Estimates of the expected recrystallization time-scale bracket the ∼1 h time-scale of coring and leave the likelihood of recrystallization uncertain. However, the observed two-maximum fabric type is not what is expected for annealing recrystallization from the sharp single-maximum fabric that would be expected in situ at the high shear strains involved (γ ∼ 20). Experimental data from Wilson (1982) suggest that, if the core did recrystallize, the prior fabric was a two-maximum fabric not substantially different from the observed one, which implies that the measured flow law and derived marginal shear stress are applicable to the in situ situation. These issues need to be resolved by further work to obtain a more definitive observational assessment of the marginal shear stress.
Distribution and fall-out of137Cs and other radionuclides over Antarctica
Authors: Pourchet M. , Bartarya S. K. , Maignan M. , Jouzel J. , Pinglot J. F. , Aristarain A.J. , Furdada G. , Kotlyakov V. M. , Mosley-Thompson E. , Preiss N. , Young N.W.
Published: September 2017

This article aims to give a comprehensive view of the distribution patterns for natural and artifical radionuclides over Antarctica. We focus this study on137Cs,210Pb and tritium. Applying various statistical methods, we show that the deposition of radionuclides reveals a structured distribution, although local drift redistribution and the snow-surface roughness disturb the representativeness of samples and produce a “noise” effect. The deposition of137Cs over Antarctica (885 TBq) represents 0.09% of the total deposition of this radionuclide in the world and the correlation between137Cs fluxes and accumulation shows two sub-populations. For the stations with a mean annual temperature above −21° C, a strong correlation is found, whereas the correlation is lower for locations with temperatures below −21° C. The flux of210Pb varies from 0.9 to 8.2 Bq m−1a−1 with values strongly correlated with the accumulation and a well-defined spatial structure. The same mechanism governs the deposition of artificial and natural tritium but it clearly differs from that of other radionuclides associated with particulate material. The “dry fall-out” accounts for between 60 and 80% of the total fall-out for the artificial radionuclides and around 40% for210Pb. This difference is likely related to a tropospheric fraction for210Pb. Despite its isolated location, the radioactive fall-out of artificial long-lived radionuclides over Antarctica has been ten times greater than for natural radionuclides.
Clast collision frequency as an indicator of glacier sliding rate
Authors: Fischer Urs Η. , Clarke Garry K. C.
Published: September 2017

The mechanical interaction between a glacier and subglacial sediment can be observed using an instrumented rod that we refer to as the UBC ploughmeter. For clast-rich sediments, the rate of collision between clasts and a rod dragged through these sediments should be related to the glacier sliding rate. By assuming that proglacial measurements of sediment granulometry represent the subglacial granulometry of Trapridge Glacier, Yukon Territory, Canada, we have used ploughmeter results to obtain an estimated sliding rate of ∼45 mm d−1, in good agreement with known rates. In addition, for a subglacial material treated as a solid-liquid dispersion having a linear viscous rheology, the force of collision experienced by the rod should be proportional to the effective sediment viscosity. Our estimate of ∼2.0 × 1010Pa s agrees well with previously, derived values.
Seasonal climatic forcing of alpine glaciers revealed with orbital synthetic aperture radar
Authors: Smith Laurence C. , Forster Richard R. , Isacks Bryan L. , Hall Dorothy K.
Published: September 2017

The evolution of four dynamic radar glacier zones at the surface of an alpine icefield in British Columbia is monitored using a time series of 35 First European Remote Sensing Satellite (ERS-1) synthetic aperture radar (SAR) images acquired from 1992 to 1994. These zones result from changing wetness and textural properties, and appear to represent: (1) cold snow with no liquid water present; (2) an initial melt front with an upper boundary near the elevation of the 0° isotherm; (3) metamorphosed, rapidly melting first-year snow with a rough or pitted surface; and (4) bare ice. This interpretation is aided by temperature and runoff data, air photographs and field measurements of snowpack properties acquired with two ERS-1 SAR scenes, ice-surface elevations derived from 1:50 000 topographic maps and simulations of radar backscatter from a geometric optics model of surface scattering. Meltwater production is affected by the development of zones (2), (3) and (4), which form, migrate up-elevation and disappear each year between April and September.
Response of sediment to ice-sheet loading in northwestern Germany: effective stresses and glacier-bed stability
Authors: Piotrowski Jan A. , Kraus Anna M.
Published: September 2017

Laboratory tests on sediment over-ridden by the last ice sheet in north-western Germany reveal very low ice-induced pre-consolidation and high palaeo-pore-water pressures. Sediment consolidation at the base of the glacier was largely controlled by hydraulic properties of the substratum. Generally low permeabilities of the bed caused sustained high pore-water pressure in over-ridden sediments close to the flotation point. This implies a serious possibility of hydraulic lifting of the ice sheet. It is believed that the reduced basal coupling limited the transformation of glacier shear stress on to the bed sediments, which is indicated by a lack of sedimentological evidence for widespread pervasive bed deformation. Ice motion was probably focused at the glacier sole by some combination of sliding and ploughing. However, isolated spots with deformation occur, so that the subglacial system in the study area can be characterized as a stable/deforming mosaic.
Ice deformation at the confluence of two glaciers investigated with conceptual map-plane and flowline models
Authors: Gudmundsson G. Hilmar
Published: September 2017

Using analytical and numerical techniques, a two-dimensional (2-D) map-plane model and a 2-D flowline model are utilized to elucidate the horizontal and vertical ice deformation at the confluence of two glaciers. For a perfectly symmetrical confluence, the junction point of the two tributaries can be modeled as a no-slip/free-slip transition. A strongly localized surface depression develops around the junction point, accompanied by two broadly elevated zones positioned close to the margins of the tributaries facing the junction point. The confluence center line is subjected to horizontal longitudinal extension and a transverse compression. The compression generally exceeds the concomitant longitudinal extension in magnitude. Depth-integrated vertical strain rates along the center line are positive (extension), but the strain-rate variation with depth depends critically on the type of basal boundary conditions at the glacier bed. For a no-slip boundary condition, vertical strain rates change from positive at the surface to negative close to the base, whereas for a free-slip boundary condition (perfect sliding) vertical strain rates are positive throughout the depth. These theoretical results are compared with field measurements from Unteraargletscher, Bernese Alps, Switzerland.
Evaluating the impact of climate on snow- and ice-melt dynamics in the Taillon basin, French Pyrénées
Authors: Hannah David M. , McGregor Glenn R.
Published: September 2017

This pilot study adopts a computer-assisted synoptic typing methodology to evaluate the totality of climatic influences on snow- and ice-melt dynamics within a small cirque basin in the French Pyrénées. The synoptic categories identified possess contrasting large-scale atmospheric circulation patterns and surface energy budgets which generate differential ablation responses. Continental air masses yield consistently high melt. Advection of moist maritime air also produces elevated but more variable ablation due to air-mass transitions. The two observed local valley circulation types show melt to be higher under nocturnal katabatic drainage than for anabatic wind flows associated with development of daytime ridge-top cumulus.
In situ thermal profiles and laboratory impact experiments on iceberg ice
Authors: Gagnon R. E. , Gammon P. H.
Published: September 2017

A series of 40 impact tests was conducted an large right-circular cylinders (68.5 cm diameter and 25.7 cm thickness) of iceberg ice collected from an iceberg in Labrador. Temperature profiles were also obtained for the iceberg and the profiles exhibited differences associated with the probe location. Temperatures as low as –15°C were measured at penetration depths of about 8 m. The impact specimens were confined at the perimeter and base by a rigid metallic ring and plate. A spherically terminated impactor, with center-mounted pressure transducer, was dropped on to the flat top surface of specimens from various heights and with various added masses. Impact velocity varied from 1.8 to 3.9 m s−1; impactor mass varied from 155 to 510 kg and the ice-specimen temperature varied from –0.5° to –14.5°C. Peak center pressures averaged from about 25 MPa at the highest temperature to about 41 MPa at the lowest temperature, with the highest recorded pressure being 50 M Pa. Crater volume increased with increasing impact energy, as expected; however, the specific energy of the ejected material was found to decrease as the energy of impact and crater volume increased. A mechanism for this observed behaviour is proposed.
A comparison between active and passive microwave measurements of the Antarctic ice sheet and their association with the surface katabatic winds
Authors: Remy F. , Minster J. F.
Published: September 2017

The intensity of the Seasat altimeter return power over Antarctica varies in strong correlation with the intensity of model katabatic winds. It is also strongly correlated with the polarization of the passive microwave signal at 37 GHz of the Nimbus-7 SMMR data. It is shown that this is most likely the result of the wind-induced micro-roughness of the ice surface.
Potential effects of subglacial water-pressure fluctuations on quarrying
Authors: Iverson Neal R.
Published: September 2017

Water-pressure fluctuations beneath glaciers may accelerate rock fracture by redistributing stresses on subglacial bedrock and changing the pressure of water in bedrock cracks. To study the potential influence of water-pressure fluctuations on the fracture of subglacial bedrock, ice flow over a small bedrock step with a water-filled cavity in its lee is numerically modeled, and stresses on the bedrock surface are calculated as a function of transient water pressures in the cavity. Stresses on the bed are then used to calculate principal stress differences within the step. Rapid reductions in cavity water pressure increase principal stress differences in the bed, increasing the likelihood of crack growth in the step and the formation of predominantly vertical fractures. Relatively impermeable bedrock may be most susceptible to fracturing during water-pressure reductions because high water pressure in cracks within the rock can be maintained, as water pressure decreases in cavities. These results, when considered in conjunction with the strong likelihood that increases in water pressure accelerate the removal of rock fragments loosened from the bed, suggest that in zones of ice-bed separation where water-pressure fluctuations typically are large, rates of quarrying may be higher than along other parts of glacier beds.
Freezing of water drops on a cold surface
Authors: Walford M. E. R. , Hargreaves D. M. , Stuart-Smith S. , Lowson M.
Published: September 2017

A drop of water falling gently on to a cold copper surface freezes to it, forming a curious minaret-shaped pellet of ice. The shear tractive force necessary then to remove the ice pellet depends on the initial temperature of the metal: it is a maximum at −22°C and falls to zero at −62°C. At impact velocities greater than approximately 0.8 ms−1, depending on the metal temperature, the droplets of water freeze to form irregular pancakes or discs of ice which adhere to the metal weakly if at all.
Deforming-bed origin for southern Laurentide till sheets?
Authors: Alley Richard B.
Published: September 2017

The widespread, uniform till sheets of the southern margin of the Laurentide ice sheet were deposited by fast-moving, wet-bedded ice over relatively short periods of time. Characteristics of these till sheets are entirely consistent with deposition from deforming subglacial sediment layers; it is difficult (although not impossible) to explain their origin through debris transport in basal ice. Careful estimation of debris budgets and studies of sorted sediments contained in the till sheets may clarify their origin further.
Surface profiles and basal shear stresses of outlet glaciers from a Late-glacial mountain ice field in western Scotland
Authors: Thorp Peter W.
Published: September 2017

Surface and basal long profiles are reconstructed for 13 outlet glaciers that drained ice from a large ice field (80 km by 120 km) that formed in the western Grampians of Scotland during part of the Late-glacial period (c, 14000–10000years BP). Basal shear stresses are calculated at 5 km intervals along the central flowlines of the reconstructed outlet glaciers. Individual basal shear stresses for the outlet glaciers range from 10 to 204 kPa. Variations in calculated basal shear stresses within and between the glaciers are mainly explained by differences in bedrock topography, extending and compressional flow, and by differences in basal boundary conditions. Low basal shear stresses (<53kPa) calculated for the terminal zones of Creran, Menteith and Lomond glaciers are partly explained by the overriding of glaciomarine clays with inferred high pore-water pressures and a low yield strength that may have led to rapid basal sliding and thinning of the ice lobes.
A three-dimensional theory of wind pumping
Authors: Clarke Garry K. C. , Waddington Edwin D.
Published: September 2017

Quantitative understanding of the processes that couple the lower atmosphere to the upper surface of ice sheets is necessary for interpreting ice-core records. Of special interest are those processes that involve the exchange of energy or atmospheric constituents. One such process, wind pumping, entails both possibilities and provides a possible mechanism for converting atmospheric kinetic energy into a near-surface heat source within the firn layer. The essential idea is that temporal and spatial variations in surface air pressure, resulting from air motion, can diffuse into permeable firn by conventional Darcy flow. Viscous friction between moving air and the solid firn matrix leads to energy dissipation in the firn that is equivalent to a volumetric heat source.

Initial theoretical work on wind pumping was aimed at explaining anomalous near-surface temperatures measured at sites on Agassiz Ice Cap, Arctic Canada. A conclusion of this preliminary work was that, under highly favourable conditions, anomalous warming of as much as 2°C was possible. Subsequent efforts to confirm wind-pumping predictions suggest that our initial estimates of the penetration depth for pressure fluctuations were optimistic. These observations point to a deficiency of the initial theoretical formulation — the surface-pressure forcing was assumed to vary temporally, but not spatially. Thus, within the firn there was only a surface-normal component of air flow. The purpose of the present contribution is to advance a three-dimensional theory of wind pumping in which air flow is driven by both spatial and temporal fluctuations in surface pressure. Conclusions of the three-dimensional analysis are that the penetration of pressure fluctuations, and hence the thickness of the zone of frictional interaction between air and permeable firn, is related to both the frequency of the pressure fluctuations and to the spatial coherence length of turbulence cells near the firn surface.
Large-scale statistical study of Scanning Multichannel Microwave Radiometer (SMMR) data over Antarctica
Authors: Fily Michel , Benoist Jean-Pierre
Published: September 2017

SMMR data over Antarctica have been statistically analysed for four different periods of 1 year (1981) and compared to geophysical data such as surface temperature, snow-accumulation rate and topography. The spatial variations of the microwave signature are stable with time. Although the ten channels are highly correlated, principal-component analysis reveals the importance of polarization and frequency. The difference between brightness temperatures at the two polarizations is found to be dependent on the atmospheric water-vapour fluxes over the ice sheet, which modify the temperature-accumulation ratio and therefore the snow stratification. The brightness-temperature gradient with frequency is related to the topography of the central plateau area. A more important subsidence over diverging areas could explain the different structure of the accumulated snow.
Steady-state characteristics of the Greenland ice sheet under different climates
Authors: Letréguilly Anne , Huybrechts Philippe , Reeh Niels
Published: September 2017

The Greenland ice sheet is modelled to simulate its extent and volume in warmer climates, and to find out whether the ice sheet would re-form on the ice-free bedrock under present climatic conditions. The ice-sheet model is a three-dimensional thermo-mechanical model with a fine-resolution grid. The bedrock surface beneath the ice sheet was mapped using radio-echo-sounding measurements by the Electromagnetic Institute, Copenhagen. The model experiments show that increased temperature will result in ice-margin retreat, but the ice sheet is relatively stable; it takes a temperature rise of at least 6 deg for the ice sheet to disappear completely, which indicates that the ice sheet probably survived the last interglacial. Furthermore, it appears that the Greenland ice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re-form on the bare bedrock under the present, or even slightly warmer, climatic conditions.
On the Determination of Horizontal Forces a Floating Ice Plate Exerts on a Structure
Authors: Kerr Arnold D.
Published: September 2017

At first, the general approach for calculating the horizontal forces an ice cover exerts on structures is discussed. Ice-force determination consists of two parts: (1) the analysis of the in-plane forces, assuming that the ice cover remains intact, and (2) the use of a failure criterion; because an ice force cannot be larger than the force capable of breaking up the ice cover. For an estimate of the largest ice force, an elastic plate analysis and a failure criterion are often sufficient. A review of the literature revealed that in the majority of the analyses, it is assumed that the failure load is directly related to a "crushing strength" of the ice cover. Observations in the field and tests in the laboratory show, however, that in some instances the ice cover failed by buckling. Subsequently the ice-force analyses based on the buckling failure mechanism are reviewed and their shortcomings are pointed out. A new method of analysis, which is based on the buckling of a floating ice wedge, is then presented.
Atmospheric Processes and the Chemistry of Snow on the Ross Ice Shelf, Antarctica
Authors: Warburton J. A.
Published: September 2017

Correlations between chemical profiles (Na, K and Mg) in three 2 m deep pits, separated by hundreds of kilometers on the Ross Ice Shelf, suggest that the passage of major storm systems is often recorded as peaks in cationic concentration in the snow-pack on the Ice Shelf. The magnitude of the peaks appears to be a function of both storm intensity and the extent of sea ice adjoining the Ross Ice Shelf. Samples were collected from a network of 21 shallow pits on the Ice Shelf. Although concentration of impurities in the snow varies as a function of distance from the sea on northern portions of the Ross Ice Shelf, a more complex relationship exists in the interior of the Shelf. A distinct chemical zone south of Roosevelt Island may reflect the presence of a "cyclone graveyard". Non-marine cationic ratios in the southern portion of the Ice Shelf suggest the significant influence of a fractionated marine aerosol and the presence of a second, continental aerosol source. Ionic ratios in rime deposited on the Ross Ice Shelf during periods of fog are interpreted as reflecting the production of fog droplets from the chemically-enriched surface microlayer of the ocean. Diffusionally grown snow crystals also have non-marine ratios. In contrast, snowfall associated with peaks in chemical concentration in particular, and the snow-pack on northern portions of the Ross Ice Shelf in general, yield near-marine ionic ratios. This indicates that the chemistry of snow which is near the coast and snow from major storms is dominated by large droplet riming and the associated presence of a high proportion of sea-salt particles.
State of Balance of the Ice Sheet in the Antarctic Peninsula
Authors: Doake Christopher S. M.
Published: September 2017

Data from ice rises on the east coast of the Antarctic Peninsula can be interpreted as showing that the ice is thinning at rates of up 0.5 m a−1. However, a level line between two nunataks in Palmer Land showed no change in surface elevation over a period of 5 a. Melt rates on George VI Ice Shelf vary with position and may indicate that parts of the ice shelf are thickening at the rate of several m a−1, presumably in response to a higher accumulation rate over the peninsula a few hundred years ago. A small valley glacier, Spartan Glacier, is wasting away at about 0.27 m a−1. Ice fronts on both east and west coasts of the peninsula have been retreating for the last 30 a. It seems that there is general glacier recession in response to a wanner climate and decreased snowfall for at least the last 30 a, while parts of the peninsula are still thickening in response to a high accumulation rate several hundred years ago.
On Modeling the Weddell Sea Pack Ice
Authors: Hibler W.D. , Ackley S.F.
Published: September 2017

Some results from a dynamic-thermodynamic simulation of the seasonal cycle of the Weddell Sea pack ice are described. The model used for the study is similar to that developed by Hibler (1979) for a numerical investigation of the Arctic ice cover. It employs a plastic ice rheology coupled to a two-level ice-thickness distribution. The thickness characteristics evolve in response to ice dynamics, and to ice growth and decay rates dictated by surface heat-budget calculations and by heat storage in a fixed depth oceanic boundary layer. Observed time-varying wind, temperature, and humidity fields based on the 1979 Australian analysis are used together with empirical radiation fields and fixed ocean currents to drive the model. Employing these fields, the model is integrated over two seasonal cycles. The second-year results are compared to observed ice-drift data obtained by Ackley (1981[b]) and to ice-edge characteristics determined from satellite imagery. In analyzing the results, particular attention is paid to ascertaining the relative roles of ice dynamics and thermodynamics in determining the ice-edge characteristics. A sensitivity analysis of the effect of a different parameterization of the atmospheric temperature and humidity fields is also carried out.

Overall, the results suggest that (1) ice dynamics are essential in describing the seasonal cycle, and (2) a feedback between the atmospheric temperature and the presence of ice may be a major cause of the rapid decay of the Antarctic ice cover during the spring-summer period.
Oceanographic Observations from George VI Ice Shelf, Antarctic Peninsula
Authors: Lennon P. , Loynes J. , Paren J.G. , Potter J.R.
Published: September 2017

Summer profiles of sea-water temperature, salinity and flow were obtained on George VI Ice Shelf near its northern ice front. At each depth, temperature salinity and density show little variation between sites. Their respective variation to 250 m depth confirms a linear temperature-salinity dependence. This is the first place in the world where observations confirm precisely the form of the T-S diagram predicted for fresh ice melting in sea-water. Both tidal and residual flow are small, except at the western margin of the ice front, where a strong outflow is concentrated immediately beneath the ice shelf. The observations lead to a simple circulation model for the ice-shelf regime. Warm Deep Water flows southwards into George VI Sound, replacing the colder water that spreads northwards in the surface outflow. Thermohaline exchanges beneath the ice shelf determine the salinity profile, which itself provides evidence of upwelling. Estimates can be made of the basal melt rate of the ice shelf. The rates vary from around 10 m a−1 at the ice front to an average value for the ice shelf of order 1 m a−1. The average value is consistent with earlier estimates from surveys of ice-shelf strain.
Antarctic Ice Elevation Maps From Balloon Altimetry
Authors: Levanon Nadav
Published: September 2017

Antarctic ice-elevation maps are presented, based on 4 000 measurement points, analysed from traverses made by constant-density balloons. These balloons were launched during the Tropical Wind, Energy Conversion and Reference Level Experiment (TWERLE). The TWERLE data yielded daily maps of the elevation of the 150 mbar pressure surface in the southern hemisphere. These maps serve as a reference level from which the altimeter readings are subtracted to yield the ice elevation.

The accuracy of the ice-elevation data is estimated at better than 60 m. The accuracy of the contouring depends on the density of measurements in the particular area. Two contouring techniques were used. One is based on generating elevation data at fixed grid-points from arbitrarily distributed measurements, using Cressman's method. The second is a surface spline interpolation technique by Duchon.

The elevation data are of special value on the inland plateau areas. There, the typical distance between balloon measurements is sufficiently small, relative to the typical distance between contour lines at 100 m intervals. Furthermore, the inland areas are the least accessible to other mapping techniques.
Numerical Modeling of Ice-Shelf Motion
Authors: MacAyeal D. R. , Thomas R. H.
Published: September 2017

Finite-element simulations of the Ross Ice Shelf flow yield good qualitative agreement with observation, but velocity magnitudes tend to be too low up-stream of ice rises and too high near the ice front. These errors will be significantly reduced by better model convergence to the flow law, more accurate values of the flow-law parameters, better resolution of the ice streams, and inclusion of subgrid scale stress variability produced by crevassing and ice-fabric orientation. A model run featuring a hypothetical ice rise down-stream of Crary Ice Rise indicates that the distinctive strain-rate patterns produced by an isolated ice rise can be cancelled by neighboring ice rises. This suggests that an isolated ice rise might migrate up-stream along sea-bed ridges unless there are neighboring ice rises acting to stabilize the surrounding ice-thickness tendencies.
Gas Extraction From Polar Ice Cores: A Critical Issue For Studying The Evolution of Atmospheric CO2 and Ice-Sheet Surface Elevation
Authors: Raynaud D. , Delmas R , Ascencio J.M. , Legrand M.
Published: September 2017

The measurement of gases enclosed in polar ice cores provides valuable Information concerning the history of the ice sheets and their environment. The extraction of gases from ice is a critical step in the experimental procedure. We found that the most efficient methods of gas extraction for 20 to 50 g samples were ice melting and controlled refreezing of the melt water for the total gas content and ice crushing far the CO2 content. These two experimental methods are described in detail.

It is shown, in particular, that ice is easily contaminated by carbonate dust during sample preparation. This contamination introduces an excess of CO2 when gases are extracted using a procedure involving ice melting.
Air Content Of The Byrd Core And Past Changes In The West Antarctic Ice Sheet
Authors: Raynaud D. , Whillans I. M.
Published: September 2017

Analyses of ice cores taken from the Antarctic ice sheet can provide information on the environmental conditions under which the ice was formed. New results from measurements of gas content and stable isotope ratios in the Byrd station ice core are discussed and interpreted in terms of past iceflow changes.

165 selected ice samples from 32 different depth levels along the core were processed for total gas content V and stable isotope ratios. This large dataset is used to discuss the variability and significance of the values of V at different depths. The short term variations of V are mainly explained by heterogeneities of the pore volume when the firn pores close off.

The general trends in the values of V with depth are then used to investigate the possibility of past changes in the ice sheet. They suggest near-steady flow during the past few tens of thousands of years and that a thickening of about 200 to 250 m occurred in this area of the ice sheet at the end of the last ice age. This thickening could be due to a change in the accumulation rate.
Preliminary Investigations on Accumulation at the Filchner/Ronne ice Shelves and Atka Bay
Authors: Reinwarth O. , Rauert W. , Stichler W. , Moser H.
Published: September 2017

In January 1980, the accumulation rates on the Filchner/Ronne ice shelves and at Atka Bay were determined by snow-pit stratigraphy (at Filchner station) and isotope analyses using a snow pit and a handdrilled core down to about 12 m from the surface. At Filchner station a mean annual net accumulation of 51 cm a−1 of snow representing a water equivalent of 20 g cm−2 was found by stratigraphic measurements. 2H, 180 and 3H analyses led to a value of 55 cm a−1 of snow for the last two decades. At Atka Bay a mean annual accumulation rate of 75 cm a−1of snow resulted from 2H and 180 analyses.
Electrical Resistivity Of George VI Ice Shelf, Antarctic Peninsula
Authors: Reynolds John M.
Published: September 2017

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−3 within 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.
Accumulation Distribution in the IAGP Area, Antarctica: 90°E-150°E
Authors: Young N. W. , Pourchet M. , Kotlyakov V. M. , Korolev P. A. , Dyugerov M. B.
Published: September 2017

The distribution of mean net accumulation rate over a large sector (90°E to 150°E) of the IAGP (International Antarctic Glaciological Project) area in Antarctica is presented in map form. The basic data have been compiled from direct measurements of accumulation at stake networks, and by dating horizons in the snow pack by gross β-activity measurements, on four long traverse routes. The spatial variability can be high, over 40%, for a single year, and typically about 20% for multiyear averages. Local surface topography in the form of undulations of several kilometres wavelength can account for about 35% of the variance. Averaging over Intervals of 50 km or more will give the smooth large-scale distribution pattern. But the resultant values can still deviate from the long-term average accumulation by 25% or more due to temporal variability over time scales of years to decades.

A very high correlation (r = 0.97) was found for the relationship a = 1414 exp (0.060 θ10) between accumulation, a kg m−2 a−1, and 10 m depth snow temperature, θ10°C, when the data set was limited to a single large drainage basin in Wilkes Land.
Seismic Investigations of The Firn-Ice Structure at Dome C, East Antarctica (Abstract only)
Authors: Blankenship Donald D. , Gassett Roger M. , Bentley Charles R.
Published: September 2017

An extensive program of seismic refraction and reflection shooting was undertaken in the vicinity of Dome C station, East Antarctica (latitude 74°39'S, longitude 124°10'E). Refraction experiments (1978–79, 1979–80) were performed at 37 different shot-point-to-center-of-spread distances along four lines of different azimuth using receiver spacings of 2 to 30 m. The principal result is an extremely well-determined velocity-depth relation for the upper few hundred meters of the ice sheet. Availability of good bore-hole control at Dome C allows us to demonstrate the validity of Kohne's (1972) density-velocity formula, which was developed for warmer ice. Also, after a careful search for azimuthal dependence of variations in the time-distance relationship along different refraction lines, deviations from transverse isotropy in the firn and upper ice are not indicated. Our reflection work (1979–80), conducted along three mutually-centered lines (10.2, 10.2, and 10.7 km in length) oriented at 60° angles to one another, used a series of 16 bore holes, each 30 m in depth, and 18 separate 24-channel recording stations. This extensive coverage combined with common reflection-point shooting geometries (to minimize topographic error) and small charge sizes (to increase resolution) yielded the highest quality set of reflection data yet obtained in East Antarctica. Significant crystalline anisotropy in the lower portion of the ice sheet is indicated. A model with 75% of the ice thickness below the firn (approximately 2 400 m) having c-axes distributed throughout a vertical cone with a semi-apex angle of 20° gives good agreement with the field observations.
Deep Geoelectric and Radar Soundings at Dome c, East Antarctica (Abstract only)
Authors: Shabtaie Sion , Thyssen Franz , Bentley Charles R.
Published: September 2017

Deep geoelectric soundings using a Schlumberger array were carried out at Dome C, Antarctica. To penetrate the 3 500 m thick ice, electrode half spacings up to 8 km (the largest yet made on polar ice) were used. A constant-current dc transmitter with voltages up to 10 kV, resulting in constant currents of up to 10 mA, was employed; potentials were measured with an electrometer and recorded continuously on an x-y recorder.

A computer program has been developed to calculate apparent resistivities on an ice sheet in which the density, temperature, and impurities, and thus the actual resistivity, vary continuously with depth. Preliminary models show that the actual resistivity at a depth of about 500 m increases downward by a factor of about three, and that elevated resistivities must persist to much greater depth. This change in resistivity appears to be linked to transition from ice-age to Holocene ice.

The cause of this resistivity increase is not well understood, and may be attributed to any of several physical and chemical changes that also occur at about the same depth.
The Heat Regime of the Central Parts of the Antarctic Ice Sheet with Changing Climate (Abstract only)
Authors: Barbash V.R. , Zotikov I.A.
Published: September 2017

The heat regime and dynamics of the Antarctic ice sheet are studied using numerical modelling for two flow lines, one of which passes Vostok station and the other Byrd station. A two-dimensional non-steady heat-transfer equation with an energy dissipation term was used. The study consists of two parts. The first is a study of velocity and temperature distributions within the glacier under steady-state conditions. The second study was performed assuming surface temperature changes intended to model palaeoclimatic changes for the last 100 ka and also to model future climate changes due to a possible "greenhouse" effect.

Computer numerical modelling shows that the Antarctic ice sheet retains a record of the climatic temperature minimum 18 ka BP. Numerical modelling of the greenhouse effect assumes a temperature increasing by 10 deg within the next 100 a; its influence increases after this even if the surface temperature then remains the same for the next 20 ka. It is shown that for the next 1 ka the temperature wave will penetrate only a thin surface layer of the ice. Even in 20 ka the bottom temperature of the ice sheet will still be unchanged. Small increases of ice velocity can produce ice-sheet thinning of the order of 10 mm a−1.
Geocryological Zones Of Antarctica (Abstract only)
Authors: Vtyurin B.I.
Published: September 2017

Criteria for the determination of geocryological zones are: (1) distribution of permafrost, (2) the mean annual temperature of permafrost, (3) thickness of the active layer, (4) types of ground ice and ice content of permafrost, (5) regularities of cryogenic structure, (6) cryogenic phenomena, and (7) types of cryogenic relief.

Interpretation of the available data allows us to delineate the following geocryological zones in the Antarctic: (1) sub-Antarctic islands, (2) coastalcontinental, and (3) intercontinental. The brief general geocryological characteristic of these zones is given in the paper.

The sub-Antarctic island zone features discontinuous and continuous permafrost. The mean annual temperature of the permafrost is near 0°C and the maximum thickness is several tens of metres. The seasonal thawed zone has a thickness of 0.4 to 1.2 m. There are visible ice inclusions and very small ice forms in the permafrost and seasonal frost. Frost action causes frost sorting, hill - slope forms, and thermokarst. Ice-wedges are not found in the sub-Antarctic zone.

The coastal-continental zone has continuous permafrost. The mean annual temperature of the permafrost therejs -1°C in the Antarctic Peninsula and up to -5 to -7°C in East Antarctica. Maximum thickness of the permafrost is over 100 m and the active layer is 0.3 to 1 m. The ground ice is mainly pore ice but in some places there is buried glacier ice in moraine. Frost action, frost sorting, creep, nivation, and pre-glacial slope forms are developed in the coastalcontinental zone.

The intercontinental zone consists of continuous permafrost only. The mean annual temperature of the permafrost there is -10°C or lower. Thickness of this permafrost is several hundreds of metres and of the active layer is 0.1 to 0.5 m. The ice content is low with only small ice forms. The cryogenic structure of the permafrost is the same as the coastal-continental zone. Because alternate freezing and thawing is infrequent in the intercontinental zone all cryogenic processes are less rapid than in the other zones. Thermokarst is not found there and 1n general the intercontinental zone is not as well studied as the two other zones.