bluuebunny/crossref_metadata_2025 huggingface dataset:
The Uplift of Unteraargletscher at the Beginning of the Melt Season—a Consequence of Water Storage at the Bed?
Authors: Iken A. , Flotron A. , Haeberli W. , Röthlisberger H.
Published: September 2017

The results of systematic movement studies carried out by means of an automatic camera on the Unteraargletscher since 1969 (Flotron, 1973) are discussed together with more recent findings from theodolite measurements made at shorter intervals and over a longer section of the glacier.

In addition to the typical spring/early-summer maximum of velocity known from other glaciers, an upward movement of up to 0.6 m has been recorded at the beginning of the melt season. It was followed, after various fluctuations of the vertical velocity, by a similar but slower downward movement which continued at an almost constant rate for about three months. The uplift was not confined to the section covered by the camera but occurred nearly simultaneously in profiles located 1 km below and 2 km above. The times of maximum upward velocity (increases of up to 140 mm/d) coincided approximately with periods of large horizontal velocity and occurred after increases of melt-rate.

The following explanations for the variations of vertical velocity are considered: (1) Changes of longitudinal strain-rate. (2) Changes of the sliding velocity in a channel of variable width and with a bed slope deviating from horizontal. (3) Changes of volume due to opening or closing of crevasses. (4) Swelling or contraction of veins at the grain edges. (5) Growth (and closure) of cavities in the interior of the glacier. (6) Changes of large-scale water storage at the bed.

Although all of the mechanisms (1)–(5) have some effect on the vertical ice movement, they cannot account for the observed variations of vertical velocity. We therefore conclude that large-scale water storage at the bed is the main cause of the uplift. Apparently the storage system is efficiently connected with the main subglacial drainage channels only during times of very high water pressure in the channels.

The findings are of some interest to the concepts of glacier sliding: As mentioned above the maxima of horizontal velocity—and thus of the sliding velocity—have not been measured at the time when the storage had attained a maximum, but at the time of maximum vertical velocity, which we assume to be the time of most rapid growth of cavities at the bed. This behaviour of the sliding velocity agrees with that predicted by a simple finite-element model of the basal ice on a wavy bed with water-filled cavities. In particular, the model shows that the sliding velocity is larger during the process of cavity growth than at the final stage when the cavities have grown to the size which is stable for the applied water pressure.
Englacial and Subglacial Hydrology, Austre Okstindbreen, Norway
Authors: Theakstone W. H. , Tvis Knudsen N.
Published: September 2017

The efficiency of drainage systems within the glacier Austre Okstindbreen apparently increases as the summer progresses. As the transient equilibrium line moves up-glacier and the main system extends headwards, several systems may join together. Much of the detail of the glacier river hydrograph depends on the development of the internal drainage systems, although its general form reflects climatic conditions. Streams flowing from both Austre Okstindbreen and the adjacent, much smaller, steeper glacier, Charles Rabots Bre respond quickly to rain, but the sustained high summer discharge of the Austre Okstindbreen river, even during periods without rainfall and ablation, indicates that much water is stored within the glacier. The volume of water leaving Austre Okstindbreen in summer partly reflects the amount of snow accumulated during the preceding winter. Surface structures and internal drainage systems convey water rapidly towards the margins of both glaciers, but their rivers do not display regular diurnal variations of level until part way into August; at glacier rivers further south, such fluctuations occur throughout the summer. Each year, in late July or early August, a lake dammed by Austre Okstindbreen drains through the glacier. Drainage may be triggered by a decline of water pressure in conduits near the lake.
Abstracts of Papers Accepted for the Symposium but not Presented: The Origin of Drumlins as an Ice-Rock Interface Problem
Authors: Baranowski S.
Published: September 2017

The origin of drumlins has long been one of the most intriguing, yet unsolved problems in glacial geology. It seems that until the mechanism responsible for drumlin formation is fully understood some of the key glaciological problems related to the glacier bed will remain obscure.
Seismic Evidence of a Wet Zone Under the West Antarctic Ice Sheet
Authors: Dewart Gilbert
Published: September 2017

It appears to be possible to identify certain conditions of thermal regime at the base of a glacier through the seismic reflection method. In some cases layers of water or wet rock debris may be identifiable. The procedure is based upon the reversal of phase of reflected dilatational waves at the interface between ice and a substratum of lower acoustic impedance. Illustrations of the method are given from the west Antarctic ice sheet, and suggestions are made for the improvement of the technique.
The Translational Lattice-Vibration Raman Spectrum of Single-Crystal Ice Ih
Authors: Faure P. , Chosson A.
Published: September 2017

We present the Raman spectra in natural and polarized light of ice Ih monocrystals in the region of the translational frequencies. These spectra are of better quality and higher resolution than previous spectra from monocrystals, and demonstrate the value of the investigation of single crystals by this technique, in spite of the proton disorder. In order to explain the observations we use the model of simultaneous activity of the modes allowed in D6h symmetry and the modes allowed by the proton disorder. By analogy with the interpretation of the phenomena observed in ordered piezoelectric crystals, we suggest that the existence of translation frequencies up to c. 320 cm-1 is due to the splitting between transverse and longitudinal optical modes. On this basis, an initial simple dynamical model using only three parameters permits an interpretation of the Raman spectrum. The probable presence of directional effects in ice Ih argues in favour of the proposed explanation.
Vacancies in Pure Ice Studied by Positron Annihilation Techniques
Authors: Mogensen O. E. , Eldrup M.
Published: September 2017

Positron annihilation techniques (PAT) are briefly discussed, and the information that may be obtained about the positronium (Ps) states is compared to that obtainable about the similar electron states. The behaviour of Ps in monocrystals of pure light and heavy ice was studied at temperatures between — 185°C and the melting point. Ps is very probably trapped in vacancies (i.e. missing water molecules) in ice. A vacancy formation energy of roughly 0.2–0.35 eV was derived in agreement with the value 0.28±0.07 eV obtained previously from studies of the annealing of irradiated ice. The vacancy concentration is at least a few parts per million at the melting point, i.e. roughly 104 times higher than normally assumed in the literature. The fact that the vacancy concentration is comparable to that of the hydrogen-bond defects will probably enforce a pronounced change in the “hydrogen-bond-defects” theory of the electric properties of ice.
Electrical Conductivity and Relaxation in Ice Crystals with Known Impurity Content
Authors: Gross Gerardo Wolfgang , Hayslip Iris Cox , Hoy Roberta N.
Published: September 2017

Three-terminal dielectric bridge measurements (in the range 20 Hz to 100 kHz between — 5°C and —90 to — 120°C) have been made of ice doped with (a) conductivity-enhancing ionic impurities (HCl, HF, NaCl, KF, NH4F) and (b) conductivity-depressing solutes (NH4OH, NH4Cl, NH5CO3, NaHCO3). Blocking electrodes were used for the first group. The true ice parameters were extracted from linearized plots of the Debye equations. Chlorides and fluorides showed very similar characteristics in their spectra and static conductivity. The results suggest that static conductivity is controlled by extrinsic protons. On the other hand, bases, or solutes that impart a positive freezing potential to the ice, suppress extrinsic protons. In this case, the static conductivity was not, or only weakly, temperature dependent and lower than in the first group. A conductivity cross-over was observed in neither case. The dielectric conductivity contribution is strongly dependent on impurity concentration but apparently less affected than the static conductivity by the nature of the solute. The principal relaxation time is reduced by most solutes, exceptions are pure (bicarbonate-free) bases, sodium bicarbonate, and carbon dioxide.
Dielectric Properties of Dislocation-free Ice
Authors: Itagaki Kazuhiko
Published: September 2017

Dielectric properties of dislocation-free hoar-frost ice crystals were measured in the audio-frequency range. Anomalously small relaxation strength was found in the dislocation-free area of the crystal samples while dislocations deliberately introduced by scratching the samples drastically modified the relaxation strength. Since measurements made in the area of high dislocation density indicated normal behavior, electrically charged dislocations are considered to be the source of the normally observed dielectric relaxation.
The Orientation Polarization in Hexagonal Ice Parallel and Perpendicular to the c-axis
Authors: Johari G. P. , Jones S. J.
Published: September 2017

The relative permittivity and loss of zone-refined single crystals of hexagonal ice have been measured in the temperature range 200–271 K and frequency range 0.5 HZ–0.2 MHz, using brass, stainless steel, and gold-foil electrodes. The c-axis of the crystal was oriented parallel to the electric field in 14 samples and perpendicular to the field in 8 samples. The equilibrium relative permittivity of orientation polarization ϵ0, parallel and perpendicular to the c-axis, is 96.5±1 and the average relaxation time τay is 36 μs at 265±0.5K; ϵ0 = 124±1.5 and τav = 30 ms, at 210 K. The magnitude of the orientation polarization obeys the Curie-Weiss equation with T0= 15±2 K for both the orientations. These values are in contrast with the c. 17% difference in ϵo for the two orientations reported in the literature. The extrapolated limiting high-frequency relative permittivity ϵ∞, measured for both the orientations, is indistinguishable within 0.5%.

The logarithmic plot of the product of τav and temperature against the reciprocal temperature is linear in the range 210–271 K and gives an activation energy and a pre-exponential factor of 51±2 kJ mol–1 and 0.93±0.22 ps K respectively, for both the orientations of the c-axis with respect to the electric field. The decrease in activation energy which has been reported to occur in polycrystalline ice and in single crystal ice near 230 K is not found until a temperature of 210 K. Single crystals of ice stored in the dielectric cell, after the completion of measurements, for periods ranging from 1–11 weeks at 253±2 K showed no change in their ϵ0, τav, ϵ∞ that could be attributed to the effect of ageing on the orientation polarization.
The Activation Energies of Temperate Snow Samples
Authors: Traub L. T. , Gribbon P. W. F.
Published: September 2017

The temperature dependence of the high-frequency conductivity of snow was studied for eight samples in the range — 10°C to — 80°C. The activation energies for granular snow varied from 0.60 eV at temperatures down to — 25°C to 0.24 eV at temperatures below — 25°C, and for dry snow from 0.42 eV to 0.18 eV in the same temperature ranges. Dry snow samples had higher conductivities and lower activation energies than granular icy samples throughout the complete temperature range.

Volume and surface conduction processes were operative. At the higher temperatures above — 25°C volume conduction was attributed to Bjerrum defect migration, while at lower temperatures Bjerrum conduction was replaced by ionic-defect conduction. Granular samples which had experienced melting and reflecting on the surface of the crystals have a structural change which decreased the ionic-defect density at the surface and lowered the sample conductivity.

Above — 25°C, the activation energies for granular icy snow were consistent with those for temperate glacier ice and for laboratory single and polycrystalline ice samples, but was not in agreement with those of either polar snow or ice. Below — 25°C, the activation energies for granular snow were consistent with those for temperate glacier ice, containing impurities, and for polar snow and ice. Fresh dry temperate snow-samples had lower activation energies than in situ polar snow.
Cooperative Movement of H2O Molecules and Dynamic Behaviour of Dislocations in Ice Ih
Authors: Perez J. , MaÏ C. , Vassoille R.
Published: September 2017

A new model of dislocations glide in ire Ih is proposed. In developing this model certain assumptions are made: (i) dislocations have a non-crystalline extended core, and (ii) transitions occur through cooperative movements of ?2? molecules in the core of dislocations. A relation between the velocity νd of linear defects and shear stress τ or temperature T is obtained. This relation shows that νd varies linearly with τ at low values of τ and (or) T but varies more rapidly at higher stresses; this non-linearity is more pronounced the higher the temperature. Such results are in agreement with experimental data.
Inelastic Behaviour of Ice Ih Single Crystals in the Low-Frequency Range Due to Dislocations
Authors: Vassoille René , Maï Christian , Perez Joseph
Published: September 2017

The inelastic behaviour of ice Ih single crystals has been investigated by an inverted torsional pendulum in the low-frequency range. Three features are distinguished:

(i) a relaxation peak previously observed by several authors in the higher-frequency range,

(ii) an internal friction increasing with temperature in the high-temperature range (230–273 K),

(iii) within this high-temperature range, internal friction becomes amplitude dependent, and this dependence becomes greater the greater the temperature.

In this case, the internal friction has been interpreted in terms of movements of dislocations. Hence, the experimental results are interpreted with a model of internal friction based on an empirical relation for the velocity of dislocations. This model of internal friction is in fair agreement with experimental data . It is possible then to get an estimate of dislocation density. Hence it is shown that internal friction experiments can be useful in the study of the plastic behaviour of ice single crystals.
Anelastic Behaviour of Polycrystalline Ice
Authors: Duval Paul
Published: September 2017

Torsion creep tests were performed on glacier ice at temperatures above -12°C. The polycrystalline ice, when unloaded, exhibits creep recovery. The time-dependent recoverable component of deformation (or anelastic strain) ϵa was found to be adequately described by a relationship of the form: ϵa = Δτ log(r + αt)/h, where Δτ is the stress decrement, α a constant, and t the time. The anelastic modulus h defined for times t in excess of 3 h is always smaller than the dynamic elastic modulus. The movement of dislocations composing the sub-boundaries or in dislocation pile-ups may produce this important reversible deformation. The time-dependent recovery is explained in a similar way to the transient creep behaviour observed at low temperatures for metals. The small temperature dependence of creep recovery would arise from the existence of a distribution of internal stresses values.
Regelation and the Deformation of Wet Snow
Authors: Colbeck S. C. , Parssinen N.
Published: September 2017

The thermodynamics of phase equilibrium control the temperature distribution around the ice particles in wet snow. When the snow is stressed, pressure melting occurs at the inter-particle contacts and the snow densifies. Densification is described by a physical model which simulates the heat flow, meltwater flow, and particle geometry. The effects of ionic impurities, liquid saturation, and particle size are demonstrated. Typical values of the temperature difference, inter-particle film size, and density are calculated as functions of time. The calculated rates of compaction are too large, hence, at some later time, the effects of simultaneous grain growth must be added to the model.
The Dislocation Formation Volume in Ice
Authors: Cotterill R. M. J. , Pedersen O. Bøcker
Published: September 2017

Relaxations around a shear dislocation loop on a basal plane in ice have been studied by molecular dynamics. The model intermolecular potential included directional components which stabilized the open ice structure. A random phase approximation was introduced to simulate the disordered arrangement of hydrogen bonds. The dislocation formation volume was found to be zero within the limits of computational error. This paper is published in full in Nuclear Metallurgy, Vol. 20, Pt. 1, 1976, p. 572-81.
Dimesional Changes of Ice Ih with Time
Authors: Camp Paul R.
Published: September 2017

Two different types of experiment were reported. Both used a pure single crystal of ice freshly grown in the laboratory at 2 mm per hour.

Direct volumetric measurements were made by submerging an ice crystal (volume 143 cm3) in mercury in a sealed steel container and electronically monitoring the height of the mercury in a manometer tube connected to it. Measurements over a 60 d period at —4.0°C showed a small gradual decrease in apparent volume. This could be due to the adsorption of perhaps 10-2 cm3 of air trapped by the mercury at the surface of the ice. The total un-certainties of the experiment are such that we believe we would have observed a volume dilation of as little as 2.5 × 10-6 per day.

Direct measurements were also made of the change in length of ice samples from the same crystal. One was cut with length parallel to c and the other perpendicular to c. Over a 28 d period, the fractional change in length at —13.7°C was less than 2 × 10-7 per day and less than 7 × 10-8 per day ║c, leading to an upper bound on volume change of 7 × 10-7 per day.

We conclude that if dilation of ice occurs with time, it is less than 10-6 per day and therefore probably not a factor which needs consideration in ordinary experiments.
An Effective Pair-Potential Study of the Interaction of a Water Monomer with the Basal-Plane Surface of Ice Ih
Authors: Hale B. N. , Kiefer J.
Published: September 2017

The central-force effective pair potential of Rahman and others (1975) is used to generate minimal binding-energy surfaces and configurations of a water monomer adsorbed on the unrelaxed basal plane surface of ice Ih. In the initial study H2O molecules arc placed with oxygen atoms fixed at the ice Ih lattice positions and associated hydrogens along the tetrahedral bond directions—restricting the H-O-H bond angles to 109.5°. A rigid-body water monomer adsorbed on the surface interacts with all the H2D molecules in the bulk ice model via the central-force effective pair potential. The center-of-mass height, z, and the dipole orientation of the adsorbed H2O molecule are varied to minimize the total binding energy of the monomer over a particular (x,y) point of the surface. Preliminary results showed that a rigid adsorbed monomer with an H-O-H angle fixed at 104.5° produced only minor deviations in the binding-energy surfaces and that a large bulk-ice model (486 molecules) gave effectively the same results as a smaller ice model (50 molecules). Studies on an infinite ice surface using periodic boundary conditions are in progress and will be used to study surface relaxation and long-range effects on the minimal energy surfaces. Three types of sites on the basal plane were considered: (1) a site with all surface molecule protons pointing out of the surface; (2) a site with all surface molecule protons pointing into the surface; and (3) a site with all rows of surface molecule protons pointing alternately into and out of the surface. A "site" generally refers to a region (about 90 Å2) on the surface over which the minimal binding-energy surface is to be determined.

Minimal binding-energy surfaces for the sites have been obtained together with plots showing the surface of the position of the center of mass as a function of x and y. This is a model calculation and is limited by the validity of the potential under close scrutiny. However it gives a qualitative picture of how complex a terrain the real ice Ih surface might present to an adsorbed water molecule and how the water molecule might diffuse from site to site. From these calculations (and in the spirit of this model potential) a value for the mean path length and the mean residence time of the adsorbed water monomer can be estimated.
Enthalpy Relaxation Phenomenon in a Heavy Ice Crystal
Authors: Haida Osamu , Suga Hiroshi , Seki Syūzō
Published: September 2017

The heat capacities of quenched and annealed heavy ice Ih were measured in the temperature range 14 to 300 K by an adiabatic calorimeter. A relaxational thermal anomaly was found at around 115 K and this phenomenon was ascribed to the onset of deuteron ordering in the crystal. The average activation enthalpy of the relaxational process was determined to be (26±5) kJ mol-1. Residual entropies of the crystal were recalculated on the basis of the present heat-capacity data combined with the revised values for enthalpy of vaporization, saturated vapour pressure, and spectroscopic entropy. They are (3.47±0.41 J K-1 mol-1 for the quenched crystal and (3.44±0.41) J K-1 mol-1 for a crystal annealed at 102-106 K for 264 h. The characteristics and the origin of the anomaly are discussed in comparison with that of ordinary ice.

This paper has been accepted for publication in full in a forthcoming issue of the Journal of Glaciology.
Reconstructed Ledges: Ice Crystal Growth without Dislocations
Authors: Bartley David L.
Published: September 2017

We give a simple explanation of recent experimental evidence that ice crystals may grow in water vapor at low supersaturation (i.e. under atmospheric conditions) without screw dislocations. Examination of the intermolecular potential shows that by assuming non-bulk-like orientations, dangling molecules at surface-cluster edges may form strong hydrogen bonds with substrate molecules. This leads to a study of ice surfaces within the framework of an Ising-like model in which molecules with nearest neighbor vacancies which can provide vertical bonding are allowed two distinct states, yielding bulk-like as well as reconstructed monolayer ledges. The surface roughening transition is examined for this model by means of (i) a Monte Carlo determination of critical points and (ii) an analytical treatment of nucleation clusters. It is found that rough surfaces and, correspondingly, (dislocation-less) surface nucleation growth, prevail at temperatures below the bulk melting point over a wide range of feasible binding energies.
The Electrical Properties of Snow and Ice
Authors: Glen J. W. , Paren J. G.
Published: September 2017

This paper reviews the electrical properties of snow and ice that are of importance in remote sensing using electrical devices. After a review of the observed laboratory behaviour of ice samples and the microscopic theory which has been advanced to explain this, the data on temperate and polar glacier ice are compared with the laboratory data. Temperate glacier ice is generally rather similar to laboratory ice, but certain relaxation processes found in the laboratory are absent from the glacier ice. Polar ice, on the other hand, is considerably different in its dielectric behaviour from "pure" laboratory ice, or temperate glacier ice; in many ways it more resembles doped laboratory ice, despite its variable, sometimes low, impurity content. It also resembles in behaviour ice produced by freezing supercooled water. The electrical behaviour of snow, and the attempts to account for this in terms of the behaviour of the ice and air components, and also of the water component in wet snow, are next discussed. Finally the implications of this work for radio-echo sounding of ice, radar reflectivity from wet and dry hydrometeors, devices for determining the water content of snow, and resistivity surveys of glaciers are discussed.
Layer echoes in polar ice sheets
Authors: Preben Gudmandsen
Published: September 2017

A multitude of extensive layers have been observed by radio-echo soundings in Greenland. By comparison with the stable isotope profile from Camp Century it is found that layering in the lop of the ice has been formed in the period since the last glaciation. Radio-echo layers observed at greater depths in central Greenland may have been created in the period of the interstadials and further down possibly in the period prior to the last glaciation. Further investigations are needed to prove this.
The Analysis of the Near-surface Energy Transfer Environment from Thermal Infrared Imagery
Authors: Outcalt Sam I.
Published: September 2017

The radiant surface temperature imaged by thermal infrared line-scanning equipment is a product of both surface temperature and emissivity. In detail it is the integrated product of the evolutionary development of the near-surface energy transfer regime. The variation of surface radiant temperature spatially and temporally contains information about the structure, composition, and thermal state of near surface materials. It is suggested that the study of ground ice, sea/lake ice, and the thermal regimes of mountain snow and ice bodies, are reasonable targets for the quantitative application of thermal mapping technology, and that considerable technical development effort be expended on spectral, spatial, and temporal operators for use in computer processing of pictures for glaciological data.
Erts Data in Glaciology—An Effort to Monitor Glacier Mass Balance from Satellite Imagery
Authors: Østrem Gunnar
Published: September 2017

Due to increased demand for electric energy, which in Norway is produced almost entirely by hydro-electric power plants, extensive glacierized basins are now considered for future power production, However, glacier behaviour has a great impact on the annual run-off from these basins, and information about expected annual deviations from a “normal” discharge must be obtained from mass-balance studies on representative glaciers within the basin. For this reason such studies are presently performed at eight selected Norwegian glaciers; the costs involved are in the order of $3 000-$10 000 annually for each observed glacier.

The transient snow line can be identified easily on conventional air photographs and its height determined by direct comparisons with reliable topographie maps (with contour lines on glaciers). The resolution in ERTS images is sufficiently good to use the satellite data for a similar height determination of the transient snow line on glaciers—at least on the larger valley glaciers and, of course, on ice caps.

Due to an existing correlation between the height of the transient snow line (at the end of the melt season) and the annual specific net mass balance, it is possible to construct a diagram expressing this relationship, provided detailed mass-balance studies have been performed during a period of several years of different mass-balance conditions (ideally comprising both years of negative and of positive net balances). Determinations of the transient snow-line height based upon ERTS data, obtained at the end of the summer season, can then be used to determine the mass balance for those glaciers where the above-mentioned relationship is established. This would be a great advantage in cases where there is a request for information on the net balance only; no separate data on winter balance or summer balance will be obtained by this method.

Experiments have been performed to delineate the transient snow line on glaciers directly from ERTS digital data (CCT magnetic tape). The results indicate that last winter’s snow is characterized by grey-levels 41-48 (of 63 possible grey-scale levels) on MSS-7, whereas exposed glacier ice is represented by levels 13—20 in the same multi-spectral band. Snow and ice can also be separated on MSS-4, but the difference in grey-scale levels between the two materials is much smaller.
Radio-Echo Sounding of Mountain Glaciers
Authors: Zotikov I. A. , Luchininov V. S. , Macheket Yu. Ya. , Suchanov L. A.
Published: September 2017

Experiments on radio-echo sounding of mountain glaciers have been done on Lednik Marukh (west Caucasus), Lednik Bezingy and Lednik Dzhankuat (central Caucasus), Lednik Gergety (east Caucasus), and Lednik IGAN (Polar Urals) in 1967-71 as a part of the I.H.D. programme. Radio altimeters operating at a frequency of 440 MHz with a pulse duration 0.5 μ5 and with an assumed radio-echo system performance of 130 dB were used. The apparatus was operated from the ice surface (using sledge or vehicle) and partly from a helicopter. Some measurements have been made while the apparatus was being moved continuously along longitudal and transverse profiles of the glacier. Some of the measurements have been made at separate points on the glacier. The methods of measurement and interpretation have been worked out. Data on ice thickness, subglacial topography, and internal structure of some mountain glaciers have been obtained and compared with data got using other geophysical methods and thermal drilling. There is agreement between the results.
The use of planimetric surface area in glacier mass-balance calculations: a potential source of errors
Authors: Jacobsen Frank M. , Theakstone Wilfred H.
Published: September 2017

Large errors in the estimation of glacier ablation and accumulation may arise from the uncritical use of planimetric surface areas in volume calculations based on specific point values. Three-dimensional digital terrain models of glacier surfaces show that the actual surface area is likely to be substantially larger than the planimetric area; with high-resolution digital terrain models, approximations of the true surface area may be as much as 20% larger. The errors are sufficient for questions to be raised about some calculations of water storage in glaciers, because incorrect surface-area values may result in ablation being underestimated substantially. Errors may also be introduced into calculations of radiation-energy inputs to a crevassed glacier surface.
Anomalous glacier responses to 20th century climatic changes in Darwin Cordillera, southern Chile
Authors: Holmlund Per , Fuenzalida Humberto
Published: September 2017

There is an asymmetric pattern response of glaciers in Darwin Cordillera (54–55° S, 69–71° W) to the climate of the 20th century. This asymmetry is suggested here as a cause of an increased wind activity which has a pronounced orographic effect. Although climatic records for the last 50 years show a warming trend, as well as no trend in precipitation in the area, some glaciers are advancing. The area is characterized by strong climatic gradients, with high rates of precipitation on the southwestern side of the range and dry conditions on the northern side. Glaciers on the northern and eastern sides show a general trend of receding fronts. With a few exceptions, these glaciers have gradually and uninterruptedly been shrinking since the turn of the century. On the southern rim, the present extents of some glaciers are similar to their 20th century maximum extents. These are, in turn, similar or close to the Holocene maximum. The most extreme sites are the glaciers on either side of Mount Darwin, which is 2469 m high. The north-facing glacier Ventisquero Marinelli has retreated several hundred metres per year over the last two decades, while the south-facing glaciers in the Pahia Pia basin have advanced during the same period.

In this study, the frontal changes over the last 50 years of 20 glaciers have been analysed. Aerial photographs (verticals) from 1943 and 1984 have been used, as well as oblique aerial photographs from 1993. The general result is that glaciers with accumulation areas facing south and west show somewhat stable fronts, while glaciers facing east and north show receding fronts.
A topographic origin for double-ridge features in visible imagery of ice divides in Antarctica
Authors: Goodwin A. H. , Vaughan D. G.
Published: September 2017

The appearance of double-ridge features on visible imagery of the ice divides of Antarctic ice rises has often been noted but, largely due to a lack of adequate ground truth, their origins have remained enigmatic. We present several examples of ice rises and other isolated ice-flow centres that apparently show double ridges. We investigate one of these in particular: Fletcher Promontory, Antarctica. A digtal-elevation model (DEM) of the summit region is derived from surface profiles obtained using the Global Positioning System (GPS) and this is correlated with Landsat MSS satellite imagery. Precise registration is achieved by correlating image-brightness values with surface slope calculated along the direction of the Sun azimuth in the image. Using a simple bi-directional relation, the DEM data are used to model the Landsat image. We therefore demonstrate that the double ridge is a product of a subtle concavity parallel to the ridge and is unlikely to be dependent on other factors. This concavity is not predicted by steady-state models of ice divides and so we suggest that the ridge may not be in a steady-state but responding to changes in the glaciological boundary conditions. We speculate that this may be an indication of ongoing migration of the ice divide.
Radiative fluxes and their impact on the energy balance of the Greenland ice sheet
Authors: Konzelmann Thomas , Ohmura Atsumu
Published: September 2017

A meteorological experiment was carried out during the summer months of 1990 and 1991 near the mean equilibrium-line altitude (ELA) on the western slope of the Greenland ice sheet (ΕΤΗ Camp; 69° 34’ N, 49° 17’ W; 1155 m a.s.l.). As a part of the project, the energy fluxes at the surface, including all components of the radiation balance, atmospheric profiles with a tower and radiosondes, and the cloud conditions were investigated in detail. Results from the radiative fluxes are compared with observations made at other locations in order to derive general characteristics of the radiation conditions on the Greenland ice sheet and their relation to the climate cf the ice sheet.

At ΕΤΗ Camp, albedo values obtained at ground level (2 m) and from a high tower (27 m) are similar during the melt season (late May to mid-August) and slightly different during pre- and post-melt seasons due to the interplay of inhomogeneous surface conditions and solar elevation. During the melt period, the decrease in global radiation due to increasing cloud amount is compensated for by an increase, m longwave incomine, radiation. Because of the steady values of longwave outgoing radiation, net radiation at the surface is characterized mainly by the albedo and its variation. The regional net radiation for summer months on the Greenland ice sheet is determined mainly by three facts: (1) a strong increase in alhedo from the ablation area to the ELA and a smaller increase Gom the ELA to the accumulation area: (2) a large increase in longwave outgoing radiation in the ablation area and at the ELA in June and July compared to the accumulation area: (3) a larger amount of cloud of the stratus type at lower areas.
Glacio-meteorological and isotopic studies along the EGIG line, central Greenland
Authors: Fischer H. , Wagenbach D. , Laternser M. , Haeberli W.
Published: September 2017

The geographical distribution of firn temperature, annual accumulation rate as well as deuterium and oxygen-18 content in the firn were determined along an east-west transect through central Greenland. This study is based on isotopic and chemical analyses of shallow firn cores at 18 sites along the EGIG line and high-precision firn-temperature measurements m 17 steam-drilled boreholes along the eastern part of the transect. The firn temperatures at 15 m depth range from -31.6°C at Dome GRIP (3230 m a.s.l.) to -11.4°C at Caecilia Nunatak (eastern ice margin at 1600 m a.sl.) and -18°C at T05 (near the western ice margin at 1900 m a.s.l.). The temperature/altitude gradient changes from -0.7°C (100 m)−1 in the ice divide region to -1.1 °C (100 m)−1 in the eastern part of the dry-snow zone. The temperature/latitude gradient in the central part of the EGIG line is -0.7° C lat−1 The average annual accumulation decreases significantly from the west (~47 cm a−1 water equivalent at T05) towards the ice divide (20–25 cm a−1 water equivalent from T99 to T43). Accumulation rates are constantly low east of the ice divide (−23–17 cm a−1 water equivalent), thus dividing central Greenland into two climatologically different regions. The average δ18O and δD values along the whole EGIG line reflect the well-known temperature-dependence for Greenland very well (e.g. ∂18O/∂Tm = 0.69%ₒ °C–1 Different regression lines for the western and eastern part, however, should be applied. Unlike the mean annual temperature, the isotopic minimum along the EGIG line lies east of the ice divide. This geographical distribution supports the choice of different water-vapour trajectories in central Greenland for the west and for the east. Significant parts of the water precipitated over the western slope are attributed to cyclonic systems entering Greenland from the west. The deuterium excess shows no significant geographical trend but a uniform seasonal variation at all sites along the EGIG line, suggesting equal contributions from vapour-source areas of the water precipitated over central Greenland.
Theory of lattice Boltzmann simulations of glacier flow
Authors: Bahr David B. , Rundle John B.
Published: September 2017

A lattice Boltzmann technique for modeling Navier–Stokes fluid flow is extended to allow steady-state simulations of glaciers and other slow-flowing solids. The technique is based on a statistical mechanical representation of flowing ice as a set of particles (populations) which translate and collide on a face-centered cubic lattice. The average trajectories of the populations give the velocities of the ice at any point in the glacier. The method has considerable advantages over other techniques, including its ability to handle complex realistic geometries without additional complications to the code Examples are presented for two-dimensional simulations.
The use of tiltmeters to study the dynamics of Antarctic ice-shelf grounding lines
Authors: Smith A. M.
Published: September 2017

New tiltmeter data are presented from Doake Ice Rumples on Ronne Ice Shelf, Antarctica. Five sites which showed a tidal ice-shelf flexure have been analysed using an elastic beam model to investigate the variation of flexure amplitude with distance from the grounding line. An earlier study on Rutford Ice Stream which also used an elastic model required an ice thickness much less than that observed. Reworking the Rutford Ice Stream data suggests that this greatly reduced ice thickness is not required, given the current sparse data coverage. The elastic model is used to improve the estimated grounding-line position on Rutford Ice Stream. Some of the difficulties in modelling ice-shelf flexure and locating grounding lines are discussed.
Measuring the dihedral angle of water at a grain boundary in ice by an optical diffraction method
Authors: Walford M.E.R. , Nye J.F.
Published: September 2017

Optical measurements have been made on the water lenses which form under pressure at grain boundaries in polycrystalline ice. Monochromatic light from a point source is focused by the lenses but, because the lenses are microscopic in size, the image is blurred by diffraction. The diffraction pattern observed under a microscope has been compared with the computed diffraction pattern to deduce the angle 2θ at the rim of each lens. This is the dihedral angle for water at a grain boundary in ice, and gives the ratio of the grain-boundary energy to that of an ice-water interface. The most sensitive measurements are those made on the rings of the virtual diffraction pattern formed on the object side of the lens. They give θ = 12.5 ± 0.5° for the grain boundary under observation, which is 26% lower than the previous value for θ found by ignoring diffraction.
Variations in grain-size distribution of suspended sediment in a glacial meltwater stream, Austre Okstindbreen, Norway
Authors: Karlsen Erik
Published: September 2017

Thirty-nine samples of suspended sediment from the meltwater stream of Austre Okstindbreen, Norway, were analysed using both moments and parameters of the hyperbolic distribution. The samples turned out to be non-normally distributed. No direct correlation was found between discharge and grain-size distribution, but it is supposed that the hydraulic influence is hidden behind factors like composition of morainic or stream-bed material. Through comparison of the grain-size parameters from two periods in the field season, it was possible to distinguish between two sediment populations.
NMR imaging of salt-water ice
Authors: Edelstein W.A. , Schulson E.M.
Published: September 2017

Salt-water ice was imaged in a 2Tesla, horizontal 310 mm bore NMR imaging system at 85 MHz. 50 mm diameter ice cylinders were placed in a temperature-controlled chamber in the NMR system and imaged at temperatures from −20° to 0°C. Paramagnetic Cu2SO4 at a low concentration was added to the solution, from which one ice sample was crystallized in order to decrease the NMR relaxation time of the entrapped brine in the ice cylinder and thereby speed up image acquisition. The Cu2SO4-spiked sample displayed what appears to be small brine pockets/channels which resemble larger drainage channels seen in thin plates of sea ice. The brine channels/pockets seen by NMR contracted as the temperature decreased. NMR imaging of salt ice appears to be an excellent way to visualize ice structure.
Some Measurements of Settlement in a Rocky Mountains Snow Cover
Authors: Bergen James D.
Published: September 2017

Snow-cover settlement was measured in a dry, annual sub-alpine snow cover in the Colorado Rockies with settlement gages. Settlement viscosities were calculated from the change in gage heights over various periods during the winter and early spring, and the associated overburden over the gages as estimated from density measurements and precipitation records. When adjustments are made for local snow temperature, viscosities are in fair agreement with values found in the literature from similar snow covers, although considerable scatter for a given snow density is found in all sets compared. The viscosity for a given density does not appear to vary systematically with grain size.
Ice Flow Along an I.A.G.P. Flow Line and Interpretation of Data From an Ice Core in Terre Adélie, Antarctica
Authors: Raynaud D. , Lorius C. , Budd W. F. , Young N. W.
Published: September 2017

An ice core has been obtained to the bedrock about 300 m deep in Terre Adélie, 5 km inland from the coast. Stable isotopes and gas content have been measured over the length of the core. The results have been interpreted in terms of the temperature and elevation of origin of the ice further inland on the ice sheet from the data obtained along an 800 km traverse towards Dome “C”, and from Dome “C”, at an elevation of about 3 200 m. The flow of the ice from Dome “C“ to the coast has been modelled to determine the ages and particle trajectories of the ice for present conditions.

It has been found that the upper isotope and gas-content values in the core can be matched with the present regime using a base for ice flow above the present bed which is suggested by moraine in the ice core. The ice in the layer from the 200 m depth, where the age is apparently more than 5 000 years, to the 250 m depth, appears to have originated from conditions which differ substantially from those existing on the present inland ice-sheet surface. The results give an indication of a colder climate and greater ice-sheet thickness in the past.
Seasonal Variations In The Surface Energy Exchanges Over Antarctic Sea Ice and Coastal Waters
Authors: Allison I. , Tivendale C.M. , Akerman G.J. , Tann J.M. , Wills R.H.
Published: September 2017

Seasonal variations in radiative and turbulent fluxes at the surface of, and in the heat transfer within, sea ice are discussed from results of energy balance studies at a site of annual ice cover near Mawson, Antarctica. In mid-summer, the open water gains heat mostly by radiation but by early February the ocean is cooling predominantly by strong turbulent losses, with some radiative heat loss occurring also by March. When an ice cover forms, turbulent fluxes decrease from several 100 W m−2 over open water to only 40 w m−2 over ice less than 0.2 m thick and even less over thicker ice.Net radiative losses over mature ice in mid-winter are balanced mostly by conduction through the ice cover but with some turbulent heat gain at the surface. By mid-spring, there is a net radiative gain, the turbulent fluxes are again outgoing, and there is little total heat transfer through the ice. At break-out, the albedo increase from ice to open water causes a large increase in the net radiative gain.

At the lower boundary of the ice, the oceanic heat flux provides an important contribution. A net advection of heat into the region is shown from temperature profiles in the water under the ice. Salinity changes in the water during the period of ice melt are also discussed.
Isotope Climatic Record Over The Last 2.5 KA from Dome C, Antarctica, Ice cores
Authors: Benoist J. P. , Jouzel J. , Lorius C. , Merlivat L. , Pourchet M.
Published: September 2017

Data on climatic changes over thousands of years is needed for a better understanding of the shorter term variations which are of interest to man. For this purpose we measured the isotope composition (δD‰) of two adjacent ice cores drilled in the Dome C area. The time scale was established using the remarkably constant mean annual accumulation rate (37 kg m−2) determined by various techniques. The detailed isotope records were smoothed to filter out the δ value fluctuations not directly related to local temperature changes. With respect to conditions over the last 2.5 ka, the combined smoothed δ curve indicates a cooler climate from about 1800 to 1200 AD and a slightly warmer period from about 1200 to 700 AD. These periods may well correspond to the suggested world-wide Little Ice Age and medieval warm phase. Using the present δD‰/T°C measured at the surface, the maximum amplitude for these two periods, after smoothing with a low pass filter of 512 a, is approximately -0.35 and +0.3°C, respectively.
The NOAA-6 Satellite Mosaic of Antarctica: A Progress Report
Authors: Berg Craig P. , Wiesnet Donald R. , Legeckis Richard
Published: September 2017

The Antarctic mosaic project is a joint National Oceanic and Atmospheric Administration/United States Geological Survey (NOAA/USGS) project to produce a photomosaic map at 1:5 000 000 scale. The mosaic will be made as a collage of rectified images from the polar-orbiting NOAA-6 satellite. The near-infrared wavelength band of 0.725 to 1.10 μm, with a spatial resolution of 1.1 km, will be used. The NOAA-6 data are obtained from the McMurdo station receiving facility and from the archive of recorded data. Examples of imagery from both sources are presented. The operational plan including the processing flow chart, rectification process, progress to date, and problems to be faced are discussed. Applications of the mosaic are discussed as well as possible NOAA-6 applications to Antarctic investigators.