bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Velocity Determination on Large Polar Glaciers by Aerial Photogrammetry
Authors: Brecher H. H.
Published: September 2017

Aerial photogrammetric block triangulation, a standard and well-developed technique for extending accurate control for mapping into the interior of a region from a few points of known position on its perimeter, can be readily adapted to determine surface velocities on bodies of ice which are too large, and often too crevassed, to be studied effectively by conventional ground surveying. Velocities are calculated from the changes in positions of the same natural surface features determined from photography of two (or more) epochs and the elapsed time. This method is capable of providing many uniformly-spaced measurements over the whole, moving, ice surface, thus allowing the production of maps of velocity and strain-rate, which are valuable in analyzing the ice-flow regime. Results from measurements completed some years ago on Byrd Glacier, one of the largest outlet glaciers from the East Antarctic plateau, are presented as an example of what the method can yield. By means of Doppler satellite surveying, relative positions of control points for each photography epoch can be determined with sub-meter accuracy, making the technique suitable also in regions where no fixed land features exist. A brief description of a project under way in such an area, on Ice Stream B in West Antarctica, is given.
The Use of Landsat Digital Data For Glacier Inventories
Authors: Howarth P.J. , Ommanney C.S.L.
Published: September 2017

Enhancement and classification of digital Landsat data has been carried out for two Canadian glaciers. The objective of the study was to determine the role that such data might play in preparing glacier inventories, It was difficult to measure accurately areas of glaciers and to map moraine-covered ice directly from information derived from digitally classified data. Digital enhancements, however, provide considerable, interpretive detail. Although Landsat imagery is not a substitute for aerial photographs in compiling glacier inventories, grey-tone prints can be used to identify changes rapidly and to provide a base map for recording information.
The Response Time of Glaciers in Iceland to Changes in climate
Authors: Jóhannesson Tómas
Published: September 2017

Records of the time variation of the terminus position of Icelandic glaciers since 1700 show clear responses to the little ice age and to the warm period from 1930 to 1960. These data are used to deduce limits for the response time of the glaciers. The response time turns out to be of the order of one or two hundred years. This is much shorter than the “long response time” of Nye’s kinematic wave theory.
Processes which Distribute Supraglacial Debris on the Khumbu Glacier, Nepal Himalaya
Authors: Nakawo M. , Iwata S. , Watanabe O. , Yoshida M.
Published: September 2017

The thickness of supraglacial debris on the Khumbu Glacier, Nepal Himalaya, has been mapped by a combination of direct measurements and morphological and lithological studies. All three processes, englacial, supraglacial, and subglacial, must be considered in establishing the distribution of debris. Taking advantage of the lithological characteristics of the debris and their bedrock source, the denudation rate of the schistose bedrock was estimated to be about 0.02 mm a−1. A rough estimate of the production rate of supraglacial debris indicated that most of the present debris has formed since the last advance of the glacier, which took place a few hundred years B.P.
Determination of Changes in Volume and Elevation of Glaciers using Digital Elevation Models for the Vernagtferner, Ôtztal Alps, Austria
Authors: Reinhardt W. , Rentsch H.
Published: September 2017

The paper deals with the determination of changes in volume and elevation of glaciers, using Digital Elevation Models (DEM). First, the generation of a DEM is briefly described and the method of determining changes in volume and elevation by using DEMs is introduced, A brief description of the determination of these changes by means of contour plots follows. A comparison of both methods with respect to accuracy and economy is carried out on part of the Vernagtferner. The results from these investigations show that a required accuracy level can be obtained more economically by using DEMs. The changes in volume and elevation for the whole glacier area are determined by means of DEMs, for 1979 and 1982. The paper concludes with comments on the results and a review of other applications of DEMs.
A Survey of the Vanderford and Adams Glaciers in East Antarctica (Abstract)
Authors: Davis E R. , Jones D.J. , Morgan V.I. , Young N.W.
Published: September 2017

A comprehensive, airborne survey of the Vanderford and Adams glaciers was started in January 1983, continued through the austral summer season 1984/5, and completed in February 1985.

Ice-thickness and surface-elevation data were collected over some 4500 square kilometres, on a grid spacing of approximately 5 kilometres.

The measurement system was based on a Bell 206 helicopter, fitted with ANARE 100 MHz ice radar, Motorola Mini-Ranger navigation equipment, and a digital, pressure altimeter. A JMR, satellite, doppler receiver was used to position the navigation ground stations precisely. Gravity measurements were used to fill in ice-thickness coverage, where the ice radar failed to produce an echo and also to help determine where the glacier was floating.

Ice-movement profiles were measured across the front sections of the glaciers and additional spot values were obtained further upstream by utilizing the 3 m accuracy of the navigation equipment to locate markers quickly at both the beginning and end of the season’s work.

A data logger in the helicopter recorded time, navigation distances, aircraft to ground clearance, and air pressure, at 10 second intervals. These data were later merged with manually-scaled, ice-thickness values, for computer processing.

The results show that the Vanderford glacier dominates the system and drains about 5 cubic kilometres of ice per annum, mainly from the inland ice sheet to the south. Ice flowing into the Adams Glacier tends to come from nearer the coast and to the south and west of the glacier. Bedrock topography beneath the Vanderford shows that the deep, inland trench, similar to that found below other outlet glaciers, drops to 2500 m below sea level, 60 kilometres from the front. The trench has steep sides to the east and gives a clearly-defined edge to the fast glacier flow. The western side, however, is much more complicated, particularly further inland, where the flow is not clearly separate from that of the Adams glacier.
Glacial Geomorphological Map (1:200 000) of Mt. Tomur Region, Tianshan (Abstract)
Authors: Benxing Zheng
Published: September 2017

The Glacial Geomorphological Map (1:200 000) of Mt, Tomur Region, Tianshan, covers 78°33′ – 81°10′E and 41° 08′ – 42° 44′N, with high mountains, deep valleys and many snow peaks, the highest being Mt. Tomur (7435.3 a.s.l.). There are many glaciers in this region with a total area of 4553.69 km2. The melt water from glaciers irrigates the large oasis of Aksu, in the piedmont region in southern Xingjiang and waters the valley plain of Teks River in the Yili area. From piedmont plain to highest mountain summit, the vertical zonality of geomorphology is quite clear, rich in various geomorphological types, representing alpine geomorphology of the arid desert in Central Asia.

The author joined the glacial/geomorphological expedition to the Mt. Tomur Region in 1963, 1973 and 1974, and, in the process of mapping, cooperated closely with mapping engineers. This involved extensive use of aerial photographs, satellite images, large-scale topographic maps, geological maps, geomorphological maps and other data, and comprehensive analyses, comparisons, and judgements of data.

Special emphasis was placed on existing glaciers and the geomorphology of Quaternary glaciers, according to form, composition and relative chronological periods. The geomorphology was divided into five great systems, i.e. glacial, fluvio-glacial, fluvial, arid and artificial. Twenty-four geomorphic types were defined as the basic elements of the geomorphological map and shown in different colours and by various marks, while old and Neozoic faults were shown by black line marks. There are representative heights on all geomorphological zones. Colour brush-shading added much to the stereo effect.

Below the main map, the longitudinal and cross sections of Quaternary geology and geomorphology of the Tialan valley, the stratigraphical columnar profile of West Zamtia and the fluvial/lacustrine deposit profile of the Loska basin were attached, showing the stratigraphical relation between the glacial and non-glacial deposit and the basis for the divisions of the glacial and inter-glacial periods.
On the Placement and Mass of Avalanche Explosives: Experience with Helicopter Bombing and Preplanted Charges
Authors: Perla R. , Everts K.
Published: September 2017

Snow avalanches threatening the road to the Sunshine ski area in Banff National Park, Alberta, Canada, are controlled by helicopter bombing and preplanted explosives. The effectiveness of these methods is evaluated using two ratios: avalanche points/bomb and avalanche points/kilogram of explosive, where avalanche points are computed on a scale of 1 to 5, according to size. Analysis of 74 helicopter missions shows a significant increase in avalanche points/bomb with increasing bomb mass. Comparison of helicopter bombing (near-surface detonations) with preplanted charges (ground detonation) shows that ground detonations are at least as effective as bombs detonated just below the snow surface.
Experimental Determination of the Buckling Loads of Floating Ice Sheets
Authors: Sodhi D. S. , Haynes F. D. , Kato K. , Hirayama K.
Published: September 2017

Experiments were performed to determine the forces required to buckle a floating ice sheet pushing against structures of different widths. The characteristic length of each ice sheet was determined to enable a comparison to be made between the theoretical and experimental results.

Most of the experimental data points are within the range of the theoretical values of normalized buckling loads for frictionless and hinged boundary conditions, which represent the extreme situations for ice-structure contact. Thus, the agreement between the theoretical and experimental buckling loads is considered to be good. Photographs of the buckled ice sheets show a resemblance to the theoretical mode of buckling.
Two Calving Laws for Grounded Iceberg-Calving Glaciers (Abstract only)
Authors: Brown C. S. , Sikonia W. G. , Post Austin , Rasmussen L. A. , Meier M. F.
Published: September 2017

Prediction of the future retreat of Columbia Glacier, Alaska, required a calving law for the boundary condition at the terminus. Qualitative observations on the variations of all major iceberg-calving glaciers of Alaska suggest that calving is high whenever glaciers terminate in deep water, and greatly reduced whenever they terminate in shallow water. Calving relations were investigated based on calculations of calving speed, defined as the volume rate of iceberg discharge from the terminus divided by the cross-sectional area of the terminus. The calving speed was determined for 12 glaciers for which measurements of glacier speed, advance and retreat rates, and other variables were obtained. To extend the range of data, four additional periods of rapid retreat were examined. Values for the terminus characteristics of water depth, cliff height, and thickness of the terminus, averaged over the width of the glacier and over a year, were then examined in relation to the calculated speeds of calving. A statistical analysis to determine the form and coefficients of an empirical calving relation that approximates the data shows that calving speed is best fitted by a simple proportionality to average water depth at the terminus:
1
where vc is the calving speed and hw the water depth, both averaged over the width and over a year, and c a constant of proportionality. This gives a variance reduction fraction (similar to the coefficient of determination r2) of 0.90.

To investigate seasonal changes in calving, data based on shorter time intervals were obtained at the head of embayments from Columbia Glacier. At intervals of approximately two months, the following expression fits intra-yearly calving at Columbia Glacier:
2
where D is the meltwater discharge from the glacier, hj is the height of the ice column unsupported by water buoyancy, a, b, c are constants, and vc and hu are evaluated at the embayment head. D was determined by correlation with a nearby glacial stream, and hu = h _ hw PW/PJ, where h is glacier thickness and pi and pw the densities of ice and water. Best-fit values of b and c are approximately 0.5 and -2, respectively. This yields a variance reduction fraction r2 of 0.83.

Equation (2) does not fit data averaged over a year and over the width of the glacier and Equation (1) does not fit data obtained over shorter periods at the head of the embayment. Although the two equations are different in form, for similar or average values of D and h - hw (ice-cliff height), they give approximately similar results over the present range of the geometry of the terminus of Columbia Glacier. Whether this will be true after rapid retreat begins remains to be seen.
Numerical Modelling of Glacier Response to a Perturbation in Thickness (Abstract only)
Authors: Echelmeyer Keith
Published: September 2017

Blue Glacier was subject to 5 to 10% increase in thickness during the period 1958 to 1978. A surface velocity increase of 15 to 50% has accompanied this change in ice thickness. A non-uniform distribution of thickening over the glacier produced a general decrease in surface slope. The flow law parameters in a power-law relation for ice can be obtained from the resulting increase in velocity.

In 1957–58 the surface velocities and surface elevation along several transverse profiles were determined by others. During the period 1977 to 1980 similar measurements were made of surface velocity, elevation, and ice thickness along profiles spatially equivalent to those of the 1957–58 survey. Using these results a detailed study of the flow response has been made. Preliminary results indicate that the controlling surface slope a is one that is averaged over approximately ten times the glacier thickness and also indicate a relatively high stress exponent n = 4 to 5.

Blue Glacier flows in a complex channel and any detailed interpretation of the flow response requires the inclusion of this geometry in a model. For this reason multi-dimensional finite-element methods using a non-linear constitutive relation were employed. Various degrees of model sophistication allowed for the specification of different parameters governing the flow of the glacier. Variations in the flow law parameters and the curvature of the channel were found to have significant effects on the velocity and stress fields, as well as on the characteristics of the flow response to the thickness perturbation. Fully three-dimensional models of the flow of Blue Glacier and its response to the thickness increase were developed. Important effects such as those arising from longitudinal thickness and surface slope variations were included in three-dimensional modeling. The three-dimensional effects were seen to play an important role in flow of a rheologically non-linear fluid such as ice.
Use of Satellite Synthetic Aperture Radar Imagery in Arctic Marine Design and Sea-Ice Studies (Abstract only)
Authors: Lapp David , Ramseier René O.
Published: September 2017

Digitally processed Seasat synthetic aperture radar images from the Beaufort Sea, recorded during August 1978, were analyzed to determine ice-floe displacements and floe-size distributions. Combining data on displacements with those on floe area and thickness yields floe kinetic energies which can then be used as input into design criteria for offshore Arctic structures. Floe-size distributions are needed to determine probabilistically the “design” mass of Ice for an offshore structure.

Vectors of floe movement show the influence of surrounding floes and the compactness of the ice. Floes nearer to more open water showed more movement in the prevailing wind direction while floe movement within the ice pack was primarily affected by floe interaction.

Different cutoff criteria in terms of number of resolution cell sizes were applied to the data on floe size. It was found that the numbers of floes dropped by up to 50% of the original count at ten resolution cells (250 m). Exponential and log-normal probability distributions were fitted to the original counts of floe size. The log-normal fit was better but this is based on one dataset at one time of year in one location. More datasets need to be analyzed to investigate this further. If a probability distribution to floe size can be generalized then only a subset of all the floes would need to be analyzed to determine numbers of floes in each size range. This would greatly speed up a tedious task and be beneficial for design and operational purposes.
Measurement of Snow Creep Pressures on an Avalanche Defence Structure (Abstract only)
Authors: Larsen J. O. , McClung D. M. , Hansen S. B.
Published: September 2017

This study presents estimates of snow creep pressures from the centre section of an avalanche defence structure in western Norway. The structure is 15 in long and is erected on a 25° slope characterized by deep snow covers. Two methods of measurement are described: (1) direct estimates from earth pressure cells, and (2) construction of force, shear and moment diagrams from strains measured using vibrating wire strain gauges mounted on the steel beams of the structure.

In addition to the estimates of pressure, relevant snowpack data were measured, including snow depth, density, temperature and rammsonde hardness profiles as well as snow crystal stratigraphy. Snow gliding was also measured, and was found to be negligible. The snowpack measurements were made at approximately monthly intervals during each of the four winters which yielded useable data for the study.

Analysis of the pressure distributions along with the snowpack data yielded the following results: (1) the average pressure on the structure is linearly proportional to the product of average density times snow depth, (2) the average pressures are predicted fairly accurately by a linear, viscous creep model, (3) the maximum pressure depends strongly on the snowpack stiffness and decreases rapidly when warming and melt soften the snowpack, and (4) the maximum pressures are of the order of 254 higher than predicted by a linear, viscous creep model.
Seismic Moment, Stress Drop, Strain Energy, Dislocation Radius, and Location of Seismic Acoustic Emissions Associated with a High Alpine Snowpack at Berthoud Pass, Colorado, U.S.A. (Abstract only)
Authors: Rosé Charles Cleland
Published: September 2017

The monitoring of the number of acoustic seismic impulses arising from snow instabilities is regarded as a relative indicator of an unstable snow slope but has not yielded a qualitative, predictive indicator. Until now, the source parameters (fracture area and length), seismic moment, energy released, stress drop, and location of acoustic seismic emissions arising from the snowpack have been neglected. A comprehension of these parameters leads to a better understanding of the event and may help in avalanche prediction.

The location of a seismic event is derived from time differences between P-wave arrivals at four sensors located at the snow-ground interface. Three methods confirm the location of an acoustic seismic snow event to within 2 to 4 cm when the event is inside a seismic net.

Spectral analyses of body waves from seismic snow events yield estimates of source parameters, stress drop and energy released. Equivalent dislocation surface radii range from 4.8 to 9.0 cm, which give stress drops of 0.20 to 0.29 bar, with a dissipated energy in the range of 0.0205 to 0.0632 J.

Spectral analysis of the acoustic seismic snow event with application of dislocation theory provides several likely methods to predict avalanches of a climax type.
Assessing Laboratory Procedures for the Decontamination of Polar Snow or Ice Samples for the Analysis of Toxic Metals and Metalloids
Authors: Boutron Claude F. , Batifol Françoise M.
Published: September 2017

Most, if not all, Antarctic and Greenland snow and ice samples to be analyzed for toxic metals and metalloids such as Pb, Hg, Sb, Cd, Ag, Se, As, Cu and Zn become more or less contaminated by these elements on their outsides, mainly during field collection. We assess here the various procedures which have been developed to try to decontaminate the samples. They include both mechanical and rinsing techniques. It appears that it is essential, but very difficult, to establish clearly the efficiency of these procedures. This can however be done by determining the geometry of contamination of the analyzed samples and by evaluating procedural blanks carefully. Such careful evaluation has been achieved at present only for mechanical procedures and for a few metals.
Gaseous Components in the Atmosphere and the Historic Record Revealed by Ice Cores
Authors: Stauffer B. , Oeschger H.
Published: September 2017

The composition of air in bubbles of ice reveals important information on the composition of the atmosphere at the time at which the ice was formed. The enclosed air has essentially an atmospheric composition if the ice formation occurred by dry sintering of snow and firn at low temperatures. The history of atmospheric CO2 concentration is of special interest due to its present increase and its climatic implications. Currently, CO2 analysis of air extracted from ice cores seems the best and most direct method of determining the natural CO2 concentration before 1950 and possible pre-industrial variations. Analyses of ice samples representing the past 40 ka show that there were significant changes in concentration of atmospheric CO2 at the end, and probably during part, of the last glaciation. δ13C measurements on CO2 extracted from ice cores can indicate possible mechanisms causing these changes in the concentration of atmospheric CO2.
Stratigraphic Noise in Time Series Derived from Ice Cores
Authors: Fisher David A. , Reeh Niels , Clausen H.B.
Published: September 2017

Because of snow drifting, two time series of any variable derived from two adjacent ice cores will differ considerably. The size and statistical nature of this noise element is discussed for two kinds of measured substance. A theory is developed and compared to data from Greenland and Canadian Arctic ice cores. In case 1, the measured substance can diffuse and the seasonal cycle degrade with time and depth, e.g. δ(18O). In case 2, the measured substance cannot diffuse, e.g. microparticles. The case 2 time series contain drift noise proportional to that in the accumulation series. For accumulation series, the spectral power is concentrated at the high frequencies, i.e. is “blue”. Such noise can be easily reduced by taking relatively short time averages. The noise in the case 1 time series, however, starts out “blue” but quickly diffuses to have a “red” character with significant power at longer wavelengths, and many decades of such series must be averaged to reduce the noise level. Because the seasonal amplitude of any given variable is an important input to the drift noise and because the seasonal amplitudes of some variable types are latitude-dependent, some sites have inherently less drift noise than others.
The Glaciochemistry of Snow-Pits from Quelccaya Ice Cap, Peru, 1982
Authors: Lyons W. Berry , Mayewski A. Paul , Thompson Lonnie G. , Allen Boyd
Published: September 2017

We present glaciochemical data from a pilot study of two snow-pits from Quelccaya ice cap, Peruvian Andes. These are the first samples to be analyzed from Quelccaya for nitrate and sulfate by ion chromatography (IC), for nitrate-plus-nitrite, reactive silicate and reactive iron by colorimetry, and for sodium by atomic absorption spectrophotometry. The 3 m pits used in this study represent a one year record of mass accumulation and the 29 samples collected provide the first glaciochemical data from this area which can be compared with glaciochemical studies from other locations.

Reactive iron, reactive silicate and sodium, and the profiles of >0.63μm microparticles from Thompson and others (1984) are coincident, suggesting that transport and deposition into this area of each species are controlled by similar processes. The common source is probably local, resulting from crustal weathering. In general, the reactive silicate values are lower than those observed in other alpine glacier ice. The highest sulfate and nitrate values were observed in the upper few centimeters of the snow-pit. Most of the sulfate concentrations were less than 3 μM and are similar to values obtained for fresh surface snows from Bolivia (Stallard and Edmond 1981). Since biological gaseous emissions are thought to be the major source of sulfur and nitrogen to the atmosphere over the Amazon basin, the sulfate and nitrate fluctuations may be due to seasonal biological input and/or seasonal shifts in wind direction bringing material to Quelccaya.

With only one exception, the colorimetric nitrate-plus-nitrite data were higher than the IC nitrate data. Unfortunately, the IC analyses were conducted 81 d after the colorimetric analyses. The difference between the two data sets could be attributable to the following: (1) the colorimetric technique may yield erroneously high results as suggested for polar ice by Herron (1982), (2) the IC technique yields erroneously low results due, in part, to the possible exclusion of nitrite concentrations, and/or (3) nitrite was lost via biological removal during the 81 d period before the IC analyses. If the IC data are correct, the mean nitrate value is 0.4μΜ (n = 29). This value is similar to those reported from pre-industrial aged polar ice (Herron 1982). If the colorimetric mean value (1.1 μM) is correct, it is similar to colorimetrically determined values from other high-elevation alpine ice (Lyons and Mayewski 1983).
Isotope Studies of Ice Cores from a Temperate Alpine Glacier (Vernagtferner, Austria) with Respect to the Meltwater Flow
Authors: Oerter H. , Baker D. , Stichler W. , Rauert W.
Published: September 2017

Core drillings were carried out in 1979 and 1983 on the temperate Alpine glacier Vernagtferner, Ötztal Alps, Austria. In addition, studies on the variation of the water table of the firn were carried out in the bore holes. The 18O, 2H and 3H content of the cores, as well as the electrical conductivity, were measured. The isotope profiles and the electrical conductivity of the 1983 core display a strong damping in comparison with the profiles from the 1979 core for the depth from 17 to 20 m (10.5 to 13 m water equivalent) below the surface. In the 1983 core, the 3H contents are lower, and the 2H and 18O contents are more homogenized. This core section lies between the lower and upper limits of the water table fluctuations from 1979 to 1982, and it is also assumed that the transition from firn to ice takes place at this depth of the glacier. The most reasonable explanation for this damping is that within the range of the firn water table important isotopic and chemical exchanges between the meltwater and the porous medium (firn) take place. It is also possible that a small amount of meltwater is included in the firn while it is changing into ice.
Airborne Pollen: A Unique Air Mass Tracer, Its Influx to the Canadian High Arctic
Authors: Bourgeois J.C. , Koerner R.M. , Alt B.T.
Published: September 2017

A study of pollen grain concentration in surface snow and ice cores at 15 sites in the Canadian high Arctic and one site near the tree line, together with published pollen deposition rates south of the tree line has shown long-range dispersal of pollen from the boreal forest to the limits of our area on the Arctic Ocean close to Svalbard and the North Pole. There are no discernible trends of deposition rates within the high Arctic which suggests extremely long trajectories with strong zonal components; some of the pollen may have an Eurasian source. We relate the trajectories to synoptic patterns in the mid- and high Arctic.
A Global Oxygen Isotope Model – Semi-Empirical, Zonally Averaged
Authors: Fisher D.A. , Alt B.T.
Published: September 2017

A simple model, which is zonally averaged, for the transport of atmospheric water vapour is presented which uses as input the zonally averaged evaporation field and the mean meridional travel distance of tropospheric water vapour as functions of latitude. The model demonstrates that for polar regions each of the 10° latitude strips poleward of 25° is of equal importance as a moisture source. The model is used to predict zonal averages of δ(18O) for the present day and 18 ka BP. Both annual average values and seasonal amplitudes are presented and compared to observations. Sea-ice cover is an important factor in determining both annual averages and seasonal amplitudes today and at 18 ka BP. An earlier model (Jouzel and others 1983) linking δ(18O), the deuterium excess, and sea-salt content in an Antarctic ice core to the relative humidity of the source region is based on a single-source atmospheric water-vapour cycle type model and is re-evaluated using the present model.
Simulation of Airborne Impurity Cycles Using Atmospheric General Circulation Models
Authors: Joussaume Sylvie
Published: September 2017

Atmospheric general circulation models are believed to be appropriate tools for studying airborne impurity cycles in order to supplement observations and to improve our knowledge of gaseous and particulate pollutant cycles in the atmosphere. The main aspects of the modelling of tracer cycles are reviewed and illustrated by two particular examples: desert dust particles in the 1 μm range and water isotope species HDO and H218O. Some results from a first simulation including desert dust and water isotope cycles using the model developed at the Laboratoire de Météorologie Dynamique (LMD) are presented and compared to observations, with particular emphasis on ice-sheet data. The relatively good agreement with observations obtained so far is encouraging and should stimulate further applications to other types of tracers.
Acid Content of Snow from a Mid-Troposphere Sampling Site on Mount Logan, Yukon Territory, Canada
Authors: Holdsworth G. , Peake E.
Published: September 2017

An ice core 103 m long was extracted in 1980 from an altitude of 5340 m on the icefield plateau of Mount Logan, Yukon Territory (lat 60°35ˈN, long 140°30ˈW). The firn-ice transition occurs at a depth of 65 m, corresponding to about the year 1880.

The chemistry of this upper 65 m is apparently dominated by acid-ion species, the peaks in which are provisionally identified with several documented volcanic events. Although the analyses cover only selected discontinuous intervals, it appears that there is no significant long-term trend in the background acidity level of the precipitation at this location over the past century, in contrast to the results from the North American Arctic and Greenland.

Nitrate ion concentration shows pseudo-seasonal variations, which may be associated with stratospheric-tropospheric interactions, although other seasonally linked mechanisms are possible. This result has also been reported for ice-core sequences from Greenland. Other nitrate pulses are tentatively associated with local volcanic events and a possible meteorite event (the entry of Tunguska in 1908). One of the largest short-term sources of sulfate ions is probably from volcanic activity on the north Pacific rim. Background volcanically-quiet nitrate and sulfate ion concentrations are compared with similar Greenland data in an attempt to throw further tight on the origin of the acids.

Since the moisture for this precipitation originates primarily in the Gulf of Alaska, the data has particular relevance to that region. Short-term climatic changes, as reflected by the oxygen isotope (δl8O) record, show some response to the major volcanic-acid events. The influences affecting the δl8O record are listed but not discussed.
The Chemistry of Snow and Meltwaters Within the Mesostructure of a Boreal Forest Snow Cover
Authors: Jones H.G.
Published: September 2017

A physical and chemical study of snow mesostructure was carried out in a boreal forest site at Lake Laflamme, Quebec in spring 1983. The concomitant physical observations and δ18O‰ data on the upper layers led to the reconstruction of recent snowfall events and meltwater movements which influenced the chemistry of snow at different levels of the snowpack. Correlations between data relating the concentrations of atmospheric pollutants in snow strata were significant (H+, , r = 0.89; H+, , r = 0.81, P ≤ 0.001). The grouping of chemical species by factor analysis distinguished clearly between ionic species originating from the long-range transport of atmospheric pollutants and those due to local deposition phenomena and organic debris from the forest canopy. Mesostructural characteristics led to heterogeneous flow patterns of meltwater and rainwater through the snow cover. Both physical and chemical characteristics of the snow mesostructure change rapidly in a non-uniform manner under such conditions. This leads to increased difficulties in the interpretation of data gathered during snow sampling studies on pack decay during the spring run-off period.
The Chemical Characteristics of Snow Cover in a Northern Boreal Forest During the Spring Run-Off Period
Authors: Jones H.G. , Sochanska W.
Published: September 2017

An intensive snow-cover survey at Lake Laflamme, Quebec, during the spring of 1983 showed that wet deposition in the form of rain, which was a dominant phenomenon during the 1983 melt season, gave rise, according to the intensity and chemical quality of the precipitation, to both losses and gains of ion loads (meq m−2) in the snowpack. Mean values for the daily wet deposition loadings (meq m−2 d−1) of ionic species associated with atmospheric aerosols (H+, , ) were of approximately the same magnitude as the daily changes in gains recorded in the snow cover during the melt period. In contrast, the mean value for the contribution by wet deposition to the total loads of K+ and in the snow cover was far outweighed by the gains which were observed at the same time. The expected losses for the snowpack, calculated from the sum of the total loads stocked in the pack at the beginning of the melt period and the total loads in precipitation during the melt period, were lower than the sum of the actual losses observed for all ionic species except H+. The increases (%) in the loads for the major anions Cl−, and were comparable (25 to 32%). The results suggested that dry deposition either directly by aerosol interaction with the snow cover or indirectly by adsorption on organic material followed by leaching during the melt period, or by a combination of both, was a major factor in the increases observed. The values for the increases in loads for Ca2+, , Mg2+ and Na+ (50 to 287%) probably represented, in addition to leaching of local debris, the exudates of cellular material from the cell plasmolysis of detrital organic debris. High rates of in-pack production, however, were characteristic of Al3+. Mn2+, K+ and which showed substantial increases in pack loads (480 to 750%). These increases cannot be accounted for by any local phenomena other than the dissolution or microbiological degradation of organic debris. It is suggested that ion exchange capacity of both particulate and soluble organic material led to a decrease in pack acidity; this phenomenon should thus be considered as a major factor in all attempts to model acid rain fluxes through boreal forest systems.
Sulphur and Heavy Metal Pollution in Urban Snow: Multi-Elemental Analytical Techniques and Interpretations
Authors: Landsberger S. , Jervis R.E.
Published: September 2017

Three multi-elemental techniques (neutron activation analysis, proton-induced X-ray emission and inductively coupled plasma-atomic emission spectrometry) are described in terms of their special advantages in determining sulphur and heavy metal pollution in urban snow. Environmental analytical interpretations, including wash-out factors, enrichment factors, inter-elemental correlations, mobilization factors, and toxicity potential, are also discussed.
The Elution of Ions Through Field and Laboratory Snowpacks
Authors: Tsiouris Sotiris , Vincent Christopher E. , Davies Trevor D. , Brimblecombe Peter
Published: September 2017

It has been recognised for many years that the first fraction of meltwater from a melting snowpack contains a much higher concentration of ions than that of the bulk (or average) snow of which the pack is comprised (Foster 1978, Johannessen and Henriksen 1978). This process leads to the so called “acid flush” in the spring and can have severe ecological effects on lakes and streams (Hagen and Langeland 1973, Leivestad and Muniz 1976, National Research Council of Canada 1981). We have studied elution of ions through a snowpack on Folgefonna near Bergen, Norway, and in the laboratory. In the field we collected meltwater samples at hourly intervals for a period of 4 d at the start of the melt season, and analyzed them for pH, , Cl−, Na+, Mg2+, Ca2+ and K+. 2 m cores were also collected at the beginning and end of the experiment in order to study bulk changes in snow composition. The meltwaters showed a diurnal cycle with high ionic concentrations around noon, with and levels rising by factors of up to four and six-fold compared to the average concentrations on the first day. Cl− levels peaked much later, after the and levels had decreased, and only reached 2.3 times their lowest concentrations. pH values were strongly correlated with and levels, suggesting that a significant proportion of these anions were in the form of strong acids.

The laboratory experiments involved slow melting of snow samples collected in the Cairngorm mountains, Scotland, and also showed that and (and also Mg2+ and K+) ions were removed from the snow preferentially whilst Na+ and Cl− tended to remain longer. The position of H+ within the ion elution sequence is unclear due to uncertainties in the absolute determination of pH in the field measurements, but the laboratory experiments confirm the differential rates of elution shown in the Norwegian snowpack and reaffirms its importance in the acidification of streams during spring.
Ice-Shelf Flow at the Boundary of Crary Ice Rise, Antarctica
Authors: Bindschadler R. A. , Vornberger P. L. , Stephenson S .N. , Roberts E. P. , Shabtaie S. , MacAyeal D. R.
Published: September 2017

Surface velocity and deformation, radar sounding, and aerial photography data are used to describe the flow of Ross Ice Shelf around Crary Ice Rise. A continuous band of crevasses around the ice rise now allows the complete boundary to be mapped for the first time. The dynamics of three distinctly different areas of ice flow are studied. Just up-stream of the ice rise, there is a region of ice rumples dominated by intense longitudinal compression (0.01 a−1) and lateral tension. On the south-west side of the ice rise, intense shear (0.03 a−1) dominates, with the boundary layer of affected ice-shelf motion extending over 20 km from the ice-rise edge into the ice shelf. North-west of the ice rise, a crevasse-free block of ice, 40 km × 7 km, appears to have separated from the main ice rise and is now moving with the ice shelf. We refer to such moving blocks of ice as rafts. The separation of this raft is calculated to have occurred 20 ± 10 years ago. Other possible rafts are identified, including one on the south-west side of the ice rise which appears to be in the process of separating. Mechanisms for the formation of rafts are discussed.
A Three-Dimensional Model of the Antarctic Ice Sheet
Authors: Herterich Klaus
Published: September 2017

A preliminary version of a three-dimensional ice-sheet model for later use in climate models, but excluding ice shelves and basal sliding, is presented and applied to the Antarctic ice sheet. In the model, the three-dimensional fields of velocity and temperature are calculated in the coupled mode, and the temperature equation is integrated for 150 000 years; the shape of the Antarctic ice sheet remains fixed. The results from the model are consistent with a stationary state in the central parts of the Antarctic ice sheet, but not in marginal areas, where the flow in the model is too small. Including a parameterized form of basal sliding that is dependent on the water pressure is likely to improve the situation.
Ice-Motion Determination by Means of Satellite Positioning Systems
Authors: Hinze Heinrich , Seeber Günter
Published: September 2017

The satellite positioning systems, NNSS or Transit system and NAVSTAR-GPS, are used successfully for the determination of ice motion. The ice motion is derived from the change in the coordinates of a station between at least two measurement epochs. Simultaneous satellite observations on solid-ground-based and on ice stations yield precise relative or local coordinates between the stations. The ice motion can be determined very accurately from the variation in these coordinates. The field observations and post-processing steps, which differ slightly for the two positioning systems, are outlined. Results for several examples are presented. Ice-motion solutions are discussed for data from Anvers Island (NNSS), from Filchner-Ronne Ice Shelf (NNSS, GPS), and from Ekström Ice Shelf (NNSS, GPS). Slow velocities of a few dm/d could be estimated in the course of one field season and the velocity values found are confirmed by annual station displacements.
Ice Thickness and Bedrock Elevation in Western Neuschwabenland and Berkner Island, Antarctica
Authors: Hoppe H. , Thyssen F.
Published: September 2017

In 1985–86, western Neuschwabenland was surveyed with an electromagnetic reflection system (EMR) over flight tracks totalling 6100 km. The area spans a triangle from Ekström Ice Shelf and Heimefront Range to the Kraul Mountains [Vestfjella] and covers 48 000 km2.

Data on surface elevation, ice thickness and bedrock topography are presented in maps. The bedrock-elevation map shows more detail than earlier compilations, with a remarkable graben-like structure north of the Heimefront Range and large areas of bedrock below sea-level.

In the same season, tracks totalling 1600 km were flown over Berkner Island. High electromagnetic reflectivity was found over the southern part of Berkner Island, whereas the northern part showed considerably lower reflectivity. We believe that this is due to melting conditions in the southern part and freezing conditions in the northern part.
Evolution of the East Antarctic Ice Sheet: A Numerical Study of Thermo-Mechanical Response Patterns With Changing Climate
Authors: Huybrechts P. , Oerlemans J.
Published: September 2017

An efficient numerical ice-sheet model, including time dependence and full thermo-mechanical coupling, has been developed in order to investigate the thermal regime and overall configuration of a polar ice sheet with respect to changing environmental conditions.

From basic sensitivity experiments, in which a schematic East Antarctic ice sheet is forced with a typical glacial–interglacial climatic shift, it is found that: (i) the mutual interaction of temperature and deformation has a stabilizing effect on its steady-state configuration; (ii) in the transient mode, this climatic transition initially leads to increased ice thickness due to enhanced accumulation, after which this trend is reversed due to a warmer base. Time-scales for this reversal are of the order of 103 years in marginal zones and of 104 years in interior regions; (iii) horizontal heat advection plays a major role in damping possible runaway behaviour due to the dissipation – strain-rate feed-back, suggesting that creep instability is a rather unlikely candidate to initiate surging of the East Antarctic ice sheet.

The model is then applied to four East Antarctic flow lines. Only the flow line passing through Wilkes Land appears to be vulnerable to widespread basal melting, due to enhanced basal warming following climatic warming. Time-dependent modelling of the Vostok flow line indicates that the Vostok Station area has risen about 95 m since the beginning of the present interglacial due to thermo-mechanical effects, which is of particular interest in interpreting the palaeoclimatic signal of the ice core obtained there.
Effect of Stratigraphy on Radar-Altimetry Data Collected Over Ice Sheets
Authors: Jezek Kenneth C. , Alley Richard B.
Published: September 2017

A method for calculating the impulse response of a layered dielectric is used to investigate the effect of near-surface density stratification on the interpretation of radar-altimetry data collected over ice sheets. Results are computed for a model consisting of a measured density profile that is artificially interrupted by an ice layer inserted at successively greater depths. The incident radar signal is modeled by a 20 ns long pulse modulated at 1 GHz. Analysis using a simple scheme for estimating the one-way travel time of the wave indicates as much as a 2 ns (equivalent to 60 cm in range) apparent time delay for a density profile that has been modified by inclusion of an ice layer relative to the ice-layer-free case. This suggests that layering may be a factor in interpreting repeated altimeter measurements of the ice sheets in terms of net growth or decay.