bluuebunny/crossref_metadata_2025 huggingface dataset:
Glaciochemical Studies and Estimated Net Mass Balances for Rennick Glacier Area, Antarctica
Authors: Allen Boyd , Mayewski Paul A. , Lyons W. Berry , Spencer Mary Jo
Published: September 2017

Two snow and ice cores from the Rennick Glacier area, Antarctica (study area center point lat 71°15ˈS, long 162°30ˈE) were analyzed for the chemical species: chloride, sodium, reactive silicate, sulfate and nitrate. Core E10 (6.35 m) was taken from Evans Névé, a large accumulation basin at the head of Rennick Glacier. Core M1 (4.35 m) was extracted from the accumulation zone on the central plateau of the Morozumi Range, a small mountain massif bordering Rennick Glacier. Cores E10 and M1 span the time periods from 1929 to 1981 and from 1971 to 1981, respectively, as dated using seasonal variations in chloride (E10) and sulfate (M1) concentrations. An estimated net balance of 50 kg m−2 a−1 was derived for site E10 and of 182 kg m−2 a−1 for site M1. The difference in net mass balance may be explained by elevational differences (M1 1400 m a.s.1., E10 2305 m a.s.1.). Recent (1973 to 1980) increases in sodium, silicate and sulfate at site E10 may be linked to decreases in Antarctic pack-ice extent (Kukla and Gavin 1981) for the same period.
Snow Stratigraphic Record at South Pole: Potential for Paleoclimatic Reconstruction
Authors: Mosley-Thompson E. , Kruss P.D. , Thompson L.G. , Pourchet M. , Grootes P.
Published: September 2017

An extensive investigation of the visible stratigraphy, microparticle concentration, liquid conductivity, oxygen isotopes and beta-radioactivity was conducted in pits excavated at Amundsen-Scott South Pole station. The objectives of the investigation were to assess the spatial representativeness of the geochemical and physical records preserved within the snow strata and to ascertain the temporal resolution which can be obtained from such ice-core records. Accurate interpretation of the time scale and reconstruction of climatic conditions from these time series requires (1) the analysis of as many stratigraphic parameters as possible and (2) the synthesis of data from a suite of cores in the study area. For periods of 10 a or less, regionally representative accumulation rates cannot be obtained from annual accumulation time series reconstructed at a single site. Although the microparticle concentrations, liquid conductivity and oxygen isotopic abundances all exhibit a seasonal cycle in the firn, the construction of an accurate time scale requires all three parameters in conjunction with the beta-radioactivity. Absolute dating will be impossible for cores from South Pole where entire accumulation years may be missing. Nevertheless, for East Antarctica, where accumulation rates are low (<0.1 m a−1 water equivalent), the good temporal resolution and the preservation of a distinct annual signal in some geochemical parameters makes the South Pole a very attractive site for deep ice-core drilling.
Investigations of the Oxygen-18 Content of Samples from Snow Pits and Ice Cores from the Filchner-Ronne Ice Shelves and Ekström Ice Shelf
Authors: Reinwarth O. , Graf W. , Stichler W. , Moser H. , Oerter H.
Published: September 2017

Since 1979–80, isotope studies with oxygen-18 (18O) have been carried out at several snow pits and ice cores near the German Georg-von-Neumayer station (Ekström ice shelf, Atka Bay), as well as from the Filchner-Ronne ice shelves, in the framework of the German Antarctic research programme. The investigations of snow pits on the Filchner-Ronne ice shelves yield a standard deviation for the annual average δ18O values of approximately 1‰ over the last five years, and a decrease of δ18O with distance from the ice edge of about 1‰ per 50 km. The variation of δ18O for stratigraphically matching snow layers from snow pits at the same location in different years is about 0.3‰ on the Filchner-Ronne ice shelves, and 0.8‰ at Georg-von-Neumayer station. The mean annual accumulation rate in the surroundings of Georg-von-Neumayer station was determined to be 34 g cm-2 for the years 1977–81. On the Filchner-Ronne ice shelves the mean annual accumulation rate (1979–83) decreases from 22 g cm−2 at Filchner station to 15 g cm−2 at traverse point T340, located 200 km southeast of Filchner station.
Closer to a True Value for Heavy Metal Concentrations in Recent Antarctic Snow by Improved Contamination Control
Authors: Wolff E.W. , Peel D.A.
Published: September 2017

Recent snow from two sites in the Antarctic Peninsula has been analyzed for Al, Cd, Cu, Pb and Zn. Measurement of full procedural blanks and of the extent of penetration of surface contamination has allowed a rigorous appraisal of both sampling and analytical methods. Whilst the particular samples of cored firn used here have been shown to be unsuitable due to penetration of surface contamination into their interiors, surface samples collected directly into acrylic tubes showed very limited penetration of contamination. The surface samples gave the following average concentrations: Al: 0.7±0.3 ng g−1, Cd: 0.26±0.09 pg g−1, Cu: 1.9±0.5 pg g−1, Pb: 6.3±3.3 pg g−1 and Zn: 3.3±1.7 pg g−1. The Pb concentration agrees well with data from other workers for recent snow from East Antarctica, while the values for Cd, Cu and Zn are about ten times lower than have been reported previously, even for ancient Antarctic ice. Although these data refer to only one site and a short time period, it is believed that they are representative of modern Antarctic snow.

The true concentrations of Cd, Cu, Pb and Zn in ancient Antarctic ice are not yet established. However the following limits are suggested for increases over natural background levels due to anthropogenic emissions: Pb 1 to 40 times, Cd 1 to 180 times, Cu 1 to 4.5 times and Zn 1 to 6 times. These results indicate that contamination may have been responsible for reports of anomalous enrichment of several heavy metals in Antarctic snow.
Atmospheric Particles: Their Physical and Chemical Characteristics, and Deposition Processes Relevant to the Chemical Composition of Glaciers
Authors: Barrie L.A.
Published: September 2017

Atmospheric particles originate from a variety of natural and anthropogenic sources. Estimates of man’s contribution to the total particle mass loading of the atmosphere range from 5 to 48%. Much of this is initially in the form of gases (SO2, NO2, hydrocarbons) that convert to particles while being transported to glacial receptors where they are incorporated into snow. The complex physical and chemical processes involved in the deposition of atmospheric particles to glaciers are reviewed. Both wet and dry deposition contribute to the pollutant loading of a snowfield. However, except in the case of low snowfall (<60 kg m−2 a−1) or exceptionally large particle sizes, such as might be released by volcanoes or when unrimed snowfall predominates, wet deposition is dominant. Estimates of the relative importance of wet and dry deposition based on scavenging ratios for rimed snowfall and dry deposition velocities agree well with observations in southern Greenland.
Relocation and Preferential Elution of Acidic Solute through the Snowpack of a Small, Remote, High-Altitude Scottish Catchment
Authors: Brimblecombe P. , Tranter M. , Abrahams P.W. , Blackwood I. , Davies T.D. , Vincent C.E.
Published: September 2017

This isolated snowpack shows wide spatial variability in composition, with 15 samples from a 700 m transect giving coefficients of variance of more than 50% for most of the major ions. Cations showed somewhat less variability than anions. Preferential elution, i.e. the more rapid loss of some ions from the pack than others, was more readily observed in the composition of meltwaters because of the high variability in snowpack composition. Preferential elution could be found in the snowpack where it was possible to resample a well-defined surface during a period of ablation. The elution sequence established from these surfaces was

although the position of the hydrogen and ammonium ions may be affected by buffering. The sequence compares reasonably well with a generalized one assembled from earlier studies, where is usually eluted quickly and sodium and chloride rather slowly. The evolution of the snowpack composition towards solute depletion, but relative richness in chloride, is clearly represented in triangular diagrams.
The Use of Continuum Thermodynamics in the Formulation of Ice-Sheet Dynamics
Authors: Hutter K. , Engelhardt H.
Published: September 2017

Ice sheets consist of several disjoint regions, each with physically distinct behavior. Parts are cold; others are temperate and either partly or completely saturated. Varying dust content, impurities, debris content, etc., may affect the ice flow. Usually, these regions are separated by material or non-material surfaces or boundaries. We use mixture concepts, involving the balances of mass, momentum, energy and entropy. When applied to regular domain points these concepts and appropriate constitutive postulates yield the field equations for the evolution of the constituents. When formulated in terms of singular surfaces, boundary and transition conditions emerge. Our presentation takes the form of an extended abstract of work that is presently under consideration (Hutter and Engelhardt 1988; Hutter and Engelhardt, in preparation).
Numerical Models of Steady-State Thickness and Basal Ice Configurations of the Central Ronne Ice Shelf, Antarctica
Authors: Lange M. A. , MacAyeal D. R.
Published: September 2017

Radar ice-thickness surveys and bore-hole measurements suggest that the central part of Ronne Ice Shelf possesses a lobe-shaped basal layer of undetermined nature (probably saline ice). This layer is characterized by high radio-wave absorbtivity and by thicknesses up to approximately 300 m. We reconstruct this basal layer and the associated ice-shelf thickness and flow distributions, using a time-dependent ice-shelf model forced with prescribed basal freezing rates. Characteristics of the basal layer are controlled by two factors: (i) long ice-column residence times in the unventilated pocket between Henry and Korff ice rises and Doake Ice Rumples, and (ii) basal freezing rates in this pocket that exceed the snow-accumulation rate (currently averaging 0.35 m/a ice equivalent across the ice shelf).
Dielectric Variability of a 130 m Antarctic Ice Core: Implications for Radar Sounding
Authors: Moore J. C.
Published: September 2017

A 130 m long ice core has been dielectrically profiled. From an analysis of the measurements, we obtain a profile of the high-frequency (radio-echo) conductivity. This profile has been represented by a simplified 700 layer model. The model has layers of differing conductivities, permittivities and thicknesses. A reflection-coefficient log can be calculated, assuming that permittivity is a smooth function of depth. Variations in conductivity are shown to be more likely sources of internal reflections from depths greater than a few hundred metres than changes in permittivity caused by density changes. The log is convoluted with input pulses of various frequencies and pulse lengths in order to produce synthetic radargrams. These show features that correspond to the internal reflections typically seen when radio echo-sounding polar ice sheets.
Characteristic Growth Processes of Ice Crystals on the Antarctic Ice Sheet
Authors: Nishimura Hiroshi , Maeno Norikazu
Published: September 2017

Characteristic growth processes were investigated by measuring cross-sectional areas of ice crystals for four 30 m snow cores drilled in Mizuho Plateau, Antarctica. Considerable difference was found in the growth rate of crystals between a temperature-gradient layer above 6 m depth and an isothermal layer below 10 m depth: the growth rate in the temperature-gradient layer was much larger than that in the isothermal layer. In the isothermal layer, temperature dependence of the growth rate K was expressed by an equation K = K0 exp(−E/RT), where R and T are the gas constant and absolute temperature respectively. The apparent activation energy E is 44.7 kJ mol−1.

On the other hand, in the temperature-gradient layer, the apparent activation energy was as small as 12 kJ mol−1: the difference was explained as due to the temperature gradient. Using the temperature profiles in snow that have been estimated from the meteorological data from several stations, the growth rates in the temperature-gradient layer were calculated. The calculated temperature dependence of the growth rates, taking into consideration vertical flux of water vapor between ice particles caused by the temperature gradient, showed good agreement with measured results. It is concluded that the growth process in the layer above 6 m depth is mainly due to vapor transport under the vertical temperature gradient.
Growth Rate of Crystals Within the Surface-Snow/Firn Layer in Wilkes Land, East Antarctica
Authors: Dahe Qin , Young Neal W. , Thwaites Richard J.
Published: September 2017

Measurements of crystal size have been made on seven firn cores drilled at sites covering a range of mean annual temperature from –12.6° to –52.5°C and a range of accumulation rate from 52 to 315 kg m−2 a−1. The sorting coefficient, which gives a measure of the dispersion of crystal sizes within a sample, shows an overall pattern when data from all cores are grouped together as a function of depth. The values are generally small near the surface, increasing to a maximum around 8 m depth, then decreasing but becoming more diffuse at greater depths. Below about 5 m depth, the crystal size increases at an essentially constant rate, which depends on temperature, but in the upper 5 or 7 m the size increases at 1.5 to 2 times this rate. The seasonal variation in temperature enhances the effective mean growth rate of crystals in the near-surface layers compared to conditions with a constant mean temperature and accounts for a part of that increase. But it is likely that vapour diffusion along strong vertical temperature gradients causes the greater part of the observed increase in growth rate. The dependence of crystal-growth rate on temperature is consistent with the Arrhenius-type relation found by other studies.
Ekström Ice Shelf, Antarctica
Authors: Thyssen F. , Grosfeld K.
Published: September 2017

In 1980–81, 1983–84 and 1985–86 airborne surveys with an electromagnetic reflection (EMR) system were made of Ekström Ice Shelf, Antarctica. The EMR data were supplemented by measurements of surface elevation with radar altimetry during flights at a constant pressure altitude. The accurate measurement of ice thickness in areas with clearly developed bottom reflectors was used to generate a plot of surface elevation against ice thickness. The effect of changing barometric pressure during the flights could be reduced by this means. Elevations were calibrated over the open sea at the beginning and end of each flight.

On the basis of these data, the surface elevation, ice thickness and isostatic anomalies have been mapped over the ice shelf.
Microearthquake Source Locations and Mechanisms: Ice Stream B, West Antarctica (Abstract)
Authors: Anandakrishnan S. , Blankenship D. D. , Bentley C. R.
Published: September 2017

An array of nine seismographic stations, each sensitive to all three components of motion, was deployed on Ice Stream B, West Antarctica, during the austral summer of 1985–86. The network was sensitive to high-frequency (=400 Hz) seismic activity within a 350 km2 area of the ice stream, and the deployment geometry allows the precise determination of depths for events beneath the 10 km2 array. Microearthquakes from both beneath and beside the ice stream were detected and recorded (Blankenship and others 1987). Inversion of P-wave and S-wave travel times and radiation patterns allows the determination of locations and fault-plane solutions for many of these events.

We find that bottom events involve low-angle thrusting, in the down-stream direction, of ice or till; displacement is ∼½ cm per event over a (15 m)2 area. Such faulting is rare and releases an insignificant part of the total energy dissipated by ice flow. However, this is a possible mechanism for plucking of the ice-stream bed.

Fault-plane solutions for most major surface events are consistent with the opening of tensional fractures oriented transverse to ice flow. Precise location of these events shows that they correspond to open crevasses, mapped by Vornberger and Whillans (1986), that are oriented transverse to ice flow.

In addition, shear-wave splitting observed on some of the microearthquakes shows that the c-axes in the ice stream are slightly, but not strongly, anisotropic. Precise location of the sources requires the use of a detailed velocity-depth profile in the firn, which was obtained by seismic short-refraction studies (Anandakrishnan and others 1988, this volume). A density-depth profile calculated from these velocities agrees well with direct density measurements on a single core nearby (Alley and Bentley 1988, this volume).
Basal Mass Balance Along a Flow Line on Ronne Ice Shelf, Antarctica (Abstract)
Authors: Jenkins A. , Doake C.S.M.
Published: September 2017

Recent glaciological work on Ronne Ice Shelf has focused on an assumed flow line which extends from Rutford Ice Stream grounding line to the ice front. Results from doppler satellite surveying and radio echo-sounding are used in kinematic calculations to determine the basal mass balance, assuming the flow line to be in a steady state. Models suggest that basal melting dominates over most of the flow line and is most pronounced at the extremities. In the region within 300 km of the grounding line and over the final 45 km before the ice front, at least 1 m/a on average must melt away to maintain the observed velocity and thickness profile. More gentle melting occurs over about half the remaining distance, but in a region between 130 and 300 km in from the ice front, basal freezing must occur at an average rate of about 0.1 m/a to maintain a steady state. The existence of a thin layer of saline ice underlying the ice shelf, which persists for a further 80 km down-stream before being melted away entirely, is consistent with the weak returns observed during both airborne and ground-based radio echo-sounding in this region.
Antarctic Icebergs – Production, Distribution and Disintegration (Abstract)
Authors: Orheim Olav
Published: September 2017

A programme of systematic iceberg observations was initiated in 1981 by Norsk Polarinstitutt through the SCAR Working Group on Glaciology. Icebergs are recorded every 6 h and in five length groups: 10-50, 50-200, 200-500 and 500-1000 m, and those over 1000 m, which are described individually. Data on more than 100 000 icebergs are now on file at Norsk Polarinstitutt, and practically all ships travelling to and from Antarctica participate in the collection of data.

This paper presents the first comprehensive analysis of the iceberg data. The quality of the data set is discussed, with consideration of potential errors in and limitations of the data, and various statistical evaluations. Representative distribution data are presented, and used to determine iceberg production, disintegration and mean residence times, and regional and total Antarctic calving rates.

The incidence of large-scale calving in particular is evaluated, including the remarkably large break-offs in recent years. These exceed both the total annual accumulation on the Antarctic continent and the mean annual calving rate as determined from ship observations.

The results show further: (1) that there are more than 200 000 icebergs south of the Antarctic Convergence, (2) that there are large regional differences in iceberg calving rates and iceberg sizes, and (3) that the calving rate from Antarctica is higher than that given in most previous estimates, which implies (4) that the mass balance of the Antarctic ice sheet is not positive as suggested by most recent estimates.
Force Budget: Numerical Methods and Application to Two-Dimensional Flow Along the Byrd Station Strain Network, West Antarctica (Abstract)
Authors: van der Veen C. J. , Whillans I. M.
Published: September 2017

Using the partitioning of full stresses into resistive and lithostatic parts, force balance for plane flow is expressed in terms of strain-rates and a vertical coordinate scaled to the ice thickness. The balance equation and constitutive relation can then be used to calculate stresses through a vertical section of a glacier. Because the flow law is highly non-linear, these calculations are done numerically. Starting at the surface, the force-balance equation is solved by using measured surface velocities to calculate vertical shearing, and this yields velocities at a depth just below the surface. These velocities are used to compute vertical shearing at that depth, from which velocities at the next deeper layer follow. In this way, going progressively downward, velocities and stresses are calculated throughout a section of a glacier.

The theory for calculating resistive stresses and velocities in a glacier is applied to the Byrd Station Strain Network. Large longitudinal variations in basal drag and in sliding velocity occur and this result is little affected by errors in the input data or by uncertainties in the constitutive relation for ice. The basal drag is usually equal to the driving stress to within 10–20%, and both vary by a factor of about 2 along the strain network. Sites of high drag and little sliding are not always correlated with basal highs, indicating that some process (for example, complex bed drainage) is controlling the friction at the bed of the West Antarctic ice sheet.
Glaciological and Chemical Characteristics of an Antarctic Inland Plateau (Abstract)
Authors: Ageta Y. , Kamiyama K. , Okuhira F. , Fujii Y. , Watanabe O.
Published: September 2017

A glaciological research project in east Queen Maud Land, Antarctica, has been carried out by the Japanese Antarctic Research Expeditions between 1982 and 1986 (JARE-23 – JARE-27).

In this paper, we deal with the area traversed by JARE-25 and JARE-26, a representative inland plateau in Antarctica. In 1984, a team from JARE-25 extended a route from Mizuho Station (MS) to an advanced camp (AC; 74°12′S, 34°59′E; 3200 m a.s.l.) and returned to MS via the Yamato Mountains region. In the following year, 1985, a team from JARE-26 reached the summit (77°22′S, 39°37′Έ; 3810 m a.s.l.) of an ice dome on the plateau behind AC and continued to Asuka camp, north of Sør-Rondane Mountains. Investigations were carried out along the routes as follows:

Geomorphological observations: the altitude along the routes was measured, together with the depth of the bedrock, which was obtained by radio echo-sounding. The shape of the dome and the position of ice divides were revealed. Gravity soundings were also carried out along the routes.

Depositional and erosional environments of the snow surface: the net accumulation rate was obtained along the routes by the stake method. Sastrugi orientations were recorded in order to gain information on the prevailing wind. At several points, vertical profiles of snow stratigraphy and snow hardness were obtained, together with snow temperatures at 10 m depth. The glaciological characteristics of the plateau are described with reference to these results.

Snow chemistry: the values of the electro-conductivity and pH of melted snow along the routes were obtained, and the results show high conductivity and low pH values around the dome region. Quantitative studies on the chemical composition of the samples are continuing.

Ice coring: at the dome camp (DC; 77°00′S, 35°00′E; 3760 m a.s.l.), coring was carried out to a depth of 40 m. In the samples, we have been studying the vertical distribution of δ18O and the products of nuclear fission, in order to determine the accumulation rate and the atmospheric environment.

On the basis of the results described above, the relationship between meteorological and glaciological conditions in the inland plateau are discussed.
Distribution of Surface Features and Surface Mass Balance of Ice Sheet, East Queen Maud Land, Antarctica (Abstract)
Authors: Fujii Yoshiyuki , Ageta Yukata
Published: September 2017

Surface features were classified morphologically and described along oversnow traverse routes from the coast to the inland high plateau of east Queen Maud Land, Antarctica, during the 1984 and 1985 summer seasons. The distribution of surface features reveals regional characteristics which reflect differences in the regional deposition-erosion process.

On the basis of observation of surface features and measurements of surface mass balance, the ice-sheet surface of east Queen Maud Land is sub-divided according to different environmental zones:

(1)

Ablation zone (below 700 m a.s.l.): melting of snow occurs. Dry snow line approximates the altitude where the maximum air temperature is 0°C.

(2)

Coastal continuous accumulation zone (700–1800 m a.s.l.): snow accumulation occurs continuously and the surface is flat because of high snow precipitation and a slight katabatic wind.

(3)

Discontinuous accumulation zone (1800–2500 m a.s.l.): a rough surface of sastrugi dominates this zone. Snow accumulation is discontinuous in space and time because of low snow precipitation and strong katabatic wind. Negative annual snow accumulation was observed at 20–30% of the stakes set every 2 km along the traverse route. Mizuho Station is located in this zone.

(4)

Long-term accumulation-free zone (2500–3400 m a.s.l.): long-term absence of snow accumulation occurs at the glazed surface, which consists of a multi-layered ice crust several millimetres thick. A glazed surface develops over a distance of 1–20 km when the surface undulation is steeper, and covers 30–50% of the area in this zone. A hiatus sequence of snow accumulation is thought to continue for about 10–100 years over the glazed surface region.

(5)

Inland continuous accumulation zone (above 3400 m a.s.l.): a flat surface dominates in this zone. Snow accumulation occurs continuously because there is a weak katabatic wind in the central high plateau in spite of a very small amount of precipitation.
Modelling the Evolution of the East Antarctic Ice Sheet: Problems and Perspectives (Abstract)
Authors: Grigoryan S. S. , Ignat’yeva I. Yu. , Krass M. S. , Shumskiy P. A.
Published: September 2017

Modelling the thermodynamics of a large ice sheet is in essence a problem of the deformation of a non-isothermal and relatively thin viscous layer. Reasons for forecasting the behaviour of a large ice sheet are: (a) to specify the relationship between the existence and development of the ice sheet and regional climatic and tectonic conditions; (b) to study the influence of variations in surface temperature, mass balance, and geothermal flux (as functions of coordinates and time) on the evolution of the thickness of the ice sheet. Hence the principal requirements for modelling are:

1.

The model must be evolutionary; in particular, various stationary stages should be derived from it (rather than postulated).

2.

The model must be non-isothermal because temperature variations amount to some tens of degrees.

3.

Two-dimensionality of the model is essential if we are to use it for making realistic forecasts.

4.

Conditions at the boundary between land ice and the sea, which are the basic factors controlling the location of the margin of the ice sheet, should be taken into account.

5.

Finally, the model must be acceptable for digital analysis by computer.

Contemporary mathematical models of the dynamics of the Antarctic and Greenland ice sheets are too simplified and do not fulfil these requirements. Our mathematical model of the evolution of the Antarctic ice sheet is based on temperature parameterization. The parameterization correctly describes the distribution of temperature and its dependence on surface temperature, advection of ice, geothermal flux, and heat losses. The problem reduces to Cauchy’s problem for a non-linear parabolic partial differential equation with three-step dependence of ice temperature on depth. A linear viscous flow law is assumed. Tests treat the whole problem of the thermo-hydromechanics of the ice sheet. The ice sheet is assumed to be bounded by a grounding line or ice wall where the ice is in hydrostatic equilibrium with the sea. In this case, the problem reduces to a non-linear parabolic partial differential equation with a complicated boundary condition at the moving edge. A digital representation of the model is presented first. Tests demonstrated the possibility of using an explicit three-layered scheme. Calculations for the East Antarctic ice sheet indicated that the ice margin should retreat slightly under contemporary climatic conditions (which corresponds to the field evidence). In future the boundary should tend towards a stationary state. A forecast of the behaviour of the ice sheet is derived. The East Antarctic ice sheet is found to be stable during various changes in climatic factors. The calculated hydromechanical characteristics of the ice sheet agree with the observed field data.
Measurements of Strength on Dakshin Gangotri Ice Shelf in East Antarctica (Abstract)
Authors: Sharma Satya S.
Published: September 2017

During the first wintering by Indian scientists in Antarctica, from December 1983 to February 1985, year-round measurements of the strength of the snow cover were carried out to a depth of 1 m on Dakshin Gangotri Ice Shelf in East Antarctica, around the Indian Antarctic research station Dakshin Gangotri (70°05′S, 12°E). The measurements covered an area of 625 km2 around Dakshin Gangotri Station. Ten to 15 snow-hardness profiles per month were taken at different locations, using a Swiss ramsonde, and the values of ram resistance so obtained at different depths were averaged for each profile at depth intervals of 15 cm. These values were later tabulated and the minimum, maximum and average values obtained for each month were calculated. The values of ram resistance so obtained for each period were then used for determining unconfined compressive-strength profiles of the snow cover during different winter periods, using the correlation function given by Abele (1963).

Based on these values, the average unconfined compressive strengths of snow cover were calculated for different depths in the ranges 0–30 cm, 0–45 cm, 0–60 cm, 45–100 cm, 60–100 cm, and 75–100 cm. Preliminary results show that the snow cover below 45 cm generally has high strength throughout the year, whereas the strength of the snow cover from 0 to 45 cm varies greatly with the time of year. This layer from 0 to 45 cm shows a general increase in strength from January to September, with peak values occurring between June and September. Strength decreases gradually from October to December, which is the warm period in Antarctica.

The hardness-profile values obtained by ramsonde, when duly converted into unconfined compressive strength, give a fair indication of trafficability of wheeled and tracked vehicles at different times of the year on the ice shelf. They also indicate the load-bearing capacity of the surface snow for landing light- to medium-weight aircraft.
Pack-Ice Drift off East Antarctica and some Implications
Authors: Ian Allison
Published: September 2017

Three satellite-tracked data buoys were deployed between 70° and 80°E south of 65°S in February-March 1985. These buoys were subsequently trapped within the expanding seasonal sea ice and drifted with the ice. The buoys measured air temperature and pressure, and water temperatures to 100 m depth. Data from the buoys are used to describe the ice drift and environment within the winter sea-ice zone in this region, both north and south of the Antarctic Divergence. Additional preliminary data from a further six buoys deployed in the same area in March 1987 are also presented.

Besides providing information on the broad-scale drift of the ice in the Prydz Bay region, data from the buoys have shown: (i) the important role that ice drift plays in determining the autumn and winter expansion of Antarctic sea ice; (ii) the highly mobile nature of the ice, even hundreds of kilometres from the ice edge; (iii) the role that ocean-bottom topography has in determining ice drift over the continental shelf; and (iv) the modifying influence that an ice cover has on regional climate.

A qualitative assessment is made of the relative importance of the major forces driving the ice, although the data are insufficient for a detailed study of the ice dynamics.
The Dynamics of Austfonna, Nordaustlandet, Svalbard: Surface Velocities, Mass Balance, and Subglacial Melt Water
Authors: Dowdeswell Julian A. , Drewry David J.
Published: September 2017

Glaciological measurements from Austfonna on Nordaustlandet, Svalbard, are needed as a prerequisite to mathematical modelling of ice-mass dynamics. Several upper and lower boundary conditions are set out in detail for a 670 km2 drainage basin (Basin 5) and are generalized to the whole ice cap where possible. The ice surface and bed topography are mapped for Basin 5. 30% of the basin lies below sea-level. Bed elevations range from -100 m to over 300 m, and maximum ice thickness is >500 m. A 21 km long trilateral network of stakes provides velocity and strain-rate data. Maximum ice-surface velocity is 47 m a−1 and maximum strain-rate is 0.64 × 10−2 a−1. Snow-line migration with time is mapped from digital Landsat MSS data, and mass-balance estimates are used to calculate balance velocities. At the equilibrium line, about 300–350 m in elevation, balance velocity and observed ice-surface velocity are comparable, indicating that the basin is approximately in balance. A first approximation is given for the rate of iceberg calving from the tide-water basin margins. Enhanced Landsat imagery also shows that turbid melt-water plumes of subglacial origin flow from the terminal ice cliffs, indicating that at least parts of the ice-cap margin are at the melting point. The margins of Basin 5, grounded below present sea-level, are likely to be underlain by deformable sediments, but inland the nature of the substrate is unknown.
Numerical Models of Ice-Shelf Flow: Ideal/Real
Authors: Lange M.A. , MacAyeal D.R.
Published: September 2017

We present model calculations that describe the flow of ice shelves of different configurations. We consider “ideal” models with well-defined boundary conditions and simple geometry in order to explore the response of an ice shelf to transient variations in ice-stream input. Gradually increasing the complexity of these simple models allows a better understanding of ice-shelf behavior without the complications that would arise in considering natural ice shelves. We find that the dissipation of ice-thickness variations caused by ice-stream transience is strongly influenced by ice rheology. The presence of an ice rise significantly alters the velocity field of the adjacent ice, when changes in ice-stream input occur. With models of “real” ice shelves, we demonstrate the ability of numerical models to test successfully working hypotheses on ice-shelf thickness distributions. Ice velocities, obtained by diagnostic models of Filchner–Ronne Ice Shelf that use different ice-thickness distributions, are compared with measured ice velocities. This comparison demonstrates that the model employing regions of thin ice in the central part of the ice shelf yields velocities significantly different from the field data. We therefore conclude that zones of thin ice on Filchner–Ronne ice Shelf are unlikely. This conclusion has recently been confirmed by field measurements.
Basin-Scale Ice Motion and Deformation in the Weddell Sea During Winter
Authors: Wadhams P. , Sear C.B. , Crane D.R. , Rowe M.A. , Morrison S.J. , Limbert D.W.S.
Published: September 2017

Ice motion in the Weddell Sea is examined for the period 19 August (Day 232) to 12 October (Day 286) 1986 using the tracks of four Argos buoys deployed during the Winter Weddell Sea Project 1986 (WWSP 86). Two were SPRI/BAS buoys, launched in December 1985 and March 1986 in the south-east and north-west Weddell Sea. The others were part of a mesoscale array deployed in the Maud Rise area by H. Hoeber of the Meteorologisches Institut der Universität Hamburg, during the WWSP 86 cruise of FS Polarstern. The four buoys operated together for 44 d, comprising a basin-scale quadrilateral from which the differential kinematic parameters of divergence, vorticity, shear, and stretch were extracted, as well as the large-scale pattern of motion. It is found that most deformation episodes were associated with atmospheric forcing events.
Recommendations for the Safe use of Ropeways Carrying Explosives in Avalanche Blasting
Authors: Brugnot Gerard , Rapin Francois
Published: September 2017

Over 15 years of experience, and a present stock of nearly 140 devices, have made us familiar with the use of avalanche-blasting ropeways (CATEX) in artificial avalanche release. Two years ago, in consultation with all other users we started to establish a list of recommendations for the safe use of CATEX, so that efficiency and reliability could be improved considerably. These guidelines have been designed to achieve safety by adapting CATEX technology to avalanche problems concerned with mechanical equipment, explosives, staff and maintenance.
Two Years Experience of Operational Avalanche Forecasting using the Nearest Neighbours Method
Authors: Buser O.
Published: September 2017

An operational version of avalanche forecasting using the nearest neighbours method was given to the Parsenndienst, the safety service in the ski area of the Parsenn region. They have tested this NXD method through two winters and have now decided to acquire their own computer with a mass storage unit in order to run the programme. The forecasting is being run by the patrolmen themselves, including the input of weather and snow data, and they also update the file of avalanche and blasting activities with the details of operations, as required for ammunition accountancy. The nearest neighbours method provides the patrolmen with a list of the avalanches that have occurred on the 10 d in the past 20 years most similar to the day being considered. These data represent the nearest neighbours of the method's name. The men are able to interpret the list correctly without any need of instruction, and rely on getting information from it which will help them to decide when and where to use (or not to use) explosives. The method of interpretation of the information supplied is illustrated by way of four specific examples.
Quantifying the Errors Involved in Transferring Suspended Sediment Rating Equations Across Ablation Seasons
Authors: Fenn C.R.
Published: September 2017

Bias-corrected suspended sediment rating equations are developed for the data from six separate ablation seasons in the Glacier de Tsidjiore Nouve basin. These equations differ significantly from one another. Suspended loads as predicted by equations used beyond their year of origin fall in the range of 34-278% of the true load. Mean absolute-percentage errors (MAPE) based on forecasts computed from each year’s model applied to the other 5 years of data range from 35 to 81%, with a mean of 52%. The equivalent MAPE for a lumped multi-year model is 38%, for an autocorrelation-correcting generalized least-squares (GLS) regression model, is 15%, and for a transfer function (TF) developed from a single 25 d period, only 5%. Simple structure-transfer functions appear to be more robust to temporal transfer than the usual type of rating equation, and offer the possibility of greatly improving upon the poor performance of OLS rating equations in providing estimates of suspended loads for periods beyond frames of origin.
Forecasting the Effects of a Planned Reservoir which will Partially Flood the Tongue of Unteraargletscher in Switzerland
Authors: Funk Martin , Röthlisberger Hans
Published: September 2017

In order to improve their hydro-electric power production in the Grimsel area, Kraftwerke Oberhasli (KWO) plan to construct a new reservoir with a storage level about 110 m higher than the existing Grimselsee. This paper deals with the expected changes of Unteraargletscher after periodical contact with the resulting water body. Upon initial flooding, the lowermost section of Unteraargletscher, about 800 m long, will float, drift away, and melt. A rough estimate of the heat balance shows that the energy input into the lake would be sufficient to melt this ice within 2–3 years, so that calving and melting will continue at a frontal ice cliff. The main effort of the study was aimed at forecasting this retreat. A pre-existing seismic survey was supplemented by new soundings by radar and seismic reflection, resulting in reliable cross-sections and information about the sub-bottom material. The forecast is based on the existing mass flux and an empirical calving rate relationship with water depth and predicts an equilibrium position of the terminus some 3–4 km further back than today, and a gain of water storage volume of 50 × 106 m3 after 10 years.
A Model of Initial Failure in Slab-Avalanche Release
Authors: Gubler H. , Bader H.-P.
Published: September 2017

At strain-rates below 1 × 10−4 s−1, low-density weak seasonal snow fails in a ductile manner. In inclined natural snow covers, local strain-rates hardly ever exceed 1 × 10−4 s−1, therefore initial shear failure, which eventually starts slow and finally fast fracture propagation causing slab releases, must be ductile. Changes in initial stability during precipitation periods are simulated using a microscopic mechanical model for weak low-density snow combined with equations describing strength increase by settling and sintering as a function of snow temperature. The results indicate, in good correspondence with experience, a strong dependence of fracture height of direct-action avalanches on precipitation intensity, snow temperature, and slope angle.
Development and Certification of A Visibility-Range Monitor By Image Processing
Authors: Ishimoto Keishi , Takeuchi Masao , Naitou Shigeyuki , Furusawa Haruki
Published: September 2017

A new visibility-range measuring system has been developed which uses a video camera, and with which visibility can be estimated by measuring the brightness contrast of a black target against a standardized background. This principle has been applied to development of the new visibility-range monitor described in this paper. In this monitor, a charge-coupled device (CCD) video camera measures the brightness of an arbitrary area in its range of vision, and visibility range measured by the video camera in blowing snow can be compared with that measured by the transmissometer-type visibility-range monitor and can also be calculated by direct observation using optical targets.

The new sytem can monitor visibility and record information about traffic on highways at 1 s intervals for a maximum of six separate positions. The vertical distribution of visibilities over a snow surface has been observed, and it has been found that the fluctuation in visibility is greatest at lower levels above the ground in blowing snow.
Extreme Avalanche Run-Out: Data from four Mountain Ranges
Authors: McClung D.M. , Mears A.I. , Schaerer P.
Published: September 2017

Avalanche run-out distances have a prominent statistical character which is not usually featured in calculations derived from avalanche dynamics models. In order to predict run-out distances in a rational manner, the statistical element should be included. Here, we present and analyze data on extreme run-out from four mountain ranges. When the data are fitted to extreme-value distributions, we are able to show how (and why) extreme-value parameters vary with terrain properties of the different ranges.
Three-Dimensional Equations for Mass Centre Motion of an Avalanche of Arbitrary Configuration
Authors: Nohguchi Yasuaki
Published: September 2017

The path over a surface with complex topography that a snow avalanche will take is usually not known in advance. To predict avalanche paths over such terrain, we propose a model for the motion of the mass centre of an avalanche over an arbitrary surface. The numerical solution for this model shows that avalanche paths over complex topography are very sensitive to small differences in the avalanche velocity.
Simulation of Snow-Avalanche Flow in Run-Out Zones
Authors: Norem Harald , Irgens Fridtjov , Schieldrop Bonsak
Published: September 2017

The authors of this paper have previously, in 1987, outlined the development of a set of constitutive equations representing the behaviour of avalanching snow, and the resulting equations for fully developed steady shear flow. The present paper considers the development of non-steady two-dimensional shear flow together with the use of a finite-difference programme to calculate snow-avalanche velocities and flow heights in the run-out zone. The numerical results thus obtained are compared with full-scale experimental data. These comparisons indicate that front velocity and run-out distance are simulated well by the model, and that the predicted snow deposits are fairly well in agreement with those actually observed.
Assessing Avalanche-Risk Levels on Walking Tracks in Fiordland, New Zealand
Authors: Owens I.F. , Fitzharris B.B.
Published: September 2017

Walking tracks which cross relatively rugged avalanche-prone terrain are becoming increasingly popular in New Zealand. Consequently, there exists the need to develop a methodology by which it will be possible objectively to assess the avalanche hazard in the vicinity of the tracks. This paper outlines some procedures that have been used to map avalanche paths, and introduces modifications to an internationally used highway hazard index employed to quantify the danger to walkers. The Fiordland region of south-west New Zealand is an area of spectacular scenic beauty, made famous by the Milford Track which has been walked by large numbers of tourists since the late nineteenth century. In recent years, avalanches have killed one person on the track, severely damaged a lodge, and destroyed several small bridges. Other walking tracks have been opened to tourists in this century and one of these, the Routeburn Track, is included in this study. Avalanche paths which affected the Milford and Routeburn Tracks were mapped in the field using well-established techniques and applying the results of previous research on the Milford Road, where historical records are available for a period of 50 years. The risk to walkers was assessed with a hazard index which depends on frequency of avalanches, numbers of paths, time taken to traverse each path, and numbers of walkers using the track. Results indicate that the avalanche hazard is low to moderate on the Milford Track and moderate on the Routeburn Track. The management implications of these findings are outlined.
A Process-Based Model of Snow Drifting
Authors: Pomeroy J.W.
Published: September 2017

This physics-based two-phase flow model of the mass balance of drifting snow calculates the transport of snow through saltation and suspension, and recognizes the important role of in-transit sublimation on surface-erosion rates. Measurements of the vertical gradient of drifting snow-mass flux and wind speed in the surface-boundary layer indicate the total flux of saltating snow increases linearly with wind speed and is sensitive to the transport threshold. The total flux of suspended snow requires saltation to become established, and increases with the cube of both the total flux of saltating snow and the wind speed. The total suspended flux quickly becomes the dominant transport mode as wind speeds increase beyond threshold levels, and comprises more than 90% of the total flux for wind speeds greater than 15 ms−1. Sublimation rates estimated from wind speed, temperature, and humidity are sufficiently balanced by snow-surface erosion rates to ablate completely snow-packs with depths of the order 200 mm, a typical value for steppe and prairie environments.