bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Ice-Stream Model: Application to Holocene Retreat in the Ross Sea, West Antarctica (Abstract)
Authors: Linglet Craig S. , Clark James A.
Published: February 2017

A numerical model of ice-stream retreat during the Holocene period of rising sea-level has been constructed, and applied to one of the ice streams draining the Ross Sea sector of the West Antarctic ice sheet. The purpose of the experiment is to assess the relative significance of eustatic sea-level rise, the response of the solid Earth to the changing ice load, and the formation of the Ross Ice Shelf on retreat of the ice-stream grounding line to its present position in the Ross embayment. An underlying hypothesis is that marine ice sheets (such as that in West Antarctica), the ocean, and the solid Earth form a coupled dynamic system in which changes, once initiated by an external event such as rising sea-level, can proceed independently of climatic change. Ice stream E (see maps by Rose 1979) was used as a test case during development of the model.
Glaciological Investigations in the Crête Area, Central Greenland: A Search for a new Deep-Drilling Site
Authors: Clausen H.B. , Gundestrup N.S. , Johnsen S.J. , Bindschadler R. , Zwally J.
Published: February 2017

The results of the 1984-85 post-GISP campaigns in central Greenland are presented. Eight ice cores were obtained, some spanning up to 360 years. We present:

I.

Geographical positions and elevations at the drill sites,

II.

Density and temperature in the bore holes,

III.

Filtered δ18O profiles and accumulation-rate variations along the ice cores.

The δ18O and accumulation profiles, along with those from the 400 m Crête ice core obtained in 1974, are compared.

The accumulation-rate series over a large region have a very high coherence. This indicates that a single bore hole in this region would give a representative accumulation time series over a long period. Further, it appears that for this region there is a linear relation between the measured annual accumulation rate and the mean annual δ18O values. Thus the area between Crête and Summit, just west of the ice divide, seems to be favorable for a deep-drilling operation.
Microparticle Concentration and Electrical Conductivity of a 700 m Ice Core from Mizuho Station, Antarctica
Authors: Fujii Yoshiyuki , Watanabe Okitsugu
Published: February 2017

The present paper gives the preliminary results of the analyses on microparticle concentration and electrical conductivity of a 700.56 m ice core from Mizuho Station, Antarctica. Concentration of microparticles coarser than 0.63 μm in diameter increases more than twofold at the 240-440 m depth interval compared with that below 440 m in depth. The higher particle concentration is well associated with higher electrical conductivity and lower δ18O. Periods of high particle concentration are estimated to be 3000-6000 years B.P. A visible volcanic dirt band was found at 500.7 m below the surface. This dirt band may be isochronous with the shallowest ash band of the Byrd Station core, found at 799 m depth. The present study indicates that large-scale environmental changes possibly occurred in the Southern Hemisphere in the middle of the Holocene.
Trace-Acid Ion Content of Shallow Snow and Ice Cores from Mountain Sites in Western Canada
Authors: Holdsworth G. , Krouse H.R. , Peake E.
Published: February 2017

An historical record of the deposition of common acids is contained in snow and ice cores taken from suitable sites in the accumulation zone of certain glaciers. Spatial and time-series data sets for trace-mineral acids have been obtained from snow-pit samples and ice cores from a number of mountain sites in Alberta, British Columbia, and the Northwest and Yukon Territories. In Alberta, it is possible to use temperate firn sites above 3460 m, although elution occurs during certain summers as indicated by isotopic and ionic data. This would also apply to sites of a similar latitude (52°±2°N) in British Columbia. In the Yukon Territory (≥60.5°N) reliable time series for the acid anions may be obtained from sites at altitudes above 3000 m. Elution provides a natural control for demonstrating that field sampling and subsequent analytical procedures do not introduce significant contamination. The Yukon data are compared with the net annual accumulation rate and with altitude. Recent data from the 5340 m Mt Logan site do not indicate any significant increase in natural background levels of snow acidity. Lightning, which is responsible for numerous forest fires in all provinces, is a possible natural source of nitric acid. Spring-summer peaks in nitrate concentration usually occur. In addition, forest-fire smoke may be a significant contributor to the mountain snow-pack chemistry in some years and must be considered when interpreting the Mt Logan core data. One Yukon profile seems to contain the signature from the 1986 Augustine volcanic eruption.
A Computer-Controlled System for Ice-Fabric Analysis on a Rigsby Stage
Authors: Lange Manfred A.
Published: February 2017

An integrated system for ice-fabric analysis on a Rigsby stage is described. The system consists of a regular Rigsby stage fitted with two opto-electronic sensors for assessment of azimuth and the tilt angle of each individual grain. Signals from the sensors are transmitted to a computer terminal via an interface box, which facilitates transformation of Gray-coded data to ASCII data records. The terminal is hooked up to a main-frame computer (VAX 750), where the digitized angles of the c-axis orientations of individual thin sections are stored in separate data files. These files are compatible with other already existing files containing additional ice-core data and thus become part of an extensive data bank. Appropriate software has been developed to produce, among other things, plots of c-axis orientations in a Schmidt net.
Mechanical Behavior of Ice Along the 2040 m Vostok Core, Antarctica
Authors: Pimienta Pierre , Duval Paul , Lipenkov V.Ya.
Published: February 2017

Uniaxial and biaxial compression tests were carried out on ice samples from the 2040 m Vostok ice core. It is shown that the ice viscosity does not significantly change with depth. As a result the high impurity content in glacial ice does not seem to influence the mechanical behavior of the Vostok ice core. The measured enhancement factor, smaller than 1, is caused by the particular orientation ofc-axes in this polar ice. It is deduced that the viscosity of Vostok ice for horizontal shear is high compared with that of other ice cores.
Air Mixing in Firn and the Age of the Air at Pore Close-Off
Authors: Schwander J. , Stauffer B. , Sigg A.
Published: February 2017

The air trapped in the bubbles of natural ice is not the same age as the surrounding ice. This is due to the fact that the air is enclosed in isolated bubbles only at the depth of the firn–ice transition. Within the overlying porous firn layer the air is able to mix and to exchange to a certain degree with the atmosphere. The age difference between ice and air is given by the age of the ice at pore close-off, less the mixing delay. Also, there is an age distribution due to diffusive smoothing and due to the gradual enclosure of the air at the firn–ice transition. Knowledge of this age relation is necessary for the interpretation of climatic parameters measured on ice cores. This work concentrates on the effect of diffusive mixing. We report on measurements of the diffusivity of CO2 and O2 (in N2) in firn samples from Siple Station, Antarctica. It is shown that the dominant mixing process is molecular diffusion. The diffusion coefficient depends approximately linearly on the porosity. A one-dimensional diffusion model has been used to calculate the air mixing in firn at Siple Station (Antarctica), at the South Pole, and at Station Crête (Greenland). An exchange time of between 10 and 50 years is obtained.
Trace Elements in Simultaneously Sampled Aerosol and Snow from the Antarctic Peninsula (Abstract)
Authors: Dick Alan L.
Published: February 2017

Ultra-clean techniques have been used to collect a series of fresh surface-snow samples on Gipps Ice Rise, Larsen Ice Shelf (68°48′S, 60°54′W) between 21 December 1984 and 12 February 1985. Aerosol samples were collected simultaneously on to pre-cleaned membrane filters to allow the direct comparison of trace-element levels in air and snow. Samples have been analysed by various techniques for cadmium, copper, lead, zinc, aluminium, calcium, potassium and sodium. For all elements, cross-sample concentration profiles have been obtained to support the data for snow samples.

The heavy-metal concentrations found in the surface snow were similar to those measured previously near Gomez Nunatak in the Antarctic Peninsula. The mean aerosol concentrations found at Gipps Ice Rise were Cd: 0.06 pg m−3, Cu: 1.0 pg m−3, Pb; 4.7 pg m−3, Zn: 6.1 pg m−3. These are the lowest concentrations measured so far in Antarctic aerosol.

The ratio of the snow concentration (pg g−1) to air concentration (ng m−3), known as the washout factor, has been calculated for each element and sampling period. The data show that, for the Antarctic Peninsula, the marine aerosol is more efficiently removed to the snow-pack than is the crustal aerosol. Heavy metals are least efficiently removed. This result suggests that the measurement of concentrations in snow and ice alone may lead to misinterpretation of atmospheric source strengths.
An experimental study of the water and heat balance in the source area of the Ürümqi River in the Tien Shan mountains
Authors: Ersi Kang , Daqing Yang , Yinsheng Zhang , Xinyuan Yang , Yafeng Shi
Published: February 2017

In the source area of the Ürümqi River, during the glacier ablation season, net radiation is the only heat input to the tundra, averaging 119W m−2 in July and August, more than twice that to the glacier, where additional heat input is contributed by sensible heat. The heat input to the tundra is mostly lost by evaporation, which accounts for 86%, while the input to the glacier is mostly lost by melting. The relatively small heat input to the glacier and the large evaporation rate of its surroundings favour the glacier’s existence. Most precipitation occurs between June and August, accounting for 66% of the annual total. Precipitation increases with altitude in average conditions during the ablation season; the annual precipitation is estimated to be about 650 mm at the mean equilibrium line altitude of 4030 m. This amount is considerably larger than that of the surrounding area. Evaporation is estimated at 270 mm a−1 on the tundra, reducing the runofTin a rather large proportion, and 120 mm a−1 on the glacier. Almost all runoff takes place between May and September, and is mostly concentrated in July and August when the glacier melt is the most intense. When air temperature is high during the ablation period, although the precipitation is less, runoff could peak because of the glacier melt. Based on the measured runoff and estimated regional precipitation and evaporation, the glacier mass balance is calculated and discussed.
Temperature regime studies and mathematical calculations for dry snow covers in the western Tien Shan mountains, China
Authors: Hong Ma , Zongchao Liu , Zhian Yang
Published: February 2017

A mathematical model is proposed to simulate the spatial and temporal variations in snow temperature. The model is based on the non-steady, one-dimensional, heat-conduction equation with internal heat source. It gives the change in time of the internal temperature field of the snow as it responds to varying surface temperature and periodic solar radiation. Verification of the model is accomplished by comparing the calculated results with observed data. The model may serve as a basis for quantitative investigations of snow temperature and temperature gradient, and relevent problems such as energy-mass transfer processes. Moreover, it allows better understanding of the relationship between external atmospheric conditions and the internal thermal regime of dry snow covers in the western Tien Shan mountains.
Industrial influence on glacial processes in mountains of circumpolar regions
Authors: Grebenets V.I. , Fedoseyev D.B.
Published: February 2017

Industrial activity in the Noril’sk mountains since the 1930s has changed the landscape and formed artificial banks, ridges and terraces. New water courses have been formed and snow has been removed to places where it has accumulated year by year. The ground temperature has increased by 0.3 to 0.5°C down to a depth of 30 to 50 m, melting has increased in the permafrost layer and artificial ground has become more unstable, leading to landslides and mudflows. Material in dumping sites has frozen and turned into rock glaciers, chemical pollutants have accumulated in snow and extremely high concentrations are observed in meltwater during spring. The gravitational instability of mountain and piedmont landscapes increases with human activities and the landscapes thus changed cause greater danger from slumps, mud flows and avalanches.
Calculation of Snow Avalanche Runout Distance
Authors: Bakkehoi S. , Domaas U. , Lied K.
Published: February 2017

Distance of maximum avalanche runout is calculated by four topographical factors. An empirical equation found by regression analysis of 206 avalanches is used to predict the maximum runout distance in terms of average gradient of the avalanche path (angle α). The correlation coefficient R = 0.92, and the standard deviation of the residuals SD = 2.3°.

The avalanche paths are further classified into different categories depending on confinement of the path, average inclination of the track 6, curvature of the path y", vertical displacement Y, and inclination of rupture zone Q. The degree of confinement is found to have no significant effect on the runout distance expressed by a. Best prediction of runout distance is found by a classification based on 5 and Y. For avalanches with β <30° and Y > 900 m, R = 0.90 and SD = 1.02°.

The population of avalanches is applied to a numerical/dynamical model presented by Perla and others (1980). Different values for the friction constantsvand M/DY are computed, based on the observed extent of the avalanches. The computations are supplied by velocity measurements v from a test avalanche where Y = 1 000 m, and vmax= 60 m s−1. The best fitted values are μ = 0.25 and M/DY = 0.5, which gives R = 0.83 and SD = 3.5°.
Modelling of Antarctic Tabular Icebergs in Ocean Waves
Authors: Kristensen Monica , Squire Vernon A.
Published: February 2017

The prediction of the motions of a tabular iceberg in a seaway is a problem which cannot be solved with a simple approach. The main difficulty lies in the size and mass of the iceberg, which produce frequency-dependent hydrodynamical effects as it moves in the water. Specifically, any solution must take into account both the added inertia and the generation of surface waves caused by the motions of the berg. Early attempts at modelling, which did not include these terms, could not accurately predict the complicated response behaviour seen in field data. In this paper we discuss some modifications to a two-dimensional simulation of floating bodies in waves, which must be applied when the motions and the hydro-dynamical pressures beneath tabular icebergs are required.
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: February 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).
Ekström Ice Shelf, Antarctica
Authors: Thyssen F. , Grosfeld K.
Published: February 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.
Absorption of Solar Radiation at the Antarctic Snow Surface (Abstract)
Authors: Grenfell Thomas C. , Warren Stephen G. , Mullen Peter C.
Published: February 2017

Solar radiation incident on, and reflected by, the snow surface was measured near the South Pole as a function of wavelength, angle, and distance from the station. The objectives of the study were: (1) to observe spectral albedos of snow across the solar spectrum, (2) to obtain depth profiles of snow-grain radius in order to construct theoretical models of spectral albedo for pure snow, (3) to document the extent and degree of soot pollution due to station activities and to assess whether it could invalidate solar-radiation measurements made close to large stations, and (4) to obtain the spectral distribution of incident solar radiation at the Antarctic surface for various cloud conditions, in order to test radiation models of the Antarctic atmosphere.

Spectral albedo, measured under diffuse lighting conditions (overcast cloud) on many days, repeatedly agreed with the results of theoretical models which predicted values approaching unity in the visible and found grain-size to be the most important variable controlling snow albedo in the near-infra-red. A representative albedo curve is shown in Figure 1.The visible albedo values were found to be 98–99% and were relatively insensitive to grain-size. (These results disagree with the only previous measurements of Antarctic snow albedo which had good spectral resolution: those of Kuhn and Siogas. Their maximum albedo was only about 90% in the visible.) The near-infra-red albedo, however, varied substantially among the experiments, due to day-to-day variations in snow grain-size, caused by precipitation and wind drifting. The experimental points in the figure match theoretical calculations for grain radius less than 50 μm at wavelengths beyond 1.5 μm, and 50–100 μm for shorter wavelengths. At the shorter wavelengths the light penetrates more deeply into the snow, so the albedo is sensitive to grains beneath the surface, whereas at the longer wavelengths the albedo is influenced only by the grains very close to the surface. The observed albedos can thus be explained by an increase in grain-size with depth.

In order that our measurements would be representative of large areas, we were concerned to avoid possible effects of pollution from the station. We collected samples from the top 20 cm of snow, melted and filtered them, and analyzed the filters. The conclusion is that the pollution is very minor. Just 500 m up-wind of the station there is normally less than 1 ng of carbon per gram of snow (1 ppb). Even down-wind of the station the carbon content did not exceed 3 ppb. For snow grain-sizes typical of Antarctica, our models predict that 15 ppb carbon would reduce snow albedo by only 1% at the most sensitive wavelength. Thus we reject our earlier suggestion that the low visible albedos of Kuhn and Siogas were due to impurities in the snow and now favor other explanations.
Basal Mass Balance Along a Flow Line on Ronne Ice Shelf, Antarctica (Abstract)
Authors: Jenkins A. , Doake C.S.M.
Published: February 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.
Air Temperature and Snow Accumulation in the Antarctic Peninsula During the Past 50 Years (Abstract)
Authors: Peel David A. , Mulvaney Robert
Published: February 2017

Trends in climate affecting the West Antarctic ice sheet may be detected first in the Antarctic Peninsula region. Although the area contains the most comprehensive weather records for any part of Antarctica, reliable snow-accumulation data are lacking.

Mainly as a result of the large snow-accumulation rate in the region (typically in the range 4.0–10.0 kg m−2 a−1), stratigraphie evidence of climate derived from ice cores can be resolved in much greater detail than is possible over most of the continent. Ice cores have been drilled at two sites, representing the extremes of climate type encountered in the region. A 133 m core has been obtained from Dolleman Island (70°35.2′S, 60°55.5′W) to represent the continental-type climate of the Weddell coast region, and an 87 m core has been obtained from the Palmer Land plateau (74°01′S, 70°38′W) to represent the more maritime regime of the west coast and central areas. Replicated cores were obtained at both sites in order to assess the contribution of local noise factors to the climatic signal preserved in the cores. Climatic trends during the period 1938–86 have been assessed on the basis of stable-isotope analysis of the top 47 m of the Palmer Land core and of the top 32 m of the Dolleman Island core.

A statistical analysis of derived profiles of mean annual δ18O and accumulation rate indicates that the local noise factors at these sites are sufficiently small that data averaged over periods as short as 5 years should reveal climatic shifts at the level of 0.2% and 5% respectively. These changes are much smaller than trends that have actually occurred during the past 50 years.

The most notable trend over the past 30 years is an increase of more than 30% in the snow-accumulation rate that has occurred in parallel with an overall temperature increase of 0.06°C/a during the same period. Increases of similar magnitude can be inferred from studies in East Antarctica, and may be related to a significant increase in precipitation rate that has been documented recently at mid-to high-latitude stations in the Northern Hemisphere. The finding may have relevance to studies of the possible consequences of a CO2-induced climate change. More extensive accumulation time series are now required from Antarctica, if satisfactory models of the long-term balance of the ice sheet are to be derived.
Measurements of Strength on Dakshin Gangotri Ice Shelf in East Antarctica (Abstract)
Authors: Sharma Satya S.
Published: February 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.
Some Dynamics Studies on Urumqi Glacier No. 1, Tianshan Glaciological Station. China
Authors: Maohuan Huang , Zhongxiang Wang , Baolin Cai , Jiankang Han
Published: February 2017

The zero isopleth of surface areal strain-rate is roughly parallel to, but below, the equilibrium line of the glacier. In the middle and lower parts of the ablation area, the basal temperature is either close to or at the melting point, whereas above and around the equilibrium line the glacier is frozen to its bed. The basal bulk ice is deforming continuously and inhomogeneously but, in the inner parts of the glacier, where the strain-rate is smaller, homogeneous deformation can only be assumed conditionally. In the ablation area, pure shear is predominant near the base of the glacier and simple shear becomes progressively more important from the inner parts of the glacier towards its margins.
Avalanche Starting-Zone Analysis by use of a Knowledge-Based System
Authors: Buisson Laurent , Charlier Claude
Published: February 2017

This paper presents the first step in the development of a new kind of computer-based tool which can help a specialist consultant in avalanche path analysis, a knowledge-based or expert system. In considering an avalanche path, the specialist often needs a simulation of possible avalanches on this path in order to obtain data for probable velocities and pressures. Use of classical numerical tools by an engineer requires a great deal of experience and knowledge. Such knowledge exists, but until the development of knowledge-based systems no computer-based tool was available.

After a short review of such systems, we describe a knowledge-based system currently being developed in CEMAGREF. Its problem-solving environment includes methods of analysis developed by a senior consultant, and also numerical and qualitative models. In the first step, which is presented here, it analyses the starting zone of an avalanche path. By means of a digital terrain model and a description of vegetation and main ridges (a model which still needs to be improved) this system can make use of the experience of specialists to produce an avalanche-starting simulation based on specified meteorological conditions. Quite simple rules are employed in order to take into account snow drift. First results are shown on accompanying maps of this qualitative modelling and these will need to be tested for validity.
Numerical, Analytical, and Laboratory Experimental Studies of Granular Avalanche Flows
Authors: Hutter Kolumban , Savage Stuart B. , Nohguchi Yasuaki
Published: February 2017

Flow avalanches may be regarded as being composed of a granular fluid. When dislodged, the snow masses accelerate down a slope until the inclination of its bed tends towards the horizontal, at which stage bed friction eventually brings the snow to rest. We present a completely new analysis of the motion of a finite mass of granular material along an inclined base.

We regard a granular snow mass as an incompressible continuum to which a Coulomb-like basal friction law can be applied. Depth-averaged equations of motion are formulated in terms of a curvilinear coordinate system along a curved bed, and incorporate an averaged longitudinal velocity and a height distribution. A numerical finite-difference technique is employed to integrate these equations. We present numerical results obtained for motion along a curved bed and compare this with the solutions of the equations with results from laboratory observations. The experiments have been performed in order to monitor the motion of a finite mass of granules, either plastic particles or glass beads, along a chute consisting of both an inclined and a horizontal zone, the two zones being connected by a curved element. The particle spread along the chute and the mass distribution of the granules in the run-out zone, as obtained from these experiments, are compared with those derived from theoretical computations. The results show that the model used predicts the motion of a granular avalanche reasonably well.

Finally, it is indicated how the basal friction law may be extended or altered in order to reproduce the dynamic processes involved in causing the abrupt cessation of the snow mass-motion characteristic in the run-out zone.
Forty Years of Mass-Balance Observations on Glacier de Sarennes, French Alps
Authors: Valla François
Published: February 2017

Located south of Grenoble, in the French Alps, Glacier de Sarennes is a small cirque glacier whose mass balance has been measured since 1948.

Field measurements are made after the accumulation period (from October to May) and during the ablation period (from June to September). The main variables for snow are depth, density, and water equivalent for accumulation, together with ice depth and water equivalent for ablation which are used to calculate mass balance and regime. We present an example of the data collected on the glacier during the 1986–87 season, the evolution of the mass balance during the summer of 1987, and the main variables followed during the 40 years of observation, 1948–88. Mass balance, accumulation, and ablation are directly related to precipitation and temperature. Glacier de Sarennes is a simple glacier which has no tongue and no ice movement, and is like a gigantic rain gauge. The evolution of its mass balance is simply related to the meteorological variables of the year. For more significant and complex glaciers, it is necessary to take account of past as well as present meteorological variables.
Evolution, Water Balance, Potential Hazards, and Control of a Pro-Glacial Lake in the French ALPS
Authors: Vallon M.
Published: February 2017

Lake Arsine, a pro-glacial lake in the French Alps, first appeared 30 years ago and has since been growing steadily. In 1985, it reached an area of 5.9 ha, a maximum depth of 39 m, and a volume of 0.8 × 106 m3. This lake is dammed partially by a glacial moraine and partially by a tongue of dead ice covered by a moraine 1–2 m thick. The glacier calves into the lake, which collects all the melt water from the surrounding glacial area of 250 ha. No open outlet exists and seepage reaches a value of 5 × 106 m3 year−1. A 1 year water balance shows that seepage increases rapidly with water level, from less than 0.03 m3 s−1to more than 0.75 m3 s−l for a rise in water level of 10 m. The seasonal lake-volume fluctuations of 0.5 × 106 m3 are small compared with the inflow volume of 5 × 106 m3.

Progressive clogging of the bottom by glacial flour has led to a gradual rise of 8 m in 16 years in the summer level, while at the same time the height of the dam has decreased by 10 m due to the melting of dead ice. Consequently, by the end of July 1985 the freeboard was only 2 m and overflow on to the dead ice was thought likely to occur in the very near future. To eliminate this flood hazard, a 250 m long channel was dug in an ice-free zone which had been profiled by geophysical prospecting. This work was carried out between 14 April and 13 June 1986, in order to benefit from the low winter water level.

Geotechnical studies of the moraine have shown that no large landslide is to be feared. A crude model of the waves created by calving shows that the new water level is safe and the channel is capable of handling the maximum likely discharge of 15 m3 s−1 resulting from the highest possible wave of 3.5 m.
On a Simple Sea-Ice Dynamics Model for Climate Studies
Authors: Flato G.M. , Hibler W.D.
Published: February 2017

Sea-ice motion and dynamic thickness build-up play an important role in the transfer of heat between the ocean and the atmosphere and so must be included in large-scale climate studies. A “cavitating-fluid” approximation allows these dynamic processes to be parameterized in a simple way by ignoring shear and tensile strength yet retaining compressive strength. A simple procedure for approximating a cavitating fluid is presented here and is compared to the more complete viscous-plastic sea-ice model by performing several three year simulations with daily varying and monthly average wind forcing. Although differences exist on a monthly basis, the two models compare favourably over a seasonal cycle, particularly when compared to a thermodynamics only model in which ice motion is ignored. The lack of shear strength in a cavitating-fluid approximation makes it less sensitive to smoothing of the wind fields (as demonstrated by the monthly average wind simulations); however it also changes the detailed circulation and thickness build-up patterns somewhat. Overall, the cavitating-fluid approximation shows considerable promise for including sea-ice dynamics in large-scale climate models, especially where averaged wind fields are employed.
The Arctic Ocean Multi-Year Ice Balance, 1979-82
Authors: Rothrock D.A. , Thomas D.R.
Published: February 2017

A method of determining the temporally varying “state” of the ice cover (the concentrations of three surface types: open water, first-year ice, and multi-year ice) is presented. The methodology is that of Kalman smoothing: a physical model and a measurement model are used to blend satellite passive microwave data and buoy data to give an optimal estimate of the ice state. The estimates are optimal only to the degree that model parameter values are known and assumptions about variances are met. Uncertainty about these values and assumptions, and lack of independent data with which to compare results,leaves self-consistency as the most important test of results. A four-year record (1979-82) of the estimated Arctic Ocean ice balance is presented and shown to be self-consistent. Results are discussed in terms of the Arctic multi-year ice balance, which may be an important factor in the interaction ofocean, sea ice and climate because of its relationship to the minimum summer ice extent. The estimated area of multi-year ice decreases each year, but the decrease is small and insignificant based on four years of results. Furthermore, the observed decrease may be due to instrument drift or changes in the multi-year ice signature.
Effects Of Eurasian Snow Cover On Atmospheric Circulation In The Northern Hemisphere
Authors: Morinaga Yuki , Yasunari Tetuzo
Published: February 2017

Effects of Eurasian snow cover were first noted by Blanford (1884) who found an inverse relationship between summer monsoon rainfall over India and winter snow cover over the Himalayas. Hahn and Shukla (1976) confirmed it by using satellite-derived data and their work stimulated succeeding studies on the interaction between large-scale snow cover and atmosphere. Matson and Wiesnet (1981) showed that interannual variation of northern hemisphere snow cover is dominated by Eurasian snow cover, both showing similar trends and fluctuations during 1967–79. Recent studies (Barnett, 1988) also noted that Eurasian snow cover has a greater feedback potential than that of North America on hemispheric-scale climatic anomalies.

Though the importance has been thus recognized, not many studies have been done on the interaction between Eurasian snow cover and large-scale atmospheric circulation anomalies. Morinaga and Yasunari (1987) studied lag correlations between satellite-derived snow-cover extent over central Asia and the 500 mb-geopotential height field in the Northern Hemisphere (1967–84), and indicated that so-called Eurasian pattern (Wallace and Gutzler, 1981) in December brings large snow-cover extent in February; in turn, February snow cover has a considerable lingering effect on the atmosphere in April.

This study present further results on the time-lag teleconnections of the atmosphere associated with Eurasian snow-cover anomalies and their physical implications including the evaluation of snow-hydrological process.
Ice-Core Evidence For Weddell Sea Ice Extent During The Past 200 Years
Authors: Mulvaney R. , Reid A.P. , Peel D A.
Published: February 2017

A continuous, detailed, 200-years record of the anionic species, chloride, nitrate and sulphate, has been measured on an ice core from Dolleman Island (70°35.2′ S, 60°55.5′ W), Antarctic Peninsula. The site lies on the east coast of the Peninsula, and the chemistry of the core is dominated by the changing pattern of sea-ice distribution and storm activity in the Wed dell Sea. Strong annual cycles in chloride and non sea salt sulphate reflect the dominance of the seasonal cycle in sea-ice distribution in the Weddell Sea, observed in time series derived from satellite imagery since the early 1970s. However, in the case of chloride there is also an exceptionally strong interannual variability, which in many parts of the core dominates the seasonal cycle.

Secular variations in the sea-ice extent appear to have a strong influence on the climate of the region and may play a major role in determining how long-term climate change in the Antarctic Peninsula relates to global climate change. The paper examines documented evidence for sea-ice extent in the Weddell Sea sector, and evaluates the usefulness of ice-core data for reconstructing this parameter in the earlier period.
High Evaporation On Glaciers On The Northwestern Tibetan Plateau
Authors: Ohata Tetsuo , Takahashi Shuhei , Ohno Hiroyuki
Published: February 2017

Quite high amounts of evaporation observed on glaciers in dry Central Asia are one important component in the mass balance of glaciers. During glaciological research at West Kunlun Mountains on the northwestern Tibetan plateau in 1987, high evaporation of more than 2 mm of water per day was observed near the equilibrium line (5800–5900 m a.s.l.) in mid-summer due to dry and windy climate. Annual evaporation is estimated by a semi-empirical method using the full year meteorological data taken by an automatic meteorological station. This value shows that evaporation occupies quite a high percentage within the mass balance near the equilibrium line and on the whole glacier. Discussions will centre on comparison with evaporation data obtained on other glaciers and on the effect of such evaporation in the climate-glacier relation.
A Detailed Oxygen-18 Profile From The Greenland Ice-Sheet Margin Through The Wisconsinan-Holocene Transition
Authors: Reeh Niels , Letréguilly Anne , Oerter Hans
Published: February 2017

About 1500 surface-ice samples for δ18O analysis were collected in the 1988 field season along a 750 m profile perpendicular to the margin of the Greenland ice sheet at Pakitsoq, ca 40 km north-east of Jakobshavn, central West Greenland. The purpose of the study was to evaluate how well the continuity of the layer sequence is preserved in ice-margin records, a question of crucial importance for evaluating the potential yield of using ice margins as “mining areas” for easily accessible old ice for climate and environmental studies.

More than half of the 1500 samples were taken continuously as 20 cm samples along a 170 m section through the Wisconsinan-Holocene transition which, previously, had been located at the surface of the ice margin. Along this transition section δ18O values decrease by about 6‰ from −31.5 to 37.5‰ on an average. Detailed studies were made of surface elevations and surface structures (e.g. blue bands) along the “horizontal core” profile which, moreover, was photographed section by section, thus enabling the δ-record to be correlated with surface features.

Results of the δ18O analyses are promising. Even though ice from the blue bands has δ-values that are 7–8‰ higher than those of the surrounding white ice, there seems to be no discontinuity in the white-ice δ-record across the blue bands.
Increased Accumulation On The Antarctic Ice Sheet Due To Climatic Warming
Authors: Warren Stephen , Frankenstein Susan
Published: February 2017

Climatic warming due to increased greenhouse gases is expected to cause increased precipitation in the next century because of the increased water content of the air, assuming constant relative humidity. Since temperatures over most of Antarctica are far below freezing even in the warmest month of the year, the increase in melting is probably negligible compared to the increase in precipitation.

Oerlemans (1982) showed that this increase of precipitation would cause a growth of the ice sheet, tending to lower sea level. This would partially counteract the rise of sea level due to increased melting on mountain glaciers and Greenland, and to a possible (and more difficult to predict) surge of ice from West Antarctica.

Oerlemans may have underestimated the increase in accumulation. He used results of General Circulation Models (GCMs) which indicated an increase of precipitation by only 12% for a temperature change ΔΤ = 3 Κ and 30% for ΔΤ = 8 K. In contrast, the change in accumulation rate at Dome C (Lorius and others, 1979) accompanying the warming from the recent ice age to the present was in accord with the simple assumption that accumulation is proportional to saturation vapor pressure at the temperature of the inversion layer, i.e. a 30% increase for ΔΤ = 3 K.

The experimental results are to be preferred to the climate model results because GCMs do not represent ice-sheet accumulation processes well. Most of the accumulation is not snow falling from clouds but instead results from clear-sky ice-crystal formation in near-surface air, or hoarfrost deposition on the surface. GCMs lack sufficient vertical resolution to represent the strong temperature inversion on which these accumulation mechanisms depend.

The figure shows that the increase of vapor pressure due to ΔΤ = 5 Κ varies from a factor of 1.9 at Τ = −60°C to a factor of 1.6 at Τ = −20°C. A climatic warming of 5 K. over Antarctica, which is possible during the next century, could thus increase the Antarctic accumulation from its present 17g cm−2 yr−1 to 30 g cm−2 yr−1, leading to a 50 cm drop in sea level in 100 years. This assumes that the simple proportionality of precipitation rate to saturation vapor pressure applies as well to the coastal regions, which is doubtful because the accumulation processes are not the same as on the plateau.

The potential importance of Antarctic accumulation changes in contributing to changes of sea level argues for further study of the mechanisms of Antarctic precipitation and for their improved representation in climate models.
Ice-Sheet Elevation Change
Authors: Zwally H. Jay
Published: February 2017

Over century time scales, the primary effect of ice-sheet/climate-change interactions is vertical growth or shrinkage of the ice in response to changes in precipitation and surface heat flux. Because the dynamic response of large ice masses is generally slower than climate variations experienced during the last few centuries, the ice sheets are unlikely to be in equilibrium with today’s climate. Uncertainty in the current mass balance has been large, at least ±30% or ±2 mm yr−1 in sea-level equivalent. Estimates of annual snow accumulation, iceberg discharge, and peripheral melting of the Antarctic ice sheet (personal communication from S. Jacobs) would suggest a negative mass-balance equivalent to +2 mm yr−1 of sea-level rise, in contrast to other estimates of a small positive balance for both Antarctica (−0.6 ±0.6 mm yr−1 sea level) and Greenland (−0.1 ±0.4 mm yr−1 sea level) (Meier and others, 1985). For some years, measurement of changes in ice-sheet surface elevation by satellite altimetry has been noted as a potential means of determining the overall ice-sheet mass balance and investigating regional variations. Difficulties in deriving elevation change from a set of sequential measurements from several satellites have been primarily a result of the limited precision (about 1–2 m) of satellite radar altimetry, residual orbit errors, and relative uncertainties in the gravity fields and geoid reference levels used for different satellites. However, recent radar altimeter measurements by the U.S. Navy Geosat to 72°N and 72°S provide a sufficient density of repeated measurements of ice elevation for analysis of elevation change during the life of the satellite. The average elevation change at 224 267 orbital crossovers over southern Greenland is +28.3 ±0.4 cm yr−1. The largest values are observed near the summit and over the southern dome, with smaller values in the saddle region and toward the margins. Local gridded values of thickening and thinning rates agree with estimates from surface studies in the vicinity of the EGIG traverse (Steckel, 1977), Dye 3 (Reeh, 1985), and the OSU survey (Kostecka and Whillans, 1988) within the error limits of the respective measurements. Comparisons with elevations measured by the Seasat altimeter in 1978 and continuing Geosat measurements provide information on the temporal continuity of the thickening. The spatial distribution of the elevation changes is used to estimate an average thickening rate and the current rate of oceanic depletion.
The Effect of Snow Distribution on Gamma-Ray Survey of Snow Cover
Authors: Johnsrud Morten
Published: February 2017

Topography and snowdrifts may cause large variations in the snow cover as well as in snow depth from one year to another. A simple model is developed to study the influence of different snow distributions and the importance of this as a source of error. The ground surface “seen” from the detector will appear as a disc that can be divided into a number of small elements where it is possible to place the wanted snow distribution. Calculations of the gamma radiation field with different snow distributions show how small changes in the snow cover and distribution will influence the measurements as a function of the average snow water equivalent.
Formation Mechanisms of Snow Crystals at Low Temperature
Authors: Sato Noboru , Kikuchi Katsuhiro
Published: February 2017

To study crystal shapes, and formation and growth mechanisms of snow crystals formed below -20 °C, a new type of diffusion chamber was constructed. Using this chamber, different kinds of “peculiar shaped” crystals previously observed in nature have been produced, together with normal types of snow crystals. Gohei twins, one of the most typical polycrystalline shapes in nature, have been produced artificially. The vapor pressure was at or near water saturation at the time of nucleation. Analysis of photomicrographs and replicas of Gohei twins that were replicated in the polar regions show that the number frequency of the tip angle has a maximum frequency at about 77° and a minor one at about 54°.

On the basis of these results, a formation mechanism for some Gohei twins is proposed in this paper.