bluuebunny/crossref_metadata_2025 huggingface dataset:
The Dynamics of the Antarctic Ice Sheet
Authors: Budd W.F. , Jenssen D.
Published: September 2017

A three-dimensional dynamic, thermodynamic ice-sheet model has been developed to simulate the past, present, and future behaviour of the Antarctic ice sheet. The present ice velocities depend on the deep ice temperatures which in turn depend on the past changes of the ice sheet, including surface temperature, accumulation rate, and ice thickness. The basal temperatures are also strongly dependent on the geothermal heat flux. The model has therefore been used to study the effect on the basal temperatures, of changes to the geothermal heat flux, as well as the past changes of surface temperature and accumulation rate based on results obtained from the Vostok deep ice core. The model is also used to compute the distribution of surface velocity required to balance the present accumulation rate and the dynamics velocity based on the stress, temperature, and flow properties of ice, for the internal deformation, plus a component due to ice sliding. These velocities are compared to observed surface velocities in East Antarctica to assess the state of balance and the performance of the dynamics formulation.
Single Folds at the Margins of Dry-Based Glaciers as Indicators of a Glacial Advance
Authors: Chinn T.J.H.
Published: September 2017

Single folds which enclose the marginal “inner moraines” of the dry-based Jeremy Sykes and Alberich Glaciers, Dry Valleys area, Antarctica, are deduced to have formed during an advance of the margins of these glaciers where the thin, stiff marginal ice has obstructed glacier flow and expansion.

It is suggested that the occurrence of this type of fold can be an indicator of an advance in many fully dry-based glaciers. On Alberich Glacier, the fold and associated margin forms suggest that a sequence of margin forms evolves when a small cirque glacier expands outward from a sloping ramp front to a tongue terminating in a calving ice cliff.
Dynamics of the Law Dome Ice Cap, Antarctica, as Found From Bore-Hole Measurements
Authors: Etheridge D.M.
Published: September 2017

The internal dynamics of the Law Dome ice cap have been investigated by measuring the deformation of three bore holes located on an approximate flow line. Bore holes BHC1 (300 m deep) and BHC2 (344 m) were drilled in the coastal area to within several metres of bedrock and BHQ (418 m) was drilled about half-way towards the dome centre to about 50% of the ice thickness. Detailed measurements of orientation (inclination and azimuth), diameter, and temperature were taken through each bore hole over a 1 year span for BHC1 and BHC2 and a 10 year span for BHQ. The orientation data were reduced to obtain ∂u/∂z, a measure of the shear strain-rate. Changes in the depth of features located by bore-hole diameter measurements were used to obtain vertical velocity profiles. Other measurements discussed are temperatures, oxygen isotopes, crystal structure, surface velocities, and surface and bedrock topography.

At the coastal sites, the ∂u/∂z profiles show two maxima in the lower third of the ice sheet. Flow due to the measured deformation accounts for about 55% of the surface velocity, the remainder being due to deformation and sliding in the basal zone. The vertical velocity profiles show mostly firn compression. The deeper ∂u/∂z maximum occurs in ice from the Wisconsin period which appears to deform more rapidly than the Holocene ice immediately above. The upper ∂u/∂z maximum may be related to the stress history of the ice, which can also explain the presence of significant shear strain and crystal-fabric development at only half the ice thickness at the BHQ site.
Isotropic and Anisotropic Flow Relations for Ice Dynamics
Authors: Jacka T.H. , Budd W.F.
Published: September 2017

A flow relation for the minimum strain-rates for isotropic ice is presented. This flow relation has been compiled from laboratory tests in shear and compression, and covers the temperature and stress ranges typical of natural ice masses. However, the ice in natural ice masses is mostly anistropic. Three cores drilled at Law Dome, Antarctica, are used as examples to illustrate some of the different anisotropies that develop in ice masses in relation to the stress configurations and accumulated strains.

For the shear- or compression-stress configurations, anistropic flow rates can be derived as enhancements of the minimum isotropic flow rates for the particular stress, temperature, and stress configuration. For compression, this enhancement asymptotically approaches 3. For shear, the enhancement may be as high as 8. For combinations of shear and compression, further tests are required.
Sources And Movement of Icebergs in the South-West Ross Sea, Antarctica
Authors: Keys Harry , Fowler Dennis
Published: September 2017

The shape, surface features, composition, and thickness of icebergs trapped annually in a 200 km long coastal strip of fast ice have been examined to determine their sources and movement. The thin western ice front of the Ross Ice Shelf seems to produce about 40% of the icebergs while local glaciers produce the remainder. The ice-shelf icebergs are carried west towards Ross Island then north up the western side of the Ross Sea. A small proportion of them gets trapped mainly by grounding on shallow areas of the sea floor which protrude across the regional long-shore currents.
Pack-Ice Motion in the Weddell Sea in Relation to Weather Systems and Determination of a Weddell Sea Sea-Ice Budget
Authors: Limbert D.W.S. , Morrison S.J. , Sear C.B. , Wadhams P. , Rowe M.A.
Published: September 2017

As part of the Winter Weddell Sea Project 1986 (WWSP 86), a buoy, transmitting via TIROS-N satellites to Service Argos, was inserted into an ice floe in the southern Weddell Sea. Operational U.K. Meteorological Office numerical surface-pressure analyses, which utilized the buoy’s measured values of air pressure and temperature, are used to assess the impact of weather systems on pack-ice movement. The motion of the buoy is shown to be related closely to the position of the circumpolar trough and to the tracks of depressions crossing the area. The tracks of this and other buoys deployed during WWSP 86 are analysed, together with the known drifts of some ice-bound vessels, to establish the overall movement of sea ice in the central and western Weddell Sea. Using these data, the area of ice transported northward out of the Weddell Sea is determined. Roughly 60% of the winter sea-ice cover is discharged out of the area, and is replaced by new ice formation in coastal polynyas and by influx of new ice from the east. In summer, a further 30% is discharged northward out of the region, leaving 40% cover and by implication a 30% loss by melting.
Model Studies on Ice-Stream Surging
Authors: Radok U. , McInnes B.J. , Jenssen D. , Budd W.F.
Published: September 2017

A self-surging glacier model (Budd and McInnes, 1974;Budd, 1975), in which basal sliding is parameterized in terms of energy per unit area dissipated by basal friction, TbVb, has been extended to model the steady-state and time-dependent behaviour of eight Antarctic ice streams. Their basic characteristics were established with the working hypothesis of steady-state mass balance for the ice sheet as a whole, using a 20 km grid digitization of the surface and bedrock-elevation contours in Antarctica: glaciological and geophysical folio (Drewry, 1983). When the viscosity of the ice is lowered to values that are somewhat unrealistic for the present Antarctic ice, all the model ice streams enter a pulsating fast-sliding mode of flow in which the velocity reaches several km/year for periods ranging from fractions οf a year to tens of years. Except for one ice stream (Slessor Glacier), no substantial surge-like advances were found, and even in that case no periodic surging regime developed. The pulses are tentatively attributed to processes at the grounding line, with the converging width-parameterization scheme in the surging velocity calculation as another complexity that is still being investigated. For the cyclic surging Medvezhi Glacier model (Budd and Mclnnes, 1978), it has been found that the model surges change to shorter pulses as the width-convergence rate is increased.

It is concluded that the special regime and topography of ice streams — net accumulation increasing along the strongly converging flow and removal of the ice by calving rather than ablation — impede the onset of periodic surging. However, more sophisticated parameterizations of the basal hydraulics now in development may well show that ice-stream surges after all are possible.
Dynamics of Ice-Island Motion Near the Coast of Axel Heiberg Island, Canadian High Arctic
Authors: Sackinger W.M. , Jeffries M.O. , Tippens H. , Li F. , Lu M.
Published: September 2017

The largest ice island presently known to exist in the Arctic Ocean has a mass of about 700 × 106 tonnes, an area of about 26 km2, and a mean thickness of 42.5 m. Known as Hobson’s Ice Island, this large ice feature has been tracked almost continuously since August 1983 with a succession of Argos buoys. In this paper, two particular ice-island movement episodes near the north-west coast of Axel Heiberg Island are described: 6–16 May 1986 and 14–21 June 1986. Each movement episode is analyzed in terms of the forces acting on the ice island, including wind shear, water drag, water shear, Coriolis force, sea-surface tilt, and pack-ice force. Ice-island movement is generally preceded by an offshore surface wind, and a threshold wind speed of 6 m s°1 appears to be necessary to initiate ice-island motion. An angle of 50° between surface wind and ice-island movement direction is noted during one episode. The pack-ice force, which appears to be the dominant arresting factor of ice-island motion for these two episodes, varies from 100° to 180° to the left of the ice-island velocity direction, depending upon whether the ice island is accelerating or decelerating.
Six Years of Snow-Fence Testing in France
Authors: Brugnot G.
Published: September 2017

Drifting snow creates problems which have practical effects in France in two situations. The first situation is when the result of wind action on snow is to cause accumulation of this snow on mountains, leeward of crests, and consequently to create the potential hazard of avalanche. The second is when the result is to pile up snow in flat regions wherever there are obstacles such as road cuttings and vegetation. This paper focuses on the second type of problem, which affects large areas of central and north-eastern France. We explain how we have chosen our test site, which initial experiments we have conducted in order to assess the general geometrical features which a snow fence must possess in order to function most effectively in collecting snow, and how subsequently we have assessed the properties and costs of different fencing systems.
Investigation on Wet-Snow Metamorphism in Respect of Liquid-Water Content
Authors: Brun E.
Published: September 2017

Up to the present time, quantitative investigations on wet-snow metamorphism have mostly been conducted on water-saturated snow, because of the difficulty in getting large enough wet-snow samples at a uniformly low liquid-water content. Using the dielectric properties of snow at a frequency in the range 20–100 kHz, a warming device has been developed which has enabled us to bring samples of 7 × 10−3 m3 snow to any desired liquid-water content. A maximum value of 8% by volume was reached within 2 h.

The warming device was used to reproduce natural wetness conditions in the laboratory in order to investigate wet snow metamorphism at low liquid-water content. Snow samples were brought to different liquid-water contents and held in that condition for about 2 weeks, during which grain-size was characterized using a picture-analysis system able to derive the mean radius of curvature of the cluster circumference. At any given liquid-water content value, the growth rate of the mean volume of the crystals building the clusters was constant, a pattern which has also been observed in water-saturated snow by previous investigators. This growth rate is well described by a power function of liquid-water content.
Avalanche Starting-Zone Analysis by use of a Knowledge-Based System
Authors: Buisson Laurent , Charlier Claude
Published: September 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.
The Agricultural Use of Melt Water in Hopar Settlement, Pakistan
Authors: Butz David
Published: September 2017

Agricultural irrigation is an important use of melt water in the Karakoram Range of Pakistan; indeed all crop cultivation relies on melt water from small glaciers and/or snow and ice patches in the zone above 3500 m. Inhabitants of Hopar settlement utilize run-off from a cirque-shaped basin covering about 11.5km2 between 3600 and 4900 m a.s.l. to irrigate 280 ha of cultivated terraces in the altitudes 2500–3000 m. The characteristics of discharge from this basin require specific adaptions to be made by irrigators. In particular, access, turbulent flow, water temperature and sediment load are problematic, although water allocation is not an important concern because supply exceeds demand for most of the local growing season. Supply characteristics are outlined in the paper and are related to features of the indigenous irrigation system.
Measurements of Friction Coefficients of Snow blocks
Authors: Casassa G. , Narita H. , Maeno N.
Published: September 2017

Snow blocks were slid down natural snow slopes and filmed with a video camera. Friction coefficients were calculated from time-distance curves and the equation of motion. Dry-friction coefficients ranged from 0.57 to 0.84, and could be separated into Coulomb friction and a friction component proportional to the contact area of the blocks (adhesion). These values are greater than the values usually used in avalanche dynamics, but are consistent with previous coefficients obtained for snow blocks sliding over snow.

When uniform ploughing occurred and a shear layer developed along the track the apparent friction coefficients increased with velocity, and could be modelled by considering the kinematic viscosity of the snow. The values of kinematic viscosity ranged from 10−3 to 10−4 m2/s and agreed well with those values obtained by other researchers.
Comparison of three Models of Avalanche Dynamics
Authors: Gubler H.
Published: September 2017

Results and characteristics of three models for estimating avalanche flow speeds, flow heights, and run-out distances are compared: (1) Voellmy–Salm equation used with the traditional release, track, and run-out segmentation method; (2) Voellmy–Salm differential equation solved numerically along longitudinal profiles of avalanche paths, combined with modified assumptions for the flow in the run-out zone; (3) a granular-flow model introduced by Salm and Gubler. Within the limits of the accuracy of the field observations, all models are able to predict run-out distances correctly, at least for large avalanches, but the Voellmy–Salm type models significantly underestimate flow speeds. Modelling different flow regimes (sliding and partial fluidization) increases the range of avalanche sizes for which correct run-out modelling is possible without recalibration of model parameters.
Effects of Solar Radiation on the Formation of Weak Wet Snow
Authors: Izumi Kaoru
Published: September 2017

Laboratory and field experiments on hardness of snow have shown that the free water contained in snow decreases its hardness, and that solar radiation further decreases hardness down to a value below the limit of that which would result only from the influence of the water content of snow. A quantitative relationship between the amount of solar radiation absorbed by snow and decrease in snow hardness was derived. Thin-section analyses of snow were used to reveal the mechanism of decrease in snow hardness which had been caused by solar radiation.
Spatial Variability of Snow-Pack Outflow at a Site in Sierra Nevada, U.S.A.
Authors: Kattelmann Richard
Published: September 2017

Water flow through natural snow-packs is generally accepted to be extremely variable even over short distances. Differences in snow properties, and discontinuities in the horizontal and vertical structures of snow-packs, are responsible for variations in the effective area of the snow surface associated with outflow from a part of the base of the snow-pack. At the Central Sierra Snow Laboratory snow-pack outflow has been monitored using four snow-melt lysimeters of 6 m2 area each; two of these collectors were subdivided into three sections of equal area.

Substantial variations in daily and monthly outflow volumes were noted between the individual collectors and also to a greater degree between the 2 m2 sub-units of the divided containers. The relative collecting efficiency of the snow-melt lysimeters also changed over time. In the deep warm snow-packs of the Sierra Nevada forest zone, snow-pack water routing appears to be highly variable, and this variability is on a much larger scale than was previously recognized. The large differences in snow-pack outflow measured in this study suggest that structural discontinuities and microtopography of snow strata can redirect percolating water over an area of several square meters.
Supporting Forces and Stability of Snow-Slab Avalanches: A Parameter Study
Authors: Lackinger Bernhard
Published: September 2017

The fracture of a slab avalanche is a multi-phase and progressive process. The different kinds of fracture and possible scenarios of avalanche release in the form of a zip effect are shown. In the course of investigations, most importance has so far been attached to shear failure along the sliding surface. Various cases of load and their effects on the stresses, on the changes of strength, and on the stability of the inclined snow-pack are discussed. The usual simple model of the shear-stability index is unsatisfactory. The present paper deals with the complex interaction of all supporting forces of a snow slab by means of simplified geotechnical considerations. For this purpose, the acting and reacting forces of a “standard avalanche” (i.e. dead load with driving and normal component, shear force, tensile force, compressive force, and flank force) are estimated from published boundary values. Using different combinations (e.g. hard slab with high circumferential forces on a weak shear surface with low shear force), it can be shown that suspension at the crown and lower and lateral support are of great importance. This applies especially to cases with low shear forces and, consequently, with low overall stability. Despite the fact that the circumferential area of the model avalanche is only 6% of the area of the shear surface, the circumferential force in this case is more than 150% of the shear force. In a parameter study with different avalanche sizes, these results are generalized and confirmed. For the assumed strength limits, critical areas and depths of possible slab avalanches can be derived. Although the supporting shear force is the major contributor to stability, particularly with larger slabs, it can be seen from the investigations that the redistributions of stress and spatial supports and suspensions of the whole slab avalanche must not be neglected in stability analyses.
Flow Characteristics of an Unconstrained, Non-Cohesive, Granular Medium Down an Inclined, Curved Surface: Preliminary Experimental Results
Authors: Lang R.M. , Leo B.R. , Hutter K.
Published: September 2017

Some preliminary experimental results are presented, which characterize the behaviour of small-scale artificial avalanches. The laboratory simulation consisted of releasing a finite mass of non-cohesive granular material to flow without restriction down an inclined surface which includes a curved part at the base where the run-out zone is encountered. Three contrasting materials, of 3 mm and 5 mm diameter size sortings, and also two different bed roughnesses were used.

Results indicate that a theoretical model which presumes a flow-regime-type avalanche may be too restrictive, in the sense that it describes a limiting case which does not often occur even under controlled conditions. Some suggestions are made for amendments to current theoretical concepts.
Calculation of Maximum Snow-Avalanche Run-Out Distance by use of Digital Terrain Models
Authors: Lied K. , Toppe R.
Published: September 2017

Digital maps and terrain models are used to calculate maximum snow-avalanche run-out distance based on topographic parameters. Maps of 1:50 000 scale are found to be accurate enough for the purpose. 113 well-known avalanches are discussed in this paper. A computer system is used to calculate terrain parameters such as rupture area (A), avalanche-path length (L), avalanche-track lengths (L1L2), and run-out lengths (L3). Maximum run-out angle (α), avalanche-track angle (β). and average angle of rupture zone (γ) are also found by computer. The use of computer and terrain model reduces subjective judgement of parameters to a minimum. Run-out distance was found to be best expressed by the regression equation:

α = 0.91β + 0.08γ–3.5°. R2 = 0.94, S = 1.4°.

L = 0.93L1 + 0.97L2 + 0.61A + 182 m. R2 = 0.96, S = 137 m.
The Internal Structure of Powder-Snow Avalanches
Authors: Nishimura K. , Narita H. , Maeno N. , Kawada K.
Published: September 2017

The internal structure of powder-snow avalanches was investigated at Kurobe Canyon in the Shiai-dani area of Japan in 1988. Internal velocity was derived for avalanches of this kind by frequency analysis of impact-force data, and was found to undergo a remarkable change with time. The shear of the avalanche flow was estimated to range from 1 to 7 s−1. The front region of the avalanche wind was observed to precede the front of the avalanche by a distance of 17.3 m. The maximum wind velocity was comparable with the internal velocity of the front region of the avalanche.
Slush-Flow Questionnaire
Authors: Onesti Lawrence J. , Hestnes Erik
Published: September 2017

Questionnaires concerning slush flows were distributed globally. The purpose of the questionnaire was to determine the geographic distribution of slush-flow activity and also to collect information concerning the most commonly used nomenclature, release conditions, the season of occurrence, the type of terrain most susceptible to slush-flow occurrences, the characteristics of starting zones, paths and run-out zones, geomorphic activity, type of damage likely to result, and hazard control.

Individuals having first-hand experience of the slush-flow process have been identified. The answers to the questionnaire established that slush flows definitely occur in lower latitudes as well as in the Arctic, and that the slush-flow hazard has not yet received the emphasis that it deserves. Heavy rainfall may cause slush flows at any time during winter, especially in areas with a marine west-coast type of climate. Stream channels and shallow depressions are the most common locations of starting zones, while slush-flow frequency seems to be closely related to the permeability of the substratum. Slush flows are a significant geomorphic agent, and it is noteworthy that there has been an increasing encroachment into potential slush-flow zones as a consequence of human activity.
Numerical Simulation of Snowdrift Development
Authors: Uematsu T. , Kaneda Y. , Takeuchi K. , Nakata T. , Yukumi M.
Published: September 2017

A two-dimensional, finite-element calculation was performed to simulate the development of a snowdrift. The underlying two-dimensional topography was taken as the lower boundary, and this changed as the drift developed. The two-dimensional wind field was calculated from the Navier–Stokes equations. The calculation was performed until a quasi-steady state was reached, and the pattern of erosion and deposition was estimated by computing the divergence of snowdrift transport. Considering a snowdrift as a new surface, the wind field was then recalculated. Simulated results were compared with outdoor observations of the wind field and snowdrifts. The results were in fairly good agreement with each other, but more detailed research is regarded as being necessary.
Effects of Spatial and Temporal Variation in Snow Melt on Nitrate Ion and Sulfate Ion Pulses in Melt Waters Within an Alpine Basin
Authors: Williams Mark W. , Melack John M.
Published: September 2017

Source areas of snow-melt run-off vary spatially and temporally, with corresponding changes in chemistry of the snow-pack, and influence both timing and quality of snow-pack run-off. In the the alpine basin of Emerald Lake, located in the southern Sierra Nevada, California, U.S.A., we have found that nitrate ion and sulphate ion concentrations in streams were correlated with the amount of snow melt in each sub-basin. Inflows to Emerald Lake had elevated concentrations of , and , which corresponded temporally with the initiation of snow melt in each sub-basin. Concentrations of both anions then decreased as snow melt progressed. The onset of snow melt shifted temporally from sub-basins with a south-westerly aspect to basins with a progressively more northerly aspect. The and pulses also moved, with time, from the sub-basins with south-westerly aspects to those with more northerly aspects. The time span over which the basin experienced these anionic pulses was longer than that for any single sub-basin. Maximum concentrations of and in the lake outflow, which also occurred at the onset of snow melt, were elevated by 100 and 40%, respectively, above their January concentrations in line with increases in inflow, but were sustained for a longer period than that of any inflow increase.
Ice Loss in the Ablation Area of a Himalayan Glacier; Studies on Miar Glacier, Karakoram Mountains, Pakistan
Authors: Young G.J. , Schmok J.P.
Published: September 2017

One of the main aims of the Snow and Ice Hydrology Project, a joint Canada-Pakistan endeavour, is to estimate ice loss in the ablation areas of glaciers in order to predict with greater confidence stream flow in the headwaters of the Indus River. To this end, Miar Glacier, located in the central Karakoram Range, north of Gilgit, was intensively studied during the summers of 1986 and 1987.

Measurements of glacier mass balance by the monitoring of accumulation and ablation at stake locations is very difficult in the Himalyan environment. It is usually almost impossible to reach elevations above the equilibrium line without major effort, and always very difficult once there to make meaningful measurements; the ablation areas are often heavily crevassed and/or debris-covered, and this poses difficult sampling problems.

The method used in this study was to monitor annual surface movement on a cross-profile as near as possible to the equilibrium line. The measurements, obtained in conjunction with depth soundings made on the same profile, allow the annual ice flux through the cross-profile to be calculated. If an approximately steady-state glacier is assumed, it would be expected that this flux would be roughly equivalent to the rate of ice loss below the profile.

The movements of wooden stakes drilled into the glacier were monitored throughout each of the summers and, since two of the stakes survived the intervening winter, this allowed calculation of annual movement. Distances between the crests of ogives were also surveyed, providing an independent assessment of glacier movement. Depth measurements by radio-echo sounder were successfully made in the summer of 1987, showing maximum ice depths of 550 m. The annual ice flux through the transverse profile was estimated as 5.67 × 107 m3, which corresponds to a mean annual ice loss from the glacier surface below the profile of 8.10 m of ice.
Lidar-Derived Particle Concentrations in Plumes from Arctic Leads
Authors: Andreas Edgar L. , Miles Martin W. , Barry Roger G. , Schnell Russell C.
Published: September 2017

With an airborne lidar, we have observed massive plumes of condensate particles rising from wintertime leads in the Arctic Ocean. Some of these plumes reached an altitude of 4 km; some extended over 200 km down-wind from their surface source. Here we invert the lidar equation and use lidar backscatter data to infer particle concentrations within two such plumes. Assuming that the plumes consist of supercooled water droplets of radius 5 μm, we estimate typical concentrations of 3–6 × 105 droplets m-3 just above the leads. Concentrations within the plumes can still be as high as 104 droplets m-3 at an altitude of 3 km and 200 km down-wind from some leads. Had we assumed that the plume particles are ice spheres of radius 40 μm, concentrations would be just 100 times less than these.
Age of Crary Ice Rise, Antarctica, Determined from Temperature-Depth Profiles
Authors: Bindschadler Robert A. , Roberts Eric P. , Iken Almut
Published: September 2017

Temperature-depth measurements from two sites on Crary Ice Rise, Antarctica are analyzed to deduce the time the ice first grounded at each location. At the thicker site (480 m), the best estimate of the time since grounding is 1100 years. At the shallower site (369 m) the grounding is more recent, 580 years ago, and there is evidence that basal cooling was delayed for 450 years while water at the base was freezing. This analysis leads to the conclusion that Crary Ice Rise was formed by at least two separate grounding events and is not a remnant of a more extensive grounded ice sheet which occupied the present position of the Ross Ice Shelf.
Recent Deposition of 210Pb on the Greenland Ice Sheet: Variations in Space and Time
Authors: Dibb Jack E.
Published: September 2017

Detailed 210Pb profiles were determined for four “Chernobyl dated” snowpits sampled during a wide-ranging survey of the Greenland ice sheet during the 1988 season. The profiles from widely separated pits show little or no coherence; even for two pits only 40 km apart the profiles differ in detail. There does not appear to have been any seasonality in the deposition of 210Pb onto the ice sheet in the two years since the Chernobyl accident. The total deposition of 210Pb during this period (10-20 bq m-2) was about 20 times less than has been observed at mid-latitude sites in the eastern United States. The three pits west of the ice-sheet divide recorded very similar depositional fluxes, while the one eastern pit had only two-thirds the average of the others, suggesting a west-to-east gradient in the deposition of 210Pb, and perhaps other continentally-derived submicron aerosols, onto the Greenland ice sheet.
On a Simple Sea-Ice Dynamics Model for Climate Studies
Authors: Flato G.M. , Hibler W.D.
Published: September 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.
Glacier and Permafrost Signals of 20th-Century Warming
Authors: Haeberli Wilfried
Published: September 2017

Currently-available evidence of 20th-century warming from glaciers and permafrost is briefly reviewed. The signals are clear and strong: warming of polar firn and permafrost, and mass losses of glaciers at lower latitudes, were most striking towards the middle of the century. The easily observable length-reduction of mountain glaciers confirms the global character of the evolution. A probably intermittent reversal of the trend was observed in places after about 1950.
Long-Term Glacier Mass-Balance Investigations in Svalbard, 1950–88
Authors: Hagen Jon Ove , Liestøl Olav
Published: September 2017

Mass-balance investigations on glaciers in Svalbard at high latitudes (78°N) show that the ice masses have been steadily decreasing during the period 1950–88. Detailed annual observations have been carried out on Brøggerbreen since 1966 and Lovénbreen since 1967. The mean specific net balances are −0.46 and −0.37 m year−1 water equivalent respectively. Only one year had positive net balance in this period. The cumulative mass lost in the period is then more than 10% of the volume in 1967. Zero net balance would be obtained if the summer temperature was lowered about 1°C or if the winter precipitation increased about 50%. There is a strong correlation between the net mass balance and the height of the equilibrium-line altitude (ELA). Because of the high amount of superimposed ice (10–30% of winter balance) stake readings are necessary to find the ELA. There is no sign of climatic warming through increased melting. The trend analysis of the data from the last 20 years shows stable conditions with a slight increase of the winter balance. The net balance is then slightly increasing and thus less negative than 20 years ago.
Paleogeographic Significance of Middle Pleistocene Glaciomarine Deposits on Baldwin Peninsula, Northwest Alaska
Authors: Huston Matt M. , Brigham-Grette Julie , Hopkins David M.
Published: September 2017

Baldwin Peninsula, northwest Alaska, is a middle Pleistocene push-moraine complex composed of marine, fluvial, and glaciogenic sediments. The peninsula was formed by three ice lobes emanating from the De Long and Baird mountains and the Selawik Lowlands in the southwest Brooks Range during the Anaktuvuk River glaciation. This glaciation was nearly an order of magnitude more areally extensive than late Pleistocene glaciations in the same region and occurred c. 500 to 600 ka B.P. based on paleomagnetism, and amino-stratigraphic and morphostratigraphic correlations with other numerically-dated northwest Alaskan deposits.

Extensive deposits of massive and laminated clayey silt with striated, faceted stones indicate that local sea level was high as glacial ice reached its maximum extent. Glacio-isostasy does not seem to have been important in maintaining a high relative sea level; therefore we infer that eustatic sea level remained high during ice advance. For this to occur, high latitude glaciation must have preceded the build-up of ice in lower latitudes. The source of moisture for such massive glaciation may have come from submerged Bering and Chukchi shelves, enhanced flow of North Pacific/southern Bering Sea winter storms, reduced intensity of the winter Arctic High, or a combination thereof.
Meridional Sea-Ice Transport and its Impact on Climate
Authors: Ledley Tamara Shapiro
Published: September 2017

Sea ice is an important factor in controlling the ocean–atmosphere energy exchange in polar regions, and has an important impact on climate. This is because sea ice insulates the relatively warm ocean from the cold winter atmosphere, and has a higher surface albedo than the ocean. In this study the effect of sea-ice transport on the energy exchange between the atmosphere and ocean, and thus on climate, is examined using a coupled energy-balance climate–thermodynamic sea-ice model.

Transport of sea ice produces a thinning of the zonally annually-averaged sea ice in the poleward-most zones, and an extension of the ice edge equatorward. Thinning of the poleward-most ice produces an increase in the annual sensible heat flux from the ocean to the atmosphere, which produces an increase in the mean annual atmospheric temperatures. Sensible heat flux is decreased in the zones that contain the ice edge. However, warming in the poleward-most zones produces an increased meridional energy convergence at the ice edge that offsets the decrease in the sensible heat flux to the atmosphere, resulting in a net warming.
Quantitative Approximation of Mountain Glacial Climates
Authors: Locke William W.
Published: September 2017

The winter precipitation at the equilibrium line altitude of a wide selection of modern mountain glaciers is well explained (r2= 0.81,n= 25) by multiple regression using summer temperature and the logarithm of continentality (distance from a moisture source) as independent variables. Continentality serves as a proxy for inland decreases in energy input through longwave radiation and condensation and increasing energy losses through evaporation and sublimation. Winter precipitation in presently inaccessible areas and former precipitation across broad regions can thus be estimated accurately from two simple variables.
Climatic Change in a High-Altitude Alpine Area Suggested by the Isotopic Composition Of Cold Basal Glacier Ice
Authors: Lorrain R. , Haeberli W.
Published: September 2017

For the first time, a cold ice cover of a summit in the central Swiss Alps has been sampled from the surface to the bed for determining its isotopic composition in δD and δ18O. Results of the analyses show a striking decrease of δ-values with depth. The δ-value differences are greater than those explicable by a direct temperature effect, but a substantial increase in melt water percolation through the firn since the formation of the deepest ice layer may explain the situation of this high-altitude ice.
Effects of Glaciation on Methane-Hydrate Stability
Authors: MacAyeal Douglas R. , Lindstrom Dean R.
Published: September 2017

Temperature and pressure changes within subglacial sediments caused by déglaciation favor a phase change from methane hydrate to methane gas. If released to the atmosphere, this gas could have contributed significantly to the increased atmospheric methane concentration during interglacial periods. Using a numerical reconstruction of sediment temperatures and ice-sheet loads, the total sediment volume in the Eurasian Arctic that is subject to this phase change is estimated to be 2.8 × 1014 m3.
Chemical Evidence in Polar Ice Cores from Dielectric Profiling
Authors: Moore J.C. , Paren J.G. , Mulvaney R.
Published: September 2017

The dielectric stratigraphy of a 130 m ice core from Dolleman Island, Antarctic Peninsula, shows large variations in the dielectric relaxation process and in conductivity. A comparison with the chemical stratigraphy of the core demonstrates the decisive role played by both acids and salts in determining the electrical behaviour of natural ice. The dielectric response is sensitive both to the type of impurity and to its distribution within the ice fabric. The evidence supports other observations of the localization of sulphuric acid at three-grain boundaries: in contrast, the salt impurity appears to be largely incorporated into the ice lattice. The overriding importance of the dielectric profiling technique is that it is the only profiling tool so far developed that is sensitive to the presence of salt in polar ice cores.
Identification of Some Global Volcanic Horizons by Major Element Analysis of Fine Ash in Antarctic Ice
Authors: Palais Julie M. , Kirchner Severine , Delmas Robert J.
Published: September 2017

Acid fallout from volcanic eruptions is well documented in the Greenland and Antarctic ice sheets (Hammer and others, 1980; Hammer, 1984; Legrand and Delmas, 1987). However, to date, no volcanic ash (tephra) layers have been positively identified in association with any of the high electrical conductivity layers that mark the volcanic acid deposition. In this paper we report the results of a study of the chemical composition of insoluble microparticles filtered from five intervals of a core from the South Pole. These five intervals were identified by Kirchner (1988) as being due to volcanic fallout, on the basis of electrical conductivity and sulfuric acid measurements.

The major element composition of tiny (<5 µm) glass shards found in these layers was determined and compared with analyses of volcanic ash from known eruptions or from volcanic sources suspected of having produced the fallout. Glass shards from volcanic eruptions of both local (Antarctic and sub-Antarctic) and of global (Indonesian/South American) importance have been identified in this study.
Modeling Mass-Balance Changes During a Glaciation Cycle
Authors: Pelto M.S. , Higgins S.M. , Hughes T.J. , Fastook J.L.
Published: September 2017

Identification of present-day climate setting and alpine glacier-balance gradients indicates that the balance gradient of alpine glaciers is primarily determined by climatic conditions. Determination of balance gradients for specific climatic settings on present-day ice sheets provides an analog for determining the mass balance on paleo and future ice sheets.
The Treatment of Shortwave Radiation and Open Water in Large-Scale Models of Sea-Ice Decay
Authors: Perovich Donald K. , Maykut Gary A.
Published: September 2017

Sea ice covering the polar oceans is only a thin veneer whose areal extent can undergo large and rapid variations in response to relatively small changes in thermal forcing. Positive feedback between variations in ice extent and global albedo has the potential to amplify small changes in climate. Particularly difficult to model is the summer decay and retreat of the ice pack which is strongly influenced by shortwave radiation entering the upper ocean through leads (Iw). Most models assume that all of this energy is expended in lateral melting at floe edges. In reality, only a portion of Iw contributes directly to lateral melting, with the remainder going to bottom ablation and warming of the water. This partitioning of Iw affects not only the magnitude, but also the character of the predicted ice decay, reducing the change in ice concentration and enhancing the thinning of the ice and the storage of heat in the water. In this paper we present an analytical model which includes many of these processes and is stable regardless of time step, making it suitable for use in climate simulations.
A Simple Parameterization of Ice Leads In a General Circulation Model, and the Sensitivity of Climateto Change in Antarctic Ice Concentration
Authors: Simmonds Ian , Budd W.F.
Published: September 2017

We present a simple parameterization of the effect of open leads in a general circulation model of the atmosphere. We consider only the case where the sea ice distribution is prescribed (i.e., not interactive) and the fraction of open water in the ice is also prescribed and set at the same value at all points in the Southern Hemisphere and a different value in the Northern Hemisphere. We approximate the distribution of sea ice over a model “grid box” as a part of the box being covered by solid ice of uniform thickness and the complement of the box consisting of open water at a fixed -1.8 C. Because of the nonlinearity in the flux computations, separate calculations are performed over the solid sea ice and over the open leads. The net fluxes conveyed to the atmosphere over the grid box are determined by performing the appropriate area-weighted average over the two surface types.

We report on an experiment designed to assess the sensitivity of the modelled climate to the imposition of a 50% concentration in the winter Antarctic sea ice. Significant warming of up to 6°C takes place in the vicinity of and above the Antarctic sea ice and is associated with significant changes in the zonal wind structure. Pressure reductions are simulated over the sea ice, being particularly marked in the Weddell Sea region, and an anomalous east-west aligned ridge is simulated at about 60°S. Very large changes in the sensible heat flux (in excess of 200 Wm−2) are simulated near the coast of Antarctica.
Effect of Area Distribution with Altitude on Glacier Mass Balance – A Comparison of North and South Klawatti Glaciers, Washington State, U.S.A.
Authors: Tangborn Wendell V. , Fountain Andrew G. , Sikonia William G.
Published: September 2017

The North and South Klawatti glaciers are adjacent glaciers in the North Cascade Mountains of Washington state. During 1947–61 North Klawatti Glacier lost volume, equivalent to a mean decrease in thickness of 8.3 m over the glacier area, whereas South Klawatti Glacier gained volume, equivalent to an increase in thickness of 5.8 m. Although the glaciers are in the same climate, they have different distributions of area with altitude, resulting in different responses to climatic variations.

A quadratic equation is assumed to approximate the relation of mass balance to altitude for both Klawatti glaciers. The coefficients of the equation are derived by comparing the calculated mass change to the mass change for each glacier estimated from topographic maps. The resultant relation of mass balance to altitude is the mean for the time period between maps (1947–61).

Steady-state longitudinal profiles of both glaciers were obtained by shifting the existing mass-balance versus altitude curve by a magnitude equal to the measured mean annual mass balance. To produce steady-state conditions, the equilibrium-line altitudes of both glaciers would need to move less than 90 m (85 m higher for South Klawatti Glacier and 88 m lower for North Klawatti Glacier).
Neoglaciation in the Southern Kenai Mountains, Alaska
Authors: Wiles Gregory C. , Calkin Parker E.
Published: September 2017

A preliminary late-Holocene glacial chronology from the west flank of the southern Kenai Mountains, Alaska, is characterized by two major episodes of advance. Outlet glaciers of both the Harding Icefield and the Grewingk-Yalik ice complex were expanding across their present positions at 545 A.D. and again during the Little Ice Age, about 1500 A.D. The earliest of these Neoglacial advances is dated by radiocarbon ages from the outer rings of tree trunks rooted near the margins of Grewingk and Dinglestadt glaciers. Subsequently, ice margins retreated some distance behind their present positions allowing marked soil development before the last readvance through mature forest. Wood preserved in lateral moraines at Grewingk Glacier and from an uprooted stump at Tustemena Glacier date this later ice advance. Tree-ring ages, correlated with lichen diameters, suggest that this last advance was widespread and culminated in its Neoglacial maximum about 1800 A.D.. Since this time, glacier retreat has dominated in the area, punctuated by at least two pauses. Historical accounts and photographs document a mean rate of retreat of 27 m a−1 for the past century with partial control exerted by calving of ice margins into proglacial lakes.