bluuebunny/crossref_metadata_2025 huggingface dataset:
Ice-Age Climate and Continental Ice Sheets: Some Experiments with A General Circulation Model
Authors: Manabe S. , Broccoli A. J.
Published: February 2017

The climatic influence of the land ice which existed 18 ka BP is investigated using a climate model developed at the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration. The model consists of an atmospheric general circulation model coupled with a static mixed layer ocean model. Simulated climates are obtained from each of two versions of the model: one with the land-ice distribution of the present and the other with that of 18 ka BP.

In the northern hemisphere, the difference in the distribution of sea surface temperature (SST) between the two experiments resembles the difference between the SST at 18 ka BP and at present as estimated by CLIMAP Project Members (1981). In the northern hemisphere a substantial lowering of air temperature also occurs in winter, with a less pronounced cooling during summer. The mid-tropospheric flow field is influenced by the Laurentide ice sheet and features a split jet stream straddling the ice sheet and a long wave trough along the east coast of North America. In the southern hemisphere of 18 ka BP, the ice sheet has little influence on temperature. An examination of hemispheric heat balances indicates that this is because only a small change in interhemispheric heat transport exists, as the In situ radiative compensation in the northern hemisphere counterbalances the effective reflection of solar radiation by continental ice sheets.

Hydrologic changes in the model climate are also found, with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in North America and Eurasia. These findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum.
Reconstruction of the Glacial Ice Covers of Greenland and the Canadian Arctic Islands by Three-Dimensional, Perfectly Plastic Ice-Sheet Modelling
Authors: Reeh N.
Published: February 2017

A three-dimensional perfectly plastic ice-sheet model, developed for determining the surface elevations and the flow pattern of an ice sheet with given bottom topography and ice-margin positions, is applied to the reconstruction of the glacial ice covers of Greenland and the Canadian Arctic islands. In the northern regions, two different reconstructions have been performed with ice margins along the present 600 and 200 m sea-depth contours, respectively. In central Greenland, the ice margin is considered to be at the outermost ice-margin deposits on the coastal shelf to the west, and at the present 200 m sea-depth contour to the east.

The main conclusions to be drawn from the reconstructions are: (1). The flow pattern of the glacial ice cover of Greenland shows a great resemblance to the present one, the central ice divide being displaced less than 50 km from its present position and being no more than 200 m higher than today. (2). The main ice divide of the ice sheet covering the Canadian Arctic islands (the Innuitian ice sheet) was located over the highlands of eastern Ellesmere Island with local domes positioned over the present ice caps, indicating that even the deep ice of Wisconsin age in these ice caps is of local origin. This is also the case for the Devon Island ice cap. (3). Even in the not very likely case of a rather extensive glacial ice cover in north-west Greenland, the ice-flow pattern upstream of the Camp Century deep drill site would not have changed radically compared to the present flow pattern. Thus it is concluded that even advanced ice margins in late-Wisconsin time could at most have resulted in an elevation of the deposition site of the late-Wisconsin ice at Camp Century 600 m higher than at present. The consequences of this conclusion are discussed.
A Model Simulation of 20 Years of Northern Hemisphere Sea-Ice Fluctuations
Authors: Walsh John E. , Hibler William D. , Ross Becky
Published: February 2017

A dynamic-thermodynamic sea-ice model (Hibler 1979) is used to simulate northern hemisphere sea ice for a 20-year period, 1961 to 1980. The model is driven by daily atmospheric grids of sea-level pressure (geo-strophic wind) and by temperatures derived from the Russian surface temperature data set. Among the modifications to earlier formulations are the inclusion of snow cover and a multilevel ice-thickness distribution in the thermodynamic computations.

The time series of the simulated anomalies show relatively large amounts of ice during the early 1960s and middle 1970s, and relatively small amounts during the late 1960s and early 1970s. The fluctuations of ice mass, both in the entire domain and in individual regions, are more persistent than are the fluctuations of ice-covered area. The ice dynamics tend to introduce more high-frequency variability into the regional (and total) amounts of ice mass. The simulated annual ice export from the Arctic Basin into the East Greenland Sea varies interannually by factors of 3 to 4.
Ice Flow Leading to the Deep Core Hole at Dye 3, Greenland
Authors: Whillans I. M. , Jezek K. C. , Drew A. R. , Gundestrup N.
Published: February 2017

Detailed studies of the last 20 km of the flow-line leading to the core hole at Dye 3 Greenland, provide a description of ice flow over and around basal hills. The surface pattern is very simple. Velocity vectors are nearly parallel to one another and the largest variations in velocity are speed changes along the direction of flow. The surface elevation is stepped and the speed is faster than average where the surface slope is steepest. These positions correspond to basal highs, and the surface velocity increases as expected, based on the decrease in ice thickness, which indicates that most of the ice thickness must vary in velocity as does surface ice. Further support for this comes from the form of an internal radio-reflecting layer, which, in general, has the same shape as the bed but with much reduced relief. The damping of the relief is the same both along and across the flowline, suggesting that lateral velocity fluctuations are not important and that flow around and between obstacles is not well developed at the surface or at depth. At two sites, however, the internal layer does not match the bed and at one of these there must be important third-dimensional flow at depth.
The IGS Symposium on Ice and Climate Modeling: An Overview
Authors: Radok Uwe
Published: February 2017

The Symposium on Ice and Climate Modeling was staged by the International Glaciological Society (IGS) with the co-sponsorship of the American Meteorological Society to bring glaciologists into direct contact with modelers of the Earth’s climates during interglacials (such as the present) and glacial episodes. The purpose of mutual familiarization was served by reviews of the hierarchies which now exist for models of atmosphere, ocean, and climate. These reviews emphasized the actual or potential uses of ice data and parameterizations, and both general and specific aspects of coupling and sensitivity testing. The glaciologists in their turn reviewed the problems of exploring different ice forms and simulating their responses to climatic forcing. Interspersed with the didactic presentations important new results were reported. The most significant concerned atmospheric concentrations of carbon dioxide deduced from ice core analyses, which were put into a wider context by a new interpretation of the ocean as a chemical system.

The presentations and discussions highlighted a wide range of problems ripe for collaborative study. Topics recommended for priority attention include contemporaneous changes in the properties of ice cores from Greenland and Antarctica, links between weather sequences and the stable isotope contents of polar precipitation, systematic intercomparisons of a wide range of model results, and the construction of intermediate-complexity sea-ice models for use in climate simulations.
Crystal Size and Orientation Patterns in the Wisconsin-Age Ice from Dye 3, Greenland
Authors: Langway C.C. , Shoji H. , Azuma N.
Published: February 2017

Crystal size and c-axis orientation patterns were measured on the Dye 3, Greenland, deep ice core in order to investigate time-dependent changes or alterations in the physical character of the core as a function of time after recovery. The physical measurements were expanded to include depth intervals not previously studied in the field. The recent study focused on core samples located between 1786 m and the bottom of the ice sheet at 2037 m.

Manual c-axis measurements were made on 23 new thin sections using a Rigsby-type universal stage. A new semi-automatic ultrasonic wave-velocity measuring device was developed in order to compare the results with the earlier manual measurements and to study an additional 114 ice-core samples in the Wisconsin-age ice. Crystal-size measurements were made on specimen surfaces by inducing evaporation grooves at crystal boundaries and measuring linear intercepts. The ultrasonically measured test samples were subsequently cleaned and analyzed by ion chromatography in order to measure impurity concentration levels of Cl−, NO3− and SO4
2− and study their effects on crystal growth and c-axis orientation.
Soluble Impurities in Four Antarctic Ice Cores Over the Last 30 000 Years
Authors: Legrand Michel R. , Delmas Robert J.
Published: February 2017

The chemical composition of soluble impurities along the Dome C ice core covering approximately the last 30 000 years is reported and interpreted in terms of atmospheric contributions. Terrestrial and sea-salt inputs are known to have been much higher during the Last Glacial Maximum (LGM) than during the Holocene period. For this reason, the gas-derived compounds (mainly H2SO4 and HNO3) which dominate the chemistry of present-day snow are minor components in LGM snow. The exact calculation of each of the various contributions has been made possible by the determination of all major ions (H+, Na+, K+, NH4
+, Mg2+, Ca2+, NO3
−, SO4
2− and Cl−) in the samples. Three additional deep ice cores from other Antarctic areas have also been analyzed, but in a less comprehensive manner than the Dome C core. The differences observed at the four study sites increase the general understanding of the past atmospheric chemistry of the Southern Hemisphere.
Anions and Cations in Ice Cores from Dolleman Island and the Palmer Land Plateau, Antarctic Peninsula
Authors: Mulvaney Robert , Peel David A.
Published: February 2017

High-resolution anion profiles of Cl-, NO3- and SO4
2− are presented for two cores from the Antarctic Peninsula. A 47.2 m core from a site on the Palmer Land plateau (74°01’S, 70°38’W), spans the period 1942–80, and a 10.5 m core from Dolleman Island (70°35.2’S, 60°55.5’W), on the east coast of the peninsula, spans the period 1973–85. The seasonal pattern of deposition of these species has been determined by reference to the oxygen-isotope composition. Averaged over 38 years, the annual cycle of SO4
2− at Gomez shows a seasonal maximum during the austral summer, and minimum during the winter, whereas the Cl- cycle is more complex and may show the influence of equinoctial storms. The Dolleman core is significantly influenced by the proximity of the Weddell Sea, with a mean Cl- concentration five times greater than in the core from the plateau, and it shows a clear seasonal maximum in late-summer snowfall. There is no significant long-term trend in the 38 years’ data from the plateau site, suggesting that global pollution does not contribute significantly to the anion budget. Both anions and the cations Na+, K+ and H+ have been measured for more than a complete year of snowfall and the balance of ionic species is excellent.
Seasonal Variations in Hydrogen Peroxide in Polar Ice Cores
Authors: Sigg Andreas , Neftel Albrecht
Published: February 2017

Hydrogen peroxide is present in polar snow and ice in remarkably high concentrations. With values up to 300 ppb, H2O2 is one of the most concentrated impurities in polar ice. We present a continuous H2O2 firn record from Siple Station (Antarctica); it covers the last 83 years with a resolution of 10–20 samples per year. A very strong seasonality is present in this record. This seasonality is also observed in a Greenland ice core from Dye 3, where we have continuously measured the top 10 m with the same resolution. The maximum concentrations correspond to summer snow layers and can exceed winter snow concentrations by a factor of 10. This property makes H2O2 a useful tracer for dating suitable cores by counting annual layers. The different steps needed to relate the atmospheric to the ice–core H2O2 concentration are discussed. As with isotopic tracers, diffusion in the firn smooths the original H2O2 concentration profile.
Co-Isotopic Signature of Two Mechanisms of Basal-Ice Formation in Arctic Outlet Glaciers
Authors: Souchez R. , Lorrain R. , Tison J.L. , Jouzel J.
Published: February 2017

Basal ice is formed by regelation as a consequence of both pressure-melting and freezing-on at the glacier sole.

A study of D/H and 18O/16O ratios in basal ice from five Arctic outlet glaciers indicates that a co-isotopic signature exists for these two mechanisms of formation.

The dispersed and stratified facies of basal ice present in these glaciers are related respectively to the occurrence of regelation and to freezing-on at the glacier base. Their origin is tentatively connected with the onset of basal sliding and the zone of bed decoupling due to basal water pressure in these Arctic outlet glaciers.
Climatic Records from the Dunde Ice Cap, China
Authors: Thompson Lonnie G. , Xiaoling Wu , Mosley-Thompson Ellen , Zichu Xie
Published: February 2017

Results from the first glaciological investigation of the Dunde ice cap demonstrate that a long, highly temporally resolvable climatic ice-core record is preserved in this ice cap. Measurements of stratigraphy, microparticle concentrations, liquid conductivity, and oxygen-isotope ratios from three snow pits in 1984 suggest that the annual accumulation is approximately 200 mm (water equivalent). Measurement of microparticle concentrations and conductivities of pit samples collected in 1986 confirm the existence of annual dust layers and an annual accumulation rate of ∼200 mm/year over the past 5 years. Bore-hole temperatures of –5.4°C at 30 m indicate that the ice cap is polar. Mono-pulse radar depth determinations yield an average thickness of 140 m, which (coupled with the smooth bedrock topography and the current accumulation rate) suggest that the Dunde ice cap should contain at least a 3000 year climatic record. A drilling program to recover that record from this subtropical location is planned for 1987.
Concentrations of Cadmium, Copper, Lead and Zinc in Snow from Near Dye 3 in South Greenland
Authors: Wolff E.W. , Peel David A.
Published: February 2017

Clean sampling and analysis procedures have been used to measure the concentrations of Al and four heavy metals in snow representing one year’s accumulation (1983-84) near Dye 3 in Greenland. Mean values were Al 17.5ng g−1, Cd 0.74 pg g−1, Cu 6.2 pg g−1, Pb 28 pg g−1 and Zn 27 pg g−1. Concentrations of the heavy metals are lower than previously reported at other Greenland sites for snowfall during the last 20 years. A distinct late-winter / early-spring maximum is seen for Al, Cu, Pb and Zn, in accord with other workers’ measurements of various species in the atmospheric aerosol in the Arctic. Cu appears to have a large crustal component, but Cd, Pb and Zn probably originate mainly from pollution. One explanation for the lower Pb values may be the considerable reduction in North American and European usage of Pb as a petrol (gasoline) additive during the last decade. These limited data emphasize the importance of obtaining a reliable century-long record of these metals in Greenland ice.
Antarctic Peninsula Climate Over the Last 400 Years, Deduced from an Ice-Core Record
Authors: Aristarain A.J. , Jouzel J. , Pourchet M. , Lorius C.
Published: February 2017

Reconstruction of the past climate of the Antarctic Peninsula is of special interest because it represents a possible link between the conditions that predominated over the Antarctic continent and those over South America, only about 1000 km away. From a detailed isotopic study on a core drilled on James Ross Island (64°12′S, 57°40′W), including a comparison with the Orcadas temperature record (which has been available since 1904), we have recently examined the climatic changes which have occurred in this region over the last 130 years (Aristarain and others 1986).

We have now extended this isotope record back to about A.D. 1600 (dating is obtained from a glaciological model). A striking feature of the resulting climatic curve is the significant cooling, estimated at about 2º C, which has been observed since the turn of the century, in comparison with the warmest period of the record (around A.D. 1850). This feature, which is at odds with Northern Hemisphere temperature data, will be examined in the context of factors affecting the Antarctic Peninsula climate. These include sea-ice extent, and the relative influence of a maritime climate in the west and of a continental climate in the east, and the generally high climatic sensitivity theoretically expected in these ice-margin areas. The whole climatic curve will also be compared with other Antarctic and Southern Hemisphere records.
The influence of humidity on the ablation of continental-type glaciers
Authors: Ohno Hiroyuki , Ohata Tetsuo , Higuchi Keiji
Published: February 2017

The annual evaporation of a continental-type glacier (43°05’ Ν, 86°48’ E) in the Chinese Tien Shan is estimated, based on data derived from four field observations carried out between summer 1987 and spring 1988, and data from a permanent weather station near the glacier. The evaporation during the melting and non-melting seasons is estimated as 81 mm and negligible, respectively. Assuming that the ablation is equivalent to the annual precipitation (650 mm) in 1987, estimated annual evaporation of 81 mm is 12% of the ablation and consumes 54% of the energy which causes the ablation. It can be said that evaporation suppresses ablation by 50% in comparison with the condition in which there is no evaporation.

The influence of fluctuations of air temperature and humidity on the ablation of the glacier were evaluated. Changes in temperature and humidity cause larger changes in ablation of glaciers in a cold and dry climate. The influence of humidity change is very important to glaciers located in a relatively warm environment.
Progress and prospect for research on mountain glaciers in China
Authors: Zichu Xie
Published: February 2017

In the past decade the interest of many scientists worldwide has been attracted to the central Asian area of China. A number of gaps in scientific knowledge have been closed, and many significant discoveries have been made.

The most important achievement is the ice-core research by the Sino-American Joint Expedition to the Dunde Ice Cap, Qilian mountains, that established a record of ten thousand years of climatic and environmental change. In addition, in cooperation with scientists from Japan, Switzerland and the Soviet Union, studies have been carried out focusing on glacier mass balance, heat balance, the mechanism and formation of glacial runoff, and high mountain climates. This work has been done in the Tien Shan, west Kunlun, Tanggula, Nyaingentanglha and Gongga mountains.

In addition, through joint efforts of scientists from China, Nepal and Canada, important advances have also been made in studies of glacier lake outburst floods and debris flows in the Karakoram and the Himalayas, and in mountainous areas in southeastern Tibet.

The glaciers in central Asia will continue to be an important research area for glaciologists from all over the world in the coming decade.
The use of microwave radiometer data for characterizing snow storage in western China
Authors: Chang A. T. C. , Foster J. L. , Hall D. K. , Robinson D.A. , Peiji Li , Meisheng Cao
Published: February 2017

In this study a new microwave snow retrieval algorithm was developed to account for the effects of atmospheric emission on microwave radiation over high-elevation land areas. This resulted in improved estimates of snow-covered area in western China when compared with the meteorological station data and with snow maps derived from visible imagery from the Defense Meteorological Satellite Program satellite. Some improvement in snow-depth estimation was also achieved, but a useful level of accuracy will require additional modifications tested against more extensive ground data.
Description and Analysis of a 20-Year (1960-79) Digital Ice-Concentration Database for the Great Lakes of North America
Authors: Assel Raymond A.
Published: February 2017

A digital ice-concentration database spanning 20 years (1960 to 1979) was established for the Great Lakes of North America. Data on ice concentration, i.e. the percentage of a unit surface area of the lake that is ice-covered, were abstracted from over 2 800 historic ice charts produced by United States and Canadian government agencies. The database consists of ice concentrations ranging from zero to 100% in 10% increments for individual grid cells of size 5 × 5 km constituting the surface area of each Great Lake. The data set for each of the Great Lakes was divided into half-month periods for statistical analysis. Maxinium, minimum, median, mode, and average ice-concentrations statistics were calculated for each grid cell and half-month period. A lakewide average value was then calculated for each of the half-month ice-concentration statistics for all grid cells for a given lake. Ice-cover variability and the normal extent and progression of the ice cover is discussed within the context of the lakewide averaged value of the minimum and maximum ice concentrations and the lakewide averaged value of the median ice concentrations, respectively. Differences in ice-cover variability among the five Great Lakes are related to mean lake depth and accumulated freezing degree-days. A Great Lakes ice atlas presenting a series of ice charts which depict the maximum, minimum, and median icecover concentrations for each of the Great Lakes for nine half-monthly periods, starting the last half of December and continuing through the last half of April will be published in 1983 by the National Oceanic and Atmospheric Administration (NOAA). The database will be archived at the National Snow and Ice Data Center of the National Environmental Satellite Data and Information Service (NESDIS) in Boulder, Colorado, USA, also in 1983.
A Turbulent Mixture Theory for the Atmospheric Mixture of Snow and Air
Authors: Decker Rand , Brown R. L.
Published: February 2017

A theory based on classical fluid mechanics for an incompressible, chemically non-reacting, atmospheric mixture of air and entrained snow particles is derived. These continuum equations of motion are then expanded to include turbulent flow. The reduced, one-dimensional equations of this theory are further refined by order-of-magnitude analysis and correlation of the turbulent terms to mean flou parameters. The resulting one-dimensional, turbulent equations of motion for the snow contain apparent turbulent forces which enhance entrainment of snow where gradients of the air flow are high. These turbulent equations of motion are then solved numerically for snow particle velocity and concentration as a function of height above the surface. The results are similar to observed profiles of snow concentration and the superposition of the solution of this turbulent mixture theory for snow entrainment with an appropriate solution for the saltation layer will eventually lead to a working continuum theory for blowing snow.
Subglacial Processes at Bondhusbreen, Norway: Preliminary Results
Authors: Hagen Jon Ove , Wold Bjørn , Liestøl Olav , Østrem Gunnar , Sollid Johan Ludvig
Published: February 2017

Subglacial hydrology, sediment transport, pressure, and temperature have been studied beneath approximately 160 m of ice at Sondhusbreen, an outlet glacier from Folgefonni in south-western Norway.

The volume of the mean annual water discharge passing through the study area is about 60x106m3. Most of this water is diverted into a tunnel system in the rock beneath the glacier and used for hydroelectric power generation. At the beginning of the melt season, this water flows in multiple small channels, but later it collects in one or two main channels. The discharge of eroded material is about 7 600 tonnes a−1. Of this, roughly 90% is transported by running water.

Pressure gauges and thermistors were installed at two sites under the glacier. Results from one of the sites indicated that ice can stagnate in some leeward positions, as almost no ice movement was recorded during most of the period of measurement and the pressure distribution was nearly hydrostatic. However, increased water pressure during the summer apparently resulted in the opening of subglacial cavities, adding a local up-glacier component to the flow at this site.

At another location, about 20 m up-glacier, non-hydrostatic differential pressures of up to 30 bar were recorded across an artificial dome-shaped obstacle. The flow at this location was more steady, in general, but rather dramatic effects were recorded when a boulder 0.3 m3in size passed over the obstacle, destroying one of the pressure sensors. This sensor recorded a pressure of 90 bar before failing. The boulder was moving at a speed of about 40 mm d-1, whereas the sliding velocity of the ice was 80 mm d-1. Temperature measurements suggest that the difference in temperature across this obstacle was less than 0.03 deg, or an order of magnitude less than expected. This may mean that water was squeezed out of the ice on the stoss side of the obstacle as suggested by Robin (1976), and thus was not available to warm the lee-side ice by refreezing.
Comparison Between Different Yield Functions for Saline Ice
Authors: Häusler F. U.
Published: February 2017

Data obtained from tests of uniaxial and multi-axial compressive strength on saline ice have been used to determine the coefficients of the Smith yield function, which uses seven parameters, and of the Pariseau yield function, which uses five. Both functions describe orthotropic materials and have been reduced for transverse isotropy. The tests of compressive strength were carried out over the past few years in the ice laboratory of the Hamburgische Schiffbau-Versuchsanstalt (HSVA) on a closed-loop controlled triaxial loading frame with brush-type loading platens. The values for tensile strength have been obtained from data published by other researchers.

The ice-strength values computed by means of the two yield functions were compared with measured ice strengths; the seven-parameter Smith yield function provides reliable results over the whole stress space, while the simpler Pariseau yield function is only applicable within a restricted area of the stress space.
The Lobe Structure in Ice Accreted on an Aluminium Conductor in The Presence of a Dc Electric Field
Authors: Phan Luan C. , Laforte Jean-Louis , Nguyen Du D.
Published: February 2017

Supercooled droplets of 38 μm mean volume diameter are accreted on a smooth aluni mum cylinder of 3.15 cm in diameter in order to study the effect of an electrostatic field upon ice formation on a power-line conductor. The results obtained show that ice grown in the presence of an applied negative field of 15 kV cm−1exhibits a cusped-lobe structure characterized by surfacial outward knobs, convex rings of fine air bubbles and radial lines of large air bubbles; in the same conditions, a positive electric field of 15 kV cm−1does not produce such lobe features. On the other hand, accretion tests performed in the absence of an electric field with a 33 μm droplet spectrum show that the well-developed cusped-lobe structure appears in ice at low ambient temperature and air velocity. In the present experimental conditions, the formation of cusped lobes observed in the presence of a negative electric field could be explained by a decrease in the temperature of the deposit due to a reduction of impact velocity of the charged droplets and/or an increase in the local heat-transfer coefficient at the surface of the ice accretion. Corona wind from ice points, always in the opposite direction to the impinging droplets, may also reduce their impact velocities. In addition, corona wind and roughness of the surface may contribute to a better evacuation of the latent heat and thus decrease the deposit temperature. The difference between the effects of a negative DC field and those of a DC positive field of the same strength comes from a stronger ionization intensity and/or a stronger deformation of water drops in the negative electric field.
Relocation and Preferential Elution of Acidic Solute through the Snowpack of a Small, Remote, High-Altitude Scottish Catchment
Authors: Brimblecombe P. , Tranter M. , Abrahams P.W. , Blackwood I. , Davies T.D. , Vincent C.E.
Published: February 2017

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

although the position of the hydrogen and ammonium ions may be affected by buffering. The sequence compares reasonably well with a generalized one assembled from earlier studies, where is usually eluted quickly and sodium and chloride rather slowly. The evolution of the snowpack composition towards solute depletion, but relative richness in chloride, is clearly represented in triangular diagrams.
Can Relict Crevasse Plumes on Antarctic Ice Shelves Reveal a History of Ice-Stream Fluctuation?
Authors: MacAyeal D. R. , Bindschadler R. A. , Jezek K. C. , Shabtaie S.
Published: February 2017

Configurations of relict surface-crevasse bands and medial moraines that emanate from the shear margins of ice streams are simulated, using a numerical model of an ideal rectangular ice shelf to determine their potential for recording a past ice-stream discharge chronology.
Mass-Balance Studies of Ice Streams A, B, and C, West Antarctica, and Possible Surging Behavior of Ice Stream Β
Authors: Shabtaie S. , Bentley C. R. , Bindschadler R. A. , MacAyeal D. R.
Published: February 2017

Recent airborne radar sounding has made it possible to map accurately three of the West Antarctic ice streams that flow into Ross Ice Shelf. In previous work we have shown that ice streams A and Β have negative mass balances, whereas inactive Ice Stream C has a strongly positive balance. In this paper we examine in more detail the balance of ice streams A and Β by constructing several gates across them where velocities and ice thicknesses have been measured. We then examine the net fluxes in blocks of the ice streams delimited by successive pairs of gates.

Ice Stream A as a whole is apparently discharging more ice than is being accumulated in the catchment area, and currently thinning at the rate of 0.08 ± 0.03 m a−1. The situation on Ice Stream Β is more complex. We have calculated separately the fluxes from tributary ice streams Bl and B2, and examined their individual fluxes within Ice Stream Β by tracing the suture zone between them down-stream of their confluence. The flow band that is the farthest up-stream (girdle), encompassing both Ice Stream Bl and Ice Stream B2, shows a strongly negative net flux that we attribute to lateral and headward expansion of the ice streams within the band. Such expansion can occur by lateral movement of an ice-stream boundary, by temporally accelerating ice flow at the head of the ice stream, or by activation of formerly slowly moving “island” or “peninsula” ice.

The imbalance in this flow band, 8 ± 2 km3 a−1 (equivalent mean rate of change in ice thickness,
is nearly half of the total excess outflow for the Ice Stream Β system (20 ± 4 km3 a−1),

— the remainder is mostly the difference between flow through the uppermost gate and mass input to the catchment area .

When

for the whole of Ice Stream Β is plotted against the distance along the entire Ice Stream B, the overall pattern appears to be of mild thinning in the catchment, intense thinning in the girdle, and thickening in the main body of the ice stream, which decreases with distance from the girdle. This global behavior is suggestive of a major transient response, resulting from either a change in the internal dynamics or an internal adjustment to a change in the external forcings. We argue that there are a number of conditions which could lead to this type of response pattern. One possibility is a surge. Although the distribution of the changes in thickness is one characteristic of a surge, we caution that this alone is not sufficient to classify the behavior as a surge. Several other possibilities that support a picture of Ice Stream Β as a system in the process of dynamic change and in unsteady state are discussed.

At present, Ice Stream C and its catchment area are thickening over their entire area

The present surface elevation does not suggest that Ice Stream Β has captured part of Ice Stream C. Moreover, the shut-down of Ice Stream C and the large mass imbalance of Ice Stream Β are not related.
Characteristics of the Initial Densification of Snow/Firn in Wilkes Land, East Antarctica (Abstract)
Authors: Dahe Qin , Young N. W.
Published: February 2017

Fourteen shallow snow/firn cores were drilled with the Polar Ice Coring Office light-weight hand-coring auger in Wilkes Land, along a line approximately long. 111°E between lat. 66° and 74°S. Five of these cores, all between 20 and 30 m deep, are studied in detail in this paper: LJ, BJ, GC30, GC40 and GC46. The physical geographical conditions differ at these five stations, but the general trend is for mean annual accumulation rate and mean annual temperature to decrease farther south, with increasing elevation. At the southernmost station, GC46, the mean annual temperature is –52.5°C, and accumulation rate is 52 kg m−2 a−1.

The density measurements of the snow/firn were made in a cold-room at temperatures from –14− to –18−C, by taking consecutive samples from the core and measuring the mass of each sample of known volume. The characteristics of the initial densification (to a density of 550 kg m−3) – variation in snow/firn density with depth, the densification rate of snow/firn, and the compactive viscosity coefficient of snow/firn – are studied, and the factors affecting this initial densification process are discussed.

The following observations were made and conclusions reached:

1.

Plots of all the measurements, from each core, of density against depth showed three different patterns. The first type, typical of the coastal areas, shows a very great variability of density at shallow depth, reducing with an increase in depth. The second, typical of the high inland stations, shows a smaller scatter of densities at shallow depth, again reducing with an increase in depth. The third type is a pattern intermediate between these two. So, the range of density fluctuation with a depth range in any core is greater at the top of the core than at the bottom, and at the same depth in different cores the variation in density is greater where the mean annual temperature is higher.

2.

The snow/firn density increases with an increase in depth at all stations, and the densification rate is higher at stations with higher mean annual temperature.

3.

The mean density of snow/firn in the top 1 m decreases farther inland, and this decrease appears to be closely related to the decrease in temperature.

4.

The mean densification rate is compared with the mean annual temperature and the mean annual accumulation rate over the past 40 years in the most southerly cores. The mean annual temperature is found to be the more important factor affecting the densification rate in the surface snow/firn on the cold ice sheet.

5.

At each station, for ρ = 550 kg m−3, a linear relationship is found between log compactive-viscosity coefficient of snow/firn and mean annual temperature for a constant density. If only stations with a mean annual temperature below –25°C (i.e. no melt features are present in the stratigraphy) are considered, then these results from Wilkes Land are very similar to the results obtained by Nishimura and others (1983) from Mizuho Plateau, East Antarctica.
Pack-Ice Drift off East Antarctica and some Implications
Authors: Ian Allison
Published: February 2017

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

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

A qualitative assessment is made of the relative importance of the major forces driving the ice, although the data are insufficient for a detailed study of the ice dynamics.
Single Folds at the Margins of Dry-Based Glaciers as Indicators of a Glacial Advance
Authors: Chinn T.J.H.
Published: February 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.
Ice-Shelf Topography and Structure Determined Using Satellite-Radar Altimetry and Landsat Imagery
Authors: Stephenson Simon N. , Jay Zwally H.
Published: February 2017

The glaciological structure and dynamics of West and Shackleton Ice Shelves, East Antarctica, are qualitatively determined using a combination of satellite remote-sensing techniques. Sketch maps traced from unenhanced imagery show the ice edge, grounding lines, flow lines, and rifts. Surface-elevation profiles and contour maps from radar altimetry provide free-board elevations of the floating ice and show flow-line undulations and rumples characteristic of grounded ice. West and Shackleton Ice Shelves consist of a combination of fast-moving ice tongues from outlet glaciers and slow-moving parts constrained by islands, ice rises, and ice rumples.
Past and Forecast Fluctuations of Glacier Blanc (French Alps)
Authors: Letréguilly Anne , Reynaud Louis
Published: February 2017

In 1980 the new advance of Glacier Blanc covered a trail leading to a mountain hut and threatened the footbridge that crosses its melt-water stream. This event prompted the Laboratoire de Glaciologie et Géophysique de l’Environnement (LGGE) to undertake a new study of the glacier. With the old Eaux et Forêts measurements, and the more recent LGGE ones, it has been possible to forecast the probable fluctuations in glacier length by two different methods: a statistical method based on a correlation between the variations in length and mass balance, and a one-dimensional numerical ice-flow model. Both methods show that a substantial glacier retreat is unlikely during the 1985–90 period.
Influence of Strong Winds on Snow Distribution and Avalanche Activity
Authors: Meister R.
Published: February 2017

In a local range, crest winds were compared with winds at lower stations to make it possible to initiate a drift-transport model which would predict snow accumulation patterns on leeward slopes. Corrections to the model input were made after consideration of detailed drift-flux measurements in the lowest 2 m above snow surface. Good agreement was found between the total length of large avalanches in a path near the crest, the appropriate wind reading and the corrected snow-depth increments in the rupture zone. Control of medium-sized avalanches likely to cause injury to skiers can be improved with the proposed method.
Geostatistics in Glaciology: Implications of a Study of Scharffenbergbotnen, Dronning Maud Land, East Antarctica
Authors: Herzfeld U.C. , Holmlund P.
Published: February 2017

Geostatistical methods are applied in the analysis of radio-echo data from Scharffenbergbotnen, Dronning Maud Land, East Antarctica, in order to allow the following investigations: detailed and reliable cartography of subglacial bed topography and ice thickness, comparison of recent ice flow patterns and ice flow during earlier glacial maxima, and mass balance studies in relation to climatic changes.
A Review of Central Asian Glaciochemical Data
Authors: Wake Cameron P. , Mayewski Paul A. , Spencer Mary Jo
Published: February 2017

The glaciers of central Asia provide suitable locations from which to recover continuous, high-resolution glaciochemical records on a continental scale. Although the glaciochemical investigations undertaken to date in central Asia are few in number and limited in terms of spatial coverage and length of record, some preliminary observations can be made concerning regional and seasonal trends in snow chemistry in this region.

The sodium chloride ratio for most snow samples collected in central Asia approaches the ratio found in sea water (0.86 in μeq kg−1), reflecting a marine source for these constituents. Sodium and chloride concentrations are, on average, 3–10 times higher in the Himalayas than in the Karakoram, demonstrating the greater influence of monsoonal sources of moisture in the Himalayas. Very high sodium concentrations from Khel Khod Glacier probably reflect a local crustal source from surrounding ice-free areas. Low nitrate concentrations were found in snow collected from the southern margin of the Himalayas and high concentrations in snow deposited on the north margin of the Himalayas. This strong regional trend in the spatial distribution of nitrate suggests the influx of continental aerosols, rich in nitrate, originating from the arid regions of central Asia. High calcium concentrations measured in snow from Mount Everest and the north-west corner of China are also indicative of dust derived from the arid regions of central Asia. Very high sulfate concentrations found in snow from the Tien Shan and the Bogda Shan most likely reflect local anthropogenic sources. The altitude effect on isotopie composition is not apparent from snow samples collected in central Asia.

Understanding the processes which control the chemical content of snow, the local-to-regional scale complexities, and the seasonal variability are fundamental steps necessary to assess the potential for recovering representative long-term glaciochemical records from central Asia.
Numerical simulations of a compact convergent system of ice floes
Authors: Hopkins M.A. , Hibler W.D.
Published: February 2017

The granular nature of the Arctic pack ice, and the plastic nature of the deformation of the pack due to ridging, has long been recognised. However, because of a lack of experimental data, assumptions must be made to define the shape of the yield curve and the associated flow rule which characterize the aggregate rheology of the ice pack. In this work, the results of numerical experiments with a simulated granular viscous-plastic material are presented. The experiments model the granular texture of the ice pack as a dense assembly of non-uniform diameter disks in a rectangular control area. Deformation of the control area is driven by constant strain rates. In the experiments, the ratio of the principal strain rates is varied from isotropic convergence through uniaxial divergence. The stresses computed in the experiments, at the various strain-rate ratios, define a yield curve in principal-stress space. The effects of different coefficients of friction and viscous damping on the shape of the yield curve are explored.
The propagation of characteristics in sea-ice deformation fields
Authors: Erlingsson Björn
Published: February 2017

The role of internal forces in determining the geometrical properties of local features such as leads and ridges in sea ice has been investigated. A description of the horizontal stress distribution in a granular material subject to two-dimensional deformations has been derived. The description yields expressions for the propagation of deformation characteristics in a granular deformation field with constant angle of internal friction. The characteristics are mathematical singularities interpreted as trajectories of constant state variables, e.g. ice concentration or ice thickness typified as leads, fractures, pressure and shear ridges. The derived descriptions are used to study the geometrical nature of curving and rectilinear lead patterns frequently observed in sea-ice deformation fields. An expression for the relationship between the arching (tangent angling) of characteristics and relative increase in shear (maximum shear stress) along them is derived. It is explained how the acute angle between large-scale rectilinear characteristics is related to the important mechanical property of the deformed material, the angle of internal friction. It is outlined how the derived results can be applied to study the horizontal distribution of internal forces in sea ice by using imagery data and stress measurements at one site only.
Ocean-atmosphere energy exchange over thin, variable concentration Antarctic pack ice
Authors: Worby A. P. , Allison Ian
Published: February 2017

Several recent studies have suggested that much of the winter-time Antarctic ice is thin (<0.3m). The presence of extensive areas of thin ice has a significant effect on ocean-atmosphere energy exchange. This is investigated using the Maykut (1978) thin-ice energy-budget model in a study for typical September Antarctic ice and climatic conditions. To study the sensitivity of turbulent heat loss to ice concentrations, the Maykut model is combined with an empirical parameterization for the turbulent fluxes from leads (Andreas, 1980) which takes account of the non-linear relationship between heat loss and lead width (or ice concentration). In this one-dimensional sensitivity study, a constant floe-size is assumed, and ice-concentration variations are simulated by changing the width of the leads between floes. The modelled results, for the floe size considered, indicate that at 80% ice concentration the turbulent heat loss through the thin ice component can be greater than that from leads. As concentration decreases, however, the fractional loss through the ice, and, hence, the ice-thickness distribution, becomes less significant. For the concentrations lower than 50%, there is little change in turbulent loss with further decrease in ice cover, as the atmosphere effectively “sees” open ocean.