bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of weather effects in the calculation of sea-ice concentration with the DMSP SSM/I
Authors: Cavalieri Donald J. , St. Germain Karen M. , Swift Calvin T.
Published: September 2017

A problem in mapping the polar sea-ice covers in both hemispheres has been the sporadic false indication of sea ice over the open ocean and at the ice edge. These spurious sea-ice concentrations result from variations in sea-surface roughening by surface winds, atmospheric water vapor and both precipitating and non-precipitating liquid water. This problem was addressed for sea-ice concentrations derived from the Nimbus-7 scanning multi-channel microwave radiometer (SMMR) data through the development of a weather filter based on spectral information from the 18.0 and 37.0 GHz vertical polarization SMMR channels. Application of a similar filter for use with sea-ice concentration maps derived with the special-sensor microwave imager (SSM/I) sensor is less successful. This results from the position of the 19.35 GHz SSM/I channels, which are closer to the center of the 22.2 GHz atmospheric water-vapor line than are the SMMR 18.0 GHz channels. Thus, the SSM/I 19.35 GHz channels are more sensitive to changes in atmospheric water vapor, which results in greater contamination problems. An additional filter has been developed, based on a combination of the 19.35 and 22.2GHz. SSM/I channels. Examples of the effectiveness of the new filter are presented and limitations are discussed.
Sub-surface melting in a seasonal snow cover
Authors: Koh Gary , Jordan Rachel
Published: September 2017

The ability of solar radiation to penetrate into a snow cover combined with the low thermal conductivity of snow can lead to a sub-surface temperature maximum. This elevated sub-surface temperature allows a layer of wet snow to form below the surface even on days when the air temperature remains sub-freezing. A high-resolution frequency-modulated continuous wave (FMCW) radar has been used to detect the onset of sub-surface melting in a seasonal snow cover. The experimental observation of sub-surface melting is shown to be in good agreement with the predictions of a one-dimensional mass- and energy-balance model. The effects of varying snow characteristics and solar extinction parameters on the sub-surface melt characteristics are investigated using model simulations.
Recent drumlins, flutes and lineations at Vestari-Hagafellsjökull, Iceland
Authors: Hart Jane K.
Published: September 2017

In the foreland of the Vestari-Hagafellsjökull glacier, Langajökull, central Iceland, three scales of subglacial bed forms are found: drumlins, flutes and lineations. The smaller bed forms are superimposed upon the larger. These three bed forms probably formed as a result of the presence of a rigid suhglacial core producing a lee-side low-pressure area into which sediment flowed and collected. The cores of the drumlins are tumuli (lava blisters), whilst the cores of the flutes and lineations were large clasts.

Differences between the three scales of bed forms are that: (a) the flutes and lineations are far more mobile features as their cores could move within the deforming layer, whilst the drumlin bedrock cores were fixed; (b) the lineations formed in association with a clast pavement.

The change in scale of the bed forms may he related to changes in thickness of the deforming layer and size of the core. At this site, smaller bed forms were superimposed upon larger bed forms and these may have formed as the deforming layer progressively thinned in association with glacial retreat.
Measuring geophysical parameters of the Greenland ice sheet using airborne radar altimetry
Authors: Ferraro Ellen J. , Swift Calvin T.
Published: September 2017

This paper presents radar-altimeter scattering models for each of the diagenetic zones of the Greenland ice sheet. AAFE radar-altimeter waveforms obtained during the 1991 and 1993 NASA multi-sensor airborne altimetry experiments over Greenland reveal that the Ku-band return pulse changes significantly with the different diagenetic zones. These changes are due to varying amounts of surface and volume scattering in the return waveform.

In the ablation and soaked zones, where surface scattering dominates the AAFE return, geophysical parameters such as rms surface height and rms surface slope are obtained by fitting the waveforms to a surface-scattering model. Waveforms from the percolation zone show that sub-sruface ice features have a much more significant effect on the return pulse than the surrounding snowpack. Model percolation waveforms, created using a combined surface- and volume-scattering model and an ice-feature distribution obtained during the 1993 field season, agree well with actual AAFE waveforms taken in the same time period. Using a combined surface- and volume-scattering model for the dry-snow-zone return waveforms, the rms surface height and slope and the attenuation coefficient of the snowpack are obtained. These scattering models not only allow geophysical parameters of the ice sheet to he measured but also help in the understanding of satellite radar-altimeter data.
Weak bands within Ice Stream B, West Antarctica
Authors: Hulbe C. L. , Whillans I. M.
Published: September 2017

Kilometer-scale variations in ice velocity and surface topography are used to investigate the style of glacier deformation in the main body of Ice Stream B, West Antarctica. The pattern is very different from that reported for other glaciers. For the 250 km2 area studied on Ice Stream B, most of the observed deformation occurs within two narrow bands, in which there is large across-flow compression and slow lateral shearing. The bands underlie valleys in the ice-surface topography. Measured upward displacement of ice adjacent to the rapidly compressing bands appears to be linked to the creation of the ice stream’s topography. The most likely cause for the observed pattern of strain rates and surface topography, and their changes over time, is deformation guided by longitudinal bands of ice with an aligned crystal fabric.
Bubbly-ice densification in ice sheets: I. Theory
Authors: Salamatin Andrey N. , Lipenkov Vladimir Ya , Duval Paul
Published: September 2017

Dry snow on the surface of polar ice ice sheets is first densified and metamorphosed to produce firn. Bubbly ice is the next stage of the transformation process which takes place below the depth of pore closure. This stage extends to the transition zone where, due to high pressures and low temperatures. air trapped in bubbles and ice begins to form the mixed air clathrate hydrates, while the gas phase progressively disappears. Here we develop a model of bubbly-ice rheology and ice-sheet dynamics taking into account glacier-ice compressibility. The interaction between hydrostatic compression of air bubbles, deviatoric (uniaxial) compressive deformation of the ice matrix and global deformations of the glacier body is considered. The ice-matrix pressure and the absolute-load pressure are distinguished. Similarity theory and scale analysis are used in examine the resultant mathematical model of bubbly-ice densification. The initial rate of bubble compression in ice sheets appears to be relatively high, so that the pressure (density) relaxation process takes place only 150-200 m in depth (below pore close-off) to reach its asymptotic phase, wherein the minimal drop between bubble and ice pressures is governed by the rate of loading (ice accumulation). This makes it possible to consider densification under stationary (present-day) conditions of ice formation as a special case of primary interest. The computational tests performed with the model indicate that both ice-porosity and bubble-pressure profiles in ice sheets are sensitive to variations of the rheological parameters of pure ice. However, only the bubble-pressure distinguishes between the rheological properties at low and high stresses. The porosity profile at the asymptotic phase is mostly determined by the air content in the ice. In the companion paper (Lipenkov and others, 1997), we apply the model to experimental data from polar ice cores and deduce, through an inverse procedure, the rhelogical properties of pure ice as well as the mean air content in Holocene and glacial ice sediments at vostok Station (Antarctica).
Across-column cracks and axial splits in S2 saline ice under compression
Authors: Schulson E. M. , Qi S. , Melton J. S. , Gratz E.T.
Published: September 2017

Experiments on plate-like specimens have established that across-column cracks from within S2 (columnar) salt-water ice when compressed uniaxially along a direction inclined to the long axis of the grains. Wing cracks initiate from the across-column cracks and lengthen into axial splits when the ice is rapidly deformed; correspondingly; the macroscopic behavior changes from ductile to brittle. The across-column cracking is attributed to grain-boundary sliding, and the splitting to the suppression of crack-tip creep.
Surge of Bering Glacier and Bagley Ice Field, Alaska: an update to August 1995 and an interpretation of brittle-deformation patterns
Authors: Herzfeld Ute Christina , Mayer Helmut
Published: September 2017

In the summers of 1993, 1994 and 1995, video and Global Positioning System location data and 35 mm photographs were collected in a series of systematic survey flights undertaken over the Bering Glacier and Bagley Ice Field system (Alaska) in an effort to characterize surge-crevasse patterns and surge propagation. During survey flights in late August 1995, we observed that the 1993–94. Bering Glacier surge was continuing and still expanding affecting new areas farther up in Bagley Ice Field. New crevasse fields, similar in pattern to the first surge crevasses we had observed in June 1993 below Khitrov Hills and in other isolated areas of central Bering Glacier and in July 1994 near the head of Bering Glacier (near the junction of Bering Glacier and Bagley Ice Field, in both upper Bering Glacier and Bagley Ice Field), were opening in eastern Bagley Ice Field and in the “Stellet” side of Bagley Ice Field. The type of crevasses seen in the new fields suggested that the surge was propagating into these areas. By analysis and interpretation of the brittle-deformation patterns apparent in the crevasse patterns, some aspects of the past kinematic framework of the surge can be deduced. This approach may lead to a more general classification of ice-surface structures and to their linkage to ongoing processes.
Glacier recession on Kilimanjaro, East Africa, 1912–89
Authors: Hastenrath Stefan , Greischar Lawrence
Published: September 2017

The varying ice extent on the Kibo cone of Kilimanjaro, East Africa, this century was reconstructed from terrestrial-photogrammetric mappings in 1912 and 1953 and satellite images in 1976 and 1989. These were all conformed to the official 1:50 000 topographic sheet. The ice distribution on Kibo is characterized by lower ice margins on the southern than on the northern flanks, and deepest-reaching glaciers to the west contrasting with least ice cover on the eastern crater rim. The meridional contrast appears to be related to the more abundant precipitation on the southern side. The even more striking zonal asymmetry in ice cover is favored by the vigorous diurnal circulations, with enhanced afternoon cloudiness blocking insolation on the western slopes. The total ice cover diminished from 12058 to 6675 to 4171 in 3305 × 103 m2 between the years 1912,1953, 1976 and 1989, and the three large coherent ice bodies disintegrated into numerous smaller ice fragments.
Climatic effects and bedrock control on rapid fluctuations of Chhota Shigri glacier, northwest Himalaya, India
Authors: Kumar Surendar , Dobhal D.P.
Published: September 2017

Active tectonism in the Himalaya, and the long-fault lineament controlling the east–west river valleys, play an important role in melt at the snouts of glaciers, or their fluctuations during the year. Lower glacier limits are controlled by high winds from the Indian plains flowing along the valleys. Fluctuations of the Chhota Shigri glacier depend on temperature variations at the junction with the Chandra River valley and in the unconsolidated morainic debris below the glacier ice. High flow rates in the ablation zone indicate that basal sliding is the main movement mechanism. Melt takes place mainly from advection, and this process of melting during the summer season occurs both day and night.
Subglacial comminution in till — evidence from microfabric studies and grain-size distributions
Authors: Chaolu Yi
Published: September 2017

Quartz, feldspar and chlorite, the principal minerals in a basal till from the Halasi River catchment in the Altay Mountains, northwestern China, are present in approximately equal concentrations in the coarse fraction of the till, 1.0-0.125 mm. Quartz concentrations are significantly higher than those of the other two minerals in the 0.125-0.016 mm size range. Feldspar and chlorite concentrations are higher than those of quartz in the finest fraction. Quartz has a strong preferred mode at 0.063-0.032 mm. Feldspar and chlorite have two weak modes in the silt-size range, one between 0.063 and 0.032 mm and the other between 0.016 and 0.004 mm.

Thin sections of oriented impregnated samples were used to study crushing and abrasion. Over 2700 daughter particles were identified as products of comminution of 925 parent grains. Quartz and feldspar are most likely to be broken into two particles of roughly equal size, as are fine chlorite grains. However, owing to their weakness and cleavage, larger grains of chlorite tend to he split into more than two daughter particles.

Sizes of the daughter grains were measured and sizes of the original parent grains were estimated. Mean parent grain-sizes for quartz, feldspar and chlorite are 0.129, 0.078 and 0.059 mm, respectively, whereas mean daughter grain-sizes are 0.068,0.041 and 0.024 mm, respectively. The greater percentage reduction in the size of chlorite reflects its tendency to break into more than two daughter particles.

Most grains tend to be crushed. Only a few large particles seem to have suffered from abrasion.
Surge-type glaciers in the Russian High Arctic identified from digital satellite imagery
Authors: Dowdeswell Julian A. , Williams Meredith
Published: September 2017

Landsat digital imagery was used to search the island archipelagos of Franz Josef Land, Severnaya Zemlya and Novaya Zemlya, Russian High Arctic, for the presence of looped moraines characteristic of past glacier surges. The imagery provides almost complete summer-time coverage of the 60 000 km2of ice in these islands. very few surge-type glaciers are identified: none in Franz Josef Land, three in Novaya Zemlya and two on Severnaya Zemlya. This contrasts greatly with Svalbard (ice-covered area 36 600 km2), to the west, where 36% of glaciers and ice-cap drainage basins are inferred to surge. The strong climatic gradient across the Eurasian High Arctic, with decreasing temperature and moisture eastward, may provide a gross control on this pattern through colder glacier thermal structure, limiting basal drainage on the thinner ice masses in particular.
The flow of a polythermal glacier: McCall Glacier, Alaska, U.S.A.
Authors: Rabus B.T. , Echelmeyer K. A.
Published: September 2017

We have analyzed the flow of polythermal McCall Glacier in Arctic Alaska. Using measurements of surface velocity from the 1970s and 1990s, together with measurements of ice thickness and surface slope, we have investigated both the present flow and seasonal and long-term flow variations. Our analysis of the present flow reveals that (i) longitudinal stress coupling is important along the entire length of the glacier, and (ii) there is significant basal sliding beneath a 2 km long section of the lower glacier. This sliding exists year-round and it accounts for more than 70% of the total motion there. We have developed a numerical model which shows that such a sliding anomaly causes an asymmetric decrease in ice thickness. Accompanying this decrease in thickness is a decrease in surface slope at the center of the anomaly and an increase in slope up-glacier from it. Both effects are reflected in the observed surface profile of McCall Glacier.The longitudinal stress-coupling length of McCall Glacier is three times the ice thickness, almost twice that typical of temperate glaciers. This is a direct effect of lower strain rates, which themselves are associated with the smaller mass-balance gradients of Arctic and continental glaciers. Long-term variations in surface velocity between the 1970s and 1990s are explained solely by the effects of changes in glacier geometry on the deformational flow contribution. This means that long-term variations in the spatial patterns of longitudinal stresses and basal sliding must have been small. Seasonally, Velocities reach their annual minimum in spring and increase during the short summer nick season by up to 75% above mean winter values. However, the extra motion associated with the period of elevated velocities is only about 5% of the total annual motion. The speed-up is due to an increase in basal sliding. This implies that most of the glacier bed is at the melting point. The zone a affected by the melt-season speed-up extends well up-glacier of any moulins or other obvious sources for melt water at the bed.
Measurements of ice deformation at the confluence area of Unteraargletscher Bernese Alps, Switzerland
Authors: Gudmundsson G. Hilmar , Iken Almut , Funk Martin
Published: September 2017

An experimental study of ice deformation at the confluence area of Unteraargletscher, Bernese Alps, Switzerland, has been carried out. Surface velocities were measured by repeatedly surveying stakes and with the use of remote-sensing methods. The variation of the vertical strain rates with depth was measured in boreholes. The confluence center line is subjected to longitudinal horizontal extension, which is exceeded in magnitude by a concomitant transverse compression. Vertical strain rates change from positive (extension) at the surface to negative (compression) in the lowest layers of the glacier.
Width and length scaling of glaciers
Authors: Bahr David B.
Published: September 2017

An analysis of hundreds of mountain and valley glaciers in the former Soviet Union and the Alps shows that characteristic glacier widths scale as characteristic glacier lengths raised to an exponent of 0.6. This is in contrast to most previous analyses which implicitly of explicitly assumed scaling exponents of either 0 or 1. The exponent 0.6 implies that average glacier widths are proportional to average glacier thicknesses. Although this seems to suggest V-shaped glacier valleys, the linear width-thickness relationship is not inconsistent with parabolic valley cross-sections, because the characteristic (or average) width of a glacier depends on many other aspects of channel and glacier morphology, including variations in the channel width with distance up- and downstream.
Glaciological studies at Siple Station (Antarctica): potential ice-core paleoclimatic record
Authors: Mosley-Thompson E. , Dai J. , Thompson L. G. , Grootes P. M. , Arbogast James K. , Paskievitch J. F.
Published: September 2017

The quality and utility of the records of oxygen-isotopic abundances, dust concentrations and anionic concentrations preserved in the ice at Siple Station (75°55′ S, 84° 15′ W) are assessed from four shallow (20 m) cores. The combination of high accumulation (0.56 m a−1 w.e.) and low mean annual temperature (—24°C) preserves the prominent seasonal variations in δ18Ο which are very spatially coherent. Sulfate concentrations vary seasonally and, in conjunction with δ18Ο, will allow accurate dating of deeper cores from Siple Station. The concentrations of insoluble dust are the lowest measured in Antarctica, making Siple Station an excellent location to examine large increases in atmospheric tubidity.

The seasonal variations and annual fluxes of the anions are examined for the last two decades (AD 1966–85) with regard to probable sources. An unusually high sulfate flux in 1976 may reflect the February 1975 eruption of Mount Ngauruhoe, New Zealand. No annual signal in nitrate concentration is confirmed and no unusually high nitrate fluxes support the suggestion of nitrate production by large solar flares. However, nitrate flux is higher for the latter half of the 1970s and early 1980s, possibly reflecting the recent loss of stratospheric ozone.

Finally, comparison of the δ18O record with available surface-temperature data (AD 1957–85) reveals that multi-year trends along the western coast of the Antarctic Peninsula are recorded at Siple. More importantly, comparison with areally weighted temperature reconstructions suggests that the δ18Ο record may reflect larger-scale, persistent trends in the high southern latitudes. The strong spatial coherence of the preserved records, the potential for accurate dating, and possible relevance to larger-scale processes make Siple Station an excellent site for paleoenvironmental reconstruction from ice cores.
Equilibrium oxygen- and hydrogen-isotope fractionation between ice and water
Authors: Lehmann M. , Siegenthaler U.
Published: September 2017

We have performed high-precision measurements of the isotope-fractionation factors between ice and water. Ice was grown from a stirred water mass on a cooling plate. The freezing velocity was varied, keeping the stirring rate of the water constant, so that the equilibrium fractionation factors could be determined by extrapolating to zero freezing velocity. The resulting values are

∝ (18O/16O) = 1.00291 ± 0.00003 and

∝ (D/H) = 1.0212 ± 0.0004.

Non-equilibrium freezing of lake and sea ice is briefly discussed as well as the significance of our results for the deuterium excess in polar precipitation.
The composition of the englacial and subglacial component in bulk meltwaters draining the Gornergletscher, Switzerland
Authors: Tranter Martyn , Raiswell Robert
Published: September 2017

A new method of hydrograph separation for bulk meltwaters draining Alpine glaciers is proposed. It is based on the two-component (subglacial and englacial) mixing model of Collins (1978), but allows the composition of the subglacial component to vary between ascending and descending lines of the hydrograph. The mean englacial component can be derived from linear relationships between sulphate concentrations and other ions in bulk meltwaters. On certain occasions during the ablation season, the maximum concentration of ions in the subglacial component can be determined from the linear relationship between bulk meltwater sulphate concentrations and discharge. The bulk discharge is then a direct measure of the mass fraction of the englacial component. At maximum discharge, the contribution of the subglacial component approaches zero, which has implications for the storage and mixing of waters in subglacial reservoirs. Further, the subglacial component is not of constant composition, and may itself be a mixture of dilute supraglacial and concentrated subglacial water.
Glacier dynamics in the Susitna River basin, Alaska, U.S.A.
Authors: Clarke Ted S.
Published: September 2017

The dynamics of the glaciers which form the headwaters of the Susitna River in central Alaska exhibit several interesting features, including a spectrum of surge-type behavior. A difference between balance flux and actual down-glacier transport, which is taken to be an indicator of surge behavior, shows West Fork Glacier and two tributaries of Susitna Glacier to be surge-type of varying strengths, while East Fork Glacier and one tributary of Susitna Glacier to be non-surge-type. The main trunk of Susitna Glacier and its two unstable tributaries surge simultaneously with a period estimated to be 50–60 years. Having last surged in 1951–52, its next surge should be expected sometime in the first decade of the next century. West Fork Glacier last surged in about 1935 and again in 1987–88, indicating a similar surge period of about 50 years. Significant seasonal velocity variations were observed during the glacier’s quiescent phases, with increases of 30–100% over background occurring early in the melt season. In some cases, the annual minimum occurred during late summer, implying that basal motion contributes measurably to winter velocity on at least some glaciers in the area. Events of rapid motion lasting a day or so also occur occasionally during the melt season and may account for brief velocity increases of up to 300%.
Analysis of glacier facies using satellite techniques
Authors: Williams Richard S. , Hall Dorothy K. , Benson Carl S.
Published: September 2017

The different snow and ice types on a glacier may be subdivided according to the glacier-facies concept. The surficial expression of some facies may be detected at the end of the balance year by the use of visible and near-infrared image data from the Landsat multispectral scanner (MSS) and thematic mapper (TM) sensors. Ice and snow can be distinguished by reflectivity differences in individual or ratioed TM bands on Brúarjökull, an outlet glacier on the northern margin of the Vatnajökull ice cap, Iceland. The Landsat scene shows the upper limit of wet snow on 24 August 1986. Landsat-derived reflectance is lowest for exposed ice and increases markedly at the transient snow line. Above the slush zone is a gradual increase in near-infrared reflectance as a result of decreasing grain-size of the snow, which characterizes drier snow. Landsat data are useful in measuring the areal extent of the ice facies, the slush zone within the wet-snow facies, the snow facies (combined wet-snow, percolation and dry-snow facies), and the respective positions of the transient snow line and the slush limit. In addition, fresh snowfall and/or airborne contaminants, such as soot and tcphra, can limit the utility of Landsat data for delineation of the glacier facies in some cases.
Observations on Submerged Glacial Ice in McMurdo Sound, Antarctica
Authors: Oliver John S. , O'Connor Edmund F. , Watson Daniel J.
Published: September 2017

Several large submerged ice masses are described from along western McMurdo Sound, Antarctica. The most important discovery is that Cape Chocolate and the adjacent island that form Salmon Bay are large, grounded ice masses mounted with morainal sediment. Both features are probably remnants of a past expansion of the Ross Ice Shelf. As such, their strata and potential temporal markers may help to unravel the glacial geological chronology of McMurdo Sound. The island was connected to Cape Chocolate during the early British Antarctic expeditions and split away between 1908 and 1956. Large sections of the Ross Ice Shelf have broken out along western McMurdo Sound several times since 1908. Ice walls grounded in shallow water were only observed near large receding ice masses. The location of these walls also corresponds to the recent calving pattern of the Ross Ice Shelf.
Thoughts on Ogive Formation
Authors: Posamentier Henry W.
Published: September 2017

The formation of ogives is examined from a structural point of view. It is suggested that the dark bands represent large-crystal, bubble-free ice which was transported from near the glacier base up toward the glacier surface by the processes of folding and/or reverse faulting due to compressive flow at the base of an ice fall, while the white bands represent relatively small-crystal, bubble-rich near-surface ice. The variation in compression to account for periodic folding and/or reverse faulting is explained by seasonal variation in flow velocity through an ice fall.
Results From The Amery Ice Shelf Project
Authors: Budd W. F. , Corry M. J. , Jacka T. H.
Published: September 2017

The major results from a comprehensive study of the Amery Ice Shelf are presented, following the work of a wintering expedition in 1968 and supplemented by further measurements during the summer seasons of 1969 to 1971. The Programme included ice-core drilling, oversnow surveys for ice movement and optical levelling, ice-thickness sounding, and measurements of snow accumulation. The new data obtained provide the basis for a more accurate assessment of the mass balance and dynamics of the ice shelf than was possible from the earlier surveys.

The results indicate a substantial growth of basal ice under the ice shelf inland where the ice thickness is greater than 450 m. Further towards the ice front the high strain thinning is approximately balanced by the horizontal ice advection.

The velocity distribution over the ice shelf is primarily governed by a substantial surface slope towards the ice front and high restraining shear stress along the sides.
Large-Scale Numerical Modelling of the Antarctic Ice Sheet
Authors: Budd W.F. , Smith I.N.
Published: September 2017

A large-scale dynamic numerical model of the Antarctic ice sheet has been developed to study its present state of ice flow and mass balance as well as its response to long-term changes of climate or sea-level.

The flow of ice over a two-dimensional grid is determined from the ice thickness, the basal shear stress, the bedrock depth, and ice flow parameters derived from velocities of existing ice sheets. The change in ice thickness with time is governed by the continuity equation involving the ice flux divergence and the ice accumulation or ablation. At the ice sheet seaward boundary, a floating criterion and floating ice thinning rate apply. Bedrock depression with a time-delayed response dependent on the history of the ice load is also included.

A 61 × 61 point grid with 100 km spacing has been used to represent the ice-sheet surface, bedrock, and accumulation rate. The model has been used to simul a te the growth of the present ice sheet and i ts reaction to changes of sea-level, bedrock depression, accumulation rate, ice flow parameters, and the iceshelf thinning rate.

Preliminary results suggest that the present ice sheet is not in equilibrium but rather is still adjusting to changes of these parameters.
Studies of the Antarctic and Present-Day Concepts of Global Glaciation
Authors: Chizhov O.P. , Kotlyakov V.M.
Published: September 2017

Antarctic researches of the last decades have provided new facts which have made scientists change their ideas. The researches have shown a great difference between the history of the Antarctic and the northern hemisphere glaciation. The former is very old and stable, while the latter was ephemeral. An analogous one to the Antarctic ice sheet in the northern hemisphere is the Greenland inland ice. Both ice sheets are of continental-insular type; the Pleistocene ice sheets were of continental type proper. Icethickness measurements showed the topography of the bed under Antarctic ice and revealed a special type of ice sheet lying partly on the sea-floor: the West Antarctic continental-marine ice sheet. Such ice sheets could exist in the northern hemisphere too. They were especially unstable and their formation and destruction could serve as a triggering mechanism in alternating glacials and interglacials. The main concept is: all the great climatic variations during the Pleistocene were glacioclimatic ones where the feedback mechanism was the most important factor. But there are many details which are uncertain. The Antarctic and Greenland ice sheets are the key regions to research so that problems of glacioclimatology could be solved.
Pine Island Glacier and Its Drainage Basin: Results From Radio Echo-Sounding
Authors: Crabtree R.D. , Doake C.S.M.
Published: September 2017

Retreat of the grounding lines of West Antarctic ice streams may lead to the collapse of the West Antarctic ice sheet. Pine Island Glacier has been pinpointed as an ice stream in which rapid retreat is likely, especially as it is not buttressed by an ice shelf. Radio echo-sounding flights have produced a longitudinal thickness profile for the glacier. The ice presently rests on a bedrock sill which may play a crucial role in controlling the position of the grounding line. The profile can be fitted to a steadystate model but this alone is not adequate to determine steady- or non-steady-state behaviour. Landsat images show that the ice front undergoes periodic calving. Mass-balance calculations suggest that accumulation in the catchment may exceed ablation by a factor of 2. However, accumulation data are poor and there is no firm evidence of a build-up of ice within the Pine Island Glacier drainage basin.
Mechanical Behaviour of Antarctic Ice
Authors: Duval P. , Le Gac H.
Published: September 2017

The mechanisms of Antarctic ice deformation are discussed. Diffusional flow (Nabarro-Herring or Coble creep) seems to dominate creep for the first 905 m near Dome C. Formation mechanisms of single-maximum fabrics are examined. Dislocation creep does not explain the preferred c-axis orientation observed in the Antarctic ice sheet. The quantitative effects of crystallographic orientation on strain-rate are given. The activation energy for dislocation creep was found to be 78 kJ mol−1 between -7.2°C and -30°C. Rate-limiting mechanisms are discussed.
Finite Element Analysis of Calving From Ice Fronts
Authors: Fastook James L. , Schmidt William F.
Published: September 2017

The Antarctic ice sheet has almost no net annual ablation on its surface, so most mass losses are by iceberg calving along its perimeter, which may be either grounded in shallow water or floating in deep water. An ice cliff forms along the perimeter in both cases. Wave action undercuts ice margins in the tide-water zone along beaches, and causes coastal calving if the rate of undercutting compares with the forward ice velocity. If the ice velocity is sufficiently greater, the ice sheet advances into deeper water and becomes a float at depths of 200 to 300 m (Robin 1979). A floating ice shelf then forms and icebergs calve along the ice front. Iceberg calving along this ice front may be due to several causes (Holdsworth 1977,Robin 1979). Since iceberg calving, either from ice shelves or in the tidewater zone of beaches between ice shelves, is the principal ablation mechanism of the Antarctic ice sheet, it is important to understand calving dynamics quantitatively. This paper presents the results of a finite-element examination of calving along floating margins of the ice sheet.
On the Joint Interpretation of Total Gas Contents and Stable Isotope Ratios in Ice Cores
Authors: Jenssen D. , Radok U.
Published: September 2017

Total gas contents of ice cores together with temperature estimates derived from 180/160 and 2D/1H values have been used to separate topographic and climatic changes in the deposition temperature history of the ice (Raynaud 1977, Jenssen 1978). The most recent analysis (Jenssen in press) made use of two linear relationships (one purely empirical, the other established empirically but subsequently justified theoretically) to derive an algebraic expression for the change of surface temperature with ice-sheet elevation. A physical line of reasoning is presented which instead infers the climatic history from changes in the surface topography of the ice sheet. This suggests that a complete interpretation of core data must go hand in hand with ice-sheet modeling.
Glaciological Investigations in the Frontal Zone of the Filchner and Ronne Ice Shelves
Authors: Kohnen H.
Published: September 2017

In the 1979–80 field season, a site survey was carried out in the southern Weddell Sea for the construction of a wintering station. The survey comprised glaciological investigations on the Filchner and Ronne ice shelves, such as ice movement, deformation, ice thickness, calving, accumulation, and snow temperature measurements which are relevant to mass-balance studies. Along with the investigations on the ice, oceanographical and bathymetrical observations were carried out along the ice front. The field data and observations lead to assumptions about the advance of the ice shelf as well as about the mass loss at the frontal zone due to calving and bottom melting. The ice-front velocity at 50°W is about 1 070 m a−1 and the bottom melting is estimated to be 3.2 m a−1 at 20 km south-west of the ice front.
The Volcanic Record of Antarctic Ice Cores: Preliminary Results and Potential for Future Investigations
Authors: Kyle P. , Palais J. , Delmas R.
Published: September 2017

Occurrences of tephra layers in four ice cores from Antarctica are reviewed. A new tephra, informally named the Vostok tephra, is described from a depth of 100.85 m in an ice core from Vostok station. Ice associated with four tephra layers at depths between 1390 and 1450 m in the Byrd station ice core shows increased levels of sulfate and nitrate which correlate well with peaks in particle concentrations. High levels of sulfate and nitrate are also associated with the Vostok tephra.

Tephra offer great potential as stratigraphic markers and should be useful in providing time planes as well as assisting in correlation between widely spaced ice cores.
Electrical Behaviour of Antarctic Ice and Radio Echo Layers in Ice Sheets
Authors: Maccagnan M. , Duval P.
Published: September 2017

Static electrical conductivity (SEC) and dielectric measurements were made on Antarctic ice cores at -15°C. The observed behaviour is markedly different from that of temperate glacier ice. The influence of impurities on the electrical properties of polar ice is discussed. Variations of SEC do not appear to be correlated with variations in the relaxation frequency when the loss factor is maximal. Different growth conditions coupled to ageing effects in the first few metres of the firn may explain variations in the electrical properties along an ice core. Moreover, it is suggested that the relaxation frequency increases as the specific surface area increases. Defects are produced in the firn near the surface and may be retained in the subsequent ice. Discontinuous changes in the high-frequency electrical conductivity between adjacent layers can induce internal reflections of radio waves within ice sheets.
Structural Studies Of Bare Ice Near The Allan Hills, Victoria Land, Antarctica: A Mechanism Of Meteorite Concentration
Authors: Nishio Fumihiko , Azuma Nobuhiko , Higashi Akira , Annexstad John O.
Published: September 2017

Structural laboratory studies were made of ice collected at the surface and from a shallow bore hole in the bare ice near the Allan Hills, Victoria Land, Antarctica. The results obtained were combined with glaciological survey data to describe the mechanism of accumulation of meteorites by ice flow in a marginal area of the East Antarctic ice sheet. The age of the bare ice, approximately 20 ka, was estimated by fabric characteristics and grain size of the ice. This conforms to the minimum value of the terrestrial age of the meteorites found in the same area. The several hundred meteorite finds concentrated in the bare-ice area can be explained by an expanded catchment area during a previous ice age, or by a correction factor for the estimate of the influx rate of meteorite fall, or more probably by a combination of both.
Snow Stratigraphic Studies At Dome C, East Antarctica: An Investigation Of Depositional and Diagenetic Processes
Authors: Palais J. M. , Whillans I. M. , Bull C.
Published: September 2017

The increased interest in past climatic changes, as revealed by studies of long ice cores from polar ice sheets, has stressed the need for a better understanding of the development of the stratigraphic record preserved in these cores. This paper presents some results of surface investigations at Dome C (74°30'S, 123°10'E), East Antarctica, carried out in austral summers 1978-79 and 1979-80. An explanation is presented of the snow stratigraphy, in terms of depositional and post-depositional processes, that is supported by detailed accumulation measurements at stakes and by snow-pit studies. Temporal and areal variability of snow accumulation are investigated to determine how representative the results interpreted from a single core might be for the Dome C region. Finally, the reliability of several stratigraphic methods for defining annual layers is assessed.

Snow-pit studies show that major depositional features are preserved with depth. Visible annual strata at Dome C are composed of thin, hard crusts overlying thicker layers of soft to medium-hard snow. Low density depth-hoar layers, when they occur, are usually found below the thin, hard crusts. Depth profiles of gross 8-radioactivity and of microparticles concentration exhibit annual cyclicity which, together with the detailed visible stratigraphy, can be used to assign dates to the layers.
Interannual Sea-Ice Variations and Sea-Ice/Atmosphere Interations in the Southern Ocean, 1973–1975
Authors: Parkinson Claire L. , Cavalieri Donald J.
Published: September 2017

Examination of satellite-derived 1973–75 sea-ice concentrations for the Southern Ocean and comparison with 1 000 mbar temperatures and sea-level pressures reveal considerable Interannual variability in both the ice and atmospheric fields plus strong suggestions of ice/atmosphere interconnections. The mean position of the ice edge undergoes a strong yearly cycle that lags the cycle of the zonally-averaged temperatures by about one month, but the mean ice edge does not contain small-term fluctuations or interannual variability to the same extent as either the temperature or the pressure. Regionally, the ice varies much more noticeably from year-to-year, with the interannual contrasts showing strong spatial dependence in all months and strong spatial coherence in winter. These are illustrated by selected maps of monthly differences in ice concentrations between 1973 and 1974 and between 1974 and 1975. It is shown that the interannual ice differences can, in many cases, be attributed to the Interannual differences in the positioning and intensity of cyclonic and anticyclonic systems.
Glacier Inventory of James Ross and Vega Islands, Antarctic Peninsula
Authors: Rabassa Jorge , Skvarca Pedro , Bertani Luis , Mazzoni Elizabeth
Published: September 2017

This paper presents the results of the glacier Inventory of James Ross and Vega islands based on topographic map sheets at 1:250 000 scale, Landsat multi-spectral scanner imagery in bands 4 and 7 at the same scale, and oblique air photographs obtained in 1979–80. Work was completed following the methodology proposed by the Temporary Technical Secretariat of the World Glacier Inventory. This is the first such inventory carried out in Antarctica.
Flow Of Ice Sheets In The Vicinity Of Subglacial Peaks
Authors: Robin G. de Q. , Millar D. H. M.
Published: September 2017

Although changes of surface slope across a subglacial peak can be explained at least semi-quantitatively on a two-dimensional basis in terms of gradients of longitudinal and shear stresses along a flow line, we lack appreciation of flow in the third dimension which may tend to cause lower layers to flow around rather than over a sharp peak. This paper collects and surveys evidence relevant to flow in the third dimension and discusses the processes involved, particularly the evidence from radio-echo layering, and also discusses possible reasons for the lack of radio-echo layers near the base of the Antarctic ice sheet.
The Unsteady State of The Ross Ice Shelf (Abstract only)
Authors: Bentley Charles R.
Published: September 2017

According to our present picture, the Ross Ice Shelf is subject to relatively rapid changes, perhaps constantly out of steady state, but not undergoing a long-term secular change. Recent supporting evidence comes from a flow band of ice extending from the edges of Beardmore Glacier as far as Nimrod Glacier. The boundaries of that band and of ice stemming from several individual glaciers within it have been traced on airborne radar records. Using measurements made as part of the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS) program, mass-flux variations along the bands have been calculated. The band from Nimrod Glacier, a major outlet glacier from the East Antarctic inland ice sheet, shows no significant deviations from zero for the sum of thence thickness change rate ∂H/∂t and bottom melt rate. ḃH. We interpret this to mean that ∂H/∂t and ḃH are separately small. Significant flux variations in the entire flow band are then attributed to relatively large variations in input flux from the alpine glaciers of the Transantarctic Mountains, and from zones between the glaciers. Although flux variations are not coherent between individual glacier bands, the average strengths of internal reflections (from bottom crevasses and/or included moraine), exhibit a semi-coherent variation with a period of 400 a that correlates with 180 variations in ice cores from Dome C and Byrd station.
A Preliminary Model of Holocene Retreat and Thinning of Ice Stream E, West Antarctica (Abstract only)
Authors: Lingle Craig S. , Bentley Charles R.
Published: September 2017

A preliminary numerical model of ice-stream grounding-line retreat and thinning as a function of eustatic sea-level rise has been developed. Grounding-line retreat is computed using the methods of Thomas and Bentley (1978). The change in thickness along the ice-stream profile is found by solving the equation of continuity in two dimensions during the time intervals corresponding to increments of grounding-line retreat. The model was applied to ice stream E, West Antarctica, assuming that the ice stream was initially grounded to the edge of the Ross Sea continental shelf.
Radar Studies of Internal Layers and Bottom Topography at Dome C, East Antarctica (Abstract only)
Authors: Jezek Kenneth C. , Shabtaie Sion , Bentley Charles R.
Published: September 2017

Extensive and detailed radar surveys at Dome C were conducted during the 1978–79 and 1979–80 austral field seasons by groups from the University of Wisconsin. Measurements were conducted within a 10 × 10 km grid centered approximately on the Dome C camp (some additional studies were carried out as far as 20 km from the camp) and involved profiling of internal layers and bottom topography. In addition, a new digital recording system for the radar was used during the first season and has yielded interesting results on internal layers near the French bore hole.

Analysis of these data has produced a local map of bottom topography showing generally rough terrain. In particular, there is a rapid deepening of the bottom topography (about 500 m over 2 km) just grid south-west of the camp. Internal layers were found to be discontinuous on a scale of tens of meters. The deepest internal layers were detected at depths of about 2 500 m although a set of remarkable layer-like returns were observed about 50 to 100 m above the interpreted base of the ice. (It is not yet clear whether these returns represent reflections from layers internal to the ice or whether they are reflections and diffractions associated with the rough terrain.) In addition the processed digital records show an abrupt decrease in the reflection strength of internal layers at about 1 700 m. Because the digitally recorded data were collected at only one site, we reserve concluding that this observation is characteristic of the entire Dome C area until more of the photographically recorded data can be reduced.