bluuebunny/crossref_metadata_2025_split huggingface dataset:
Short-term velocity and water-pressure variations down-glacier from a riegel, Storglaciären, Sweden
Authors: Hanson Brian , LeB. Hooke Roger , Grace Edmund M. 
Published: September 2017

AbstractDuring the 1991 94 summer held seasons, time-correlated measure-merits of water pressure and surface speed were made over and down-glacier from a major riegel on Storglaciären, Sweden. Measurements were made at sub-hourly time-scales in order to discern details in the diurnal cycle. Large water-input events, typically associated with rain storms, produced coherent, lagged surface-velocity responses that could be understood in terms of till deformation or decoupling, and these have been discussed elsewhere. The consequences of smaller diurnal water-pressure events w ere more enigmatic, in that acceleration of ice flow generally preceded the onset of the local water-pressure rise. From consideration of these data and other work done on the hydrology of Storglaciären, we infer that the ice in this area is generally pushed from behind via a relaxation in extensional strain across the riegel. Hence, accelerations occur in response to increases in water pressure that occur up-glacier and that precede local water-pressure rises. In addition, following a period of large storm events, surface speeds became more spatially coherent and were in phase with the diurnal water-pressure cycle. This suggests that the large water-pressure events lead to a spatially more homogeneous subglacial drainage system. Sliding laws need to take into account such temporal changes in spatial coherence of the subglacial drainage system.
Comparison of a three-dimensional model for glacier flow with field data from Haut Glacier d’Arolla, Switzerland
Authors: Hubbard Alun , Blatter Heinz , Nienow Peter , Mair Douglas , Hubbard Bryn 
Published: September 2017

AbstractA three-dimensional, finite-difference model based on a first-order solution of the ice-flow equations is applied to Haut Glacier d’Arolla, Switzerland. The numerical model successfully converges at horizontal resolutions down to 70 m, so a number of detailed comparisons with field data can be made. Modelled surface velocities with no basal sliding component are compared with surface velocities observed on the glacier over four different time periods. The best fit is achieved with over-winter surface velocities (R2 = 0.75) using a rate factor, A, in Glen’s flow law of 0.063 a−1 bar−3. Surface zones of maximum computed effective stress display a high level of coincidence with observed crevassing, the orientation of which is successfully predicted by the direction of the tensile component of the computed principal surface stress. Comparison of the relative magnitude and direction of computed principal stresses with principal strains measured at the ice surface also correspond closely. In an attempt to simulate the observed annual velocity distribution within a cross-section of the glacier tongue, we incorporate two basal-motion patterns into the model. By treating net annual ice motion as a time-weighted composite of three separate flow situations: normal sliding, enhanced sliding and no sliding, we are able to reproduce the key features of the observed cross-sectional ice and basal slip velocity distributions. These experiments indicate there may be substantial decoupling taking place along an elongated narrow zone at the bed of Haut Glacier d’Arolla and that this decoupling interacts in a complex manner with the englacial stress and strain field.
Site information and initial results from deep ice drilling on Law Dome, Antarctica
Authors: Morgan V.I. , Wookey C.W. , Li J. , van Ommen T.D. , Skinner W. , Fitzpatrick Μ.F. 
Published: September 2017

AbstractThe aim of deep ice drilling on Law Dome, Antarctica, has been to exploit the special characteristics of Law Dome summit, i.e. low temperature and high accumulation near an ice divide, to obtain a high-resolution ice core for climatic/environmental studies of the Holocene and the Last Glacial Maximum (LGM). Drilling was completed in February 1993, when basal ice containing small fragments of rock was reached at a depth of 1196 m. Accurate ice dating, obtained by counting annual layers revealed by fine-detail δ18О, peroxide and electrical-conductivity measurements, is continuous down to 399 m, corresponding to a date of AD 1304. Sulphate concentration measurements, made around depths where conductivity tracing indicates volcanic fallout, allow confirmation of the dating (for Agung in 1963 and Tambora in 1815) or estimates of the eruption date from the ice dating (for the Kuwae, Vanuatu, eruption ~1457). The lower part of the core is dated by extrapolating the layer-counting using a simple model of the ice flow. At the LGM, ice-fabric measurements show a large decrease (250 to 14 mm2) in crystal size and a narrow maximum in c-axis vertically. The main zone of strong single-pole fabrics however, is located higher up in a broad zone around 900 m. Oxygen-isotope (δ18O) measurements show Holocene ice down to 1113 m, the LGM at 1133 m and warm (δ18O) about the same as Holocene) ice near the base of the ice sheet. The LGM/Holocene δ18O shift of 7.0‰, only ~1‰ larger than for Vostok, indicates that Law Dome remained an independent ice cap and was not overridden by the inland ice sheet in the Glacial.
Response of the longwave radiation over melting snow and ice to atmospheric warming
Authors: Meesters Antoon , van den Broeke Michiel 
Published: September 2017

AbstractParameterizing the incoming longwave radiation L ↓ in terms of the fourth power of the absolute temperature at the reference height is used in glaciology for several purposes. In this paper, the validity of this kind of parameterization is investigated for the Greenland ice sheer, both by observations and by numerical simulation with a meso-scale model, It is found that such a parameterization severely underestimates the increase of L ↓ in response to large-scale warming in an area where surface melting is important. This is explained by the systematic influence that is exerted on the shape of the temperature profiles by surface melting.
Seasonal variations in the properties and structural composition of sea ice and snow cover in the Bellingshausen and Amundsen Seas, Antarctica
Authors: Jeffries M. O. , Morris K. , Weeks W.F. , Worby A. P. 
Published: September 2017

AbstractSixty-three ice cores were collected in the Bellingshausen and Amundsen Seas in August and September 1993 during a cruise of the R.V. Nathaniel B. Palmer. The structure and stable-isotopic composition (18O/16O) of the cores were investigated in order to understand the growth conditions and to identify the key growth processes, particularly the contribution of snow to sea-ice formation. The structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the Bellingshausen Sea in March 1992 are reassessed. Frazil ice and congelation ice contribute 44% and 26%, respectively, to the composition of both the winter and summer ice-core sets, evidence that the relatively calm conditions that favour congelation-ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil-ice growth and pancake-ice formation. Both frazil- and congelation-ice layers have an av erage thickness of 0.12 m in winter, evidence that congelation ice and pancake ice thicken primarily by dynamic processes. The thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover. Snow-ice layers have a mean thickness of 0.20 and 0.28 m in the winter and summer cores, respectively, and the contribution of snow ice to the winter (24%) and summer (16%) core sets exceeds most quantities that have been reported previously in other Antarctic pack-ice zones. The thickness and quantity of snow ice may be due to a combination of high snow-accumulation rates and snow loads, environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow/ice interface, and bottom melting losses being compensated by snow-ice formation. Layers of superimposed ice at the top of each of the summer cores make up 4.6% of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice. The accumulation of superimposed ice is evidence that melting in the snow cover on Antarctic sea-ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass.
The Dominion Range Ice Core, Queen Maud Mountains, Antarctica - General Site and Core Characteristics with Implications
Authors: Mayewski Paul A. , Twickler Mark S. , Lyons Wm Berry , Spencer Mary Jo , Meese Debra A. , Gow Anthony J. , Grootes Pieter , Sowers Todd , Watson M.Scott , Saltzman Eric 
Published: September 2017

AbstractThe Transantarctic Mountains of East Antarctica provide a new milieu for retrieval of ice-core records. We report here on the initial findings from the first of these records, the Dominion Range ice-core record. Sites such as the Dominion Range are valuable for the recovery of records detailing climate change, volcanic activity, and changes in the chemistry of the atmosphere. The unique geographic location of this site and a relatively low accumulation rate combine to provide a relatively long record of change for this potentially sensitive climatic region. As such, information concerning the site and general core characteristics are presented, including ice surface, ice thickness, bore-hole temperature, mean annual net accumulation, crystal size, crystal fabric, oxygen-isotope composition, and examples of ice chemistry and isotopic composition of trapped gases.
Icequakes On Ekström Ice Shelf Near Atka Bay, Antarctica
Authors: Osten-Woldenburg H. Von Der 
Published: September 2017

AbstractTwo seismic arrays recorded in an 11 month field experiment in 1985 the seismicity of Ekström Ice Shelf in the area of an ice rumple and an inlet, situated respectively about 10 km north-west and 7 km north of the German Antarctic station Georg von Neumayer (lat. 70°37′S., long. 08°22′W). Most of the focal depths of the icequakes considered until now are in the range 5–9 m; the ice-rumple area shows extremely high seismic activity. Tensile fracture is the most frequent fault mechanism, although there are a few shear-fracture events. The ice rumple’s seismicity provides information on the dynamics of the ice shelf in this area. A comparison of this time-dependent seismicity with tides suggests that most of this seismicity is induced by tides. The most active period of this seismicity starts at the beginning of low tide and ends at low tide. The location of the epicentres of icequakes recorded at that time and the digital recording on tapes of the seismicity without interruption for 396 h shows a jerky vertical movement of the ice shelf in response to tides; this can be interpreted as a kind of “grater effect”, especially at the southern ice-rock boundary of the ice rumple.The seismicity in the inlet is much less and tensile fracture seems to be the only fault mechanism.
On the Numerical Solution of Stefan Problems in Temperate Ice
Authors: Hutter Kolumban , Zryd Amédé , Röthlisberger Hans 
Published: September 2017

AbstractFreezing processes in temperate ice consisting of a mixture of pure ice with water inclusions are studied for the case that the initial amount of moisture content is uniform. By introducing a cold source at the center of the ice specimen, the cold front propagates outwards leaving behind pure cold ice with a temperature distribution dictated by the exact set-up of the cold source. The speed of the front is directly related to the water content of the temperate ice and depends essentially on the Stefan condition.Three types of initial and boundary conditions are considered and realized in uniaxial, cylindrical, and/or spherical symmetry: (1) a metallic core at a temperature below the freezing point is initially brought into contact with the ice and the system is left free to evolve; (2) the metallic core is kept at constant temperature below freezing; (3) Case (2) is repeated with an insulating air layer between the metallic core and the ice.
Jakobshavns Isbræ, West Greenland: Seasonal Variations in Velocity - or Lack Thereof
Authors: Echelmeyer Keith , Harrison William D. 
Published: September 2017

AbstractThe lower 80 km of the fast-moving Jakobshavns Isbræ, West Greenland, is subject to significant melting during the summer season. The melt water drains into large supraglacial rivers which pour into moulins or feed into beautiful supraglacial lakes, some of which are observed to drain periodically. Except for a few streams that drain directly off the margins of the ice sheet within the drainage basin of this glacier, the fate of this melt water is unknown. However, a localized upwelling of highly turbid water is often observed during the melt season in the fjord adjacent Io the terminal cliff of the glacier, indicating that water from some source does move along the glacier bed.As part of an investigation on the mechanisms of rapid flow on Jakobshavns Isbræ, measurements of surface velocity at several (∼25) locations along the ice stream at and below the equilibrium line were made in order to investigate the effects of this seasonally varying input of melt water on the speed of the glacier.No significant seasonal variation in speed was found at any location. This indicates that, unlike many other sub-polar and temperate glaciers, surface melt-water production does not affect the motion of this glacier on a seasonal basis, and, thus, does not cause a significant temporal variation in basal sliding. This finding has important ramifications on the mechanisms of flow for this ice stream.
Configuration of the Drainage System of Midtdalsbreen, Norway, as Indicated by Dye-Tracing Experiments
Authors: Willis Ian C. , Sharp Martin J. , Richards Keith S. 
Published: September 2017

AbstractDuring the summers of 1987 and 1988, 15 dye-tracer tests from a total of eight injection points were conducted in the ablation area of Midtdalsbreen, a northern outlet of Hardangerjokulen, southern Norway. The spatial and temporal patterns of water discharge, shapes of the dye-return curves, through-flow velocities, dye-recovery rates, dispersivities, and velocity/discharge relationships suggest the existence of distinct catchments beneath the eastern and western halves of the glacier which are characterized by different types of drainage sytem. Experiments on the eastern side were associated with high melt-water discharges and produced short-lived and highly peaked dye-return curves, fast through-flow velocities, high dye-recovery rates, low dispersivity values which decreased through the melt season, and a velocity/discharge relationship with an exponent of 1.0. Experiments on the western side were associated with low melt-water discharges and produced flat, extended dye-return curves which often displayed secondary peaks, slow through-flow velocities, low dye-recovery rates, high dispersivity values which increased during the melt season, and a velocity/discharge relationship with an exponent of 0.6. Comparison of observed through-flow velocities with values calculated theoretically using various hypothetical drainage-system structures suggests that water flows in a major sinuous conduit beneath the eastern half of the glacier and in a system of linked cavities beneath the western half. A model for the seasonal evolution of the whole drainage network is postulated which has important implications for temporal variations in subglacial water pressures and glacier-sliding velocity.
Drift-Ice Abrasion Marks along Rocky Shores
Authors: Dionne Jean-Claude 
Published: September 2017

AbstractDrift-ice abrasion marks are common along present-day rocky shorelines in cold regions. They include polished surfaces, scratches, striations, small grooves, and minor friction cracks. Most are found on relatively soft rocks like shale, sandstone, limestone, dolomite, and basalt, and occasionally on harder rocks like granite and gneiss. They were made by rock fragments frozen at the base of ice cover or by ice floes pushed onshore by wind or dragged along the bottom by waves, tides, and currents. They are found both in the modern and Pleistocene marine, lacustrine, and fluvial environments. Along the Hudson Bay eastern shoreline, these abrasion marks are superimposed on glacially polished and striated surfaces. Along the St. Lawrence Estuary, they are more common on boulders in the tidal zone. Characteristics of drift-ice abrasion marks are described and their significance is pointed out.
The Mathematical Model of Ice Sheets and the Calculation of the Evolution of the Greenland Ice Sheet
Authors: Grigoryan S.S , Buyanov S.A , Krass M.S , Shumskiy P.A 
Published: September 2017

AbstractAn evolutionary mathematical model of ice sheets is presented. The model takes into account the basic climatic and geophysical parameters, with temperature parameterization. Some numerical data derived from experiments on the Greenland ice sheet are received. At present the Greenland ice sheet is found to be in a state essentially different from a stationary one corresponding to modern climatic conditions.
Greenland ice-sheet surface properties observed by the Seasat-A scatterometer at enhanced resolution
Authors: Long David G. , Drinkwater Mark R. 
Published: September 2017

AbstractFor 3 months in 1978, the 14.6 GHz Seasat-A scatterometer (SASS) measured the normalized microwave-radar back-scatter coefficient of the Earth’s surface for the purpose of estimating near-surface vector winds over the ocean. SASS also made back-scatter measurements over land and ice regions; however, the application of this data has been limited due to the low (50 km) resolution of the measurements. Using a new technique for generating 6 km enhanced-resolution SASS images of the radar back-scatter characteristics, we present a study of the 1978 condition of the Greenland ice sheet. We derive a time-series of back-scatter images spanning the period July–September 1978. These images show the extent of summer ablation along the ice-sheet periphery. Using the data and models relating firn structure and condition to radar back-scatter characteristics, we delineate and map the seasonal extent of zones which appear to correspond to dry-snow, percolation, wet-snow, and ablation facies, over virtually the entire ice sheet. The results provide a base line with which to compare current (ERS-1) and future Greenland radar maps of snow-and ice-surface conditions.
TV-video observations of englacial voids in Storglaciären, Sweden
Authors: Allan Pohjola Veijo 
Published: September 2017

AbstractTV-video observations of four boreholes in Storglaciären, Sweden, revealed that 1.3% of the observed ice column was composed of englacial voids. The form of the voids is presented by photographs from the video. It is suggested that they are openings into englacial channels and cavities which were intersected during drilling. The observations further showed that about 11% of the ice column consisted of air-bubble-poor blue-ice inclusions. The observations show a relation between the blue-ice inclusions and the voids, which indicates that the origin and development of these features are coupled to each other. It is suggested that crevasses in the accumulation area are an important factor in this process.
Glacial land forms indicative of a partly frozen bed
Authors: Kleman Johan , Borgström Ingmar 
Published: September 2017

AbstractIn parts of the core area of the Fennoscandian ice sheet relict periglacial surfaces occur. The boundary between periglacial and glacial landscapes is often sharp and erosional, with fluting truncating patterned ground. The periglacial surfaces are older than the last ice sheet and are interpreted to represent patches of continuous frozen-bed conditions. A specific land-form assemblage occurs at the edges of such patches. On the basis of three type localities along the eastern rim of the Scandinavian mountains, four thermal boundary land forms, characteristic of the frozen-patch environment, are defined. Stoss-side moraines and transverse till scarps, not previously described, are interpreted to have formed in detachment zones where soil frozen to the glacier overlies thawed soil. The detachment zones are located where subglacial warming raises the phase-change surface (water/ice) until it intersects the soil layer up-and down-glacier from residual frozen-bed patches. The up-glacier ends of frozen-bed patches are located on topographic highs, but down-glacier the location of lateral sliding boundaries is occasionally independent of topography. The identification of relict surfaces and thermal boundary forms can improve paleo-ice-sheet models by providing estimates of the extent of frozen-bed conditions.
Brittle compressive failure of salt-water columnar ice under biaxial loading
Authors: Smith T. R. , Schulson E. M. 
Published: September 2017

AbstractThe brittle failure of saline columnar ice was investigated under biaxial compression at and −10° and −40°C over the range 0 ≤ RA < 1 where RA is the ratio of the intermediate to major principal compressive stress. The major principal stress and the intermediate (confining) stress were orthogonal to the columnar axes (type-A confinement); both stresses and the c-axes of the grains were co-planar. The results confirm earlier work by Hausier (1981) and Timco and Frederking (1983, 1986) on saline ice and follow similar behavior to fresh-water columnar ice found by Smith and Schulson (1993) and Frederking (1977). Failure stress and failure mode are sensitive to the confinement and two regimes of behavior are found: the failure stress first rapidly increases with RA in the range 0 ≤ RA < RT and then tends to decrease for RA > Rt. The transition stress ratio, Rt changes from ≈0.2 at −10°C to ≈0.1 at −40°C. The failure mode changes from axial splitting to shear faulting in the loading plane for 0 < RA < Rt. Above Rt failure changes to a combined mode of splitting across the columns and shear faulting out of the loading plane. The failure-stress envelope is of a truncated Coulomb-type. Damage studies show wing cracks and local fragmentation of grains involving the brine pockets. The results are explained in terms of Coulombic sliding and Hertzian crack mechanics.
Mass-balance estimates on the glacier complex Kongsvegen and Sveabreen, Spitsbergen, Svalbard, using radioactive layers
Authors: Lefauconnier Bernard , Hagen Jon Ove , Pinglot Jean Francis , Pourchet Michel 
Published: September 2017

AbstractAnalyses of total β and γ radioactivity have been carried out on ten shallow ice cores collected in 1989 and 1990 on Kongsvegen and Sveabreen, Spitsbergen. No peak of total β radioactivity, corresponding to the Chernobyl accident (1986), can be identified. Chernobyl layers were identified by 137Cs and 134Cs activities, and a signal from the nuclear tests in Novaya Zemlya (1961–62), was detected at one location by 137Cs activity. The mean net accumulation for the periods 1986–89 and 1962–88 was estimated for both glaciers. Using topographic data, the mean net ablation on Kongsvegen was estimated for the period 1964–90 and the mean net balances were calculated. The results agree with recent direct glaciological balance measurements. For the period 1986–89, the net accumulation was higher on Sveabreen than on Kongsvegen, and the equilibrium-line altitudes (ELA) were around 450 and 520 m a.s.l., respectively. Kongsvegen had a positive balance of 0.11 m w.eq. and Sveabreen was in equilibrium, whereas for the last 26 years the balance of Kongsvegen was slightly negative (−0.10 m w.eq.) and the ELA was around 560 m a.s.l.