bluuebunny/crossref_metadata_2025_split huggingface dataset:
Grain area as a statistical weight for polycrystal constituents
Authors: Gagliardini Olivier , Durand Gaël , Wang Yun 
Published: November 2007

AbstractBy using recently developed automatic instruments for fabric and texture measurements on ice, both the c-axis orientation and area of the individual crystals can be determined. Each grain can then be associated with its volume fraction, defined as a function of its measured cross-sectional area, to describe the microstructure of a poly-crystal. The relevance of this approach is studied using a three-dimensional microstructure obtained from the Potts model. In particular, the area weighting is compared to the classical implicit equal weighting used by glaciologists, which assumes that all the grains have the same volume fraction (discrete uniform distribution). Then, using the measurements of c-axis orientation and crystal size performed on the North Greenland Icecore Project (NorthGRIP) ice core, we compare area-weighted and equal-weighted fabrics. All these comparisons are made with respect to the orientation tensor. According to the ability of the Potts model to reproduce the ice microstructure, it is shown that using the grain cross-sectional area to infer its volume fraction improves the description of the actual polycrystal fabric.
The retreat of Jones Ice Shelf, Antarctic Peninsula
Authors: Fox Adrian J. , Vaughan David G. 
Published: November 2007

AbstractIn recent decades, several ice shelves along the Antarctic Peninsula have diminished in size as a result of climate warming. Using aerial photographic, satellite and survey data we document a similar retreat of Jones Ice Shelf, which was another small ice shelf on the west coast of the Antarctic Peninsula. This ice shelf was roughly stable between 1947 and 1969, but in the early 1970s it began to retreat and had completely disappeared by early 2003. Jones Ice Shelf has two ice fronts only a few kilometres apart and its retreat provides a unique opportunity to examine how different ice fronts retreat when subjected to similar climate forcing. We mapped the retreat of both the east and west ice fronts of Jones Ice Shelf and found that, although individual episodes of retreat may be related to particularly warm summers, the overall progress of retreat of the two ice fronts has been rather different. This suggests that in this case the course of retreat is controlled by the geometry of the embayment and location of pinning points as well as climatic events.
Fluctuation of the seasonal snowpack in a mountainous area of the heavy-snow district in the warm-temperate zone of Japan
Authors: Matsuura Sumio , Matsuyama Koji , Asano Shiho , Okamoto Takashi , Takeuchi Yoshitsugu 
Published: November 2007

AbstractThe seasonal snowpack and meteorological factors associated with the accumulation and ablation of the snowpack were monitored for 11 years in a mountainous area in the warm-temperate zone of Japan. No notable rise was observed in mean wintertime air temperature, but an increase was seen in the difference between the maximum and minimum air temperatures. Precipitation exhibited annual variability but no notable reduction over the measurement period. The length of the continuous snow-cover period increased slightly over the 11 years, but no trend in variability was observed. The maximum snow depth and maximum water equivalent of snow varied greatly from year to year, depending on the amount of snowfall. In a heavy-snow year, about 1600 mm of water, which is almost the mean annual precipitation for the whole of Japan, was found to be temporarily stored in the snowpack.
Glacier area changes in the Pumqu river basin, Tibetan Plateau, between the 1970s and 2001
Authors: Jin Rui , Li Xin , Che Tao , Wu Lizong , Mool Pradeep 
Published: November 2007

AbstractGlacier area changes in the Pumqu river basin, Tibetan Plateau, between the 1970s and 2001 are analyzed, based on the Chinese Glacier Inventory and ASTER images. A new glacier inventory is obtained by visually interpreting the remote-sensing images and the digital elevation model. By comparing the two inventories, glacier area changes over the past 30 years are revealed. The results show that the area loss is about 9.0% and the shrinkage trend continues according to the meteorological data.
Application of micro-X-ray fluorescence to chemical mapping of polar ice
Authors: Fourcade M.C. Morel , Barnola J.M. , Susini J. , Baker R. , Durand G. , de Angelis M. , Duval P. 
Published: November 2007

AbstractSynchrotron-based micro-X-ray fluorescence (μXRF) equipment has been used to analyze impurities in polar ice. A customized sample holder has been developed and the μXRF equipment has been adapted with a thermal control system to keep samples unaltered during analyses. Artificial ice samples prepared from ultra-pure water were analyzed to investigate possible contamination and/or experimental artefacts. Analyses of polar ice from Antarctica (Dome C and Vostok) confirm this μXRF technique is non-destructive and sensitive. Experiments can be reproduced to confirm or refine results by focusing on interesting spots such as crystal grain boundaries or specific inclusions. Integration times and resolution can be adjusted to optimize sensitivity. Investigation of unstable particles is possible due to the short analysis time. In addition to identification of elements in impurities, μXRF is able to determine their speciations. The accuracy and reliability of the results confirm the potential of this technique for research in glaciology.
The application of a non-linear back-propagation neural network to study the mass balance of Grosse Aletschgletscher, Switzerland
Authors: Steiner Daniel , Walter A. , Zumbühl H.J. 
Published: November 2007

AbstractGlacier mass changes are considered to represent key variables related to climate variability. We have reconstructed a proxy for annual mass-balance changes in Grosse Aletschgletscher, Swiss Alps, back to AD 1500 using a non-linear back-propagation neural network (BPN). The model skill of the BPN performs better than reconstructions using conventional stepwise multiple linear regression. The BPN, driven by monthly instrumental series of local temperature and precipitation, provides a proxy for 20th-century mass balance. The long-term mass-balance reconstruction back to 1500 is based on a multi-proxy approach of seasonally resolved temperature and precipitation reconstructions (mean over a specific area) as input variables. The relation between the driving factors (temperature, precipitation) used and the reconstructed mass-balance series is discussed. Mass changes in Grosse Aletschgletscher are shown to be mainly influenced by summer (June–August) temperatures, but winter (December–February) precipitation also seems to contribute. Furthermore, we found a significant non-linear part within the climate–mass-balance relation of Grosse Aletschgletscher.
Hydrogeological analysis of slug tests in glacier boreholes
Authors: Kulessa Bernd , Hubbard Bryn , Williamson Mike , Brown Giles H. 
Published: November 2007

AbstractSlug testing allows estimation of subglacial hydraulic properties by evaluating the response of a coupled borehole–subglacial flow system to an artificial displacement of its steady-state hydraulic head. However, existing models developed specifically for application to slug-test data collected in glacier boreholes are challenging to apply in practice. Here, we demonstrate that conventional linear methods, which are relatively readily applicable and widely used in groundwater studies, can also be used to estimate subglacial hydraulic properties. Overdamped, underdamped and critically damped slug-test data were recorded in fluctuating boreholes drilled to the bed of Haut Glacier d’Arolla, Valais, Switzerland. We find that non-linear effects in the data are negligible, supporting the application of conventional hydrogeological methods. Results suggest that the hydraulic conductivity of the unconsolidated sediments within the area influenced by a major subglacial drainage channel is enhanced (several 10–2 m s–1; typical of gravelly sand) compared to areas outside the zone of influence (~0.1 × 10–2ms–1; typical of silty sand). A distance to a flow boundary within the subglacial aquifer, inferred on the basis of slug-test analysis, was found to coincide with the actual location of the subglacial channel. Sensitivity analyses reveal that uncertainties in borehole and filter radii, as well as the storage coefficient of the subglacial aquifer, are more likely to affect the accuracy of the hydraulic and distance estimates than uncertainties regarding the repeatability of the slug-test responses and curve-fitting procedures involved in the conventional hydrogeological methods.
Influx of meltwater to subglacial Lake Concordia, East Antarctica
Authors: Tikku Anahita A. , Bell Robin E. , Studinger Michael , Clarke Garry K. C. , Tabacco Ignazio , Ferraccioli Fausto 
Published: November 2007

AbstractWe present evidence for melting at the base of the ice that overlies Lake Concordia, an 800 km2 subglacial lake near Dome Concordia, East Antarctica, via a combination of glaciohydraulic melting (associated with the tilted ice ceiling and its influence on lake circulation/melting temperature) and melting by extreme strain heating (where the ice sheet is grounded). An influx of water is necessary to provide nutrients, material and biota to support subglacial lake ecosystems but has not been detected previously. Freezing is the dominant observed basal process at over 60% of the surface area above the lake. The total volume of accreted ice above the lake surface is estimated as 50-60 km3, roughly 25-30% of the 200 ± 40 km3 estimated lake volume. Estimated rates of melting and freezing are very similar, ±2-6 mm a-1. The apparent net freezing may reflect the present-day response of Lake Concordia to cooling associated with the Last Glacial Maximum, or a large influx of water either via a subglacial hydrological system or from additional melting of the ice sheet. Lake Concordia is an excellent candidate for subglacial exploration given active basal processes, proximity to the Dome Concordia ice core and traverse resupply route.
Modelling the evolution of supraglacial lakes on the West Greenland ice-sheet margin
Authors: Lüthje M. , Pedersen L.T. , Reeh N. , Greuell W. 
Published: November 2007

AbstractWe present a model study investigating the summer evolution of supraglacial lakes on the Greenland ice margin. Using a one-dimensional (1-D) model we calculate the surface ablation for a bare ice surface and beneath supraglacial lakes for 30 days in the summers of 1999 and 2001. The surface ablation beneath the lake was enhanced by 110% in 1999 and 170% in 2001 compared with the ablation for bare ice. We then use the results from the 1-D model to further model the vertical and horizontal evolution of the supraglacial lakes, the results of which are compared with satellite images. Within the region of the ice sheet where supraglacial lakes presently occur, the area covered by supraglacial lakes is found to be more or less independent of the summer melt rate but controlled by topography. We therefore predict that, inside this region, the area covered by supraglacial lakes will remain constant even in a warmer climate. However, in a warmer climate, surface melting will occur higher on the ice sheet where small surface slopes favour formation of large supraglacial lakes. Enhanced surface melting beneath such lakes is a hitherto overlooked feedback mechanism related to climate warming.
Using electron backscatter diffraction patterns to examine recrystallization in polar ice sheets
Authors: Obbard Rachel , Baker Ian , Sieg Katherine 
Published: November 2007

AbstractThe fabric of polycrystalline ice is typically described using the c-axis orientation alone, but this is insufficient for a full description of grain orientations in this hexagonal material. Electron backscatter diffraction (EBSD) provides full c- and a-axis orientation of individual grains, and is used here to study Greenland Ice Sheet Project 2 (GISP2) ice specimens from depths of 1551, 1642 and 1745 m. Complete orientation data are used to compare nearest-neighbor relationships to overall fabric and to differentiate between recrystallization mechanisms. Changes in orientation between grains and subgrains in GISP2 specimens were correlated with the appearance of grain boundaries on thin sections and used to identify grain sets that were probably produced by polygonization. Comparison of grain misorientations that take into account both c- and a-axis differences with those derived from c-axis directions alone reveals the presence of polygonization and illustrates the usefulness of this technique.
Time-dependent basal stress conditions beneath Black Rapids Glacier, Alaska, USA, inferred from measurements of ice deformation and surface motion
Authors: Amundson Jason M. , Truffer Martin , Lüthi Martin P. 
Published: November 2007

AbstractObservations of surface motion and ice deformation from 2002–03 were used to infer mean stress fields in a cross-section of Black Rapids Glacier, Alaska, USA, over seasonal timescales. Basal shear stresses in a well-defined zone north of the center line (orographic left) were approximately 7% and 16% lower in spring and summer, respectively, than in winter. Correspondingly higher stresses were found near the margins. These changes in the basal shear stress distribution were sufficiently large to cause mean surface velocities to be 1.2 and 1.5 times larger in spring and summer than in winter. These results were inferred with a simple inverse finite-element flow model that can successfully reproduce bulk surface velocities and tiltmeter data. Stress redistribution between the well-defined zone and the margins may also occur over much shorter time periods as a result of rapidly changing basal conditions (ice–bed decoupling or enhanced till deformation), thereby causing large variations in surface velocity and strongly influencing the glacier’s net motion during summer.
Local response of a glacier to annual filling and drainage of an ice-marginal lake
Authors: Walder Joseph S. , Trabant Dennis C. , Cunico Michelle , Fountain Andrew G. , Anderson Suzanne P. , Anderson Robert S. , Malm Andrew 
Published: November 2007

AbstractIce-marginal Hidden Creek Lake, Alaska, USA, outbursts annually over the course of 2–3 days. As the lake fills, survey targets on the surface of the ‘ice dam’ (the glacier adjacent to the lake) move obliquely to the ice margin and rise substantially. As the lake drains, ice motion speeds up, becomes nearly perpendicular to the face of the ice dam, and the ice surface drops. Vertical movement of the ice dam probably reflects growth and decay of a wedge of water beneath the ice dam, in line with established ideas about jökulhlaup mechanics. However, the distribution of vertical ice movement, with a narrow (50–100 m wide) zone where the uplift rate decreases by 90%, cannot be explained by invoking flexure of the ice dam in a fashion analogous to tidal flexure of a floating glacier tongue or ice shelf. Rather, the zone of large uplift-rate gradient is a fault zone: ice-dam deformation is dominated by movement along high-angle faults that cut the ice dam through its entire thickness, with the sense of fault slip reversing as the lake drains. Survey targets spanning the zone of steep uplift gradient move relative to one another in a nearly reversible fashion as the lake fills and drains. The horizontal strain rate also undergoes a reversal across this zone, being compressional as the lake fills, but extensional as the lake drains. Frictional resistance to fault-block motion probably accounts for the fact that lake level falls measurably before the onset of accelerated horizontal motion and vertical downdrop. As the overall fault pattern is the same from year to year, even though ice is lost by calving, the faults must be regularly regenerated, probably by linkage of surface and bottom crevasses as ice is advected toward the lake basin.
Improved method to determine radio-echo sounding reflector depths from ice-core profiles of permittivity and conductivity
Authors: Eisen Olaf , Wilhelms Frank , Steinhage Daniel , Schwander Jakob 
Published: November 2007

AbstractWe present a technique that modifies and extends down-hole target methods to provide absolute measures of uncertainty in radar-reflector depth of origin. We use ice-core profiles to model wave propagation and reflection, and then cross-correlate the model results with radio-echo sounding (RES) data to identify the depth of reflector events. Stacked traces recorded with RES near the EPICA drill site in Dronning Maud Land, Antarctica, provide reference radargrams, and dielectric properties along the deep ice core form the input data to a forward model of wave propagation that produces synthetic radargrams. Cross-correlations between synthetic and RES radargrams identify differences in propagation wave speed. They are attributed to uncertainties in pure-ice permittivity and are used for calibration. Removing conductivity peaks results in the disappearance of related synthetic reflections and enables the unambiguous relation of electric signatures to RES features. We find that (i) density measurements with g-attenuation or dielectric profiling are too noisy below the firn–ice transition to allow clear identification of reflections, (ii) single conductivity peaks less than 0.5 m wide cause the majority of prominent reflections beyond a travel time of about 10 µs (~900m depth) and (iii) some closely spaced conductivity peaks within a range of 1–2m cannot be resolved within the RES or synthetic data. Our results provide a depth accuracy to allow synchronization of age–depth profiles of ice cores by RES, modeling of isochronous internal structures, and determination of wave speed and of pure-ice properties. The technique successfully operates with dielectric profiling and electrical conductivity measurements, suggesting that it can be applied at other ice cores and drill sites.
In situ measurements of till deformation and water pressure
Authors: Truffer Martin , Harrison William D. 
Published: November 2007

AbstractA newly developed hammer was used to insert two autonomous probes 0.8 m and 2.1 m into clast-rich subglacial till under Black Rapids Glacier, Alaska, USA. Both probes were instrumented with a dual-axis tilt sensor and a pore-water pressure transducer. The data are compared to a 75 day record of surface velocities. Till deformation at depth was found to be highly seasonal: it is significant during an early-season speed-up event, but during long periods thereafter measured till deformation rates are negligible. Both tilt records show rotation around the probe axis, which indicates a change in tilt direction of about 30°. The tilt records are very similar, suggesting spatial homogeneity on the scale of the probe separation (4 m horizontal and 3.3 m vertical). There is evidence that during much of the year sliding of ice over till or deformation of a thin till layer (<20 cm) accounts for at least two-thirds of total basal motion. Basal motion accounts for 50–70% of the total surface motion. The inferred amount of ice–till sliding is larger than that found at the same location in a previous study, when surface velocities were about 10% lower. We suggest that variations in ice–till coupling account for the observed variations in mean annual speed.
Dynamics of tidewater glaciers: comparison of three models
Authors: Nick F.M. , Oerlemans J. 
Published: November 2007

AbstractA minimal model of a tidewater glacier based solely on mass conservation is compared with two one-dimensional numerical flowline models, one with the calving rate proportional to water depth, and the other with the flotation criterion as a boundary condition at the glacier terminus. The models were run with two simplified bed geometries and two mass-balance formulations. The models simulate the full cycle of length variations and the equilibrium states for a tidewater glacier. This study shows that the branching of the equilibrium states depends significantly on the bed geometry. The similarity between the results of the three models indicates that if there is a submarine undulation at the terminus of a tidewater glacier, any model in which the frontal ice loss is related to the water depth yields qualitatively the same non-linear behaviour. For large glaciers extending into deep water, the flotation model causes unrealistic behaviour.
Thermo-erosional notch development at fresh-water-calving Tasman Glacier, New Zealand
Authors: Röhl Katrin 
Published: November 2007

AbstractControls on glacier calving rates are receiving increased scientific interest. At fresh-watercalving glaciers, limnological factors might be more important than glaciological ones. Measurements of thermo-erosional notch development at the calving ice cliff of Tasman Glacier, New Zealand, suggest that the calving rates at this glacier are directly controlled by the rate of thermal undercutting. Notch formation rates typically vary between 10 and 30 cm d–1 (maximum rate 65cmd–1) in summer, corresponding to an average calving rate of 34 m a–1. Notch formation is slower than waterline melt and is controlled by water temperatures and circulation, cliff geometry, debris supply and water-level fluctuations. The latter shift the position of undercutting, resetting the level of the notch formation process and thereby slowing it. The geometry of the notch and the debris supply determine the extent of influence of the lake on notch water temperatures and circulation. Hence, water temperatures in the lake are not necessarily indicative of the rate of notch formation. The prediction of rate of notch formation from far-field variables is hampered by the complex interaction of the influencing factors. The significance of thermal undercutting as a calving rate-controlling process decreases with increasing ice velocities, calving rates and surface gradients.
Glacier change (1958–1998) in the North Cascades National Park Complex, Washington, USA
Authors: Granshaw Frank D. , G. Fountain Andrew 
Published: November 2007

AbstractThe spatial characteristics for all glaciers in the North Cascades National Park Complex, USA, were estimated in 1958 and again in 1998. The total glacier area in 1958 was 117.3 ± 1.1 km2; by 1998 the glacier area had decreased to 109.1 ± 1.1 km2, a reduction of 8.2 ± 0.1 km2 (7%). Estimated volume loss during the 40 year period was 0.8 ± 0.1 km3 of ice. This volume loss contributes up to 6% of the August–September stream-flow and equals 16% of the August–September precipitation. No significant correlations were found between magnitude of glacier shrinkage and topographic characteristics of elevation, aspect or slope. However, the smaller glaciers lost proportionally more area than the larger glaciers and had a greater variability in fractional change than larger glaciers. Most of the well-studied alpine glaciers are much larger than the population median, so global estimates of glacier shrinkage, based on these well-studied glaciers, probably underestimate the true magnitude of regional glacier change.