bluuebunny/crossref_metadata_2025_split huggingface dataset:
Towards a snow-depth distribution model in a heterogeneous subalpine forest using a Landsat TM image and an aerial photograph
Authors: Stähli Manfred , Schaper Jesko , Papritz Andreas 
Published: November 2007

AbstractFor landscapes with a complex topography and a heterogeneous forest mosaic it is not feasible to map the snow depth directly from optical satellite images. In this paper, an indirect method to predict the snow-depth distribution is presented and applied to a 0.7 km2subalpine catchment in central Switzerland. The method consists of (a) a parsimonious linear regression model which includes the attributes of topography and vegetation indices (derived from a Landsat Thematic Mapper (TM) image) as explanatory variables, and (b) geostatistical interpolationtechniques. A previous analysis of the forest mosaic revealed two main scales showing up in the Landsat TM image and an aerial photograph. This discrepancy in scale was assumed to be the major reason why the vegetation indices derived from the Landsat TM image were only weak explanators of the snow-depth variation measured at 100–200 locations within the catchment. Surprisingly, the geostatistical interpolation (universal kriging) was not able to improve the prediction of the snow-depth distribution significantly. The residuals of the regression model showed hardly any spatial dependence for single snow-measurement dates.
The new remote-sensing-derived Swiss glacier inventory: I. Methods
Authors: Paul Frank , Kääb Andreas , Maisch Max , Kellenberger Tobias , Haeberli Wilfried 
Published: November 2007

AbstractA new Swiss glacier inventory is to be compiled from satellite data for the year 2000. The study presented here describes two major tasks: an accuracy assessment of different methods for glacier classification with Landsat Thematic Mapper (TM) data and a digital elevation model (DEM); the geographical information system (GIS)-based methods for automatic extraction of individual glaciers from classified satellite data and the computation of three-dimensional glacier parameters (such as minimum, maximum and median elevation or slope and orientation) by fusion with a DEM. First results obtained by these methods are presented in Part II of this paper (Kääb and others, 2002). Thresholding of a ratio image from TM4 and TM5 reveals the best-suited glacier map. The computation of glacier parameters in a GIS environment is efficient and suitable for worldwide application. The methods developed contribute to the U. S. Geological Survey-led Global Land Ice Measurements from Space (GLIMS) project which is currently compiling a global inventory of land ice masses within the framework of global glacier monitoring (Haeberli and others, 2000).
Acceleration of Pine Island and Thwaites Glaciers, West Antarctica
Authors: Rignot Eric , Vaughan David G. , Schmeltz Marjorie , Dupont Todd , Macayeal Douglas 
Published: November 2007

AbstractRecent satellite investigations revealed that in the 1990s the grounding line of Pine Island and Thwaites Glaciers, West Antarctica, retreated several km, the ice surface on the interior of the basins lowered 10 cm a–1, and Pine Island Glacier thinned 1.6 ma–1. These observations, however, were not sufficient to determine the cause of the changes. Here, we present satellite radar interferometry data that show the thinning and retreat of Pine Island Glacier are caused by an acceleration of ice flow of about 18 ± 2% in 8 years. Thwaites Glacier maintained a nearly constant flow regime at its center, but widened along the sides, and increased its 30 ± 15% mass deficit by another 4% in 4 years. The combined mass loss from both glaciers, if correct, contributes an estimated 0.08 ± 0.03 mma–1 global sea-level rise in 2000.
Seasonal comparison of ice-surface structures in the ablation area of Jakobshavn Isbræ drainage system, West Greenland
Authors: Herzfeld Ute Christina , Mayer Helmut 
Published: November 2007

AbstractIce surface roughness is a parameter of importance to many glaciological studies. Surface roughness, a derivative of microtopography, provides the high-resolution information necessary to characterize morphological types of ice surfaces and complements satellite data in investigations of surface features across scale. There has been a gap in observational scale between high-resolution satellite data, aircraft data and analyses at microscopic scale, the latter investigating material properties rather than micromorphology. To fill this gap, we designed and built the Glacier Roughness Sensor (GRS), a towed instrument that collects surface roughness data mechanically in swath-survey style with 0.1 m along-track spacing, 0.2 m across-track spacing, and sub-centimeter accuracy for areas typically 100 m by 175 m. As a result of this instrument development, the variable ice surface roughness has been added as a geophysical observable in the study of glaciers and ice sheets. The method utilized for analysis of GRS surface roughness data is geostatistical classification employing a range of parameters extracted from vario functions, which are generalized spatial structure functions. In a seasonal comparison of data from spring (May 1997) and summer (late July 1999), characteristic parameters of the spring and summer ice surface were calculated, and, as a result, an answer to the morphogenetic question of ice surface processes could be derived: in this part of the Jakobshavn Isbræ drainage basin, ice-surface structures develop in an interplay of ablation, refreezing, snowfall, wind and (distant) crevassing, each process yields characteristically different components of the surface structure, and ablat ion is the dominant morphogenetic process.
The application of an automated fabric analyzer system to the textural evolution of folded ice layers in shear zones
Authors: Wilson Christopher J. L. , Russell-Head David S. , Sim Hadi M. 
Published: November 2007

AbstractLayered ice has been used to investigate the initiation of fabrics in shear zones where there is preservation of a refolded layering The fabrics were measured using an apparatus that acquires pixel-based images that illustrate the variation of c-axis orientation within and between grains. In the centre of the shear zones there is dynamic recrystallization with the production of an asymmetric two-maxima fabric. The way dynamic recrystallization modifies the inherited folds and microstructure suggests that there is little effect of inheritance from a precursor grain microstructure or fabric No obvious evidence has been found for the occurrence of sub-grains, which implies that the role of sub-grain rotation is minimal or is obliterated by the recrystallization process. The final c-axis pattern is asymmetric with respect to the direction of shortening, with a strong maximum at ~5° to the pole of the shear zone, and a sense of asymmetry in the direction of the shear, and a secondary maximum inclined at ~45° to the plane of shearing. Distinct sets of nearest-neighbour c-axis distributions, namely, intermediate-angle (10–25°), high-angle (50–65°) and very high-angle (120–150°), suggest there may be special grain-boundary relationships.
A regression model for the mass-balance distribution of the Vatnajökull ice cap, Iceland
Authors: Aðalgeirsdóttir Guðefinna , Gudmundsson G. Hilmar , Björnsson Helgi 
Published: November 2007

AbstractA non-linear regression model describing the mass-balance distribution of the whole Vatnajökull ice cap, Iceland, for the years 1992–2000 is presented. All available data from some 40 locations over this 9 year period were used to determine the parameters of the model. The regression model uses six adjustable parameters which all have a clear physical interpretation. They are the slope, direction and the height of the equilibrium-line altitude (ELA) plane, two altitude mass-balance gradients, and a maximum value of the surface mass balance. It is found that the temporal variation of the observed mass-balance distribution can be accurately described through annual shifts of the ELA. Annual shifts in ELA are on the order of 100 m, which is of the same magnitude as the change expected to be caused by the climate variation predicted during the next decades. A slight trend towards a more negative mass balance is detected during this 9 year period.
Spatial variability in the water content and rheology of temperate glaciers: Glacier de Tsanfleuron, Switzerland
Authors: Hubbard Bryn P. , Hubbard Alun , M. Mader Heidy , Tison Jean-Louis , Grust Karin , Nienow Peter W. 
Published: November 2007

AbstractThe physical properties of eight ice cores recovered from along a flowline at Glacier de Tsanfleuron, Switzerland, have led to the identification of three distinctive internal zones. We use variations in the bulk ionic chemistry of these zones to approximate their relative liquid-water concentrations and ice viscosities. Results suggest that relative bulk water concentration and ice softness vary by over an order of magnitude between the zones. Implications of this variability for predictions of the glacier’s response to climate change are evaluated by incorporating these relative softnesses into a multi-layered (two-dimensional) model of ice flow. Model output is compared with that from an identical model constrained with a spatially uniform ice viscosity under advance and retreat modelling scenarios. The former scenario is used to tune viscosity by growing a glacier to its present long-section geometry, resulting in best-fit ice hardness values of 1.2 a1 bar–3 for the englacial ice in the multi-layered model and 7.0 a–1 bar–3 for all of the ice in the single-layered model. Both result in close approximations to the current long profile, yielding rms deviationsbetween measured and modelled ice thicknesses that are 5 5 m. In contrast, a single-layered model constrained with a hardness of 1.2 a–1 bar–3 overestimates the current measured long-section area by 31%, having a rms ice-thickness error of 15.0 m. Under the retreat modelling scenario, which gauges the response of the glacier to an imposed 75 m rise in equilibrium-line altitude (ELA), the multi-layered model predicts a long-section area reduction of 78%. This contrasts with a reduction of 64% for the single-layered model (hardness = 7.0 a–1 bar–3) and 85% for the single-layered model (hardness = 1.2 a–1 bar–3).
Basal melt at NorthGRIP modeled from borehole, ice-core and radio-echo sounder observations
Authors: Dahl-Jensen Dorthe , Gundestrup Niels , Gogineni S. Prasad , Miller Heinz 
Published: November 2007

AbstractFrom temperature measurements down through the 3001 m deep borehole at the North Greenland Icecore Project (NorthGRIP) drill site, it is now clear that the ice at the base, 3080 m below the surface, is at the pressure-melting point. This is supported by the measurements on the ice core where the annual-layer thicknesses show there is bottom melting at the site and upstream from the borehole. Surface velocity measurements, internal radio-echo layers, borehole and ice-core data are used to constrain a time-dependent flow model simulating flow along the north-northwest-trending ice-ridge flow-line, leading to the NorthGRIP site. Also time-dependent melt rates along the flowline are calculated with a heat-flow model. The results show the geothermal heat flow varies from 50 to 200 mW m–2 along the 100km section of the modeled flowline. The melt rate at the NorthGRIP site is 0.75 cm a–1, but the deep ice in the NorthGRIP core originated 50 km upstream and has experienced melt rates as high as 1.1 cm a–1.
On the inclusion of recrystallization processes in the modeling of induced anisotropy in ice sheets: a thermodynamicist’s point of view
Authors: Faria Sérgio H. , Kremer Gilberto M. , Hutter Kolumban 
Published: November 2007

AbstractIn spite of the clear fact that annealing and recrystallization phenomena in ice sheets have their roots in the thermodynamics of polycrystalline media, most approaches seem to neglect it by proposing ad hoc theories which can eventually violate fundamental thermodynamic principles. The current work presents a useful fusion of modern concepts from the thermodynamics of mixtures with continuous diversity with recent developments in the modeling of induced anisotropy and recrystallization in ice sheets. The fabric (also called texture) of the medium is described by a continuous distribution of crystallographic c axes, while recrystallization processes are assumed to be essentially driven by an internal variable representing the density of dislocations within the material. Among other results of this coalition, a balance equation for the dislocation density is formulated, as well as additional terms in the balance equations of mass, momenta, energy and entropy, associated with specific microstructural processes. By picturing the polycrystal as a mixture with continuous diversity, we discuss how the modeling of recrystallization processes in ice sheets could profit from powerful notions of chemical kinetics, which are related to the so-called dynamics of continuous reactions. Additionally, further topics like homogenization, comparison with earlier work, and directives for the construction of constitutive theories are addressed.
Ice dynamics and basal properties of Sofiyskiy glacier, Altai mountains, Russia, based on DGPS and radio-echo sounding surveys
Authors: Pattyn Frank , De Smedt Bert , De Brabander Sang , Van Huele Wim , Agatova Anna , Mistrukov Anatoliy , Decleir Hugo 
Published: November 2007

AbstractCentral Asian glaciers, compared to other glaciers in the world, should exhibit a different response to changing climate owing to (i) the extreme continentality that gives rise to aridity and large seasonal temperature variations, and (ii) the coincidence of accumulation and ablation seasons in summer. A detailed 4year field survey has been carried out on Sofiyskiy glacier in the south Chuya range(Altai mountains), Russia. Field observations reveal that this glacier retreated steadily during the 20th century at a rate of 18.3 m a–1, considerably faster than Maliy Aktru glacier, 30km to the north. Based on radio-echo sounding (RES), the subglacial topography of Sofiyskiy glacier has been reconstructed, and stake and snow-pit measurements enable the determination of surface velocity and mass balance. Basal sliding plays an important role in Sofiyskiyglacier’s behaviour, as is shown by a force-balance analysis. An analysis of RES measurements yields the bed reflection power (BRP). Using the three-layer reflectivity model of Born and Wolf (1986), the BRP is compared with the theoretical bed reflectivity for two contrasting layers of varying porosity and thickness. Results indicate that Sofiyskiy glacier possibly exhibits a polythermal regime.
Thermomechanical coupling of ice flow with the bedrock
Authors: Hindmarsh Richard C.A. 
Published: November 2007

AbstractTwo aspects of thermal coupling with bedrock are considered: the coupled time-dependent problem of co-evolving temperatures in lithosphere and ice; and the influence of basal topography on steady temperature distribution within the ice. The nature of the time-dependent coupling is found to depend on the horizontal velocity. As has been suggested, there is a cooling of steady temperatures on bedrock highs, but this is phase-shifted downstream when horizontal velocities increase. This observation may have consequences for geomorphological processes such as plucking and protection. The effect of bedrock channelling on steady temperature is considered. The positive anomaly of basal temperature due to channelling increases as the transverse wavelength decreases, but not monotonically, reaching a plateau when both the wavelengths of the basal topography are around 100 km.
Firn–ice transition-zone features of four polythermal glaciers in Svalbard seen by ground-penetrating radar
Authors: Pälli Anja , Moore John C. , Rolstad Cecilie 
Published: November 2007

AbstractDetailed ground-penetrating radar (GPR) surveys on the firn–ice transition zones of Kongsvegen, Nordenskjoldbreen, Hansbreen and Werenskioldbreen, Svalbard, are presented. We discuss features seen in GPR radargrams in all polythermal glaciers down-glacier of the firn line. The firn line of a polythermal glacier in GPR data is easily detected with both 50 and 200 MHz radar. By comparison with satellite images, characteristic patterns of reflection are shown to be caused by superimposed ice, but the reflections from the interface between the superimposed ice and the underlying glacier ice are of unknown origin. Layered reflections within the superimposed ice and firn area are likely from layers of ice lenses and relatively low-density firn in the firn area, and from bubble-rich and bubble-poor ice in the superimposed-ice zone. Dipping foliations in the glacier ice down-glacier of the firn line show that the layered reflections from the firn line are preserved, though in much weaker form, even when the firn has been transformed to solid ice.
Ice surface velocity patterns on Seward Glacier, Alaska/Yukon, and their implications for regional tectonics in the Saint Elias Mountains
Authors: Ford Andrew L.J. , Forster Richard R. , Bruhn Ronald L. 
Published: November 2007

AbstractSeward Glacier, on the Alaskan/Yukon border along the Gulf of Alaska, sits atop an important structural and morphological junction in the Saint Elias orogen. It is situated at the intersection between the Fairweather and Bagley strike–slip faults, and in the hanging wall of the Malaspina and Chugach–Saint Elias thrust faults. An ice surface velocity map of Seward Glacier derived from interferometric synthetic aperture (InSAR) reveals a complex flow pattern, which implies there is a previously unmapped northwest-trending supra-/subsurface ridge crossing the Seward. Analysis of additional remote-sensing images, ASTER, ERS SAR and the InSAR coherence map, confirms this observation. The presence of this ridge leads to a set of tectonic models describing the possible interaction of the underlying faults.
Liligo Glacier, Karakoram, Pakistan: a reconstruction of the recent history of a surge-type glacier
Authors: Diolaiuti Guglielmina , Pecci Massimo , Smiraglia Claudio 
Published: November 2007

AbstractLiligo Glacier is a small glacier located in a transverse valley, which flows on the south side of Baltoro Glacier, Karakoram, Pakistan. Terminus variations of Liligo Glacier since 1892 were reconstructed using various methods and sources (historical documents, cartography, photographs, satellite images and field surveys). The glacier is characterized by two phases of strong advance (beginning and end of the 20th century), separated by at least half a century of retreat. The advance rates, together with some ice-surface features such as the heavily crevassed surface and terminus morphology, are considered to be indicative of a surge-type glacier.
Subaqueous melt rates at calving termini: a laboratory approach
Authors: Eijpen Kimjardine , R.Warren Charles , Benn Douglas I. 
Published: November 2007

AbstractNumerous field and theoretical studies have pointed to an important role for subaqueous and waterline melting in the dynamics of calving glaciers. These processes remain unquantified because of the dangerous nature of the environment, a data gap which hampers both theoretical and numerical modelling studies. Here we report laboratory experiments designed to quantify waterline and subaqueous ice-melt rates in saline and fresh water. Experiments were conducted at temperatures of 1–10°C, a range typical of ice-contact environments, and at salinities of 0,17.5 and 35 ppt. Results indicate that melt rates are slightly faster under fresh-water conditions, and that different thermohaline combinations can produce contrasting ice-front geometries. Thermo-notches develop quickly at higher temperatures ( >4°C), and form most rapidly and to a greater extent in saline water. Contrasts in melt rates and ice-front geometry are controlled by temperature-driven density contrasts and circulation patterns. Rates of up to 0.8 md–1 suggest that mass loss by subaqueous melting is a significant process at calving termini.
Subglacial thermal balance permits ongoing grounding-line retreat along the Siple Coast of West Antarctica
Authors: Parizek Byron R. , Alley Richard B. , Hulbe Christina L. 
Published: November 2007

AbstractChanges in the discharge of West Antarctic ice streams are of potential concern with respect to global sea level. The six relatively thin, fast-flowing Ross ice streams are of interest as low-slope end-members among Antarctic ice streams. Extensive research has demonstrated that these “rivers of ice” have a history of relatively high-frequency , asynchronous discharge variations with evolving lateral boundaries. Amidst this variability, a ∼1300 km grounding-line retreat has occurred since the Last Glacial Maximum. Numerical studies of Ice Stream D (Parizek and others, 2002) indicate that a proposed thermal-regulation mechanism (Clarke and Marshall, 1998; Hulbe and MacAyeal, 1999; Tulaczyk and others, 2000a, b), which could buffer the West Antarctic ice sheet against complete collapse, may be over-ridden by latent-heat transport within melt-water from beneath inland ice. Extending these studies to Ice Stream A, Whillans Ice Stream and Ice Stream C suggests that further grounding-line retreat contributing to sea-level rise is possible thermodynamically However, the efficiency of basal water distribution may be a constraint on the system. Because local thermal deficits promote basal freeze-on (especially on topographic highs), observed short-term variability is likely to persist.
Bed reflectivity beneath inactive ice streams in West Antarctica
Authors: Catania Ginny A. , Conway Howard B. , Gades Anthony M. , Raymond Charles F. , Engelhardt Hermann 
Published: November 2007

AbstractRadio-echo sounding (RES) techniques are used to examine spatial changes in bed reflectivity across relict ice streams inWest Antarctica. Measurements from adjacent interstream ridges are used to correct the measured power returned from the bed for attenuation and losses due to geometric spreading, scattering and absorption. RES measurements near boreholes drilled on Ice Stream C (ISC) indicate high coefficients of bed reflectivity (R > 0.1) in locations where the bed was thawed and boreholes connected to the basal water system, and low reflectivity coefficients (R < 0.02) at locations that were frozen and not connected. Intermediate values of bed reflectivity were measured at locations where the connection to the basal water system was weak. Measurements across four relict margins show that bed reflectivity usually jumps from low to high values several kilometers inside the outermost buried crevasses. We interpret this to be a transition from frozen to thawed basal conditions and discuss implications of these observations.