bluuebunny/crossref_metadata_2025_split huggingface dataset:
The regional distribution of the dry-snow zone on the Antarctic Peninsula north of 70˚ S
Authors: Rau Frank , Braun Matthias 
Published: November 2007

AbstractIn order to estimate the contribution of the Antarctic Peninsula to global sea-level rise as a result of the observed warming in this region, the spatial extent of snow-melt-producing areas needs to be quantified. By using the dry-snow line derived from synthetic aperture radar (SAR) imagery as the uppermost limit of frequent or occasional surface melt, an estimation of the spatial extent of areas with non-zero ablation rates is facilitated. Three calibrated RADARSAT ScanSAR mosaics covering the northern Antarctic Peninsula were analyzed applying a threshold of –14 dB to identify the dry-snow line. The area of the dry-snow radar zone was determined to be 23300±2000 km2.Areas affected frequently or occasionally by snowmelt cover 85 000±9000 km2. In addition, the dry-snow line as derived from multi-temporal ERS-1/-2 imagery serves as an indicator of climate variability in the uppermost areas of polar glaciers and ice sheets. The upward shift of the dry-snow line between 1992 and 1998 on the eastern side of the Antarctic Peninsula at 68˚ S is interpreted as a direct response to the increasing number of high-temperature events during the 1991–2000 decade.
In situ and satellite surface temperature records in Antarctica
Authors: Shuman Christopher A. , Comiso Josefino C. 
Published: November 2007

AbstractAir-temperature records (TA) during 1992 from five inland Antarctic automatic weather station (AWS) sites were compared with the best available infrared temperatures (TIR) from the Advanced Very High Resolution Radiometer (AVHRR) as well as calibrated passive-microwave temperatures (TC) from the Special Sensor Microwave/Imager (SSM/I). Daily and monthly average TA, TIR, and TC data indicate that each approach captures generally similar trends at each site but each approach also has limitations. AWS TA data are considered the most accurate but represent spatially restricted areas and may have long gaps due to sensor or transmission problems. AVHRR TIR data have daily variability similar to the TA record but have numerous small gaps due to cloud cover or observation interruptions. An offset between TA and TIR (>4 K) at the South Pole site was identified that may be due to the inclusion of data with large satellite scan angles necessary to cover this area. SSM/I TC data have the most continuity but exhibit calibration problems, a significantly damped daily response and do not cover all of Antarctica. Individual daily differences between TA and TIR as well as TA and TC can exceed 17 K, but all sites have mean daily differences of about 1 Kor better, after compensating for the offset at South Pole, and standard deviations of <6K. Monthly temperature differences are typically 5 K or better, with standard deviations generally <3K. And finally, using the available data, the 1992 average temperature differences are <1 K.
RADARSAT-1 Antarctic Mapping Project: change-detection and surface velocity campaign
Authors: Jezek Kenneth C. 
Published: November 2007

AbstractThe RADARSAT-1 Antarctic Mapping Project (RAMP) is a collaboration between NASA and the Canadian Space Agency to map Antarctica using synthetic aperture radar (SAR). The first Antarctic Mapping Mission (AMM-1) was successfully completed in October 1997. Data from the acquisition phase of the 1997 campaign have been used to achieve the primary goal of producing the first high-resolution SAR image map of Antarctica. The Modified Antarctic Mapping Mission (MAMM) occurred during the fall of 2000. The acquisition strategy concentrated on collecting highest- resolution RADARSAT-1 data of Antarctica’s fast glaciers for change detection and feature-retracking estimates of surface velocity. Additionally, extensive data were acquired for interferometric analysis over the entire viewable region, which extends north of 80.1˚ S latitude. This paper summarizes the goals and strategy behind MAMM. It goes on to discuss ice-sheet margin changes observed on several ice shelves around the continent. Margin changes are documented by comparing AMM-1 and MAMM data with earlier datasets including European Remote-sensing Satellite-1 SAR imagery, Landsat imagery, the Antarctic Digital Database (version 1) coastline and Declassified Intelligence Satellite Photography. Analysis reveals a complex pattern of ice-margin advance and retreat without indicating any systematic behavior in ice-sheet extent about the ice-sheet perimeter.
Correlation and trend studies of the sea-ice cover and surface temperatures in the Arctic
Authors: Comiso Josefino C. 
Published: November 2007

AbstractCo-registered and continuous satellite data of sea-ice concentrations and surface ice temperatures from 1981 to 2000 are analyzed to evaluate relationships between these two critical climate parameters and what they reveal in tandem about the changing Arctic environment. During the 19 year period, the Arctic ice extent and actual ice area are shown to be declining at a rate of –2.0±0.3% dec –1 and 3.1 ±0.4% dec–1, respectively, while the surface ice temperature has been increasing at 0.4 ±0.2 K dec–1, where dec is decade. The extent and area of the perennial ice cover, estimated from summer minimum values, have been declining at a much faster rate of –6.7±2.4% dec–1 and –8.3±2.4% dec–1, respectively, while the surface ice temperature has been increasing at 0.9 ±0.6K dec–1. This unusual rate of decline is accompanied by a very variable summer ice cover in the 1990s compared to the 1980s, suggesting increases in the fraction of the relatively thin second-year, and hence a thinning in the perennial, ice cover during the last two decades. Yearly anomaly maps show that the ice-concentration anomalies are predominantly positive in the 1980s and negative in the 1990s, while surface temperature anomalies were mainly negative in the 1980s and positive in the 1990s. The yearly ice-concentration and surface temperature anomalies are highly correlated, indicating a strong link especially in the seasonal region and around the periphery of the perennial ice cover. The surface temperature anomalies also reveal the spatial scope of each warming (or cooling) phenomenon that usually extends beyond the boundaries of the sea-ice cover.
The influence of temperature on the small-strain viscous deformation mechanics of snow: a comparison with polycrystalline ice
Authors: Scapozza Carlo , Bartelt Perry A. 
Published: November 2007

AbstractGlen’s law is commonly used to model the viscous deformation of polycrystalline ice. It is a power law that relates stress to viscous strain rate and contains three material parameters: n, a power-law exponent, Q, an activation energy, and A0, a material constant. Because polycrystalline ice is the constituent material of snow, it is to be expected that the viscous deformation mechanics of snow are related to the viscous behaviour of polycrystalline ice, especially under small strains and low strain rates when kinematic effects in the ice matrix like bond breakage, bond formation and grain sliding are of secondary importance. Based on 64 deformation-controlled compression tests on fine-grained snow in the density range 200–430kg m–3 and temperature range T = –20 to –2°C, we show that Glen’s law—with material parameters similar to those for polycrystalline ice—can be applied to model the viscous deformation of high-density snow However, the values of the ice material parameters are valid for densities above a relatively low density of 400 kg m–3; they are not valid for snow with densities below 360 kg m–3. We present the variation of n, Q and A for snow as a function of density and temperature. A possible explanation for this behaviour is that the ice grains in low-density snow are less constrained. Therefore, deformation mechanisms, such as grain-boundary sliding, increase in overall importance, leading to smaller n values and higher activation energies, Q. Although the material behaviour of low-density snow can be accurately modelled using a power law, the power-law parameters depart substantially from those of polycrystalline ice. The large variation of n and Q with temperature and density underscores the difficulty of predicting snow avalanches.
Simulation of fast-flow features of the Fennoscandian ice sheet during the Last Glacial Maximum
Authors: Forsström Pirjo-Leena , Sallasmaa Olli , Greve Ralf , Zwinger Thomas 
Published: November 2007

AbstractIn order to reconstruct the palaeoglaciation in Fennoscandia and northern Asia during the late-Weichselian ice-age phase, simulations with the dynamic and thermodynamic ice-sheet model SICOPOLIS are carried out. Our focus is on the Last Glacial Maximum (LGM) around 20 kyr BP. Climate forcing is based on mean annualsur-face temperature and precipitation derived from present data and Palaeoclimatic Modelling Intercomparison Project (PMIP) UKMO21 results for the LGM. These distributions are interpolated via a glacial index defined by the Greenland Icecore Project (GRIP) δ18O record. The extent of the Scandinavian and the Barents ice sheets is reproduced in good agreement with the Quaternary Environments of the Eurasian North (QUEEN) reconstruction, but the Kara Sea and Taymyr Peninsula areas are excessively glaciated. The fast-flow regions derived from the simulations, which are generally connected to regions with a temperate base and temperate ice above, are compared to hypothesized palaeo-ice-stream locations, especially in the Norwegian Channel and the Baltic area. In the Norwegian Channel, temperate basal conditions with temperate ice above prevail and favour fast flow. In the Baltic area, ice-sheet advance is generally accompanied by slow ice velocities (<200 m a–1). Some temporary fast-flow features occur due to transitional temperate-base conditions, and higher velocities arise in retreat phases.
Laboratory studies of the flow rates of debris-laden ice
Authors: Jacka Tim H. , Shavawn Donoghue  , Li Jun , William F. Budd  , Anderson Ross M. 
Published: November 2007

AbstractIce-sheet basal ice is warmer than that above because of the heat from the Earth’s interior. The stresses acting on the basal ice are greatest. In addition, the basal ice often contains debris consisting of silt and small stones picked up from the rock over which the ice flows. Because the base is the warmest part of an ice sheet and the stress there is greatest, flow rates in the basal ice are large and often contribute most of the ice movement. It is therefore important, for accurate modelling of the ice sheets, to know whether the debris within the basal ice enhances or retards the flow of the ice. In this paper, we describe laboratory deformation tests in uniaxial compression and in simple shear, on sand-laden ice. We find no significant dependence of flow rate on sand content (up to 15% volume) in the stress range 0.13–0.5 MPa and temperature range –0.02 to –18.0°C. Further work needs to include laboratory tests on debris-laden ice extracted from the polar ice sheets. This work is underway.
Glacier changes in southern Spitsbergen, Svalbard,1901–2000
Authors: Pälli Anja , Moore John C. , Jania Jacek , Glowacki Piotr 
Published: November 2007

AbstractHigh-resolution ground-penetrating radar surveys at 50 MHz on the polythermal glaciers Hornbreen, Hambergbreen and several surrounding glaciers in southern Spitsbergen, Svalbard, are presented and interpreted. Accurate positioning was obtained using differential global positioning system (DGPS). Digital elevation models (DEMs) of the bedrock and surface were constructed. Comparison of DGPS data and surface DEMs with data from the topographic mappings from 1936 oblique stereoscopic aerial photographs and from Mission Russe in 1899–1901 shows that the Hornbreen and Hambergbreen surfaces are about 60–100 m thinner today in the upper part than at the beginning of the 20th century. Hornbreen has retreated by 13.5 km from the central part of the front, and Hambergbreen by 16 km. All the fronts of the nearby east-coast glaciers in this area have retreated. The bedrock DEM shows that the Hornbreen and Hambergbreen beds lie at –25 to 25 m a.s.l. The combination of sub-sea-level fronts and increasing steepness of the glaciers suggests that the low-lying glaciated valley filled by Hornbreen and Hambergbreen may become a partially inundated ice-free isthmus within perhaps 100 years.
Seasonal variability in ice crystal properties at NorthGRIP: a case study around 301 m depth
Authors: Svensson Anders , Baadsager Pauli , Persson Asbjørn , Schøtt Hvidberg Christine , Siggaard-Andersen Marie-Louise 
Published: November 2007

AbstractThe aim of this case study is to quantify the seasonal variability in crystal properties and to discuss the reason for the variability. A continuous 1.10 m long vertical thin-section profile covering approximately five annual cycles has been obtained from the North Greenland Icecore Project (NorthGRIP) ice core at around 301 m depth. The crystal outline and the c-axis orientation of more than 13000 crystals in the profile have been measured on a new Australian automated ice-crystal analyzer. In 2.5 cm resolution we observe a strong seasonal variability in crystal areas of >30%deviation from the average value of 6.7 mm2. Each year, a band of smaller crystals is observed in ice deposited during spring. The area distribution function is found to be close to a lognormal distribution. The crystal areas are compared to the concentration of chemical impurities in the ice; at a 5 cm resolution, the best correlation is found with the concentration of Ca2+. Our results show no seasonal variability of the average c-axis orientation of ice crystals.
Anisotropic ice flow leading to the onset of Ice Stream D, West Antarctica: numerical modelling based on the observations from Byrd Station borehole
Authors: Wang Weili , Jay Zwally H. , Hulbe Christina L. , Siegert Martin J. , Joughin Ias 
Published: November 2007

AbstractAn ice-sheet flowline model is used to simulate the flow of ice along two particle paths toward the onset to Ice Stream D, West Antarctica. One path is near the centre line of the main tributary to the ice stream, while the second passes by the Byrd Station borehole site. In this paper, we analyze the flow of the moderately fast-flowing tributaries in terms of ice-fabric anisotropy and estimate the steady-state ice-flow regions with the compatible developed crystal orientation fabrics along two particle paths. Comparison between modelled isochrones and internal layers detected from radio-echo sounding surveys in the area is used to suggest that flow upstream of the onset to Ice Stream D appears to have been stable since at least the Last Glacial Maximum.
Properties of ice crystals in NorthGRIP late- to middle-Holocene ice
Authors: Svensson Anders , Schmidt Karen G. , Dahl-Jensen Dorthe , Johnsen Sigfús J. , Wang Yun , Kipfstuhl Sepp , Thorsteinn Thorsteinsson  
Published: November 2007

AbstractDetailed measurements of crystal outlines and fabrics have been performed on 35 000 crystals in fifteen 10 × 20 cm2 vertical thin sections from the North Greenland Icecore Project (NorthGRIP) ice core, evenly distributed in the depth interval 115–880m. The crystals exhibit important changes over this period. As the ice gets older the mean crystal area increases towards a constant value, the shape of the crystals becomes increasingly irregular, and the area distribution of crystals develops from a single log-normal distribution into a bimodal lognormal distribution. The c-axis fabric of the ice shows a smooth development of an increasingly stronger vertical fabric with depth, and the formation of a weak vertical girdle. Already in the younger samples the fabric is rather strongly oriented towards vertical. The fabric and the area of individual crystals are found not to correlate. A simple model, which takes into account the vertical strain of the ice, is applied in an attempt to determine the crystal growth rate at NorthGRIP.
Effects of first-order stress gradients in an ice sheet evaluated by a three-dimensional thermomechanical coupled model
Authors: Saito Fuyuki , Abe-Ouchi Ayako , Blatter Heinz 
Published: November 2007

AbstractA three-dimensional thermomechanically coupled ice-sheet model including calculation of the first-order stress gradients is developed to perform numerical studies on the effects of stress components neglected in the zeroth-order shallow-ice approximation. Steady-state solutions are obtained with both a shallow-ice and a first-order ice-sheet model for several idealistic, radially symmetric ice-sheet configurations. The results show that the effects of the normal deviatoric-stress gradients on ice thickness are generally small, but the influence on basal temperatures and age profiles at an ice divide is significant.
An ice crystal model for Jupiter’s moon Europa
Authors: K Schmidt Karen Guldbæ , Dahl-Jensen Dorthe 
Published: November 2007

AbstractA simple model for crystal growth in the ice shell of Europa has been made in order to estimate the size of ice crystals at Europa’s surface. If mass is lost from the surface of Europa due to sputtering processes, and the ice thickness is constant in time, ice crystals will be transported upwards in the ice shell. The crystals will therefore grow under varying conditions through the shell. The model predicts that ice crystals are 4 cm– 80 m across at the surface. For the preferred parameter values, a crystal size of the order of 7 m is calculated.
Lakes and subglacial hydrological networks around Dome C, East Antarctica
Authors: Rémy Frédérique , Testut Laurent , Legrésy Benoît , Forieri Alessandro , Bianchi Cesido , Tabacco Ignazio E. 
Published: November 2007

AbstractPrecise topography from European Remote-sensing Satellite radar altimetry and high density of airborne radio-echo sounding in the area surrounding Dome C, Antarctica, show a link between surface features and subglacial lakes. In this paper, we extend the study to fine structures by computing a curvature-based coefficient (cy) related to surface undulations. These coefficient variations reveal many surface undulations, and some elongated features of this parameter seem to link known subglacial lakes. A population of high values of this coefficient, assumed to correspond to transitions between sliding and non-sliding flow regime, strengthen the appearance of a network which would link most of the lakes in the area. The existence of such a network impacts on ice-flow dynamics and on subglacial-lake studies.
The ice-thickness distribution of Unteraargletscher, Switzerland
Authors: Bauder Andreas , Funk Martin , Gudmundsson G. Hilmar 
Published: November 2007

AbstractResults from 15 years of work on glacier-bed mapping by radio-echo soundings on Finsteraar-, Lauteraar- and Unteraargletscher, Switzerland, are summarized, and a new and greatly improved map of the ice-thickness distribution presented. In contrast to the tongue of Unteraargletscher, its two main tributaries, Lauteraar and Finsteraar, are both deep and narrow, and ice-thickness determination depends on the detection of more than just the primary reflection. Migrating the data led to considerably improved bed determination. Wherever possible, additional information on ice thicknesses gained from numerous hot-water drillings to the glacier bed is used as an independent verification of the results of the radar measurements, and a fair agreement is found.
Modeling the marine extent of Northern Hemisphere ice sheets during the last glacial cycle
Authors: Zweck Chris , Huybrechts Philippe 
Published: November 2007

AbstractMechanisms that determine time-dependent changes of the marine ice margin in dynamic ice-sheet models are important but poorly understood. Here we derive an empirical formulation for changes in the marine extent when modelling the Northern Hemisphere ice sheets over the last glacial cycle in a three-dimensional thermomechanically coupled ice-sheet model. We assume that the strongest control on changes in marine extent is ice calving, and that the variable most crucial to calving is water depth. The empirical marine-extent relationship is tuned so that the major marine-retreat history of the Laurentide and Eurasian ice sheets is modelled accurately in time and space. We find that this empirical treatment relating marine extent to water depth is sufficient to reproduce the observations, and discuss the implications for the physics of marine margin changes and the dynamics of the Northern Hemisphere ice sheets since the Last Glacial Maximum.
On the rheology of till
Authors: Fowler Andrew C. 
Published: November 2007

AbstractThe deformation of subglacial till is instrumental in causing certain glacier surges, the motion of rapid ice streams in ice sheets, and ice-sheet surges which are associated with Heinrich events, and consequent rapid climatic shifts, during the last ice age. It may also be the means whereby drumlins are formed, and these in turn may act as a brake on large-scale ice flow. It is therefore important in building models to understand the rate at which till deforms, and how this controls the basal ice velocity. In recent years, two paradigms have emerged. On the one hand, theoreticians have tended to use a viscous rheology, though this lacks quantitative support. On the other hand, field and laboratory studies suggest that till behaves plastically. In this paper I will examine some of the dynamic consequences of this latter assumption, and show how the dichotomy between viscous and plastic may be less clear-cut than previously thought.
Effects of basal sliding on isochrones and flow near an ice divide
Authors: Pettit Erin C. , Jacobson H. Paul , Waddington Edwin D. 
Published: November 2007

AbstractIf an ice sheet is frozen to its bed, deep ice directly under a divide experiences low deviatoric stress and is relatively hard, because the rheology of polar ice is described by a power-law constitutive relation. In steady state, stratigraphic layers tend to form an arch (“Raymond bump”) in this region. However, when the basal ice can slide, the stresses are redistributed, and longitudinal extension due to sliding is associated with increased deviatoric stress in the deep ice under the divide. This increased deviatoric stress weakens the tendency to form a Raymond bump. To find a realistic spatial distribution of sliding under an ice divide, we incorporate a thin layer of viscous till in a finite-element plane-strain flow model. The resulting basal “sliding” velocity varies approximately linearly with distance from the ice divide. By varying the till viscosity, we can adjust the amount of basal motion. We find that the Raymond bump decays exponentially with the fraction of total ice flux carried by sliding: the arch is 50% smaller when the sliding flux is only 7% of the total ice flux. This implies that the possibility of a wet bed must be considered when inferring past ice-divide locations from radar internal layering.
Spatial stability of Ice Stream D and its tributaries, West Antarctica, revealed by radio-echo sounding and interferometry
Authors: Siegert Martin J. , Payne Antony J. , Joughin Ian 
Published: November 2007

AbstractIt has been shown recently that ice streams are fed by fast-flowing tributaries occupying well-defined subglacial troughs and with shared source areas. Here, ice-penetrating radio-echo sounding (RES) data are analyzed in conjunction with ice surface velocities derived from interferometric synthetic aperture radar (InSAR), to determine the englacial properties of tributaries feeding Ice Stream D, West Antarctica. All of Ice Stream D’s tributaries are coincident with “buckled” internal ice-sheet layers, most probably deformed by the processes responsible for enhanced ice flow. Between the tributaries well-preserved internal layers occur. The data reveal that no lateral migration of the ice-stream tributaries has occurred recently. This is consistent with thermomechanical ice-flow modelling, which indicates that the flow of Ice Stream D is controlled by a subglacial trough and is unaffected by changes to the flow of neighbouring Ice Stream C.