bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical characteristics of cryoconite (surface dust) on glaciers: the relationship between light absorbency and the property of organic matter contained in the cryoconite
Authors: Takeuchi Nozomu 
Published: November 2007

AbstractOptical characteristics of the cryoconite collected from nine glaciers in the Himalaya, Tibet and the Arctic (Canada and Svalbard) were analyzed. The spectral light reflectance (visible region) of the cryoconite on the six glaciers in the Arctic and the Himalayawas generally low, indicating high light absorbency (dark coloration) of the cryoconite. In contrast, the spectral reflectances of the cryoconite on the three glaciers in Tibet were significantly higher than on the other glaciers. There was no significant difference in the spectral reflectance of mineral particles contained in the cryoconite between the Tibetan and the other glaciers, indicating that the difference in the albedo of the cryoconites is not due to the mineral particles, but due to organic matter contained in the cryoconite. Chemical analysis of the organic matter in the cryoconites revealed that the light absorbency of cryoconites is due to the amount of humic substances, which are dark-colored organic substances, the residue of bacterial decomposition of organic matter. The cryoconite of the three glaciers in Tibet contained significantly smaller amounts of humic substances than that of the other glaciers, probably due to different biological or chemical conditions. Results show that the formation of the humic substances in the cryoconite affects its optical characteristics, and possibly affects the surface albedo of the glaciers.
The impact of cloud cover on the net radiation budget of the Greenland ice sheet
Authors: Cawkwell F. G. L. , Bamber J. L. 
Published: November 2007

AbstractEnergy-balancemodels driven by radiation and turbulent heat fluxes have been widely applied to predicting the response of the Greenland ice sheet to climate change. However, a lack of knowledge of the temporal and spatial distribution of cloud amount and type has necessitated the use of parameterizations or statistical models of cloud cover. This deficiency results in large uncertainties in both shortwave and longwave radiation fluxes. Stereo-matching of nadir and forward view AlongTrack Scanning Radiometer-2 (ATSR-2) image pairs has been shown to be a reliable method of retrieving cloud top height, and further cloud properties can be derived from thermal imagery allowing classification into cloud type. A 1 year cloud record for a transect across southern Greenland derived from stereo-matching is presented here, and comparisons are made with climate re-analysis data and ground observations. The cloud-cover data were used in a simple radiative transfer model, and the impact of clouds on the net radiation fluxes was found to be considerable. Different cloud scenarios produced up to 40 Wm–2 difference in net radiation balance. In the ablation zone, where the albedo is lower and most variable, the sensitivity to cloud-cover fraction was less marked, but the higher spatial resolution of the ATSR-2 cloud record was reflected by a much more varied trend in radiation balance. Whether the net radiation balance increases or decreases with increased cloud cover was found to be a function of the cloud amount and type and also the surface albedo. The sensitivity of the model to a ±5% change in cloud amount was found to be comparable to a 1 K change in temperature. This clearly demonstrates the importance of reliable, quantitative cloud data in mass-balance and other glaciological studies.
Mapping of a hydrological ice-sheet drainage basin on the West Greenland ice-sheet margin from ERS-1/-2 SAR interferometry, ice-radar measurement and modelling
Authors: Ahlstrøm A. P. , Bøggild C. Egede , Mohr J. J. , Reeh N. , Christensen E. Lintz , Olesen O. B. , Keller K. 
Published: November 2007

AbstractThe hydrological ice-sheet basin draining into the Tasersiaq lake, West Greenland (66°13’ N, 50°30’W), was delineated, first using standard digital elevation models (DEMs) for ice-sheet surface and bedrock, and subsequently using a new high-resolution dataset, with a surface DEM derived from repeat-track interferometric synthetic aperture radar (SAR) and a bedrock topography derived from an airborne 60 MHz ice-penetrating radar. The extent of the delineation was calculated from a water-pressure potential as a function of the ice-sheet surface and bedrock elevations and a hydraulic factor k describing the relative importance of the potential of the ice overburden pressure compared to the bedrock topography. Themeltwater run-off for the basin delineations was modelled with an energy-balance model calibrated with observed ice-sheet ablation and compared to a 25 year time series of measured basin run-off. The standard DEMs were found to be inadequate for delineation purposes, whereas delineations from high-resolution data were found to be very sensitive to changes in k in a non-linear way, causing a factor 5 change of basin area, corresponding to a doubling of the modelled runoff. The 50% standard deviation of the measured basin run-off could thus be explained by small year-to-year variations of the k-factor.
Scattering of VHF radio waves from within the top 700 m of the Antarctic ice sheet and its relation to the depositional environment: a case-study along the Syowa–Mizuho–Dome Fuji traverse
Authors: Fujita Shuji , Maeno Hideo , Furukawa Teruo , Matsuoka Kenichi 
Published: November 2007

AbstractRadio-wave scattering is a convenient method to image the properties of large internal regions of ice sheets. We used a ground-based radar system with short pulses of 60 and 179MHz frequencies to scatter off internal strata within 100–700 m of the surface in the ice sheet of East Antarctica. Data were examined along an 1150 kmlong traverse line that was approximately along the ice flowline from inland of Dome Fuji station to the coast. The scattered waves are from strata, and the dominant cause of the scattering was changes in dielectric permittivity across the strata. Therefore, density fluctuations primarily cause the scattering, although variations in ice-crystal fabrics and acidity could also have effects. The power scattered from the same depths varied by > 15 dB from one location to another. These variations correlate with the accumulation rate, changes in the surface slope, and subglacial bedrock undulations. Variations of the scattered power suggest that density contrasts in the strata are highly variable depending on these interdependent local conditions. The distribution of strata along the route allowed estimates of the ice-flow trajectories to depths of about 250 m.
50 years of ice-front changes between the Adélie and Banzare Coasts, East Antarctica
Authors: Frezzotti Massimo , Polizzi Marco 
Published: November 2007

AbstractIce-front change may well be a sensitive indicator of regional climate change. We studied the coastal sector of Wilkes Land, East Antarctica, along the Adélie and Banzare Coasts, extending from Buchanan Bay (67°05’ S, 144°30’ E) to Porpoise Bay (67°S, 128°E). The glaciers in this area drain the northern part of Dome C (area 270 000 km2). A comparison of maps, photographs and satellite images, dated several years apart, led to an estimation of the fluctuations of 18 ice fronts over the 50 years 1947–97 .The area of the floating glaciers in 1963 was 3035 km2, and in 1989, 2785 km2. The main glaciers in the area are Zélée, Astrolabe, du Français, Commandant Charcot and Pourquoi Pas for the Adélie Coast, and Dibble, May, Sandford and Frost Glaciers for the Clarie and Banzare Coasts. Most of the floating glaciers have shown cyclical behaviour without a marked trend, but a general reduction since 1947. The reduction in the area of floating glaciers since the 1950s may be linked to changes in ice–ocean interaction, as noted for the floating glaciers of the George V Coast and the Cape Adare area, and sea-ice extent. The calving behaviour of the main glacier tongues is characterized by an accumulation of icebergs projecting from the coast to form iceberg tongues, held in place by grounding and joined together by annual or perennial fast ice.
Crevasse ages on the northern margin of Ice Stream C, West Antarctica
Authors: Smith B. E. , Lord N. E. , Bentley C. R. 
Published: November 2007

AbstractIn the 1997/98 austral summer field season, we conducted a ground-penetrating radar survey on the northern shear margin of Ice Stream C, West Antarctica. The radar data were used to identify features near the surface of the ice, including internal layers and buried crevasses. The survey was intended to determine the variation in the age of buried crevasses along the ice stream. A procedure was developed by which the accumulation rate and the age of buried crevasses can be estimated based on radar records, firn-core measurements and the assumption that the crevasses were once open to the surface. With this method we were able to determine the age of buried crevasses with a standard error of 15–20%. We discuss our new results in conjunction with those of Retzlaff and Bentley (1993) on the southern margin of the ice stream. Typical crevasse ages were found to range from 120 to 200 years, although crevasses in a few areas were significantly younger. The youngest crevasses are at the extreme upstream end of the survey, but the next youngest were found midway along the ice stream. Crevasses upstream and downstream are older, with ages 40–80 years greater than those in the middle. Crevasses on the northern shear margin of tributary C2 were 30–50 years older than those on the southern margin. These patterns of crevassing suggest that variability in shear margin response to changes in ice-stream flow played an essential role in determining the time at which crevassing became inactive.
An image-enhanced DEM of the Greenland ice sheet
Authors: Scambos Ted A. , Haran Terry 
Published: November 2007

AbstractWe have assembled an elevation grid for the Greenland ice sheet using a combination of the best current digital elevation model (DEM) (Bamber and others, 2000a, 2001) and 44 Advanced Very High Resolution Radiometer satellite images acquired in spring 1997. The images are used to quantitatively enhance the representation of surface undulations through photoclinometry. Gridcell spacing of the new DEM is 625 m. To validate the new DEM, we compared profiles extracted from it and the Bamber and others DEM with airborne laser altimetry profiles collected in the 1990s by the Airborne Topographic Mapper (Krabill and others, 1995). The image-enhanced DEM has a greatly improved representation of decameter-relief surface features <15 km in lateral extent, and reduces the mean elevation error in regions having these features by 20–50%. Root-mean-squared errors are typically 7–15m in the Bamber DEM, and 4–10m after image enhancement. However, the photoclinometry process adds some noise. In very smooth portions of the ice sheet where decameter undulationsare absent, the photoclinometry process caused a slight increase in the rms error, from ~1 min the Bamber and others DEM to ∼2.5 min the image-enhanced DEM. The image-enhanced DEM will be useful for inferring accumulation-rate variations over the undulation field, or for improving maps of bedrock elevation through inversion of surface elevation, for example. We briefly explore the preliminary steps of this latter application.
Ice-sheet velocity mapping: a combined interferometric and speckle-tracking approach
Authors: Joughin Ian 
Published: November 2007

AbstractThe first and second RADARSAT Antarctic Mapping Missions (AMM-1 and -2) have now acquired interferometric synthetic aperture radar (SAR) overmuch of the ice sheet. The RADARSAT 24 day repeat cycle is nearly ideal for measuring slow ice motion (e.g. <100ma–1), but application of SAR interferometry is limited in faster-moving areas. With a 1day repeat period, ERS-1/-2 tandem SAR data are much better matched to fast motion, but are not always available. Fortunately, several authors have demonstrated the ability to measure velocity in fast-moving areas by tracking SAR speckle from image to image, which works well even in the absence of visible features. While these estimates have intrinsically lower resolution and poorer accuracy than direct phase measurements, they serve well in areas where there are no data suitable for conventional interferometry. This paper describes algorithms I have developed for merging interferometric and speckle-tracking data from multiple swaths to form a single seamless mosaic of velocity. At each point in the mosaic, all the available data are combined to produce estimates of the velocity and the associated error. This technique is demonstrated using RADARSAT data collected over Lambert Glacier, Antarctica, during AMM-1 and -2.
Reflectance of Antarctica from 3 to 5 μm: discrimination of surface snow and cloud properties
Authors: Calvin Wendy M. , Milman Margaret , Kieffer Hugh H. 
Published: November 2007

AbstractCurrent techniques of cloud discrimination in polar regions, ice surface temperature measurement, sea-ice and snowfield extent mapping often rely on data acquired in the region from 3 to 5 mm. The Advanced Very High Resolution Radiometer (AVHRR) and the recently launched Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on Terra have spectral bands in this region used for these purposes. Approaches often consider the radiance value in this spectral range in terms of a single equivalent brightness temperature. However, this spectral region contains contributions from both solar-reflected and thermal-emitted radiance, and a water ice reflectance peak at 3.7 μm can be highly variable and a sensitive indicator of grain-size in icy particles either in clouds or as surface snow. In December 1992 the Galileo spacecraft, on its way to Jupiter, flew by and acquired images of Antarctica that included spectral coverage in 408 channels in the wavelength range 1–5 μm with the Near Infrared Mapping Spectrometer (NIMS). The NIMS spectra provide a basis for the separation of the reflected and emitted components in this wavelength region. This separation then allows the examination of the observed variation of the reflected component with respect to cloud and surface ice properties. This analysis may help refine current algorithms for cloud discrimination in AVHRR and MODIS using channels from 3 to 5 μm.
Synthetic aperture radar detection of the snowline on Commonwealth and Howard Glaciers, Taylor Valley, Antarctica
Authors: Bardel Patrick , Fountain Andrew G. , Hall Dorothy K. , Kwok Ron 
Published: November 2007

AbstractSynthetic aperture radar (SAR) images of Taylor Valley, Antarctica, were acquired in January 1999 in coordination with ground-based measurements to assess SAR detection of the snowline on dry polar glaciers. We expected significant penetration of the radar wave resulting in an offset of the SAR-detected snowline relative to the true snowline. Results indicated no detectable displacement of the SAR snowline. Snow depths of 15 cm over ice can be detected on the imagery. We hypothesize that the optical depth of thin snowpacks is enhanced by reflection and refraction of the radar beam by internal snow layers. The enhanced optical depth increases the volume scattering, and thereby enhances backscatter sufficiently to be detected by the SAR. Consequently, SAR imagery may be used directly to image the position of transient snowlines in dry polar regions.
Experimental study on the micro-fabric of frozen sediment using triaxial deformation and computerized tomography
Authors: Jilin Qi , Yuanming Lai , Yibing Pu 
Published: November 2007

AbstractThe micro-fabric of frozen sediment was studied using a triaxial deformation machine with computerized tomography (CT) to describe a quantitative relationship between microstructure and mechanical behaviour at different temperatures and confining pressures. Micro-fabric changes were described by CT images and CTvalues. Relationships between CT values and the stress–strain curves were analyzed. It was shown that CTvalues can describe the deformation quantitatively.
Spatial and temporal scales of anisotropic effects in ice-sheet flow
Authors: Thorsteinsson Throstur , Waddington Edwin D. , Fletcher Raymond C. 
Published: November 2007

AbstractAlong most particle paths in polar ice sheets, ice experiences a slowly changing local deviatoric-stress pattern, and develops a fabric characteristic of its current stress state, in which there is generally a correspondence between non-zero strain-rate components and non-zero deviatoric-stress components. Where the stress pattern changes rapidly in special transition zones, fabric may evolve more slowly than the local stress field, and unusual or unexpected deformation patterns can result. The degree to which fabric tracks the local stress is determined by the relative characteristic times for changes in stress, given by the transition-zone width and ice velocity, and for changes in crystal orientation, given, in the absence of recrystallization, by the inverse of the local strain rate due to the principal stress. Recrystallization can significantly reduce the time-scale of fabric adjustment. We examine transition zones where ice (a) enters ice-stream margins, (b) is overrun by a migrating divide, and (c) flows through a strong saddle. Stress and fabric tend to be significantly misaligned in ice-stream margins and in flow through a saddle. When stresses that are markedly different from in situ stresses are applied to ice specimens during creep tests, deformation may be difficult to interpret.
A new bedrock and surface elevation dataset for modelling the Greenland ice sheet
Authors: Bamber Jonathan L. , Baldwin Duncan J. , Gogineni S. Prasad 
Published: November 2007

AbstractA new digital elevation model of the surface of the Greenland ice sheet and surrounding rock outcrops has been produced from a comprehensive suite of satellite and airborne remote-sensing and cartographic datasets. The surface model has been regridded to a resolution of 5 km, and combined with a new ice-thickness grid derived from ice-penetrating radar data collected in the 1970s and 1990s. A further dataset, the International Bathymetric Chart of the Arctic Ocean, was used to extend the bed elevations to include the continental shelf. The new bed topography was compared with a previous version used for ice-sheet modelling. Near the margins of the ice sheet and, in particular, in the vicinity of small-scale features associated with outlet glaciers and rapid ice motion, significant differences were noted. This was highlighted by a detailed comparison of the bed topography around the northeast Greenland ice stream.
Ice-core insights into the flow and shut-down of Ice Stream C, West Antarctica
Authors: Voigt Donald E. , Alley Richard B. , Anandakrishnan Sridhar , Spencer Matthew K. 
Published: November 2007

AbstractVigorous flow of central regions of Ice Stream C, West Antarctica, near the UpC camp ended about the year 1830, based on analysis of a firn and ice core taken at the camp. Ice-stream flow was characterized by repeated fracturing and healing, probably subsurface, especially near the onset of streaming flow. High longitudinal stresses caused fracturing, recrystallization of the ice and elongation of bubbles, and enhanced densification rates of high-density firn indicating power-law-creep behavior.
Comparison of modelled and observed responses of a glacier snowpack to ground-penetrating radar
Authors: Kohler Jack , Moore John C. , Isaksson Elisabeth 
Published: November 2007

AbstractThe upper 10 m of the firn of a Svalbard glacier is imaged along the centre line using a 500 MHz ground-penetrating radar, and a 10 m firn core taken along the profile. Complex reflection coefficients are calculated from the high-resolution capacitance and conductance measurements made on the snow core. The reflection coefficient depth series is converted to the time domain and convolved with model radar monopulses to synthesize traces that compare well with radar traces recorded near the ice core. Differences are probably due to cm-scale physical and chemical inhomogeneities that are smoothed when imaged by the radar beam, which integrates information over areas that are of the same order of magnitude as the depth to the layer.
A dislocation-based analysis of the creep of granular ice: preliminary experiments and modeling
Authors: Cole David M. 
Published: November 2007

AbstractThe nature of the fall-off at lower stresses from power-law behavior to a lower-order stress dependency is of particular interest in glacier and ice-sheet modeling. Preliminary experiments show that the stress level at which the fall-off occurs is a function of the specimen’s dislocation density. The analysis employs a dislocation-based model of anelasticity that provides a quantitative relationship between the effective dislocation density and the area of hysteresis loops observed in cyclic loading experiments. Combining this technique with a staged creep experiment makes it possible to calculate the dislocation density as a function of strain, thereby supporting a quantitative dislocation analysis of the deformation process.Work on saline ice established that the threshold stress associated with power-law behavior increased as a result of prior straining, power-law behavior emerged when the effective dislocation density increased measurably during deformation, and approximately linear behavior was evident when the dislocation density remained relatively constant. Those findings motivated the experiments on fresh-water ice presented here. The preliminary experiments show that pre-straining increases the stress associated with the fall-off from power-law behavior, and the results are interpreted in the context of a dislocation-based constitutive model developed for sea ice.
Numerical modelling of historical front variations and dynamic response of Sofiyskiy glacier, Altai mountains, Russia
Authors: De Smedt Bert , Pattyn Frank 
Published: November 2007

AbstractThe recent fluctuation of the central Asian climate, and its effect on the region’s glaciers, is poorly known, largely because of a lack of knowledge of the dynamic behaviour of so-called summer-accumulation-type glaciers. In this study, a one-dimensional numerical glacier model is used to simulate the dynamic response of Sofiyskiy glacier, Altai mountains, Russia, to climate forcing. A successful simulation of the observed historical front variations was accomplished by dynamic calibration. This resulted in a reconstruction of the recent mass-balance history of the glacier, showing a distinct decline in surface mass balance in the second half of the 19th century, a slightly higher mass balance at the beginning of the 20th century, followed by a steady decline towards present conditions. The future response of Sofiyskiy glacier was projected for six 21st-century climate scenarios. Under a “no-change” scenario, the glacier will retreat > 2 km by 2100. If air temperature gradually rises by > 5°C during this century, the glacier will vanish around 2100. Basic response characteristics of Sofiyskiy glacier were determined. These indicate rather low mass-balance sensitivity to temperature change, but a strong front reaction due to geometric conditions.