bluuebunny/crossref_metadata_2025_split huggingface dataset:
A borehole camera system for imaging the deep interior of ice sheets
Authors: Carsey Frank , Behar Alberto , Lonne Lane A. , Realmuto Vince , Engelhardt Hermann 
Published: November 2007

AbstractThe design and first deployment is described for the Jet Propulsion Laboratory–California Institute of Technology ice borehole camera system for acquisition of down-looking and side-looking images in a borehole made by a hot-water drill. The objective of the system is to acquire images in support of studies of the basal dynamics and thermodynamics of West Antarctic ice streams. A few sample images, obtained during the 2000/01 Antarctic field season, are shown from the basal layers of Ice Stream C.
Flow mechanism of the Des Moines lobe of the Laurentide ice sheet
Authors: Hooyer Thomas S. , Iverson Neal R. 
Published: November 2007

AbstractRapid flow of the Des Moines lobe of the Laurentide ice sheet may have been related to its unlithified substrate. New reconstructions of the lobe, based on moraine elevations, sediment subsidence during moraine deposition, and flow-direction indicators, indicate that the lobe may have been ∼3 times thicker than in previous reconstructions. Nevertheless, implied basal shear stresses are <15 kPa, so internal ice deformation was not significant. Instead, the lobe likely moved by a combination of sliding, plowing of particles through the bed surface, and bed shear. Consolidation tests on basal till yield preconsolidation stresses of 125–300 kPa, so effective normal stresses on the bed were small. A model of sliding and plowing indicates that at such stresses most particles gripped by the ice may have plowed easily through the till bed, resulting in too small a shear traction on the bed to shear it at depth. Consistent with this prediction, measurements of orientations of clasts in basal till yield a weak fabric, implying pervasive bed shear strain less than ∼2, although some stronger fabrics have been reported by others. We infer, tentatively, that movement was principally at the bed surface by plowing.
Healed cracks in iceberg ice
Authors: Barrette Paul D. , Jordaan Ian J. 
Published: November 2007

AbstractA noticeable trait of iceberg ice is the presence of several sets of planar features cross-cutting each other at various angles. Close-up views of these features show that they consist of an array of individual air inclusions that differ in size, shape and spatial distribution. In none of the cases resolvable at the scale of our observations were these inclusions physically linked to form a continuous fracture plane, although they may have originated as such. All postdate the formation of ice veins.
On the representation of ice-shelf grounding zones in SAR interferograms
Authors: Rabus Bernhard T. , Lang Oliver 
Published: November 2007

AbstractWe investigate limitations of the one-dimensional elastic-beam model to detect grounding line and thickness of an ice shelf from a differential interferogram. Spatial limitations due to grounding-line curvature and variable ice thickness are analyzed by comparison with two-dimensional plate flexure. Temporal limitations from the tide-dependent shift of the grounding line are analyzed by superpositions of four tidal flexure profiles representing differential interferograms. (i) At scales greater than one ice thickness, seaward protrusions of the grounding line are well represented by the elastic-beam model, while landward embayments of the same scale produce significant misplacements >10% of the ice thickness. (ii) For reasonable spatial variations of shelf thickness, the elastic-beam model gives reliable estimates of grounding-line position and unfractured mean ice thickness near the grounding line. (iii) For about 20% of superpositions of four tidal flexure profiles, the resulting grounding-line misplacements exceed the physical tidal shift of the grounding line by factors >2. For differential tide levels <10% of a 1 m tide dynamics, a physical shift of the grounding line of 0.3 km per metre of tide can lever misplacements of >2 km. Examples of real interferometric profiles from West Antarctic ice shelves corroborate our results.
Patterning mechanisms in subglacial carbonate dissolution and deposition
Authors: NG Felix , Hallet Bernard 
Published: November 2007

AbstractDeglaciated bedrock surfaces in limestone areas often exhibit extensive patterning by solutional furrows and carbonate deposits that occur in close association with undulations in the bed topography. These features clearly result from subglacial dissolution and precipitation of calcite on the bed — induced, for instance, by melting and freezing in a regelation water film — but little is known about the observed morphology. In particular, it is intriguing that (i) the solutional furrows, whose formation requires explanation, are collectively organized into arcuate patterns, with characteristic spacing, and (ii) a fluted or “spiculed” surface texture is ubiquitous on the calcite deposits. Herein, we propose specific mechanisms for such patterning based on a theory where chemical processes in the water film are coupled to regelation physics. Solutional furrows reflect locally enhanced dissolution along stoss surfaces, where CO2-rich bubbles advected in the ice from up-glacier come into contact with the bed. The bubbles form as CO2is exsolved from freezing film water at the lee of bed bumps. The flutings on the deposit are inherently the manifestation of a spatial instability at the interface where calcite precipitation occurs. Complex interactions underlie some of the striking glacier-bed features shaped by subglacial chemical processes.
Transient glacier response with a higher-order numerical ice-flow model
Authors: Pattyn Frank 
Published: November 2007

AbstractIn this paper, a higher-order numerical flowline model is presented which is numerically stable and fast and can cope with very small horizontal grid sizes (<10 m). The model is compared with the results from Blatter and others (1998) on Haut Glacier d’Arolla, Switzerland, and with the European Ice-Sheet Modelling Initiative benchmarks (Huybrechts and others, 1996). Results demonstrate that the significant difference between calculated basal-drag and driving-stress profiles in a fixed geometry disappears when the glacier profile is allowed to react to the surface mass-balance conditions and reaches a steady state. Dynamic experiments show that the mass transfer in higher-order models occurs at a different speed in the accumulation and ablation areas and that the front position is more sensitive to migration compared to the shallow-ice approximation.
Last Glacial Maximum equilibrium-line altitudes and paleoclimate, northern Uinta Mountains, Utah, U.S.A.
Authors: Munroe Jeffrey S. , Mickelson David M. 
Published: November 2007

AbstractNineteen former valley glaciers were reconstructed for their Last Glacial Maximum (LGM) extents in the northern Uinta Mountains, Utah, U.S.A. Mean equilibrium-line altitudes (ELAs) calculated by four methods (accumulation–area ratio, toe–headwall altitude ratio, lateral moraines and cirque floors) range from 3050 to 3300 m a.s.l. Modern mean summer temperatures (Ts) at the ELAs range from 8.7° to 11.2°C, while modern winter precipitation (P) ranges from 354 to 590 mm snow water equivalent (SWE). Based on the difference in elevation of mean ELAs across the range, LGM P values must have ranged from 940 to 3040 mm SWE, assuming the modern summer lapse rate was the same during the LGM. A Ts depression of 5.5°C is required for these precipitation values to plot in the range of modern ELA values. The reconstructed increase in P at the western end of the range is 10 times the modern increase, reflecting the influence of pluvial Lake Bonneville. Assuming ELA depression (ΔELA) resulted from this P increase and a uniform 5.5°C Ts decrease, the regional LGM ΔELA was approximately 900 m.
Discharge of debris from ice at the margin of the Greenland ice sheet
Authors: Knight Peter G. , Waller Richard I. , Patterson Carrie J. , Jones Alison P. , Robinson Zoe P. 
Published: November 2007

AbstractSediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin. These data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the Greenland ice sheet.
A method for monitoring glacier mass balance using satellite albedo measurements: application to Vatnajökull, Iceland
Authors: De Ruyter De Wildt Martijn S. , Oerlemans Johannes , Björnsson Helgi 
Published: November 2007

AbstractWe compare satellite albedo images of Vatnajökull, Iceland, with mass-balance measurements for the years 1991–99. We find that the equilibrium line is mostly not visible when it is located above its position of the previous year(s). Equilibrium-line detection is further hindered by clouds and a gradual transition between ice and firn or snow. Consequently, firn-line elevation at the end of the melting season is not particularly useful for estimating the annual mass balance. Instead, we propose to study the mean albedo of the entire ice cap throughout the melting season so that all available information about the surface albedo is taken into account. The mean net potential global radiation, which can be estimated from the mean surface albedo alone, both depends on and influences summer melt. It also depends on winter precipitation and, integrated over the melting season, is found to relate linearly to the specific mass balanceB(r= 0.87 and 0.94 for different outlets of Vatnajökull).Bcan be estimated quantitatively when this relation is known and qualitatively when it is not. The uncertainty in the satellite-derived value ofBis 0.5–0.8 m w.e., which for Vatnajökull corresponds to about 27% of the interannual variability ofB.
Measurement of snow density and microstructure using computed tomography
Authors: Lundy Chris C. , Edens Michael Q. , Brown Robert L. 
Published: November 2007

AbstractIn the past, two-dimensional images of internal snow structure have been obtained through plane surface sections or thin sections. These techniques are time-consuming and necessarily destroy the snow specimen. Computed tomography (CT) allows similar images to be obtained, but in a more efficient and non-destructive manner. To demonstrate the methodology, a CT scanner was used to obtain cross-sectional images over time of a snow sample undergoing kinetic-growth metamorphism. Densities calculated from the CT images correlated well to density measured using a traditional method. A procedure was developed that allows the CT image to be converted to binary in an objective manner. Employing innovative stereological software, the microstructural properties (grain diameter, bond diameter, neck length and intercept length) of the snow were then measured from the two-dimensional CT images. The presented methodology provides significant improvements over previous techniques, requiring less time and labor to obtain high-quality microstructural data.
Formation of band ogives and associated structures at Bas Glacier d’Arolla, Valais, Switzerland
Authors: Goodsell Becky , Hambrey Michael J. , Glasser Neil F. 
Published: November 2007

AbstractStructural glaciological, sedimentological and geophysical techniques are used to provide new insight concerning the formation of band ogives and associated structures at Bas Glacier d’Arolla, Switzerland. Sedimentary stratification, crevasse traces and transverse foliation are identified as planar structures in the lower icefall and glacier tongue. Stratification and crevasse traces are progressively deformed into, and enhance, the transverse foliation found in the glacier tongue. Three-dimensional geometry has been defined using ground-penetrating radar, which portrays four main characteristics: (i) deep reflectors interpreted as the ice/bed interface, (ii) alternating reflection-rich and reflection-poor zones interpreted as ogives, (iii) up-glacier-dipping reflectors, interpreted as planar structures, and (iv) down-glacier-dipping reflectors of uncertain origin. At the glacier surface, each band ogive consists of a light and dark band. The dark bands contain more intense foliation which, on differential weathering, traps fine debris. Clasts and clear ice of basal character within dark ogive bands suggest that basal ice has been raised to the glacier surface. The most applicable model for the formation of band ogives at Bas Glacier d’Arolla is a refinement of Posamentier’s (1978) “reverse faulting” hypothesis. In this context, multiple shear zones are formed, through which basal ice is uplifted to the glacier surface to produce the dark, foliated ogive bands. This model fits observations reported from other glaciers with band ogives.
Force balance along an inland tributary and onset to Ice Stream D, West Antarctica
Authors: Price Stephen F. , Bindschadler Robert A. , Hulbe Christina L. , Blankenship Donald D. 
Published: November 2007

AbstractThe transition from inland- to streaming-style ice flow near to and upstream from the onset to Ice Stream D, West Antarctica, is investigated using the force-balance technique. Basal drag provides the majority of the flow resistance over the study area but is substantially modified by non-local stress gradients. Lateral drag increases with distance downstream, balancing ∼50–100% of the driving stress at the onset. Longitudinal stress gradients (LSG) are also found to be significant, an observation that distinguishes ice flow in this region from the inland- and streaming-flow regimes that bound it, in which LSG are usually negligible. LSG decrease the spatial variability in basal drag and sliding speed and increase the area of the bed over which frictional melting occurs. Overall, LSG decrease the resistive influence of basal stress concentrations and increase the spatial uniformity of basal sliding. These observations suggest that streaming flow develops as an integrated response to the physical interaction between the ice and its bed over an extended region upstream from the onset, rather than being solely due to changes in basal characteristics at the onset. An implication is that non-steady-flow behavior upstream from the onset may ultimately propagate downstream and result in non-steady behavior at the onset.
Performance and applications of an automated c-axis ice-fabric analyzer
Authors: Hansen Dirk P. , Wilen Larry A. 
Published: November 2007

AbstractA completely automated instrument for ice-fabric analysis has been built, tested and applied. The analysis of a thin section is performed in two steps. First, the section is loaded into the machine and is automatically imaged in about 16 min. Then, at a later time and convenient location, the grains in the section are identified from a stored image (either automatically or by the user), and the c-axis orientation of each grain is calculated at a rate of 1200 grains h−1. Comparison of automated results with manual Rigsby stage results shows excellent agreement. Diagnostics indicate that the accuracy of the new technique is 0.5° in the c-axis orientation. Two specific applications are demonstrated: (1) the ability to measure internal grain orientations that may reveal internal stress, and (2) the ability to measure very thin thin sections. The latter, combined with the ability to zoom in on small regions of a section, will be useful for examining the fabric of fine-grained (< 1 mm size grains) ice.
A century reconstruction of the mass balance of Glacier de Sarennes, French Alps
Authors: Torinesi Olivier , Letréguilly Anne , Valla François 
Published: November 2007

AbstractThe 50 year time series of mass balance on Glacier de Sarennes is one of the longest in the French Alps, and so is often used as a reference for glacier variations in the French Alps. Meteorological data can be used to extend the series backwards in time. Martin (1978) proposed such a reconstruction for the 1882–1977 period. With 50 years of observations, we show that the classical method used by Martin is too dependent on the calibration period. We therefore try to improve the accuracy of this reconstruction using the Vincent and Vallon (1997) method which takes into account the albedo change of the surface during the ablation period (this is called the daily method). This new method appears to be stable in time. Once calibrated, the daily method is applied to reconstruct the 1881–1949 period. The new reconstruction is compared to a volumetric balance between two maps from 1906 and 1981. It appears that both reconstructions (classical and daily) fail to render the trend correctly over a long period of time. The cumulative centred mass balance correlates well (r2 = 0.62) with the hydrological mass-balance series of Aletschgletscher, Switzerland.
Direct measurement of basal motion at a hard-bedded, temperate glacier: Glacier de Tsanfleuron, Switzerland
Authors: Hubbard Bryn 
Published: November 2007

AbstractA rigid mast, equipped with five multi-turn potentiometers, was bolted to the bedrock floor of a frontal cavity at Glacier de Tsanfleuron, Switzerland. Each potentiometer was linked by a thin cord to an anchor emplaced in the adjacent ice wall, enabling basal ice motion to be measured continually over a 6 day period in the late summer. Results indicate that basal ice velocity increased quasi-linearly away from the glacier bed, rising from 10.66 to 11.82 mm d−1 between 25 and ∼ 265 mm above the ice– bed interface. Extrapolation of this gradient indicates that ∼ 10.55 mm d−1 may have been accommodated by pure slip between the ice and the glacier bed. Basal ice motion is temporally variable, generally being characterized by tens of minutes to hours of little or no motion interspersed with rapid-motion “events” lasting for between < 120 s (a single measurement interval) and 360 s. These motion events were responsible for speeds of up to > 400 mm d−1 over individual measurement intervals. The magnitude–frequency distribution of these events is consistent with a pattern of infrequent and large “slips” initiated at the ice–bed interface, that are manifested as more frequent and smaller motion events some tens of cm above that interface.
Basal conditions and glacier motion during the winter/spring transition, Worthington Glacier, Alaska, U.S.A.
Authors: Harper Joel T. , Humphrey Neil F. , Greenwood Mark C. 
Published: November 2007

AbstractObservations of the motion and basal conditions of Worthington Glacier, Alaska, U.S.A., during late-winter and spring melt seasons revealed no evidence of a relationship between water pressure and sliding velocity. Measurements included borehole water levels (used as a proxy for basal water pressure), surface velocity, englacial deformation, sliding velocity, and time-lapse videography of subglacial water flow and bed characteristics. The boreholes were spaced 10–15 m apart; six were instrumented in 1997, and five in 1998. In late winter, the water-pressure field showed spatially synchronous fluctuations with a diurnal cycle. The glacier’s motion was relatively slow and non-cyclic. In spring, the motion was characterized by rapid, diurnally varying sliding. The basal water pressure displayed no diurnal signal, but showed high-magnitude fluctuations and often strong gradients between holes. This transition in character of the basal water-pressure field may represent a seasonal evolution of the drainage system from linked cavities to a network of isolated patches and conduits. These changes occurred as the glacier was undergoing a seasonal-velocity peak. The apparent lack of correlation between sliding velocity and water pressure suggests that local-scale water pressure does not directly control sliding during late winter or early in the melt season.
Altitudinal variation of the stable isotopes of snow in regions of high relief
Authors: Holdsworth Gerald , Roy Krouse H. 
Published: November 2007

AbstractA major discontinuity in the variation of δ18O (δD) with altitude in high mountains was first seen in data from Mount Logan, YukonTerritory, Canada (Holdsworth and others, 1991). The profile of δ vs altitude revealed three well-defined regions: (1) a lower, monotonic, fractionation sequence below ∼3 km; (2) a middle layer, typically 1–2 km thick, within which δ values are nearly constant or stepped with altitude, and (3) part of another fractionation sequence in the “quasi-geostrophic flow region” above ∼5.3 km. The middle region was inferred to be a “mixed layer”, combining moisture from regions (1) and (3). This type of structure is now seen to occur on other high-altitude mountains, including Cerro Aconcagua, Argentina, where observations reach almost 7 km. The new observations confirm the general occurrence of a multi-layered atmosphere during precipitation at high-altitude glacier sites. This structure is linked to synoptic-scale polar cyclones, where the middle layer is identified as being the signature of the warm-front zone. These results have implications for the common practice of using a specific, spatially derived, isotopic thermometer in the time domain for the paleoclimatic interpretation of high-altitude ice-core δ records.
Computing marine-ice thickness at an ice-shelf base
Authors: Holland David M. 
Published: November 2007

AbstractThe freezing of sea water to the base of an ice shelf can give rise to large patches of accumulated ice, a phenomenon known as marine ice. In this study a numerical method is presented for calculating the thickness of the marine-ice layer using an ice- shelf-ocean model. The present-day modeling paradigm of ice-shelf–ocean interaction usually involves the fixed specification of the ice-shelf geometry while the ocean circulation in the cavity beneath the ice shelf evolves freely. This approach relies on several assumptions, such as steady-state ice-shelf thickness and ice-shelf flow fields, in order to make reasonable quantitative estimates of the thermodynamic exchange processes occurring at the ice-shelf base. This paper discusses the impact of these and other assumptions on the estimation of the thickness of the marine-ice layer. Model simulation results are presented for an idealized ice-shelf–ocean configuration as a demonstration of the feasibility of the numerical method. A sensitivity analysis is given so as to quantify the relative uncertainty in the marine-ice thickness that arises from uncertainties in the model input parameters, these being principally the ice-shelf flow field, the basal accumulation rate and the ice-shelf thickness field.