bluuebunny/crossref_metadata_2025_split huggingface dataset:
Short-term flow dynamics of a retreating tidewater glacier: LeConte Glacier, Alaska, U.S.A.
Authors: O’Neel S. , Echelmeyer K. A. , Motyka R. J. 
Published: November 2007

AbstractAn analysis of motion in the terminus region of LeConte Glacier, Alaska, U.S.A., delineates mechanisms that are important to tidewater glacier stability. This glacier is undergoing rapid retreat. Since 1995 it has retreated 2 km and thinned >125 m at the present location of the terminus. Ice velocities in this region are quite high; at the terminus they exceed 27 m d−1. Our analysis reveals that fluctuations in speed and surface elevation are forced by ocean tides, surface melt and precipitation. The nearterminus ice speed is 180° out of phase with the tide, such that high tide corresponds to low speed. Smaller, melt-forced diurnal variations in speed are present throughout the lowermost 7 km. Speed-ups in excess of 10% of the mean often occur after rainstorms as a result of increased basal water pressure and storage, but the relation is not simple. The velocity does not vary over the spring and summer seasons.
Surface properties and processes of perennial Antarctic sea ice in summer
Authors: Haas Christian , Thomas David N. , Bareiss Jörg 
Published: November 2007

AbstractIce-core and snow data from the Amundsen, Bellingshausen and Weddell Seas, Antarctica, show that the formation of superimposed ice and the development of seawater-filled gap layers with high algal standing stocks is typical of the perennial sea ice in summer. The coarse-grained and dense snow had salinities mostly below 0.1‰. A layer of fresh superimposed ice had a mean thickness of 0.04–0.12 m. Gap layers 0.04–0.08 m thick extended downwards from 0.02 to 0.14 m below the water level. These gaps were populated by diatom standing stocks up to 439 μg L−1 chlorophyll a. We propose a comprehensive heuristic model of summer processes, where warming and the reversal of temperature gradients cause major transformations in snow and ice properties. The warming also causes the reopening of incompletely frozen slush layers caused by flood-freeze cycles during winter. Alternatively, superimposed ice forms at the cold interface between snow and slush in the case of flooding with negative freeboard. Combined, these explain the initial formation of gap layers by abiotic means alone. The upward growth of superimposed ice above the water level competes with a steady submergence of floes due to bottom and internal melting and accumulation of snow.
Basal-crevasse-fill origin of laminated debris bands at Matanuska Glacier, Alaska, U.S.A.
Authors: Ensminger Staci L. , Alley Richard B. , Evenson Edward B. , Lawson Daniel E. , Larson Grahame J. 
Published: November 2007

AbstractThe numerous debris bands in the terminus region of Matanuska Glacier, Alaska, U.S.A., were formed by injection of turbid meltwaters into basal crevasses. The debris bands are millimeter(s)-thick layers of silt-rich ice cross-cutting older, debris-poor englacial ice. The sediment grain-size distribution of the debris bands closely resembles the suspended load of basal waters, and of basal and proglacial ice grown from basal waters, but does not resemble supraglacial debris, till or the bedload of subglacial streams. Most debris bands contain anthropogenic tritium (3H) in concentrations similar to those of basal meltwater and ice formed from that meltwater, but cross-cut englacial ice lacking tritium. Stable-isotopic ratios (δ18O and δD) of debris-band ice are consistent with freezing from basal waters, but are distinct from those in englacial ice. Ice petrofabric data along one debris band lack evidence of active shearing. High basal water pressures and locally extensional ice flow associated with overdeepened subglacial basins favor basal crevasse formation.
Greenland ice-sheet mass-balance distribution: a variance analysis of existing field data
Authors: Six Delphine , Letréguilly Anne , Reynaud Louis 
Published: November 2007

AbstractA large number of mass-balance measurements have been carried out on the Greenland ice sheet, but few of the series obtained are well suited for statistical studies. Rather than looking at the global mass-balance value, this paper deals with the spatial and temporal mass-balance variability on the ice sheet. Two sorts of analysis are possible: direct comparisons of the series measured at a given site, or a broader approach involving comparisons between different sites using variance analysis. For glaciers in the southwest ablation area, a significant interannual variability (around 1.0 m w.e.) is found. This variability is spatially consistent. In the accumulation area, the results are more complex. For example, there is consistent evidence of year-to-year variations on the west–east Expéditions Glaciologiques Internationales au Groenland (EGIG) profile, but other closer sites are weakly correlated. These results emphasize the need for a better coverage of measurements over the entire ice sheet, as well as longer and more continuous measurement series.
A high-altitude snow chemistry record from Amundsenisen, Dronning Maud Land, Antarctica
Authors: Isaksson Elisabeth , Karlén Wibjörn , Mayewski Paul , Twickler Mark , Whitlow Sallie 
Published: November 2007

AbstractIn this paper a detailed record of major ions from a 20 m deep firn core from Amundsenisen, western Dronning Maud Land, Antarctica, is presented. The core was drilled at 75° S, 2° E (2900 m a.s.l.) during austral summer 1991/92. The following ions were measured at 3 cm resolution: Na+, Mg2+, Ca2+, Cl−, NO3−, S042− and CH3SO3H (MSA). The core was dated back to 1865 using a combination of chemical records and volcanic reference horizons. The volcanic eruptions identified in this core are Mount Ngauruhoe, New Zealand (1974–75), Mount Agung, Indonesia (1963), Azul, Argentina (1932), and a broad peak that corresponds in time toTarawera, New Zealand (1886), Falcon Island, South Shetlands, Southern Ocean (1885), and Krakatau, Indonesia (1883). There are no trends in any of the ion records, but the annual to decadal changes are large. The mean concentrations of the measured ions are in agreement with those from other high-altitude cores from the Antarctic plateau. At this core site there may be a correspondence between peaks in the MSA record and major El Niño–Southern Oscillation events.
Frazil-ice entrainment of sediment: large-tank laboratory experiments
Authors: Smedsrud Lars Henrik 
Published: November 2007

AbstractLaboratory experiments that simulate natural ice-formation processes and sediment entrainment in shallow water are presented. A 10–30 cm s−1 current was forced with impellers in a 20 m long, 1 m deep indoor tank. Turbulence in the flow maintained a suspension of sediments at concentrations of 10–20 mg L−1 at 0.5 m depth. Low air temperatures (∼−15°C) and 5 m s−1 winds resulted in total upward heat fluxes in the range 140–260 W m−2. The cooling produced frazil-ice crystals up to 2 cm in diameter with concentrations up to 4.5 g L−1 at 0.5 m depth. Considerable temporal variability with time-scales of <1 min was documented. A close to constant portion of the smaller frazil crystals remained in suspension. After some hours the larger crystals, which made up most of the ice volume, accumulated as slush at the surface. Current measurements were used to calculate the turbulent dissipation rate, and estimates of vertical diffusion were derived. After 5–8 hours, sediment concentrations in the surface slush were normally close to those of the water. After 24 hours, however, they were 2–4 times higher. Data indicate that sediment entrainment depends on high heat fluxes and correspondingly high frazil-ice production rates, as well as sufficiently strong turbulence. Waves do not seem to increase sediment entrainment significantly.
The surges of Variegated Glacier, Alaska, U.S.A., and their connection to climate and mass balance
Authors: Eisen O. , Harrison W. D. , Raymond C. F. 
Published: November 2007

AbstractOne of the questions still unanswered concerning the surge behavior of glaciers concerns their quasi-periodic occurrence. Some results on the phenomenological connection between local cumulative balance and surge initiation of Variegated Glacier, Alaska, U.S.A., are discussed here. Based on climate data from neighboring weather stations, an empirical relation between precipitation, temperature and local mass balance is established and used to reconstruct the annual balance at a location in the accumulation area back to 1905. Between the last four surges in 1946/47, 1964/65, 1982/83 and 1994/95, the ice-equivalent cumulative balance was 43.5 m on average, with a 1σ error of 1.2 m. Although the existence of a surge level cannot be directly interpreted in physical terms, it explains the variable length of the quiescent periods of Variegated Glacier by variations in the accumulation rate prior to the surge. We use the surge level to hindcast former unobserved surges, to compare the results with other surge datings obtained from photographs and to establish a complete surge history for Variegated Glacier for the 20th century.
Post-stagnation behavior in the upstream regions of Ice Stream C, West Antarctica
Authors: Price S. F. , Bindschadler R. A. , Hulbe C. L. , Joughin I. R. 
Published: November 2007

AbstractThe region where two active tributaries feed into the now stagnant Ice Stream C (ISC), West Antarctica, is thickening. In this region, we observe a correlation between faster ice flow (the tributaries) and elevated topography. We conclude that stagnation of ISC resulted in compression and thickening along the tributaries, eventually forming a “bulge” on the ice-sheet surface. Modern hydraulic potential gradients would divert basal meltwater from ISC to Ice Stream B (ISB). These gradients are primarily controlled by the bulge topography, and so likely formed subsequent to trunk stagnation. As such, we argue against “water piracy” as being the cause for ISC’s stagnation. Kinematic-wave theory suggests that thickness perturbations propagate downstream over time, but that kinematic-wave speed decreases near the stagnant trunk. This and modest diffusion rates combine to trap most of the tributary-fed ice in the bulge region. Using interfero-metric synthetic aperture radar velocity measurements, we observe that half of the ice within ISC’s southern tributary flows into ISB. That flow pattern and other observations of non-steady flow in the region likely result from stagnation-induced thickening along upper ISC combined with a longer period of thinning on upper ISB. If current trends in thickness change continue, more ice from upper ISC will be diverted to ISB.
Dynamical processes involved in the retreat of marine ice sheets
Authors: Hindmarsh Richard C.A. , Meur E. Le 
Published: November 2007

AbstractMarine ice sheets with mechanics described by the shallow-ice approximation by definition do not couple mechanically with the shelf. Such ice sheets are known to have neutral equilibria. We consider the implications of this for their dynamics and in particular for mechanisms which promote marine ice-sheet retreat. The removal of ice-shelf buttressing leading to enhanced flow in grounded ice is discounted as a significant influence on mechanical grounds. Sea-level rise leading to reduced effective pressures under ice streams is shown to be a feasible mechanism for producing postglacial West Antarctic ice-sheet retreat but is inconsistent with borehole evidence. Warming thins the ice sheet by reducing the average viscosity but does not lead to grounding-line retreat. Internal oscillations either specified or generated via a MacAyeal–Payne thermal mechanism promote migration. This is a noise-induced drift phenomenon stemming from the neutral equilibrium property of marine ice sheets. This migration occurs at quite slow rates, but these are sufficiently large to have possibly played a role in the dynamics of the West Antarctic ice sheet after the glacial maximum. Numerical experiments suggest that it is generally true that while significant changes in thickness can be caused by spatially uniform changes, spatial variability coupled with dynamical variability is needed to cause margin movement.
Longitudinal variations in cross-section morphology along a glacial valley: a case-study from the Tien Shan, China
Authors: Yingkui Li , Gengnian Liu , Zhijiu Cui 
Published: November 2007

AbstractA new model, the variable width/depth ratio (VWDR) model, is used to analyze longitudinal variations in cross-section morphology along glacial valleys. In the VWDR, the cross-sectional shape of a valley is expressed as a function of the width/depth ratio at various heights above the valley floor. Two parameters, m, a measure of the breadth of the valley floor, and n, a measure of the steepness of the valley sides, appear in the model. We have used the VWDR model to study morphological variations of cross-sections along glacial valleys in the middle Tien Shan mountains, China, and find that: (1) in valleys without tributaries, m increases (the valley floor becomes wider) and n becomes more negative (valley sides become steeper) from the head of the valley to the equilibrium line, and then m decreases and n becomes less negative to the end of the valley; (2) in valleys with tributaries, a similar pattern is observed, with an oscillating maximum in m and minimum in n in those sections where a tributary enters the main valley. These characteristics are believed to reflect a maximization of glacial erosion potential in the vicinity of the equilibrium line and in locations of confluence.
Glacier-climate interaction at low latitudes
Authors: Kaser Georg 
Published: November 2007

AbstractIn the low latitudes there is an absence of major thermal seasonality, yet there are three different climate regimes related to global circulation patterns and their seasonal oscillation: the humid inner tropics, the dry subtropics and, intermediate between these two, the outer tropics. For the respective glacier regimes the vertical profiles of specific mass balance (VBPs) are modeled considering vertical gradients of accumulation, air temperature and albedo, the duration of the ablation period and a factor for the ratio between melting and sublimation. The model is first calibrated with data from Hintereisferner, Austrian Alps, and is then applied to tropical conditions. The simulated VBP matches well the measured profiles from Irian jaya and Mount Kenya. Due to lack of field evidence, the subtropical VBP cannot be verified directly. However, application of the respective model versions separately to the humid and dry seasons of the outer-tropical Glaciar Uruashraju, Cordillera Blanca, Peru, provides reasonable results. Glaciers in the humid inner tropics are considered to be most sensitive to variations in air temperature, while dry subtropical glaciers are most sensitive to changes in air humidity. The two seasons of the outer tropics have to be viewed from these different perspectives.
A new ice-core record from Lomonosovfonna, Svalbard: viewing the 1920–97 data in relation to present climate and environmental conditions
Authors: Isaksson Elisabeth , Pohjola Veijo , Jauhiainen Tauno , Moore John , Pinglot Jean Francis , Vaikmäe Rein , van De Wal Roderik S.W. , Hagen Jon Ove , Ivask Jüri , Karlöf Lars , Martma Tõnu , Meijer Harro A.J. , Mulvaney Robert , Thomassen Martijn , van den Broeke Michiel 
Published: November 2007

AbstractIn 1997 a 121 m ice core was retrieved from Lomonosovfonna, the highest ice field in Spitsbergen, Svalbard (1250 m a.s.l.). Radar measurements indicate an ice depth of 126.5 m, and borehole temperature measurements show that the ice is below the melting point. High-resolution sampling of major ions, oxygen isotopes and deuterium has been performed on the core, and the results from the uppermost 36 m suggest that quasi-annual signals are preserved. The 1963 radioactive layer is situated at 18.5–18.95 m, giving a mean annual accumulation of 0.36 m w.e. for the period 1963–96. The upper 36 m of the ice core was dated back to 1920 by counting layers provided by the seasonal variations of the ions in addition to using a constant accumulation rate, with thinning by pure shear according to Nye (1963). The stratigraphy does not seem to have been obliterated by meltwater percolation, in contrast to most previous core sites on Svalbard. The anthropogenic influence on the Svalbard environment is illustrated by increased levels of sulphate, nitrate and acidity. Both nitrate and sulphate levels started to increase in the late 1940s, remained high until the late 1980s and have decreased during the last 15 years. The records of δ18O, MSA (methane-sulphonic acid), and melt features along the core agree with the temperature record from Longyearbyen and the sea-ice record from the Barents Sea at a multi-year resolution, suggesting that this ice core reflects local climatic conditions.
Cold firn and ice of high-altitude glaciers in the Alps: measurements and distribution modelling
Authors: Suter Stephan , Laternser Martin , Haeberli Wilfried , Frauenfelder Regula , Hoelzle Martin 
Published: November 2007

AbstractThe thermal regime of high-altitude accumulation areas in the Swiss Alps was systematically investigated on the Jungfraufirn, Bernese Alps, on the Breithornplateau, Valais Alps, and on Grenzgletscher, Valais Alps. In 1991, 1992 and 1994, temperatures were measured in a deep hole (120 m deep) and in several shallow holes (14–30 m deep). Whereas the wide névé of the Jungfraufirn at 3400–3600 m a.s.l. and the 3800 m high Breithornplateau seems to be predominantly temperate, cold firn and ice temperatures were measured throughout on Grenzgletscher (3900–4450 m a.s.l.). Mean firn temperatures on Grenzgletscher vary strongly and range between −3° and −14°C. A comparison between the measured temperature profiles and a one-dimensional heat-conduction calculation shows that the release of latent heat by penetrating and refreezing meltwater decisively influences the thermal pattern of the firn pack. A multiple linear regression model, based on measured firn temperatures from the European Alps and the parameters altitude and aspect, yields aspect-dependent lower boundaries for the occurrence of cold firn ranging between 3400 (northerly aspects) and 4150 m a.s.l. (southerly aspects). A total of 120 glaciers with cold-firn areas are found when applying the model to glacier inventory data from the European Alps.
Prevention of outburst floods from periglacial lakes at Grubengletscher, Valais, Swiss Alps
Authors: Haeberli Wilfried , Kääb Andreas , Mühll Daniel Vonder , Teysseire Philip 
Published: November 2007

AbstractFlood and debris-flow hazards at Grubengletscher near Saas Balen in the Saas Valley, Valais, Swiss Alps, result from the formation and growth of several lakes at the glacier margin and within the surrounding permafrost. In order to prevent damage related to such hazards, systematic investigations were carried out and practical measures taken. The evolution of the polythermal glacier, the creeping permafrost within the large adjacent rock glacier and the development of the various periglacial lakes were monitored and documented for the last 25 years by photogrammetric analysis of annually flown high-resolution aerial photographs. Seismic refraction, d.c. resistivity and gravimetry soundings were performed together with hydrological tracer experiments to determine the structure and stability of a moraine dam at a proglacial lake. The results indicate a maximum moraine thickness of > 100 m; extremely high porosity and even ground caverns near the surface may have resulted from degradation of sub- and periglacial permafrost following 19th/20th-century retreat of the partially cold glacier tongue. The safety and retention capacity of the proglacial lake were enhanced by deepening and reinforcing the outlet structure on top of the moraine complex. The water level of an ice-dammed lake was lowered and a thermokarst lake artficially drained.
Snow grain-size measurements in Antarctica
Authors: Gay Michel , Fily Michel , Genthon Christophe , Frezzotti Massimo , Oerter Hans , Winther Jan-Gunnar 
Published: November 2007

AbstractGrain-size is an important but not well-known characteristic of snow at the surface of Antarctica. In the past, grain-size has been reported using various methods, the reliability, reproducibility and intercomparability of which is not warranted. In this paper, we present and recommend, depending on available logistical support, three techniques of snow-grain sampling and/or imaging in the field as well as an original digital image-processing method, which we have proved provides reproducible and intercomparable measures of a snow grain-size parameter, the mean convex radius. Results from more than 500 samples and 3000 images of snow grains are presented, which yield a still spatially limited yet unprecedentedly wide picture of near-surface snow grain-size distribution from fieldwork in Antarctica. In particular, except at sites affected by a very particular meteorology, surface grains in the interior of the ice sheet are uniformly small (0.1–0.2 mm). The climate-related increase of grain-size with depth through metamorphism is, as expected, not spatially uniform. Our Antarctic snow grain-size database will continue to grow as field investigations bring new samples, images and measures of snow grain.
Stable-isotopic composition of precipitation over the northern slope of the central Himalaya
Authors: Kang Shichang , Kreutz Karl J. , Mayewski Paul A. , Qin Dahe , Yao Tandong 
Published: November 2007

AbstractStable-water-isotope data (δD and δ18O) from three groups of samples (fresh-snow and snow-pit samples collected on Qomolangma (Mount Everest) and Xixa-bangma during field seasons 1997, 1998 and 2001, and precipitation samples collected at Tingri station during summer 2000) are presented and used to survey the isotopic composition of precipitation over the northern slope of the central Himalaya. Multi-year snow-pit samples on Qomolangma have a local meteoric water-line (slope = 8) close to the global value. Deuterium excess (d = δD – 8δ18O) values at Tingri are much lower than those in fresh snow from Qomolangma, probably due to differences in moisture source and air-mass trajectories as well as local weather conditions. There is no obvious seasonal trend for d values in the Qomolangma region. A negative relationship exists between δ18O and d values in both fresh snow on Qomolangma and precipitation at Tingri. Fresh-snow samples collected from different altitudes on Xixabangma allow us to investigate the altitude effect on δ18O values in snow. Of four storm events, only one has an obvious altitude effect on δ18O variation and a very low gradient of −0.1 % per 100 m elevation.
Ice-dynamic conditions of Shirase Glacier, Antarctica, inferred from ERS SAR interferometry
Authors: Pattyn Frank , Derauw Dominique 
Published: November 2007

AbstractThe surface velocity field of Shirase Glacier, a fast-flowing East Antarctic outlet glacier, is determined from ERS synthetic aperture radar (SAR) images by means of speckle tracking using phase correlation, a technique which matches small image kernels of two complex SAR images by maximization of the local coherence. Velocity estimates are used to calculate surface strain rates, which are then used to calculate the large-scale, vertically integrated force balance and to determine the major stress components resisting the driving stress. For the whole glacier system, the driving stress is largely balanced by the basal drag, but with contributions from lateral drag up to 15% of the driving stress at the grounding line. Longitudinal stress gradients have only local importance to the balance of forces, limited to an area of a few square kilometers near the grounding line, where they resist the driving stress. In the grounded part of the glacier, >90% of the total ice velocity is due to basal sliding. Comparison with a balance-flux distribution of the Antarctic ice sheet suggests that the glacier in the downstream part of the Shirase drainage basin is close to equilibrium, showing a slight negative imbalance.