bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal and spatial variation of the surface albedo of Morteratschgletscher, Switzerland, as derived from 12 Landsat images
Authors: (Lisette) Klok E. J. , Greuell Wouter , Oerlemans Johannes
Published: November 2007

This investigation uses Landsat images from 12 days in 1999 and 2000 to study the spatial and temporal variation in surface albedo of a glacier with a rugged topography: Morteratschgletscher, Switzerland. Our retrieval method considers all processes that substantially influence the relationship between the satellite signal and the surface albedo. The correction for the anisotropy of the reflected radiation field of ice and snow ranges up to 0.10, depending on wavelength band, solar zenith angle and surface type. We analyzed the uncertainties in the retrieval method and mainly expect errors in satellite-derived albedos for areas with large variation in topography and high albedos. The latter is due to application of bidirectional reflectance distribution function (BRDF) parameterizations for the anisotropic correction to albedos outside the parameterizations’ validity. On average, satellite-derived albedos exceed the measured surface albedo by 0.03. The glacier tongue is characterized by bands of low and high albedo, relating to ice with higher and lower concentrations of debris. The ice albedo shows no dependence on altitude, except at 2000–2200 m a.s.l. It increases during summer, which is likely associated with rainfall, as concluded from a comparison between summer rainfall and measured albedos.
Subglacial environment inferred from bedrock-coating siltskins, Mendenhall Glacier, Alaska, U.S.A.
Authors: Carter Carissa L. , Dethier David P. , Newton Robert L.
Published: November 2007

Retreat of Mendenhall Glacier nearJuneau, Alaska, U.S.A., has exposed a bedrock ridge spotted with “siltskins”, patchy coatings of calcite-cemented clay-to sandsized lithic grains. Coatings 0.5–20 mm thick occur in two distinct morphologies. Thin, striated siltskins coat mainly stoss faces. Thicker, corrugated siltskins on lee faces consist of parallel micro-ridges elongated downslope. Thin-section analysis shows that siltskins consist of a basal, calcite-rich layer overlain by microlaminated layers of calcite-cemented lithic grains. Scanning electron microscope (SEM) energy-dispersive spectrometer (EDS) analysis of laminae and surfaces shows laterally persistent Ca/Si differences. Isotopic values for δO18 and δO13 ranged from −19.52‰ to −12.74‰ and −6.18‰ to −3.44‰, respectively, consistent with deposition from subglacial waters of varying isotopic composition and with derivation of carbon from inorganic sources. Corrugated siltskins are complex depositional features modified by erosional processes. Parallel micro-ridges spaced 1–10 mm apparently formed as sediment-rich water dripped down lee-slope rock faces. Ice–rock separation, flow energy and the transported sediment controlled the layering and depositional forms. Siltskins probably formed when a subglacial cavity system was active on the rock ridge and provide clues about how microscale hydrologic processes interact with larger-scale subglacial systems.
A two-dimensional shallow ice-flow model of Glacier de Saint-Sorlin, France
Authors: Meur Emmanuel Le , Vincent Christian
Published: November 2007

A two-dimensional ice-flow model based on the shallow-ice approximation (SIA) is used to investigate the dynamics of Glacier de Saint-Sorlin, France. This glacier is well suited for this kind of study. First, the particular geometry of the glacier itself as well as that of the bedrock surface allows for correct applicability of the SIA (zeroth-order equations), provided that thickness changes and termini positions rather than short-scale dynamics are considered. Secondly, the wealth of available data for the glacier including mass-balance series and records of glacier changes provides a reliable forcing and a powerful constraining set for the model. Steady-state simulations show realistic results and the capabilities of the model in reproducing the glacier extent at the beginning of the 20th century. An extensive parameter study of ice rheology and sliding intensity is also carried out and the results are checked against the thickness changes as well as the glacier termini positions since 1905. It is possible to find a parameter combination that best matches these two types of data with an ice-flow rate factor of 2 × 10−24 Pa−3 s−1 and a Weertman-type sliding factor of 5 × 10−14 m8 N−3 a−1 which both appear to be in agreement with similar inferences from recent modelling attempts.
Energy exchange processes in the marginal ice zone of the Barents Sea, Arctic Ocean, during spring 1999
Authors: Ivanov Boris V. , Gerland Sebastian , Winther Jan-Gunnar , Goodwin Harvey
Published: November 2007

We present some new results describing energy exchange processes of drifting sea ice in the marginal ice zone (MIZ) in the Barents Sea, Arctic Ocean. All measurements and observations of meteorological parameters and ice conditions were taken on board the Norwegian research vessel Lance from 3 to 22 May 1999. Components of surface heat balance were measured and correlated with ice conditions and synoptic observations. These results can be used in atmospheric boundary layer modelling as lower boundary conditions. A relationship was found between modelled turbulent heat fluxes and observed sea-ice concentrations.
Glaciological response to distal tephra fallout from the 1947 eruption of Hekla, south Iceland
Authors: Kirkbride Martin P. , Dugmore Andrew J.
Published: November 2007

Glacier responses to tephra deposition are shown to be highly variable where wind-transported eruption plumes produce narrow distal fallout zones with steep lateral thickness gradients. Significant but short-lived advances of faster-flowing glaciers can be triggered by deposition from modest eruptions. The 1947 eruption of Hekla, south Iceland, covered nearby glaciers with variable thicknesses of tephra, causing dramatic spatial variations in ablation rate. Relative snow ablation increased by an estimated >80% at the eastern margin of Eyjafjallajökull, but decreased by >54% at the western margin. Relative ice ablation increased by only 4% in the east but decreased by >75% at the western margin, only 15 km distant. The effect on mass balance therefore depends on tephra distribution as well as on the nature of the glacier surface. On Gígjökull, retardation of ablationwas greatest at the terminus, associated with an anomalous advance of ≥328 m between 1947 and 1954. Other glaciers in the fallout zone show either no recognizable response, or accelerated retreat. Advances will be short-lived due to the rapid redistribution of supraglacial tephra in a maritime climate, and the potential for discriminating between volcanically and climatically forced advances in the glacio-geomorphological record is low. The long-term glaciological effect of volcanism is to create thin, low-albedo covers after reworking, which make conditions less favourable for glaciation.
Surge-related topographic change of the glacier Sortebræ, East Greenland, derived from synthetic aperture radar interferometry
Authors: Pritchard Hamish , Murray Tavi , Strozzi Tazio , Barr Stuart , Luckman Adrian
Published: November 2007

A major surge of the glacier complex of Sortebræ, East Greenland, occurred between 1992 and 1995. The impact of this surge on the topography of Sortebræ was examined through the production of a pre-surge (1981) digital elevation model (DEM) from interpolated digital map data, and a post-surge DEM from differential synthetic aperture radar interferometry using European Remote-sensing Satellite (ERS) imagery. The combined vertical error is typically 30–40 m; however, downdraw of up to 270 m in the reservoir zone, and uplift of up to 145 m in the receiving zone were measured. The upper glacier reservoir area discharged in excess of 24.3 ± 9.5 km3volume over the surge, of which ∼12.5 km3was stored in the advanced lower glacier, the balance being lost, predominantly to calving.
On friction and surface cracking during sliding of ice on ice
Authors: Montagnat Maurine , Schulson Erland M.
Published: November 2007

As a complement to earlier measurements on the friction of both granular fresh-water ice and S2 columnar salt-water ice, new experiments were performed on the friction of S2 columnar fresh-water ice sliding against itself at low velocities (5 × 10−7 to 5 × 10−1 m s−1) and at −10°C, using the same double-shear device as was used earlier. The results showed that under a given set of experimental conditions the kinetic coefficient of friction of S2 fresh-water ice compares favorably with that of the other two variants.The experiments also revealed friction-induced surface cracks and recrystallized grains.These deformation features are explained, respectively, in terms of fracture mechanics and an earlier model of dynamic recrystallization in ice.
Variations of Glaciar Coronas, Pyrenees, Spain, during the 20th century
Authors: Chueca Javier , Julián Asunción , López Ignacio
Published: November 2007

Glaciar Coronas is one of the small cirque glaciers located in the Maladeta Range, central Spanish Pyrenees. The ice extends from 3220 to 3065 m a.s.l. Using early and modern photographs and aerial photographs, we study the evolution of the glacier during the 20th century, with particular focus on evaluating the variations in area, ice thickness and the withdrawal of the ice front. This information is compared with some basic climatic data (quarterly and annual evolution of temperatures and precipitation) recorded in the nearby Seira observatory. The results show that ice wastage, clearly associated with the main regional climatic evolution, has been dominant during the 20th century at Glaciar Coronas, but the rate has varied and has not been continuous. Three periods have been detected: (1) 1920s–early 1960s: ice depletion period; (2) early 1960s–mid-1980s: stabilization of the deglaciation process; (3) mid-1980s–1998: marked ice depletion period. The study shows a decrease in area of Glaciar Coronas from 19 ha in 1928 to 2.4 ha in 1998. The decrease in length from 1928 to 1998 has been 325 m.
Thickness changes on Whillans Ice Stream and Ice Stream C, West Antarctica, derived from laser altimeter measurements
Authors: Spikes Vandy Blue , Csatho Beáta M. , Hamilton Gordon S. , Whillans Ian M.
Published: November 2007

Repeat airborne laser altimeter measurements are used to derive surface elevation changes on parts of Whillans Ice Stream and Ice Stream C, West Antarctica. Elevation changes are converted to estimates of ice equivalent thickness change using local accumulation rates, surface snow densities and vertical bedrock motions. The surveyed portions of two major tributaries of Whillans Ice Stream are found to be thinning almost uniformly at an average rate of ∼1 m a−1. Ice Stream C has a complicated elevation-change pattern, but is generally thickening. These results are used to estimate the contribution of each surveyed region to the current rate of global sea-level rise.
Oxygen isotopes in glacier-river water, Austre Okstindbreen, Okstindan, Norway
Authors: Theakstone Wilfred H.
Published: November 2007

There is no discernible river discharge from Austre Okstindbreen, Norway, in winter; any water formed by basal melting is likely to be stored in isolated cavities or sediments at the bed. In summer, a baseflow component of discharge, relatively depleted of 18O, is diluted by water more enriched in 18O. Glacier ice meltwater with a high δ18O value passes rapidly through channelized systems, and emerges in the glacier river within a few hours. Headward extension of the systems in late summer may tap water stored within the glacier since the previous summer’s close-down. Stored water also is released during early melt-season events, when the low-capacity drainage systems cannot accommodate inputs. The high δ18O value indicates that the probable source of the released water is glacier ice or low-altitude snowfall. Stratigraphic variations of δ18O values, resulting from changing weather conditions, characterize the accumulating winter snowpack. During the melt season, the mean δ18O value of the residual pack rises. The water leaving it, depleted of 18O, passes slowly through the glacier, smoothing out variations of supply. δ18O values of rain vary between and within events, and their effect on glacier-river δ18O values is unpredictable.
Tropical glacier meltwater contribution to stream discharge: a case study in the Cordillera Blanca, Peru
Authors: Mark Bryan G. , Seltzer Geoffrey O.
Published: November 2007

Discharge measurements, climate observations and hydrochemical samples gathered monthly (1998/99) in the Yanamarey and Uruashraju glacier-fed catchments of the Cordillera Blanca, Peru, permit an analysis of the glacier meltwater contribution to stream-flow. These glacier catchments feed the Río Santa, which discharges into the Pacific Ocean. Based on a water-balance computation, glacier melt contributes an estimated 35% of the average discharge from the catchments. For comparison, a volumetric end-member mixing model of oxygen isotopes shows glacier melt contributes 30–45% to the total annual discharge. Based on stream geochemistry, discharge from the Yanamarey glacier catchment provides 30% of the annual volume discharged from the Querococha watershed, which is <10% glacierized. By analogy, the larger Río Santa watershed, also <10% glacierized, receives at least 12% of its annual discharge from melting glacier ice. Tributary watersheds to the Río Santa with larger fractions of glacier cover have less variable runoff and enhanced discharge, demonstrating that the glaciers effectively buffer stream discharge seasonally. With continued glacier melting, stream-flow will likely become more variable, and there will be less dry-season runoff.
Investigation of surface melting and dynamic thinning on Jakobshavn Isbræ, Greenland
Authors: Thomas Robert H. , Abdalati Waleed , Frederick Earl , Krabill William B. , Manizade Serdar , Steffen Konrad
Published: November 2007

Jakobshavn Isbræ is the most active glacier in Greenland, with an annual discharge of about 30 km3 of ice, and it is one of the few recently surveyed glaciers to thicken between 1993 and 1998, despite locally warm summers. Repeated airborne laser-altimeter surveys along a 120 km profile in the glacier basin show slow, sporadic thickening between 1991 and 1997, suggesting a small positive mass balance, but since 1997 there has been sustained thinning of several m a−1 within 20 km of the ice front, with lower rates of thinning further inland. Here, we use weather-station data from the coast and the ice sheet to estimate the effects on surface elevation of interannual variability in snowfall and surface melt rates, and thus to infer the temporal and spatial patterns of dynamic thinning. These show the glacier to have been close to balance before 1997 followed by a sudden transition to rapid thinning, initially confined to the lower reaches of the glacier (below about 500 m elevation), but progressively spreading inland until, between 1999 and 2001, thinning predominated over the entire surveyed region, up to 2000 m elevation. If this continues, the glacier calving front and probably its grounding line will retreat substantially in the very near future.
SEM/EDS observations of impurities in polar ice: artifacts or not?
Authors: Baker Ian , Cullen Daniel
Published: November 2007

A series of experiments was undertaken to determine the origin of filaments found in grain boundaries and impurity spots found in grain interiors of polar ice during observation in the scanning electron microscope. It is shown that although the filaments are artifacts, they demonstrate the presence of impurities segregated to the grain boundary planes. It is also demonstrated that the impurities observed in the grain interior reside there and were not transported from the grain boundaries during specimen preparation or observation.
Accuracy of three-dimensional glacier surface velocities derived from radar interferometry and ice-sounding radar measurements
Authors: Mohr Johan Jacob , Reeh Niels , Madsen Søren Nørvang
Published: November 2007

We present a method for analyzing the errors involved in measuring three-dimensional glacier velocities with interferometric radar. We address the surface-parallel flow assumption and an augmented approach with a flux-divergence (FD) term. The errors in an interferometric ERS-1/-2 satellite radar dataset with ascending- and descending-orbit data covering Storstrømmen glacier, northeast Greenland, are assessed. The FD error assessment is carried out on airborne 60 MHz ice-sounding radar data from the same area. A simple model of an interferometric radar system is developed and analyzed. The error sources considered include phase noise, atmospheric distortions, baseline calibration errors, a dry snow layer, and the stationary-flow assumption used in differential interferometry. The additional error sources in the analysis of FD errors are noise, bias and unknown variations of the ice thickness, and approximations of the ice-flow model. The example glacier is now building up following a surge. The analysis shows that in the case study presented the errors are small enough to justify the use of both the estimated surface-parallel flow term of the vertical velocity and the estimated FD term of the vertical velocity.
Initial investigations of dynamics of the maritime Koryto glacier, Kamchatka, Russia
Authors: Yamaguchi Satoru , Naruse Renji , Sugiyama Shin , Matsumoto Takane , Murav’yev Yaroslav D.
Published: November 2007

Ice-flow velocities were measured at Koryto glacier on Kamchatka Peninsula, Russia, during a 37 day period in the middle of the 2000 melt season. Six survey points from the upper to the lower reaches of the glacier exhibited daily fluctuations in surface horizontal speed with major peaks that appeared at all points.We argue that basal motion is the major cause of flow on Koryto glacier. Downward vertical velocities measured over most of the glacier during the survey period are likely due to shrinking of englacial and subglacial cavities. This result may imply that a large amount of water is deposited in the early summer. Since 1960, Koryto glacier has retreated by 450 m and this retreat has accelerated following a decrease in winter precipitation after the mid 1970s.The glacier has thinned by 10–50 m during the last 40 years.
Three-dimensional surface velocities of Storstrømmen glacier, Greenland, derived from radar interferometry and ice-sounding radar measurements
Authors: Reeh Niels , Mohr Johan Jacob , Madsen Søren Nørvang , Oerter Hans , Gundestrup Niels S.
Published: November 2007

Non-steady-state vertical velocities of up to 5 m a−1exceed the vertical surface-parallel flow (SPF) components over much of the ablation area of Storstrømmen, a large outlet glacier from the East Greenland ice sheet. Neglecting a contribution to the vertical velocity of this magnitude results in substantial errors (up to 20%) also on the south–north component of horizontal velocities derived by satellite synthetic aperture radar interferometry (InSAR) measurements. In many glacier environments, the steady-state vertical velocity component required to balance the annual ablation rate is 5–10 m a−1or more. This indicates that the SPF assumption may be problematic also for glaciers in steady state. Here we derive the three-dimensional surface velocity distribution of Storstrømmen by using the principle of mass conservation (MC) to combine InSAR measurements from ascending and descending satellite tracks with airborne ice-sounding radar measurement of ice thickness. The results are compared to InSAR velocities previously derived by using the SPF assumption, and to velocities obtained by in situ global positioning system (GPS) measurements. The velocities derived by using the MC principle are in better agreement with the GPS velocities than the previously calculated velocities derived with the SPF assumption.
A mechanism for differential frost heave and its implications for patterned-ground formation
Authors: Peterson Rorik A. , Krantz William B.
Published: November 2007

The genesis of some types of patterned ground, including hummocks, frost boils and sorted stone circles, has been attributed to differential frost heave (DFH). However, a theoretical model that adequately describes DFH has yet to be developed and validated. In this paper, we present a mathematical model for the initiation of DFH, and discuss how variations in physical (i.e. soil/vegetation properties) and environmental (i.e. ground/air temperatures) properties affect its occurrence and length scale. Using the Fowler and Krantz multidimensional frost-heave equations, a linear stability analysis anda quasi-steady-state real-time analysis are performed. Results indicate that the following conditions positively affect the spontaneous initiation of DFH: silty soil, small Young’s modulus, small non-uniform surface heat transfer or cold uniform surface temperatures, and small freezing depths. The initiating mechanism for DFH is multidimensional heat transfer within the freezing soil. Numerical integration of the linear growth rates indicates that expression of surface patterns can become evident on the 10–100 year time-scale.
Development, structure and composition of land-fast sea ice in the northern Baltic Sea
Authors: Granskog Mats A. , Martma Tõnu A. , Vaikmäe Rein A.
Published: November 2007

The structural and stable-oxygen-isotopic properties of sea-ice samples collected on land-fast sea ice in the northern Baltic Sea, at 60.2–65.7° N, 21.3–26.9° E, were used to estimate the contribution of snow ice to the total sea-ice thickness, and the fraction of snow in the snow-ice layers and in the total sea-ice thickness. The textural analysis of the sea-ice cores revealed a general structure of a granular surface layer and a columnar basal layer. Using different isotopic criteria to distinguish snow-ice layers, we estimate that snow-ice layers contributed on average 24–32% of the total ice thickness in the study region. Transition ice (intermediate granular–columnar ice) also contributed significantly to the total ice thickness. The snow in the snow-ice layers contributed on average 18–21% of the total sea-ice thickness (by mass), a significant contribution when compared to other regions with sea-ice cover. The methods used could be improved to give more accurate estimates, especially by improving knowledge of the temporal variability of the isotopic properties of the snow incorporated into the sea-ice cover. However, our results can be regarded as plausible estimates for the contribution of snow ice and snow to sea-ice growth in the study area.
Triaxial tests on snow at low strain rate. Part I. Experimental device
Authors: Moos Markus von , Bartelt Perry , Zweidler Adrian , Bleiker Ernst
Published: November 2007

A deformation-controlled triaxial apparatus has been developed in order to investigate the mechanical behaviour of alpine snow. Cylindrical specimens (58 mm in diameter, 126 mm in height) can be axially deformed by applying tensile or compressive strain rates between 2.4 × 10−7s−1and 2.4 × 10−2s−1. Compressed air is used to laterally load the snow specimens with pressures of up to 40 k Pa.The volumetric deformation is found by carefully encapsulating the snow samples in an airtight Mylar foil and measuring the expelled pore air during sample deformation. The multidimensional stress–strain behaviour can therefore be determined, and constitutive theories of snow advanced. The device is located in the cold rooms of the Weissfluhjoch research station of the Swiss Federal Institute for Snow and Avalanche Research. Some 180 tests have been performed over the last four winters. The density of the snow specimens varied between 190 and 435 kg m−3. Part I of this two-part paper discusses the development of the apparatus and the applied testing methodology. Qualitative results are provided. In Part II, a detailed analysis of the results is presented and the viscoelastic properties of snow quantified.
Ice cores from Arctic sub-polar glaciers: chronology and post-depositional processes deduced from radioactivity measurements
Authors: Pinglot Jean Francis , Vaikmäe Rein A. , Kamiyama Kokichi , Igarashi Makoto , Fritzsche Diedrich , Wilhelms Frank , Koerner Roy , Henderson Lori , Isaksson Elisabeth , Winther Jan-Gunnar , Van de wal Roderik S.W. , Fournier Marc , Bouisset Patrick , Meijer Harro A.J.
Published: November 2007

The response of Arctic ice masses to climate change is studied using ice cores containing information on past climatic and environmental features. Interpretation of this information requires accurate chronological data. Absolute dating of ice cores from sub-polar Arctic glaciers is possible using well-known radioactive layers deposited by atmospheric nuclear tests (maximum fallout in 1963) and the Chernobyl accident (1986). Analysis of several isotopes (3H, 137Cs) shows that 3H provides the most accurate dating of the 1963 maximum, as indicated also in comparison with results from total-beta measurements (90Sr and 137Cs). Mean annual net mass balances are derived from the dated ice cores from 1963 up to the date of the drillings. The 137Cs and 3H deposited by nuclear tests, after decay correction, are used to define a melt index for all 13 ice cores studied. The relative strength of melting and percolation post-depositional processes is studied on the basis of these 137Cs and 3H deposits.
Responses of various-sized alpine glaciers and runoff to climatic change
Authors: Baisheng Ye , Yongjian Ding , Fengjing Liu , Caohai Liu
Published: November 2007

This paper presents a glacier ice-flow model that simulates changes to alpine glaciers of various sizes and their runoff response to climate change in the Yili river basin in the Tien Shan mountains, northwestern China. It is suggested that the sensitivity of glaciers to climatic change is determined by glacier size. The change in glacial runoff does not keep pace with climatic change. As climate warms and glaciers retreat, the glacier runoff tends to increase and then decrease. The runoff peak and its timing depend not only on glacier size but also on the rate of air-temperature rise.
Quiescent-phase dynamics and surge history of a polythermal glacier: Hessbreen, Svalbard
Authors: Sund Monica , Eiken Trond
Published: November 2007

Hessbreen is a 5km2, polythermal glacier in southern Spitsbergen. It is believed to have surged at the end of the 19th century, and another surge started in 1969, not in 1972 as earlier studies suggested. The surge was probably triggered in the middle section of the glacier and affected the upper part approximately 4 years before including the whole glacier. Present velocities are low, increasing from 0.3m a-1 at the snout to 4.8 m a-1 above the equilibrium line. A distinct velocity reduction occurs where the glacier narrows. This suggests the velocities here are affected by the cold marginal and frontal ice. Large seasonal variations, with summer velocities of more than twice the winter velocities in the middle part of the glacier, indicate a seasonal change in the drainage system in this area. In the lower part there is no apparent sliding. The balance-flux estimate indicates that the actual ice flux is only about 50% of that required for steady state, so Hessbreen appears to be building up in the accumulation area. The surge duration is now estimated to be 8 years.
Probing the till beneath Black Rapids Glacier, Alaska, USA
Authors: Harrison William D. , Truffer Martin , Echelmeyer Keith A. , Pomraning Dale A. , Abnett Kevin A. , Ruhkick Richard H.
Published: November 2007

A heavy down-hole hammer actuated from the surface by a light composition rope was used to place instrumented probes into the active, 7m thick, clast-rich till underlying a site on Black Rapids Glacier, Alaska, USA, where the ice is 500m thick. A till penetration of about 2.5m was obtained, and greater depths seem possible. The probes measured pore-water pressure and two axes of tilt, which they broadcasted, without wires, to a receiver just above the ice–till interface.
Can climate warming induce glacier advance in Taylor Valley, Antarctica?
Authors: Fountain Andrew G. , Neumann Thomas A. , Glenn Paul L. , Chinn Trevor
Published: November 2007

Changes in the extent of the polar alpine glaciers within Taylor Valley, Antarctica, are important for understanding past climates and past changes in ice-dammed lakes. Comparison of ground-based photographs, taken over a 20 year period, shows glacier advances of 2-100 m. Over the past ~103years the climate has warmed. We hypothesize that an increase in average air temperature alone can explain the observed glacier advance through ice softening. We test this hypothesis by using a flowband model that includes a temperature-dependent softness term. Results show that, for a 2˚C warming, a small glacier (50 km2) advances ~25m and the ablation zone thins, consistent with observations. A doubling of snow accumulation would also explain the glacial advance, but predicts ablation-zone thickening, rather than thinning as observed. Problems encountered in modeling glacier flow lead to two intriguing but unresolved issues. First, the current form of the shape factor, which distributes the stress in simple flow models, may need to be revised for polar glaciers. Second, the measured mass-balance gradient in Taylor Valley may be anomalously low, compared to past times, and a larger gradient is required to develop the glacier profiles observed today.
The Kolka-Karmadon rock/ice slide of 20 September 2002: an extraordinary event of historical dimensions in North Ossetia, Russian Caucasus
Authors: Haeberli Wilfried , Huggel Christian , Kääb Andreas , Zgraggen-Oswald Sonja , Polkvoj Alexander , Galushkin Igor , Zotikov Igor , Osokin Nikolay
Published: November 2007

On 20 September 2002, an enormous rock/ice slide and subsequent mud-flow occurred on the northern slope of the Kazbek massif, Northern Ossetia, Russian Caucasus. It started on the north- northeast wall of Dzhimarai-Khokh (4780 ma.s.l.) and seriously affected the valley of Genaldon/ Karmadon. Immediate governmental actions, available scientific information, first reconstructions, hazard assessments and monitoring activities as well as initial expert judgments/recommendations are documented in order to enable more detailed analyses and modelling of the event by the wider scientific community. Among the most remarkable aspects related to this event are (1) the relation between the recent event and somewhat smaller but quite similar events that occurred earlier in historical times (1835, 1902), (2) the interactions between unstable local geological structures and complex geothermal and hydraulic conditions in the starting zone with permafrost, cold to polythermal hanging glaciers and volcanic effects (hot springs) in close contact with each other, (3) the erosion and incorporation of a debris-covered valley glacier largely enhancing the sliding volume of rocks, ice, firn, snow, water and probably air to a total of about 100 × 106m3, and (4) the astonishingly high flow velocities (up to 300 km h-1) and enormous length of travel path (18 km plus 15 km of debris/mud-flow). This extraordinary case illustrates that large catastrophic events in high mountain regions typically involve a multitude of factors and require integrated consideration of complex chains of processes, a task which must be undertaken by qualified groups of experts.
West Antarctic ice-stream discharge variability: mechanism, controls and pattern of grounding-line retreat
Authors: Hulbe Christina L. , Fahnestock Mark A.
Published: November 2007

West Antarctic ice streams show pronounced flow variability in their downstream reaches, with changes stranding formerly fast-flowing ice and redirecting discharge. A simple model, in which the temperature gradient in basal ice provides control of fast sliding in the downstream reach, can explain this behavior. Downstream thinning steepens the temperature gradient near the bed, increasing upward heat flow and the tendency toward basal freezing. The basal temperature gradient is steepest and the tendency toward basal freezing the strongest in ice that has experienced the most rapid downstream thinning, that is, the fastest-flowing ice. The most ‘successful’ rapid outflows are regions where basal water from elsewhere is likely to be consumed. Freezing here leads to episodic slow-downs and redirections of flow, the history of which appears in satellite imagery as ice rises, distorted streaklines, and margin jumps created when discharge migrates to areas with more favorable basal conditions. One compelling consequence of this process is that it makes catastrophic collapse less likely; if discharge currents are forced to slow when they become too fast (thin), then there may be an upper bound on the retreat rate and discharge flux of the West Antarctic ice sheet (WAIS) ice-stream system under the present climate.
A comparison of three methods of mass-balance determination in the Tuyuksu glacier region, Tien Shan, Central Asia
Authors: Hagg Wilfried J. , Braun Ludwig N. , Uvarov Vladimir N. , Makarevich Konstantin G.
Published: November 2007

A photogrammetric survey in 1998 formed the basis for compiling a map of the Tuyuksu glacier region in the northern Tien Shan, Central Asia. Comparison with a map from 1958 enables calculation of the change in glacier volume over 40 years. The results are compared with direct annual measurements carried out continuously since 1956. Central Tuyuksu glacier shows a mass balance of –12.6 mw.e. for the geodetic method and –16.8 m for glaciological measurements. In view of the high accuracy of the maps, the discrepancy can be explained mainly by deficiencies in the glaciological measurements. Application of the precipitation–runoff model HBV-ETH represents the hydrological method of mass-balance determination and delivers specific mass-balance losses almost twice those indicated by the geodetic observations. This discrepancy is suspected to be caused by erroneous runoff measurements. The volume balance derived by the geodetic method is used to calibrate both the glaciological and the hydrological method.
Ice-flow-induced scattering zone within the Antarctic ice sheet revealed by high-frequency airborne radar
Authors: Matsuoka Kenichi , Uratsuka Seiho , Fujita Shuji , Nishio Fumihiko
Published: November 2007

To better understand how internal radar echoes depend on ice-flow conditions and radar polarization, we surveyed two basins in East Antarctica using 179 MHz airborne radar. We compared radar echoes from three ice-flow conditions: parallel sheet flow in the main stream of a basin, convergent flow towards an ice stream, and longitudinal compression by nunataks. We detected a distinct zone of high radar scattering several hundred meters thick at middle depths in the latter two regions. This high-scattering zone was detected only when the radar polarization plane was parallel to the compression axis in ice. Such a high-scattering zone was not found in the parallel-flow region, regardless of the polarization. Using a recently developed theory of radar scattering in ice, we interpret the high-scattering zone as being caused by crystal-orientation-fabric alternations among adjacent ice layers due to difference in horizontal strain components. We argue that the spatial variation of the high-scattering zone is crucial for understanding past and present flow features.
Distribution of soluble impurities in cold glacial ice
Authors: Barnes Piers R.F. , Wolff Eric W.
Published: November 2007

Understanding the microstructure of ice underpins the interpretation of ice-core measurements and many ice-sheet properties. A detailed study of polar snow and ice using scanning electron microscope (SEM) and X-ray analysis revealed the micro-structural distribution of soluble impurities. Sublimation under vacuum (etching) concentrated impurity from both the bulk and grain boundaries on to the specimen surfaces in detectable quantities. Sublimation in the cold room before examination (pre-etching) collected previously unobservable quantities of impurity at triple junctions. A heterogeneous distribution of impurities was observed. Chloride was frequently found to originate from the lattice, but not usually at triple junctions. Other impurities, particularly sodium chloride, were detected at grain boundaries and bubble surfaces. Sulphate was often found at triple junctions in specimens containing a high bulk concentration of the acid, frequently in conjunction with cations. This suggests the possibility that veins were only filled with significant amounts of impurity when the surrounding grain boundaries were saturated. The model of impurity arrangement inferred from the results reconciles differences between previous SEM studies; additionally it is consistent with and explains recent electrical conduction observations. The disconnected arrangement of impurity-filled grain boundaries and veins limits opportunities for significant post-depositional solute movement.
Vertical-strain measurements in firn at Siple Dome, Antarctica
Authors: Hawley Robert L. , Waddington Edwin D. , Lamorey Gregg W. , Taylor Kendrick C.
Published: November 2007

We measured vertical strain in the firn at Siple Dome, Antarctica, using two systems, both of which measure relative displacements over time of metal markers placed in an air-filled borehole. One system uses a metal-detecting tuned coil, and the other uses a video camera to locate the markers. We compare the merits of the two systems. We combine steady-state calculations and a measured density profile to estimate the true vertical-velocity profile. This allows us to calculate a depth-age scale for the firn at Siple Dome. Our steady-state depth-age scale has ages ≈10-15% younger at any given depth when compared to depth-age scales derived by layer counting in a core 40 m away. The age of a visible ash layer at 97 m in the core is 665 ± 30 years, in agreement with a similar analysis conducted at Taylor Dome, Antarctica, where the same ash is also seen, providing an additional dated tie point between the two cores.
Two-dimensional electrical stratigraphy of the Siple Dome (Antarctica) ice core
Authors: Taylor Kendrick C. , Alley Richard B.
Published: November 2007

A two-dimensional array of electrical conductivity measurements (ECM) has been used to image the acidity of the Siple Dome (Antarctica) ice core in a vertical plane. Annual layering and possible stratigraphic discontinuities are apparent. A brief disruption to the chemical stratigraphy is detected at 680 m. Below 800 m, weaker layering occurs and is interpreted as the result of post-depositional migration of chemical species. This technique provides a way to observe the horizontal continuity of chemical layers in an ice core and identify some types of flow irregularity.
Chemical properties of brackish water ice in the Bothnian Bay, the Baltic Sea
Authors: Granskog Mats A. , Virkkunen Kristiina , Thomas David N. , Ehn Jens , Kola Harri , Martma Tõnu
Published: November 2007

The behavior of majorions, δ18O, dissolved organic carbon (DOC) and trace elements was studied during the initial freezing of low-saline water (3 practical salinity units) in a freezing experiment. Samples were also collected from first-year sea ice from pack ice in the Bothnian Bay, northern Baltic Sea. During initial ice formation, the major-ion ratios in sea ice indicated variable behavior, with some ions showing relative enrichment (sulfate, calcium and magnesium), conservative behavior (sodium) or relative depletion (potassium) compared to sea water at the same salinity. DOC, iron and aluminum showed enrichment in the ice, while zinc was depleted to salinity. Lead was detected in surface snow-ice layers only, implying atmospheric accumulation. First-year sea ice, with a variable growth and thermal history, showed behavior for major ions similar to that observed in new ice. However, for trace elements the picture was much more complicated, most likely due to active secondary processes such as atmospheric supply and biological activity. Ice growth has a potential impact on the chemical budgets and cycling of some elements, especially those which are selectively rejected/retained during sea-ice formation, particularly in the shallow parts of the Bothnian Bay covered with a land-fast ice cover.
The basal speed of valley glaciers: an inverse approach
Authors: Truffer Martin
Published: November 2007

Geophysical inverse methods are used to calculate the basal motion of a glacier. They are applied to a one-dimensional forward model that can be linearized to make the analysis simpler. The inverse method finds a solution that fits the data within a given error. It selects for smooth solutions to discriminate against unrealistic oscillations. The method is applied to a simple model glacier of uniform shape and thickness to test how well a given basal motion field can be reconstructed. It shows, as expected, that optimizing for smoothness lowers maxima and increases minima of the solution. A step change in basal velocity is drawn out in the inversion over a distance that is given by the half-width of a resolving function. This is typically about three times the ice thickness, but is also affected by the sampling rate of the data. The method is then applied to two glaciers where suitable data are available: Brown Glacier on Heard Island, southern Indian Ocean, and McCall Glacier in the Brooks Range, Alaska, U.S.A. The McCall results agree well with earlier estimates of basal motion.
Automatic glacier ablation measurements using pressure transducers
Authors: Bøggild Carl Egede , Olesen Ole B. , Andreas P.Ahlstrøm , Jørgensen Peer
Published: November 2007

An instrument is described that automatically records ice ablation while eliminating the need for ablation stakes. A pressure transducer placed at the bottom of a hole drilled into the ice is connected by a hose to a bladder lying on the surface. Ice ablation is detected as a reduction in the hydrostatic pressure measured by the transducer.
A sedimentological and isotopic study of the origin of supraglacial debris bands: Kongsfjorden, Svalbard
Authors: Hubbard Bryn , Glasser Neil , Hambrey Michael , Etienne James
Published: November 2007

Debris bands associated with supraglacial moraines and associated basal deposits have been logged and sampled for their ice and debris at three glaciers in northwest Spitsbergen, Svalbard. Physical properties, including sediment concentrations, sediment particle-size distributions, clast macro-fabrics, and oxygen isotope compositions, indicate that all transverse and some longitudinal debris bands originate from the basal zone of these glaciers. Transverse supraglacial bands are composed of extensive stratified-facies basal ice that is enriched in 18O and which contains polymodal debris with spatially consistent clast fabrics. These properties suggest initial formation as basal ice and subsequent elevation into an englacial position by thrusting rather than formation as crevasse fills. The formation of longitudinal debris bands results from laterally compressive folding in response to the convergence of multiple flow units into a narrow glacier tongue. In common with transverse debris bands, longitudinal bands appear to be composed of stratified basal ice. The bands exposed at the surface of austre Brøggerbreen comprise two subfacies, strongly suggesting that the glacier was at least partially warm-based in the past, when the basal ice formed.
Recumbent folding in ice sheets: a core-referential study
Authors: Paul Jacobson H. , Waddington Edwin D.
Published: November 2007

To better understand apparent stratigraphic disturbances in ice cores such as Greenland Ice Sheet Project 2 (GISP2), we examine how ice-sheet flow can transform gentle open folds into order-disturbing recumbent folds. The initial disturbances in the stratigraphy have their roots in transient dynamic processes and local rheological inhomogeneities, but the kinematics of even a simple ice-flow model can deform these disturbances enough to alter paleoclimatic interpretation of an ice core. The local vorticity number suggests which structures can be passively overturned, but analyzing the finite strain along particle paths gives a more complete picture, especially when taken relative to a hypothetical core location. Core-relative isochrones, or “pre-cores”, predict which stratigraphic disturbances will appear as obviously overturned layers in a core. The deformation-gradient tensor along particle paths allows us to calculate the rotation of segments of various reference slopes. These calculations suggest that observed 20° dips in the GISP2 core are rotating on a time-scale of a few hundred years and could result from distortions with much smaller slopes produced upstream. The time during which they can be recognized to be overturning is short because the rotation rate is high. Once overturned they are flattened further and may be hard to recognize, especially in the small cross-section of a core.
The flow of Fireweed rock glacier, Alaska, U.S.A.
Authors: Bucki Adam K. , Echelmeyer Keith A.
Published: November 2007

Fireweed rock glacier is a large rock glacier in south central Alaska, U.S.A. It flows relatively fast, with velocities up to 3.5 ma–1, and exhibits both seasonal and annual velocity variations, some of which are related to periodic terminus calving and increased rainfall. Our analysis reveals that motion is likely concentrated in a pseudo-rectangular channel within the larger parabolic channel with a “shear plane” at ~27 m depth. There is likely motion along the shear plane as well as internal deformation above it. We estimate that the ice—rock mixture is up to seven times softer than clean glacier ice with a temperature of –2°C. Calving at the terminus is an important component of the mass balance of this rock glacier.
Evolution of cryoconite holes and their contribution to meltwater runoff from glaciers in the McMurdo Dry Valleys, Antarctica
Authors: Fountain Andrew G. , Tranter Martyn , Nylen Thomas H. , Lewis Karen J. , Mueller Derek R.
Published: November 2007

Cryoconite holes are water-filled holes in the surface of a glacier caused by enhanced ice melt around trapped sediment. Measurements on the ablation zones of four glaciers in Taylor Valley, Antarctica, show that cryoconite holes cover about 4–6% of the ice surface. They typically vary in diameter from 5 to 145 cm, with depths ranging from 4 to 56 cm. In some cases, huge holes form with 5 m depths and 30 m diameters. Unlike cryoconite holes elsewhere, these have ice lids up to 36 cm thick and melt from within each spring. About one-half of the holes are connected to the near-surface hydrologic system and the remainder are isolated. The duration of isolation, estimated from the chloride accumulation in hole waters, commonly shows ages of several years, with one hole of 10 years. The cryoconite holes in the McMurdo Dry Valleys create a near-surface hydrologic system tens of cm below the ice surface. The glacier surface itself is generally frozen and dry. Comparison of water levels between holes a few meters apart shows independent cycles of water storage and release. Most likely, local freeze–thaw effects control water passage and therefore temporary storage. Rough calculations indicate that the holes generate at least 13% of the observed runoff on the one glacier measured. This hydrologic system represents the transition between a melting ice cover with supraglacial streams and one entirely frozen and absent of water.