bluuebunny/crossref_metadata_2025 huggingface dataset:
Does englacial water storage drive temperate glacier surges?
Authors: Lingle Craig S. , Fatland Dennis R.
Published: November 2007

Hydrological studies of surge-type and steady-flow glaciers, combined with recent space-borne synthetic aperture radar interferometry measurements of the motion of Bagley Ice Valley, Alaska, U.S.A., during its 1993–95 surge, suggest a temperate-glacier surge hypothesis that is consistent with observational evidence and appears capable of shedding light on several aspects of surge behavior. We propose that the fundamental driver of temperate-glacier surges is englacial storage of water, combined with gravity-driven movement of stored water to the bed during winter. Whether a given glacier is surge-type is a matter not of whether, but of the degree to which, these processes occur. A surge-type glacier must have sufficient storage capacity for continued downward movement of englacially stored water during winter to finally overwhelm the constricted basal drainage system, thereby forcing pervasive failure of the subglacial till — or, alternatively, widespread and rapid basal sliding — thus initiating a surge. We further propose that the “sufficient storage capacity” requirement is most easily met by glaciers with large thickness, which are therefore likely to be long and to have, on average, low surface slopes. The average length \of the surge cycle in a given region appears to be a function of the mass balances, which, after each surge, determine the time required to restore glaciers to their pre-surge geometries. We suggest that the stochastic timing of surge onset for a particular glacier, however, is a result of the uncertainty of the meteorological conditions required to cause englacial storage of a sufficiently large volume of water.
Stratigraphic analysis of Dome Fuji Antarctic ice core using an optical scanner
Authors: Takata Morimasa , Iizuka Yoshinori , Hondoh Takeo , Fujita Shuji , Fujii Yoshiyuki , Shoji Hitoshi
Published: November 2007

Long-term changes of snow-accumulation rate in Antarctica are a major uncertainty in our understanding of past climate. Because the visible strata in polar ice are due to variations in the sizes and concentrations of air inclusions and microparticles, the scattered light intensity from an ice core yields valuable information on the stratification, which is likely to provide estimates of the annual accumulation rates. Identification of each layer is therefore necessary, and we developed an optical scanner apparatus to record detailed visible strata of ice cores. The apparatus records the two-dimensional distribution of light-scattering intensity along ice-core samples and produces an image of the whole ice-core sample by an image analysis process. These images showed that ice from Dome Fuji ice core contained a large number of layers. Volcanic layers were also well identified. We processed the scattering intensity on the enhanced intensity images to produce an intensity profile. This profile showed that the period of the intensity variations is consistent with a core-dating model applied to the Dome Fuji ice core. We also found that the intensity peaks are closely correlated to peaks in Ca2+ ion concentrations. Thus, our scanning method is a promising approach to measuring annual-layer thickness and, as a result, may be used to infer past accumulation rates in Antarctica.
A further assessment of surface temperature changes at stations in the Antarctic and Southern Ocean, 1949–2002
Authors: Jacka Tim H. , Budd William F. , Holder Andrew
Published: November 2007

Statistical analyses are carried out, of the annual mean surface air temperature at occupied stations and automatic weather stations in the Antarctic and Southern and Pacific Oceans. The data are studied in four groupings: coastal Antarctica (excluding the Antarctic Peninsula), inland Antarctica, the Antarctic Peninsula and the Southern Ocean/Pacific Ocean islands. We find that within each of these four groupings the average trend indicates warming. For coastal Antarctica the trend is ∼0.8°C(100 a)–1. Inland, the results are less clear, but the mean trend is to a warming of ∼1.0°C(100 a)–1. For the Peninsula stations it is ∼4.4°C(100 a)–1, and for the ocean stations the average trend is ∼0.8°C(100 a)–1. The results indicate a reduction in the warming trend since our last analysis 6 years ago. While the Pinatubo (Philippines) volcanic eruption may have had some influence on this reduction in the warming rate, examination of the interannual variations in the temperature record shows variability has continued high since the recovery from any such effect. There has been a further period of cooler temperatures in coastal and inland Antarctica in that time, yet a warmer period in the Peninsula and ocean islands.
Chemical composition of volcanic glasses in visible tephra layers found in a 2503 m deep ice core from Dome Fuji, Antarctica
Authors: Kohno Mika , Fujii Yoshiyuki , Hirata Takafumi
Published: November 2007

Twenty-six ash layers were found in a 2503 m deep ice core from Dome Fuji station, East Antarctica. In order to gain information about the sources of ash particles found in the layers, major and trace element abundances have been measured. The particles found in 21 of the 26 layers were commonly a few tens of μm in size, suggesting that they originated from volcanoes located in and around the Antarctic. On the basis of comparison of the major-element compositions of these tephras with reference to volcanic rocks and ash, the tephras were divided into three types: (1) tholeiitic basalt to dacite, (2) calc-alkaline andesite, and (3) trachyandesite to trachyte. The source regions appear to be (1) South Sandwich Islands, Southern Ocean, (2) South Shetland Islands, Antarctica, and/or a southern part of the volcanic zone of the Andes, and (3) Marie Byrd Land and/or Victoria Land, Antarctica, respectively. The tephras found in the other five ash layers were significantly smaller (< 5 μm), suggesting that they traveled over longer distances. Abundances of trace elements for the alkaline tephra collected from one layer revealed a possible genetic link to volcanic rocks from Marie Byrd Land. In order to correlate between ice cores from Dome Fuji and Vostok, Antarctica, which are widely separated, we found coeval ash layers serving as stratigraphic markers of Antarctic ice cores. A comparison of profiles of 18O/16O (δ18O) and 2H/1H (δD) for the Dome Fuji and Vostok cores indicates that eight ash layers are equivalent in the two cores. A clear correlation was found for the chemical compositions of six of these ash layers, indicating a high potential for key correlation beds between the deep ice cores from Dome Fuji and Vostok.
Climate variability along latitudinal and longitudinal transects in East Antarctica
Authors: Magand Olivier , Frezzotti Massimo , Pourchet Michel , Stenni Barbara , Genoni Laura , Fily Michel
Published: November 2007

In the framework of the International Trans-Antarctic Scientific Expedition (ITASE) programme, France and Italy carried out a traverse along one west–east and two north–south transects in East Antarctica from November 2001 to January 2002. Eighteen shallow snow–firn cores were drilled, and surface snow samples were collected every 5km along the traverse. Firn temperatures were measured in boreholes down to 30 m. The cores were analyzed for β radioactivity to obtain snow accumulation-rate data. The surface snow samples were analyzed for δ18O to correlate isotopic values with borehole temperatures. Multiple regression analysis shows a global near-dry-adiabatic lapse rate and a latitudinal lapse rate of 1.05˚C(˚ lat. S)–1, in the Dome C drainage area. Analysis of firn temperatures reveals a super-adiabatic lapse rate along the ice divide between Talos Dome and the Southern Ocean coast, and in some sectors along the ice divide between the Astrolabe Basin and D59. Snow accumulation rates and firn temperatures show warmer temperatures and higher accumulation values close to the ice divides extending from Talos Dome and Dome C to the Southern Ocean. The spatial pattern of data is linked with a katabatic-wind-source basin and moisture-source region.
The effect of anisotropic flow properties on ice-sheet surface elevation change
Authors: Wang Weili , Li Jun , Zwally Jay , Morgan Vin , Van Ommen Tas D.
Published: November 2007

An ice-flow model has been developed and applied to Law Dome, East Antarctica, at the location of the Dome Summit South deep borehole. The results are used to reconstruct an ice-sheet history of accumulation rate, ice thickness and the rate of change in ice thickness. The focus of this study is on the effect of the variation in anisotropic flow properties on the ice-sheet surface elevation change. The enhancement factor, defined as the ratio of the strain rate for anisotropic ice to the strain rate for isotropic ice, is used in the ice-flow relations to account for the anisotropic properties of the ice with fabric development. The model is run with the various ice rheologies which represent anisotropic or isotropic ice-flow properties. The results show that the model incorporating anisotropic flow properties of the ice is more sensitive to the climate-change history.
Electromagnetic reflecting properties of sub-ice surfaces
Authors: Bianchi Cesidio , Forieri Alessandro , Tabacco Ignazio E.
Published: November 2007

The power strength of the radio-echo signal coming from reflecting sub-ice surfaces is used to determine the nature of the reflecting surface, i.e. rock, water or sea water. Electromagnetic analysis shows that the amplitude variations detected by radio-echo sounding are mainly due to the nature of the interface as well as the concave or convex shape of the reflectors. In this paper, some relevant profiles showing the power variations due to the different nature of the interface and the shape of the reflectors are presented. These results are important both for surface shape determination and for subglacial lake detection.
Vostok (Antarctica) ice-core time-scale from datings of different origins
Authors: Salamatin Andrey N. , Tsyganova Elena A. , Lipenkov Vladimir Ya. , Petit Jean Robert
Published: November 2007

Three different approaches to ice-core age dating are employed to develop a depth–age relationship at Vostok, Antarctica: (1) correlating the ice-core isotope record to the geophysical metronome (Milankovich surface temperature cycles) inferred from the borehole temperature profile, (2) importing a known chronology from another (Devils Hole, Nevada, USA) paleoclimatic signal, and (3) direct ice-sheet flow modeling. Inverse Monte Carlo sampling is used to constrain the accumulation-rate reconstruction and ice-flow simulations in order to find the best-fit glaciological time-scale matched with the two other chronologies. The general uncertainty of the different age estimates varies from 2 to 6 kyr on average and reaches 6–15 kyr at maximum. Whatever the causes of this discrepancy might be, they are thought to be of different origins, and the age errors are assumed statistically independent. Thus, the average time-scale for the Vostok ice core down to 3350m depth is deduced consistent with all three dating procedures within the standard deviation limits of ±3.6 kyr, and its accuracy is estimated as 2.2 kyr on average. The constrained ice-sheet flow model allows, at least theoretically, extrapolation of the ice age–depth curve further to the boundary with the accreted lake ice where (at 3530m depth) the glacier-ice age may reach ∼2000 kyr.
The EPICA ice core from Dronning Maud Land: first results from stable-isotope measurements
Authors: Oerter Hans , Graf Wolfgang , Meyer Hanno , Wilhelms Frank
Published: November 2007

The European Project for Ice Coring in Antarctica (EPICA) focuses on the drilling of two deep ice cores, the first at Dome C and the second at Kohnen station (75°00’ S, 0°04’ E) in Dronning Maud Land (DML). This paper deals with stable-isotope records from ice cores drilled in DML. In the first season, the deep EPICA DML core reached a depth of 450 m, recovering ice approximately 7000 years old. Generally, the δ18O record indicates a stable Holocene climate and shows low variability. However, during the last 4000 years (based on a preliminary time-scale) the δ18O values decrease continuously by about 0.6%, and the deuterium excess values increase by about 0.5%. The correlation between δ18O and the deuterium excess d is investigated for a 50m long core section and the near-surface snow. High-pass filtered profiles are positively correlated, whereas the correlation between low-pass filtered profiles is negative. A post-depositional effect due to diffusion processes can be seen in a sub-annually resolved profile from snow-pit samples. Changes in the seasonality of the evolution of the snow cover and the consequences for stable-isotope content are demonstrated with data from ice core B31.
Ground ice in permafrost on Seymour (Marambio) and Vega Islands, Antarctic Peninsula
Authors: Ermolin Evgeniy , De Angelis Hernán , Skvarca Pedro , Rau Frank
Published: November 2007

Seymour (Marambio) and Vega Islands occur within the continuous permafrost zone of the northeastern Antarctic Peninsula. Results are presented of investigations on the occurrence, distribution, morphology and genesis of ground ice, a key aspect of permafrost research in this region. According to its morphology, ice content, buried ice type and possible upper Quaternary conditions, permafrost is divided into two cryoformations: epigenetic and syngenetic. Based on field and remote-sensing data, 76.6 km2 of Seymour Island and 81.0 km2 of Vega Island are characterized by permafrost, with estimated ice contents of 0.06 and 1.41 km3, respectively. Different genetic ground-ice types are distinguished and a regional morphogenetic classification of ground ice is proposed.
Accumulation variability derived from an ice core from coastal Dronning Maud Land, Antarctica
Authors: Kaczmarska Marzena , Isaksson Elisabeth , Karlöf Lars , Winther Jan-Gunnar , Kohler Jack , Godtliebsen Fred , Olsen Lena Ringstad , Hofstede Coen M. , Van Den Broeke Michiel R. , Van De Wal Roderik S. W. , Gundestrup Niels
Published: November 2007

A 100 m long ice core was retrieved from the coastal area of Dronning Maud Land (DML), Antarctica, in the 2000/01 austral summer. The core was dated to AD 1737 by identification of volcanic horizons in dielectrical profiling and electrical conductivity measurement records in combination with seasonal layer counting from high-resolution oxygen isotope (δ18O) data. A mean long-term accumulation rate of 0.29 ma–1w.e. was derived from the high-resolution δ18O record as well as accumulation rates during periods in between the identified volcanic horizons. A statistically significant decrease in accumulation was found from about 1920 to the present. A comparison with other coastal ice cores from DML suggests that this is a regional pattern.
The influence of precipitation origin on the δ18O–Trelationship at Neumayer station, Ekstrmisen, Antarctica
Authors: Schlosser Elisabeth , Reijmer Carleen , Oerter Hans , Graf Wolfgang
Published: November 2007

The relationship between δ18O and air temperature at Neumayer station, Ekstrmisen, Antarctica, was investigated using fresh-snow samples from the time period 1981–2000. A trajectory model that calculated 5 day-backward trajectories was used to study the influence of different synoptic weather situations and thus of different moisture sources on this correlation. Generally a high correlation between air temperature and δ18O was found, but the quality of the δ18O–Trelationship varied with the different trajectory classes. Additionally, the sea-ice coverage on the travel path of the moist air was considered. The amount of open ocean water underneath the trajectory has a large influence on the δ18O–Trelationship. For trajectories that lead completely above open water, no significant correlation between δ18O andTwas found, because mixing with air masses containing additionally evaporated water vapour from the ocean influences the isotope ratio of precipitation. A very high correlation, however, was found for transports over the completely ice-covered Weddell Sea.
Space–time Antarctic surface mass-balance variability from climate models
Authors: Genthon Christophe
Published: November 2007

The interannual to interdecadal variability and space–time statistics (including radius of decorrelation) of the Antarctic surface mass balance (SMB) are evaluated from climate models and meteorological analyses. At model resolution scales (>100 km), the interannual relative standard deviation of precipitation ranges from ∼5% (remotest interior) to ∼40% and possibly more. Time variability is spatially coherent at distances of ∼500km on average, less than 300 km in the interior near ridges, but in excess of 700 km in some regions. As far as spatial distributions are concerned, interannual statistics can be broadly transposed to interdecadal time-scales. The amplitude of variability may also be extrapolated across time-scales, using a ‘white’ spectrum hypothesis according to one coupled ocean– atmosphere model, but a significantly ‘red’ spectrum hypothesis according to another. Surface sublimation and blowing-snow processes are estimated to have limited contributions to the statistics of the SMB at model-resolved scales. Precipitation statistics can thus largely be transposed to SMB. The information reported here is expected to be useful for defining the details of field programmes such as the International Trans-Antarctic Scientific Expedition (ITASE), for extrapolating the spatial significance of field SMB data and for better interpreting Antarctic ice-sheet surface elevation changes from satellite altimetry.
Preliminary results of ionic concentrations in snow pits along the Zhongshan–Dome A traverse route, Antarctica
Authors: Jiawen Ren , Junying Sun , Dahe Qin
Published: November 2007

During an inland traverse expedition along the route from Zhongshan station on the coast to Dome A (about 4200ma.s.l.; 1400 km from Zhongshan) in East Antarctica in 1998/99, three snow pits with a depth of 2.1–3.3m were sampled continuously. Snow pits were located at sites 800–1100km from the coast, with altitudes varying from 2850 to 3760 m. The samples were analyzed for stable oxygen isotope and major ions. Seasonal variations in δ18O are not clear, so initial dating was made through comparison of concentration profiles of major ions and then adjusted according to the visible stratigraphy. Generally, average ionic concentrations decrease with increasing altitude and hence distance from the coast, but NH4+ and Ca2+ have relatively high values at a site 1000 km inland. Ionic concentrations tend to increase with depth at lower altitudes, but the opposite is true at higher altitudes. Accumulation rates increase with depth at site DT401 (3760ma.s.l.; 1097 km from Zhongshan) and decrease at DT364 (3380ma.s.l.; 1022 km from Zhongshan) and DT263 (2850ma.s.l.; 820 km from Zhongshan), suggesting that differences in regional trends exist. In all snow pits, Na+ and Cl– concentration profiles have a very good positive correlation. Profiles of nssSO42– in the pits show quite different features. At 3760ma.s.l, no remarkable nssSO42– peaks can be distinguished, but one and three peak sets are quite striking at 3380 and 2850 m, respectively.
Subglacial hydrological networks in Antarctica and their impact on ice flow
Authors: Remy Frédérique , Legresy Benoît
Published: November 2007

Deep beneath the thick ice cover of the Antarctic continent there exist subglacial hydrological networks, within which basal meltwater can flow. In this paper, we use surface elevation data from European Remote-sensing Satellite radar altimetry to map these subglacial hydrological networks for the whole continent. We observe a confused pattern of subglacial systems, linking regions where basal melting takes place. In some regions, channels can be followed over some hundreds of kilometres. Some of these meet the ice-sheet margin, suggesting that meltwater can be transported all the way to the ocean. We observe an east–west gradient in the distribution of hydrological networks that could be explained by the geothermal flux pattern.
Force-perturbation analysis of Pine Island Glacier, Antarctica, suggests cause for recent acceleration
Authors: Thomas Robert , Rignot Eric , Kanagaratnam Pannirselvam , Krabill William , Casassa Gino
Published: November 2007

Pine Island Glacier, flowing into the Amundsen Sea from West Antarctica, thinned substantially during the 1990s, its grounding line receded by several km, and its velocity increased by >10% to values approaching 3 km a–1. Here, we use these observations, together with estimates of ice thickness and surface strain rates, to estimate the perturbation in forces resisting ice flow compatible with the observations. The analysis assumes that such perturbations are transmitted far upstream from where they originate, and that creep response to the perturbations can be described by equations similar to those that govern ice-shelf creep. It indicates that observed acceleration between 1996 and 2000 could have been caused by progressive ungrounding within the most seaward 25 km ‘ice plain’ of the grounded glacier. Earlier retreat and thinning of the glacier’s floating ice shelf may have provided the conditions that initiated ungrounding of the ice plain. Our analysis indicates that continued ice-plain thinning at the current rate of about 2 ma–1 will result in a velocity increase by 1 km a–1 within the next 11 years as the ice plain becomes totally ungrounded.
Reconstructing ice-sheet accumulation rates at ridge B, East Antarctica
Authors: Leysinger Vieli Gwendolyn J.-M. C. , Siegert Martin J. , Payne Antony J.
Published: November 2007

Understanding how ice sheets responded to past climate change is fundamental to forecasting how they will respond in the future. Numerical models calculating the evolution of ice sheets depend upon accumulation data, which are principally available from ice cores. Here, we calculate past rates of ice accumulation using internal layering. The englacial structure of the East Antarctic ice divide at ridge B is extracted from airborne ice-penetrating radar. The isochronous surfaces are dated at their intersection with the Vostok ice-core site, where the depth–age relationship is known. The dated isochrons are used as input to a one-dimensional ice-flow model to investigate the spatial accumulation distribution. The calculations show that ice-accumulation rates generally increase from Vostok lake towards ridge B. The western flank of the ice divide experiences markedly more accumulation than in the east. Further, ice accumulation increases northwards along the ice divide. The results also show the variability of accumulation in time and space around the ridge B ice divide over the last 124 000 years.
Ice-lattice distortion along the deepest section of the Vostok core from X-ray diffraction measurements
Authors: Hori Akira , Hondoh Takeo , Oguro Mitsugu , Lipenkov Vladimir Ya.
Published: November 2007

We performed X-ray diffraction measurements on eight ice samples taken between 3200 and 3611 m depth of the Vostok (Antarctica) ice core to observe lattice distortions of ice crystals. Selected samples represent three distinct sections of the core: (i) glacier (meteoric) ice with well-preserved climatic record (down to 3310 m), (ii) ‘shear zone’ at the base of the glacier ice (3450– 3537 m) within which the climatic record is disturbed by ice deformation, and (iii) accretion ice formed by freezing of subglacial Vostok lake waters at the base of the ice sheet (from about 3537 m depth to the bottom of the core). The dislocation density decreases from 1012 to 108m–2 with increasing depth. In the accretion ice, lattice distortion tends to decrease with depth. However, the dislocation density does not reach a level typical for laboratory-grown columnar ice even at 3610 m. This reflects plastic deformation which accretion ice has undergone after its formation.
Three-dimensional modelling of the dynamics of Johnsons Glacier, Livingston Island, Antarctica
Authors: Martín Carlos , Navarro Francisco , Otero Jaime , Cuadrado María L. , Corcuera María I.
Published: November 2007

A new three-dimensional finite-element model of the steady-state dynamics of temperate glaciers has been developed and applied to Johnsons Glacier, Livingston Island, Antarctica, with the aim of determining the velocity and stress fields for the present glacier configuration. It solves the full Stokes system of differential equations without recourse to simplifications such as those involved in the shallow-ice approximation. Rather high values of the stiffness parameter B (∼0.19–0.23MPaa1/3) are needed to match the observed ice surface velocities, although these results do not differ much from those found by other authors for temperate glaciers. Best-fit values of the coefficient k in the sliding law (*2.2–2.7 x 103m a–1MPa–2) are also of the same order of magnitude as those found by other authors. The results for velocities are satisfactory, though locally there exist significant discrepancies between computed and observed ice surface velocities, particularly for the vertical ones. This could be due to failures in the sliding law (in particular, the lack of information on water pressure), the use of an artificial down-edge boundary condition and the fact that bed deformation is not considered. For the whole glacier system, the driving stress is largely balanced by the basal drag (80% of the driving stress). Longitudinal stress gradients are only important in the divide areas and near the glacier terminus, while lateral drag is only important at both sides of the terminal zone.
Chemical and isotopic snow variability in East Antarctica along the 2001/02 ITASE traverse
Authors: Becagli Silvia , Proposito Marco , Benassai Silvia , Flora Onelio , Genoni Laura , Gragnani Roberto , Largiuni Ombretta , Pili Simone Luca , Severi Mirko , Stenni Barbara , Traversi Rita , Udisti Roberto , Frezzotti Massimo
Published: November 2007

As part of the International Trans-Antarctic Scientific Expedition (ITASE) project, a traverse was carried out from November 2001 to January 2002 through Terre Adélie, George V Land, Oates Land and northern Victoria Land, for a total length of about 1875 km. The research goal is to determine the latitudinal and longitudinal variability of physical, chemical and isotopic parameters along three transects: one west–east transect (WE), following the 2150m contour line (about 400 km inland of the Adélie, George V and Oates coasts), and two north–south transects (inland Terre Adélie and Oates Coast–Talos Dome–Victoria Land). The intersection between the WE and Oates Coast–Victoria Land transects is in the Talos Dome area. Along the traverse, eight 2 m deep snow pits were dug and sampled with a 2.5 cm depth resolution. For spatial variability, 1 m deep integrated samples were collected every 5 km (363 sampling sites). In the snow-pit stratigraphy, pronounced annual cycles, with summer maxima, were observed for nssSO42–, MSA, NO3– and H2O2. The seasonality of these chemical trace species was used in combination with stable-isotope stratigraphy to derive reliable and temporally representative snow-accumulation rates. The study of chemical, isotopic and accumulation-rate variability allowed the identification of a distribution pattern which is controlled not only by altitude and distance from the sea, but also by the complex circulation of air masses in the study area. In particular, although the Talos Dome area is almost equidistant from the Southern Ocean and the Ross Sea, local atmospheric circulation is such that the area is strongly affected only by the Ross Sea. Moreover, we observed a decrease in concentration of aerosol components in the central portion of the WE transect and in the southern portion of the Talos Dome transect; this decrease was linked to the higher stability of atmospheric pressure due to the channelling of katabatic winds.
Mass balance of ‘Glaciar Bahía del Diablo’, Vega Island, Antarctic Peninsula
Authors: Skvarca Pedro , De Angelis Hernán , Ermolin Evgeniy
Published: November 2007

Given the pronounced atmospheric warming recorded in recent decades on the Antarctic Peninsula (AP), knowledge of glacier mass balance in this region is especially important for assessing the impact of climatic warming on ice masses. ‘Glaciar Bahía del Diablo’ (GBD) on Vega Island, northeastern AP, is a glacier that terminates on land, so its mass balance is directly linked to climate. GBD is a polythermal outlet glacier, 14.3 km2 in area with an accumulation–area ratio of 0.39. Increased ablation rates and glacier thinning motivated us to select GBD as a test site for mass-balance studies within the region. Calculations based on the stratigraphic annual method yielded a mean annual loss of 0.32 mw.e. a–1 for the annual net mass balance (bn) between 1999 and 2003. A strong correlation was observed between bn and mean summer temperatures, confirming that GBD is highly sensitive to climate. The study of GBD aims at establishing a suitable reference database for ice–climate studies in a region of dramatic changes in Antarctica.
Operational sub-pixel snow mapping over the Alps with NOAA AVHRR data
Authors: Foppa Nando , Wunderle Stefan , Oesch David , Kuchen Florian
Published: November 2007

This study is part of research activities concentrating on the real-time application of the U.S. National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) sensor for snow-cover analysis of the European Alps. For mapping snow cover in heterogeneous terrain, we implement the widely used linear spectral mixture algorithm to estimate snow cover at sub-pixel scale. Principal component analysis, including the reflective part of AVHRR channel 3, is used to estimate fractions of “snow” and “not snow” within a pixel, using linear mixture modeling. The combination of these features leads to a fast, simple solution for operational and near-real-time processing. The presented algorithm is applied on the European Alps on 17 January 2003 and successfully maps snow at sub-pixel scale. The detailed snow-cover information makes it easy to recognize the complex topography of the Alps, more so than with either a classic binary map or a Moderate Resolution Imaging Spectroradiometer (MODIS) snow product. The sub-pixel algorithm reasonably identifies snow-cover fractions in regions and at altitudes where neither the classic binary map nor the MODIS algorithm detects any snow. Differences concerning the snow distribution are found in forested areas as well as in the lowest-elevation zones. The algorithm substantially improves snow mapping over complex topography for operational and near-realtime applications.
Experimental and numerical study of granular flow and fence interaction
Authors: Faug Thierry , Naaim Mohamed , Naaim-Bouvet Florence
Published: November 2007

Dense snow avalanches are regarded as dry granular flows. This paper presents experimental and numerical modelling of deposition processes occurring when a gravity-driven granular flow meets a fence. A specific experimental device was set up, and a numerical model based on shallow-water theory and including a deposition model was used. Both tools were used to quantify how the retained volume upstream of the fence is influenced by the channel inclination and the obstacle height. We identified two regimes depending on the slope angle. In the slope-angle range where a steady flow is possible, the retained volume has two contributions: deposition along the channel due to the roughness of the bed and deposition due to the fence. The retained volume results only from the fence effects for higher slopes. The effects of slope on the retained volume also showed these two regimes. For low slopes, the retained volume decreases strongly with increasing slope. For higher slopes, the retained volume decreases weakly with increasing slope. Comparison between the experiments and computed data showed good agreement concerning the effect of fence height on the retained volume.
Statistical avalanche-runout estimation for short slopes in Canada
Authors: Jones Alan S.T. , Jamieson Bruce
Published: November 2007

To develop avalanche runout models for short slopes, field measurements were made at 48 short-slope avalanche paths located in the Coast, Columbia and Rocky Mountains of western Canada, and at several paths in eastern Canada. Field studies included detailed topographic surveys and estimation of the extreme runout position in each path. A statistical runout model was developed using the runout ratio method, for which runout ratios from the four mountain ranges are well fit by an extreme-value type I (Gumbel) distribution when the β point is defined at the uppermost point where the slope is 24°. A second model was developed by regressing the α angle for the extreme runout position on numerous terrain variables. This regression model uses three predictor variables that can be easily measured in the field or on topographic maps. Length-scale effects were noted in both models, but are more pronounced in the runout ratio model. A comparison of models developed using the two methods shows that the runout ratio model estimates more conservative (longer) runout distances than the regression model for most threshold probabilities. Data from 13 additional paths from Switzerland and Québec, Canada, are used to test the models.
Large-scale snow instability patterns in western Canada: first analysis of the CAA–InfoEx database 1991–2002
Authors: Gruber Urs , Hägeli Pascal , McClung David M. , Manners Evan
Published: November 2007

Daily weather measurements, snow stability assessments and recorded weak layers of 23 stations covering an observation area of approximately 40 000 km2 in western Canada were analyzed. The study area includes three major mountain ranges with different snow climates. All stations included assess the stability of the snow cover. However, the focus of the avalanche safety program of the different types of operation (heli-ski operation, ski resorts and parks) varies significantly. The three stations in the Coast Mountains show the highest snow stability, followed by the South Columbia Mountains and then the North Columbia and Rocky Mountains. The weather data were analyzed to try to explain some of these differences. Intensive snowfall at relatively high temperatures proved to be important for the higher snow stability over the season in the Coast Mountains. Theweak-layer data were used to complement the snow stability assessments. Most persistent weak layers were reported in the Columbia Mountains, followed by the three stations in the Coast Mountains and trailed by the Rocky Mountains. Although some weather observations indicate climatic reasons for the smaller number of weak layers in the Rocky Mountains, it cannot be excluded that these differences are also related to the different type of operations.
Calculation of two-dimensional avalanche velocities from optoelectronic sensors
Authors: McElwaine Jim N.
Published: November 2007

Optoelectronic sensors using infrared light-emitting diodes and photo-transistors have been used for measuring velocities in snow avalanches for more than 10 years in America, Europe and Japan. Though they have been extensively used, how they should be designed and how the data should be processed has received little discussion. This paper discusses how these sensors can be applied to measure two-dimensional velocities. The effects of acceleration and structure in the underlying field of reflectance are carefully accounted for. An algorithm is proposed for calculating the continuous velocity vector of an avalanche, and a sketch of the mathematical analysis given. The paper concludes by suggesting design criteria for such sensors.
Effect of summer snowfall on glacier mass balance
Authors: Oerlemans Johannes , Klok E. J. (Lisette)
Published: November 2007

It has been postulated that heavy summer snowfalls have a large impact on the mass balance of mid-latitude glaciers, because they simultaneously add mass to the glacier and reduce the amount of absorbed solar radiation. An automatic weather station (AWS) on the snout of Morteratschgletscher, Switzerland, registered a large summer snowfall event on 10–11 July 2000. Sonic rangers recorded about 20 cm of new snow on the snout and about 50 cm near the equilibrium line. We have used data from the AWS to study the impact on the melt process. The data show that in the ablation zone of the glacier the snow has melted and the effect on the albedo has disappeared after about 5 days. The suppression of the melt by the high albedo of the fresh snow is an important effect. For the ablation zone we find a feedback factor of about four, that is, the total effect of the snowfall event on the annual specific balance is about four times the amount of mass added during the event. We have also used a mass-balance model with 25 m spatial resolution to assess the impact of the snowfall on the net balance of the entire glacier. We find the strongest effects just below the equilibrium line. Averaged over the glacier, the amount of snow deposited was 224 mm w.e. The calculated effect on the total mass balance of the glacier is 354 mm w.e.
Changes in the shear strength and micro-penetration hardness of a buried surface-hoar layer
Authors: Birkeland Karl W. , Kronholm Kalle , Schneebeli Martin , Pielmeier Christine
Published: November 2007

We investigated a buried surface-hoar layer using the SnowMicroPen (SMP), an instrument designed to measure detailed snowpack profiles.We collected data from two adjacent parts of a slope 6 days apart. In addition, one manual snowpack profile was sampled each day, as well as 50 quantified loaded column tests (QLCTs) which provided an index of shear strength. For the SMP data, a 900 m2 area was sampled on both days in a grid with points 3 mapart, with some sub-areas of more closely spaced measurements. We collected 86 SMP profiles on the first day and 129 on the second day. Our analyses involved manually locating layer boundaries and calculating statistics for the force signal through the surface-hoar layer. The shear strength index increased by 40% between the two sampling days, but the SMP data show no statistical difference in layer thickness, and the mean, minimum, median, and a variety of percentile measures of the SMP force signal through the layer also do not change. Interestingly, the maximum hardness, and the variance and coefficient of variation of the SMP signal, increased. Since the small SMP tip might only break one or a couple of bonds as it passes through the weak layer, we interpret these changes as being indicative of increasing bond strength. Though we cannot specifically tie the increasing maximum hardness of the SMP signal to our QLCT results, our work suggests that the maximum SMP signal within buried surface-hoar layers may be useful for tracking increases in the shear strength of those layers.
Numerical study of the time development of drifting snow and its relation to the spatial development
Authors: Nemoto Masaki , Nishimura Kouichi , Kobayashi Syunichi , Izumi Kaoru
Published: November 2007

The time evolution of drifting snow under a steady wind is estimated using a new numerical model of drifting snow. In the model, Lagrangian stochastic theory is used to incorporate the effect of turbulence on the motion of drifting-snow particles. This method enables us to discuss both the saltation and the suspension process. Aerodynamic entrainment, grain/bed collision (splash process), wind modification and particle size distribution are also taken into account. The calculations show that the time needed by the total mass flux to reach a steady state appears to be 3–5 s. Vertical profiles of horizontal mass flux near the surface show a similar tendency. In contrast, it takes >50 s for the wind speed and the whole mass-flux profile to reach a steady state. This longer time depends on the time-scale of the turbulent diffusion, which is responsible for the mass flux extending to an order of a few meters in height. Applying Taylor’s hypothesis, the estimated length scale at which drifting snow reaches equilibrium is around 400 m. This result is comparable with previously reported field observations.
Hierarchy theory as a conceptual framework for scale issues in avalanche forecast modeling
Authors: Hägeli Pascal , McClung David M.
Published: November 2007

Although scale issues have been defined to be one of the most crucial topics in geosciences, they have received only limited attention in avalanche research. A thorough understanding of these issues in avalanche forecasting, however, is fundamental for the development of useful prediction models. After the definition of relevant terms, the different aspects of scale issues are introduced in detail. We present hierarchy theory (Ahl and Allen, 1996) as a potential framework for the multi-scale characteristics of the avalanche phenomenon. We suggest a temporal hierarchy, where the main contributing factors are ordered into seven levels according to their temporal-scale characteristics with respect to avalanche forecasting. Within each level there are individual spatial hierarchies, which result in a two-dimensional structure. This process-oriented framework is compared to the data classification scheme of La Chapelle (1980), which is based on informational entropy. Scale issues in prediction modeling and the consequences of the new framework for modeling efforts are discussed in detail.
Implications of spatial distributions of snow mass and melt rate for snow-cover depletion: theoretical considerations
Authors: Essery Richard , Pomeroy John
Published: November 2007

Snow becomes patchy while melting, giving a heterogeneous surface with large contrasts in characteristics such as albedo. It is therefore necessary for surface schemes used in atmospheric and hydrological models to represent the influence of heterogeneities in snow cover on scales smaller than the model grid; this is typically done by introducing a snow-cover depletion (SCD) curve relating fractional snow cover to average depth. Here, ad hoc functional forms which have been used for this relationship are first compared with forms obtained for an assumed initial snow distribution undergoing homogeneous melt. The energy available for melt may be heterogeneous, however, and can be influenced by factors that also influence snow distribution, such as slope, aspect and vegetation cover. The modification of SCD curves by spatial variations in melt energy is investigated, and resulting curves are found to be similar to those which would be given by homogeneous melting of a snow cover with greater initial variance. This influence is increased by any negative correlation between snow depth and melt rate.
Glacier winds on Vatnajökull ice cap, Iceland, and their relation to temperatures of its lowland environs
Authors: Björnsson Helgi , Gudmundsson Sverrir , Pálsson Finnur
Published: November 2007

During the ablation season, the ice cap Vatnajökull (8100 km2) develops its own microclimate that we describe by meteorological data collected during the summers of 1994-2003. Persistent glacier winds are generated down the melting ice cap, whose variations in speed can be related empirically to the temperature fluctuations of the lowland environs of the ice cap. This suggests that climate warming would be accompanied by stronger glacier winds down the outlets of Vatnajökull, producing stronger turbulent fluxes that might amplify the melting rates in the lower ablation areas.
Multi-decadal record of ice dynamics on Daugaard Jensen Gletscher, East Greenland, from satellite imagery and terrestrial measurements
Authors: Stearns Leigh A. , Hamilton Gordon S. , Reeh Niels
Published: November 2007

The history of ice velocity and calving front position of Daugaard Jensen Gletscher, a large outlet glacier in East Greenland, is reconstructed from field measurements, aerial photography and satellite imagery for the period 1950-2001. The calving terminus of the glacier has remained in approximately the same position over the past ∼50 years. There is no evidence of a change in ice motion between 1968 and 2001, based on a comparison of velocities derived from terrestrial surveying and feature tracking using sequential satellite images. Estimates of flux near the entrance to the fjord vs snow accumulation in the interior catchment show that Daugaard Jensen Gletscher has a small negative mass balance. This result is consistent with other mass-balance estimates for the inland region of the glacier.
Estimating the mass balance of Vatnajökull, Iceland, from NOAA AVHRR imagery
Authors: Calluy G.H.K. , Björnsson H. , Greuell J.W. , Oerlemans J.
Published: November 2007

We investigate the possibility of obtaining the mass balance of Vatnajökull, Iceland, from US National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) albedo images for the years 1991-2002. De Ruyter de Wildt and others (2002) demonstrated that the mean potential absorbed radiation (〈Qpot,net〉) averaged over the melting season correlates well with the mean specific mass balance and that 〈Qpot,net〉 can be estimated from the evolution of the surface albedo. Here, we improve the retrieval method of de Ruyter de Wildt and others (2002) by introducing the more realistic 6S atmospheric transfer model and by adding the latest narrow-to-broadband (NTB) albedo conversion equations. Bidirectional reflectance distribution functions for both ice and snow are used where appropriate. We show that the choice of the NTB conversion equations greatly influences the calculated 〈Qpot,net〉. Measured mass balance correlates well with 〈Qpot,net〉 if enough cloud-free images can be found through the year and if the spatial variation in measured mass balances is high enough. The correlation coefficient for all drainage basins combined is 0.92, with a residual standard deviation of 0.18 m w.e. We present an estimated mass-balance series for the whole of Vatnajökull based on our findings. Switching between different AVHRR instruments over time may cause serious errors in the calculated mass balance.
Analysis of the first jökulhlaup at Blåmannsisen, northern Norway, and implications for future events
Authors: Engeset Rune Verpe , Schuler Thomas Vikhamar , Jackson Miriam
Published: November 2007

The first known jökulhlaup from the Blåmannsisen ice cap in northern Norway began on 6 September 2001. It lasted 35 hours and emptied the lake Øvre Messingmalmvatn (∼4.0 × 107m3). Before the event, the lake drained steadily via a rock spillway into Sweden. The water from the jökulhlaup drained into the hydropower reservoir Sisovatn, and so was financially beneficial to Norway. Glaciological data show evidence of glacier retreat and thinning during the last four decades. Glacier thickness decreased in the ablation zone, reducing ice-barrier stability. The lake drained at a water level 40 m below that required to equalize the ice overburden pressure. Measurements show an ice-barrier thinning of 3.5 m since the jökulhlaup occurred. Climate scenarios indicate future negative mass balance and further thinning. The lake volume was 82% full 2.5 years after the event, suggesting a probable repeat interval of 3 years. Future jökulhlaups may be triggered at lower water levels and produce lower discharges.