bluuebunny/crossref_metadata_2025 huggingface dataset:
Variability in accumulation rates from GPR profiling on the West Antarctic plateau
Authors: Spikes Vandy B. , Hamilton Gordon S. , Arcone Steven A. , Kaspari Susan , Mayewski Paul A.
Published: November 2007

Isochronal layers in firn detected with ground-penetrating radar (GPR) and dated using results from ice-core analyses are used to calculate accumulation rates along a 100 km across-flow profile in West Antarctica. Accumulation rates are shown to be highly variable over short distances. Elevation measurements from global positioning system surveys show that accumulation rates derived from shallow horizons correlate well with surface undulations, which implies that wind redistribution of snow is the leading cause of this variability. Temporal changes in accumulation rate over 25–185 year intervals are smoothed to along-track length scales comparable to surface undulations in order to identify trends in accumulation that are likely related to changes in climate. Results show that accumulation rates along this profile have decreased in recent decades, which is consistent with core-derived time series of annual accumulation rates measured at the two ends of the radar profile. These results suggest that temporal variability observed in accumulation-rate records from ice cores and GPR profiles can be obscured by spatial influences, although it is possible to resolve temporal signals if the effects of local topography and ice flow are quantified and removed.
Aluminium and iron record for the last 28 kyr derived from the Antarctic EDC96 ice core using new CFA methods
Authors: Traversi Rita , Barbante Carlo , Gaspari Vania , Fattori Ilaria , Largiuni Ombretta , Magaldi Lorenzo , Udisti Roberto
Published: November 2007

Spectrofluorimetric and spectrophotometric continuous flow analysis (CFA) methods were developed and applied to the determination of aluminium and iron in EPICA Dome C (East Antarctica) ice-core samples (6–585m depth). The methods are able to measure the fraction of Al and Fe which can be detected once the sample is filtered on a 5.0 μm membrane and acidified to pH 2. Both the methods present high sensitivity (detection limit of 10 ng L–1 for Al and 50 ng L–1 for Fe) and reproducibility (5% at sub-ppb level). The Fe and Al profiles show sharp decreases in concentrations in the last glacial/interglacial transition, reflecting the decreasing dust aerosol load. The two elements show a different pattern during the Antarctic Cold Reversal (ACR) climatic change, with high iron concentrations (similar to the glacial period) and low but increasing Al content during the ACR minimum. In order to interpret the Al and Fe data obtained by CFA, a comparison with Al and Fe composition, as measured by inductively coupled plasma sector field mass spectrometry (ICP-SFMS), was performed for Holocene, ACR and glacial periods. The percentage of CFA-Al with respect to ICP-SFMS-Al in the three periods shows a lower variability than CFA-Fe (3% in the glacial period and 64% in the ACR). This pattern may be explained by the different dominant iron sources in the different climatic periods. During the Last Glacial Maximum, Fe is proposed to arise mainly from insoluble continental dust, while a variety of ocean-recycled Fe, mainly distributed in fine particles and as more soluble species, shows a higher contribution in the ACR and, to a lesser extent, in the Holocene.
New bedrock map of Dome C, Antarctica, and morphostructural interpretation of the area
Authors: Forieri Alessandro , Zuccoli Luisa , Bini Alfredo , Zirizzotti Achille , Remy Frédérique , Tabacco Ignazio E.
Published: November 2007

A new bedrock map of the Dome C area is presented, based on all radar data collected during Italian Antarctic Expeditions in 1995, 1997, 1999 and 2001. The map clearly distinguishes the Dome C plateau, along with valleys and ridges. The plateau develops at three different altimetric levels, and its morphology is characterized by hills and closed depressions. There are no visible features which can be ascribed to glacial erosion or deposition. The major valley is 15 km wide and 500 m deep; its axis is parallel to that of other valleys and ridges in the plateau. The valley bottom is not flat, but contains a saddle at its centre. The morphology of the major valley may be considered a relict one which was not modified by the overlying ice cap. Two large ridges, characterized by hills, saddles and depressions, lie near the boundaries of the area. The map is used to recalculate ice thickness below the European Project for Ice Coring in Antarctica (EPICA) borehole. The new thickness is 3300 m, 50m greater than before, implying that the expected palaeoclimate record from the ice core could extend back >800 kyr.
The carbon isotopic composition of dissolved inorganic carbon in perennially ice-covered Antarctic lakes: searching for a biogenic signature
Authors: Neumann Klaus , Lyons W. Berry , Priscu John C. , Desmarais David J. , Welch Kathleen A.
Published: November 2007

The stable-isotopic signature of dissolved inorganic carbon (DIC) has been routinely used in temperate lake systems to investigate the biogeochemical dynamics of carbon. We studied seven perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, to ascertain how carbon cycling affects the δ13C of DIC in water columns of these systems. Unlike temperate lakes and, in fact, most polar lake systems, the permanent ice covers of these lakes eliminate physical mixing (turnover) and hence redistribution of DIC in the lakes, as well as minimize CO2 exchange with the atmosphere. These important and unique physical constraints have significant impact on carbon dynamics in the lakes, and important consequences for the δ13C distribution. The geochemistry in these lakes is influenced in varying amounts by landscape position, hydrologic input and their evolutionary history. Five of these lakes (both lobes of Lake Bonney, and Lakes Fryxell, Miers and Vanda) have surface water δ13C ratios of 0–4‰, Lake Hoare has more negative values, while Lake Joyce, the highest-elevation lake, has a much higher value (10.5‰). All of the lakes have upper- to mid-depth δ13C maxima reflecting biological uptake of 12C. Only four of the lakes (Lakes Vanda, Joyce, Hoare and Fryxell) have deep waters with negative values of δ13C, implying rigorous remineralization of 12C at depth. Lake Miers, the only lake that is not closed basin, has the smallest δ13C variation with depth, indicating that hydrologic exchange greatly influences the δ13C signal.
Elemental indicators of natural and anthropogenic aerosol inputs to Law Dome, Antarctica
Authors: Vallelonga Paul , Barbante Carlo , Cozzi Giulio , Gaspari Vania , Candelone Jean-Pierre , Van De Velde Katja , Morgan Vin I. , Rosman Kevin J. R. , Boutron Claude F. , Cescon Paolo
Published: November 2007

A selection of elements (Bi, Ca, Cd, Co, Cu, Mn, Na, Sr, U, V, Zn) were measured by high-resolution inductively coupled plasma sector-field mass spectrometry in firn- and ice-core samples from Law Dome, Antarctica, corresponding to the period 4500 BC to AD 1989. Concentrations of rock dust and sea salts were calculated for each sample and then used to determine concentrations of each element originating from crustal and marine aerosol emissions, respectively. Where calculated contributions from crustal and marine aerosol sources failed to account for the total measured concentration of an element, the remainder was apportioned to volcanic and/or anthropogenic sources and defined as an enrichment. On this basis, it was determined that Bi and Cd concentrations in Law Dome ice are overwhelmingly influenced by volcanic emissions (enrichments 150–250x crustal and marine inputs); Co, Cu, Pb and Zn concentrations in Law Dome ice are largely influenced by volcanic emissions (enrichments 16–36x crustal and marine inputs); and Mn, Sr, U and V concentrations in Law Dome ice are minimally influenced by volcanic emissions (enrichments 1.5–4x crustal and marine inputs). During the 20th century, enrichments of Pb and Cu concentrations were observed to be greater than in earlier centuries, consistent with increasing anthropogenic emissions of Pb and Cu in the Southern Hemisphere over that period.
Investigating the potential to determine the upstream accumulation rate, using mass-flux calculations along a cross-section on a small tributary glacier in Heimefrontfjella, Dronning Maud Land, Antarctica
Authors: Pohjola Veijo Allan , Hedfors Jim , Holmlund Per
Published: November 2007

How well can we estimate the incoming ice flux by calculating the ice flux through a well-defined cross-section? We test this by comparing calculated ice flux out from the small glacier Bonnevie-Svendsenbreen with the measured accumulation rate integrated over the well-defined catchment area in the Sivorgfjella plateau, Dronning Maud Land, Antarctica (74˚45’ S, 11˚10’ W). The ice flux is calculated using ice-dynamical properties from an ice temperature model and the distribution of forces calculated using a force-budget model. The input we use includes velocity data of the glacier surface, combined with ice-thickness measurements. The result is an accumulation rate on the Sivorgfjella plateau of 0.50 ± 0.05 mw.e. a–1. We find that this is similar to the accumulation rate recorded by ground-penetrating radar work in the area. We therefore find the balance-flow method, in combination with the force-budget technique and ice temperature modeling, to be a useful tool for studies of mass fluxes in a catchment area. The most important source of uncertainty in these calculations is the quality and the spatial distribution of the ice surface velocity data. The high accumulation rate shows the effect of orographic enhancement on accumulation in montane areas in Antarctica.
Climatic conditions, mass balance and dynamics of Larsen B ice shelf, Antarctic Peninsula, prior to collapse
Authors: Skvarca Pedro , De Angelis Hernán , Zakrajsek Andrés F.
Published: November 2007

Following the collapse of Larsen A in 1995, about 3200 km2 of Larsen B ice shelf disintegrated in early 2002 during the warmest summer recorded on the northeastern Antarctic Peninsula. Immediately prior to disintegration the last field campaign was carried out on Larsen B. Measurements included surface net mass balance, velocity and strain rate on a longitudinal transect along Crane Glacier flowline and over a remnant section confined within Seal Nunataks that survived the collapse. In addition, an automatic weather station located nearby allowed derivation of melt days relevant to the formation and extent of surface meltwater. Repeated surveys allowed us to detect a significant acceleration in ice-flow velocity and associated increasing strain rates along the longitudinal transect. It may be possible to use this acceleration as a predictor of imminent ice-shelf collapse, applicable to ice shelves subject to similar climatic conditions. Additional information on recent ongoing changes was provided by a visible satellite image acquired in early 2003.
Geophysical survey at Talos Dome, East Antarctica: the search for a new deep-drilling site
Authors: Frezzotti Massimo , Bitelli Gabriele , De Michelis Paola , Deponti Alberto , Forieri Alessandro , Gandolfi Stefano , Maggi Valter , Mancini Francesco , Remy Frédérique , Tabacco Ignazio E. , Urbini Stefano , Vittuari Luca , Zirizzottl Achille
Published: November 2007

Talos Dome is an ice dome on the edge of the East Antarctic plateau; because accumulation is higher here than in other domes of East Antarctica, the ice preserves a good geochemical and palaeoclimatic record. A new map of the Talos Dome area locates the dome summit using the global positioning system (GPS) (72˚47’ 14’’S, 159˚04’ 2’’ E; 2318.5m elevation (WGS84)). A surface strain network of nine stakes was measured using GPS. Data indicate that the stake closest to the summit moves south-southeast at a few cm a–1. The other stakes, located 8 km away, move up to 0.33ma–1. Airborne radar measurements indicate that the bedrock at the Talos Dome summit is about 400m in elevation, and that it is covered by about 1900 m of ice. Snow radar and GPS surveys show that internal layering is continuous and horizontal in the summit area (15 km radius). The depth distribution analysis of snow radar layers reveals that accumulation decreases downwind of the dome (north-northeast) and increases upwind (south-southwest). The palaeomorphology of the dome has changed during the past 500 years, probably due to variation in spatial distribution of snow accumulation, driven by wind sublimation. In order to calculate a preliminary age vs depth profile for Talos Dome, a simple one-dimensional steady-state model was formulated. This model predicts that the ice 100m above the bedrock may cover one glacial–interglacial period.
Spatial distribution of surface mass balance on Amundsenisen plateau, Antarctica, derived from ice-penetrating radar studies
Authors: Rotschky Gerit , Eisen Olaf , Wilhelms Frank , Nixdorf Uwe , Oerter Hans
Published: November 2007

The distribution of surface mass balance on Amundsenisen, Dronning Maud Land, Antarctica, is investigated along a continous profile line. Ice-penetrating radar is used to map variations in ice-layer thickness within the upper 100 m of the ice sheet. The route passes several firn- and ice-core drilling sites over a distance of 320 km. Dielectric-profiling data of ice cores are used to calculate the depths of selected reflection horizons and the cumulative mass of the ice column. The local surface mass balance is determined as a temporal average, covering a time-span of almost two centuries. The findings indicate a complex accumulation pattern superimposed on a generally low surface mass balance, which is related to small-scale surface undulations. The results of the radar soundings are in general in good agreement with surface mass-balance data derived from firn-core studies. Discrepancies between these two datasets can be explained by spatial mismatch or by minor quality of either ice-core profiles or radar data. For regional comparison of radar-based accumulation data we use an accumulation distribution interpolated from point measurements. The surface mass balance varies up to 50% over short distances, with correlation lengths of <10 km. We conclude that the current utilization schemes of point sampling are only capable of reproducing local values and regional trends but provide no information on the small-scale variability of surface mass balance.
Antarctic ice volume and deep-sea temperature during the last 50 Myr: a model study
Authors: Oerlemans Johannes
Published: November 2007

A simple quasi-analytical model is used to study the sensitivity of the Antarctic ice sheet to climate change. The model is axisymmetrical and has a profile that only depends on the ice-sheet radius. The climatic conditions are represented by three parameters: the altitude of the runoff line, the accumulation rate above the runoff line, and the balance gradient below the runoff line. The ice sheet may extend into the sea. At the grounding line the ice velocity is assumed to be proportional to the water depth. For this set-up, an explicit algebraic expression for the total mass budget of the ice sheet can be derived. After calibration of the model with respect to the present-day ice sheet, equilibrium states are studied for a wide range of temperatures. The model predicts a maximum ice volume (+3.4%) for a temperature that is 2.5 K above the present value. For a temperature increase of 7 K, mass loss by runoff and calving are about the same. In this case the ice volume is about 82% of the current value. The ice-sheet model is used to correct the Cenozoic deep-sea temperature record (δ18O record from benthic foraminifera in ocean sediments) for Antarctic ice volume. The model is forced with the oxygen isotope record, which is then corrected for the calculated ice volume. Therefore, the resulting deep-sea temperature and Antarctic ice-volume curves are mutually consistent. It is concluded that for the last 35×106 years the δ18O record truly is a mixed temperature/ice-volume record, in which the contributions from these parameters have the same order of magnitude.
Two-dimensional numerical modelling of surface wind velocity and associated snowdrift effects over complex mountainous topography
Authors: Durand Yves , Guyomarc’h Gilbert , Mérindol Laurent , Corripio Javier G.
Published: November 2007

A new experimental software for blowing snow, SYTRON2, is presented. It takes advantage of the previous limited realization SYTRON1 and of the entire real-time operational environment of the automatic chain SAFRAN–Crocus–MÉPRA (SCM). It runs presently on a rectangular grid, with a mesh size of about 45 m, covering an area of 3.0 × 3.0km2 around the observation test site Col du Lac Blanc, French Alps (2700m a.s.l., near the Alpe d’Huez ski resort). SYTRON2 is initialized with a realistic snowpack representation derived from the SCM outputs and coupled to a wind field computed by the new SAMVER model. The final aim is to build a fully embedded tool, suitable for representing snowdrift effects with a better resolution at different specific locations. The different tools and operators used are described, as well as the field validation processes which are based on remote identification of the eroded and accumulated areas using digital pictures.
Validation of the energy budget of an alpine snowpack simulated by several snow models (Snow MIP project)
Authors: Etchevers Pierre , Martin Eric , Brown Ross , Fierz Charles , Lejeune Yves , Bazile Eric , Boone Aaron , Dai Yong-Jiu , Essery Richard , Fernandez Alberto , Gusev Yeugeniy , Jordan Rachel , Koren Victor , Kowalczyk Eva , Nasonova N. Olga , Pyles R. David , Schlosser Adam , Shmakin Andrey B. , Smirnova Tatiana G. , Strasser Ulrich , Verseghy Diana , Yamazaki Takeshi , Yang Zong-Liang
Published: November 2007

Many snow models have been developed for various applications such as hydrology, global atmospheric circulation models and avalanche forecasting. The degree of complexity of these models is highly variable, ranging from simple index methods to multi-layer models that simulate snow-cover stratigraphy and texture. In the framework of the Snow Model Intercomparison Project (SnowMIP), 23 models were compared using observed meteorological parameters from two mountainous alpine sites. The analysis here focuses on validation of snow energy-budget simulations. Albedo and snow surface temperature observations allow identification of the more realistic simulations and quantification of errors for two components of the energy budget: the net short- and longwave radiation. In particular, the different albedo parameterizations are evaluated for different snowpack states (in winter and spring). Analysis of results during the melting period allows an investigation of the different ways of partitioning the energy fluxes and reveals the complex feedbacks which occur when simulating the snow energy budget. Particular attention is paid to the impact of model complexity on the energy-budget components. The model complexity has a major role for the net longwave radiation calculation, whereas the albedo parameterization is the most significant factor explaining the accuracy of the net shortwave radiation simulation.
Estimating snow conditions in Finland in the late 21st century using the SNOWPACK model with regional climate scenario data as input
Authors: Rasmus Sirpa , Räisänen Jouni , Lehning Michael
Published: November 2007

An assessment of possible snow changes in a changing climate for Finland is presented. The snowpack structure model SNOWPACK (developed at the Swiss Federal Institute for Snow and Avalanche Research) was used for calculating snow conditions at six different locations in Finland for the decades 1980–89 and 2080–89. Regional climate model (RCAO) data from the Rossby Centre, Sweden, were used as input to the SNOWPACK model. Ten years from the RCAO control run and scenario run were chosen, and the snow conditions for different snow zones were calculated for these winters. The snow-cover depth and duration decreased at all locations in the scenario run cases, and the snow-cover quality also changed between the control and scenario runs: grains were bigger, snow was warmer and denser, and the fraction of faceted snow decreased while the fraction of icy or melting snow increased, even in mid-winter. Finally, the variability between different global climate predictions was analyzed. Significant differences were found between different climate-model outputs. The inter-model variability is comparable to the interannual variability of a single model. The qualitative conclusions from the scenario run do not critically depend on the climate-model variability.
Slushflow hazard prediction and warning
Authors: Hestnes Erik , Bakkehøi Steinar
Published: November 2007

Parameters critical to slushflow release have been studied during 11 winters in Rana, North Norway. Slushflows occurred during 16 periods within the research areas and during another 13 in the district. A noticeable rise of water in snowpack was registered 49 times. Field predictors of acute-hazard and critical water influxes related to different snowpack conditions are identified. Threshold values for acute-hazard prediction based on five main combinations of winter snowpack and current rise of water in snowpack were identified and checked against the registered slushflows, with promising results. Cohesionless new snow and coarse-grained snow are most liable to start flowing. A snowpack reinforced by layers of crust and ice is normally the most stable. An automatic system for supervising slushflow hazard based on the defined criteria is presented. The system can be tailored for any location and problem owner.
The mass balance of a dry snow surface during a snowstorm
Authors: Bintanja Richard
Published: November 2007

This paper focuses on the surface mass balance of a horizontally homogeneous snowfield, with emphasis on the effects of snowdrift sublimation. A one-dimensional model of the atmospheric boundary layer that includes snowdrift physics and thermodynamics is used. In sufficiently strong winds, snow particles are eroded from the surface. Once airborne, they are susceptible to sublimation. Averaged over longer time periods, the net erosive flux equals sublimation of snowdrift. However, model results show that there is no such balance in the course of a snowstorm event. They also indicate that snowdrift sublimation tends to enhance net erosion, but the increase occurs more slowly than the mass transfer by snowdrift sublimation, and the maximum is smaller. This difference in temporal behaviour influences the average erosion rate owing to non-linear interactions between snowdrift sublimation, drift density and erosion. Since the increase in relative humidity due to snowdrift diminishes surface sublimation, the average change in total ablation induced by snowdrift sublimation remains small. Observations made during snowdrift episodes in Antarctica agree qualitatively with some of the model results.
Three-dimensional geometric measurements of snow microstructural evolution under isothermal conditions
Authors: Flin Frédéric , Brzoska Jean-Bruno , Lesaffre Bernard , Coléou Cécile , Pieritz Romeu André
Published: November 2007

Snow, from its fall until its full melting, undergoes a structural metamorphism that is governed by temperature and humidity fields. Among the many possible mechanisms that contribute to snow metamorphism, those that depend only on curvature are the most accessible to modelling. In this paper, techniques of volume data analysis adapted to the complex geometry of snow are introduced and then applied to experimental tomographic data coming from the isothermal metamorphism of snow near 0°C. In particular, an adaptive algorithm of curvature computation is described. Present results on the evolution of specific surface area and anisotropy already show that such image-analysis methods are relevant tools for the characterization of real snow microstructures. Moreover, the evolution of the curvature distribution with time provides valuable information for the development of sintering models, in the same way as a possible quantitative calibration of snow-grain coarsening laws.
Dendrochronological study of the Canal del Roc Roig avalanche path: first results of the Aludex project in the Pyrenees
Authors: Muntán Elena , Andreu Laia , Oller Pere , Gutiérrez Emilia , Martínez Pere
Published: November 2007

Historical data about ancient avalanches are scarce in the Pyrenees. Dendrochronology can provide new data about past avalanches and their return period, but up to now little research has been carried out with this purpose. The Aludex project aims to obtain information about the frequency and extent of extreme avalanches, using a dendrochronological and a nivo-meteorological approach. In this paper, we present the results of a dendrochronological study of the Canal del Roc Roig avalanche path which was affected by two extreme avalanches in February 1996. This first dendrochronological study has permitted us to assess the tree-ring signals due to avalanche events in 53 out of 132 dated trees. The trees presented a variety of responses to the 1996 avalanche events. It is shown that the type of tree-ring signal depends on tree age. The methodology has proved successful in detecting the 1996 and 1972 documented avalanche events, and provided outstanding evidence of undocumented past events such as one in 1930.
Verification of nearest-neighbours interpretations in avalanche forecasting
Authors: Heierli Joachim , Purves Ross S. , Felber Andreas , Kowalski Julia
Published: November 2007

This paper examines the positive and negative aspects of a range of interpretations of nearest-neighbours models. Measures-oriented and distribution-oriented verification methods are applied to categorial, probabilistic and descriptive interpretations of nearest neighbours used operationally in avalanche forecasting in Scotland and Switzerland. The dependence of skill and accuracy measures on base rate is illustrated. The purpose of the forecast and the definition of events are important variables in determining the quality of the forecast. A discussion of the application of different interpretations in operational avalanche forecasting is presented.
Experimental study of dense snow avalanches: velocity profiles in steady and fully developed flows
Authors: Bouchet Alexi , Naaim Mohamed , Bellot Hervé , Ousset Frédéric
Published: November 2007

In order to study channelled snow flows over rough surfaces, a laboratory-scale experiment was installed at the “Col du Lac Blanc”, a 2800 m high pass in the French Alps, near the Alpe d’Huez ski resort. It consists of a 0.2 mwide, 10 m long channel fed with snow by a motorized hopper. Both the slope of the channel and the feeding rate of the hopper can be modified. Sensors in the channel provide measurements of the velocity profile, the flow height and the shear and normal stresses at the bottom of the flow. Velocity profiles for different slopes are presented in this paper. Results indicate the presence of a highly active layer at the bottom. This layer is mainly responsible for the avalanche velocity, while the upper layer has a much smaller velocity gradient. A first interpretation of both layers is given.
Development of saltation layer of drifting snow
Authors: Sato Takeshi , Kosugi Kenji , Sato Atsushi
Published: November 2007

The saltation length of aeolian snow particles and a new parameter, the ejection factor, which expresses the degree of erosion due to drifting snow, were obtained as functions of friction velocity by means of wind-tunnel experiments for semi-hard snow cover. The saturated-snowdrift transport rate was also obtained experimentally as a function of friction velocity. Based on these characteristics and the parameter, the development of the saltation layer of drifting snow along the fetch was simulated under various conditions such as snow hardness, wind speed and snowfall intensity. The main results are as follows. The developing distance denoting the distance required for the saltation layer to attain saturation, X sat, is determined by saltation length, ejection factor and saturated-snowdrift transport rate, all of which depend on wind speed. It is also affected by the magnitude of snowdrift transport rate at the starting point and by the intensity of snowfall if it exists. The dependence of Xsat on wind speed is not simple in the case of semi-hard snow cover: Xsat increases with wind speed under weak to moderate wind conditions and then decreases under moderate to strong wind conditions. It is sensitive to snow hardness: it is about one order longer on hard snow cover than on semi-hard snow cover. Snowfall reduces not only the value of Xsat but also its dependence on snow hardness.
Spatial variability of micropenetration resistance in snow layers on a small slope
Authors: Kronholm Kalle , Schneebeli Martin , Schweizer Jürg
Published: November 2007

The mechanisms leading to dry-snow slab release are influenced by the three-dimensional variability of the snow cover. We measured 113 profiles of penetration resistance with a snow micropenetrometer on an alpine snow slope. Seven distinct layers were visually identified in all snow micropenetrometer profiles. The penetration resistance of adjacent layers did not change abruptly, but gradually across layer boundaries that were typically 2 mm thick. In two layers, penetration resistance varied around 200% over the grid, possibly due to wind effects during or after layer deposition. Penetration resistance varied around 25%in five layers. Statistically significant slope-scale linear trends were found for all layers. The semivariogram was used to describe the spatial variation. Penetration resistance was autocorrelated, but the scale of variation was layer-specific. A buried layer of surface hoar was the most critical weak layer. It had little spatial variation. The layers in the slab above had higher spatial variation. The penetration resistance of each snow layer had distinct geostatistical properties, caused by the depositional processes.
Impact of artificial snow and ski-slope grooming on snowpack properties and soil thermal regime in a sub-alpine ski area
Authors: Keller Thomas , Pielmeier Christine , Rixen Christian , Gadient Florian , Gustafsson David , Stähli Manfred
Published: November 2007

Earlier studies have indicated that the soil on groomed ski slopes may be subjected to more pronounced cooling than the soil below a natural snowpack. We analyzed the thermal impacts of ski-slope preparation in a sub-alpine ski resort in central Switzerland (1100ma.s.l.) where artificial snow was produced. Physical snow properties and soil temperature measurements were carried out on the ski slope and off-piste during winter 1999/2000. The numerical soil–vegetation–atmosphere transfer model COUP was run for both locations, with a new option to simulate the snowpack development on a groomed ski slope. Snow density, snow hardness and thermal conductivity were significantly higher on the ski slope than in the natural snowpack. However, these differences did not affect the cooling of the soil, since no difference was observed between the ski slope and the natural snow cover. This might be because cold periods were rare and short and thus any snowpack could protect the soil from freezing. The major impact of the ski-slope grooming was a 4 week delay in snowmelt and soil warming at the end of the season. The newly implemented option proved to be a useful strategy for simulating the snowpack of a ski slope. However, snow density was underestimated by the model as it could not account adequately for compaction due to grooming traffic. Our study demonstrates that there is no site-independent answer as to whether a groomed snowpack affects the thermal conditions in the soil.
Ice fabric evolution process understood from anisotropic distribution of a-axis orientation on the GRIP (Greenland) ice core
Authors: Miyamoto Atsushi , Shoji Hitoshi , Hori Akira , Hondoh Takeo , Clausen Henrik B. , Watanabe Okitsugu
Published: November 2007

To better understand how ice fabric evolves in polar ice sheets, we use X-ray diffraction to measure ice crystal orientations. X-ray measurement equipment which can measure the orientation of the c axis and a axis of each crystal in a thin section with high measurement accuracy was developed. In this study, we present a-axes orientation distribution of the deep part of the GRIP (Greenland summit) ice core. At some depths, we find an anisotropic distribution of a-axes orientation. Long-term uniaxial compression tests are also carried out on the GRIP ice core to investigate the ice fabric evolution process. The c-axis orientation distribution develops into a stronger single maximum as the strain increases up to about 20% strain. We find that the a axes of each grain also tend to cluster close to nearly a mutual direction. We discuss the development process of ice fabrics, taking into consideration the distribution of the a-axis orientations. It is suggested that these fabrics may be attributed to a local simple shear deformation in the deep part of an ice sheet.
Relation of measured basal temperatures and the spatial distribution of the geothermal heat flux for the Greenland ice sheet
Authors: Greve Ralf
Published: November 2007

The thermomechanical, three-dimensional ice-sheet model SICOPOLIS is applied to the Greenland ice sheet. Simulations over two glacial–interglacial cycles are carried out, driven by a climatic forcing interpolated between present conditions and Last Glacial Maximum anomalies. Based on the global heat-flow representation by Pollack and others (1993), we attempt to constrain the spatial pattern of the geothermal heat flux by comparing simulation results to direct measurements of basal temperatures at the GRIP, NorthGRIP, Camp Century and Dye 3 ice-core locations. The obtained heat-flux map shows an increasing trend from west to east, a high-heat-flux anomaly around NorthGRIP with values up to 135 mWm–2 and a low-heat-flux anomaly around Dye 3 with values down to 20 mW m–2. Validation is provided by the generally good fit between observed and measured ice thicknesses. Residual discrepancies are most likely due to deficiencies of the input precipitation rate and further variability of the geothermal heat flux not captured here.
Seismic emissions from a surging glacier: Bakaninbreen, Svalbard
Authors: Stuart Graham , Murray Tavi , Brisbourne Alex , Styles Peter , Toon Sam
Published: November 2007

Bakaninbreen is a polythermal glacier in southern Spitsbergen, Svalbard, which surged between 1985 and 1995. For 9 days in spring 1987, when the surge front was travelling at ∼2.5-3.0 m d–1, three single-component geophones and two accelerometers were deployed in a T-shaped array immediately downstream of the surge front to record seismic emissions. The events were characterized by their waveforms and spectral content. At least three different categories have been identified: impulsive P- and S-waveforms, surface P- and S-wave trains, and harmonic (75-130 Hz) events. We interpret the impulsive events to originate at the base of the glacier, at or downstream of the surge front; the surface P- and S-wave trains from near-surface brittle fracture associated with the surface expression of the surge front itself; and the harmonic events from deep sources that involve resonance in a water-filled fracture, associated with the base of the surge front. We believe the basal events are related to the activation of stagnant ice downstream of the surge front, which allows water to access the bed and provides the mechanism for its propagation.
Regional and temporal variation of accumulation around NorthGRIP derived from ground-penetrating radar
Authors: Steinhage Daniel , Eisen Olaf , Clausen Henrik Brink
Published: November 2007

During the summer of 2003, a ground-penetrating radar survey around the North Greenland Icecore Project (NorthGRIP) deep ice-core drilling site (75˚06’N, 42˚20’W; 2957ma.s.l.) was carried out using a shielded 250 MHz radar system. The drill site is located on an ice divide, roughly 300 km north-northwest of the summit of the Greenland ice sheet. More than 430 km of profiles were measured, covering a 10 km by 10 km area, with a grid centered on the drilling location, and eight profiles extending beyond this grid. Seven internal horizons within the upper 120 m of the ice sheet were continuously tracked, containing the last 400 years of accumulation history. Based on the age-depth and density-depth distribution of the deep core, the internal layers have been dated and the regional and temporal distribution of accumulation rate in the vicinity of NorthGRIP has been derived. The distribution of accumulation shows a relatively smoothly increasing trend from east to west from 145 kgm–2a–1 to 200 kg m–2 a -1 over a distance of 50 km across the ice divide. The general trend is overlain by small-scale variations on the order of 2.5 kgm–2a-1 km- 1 , i.e. around 1.5% of the accumulation mean. The temporal variations of the seven periods defined by the seven tracked isochrones are on the order of ± 4% of the mean of the last 400 years, i.e. at NorthGRIP ± 7 kg m–2 a-1. If the regional accumulation pattern has been stable for the last several thousand years during the Holocene, and ice flow has been comparable to today, advective effects along the particle trajectory upstream of NorthGRIP do not have a significant effect on the interpretation of climatically induced changes in accumulation rates derived from the deep ice core over the last 10 kyr.
On the growth of ice cover in the Sea of Okhotsk with special reference to its negative correlation with that in the Bering Sea
Authors: Rikiishi Kunio , Takatsuji Shinya
Published: November 2007

Characteristic features of the growth of sea-ice extent in the Sea of Okhotsk are discussed statistically in relation to the surface wind and air temperature over the Okhotsk basin. It is shown that cold-air advection from the continent is not the only factor for the growth of ice extent: air-mass transformation with fetch (downwind distance from the coast) is another important factor. Using weekly growth rates of ice extent and objectively analyzed meteorological data, it is shown that the ice cover extends when cold northerly/northwesterly winds blow, whereas the ice cover retreats when warm northeasterly/easterly winds blow. It is concluded that the advance/retreat of the Sea of Okhotsk ice cover is largely determined by the atmospheric circulation, which is in turn controlled by the position and intensity of the Aleutian low. Occasional out-of-phase fluctuations between the Sea of Okhotsk and Bering Sea ice covers are found to occur when an intensified Aleutian low is located in the mid-western part of the Bering Sea and induces cold northwesterly winds to the Okhotsk basin and warm southeasterly winds to the Bering Sea, or when a weakened Aleutian low is displaced eastward and induces cold northeasterly winds to the Bering Sea and warm northeasterly winds to the Okhotsk basin.
The influence of drifting snow on the location of glaciers on western Spitsbergen, Svalbard
Authors: Jaedicke Christian , Gauer Peter
Published: November 2007

On western Spitsbergen, Svalbard, the amount of winter precipitation is insufficient to maintain the present-day mass balance of the local glaciers. Additional snow mass must be added to the precipitation to reach the observed accumulation rates of the glaciers. It was assumed in previous work that this additional mass is transported onto the glaciers by drifting snow and snow avalanches. This study is a first attempt to quantify the amount of snow mass added to the glacier mass balance by wind-transported snow. The wind field over an area of 60 × 50 km2 on western Spitsbergen was simulated for 24 idealized weather types by a mesoscale meteorological model on a 750 m grid. The resulting wind velocities and directions were coupled to a two-level snowdrift model. The model output clearly shows erosion and accumulation areas in the terrain. Comparison with the present glacier locations suggests that the glacier accumulation areas coincide with low wind speeds. Moreover, exposed areas with high wind speeds are mostly glacier-free in reality. Thus, the wind field and corresponding snowdrift gives an indication of the location of the present glaciers on western Spitsbergen.
ICESat measurement of Greenland ice sheet surface slope and roughness
Authors: Yi Donghui , Jay Zwally H. , Sun Xiaoli
Published: November 2007

The Ice, Cloud and land Elevation Satellite (ICESat) in its 8 day repeat orbit mode provided data not only on the along-track surface slope, but also on the cross-track surface slope from adjacent repeat ground tracks. During the first 36 days of operation, four to five such repeat orbits occurred within 1 km in the cross-track direction. This provided an opportunity to use ICESat data to measure surface slope in the cross-track direction at 1 km scale. An algorithm was developed to calculate the cross-track surface slope. Combining the slopes in the cross-track and along-track directions gives a three-dimensional surface slope at 1 km scale. The along-track surface slope and surface roughness at 10km scale are also calculated. A comparison between ICESat surface elevation and a European Remote-sensing Satellite (ERS-1) 5 km digital elevation model shows a difference of 1–2 m in central Greenland where the surface slope is small, and >20m at the edge of Greenland where the surface slope is large. The large elevation difference at the edge is most likely due to the slope-induced error in radar altimeter measurement. Accurate surface slope data from ICESat will help to correct the slope-induced error of radar altimeter missions such as Geosat, ERS-1 and ERS-2.
High-resolution reconstruction of Polar Ural glacier mass balance for the last millennium
Authors: Kononov Yuriy M. , Ananicheva Maria D. , Willis Ian C.
Published: November 2007

Our ultimate objective is to study the mass-balance variations of Polar Ural glaciers during the last millennium. We use mass-balance data for two glaciers between 1957 and 1981, climate data obtained by instrumental observations during the 20th century, and tree-ring data compiled for the last 1000 years. Because there is a high correlation between measured glacier mass-balance and climate variables, we reconstruct glacier mass balance for the 20th century using regression equations. Similarly, we use regression equations relating measured climatic variables to tree-ring widths to reconstruct glacier mass balance for the last millennium. According to our reconstructions, the most extensive period of negative mass balance occurred in the late 10th/early 11th century AD, which corresponds to the Medieval Warm Period. A prolonged period of positive glacier mass balance began after the mid-11th century, a time commonly accepted as the onset of the Little Ice Age. This cooling period has three maxima, the last from the early 17th to mid-19th century. Until the beginning of the 20th century, cumulative mass balance over the last millennium varied between ±8mw.e. However, glacier mass balance in the second half of the 20th century is lower than it has been for the past millennium, and cumulative mass balance is now -10mw.e. Polar Ural glaciers are important indicators of regional climate change and should be incorporated into a worldwide glacier-monitoring programme.
Interannual variability in the spatial distribution of winter accumulation at a high-Arctic glacier (Finsterwalderbreen, Svalbard), and its relationship with topography
Authors: Hodgkins Richard , Cooper Richard , Wadham Jemma , Tranter Martyn
Published: November 2007

Glacier mass balance and hydrology are strongly influenced by the distribution of snow accumulation at the start of the melt season. Two successive end-of-winter snow-cover surveys at Finsterwalderbreen, Svalbard, are here used to investigate the interannual variability in the spatial distribution of accumulation, and its relationship with topography. 40–62% of the variance in snow depth was not determined by elevation (assessed by linear regression of snow depth on surface elevation), which could not therefore necessarily be used as a sole predictor of the spatial distribution of accumulation here. Principal components (PC) analysis of the topographic variables elevation, slope, north–south and east–west aspects shows that only two of six PCs, determined for 2years’ sampling locations, had maximum loadings on altitude; aspect was more important, with maximum loadings on four PCs. Hierarchical cluster analysis was then applied to these PCs: significant correlations with accumulation in each of two terrain clusters were given by (1) elevation and slope, (2) east–west aspect only (1999); (1) elevation only, (2) no significant correlations (2000). There is strong interannual variability not only in the magnitude of winter accumulation (0.41 mw.e. in 1999, 0.58 mw.e. in 2000), but also in its spatial distribution, and its relationship with topography.
Geometry changes on Svalbard glaciers: mass-balance or dynamic response?
Authors: Hagen Jon Ove , Eiken Trond , Kohler Jack , Melvold Kjetil
Published: November 2007

The geometry of glaciers is affected by both the mass balance and the dynamics. We present repeated GPS measurements of longitudinal altitude profiles on three glaciers in Svalbard and show that surface altitude changes alone cannot be used to assess the mass balance. The three measured glaciers are in different dynamic modes, and the observed changes in geometry are strongly affected by the dynamics. Nordenskiöldbreen shows no significant change in the geometry, indicating that the mass balance is in steady state with the dynamics. On Amundsenisen the surface has lowered by 1.5–2.0 ma–1 in the lower part of the accumulation area at 520–550m a.s.l., indicating that the ice flux is higher than the mass-balance input, probably due to a surge advance of the glacier further downstream affecting the higher part of the drainage area. On Kongsvegen the opposite situation was found. Here the geometry of the profile showed a clear build-up of 0.5 ma–1 in the accumulation area and a lowering of 1 ma–1 in the lower part of the ablation area. The ice velocity is very low, giving a negligible vertical velocity component and an ice flux that is far smaller than the mass-balance flux, indicating that the glacier is building up towards a surge advance. Our results show that if mapping of height changes is to be used to monitor the response of the glaciers to climate change, both surface net mass-balance data and dynamic data are needed.
Interpretation of the anomalous growth of Austfonna, Svalbard, a large Arctic ice cap
Authors: Raper Vivienne , Bamber Jonathan , Krabill William
Published: November 2007

As previously reported, repeat-pass airborne laser altimetry measurements made in May 1996 and May 2002 show a large positive ice-surface elevation change rate over parts of the accumulation area of Austfonna, eastern Svalbard. The maximum growth rate is estimated to be equivalent to a 35–40% increase in snowfall over the area of thickening. Thinning is observed at lower elevations. Here we discuss in detail the possible causes of these elevation changes, including ice-cap dynamics and/or firn density changes, and conclude that sea-ice loss producing a localized increase in precipitation over Austfonna remains the most convincing explanation. This study highlights the problems of interpreting relatively short-term altimetry measurements where auxiliary data are limited in both spatial and temporal extent.