bluuebunny/crossref_metadata_2025 huggingface dataset:
20th-century sea-ice variations from observational data
Authors: Walsh John E. , Chapman William L.
Published: November 2007

In order to extend diagnoses of recent sea-ice variations beyond the past few decades, a century-scale digital dataset of Arctic sea-ice coverage has been compiled. For recent decades, the compilation utilizes satellite-derived hemispheric datasets. Regional datasets based primarily on ship reports and aerial reconnaissance are the primary inputs for the earlier part of the 20th century. While the various datasets contain some discrepancies, they capture the same general variations during their period of overlap. The outstanding feature of the time series of total hemispheric ice extent is a decrease that has accelerated during the past several decades. The decrease is greatest in summer and weakest in winter, contrary to the seasonality of the greenhouse changes projected by most global climate models. The primary spatial modes of sea-ice variability diagnosed in terms of empirical orthogonal functions, also show a strong seasonality. The first winter mode is dominated by an opposition of anomalies in the western and eastern North Atlantic, corresponding to the well-documented North Atlantic Oscillation. The primary summer mode depicts an anomaly of the same sign over nearly the entire Arctic and captures the recent trend of sea-ice coverage.
The Ronne polynya of 1997/98: observations of air-ice-ocean interaction
Authors: Ackley S. F. , Geiger C. A. , King J. C. , Hunke E. C. , Comiso J.
Published: November 2007

The Ronne polynya formed in the Weddell Sea, Antarctica, during the period November 1997−February 1998 to an extent not seen previously in the 25 years of all-weather satellite observations. The vessel HMS Endurance traversed the polynya region and took sea-ice, physical oceanographic and meteorological measurements during January and early February 1998. These observations, together with satellite imagery and weather records, were analyzed to determine the causes of the anomalous condition observed and to provide comparisons for numerical modeling experiments. The polynya area, analyzed from satellite imagery, showed a linear, nearly constant, increase with time from mid-November 1997 through February 1998. It had a maximum open-water area of 3 × 105 km2 and extended 500 km north of the Ronne Ice Shelf (at 76° S) to 70° S. The ice and snow structure of floes at the northern edge of the polynya showed the ice there had formed in the previous mid- to late winter (October 1997 or earlier) and had been advected there either from the eastern Weddell Sea or from the front of the Ronne Ice Shelf. Analyses of the wind fields showed anomalous spring-summer wind fields in the polynya year, with a strong southerly to southwesterly component compared to the mean easterly winds typical of summer conditions. These southerly wind conditions, in both magnitude and direction, therefore account for the drift of ice northward. The predominant summer easterly winds usually fill the southern Weddell Sea with ice from the east, and the high-albedo surfaces reflect the solar radiation, preventing warming of the surface ocean waters and consequent sea-ice melt. Instead, high incident solar radiation from November 1997 to February 1998 was absorbed by the open water, rather than being reflected, thereby both melting ice and preventing ice formation, and thereby sustaining the polynya. We conclude that open-water-albedo feedback is necessary to allow the observed polynya formation, since similar drift conditions prevail in winter (arising from southerly winds also) and usually result in extensive new ice formation in front of the Ronne Ice Shelf. The strong southerly winds therefore have quite opposing seasonal effects, leading to high ice production in winter as usually found, and extensive open water if they occur in spring and summer, as seen in this atypical event in 1997/98. In this case, the atypical southerly winds may be associated with an El Niño-Southern Oscillation (ENSO)-induced atmospheric circulation pattern.
Measurement of all-wave and spectral albedos of snow-covered summer sea ice in the Ross Sea, Antarctica
Authors: Zhou Xiaobing , Li Shusun , Morris Kim
Published: November 2007

All-wave albedo and spectral albedo data were collected over snow-covered pack-ice floes during summer 1999 (January and February) in the Ross Sea, Antarctica. Temporal variation of the all-wave albedo and spectral albedo was measured from the northern edge to the southern edge of the pack ice along three lines of longitude: 165° W, 150° Wand 135° W. Snow depth, snow-cover stratification, snow-temperature profiles, and grain-size and morphology were also documented. It was observed that daily-averaged albedos were 0.70−0.86 for cloudy conditions over the pack ice. Only two sets of daily-averaged albedo were collected for clear-sky conditions (0.788 and 0:825). Albedo was lower at the marginal edges of the pack ice than in the central pack ice. Albedo was higher over the southern part of the central pack ice than over the northern part. Clear- and cloudy-sky albedos measured on the same site indicate that the average increase in albedo due to clouds is 1.4% (maximum 4.0%). Spectral albedos of the pack-ice floes were similar under clear-sky and cloudy conditions. Both are mainly controlled by the snow grain-size, especially in the top snow layer. All-wave albedos derived from measured visible and near-infrared spectral albedos, with extrapolation to ultraviolet and shortwave infrared regions for both clear- and cloudy-sky conditions, agreed well with all-wave albedos from direct measurements.
Snow-ice growth: a fresh-water flux inhibiting deep convection in the Weddell Sea, Antarctica
Authors: Lytle V.I. , Ackley S.F.
Published: November 2007

During a field experiment in July 1994, while the R.V. Nathaniel B. Palmer was moored to a drifting ice floe in the Weddell Sea, Antarctica, data were collected on sea-ice and snow characteristics. We report on the evolution of ice which grew in a newly opened lead. As expected with cold atmospheric conditions, congelation ice initially formed in the lead. Subsequent snow accumulation and large ocean heat fluxes resulted in melt at the base of the ice, and enhanced flooding of the snow on the ice surface. This flooded snow subsequently froze, and, 5 days after the lead opened, all the congelation ice had melted and 26 cm of snow ice had formed. We use measured sea-ice and snow salinities, thickness and oxygen isotope values of the newly formed lead ice to calculate the salt flux to the ocean. Although there was a salt flux to the ocean as the ice initially grew, we calculate a small net fresh-wlter input to the upper ocean by the end of the 5 day period. Similar processes of basal melt and surface snow-ice formation also occurred on the surrounding, thicker sea ice. Oceanographic studies in this region of the Weddell Sea have shown that salt rejection by sea-ice formation may enhance the ocean vertical thermohaline circulation and release heat from the deeper ocean to melt the ice cover. This type of deep convection is thought to initiate the Weddell polynya, which was observed only during the 1970s. Our results, which show that an ice cover can form with no salt input to the ocean, provide a mechanism which may help explain the more recent absence of the Weddell polynya.
Sea-ice thickness and roughness in the Ross Sea, Antarctica
Authors: Tin Tina , Jeffries Martin O.
Published: November 2007

Sea-ice thickness and roughness data collected on three cruises in the Ross Sea, Antarctica, showed interseasonal, regional and interannual variability. Variability was reduced to season, or age of ice floe, when sea-ice roughness values from around Antarctica were compared. There were statistically significant correlations between mean snow elevation and mean ice thickness; snow surface roughness and mean ice thickness; and snow surface roughness and ice bottom roughness, which appeared to be independent of season, geographical location and deformation history of ice floes. Our field data indicate that ice thickness can be predicted from snow elevation measurements with higher accuracy in summer. The feasibility of using snow surface roughness to infer ice thickness and ice bottom roughness is promising, and can provide us with a means to study the thickness and underside of Antarctic sea ice at good spatial and temporal resolution.
The albedo of Arctic leads in summer
Authors: Pegau W. Scott , Paulson Clayton A.
Published: November 2007

Leads act as windows through which solar radiation enters the upper ocean. Studies of the heat budget and ice melt require accurate parameterization of the albedo. Results from summertime measurements of albedo over leads show that under cloudy conditions the average albedo is 0.066 with a standard deviation of 0.007. The clear-sky case is more complex because the albedo is strongly dependent on wind speed at large solar zenith angles. This dependence has not been included in prior modeling efforts. We suggest a simple modification to an existing parameterization of the albedo" which includes the effect of wind speed.
Understanding climatic controls on sea-ice transport pathways in the Arctic Ocean
Authors: Proshutinsky Andrey , Johnson Mark , Proshutinsky Tatiana
Published: November 2007

The primary goal of this paper is to demonstrate the dependence of Arctic Ocean sea-ice transport pathways on climate variations. We build our analysis on the results of Proshutinsky and Johnson (1997), Johnson and others (1999), Polyakov and others (1999) and Proshutinsky and others (1999), where we have shown that wind-driven ice motion and upper ocean circulation alternate between anticyclonic and cyclonic states. Shifts between regimes occur at 5−7 year intervals, resulting in a 10−15 year period. The anticyclonic circulation regime has been observed in our model results for 1946−52,1958−62,1972−79,1984−88 and 1998−present. The cyclonic circulation regime prevailed during 1953−57,1963−71,1980−83 and 1989−97. The regime shifts are fundamentally important to understanding the Arctic’s general circulation and particularly useful for estimating pollution transport by sea ice and surface waters. It is important to pollution studies to understand which circulation regime prevails. Initially, we simulate trajectories of a non-reactive, conservative soluble tracer. Results from this research demonstrate realistic potential flow pathlines and we describe how those pathlines change in response to climate forcing. These results can be used to aid current and future scenario risk assessments and may provide management agencies with the tools to determine where risks from contaminants might exist.
Solar radiative heating in first-year sea ice
Authors: McGuinness M. J. , Landman K. A. , Trodahl H. J. , Pantoja A. E.
Published: November 2007

Temperature measurements taken in young, landfast Antarctic sea ice show daily oscillations consistent with heating by solar radiation. We present and solve a heat conduction model for the temperature with a non-linear thermal capacity and a distributed source term for solar power absorption based on Monte Carlo scattering simulations of penetrating photons. We observe two characteristic modes for solar heating in sea ice, one dominated by travelling thermal waves or conduction in the upper half, and the other dominated by in-place solar heating in the lower half. We note that deep thermal responses to solar radiation are larger by a factor of ∼ 10 than predicted by scattering measurements, due possibly to the presence of algae and/or dissolved organic material.
The proposed open-pit protection of Bolungarvík, Iceland
Authors: Jónsson Árni , Hestnes Erik
Published: November 2007

Snow avalanches threaten a large part of the residential area of Bolungarvik, a town of 1100 inhabitants located in the Vestfirðir peninsula, northwest Iceland. Methods for the complete protection of all the houses were requested by the Ministry of Environment. As conventional deflecting and catching dams were not feasible due to avalanche velocities of > 40 m s–1 in the actual defence area, a huge open pit built into the lower mountainside was proposed. The pit is designed to dissipate the energy of avalanches of any expected size. It is 1000 m long, and the upper and lower pit walls are 30–40 and 15–20 m high, respectively. The downhill side of the pit is increased to 30 m by a nearly vertical, 10–15 m high dam. The bottom is 25–40 m wide, and the effective cross-sections are 700–2300 m2. The total storage capacity is approximately 106 m3. Cost-benefit analyses indicate that the development cost of the pit protection is favourable compared to the value of the houses as well as alternative safety solutions.
Observations of snowdrift over Antarctic snow and blue-ice surfaces
Authors: Bintanja Richard , Lilienthal H. , Tüg H.
Published: November 2007

Vertical profiles of snowdrift density and concurrent meteorological data were measured over Antarctic snow and blue ice during a 1 month field experiment in austral summer 1997/98. It is found that drift densities and transport rates over blue ice are significantly smaller than over snow, which can be attributed mainly to the limited availability of snow particles at the blue-ice surface. Hence, over blue ice, near-surface drift densities and vertical gradients in drift density are relatively small. Over blue ice, snowdrift can occur in very weak winds, presumably because of the smoothness of the surface. Over snow, in contrast, drift occurs only in much stronger winds, such that the shear stress applied by the flow can overcome the cohesive interparticle bonds.
Avalanche of 18 January 1997 on Brenva glacier, Mont Blanc Group, Western Italian Alps: an unusual process of formation
Authors: Giani Gian Paolo , Silvano Sandro , Zanon Giorgio
Published: November 2007

At 1455 h on 18 January 1997, an airborne powder avalanche with a volume of about 3 × 106 m3 flowed along the tongue of Brenva glacier, high Aosta valley, on the southern flank of Val Veny, Italy It descended 2000 m and covered a distance of 5.5 km, with a rate of movement on the intermediate stretch of > 70 m s–1. It killed two skiers following a valley-bottom piste, damaged a hotel, destroyed a wide belt of woodland on the opposite slope and caused other minor damage. The avalanche occurred immediately after a large rockfall on the southern slope of the Sperone della Brenva (3567 m a.s.L). However, the relationship between the two events can only be considered indirect, since the main mass of the rockfall stopped at the base of the scar, on a large plateau on the glacier surface. The rockfall and subsequent shock caused the contemporaneous detachment of masses of ice and/or firn from hanging glaciers at the head of a nearby cirque, leading to the formation of the avalanche. The complex mechanism of detachment hypothesized was induced from available documentation and from in situ investigations. Its phases also coincide with seismograms recorded at a station 45 km from the avalanche area. Finally, a mathematical model of the avalanche was used to reconstruct its dynamics and path.
Flow of dense avalanches past obstructions
Authors: Tai Y. C. , Gray J. M. N.T. , Hutter K. , Noelle S.
Published: November 2007

One means of preventing areas from being hit by avalanches is to divert the flow by straight or curved walls or tetrahedral or cylindrical-type structures. Thus, there arises the question how a given avalanche flow is changed regarding the diverted-flow depth and flow direction. In this paper a report is given on laboratory experiments performed for gravity-driven dense granular flows down an inclined plane obstructed by plane wall and tetrahedral wedge. It was observed that these flows are accompanied by shocks induced by the presence of the obstacles. These give rise to a transition from super-to subcritical flow of the granular avalanche, associated with depth and velocity changes. It is demonstrated that with an appropriate shock-capturing integration technique for the Savage-Hutter theory, the shock formation for a finite-mass granular flow sliding from an inclined plane into a horizontal run-out zone is well described, as is the shock formation of the granular flow on either side of a tetrahedral protection structure.
The effect of wind direction on drift control by snow fences
Authors: Takeuchi Yukari , Kobayashi Shun’ichi , Sato Takeshi , Izumi Kaoru , Kosugi Kenji , Xin Wang , Jiapin Zhang , Yongheng Peng
Published: November 2007

Snowdrifting processes and the wind-velocity profiles around a collector and a blower snow fence were investigated in a cold wind tunnel. The purpose was to ascertain the effect of wind direction on drift control by snow fences. Three different cases were studied for both types of snow fence, and the resultant snowdrifts were compared. In the first case, the snow fence was perpendicular to the wind direction. In the second and third cases, it was tilted by 30° and 45°. When the collector snow fence was tilted, the amounts of snowdrift were much less than when the fence was perpendicular to the wind direction, because the area with low wind velocity was reduced to half behind the tilted fence. On the other hand, the blowing effect of the blower snow fence increased when it was set up at an angle to the wind direction. It is necessary to investigate the position where the blown snow is deposited by the tilted blower snow fence.
Saltation-layer structure of drifting snow observed in wind tunnel
Authors: Sato Takeshi , Kosugi Kenji , Sato Atsushi
Published: November 2007

The saltation-layer structure of drifting snow was investigated using the wind tunnel in a cold room. Experiments were conducted under various snow-temperature and wind-speed conditions over loose and hard snow covers. Snow was seeded at the upwind end of the wind tunnel. Mass-flux profiles of drifting snow were measured with a snow-particle counter. The theoretical expression for the mass flux of saltating sand (Kawamura, 1948) was fitted to the measured profiles, and two parameters in the theoretical expression, saltation height h0 and mass flux at the surface q0, were determined. The main results are as follows: (1) In the case of hard snow cover, snow particles are hardly ejected and drifting snow is maintained by the seeded snow. The value of h0 linearly increases with wind speed and decreases with snow temperature, and q0 decreases with wind speed and is in proportion to seeding rate. (2) In the case of loose snow cover, erosion occurs under high-wind conditions and the contribution of the ejected snow particles to drifting snow is remarkable. The h0 linearly increases with wind speed, but its value is smaller than the value over hard snow cover. Due to erosion, q0 increases with wind speed. Snowdrift transport rate and q0 do not change with seeding rate under low-wind conditions, because the drifting snow is saturated. Under high-wind conditions, however, both snowdrift transport rate and q0 slightly increase with seeding rate.
Creep experiments and numerical simulations of very light artificial snowpacks
Authors: Abe Osamu
Published: November 2007

This paper reports on the measurement of the viscosity coefficient of very light artificial snow with H. density of < 100 kg m−3. The temperature dependency on the viscosity coefficients of the snow was also obtained, and these results were applied to the problem of snow creep. General comparison between experimental and computed results shows good agreement, but differences between the two creep flows along the slope indicate that low-density snow near the freezing point should be considered as an orthotopic material.
Effect of western U.S. snow cover on climate
Authors: Marshall Susan , Oglesby Robert J. , Nolin Anne W.
Published: November 2007

The purpose of this study is to identify characterize and quantify local, regional and remote effects of snow cover on western U. S. climate and water resources. An ensemble of predictability and sensitivity studies was made with the U.S. National Center for Atmospheric Research (NCAR) Community Climate Model, version 3 (CCM3) to investigate the relative roles of snow-cover anomalies and initial atmospheric states in the subsequent accumulation and ablation seasons. The suite of model experiments focuses on the direct effect of snow on regional climate anomalies and ultimately will be used to examine the lagged effect of anomalous snow cover on the climate. The set of ensemble simulations presented here looks at the climate-system response to anomalously high and low snow cover at the start of the ablation season over the western U.S.A. These current results suggest that the initial state of snow cover is more important than the initial state of the atmosphere or of sea-surface temperatures because of direct thermal effects on the surface and subsequent indirect, dynamical effects on the atmospheric circulation.
Prediction of avalanche paths deviated from the stream by center-of-mass model
Authors: Nagasaki Tomoharu , Izumi Kaoru , Kobayashi Shun’ichi , Yamada Takatsugu
Published: November 2007

We developed a method that predicts avalanche paths deviating from a stream on complex surfaces. This method is based on Nohguchi’s center-of-mass model with simple dynamic resistance. Avalanche paths from many starting points were calculated at two sites in Japan where avalanche disasters have occurred, and paths causing unexpected disaster are presented. The characteristics of avalanche paths at these sites are shown. Small differences of the release positions sometimes cause great changes in avalanche meanderings.
Three-dimensional snow images by X-ray microtomography
Authors: Coléou Cécile , Lesaffre Bernard , Brzoska Jean-Bruno , Ludwig Wolfgang , Boller Elodie
Published: November 2007

For the first time, three-dimensional (3-D) high-resolution images of snow were obtained using X-ray absorption tomography. Images with a spatial resolution of 10 μm were taken on four different cylindrical snow samples (9 mm high, 9 mm diameter). About 1000 two-dimensional X-ray absorption images were recorded at angular positions of the object around an axis spanning 180°. An appropriate algorithm was then used for these data to reconstruct a 3-D image. In the case of snow, experimental problems have been solved to prepare the samples and prevent both melting and metamorphism of snow during the experiments. This tomographic method provided 3-D data files from which images of 6003 voxels were extracted Several physical parameters of snow microstructure can be processed from these data. Porosity P and discrete local (3-D) curvature C of the grain/pore interface were computed for the four snow samples. Representative elementary volume (REV, in the sense of porous media) is a relevant index to the significance of the sample size with respect to a given parameter. From each image, the values of P and C are compared for subsamples of different size, as an attempt to assess the REVs for porosity and curvature. Results show that the observed volume of snow is statistically significant to achieve the porosity and the curvature distribution.
Numerical experiments of wind transport over a mountainous instrumented site: I. Regional scale
Authors: Durand Yves , Guyomarc’h Gilbert , Mérindol Laurent
Published: November 2007

For about ten winter seasons, the Centre d’Etudes de la Neige and CEMAGREF have performed intensive field measurement campaigns concerning various snow and weather parameters during blowing-snow events. The observation sites are located near the ski resort, Alpe d’Huez, Col du Lac Blanc, France (2700–2800 m a.s.L). Our first objective is to include the main effects of the wind in the operational avalanche-hazard forecast at the massif scale, taking into account the effects of local winds on our snow-cover estimation without simulating the phenomena exactly. Only the effects on snow accumulation or erosion and snow characteristics are measured, without any direct link with a precise field location except for the validation. The underlying numerical simulations have been tested on the instrumented site and include an assessment of the appropriate shear velocity, an evaluation of the occurrence of transport related to the snow characteristics provided by the software PROTEON and an estimation of the transport rates. These different computations are embedded in the new software, SYTRON, which is inserted in the SAFRAN/Crocus/MEPRA operational chain! Different validations of this new application are presented in terms of shear velocities, observed transport periods and snow depths. The encouraging results augur well for an operational implementation next winter
Evaluation of the shear frame test for weak snowpack layers
Authors: Jamieson Bruce , Johnston Colin D.
Published: November 2007

The shear frame allows testing of thin weak snowpack layers that are often critical for slab avalanche release. A shear metal frame with an area of 0.01–0.05 m2 is used to grip the snow a few mm above a buried weak snowpack layer. Using a force gauge, the frame is pulled until a fracture occurs in the weak layer within 1 s. The strength is calculated from the maximum force divided by the area of the frame. Finite-element studies show that the shear stress in the weak layer is concentrated below the cross-members that subdivide the frame and where the weak layer is notched at the front and back of the frame. Placing the bottom of the frame in the weak layer increases the stress concentrations, and results in significantly lower strength measurements than placing the bottom of the frame a few mm above the weak layer. Based on over 800 sets of 7–12 tests in western Canada, coefficients of variation average 14% and 18% from level study plots and avalanche start zones, respectively. Consequently,sets of 12 tests typically yield a precision of the mean of 10% with 95% confidence, which is sufficient for monitoring of strength change of weak layers over time in study plots. With consistent technique, there is no significant difference in mean strength measurements obtained by different experienced shear frame operators using the same approximate loading rate and technique for placing the frame. Although fracture surfaces are usually planar, only one of eleven shapes of non-planar fracture surfaces showed significantly different strength compared to planar fracture surfaces. For weak layers thick enough for density measurements, the shear strength is plotted against density and grain form. From these data, empirical equations are determined to estimate the shear strength of weak snowpack layers.
On the correlation between tensile strength and stress wave velocities of dry coherent snow based on its structural model
Authors: Golubev Vladimir N. , Frolov Anatoly D.
Published: November 2007

The various mechanical properties of dry coherent snow are determined by the same structural peculiarities of this medium, that can be described using the model of regular packed grains connected by rigid bonds. Analytic expressions for the many important snow mechanical parameters density elastic moduli, stress wave velocities, strength, etc.) are derived using the model by introducing three non-dimensional principal structural factors: texture friability, bond rigidity and coordination number. Analytic expressions that relate tensile strength to P and S stress wave velocities are proposed and used to examine the interrelations between the internal structure and tensile strength for snow-ice formations in a wide density range. The theoretically derived results and available experimental data are well correlated and form the basis for the development of non-destructive testing methods to evaluate the strength characteristics of snow, using seismic and acoustic measurements.
Measurements and one-dimensional model calculations of snow transport over a mountain ridge
Authors: Doorschot J. , Raderschall N. , Lehning M.
Published: November 2007

Wind transport of snow can cause an additional snow load on leeward slopes, which often has a considerable influence on avalanche danger. For a quantitative assessment of this process, a model is proposed which calculates the snow transport over a two-dimensional mountain ridge, based on input measurements of wind speed and precipitation. Since the topography is idealized, the model is focused on the snow mass that is transported over the ridge, and no statements are made about the exact snow distribution over the slopes. Three transport modes are distinguished: snow transport in saltation, snow transport in Suspension, and preferential deposition of precipitation. Suspension is modelled with a one-dimensional diffusion equation, and for the saltation layer a newly developed model, based on the microscale physical processes, is implemented. The effect of speed-up of the wind over the ridge is included by assuming an analytical wind profile with a maximum wind speed at a few meters above the ridge Advective effects are taken into account in a parameterization of the turbulent shear stress profile. The model is compared with measurements taken at the experimental snowdrift site Gaudergrat in the Parsenn area, Switzerland, and good agreement is obtained between calculated and measured results.
Photogrammetric avalanche volume measurements at Vallée de la Sionne, Switzerland
Authors: Vallet Juauien , Gruber Urs , Dufour François
Published: November 2007

During winter 1999 three large avalanche events were triggered by explosives at SLF’s avalanche test site, Vallée de la Sionne, canton Valais, Switzerland. One important goal of these large-scale field experiments was to measure the release and deposition volumes of avalanches by photogrammetric methods. In this paper, the photogrammetric measurements of all three avalanches are summarized. For one avalanche event it was possible to realize the whole measuring procedure as planned, and to obtain volume measurements before and after the avalanche triggering In the other two avalanche events, the photographs before the triggering of the avalanche failed. Nevertheless the photographs taken after the avalanche provide valuable information on the fracture depth at the fracture line. The mean fracture depth of the largest avalanche was about 2.10 m, varying between 1 and 3.5 m over a width of > 1000 m. The total volume of the deposition of all three avalanche events was about 1300 000 m3. The deposits are distributed over a length of > 1000 m with depths up to 30 m. The difference between the released and deposited volumes proved that avalanches entrain a large amount of snow along the avalanche track. Furthermore, the snow distribution in the deposition zone provides important information about the behaviour of a dense flowing avalanche in the runout zone.
Distribution of slushflows in northern Europe and their potential change due to global warming
Authors: Sidorova T. , Belaya N. , Perov V.
Published: November 2007

The distribution of slushflows in northern Europe is described. Schematic maps of the beginning and ending periods of slushflow risk are presented. The months with maximum slufhflow activity are also shown. Potential changes in the geographic and temporal distribution of slushflows due to global warming were analyzed for this region. Calculations for the year 2050 were done on the basis of climatic changes given by three global circulation models. The method of calculation was based on the general relationships between climatic parameters and the geographical and temporal distribution of slushflows. Schematic maps of potential distribution of slushflows show changes when calculated according to the most extreme of the three climatic-change scenarios.
A glacio-chemical characterization of the new EPICA deep-drilling site on Amundsenisen, Dronning Maud Land, Antarctica
Authors: Göktas Fidan , Fischer Hubertus , Oerter Hans , Weller Rolf , Sommer Stefan , Miller Heinz
Published: November 2007

In the framework of the European Project for Ice Coring in Antarctica (EPICA) a glacio-chemical pre-site survey was carried out in Dronning Maud Land (DML), Antarctica, to investigate seasonal and spatial variations. All ion species show pronounced seasonal cycles with the exception of nitrate, which is subject to post-depositional alterations. Sea salt reaches maximum concentrations in late winter/spring, while sulphate, being mainly of marine biogenic origin, shows a double peak with high concentrations both in autumn and in late spring/summer. Methanesulphonate (MSA) also shows a strong autumn peak but only slight indications of a second peak in late spring/summer, as seen for sulphate. Due to post-depositional changes, the seasonal cycle of MSA vanishes further down in the firn. These changes are also reflected in the spatial distribution of MSA. While surface MSA concentrations decline with altitude and higher accumulation rates, concentrations of aged snow show a strong increase with higher accumulation rates in our ice cores. Non-sea-salt sulphate shows a 40% decrease with an increase in snow accumulation of about 80% in recent and aged snow. While the geographical variation is negligible for average nitrate concentrations, sea salt shows an exponential decline with altitude. the outcome of this study confirms that the data of the new EPICA deep drilling site in DML (75˚00.10’ S, 0˚04.07’ E) will be representative for this region, and high-resolution analytical methods will allow accurate stratigraphic dating of a deep ice core.
Lithium in Greenland ice cores measured by ion chromatography
Authors: Siggaard-Andersen Marie-Louise , Steffensen Jørgen Peder , Fischer Hubertus
Published: November 2007

Ion chromatography (IC) is a widely used technique for analyzing ice cores for ions like Na+, NH4+, K+, Mg2+, Ca2+, F–, MSA–, Cl–, NO2– and SO42– that are present in polar ice cores at ppb level. By using sample preconcentration and an optimized separation technique, we have been able to detect Li+ in ice-core samples in concentrations as low as 0.0001 μeq kg–1 or 0.7 ppt by IC. During routine analysis of ions in ice cores, the lithium content has been evaluated and recorded. the IC technique used in these measurements and some exemplary IC data from the Greenland Icecore Project (GRIP) and the North Greenland Icecore Project (NorthGRIP) ice cores are presented. By these data we introduce Li+ concentration as a new parameter in the analysis of ice cores. Like other ions, Li+ reflects climatic changes and shows seasonal cycles. on the basis of the geochemistry of lithium, we suggest that Li+ measured in the Greenland ice cores is derived from mineral dust. However, data from the NorthGRIP ice core representing the 8.2 kyr BPHolocene cold event show a strong Li+ signal that does not correlate with any other ionic component measured. This means that the lithium content in ice cores is a signal with its own pattern, which is not yet understood.
Mass balance and ice flow along the north-northwest ridge of the Greenland ice sheet at NorthGRIP
Authors: Hvidberg Christine Schøtt , Keller Kristian , Gundestrup Niels S.
Published: November 2007

The North Greenland Icecore Project (NorthGRIP) deep drilling site (75˚05’47’’N, 42˚19’42’’ W) is located at the north-northwest ridge of the Greenland ice sheet, 320 km from Summit. A strain net has been established around the NorthGRIP site and surveyed with global positioning system. Our results show that ice flows with a horizontal surface velocity of 1.329 ±0.015ma–1 along the ridge. Estimated principal surface strain rates at NorthGRIP are and in the directions along and transverse to the north-northwest ridge, respectively, i.e. ice is compressed along the ridge but stretched transverse to the ridge. Possible implications of the observed flow pattern for the stratigraphy are discussed. the average thickening rate in the strain-net area is found to be ∂H/∂t = 0.00 ±0.04ma– 1, in agreement with previous estimates of mass balance in high-elevation areas of Greenland.
Past 43 year oxalate record: Ürümqi glacier No. 1, Tien Shan, China, and its link with Far East Rongbuk Glacier, Qomolangma (Mount Everest)
Authors: Xinqing Lee , Dahe Qin , Jiawen Ren , Keqin Duan , Shichang Kang , Hui Zhou
Published: November 2007

A 43 year oxalate record has been recovered in a 14.08m ice core from Ürümqi glacier No. 1 (43˚06’N, 86˚49’ E), a mid-latitude glacier at Ürümqi river head, Tien Shan, western China. Averaging 3.6±9.2 ng g–1 the oxalate has a background level <2 ng g–1 with sporadic concentration enhancements. Most of the spikes reach beyond 10 ng g–1 and have durations 51 year. the oxalate variation correlates with that in Far East Rongbuk Glacier (27˚59’N, 86˚55’ E), Qomolangma (Mount Everest), which is located 1600 kmawayacross the Qinghai–Tibetan Plateau and Taklimakandesert. Although the concentration enhancement in the latter is much higher, and lasts longer, oxalate reaches its highest concentration in both cores at the same time, during winter. the correlation of oxalate records suggests that the two areas may have had the same kind of local sources, but with a much larger (COO)22– flux in the Qomolangma area, or that they may have had a common source in the Indian subcontinent through the longitudinal atmospheric circulation. the concentration variation in the past 40 years coincides with industrial/economic development in southern Asia, and is mainly due to anthropogenic pollution.
The structure and chemistry of 94 m Greenland Ice Sheet Project 2 ice
Authors: Baker Ian , Cullen Daniel
Published: November 2007

Optical microscopy, X-ray topography, scanning electron microscopy and X-ray spectroscopy have been used for microstructural analysis of ice from 94 m depth from Greenland Ice Sheet Project 2. the ice had a high density of air bubbles, a 2 mm grain-size and contained a high dislocation density in most grains (>1×1010 m–2), although a few lower-dislocation-density grains were present. the main impurities, Na and Cl, were found in several grain boundaries and triple points, often as filaments. Na and Cl were also found in the lattice, but to a lesser extent, along with S, Mg, K and Ca. These observations are compared to previous studies of dislocations and impurity locations in natural ice.
A site for deep ice coring in West Antarctica: results from aerogeophysical surveys and thermo-kinematic modeling
Authors: Morse David L. , Blankenship Donald D. , Waddington Edwin D. , Neumann Thomas A.
Published: November 2007

The U.S. Science Plan for Deep Ice Coring in West Antarctica calls for two ice cores to be collected. the first of these cores, from Siple Dome, was completed during the 1997/98 field season. the second core is to be collected from a site near the divide that separates ice flowing to the Ross Sea and to the Amundsen Sea.Using high-resolution, grid-based aerogeophysical surveys of the Ross/Amundsen ice-divide region, we identify seven candidate sites and assess their suitability for deep coring. We apply ice-flow and temperature calculations to predict time-scales and annual-layer resolution, and to assess the potential for basal melting for several selected sites. We conclude that basal melting is likely for sites with very thick ice, as was observed at the Byrd core site. Nevertheless, these sites are most attractive for coring since they promise recovery of a long climate record with comparatively high time resolution during the last glacial period.
Surface mass balance of the Greenland ice sheet from climate-analysis data and accumulation/runoff models
Authors: Hanna Edward , Huybrechts Philippe , Mote Thomas L.
Published: November 2007

We used surface climate fields from high-resolution (~0.5660.56˚) European Centre for Medium-RangeWeather Forecasts (ECMWF) operational analyses (1992–98), together with meteorological and glaciological models of snow accumulation and surface meltwater runoff/retention, to produce novel maps of Greenland ice sheet (GIS) net accumulation, net runoff and surface mass balance (SMB). We compared our runoff maps with similar-scaled runoff (melt minus refreezing) maps based on passive-microwave satellite data. Our gross spatial/temporal patterns of runoff compared well with those from the satellite data, although amounts of modelled runoff are likely too low. Mean accumulation was 0.287 (0.307)ma–1, and mean runoff was 0.128 (0.151)ma–1, averaged across the W. Abdalati (T. L. Mote) GIS mask. Corresponding mean SMB was 0.159 (0.156)ma–1, with considerable interannual variability (standard deviation ~0.11ma–1) primarily due to variations in runoff. Considering best estimates of current iceberg calving, overall the GIS is probably currently losing mass. Our study shows great promise for meaningfully modelling SMB based on forthcoming ``second-generation’’ ECMWF re-analysis (ERA-40) data, and comparing the results with ongoing laser/radarmeasurements of surface elevation. This should help elucidate to what extent surface elevation changes are caused by short-term SMB variations or other factors (e.g. ice dynamics).
Reconstruction of three centuries of annual accumulation rates based on the record of stable isotopes of water from Lomonosovfonna, Svalbard
Authors: Pohjola Veijo A. , Martma Tõnu A. , Meijer Harro A. J. , Moore John C. , Isaksson Elisabeth , Vaikmäe Rein , van de Wal Roderik S.W.
Published: November 2007

We use the upper 81 mof the record of stable isotopes of water from a 122m long ice core from Lomonosovfonna, central Spitsbergen, Svalbard, to construct an ice-core chronology and the annual accumulation rates over the icefield. the isotope cycles are counted in the ice-core record using a model that neglects short-wavelength and low-amplitude cycles. We find approximately the same number of δ18O cycles as years between known reference horizons, and assume these cycles represent annual cycles. Testing the validity of this assumption using cycles in δD shows that both records give similar numbers of cycles. Using the δ18O chronology, and decompressing the accumulation records using the Nye flow model, we calculate the annual accumulation for the ice-core site back to AD 1715. We find that the average accumulation rate from 1715 to 1950 was on average 0.30 mw.e. Accumulation rates increased about 25% during the later part of the 20th century to an average of 0.41 mw.e. for the period 1950–97. the accumulation rates show highly significant 2.1 and 21 year periodicities, which gives credibility to our time-scale.
Antarctic volcanic flux ratios from Law Dome ice cores
Authors: Palmer Anne S. , Morgan Vin I. , Curran Mark A. J. , van Ommen Tas D. , Mayewski Paul A.
Published: November 2007

Explosive volcanic eruptions can inject large quantities of sulphur dioxide into the stratosphere. the aerosols that result from oxidation of the sulphur dioxide can produce significant cooling of the troposphere by reflecting or absorbing solar radiation. It is possible to obtain an estimate of the relative stratospheric sulphur aerosol concentration produced by different volcanoes by comparing sulphuric acid fluxes determined by analysis of polar ice cores. Here,we use a non-sea-salt sulphate time series derived from three well-dated Law Dome ice cores to investigate sulphuric acid flux ratios for major eruptions over the period AD 1301–1995. We use additional data from other cores to investigate systematic spatial variability in the ratios. Only for the Kuwae eruption (Law Dome ice date AD 1459.5) was the H2SO4 flux larger than that deposited by Tambora (Law Dome ice date AD 1816.7).
Features of meteorological events preserved in a high-resolution Law Dome (East Antarctica) snow pit
Authors: McMorrow Alison J. , Curran Mark A. J. , Van Ommen Tas D. , Morgan Vin I. , Allison Ian
Published: November 2007

Snow-pit and shallow firn-core records of oxygen isotope ratios (δ18O) and trace ion species were generated at a high-accumulation site on Law Dome, East Antarctica. Concordance between accumulation events identified in records up to 7.7 km a part confirms that the observed glaciochemical variations are the result of regional rather than local surface effects. This allows calibration of the snow-pit records with measured meteorological parameters. Net accumulation periods that comprise the snow-pit record are identified using hourly snow-accumulation measurements from a co-located automatic weather station (AWS). Particular focus is given to three net accumulation periods preserved during austral summer 1999/2000 that correspond to the top 0.5 m of the snow pit. Local meteorological conditions recorded during the summer accumulation periods by the AWS are combined with regional and synoptic-scale meteorology derived from Casey station (110 km away) and Advanced Very High Resolution Radiometer satellite imagery to identify potential source regions for chemical signals preserved in summer snow at Law Dome.
Preliminary results from the chemical records of an 80.4 m ice core recovered from East Rongbuk Glacier, Qomolangma (Mount Everest), Himalaya
Authors: Dahe Qin , Shugui Hou , Dongqi Zhang , Jiawen Ren , Shichang Kang , Mayewski Paul A. , Wake Cameron P.
Published: November 2007

High-resolution chemical records from an 80.4m ice core from the central Himalaya demonstrate climatic and environmental changes since 1844. the chronological net accumulation series shows a sharp decrease from the mid-1950s, which is coincident with the widely observed glacier retreat. A negative correlation is found between the ice-core δ18O record and the monsoon precipitation for Indian region 7. the temporal variation of the terrestrial ions (Ca2+ and Mg2+) is controlled by both the monsoon precipitation for Indian regions 3,7 and 8, located directly south and west of the Himalaya, and the dust-storm duration and frequency in the northern arid regions, such as the Taklimakan desert, China. the NH4+ profile is fairly flat until the 1940s, then substantially increases until the end of the 1980s, with a slight decrease during the 1990s which may reflect new agricultural practices. the SO42– and NO3– profiles show an apparent increasing trend, especially during the period 1940s–80s. Moreover, SO42– concentrations for the East Rongbuk Glacier core are roughly double that of the nearby Dasuopu core at Xixabangma, Himalaya, due to local human activity including that of climbing teams who use gasoline for cooking, energy and transport.
Properties of GRIP ice crystals from around Greenland interstadial 3
Authors: Hansen Kaj M. , Svensson Anders , Wang Yun , Steffensen Jørgen Peder
Published: November 2007

Ice-crystal textures (sizes and shapes) and fabrics (c-axis orientations) have been determined in 3 m of vertical thin sections from the Greenland Icecore Project (GRIP) ice core. the samples cover ice from before, during and after Greenland interstadial 3 (IS3) that occurred about 25 kyr BP. the texture of 60 000 crystals has been obtained from stacked digital images by semi-automated methods, and the fabric of 5000 selected crystals has been measured on the Automatic Ice Fabric Analyzer at the Alfred Wegener Institute, Bremerhaven. the area distribution function of the crystals is close to a log normal distribution, and the mean area is found to be 3.36 mm2 in ice from IS3, and 3.04 mm2 in ice from colder periods before and after IS3. the overall c-axis orientations show a strong single maximum with vertical orientation. These results agree well with earlier GRIP fabric studies obtained by manual methods. from comparisons of crystal areas with the concentrations of dust, Ca2+, SO42–, Cl– and NO3– in the ice we determine that NO3– correlates best with crystal areas. Crystals within clearly visible cloudy bands are significantly smaller than the surrounding crystals, and their c-axis orientations are less well confined than the average.