bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the ground surface Enthalpy balance from bedrock temperatures (Livingston Island, Maritime Antarctic)
Authors: Ramos M. , Vieira G.
Published: April 2010

Abstract. The annual evolution of the ground temperatures from Incinerador borehole in Livingston Island (South Shetlands, Antarctic) is studied. The borehole is 2.4 m deep and is located in a massive quartzite outcrop with negligible water content, in the proximity of the Spanish Antarctic Station Juan Carlos I. In order to model the movement of the 0°C isotherm (velocity and maximum depth) hourly temperature profiles from: (i) the cooling periods of the frost season of 2000 to 2005, and (ii) the warming periods of the thaw season of 2002–2003, 2003–2004 and 2004–2005, were studied. In this modelling approach, heat gains and losses across the ground surface are assumed to be the causes for the 0°C isotherm movement. A methodological approach to calculate the ground Enthalpy change based on the thermodynamic analysis of the ground during the cooling and warming periods is proposed. The Enthalpy change into the rock is equivalent to the heat exchange through the ground surface during each season, thus enabling to describe the interaction ground-atmosphere and providing valuable data for studies on permafrost and periglacial processes. The bedrock density and thermal conductivity are considered to be constant and initial isothermal conditions at 0°C are assumed (based in collected data and local meteorological conditions in this area) to run the model in the beginning of each season. The final stages correspond to the temperatures at the end of the cooling and warming periods (annual minima and maxima). The application of this method avoids error propagation induced by the heat exchange calculations from multiple sensors using the Fourier method.
Frost flower chemical signature in winter snow on Vestfonna ice cap, Nordaustlandet, Svalbard
Authors: Beaudon E. , Moore J.
Published: April 2010

Abstract. The chemistry of snow and ice cores from Svalbard is influenced by variations in local sea ice margin and distance to open water. Snow pits sampled at two summits of Vestfonna ice cap (Nordaustlandet, Svalbard), exhibit spatially heterogeneous soluble ions concentrations despite similar accumulation rates, reflecting the importance of small-scale weather patterns on this island ice cap. The snow pack on the western summit shows higher average values of marine ions and a winter snow layer that is relatively depleted in sulphate. One part of the winter snow pack exhibits a [SO42-/Na+] ratio reduced by two thirds compared with its ratio in sea water. This low sulphate content in winter snow is interpreted as the signature of frost flowers, which are formed on young sea ice when offshore winds predominate. Frost flowers have been described as the dominant source of sea salt to aerosol and precipitation in ice cores in coastal Antarctica but this is the first time their chemical signal has been described in the Arctic. The eastern summit does not show any frost flower signature and we interpret the unusually dynamic ice transport and rapid formation of thin ice on the Hinlopen Strait as the source of the frost flowers.
Glacier volume response time and its links to climate and topography based on a conceptual model of glacier hypsometry
Authors: Raper S. C. B. , Braithwaite R. J.
Published: April 2010

Abstract. Glacier volume response time is a measure of the time taken for a glacier to adjust its geometry to a climate change. It has been previously proposed that the volume response time is given approximately by the ratio of glacier thickness to ablation at the glacier terminus. We propose a new conceptual model of glacier hypsometry (area-altitude relation) and derive the volume response time where climatic and topographic parameters are separated. The former is expressed by mass balance gradients which we derive from glacier-climate modelling and the latter are quantified with data from the World Glacier Inventory. Aside from the well-known scaling relation between glacier volume and area, we establish a new scaling relation between glacier altitude range and area, and evaluate it for seven regions. The presence of this scaling parameter in our response time formula accounts for the mass balance elevation feedback and leads to longer response times than given by the simple ratio of glacier thickness to ablation at the terminus. Volume response times range from decades to thousands of years for glaciers in maritime (wet-warm) and continental (dry-cold) climates respectively. The combined effect of volume-area and altitude-area scaling relations is such that volume response time can increase with glacier area (Axel Heiberg Island and Svalbard), hardly change (Northern Scandinavia, Southern Norway and the Alps) or even get smaller (The Caucasus and New Zealand).
Quantifying changes and trends in glacier area and volume in the Austrian Ötztal Alps (1969-1997-2006)
Authors: Abermann J. , Lambrecht A. , Fischer A. , Kuhn M.
Published: April 2010

Abstract. In this study we apply a simple and reliable method to derive recent changes in glacier area and volume by taking advantage of high resolution LIDAR (light detection and ranging) DEMs (digital elevation models) from the year 2006. Together with two existing glacier inventories (1969 and 1997) the new dataset enables us to quantify area and volume changes over the past 37 years at three dates. This has been done for 81 glaciers (116 km2) in the Ötztal Alps which accounts for almost one third of Austria's glacier extent. Glacier area and volume have reduced drastically with significant differences within the individual size classes. Between 1997 and 2006 an overall area loss of 10.5 km2 or 8.2% occurred. Volume has reduced by 1.0 km3 which accounts for a mean thickness change of −8.2 m. The availability of three comparable inventories allows a comprehensive size and altitude dependent analysis of glacier changes but lacks a high temporal resolution. For the comparison of rates of changes between the two different periods (1969 to 1997 with 1997 to 2006) we propose two approaches in this study: a) to estimate mean overall rates of changes (including a period of advance) and b) to extract periods of net-retreat by using additional information (length change and mass balance measurements). Analysis of the resulting acceleration factors reveals that the retreat of volume and mean thickness changes has accelerated significantly more than that of area changes.
Mapping glaciers in Jotunheimen, South-Norway, during the "Little Ice Age" maximum
Authors: Baumann S. , Winkler S. , Andreassen L. M.
Published: April 2010

Abstract. The maximum glacier extent during the "Little Ice Age" (mid 18th century AD) in Jotunheimen, southern Norway, was mapped using remote sensing techniques. Interpretation of existing glaciochronological studies, analysis of geomorphological maps, and own GPS-field measurements were applied for validation of the mapping. The length of glacier centrelines and other inventory data were determined using a Geographical Information System (GIS) and a Digital Elevation Model. "Little Ice Age" maximum extent for a total of 233 glaciers comprising an overall glacier area of about 290 km2 was mapped. Mean length of the centreline was calculated to 1.6 km. Until AD 2003, the area and length shrank by 35% and 34%, respectively, compared with the maximum "Little Ice Age" extent.
Three examples where the specific surface area of snow increased over time
Authors: Domine F. , Taillandier A.-S. , Cabanes A. , Douglas T. A. , Sturm M.
Published: April 2010

Abstract. Snow on the ground impacts climate through its high albedo and affects atmospheric composition through its ability to adsorb chemical compounds. The quantification of these effects requires the knowledge of the specific surface area (SSA) of snow and its rate of change. All relevant studies indicate that snow SSA decreases over time. Here, we report for the first time three cases where the SSA of snow increased over time. These are (1) the transformation of a melt-freeze crust into depth hoar, producing an increase in SSA from 3.4 to 8.8 m2 kg−1. (2) The mobilization of surface snow by wind, which reduced the size of snow crystals by sublimation and fragmented them. This formed a surface snow layer with a SSA of 61 m2 kg−1 from layers whose SSAs were originally 42 and 50 m2 kg−1. (3) The sieving of blowing snow by a snow layer, which allowed the smallest crystals to penetrate into open spaces in the snow, leading to an SSA increase from 32 to 61 m2 kg−1. We discuss that other mechanisms for SSA increase are possible. Overall, SSA increases are probably not rare. They lead to enhanced uptake of chemical compounds and to increases in snow albedo, and their inclusion in relevant chemical and climate models deserves consideration.
Polynyas in a dynamic-thermodynamic sea-ice model
Authors: Ólason E. Ö. , Harms I.
Published: April 2010

Abstract. The representation of polynyas in viscous-plastic dynamic-thermodynamic sea-ice models is studied in a simplified test domain, in order to give recommendations about parametrisation choices. Bjornsson et al. (2001) validated their dynamic-thermodynamic model against a polynya flux model in a similar setup and we expand on that work here, testing more sea-ice rheologies and new-ice thickness formulations. The two additional rheologies tested give nearly identical results whereas the two new-ice thickness parametrisations tested give widely different results. Based on our results we argue for using the new-ice thickness parametrisation of Hibler (1979). We also implement a new parametrisation for the parameter h0 from Hibler's scheme, based on ideas from a collection depth parametrisation for flux polynya models.
On the potential of very high-resolution repeat DEMs in glacial and periglacial environments
Authors: Abermann J. , Fischer A. , Lambrecht A. , Geist T.
Published: April 2010

Abstract. The potential of high-resolution repeat DEMs was investigated for glaciological applications including periglacial features (e.g. rock glaciers). It was shown that glacier boundaries can be delineated using airborne LIDAR-DEMs as a primary data source and that information on debris cover extent could be extracted using multi-temporal DEMs. Problems and limitations are discussed, and accuracies quantified. Absolute deviations of airborne laser scanning (ALS) derived glacier boundaries from ground-truthed ones were below 4 m for 80% of the ground-truthed values. Overall, we estimated an accuracy of +/−1.5% of the glacier area for glaciers larger than 1 km2. The errors in the case of smaller glaciers did not exceed +/−5% of the glacier area. The use of repeat DEMs in order to obtain information on the extent, characteristics and activity of rock glaciers was investigated and discussed based on examples.
Forecasting temperate alpine glacier survival from accumulation zone observations
Authors: Pelto M. S.
Published: April 2010

Abstract. Temperate alpine glacier survival is dependent on the consistent presence of an accumulation zone. Frequent low accumulation area ratio values, below 30%, indicate the lack of a consistent accumulation zone, which leads to substantial thinning of the glacier in the accumulation zone. This thinning is often evident from substantial marginal recession, emergence of new rock outcrops and surface elevation decline in the accumulation zone. In the North Cascades 9 of the 12 examined glaciers exhibit characteristics of substantial accumulation zone thinning; marginal recession or emergent bedrock areas in the accumulation zone. The longitudinal profile thinning factor, f, which is a measure of the ratio of thinning in the accumulation zone to that at the terminus, is above 0.6 for all glaciers exhibiting accumulation zone thinning characteristics. The ratio of accumulation zone thinning to cumulative mass balance is above 0.5 for glacier experiencing substantial accumulation zone thinning. Without a consistent accumulation zone these glaciers are forecast not to survive the current climate or future additional warming. The results vary considerably with adjacent glaciers having a different survival forecast. This emphasizes the danger of extrapolating survival from one glacier to the next.
Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years
Authors: Cook A. J. , Vaughan D. G.
Published: April 2010

Abstract. In recent decades, seven out of twelve ice shelves around the Antarctic Peninsula (AP) have either retreated significantly or have been almost entirely lost. At least some of these retreats have been shown to be unusual within the context of the Holocene and have been widely attributed to recent atmospheric and oceanic changes. To date, measurements of the area of ice shelves on the AP have either been approximated, or calculated for individual shelves over dissimilar time intervals. Here we present a new dataset containing up-to-date and consistent area calculations for each of the twelve ice shelves on the AP over the past five decades. The results reveal an overall reduction in total ice-shelf area by over 28 000 km2 since the beginning of the period. Individual ice shelves show different rates of retreat, ranging from slow but progressive retreat to abrupt collapse. We discuss the pertinent features of each ice shelf and also broad spatial and temporal patterns in the timing and rate of retreat. We believe that an understanding of this diversity and what it implies about the underlying dynamics and control will provide the best foundation for developing a reliable predictive skill for ice-shelf change.
Evaluation of the ground surface Enthalpy balance from bedrock shallow borehole temperatures (Livingston Island, Maritime Antarctic)
Authors: Ramos M. , Vieira G.
Published: April 2010

Abstract. The annual evolution of the ground temperatures from Incinerador borehole in Livingston Island (South Shetlands, Antarctic) is studied. The borehole is 2.4 m deep and is located in a quartzite outcrop in the proximity of the Spanish Antarctic Station Juan Carlos I. In order to model the movement of the 0°C isotherm (velocity and maximum depth) hourly temperature profiles from: (i) the cooling periods of the frost seasons of 2000 to 2005, and (ii) the warming periods of the thaw seasons of 2002–2003, 2003–2004 and 2004–2005, were studied. In this modelling approach, heat gains and losses across ground surface are considered to be the causes for the 0°C isotherm movement. A methodological approach to calculate the Enthalpy change based on the thermodynamic analysis of the ground during the cooling and warming periods is proposed. The Enthalpy change is equivalent to the heat exchange through the ground surface during each season, thus enabling to describe the interaction ground-atmosphere and providing valuable data for studies on permafrost and periglacial processes. The bedrock density is considered to be constant in the borehole and initial isothermal conditions at 0°C are assumed to run the model. The final stages correspond to the temperatures at the end of the cooling and warming periods (annual minima and maxima).
Analytical analysis of small-amplitude perturbations in the shallow ice stream approximation
Authors: Gudmundsson G. H.
Published: April 2010

Abstract. New analytical solutions describing the effects of small-amplitude perturbations in boundary data on flow in the shallow ice stream approximation are presented. These solutions are valid for a non-linear Weertman-type sliding law and for Newtonian ice rheology. Comparison is made with corresponding solutions of the shallow ice sheet approximation, and with solutions of the full Stokes equations. The shallow ice stream approximation is commonly used to describe large-scale ice stream flow over a weak bed, while the shallow ice sheet approximation forms the basis of most current large-scale ice sheet models. It is found that the shallow ice stream approximation overestimates the effects of bedrock perturbations on surface topography for wavelengths less than about 5 to 10 ice thicknesses, the exact number depending on values of surface slope and slip ratio. For high slip ratios, the shallow ice stream approximation gives a very simple description of the relationship between bed and surface topography, with the corresponding transfer amplitudes being close to unity for any given wavelength. The shallow ice stream estimates for the timescales that govern the transient response of ice streams to external perturbations are considerably more accurate than those based on the shallow ice sheet approximation. In contrast to the shallow ice sheet approximation, the shallow ice stream approximation correctly reproduces the short-wavelength limit of the kinematic phase speed. In accordance with the full system solutions, the shallow ice sheet approximation predicts surface fields to react weakly to spatial variations in basal slipperiness with wavelengths less than about 10 to 20 ice thicknesses.
The new Landsat-derived glacier inventory for Jotunheimen, Norway, and deduced glacier changes since the 1930s
Authors: Andreassen L. M. , Paul F. , Kääb A. , Hausberg J. E.
Published: April 2010

Abstract. A Landsat Thematic Mapper (TM) scene from 2003 covering the Jotunheimen and Breheimen region has been used to map the recent glacier extents using thresholded ratio images (TM3/TM5). Orthoprojected aerial photographs and glacier outlines from digital maps have been used to validate the method and control the results. We further calculated glacier changes by comparing the Landsat-derived 2003 glacier outlines with previous maps and inventories from the 1930s, 1960s and 1980s. Our results confirm that the applied automatic mapping method is very robust and agrees precisely with the reference data used. Some manual editing was necessary to correct the outline at ice-lake contacts and at debris covered glaciers. However, for most of the glaciers no corrections were required. The most laborious task has been to assign ID numbers and couple the new Landsat inventory to previous inventories to assess area changes. The glaciers investigated shrank since the 1930s with an overall area reduction of about 23% for 38 glaciers. Since the 1960s the area reduction was 12% for 164 glaciers. Although the general trend is glacier retreat and area reduction, some glaciers have increased their size or remained nearly unchanged over the last decades.
On the limit to resolution and information on basal properties obtainable from surface data on ice streams
Authors: Gudmundsson G. H. , Raymond M.
Published: April 2010

Abstract. An optimal estimation method for simultaneously determining both basal slipperiness and basal topography from variations in surface flow velocity and topography along a flow line on ice streams and ice sheets is presented. We use Bayesian inference to update prior statistical estimates for basal topography and slipperiness using surface measurements along a flow line. The methods requires no smoothing of surface data. Our main focus here is on how errors and spacing of surface data affects estimates of basal quantities and on possibly aliasing/mixing between basal slipperiness and basal topography. We find that the effects of spatial variations in basal topography and basal slipperiness on surface data can be accurately separated from each other, and mixing in retrieval does not pose a serious problem. For realistic surface data errors and density, small-amplitude perturbations in basal slipperiness can only be resolved for wavelengths larger than about 50 times the mean ice thickness. Bedrock topography is well resolved down to horizontal scale equal to about one ice thickness. Estimates of basal slipperiness are not significantly improved by accurate prior estimates of basal topography. Retrieval of basal slipperiness is found to be highly sensitive to unmodelled errors in basal topography.
On the use of incoming longwave radiation parameterizations in a glacier environment
Authors: Sedlar J. , Hock R.
Published: April 2010

Abstract. Energy balance based glacier melt models require accurate estimates of incoming longwave radiation since it is generally the largest source of energy input. Multi-year near-surface meteorological data from Storglaciären, northern Sweden, were used to evaluate commonly used longwave radiation parameterizations in a glacier environment under clear-sky, overcast-sky and all-sky conditions. The tested parameterization depending solely on air temperature performed worse than those including also air humidity. Adopting parameter values from the literature instead of fitting them to the data resulted in similar correlation coefficients between modeled and measured radiation, but generated larger biases, emphasizing the need to derive site-specific coefficients. Nearly all models including those fitted to the data tended to overestimate longwave radiation during periods of low longwave radiation, and vice versa when radiation input was high. An attempt was made to parameterize cloud cover using top of atmosphere and measured global radiation. Both hourly and daily calculations of incoming longwave radiation using the cloud parameterization provided similar, or even stronger, correlations to the measurements compared to using observed cloud fraction as input. Using the global radiation cloud parameterization is promising for use in high-latitude regions where global radiation measurements exist but cloud observations do not.
Applicability of the Shallow Ice Approximation inferred from model inter-comparison using various glacier geometries
Authors: Schäfer M. , Gagliardini O. , Pattyn F. , Le Meur E.
Published: April 2010

Abstract. This paper presents an inter-comparison of three different models applied to various glacier geometries. The three models are built on different approximations of the Stokes equations, from the well known Shallow Ice Approximation (SIA) to the full-Stokes (FS) solution with an intermediate higher-order (HO) model which incorporates longitudinal stresses. The studied glaciers are synthetic geometries, but two of them are constructed so as to mimic a valley glacier and a volcano glacier. For each class of glacier, the bedrock slope and/or the aspect ratio are varied. First, the models are compared in a diagnostic way for a fixed and given geometry. Here the SIA surface velocity can overestimate the FS velocity by a factor of 5 to a factor of 10. Then, the free surface is allowed to evolve and the time-dependent evolution of the glacier is studied. As a result, the difference between the models decreases, but can still be as large as a factor of 1.5 to 2. This decrease can be explained by a negative feedback for the SIA which overestimates velocities.
Three examples where the specific surface area of snow increased over time
Authors: Domine F. , Taillandier A.-S. , Cabanes A. , Douglas T. A. , Sturm M.
Published: April 2010

Abstract. Snow on the ground impacts climate through its high albedo and affects atmospheric composition through its ability to adsorb chemical compounds. The quantification of these effects requires the knowledge of the specific surface area (SSA) of snow and its rate of change. All relevant studies indicate that snow SSA decreases over time. Here, we report for the first time three cases where the SSA of snow increased over time. These are (1) the transformation of a melt-freeze crust into depth hoar, producing an increase in SSA from 3.4 to 8.8 m2 kg−1. (2) The mobilization of surface snow by wind, which reduced the size of snow crystals by sublimation and fragmented them. This formed a surface snow layer with a SSA of 61 m2 kg−1 from layers whose SSAs were originally 42 and 50 m2 kg−1. (3) The sieving of blowing snow by a snow layer, which allowed the smallest crystals to penetrate into open spaces in the snow, leading to an SSA increase from 32 to 61 m2 kg−1. We discuss that other mechanisms for SSA increase are possible. Overall, SSA increases are probably not rare. They may lead to enhanced uptake of chemical compounds and to increases in snow albedo, and thus should be included in relevant chemical and climate models.
A new 1 km digital elevation model of the Antarctic derived from combined satellite radar and laser data – Part 1: Data and methods
Authors: Bamber J. L. , Gomez-Dans J. L. , Griggs J. A.
Published: April 2010

Abstract. Digital elevation models (DEMs) of Antarctica have been derived, previously, from satellite radar altimetry (SRA) and limited terrestrial data. Near the ice sheet margins and in other areas of steep relief the SRA data tend to have relatively poor coverage and accuracy. To remedy this and to extend the coverage beyond the latitudinal limit of the SRA missions (81.5° S) we have combined laser altimeter measurements from the Geosciences Laser Altimeter System onboard ICESat with SRA data from the geodetic phase of the ERS-1 satellite mission. The former provide decimetre vertical accuracy but with poor spatial coverage. The latter have excellent spatial coverage but a poorer vertical accuracy. By combining the radar and laser data using an optimal approach we have maximised the vertical accuracy and spatial resolution of the DEM and minimised the number of grid cells with an interpolated elevation estimate. We assessed the optimum resolution for producing a DEM based on a trade-off between resolution and interpolated cells, which was found to be 1 km. This resulted in just under 35% of grid cells having an interpolated value. The accuracy of the final DEM was assessed using a suite of independent airborne altimeter data and used to produce an error map. The RMS error in the new DEM was found to be roughly half that of the best previous 5 km resolution, SRA-derived DEM, with marked improvements in the steeper marginal and mountainous areas and between 81.5 and 86° S. The DEM contains a wealth of information related to ice flow. This is particularly apparent for the two largest ice shelves – the Filchner-Ronne and Ross – where the surface expression of flow of ice streams and outlet glaciers can be traced from the grounding line to the calving front. The surface expression of subglacial lakes and other basal features are also illustrated. We also use the DEM to derive new estimates of balance velocities and ice divide locations.
Comparison of the meteorology and surface energy balance at Storbreen and Midtdalsbreen, two glaciers in southern Norway
Authors: Giesen R. H. , Andreassen L. M. , van den Broeke M. R. , Oerlemans J.
Published: April 2010

Abstract. We compare 5 years of meteorological records from automatic weather stations (AWSs) on Storbreen and Midtdalsbreen, two glaciers in southern Norway, located approximately 120 km apart. The records are obtained from identical AWSs with an altitude difference of 130 m and cover the period September 2001 to September 2006. Air temperature at the AWS locations is found to be highly correlated, even with the seasonal cycle removed. The most striking difference between the two sites is the difference in wind climate. Midtdalsbreen is much more under influence of the large-scale circulation with wind speeds on average a factor 1.75 higher. On Storbreen, weaker katabatic winds are dominant. The main melt season is from May to September at both locations. During the melt season, incoming and net solar radiation are larger on Midtdalsbreen, whereas incoming and net longwave radiation are larger on Storbreen, primarily caused by thicker clouds on the latter. The turbulent fluxes are a factor 1.7 larger on Midtdalsbreen, mainly due to the higher wind speeds. Inter-daily fluctuations in the surface energy fluxes are very similar at the AWS sites. On average, melt energy is a factor 1.3 larger on Midtdalsbreen, a result of both larger net radiation and larger turbulent fluxes. The relative contribution of net radiation to surface melt is larger on Storbreen (76%) than on Midtdalsbreen (66%). As winter snow depth at the two locations is comparable in most years, the larger amount of melt energy results in an earlier disappearance of the snowpack on Midtdalsbreen and 70% more ice melt than on Storbreen. We compare the relative and absolute values of the energy fluxes on Storbreen and Midtdalsbreen with reported values for glaciers at similar latitudes. Furthermore, a comparison is made with meteorological variables measured at two nearby weather stations, showing that on-site measurements are essential for an accurate calculation of the surface energy balance and melt rate.
Polynyas in a dynamic-thermodynamic sea-ice model
Authors: Ólason E. Ö. , Harms I.
Published: April 2010

Abstract. The response of a viscous-plastic dynamic-thermodynamic sea-ice model to a constant wind forcing is tested in an idealised setting. Bjornsson et al. (2001) have shown that the granular model of Tremblay and Mysak (1997) gives good results in such a set-up compared to a polynya flux model. Here it is shown that these results can be duplicated using the computationally more efficient elliptic yield curve approach by Hibler (1979) and modified Coulombic yield curve by Hibler and Schulson (2000). Some care is, however, required regarding the parametrisations of the ellipse. In addition it is shown that the new ice thickness formulation of Mellor and Kantha (1989) does not allow for proper polynya formation in the bay. In contrast the new ice thickness formulation of Hibler (1979) is found to give good results. Finally we propose a parametrisation of the ice demarcation thickness (h0) in Hibler's formulation, based on wind speed and ice thickness.
Climatology and ablation at the South Greenland ice sheet margin from automatic weather station observations
Authors: van As D. , Bøggild C. E. , Nielsen S. , Ahlstrøm A. P. , Fausto R. S. , Podlech S. , Andersen M. L.
Published: April 2010

Abstract. We describe the climatology from a meteorological dataset acquired from automatic weather station observations done in the ablation zone of the Greenland Ice Sheet between 2001 and 2007. Stations were placed in three regions below the polar circle: on the southern tip of the ice sheet, on a calving glacier in the Nuuk fjord, and on the south-eastern ice margin near Tasiilaq. The yearly cycles in temperature, relative humidity and wind speed reveal the largest variability in wintertime, causing annual values to depend largely on winter values. Adding to wintertime variability are extremely strong and cold katabatic wind events in the southeast ("piteraqs"). During summer no pronounced daily cycle in near-surface atmospheric parameters is recorded in the three regions, in spite of a large cycle in solar radiation, dominantly regulating surface melt. Net ablation is largest at the southernmost station due to low surface albedo, and can be up to six metres per year, but is highly sensitive to the timing of the start of the ice ablation season. Illustrative of this is that similar ablation amounts are found in the Nuuk fjord region where little or no snow accumulates in winter.
Frost flower chemical signature in winter snow on Vestfonna ice cap (Nordaustlandet, Svalbard)
Authors: Beaudon E. , Moore J.
Published: April 2010

Abstract. The chemistry of snow and ice cores from Svalbard is influenced by variations in local sea ice margin and distance to open water. Snow pits sampled at two summits of Vestfonna ice cap (Nordaustlandet, Svalbard), exhibit spatially heterogeneous soluble ions concentrations despite similar accumulation rates, reflecting the importance of small-scale weather patterns on this island ice cap. The snow pack on the western summit shows higher average values of marine species and a winter snow layer that is relatively depleted in sulphate. One part of the winter snow pack exhibits [SO42-/Na+] ratio reduced by two thirds compared with its ratio in sea water. This low sulphate content in winter snow is interpreted as the signature of frost flowers, which are formed on young sea ice when offshore winds predominate. Frost flowers have been described as the dominant source of sea salt to aerosol and precipitation in ice cores in coastal Antarctica but this is the first time their chemical signal has been described in the Arctic. The eastern summit does not show any frost flower signature and we interpret the unusually dynamic ice transport and rapid formation of thin ice on the Hinlopen Strait as the source of the frost flowers.
Rapid and accurate measurement of the specific surface area of snow using infrared reflectance at 1310 and 1550 nm
Authors: Gallet J.-C. , Domine F. , Zender C. S. , Picard G.
Published: April 2010

Abstract. Even though the specific surface area (SSA) of snow is a crucial variable to determine the chemical and climatic impact of the snow cover, few data are available on snow SSA because current measurement methods are not simple to use in the field or do not have a sufficient accuracy. We propose here a novel determination method based on the measurement of the hemispherical reflectance of snow in the infrared using the DUFISSS instrument (DUal Frequency Integrating Sphere for Snow SSA measurement). DUFISSS uses 1310 and 1550 nm radiation provided by laser diodes, an integrating sphere 15 cm in diameter, and InGaAs photodiodes. For SSA<60 m2 kg−1, we use the 1310 nm radiation, reflectance is in the range 15 to 50% and the accuracy is 10%. For SSA>60 m2 kg−1, snow is usually of low to very low density (typically 30 to 100 kg m−3) and this produces artifacts caused by the e-folding length of light in snow being too long. We therefore use 1550 nm radiation for SSA>60 m2 kg−1. Reflectance is then in the range 5 to 12%, and the accuracy is 12%. No effect of crystal shape on reflectance was detected. We propose empirical equations to determine SSA from reflectance at both wavelengths, with that for 1310 nm taking into account the snow density. DUFISSS has been tested in the Alps to measure the snow area index (SAI) of the Alpine snowpack in a south facing area at 2100 m elevation. This was done by measuring the SSA, thickness and density of the seven main layers of the snowpack in just 30 min, and a value of 5350 was found, significantly greater than in Arctic and subarctic regions. DUFISSS can now be used to help study issues related to polar and Alpine atmospheric chemistry and climate.
Mapping and morphometric analysis of glaciers in Jotunheimen, South Norway, during the "Little Ice Age" maximum
Authors: Baumann S. , Winkler S.
Published: April 2010

Abstract. This study provides mapping and analysis of the maximum glacier extent during the "Little Ice Age" in Jotunheimen, Southern Norway, on a regional scale. Remote sensing techniques were used to map the glacier area at the maximum of the "Little Ice Age" (mid 18th century AD). For validation of the mapping, interpretation of existing glaciochronological studies, analysis of geomorphological maps and our own field measurements using GPS have been applied. The flow length of the glaciers and other inventory data were determined by using a Geographical Information System and a digital elevation model. A total of 233 glaciers existed during the "Little Ice Age" maximum in Jotunheimen, comprising an overall glacier area of about 290 km2. Mean glacier flow length was calculated as about 1.6 km. Until AD 2003, the area shrank by about 35% and the mean flow length decreased by about 34%, compared with the maximum "Little Ice Age" extent.
Simulation of the specific surface area of snow using a one-dimensional physical snowpack model: implementation and evaluation for subarctic snow in Alaska
Authors: Jacobi H. W. , Domine F. , Simpson W. R. , Douglas T. A. , Sturm M.
Published: April 2010

Abstract. The specific surface area (SSA) of the snow constitutes a powerful parameter to quantify the exchange of matter and energy between the snow and the atmosphere. However, currently no snow physics model can simulate the SSA. Therefore, two different types of empirical parameterizations of the specific surface area (SSA) of snow are implemented into the existing one-dimensional snow physics model CROCUS. The parameterizations are either based on diagnostic equations relating the SSA to parameters like snow type and density or on prognostic equations that describe the change of SSA depending on snow age, snowpack temperature, and the temperature gradient within the snowpack. Simulations with the upgraded CROCUS model were performed for a subarctic snowpack, for which an extensive data set including SSA measurements is available at Fairbanks, Alaska for the winter season 2003/2004. While a reasonable agreement between simulated and observed SSA values is obtained using both parameterizations, the model tends to overestimate the SSA. This overestimation is more pronounced using the diagnostic equations compared to the results of the prognostic equations. Parts of the SSA deviations using both parameterizations can be attributed to differences between simulated and observed snow heights, densities, and temperatures. Therefore, further sensitivity studies regarding the thermal budget of the snowpack were performed. They revealed that reducing the heat conductivity of the snow or increasing the turbulent fluxes at the snow surfaces leads to a slight improvement of the simulated thermal budget of the snowpack compared to the observations. However, their impact on further simulated parameters like snow height and SSA remains small. Including additional physical processes in the snow model may have the potential to advance the simulations of the thermal budget of the snowpack and, thus, the SSA simulations.
A sea ice thickness retrieval model for 1.4 GHz radiometry and application to airborne measurements over low salinity sea ice
Authors: Kaleschke L. , Maaß N. , Haas C. , Hendricks S. , Heygster G. , Tonboe R. T.
Published: April 2010

Abstract. In preparation for the European Space Agency's (ESA) Soil Moisture and Ocean Salinity (SMOS) mission we investigated the potential of L-band (1.4 GHz) radiometery to measure sea ice thickness. Sea ice brightness temperature was measured at 1.4 GHz and ice thickness were measured along nearly coincident flight tracks during the SMOS Sea-Ice campaign in the Bay of Bothnia in March 2007. A research aircraft was equipped with the L-band Radiometer EMIRAD and coordinated with helicopter based electromagnetic induction (EM) ice thickness measurements. We developed a three layer (ocean-ice-atmosphere) dielectric slab model for the calculation of ice thickness from brightness temperature. The dielectric properties depend on the relative brine volume which is a function of the bulk ice salinity and temperature. The model calculations suggest a thickness sensitivity of up to 1.5 m for low-salinity (multi-year or brackish) sea ice. For Arctic first year ice the modeled thickness sensitivity is roughly half a meter. It reduces to a few centimeters for temperatures approaching the melting point. Although the campaign was conducted under such unfavorable melting conditions and despite limited spatial overlap between the L-band and EM-measurements was small we demonstrate a large potential for retrieving the ice thickness in the range of 0.2 to 1.5 m. Furthermore, we show that the ice thickness derived from SMOS measurements would be complementary to ESA's CryoSat-2 mission in terms of the error characteristics and the spatio-temporal coverage.
Brief communication: ikaite (CaCO3*6H2O) discovered in Arctic sea ice
Authors: Dieckmann G. S. , Nehrke G. , Uhlig C. , Göttlicher J. , Gerland S. , Granskog M. A. , Thomas D. N.
Published: April 2010

Abstract. We report for the first time on the discovery of calcium carbonate crystals as ikaite (CaCO3*6H2O) in sea ice from the Arctic (Kongsfjorden, Svalbard). This finding demonstrates that the precipitation of calcium carbonate during the freezing of sea ice is not restricted to the Antarctic, where it was observed for the first time in 2008. This finding is an important step in the quest to quantify its impact on the sea ice driven carbon cycle and should in the future enable improvement parametrization sea ice carbon models.
An explanation for the dark region in the western melt zone of the Greenland ice sheet
Authors: Wientjes I. G. M. , Oerlemans J.
Published: April 2010

Abstract. The western part of the Greenland ice sheet contains a region that is darker than the surrounding ice. This feature has been analysed with the help of MODIS images. The dark region appears every year during the summer season and can always be found at the same location, which makes meltwater unlikely as the only source for the low albedos. Spectral information indicates that the ice in this region contains more debris than the ice closer to the margin. An ASTER image reveals wavy patterns in the darker ice. Based on these findings we conclude that ice, containing dust from colder periods, is presently outcropping near the margin, leading to albedos lower than observed for the remaining ablation area. Therefore it can be concluded that the accumulation of melt water is a result rather than a cause of the darkening.
The relation between sea ice thickness and freeboard in the Arctic
Authors: Alexandrov V. , Sandven S. , Wahlin J. , Johannessen O. M.
Published: April 2010

Abstract. Retrieval of Arctic sea ice thickness from radar altimeter freeboard data, to be provided by CryoSat-2, requires observational data to verify the relation between the two variables. In this study in-situ ice and snow data from 689 observation sites obtained during the Sever expeditions in the 1980s have been used to establish an empirical relation between ice thickness and freeboard. Estimates of mean and variability of snow depth, snow density and ice density were produced based on many field observations, and have been used in the isostatic equilibrium equation to estimate ice thickness as a function of ice freeboard, snow depth and snow/ice density. The accuracy of the ice thickness retrieval has been calculated from the estimated variability in ice and snow parameters and error of ice freeboard measurements. It is found that uncertainties of ice density and freeboard are the major sources of error in ice thickness calculation. For FY ice, retrieval of ≈1.0 m (2.0 m) thickness has an uncertainty of 60% (41%). For MY ice the main uncertainty is ice density error, since the freeboard error is relatively smaller than for FY ice. Retrieval of 2.4 m (3.0 m) thick MY ice has an error of 24% (21%). The freeboard error is ±0.05 m for both the FY and MY ice. If the freeboard error can be reduced to 0.01 m by averaging a large number of measurements from CryoSat, the error in thickness retrieval is reduced to about 32% for a 1.0 m thick FY floe and to about 18% for a 2.3 m thick MY floe. The remaining error is dominated by uncertainty in ice density. Provision of improved ice density data is therefore important for accurate retrieval of ice thickness from CryoSat data.
Applicability of time-lapse refraction seismic tomography for the detection of ground ice degradation
Authors: Hilbich C.
Published: April 2010

Abstract. The ice content of the subsurface is a major factor controlling the natural hazard potential of permafrost degradation in alpine terrain. Monitoring of changes in ground ice content is therefore similarly important as temperature monitoring in mountain permafrost. Although electrical resistivity tomography monitoring (ERTM) has proved to be a valuable tool for the observation of ground ice degradation, results are often ambiguous or contaminated by inversion artefacts. In theory, the P-wave velocity of seismic waves is similarly sensitive to phase changes between unfrozen water and ice. Provided that the general conditions (lithology, stratigraphy, state of weathering, pore space) remain unchanged over the observation period, temporal changes in the observed travel times of repeated seismic measurements should indicate changes in the ice and water content within the pores and fractures of the subsurface material. In this paper, the applicability of refraction seismic tomography monitoring (RSTM) as an independent and complementary method to ERTM is analysed for two test sites in the Swiss Alps. The development and validation of an appropriate RSTM approach involves a) the comparison of time-lapse seismograms and analysis of reproducibility of the seismic signal, b) the analysis of time-lapse travel time curves with respect to shifts in travel times and changes in P-wave velocities, and c) the comparison of inverted tomograms including the quantification of velocity changes. Results show a high potential of the RSTM approach concerning the detection of altered subsurface conditions caused by freezing and thawing processes. For velocity changes on the order of 3000 m/s even an unambiguous identification of significant ground ice loss is possible.
Cesium and Cesium Compounds
Authors: Bick Manfred , Prinz Horst , Steinmetz Anja
Published: April 2010

The article contains sections titled:1.Physical and Chemical Properties2.Resources3.Production4.Cesium Compounds5.Quality Specifications6.Chemical Analysis7.Storage and Transportation8.Uses9.Economic Aspects10.Toxicology and Occupational Health
Ethers, Aliphatic
Authors: Sakuth Michael , Mensing Thomas , Schuler Joachim , Heitmann Wilhelm , Strehlke Günther , Mayer Dieter
Published: April 2010

The article contains sections titled:1.Introduction2.Properties2.1.Physical Properties2.2.Chemical Properties2.2.1General Aspects2.2.2Peroxide Formation Tendency of Ethers3.Synthesis4.Individual Aliphatic Ethers4.1.Diethyl Ether4.2.Diisopropyl Ether4.3.Other Aliphatic Ethers4.3.1.Di‐n‐propyl Ether4.3.2.Di‐n‐butyl Ether4.3.3.Diamyl Ether4.4.Chloroalkyl Ethers4.4.1.Bis(chloromethyl) Ether4.4.2.Bis(2‐chloroethyl) Ether4.4.3.Bis(2‐chloroisopropyl) Ether5.Toxicology
Hafnium and Hafnium Compounds
Authors: Nielsen Ralph H. , Wilfing Gerhard
Published: April 2010

The article contains sections titled:1.Introduction2.Physical Properties3.Chemical Properties4.Occurrence and Raw Materials5.Production5.1.Ore Cracking5.2.Separation of Zirconium5.3.Winning of Metallic Hafnium5.4.Refining6.Environmental Protection7.Quality Specifications8.Analysis9.Storage and Transportation10.Uses11.Economic Aspects12.Hafnium Compounds12.1.Hafnium Borides12.2.Hafnium Tetrahydroborate12.3.Hafnium Carbide12.4.Hafnium Halides12.5.Hafnium Hydride12.6.Hafnium Nitride12.7.Hafnium Dioxide12.8.Other Derivatives13.Toxicology and Occupational Health
Metallic Soaps
Authors: Nora Angelo , Koenen Gunther
Published: April 2010

The article contains sections titled:1.Introduction2.Production2.1.Raw Materials2.2.Industrial Processes2.2.1.Double Decomposition2.2.2.Direct Reaction with Metal Compounds2.2.3.Direct Reaction with Metals2.3.Plant Equipment2.4.Storage3.Fire and Explosion Protection4.Occupational Health and Environmental Protection5.Individual Metallic Soaps5.1.Sodium Soaps5.2.Potassium Soaps5.3.Lithium Soaps5.4.Magnesium Soaps5.5.Calcium Soaps5.6.Barium Soaps5.7.Aluminum Soaps5.8.Lead Soaps5.9.Copper Soaps5.10.Zinc Soaps5.11.Cadmium Soaps5.12.Manganese Soaps5.13.Iron Soaps5.14.Cobalt Soaps5.15.Nickel Soaps6.Quality Specifications
Organometallic Compounds
Authors: Salzer Albrecht
Published: April 2010

The article contains sections titled:1.Introduction2.Main Group Compounds2.1.Group 12.2.Group 112.3.Group 22.4.Group 122.5.Group 132.6.Group 143.Transition Metal Compounds3.1.Alkyls and Aryls3.2.Carbenes and Carbynes3.3.Carbonyls and Related Compounds3.4.π‐Complexes4.Lanthanoid and Actinoid Compounds