bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal evolution of aerosol stratigraphy in Ürümqi glacier No. 1 percolation zone, eastern Tien Shan, China
Authors: Wang Feiteng , Li Zhongqin , You Xiaoni , Li Chuanjin , Li Huilin , Li Xiangying , Zhu Yuman
Published: November 2007

The processes involved in the evolution of vertical profiles of Mg2+, Ca2+ and microparticle concentrations, as well as their seasonal variation in surface snow, were studied by weekly sampling from September 2003 to September 2004 of a snow pit on Ürümqi glacier No. 1, eastern Tien Shan, China. The development of the microparticle and Mg2+ and Ca2+ stratigraphy in the snow pit is closely related to the physical development of the snow–firn pack. The sampling site is located at 4130 ma.s.l. in the percolation zone of the glacier, and in addition to the effects of sublimation and wind erosion, melting plays a crucial role in both the physical and chemical evolution processes. During the winter, soluble aerosol concentrations in the surface layers are altered slightly by sublimation and wind erosion, and the concentrations are further modified as the wet season begins in late April. In contrast, soluble aerosol stratigraphy in the deeper layers remains relatively unchanged through the winter. In early summer, as melting occurs in the upper part of the snow–firn pack, meltwater carries chemical species to different depths in the underlying snow–firn layers, such that at the end of the ablation season, all of the surface cations might be leached out from the upper layers. In addition, the possible source of calcium and magnesium is discussed in this paper.
Modeling the response of glacier systems to climate warming in China
Authors: Xie Zi-Chu , Wang Xin , Feng Qing-Hua , Kang Er’si , Liu Chao-Hai , Li Qiao-Yuan
Published: November 2007

A glacier system is regarded as the ensemble of many glaciers sharing the same region, influenced by a similar climate and organized by certain intrinsic laws. It can be either ‘sensitive’ or ‘steady’. On the basis of the structure of the glacier system and the nature of the equilibrium-line altitudes at the steady state, functional models of a glacier system responding to climate warming were established, using the Kotlyakov–Krenke equation relating annual glacier ablation and mean summer temperature and the glacier system’s median size. The modeling results under the climatic scenarios with a rate of temperature increase of 0.01, 0.03 and 0.05 K a-1 indicate that by the end of this century the glacial area of China will be reduced by –14%, –40%and –60% respectively. However, model results show distinct differences between the sensitive glacier system and the steady glacier system.
Elemental and organic carbon measurements with a two-step heating-gas chromatography system in snow samples from the Tibetan Plateau
Authors: Xu Baiqing , Yao Tandong , Liu Xianqin , Wang Ninglian
Published: November 2007

In this study, an optimized two-step heating-gas chromatography system is used to measure elemental carbon (EC) and organic carbon (OC) content in snow and ice, with the ability to quantify the elemental and organic carbon species in a snow or ice sample of 60−80 g. In this system, OC and EC are transformed into CO2 in a stream of oxygen at 340°C and 650°C, respectively. The resulting CO2 is accumulated in two molecular-sieve traps, and then put into a gas chromatograph equipped with a flame ionization detector by heating the traps to 200°C in a helium stream. Background contamination (mainly caused by impurities in the oxygen stream) and accuracy are dominated by the variability of the blank loads on the pre-cleaned filters, which are 0.50 ± 0.04 (1σ) μgC for OC, and 0.38 ± 0.04 (1σ) μgC for EC. The system is suitable for snow and ice sample measurements, with the same precision as shown for the blank tests. EC and OC concentrations have been measured in snow samples collected from different glaciers on the Tibetan Plateau. The results allow quantification for the first time of the different carbonaceous particle contents on the Tibetan Plateau and other regions. The concentrations of EC and OC particles in snow show a clearly decreasing trend from east to west and from north to south on the plateau, excluding the Pamirs region. The highest mean EC content, 79.2 ngg-1, was found in the northeast region, and the lowest, 4.3 ngg-1, was found in the western Himalaya. We note that even slight surface melting results in fresh snow getting dirtier, especially in regions with higher pollution such as seen on a glacier in the Qilian Shan. Here, the EC and OC concentrations in the fresh snow average 6.6 and 87.5 ngg-1, but after 2 days of surface melting they increased to 52.6 and 195.5 ngg-1. This suggests that surface snow melting can reduce snow albedo due to the accumulation of carbonaceous particles.
Recent changes of atmospheric heavy metals in a high-elevation ice core from Muztagh Ata, east Pamirs: initial results
Authors: Li Yuefang , Yao Tandong , Wang Ninglian , Li Zhen , Tian Lide , Xu Baiqing , Wu Guangjian
Published: November 2007

Al, Mn, Rb, Sr, Ba, Cs, Bi and Sb were measured at various depth intervals of a 41.6 m firn/ ice core drilled at an elevation of 7010 m near the top of Muztagh Ata glacier, east Pamirs (38˚17’ N, 75˚06’ E), central Asia. These data, spanning the mid-1950s to 2000, were obtained by analyzing 101 sections using a sector-field double-focusing inductively coupled plasma mass spectrometer (ICP-MS) instrument. This study provides the first time series for these metals from central Asia. Concentrations are 11.7–329 ng mL−1 for Al, 0.33–42.7 ng mL−1 for Mn, 0.42–17.8 ng mL−1 for Sr, 0.04–1.4 ng mL−1 for Rb, 0.18–10.4 ng mL−1 for Ba, 2–167 pg mL−1 for Cs, 2–51 pg mL−1 for Sb and 1–31 pg mL−1 for Bi. Large variations in metal concentrations were found during the study period. Pronounced increases in concentrations were observed for Sb and Bi from the mid-1960s to the beginning of the 1990s, suggesting increased anthropogenic sources of Sb and Bi in central Asia during the same period. However, the decrease of Sb and Bi concentrations during the mid- to late 1990s reflects a reduction in anthropogenic activities in central Asia.
Recent changes of glacier coverage in the western Terskey-Alatoo range, Kyrgyz Republic, using Corona and Landsat
Authors: Narama Chiyuki , Shimamura Yuichi , Nakayama Daichi , Abdrakhmatov Kanatbek
Published: November 2007

Corona images from 1971 and a Landsat image from 2002 are used to assess glacier variations in the last 30 years in the western Terskey-Alatoo range (a part of the Tien Shan), in the northeast of the Kyrgyz Republic. The glaciers have shrunk during this period. The 269 mountain glaciers measured in the study area had an original combined area of 245 km2, which has decreased 18.4 km2, representing a loss of 8% of the original glacier coverage in 1971. Individual glaciers covering <1km2 account for 28% of the combined glacial coverage, but loss from these small glaciers represents 38% of the total decrease in area. The relative change of area is larger for small-scale glaciers, and its contribution to shrinkage of glacier area is high. This shrinkage has been linked to climate changes as recorded at local stations. Many small-scale glaciers are distributed around Issyk-Kul lake, and rapid glacier reduction is expected in this area in the future.
Influence of air temperature on a glacier’s active-layer temperature
Authors: Zagorodnov V. , Nagornov O. , Thompson L.G.
Published: November 2007

Seasonal temperature variations occur in the glacier layer about 15–20 m below the surface, while at greater depths the glacier temperature depends on the long-term surface conditions. It is generally accepted that for glaciers without surface melting the temperature at 10 m depth (T10) is close to the mean annual air temperature at standard screen level (Ta), i.e. T10 =Ta. We found that this relationship is not valid for Ta above –17˚C and below –55˚C. The goal of our investigation is to find a better temperature transfer function (TTF) between Ta and temperature at the boundary of the active layer in accumulation areas of polar and tropical glaciers. Low-precision T10 temperatures from boreholes, obtained at 41 sites, are compared with air temperatures (Ta) measured in the vicinity of these sites for at least a 1 year period. We determine that when Ta falls into the temperature range –60 to –7˚C, empirical values can be approximated as T10 = 1:2Ta + 6:7. Analysis of these data suggests that high T10 occurs in the areas of the glacier that collect meltwater.
Changes in mountain glaciers and ice caps during the 20th century
Authors: Ohmura Atsumu
Published: November 2007

The global mass balance of the glaciers outside Greenland and Antarctica is evaluated based on long-term mass-balance observations on 75 glaciers. The cause of the mass-balance change is investigated by examining winter and summer balances from 34 glaciers. The main finding is a common development in mass-balance changes shared by a number of glaciers separated by large distances and climatic conditions. The average mass balance for the second half of the 20th century was negative at –270 to –280 mma−1. The negative mass balance was found to be intensified at –10mm a−2. Increasing summer melt plays a dominant role in determining the long-term trend in mass balance. During the same period the mean winter mass balance increased slightly, indicating an acceleration (3 mma−2) of the hydrological cycle. On some Scandinavian glaciers the mean mass balance was not only positive but its tendency was accelerating. This trend is due to the strong precipitation increase in the last four decades. The melt/temperature relationships for the two warmer periods in the 20th century, one centred around the 1940s and the other ongoing, are different. Reduced melt in the modern warm period, in comparison with the earlier warm phase of the 1940s, is caused by the global dimming which reduced the solar radiation at the Earth’s surface during the second half of the 20th century.
Snow algae in a Himalayan ice core: new environmental markers for ice-core analyses and their correlation with summer mass balance
Authors: Yoshimura Yoshitaka , Kohshima Shiro , Takeuchi Nozomu , Seko Katsumoto , Fujita Koji
Published: November 2007

Snow algae in a shallow ice core (6.98 m long) from Yala glacier in the Langtang region of Nepal were examined for potential use as environmental markers in ice-core analysis. The ice core, taken at 5350m a.s.l. in 1994, was estimated to contain 11 annual layers from 1984 to 1994 from the profile of algal biomass. Algal biomass in each annual layer was noted to be correlated with air temperature, and the following two environmental indices which were calculated from air temperature and precipitation at Kyangjing (3920m a.s.l.), the village nearest to Yala glacier: estimated mean snow-cover thickness (MST) and estimated summer mass balance (SMB). Both parameters reflect snow-cover thickness on algal layers, which would be a major determinant of the light available for algal growth on the glacier. Snow algal biomass in the ice core appears to be a good environmental marker for indicating air temperature and accumulation during summer, which is important for understanding the mass balance of summer-accumulation-type glaciers in this region.
Distributed glacier mass-balance modelling as an important component of modern multi-level glacier monitoring
Authors: Machguth Horst , Paul Frank , Hoelzle Martin , Haeberli Wilfried
Published: November 2007

Modern concepts of worldwide glacier monitoring include numerical models for (1) interconnecting the different levels of observations (local mass balance, representative length change, glacier inventories for global coverage) and (2) extrapolations in space (coupling with climate models) and time (backward and forward). In this context, one important new tool is distributed mass-balance modelling in complex mountain topography. This approach builds on simplified energy-balance models and can be applied for investigating the spatio-temporal representativity of the few mass-balance measurements, for estimating balance values at the tongue of unmeasured glaciers in order to derive long-term average balance values from a great number of glaciers with known length change, and for assessing special effects such as the influence of Sahara dust falls on the albedo and mass balance or autocorrelation effects due to surface darkening of glaciers with strongly negative balances. Experience from first model runs in the Swiss Alps and from applications to the extreme conditions in summer 2003 provides evidence about the usefulness of this approach for glacier monitoring and analysis of glacier changes in high-mountain regions. The main difficulties concern the spatial variability of the input parameters (e.g. precipitation, snow cover and surface albedo) and the uncertainties in the parameterizations of the components of the energy balance. Field measurements remain essential to tie the models to real ground conditions.
Accumulation at the equilibrium-line altitude of glaciers inferred from a degree-day model and tested against field observations
Authors: Braithwaite Roger J. , Raper Sarah C.B. , Chutko Krys
Published: November 2007

We extrapolate temperature data from a gridded climatology to the equilibrium-line altitude (ELA) of a glacier and tune a degree-day model by adjusting precipitation to give zero mass balance at the ELA. We verify the tuned model by comparing modelled accumulation with winter balance where this has been measured (presently for 180 glaciers). The modelled accumulation naturally depends upon the vertical lapse rate (VLR) for temperature and the degree-day factor (DDF) for snowmelt. Both are somewhat uncertain in high-mountain areas, but modelled accumulation and measured winter balance are in reasonable agreement for most glaciers. The degree-day model predicts a non-linear relation between accumulation and summer temperature at the ELA as assumed by many workers, but we find a family of curves rather than a single universal curve. Maritime glaciers with low annual temperature range have proportionally more accumulation than continental glaciers with high annual temperature range for a similar summer mean temperature. Averages of winter balance for the five main geographical regions where mass-balance data are available agree well with annual accumulation from the degree-day model.
Wavelet analysis reveals periodic oscillations in a 1700 year ice-core record from Guliya, China
Authors: Yang Meixue , Yao Tandong , Gou Xiaohua , Wang Huijun , Neumann Thomas
Published: November 2007

Ice cores contribute important records of past climate changes. As one of the thickest ice caps in central Asia, the Guliya ice cap (35°17′ N, 81°29′ E) provides valuable information for this critical region about the past climate and environment changes. We used wavelet analysis to examine periodic temperature and precipitation oscillations over the past 1700 years recorded in the Guliya ice core. The results show non-linear oscillations in the ice-core records, with multiple timescales. Temperature records indicate persistent oscillations with periodicities of approximately 200, 150 and 70 years. Precipitation records show significant periodicities at 200, 100, 150 and 60 years. However, the amplitude modulation and frequency vary with time. Wavelet analysis can explore these time series in greater detail and furnish additional useful information.
Oxygen-18 isotopes in precipitation on the eastern Tibetan Plateau
Authors: Wusheng Yu , Tandong Yao , Lide Tian , Yu Wang , Zexia Li , Weizhen Sun
Published: November 2007

This study examines precipitation samples collected at the Yushu meteorological station on the eastern Tibetan Plateau from November 2000 to November 2002. Results show that air-temperature effects control δ18O in precipitation in this area. Values of δ18O in precipitation positively correlate with air temperature, especially for monthly averages. Our data also show δ18O values in precipitation positively correlate with dew point and surface pressure in the Yushu region. Similar to other stations (Tuotuohe, Nagqu, Gaize and Shiquanhe) lying in the transition zone between the regions in the south dominated by the monsoon and those in the north dominated by the westerlies, because of the effect of monsoon precipitation, precipitation rates are high, and heavy isotopes are more depleted in summer at the Yushu station. Accordingly, values of δ18O in precipitation correlate more strongly with air temperature and dew point before the monsoon onset and after the monsoon retreat than during the monsoon period. That is, intense monsoon activities weaken the correlations between δ18O and air temperature and dew point. Clearly, dew point, surface pressure and the monsoon intensity contribute to controlling the δ18O values in precipitation at the Yushu station.
Glacier changes in the central and northern Tien Shan during the last 140 years based on surface and remote-sensing data
Authors: Aizen Vladimir B. , Kuzmichenok Valeriy A. , Surazakov Arzhan B. , Aizen Elena M.
Published: November 2007

This research presents a precise evaluation of the recession of Akshiirak and Ala Archa glaciers, Tien Shan, central Asia, based on data of geodetic surveys from 1861–69, aerial photographs from 1943, 1963, 1977 and 1981, 1:25000 scale topographic maps and SRTM and ASTER data from 2000–03. The Akshiirak glacierized massif in the central Tien Shan contains 178 glaciers covering 371.6 km2, and the Ala Archa glacier basin in the northern Tien Shan contains 48 glaciers covering 36.31 km2. The Tien Shan glaciers retreated as much as 3 km from the 1860s to 2003. Area shrinkage of Akshiirak and Ala Archa was 4.2% and 5.1%, respectively, from 1943 to 1977, and 8.7% and 10.6%, respectively, from 1977 to 2003. The volume of the Akshiirak glaciers was reduced by 3.566 km3 from 1943 to 1977 and 6.145 km3 from 1977 to 2000. The total reduction of the Tien Shan glaciers is 14.2% during the last 60 years (1943–2003). The northern and central Tien Shan have not experienced a significant precipitation increase during the last 100 years, but they have experienced an increase in summer air temperatures, especially observable since the 1970s, which accelerated the recession of the Tien Shan glaciers.
Study of Lange Glacier on King George Island, Antarctica
Authors: Macheret Yu.Ya. , Moskalevsky M.Yu.
Published: November 2007

The results of ground-based radio-echo sounding collected in 1995 and 1996-97 in the drainage basin of Lange Glacier, a tidewater outlet glacier on King George Island, Antarctica, are presented and discussed. Ice-thickness and bedrock-elevation maps, constructed for the upper non-crevassed part of the glacier, show a close relation between its surface and subglacial topography and indicate the main directions of ice runoff from this area where the ice thickness reaches 308 m. A retreat of the glacier front by 1 km since 1956 occurred against a background of climate warming by 1.4°C on the South Shetland Islands during the last five decades, while a neighboring unnamed glacier advanced by 0.6 km and the northern ice-cap margin on King George Island was approximately stationary. To understand the reasons for the different responses of these ice masses to current climate warming in this region of West Antarctica, further studies including mass-balance and ice-velocity observations and numerical modeling are needed.
Ice-sheet flow conditions deduced from mechanical tests of ice core
Authors: Miyamoto Atsushi , Narita Hideki , Hondoh Takeo , Shoji Hitoshi , Kawada Kunio , Watanabe Okitsugu , Dahl-Jensen Dorthe , Gundestrup Niels S. , Clausen Henrik B. , Duval Paul
Published: November 2007

Uniaxial compression tests were performed on samples of the Greenland Ice Gore Project (GRIP) deep ice core, both in the field and later in a cold-room laboratory, in order to understand the ice-flow behavior of large ice sheets. Experiments were conducted under conditions of constant strain rate (type A) and constant load (type B). Fifty-four uniaxial-compression test specimens from 1327-2922 m were selected. Each test specimen (25 mm x 25 mm x 90 mm) was prepared with its uniaxial stress axis inclined 45° from the core axis in order to examine the flow behavior of strong single-maximum ice-core samples with basal planes parallel to the horizontal plane of the ice sheet. The ice-flow enhancement factors show a gradual increase with depth down to approximately 2000 m. These results can be interpreted in terms of an increase in the fourth-order Schmid factor. Below 2000 m depth, the flow-enhancement factor increases to about 20-30 with a relatively high variability When the Schmid factor was > 0.46, the enhancement factor obtained was higher than expected from the .-axis concentrations measured. The higher values of flow-enhancement factor were obtained from specimens with a cloudy band structure. It was revealed that cloudy bands affect ice-deformation processes, but the details remain unclear.
Surface accumulation on Foundation Ice Stream, Antarctica
Authors: Graf Wolfgang , Reinwarth Oskar , Oerter Hans , Mayer Christoph , Lambrecht Astrid
Published: November 2007

This paper presents new data, derived from an analysis of 16 firn cores, on the distribution of the accumulation rate and 18O content of near-surface layers in the eastern part of the Ronne Ice Shelf, Antarctica. The firn cores were drilled along the traverse route of the Filchner-V-Campaign in 1995. The traverse followed an ice flowline of the Foundation Ice Stream and reached the margin of the inland ice, an area which has not yet been investigated. On the ice shelf the accumulation rates decrease with distance from the coast. Ascending to the inland ice the accumulation rates again reach almost coastal values. This regional distribution is in agreement with the temperature gradient along the traverse. The 18 content of the near-surface layers is closely related to the 10 m firn temperature. They strongly decrease from the grounding line towards the inland ice. At the southernmost site at 1100 ma.s.l, the mean δ18O value of the firn decreases to –40‰. Ice with that isotopic signature was found in cores from the central part of the Ronne Ice Shelf just above the marine ice layer, indicating that it originates from this area. All ice deposited as snow further south was melted beneath the ice shelf after passing the grounding-line area. The time series of accumulation rate and 18O content reveal no climatic trend during the last 30-50 years.
A new automatic ice-fabric analyzer which uses image-analysis techniques
Authors: Yun Wang , Azuma Nobuhiko
Published: November 2007

An automatic ice-fabric analyzer has been developed, which can determine individual ,-axis orientations by image-analysis techniques. The analyzer consists of four major components: a sample stage, a pair of crossed polaroids, a charge coupled device (CCD) camera and a light source. Both the sample stage and the crossed polaroids can be rotated independently of each other by the stepping motors controlled by a personal computer (PC). Measurements are conducted as follows. An ice thin section is set on the sample stage and then the crossed polaroids are rotated. Thin-section images are recorded by the PC at intervals of 2° of rotation. From the image-intensity (gray value) dataset of each crystal in the thin section the extinction angles of individual crystals can be determined. Similarly, eight other extinction angles of individual crystals are obtained from eight other CCD camera positions with respect to the thin section: Finally, the .-axis orientation of individual crystals is calculated by using these extinction angles. With this technique, all crystals within the view of the CCD camera can be analyzed at the same time. In addition, with image-processing techniques the individual crystals are recognized automatically and other parameters, such as grain-size and grain shape, can be measured simultaneously. Textural studies of Dome Fuji (Antarctica) ice cores have been conducted with this analyzer.
Variations of snow accumulation and temperature over past decades in the Lambert Glacier basin, Antarctica
Authors: Jiawen Ren , Dahe Qin , Allison Ian
Published: November 2007

The Lambert Glacier basin is a region of the East Antarctic ice sheet with a distinctive topography. Accumulation data derived from cane measurements are available from recent inland traverses in the western part of the basin, together with data on stable isotopes and visible stratigraphy of shallow cores and snow pits. These data suggest that snow accumulation has decreased since the 1930s by 16-37%, but that since the late 1980s it has been increasing. Temperature records from the nearby coastal station, Mawson, show no clear trend. Although the data are from only the western part of the basin, these results are quite different from those in many other regions of Antarctica. Further investigations are needed in this potentially exceptional region.
Morphology and variations of glacial drainage basins in the King George Island ice field, Antarctica
Authors: Simões Jefferson C. , Bremer Ulisses F. , Aquino Francisco E. , Ferron Francisco A.
Published: November 2007

A Système probatoire pour l’observation de la terre (SPOT) mosaic of King George Island, the largest (1250 Km2) of the South Shetland Islands, West Antarctica, shows its major morphological features. Three main ice domes and 70 glacier drainage basins, covering 92.7% of the King George Island area, strongly controlled by the subglacial morphology and drained by relatively fast-moving tidewater outlet glaciers, were delineated. A general retreat of ice fronts through four decades, more intensely on the eastern side of the island (to the Bransfield Strait), resulted in the loss of about 7% of the glacial cover area. Superficial snow fades were derived from SPOT multispectral imagery and, together with field observations, allowed the transient-snowline elevation to be obtained The latter is estimated to have risen from about 200-250 m in the mid-1950s to 300-350 m by 1988. Spot radio-echo sounding surveys give an overview of the bedrock morphology.
Permafrost as a climatic indicator in northern Victoria Land, Antarctica
Authors: Guglielmin M. , Dramis F.
Published: November 2007

Knowledge of permafrost characteristics and distribution in Antarctica and their relationships with present and past climates is still poor. This paper reports investigations on permafrost in an area located between Nansen Ice Sheet to the south and Mount Melbourne (2732 m a.s.l.) to the north. Investigation methods included geomorphological surveys and geoelectrical soundings as well as crystallography, chemical and isotopic analyses of the ground ice. Geomorphological surveys helped to explain the relationships between periglacial landforms (e.g. rock glaciers and patterned ground) and the glacial history of the area. Geoelectrical soundings allowed us to define different ground-ice units in the ice-free areas. Each unit was characterised by a different type of permafrost (dry or ice-poor permafrost, marine or continental massive buried ice and sub-sea permafrost). To identify the nature of ground ice, trenches were dug and some shallow boreholes were drilled to a maximum depth of-3.6 m in massive buried ice. Samples of both ice-poor permafrost and massive ice were collected and analyzed. Chemical, isotopic δ18O and crystal analyses were also carried out. The relationships between climate and thermal regimes of the active layer and the upper part of permafrost were determined using a monitoring station for ground temperatures at Boulder Clay Glacier, near the Italian Antarctic station. During winter, there were several significant thermal-inversion events in the ground, which cannot be explained only by air-temperature changes, suggesting a possible influence of winter snowfall, even if these events are usually considered very rare.
Chemical characterisation of a volcanic event (about AD 1500) at Styx Glacier plateau, northern Victoria Land, Antarctica
Authors: Udisti R. , Barbante C. , Castellano E. , Vermigli S. , Traversi R. , Capodaglio G. , Piccardi G.
Published: November 2007

A dark layer (∼1 cm thick, 93.41 m deep) was identified in an ice core (116 m deep, covering the period -1350-1995) drilled at Styx Glacier plateau, northern Victoria Land, Antarctica. The ice-core section was dated around AD 1500 ± 20 by a firn-densification model. A chemical characterisation was performed on ten subsamples (resolution 3 cm) located around the dark layer by ion chromatography. The concentration/depth profiles of anions (Cl-, Br-, NC3-, H2PO4-, SO42-), cations (Na+, NH4+, K+, Mg*+, Ga2^) and some organic anions (acetate, formate, propionate and methanesulphonate (MSA)) indicate very high concentration peaks for all the components. However, non-sea-salt sulphate (nssSo/-) and F- show the greatest increase with respect to background values (370 and 860 times, respectively). A crustal contribution is attributed to Ga2+ and MSA. The profiles of gas-phase emitted substances (HF, HBr, HNOs and carboxylic acid) suggest gas emission just before the volcanic eruption. Chloride depletion is evident in the dark layer with respect to Na+/Cl- sea-water ratio. At present, it is not possible to attribute an unambiguous source to the volcanic event, but several pieces of evidence lead us to believe that this may be a time-limited local event.
The newly developed airborne radio-echo sounding system of the AWI as a glaciological tool
Authors: Nixdorf U. , Steinhage D. , Meyer U. , Hempel L. , Jenett M. , Wachs P. , Miller H.
Published: November 2007

Since 1994 the Alfred Wegener Institute (AWI) has operated an airborne radio-echo sounding system for remote-sensing studies of the polar ice caps in Antarctica and in Greenland. It is used to map ice thicknesses and internal layernigs of glaciers, ice sheets and ice shelves, and is capable of penetrating ice thicknesses of up to 4 km. The system was designed and built by AWI in cooperation with Aerodata Flugmeßtechnik GmbH, Technische Umversitat Hamburg-Harburg and the Deutsches Zentrum fur Luft- und Raumfahrt e.V. The system uses state-of-the-art techniques, and results in high vertical (5 m) as well as along-track (3.25 m) resolution. The radar signal is a 150 MHz burst with a duration of 60 or 600 ns. The peak power is 1.6 kW, and the system sensitivity is 190 dB. The short backfire principle has been adopted and optimized for antennae used on Polar2, a Dormer 228-100 aircraft, resulting in an antenna gain of 14 dB each. Digital data recording allows further processing. The quality of the recorded data can be monitored on screen and as online analogue plots during the flight.
Density log of a 181 m long ice core from Berkner Island, Antarctica
Authors: Gerland S. , Oerter H. , Kipfstuhl J. , Wilhelms F. , Miller H. , Miners W. D.
Published: November 2007

A 181 m long ice core was drilled at 79°36’51"S, 45°43’28" W, near the summit of Berkner Island, Antarctica (886 m a.s.L). Berkner Island is located between the Filchner and Ronne Ice Shelves, and the ice near the summit shows little lateral flow. The density of the ice core was measured every 3 mm along its length, using attenuation of a gamma-ray beam, which gave an absolute accuracy of 2%. As expected, there is a general density increase with depth, the maximum densities of > 900 kg m−3 being reached just above 100 m depth. Comparison with the electrical conductivity method (ECM) shows density variations with the same wavelength as the annual signals, which can be seen in the ECM log (higher acidity during summer). In the shallowest part of the core, the density of winter layers is higher than that of summer layers, a relationship which is reversed at greater depth. We assume that the densification rates for the two types of firn are different. Similar density phenomena were observed on ice cores from Greenland, showing that such phenomena are not a local effect.
Simulations of Southern Hemisphere warming and Antarctic sea-ice changes using global climate models
Authors: Wu Xingren , Budd W. F. , Jacka T. H.
Published: November 2007

A combination of modelling techniques is used in conjunction with the limited available observational data to examine Antarctic sea-ice changes with global warming over the past century. Firstly a coupled global climate model is forced by prescribing the effect of increasing greenhouse gases from last century to the present. Secondly the GISST (U.K. Meteorological Office global sea-ice and sea surface temperature) observational dataset is used to force an atmosphere-sea-ice model to compute changes in the Antarctic sea ice from last century to the present. Thirdly the global sea-surface-temperature (SST) anomalies derived from the coupled model are used to force the atmosphere-sea-ice model over the same period. The change in the Southern Hemisphere annual mean surface temperature simulated by the coupled model with greenhouse-gas forcing is about 0.6°C, which is similar to the observed change. Over the Antarctic (poleward of 60° S) the corresponding simulated change is about 0.7°C, which also appears compatible with observations. The reduction in summer sea-ice extent simulated by the CSIRO (Commonwealth Scientific and Industrial Research Organisation) coupled model is 0.44° lat. which is, in general, less than the observed change. For the two SST forcing cases the changes are, in general, larger than indicated by the observations. It is concluded that future changes of reduced sea-ice extent from increasing greenhouse gases as simulated by the CSIRO coupled model are not expected to be overestimates.
Climatic stability of the geographic origin of Antarctic precipitation simulated by an atmospheric general circulation model
Authors: Delaygue Gilles , Masson Valérie , Jouzel Jean
Published: November 2007

The geographic origin of Antarctic precipitation is important for ice-core isotopic interpretation as well as ice-sheet mass-balance calculations. Here we estimate these moisture origins with the NASA/Goddard Institute of Space Studies atmospheric general circulation model, under different climatic conditions. This model reasonably simulates the broad features of the present-day observed hydrological cycle, and indicates a subtropical to subglacial (30-60° S) latitudinal origin for the Antarctic precipitation. We use different climatic reconstructions, all based on CLIMAP, for the Last Glacial Maximum (about 21000 years ago), which differ by the latitudinal sea-surface temperature gradient and seasonality. CLIMAP conditions increase the latitudinal gradient and the sea-ice extent, with the consequence of slightly enhancing the low-latitude origins. Shifting the seasonal cycle of oceanic prescribed conditions has an important effect on the hydrological cycle but less on the precipitation origin. Prescribing cooler tropical sea-surface temperatures, which decreases the latitudinal gradient, makes the latitudinal contributions closer to modern ones and increases the dominant oceanic sources. Globally the origins of Antarctic precipitation do not change significantly, either annually or seasonally.
Simulated features of the air-hydrate formation process in the Antarctic ice sheet at Vostok
Authors: Salamatin Andrey N. , Lipenkov Vladimir Ya. , Hondoh Takeo , Ikeda Tomoko
Published: November 2007

A recently developed theory of post-nucleation conversion of an air bubble to air-hydrate crystal in ice is applied to simulate two different types of air-hydrate formation in polar ice sheets. The work is focused on interpretation of the Vostok (Antarctica) ice-core data. The hydrostatic compression of bubbles is the rate-limiting step of the phase transformation which is additionally influenced by selective diffusion of the gas components from neighboring air bubbles. The latter process leads to the gas fractionation resulting in lower (higher) N2/O2 ratios in air hydrates (coexisting bubbles) with respect to atmospheric air. The typical time of the post-nucleation conversion decreases at Vostok from 1300-200 a at the beginning to 50-3 a at the end of the transition zone. The model of the diffusive transport of the air constituents from air bubbles to hydrate crystals is constrained by the data of Raman spectra measurements. The oxygen and nitrogen self-diffusion (permeation) coefficients in ice are determined at 220 K as 4.5 × 10−8 and 9.5 × 10−8 mm2 a−1, respectively while the activation energy is estimated to be about 50 kJ mol−1. The gas-fractionation time-scale at Vostok, τF ∼300 a, appears to be two orders of magnitude less than the typical time of the air-hydrate nucleation, τz ∼30-35 ka, and thus the condition for the extreme gas fractionation, τF ≪ τz is satisfied. Application of the theory to the GRIP and GISP2 ice cores shows that on average, a significant gas fractionation cannot be expected for air hydrates in central Greenland. However, a noticeable (statistically valid) nitrogen enrichment might be observed in the last air bubbles at the end of the transition.
Distribution and glaciological implications of relict surfaces on the Ultevis plateau, northwestern Sweden
Authors: Clarhäll Anders , Kleman Johan
Published: November 2007

The Ultevis plateau, northwestern Sweden, has a relief of less than 200 m, yet bears three different kinds of landscape, classified according to the degree of glacial erosion. The first type is restricted mainly to topographic highs and has almost entirely escaped erosion, despite complete and prolonged ice cover during the late Weichselian. The other two landscape types are distinguished depending on whether older land- forms have been completely erased or not. The latter two appear to have undergone erosion only briefly. The transitions between landscape zones are usually sharp, and specific boundary landforms occur. The Scandinavian ice sheet was cold-based in its central areas during its maximum. During the deglaciation, both the dry/wet-base boundary and ice margin migrated inwards, at different speeds. When the ice front retreated faster than the thermal transition zone, the wet-base marginal zone shrank and erosion was reduced or avoided. Where the wet-base zone was of limited longitudinal extent, as on the Ultevis plateau, conversion from a frozen to a thawed bed was incomplete, leaving a patchwork of preserved glacial and non-glacial morphologies.
Zooming in on frozen-bed patches: scale-dependent controls on Fennoscandian ice sheet basal thermal zonation
Authors: Kleman Johan , Hättestrand Clas , Clarhäll Anders
Published: November 2007

In this paper, we explore geomorphological evidence allowing a first- order reconstruction of the extent and pattern of frozen-bed conditions under the last Fennoscandian ice sheet. We mapped relict landscapes, i.e. glacial landforms and subaerially developed ground surfaces predating the last ice sheet and marking sustained frozen- bed conditions, at four different spatial scales. At the ice-sheet scale, relict landscapes are most abundant between the Last Glacial Maximum ice divide and the elevation axis of the Scandinavian mountain range. The location of frozen-bed zones was mainly a function of dispersal centre location (low surface temperatures and small strain heating) and small ice thickness over the eastern flank of the mountain range. At the mesoscale (260 × 360 km map area), the pattern of relict surfaces is governed by inward-cutting ice-stream erosion.Topographical control was weak, but relation to flow pattern was strong, with the major frozen-bed zone located where ice flow was strongly divergent. At the regional scale (40 × 65 km map area) in hilly terrain, topographical control was strong with relict surfaces only appearing above a plane dipping in the up-ice direction. At the local scale (12 × 14 km map area), control by topography was likewise strong, but the detailed boundary pattern was irregular, with specific landforms occurring both up- and down-ice of frozen patches.
Thermomechanical modelling of the Scandinavian ice sheet: implications for ice-stream formation
Authors: Payne A. J. , Baldwin D.J.
Published: November 2007

This work attempts to explain the fan-like landform assemblages observed in satellite images of the area covered by the former Scandinavian ice sheet (SIS). These assemblages have been interpreted as evidence of large ice streams within the SIS. If this interpretation is correct, then it calls into doubt current theories on the formation of ice streams. These theories regard soft sediment and topographic troughs as being the key determinants of ice-stream location. Neither can be used to explain the existence of ice streams on the flat, hard-rock area of the Baltic Shield. Initial results from a three-dimensional, thermomechanical ice-sheet model indicate that interactions between ice flow, form and temperature can create patterns similar to those mentioned above. The model uses a realistic, 20 km resolution gridded topography and a simple parameterization of accumulation and ablation. It produces patterns of maximum ice-sheet extent, which are similar to those reconstructed from the area’s glacial geomorphology. Flow in the maximum, equilibrium ice sheet is dominated by wedges of warm, low-viscosity, fast-flowing ice. These are separated by areas of cold, slow-flowing ice. This patterning appears to develop spontaneously as the modelled ice sheet grows.
Glacial landform-sediment assemblages in the Canadian High Arctic and their implications for late Quaternary glaciations
Authors: Ó Cofaigh C. , Lemman D.S. , Evans D.J.A. , Bednarski J.
Published: November 2007

Modern terrestrial glaciers in the Canadian High Arctic range from polythermal to cold-based. Where polythermal glaciers override thick unconsolidated sediment, longitudinal compression and glaciotectonic thrusting produce thrust-block moraines. In contrast, the dominant geomorphic record of cold-based glaciers consists of lateral and proglacial meltwater channels. Geomorphic and sedimentary evidence indicates that late Quaternary fiord glaciers were also characterized by variations in basal thermal regime. Erratic dispersal trains and striated bedrock record the flow of warm- based ice during the Last Glacial Maximum. Emergent grounding-line fans and morainal banks, deposited during deglaciation, consist of heterogeneous glaciomarine deposits that record well-developed subglacial drainage and high sedimentation rates. However, in other fiords, subaqueous outwash and fine-grained glaciomarine deposits are absent and deglaciation is recorded by lateral meltwater channels graded to raised glaciomarine deltas, suggesting these glaciers were predominantly cold-based during retreat. Regionally, deglacial depocentres are located at pinning points within fiords and a prominent belt of glaciogenic landforms at fiord heads records stabilization of ice margins during early Holocene retreat, rather than the limit of late Quaternary glaciation. Collectively, these observations refute previous reconstructions which inferred a climatically controlled switch from cold- to warm-based thermal conditions in fiord glaciers during early Holocene deglaciation, and indicate that the dominant controls on thermal regime were glaciological.
Glaciated landscapes along Smith Sound, Ellesmere Island, Canada and Greenland
Authors: Blake Weston
Published: November 2007

Both the Ellesmere Island and Greenland coasts of Smith Sound, at 78°20' N to 78°50' N, exhibit exceptionally well-sculptured and heavily striated Precambrian bedrock. The glacial features were created by the southward flow of the “Smith Sound Ice Stream”, which overrode Pim Island (550 m), where Smith Sound is > 500 m deep and 40 km wide. The Smith Sound Ice Stream was the drainageway to Baffin Bay for ice derived from the coalescence of the Innuitian and Greenland ice sheets over Kane Basin, the shallowest part (much of it <200m) of the Nares Strait system, in late-Wisconsinan (Weichselian) time. The north-south oriented glacial features along the outermost coasts of Smith Sound contrast markedly with the present-day eastward flow of outlet glaciers from the Prince of Wales Icefield (Ellesmere Island) and the westward flow of outlet glaciers from the Greenland ice sheet (Inglefield Land). The oldest 14C ages on marine shells and lake sediments show that glacier ice had receded from the Ellesmere Island coast of Smith Sound by 9000 14C yr BP. The heads of the three longest fiords, 120-140 km to the west and northwest, did not become ice-free until 450014C yr BP.
Glaciodynamic context of subglacial bedform generation and preservation
Authors: Clark Chris D.
Published: November 2007

Subglacially-produced drift lineations provide spatially extensive evidence of ice flow that can be used to aid reconstructions of the evolution of former ice sheets. Such reconstructions, however, are highly sensitive to assumptions made about the glaciodynamic context of lineament generation; when during the glacial cycle and where within the ice sheet were they produced. A range of glaciodynamic contexts are explored which include: sheet-flow submarginally restricted; sheet-flow pervasive; sheet- flow patch; ice stream; and surge or re-advance. Examples of each are provided. The crux of deciphering the appropriate context is whether lineations were laid down time-trans-gressively or isochronously. It is proposed that spatial and morphometric characteristics of lineations, and their association with other landforms, can be used as objective criteria to help distinguish between these cases.

A logically complete ice-sheet reconstruction must also account for the observed patches of older lineations and other relict surfaces and deposits that have survived erasure by subsequent ice flow. A range of potential preservation mechanisms are explored, including: cold- based ice; low basal-shear stresses; shallowing of the deforming layer; and basal uncoupling.
The glacial impact on an exhumed sub-Mesozoic etch surface in southwestern Sweden
Authors: Olvmo Mats , Lidmar-Bergström Karna , Lindberg Göran
Published: November 2007

Along the northern part of the western coast of Sweden, the landscape is characterized by joint-aligned valleys with intervening rock hills. Precambrian bedrock is exposed over large areas and the Quaternary cover is mainly restricted to the bottom of narrow valleys. The well-exposed bedrock exhibits many glacial forms, but recently the major landforms have been interpreted as exhumed sub-Mesozoic etch forms. To gain insight into the relative roles of different processes in shaping the present forms, we studied a granite area where the rock hills contain fractures and narrow clefts with weathering forms and saprolite remnants. Marks of glacial erosion are found only in the upper parts of the clefts, where erosion by subglacial meltwater has exploited weathered preglacial sheeting structures to form furrows with concave cross profiles (p forms). On the summit surfaces, glacial erosion has been of greater importance, but the roche moutonnees found here are also structurally controlled. The main impact of glacial erosion is plucking on the order of tens of metres. Thus, landscapes labelled “areally scoured glacial terrain” can, at some locations, also be described as stripped and slightly incised etch surfaces.