bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial patterns and seasonal variation of snowpack sulphate isotopes of the Prince of Wales Icefield, Ellesmere Island, Canada
Authors: Wasiuta Vivian , Norman Ann-Lise , Marshall Shawn
Published: November 2007

Ion-chemistry and sulphate-isotope values for snow samples from the Prince of Wales Icefield, Ellesmere Island, Canada, show distinct seasonal trends and spatial patterns. Sixteen surface snow samples from two transects, and 30 samples from five depth profiles, representing fall 2003 to spring 2004 accumulation, have been analyzed. Surface snow samples show decreasing SO42– and Na+ concentrations along with decreasing δ34S values with distance inland and increased elevation. These trends follow an expected pattern of decreasing sea-salt aerosol impact with greater vertical and horizontal distance from sea-water sources. Depth-profile total sulphate and non-sea-salt sulphate increase in concentration with height in the snowpack, and these results, combined with δ34S values that are more positive in fall snow, are consistent with increased amounts of anthropogenic sulphate in surface spring snow. Sulphate apportionment was performed on surface snow assuming an isotopically light sulphate source (anthropogenic plus volcanic) mixed with isotopically heavier sulphate from dimethylsulphide (DMS) oxidation and sea water. Isotopically light sulphate in surface snow was apparent at all elevations at a reasonably uniform concentration. DMS sulphate, however, decreased exponentially with altitude, reflecting an ocean level source with oxidation occurring during transport and deposition. The significance to multi-year deposition studies is that sulphate from DMS oxidation may be related to sea-ice conditions in the region.
Application of a degree-day model for the determination of contributions to glacier meltwater and runoff near Keqicar Baqi glacier, southwestern Tien Shan
Authors: Zhang Yong , Liu Shiyin , Xie Changwei , Ding Yongjian
Published: November 2007

A so-called ‘warm and wet transition’ of climate has occurred in the arid part of northwestern China since the late 1980s. A result of this climatic transition is an increase in runoff in Xinjiang and neighboring regions. In a warming and wetting change-of-climate scenario, we attempt to evaluate the impact of glacier meltwater and precipitation on the increase in outlet discharge (runoff) from Keqicar Baqi glacier, southwestern Tien Shan, China. In our research we have applied a degree-day model which is one of the most widely used methods of ice- and snowmelt computations for a multitude of purposes such as hydrological modeling, ice-dynamic modeling and climate sensitivity studies. It is concluded that under the warming and wetting scenario, the primary supply for the runoff in this catchment is glacier meltwater, with precipitation being the dominant secondary source; 84% and 8% of total runoff, respectively.
Strong negative correlation between dust event frequency and air temperature over the northern Tibetan Plateau reflected by the Malan ice-core record
Authors: Wang Ninglian , Yao Tandong , Thompson L.G. , Davis M.E.
Published: November 2007

In this paper, the ratio of dust layer thickness to ice thickness, i.e. the dust ratio, is used as a proxy for dust event frequency in the Malan ice core from the northern Tibetan Plateau. We reconstructed a ∼900 year record that reveals that the 1770s–1880s was a prolonged period of high dust ratios, which indicates that dust events occurred frequently from the late 18th century through the 19th century. Statistical analysis of the variations in the dust ratios and δ18O (which is a good proxy for air temperature) in the Malan ice core shows that there is a strong negative correlation between them. This suggests that dust events occur more frequently in cold periods than in warm periods.
Glacier changes during the past century in the Gangrigabu mountains, southeast Qinghai–Xizang (Tibetan) Plateau, China
Authors: Liu Shiyin , Shangguan Donghui , Ding Yongjian , Han Haidong , Xie Changwei , Zhang Yong , Li Jing , Wang Jian , Li Gang
Published: November 2007

The present research focuses on glacier changes in the southeast of the Qinghai–Xizang (Tibetan) Plateau, where most of the temperate glaciers in China are located. Our results show that the 102 measured glaciers in the region have all retreated between 1915 and 1980, with total area and volume decreases of 47.9 km2 and 6.95 km3, respectively. The extrapolated mass loss of all glaciers in the Gangrigabu mountains amounted to 27 km3, 9.8% of the ice mass in 1915. Between 1980 and 2001, glaciers in the region have also experienced a general retreat; however, up to 40% of the glaciers were advancing. Our analysis demonstrates that precipitation in the studied area has increased substantially since the mid-1980s. This precipitation increase is likely to bring about a positive mass balance for glaciers in the region, so that the retreat of retreating glaciers might slow down or even turn into advance. Considering the sensitivity of the temperate glaciers in the region and the uncertainty in climate projections, more attention must be paid to glacier changes in the southeast Tibetan Plateau region.
Holocene climate variability archived in the Puruogangri ice cap on the central Tibetan Plateau
Authors: Thompson Lonnie G. , Tandong Yao , Davis Mary E. , Mosley-Thompson Ellen , Mashiotta Tracy A. , Lin Ping-Nan , Mikhalenko Vladimir N. , Zagorodnov Victor S.
Published: November 2007

Two ice cores (118.4 and 214.7 m in length) were collected in 2000 from the Puruogangri ice cap in the center of the Tibetan Plateau (TP) in a joint US-Chinese collaborative project. These cores yield paleoclimatic and environmental records extending through the Middle Holocene, and complement previous ice-core histories from the Dunde and Guliya ice caps in northeast and northwest Tibet, respectively, and Dasuopu glacier in the Himalaya. The high-resolution Puruogangri climate record since AD 1600 details regional temperature and moisture variability. The post-1920 period is characterized by above-average annual net balance, contemporaneous with the greatest 18O enrichment of the last 400 years, consistent with the isotopically inferred warming observed in other TP ice-core records. On longer timescales the aerosol history reveals large and abrupt events, one of which is dated ∼4.7 kyr BP and occurs close to the time of a drought that extended throughout the tropics and may have been associated with centuries-long weakening of the Asian/Indian/African monsoon system. The Puruogangri climate history, combined with the other TP ice-core records, has the potential to provide valuable information on variations in the strength of the monsoon across the TP during the Holocene.
Monitoring the glacier changes in the Muztag Ata and Konggur mountains, east Pamirs, based on Chinese Glacier Inventory and recent satellite imagery
Authors: Shangguan Donghui , Liu Shiyin , Ding Yongjian , Ding Lianfu , Xiong Libing , Cai Dihua , Li Gang , Lu Anxin , Zhang Shiqiang , Zhang Yong
Published: November 2007

Glaciers in the Muztag Ata and Konggur mountains of the eastern Pamir plateau, northwestern China, have been monitored by applying aerial photo stereo models (1962/66) and Landsat TM (1990) and ETM+ (1999) images, all of which have been compared in order to detect areal and frontal changes through the past four decades. The mean frontal retreat of glaciers in the Muztag Ata and Konggur mountains increased from 6.0 ma−1 between 1962/66 and 1990 to 11.2ma−1 between 1990 and 1999, with an overall glacier length reduction of 9.9% for the whole study period. The glacier area has decreased by 7.9%, mainly due to changes observed in the most recent period (1990–99), when the annual area loss almost tripled to 1.01 km2 a−1. Based on meteorological data from Taxkogan station since 1957, we conclude that climate change, particularly the rise in summer temperature after 1994, is the main forcing factor in glacier shrinkage.
Atmosphere-to-snow-to-firn transfer of NO3− on Ürümqi glacier No. 1, eastern Tien Shan, China
Authors: Zhao Zhongping , Li Zhongqin , Edwards Ross , Wang Feiteng , Li Huilin , Zhu Yuman
Published: November 2007

In order to investigate the relationship between atmospheric nitrate and nitrate records in glacial snow and firn, nitrate was investigated in atmospheric aerosol, surface snow and the snow–firn pack on Ürümqi glacier No. 1 , eastern Tien Shan, China, from September 2002 to September 2004. The study found that vertical nitrate stratigraphy in the upper snowpack is formed during the winter by dry deposition and compaction and sublimation of the snowpack. During the summer the snowpack nitrate is redistributed through the percolation of meltwater. Nitrate was found to be highly mobile in the snowpack relative to magnesium.
A comparison of tree-ring records and glacier variations over the past 700 years, northeastern Tibetan Plateau
Authors: Gou Xiaohua , Chen Fahu , Yang Meixue , Jacoby Gordon , Peng Jianfeng , Zhang Yongxiang
Published: November 2007

The ecological environment of the headwater area of the Yellow River, west China, is seriously deteriorating because of the harsh natural environment, weakened ecological systems and intensified human activities as well as regional climate changes. Forests and glaciers coexist in this area. Glaciers in the area have retreated over the last decade because of climate change. Most glaciers on the Tibetan Plateau (TP) tend to retreat during warm intervals and advance during cold intervals. Tree-ring records provide an important index for examining past climate changes. A total of 139 core samples from 97 living cypresses (Juniperus przewalskii) in the central region of the Yellow River headwater area, the Animaqin mountains, northeastern TP, were sampled from three sites that are close to each other. The chronologies were developed using the ARSTAN program. Analyses indicate that these tree-ring width records reflect the summer maximum temperature of the study area over the past 700 years. The tree-ring records and the glacier advances recorded by terminal moraines are compared. Inferred summer maximum temperatures suggest three cold periods during the Little Ice Age, around AD1500, 1700 and 1850. These cold intervals are consistent with the glacier moraine record from the region.
Accumulation studies on Amundsenisen, Dronning Maud Land, Antarctica, by means of tritium, dielectric profiling and stable-isotope measurements: first results from the 1995–96 and 1996–97 field seasons
Authors: Oerter Hans , Graf Wolfgang , Wilhelms Frank , Minikin Andreas , Miller Heinz
Published: November 2007

The paper focuses on studies of snow-pit samples and shallow firn cores taken during the 1995-96 and 1996-97 field seasons at Amundsenisen, Dronning Maud Land, Antarctica. The dating of the firn is based on the artificial tritium distribution in the snow cover and on several reference horizons identified by electrical measurements. The early 1964 through 1965 horizon is marked by the deposition of sulfate released to the atmosphere during the eruption of the Agung volcano in March 1963; this horizon was detected by dielectric profiling and electrical conductivity measurements: the proof by chemical analysis has still to be seen. At the ten investigated sites on Amundsenisen the 1964-65 horizon was identified 4.1-5.7 m below the surface. The accumulation rates on Amundsenisen are 41-91kg m-2 a−1 The cores are up to 100 years old A relationship between isotope content and the mean air temperature on a regional scale can be based on measurements of firn temperature at 10 m depth at the drilling sites Between Neumayer station at the coast and Heimefrontfiella, the temperature gradient of the deuterium content is 9.6%0 K−1. South of Heimefrontfiella, on the Amundsenisen plateau, it is only 5.5‰ K−1. Time series of yearly accumulation rates show no significant trend For the isotope records a significant trend to higher values with gradients of 0.1-0.2 δ2H‰a−1 can be seen in five of the ten time series
Sea-spray and marine biogenic seasonal contribution to snow composition at Terra Nova Bay, Antarctica
Authors: Udisti R. , Becagli S. , Castellano E. , Traversi R. , Vermigli S. , Piccardi G.
Published: November 2007

Primary and secondary marine aerosol contributions to snow composition in Terra Nova Bay Antarctica, were evaluated by chemical analysis of surface and snow-pit samples. A seasonal pattern of marine inputs, very clear for secondary aerosol (mainly constituted by nssSO4- and methanesulphonic acid (MSA) coming from phytoplanktonic activity) and less evident for sea spray (Na+, CF, Mg2+) was shown by snow-pit samples. Altitude and distance from the coast were found to be the main parameters affecting seasonal change in the composition of snow collected within about a 200 km radius of the Terra Nova Bay Italian base. Using Na+ as a sea-spray indicator and MSA as a biogenic marker, fractionating aerosol effects (which are altitude-induced) as well as source contributions for Cl- and nssSO42- were found. A nssSO42- /MSA ratio of 2.7 (w/w), indicating their distribution from the common source dimethylsulphide, was calculated from Analysis of fresh summer snow collected in horizontal and vertical transects in northern Victoria Land.
Sulfur-containing species in a snow pit in the Lambert Glacier basin, East Antarctica
Authors: Junying Sun , Jiawen Ren , Dahe Qin , Xiaoxiang Wang
Published: November 2007

A 2.7 m snow pit was sampled in the Lambert Glacier basin, about 650 km from the coast. Concentrations of methanesulfonic acid (MSA) and non-sea-salt SO42- (nssSO42-) show distinct variation with depth in the snow pit. The seasonal variation of MSA is used to date the snow-pit samples. MSA concentration is in the range 1.922.0 μgkg−1 with a mean of 7.0 μgkg-1. The mean nssSO42- concentration is 41.5 μgkg−1 with a range of 0-87 μgkg−1. The nssSO42- ∼ concentration was calculated by subtracting the sea-salt sulfate contribution using Nai as a conservative tracer. The nssSO42– contributes about 80% of the total sulfate in the snow pit. The mean mass ratio of MSA to nssSO42- 0.176, is much higher than that measured in the low to mid-latitudes, but is very close to the ratio in snow at the South Pole. El Chichon and Hudson volcanic eruptions do not significantly perturb the nssS042- concentrations at this site. MSA concentrations are anticorrelated with sea-ice area for the South Indian Ocean sector between 40° and 90° E, suggesting enhanced MSA production accompanying low sea-ice coverage.
Investigations of the mass balance of the southeastern Ronne Ice Shelf, Antarctica
Authors: Lambrecht A. , Mayer C. , Oerter H. , Nixdorf U.
Published: November 2007

Data from the Filchner V Campaign were used to investigate the mass-balance conditions in the southeastern Ronne Ice Shelf (RIS), Antarctica. Radio-echo sounding and seismic measurements over this area show a maximum ice thickness of >2000 m close to the grounding line of Foundation Ice Stream. The measurements also revealed that the position of this grounding line is 40 km further south than previously thought. New mass-flux calculations result in an estimate of 51 km3 a−1 for the ice-stream transport from the ice sheet into the eastern ice shelf. The Mollereisstrom (MES), west of Foundation Ice Stream, shows a maximum ice thickness of 1100-1200 m in the grounding-line area and a mass flux of 23 km3 a−1.

Assuming steady-state conditions, mass-balance calculations based on the new data result in a mean melt rate of about 1 ma−1 at the ice-shelf base for the entire southeastern part of the RIS. The melt rate in the grounding-line area of Foundation Ice Stream exceeds 9 m a−1. In contrast, other ice streams draining into the Filchner-Ronne Ice Shelf show maximum melt rates from 1-2 ma-1. (MES) to 4 ma−1 (Rutford Ice Stream). Our calculations indicate that nearly all of the ice deposited in the drainage area of the eastern RIS on the ice sheet does not reach the ice-shelf front as original meteoric ice, but is melted at the ice-shelf base.
Variability in snow layering and snow chemistry in the vicinity of two drill sites in western Dronning Maud Land, Antarctica
Authors: Stenberg Malin , Hansson Margareta , Holmlund Per , Karlöf Lars
Published: November 2007

As part of the pre-site survey in Dronning Maud Land for the European Project for Ice Goring in Antarctica (EPICA), the spatial variability of snow-layer thickness and snow chemistry was studied at two geographically different ice-core drill sites. The study aimed to quantify error bars on accumulation rates derived from firn and ice cores. One site is located on the polar plateau at Amundsenisen (76° S, 8° W) and the other in the coastal area at Maudheimvidda (73° S, 13° W). Medium-deep ice cores (100 m) and shallow firn cores (10-20 m) were drilled and snow pits (0.5-2 5 m) were dug at each site. At Amundsenisen a large (16 m x 6 m x 2.5 m deep) snow pit was dug. Snow structure in this large snow pit was mapped using optical surveying equipment, and photographically documented. Samples for analysis of nine ions and oxygen isotopes were collected along one depth profile. Density and in situ electrical conductivity measurements were made along three depth profiles! Snow-layer variability was studied in two different areas and at two different scales. At a regional scale, measured by snow-radar soundings, the variability was 8% on the polar plateau and 45% in the coastal area. The variability at a micro-scale in the large snow pit was 9%. The results indicate that ice cores from the polar plateau are more representative for a larger area than ice cores drilled in the coastal area There is no doubt that there are significant error bars on high-resolution accumulation data received from firn and ice cores, especially from the coastal area, but averaging over tens of years reduces the error in accumulation estimates.
New evidence for enhanced cosmogenic isotope production rate in the atmosphere ∼37 ka BP
Authors: Ninglian Wang , Tandong Yao , Dahe Qin , Thompson L. G. , Mosley-Thompson E. , Cole-Dai J. , Davis M. E. , Lin P.-N.
Published: November 2007

A 36C1 peak has been found at about 37 ka BP in the Guliya ice core, drilled from the Qinghai-Tibetan Plateau. This peak is indicative of enhanced cosmogenic isotope production in the atmosphere, rather than a change in accumulation rate. Comparison with the records of 10Be and 36C1 in ice cores from Antarctica and Greenland indicates that peaks of the cosmogenic isotopes are global, and that they can be used as time markers for dating ice cores. Interestingly, the 37 ka BP global event coincided with a cold period.
Monte Carlo inverse modelling of the Law Dome (Antarctica) temperature profile
Authors: Dahl-Jensen Dorthe , Morgan Vin I. , Elcheikh Alan
Published: November 2007

The temperature profile in the 1200 m deep Dome Summit South (DSS) borehole near the summit of Law Dome, Antarctica, was measured in 1996, 3 years after the termination of the deep drilling.

The temperature profile contains information on past surface temperature over the last 4ka. This temperature history is determined by the use of a Monte Carlo inverse method in which no constraints are placed on the unknown temperature history and no solution is assumed to be unique. The temperature history is obtained from a selection of equally well-fitting solutions by a statistical treatment.

The results show that solutions covering the last 4ka have a well-developed central value, a most likely temperature history. The temperature record has two well-developed minima at AD 1250 and 1850. From 1850 to the present, temperatures have gradually increased by 0.7 K. The reconstructed temperatures are compared with the stable oxygen isotope (δ18O) from the DSS ice core.
Volcanic eruptions recorded in an ice core from Collins Ice Cap, King George Island, Antarctica
Authors: Jiankan Han , Zichu Xie , Fengnian Dai , Wanchang Zhang
Published: November 2007

Careful mineral and structural analyses have revealed the characteristics of volcanic ash in the nine horizons of an 80.2 m ice core from Collins Ice Cap, King George Island, Antarctica.

Under the assumption of steady state, the Dansgaard-Johnsen flow model was employed to date the core. The volcanic eruptive sequence established for the South Shetland Islands region since AD 1650 shows seven volcanic eruptive cycles during the past 340 years covered by the ice core. It seems that during the period 1875-1925 there was frequent volcanic activity, with perhaps many eruptions at Deception Island. The years 1650-1800 appear to have been a quiet period, followed by a more turbulent century. The past century is basically a tranquil era except for two turbulent epochs at the beginning of the century and in the 1950s-70s.

Many of the volcanic eruptions in the ice-core sequence are found in the previously reported records for this region. The few that are not in the records should be further investigated. The absence of any 1967-70 eruption trace in the core suggests that this period may represent a minimum in volcanic activity.
Textures and fabrics in the Dome F (Antarctica) ice core
Authors: Azuma N. , Wang Y. , Mori K. , Narita H. , Hondoh T. , Shoji H. , Watanabe O.
Published: November 2007

A comprehensive study of ice-crystal fabrics and textures was conducted on the Dome F (Antarctica) ice core. Crystal ,-axis orientations, crystal sizes and crystal shape were measured on thin sections with an automatic ice-fabric analyzer. The general feature of textural and fabric development through a 2500 m long core was obtained by a 20 m interval study. Crystal size steadily increases with depth except for depths of about 500,1800, 2000, 2200 and 2300 m, at which depths crystal size decreases suddenly. There is a clear correlation between crystal-size and ´18O values. Crystals tend to elongate horizontally with depth, and the aspect ratio (long axis vs short axis of a grain) increases twofold at 1600 m depth and fluctuates below that depth. The .-axis orientation fabrics gradually change with depth from a random orientation pattern near the surface to a strong vertical single maximum at 2500 m. These are very similar to those from the GRIP (Greenland) core The observations of crystal shape and the fabric measurements indicate that nucleation-recrystallization does not take place at Dome F.
Seasonal variations of glaciochemical, isotopic and stratigraphic properties in Siple Dome (Antarctica) surface snow
Authors: Kreutz K. J. , Mayewski P. A. , Twickler M. S. , Whitlow S. I. , White J. W. C. , Shuman C. A. , Raymond C. F. , Conway H. , McConnell J. R.
Published: November 2007

Six snow-pit records recovered from Siple Dome, West Antarctica, during 1994 are used to study seasonal variations in chemical (major ion and H202), isotopic (deuterium) and physical stratigraphic properties during the 1988-94 period. Comparison of δD measurements and satellite-derived brightness temperature for the Siple Dome area suggests that most seasonal SD maxima occur within ±4 weeks of each 1 January. Several other chemical species (H2O2, non-sea-salt (nss) SO42-, methanesulfonic acid and NO3-) show coeval peaks with SD, together providing an accurate method for identifying summer accumulation. Sea-salt-derived species generally peak during winter/spring, but episodic input is noted throughout some years. No reliable seasonal signal is identified in species with continental sources (nssCa2+ nss Mg2+), NH4+ or nssCl-. Visible strata such as large depth-hoar layers (>5 cm) are associated with summer accumulation and its metamorphosis, but smaller hoar layers and crusts are more difficult to interpret. A multi-parameter approach is found to provide the most accurate dating of these snow-pit records, and is used to determine annual layer thicknesses at each site Significant spatial accumulation variability exists on an annual basis, but mean accumulation in the sampled 10 km2 grid for the 1988-94 period is fairly uniform.
The response of the Ekströmisen (Antarctica) grounding zone to tidal forcing
Authors: Riedel Björn , Nixdorf Uwe , Heinert Michael , Eckstaller Alfons , Mayer Christoph
Published: November 2007

During the austral summer 1996–97 an extensive field program with geophysical and geodetic observations was carried out in the vicinity of the grounding line of Ekstromisen, Dronning Maud Land, Antarctica. The main emphasis of the joint program was placed on continuous observations of the horizontal as well as the vertical component of the ice displacement across the grounding zone. Data-processing methods for the in parts discontinuous time series and the vertical displacements in the area of the grounding zone are described, and first results presented, with the focus on the influence of the ocean tides on grounded ice. Tidal-induced deflections with amplitudes of up to 0.15 m were recorded at a station on grounded ice 1 km from the grounding line.
34 year satellite time series to monitor characteristics, extent and dynamics of Larsen B Ice Shelf, Antarctic Peninsula
Authors: Skvarca Pedro , Rack Wolfgang , Rott Helmut
Published: November 2007

A variety of data are used to investigate Larsen B, which is at present the northernmost section of the Larsen Ice Shelf, Antarctic Peninsula. Recently declassified U.S. Argon satellite photographs from 1963 Kosmos photographs from 1975, Landsat images from 1986,1988 and 1990, ERS-1/2 synthetic aperture radar images from 1992-97, Radarsat from 1998 and field surveys are used to analyze the areal extent, surface characteristics and dynamic behaviour of this ice-shelf section over more than three decades. Visible and radar imagery together with field observations are used synergistically to describe the ice-shelf morphology, including meltwater features and rifts. In contrast to the retreat of the ice-shelf sections in the north, Larsen B advanced steadily from 1963 to early 1995, when the area decreased significantly due to a major calving event. Analysis of different satellite images indicates that melting is proceeding further south in accordance with the regional warming trend. In addition? fracturing processes and rapid development of new rifts are observed, associated with recent acceleration of ice motion close to the front. All observations predict major calving events for this ice-shelf section in the near future.
Near-surface temperatures in the Dome Summit South (Law Dome, East Antarctica) borehole
Authors: van Ommen T. D. , Morgan V. I. , Jacka T. H. , Woon S. , Elcheikh A.
Published: November 2007

Firn temperatures at the Dome Summit South drill site, East Antarctica, are simulated by driving a thermal model of the ice sheet with observed instrumental records over the period 1960-96. The model incorporates firn density and thermal properties to reproduce measured borehole temperatures as shallow as 5 m below the surface, where the seasonal temperature wave is readily apparent. The study shows that ice-sheet temperatures are approximately 0.8°C cooler than mean 4 m air temperatures. It also finds that non-conductive processes such as ventilation and radiation can be simulated at this site by assuming perfect thermal contact between the top ∼1 m of firn and the atmosphere on monthly time-scales.
The paleoclimate record in the ice core at Dome Fuji station, East Antarctica
Authors: Watanabe Okitsugu , Kamiyama Kokichi , Motoyama Hideaki , Fujii Yoshiyuki , Shoji Hitoshi , Satow Kazuhide
Published: November 2007

The Antarctic ice sheet preserves paleoclimate information in the form of physical and chemical stratigraphy. A deep ice core down to 2503 m depth was drilled at Dome Fuji station, East Antarctica, during the 1993-96 Japanese Antarctic Research Expedition inland operations. Oxygen isotope measurements were conducted on 50 cm long samples selected from the entire core length. A palco-temperature profile was obtained for the past 340 ka by assuming the same conversion factors for the past relation as exist today between isotope ratio and both surface temperature and accumulation rate, in the inland region of Dronning Maud Land. The environmental-index profiles such as major chemical and dust contents coincide quite well withVostok ice-core data in general but not in detail. Detailed analysis of these climatic and environmental signals is in progress.
Evidence for water storage and drainage at the base of the Laurentide ice sheet, south-central Alberta, Canada
Authors: Munro-Stasiuk Mandy J.
Published: November 2007

Glaciogenic sediment up to 70 m thick is exposed in preglacial valley fills in south-central Alberta. The two youngest facies are comprised of glaciolacustrine sediments overlain by a subglacial till. Conformable relationships with the till and topographic relationships support a subglacial origin for the lake sediments. As these facies are restricted to the preglacial valley system, it is suggested that the preglacial valleys of south-central Alberta acted as natural cavities at the base of the Laurentide ice sheet. Sedimentology suggests these filled and drained often.
Paleoclimatic interpretation of the early Late-glacial glacier in the Gschnitz valley, central Alps, Austria
Authors: Kerschner Hanns , Ivy-Ochs Susan , Schlüchter Christian
Published: November 2007

The former glacier at the type locality of the “Gschnitz Stadial” of the Alpine Late-glacial chronology is interpreted from a paleoglaciological and paleoclimatological point of view. The equilibrium-line altitude, ice flux through selected cross sections and mass-balance gradients are calculated from reconstructed glacier topography. They are used to determine total net ablation and accumulation and precipitation under the assumption of steady-state. The former temperature at the ELA and temperature change is estimated using various glacier—climate models. Precipitation was less than one-third of today’s values, and summer temperature was roughly 10°C lower than today. The climate during the Gschnitz Stadial appears to have been cold and continental, and was more similar to full glacial conditions than to the Younger Dryas climate in the Alps. This is further evidence for an older age of the Gschnitz Stadial.
Occurrence of rocky and sedimentary glacier beds in the Swiss Alps as estimated from glacier-inventory data
Authors: Maisch Max , Haeberli Wilfried , Hoelzle Martin , Wenzel Jörg
Published: November 2007

The occurrence of rocky and sedimentary glacier beds in the Swiss Alps was investigated using two approaches: (1) a detailed and systematic classification of glacier forefields in the completely revised Swiss glacier inventory; and (2) the application of an algorithm for estimating bed characteristics from glacier-inventory data. The algorithm is based on the assumption that the sediment balance of a glacierized catchment, i.e. the ratio between debris input from the surrounding rock walls and debris evacuation by the meltwater stream, determines the occurrence of rocky, sedimentary or mixed beds. The processes which govern the sediment balance within a glacierized catchment cannot be easily observed or measured in the field. However, the main factors reflecting them can be organized in the form of an erosion—sedimentation index. This index discriminates between glaciers eroding into bedrock and those building up thick sediment beds and, thus, allows for rough assessments concerning bed characteristics. Sedimentary and mixed sedimentary—rocky glacier beds clearly predominate in the Swiss Alps, but more detailed spatial analysis is required for better predictions.
Characteristics of Khumbu Glacier, Nepal Himalaya: recent change in the debris-covered area
Authors: Nakawo M. , Yabuki H. , Sakai A.
Published: November 2007

Using satellite data, the longitudinal distribution of the ablation rate and flow velocity were estimated for the ablation area, where glacier ice is covered with supraglacial debris. The ablation rate, small around Everest Base Camp (EBC) just below the equilibrium line, increased down-glacier for about 3 km, then decreased gradually toward the apparent terminus, located about 10 km from EBC. The velocity decreased almost linearly from EBC to the terminus. The results allowed estimation of the recent change of ice thickness using the continuity equation. The glacier has thinned recently in the ablation area. The rate of thinning was large near EBC, where the surface is either bare ice or covered with very thin debris cover, but relatively small and rather uniform at lower sites, where the supraglacial debris layer was thick and supraglacial lakes and ice cliffs predominate. The general pattern is compatible with field observations.
Basal ice temperatures during late Weichselian deglaciation: comparison of landform assemblages in west-central Sweden
Authors: Borgström Ingmar
Published: November 2007

The mountainous area of west-central Sweden has a varied glacial morphology and three unique landform assemblages appear to mark areas of different basal thermal conditions during the decay of late Weichselian ice. A glacial geomorphological map was constructed through interpretation of aerial photographs at a scale 1:60 000. The relative abundance of landforms interpreted to indicate a frozen bed, a thawed bed, and late-frozen to thawed-bed conditions were used for a first-order reconstruction of the basal temperature pattern of the decaying ice sheet. The features used to outline areas with different temperature regimes during deglaciation are glacial scouring, flutings, eskers, meltwater channels, boulder blankets, Rogen moraines, relict surfaces and thermoerosion features.

In the northern part of the area, as well as along most of the water divide to the Atlantic Ocean, the ice was warm-based during deglaciation. Glacially scoured bedrock, fluting/ drumlinization, subglacial eskers and extensive glacial lake sediments characterize the area. In the high mountain area, lateral meltwater channels are short and curve downslope to form chutes or eskers. The basal ice conditions changed from frozen- to thawedbed in a late stage of the late Weichselian cycle in most of the southern part of the area, shown by the Rogen moraines on both sides of the ice divide. However, substantial areas in the eastern and southern low mountains had frozen-bed conditions during the complete late Weichselian. In the high mountains in the north, only the summits were frozen.
Grain textural analysis across a range of glacial facies
Authors: Khatwa A. , Hart J. K. , Payne A. J.
Published: November 2007

A technique proposed by Hooke and Iverson (1995) to identify deformed subglacial sediments is reviewed and tested, based on two main objectives. First, an investigation of whether the fractal dimension can distinguish between non-deformed and deformed facies; for which we compare supraglacial and subglacial facies explicitly. Second, an evaluation of whether the fractal dimension can be used as a diagnostic criteria to discriminate between different styles and degrees of basal deformation. This is tested using a range of sediments from the deformation continuum suggested by Hart and Boulton (1991b). Sixteen subglacial samples were selected from Quaternary sites in England and three supraglacial samples from the modern Haut Glacier d’Arolla, Switzerland. The mean fractal dimension for the subglacial diamicton matrix facies was 2.92, similar to findings of 2.90 by Hooke and Iverson (1995) for their basal tills. The supraglacial facies displayed a mean fractal dimension of 2.83, which is unusually high for facies which are assumed to be undeformed. A Mann—Whitney U test showed that fractal dimensions of supraglacial and subglacial diamicton matrix facies were not significantly different. No significant difference was found between the fractal dimensions of the different tectonic facies within the subglacial group. It may be impossible to separate the subglacial and supraglacial facies because of complex debris paths within the glacier. Grain fracture or parent lithology may affect the particle-size distribution of subglacial facies.
Palimpsest tunnel valleys: evidence for relative timing of advances in an interlobate area of the Laurentide ice sheet
Authors: Kehew Alan E. , Nicks Linda P. , Straw W. Thomas
Published: November 2007

During retreat from the lateWisconsinan maximum advance in the Great Lakes region of North America, the Laurentide ice sheet margin became distinctly lobate. The Lake Michigan, Saginaw, and Huron—Erie lobes converged in southern Michigan and Indiana, U.S.A. to form a complex interlobate region. Some time after the glacial maximum, the Lake Michigan lobe advanced over landscapes previously formed by the Saginaw lobe. This can be explained by an asynchronous advance of the Lake Michigan lobe during a Saginaw lobe retreat or by an increase in size of the Lake Michigan lobe relative to the Saginaw lobe during a synchronous readvance.

Cross-cutting relationships in southwestern Michigan, including palimpsest tunnel valleys, document the overriding of Saginaw lobe terrain. Deep, generally straight trenches parallel to glacial flow lines with hummocky, irregular sides and bottoms are interpreted as tunnel valleys. Saginaw lobe tunnel valleys trend northeast—southwest and Lake Michigan lobe tunnel valleys generally trend east—west.

At some time after a Saginaw lobe retreat in southern Michigan, the drumlinized landscape was overridden by an advance of the Lake Michigan lobe to an ice-marginal position at the Tekonsha moraine. Saginaw lobe tunnel valleys in the overridden area were completely filled with ice and debris from the Saginaw lobe retreat at the time of the Lake Michigan lobe advance. Supraglacial and proglacial sediments were deposited over the buried valleys by the Lake Michigan lobe, sometimes by meltwater streams that flowed at high angles to the trends of the valleys. After entrenchment of the Kalamazoo River valley, probably by a subglacial outburst flood, short tributaries were cut nearly at right angles across and through the debris and ice within several buried Saginaw lobe tunnel valleys. After the retreat of the Lake Michigan lobe, subsequent melting of ice in the palimpsest tunnel valleys exhumed the valleys, creating the cross-cutting relationships with the Lake Michigan lobe deposits.
Assessment of requirements for cirque formation in northern Sweden
Authors: Jansson Peter , Richardson Cecilia , Jonsson Stig
Published: November 2007

Cirques in the Rassepautasjtjåkka massif currently lack glaciers and the geomorphology indicates that no glaciers occupied the cirques during the Holocene. The current climatic conditions in the cirques can be assessed using available climatic data; air temperature at Rassepautasjtjåkka, summer and winter balances of adjacent glaciers, and general precipitation patterns in northern Sweden. The data suggest that either a significant change in precipitation and wind regime or a moderate change in temperature is required to initiate a cirque glacier in the massif. Formation of a wet-based erosive glacier requires warmer winters with higher accumulation rates, equivalent to a more maritime influence in the area. Studies of current atmospheric circulation suggest that strong west- east circulation, associated with a northerly position of the polar front, is favourable for increased accumulation. Using typical erosion rates from present glaciers, we see that ~ 10% of the last 3 Myr may be required for forming the Rassepautasjtjåkka cirques. This is a significant portion of time since most of the glacial cycles are spent in states of interglacials, maximum glaciation or mountain-based glaciation. Marine sediments from the Norwegian Sea provide indications of minor glaciations back to ~12.6 Myr and, hence, cirque-formation periods are not restricted to Quaternary. Thus, it is possible that many cirque forms have a much longer history than previously recognized.
Ice composition evidence for the formation of basal ice from lake water beneath a cold-based Antarctic glacier
Authors: Lorrain R. D. , Fitzsimons S. J. , Vandergoes M. J. , Stiévenard M.
Published: November 2007

Entrainment of debris by cold-based glaciers having basal temperatures as low as — 17°C can be observed in the Dry Valleys of south Victoria Land, Antarctica. The classical models developed to explain debris incorporation at the glacier base are inappropriate in such cases, since the basal temperature is well below the freezing point. An alternative model, based on the presence of ice-marginal lakes, has recently been proposed by one of the authors (S. F.). In this model, transient wet-base conditions can occur as ice flows onto the unfrozen sediments of the lake bottom, creating conditions favorable to the entrainment of sediments and to ice accretion by water freezing.

Here we describe a situation where this model is consistent with an ice-composition study of the basal part of Suess Glacier, Taylor Valley. The stable isotope composition indicates that water freezing, most probably lake water, plays a major role in the formation of the basal ice layers. Total gas content of this basal ice is considerably depleted when compared to meteoric glacier ice, in accordance with a rejection mechanism during freezing. Its gas composition, strongly enriched in CO2, is also indicative of the presence of a former liquid phase.
Plateau icefields as contributing areas to valley glaciers and the potential impact on reconstructed ELAs: a case study from the Lyngen Alps, North Norway
Authors: Rea Brice R. , Whalley W. Brian , Dixon Tom S. , Gordon John E.
Published: November 2007

Plateau icefields occur commonly in glacierized areas and not uncommonly in glaciated mountains. We report on a glacierized area of plateaux and valleys centred round the highest peak Jiehkkevárri (1833 m) in the maritime Lyngen Alps, North Norway. Some valley glaciers are fed by steep, narrow plateau glacier outlets and/or ice avalanching from the plateaux over precipitous cliffs. Plateaux must therefore be considered as “contributing areas”, if they supply ice to valley systems below. Equilibrium line altitudes (ELAs) are calculated for the valley glaciers during the Little Ice Age (LIA), accounting for both input and no input of ice from plateaux above. The results show that ELAs may be at significantly higher altitudes when plateau/x are contributing ice mass. The response of plateau glaciers to climate amelioration since the end of the LIA is somewhat different to that of valley glaciers, which appear to be retreating markedly. These findings have significant implications for the interpretation of moraine systems, glacier dynamics, the construction and reconstruction of present and former ELAs, and palaeoclimates in glacierized and glaciated mountain plateau areas.
Multi-scale analyses of subglacial and glaciomarine deposits from the Ross Sea continental shelf, Antarctica
Authors: Kluiving S. J. , Bartek L. R. , van der Wateren F. M.
Published: November 2007

Piston cores collected from the Ross Sea continental shelf, Antarctica, were studied as part of a multi-scale analysis of glacial and glaciomarine stratigraphy and sedimentology. The objective of these analyses was to differentiate glaciomarine sediments from subglacially deformed tills. Results from analyses of microstructures, lithofacies and seafloor morphology indicate that glaciomarine and subglacially deformed sediments can be clearly distinguished and further characterized by variations in textural parameters. Overcompaction, as well as presence of stratification in sediments, are not considered critical criteria for distinguishing subglacial from glaciomarine deposits. Trough-shaped morphologies and fluted terrain strongly correlate with S-C and S-C-C- type shear-zone microstructures and indicate that subglacial deformation is an important process in these areas, confirming the presence of grounded ice on the shelf during formation of these landforms and deposits. Flat, smooth topographies, as well as (low-angle) slope environments, correspond to microfabrics which lack microscopic shear-zone geometries and contain dropstones, angular-sediment clasts, large-shell fragments and slight sorting in sandy layers, which imply ice-shelf or open-water conditions present during deposition.
Measurement and parameterization of albedo variations at Haut Glacier d’Arolla, Switzerland
Authors: Brock Ben W. , Willis Ian C. , Sharp Martin J.
Published: November 2007

Spatial and temporal variations of surface albedo on Haut Glacier d’Arolla, Switzerland, during the 1993 and 1994 ablation seasons are described. Correlation and regression analyses are used to explain the albedo variations in terms of independent meteorological and surface property variables. Parameterizations are developed which allow estimation of albedo variation in surface energy-balance models. Snow albedo is best estimated from accumulated daily maximum temperatures since snowfall. On “deep” snow (≥0.5 cm w.e. depth) a logarithmic function is used, while on “shallow” snow (<0.5 cm w.e. depth) an exponential function is used to enable the albedo to decay to the underlying ice or debris albedo. The transition from “deep” to “shallow” snow is calculated as a function of decreasing snow depth (combined r2 = 0.65). This new parameterization performs better than earlier schemes because accumulated daily maximum temperatures since snowfall correlate strongly with snow grain-size and impurity concentration, the main physical controls on snow albedo. Ice albedo may be parameterized by its relationship to elevation (r2 = 0.28), but this approach results in only a small improvement over the assumption of a constant mean ice albedo.
Sliding versus till deformation in the fast motion of an ice stream over a viscous till
Authors: Thorsteinsson Throstur , Raymond Charles F.
Published: November 2007

The partitioning between till deformation and sliding in the fast flow of ice streams with active basal melting is examined assuming no adhesion of the till to the ice base and incompressible viscous fluid behavior for the till. For deforming-till thickness of 10 m or less the predicted contribution to basal motion by sliding is larger than shearing in the till unless there is short-scale roughness with wavelengths less than order 0.1 m on the ice sole. At such short scales strain heating within the till and focused melting on the ice sole would quickly eliminate the roughness. Thus, fast flow over a till bed would be expected to be mostly by sliding over the subglacial till. More realistic continuum behavior of the till including non-linear and compressible deformation strengthens the conclusion. If sliding is not dominant, then there must be adhesion of the till to the ice base, some mechanism that continuously generates short-scale roughness on the ice–till interface, or very weak internal slip boundaries within the till.
The effects of sulfuric acid on the mechanical properties of ice single crystals
Authors: Trickett Y. L. , Baker I. , Pradhan P. M. S.
Published: November 2007

Ice single crystals of various orientations containing various concentrations of H2SO4 up to 11.5 ppm were cut from large pucks of laboratory-grown ice. Constant-strain-rate compression tests were performed on the doped ice crystals both at −20°C at an axial strain rate of 1 × 10−5 s−1 and at −10°C at 1 × 106 s−1. The stress–strain curves showed a linearly rising stress with increasing strain, followed by a sharply declining stress after reaching a peak. With further strain, the sharp decline in stress slowed. The tests clearly showed, for the first time, that this naturally occurring impurity dramatically decreases both the peak stress and the subsequent flow stress of ice single crystals. The decrease in the peak strength was related to the square root of the concentration of H2SO4 up to 11.5 ppm, suggesting that the solubility limit of H2SO4 in ice is at least 11.5 ppm. The sulfuric acid also appeared to increase the ductility of the ice. Preliminary examination of a doped ice single crystal by synchrotron X-ray topography suggested that sulfuric acid dramatically increases the grown-in dislocation density.