bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessment of the surface mass balance along the K-transect (Greenland ice sheet) from satellite-derived albedos
Authors: Greuell Wouter , Oerlemans Johannes 
Published: November 2007

AbstractThis paper explores the potential of using satellite-derived albedos to estimate the surface mass balance of the Kangerlussuaq transect (K-transect; Greenland ice sheet). We first retrieved surface albedos from Advanced Very High Resolution Radar data by using, among other techniques, a new cloud detection algorithm based on the relation between brightness temperature and surface elevation. We then computed the ‘satellite-derived mass balance’ (bsat) from the mean albedo for the transect, by taking fixed values for atmospheric transmissivity and the longwave and turbulent fluxes. We found that bsat explains 7 1% of the variance in 13 years of stake mass-balance measurements (bm). Our method also provides good estimates of the magnitude of the interannual variability in bm. The performance of the method degrades considerably without correction for anisotropic reflection at the surface and recalibration of the satellite sensors with dry snow at the top of the ice sheet. Sensitivity tests indicate that the method’s performance is hardly sensitive to uncertainties in parameters. Therefore, we expect that the method could be successfully applied on other glaciers and parts of ice sheets and ice caps, especially where accumulation rates are relatively small. We show that the investigated method performs best just below the mean equilibrium-line altitude.
Variation in glacier length and ice volume of Rabots Glaciär, Sweden, in response to climate change, 1910–2003
Authors: Brugger Keith A. , Refsnider Kurt A. , Whitehill Matthew F. 
Published: November 2007

AbstractHistorical records, photographs, maps and measurements were used to determine changes in the length, geometry and volume of Rabots Glaciär, Sweden, in response to a ∼1°C warming that occurred early in the 20th century. The glacier’s initial rate of retreat from its 1910 maximum was ~2.0 m a–1. After a sharp increase to ∼11.7 m a–1 between 1933 and 1946, the mean retreat rate decreased to ∼5.5 m a-1 between 1946 and 1959. Thereafter the rate of retreat increased to ∼11.0 m a-1 and has remained relatively constant to the present time. Concomitant decreases in ice volume were estimated to be 77.3 × 106m3 between 1910 and 1959, 51.1 × 106m3 between 1959 and 1980, at least 10.4 × 106m3 between 1980 and 1989, and 14.4 × 106m3 between 1989 and 2003. The total volume change over the last 93 years is estimated at ∼153.2 × 106m3 corresponding to 1.6 × 106m3a–1.. The magnitude of the ongoing changes in length and volume suggests that Rabots Glaciär has not yet completed its response to the earlier climatic warming. In contrast, several nearby glaciers, most notably Storglaciären, have completed their adjustments and established new steady-state profiles as a result of having shorter response times.
Re-evaluation of paleo-accumulation parameterization over Northern Hemisphere ice sheets during the ice age examined with a high-resolution AGCM and a 3-D ice-sheet model
Authors: Yamagishi Takateru , Abe-Ouchi Ayako , Saito Fuyuki , Segawa Tomonori , Nishimura Teruyuki 
Published: November 2007

AbstractSimulations of the Northern Hemisphere ice sheet at the Last Glacial Maximum (LGM; 21 kyr BP) are performed using a high-resolution atmospheric general circulation model (AGCM) in order to re-evaluate the conventional surface temperature- or elevation-based parameterization. The influence of precipitation change on the steady-state topography of the Laurentide ice sheet at the LGM is estimated using an AGCM with a horizontal resolution of ∼1° and a three-dimensional thermomechanically coupled ice-sheet model. The ice volume estimated by the AGCM simulation is much larger than that indicated by the conventional parameterization. Through sensitivity analysis of the AGCM and ice-sheet model, it is found that the rate of precipitation change depends on the location of the ice sheet, and that the rate of precipitation change due to surface elevation change is higher than the rate unrelated to surface elevation change on the Laurentide ice sheet. The rate of precipitation is also shown to exhibit seasonality and regionality due to effects such as interior desertification and the concentration of storm tracks.
A magnetic resonance study of temperature-dependent microstructural evolution and self-diffusion of water in Arctic first-year sea ice
Authors: Bock C. , Eicken H. 
Published: November 2007

AbstractThe microstructural evolution of brine inclusions in granular and columnar sea ice has been investigated through magnetic resonance imaging (MRI) for temperatures between –28 and –3˚C. Thin-section and salinity measurements were completed on core samples obtained from winter sea ice near Barrow, Alaska, USA. Subsamples of granular (2–5cm depth in core) and columnar sea ice (20–23 cm depth) were investigated with morphological spin-echo and diffusion-weighted imaging in a Bruker 4.7T MRI system operating at field gradients of 200 mTm–1 at temperatures of approximately –28, –15, –6 and –3˚C. Average linear pore dimensions range from 0.2 to 1 mm and increase with bulk liquid volume fraction as temperatures rise from –15 to –3˚C. Granular ice pores are significantly larger than columnar ice pores and exhibit a higher degree of connectivity. No evidence is found of strongly non-linear increases in pore connectivity based on the MRI data. This might be explained by shortcomings in resolution, sensitivity and lack of truly three-dimensional data, differences between laboratory and field conditions or the absence of a percolation transition. Pore connectivity increases between –6 and –3˚C. Pore-number densities average at 1.4±1.2mm–2. The pore-number density distribution as a function of cross-sectional area conforms with power-law and lognormal distributions previously identified, although significant variations occur as a function of ice type and temperature. At low temperatures (< –26˚C), pore sizes were estimated from 1H self-diffusivity measurements, with self-diffusivity lower by up to an order of magnitude than in the free liquid. Analysis of diffusional length scales suggests characteristic pore dimensions of <1 μm at < –26˚C.
Concentrations and source variations of n-alkanes in a 21 m ice core and snow samples at Belukha glacier, Russian Altai mountains
Authors: Miyake Takayuki , Nakazawa Fumio , Sakugawa Hiroshi , Takeuchi Nozomu , Fujita Koji , Ohta Keiichi , Nakawo Masayoshi 
Published: November 2007

AbstractIce-core and snow samples collected on Belukha glacier, Russian Altai mountains, were analyzed for n-alkanes by gas chromatography. On the basis of the total concentrations (T-HCs), carbon preference index (CPI) values and the plant wax contributions (WaxCn), it is suggested that mountain glaciers on the Asian continent received higher loading of n-alkanes from natural and anthropogenic sources than the Greenland ice sheet. It appears that the loading and variation of n-alkanes on glaciers in the Altai are approximately the same as those of the mountain in general, because the concentrations, CPI values and WaxCn percentages of n-alkanes in Sofiyskiy glacier, also in the Russian Altai, are at the same levels as or slightly greater than those in ice-core and snow samples from Belukha glacier. It seems that the n-alkanes on Belukha glacier are derived mainly from higher plant wax and petroleum exhaust other than from diesel engines. Vertical profiles of T-HCs and CPI values of n-alkanes show that the non-WaxCn portions and T-HCs have recently increased with a decrease in CPI values on Belukha glacier. A similar trend of n-alkanes was reported for Sofiyskiy glacier, indicating that the influence of human activities has gradually increased around the Altai.
Prediction of thermodynamic state of the Gregoriev ice cap, Tien Shan, central Asia, in the future
Authors: Nagornov Oleg , Konovalov Yuri , Mikhalenko Vladimir 
Published: November 2007

AbstractWe use a two-dimensional flowline model to study the flow of the Gregoriev ice cap, Tien Shan, central Asia. The model takes into account the transverse change of glacier width, data on the measured thickness of the glacier, the surface velocity at the glacier front, and mass-balance measurements in 1987 and 1988. The calculated ice velocity varies from 0 to 3 ma−1 along the glacier flowline. The velocity maximum is shifted from the lowest part towards the middle part of the ice cap for the time interval considered (1980–2050) in the study. The derived changes of the glacier show the degradation and decrease of glacier extent on the south slope of Terskey Ala Tau, Tien Shan. Seasonal variations of temperature in the subsurface layer result in oscillations of stresses and velocities that are due to seasonal changes of viscosity. The consequent stresses can exceed the compressive/tensile strength that would produce crevasses.
An Andean ice-core record of a Middle Holocene mega-drought in North Africa and Asia
Authors: Davis Mary E. , Thompson Lonnie G. 
Published: November 2007

AbstractAn ice core from the Nevado Huascaran col in the Cordillera Blanca of northern Peru contains high-resolution time series of dust concentrations and size distributions since the end of the last glacial stage. A large dust peak, dated ∼4500 years ago, is contemporaneous with a widespread and prolonged drought that apparently extended from North Africa to eastern China, evidence of which occurs in historical, archeological and paleoclimatic records. This event may have been associated with several centuries of weak Asian/Indian/African monsoons, possibly linked with a protracted cooling in the North Atlantic. During the second half of the 20th century, high austral-summer dust concentrations in the Huascaran record are significantly correlated with atmospheric conditions, such as sea-level pressure and zonal wind velocities that are consistent with El Nino-Southern Oscillation (ENSO) and positive North Atlantic Oscillation (NAO) indices, and with aridity in North Africa, southwest Asia and the Middle East. Therefore, the dominant submicron fraction of the dust may have been transported by more intense northeasterly trade winds from the African dry regions across the tropical Atlantic during a period of frequent and/or intense ENSO activity. The proposed ENSO conditions that may have been linked with drought in the monsoon region may also have contributed to aridity in tropical South America, including the Cordillera Blanca.
Tephra layers in the Dome Fuji (Antarctica) deep ice core
Authors: Fujii Y. , Kohno M. , Motoyama H. , Matoba S. , Watanabe O. , Fujita S. , Azuma N. , Kikuchi T. , Fukuoka T. , Suzuki T. 
Published: November 2007

AbstractA deep ice core drilled to 2503 m depth at Dome Fuji, Antarctica, contains 25 visible tephra layers during the past 340 ka. The thickness of tephra layers is in the range 1-24 mm. The thickness and duration at deposition, determined by a simple ice-flow model, suggests that a violent volcanic eruption caused ash to fall onto the Antarctic ice sheet for ~5 years and to form a ~100 mm thick tephra layer at 117 ka BE Two tephra layers at depths of 573 and 2202 m probably originated from volcanoes in the South Sandwich Islands, Southern Ocean, given the size of tephra shards, >20μm in diameter, and their major chemical composition. Only eight of the 25 tephra layers can also be recognized in the Vostok (Antarctica) ice core, but all correspond to the Vostok tephras if we consider cloudy bands to be volcanic.
Antarctic aerosol and snowfall chemistry: implications for deep Antarctic ice-core chemistry
Authors: Legrand Michel , Wolff Eric , Wagenbach Dietmar 
Published: November 2007

AbstractIn this paper we first summarise major findings of recent atmospheric studies of nitrogen and sulphur species present in the boundary layer of coastal Antarctic regions. We then discuss the implications of such atmospheric data for the interpretation of nitrate, ammonium, methanesulphonate and sulphate records in deep ice cores extracted from central Antarctica in terms of past atmospheric chemistry changes.
The motion field of northern Larsen Ice Shelf, Antarctic Peninsula, derived from satellite imagery
Authors: Rack Wolfgang , Rott Helmut , Siegel Andreas , Skvarca Pedro 
Published: November 2007

AbstractThe motion field of the northern Larsen Ice Shelf, Antarctic Peninsula, was analyzed, based on Landsat data from 1986 to 1989, Earth Resources Satellite (ERS) synthetic aperture radar (SAR) data from 1992 to 1997, and comparative field measurements along three transects. During this period the northern sections of the ice shelf showed steady retreat, which culminated in the disintegration of the two ice-shelf sections north of Seal Nunataks in January 1995. Velocities of these two sections were derived by cross-correlation, using SAR images of 1 year time intervals and Landsat images of 1-3 year intervals. A slight increase of velocity was observed as crevasses and rifts opened before the final disintegration. In addition, an interferometric motion analysis was carried out for the ice shelf around and south of Seal Nunataks, based on an image pair from the ERS-1/2 Tandem Mission in 1995. This analysis reveals a complex pattern of tidal flexure in the grounding zones, as well as rifting and shear zones on the ice shelf. In addition, the motion of the main input glaciers was derived.
200 years of isotope and chemical records in a firn core from Hercules Névé, northern Victoria Land, Antarctica
Authors: Stenni B. , Caprioli R. , Cimino L. , Cremisini C. , Flora O. , Gragnani R. , Longinelli A. , Maggi V. , Torcini S 
Published: November 2007

AbstractA 42.2 m firn core was collected at the Hercules Névé plateau (100 km inland and 2960 m a.s.L), northern Victoria Land, during the 1994-95 Italian Antarctic Expedition. Chemical (Cl–, NO3–, SO42–’; δ18O δ18O δ18O; m-2a-1) and isotope (5180) analyses were performed to evaluate the snow-accumulation rate at this site. Tritium measurements were performed in the upper part of the core to narrow down the dating of the core.High nssSO42- concentrations seem to be related to some explosive volcanic eruptions, such as Tambora (AD 1815) and the preceding event called "Unknown" (AD 1809), Coseguina (AD 1835), Makjan (AD 1861), Krakatoa (AD 1883) and Tarawera (AD 1886).A comparison between the seasonal variations observed in the isotope and chemical profiles was carried out in order to reduce the dating uncertainty, using the tritium and the volcanic markers as time constraints. A deposition period of 222 years was determined.The 3 year smoothed «5180 profile shows more negative values from the bottom of the core (dated AD 1770) throughout the 19th century, suggesting "cooler" conditions, in agreement with other East Antarctic ice-core records! Subsequently, a general increase in δ180-values is observed.The calculated average snow-accumulation rates between the above-mentioned time markers are 111-129 kg m-2a-1.
Crystal-growth rates in firn and shallow ice at high-accumulation sites
Authors: Jun Li , Jacka T.H. 
Published: November 2007

AbstractCrystal growth in firn and shallow ice is studied by examining crystal size and ,c-axis orientation fabrics in two ice cores drilled at sites Dome Summit South and DE08, near the summit of Law Dome, East Antarctica. The snow-accumulation rates at the core sites are particularly high (640 and 1160 kg m−2 a−1, respectively) compared to other Antarctic sites. Crystal-growth rates above the firn/ice transition depth (at 70-80 m) are found to be in agreement with the generally used growth-rate-temperature relation (Stephenson, 1967; Gow, 1969), sometimes referred to as "normal grain growth". In the shallow ice layers below this depth and down to about 300 m, the observed crystal-growth rates are enhanced compared to normal grain growth. Also in this shallow ice, crystal ,c-axis orientation measurements show development of anisotropic fabrics indicative of ice flow at strains well above 1%.In earlier work, Jacka and Li (1994) described the development in clean ice of steady-state ice-crystal size (inversely proportional to the stress and largely independent of temperature) during the onset of flow-related crystal anisotropy, i.e. dynamic recrystallisation. It is concluded here that as a consequence of the high accumulation rates, relatively high deformation rates are generated in the shallow ice. The deformation rates are sufficiently high that "dynamic recrystallisation" takes over from "normal crystal growth" as the dominant crystal-growth mechanism. This leads to a rapid increase in crystal size from the slow-growing small firn crystals towards the larger size appropriate to the stress.
Equilibrium-line altitudes and rock glaciers during the Younger Dryas cooling event, Ferwall group, western Tyrol, Austria
Authors: Sailer Rudolf , Kerschner Hanns 
Published: November 2007

AbstractThree cirques in the Ferwall group, western Tyrol, Austria, which are characterized by distinct Late-glacial moraines and rock glaciers, are discussed. The morphology of the moraines and the depression of the equilibrium-line altitude suggest they were deposited during the Egesen Stadial (Younger Dryas), which can be subdivided into three substages. Rock-glacier formation was initialized during or after the Egesen II substage. They became inactive at the Pleistocene—Holocene transition. ELA values are 290–320 m lower than the Little Ice Age ELA during the Egesen I substage, 190–230 m lower during the Egesen II substage and 120 —160 m lower during the Egesen III substage. The lowering of the rock-glacier belt (discontinuous permafrost) during and after the Egesen II substage is about 400 m, indicating a mean annual air-temperature depression in the order of 3 K. During the Egesen I (earlyYounger Dryas), the climate seems to have been rather cold and wet with precipitation similar to present-day values. During later phases (Egesen II and III), the climate remained cold and became increasingly drier. The rise of the ELA during the Egesen I—III substages seems to have been mainly caused by a decrease in precipitation.
Geomorphology and sedimentology of surging glaciers: a land-systems approach
Authors: Evans David J.A. , Rea Brice R. 
Published: November 2007

AbstractThe identification of surging glaciers and ice streams in glaciated landscapes is of major importance to the understanding of ice-sheet dynamics and for reconstructing ice sheets and climate. No single landform or diagnostic criterion has yet been found with which to identify surging glaciers. A surging-glacier land-system model is constructed using observations and measurements from contemporary surging-glacier snouts in Iceland, Svalbard, U.S.A. and Canada for differentiating ancient surging margins from other non-surging palaeoglaciers. This integrates the suite of landforms, sediments and stratigraphy produced at surging-glacier margins. Landforms produced during surging include thrust moraines, concertina eskers and subglacial crevasse-squeeze ridges. Sedimentary sequences are usually characterized by multiple stacked diamictons and stratified interbeds, which display severe glaciotectonic contortion and faulting. Hummocky moraine, comprising interbedded stratified sediments and mass-flow diamictons, has also been associated with surge margins where large quantities of supraglacial and englacial debris entrained during the surge event have melted out in situ. An example of the application of the land-system model is presented for east-central Alberta, Canada. A surging palaeo-ice stream is identified within this part of the southwestern Laurentide ice sheet, where thrust-block moraines, crevasse-squeeze ridges, flutings, hummocky moraine and glaciotectonized sediments are juxtaposed.
Digital elevation models for the Lambert Glacier–Amery Ice Shelf system, East Antarctica, from ERS-1 satellite radar altimetry
Authors: Fricker Helen A. , Hyland Glenn , Coleman Richard , Young Neal W. 
Published: November 2007

AbstractThe Lambert Glacier–Amery Ice Shelf system is a major component of the East Antarctic ice sheet. This paper presents two digital elevation models (DEMs) that have been generated for the Lambert–Amery system from validated European Remote-sensing Satellite (ERS-1) radar altimeter waveform data. The first DEM covers the Amery Ice Shelf only, and was produced using kriging on a 1 km grid. The second is a coarser (5 km) DEM of the entire Lambert–Amery system, generated via simple averaging procedures. The DEMs provide unprecedented surface elevation information for the Lambert–Amery system and allow new insight into the glaciology of the region.
Acoustic televiewer logging in glacier boreholes
Authors: Morin Roger H. , Descamps Guillaume E. , DeWayne Cecil L. 
Published: November 2007

AbstractThe acoustic televiewer is a geophysical logging instrument that is deployed in a water-filled borehole and operated while trolling. It generates a digital, magnetically oriented image of the borehole wall that is developed from the amplitudes and transit times of acoustic waves emitted from the tool and reflected at the water–wall interface. The transit-time data are also converted to radial distances, from which cross-sectional views of the borehole shape can be constructed. Because the televiewer is equipped with both a three-component magnetometer and a two-component inclinometer, the borehole’s trajectory in space is continuously recorded as well. This instrument is routinely used in mining and hydrogeologic applications, but in this investigation it was deployed in two boreholes drilled into Upper Fremont Glacier, Wyoming, U.S.A. The acoustic images recorded in this glacial setting are not as clear as those typically obtained in rocks, due to a lower reflection coefficient for water and ice than for water and rock. Results indicate that the depth and orientation of features intersecting the boreholes can be determined, but that interpreting their physical nature is problematic and requires corroborating information from inspection of cores. Nevertheless, these data can provide some insight into englacial structural characteristics. Additional information derived from the cross-sectional geometry of the borehole, as well as from its trajectory, may also be useful in studies concerned with stress patterns and deformation processes.
Monsoon and dust signals recorded in Dasuopu glacier, Tibetan Plateau
Authors: Shichang Kang , Wake Cameron P. , Dahe Qin , Mayewski Paul A. , Tandong Yao 
Published: November 2007

AbstractDuring summer 1997, a 15 m firn core was recovered from Dasuopu glacier (28°23′ N, 85°44′ E; 7000 m a.s.l.) on the northwest margin of Xixabarngma Feng in the central Himalaya. Oxygen isotope values and concentrations of Ca2+, Mg2+, NH4+, SO42− and NO3− were measured over the 10 years of snow accumulation captured in the firn core. The seasonal variations of δ18O values and major-ion concentrations in the Dasuopu core indicate that summer monsoon and dust signals are clearly recorded in Dasuopu glacier. Annual variations in δ18O values are controlled by the amount effect, with more negative (i.e. lighter) δ18O values representing summer monsoon precipitation characteristic of tropical regions. Higher concentrations of Ca2+, Mg2+ and SO42− reflect the influx of mineral aerosols from the vast arid and semi-arid desert regions to the north and west during the spring dust-storm period. High spring concentrations of NH4+ and NO3− appear to reflect changes in regional biogenic-source strength.