bluuebunny/crossref_metadata_2025_split huggingface dataset:
An empirical firn-densification model comprising ice lenses
Authors: Reeh Niels , Fisher David A. , Koerner Roy M. , Clausen Henrik B. 
Published: November 2007

AbstractIn the past, several empirical firn-densification models have been developed fitted to measured density–depth profiles from Greenland and Antarctica. These models do not specifically deal with refreezing of meltwater in the firn. Ice lenses are usually indirectly taken into account by choosing a suitable value of the surface snow density. In the present study, a simple densification model is developed that specifically accounts for the content of ice lenses in the snowpack. An annual layer is considered to be composed of an ice fraction and a firn fraction. It is assumed that all meltwater formed at the surface in one year will refreeze in the corresponding annual layer, and that no additional melting or refreezing occurs in deeper layers. With this assumption, further densification is solely controlled by compaction of the firn fraction of the annual layer. Comparison of modelled and observed depth–density profiles from Canadian Arctic ice-core sites with large melting–refreezing percentages shows good agreement. The model is also used to estimate the long-term surface elevation change in interior Greenland that will result from temperature-driven changes of density–depth profiles. These surface elevation changes reflect a volume change of the ice sheet with no corresponding change of mass, i.e. a volume change that does not influence global sea level.
Elevation changes on the Greenland ice sheet from comparison of aircraft and ICESat laser-altimeter data
Authors: Thomas R. , Frederick E. , Krabill W. , Manizade S. , Martin C. , Mason A. 
Published: November 2007

AbstractPrecise measurements of surface elevation on the Greenland ice sheet have been made almost every year since 1991 by an airborne scanning laser altimeter operated by NASA/Wallops Flight Facility. Results show substantial thinning over large areas near the coast, with a general increase in thinning rates since 1997, in the drainage basins of thinning glaciers, and a recent thickening in the southeast associated with very high snowfall in this region during 2003. Here, we present first results from the comparison of the aircraft data with similar measurements from the laser altimeter aboard NASA’s Ice, Cloud and land Elevation Satellite (ICESat), which was launched in January 2003. These show very close agreement with results inferred solely from the aircraft measurements, indicating that accuracies are similar for both datasets. Broad spatial coverage by satellite, together with the baseline dataset of aircraft measurements, offers the prospects of routine surveys of ice-sheet elevation changes by ICESat and follow-on missions.
Elevation changes measured on Svalbard glaciers and ice caps from airborne laser data
Authors: Bamber Jonathan L. , Krabill William , Raper Vivienne , Dowdeswell Julian A. , Oerlemans J. 
Published: November 2007

AbstractPrecise airborne laser surveys were conducted during spring in 1996 and 2002 on 17 ice caps and glaciers in the Svalbard archipelago covering the islands of Spitsbergen and Nordaustlandet. We present the derived elevation changes. Lower-elevation glaciers in south Spitsbergen show the largest thinning rates of ∼ 0.5 m a-1, while some of the higher, more northerly ice caps appear to be close to balance. The pattern of elevation change is complex, however, due to several factors including glacier aspect, microclimatological influences and the high natural annual variability in local accumulation and ablation rates. Anomalous changes were observed on Fridtjovbreen, which started surging in 1996, at the start of the measurement period. On this glacier, thinning (of > 0.6 m a-1) was observed in the accumulation area, coincident with thickening at lower elevations. Asymmetric thinning was found on two ice caps on Nordaustlandet, with the largest values on the eastern side of Vestfonna but the western slopes of Vegafonna. The mean elevation change for all ice masses was -0.19 m a-1 w.e., which is 1.6 times the net mass-balance value determined for the last 30 years. Using mass-balance sensitivity estimates for Svalbard suggests that the implied increase in negative balance is linked to warmer air temperatures in the late 1990s. Multiple linear regression suggests that mass balance is most closely correlated with latitude, rather than mean altitude or longitude.
Simulation of the net snow accumulation along the Wilkes Land transect, Antarctica, with a regional climate model
Authors: Gallée Hubert , Peyaud Vincent , Goodwin Ian 
Published: November 2007

AbstractRegional climate modelling in conjunction with accumulation measurements collected on Antarctic traverses of the International Trans-Antarctic Scientific Expedition (ITASE) is presented as a tool for extending the spatial coverage of field measurements. The modelling of part of East Antarctica spanned the 7 year epoch 1980–86 where data covering the same period are available. The agreement between simulation and observation is improved when a parameterization of the snow surface redistribution processes, such as wind erosion, is included in the regional climate model. The modelled spatial distribution of the net snow mass transported in the boundary layer over coastal East Antarctica indicates that this mass is a significant component of the surface mass balance.
Phase structure of radar stratigraphic horizons within Antarctic firn
Authors: Arcone Steven A. , Spikes Vandy B. , Hamilton Gordon S. 
Published: November 2007

AbstractWe have recorded reflection profiles of firn through large areas of West Antarctica and part of the East Antarctic plateau using 400MHz short-pulse radar. The locations show accumulation rates that vary from well above to well below the vertical radar resolution. Most reflection horizons have extensive lateral continuity, and are composed of distinctive wavelets with a consistent phase polarity sequence within their successive half-cycles. We modeled these waveforms, and conclude that they arise from thin, double layers of ice over hoar, which is consistent with the standard model of firn stratification. In addition, we conclude that ice/hoar layers are extensive throughout West Antarctica and also present (although more sparsely) beneath the Antarctic Plateau.
Characteristics of accumulation around the EPICA deep-drilling site in Dronning Maud Land, Antarctica
Authors: Eisen Olaf , Rack Wolfgang , Nixdorf Uwe , Wilhelms Frank 
Published: November 2007

AbstractBased on ground-penetrating radar profiles, we analyze area-wide spatial and temporal characteristics of accumulation rate in the vicinity of the EPICA (European Project for Ice Coring in Antarctica) deep-drilling site in Dronning Maud Land, Antarctica (EDML). An area of 1600km2 is covered by 500km of radar profiles, organized in a star-like pattern with eight 20–25km legs and a 10km grid with 1–3km spacing, each pattern being centred on the EDML drilling location. Distributions of density, cumulative mass, age and the electromagnetic wave speed with depth are available from physical ice-core records. Nine internal reflection horizons are continuously tracked within the upper 110m of ice over the whole area, yielding a spatial picture of accumulation rate history over >1000 years. The mean accumulation rate over the last 153 years varies between 50 and 75 kgm–2 a–1 over 50 km perpendicular to the ice divide; the spatial average is ~61 kgm–2 a–1. This general pattern is overlain by small-scale variations of accumulation rate on the order of 10% of the mean. Maximum local gradients in accumulation rate are ~2–3 kgm–2 a–1 km–1, about five times the regional accumulation rate gradient. Comparison of topography and accumulation rate along a 20 km profile in the direction of the mean winds indicates that variations in accumulation rate over short distances are linked to surface undulations. Our results show that advected spatial variations of accumulation rate are on the same order and even exceed temporal changes over the investigated periods. Ice flow and upstream effects therefore might influence accumulation rates reconstructed from the EDML ice core.
Characteristics of the Antarctic surface mass balance, 1958–2002, using a regional atmospheric climate model
Authors: Van De Berg W.J. , Van Den Broeke M.R. , Reijmer C.H. , Van Meijgaard E. 
Published: November 2007

AbstractTemporal and spatial characteristics of the Antarctic specific surface mass balance (SSMB) are presented, including its components solid precipitation, sublimation/deposition and melt. For this purpose, we use the output of a regional atmospheric climate model (RACMO2/ANT, horizontal resolution of ~55 km) for the period 1958–2002. RACMO2/ANT uses European Centre for Medium-Range Weather Forecasts (ECMWF) 40 year re-analysis (ERA-40) fields as forcing at the lateral boundaries. RACMO2/ANT underestimates SSMB in the high interior of East and West Antarctica and overestimates SSMB on the steep coastal slopes. Otherwise, the modeled spatial pattern of SSMB is in good qualitative agreement with recent compilations of in situ observations. Large-scale patterns, like the precipitation shadow effect of the Antarctic Peninsula, are well reproduced, and mesoscale SSMB patterns, such as the strong precipitation gradients on Law Dome, are well represented in the model. The integrated SSMB over the grounded ice sheet is 153mmw.e. a–1 for the period 1958–2002, which agrees within 5% with the latest measurement compilations. Sublimation and melt remove 7% and <1% respectively of the solid precipitation. We found significant seasonality of solid precipitation, with a maximum in autumn and a minimum in summer. No meaningful trend was identified for the SSMB, because the time series of solid precipitation and SSMB are affected by an inhomogeneity in 1980 within the ERA-40 fields that drive RACMO2/ANT. Sublimation, melt and liquid precipitation increase in time, which is related to a modeled increase in 2m temperature.
A 200 year sulfate record from 16 Antarctic ice cores and associations with Southern Ocean sea-ice extent
Authors: Dixon Daniel , Mayewski Paul A. , Kaspari Susan , Kreutz Karl , Hamilton Gordon , Maasch Kirk , B. Sneed Sharon , J. Handley Michael 
Published: November 2007

AbstractChemistry data from 16, 50–115m deep, sub-annually dated ice cores are used to investigate spatial and temporal concentration variability of sea-salt (ss) SO42– and excess (xs) SO42– over West Antarctica and the South Pole for the last 200 years. Low-elevation ice-core sites in western West Antarctica contain higher concentrations of SO42– as a result of cyclogenesis over the Ross Ice Shelf and proximity to the Ross Sea Polynya. Linear correlation analysis of 15 West Antarctic ice-core SO42– time series demonstrates that at several sites concentrations of ssSO42– are higher when sea-ice extent (SIE) is greater, and the inverse for xsSO42–. Concentrations of xsSO42– from the South Pole site (East Antarctica) are associated with SIE from the Weddell region, and West Antarctic xsSO42– concentrations are associated with SIE from the Bellingshausen–Amundsen–Ross region. The only notable rise of the last 200 years in xsSO42–, around 1940, is not related to SIE fluctuations and is most likely a result of increased xsSO42– production in the mid–low latitudes and/or an increase in transport efficiency from the mid–low latitudes to central West Antarctica. These high-resolution records show that the source types and source areas of ssSO42– and xsSO42– delivered to eastern and western West Antarctica and the South Pole differ from site to site but can best be resolved using records from spatial ice-core arrays such as the International Trans-Antarctic Scientific Expedition (ITASE).
Solar forcing of the polar atmosphere
Authors: Mayewski Paul Andrew , Maasch Kirk A. , Yan Yuping , Kang Shichang , Meyerson Eric A. , Sneed Sharon B. , Kaspari Susan D. , Dixon Daniel A. , Osterberg Erich C. , Morgan Vin I. , Ommen Tas van , Curran Mark A.J. 
Published: November 2007

AbstractWe present highly resolved, annually dated, calibrated proxies for atmospheric circulation from several Antarctic ice cores (ITASE (International Trans-Antarctic Scientific Expedition), Siple Dome, Law Dome) that reveal decadal-scale associations with a South Pole ice-core 10Be proxy for solar variability over the last 600 years and annual-scale associations with solar variability since AD 1720. We show that increased (decreased) solar irradiance is associated with increased (decreased) zonal wind strength near the edge of the Antarctic polar vortex. The association is particularly strong in the Indian and Pacific Oceans and as such may contribute to understanding climate forcing that controls drought in Australia and other Southern Hemisphere climate events. We also include evidence suggestive of solar forcing of atmospheric circulation near the edge of the Arctic polar vortex based on ice-core records from Mount Logan, Yukon Territory, Canada, and both central and south Greenland as enticement for future investigations. Our identification of solar forcing of the polar atmosphere and its impact on lower latitudes offers a mechanism for better understanding modern climate variability and potentially the initiation of abrupt climate-change events that operate on decadal and faster scales.
Glacier wastage on southern Adelaide Island, Antarctica, and its impact on snow runway operations
Authors: Rivera A. , Casassa G. , Thomas R. , Rignot E. , Zamora R. , Antúnez D. , Acuña C. , Ordenes F. 
Published: November 2007

AbstractThe variations and dynamics of the southern edge of Fuchs Ice Piedmont, Adelaide Island (67˚45’ 09’ S, 68˚55’ 04’ W), Antarctic Peninsula, are presented. The snow-covered surface of the glacier has been used since the 1960s for landing aeroplanes in support of British, and more recently Chilean, operations at nearby Teniente Carvajal station (formerly known as Adelaide T). In recent years, snow conditions in the runway area have progressively deteriorated, due to increasingly early summer melting. Radio-echo sounding, global positioning system and remotely sensed data have been analyzed for mapping the crevasse and ice velocity fields, as well as the surface and subglacial topography of the area. The results show that the runway area is located on a local ice divide surrounded by crevasses which are appearing on the glacier surface progressively earlier in the summer, presumably due to higher snowmelt and perhaps higher ice velocities, in response to regional atmospheric warming. In the near future, landing operations will be further affected as more crevasses will appear in the runway area if present warming trends persist. This situation affects all coastal areas in the Antarctic Peninsula, hence the need to search for possible new locations of crevasse-free runways at higher elevations.
Slip event propagation direction in transition region of low surface slope
Authors: Weertman Johannes 
Published: November 2007

AbstractThe base of the ice in the transition zone between an ice stream and an ice shelf is likely to be well lubricated by broadly distributed water, a condition which should permit fast sliding motion. It has been observed that motion takes place not smoothly but by localized stick–slip events that propagate in the downstream direction towards the ice shelf and at velocities approximately that expected for shear wave velocity of the basal till. Thus slip packets of gliding edge dislocations are likely to move at the base. I show here that subsonic dislocations should move upstream, rather than downstream, if frictional resistance is determined by normal traction stress change at the base. Transonic dislocations are expected to move in the downstream direction. However, if frictional resistance is lowered by hydrostatic pressure reduction at the base, the subsonic dislocation should move downstream.
The dynamic response of Kennicott Glacier, Alaska, USA, to the Hidden Creek Lake outburst flood
Authors: Anderson Robert S. , Walder Joseph S. , Anderson Suzanne P. , Trabant Dennis C. , Fountain Andrew G. 
Published: November 2007

AbstractGlacier sliding is commonly linked with elevated water pressure at the glacier bed. Ice surface motion during a 3 week period encompassing an outburst of ice-dammed Hidden Creek Lake (HCL) at Kennicott Glacier, Alaska, USA, showed enhanced sliding during the flood. Two stakes, 1.2 km from HCL, revealed increased speed in two episodes, both associated with uplift of the ice surface relative to the trajectory of bed-parallel motion. Uplift of the surface began 12 days before the flood, initially stabilizing at a value of 0.25 m. Two days after lake drainage began, further uplift (reaching 0.4 m) occurred while surface speed peaked at 1.2 md–1. Maximum surface uplift coincided with peak discharge from HCL, high water level in a down-glacier ice-marginal basin, and low solute concentrations in the Kennicott River. Each of these records is consistent with high subglacial water pressure. We interpret the ice surface motion as arising from sliding up backs of bumps on the bed, which enlarges cavities and produces bed separation. The outburst increased water pressure over a broad region, promoting sliding, inhibiting cavity closure, and blocking drainage of solute-rich water from the distributed system. Pressure drop upon termination of the outburst drained water from and depressurized the distributed system, reducing sliding speeds. Expanded cavities then collapsed with a 1 day time-scale set by the local ice thickness.
Fault-dominated deformation in an ice dam during annual filling and drainage of a marginal lake
Authors: Walder Joseph S. , Trabant Dennis C. , Cunico Michelle , Anderson Suzanne P. , Anderson Robert S. , Fountain Andrew G. , Malm Andrew 
Published: November 2007

AbstractIce-dammed Hidden Creek Lake, Alaska, USA, outbursts annually in about 2–3 days. As the lake fills, a wedge of water penetrates beneath the glacier, and the surface of this ‘ice dam’ rises; the surface then falls as the lake drains. Detailed optical surveying of the glacier near the lake allows characterization of ice-dam deformation. Surface uplift rate is close to the rate of lake-level rise within about 400 m of the lake, then decreases by 90% over about 100 m. Such a steep gradient in uplift rate cannot be explained in terms of ice-dam flexure. Moreover, survey targets spanning the zone of steep uplift gradient move relative to one another in a nearly reversible fashion as the lake fills and drains. Evidently, the zone of steep uplift gradient is a fault zone, with the faults penetrating the entire thickness of the ice dam. Fault motion is in a reverse sense as the lake fills, but in a normal sense as the lake drains. As the overall fault pattern is the same from year to year, even though ice is lost by calving, the faults must be regularly regenerated, probably by linkage of surface and bottom crevasses as ice is advected toward the lake basin.
Estimating alpine snowpack properties using FMCW radar
Authors: Marshall Hans-Peter , Koh Gary , Forster Richard R. 
Published: November 2007

AbstractLarge variations in both snow water equivalent (SWE) and snow slope stability are known to exist in the alpine snowpack, caused by wind, topographic and microclimatic effects. This variability makes extrapolation of point measurements of snowpack properties difficult and prone to error, but these types of measurements are used to estimate SWE and stability across entire mountain ranges. Radar technology provides a promising alternative to point measurements, because large areas can be covered quickly and non-intrusively. There is great potential for obtaining information on a large spatial scale from airborne applications. Frequency-modulated continuous wave (FMCW) radar measurements were made from the ground in several different alpine snowpacks, along with manual and in situ electrical measurements. The surface and ground reflections from the radar data, combined with an average density estimate, can provide a useful estimate of SWE. In addition, the locations of internal reflections are highly correlated with both visually identified layers and measured changes in in situ dielectric properties.
Culturable yeasts in meltwaters draining from two glaciers in the Italian Alps
Authors: Buzzini Pietro , Turchetti Benedetta , Diolaiuti Guglielmina , D’Agata Carlo , Martini Alessandro 
Published: November 2007

AbstractThe meltwaters draining from two glaciers in the Italian Alps contain metabolically active yeasts isolable by culture-based laboratory procedures. The average number of culturable yeast cells in the meltwaters was 10–20 colony-forming units (CFU) L–1, whereas supraglacial stream waters originating from overlying glacier ice contained <1 CFUL–1. Yeast cell number increased as the suspended-sediment content of the water samples increased. Basidiomycetous yeasts represent >80% of isolated strains (Cryptococcus spp. and Rhodotorula spp. were 33.3% and 17.8% of total strains, respectively). Culturable yeasts were psychrotolerant, predominantly obligate aerobes and able to degrade organic macromolecules (e.g. starch, esters, lipids, proteins). To the authors’ knowledge, this is the first study to report the presence of culturable yeasts in meltwaters originating from glaciers. On the basis of these results, it is reasonable to suppose that the viable yeasts observed in meltwaters derived predominantly from the subglacial zone and that they originated from the subglacial microbial community. Their metabolic abilities could contribute to the microbial activity occurring in subglacial environments.
The origin of channels on lower Taylor Glacier, McMurdo Dry Valleys, Antarctica, and their implication for water runoff
Authors: Johnston Robin R. , Fountain Andrew G. , Nylen Thomas H. 
Published: November 2007

AbstractWell-developed surface channels on Taylor Glacier, McMurdo Dry Valleys, Antarctica, begin as medial moraines incised as shallow, narrow surface depressions, and retain this geometry for tens of km. Over a distance of 1100 m, the channel geometry dramatically changes, reaching depths >20m and widths >100 m. After rapidly enlarging, the channels appear to evolve toward a new equilibrium geometry. Compared to the glacier surface, the air temperature in the channels is warmer by ∼1.7˚C, wind speed is reduced by ∼2.4ms–1 and net shortwave radiation is greater by ∼14Wm–2. The microclimate in the channel shifts the energy balance towards enhanced melt. Field evidence and energy-balance modeling indicate ablation in the deep channels is ∼4.5 times greater than the local horizontal glacier surface and that melt accounts for ∼99% of the summer ablation, compared to ∼75% on the adjacent horizontal glacier surface. Melt in these channels supplies 65% of the unaccounted water discharge into the neighboring lake. In large part, the channels generate the water they carry, rather than merely route water generated elsewhere.