bluuebunny/crossref_metadata_2025_split huggingface dataset:
A multi-century ice-core perspective on 20th-century climate change with new contributions from high-Arctic and Greenland (PARCA) cores
Authors: Mosley-Thompson Ellen , Thompson Lonnie G. , Lin Ping-Nan 
Published: November 2007

AbstractA global collection of high temporally resolved ice-core-derived δ18O records is examined to assess whether the proxy records are consistent with contemporaneous observed temperature variations in their respective regions. This is prerequisite to using the older parts of the proxy (δ18O) records to assess whether 20th-century temperatures remain within the range of longer-term natural variability. Excluding the high plateaus in East and West Antarctica where 20th-century temperatures show modest cooling, the ice-core records from other regions suggest modest to strong 20th-century warming. The recent warming over Greenland has been modest and spatially variable. The 20th-century warming over both the Barents Sea region and the Tibetan Plateau now falls well outside the range of prior longer-term temperature variability. Similarly, over the South American Andes and the Antarctic Peninsula the recent warming exceeds the long-term mean for the last 1000 and 500 years, respectively. The ice fields in these regions are in danger of being compromised or lost if the present warming trend in these regions persists.
Fast shrinkage of tropical glaciers in Colombia
Authors: Ceballos Jorge Luis , Euscátegui Christian , Ramírez Jair , Cañon Marcela , Huggel Christian , Haeberli Wilfried , Machguth Horst 
Published: November 2007

AbstractAs a consequence of ongoing atmospheric temperature rise, tropical glaciers belong to the unique and threatened ecosystems on Earth, as defined by the Intergovernmental Panel on Climate Change (Houghton and others, 2001). Worldwide glacier monitoring, especially as part of the Global Climate Observing System (GCOS), includes the systematic collection of data on such perennial surface ice masses. Several peaks in the sierras of Colombia have lost their glacier cover during recent decades. Today, high-altitude glaciers still exist in Sierra Nevada de Santa Marta, in Sierra Nevada del Cocuy and on the volcanoes of Nevados del Ruiz, de Santa Isabel, del Tolima and del Huila. Comparison of reconstructions of maximum glacier area extent during the Little Ice Age with more recent information from aerial photographs and satellite images clearly documents a fast-shrinking tendency and potential disappearance of the remaining glaciers within the next few decades. In the past 50 years, Colombian glaciers have lost 5 0% or more of their area. Glacier shrinkage has continued to be strong in the last 15 years, with a loss of 10−50% of the glacier area. The relationship between fast glacier retreat and local, regional and global climate change is now being investigated. Preliminary analyses indicate that the temperature rise of roughly 1°C in the last 30 years recorded at high-altitude meteorological stations exerts a primary control on glacier retreat. The investigations on the Colombian glaciers thus corroborate earlier findings concerning the high sensitivity of glaciers in the wet inner tropics to temperature rise. To improve understanding of fast glacier retreat in Colombia, a modern monitoring network has been established according to the multilevel strategy of the Global Terrestrial Network for Glaciers (GTN-G) within GCOS. The observations are also contributions to continued assessments of hazards from the glacier-covered volcanoes and to integrated global change research in mountain biosphere reserves.
Lead pollution in Antarctic surface snow revealed along the route of the International Trans-Antarctic Expedition
Authors: Dahe Qin , Mayewski Paul A. , Berry Lyons W. , Junying Sun , Shugui Hou 
Published: November 2007

AbstractThis paper reports the lead concentration and flux (where accumulation rate is available) along the route of the 1990 International Trans-Antarctic Expedition. The lead concentration in Larsen Ice Shelf and Antarctic Peninsula, the western part of the route, was 7.4 ± 4.1 pg g−1. The lead concentration in East Antarctic snow (South Pole to Mirny station) was 2 3 times higher than that in West Antarctica (Larsen Ice Shelf to South Pole). Taking into account the difference in site conditions, the difference between the above value over this area in 1989 and the value of 6.3 ±3.3 pg g−1 at a site within this area in 1980 (Wolff and Peel, 1985) is not significant. Because the relative contribution of soil dust, volcanoes and the oceans to lead concentration in Antarctica is about 0.5 pg g−1 under modern climatic conditions (Boutron and Patterson, 1987), it is believed that the lead in Antarctic surface snow is dominated by pollution input. The lead-concentration increase from west to east over the trans-Antarctic route suggests that remote Antarctica has been impacted by anthropogenic activities. The lowest lead flux (0.064 ng cn-2 a−1) was on the Antarctic Plateau, mainly reflecting the background global pollution. The mean flux of 0.273 ng cnT2 a−1 in the western part of the route (Larsen Ice Shelf to the Ellsworth Mountains) may result from the pollution input from the Southern Hemisphere. In addition to the influence of global and/or hemispheric pollution, local activities (notably the use of leaded gasolene) appear to have affected the region from Pionerskaya to Mirny.
Glaciological properties of the Antarctic ice sheet from RADARSAT-1 synthetic aperture radar imagery
Authors: Jezek Kenneth C. 
Published: November 2007

AbstractThe RADARSAT-1 Antarctic Mapping Project (RAMP) is a partnership between the Canadian Space Agency and the US. National Aeronautics and Space Administration. The goal of the project is to create the first complete high-resolution radar mosaic of all of Antarctica for studies of Antarctic glaciology, geology coastal processes and climate. The major participants in RAMP are the Ohio State University the Alaska SAR Facility, the Jet Propulsion Laboratory, Pasadena, GA, and Vexcel Corporation. Phase one of the project was the Antarctic Imaging Gampaign-1 (AIG) which occurred during the period 9 September-20 October 1997. The AIG relied on the abilities of the Canadian RADARSAT-1 to rotate in orbit and to image with a variety of look angles to acquire imagery from the Antarctic coast to the pole. Its primary goal was the acquisition of image data. The nearly flawless execution of the mission also enabled additional collections of exact repeat orbit data. These data, covering a large part of the interior Antarctic, are potentially suitable for interferometric analysis of surface velocity. This paper describes the AIG and the various datasets obtained! It also reviews early scientific findings on the large-scale characteristics of the ice sheet including ice divides and ice streams. The overall conclusion is that these data, which constitute complete high-resolution microwave coverage, represent a new view of the Antarctic, revealing in considerable detail the glaciology, coastal processes and geology of the Southern Continent.
A detailed density profile of the Dome Fuji (Antarctica) shallow ice core by X-ray transmission method
Authors: Hori A. , Tayuki K. , Narita H. , Hondoh T. , Fujita S. , Kameda T. , Shoji H. , Azuma N. , Kamiyama K. , Fujii Y. , Motoyama H. , Watanabe O. 
Published: November 2007

AbstractAn X-ray transmission method has been developed to obtain a continuous profile of bulk densities of ice cores. Intensities of X-rays transmitted through an ice-core sample were continuously measured by an X-ray detector during translation of the sample across the X-ray beam. A thick section of an ice core with a constant thickness was prepared by band-sawing followed by microtome planing. The X-ray intensity profile obtained was converted to a density profile using a calibration curve for X-ray absorption vs ice thickness. Using this method, spatial resolution of the density profile was down to 1 mm. X-ray radiographs were also taken on a two-dimensional detector imaging plate, in order to observe layer structures of the ice cores.The method was applied to Dome Fuji (Antarctica) ice cores from the surface to 110 m depth. From the density profile obtained we calculated the power spectrum of the density variation by the discrete Fourier transform, and obtained several peaks at different frequencies. The center period in the spectrum was close to the annual accumulation thickness at the drill site.
The annual cycle of meteorological variables and the surface energy balance on Berkner Island, Antarctica
Authors: Reijmer Carleen , Greuell Wouter , Oerlemans Johannes 
Published: November 2007

AbstractIn February 1995 an automatic weather station (AWS) was placed on Thyssen Hohe, the south dome of Berkner Island, Antarctica. A fairly complete 3 year meteorological dataset of hourly average data was obtained. The mean annual temperature is about –24°C. The annual mass balance is about +180 mm we. Summer temperatures stay below 0°C, which implies that no melt takes place. Because the AWS is located on a dome, katabatic winds are not active, the wind direction is variable (directional constancy 0.38) and the wind speed relatively low (4.5 ms−1). Annual average variables are compared with data from Recovery Glacier AWS and Halley station.The measurements are used to evaluate the surface energy fluxes for the 3 year period by using a surface energy-balance model. The annual average gain of energy from the sensible-heat flux ( + 10.8 W m–2) is balanced by a negative net radiative flux (–9.1 W m−2) and a small negative latent-heat flux (-1.7 W rrT2). The annual subsurface flux is small.
Landform modification by palaeo-ice streams in east-central Ireland
Authors: Knight Jasper , Stephen G. McCarron , McCabe A. Marshall 
Published: November 2007

AbstractIn eastern Ireland, subglacial bedforms including drumlins and Rogen moraines were modified by headward erosion along two ice streams which had overlapping flow tracks. The ice streams, which had tidewater termini, are dated by geochronometric and morphostratigraphic methods to <15.014 C kyr BP (Castleblaney ice stream) and ~13.814C kyr BP (Armagh ice stream). Bedforms along ice-stream tracks show a morphological continuum which reflects a down-ice increase in the degree of modification by ice-stream activity (i.e. resulting in unmodified →remoulded/overprinted →crosscut →streamlined bedforms). The down-ice changes in bedform types are inferred to relate to changes in subglacial drainage and sediment-transport mechanisms. Bedform and sedimentary evidence suggest that discrete subglacial meltwater channels which developed up- ice changed in a down-ice direction to unchannelized flows which deepened towards the ice margin. Meltwater release from subglacial cavities, and produced by strain heating at sheared ice-stream margins, probably helped support ice-stream flow, which ended as the volume of subglacial meltwater discharge decreased. Dated millennial-scale cycles of ice activity may be related to instability at tidewater margins, followed by complex thermal and hydraulic responses within the ice mass.
Dendrogeomorphological study of glacier fluctuations in the Italian Alps during the Little Ice Age
Authors: Pelfini Manuela 
Published: November 2007

AbstractIn the Italian Alps, the maximum advance of the Holocene usually coincided with the Little Ice Age (LIA), which reached a climax for most glaciers during the first two decades of the 19th century. Moraines deposited during the peak of the LIA usually obliterated glacial deposits from previous advances. Using dendrogeomorphology, it is possible to date glacier advances before the LIA peak. In the central Italian Alps, it was possible to pinpoint an advance of Ghiacciaio del Madaccio, which took place in the first two decades of the 17th century. With dendrogeomorphology, it is also possible to reconstruct in detail the behaviour of glaciers during the Little Ice Age climax. Trees growing on the margin of glacier tongues may have suffered damage, recognizable by the presence of wood scars and the formation of particularly thin rings; their dating allows both ice advances and retreats to be dated. This is the case for Ghiacciaio Grande di Verra in the western Italian Alps; owing to the rapid decrease of the tree ring widths, it is possible to recognize climate changes responsible for both lower wood production and, sometimes, subsequent glacier advances, although the latter take place with a certain delay. For Ghiacciaio del Lys in the western Italian Alps, a response time of five years was determined.
Deglaciation of the Northern Hemisphere at the onset of the Eemian and Holocene
Authors: Greve Ralf , Wyrwoll Karl-Heinz , Eisenhauer Anton 
Published: November 2007

AbstractHigh resolution (TIMS) U-series dating of sea-level events obtained from coral-reef complexes suggests that global deglaciation from the Saale (penultimate) glacial to the Eem Interglacial (marine δ18O stages 6/5) may have occurred earlier in relation to Milankovitch insolation forcing than that from the Wisconsinan glacial to the Holocene Interglacial (marine δ18O stages 2/1). However, the interpretation of these data has been problematic because of the possibility of isotope exchange. In order to investigate whether these different lead—lag relations between Milankovitch forcing and ice volume are feasible from the point of view of large-scale ice-sheet dynamics and thermodynamics, the three-dimensional polythermal ice-sheet model SICOPOLIS (Simulation Code for Poly- thermal Ice Sheets) is applied to the entire Northern Hemisphere (which gives the major contribution to global ice-volume changes due to the relative stability of the Antarctic ice sheet) and simulations through the last two climatic cycles are conducted. The simulations cover the interval from 250 kyr BP until today and are driven by surface-temperature reconstructions of deep ice cores (GRIP, Vostok) and simple parameterizations for the change of precipitation with time. Discussion of the results is focused on the Saale/Eem and the Wisconsinan/Holocene transitions. The amount and rate of deglaciation are in good agreement with the SPECMAP record for both cases, and the evidence of the data for an early start of the Eem Interglacial is supported.
Size distribution of two cross-cutting drumlin systems in northern Sweden: a measure of selective erosion and formation time length
Authors: Hättestrand Clas , Goodwillie Dermot , Kleman Johan 
Published: November 2007

AbstractNearly 9000 individual lineations (drumlins and flutes) from two ice- flow systems have been mapped over a 22 500 km2 area of northern Sweden by interpretation of aerial photographs.The lineations were classified according to their size and orientation to allow a quantitative analysis of their distribution. The two glacial lineation systems, separated in time by at least 100 000 years and two individual overriding ice sheets, cross-cut at a high angle. The older system occurs over the entire study area and is interpreted to have formed by prolonged sheet flow during Marine Isotope Stage 5d, while the youngest system is spatially restricted, marking the presence of a laterally constrained zone of faster ice flow, developed near the end of the last deglaciation. The effect of the younger ice flow was erosion and elimination of smaller lineations in the older system, while the larger drumlinoid forms survived more or less intact, thus creating an apparent increase in average drumlin size of the older lineation system. One possible explanation for the unaltered shape of these larger drumlins is that the glacier bed of the younger ice sheet only reached the pressure melting point in the lower parts of the terrain, thus eroding the smaller forms, while the larger forms protruded into colder parts of the ice mass and were protected from erosion and deformation. There was no evidence of the deformation of older drumlins into barchanoid shapes or the development of lee-side tail features on the distal side of pre-existing lineations, as has previously been described for crossing drumlin systems. The lack of any such deformational features suggests that the younger lineation system was formed by net erosion, rather than deformation or deposition.
Tracer experiments and borehole observations in the over-deepening of Aletschgletscher, Switzerland
Authors: Hock Regine , Iken lmut , Wangler Alexander 
Published: November 2007

AbstractThe subglacial drainage in a pronounced overdeepening of Grosser Aletschgletscher, Switzerland was investigated by borehole water-level observations and dye-tracer injections. In August 1990 and 1991, tracer was injected at the bottom of a borehole (depth 904 m and 710 m, respectively), and simultaneously in a nearby moulin. The moulin and borehole injections identified two different flow systems coexisting within the overdeepening. The moulin injection yielded short-lived, highly peaked break-through curves with high velocities, indicating a hydraulically efficient channelized system. The borehole-tracer return occurred in broad multiple peaks characterized by a striking diurnal periodicity and, in general, correlated inversely with discharge. Water level in the borehole experienced high diurnal variations in phase with discharge at the snout indicating “closed channel flow” over large parts of the glacier. We infer that the boreholes drained subglacially and were connected to a drainage system with significant long-term storage capacity. Release of labelled water was triggered by daily water-pressure cycles.
Rheology of ice at the bed of Engabreen, Norway
Authors: Cohen Denis 
Published: November 2007

AbstractA three-dimensional finite-element model is used to analyze field data collected as dirty basal ice flowed past an instrumented obstacle at the bed of Engabreen, a temperate glacier in northern Norway The ice is modeled as an incompressible power-law fluid, with viscosity , where ΠD is the second invariant of the stretching tensor, and B and n are two parameters. Using measurements obtained in 1996 and 1997, two values of B are obtained, one using the measured normal stress difference across the obstacle, and the other using the measured bed-parallel force over the instrument. These two values are not equal, probably owing to small frictional forces at the bed unaccounted for in the numerical model. Hence, B ranges between 1.9 × 107 and 3.2 × 107 Pa s1/3 in 1996, and between 2.2 × 107 and 4.1 × 107 Pa s1/3 in 1997. These values are smaller than measured elsewhere for clean glacier or laboratory ice. Field measurements of water content, fabric and texture of the basal ice suggest that unbound water between thin sediment layers and lamellae of clean ice may act as a lubricant and significantly weaken the ice. Near-isotropic fabrics indicate that preferred fabric orientation does not enhance the deformation.
Glacier calving: a numerical model of forces in the calving-speed/water-depth relation
Authors: Hanson Brian , Hooke Roger LeB. 
Published: November 2007

AbstractEmpirical data suggest that the rate of calving of grounded glaciers terminating in water is directly proportional to the water depth. Important controls on calving may be the extent to which a calving face tends to become oversteepened by differential flow within the ice and the extent to which bending moments promote extrusion and bottom crevassing at the base of a calving face. Numerical modelling suggests that the tendency to become oversteepened increases roughly linearly with water depth. In addition, extending longitudinal deviatoric stresses at the base of a calving face increase with water depth. These processes provide a possible physical explanation for the observed calving-rate/water-depth relation.
Radar glacier zones in southeast Alaska, U.S.A.: field and satellite observations
Authors: Ramage Joan M. , Isacks Bryan L. , Miller Maynard M. 
Published: November 2007

AbstractThe ability of synthetic-aperture radar (SAR) to record change in glaciers and icefields on seasonal to interannual time-scales is useful in maritime mountain regions where visible data are often obscured by clouds. A time series of RADARSAT and second European Remote-sensing Satellite (ERS-2) SAR images shows dramatic changes related to the onset and progression of glacier melting on the Juneau Icefield, southeast Alaska, U.S.A. Four “radar glacier zones” are interpreted from SAR images as snow that is dry during winter, an early snowmelt (M), a second phase of snowmelt (M2) and bare ice. These zones develop every year on the Juneau Icefield and other mid-latitude glaciers. Summer field observations on the Juneau Icefield during 1997 and 1998 constrain interpretations of the C-band radar glacier zones. Of the two zones that occur in melting snow (M, M2), M has low radar backscatter coefficients (σ° < −12), in contrast to the higher backscatter coefficients (σ° > −12) of the subsequent M2 zone. Snow moisture and surface roughness at the scale of the radar wavelength (5.6 cm) were measured to characterize the melt zones. Correlation length, wetness and grain-size in the two zones are not distinguishable in the late ablation season. Mean surface roughness, due to the presence of suncups, is higher in the M2 zone than in the M zone and probably causes the higher backscatter due to greater scattering.
Ice discharge of eastern Dome C drainage area, Antarctica, determined from airborne radar survey and satellite image analysis
Authors: Frezzotti Massimo , Tabacco Ignazio Ezio , Zirizzotti Achille 
Published: November 2007

AbstractEastern Dome C, southern Talos Dome and northern Taylor Dome are drained by the Priestley, Reeves, David, Mawson and Mackay outlet glaciers, which flow into the Scott Coast on the west side of the Ross Sea, Antarctica. Airborne radar surveys were conducted on these glaciers to determine ice thickness and bed morphology along transverse and longitudinal profiles of the grounded and floating segments. A new analysis of a Landsat Thematic Mapper satellite image using a tracking technique was used to measure ice velocity at grounding lines and along ice tongues. The integration of radar and satellite data helped to locate grounding lines and to calculate the ice discharge. Changes in ice fluxes of floating glaciers were used to determine basal melting and freezing rates. The ice discharge calculated is less than half that required for a zero net surface mass balance according to the inputs given by the accumulation estimates widely adopted at present. The basal melting rates of meteoric ice represent 50% of the net ablation rate.
Results from the EISMINT model intercomparison: the effects of thermomechanical coupling
Authors: Payne A. J. , Huybrechts P. , Abe-Ouchi A. , Calov R. , Fastook J. L. , Greve R. , Marshall S. J. , Marsiat I. , Ritz C. , Tarasov L. , Thomassen M. P. A. 
Published: November 2007

AbstractThis paper discusses results from the second phase of the European Ice Sheet Modelling Initiative (EISMINT). It reports the intercomparison of ten operational ice-sheet models and uses a series of experiments to examine the implications of thermomechanical coupling for model behaviour. A schematic, circular ice sheet is used in the work which investigates both steady states and the response to stepped changes in climate. The major finding is that the radial symmetry implied in the experimental design can, under certain circumstances, break down with the formation of distinct, regularly spaced spokes of cold ice which extended from the interior of the ice sheet outward to the surrounding zone of basal melt. These features also manifest themselves in the thickness and velocity distributions predicted by the models. They appear to be a common feature to all of the models which took part in the intercomparison, and may stem from interactions between ice temperature, flow and surface form. The exact nature of these features varies between models, and their existence appears to be controlled by the overall thermal regime of the ice sheet. A second result is that there is considerable agreement between the models in their predictions of global-scale response to imposed climate change.