bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of A 870 M Deep Temperature Profile at Dome C
Authors: Ritz Catherine , Lliboutry Louis , Rado Claude 
Published: February 2017

The French 870 m deep temperature profile gives us temperature differences with an accuracy of 0.01 deg (to obtain such an accuracy, the sensors must be applied against the walls of the bore hole). The error on the vertical gradient T' cannot be lessened by weighted running means. Thus, only a mean value of its derivative T" can be reached.Data have been analysed by assuming a two-dimensional flow over a plane horizontal bedrock. As a first step, the steady state at an ice divide has been calculated by solving the complete set of equations. The vertical strain-rate is a constant over two-thirds of the ice sheet. It appears that, at Dome C, sliding and no-sliding solutions are plausible, as well as cyclic oscillations between them. Next, the temperature response of the ice sheet to an impulse for the surface temperature has been computed, and convolved with surface palaeotemperatures deduced from the180 profile, to obtain the time derivative Ṫ.Mean values of T', T" and Ṫ allow an estimation of the vertical velocity, which is much smaller than the balance one. Therefore, the ice sheet has thickened by 200 to 280 m during the last 10 ka.
Sensitivity of Late-Glacial and Holocene Climates to the Combined Effects of Orbital Parameter Changes and Lower Boundary Condition Changes: “Snapshot” Simulations with A General Circulation Model for 18, 9, AND 6 ka BP
Authors: Kutzbach John E. , Guetter P. J. 
Published: February 2017

Sensitivity experiments can be used to illustrate the response of the general circulation to prescribed changes in lower boundary conditions (such as ocean temperature) or external forcing conditions (such as solar radiation). The climatic record from the late-glacial and the Holocene provides examples for both types of prescribed change experiments. A number of general circulation model experiments have been carried out. These are reviewed.At 18 ka 8P, orbital parameter values were very much like those of today, but the lower boundary conditions (ocean temperature, ice-sheet extent, etc.) were very different. The change in ocean temperature, and ice-sheet extent and thickness, were prescribed from the results of the Climate: Long-range Investigation Mapping and Prediction (CLIMAP) project.At 9 ka BP, orbital parameter values were very different from present, leading to increased radiation in July and decreased radiation in January (compared to present). The North American ice sheet still covered a significant area, so that lower boundary conditions also differed from the present ones. The combined and individual effects of these prescribed changes on the general circulation are reviewed, particularly in the context of changes of the monsoon circulation.At 6 ka BP, the solar radiation distribution differed from that of today in much the same fashion as at 9 ka BP, although the magnitude of the change was reduced. Lower boundary conditions were probably very similar to those of today.A series of experimental results from 18, 9, and 6 ka BP are presented as “snapshot” estimates of the paleoclimate of those times. The results are based upon simulations with the community climate model of the National Center for Atmospheric Research.
Impurities in Snow: Effects on Albedo and Snowmelt (Review)
Authors: Warren Stephen G. 
Published: February 2017

Very small (ppm) amounts of soil dust in snow can significantly reduce snow albedo and thereby affect the snow-surface energy budget. Ice cores from Greenland show enhanced dust concentrations in ice from the last glacial maximum, in amounts capable of causing measurable effects on snow albedo. This enhanced dust is probably due in part to the expanded desert areas at that time.Volcanic ash layers visible in the Byrd station core reduced the snow albedo in West Antarctica when they were on the surface. The ash is unlikely to have had a long-term effect on albedo because of the episodic nature of volcanic eruptions.Very large amounts of dust on snow can inhibit snow-melt by insulating the snow. A debris cover probably slowed the melting of parts of the North American ice sheet during its most recent decay phase.Snow in the Arctic Ocean is presently suffering large-scale contamination by carbon soot from anthropogenic sources. Preliminary estimates indicate that soot concentrations in Arctic snow are sufficient to reduce snow albedo measurably.
The Laki and Tambora Eruptions as Revealed in Greenland Ice Cores from 11 Locations
Authors: Clausen H.B. , Hammer C.U. 
Published: February 2017

Major volcanic eruptions deposit large amounts of strong acids in polar ice. Two such volcanic eruptions are Laki, A.D. 1783, at high latitude (64 °N), and Tambora,A.D.1815, close to the Equator (8°S). The acid ice layers from these eruptions are easily reached by shallow drilling, and the acidity of the ice cores obtained has been determined by a solid electrical conductivity method (ECM), and in some cases by liquid pH measurements. The strong acid is identified by chemical anion analysis. Sulfate is the dominant anion in both of these volcanic events.Atmospheric thermonuclear-bomb tests ejected radioactive debris into the atmosphere. Two major groups of such tests are those carried out by the Americans in 1952-54 at low latitude (11°N) and by the Russians in 1961-62 at high latitude (75°N). Radioactive debris from these events was deposited in polar snow, and can be detected by specific total β activity measurements. The radioactive layers serve as dating horizons in the firn. The total β activities were measured at least 10 years after ejection, thus the measured activities were mainly due to90Sr and137Cs.The amount of90Sr and137Cs ejected into the atmosphere is known. We assumed a similar global distribution pattern of bomb-produced total β activity and strong acids from violent volcanic activity, and were able to calculate that both major volcanic events produced some 300 million tons of sulphuric acid. This is in agreement with other estimates of the Tambora eruption, which are based on studies of ice cores from Antarctica.
Preliminary Results of Analyses of 700 m Ice Cores Retrieved at Mizuho Station, Antarctica
Authors: Higashi A. , Nakawo Masayoshi , Narita Hideki , Fujii Yoshiyuki , Nishio Fumihiko , Watanabe Okitsugu 
Published: February 2017

Preliminary results of the analyses on 700 m ice cores retrieved from Mizuho Station, Antarctica, in 1983 and 1984 are presented. The majority of the physical properties, density, grain-size and shape, and total gas content, were measured at the drilling site. Fabrics, microparticle concentration, electrical conductivity, and stable-isotope concentration δ18O were measured in laboratories after the cores had been taken to Japan.
In spite of inaccuracy in measuring both density and total gas content in the ice, due to interlocking cracks in cores, several attempts were made to correct the data. The coincidence between the incremental peaks in the depth profile of the microparticle concentration, as well as in the electrical conductivity and the warm trend indicated by the δ18O profile is discussed. The shape of the δ18O profile is characterized by two inflection points and is compared with results obtained from the Byrd Station, Dome C and Vostok cores. From this comparison, it is tentatively concluded that the bottom of the Mizuho core may be an age of the order of 10 ka B.P.
Stable-Isotope/Air-Temperature relationships in Ice Cores from Dolleman Island and the Palmer Land Plateau, Antarctic Peninsula
Authors: Peel David A. , Mulvaney Robert , Davison Brian M. 
Published: February 2017

Whilst stable-isotope analysis of ice cores yields the best quantitative evidence for past climate, there remains considerable uncertainty about the detailed relationship between the isotopic composition and air temperature. Analysis of two ice cores from the Antarctic Peninsula (a 47.2 m core from the Palmer Land plateau – 74°01’S, 70°38’W, and a 32 m core from Dolleman Island–70°35.2’S, 60°55.5’W) has shown that an oxygen-isotope/ temperature relationship exists at a resolution of inter-annual variations during the period 1938–86. All the major regional temperature anomalies, known from climatic records at several stations, are visible in the isotope profiles, including the overall temperature increase between 1960 and 1980.
An isotope–temperature gradient of 0.5–0.6‰/°C is indicated for the climatic interpretation of isotopic fluctuations in ice cores recovered from the region. This gradient is considerably smaller than that (0.95‰/°C) obtained from a comparison of spatial variations in the mean annual parameters. The discrepancy appears to be due mainly to an inherent biasing in the isotope profiles, which record temperature only during periods of snowfall. The effect is particularly severe in the winter months and can be expected in other areas of Antarctica where a significant part of the snow accumulation is cyclonic.
Changes in areal extent, elevation and volume of Athabasca Glacier, Alberta, Canada, as estimated from a series of maps produced between 1919 and 1979
Authors: Reynolds J. R. , Young G. J. 
Published: February 2017

Changes in planimetric area, elevation and volume were calculated for Athabasca Glacier, Alberta, Canada, below 2400 m elevation for the period 1919–79 from maps produced using aerial or terrestrial photogrammetry. Map contours were digitized and converted into raster digital elevation models (DEMs). Comparison of the models allowed changes in volume and elevation to be estimated. In the time of record, the glacier lost 2.344 × 108 m3 of volume and downwasted significantly.
There are several sources of error associated with DEM generation and construction: source maps have spatially variable uncertainty in vertical estimation, associated with the photogrammetric process used; small errors are introduced in the creation of raster DEMs as a result of fitting surfaces to digitized contours; errors of registration, leading to errors in estimation of vertical change over time, can be of significance, especially when comparing maps produced by different photogrammetric techniques.
These errors are quantified and displayed in transect and map form. Especially with maps only 2 years apart in time, errors are often greater than actual changes in surface elevation. The magnitude of the errors involved in the comparison of maps made with a 2 year interval would suggest that 5 or 10 years between successive mappings might have been more scientifically justifiable and more cost effective.
Description of a program for SAR investigation of the Greenland ice sheet and an example of margin change detection using SAR
Authors: Fahnestock Mark A. , Bindschadler Robert A. 
Published: February 2017

In order to interpret changes in the Greenland ice sheet as indications of climatic variation, it is necessary to place observations of local changes in a regional context. This requires a comprehensive monitoring effort which addresses both the inland ice and changes in the ice margin. This paper describes the design of a program for regional investigation of the Greenland ice sheet using synthetic aperture radar (SAR), and discusses the utility of SAR data for detection of change in the ice sheet margin.
Comprehensive coverage of the Greenland ice sheet by ERS-1 SAR will allow us to map the boundaries of snow facies on the ice sheet and investigate recent changes in the ice margin. We will use geo-referenced images to map the current boundaries of snow facies, providing a baseline which can be used to detect future change.
We demonstrate the utility of SAR for detecting recent changes in the ice margin. SAR images clearly show the ice edge, moraines, and ice marginal lakes. These features can be compared with published maps and earlier images in order to document changes in the margin of the ice sheet. We show evidence for recession of a section of the western margin of the ice sheet. The recession, which occurred between 1938 and 1978, ranges from a few hundred meters at high elevations to several kilometers at calving faces in both ice marginal lakes and fjords.
ERS-1 SAR will provide the first opportunity to pursue a comprehensive investigation of the state of the Greenland ice sheet. The ability to address conditions on the ice and to look at margin changes in a systematic way will allow us to develop a stronger framework for interpreting changes in the ice sheet in terms of climatic variation.
A digital elevation model of the Antarctic ice sheet derived from ERS-1 altimeter data and comparison with terrestrial measurements
Authors: Bamber Jonathan L. 
Published: February 2017

The launch of ERS-1 provides coverage, by satellite altimetry, of 80% of the Antarctic ice sheet, allowing topographic mapping of areas which previously had a dearth of accurate elevation data. Four 35 d repeat cycles of fastdelivery altimeter data were used in this study, comprising a total of approximately 1000000 height estimates. About 40% of these were rejected during a careful filtering procedure designed to remove erroneous values caused by poor tracking or complete loss of the returned echo. The OSU-91A geopotential model was used to convert ellipsoidal elevations to geoidal values. Corrections for surface slope were applied and a Digital Elevation Model (DEM) was produced with a grid spacing of 20km.The precision of the data was assessed from an analysis of crossing points of ascending and descending tracks. For 43864 cross-overs, the standard deviation was 6.8m. Regional biases associated with geoid, orbit and topography-induced errors reduce the accuracy of the height measurements. This was assessed by a comparison with ground-survey data. The DEM was compared with a 700km levelling survey, with an accuracy ranging from 1 to 5m, from the Lambert Glacier basin region (≈73° S, 55° E). The mean difference was found to be-1.6m with a standard deviation of 14m. A similar result was obtained for a 600km traverse line in Wilkes Land (75° S,≈1l0° E).The DEM was then compared with a digitized version of the Scott Polar Research Institute (SPRI) Antarctic folio map. This map was derived from orthometric measurements of surface elevation, primarily from pressure altimetry. Differences in excess of 300 m were observed between the two data sets. Only 37% of the region covered showed agreement to better than 50m, and a significant proportion ofthis was composed of the Ross and Filchner-Ronne Ice Shelves. The largest discrepancies occurred in marginal areas where there is poor coverage by both satellite altimetry and terrestrial data. Inland, significant differences were also found.
Ice Stream C, Antarctica, sticky spots detected by microearthquake monitoring
Authors: Anandakrishnan S. , Alley R. B. 
Published: February 2017

Microearthquakes at the base of slow-moving Ice Stream C occur many times more frequently than at the base of fast-moving Ice Stream B. We suggest that the microearthquake source sites are so-called “sticky spots”, defined as limited zones of stronger Subglacial material interspersed within a weaker matrix. The fault-plane area of the microearthquakes (O(102m2)) is therefore a measure of the size of the sticky spots. The spatial density of the microearthquakes (O(10 km-2)) is a measure of the distribution of sticky spots.The average stress drop associated with these microearthquakes is consistent with an ice-stream bed model of weak subglacial till interspersed with stronger zones that support much or all of the basal shear stress. We infer a weak inter-sticky-spot material by the large distances (O(103m)), relative to fault radius, to which the microearthquake stress change is transmitted.
Seasonal variations of major ionic concentration levels in drifting-snow samples obtained from east Dronning Maud Land, East Antarctica
Authors: Osada Kazuo 
Published: February 2017

Drifting-snow samples were collected at Mizuho Station (74°42' S, 44°20' E, 2230 m a.s.1.) from February to October 1986 and along traverse routes in east Dronning Maud Land (1800-3000 m a.s.1.), East Antarctica, from October 1986 to January 1987. The typical sampling interval was about once a week but two sets of intensive sampling were made at the end of February and November at between 2 h and 1 d intervalsMeasurements for CI-, NO3,SO42and Na+ were made on the drifting-snow samples by ion chromatography. Oxygen-isotope ratios were .also measured .on the samples. Concentrations levels ofNO3-and SO4-show distinctive seasonal variations: high in summer (4.6 neq g-1 for NO3and 3.3 neq g1 for SO42) and low in winter during mid-March to mid-November(1.0 neq g1 for NO3 and 0.5 neq g1 for SO42). Results obtained at Mizuho Station show that the transition from the summer high values to winter low values takes about 20 d for NO3 and SO42-.The variations in Cl and Na+ concentration levels are small in both autumn and spring (averages are about 1 neq g-l) with greater variability throughout the rest of the year. The intensive sampling data set shows that there is considerable variability within a day with NO3 and SO42-concentration levels up to about a factor of 4 associated with a 10%0 change in 3180 ratios.
A numerical model of blowing snow around an Antarctic building
Authors: Moore I. , Mobbs S.D. , Ingham D.B. , King J.C. 
Published: February 2017

The accumulation of drifting snow around buildings in regions of severe climate has important implications on their design and location. This paper studies one such building, at a station run by the British Antarctic Survey and located on the Brunt Ice Shelf at the edge of the Antarctic continent. Four previous stations have been built in the area, the buildings of which were designed to become covered in snow and all have been crushed within a few years. The current station, Halley V, consists of three buildings which are all raised from the ice shelf by means of legs. They were designed in such a way that the action of the wind blowing underneath the buildings would keep them-clear of snow.
This paper describes a model which predicts the shape and position of drift formation, and then compares the results with those observed at Halley. This model is a first attempt to address the problem and as such the paper can be considered to be a progress report; improvements arc currently being made as part of continuing research. It is found that there is some qualitative agreement and possible reasons for a few quantitative discrepancies are discussed. Both the model and the true data show clearly that the new design is very effective in prolonging the useful life of the buildings.
Validating and improving elevation data of a satellite-image map of Filchner,Ronne Ice Shelf, Antarctica, with Results from ERS-1
Authors: Sievers J. , Doake C.S.M. , Ihde J. , Mantripp D.R. , Pozdeev V.S. , Ritter B. , Schenke H.W. , Thyssen F. , Vaughan D.G. 
Published: February 2017

A satellite-image map with surface-elevation contours of Filchner Ronne Ice Shelf has been published previously as a topographic map. The image map was constructed from a mosaic of 69 Landsat Multispectral Scanner (MSS) images and NOAA AVHRR data. The standard deviation in position in the central part of the mosaic is ±125m. Topographic-glaciologic features were taken from Landsat scenes and represent the best coastline of this region. Surface elevations have been calculated from airborne and ground measurements of either ice thickness (by assuming hydrostatic equilibrium) or barometric pressure. Accuracies vary from ±2 to ±7 m, Oversnow trigonometric levelling in the northeastern part of the ice shelf, tied to sea level at the ice front, has given accuracies of ± 1m. Accuracies reduce to about ±20 m in the grounded ice areas,
ERS-I radar-altimeter data over the ice shelf have been processed to give ellipsoidal heights elevation above the ellipsoid), Geoidal reductions have been used to convert these to orthometric heights (elevation above sea level). No tidal corrections have been applied. The overall accuracy of the radar-altimeter-derived elevations is estimated to be better than ±5m. There are noticeable differences from the topographic map in the central part where the radar data indicate a lower surface. However, the maps agree to within the stated error figures.
Investigating tidal flexure on an ice shelf using kinematic GPS
Authors: Vaughan David G. 
Published: February 2017

The positions of ice-stream grounding zones are uniquely sensitive to changes in the mass balance of the ice sheet. Present methods for locating groundingzone features are either imprecise or require considerable effort in interpretation and so are of little value for change studies. We present a new method which uses the kinematic GPS technique to locate the position of the limit of tidal flexure. The method involves the collection of at least two surface-elevation profiles along the same track through the grounding zone, at different times during the tidal cycle. The elevation profiles obtained coincide upstream of the: limit of flexure but diverge downstream of the limit of flexure. Subtracting the profiles produces a tidal-def1ection profile which shows directly the response of the ice shelf to the tidal forcing.We present two examples of the use of this method, both on Rutford Ice Stream. Antarctica. The first is across the grounding zone and shows that the method is capable of measuring grounding positions to around 200 m precision. The second, taken across an active shear margin, shows a tidal-deflection profile, with an absence of steps that would indicate the presence of fracture planes penetrating from the ice base to sea level.
Temperature investigation and modeling on the Filchner-Ronne Ice Shelf, Antarctica
Authors: Grosfeld K. , Thyssen F. 
Published: February 2017

During the German Antarctic Expedition field season 1989–90. hotwater drilling was undertaken on the Filchner-Ronne Ice Shelf (FRIS) at 77° S 52°c W to investigate the temperature-depth profile and the bottom-melting rate, which arc significant parameters for mass- and energy-balance studies of the ice shelf. Remeasurements of installed chains in 1991-92 yie1ded reliable results.
Taking glaciological, geodetic and geophysical data on a flowline through the central part of FRIS. we developed a two-dimensional thermal model to reconstruct the measurernents from a steady-state temperature depth profile about 550 km upstream on Möllereisstrom. Considering mass and energy conservation, a basal layer of 350 m of marine ice was calculated with thermal properties, depending on salinity and temperature. In areas with strong basal freezing, almost isothermal depth profiles in the marine ice layer are derived. Further downstream, in areas of basal melting, a nearly cubic temperarure-depth profile is observed.