bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Surface Characteristics of the Antarctic Ice Sheet with Satellite Observations (Abstract)
Authors: Young N. , Goodwin I.
Published: February 2017

Ground surveys of the ice sheet in Wilkes Land, Antarctica, have been made on oversnow traverses operating out of Casey. Data collected include surface elevation, accumulation rate, snow temperature, and physical characteristics of the snow cover. By the nature of the surveys, the data are mostly restricted to line profiles. In some regions, aerial surveys of surface topography have been made over a grid network.

Satellite imagery and remote sensing are two means of extrapolating the results from measurements along lines to an areal presentation. They are also the only source of data over large areas of the continent. Landsat images in the visible and near infra-red wavelengths clearly depict many of the large- and small scale features of the surface. The intensity of the reflected radiation varies with the aspect and magnitude of the surface slope to reveal the surface topography. The multi-channel nature of the Landsat data is exploited to distinguish between different surface types through their different spectral signatures, e.g. bare ice, glaze, snow, etc. Additional information on surface type can be gained at a coarser scale from other satellite-borne sensors such as ESMR, SMMR, etc. Textural enhancement of the Landsat images reveals the surface micro-relief.

Features in the enhanced images are compared to ground-truth data from the traverse surveys to produce a classification of surface types across the images and to determine the magnitude of the surface topography and micro-relief observed. The images can then be used to monitor changes over time.
Surface Velocity Determination on Large Polar Glaciers by Aerial Photogrammetry
Authors: Brecher H. H.
Published: February 2017

Aerial photogrammetric block triangulation, a standard and well-developed technique for extending accurate control for mapping into the interior of a region from a few points of known position on its perimeter, can be readily adapted to determine surface velocities on bodies of ice which are too large, and often too crevassed, to be studied effectively by conventional ground surveying. Velocities are calculated from the changes in positions of the same natural surface features determined from photography of two (or more) epochs and the elapsed time. This method is capable of providing many uniformly-spaced measurements over the whole, moving, ice surface, thus allowing the production of maps of velocity and strain-rate, which are valuable in analyzing the ice-flow regime. Results from measurements completed some years ago on Byrd Glacier, one of the largest outlet glaciers from the East Antarctic plateau, are presented as an example of what the method can yield. By means of Doppler satellite surveying, relative positions of control points for each photography epoch can be determined with sub-meter accuracy, making the technique suitable also in regions where no fixed land features exist. A brief description of a project under way in such an area, on Ice Stream B in West Antarctica, is given.
Glacier Volume Estimation on Cascade Volcanoes: An Analysis and Comparison with Other Methods
Authors: Driedger C.L. , Kennard P.M.
Published: February 2017

During the 1980 eruption of Mount St. Helens, the occurrence of floods and mudflows made apparent a need to assess mudflow hazards on other Cascade volcanoes. A basic requirement for such analysis is information about the volume and distribution of snow and ice on these volcanoes.

An analysis was made of the volume-estimation methods developed by previous authors and a volume- estimation method was developed for use in the Cascade Range. A radio echo-sounder, carried in a backpack, was used to make point measurements of ice thickness on major glaciers of four Cascade volcanoes (Mount Rainier, Washington; Mount Hood and the Three Sisters, Oregon; and Mount Shasta, California), These data were used to generate ice-thickness maps and bedrock topographic maps for developing and testing volume-estimation methods. Subsequently, the methods were applied to the unmeasured glaciers on those mountains and, as a test of the geographical extent of applicability, to glaciers beyond the Cascades having measured volumes.

Two empirical relationships were required in order to predict volumes for all the glaciers. Generally, for glaciers less than 2.6 km in length, volume was found to be estimated best by using glacier area, raised to a power. For longer glaciers, volume was found to be estimated best by using a power law relationship, including slope and shear stress. The necessary variables can be estimated from topographic maps and aerial photographs.
Glacier Mapping to Confirm Results from Mass-Balance Measurements
Authors: Haakensen Nils
Published: February 2017

Annual mass-balance measurements have been made at a number of glaciers in Norway since the beginning of the 1960s, A detailed and reliable map is necessary as a base for field work and more than twenty glacier maps have been constructed photogrammetrically at scales of 1:10 000 or 1:20 000 since 1952. For some of the glaciers more than one map has been constructed and changes in glacier volume can be calculated, provided the maps have sufficient accuracy.

For the glaciers, Nigardsbreen, Hellstugubreen, and Gråsubreen, two or more good maps are available and these form a good basis for comparisons and calculations of changes in volume between the years when the air photographs were taken.

Comparisons have been made for Gråsubreen between 1968 and 1984, for Hellstugubreen between 1968 and 1980, and for Nigardsbreen between 1964 and 1984.

The calculations are made by placing a 100 m grid on the glacier maps and comparing the altitude for corresponding points. The changes in height are regarded as representative for the 0.01 km2 glacier areas represented by each point.

Results from the investigation have been used to check the accuracy in cumulative mass balance for corresponding periods.

Repeated air photography, at intervals of 5—10 years, can be used in the future to find the cumulative mass balance for a great number of glaciers at lower cost than “normal” mass-balance work.
Survey and Mapping of Recent Ice Shelf Changes and Landfast Sea Ice Growth Along the North Coast of Ellesmere Island, NWT, Canada
Authors: Jeffries M.O. , Serson H.V.
Published: February 2017

Ground and aerial surveys along the north coast of Ellesmere Island confirm that a considerable area of shelf ice remains, although it is not as extensive as it once was due to periodic ice island calvings. However, the lost ice shelf is quickly replaced by landfast sea ice. The sea ice often persists for many years and thickens sufficiently to be considered as the restoration of former ice shelf. The landfast ice quickly assumes an undulating topography, similar to the ice shelves, the development of which is encouraged by melt water and wind action. Even under the present conditions of negative mass balance, the sea ice reaches considerable, undeformed thicknesses. The thick sea ice forming today could be the precursor of an expansion of the ice shelves.
Main Results of Mapping Glacio-Nival Systems in the World Atlas of Snow and Ice Resources
Authors: Kotlyakov Vladimir M. , Dreyer Natalia N. , Kravtsova Valentina I.
Published: February 2017

The compilation of the Atlas was based on the concept of glacio-nival systems (and the fields of these systems), developed in the U.S.S.R. It became possible to map glacionival systems by using all available data and by the development of indirect methods of obtaining regime parameters, characterising the glacio-nival zones. This, in turn, made it possible to show, on maps of different scales, properties relating to glacio-nival phenomena and processes, such as air temperature in a glacierized zone, the amount of solid and liquid precipitation, snow storage, the accumulation and surface ablation of glaciers and melt run-off.

The compilation of these maps has demonstrated their conformity and complementary nature, the principles of which were worked out in the course of creating the Atlas.

Based on the experience of compiling hundreds of various maps, the paper describes some peculiarities of depicting different elements of glacio-nival systems on maps of different scales and shows ways to overcome shortages of data in preparing the maps.
Photogrammetric and Satellite Mapping of the Margin of the Inland Ice, West Greenland
Authors: Thomsen H.H.
Published: February 2017

Glaciological investigations have been carried out in areas proposed for local hydro-power stations in Greenland, A mapping programme was set up, to provide data for mass balance and simulation of run-off, as well as glacier dynamics.

Two types of glacier map have been produced, covering the margin of the Inland Ice: detailed photogrammetric maps, based on plotting from vertical aerial photographs and a new type of surface feature map, based on digitally-processed Landsat data. The photogrammetric maps, plotted on a scale of 1:25 000, include surface topography and surface features, such as crevasses, lakes, moraines etc. The surface feature maps, plotted on a scale of 1:100 000, show surface features related to ice and melt-water drainage, as well as subtle, topographic features, related to the subglacial topography.

The maps have so far been used for preliminary delineation of drainage areas on the Inland Ice and for planning tracks of radio echo-soundings.
Topographic Characteristics in the Ablation Area of the Khumbu Glacier, Nepal Himalaya
Authors: Watanabe O. , Iwata S. , Fushimi H.
Published: February 2017

Topographic sketch mapping of the whole ablation area of the Khumbu Glacier, East Nepal Himalaya, is performed, using a simple, stereo-photogrammetric method. This map shows that the surface morphology can be classified into 11 morphologic characteristics. Depending on their distribution and combination, the ablation area can be divided into four morphologic areas. Detailed maps, on a scale of 1:1000–2500, of these four areas indicate that the distribution and combination of these 11 morphologic characteristics result from thickness of the debris cover, supraglacial streams and ponds, and glacier dynamics. The irregularity in the ablation area of the Khumbu Glacier can be considered to be a consequence of the mass balance between rate of ice charge from upstream and irregular distribution of ablation rate, depending on debris-cover characteristics in situ.
Cartographic Methods for Large Scale Glacier Maps
Authors: Shicong Yin , Jianming Chen
Published: February 2017

Glacier mapping is steadily developing, along with the continuous expansion of glaciological research, in China. In the last 20 years we have made surveys and drawn up glacial topographic maps on large scales, of various study areas in Tianshan and the Qinghai-Xizang Plateau. This paper discusses the cartographic techniques, in the form of points, lines, symbols, brush-shading, colours, etc., used to create a vivid reproduction of the special natural landscape of glaciers on maps for the use of glaciologists and other scientists. For example, variations in rock symbols may be used to show the exposed bedrock, the glacial abrasion and the cryogenetic weathering. Different colours and points are used to indicate the various depositional landforms which are also enhanced by the method of brush-shading and the use of differently coloured contour lines. In addition, the paper discusses the technical and theoretical problems of glacier mapping.
Ice-Sheet Thickening Observed by Satellite Altimetry (Abstract)
Authors: Zwally H.J.
Published: February 2017

The first set of sequential measurements by two different sets of satellite altimetry data indicate that the Greenland ice sheet, south of 65.1° north latitude, thickened at the rate of 35 ± 17 cm a−1 during 1975 to 1978. The average change in surface elevation was calculated from the elevation differences determined at 525 locations observed by both GEOS-3 and Seasat radar altimeters. The observed thickening is consistent with the 8 cm a−1 thickening previously measured in the accumulation zone, approximately 900 km farther north, during conventional, surface, survey methods. The increase in ice thickness suggests a higher precipitation than the long-term average, which is one possible result of a warmer climate in polar regions. The excess ice accumulation, in the 10 % of the Greenland ice sheet observed, is estimated to be 53 km3 a−1, which is equivalent to a sea-level reduction of 0.15 mm a−1. Additional, high-precision, sequential, altimetric measurements could be used to determine the overall mass balance of the Greenland and Antarctic ice sheets.
Mapping Coastal Ice Cliffs and Icebergs From Altimetry Data (Abstract)
Authors: Thomas R.H. , Zwally H. Jay
Published: February 2017

In a recent paper, Thomas et.al. (1984) showed how the coast of Antarctica could be mapped using satellite altimetry data. As the satellite approached the continent from the ocean, the Seasat altimeter obtained strong reflections from sea ice, even for a short time after passing over the ice front. Measured ranges are actually oblique distances to the nearest portion of sea ice, yielding a false drop in surface elevation. From the sequence of oblique ranges during a single orbit crossing of the ice cliff, the horizontal position of a segment of the ice cliff is mapped. Currently, the entire Seasat data set is being analyzed to map most of the Antarctic coastline north of 72 °S to an accuracy of ± 0.1 to 1 km, which is a major improvement over existing surveys. The altimeter waveforms corresponding to each range measurement are computer analyzed (“retracked”), using procedures that account for the specular reflections from sea ice and the diffuse reflections from firn. Each waveform analysis, along with the corrected range for data obtained in the vicinity of an ice cliff crossing, is verified or recomputed on an interactive computer, which also computes and maps the position of the ice front. The locations of several tabular icebergs have also been mapped with the same procedures, which can ultimately be used to obtain an estimate of iceberg population density in polar waters, initial results include the mapping of the Larsen ice shelf on the eastern side of the Antarctic Peninsula, showing, for example, the protrusion at approximately 68.5 °S. Estimates of errors in the derived horizontal position are obtained from the analysis of data from repeating orbit tracks. Comparison of these results with results from future altimetry missions will reveal changes in the position of coastal ice cliffs, due to ice movement and/or iceberg calving. Systematic measurements over several years would probably distinguish the effects of iceberg calving, which is intermittent, from those of ice movement, which is continuous.
Polar Firn Densification and Grain Growth
Authors: Alley Richard B. , Bolzan John F. , Whillans Ian M.
Published: February 2017

A 50 m firn core from Dome C, East Antarctica, was found to consist of coarse firn, which comprised 90 to 95% of the core, and fine firn. Coarse firn was characterized by large crystals with a vertical shape orientation near the surface, connected to nearest neighbors by relatively large necks in a structure different from closest packing. Fine firn was of higher density and consisted of smaller, more spherical crystals connected by relatively narrow necks in a more nearly closest-packed configuration.

Higher surface free energy in fine firn causes crystals and necks to grow more rapidly than in coarse firn. However, we find that coarse firn densifies more rapidly with time, contrary to the predictions of unconfined sintering models. Load-driven densification due to a power-law creep mechanism is found to account for the larger coarse-firn densification rate. However, if the exponent in the power law exceeds one, then densification rates are predicted to increase with depth due to increasing load, contrary to observed behavior. We speculate that different mechanisms may control the densification process in fine and coarse firn.
Late Glacial Input of Eolian Continental Dust in the Dome C Ice Core: Additional Evidence from Individual Microparticle Analysis
Authors: Briat M. , Royer A. , Petit J. R. , Lorius C.
Published: February 2017

399 individual microparticles in nine samples from the Dome C ice core were studied under scanning electron microscope and analysed by an energy dispersive X-ray system. The studied particles were either continental quartz or various silico-aluminates of continental or volcanic origin. Observations lead to the conclusion that the increase in micro particle concentration by a factor of 10 to 20 during the last glacial stage is explained by a large input of continental dust, as already indicated by trace element analysis (Petit and others 1981) and previously suggested by chemical analysis of other polar ice cores (Cragin and others 1977).This increase is considered to be a consequence of the ice-age climate and earth surface conditions which were characterized by the increase of arid regions and more vigorous atmospheric circulation. Both these conclusions are further supported by the existence of a higher quartz content in the Antarctic ice core as was already found in tropical deep-sea core studies.
Satellite Altimeter Results Over East Antarctica
Authors: Brooks R. L.
Published: February 2017

During the operational lifetime of the Seasat altimeter from 3 July to 10 October 1978, more than 450 overflights were made over East Antarctica inland to latitude 72°S. An analysis of selected passes over a variety of ice features demonstrates that the oceanographic altimeter performed surprisingly well over the ice sheet and ice shelves, acquiring useful measurements during approximately 70% of each pass. The altimeter's onboard tracking system dampened out the ice-surface elevations, but post-flight retracking of the stored return waveforms reveals excellent ice-surface details. After waveform retracking, the altimeter repeatability is better than ±1 m.
Driving Stresses in the Antarctic Ice Sheet
Authors: Cooper A. P. R. , Mclntyre N. F. , Robin G. de Q.
Published: February 2017

Radio echo-soundings obtained during joint programmes of the US National Science Foundation (NSF), the Scott Polar Research Institute (SPRI), and the Technical University of Denmark (TUD) have provided sufficient data of good quality to map driving stress over approximately one half of the Antarctic ice sheet. Computerized averaging of data over 1 degree of latitude squares has largely eliminated local effects of longitudinal stress variations on surface slope. Methods of data handling are outlined. Variations in driving stresses between different regions are discussed in relation to the balancing restraining forces. These are primarily related to ice velocity and thickness, bedrock topography, the presence of basal water and possibly to the development of easy-glide fabric in the ice mass, to the temperature of basal ice layers, and to the excess hydrostatic pressure in areas where ice rests on bedrock well below sea-level.
Did the West Antarctic Ice Sheet Create the East Antarctic Ice Sheet?
Authors: Hughes T. J.
Published: February 2017

The mostly terrestrial East Antarctic ice sheet is ten times larger and probably more stable than the mostly marine West Antarctic ice sheet. It is natural to suppose that the former appeared first, and that perhaps the latter was partially formed from an outflow of East Antarctic ice onto the West Antarctic continental shelf. Alternatively, the largely marine West Antarctic ice sheet may have appeared first, provided that post-Eocene continental drift allowed heavy snow precipitation over the West Antarctic island archipelago, but prevented warm South Pacific ocean currents from entering. Sea ice could then thicken and ground from surface accumulation and basal freezing, creating broad marine ice domes in shallow West Antarctic embayments. These marine ice domes could then merge with ice caps on the islands to create a marine ice sheet that could expand into East Antarctica and merge with highland ice caps to form the terrestrial East Antarctic ice sheet. A Cenozoic glacial history of Antarctica is outlined, based on this marine ice transgression hypothesis.
Glaciological Investigations in the Frontal Zone of the Filchner and Ronne Ice Shelves
Authors: Kohnen H.
Published: February 2017

In the 1979–80 field season, a site survey was carried out in the southern Weddell Sea for the construction of a wintering station. The survey comprised glaciological investigations on the Filchner and Ronne ice shelves, such as ice movement, deformation, ice thickness, calving, accumulation, and snow temperature measurements which are relevant to mass-balance studies. Along with the investigations on the ice, oceanographical and bathymetrical observations were carried out along the ice front. The field data and observations lead to assumptions about the advance of the ice shelf as well as about the mass loss at the frontal zone due to calving and bottom melting. The ice-front velocity at 50°W is about 1 070 m a−1and the bottom melting is estimated to be 3.2 m a−1at 20 km south-west of the ice front.
Nitrate Fluctuations in Antarctic Snow and Firn: Potential Sources and Mechanisms of Formation
Authors: Parker Bruce C. , Zeller Edward J. , Gow Anthony J.
Published: February 2017

We summarize here data on in situ nitrate ion concentrations in snow pits and firn cores over the last ∼3 250 a. Nitrate fluctuations show seasonal, 11 and 22 a periodicities, and long-term changes both at South Pole station and Vostok. High nitrate levels conform to winter darkness and solar activity peaks. Long-term lows and highs conform to solar activity minima and maxima. The data available support the hypothesis that nitrate is fixed in the upper atmosphere by some solar-mediated phenomenon causing a periodicity in East Antarctica snow. Background levels and non-periodic spikes in nitrate come from other sources.
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.
A Preliminary Model of Holocene Retreat and Thinning of Ice Stream E, West Antarctica (Abstract only)
Authors: Lingle Craig S. , Bentley Charles R.
Published: February 2017

A preliminary numerical model of ice-stream grounding-line retreat and thinning as a function of eustatic sea-level rise has been developed. Grounding-line retreat is computed using the methods of Thomas and Bentley (1978). The change in thickness along the ice-stream profile is found by solving the equation of continuity in two dimensions during the time intervals corresponding to increments of grounding-line retreat. The model was applied to ice stream E, West Antarctica, assuming that the ice stream was initially grounded to the edge of the Ross Sea continental shelf.
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.
Dynamical Heat-Flux Feedbacks and Global Climate Stability
Authors: Molnar Gyula , Wang Wei-Chyung
Published: February 2017

In the face of the faint young sun-climate paradox, the plausible effects of dynamical heat-flux feedbacks on global stability were examined using a coupled high- and low-latitude radiative-dynamical model. The global stability is found to depend very strongly on the vertical heat transport, which is also closely coupled to the meridional heat transport. This coupling and the associated dynamical heat-flux feedbacks, treated within the framework of the radiative-dynamical model, was found to produce a fairly strong negative feedback. Our results indicate that the dynamical heat-flux feedbacks inherent in the climate system may potentially enhance the global stability.
Modeling the Ocean in Climate Studies
Authors: Semtner Albert J.
Published: February 2017

A number of processes in the ocean must be modeled properly in order to produce valid estimates of oceanic heat transport, sea-surface temperature, and sea-ice extent in climate studies. These include: wind-driven turbulent mixing and water transport in the surface layer, internal vertical mixing due to several small-scale mechanisms, horizontal and vertical exchanges by mesoscale eddies, mixing along isopycnals, large-scale transport by currents, deep convection in polar regions, and boundary exchanges with atmosphere, ice, and land. Techniques to model these processes are described. Prospects are given for parameterizing the effects of phenomena that cannot be resolved in climate studies, particularly mesoscale eddies. Past simulations of the ocean in climate studies are reviewed. A modeling strategy is outlined for an improved treatment of the ocean, consistent with the computational power soon to be available.
Flow Behavior of Basal Ice as Related to Modeling Considerations
Authors: Shoji Hitoshi , Langway Chester C.
Published: February 2017

Simple shear tests on the bottom 17 m of basal ice from Camp Century, Greenland, were carried out in order to study the flow behavior near the bottom of an ice sheet and its implications for ice-sheet modeling. The ice core was recovered in 1966. Our experimental results show that the basal ice tested, (which contained alternating bands of dirty and clean ice) has the highest strain-rate ever reported for polycrystalline ice under simple shear. The enhancement factors obtained are interpreted in terms of fabric, ageing, and impurity. Horizontal velocity profiles are calculated using data reported previously for Camp Century and Dye 3 stations. Various depth-age relationships are compared with these data. The higher than expected shear strain-rates measured on samples of near-bottom ice from Camp Century may very well exist at other locations. If such high shear strain-rates are more prevalent than presently thought, they could have an important bearing on ages calculated by physical or mathematical models of ice sheets.
Transient Temperature Changes Due to Increasing CO2 Using Simple Models
Authors: Siegenthaler U. , Oeschger H.
Published: February 2017

The effect of the oceanic heat capacity on global temperature response to external forcing is studied by considering a CO2-induced warming. The heat flux into the ocean is calculated using a box-diffusion model, earlier established for simulating the global carbon cycle. The calculated transient warming due to CO2 produced by fossil fuel until 1980 is 0.20 to 0. 26K, or about 50% of the value for radiative equilibrium, corresponding to a delay of 16 to 24 years. Analyses of CO2 in ice cores suggest a lower pre-industrial concentration, e.g. 265 ppm, than previously assumed (c. 290 ppm). The transient temperature increase until 1980 calculated for this case is about twice that for a case which starts from 297 ppm. Comparison with observations since 1880 shows that a long-term warming trend might be due to CO2, but the residual scatter unexplained by CO2 is still large. Finally the different thermal behaviour of oceans and continents is accounted for in a schematic way, considering heat exchange between them. The results indicate stronger temperature variations over the continents than over the sea.
Glacier Flexure and the Position of Grounding Lines: Measurements By Tiltmeter on Rutford Ice Stream, Antarctica
Authors: Stephenson S. N.
Published: February 2017

Two methods were used to locate the grounding line on the Rutford Ice Stream. The first method determined where the glacier was floating in hydrostatic equilibrium, while the second method measured the flexing close to the grounding line due to ocean tides. The ratio of surface elevation to ice thickness of the glacier goes through the hydrostatic equilibrium value 1 to 2 km downstream of where tidal flexing was recorded. This behaviour can be explained if the upward pressure of the sea at the base of the ice is augmented by a vertical shear-stress gradient within the glacier to overcome its weight. Simple el as tie-beam theory matches the flexure profile data if a modified elastic modulus and effective thickness are used. Tiltmeters can he used to monitor the position of the grounding line if the geometry of the flexing region can be defined.
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.
Observing Polar-Ice Variability
Authors: Zwally H. Jay
Published: February 2017

The repetitive synoptic ice data obtainable by satellite sensing provide a means of studying the time-dependent behavior of both sea ice and ice sheets on climatic time scales. Examples of sea-ice parameters which may be measured are extent, concentration, and multiyear fraction; and examples of ice-sheet/ice-shelf parameters are surface elevation, ice-front position, extent and duration of summer melting, and ice accumulation rates. Desired snow-cover parameters include extent and snow depth or water-equivalent depth. The unique ability of satellites to measure such ice parameters and the characteristics of the consequent data sets significantly influence the structure of ice models that can be successfully used with the data. Ice data sets recently acquired by satellite sensing are described. The past decade of sea-ice data provides a detailed description of the interannual variability of sea ice on a regional and seasonal basis. Because of the longer time scales involved in ice-sheet variations, a comparable record of ongoing ice-sheet variations has not yet been established, but important baseline data sets are being developed.
Ice-Core Analysis at Site A, Greenland: Preliminary Results
Authors: Alley R.B. , Koci B.R.
Published: February 2017

Ice-core drilling at Site A, Greenland (70°45′N, 35° 57.5′W; 3145m a.s.l.) by the Polar Ice Coring Office recovered two cores of about 100 m each, which are now in storage awaiting further analysis. Field studies show that visible strata in the cores record both individual storms and individual years; a typical year comprises 15 storm deposits. Pore close-off occurs between 75 and 80 m depth. The grain-growth rate in isothermal firn and ice is about 7.8 × 10−3mm2a−1, the 10 m temperature is about –29.5°C, and the accumulation rate over the last 200 years is about 290 mm a−1 ice. Melt events occur about once every 40 years, and major events can be correlated between cores separated by 20 m.
Atmospheric Lead in Antarctic Ice during the Last Climatic Cycle
Authors: Boutron Claude F. , Patterson Clair C. , Lorius Claude , Petrov V.N. , Barkov N.I.
Published: February 2017

Concentrations of lead (Pb) have been measured by the ultra-clean isotope dilution mass spectrometry technique in various sections of the Antarctic Dome C and Vostok deep ice cores, whose ages range from 3.85 to 155 ka B.P., in order to assess the natural, pre-human, sources of this toxic heavy metal in the global troposphere. Pb concentrations were very low, as low as about 0.3 pg Pb/g during the Holocene and probably during the last interglacial and part of the last ice age. On the other hand, they were quite high, up to about 40 pg Pb/g, during the Last Glacial Maximum and at the end of the penultimate ice age. Wind-blown dust from crustal rock and soil appears to be the main natural source of Pb in the global troposphere. Pb contribution from volcanoes is significant during periods of low Pb only. Contribution from the oceans is insignificant.
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.
The Effects of Wind on δ(18O) and Accumulation Give an Inferred Record of Seasonal δ Amplitude From the Agassiz Ice Cap, Ellesmere Island, Canada
Authors: Fisher D.A. , Koerner R.M.
Published: February 2017

Wind plays an important role in determining accumulation and δ(18O) on some ice caps. Three surface-to-bed cores spaced about 1 km apart have been taken on a flow line of the Agassiz Ice Cap, Ellesmere Island. The A84 core comes from the top of a local dome. The A79 core is 1200 m down the flow line, but very close to the ridge through the local dome. The A77 core is 1100m from A79 and well away from the ridge. The ridge causes wind turbulence, which removes or scours the soft winter snow from the A84 and A79 sites. No snow is scoured from the A77 site. Because of scour the retained accumulation and average δ(l8O) are different. The accumulations are 17.5, 11.5, 9.7 cm/a (ice equivalent) at A77, A79 and A84 respectively and the corresponding surface δs are –30.40, -27.90 and –27.05‰. The core records were dated by annual layer thicknesses and by identification of electrical conductivity measurement (ECM) acid peaks. With the three cores accurately aligned we examine the (δA84-δA77) and (δA84-δA79) time series. Significant variations in these difference series are interpreted as being caused by changes in the seasonal δ amplitude, which is then explained by changes in sea-ice cover. A seasonal δ amplitude series independently obtained from the Devon Island ice cap δ noise record is consistent with that from the Agassiz Ice Cap sites.
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.
Nitrous Oxide: Trends and Global Mass Balance Over the Last 3000 Years
Authors: Khalil M.A.K. , Rasmussen R.A.
Published: February 2017

We analyzed ice cores from both northern and southern polar regions to determine the concentrations of nitrous oxide in the pre-industrial and ancient atmospheres from about 150 years to 3000 yearsB.P.We found that the pre-industrial concentration of nitrous oxide remained constant over the period we studied and that the average atmospheric concentration was 285 ± 1 ppb volume (90% confidence limits), representing about 2100 Tg (2100 × 1012g) of N20 in the atmosphere, whereas the average concentration in 1984 was about 307 ppb volume or 2260 Tg. This is a change of 22 ppb volume (160 Tg), or about 8%, between pre-industrial and present times. Now the rate of change is between 0.7 and 0.9 ppb volume/year or 5 and 6.5 Tg/year, which is a slow increase of about 0.3% per year. The changes observed are probably caused by increasing use of fossil fuels, particularly coal and oil, and perhaps to a lesser extent by the use of nitrogen fertilizers in recent years. The atmospheric lifetime of N2O is probably between 100 and 150 years. The pre-industrial concentrations, present levels, and a lifetime of 100 years are consistent with natural sources, mostly soils and oceans, of about 22 Tg/year and the present anthropogenic sources of about 8.7 Tg/year. In the next 50 years we expect nitrous oxide levels to reach 360–390 ppb volume, or about 16–25% more than present.
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.
Flow-Law Parameters of the Dye 3, Greenland, Deep Ice Core
Authors: Shoji H. , Langway C.C.
Published: February 2017

Uniaxial compression tests under constant crosshead speed were carried out on 22 new specimens from the 268, 1890, 1944 and 2006 m depths of the Dye 3, Greenland, ice core. The measurements were made in a laboratory cold-room, using an Instron model 1131 apparatus. Test temperatures were held constant between −17° and −13° C, the approximate sample in-situ temperature. Specimens were prepared with various test orientations in relation to the long vertical core axis. The specimens were analyzed in terms of the content of dust, Cl−, NO3
− and SO4
2− concentrations and various other physical parameters, such as ultrasonic wave velocities, c-axis orientation patterns and grain-size. The results of the previous uniaxial compression tests show that most of the flow occurs in the Wisconsin-age ice between 1786 m and the bottom of the ice sheet. This entire depth interval is strongly anisotropic, with a vertical c-axis fabric pattern. The enhancement factor, E, which was calculated from these tests ranges from 0.03 to 17. The Wisconsin-age ice is about ten times softer (Es = 10) than artificially made laboratory ice (E = 1). The combined results of the multi-parameter correlation analyses show that E is controlled primarily by the orientation strength of c-axes and that the impurity concentration-level variations contribute to a lesser degree.
Analysis of the Seasonal Variation in Dust, Cl−, NO3
−, and SO4
2− in Two Central Greenland Firn Cores
Authors: Steffensen J.P.
Published: February 2017

The concentrations of dust, Cl−, NO3
−, and SO4
2− in two firn cores covering the period A.D. 1891 to 1910 have been analyzed and compared. The cores were drilled 130 km apart – one west and one east of the north-south ice crest in central Greenland. The dust concentration is higher at the western site. This suggests a greater influence of continental aerosols in precipitation there, and that most of the dust comes from the west. The Cl− concentration is higher at the eastern site in some years, probably because of greater marine influence on that site. Both sites have similar concentrations of NO3
− and SO4
2−. A rise in SO4
2− concentration in the middle of the period is explained by volcanic activity and increasing anthropogenic influence. The seasonal variation in each component is discussed, and explained within the framework of an Arctic aerosol-reservoir model.
Airborne Pollen: A Unique Air Mass Tracer, Its Influx to the Canadian High Arctic
Authors: Bourgeois J.C. , Koerner R.M. , Alt B.T.
Published: February 2017

A study of pollen grain concentration in surface snow and ice cores at 15 sites in the Canadian high Arctic and one site near the tree line, together with published pollen deposition rates south of the tree line has shown long-range dispersal of pollen from the boreal forest to the limits of our area on the Arctic Ocean close to Svalbard and the North Pole. There are no discernible trends of deposition rates within the high Arctic which suggests extremely long trajectories with strong zonal components; some of the pollen may have an Eurasian source. We relate the trajectories to synoptic patterns in the mid- and high Arctic.
The Chemistry of Snow and Meltwaters Within the Mesostructure of a Boreal Forest Snow Cover
Authors: Jones H.G.
Published: February 2017

A physical and chemical study of snow mesostructure was carried out in a boreal forest site at Lake Laflamme, Quebec in spring 1983. The concomitant physical observations and δ18O‰ data on the upper layers led to the reconstruction of recent snowfall events and meltwater movements which influenced the chemistry of snow at different levels of the snowpack. Correlations between data relating the concentrations of atmospheric pollutants in snow strata were significant (H+,, r = 0.89; H+,, r = 0.81, P ≤ 0.001). The grouping of chemical species by factor analysis distinguished clearly between ionic species originating from the long-range transport of atmospheric pollutants and those due to local deposition phenomena and organic debris from the forest canopy. Mesostructural characteristics led to heterogeneous flow patterns of meltwater and rainwater through the snow cover. Both physical and chemical characteristics of the snow mesostructure change rapidly in a non-uniform manner under such conditions. This leads to increased difficulties in the interpretation of data gathered during snow sampling studies on pack decay during the spring run-off period.