bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of under Water Sides of Ice Shelves and Icebergs
Authors: Orheim Olav
Published: February 2017

A systematic programme of side-scan sonar and plumb- line soundings was carried out in the Weddell Sea area in 1985 to measure the under-water sides of ice shelves and icebergs. From these observations the following model is suggested for the evolution of the ice front:

(1)

Initial stage: fracturing of the ice shelves takes place along smooth, curvi-linear segments with vertical faces.

(2)

Formative stage: the freshly formed vertical face is eroded both by wave and swell action around the water line, by small calvings from the undercut, overhanging subaerial face, and by submarine melting. The melting has a minimum at 50–100 m depth, and increases with depth to a rate of around 10 m a−1at 200 m, This is about twice the rate of erosion at the water line. The variation in melting with depth results from a combination of summer melting by near-surface water, and year-round melting by water masses that are increasingly warmer than the pressure melting-point with depth.

(3)

Mature stage: this stage is reached after a few years of exposure. The backward erosion of the face leads to a shape with a prominent under-water “nose” with a maximum projection to more than 50 m at 50–100 m depth. The ramp above this slopes upwards to meet the vertical wall about 5 m below the water line. The ice below the nose is melted back beyond the above-water face. There is no net buoyancy and ice shelves at this mature stage are generallynotup-warped at the front.
Mapping of Amery Ice Shelf, Antarctica, Surface Features by Satellite Altimetry
Authors: Partington K.C. , Cudlip W. , McIntyre N.F. , King-Hele S.
Published: February 2017

Ice shelves are important regions to observe because they are likely to be sensitive indicators of climatic change. The satellite-borne radar altimetry is highly suited to ice-shelf monitoring; experience with Seasat, which flew in 1978, has demonstrated that a height-measurement precision of the order of 1 m can be obtained over ice surfaces (Brooks and Others 1983).

We identify subtle changes in altimeter wave forms associated with crevassed zones and the grounding line. Normal retracking procedures are shown to be inadequate in detecting such changes, and so methods which provide sensitive indication of the presence of these features in the sampled areas are devised. By ranging to the first return in the echo, the grounding line is identified, and by differencing this measurement with the half-peak power range, a measure of surface roughness is obtained which can be used to detect crevassed zones.

Detection of crevassed shear zones allows delimitation of distinct zones of flow in the ice shelf which can be monitored by future altimeter missions. Monitoring of the grounding-line position can provide sensitive indication of mass-balance conditions over the grounded part of the drainage basin.
Possibilities and Limits of Synthetic Aperture Radar for Snow and Glacier Surveying
Authors: Rott H. , Mätzler C.
Published: February 2017

The physical background for the interpretation of microwave measurements on snow and ice is summarized. The angular and spectral behaviour of backscattering is shown for various snow types based on measurements carried out in the Swiss Alps. The information content of SAR images in regard to snow and glacier applications is discussed, and examples are shown for Seasat SAR and airborne SAR images. The preliminary specifications are given for an optimum SAR system for snow and glacier monitoring. The main advantage of SAR is due to its weather independence; for special applications the SAR information on the physical state of snow and ice may be of interest. Future SAR sensors can become important components in a snow and glacier monitoring system, but in order to fulfil all tasks, high-resolution optical sensors and improved passive microwave sensors will also be required.
Fractures in Arctic Winter Pack Ice (North Water, Northern Baffin Bay)
Authors: Steffen K.
Published: February 2017

Profiles of the ice cover in the North Water area were obtained in the winter of 1980/81 by using low-level infrared thermometry. The flight measurements were carried out from December to March. The statistical analysis of the sea ice surface temperature was carried out to yield distributions, frequencies and widths of fractures. Ice-free as well as ice-covered fractures with a maximum ice thickness of 0.4 m were analysed. Typical fracture frequencies were 0.25 per km for Lancaster Sound and 0.14 per km for Baffin Bay and the North Water area, with 90% of fractures being less than 0.6 km wide. From December to March, the fractures occupied 8.8% of the Ice cover in the North Water area, 8.7% along the Baffin Bay profile and 10% in the Lancaster Sound. In the North Water area the distance (y) between fractures for different fracture widths (x) is an exponential function of the form y=Aexp(ax) (A,a are constants), for fractures between 50 and 800 m wide. In the North Water area during winter, fractures of all widths occur 5 times more frequently than in M’Clure Strait and about 7 times more frequently than in southern Beaufort Sea. The heat loss in Lancaster Sound at the ice-air interface was found to be 40 to 100% larger due to the fractures compared to a fast ice situation in the same winter.
Bottom Topography and Internal Layers in East Dronning Maud Land, East Antarctica, from 179 MHz Radio Echo-Sounding
Authors: Yoshida Minoru , Yamashita Kazunobu , Mae Shinji
Published: February 2017

Extensive echo-sounding was carried out in east Dronning Maud Land during the 1984 field season. A 179 MHz radar with separate transmitting and receiving antennae was used and the echoes were recorded by a digital system to detect minute reflections. The results gave cross-sections of the ice sheet along traverse routes from lat. 69 °S. to 75°S, Detailed observations on the ground at Mizuho station showed that there was elliptical polarization in the internally reflected echoes when two antennae, kept in parallel with each other, were rotated horizontally. The internal echoes were most clearly distinguished when the antenna azimuth was oriented perpendicular to the flow line of the ice sheet. The internal echoes with a high reflection coefficient were detected at depths of 500–700 m and 1000–1500 m at Mizuho station. Since a distinct internal echo at a depth of 500 m coincides with a 5 cm thick volcanic ash-laden ice layer found in the 700 m ice core taken near the observation site, these echoes may correspond to the acidic ice layers formed by past volcanic events in east Dronning Maud Land.
Satellite Snow-Cover Monitoring in the Qilian Mountains and an Analysis for Characteristics of Stream Snow-Melt Run-Off in the Hexi Region, Gansu, China
Authors: Qunzhi Zeng , Shunying Zhang , Xianzhang Chen , Jian Wang
Published: February 2017

The images of NOAA/TIROS-N APT, AVHRR and a few Landsat MSS obtained from 1980 to 1985 are analysed in this paper. It is found that the snow-cover distribution in Qilian Mountains is above 3700 m a.s.l. during winter to spring every year. There are two concentrations of snow cover. One is on Mount Leng Longling in the upper reaches of the Shiyang River and the other is located between Hala Lake and Mount Danghe Nanshan.

Based on preliminary investigations, it is known that the surface water resource in the Hexi region is 68 8 × 108m3, of which about 24.8% is from glaciers and melting, and the snow-melt run-off is 7.63 × 108m3, equal to 62.6% of the total amount of spring run-off.

The average value of Cv for spring run-off in the Shiyang River, Heihe River, and Shule River is 0 32 and the Cv value of snow-melt run-off in spring is 0.41, about three times as much as that of the annual run-off in the Hexi, region. A prediction model of spring snow-melt run-off at the Ying Louxia Hydrometric station in the Heihe River area can be constructed by using hydrometeorological data and snow-cover percentage for the Heihe River basin obtained from NOAA/TIROS-N APT, and AVHRR images. The prediction models (2) and (3) have been tested by the Water Resources Management Office of the Heihe River basin in the Zhangye and Flood Prevention Office of Gansu Province. The prediction accuracy is suitable for demands.
Acoustical Reflection and Scattering from the Underside of Laboratory-Grown Sea Ice: Measurements and Predictions (Abstract)
Authors: Jezek K.C. , Stanton T.K. , Gow A.J.
Published: February 2017

We have studied acoustical reflection and scattering properties of the underside of laboratory-grown sea ice. Our purpose was to determine the morphologic characteristics of undeformed sea ice that control acoustic scattering and reflection. So our experiments included both detailed studies of the structure of the ice as well as the application of a variety of acoustic methods.

Ice sheets were grown in an outdoor pond (about 6 m by 13 m by 1.5 m) and exhibited features characteristic of undeformed, cold sea ice: an upper granular zone; a columnar zone of crystals with cross-sectional areas of about 1 cm2; vertical sheets of brine pockets; a bulk salinity of 9.1‰ distributed over 9 cm of ice; a dendritic interface at the ice/water boundary with dendrites about 0.5 mm across at the time of our measurements. Echo-amplitude fluctuations of normal-incidence sonar pings (100 kHz to 800 kHz) were measured as the sonars moved horizontally under the ice and accumulated into echo-amplitude histograms. (Data from a deteriorating ice sheet as well as data on lake ice were also collected.) We fitted the Rice probability density function (PDF) to the data and combined the resultant statistical parameter with Eckart acoustic scattering theory. The reflection coefficients calculated using this method ranged from 0.06 to 0.12, depending on environmental conditions. RMS roughness calculated using data from new sea ice was estimated to be about 0.3 mm. Because our ice thin sections show the ice to be porous and permeable at the interface with dendrites 0.5 mm thick, we suspect that the dendrites control the scattering as described by the echo-amplitude histograms. Further, we attribute the low reflection coefficients to the dendritic structure which may act as an impedance-matching zone into the columnar section of the sea ice.

Transmission measurements were performed by positioning a transducer located at the ice/air interface directly over the transducer located in the water. The total attenuation through 18 cm of ice ranged from 12 dB at 50 kHz to 70 dB at 420 kHz (signal levels were measured relative to the same path in water).
Satellite-Altimeter Measurements of Surface Height in Sea-Ice Areas
(Abstract)
Authors: Laxon S.W. , Rapley C.G.
Published: February 2017

The Seasat radar altimeter was designed to operate over the open ocean and encountered problems over sea ice. In particular, the on-board measurements of surface height were noisy and unreliable. As a consequence, published mean sea-surface and geoid maps based on the Seasat on-board height estimates either omit sea-ice-covered areas or include suspect data. We have identified and investigated the problems encountered by the Seasat altimeter over sea ice and have developed a technique for extracting accurate surface-height values from the sea-ice echo wave-form data. The retracking method is based upon fitting real wave forms to a library of model returns.
Analysis of Simulated Radar Altimetric Wave Forms for Polar Ice and Snow Surfaces (Abstract)
Authors: Novotny Eva
Published: February 2017

The radar altimeter of the satellite Seasat has proved that ice and snow surfaces in the polar regions can return meaningful signals if the terrain is not excessively rugged or sloping. Because the use of the leading edge of the wave forms for height determination entails inherent uncertainties and, at best, provides only a single datum per wave form, the entire wave forms should be studied. Excesses or deficiencies in amplitude at various ranges within a single wave form, and the changes that occur in successive wave forms, can be analysed to yield information on the geometric and scattering properties of features observed by the altimeter.

Results from computer simulations are presented, showing how (1) a margin of sea ice (sinusoidal in the model) can be mapped, (2) the boundaries of two isolated ice floes can be outlined, (3) sea-ice concentrations can be derived within annuli about the nadir of an individual footprint, and (4) for land ice, the elevations of topographic features, together with the general slope of the ground, can be determined if an imaging instrument that operates simultaneously with the altimeter provides the outlines of these features. In examples (1) and (2), it is assumed that the ice is contiguous wherever that is possible, to permit the analytical reconstruction of the ice margin or individual ice floes in the presence of the inevitable ambiguity in the position of any feature with respect to the two sides of the satellite track. Example (4) requires that the altimeter record correctly records the strongest signals returned by ice-packs. This condition is not fulfilled by any existing radar altimeter, but it may be achieved in the next generation of these instruments. In additional examples of information from entire wave forms, the effects of crevasses and sastrugi in reducing or re-distributing the energy of the returned signals are also illustrated.

Full details of these analyses and results will be published at a later date.
The Timing of Initial Spring Melt in the Arctic from Nimbus-7 SMMR Data (Abstract)
Authors: Anderson Mark R.
Published: February 2017

The ablation of sea ice is an important feature in the global climate system. During the melt season in the Arctic, rapid changes occur in sea-ice surface conditions and areal extent of ice. These changes alter the albedo and vary the energy budgets. Understanding the spatial and temporal variations of melt is critical in the polar regions. This study investigates the spring onset of melt in the seasonal sea-ice zone of the Arctic Basin through the use of a melt signature derived by Anderson and others from the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) data. The signature is recognized in the “gradient ratio” of the 18 and 37 GHz vertical brightness temperatures used to distinguish multi-year ice. A spuriously high fraction of multi-year ice appears rapidly during the initial melt of sea ice, when the snow-pack on the ice surface has started to melt. The brightness-temperature changes are a result of either enlarged snow crystals or incipient puddles forming at the snow/ice interface.

The timing of these melt events varies geographically and with time. Within the Arctic Basin, the melt signatures are observed first in the Chukchi and Kara/Barents Seas. As the melt progresses, the location of the melt signature moves westward from the Chukchi Sea and eastward from the Kara/Barents Seas to the Laptev Sea region. The timing of the melt signal also varies with year. For example, the melt signature occurred first in the Chukchi Sea in 1979, while in 1980 the signature was first observed in the Kara Sea.

There are also differences in the timing of melt for specific geographic locations between years. The melt signature varied almost 25 days in the Chukchi Sea region between 1979 and 1980. The other areas had changes in the 7–10 day range.

The occurrence of these melt signatures can be used as an indicator of climate variability in the seasonal sea-ice zones of the Arctic. The timing of the microwave melt signature has also been examined in relation to melt observed on short-wave imagery. The melt events derived from the SMMR data are also related to the large-scale climate conditions.
Methods for Snow Mapping from Meteorological Satellite Imagery of the Qilian Mountains, North-West China (Abstract)
Authors: Liu Z.K. , Chang S.Y.
Published: February 2017

A snow survey in north-west China has been carried out using meteorological satellite NOAA-9 imagery. A two-step geometric correction method is presented. The first step involves a large-scale geometric correction, and the second step concentrates on a small area of interest, using the control-point correction method. A high precision of geometric correction can beachieved by using this method. The snow-covered area of the Qilian Mountains basin is calculated.
Surface and Bedrock Topography of Ice Caps in Iceland, Mapped by Radio Echo-Sounding
Authors: Björnsson Helgi
Published: February 2017

Since 1977, large areas on western Vatnajökull have been surveyed by ground-based, radio echo-sounding and the whole ice cap, HofsjökuIl, was surveyed in 1983. Detailed maps of the glacier-surface elevation and the sub-ice bedrock have been compiled. The instrumentation includes a 2–5 MHz, mono-pulse echo-sounder, for continuous profiling, a satellite geoceiver and Loran-C equipment, for navigation, and a precision pressure altimeter. The maps of western Vatnajökull cover about 1500 km2 and are compiled from 1500 km-long sounding lines, which yielded about 50 000 data points for ice thickness and 20 000 points for ice-surface elevation. The maps of HofsjökuIl cover 923 km2, the sounding lines were 1350 km long; 42 000 points were used for determining ice thickness and 30 000 for surface elevation. The maps obtained from these data are the first ones of the ice caps with surface elevation of known accuracy. The bedrock map of western Vatnajökull shows details of volcanic ridges and subglacial valleys, running north-east to south-west, as well as the central, volcanic complexes, Hamarinn, Bárdarbunga, and Grimsvtön and the related fissure swarms. The map of Hofsjökull reveals a large volcanic complex, with a 650 m deep caldera. The landforms in southern Hofsjökull are predominantly aligned from north to south, but those in the northern ice cap run north by 25° east.
Photo-Interpretation, Digital Mapping, and the Evolution of Glaciers in Glacier National Park, B.C.
Authors: Champoux André , Ommanney C.S.L.
Published: February 2017

The inventory of Glacier National Park, B.C., has provided an opportunity to test a number of new procedures which might be applied to future Canadian glacier inventories. The objectives of this particular study were to complete a tripartite inventory based on available map and photo sources and develop an automated system of data acquisition and processing. The conjunction of the two has permitted an analysis of the evolution of the glaciers in this area during the last 100 years. The techniques used and a summary of the results are reported.
Digital Mapping of the Nordaustlandet Ice Caps from Airborne Geophysical Investigations
Authors: Dowdeswell J.A. , Drewry D.J. , Cooper A.P.R. , Gorman M.R. , Liestøl O. , Orheim O.
Published: February 2017

Airborne geophysical investigations of the previously tittle-studied Nordaustlandet ice caps (11 150 km2) took place in 1983, using SPRI 60 MHz radio echo-sounding (RES) equipment of 160 dB system performance. RES and navigational data were recorded digitally. Navigation used a ranging system (accurate to ±30 m) from aircraft to ground-based transponders, located by satellite geoceivers, supplemented by the aircraft’s navigational instruments and timed crossings of known features. Ice surface and bedrock elevations were measured, using aircraft pressure altitude, terrain clearance, and ice thickness data. The mean error of 251 crossing points on Austfonna was 11 m. The reduced geophysical data are stored on a direct-access computer database. During 3400 km of flying, Austfonna (8105 km2) was covered by traverses a nominal 5 km apart, whereas a 15 km-spaced grid was flown over Vestfonna (2510 km2). Maps of ice surface morphology and subglacial, bedrock topography were produced for Austfonna and Vestfonna, along with an ice thickness map of Austfonna, Austfonna reaches a maximum surface elevation of 791 m and ice thickness of 583 m. 28% of the bedrock area beneath Austfonna lies below sea level. RES yielded bedrock echoes for 91% of track over Austfonna, but only 52% over Vestfonna. This was probably due to warmer conditions on Vestfonna, resulting in greater absorption and scattering of electro-magnetic energy. Ice surface elevations are a principal data source in the revision of official Norwegian maps of Nordaustlandet.
Recession of Grasshopper Glacier, Montana, Since 1898
Authors: Ferrigno Jane G.
Published: February 2017

Grasshopper Glacier is a cirque glacier in the central Rocky Mountains of the United States. It is a remnant of the “Little Ice Age”, rather than the more widespread and older Pinedale Glaciation. The glacier has not been monitored on a regular basis and very few maps have been published of the area, but it has been studied, photographed, occasionally mapped, and described by scientific and non-scientific groups, at different times since 1898. These photographic, cartographic, and written records make it possible to trace the fluctuations of this glacier since 1898. Grasshopper Glacier has had periods of positive mass balance, but the overall trend has been negative, with accelerated melting in recent years. It is estimated that Grasshopper Glacier has lost about 50% of its area and as much as 90% of its volume, since 1898. Other Rocky Mountain glaciers are experiencing similar wastage and, if current conditions continue, these glaciers will disappear by the middle of the next century.
The Response Time of Glaciers in Iceland to Changes in climate
Authors: Jóhannesson Tómas
Published: February 2017

Records of the time variation of the terminus position of Icelandic glaciers since 1700 show clear responses to the little ice age and to the warm period from 1930 to 1960. These data are used to deduce limits for the response time of the glaciers. The response time turns out to be of the order of one or two hundred years. This is much shorter than the “long response time” of Nye’s kinematic wave theory.
Glacier Mapping for an Inventory of the Indus Drainage Basin: Current State and Future Possibilities
Authors: Kick W.
Published: February 2017

A large problem of the World Glacier Inventory is the Pakistan part which is still missing. The available official quarter-inch and half-inch maps of the Survey of India and Pakistan are not adequate for the purpose. The maps of some expeditions provide reliable data for a few areas. Landsat imagery does not yield heights and has other disadvantages. At the present time, the Spacelab mission, in September 1986, with its metric camera, seems to offer a rather good opportunity.
Processes which Distribute Supraglacial Debris on the Khumbu Glacier, Nepal Himalaya
Authors: Nakawo M. , Iwata S. , Watanabe O. , Yoshida M.
Published: February 2017

The thickness of supraglacial debris on the Khumbu Glacier, Nepal Himalaya, has been mapped by a combination of direct measurements and morphological and lithological studies. All three processes, englacial, supraglacial, and subglacial, must be considered in establishing the distribution of debris. Taking advantage of the lithological characteristics of the debris and their bedrock source, the denudation rate of the schistose bedrock was estimated to be about 0.02 mm a−1. A rough estimate of the production rate of supraglacial debris indicated that most of the present debris has formed since the last advance of the glacier, which took place a few hundred years B.P.
Results from the Radio Echo-Sounding on Parts of the Jostedalsbreen Ice Cap, Norway
Authors: Saetrang Arne Chr. , Wold Bjørn
Published: February 2017

The paper describes instrumentation, navigation methods, and interpretation problems from radio echo-sounding on parts of Jostedalsbreen. A map of the subglacial topography is presented. Ice thickness ranges from 60 m to 600 m with most sections between 150 m and 300 m.
Ice Divide Migration at Blue Glacier, U.S.A.
Authors: Waddington E.D. , Marriott R.T.
Published: February 2017

A 1984 strain net on the Snowdome of Blue Glacier showed that the surface slope is a good estimator of ice flow direction and divide location. Topographic maps from 1939, 1952, 1957, 1979, and 1984 show that the flow divide migrates within a zone up to 350 m wide, in response to changes in east-west gradient in snowfall. This zone encloses 6% of the Blue Glacier accumulation area and up to 10% of the year-end residual snow. An ongoing 28-year mass-balance study has used an extreme, westerly divide, giving systematically high net balance estimates. The correct catchment area, for a given balance year calculation, depends on the future migration sequence of the ice divide, with a time constant of about 30 years.
The Problem of “Hidden” Ice in Glacier Mapping
Authors: Whalley W.B. , Martin H. Elizabeth , Gellatly Anne F.
Published: February 2017

Ice can become “hidden”, i.e. buried, by the superimposition of rock debris on a glacier or where rock debris may incorporate interstitial ice. Because it is obscured, problems result from a lack of understanding of the extent and continued activity of such ice. Landforms may be associated with this phenomenon and can be used as indirect evidence of its existence. A rock glacier can contain glacially-derived, buried ice as well as interstitial ice. We show, with examples, how such rock glaciers can be identified and provide information on the extent and possible volume of hidden ice in marginally glacierized and permafrost areas. In most cases, recognition of topography is sufficient, although time-separated aerial photographs may be necessary to locate the extent of ice. These are generally preferable to, and more cost effective than, most detailed on-site determinations of ice extent. It is possible to incorporate and extend knowledge of hidden ice in glacier mapping and inventory projects.
Glacier Inventories of Iceland: Evaluation and Use of Sources of Data
Authors: Williams R.S.
Published: February 2017

All sources of cartographic, aerial photographic, satellite image, and related data, from the 18th century to the present, for the eight geographic groups of Iceland’s glaciers, were evaluated for use in preparing a preliminary inventory of Iceland’s glaciers, based on information requirements of the Temporary Technical Secretariat for World Glacier Inventory. On the basis of an evaluation of all sources of historic and modern data for the Langjökull Group, the 1:50 000 scale U.S. Army Map Service Series C762 maps of Iceland were determined to be the best maps from which to derive information for a preliminary inventory, as long as the limitations of these maps are considered and accommodated. The fluctuations of Langjökull’s principal outlet glaciers on maps and Landsat images were found to be consistent with field observations at the International Hydrological Decade monitoring stations. Accumulation area ratios were calculated from late summer snow lines on 1973 Landsat images of Vatnajökull (0.70), Langjökull (0.78), and Mýrdalsjökull (0.35), Measurements of the area of the now stagnant glacier on Ok showed a rapid reduction in area (68 per cent) between 1910 and 1960, but a decline in rate of wastage since 1960 (73 per cent between 1910 and 1978). From 1910 and 1945 topographic maps, the volume of the glacier on Ok was found to be reduced by 0.62 km3.
Glaciological and Hydrological Map of the Hornsund Fiord Area: 1:75 000 (Abstract)
Authors: Jania J. , Pulina M.
Published: February 2017

The problem of how to select and synthesize glaciological and hydrological information for the map of South Spitsbergen is discussed. The area of interest covers aproximately 1700 km2, but not all of it has been explored equally well so far. The map is under preparation for printing. It is one of a series of environmental maps of Hornsund at 1:75 000. Geomorphology and geology have been completed already. The general objective was to reveal the spatial differentiation of glacial and hydrological phenomena in the vicinity of the Hornsund Fiord but particular interest was focused on providing synthesized information about glacial and hydrological phenomena and processes, which had been considered in the context of natural hydrological basins.

The result is a specification of the phenomena represented in the map. It had been divided into five parts;

(1)

elements of geomorphology, geology (lithology) and topography (basemap);

(2)

features of glaciers and glacial phenomena on land;

(3)

physical and chemical properties of on-land streams and glacier streams;

(4)

features of marine environment and Hornsund Fiord bottom (during contruction); and

(5)

general characterization and classification of phenomena occurring in hydrological basins.

The first is of a general nature. Parts two, three and four include detailed, analytical information. Part five comprises synthesized data.

The glaciers of Hornsund are specified by morphological classification, according to PSFG of the IAHS, by the position of the mean firn line and major glacier zones, and by the pattern of the ice flow-lines, along with some information on the velocity of flow. Thermal classification of the glaciers, and data on the oscillations of the glacier fronts in the 20th century are presented.

Of the Hornsund glaciers, Werenskioldbreen (approximately 27 km2)has been exposed in the map at 1.25 000. It has roused the interest of many investigators and is amongst the best explored examples. The available set ot data pertaining to this glacier consists predominantly of analytical, quantifying information, e.g. on the changes of the glacier surface altitude which occurred from 1957 to 1983, on the net balance at selected points of the glacier, on the pattern of englacial and subglacial channels, on the discharge in glacial streams, and on the quantity and degree of mineralization and chemical content of glacial streams, etc.

The result is a coloured map which aims at representing, in a systematic and synthesized manner, contemporary phenomena and processes associated with the glaciers and the water system of the Hornsund Fiord basin.
Isotope Climatic Record Over The Last 2.5 KA from Dome C, Antarctica, Ice cores
Authors: Benoist J. P. , Jouzel J. , Lorius C. , Merlivat L. , Pourchet M.
Published: February 2017

Data on climatic changes over thousands of years is needed for a better understanding of the shorter term variations which are of interest to man. For this purpose we measured the isotope composition (δD‰) of two adjacent ice cores drilled in the Dome C area. The time scale was established using the remarkably constant mean annual accumulation rate (37 kg m−2) determined by various techniques. The detailed isotope records were smoothed to filter out the δ value fluctuations not directly related to local temperature changes. With respect to conditions over the last 2.5 ka, the combined smoothed δ curve indicates a cooler climate from about 1800 to 1200 AD and a slightly warmer period from about 1200 to 700 AD. These periods may well correspond to the suggested world-wide Little Ice Age and medieval warm phase. Using the present δD‰/T°C measured at the surface, the maximum amplitude for these two periods, after smoothing with a low pass filter of 512 a, is approximately -0.35 and +0.3°C, respectively.
Radiative Transfer Modeling of Microwave Emission and Dependence on Firn Properties
Authors: Comiso J. C. , Zwally H. J. , Saba J. L.
Published: February 2017

The microwave emission from a model polar firn was calculated using a numerical solution of the radiative transfer equation that included angledependent Rayleigh scattering. The depth-dependent parameters in the equation were physical temperature and the coefficients of scattering and absorption. The coefficients were based on Rayleigh scattering from the snow grains. The bulk emissivity and the seasonal dependence of brightness temperature were calculated for seven locations at which grain sizes were measured as a function of depth. When the absorption and scattering coefficients are adjusted, the modeled emissivities agree with observed emissivities at these locations. The modeled seasonal dependence of brightness temperatures also compares well with values obtained at 1.55 cm wavelength by the Nimbus-5 satellite. Good agreement with data did not occur when the imaginary part of the index of refraction (and, hence, the absorption coefficient) had a significant temperature dependence between 210 and 250 K.
State of Balance of the Ice Sheet in the Antarctic Peninsula
Authors: Doake Christopher S. M.
Published: February 2017

Data from ice rises on the east coast of the Antarctic Peninsula can be interpreted as showing that the ice is thinning at rates of up 0.5 m a−1. However, a level line between two nunataks in Palmer Land showed no change in surface elevation over a period of 5 a. Melt rates on George VI Ice Shelf vary with position and may indicate that parts of the ice shelf are thickening at the rate of several m a−1, presumably in response to a higher accumulation rate over the peninsula a few hundred years ago. A small valley glacier, Spartan Glacier, is wasting away at about 0.27 m a−1. Ice fronts on both east and west coasts of the peninsula have been retreating for the last 30 a. It seems that there is general glacier recession in response to a wanner climate and decreased snowfall for at least the last 30 a, while parts of the peninsula are still thickening in response to a high accumulation rate several hundred years ago.
Techniques for Thermal Conductivity Measurements in Antarctica
Authors: Ewing Richard E. , Falk Richard S. , Bolzan John F. , Whillans Ian M.
Published: February 2017

An accurate knowledge of the thermal properties of firn and ice within a glacier is essential for any reliable mathematical model of heat transfer. This paper considers the problem of determining the thermal properties of firn at Dome C, Antarctica, for use in such a model.

First, the difficulties in accurately determining thermal properties are discussed. Then a physical experiment which can be performed under field conditions, but which will yield a well-posed mathematical problem for determining the unknown properties, is presented. Next, two different numerical techniques for solving the mathematical problem are discussed. Finally, some numerical approximations and error estimates are presented for the results of applying our numerical procedure to data from Dome C. Although insufficient data were obtained to test our methods fully, we have established a measurement procedure and a method of analysis which appear to be promising.
Possible Causes of the Variation in Microparticle Concentration in an Ice Core from Mizuho Station, Antarctica
Authors: Fujii Yoshiyuki , Ohata Tetsuo
Published: February 2017

Variation of the microparticle concentration in an ice core from Mizuho station, East Antarctica, does not show the annual cycle that has been demonstrated for ice cores from Antarctica and Greenland by other authors. Possible reasons for the lack of a annual cycle are considered and two causes are suggested. (1) Semi-annual variation of microparticle concentration as observed in drift-snow. The low particle concentration in March and in August to October is not due to minor particle transport, but to the dilution of microparticles transported mainly from arid regions in the southern hemisphere through the troposphere by falling snow. (2) Discontinuous surface-layer formation. A seasonal or an annual sequence of the variation in microparticle concentration in surface snow layers may be interrupted by the absence of surface snow-layer formation.
On the Joint Interpretation of Total Gas Contents and Stable Isotope Ratios in Ice Cores
Authors: Jenssen D. , Radok U.
Published: February 2017

Total gas contents of ice cores together with temperature estimates derived from 180/160 and 2D/1H values have been used to separate topographic and climatic changes in the deposition temperature history of the ice (Raynaud 1977, Jenssen 1978). The most recent analysis (Jenssen in press) made use of two linear relationships (one purely empirical, the other established empirically but subsequently justified theoretically) to derive an algebraic expression for the change of surface temperature with ice-sheet elevation. A physical line of reasoning is presented which instead infers the climatic history from changes in the surface topography of the ice sheet. This suggests that a complete interpretation of core data must go hand in hand with ice-sheet modeling.
The Volcanic Record of Antarctic Ice Cores: Preliminary Results and Potential for Future Investigations
Authors: Kyle P. , Palais J. , Delmas R.
Published: February 2017

Occurrences of tephra layers in four ice cores from Antarctica are reviewed. A new tephra, informally named the Vostok tephra, is described from a depth of 100.85 m in an ice core from Vostok station. Ice associated with four tephra layers at depths between 1390 and 1450 m in the Byrd station ice core shows increased levels of sulfate and nitrate which correlate well with peaks in particle concentrations. High levels of sulfate and nitrate are also associated with the Vostok tephra.

Tephra offer great potential as stratigraphic markers and should be useful in providing time planes as well as assisting in correlation between widely spaced ice cores.
Oceanographic Observations from George VI Ice Shelf, Antarctic Peninsula
Authors: Lennon P. , Loynes J. , Paren J.G. , Potter J.R.
Published: February 2017

Summer profiles of sea-water temperature, salinity and flow were obtained on George VI Ice Shelf near its northern ice front. At each depth, temperature salinity and density show little variation between sites. Their respective variation to 250 m depth confirms a linear temperature-salinity dependence. This is the first place in the world where observations confirm precisely the form of the T-S diagram predicted for fresh ice melting in sea-water. Both tidal and residual flow are small, except at the western margin of the ice front, where a strong outflow is concentrated immediately beneath the ice shelf. The observations lead to a simple circulation model for the ice-shelf regime. Warm Deep Water flows southwards into George VI Sound, replacing the colder water that spreads northwards in the surface outflow. Thermohaline exchanges beneath the ice shelf determine the salinity profile, which itself provides evidence of upwelling. Estimates can be made of the basal melt rate of the ice shelf. The rates vary from around 10 m a−1at the ice front to an average value for the ice shelf of order 1 m a−1. The average value is consistent with earlier estimates from surveys of ice-shelf strain.
Microparticle Analysis of the Ross Ice Shelf Q-13 Core and Preliminary Results From THE J-9CORE
Authors: Mosley-Thompson Ellen , Thompson Lonnie G.
Published: February 2017

The concentration and size distribution of microparticles are measured on the Ross Ice Shelf at three sites: Q-13, base camp, and J-9. Results from the analysis of 2 611 samples representing the 100 m core from site Q-13 are presented. Increasing particle concentrations since 1800 are interpreted as a reflection of the gradual movement of the Q-13 drill site northward toward the Ross Sea under greater influence of the dissipating cyclonic storms in the Ross embayment. A substantial increase in particle concentrations found between 1920–40 may reflect an increase in the frequency and/or intensity of cyclonic storms dissipating in the Ross Sea. This is under investigation. Preliminary microparticle analyses of a small portion of each of 39 sections from the 416 m J-9 core indicate a substantial increase in particle concentrations between 250 and 350 m, possibly signaling the presence of late glacial, or Wisconsin, ice
Recent Variations in Heavy Metal Concentrations in Firn and Air From the Antarctic Peninsula
Authors: Peel D. A. , Wolff E. W.
Published: February 2017

A snow-pit and hand-drilled core have been sampled at Spaatz Island in the Antarctic Peninsula to obtain evidence on the importance of short-term fluctuations of heavy metal (Cd, Cu, Pb, and Zn) concentrations. A programme of air sampling was undertaken at the same time to investigate directly the link between concentrations in air and in snow. The snow samples and air filters have been analysed by atomic absorption spectrometry (AAS) following preconcentration on tungsten wires and by differential pulse anodic stripping voltammetry (DPASV). One sequence of snow samples was preconcentrated in the field and analysed later for Cd in the laboratory.

The snow analyses confirm that year-to-year variations in heavy metal concentrations may be comparable with changes due to long-term variations in global emission rates to the atmosphere from industrial sources. The importance of understanding these apparently meteorologically controlled processes is underlined. Averaged data from the combined air/snow sampling programme show a satisfactory linear relationship between concentrations in air and in snow for both the heavy metals and for the cation component of the marine aerosol. The results, considered in the light of Junge's model for static rainout, give a ratio for concentration in air (ng m−3)/concentration in snow (ng g−1) of 0.6±0.3.
Air Content Of The Byrd Core And Past Changes In The West Antarctic Ice Sheet
Authors: Raynaud D. , Whillans I. M.
Published: February 2017

Analyses of ice cores taken from the Antarctic ice sheet can provide information on the environmental conditions under which the ice was formed. New results from measurements of gas content and stable isotope ratios in the Byrd station ice core are discussed and interpreted in terms of past iceflow changes.

165 selected ice samples from 32 different depth levels along the core were processed for total gas content V and stable isotope ratios. This large dataset is used to discuss the variability and significance of the values of V at different depths. The short term variations of V are mainly explained by heterogeneities of the pore volume when the firn pores close off.

The general trends in the values of V with depth are then used to investigate the possibility of past changes in the ice sheet. They suggest near-steady flow during the past few tens of thousands of years and that a thickening of about 200 to 250 m occurred in this area of the ice sheet at the end of the last ice age. This thickening could be due to a change in the accumulation rate.
Subglacial Water flow Under Ice Streams and West Antarctic Ice-Sheet Stability
Authors: Weertman J. , Birchfield G. E.
Published: February 2017

An analysis is made of the steady-state width of an ice sheet whose base is below sea-level, whose basal temperatures are such that appreciable melting occurs at the base, and which is fringed by fastmoving ice streams that drain most of the outward ice flux. The fast ice velocities of the ice streams are considered to be a consequence of substantial subglacial water flow underneath the ice streams. The source of this water is the water melted from the base of the ice sheet which is diverted to flow beneath the ice streams. If the depth of the sea at the edge of the ice sheet is not a function of the width of the ice sheet, then an ice sheet with a steady-state width is in a situation of unstable equilibrium. Only if the sea-level depth at the edge of the ice sheet increases as a function of ice-sheet width at a rate greater than the 2/3rd power of the width can a stable, steady-state ice sheet exist. This condition (taking into account elastic rebound) is not satisfied for the West Antarctic ice sheet along an ice-flow path from the ice divide above Byrd station out to the Ross Sea. An increase of the mean precipitation, such as might occur under a C02-induced climatic warming, would cause growth of both stable or unstable steady-state ice sheets.
Implications for the Late Wisconsin-holocene Extent of the West Antarctic Ice Sheet from Regional Free-air Gravity Anomalies in the Ross Embayment (Abstract only)
Authors: Greischar Larry L. , Bentley Charles R.
Published: February 2017

Gravity data from cruises 32, 51, and 52 of the USNS Eltanin (Hayes and Davey 1975), approximately adjusted to the new gravity datura (IGSN 71) and reference system (GRS 67), have been used to extend the Ross Ice Shelf gravity map to the edge of the Ross Sea continental shelf. Various regional gravity anomaly fields obtained by applying low-pass filters to these data are strongly negative over the entire Ross embayment; values increase gradually from approximately -300 gu (-30 mgal) near the Siple Coast to -150 gu (-15 mgal) near the edge of the Ross Sea continental shelf.
Field Studies of Bottom Crevasses in the Ross Ice Shelf, Antarctica (Abstract only)
Authors: Jezek Kenneth C. , Bentley Charles R.
Published: February 2017

Surface and airborne radar sounding data were used to identify and map fields of bottom crevasses on the Ross Ice Shelf. Two major concentrations of crevasses were found, one along the grid-eastern grounding line and another, made up of eight smaller sites, grid-west of Crary Ice Rise.

Based upon an analysis of bottom crevasse heights and locations, and of the strength of radar waves diffracted from the apex and bottom corners of the gridcrevasses, we conclude that the crevasses are formed at discrete locations on the ice shelf. By comparing the locations of crevasse formation with ice thickness and bottom topography, we conclude that most of the crevasse sites are associated with grounding. Hence we have postulated that six grounded areas, in addition to Crary Ice Rise and Roosevelt Island, exist in the grid-western sector of the ice shelf. These pinning points may be important for interpreting the dynamics of the West Antarctic ice sheet.
Measurement of Radio Wave Velocities in the Firn Zones of Polar Ice Sheets (Abstract only)
Authors: Shabtaie Sion , Bentley Charles R.
Published: February 2017

A common-reflection point profiling experiment to obtain electromagnetic wave velocities in the ice at Dome C at 35 MHz was carried out to a maximum antenna separation of 2 km. Four different recording systems were used for this experiment. The echoes from numerous internal reflecting horizons within the ice and the bedrock were recorded in four different ways: in A-display form on film using an oscilloscope, in intensity-modulated form using the Honeywell Visi-corder and thermal intensifier on heat-sensitive silver paper, and in both raw and signal-averaged form on magnetic tape.

Travel times of oblique reflections from nearly 160 internal layers down to a depth of 2 600 m and reflections from the ice bottom were measured at each station along the profile. The average wave velocities from the surface of each internal layer were measured to obtain a continuous mean velocity vs depth profile.

Velocity-density models derived from the dielectric mixture equations of Looyenga, Böttcher, Lichtenrecker, Hanai-Bruggeman and Wiener were compared against the measurements. In addition Robin's empirical relationship was also used in this study. The preliminary results show that the observed velocity depth profile for the ice column is compatible with Wiener's equation (with Formzahl = 0) and a newly derived empirical relationship (from this study) ofwhere γiis ice density, γffirn density, ε dielectric constant of mixture, and εidielectric constant of ice; γf>0.55 kg m−3. It appears that the electromagnetic wave velocity in the firn is 20 m MS−1or more, which is higher than previously assumed.

The above models were also compared with velocity measurements in the Devon Island bore holes (Robin 1975) and at several sites on the Ross Ice Shelf where the ice is relatively thin compared to Dome C so that the effect of firn on mean velocities is more pronounced. The results for these sites suggest again that Wiener's equation and empirical relationship from this study produce velocities compatible with the observed values.