bluuebunny/crossref_metadata_2025_split huggingface dataset:
A method for determining the average height of a large topographic ice sheet from observations of the echo received by a satellite altimeter
Authors: Wingham D.J. 
Published: September 2017

AbstractIce-sheet surfaces have scales of fluctuation that arc similar to the diameter of the area illuminated by a satellite radar altimeter. The present theory of altimeter, developed to describe scattering from the ocean surface, does not deal properly with the geometry of ice-sheet surfaces. In this paper, the theory of altimeter is extended to cover this geometry. A general relation for the altimeter echo from a surface of unknown geometry is developed, including the effects of the penetration of the surface by the radar waves. This expression is linearized, using the characteristic operating geometry of satellite altimeters and the gentle nature of ice-sheet gradients. From this expression, an integral equation is derived, from whose solution the spatial average of the height of the surface relative to a spherical datum can be determined. The integral equation is of a Volterra type, which permits the uniqueness of the solution for the average height to be investigated simply. The method is extended to provide a solution for the spatial average of the height of a local region of the ice sheet, provided the region remains large in comparison with the area illuminated by the altimeter, and to deal with variations in the antenna bore-sight alignment. The results have a number of implications for the collection and reduction of echoes in an experiment to determine the average height of an ice sheet. The unique determination of the average height requires the echo to be known over a time interval that depends on the extrema of the surface, which therefore must be known a priori. The average height itself can be determined by the operation on the echo of a linear operator whose kernel is derived from the solution of the Volterra-type equation. This marks a change from the procedures currently used in practice to reduce echoes from ice sheets.
Positive degree-day factors for ablation on the Greenland ice sheet studied by energy-balance modelling
Authors: Braithwaite Roger J. 
Published: September 2017

AbstractIce ablation is related to air temperature by the positive degree-day factor. Variations of the positive degree-day factor in West Greenland are studied using an energy-balance model to simulate ablation under different conditions. Degree-day factors for simulated and measured ice ablation at Nordbogletscher and Qamanârssûp sermia agree well with values around 8 mm d−1 °C−1. Degree-day factors for snow are less than half those for ice. Energy-balance modelling shows that degree-day factors vary with summer mean temperature, surface albedo and turbulence but there is only evidence of large positive degree-day factors at lower temperatures and with low albedo (0.3). The greatest effect of albedo variations (0.3–0.7) is at lower temperatures while variations in turbulence have greater effect at higher temperatures. Current models may underestimate runoff from the Greenland ice sheet by several tenths because they use a degree-day factor for melting ice that is too small for the colder parts of the ice sheet, i.e. the upper ablation area and the northerly margin.
The Equation of Continuity and its Application to the Ice Sheet Near “byrd” Station, Antarctica
Authors: Whillans I. M. 
Published: September 2017

AbstractThe continuity relationship that is often used in the study of ice sheets and ice shelves is developed by integrating the equation of continuity through the ice thickness. This equation is then integrated again with respect to horizontal distance from an ice divide, showing that the difference between the true ice velocity and the balance velocity, which is defined, is a measure of the time chance of the mass of a column through the ice thickness.The relationship is applied using data from along the “Byrd” station strain network, Antarctica. This region is found to be thinning slowly (0.03 m a−1 of ice of mean density) and uniformly, but it is still close to steady-state. The calculations would show a larger thinning rate if bottom sliding contributed more to the ice movement and integral shear contributed less, but the “Byrd” station bore-hole tilting results of Garfield and Ueda (1975, 1976), together with surface velocity measurements at “Byrd” station, indicate that most of the ice flow is by deformation within the ice mass. This large amount of internal deformation is more than that predicted by most “flow laws”, probably because of the strongly oriented ice-crystal fabric in the ice sheet. The cause of ice thinning is probably decreased surface mass balance beginning before A.D. 1550.The consistent relationship between measured velocity and balance velocity indicates that the ice flow is simple and that flow lines are in the same direction at depth as at the surface when considered smoothed over a distance of 10 km. Because the ice sheet is at present thinning, the balance velocity, calculated only from flow line and surface mass-balance data, and the somewhat mistaken assumption of steady-state is 15% less than the true ice velocity. This rather small difference confirms the use of balance-velocity estimates where velocity measurements are not available.
The Optical Properties of Ice and Snow in the Arctic Basin
Authors: Grenfell Thomas C. , Maykut Gary A. 
Published: September 2017

AbstractMeasurements of light transmission and reflection were carried out on first-year sea ice near Point Barrow, Alaska, and on multi-year ice near Fletcher’s Ice Island in the Beaufort Sea (lat. 84° N., long. 77°W.). Spectral albedos (400-1 000 nm) and extinction coefficients (400-800 nm) were determined for melt ponds, snow, and various types of bare ice. Albedos were largest in the 400-600 nm range, decreasing toward longer wavelengths at a rate which appeared to be related to the liquid-water content of the near-surface layers. Extinction coefficients remained nearly constant between 400 and 550 nm, but increased rapidly above 600 nm. At 500 nm, albedos ranged from 0.25 over mature melt ponds to 0.93 over dense dry snow, while the corresponding extinction coefficients ranged from 0.6 to 16 m-1. Intensity profiles taken in the upper 50 cm of the ice indicated that the extinction coefficient at a particular wavelength was nearly constant with depth below 15 cm, although the bulk extinction coefficient decreased with depth because of the strong attenuation in the red. Near the surface it was found that multi-year ice absorbed slightly more energy than did first-year blue ice, but at depths below 10 cm the flux divergence in the first-year ice was three to four times larger than that in the multi-year ice. A simple procedure is described for estimating light transmission and absorption within the ice under clear or cloudy skies from total flux measurements at the surface. Methods by which satellite data could be used to estimate regional albedos, melt-pond fraction, and lead area are also presented.
Secular Trends of Accumulation Rates at Three Greenland Stations
Authors: Reeh N. , Clausen H.B. , Dansgaard W. , Gundestrup N. , Hammer C.U. , Johnsen S.J. 
Published: September 2017

AbstractThe annual layer thickness profiles along three 400 m ice cores are transferred into accumulation-rate records. A linear decrease of 3±2% per millenium is found in mid-Greenland. Intermediate-term (periods longer than 120 years) deviations from the linear trend lines are less than 5% in mid-Greenland but reach 11% at Dye 3 around A.D. 1700 and 1400. Short-term (periods between 120 and 30 years) oscillations are generally in phase at Milcent and Crête.
Ivory Glacier, New Zealand, an I.H.D. Representative Basin Study
Authors: Anderton P.W. , Chinn T.J. 
Published: September 2017

AbstractMass, water, and energy balances were measured lit the Ivory Glacier, South Island, New Zealand from 1969 to 1975 as part of an I.H.D. programme of representative basin studies. Ivory Glacier is a small cirque glacier within the high-precipitation maritime environment of Westland and was chosen initially for convenience of study rather than representativeness. Mass-balance investigations included a detailed study of the sampling efficiency of a pole network. Annual mass balance was consistently negative during the study period. The run-off pattern was dominated by rain. The estimated annual mean precipitation is 9630 mm for 1971-75. Snow represents about 25% of annual precipitation. Melt contributed 21% of run-off including 9% contributed by melt of perennial snow and ice. The relative contributions of different fluxes to the energy balance during summer are: net radiation 52%, sensible heat 29%, and latent heat 17%. Heat content of precipitation contributes significantly to the energy balance during individual rain-storms and is probably significant during periods of high precipitation in spring and autumn. Climatic characteristics and behaviour of Ivory Glacier appear to follow regional trends in the Southern Alps and the glacier is considered to be reasonably representative.
Sediment Concentration in Melt Waters as an Indicator of Erosion Processes Beneath an Alpine Glacier
Authors: Collins David N. 
Published: September 2017

AbstractSuspended-sediment concentrations in melt waters from the Gornera, Gornergletscher, Switzerland, were determined at hourly intervals for periods during the ablation seasons of 1974 and 1975. Rapid erratic fluctuations of suspended-sediment concentration produced peaks which occurred both before and after highest daily flows. Clockwise daily hysteresis rating loops between sediment concentration and discharge included many involutions. Suspended-sediment-concentration-discharge rating curves were different for rising and falling limbs of individual diurnal hydrographs and varied from day to day. Close-interval measurements of sediment concentration and discharge records allow interpretation of the nature of ice–water–sediment interactions at the bed of an Alpine glacier. At Gornergletscher, subglacial sediment is delivered to melt waters flowing in the smaller basal conduits, which often change course suddenly, entraining unworked sediment stored at the bed. During diurnal discharge maxima, sediment concentration in the Gornera is reduced because the rate of increase of water volume outstrips the rate of supply of sediment. The drainage of the ice-dammed lake Gornersee, producing exceptionally high flows, extended the drainage network over large areas of the glacier bed, and evacuated much sediment.
Plough Marks in the Weddell Sea
Authors: Orheim Olav 
Published: September 2017

AbstractThe 1976/77 Norwegian Antarctic Research Expedition carried out studies of the sea bed by side-scan sonar. The equipment was operated from the expedition vessel down to about 350 m depth by personnel from the Continental Shelf Institute, Trondheim. Various types of plough marks mostly ranging from 10 to 100 m in width were observed. These included several generations of crossing plough marks as well as plough marks with abrupt changes in trend reflecting changing iceberg motion. The investigations will be expanded during the 1978/79 expedition to include towing at greater depths, and mapping of sea-bed morphology by mosaic towing patterns.
Water Movement At The Base Of Ice Sheets
Authors: Whillans I. M. 
Published: September 2017

AbstractFlat-surfaced subglacial lakes, such as those discovered by Oswald (1975), can form where basal sliding velocities are low. As the glacier moves onto a subglacial lake, its underside retains the shape of the vertical relief at the lake edge. Differential heat transfer from the lake into high and low points in the interface flattens the surface by extra melting of the downward projections or freezing in the high areas. A time of the order of 103 years is required to flatten the fluting, and the down-glacier part of a subglacial lake can be flat-surfaced if the glacier takes longer than some 103 years to traverse the lake. Such a slow traverse time is expected near ice-drainage divides, and it is there that flat-surfaced lakes were discovered by radar sounding.
Ice At Melting Point Sliding Over A Pebble Slab–A Film
Authors: Budd W. F. , Blundy N. A. 
Published: September 2017

AbstractA time-lapse movie technique has been developed to study processes taking place near the interface when ice under high normal stress slides over a rough slab for shear stresses and sliding velocities comparable to those of real glaciers.The “sledge rig” described by Budd and others (1979) was set up with one of the strips of ice (160 mm long and 23 mm wide) close to the edge of the pebble slab on which it rested. The normal stress was applied by loading the rig with lead to 5 bars. The shear stress was applied by a direct load on a cable over a pulley while the rig rested on the slab on a strong table. Shear stresses in the range 1 to 2 bars were used giving velocities from about 50 to 500 m a–1. Beyond 2 bars it was found that acceleration would set in, so this was avoided.A time-lapse movie camera was set up beside the rig to focus first on the whole configuration and then on the ice and interface as a close-up. A flash light was set up behind the rig to shine through the ice strip. A scale rule was placed along the slab under the ice strip. A dial-gauge micrometer was also used to monitor displacement.A time-lapse frequency of about 1 frame per 8 s was found to give a suitable speed. An automatic control triggered the camera and flash and also recorded the number of frames. A number of different markings were tried on the ice to indicate the relative ice deformation. Small graphite particle tracers were found the most successful.A number of runs have been filmed showing the ice sliding speed increasing with increasing shear stress. The tests were carried out in a cold room at a temperature close to 0°C.Copies of the film can be made available at cost.The authors were greatly assisted by Mr David Gardner of the Department of Educational Technology of Melbourne University by the provision of the filming equipment and general support for the operation.
Abstracts of Papers Presented at the Symposium But Not Published in Full in this Volume: Subglacial, Englacial, and Supraglacial Sediment Differentiation and Erosion in Glacial Basins
Authors: Rogerson R. J. , Eyles N. 
Published: September 2017

AbstractIf sediments being transported by glaciers in subglacial, englacial, and supraglacial situations can be differentiated on the basis of their textural characteristics, some potential exists for interpreting the relative importance of subglacial and sub-aerial periglacial processes in the excavation of glacial valleys, by examining the sediments in abandoned or active terminal moraines. Caution should be used with compound glacial valleys where subglacially eroded debris may become englacial as ice streams merge, be subsequently transported passively, and in terminal moraine deposits appear to represent sub-aerially derived sediments.
Erosion of Grooves by Subglacial Melt-Water Streams
Authors: Whillans I. M. 
Published: September 2017

AbstractThe shape of the former Laurentide ice sheet in what is now northern Ohio and southern Ontario is calculated and the subglacial hydrological potential field computed. Subglacial water flow is found to be concentrated over high points in the bed, such as what is now Kelleys Island in Lake Erie. Some 1010 litres of subglacial melt water per year passed over Kelleys Island.It is argued that the “glacial” grooves on Kelleys Island are subglacial melt-water channels. Assuming that the subglacial melt water attained saturation with respect to CaCO3, in passing over the limestone of Kelleys Island, the material formerly occupying the grooves could have been dissolved in 102 years. This is a much shorter time than glacier occupancy and the assumption of chemical equilibrium is not critical.The features on Kelleys Island are fluted valleys about 6 m across and each flute is about 0.1 m in width. Each flute represents a subglacial channel but only one or two of these channels operated at any one time. Blockages, perhaps caused by basal debris, caused the rivers to make minor course changes and in many instances it is possible to determine the order of channel occupancy. The channels were striated after abandonment by water when moving basal debris or debris-laden ice occupied the channels. From the Gauckler-Manning formula and the potential gradient obtained from the ice-sheet model the river velocity is calculated to be about 4 m s–1, in rough agreement with the water flux calculated earlier.The grooves support the concept that subglacial water flows in “Nye” channels, and raise the suggestion that subglacial erosion by solution is of widespread importance.
The Uplift of Unteraargletscher at the Beginning of the Melt Season—a Consequence of Water Storage at the Bed?
Authors: Iken A. , Flotron A. , Haeberli W. , Röthlisberger H. 
Published: September 2017

AbstractThe results of systematic movement studies carried out by means of an automatic camera on the Unteraargletscher since 1969 (Flotron, 1973) are discussed together with more recent findings from theodolite measurements made at shorter intervals and over a longer section of the glacier.In addition to the typical spring/early-summer maximum of velocity known from other glaciers, an upward movement of up to 0.6 m has been recorded at the beginning of the melt season. It was followed, after various fluctuations of the vertical velocity, by a similar but slower downward movement which continued at an almost constant rate for about three months. The uplift was not confined to the section covered by the camera but occurred nearly simultaneously in profiles located 1 km below and 2 km above. The times of maximum upward velocity (increases of up to 140 mm/d) coincided approximately with periods of large horizontal velocity and occurred after increases of melt-rate.The following explanations for the variations of vertical velocity are considered: (1) Changes of longitudinal strain-rate. (2) Changes of the sliding velocity in a channel of variable width and with a bed slope deviating from horizontal. (3) Changes of volume due to opening or closing of crevasses. (4) Swelling or contraction of veins at the grain edges. (5) Growth (and closure) of cavities in the interior of the glacier. (6) Changes of large-scale water storage at the bed.Although all of the mechanisms (1)–(5) have some effect on the vertical ice movement, they cannot account for the observed variations of vertical velocity. We therefore conclude that large-scale water storage at the bed is the main cause of the uplift. Apparently the storage system is efficiently connected with the main subglacial drainage channels only during times of very high water pressure in the channels.The findings are of some interest to the concepts of glacier sliding: As mentioned above the maxima of horizontal velocity—and thus of the sliding velocity—have not been measured at the time when the storage had attained a maximum, but at the time of maximum vertical velocity, which we assume to be the time of most rapid growth of cavities at the bed. This behaviour of the sliding velocity agrees with that predicted by a simple finite-element model of the basal ice on a wavy bed with water-filled cavities. In particular, the model shows that the sliding velocity is larger during the process of cavity growth than at the final stage when the cavities have grown to the size which is stable for the applied water pressure.
Englacial and Subglacial Hydrology, Austre Okstindbreen, Norway
Authors: Theakstone W. H. , Tvis Knudsen N. 
Published: September 2017

AbstractThe efficiency of drainage systems within the glacier Austre Okstindbreen apparently increases as the summer progresses. As the transient equilibrium line moves up-glacier and the main system extends headwards, several systems may join together. Much of the detail of the glacier river hydrograph depends on the development of the internal drainage systems, although its general form reflects climatic conditions. Streams flowing from both Austre Okstindbreen and the adjacent, much smaller, steeper glacier, Charles Rabots Bre respond quickly to rain, but the sustained high summer discharge of the Austre Okstindbreen river, even during periods without rainfall and ablation, indicates that much water is stored within the glacier. The volume of water leaving Austre Okstindbreen in summer partly reflects the amount of snow accumulated during the preceding winter. Surface structures and internal drainage systems convey water rapidly towards the margins of both glaciers, but their rivers do not display regular diurnal variations of level until part way into August; at glacier rivers further south, such fluctuations occur throughout the summer. Each year, in late July or early August, a lake dammed by Austre Okstindbreen drains through the glacier. Drainage may be triggered by a decline of water pressure in conduits near the lake.
Abstracts of Papers Accepted for the Symposium but not Presented: The Origin of Drumlins as an Ice-Rock Interface Problem
Authors: Baranowski S. 
Published: September 2017

AbstractThe origin of drumlins has long been one of the most intriguing, yet unsolved problems in glacial geology. It seems that until the mechanism responsible for drumlin formation is fully understood some of the key glaciological problems related to the glacier bed will remain obscure.
Seismic Evidence of a Wet Zone Under the West Antarctic Ice Sheet
Authors: Dewart Gilbert 
Published: September 2017

AbstractIt appears to be possible to identify certain conditions of thermal regime at the base of a glacier through the seismic reflection method. In some cases layers of water or wet rock debris may be identifiable. The procedure is based upon the reversal of phase of reflected dilatational waves at the interface between ice and a substratum of lower acoustic impedance. Illustrations of the method are given from the west Antarctic ice sheet, and suggestions are made for the improvement of the technique.
The Translational Lattice-Vibration Raman Spectrum of Single-Crystal Ice Ih
Authors: Faure P. , Chosson A. 
Published: September 2017

AbstractWe present the Raman spectra in natural and polarized light of ice Ih monocrystals in the region of the translational frequencies. These spectra are of better quality and higher resolution than previous spectra from monocrystals, and demonstrate the value of the investigation of single crystals by this technique, in spite of the proton disorder. In order to explain the observations we use the model of simultaneous activity of the modes allowed in D6h symmetry and the modes allowed by the proton disorder. By analogy with the interpretation of the phenomena observed in ordered piezoelectric crystals, we suggest that the existence of translation frequencies up to c. 320 cm-1 is due to the splitting between transverse and longitudinal optical modes. On this basis, an initial simple dynamical model using only three parameters permits an interpretation of the Raman spectrum. The probable presence of directional effects in ice Ih argues in favour of the proposed explanation.