bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of glacier retreat on the outbursts of Goësvatnet, southwest Spitsbergen, Svalbard
Authors: Schöner W. , Schöner M. 
Published: September 2017

AbstractEffects of the retreat of Gåsbreen, southwest Spitsbergen, Svalbard, on the evolution of the ice-dammed lake Goësvatnet are shown for the period 1899-1991. The retreat and lowering of the damming ice masses have changed not only the stored lake volume, the lake geometry and the elevation, slope and length of the subglacial outlet tunnel, but also the frequency and magnitude of outburst floods of Goësvatnet. For the estimation of peak discharges of outburst floods we computed an unbiased regression equation related to the progressive enlargement of subglacial tunnels using lake volume data and peak discharge data from the literature. The derived equation is very similar to the original form of the Clague-Mathews formula and answers the question why this formula has worked well in many cases. Peak discharges of Goësvatnet in various years were estimated by means of the derived equation. Effects of the changed lake geometry as well as the changed length and slope of the subglacial outlet tunnel on the discharge during outbursts will be discussed by means of the Nye-Clarke model. Observation of an outburst of Goësvatnet in summer 1991 indicates that the outbursts may have been triggered by pressure decrease in the subglacial outlet tunnel during increased discharge, whereas flotation of the ice dam can be excluded.
Large-scale ice-sheet modelling as a means of dating deep ice cores in Greenland
Authors: Greve Ralf 
Published: September 2017

AbstractThe three-dimensional ice-sheet model SICOPOLIS is used to simulate the dynamic/thermody namic behaviour of the entire Greenland ice sheet from 250 000 a BP until today. External forcing consists of a surface-temperature history constructed from δ18O data of the GRIP core, a snowfall history coupled linearly to that of the surface temperature, a piecewise linear sea-level scenario and a constant geothermal heat flux. The simulated Greenland ice sheet is investigated in the vicinity of Summit, the position where the maximum elevation is taken, and where the two drill sites GRIP and GISP2 are situated 28km apart from each other. In this region, the agreement between modelled and observed topography and ice temperature turns out to be very good. Computed age-depth profiles for GRIP and GISP2 are presented, which can he used to complete the dating of these cores in the deeper regions where annual-layer counting is not possible. However, artificial diffusion influences the computed ages in a near-basal boundary layer of approximately 15% of the ice thickness, so that the age at the bottom of the cores cannot be predicted yet.
A low-cost electrical conductivity profiler for glacier boreholes
Authors: Smart C. C. , Ketterling D. B. 
Published: September 2017

AbstractElectrical conductivity profiling allows definition of the hydrology of glacier boreholes occupied by contrasting water types. An inexpensive, robust conductivity profiling system is described that allows detailed description of borehole hydrostratigraphy with reasonable reproducibility. Field dato demonstrate the need to distinguish between bottom water in boreholes and basal water in drainage systems at the glacier bed.
A force-balance study of ice flow and basal conditions of Jutulstraumen, Antarctica
Authors: Armand Høydal Øyvind 
Published: September 2017

AbstractStresses and velocities at depth are calculated across Jutulstraumen, an ice stream in Dronning Maud Land, draining about 1% of the Antarctic ice sheet. The force-balance study is based on data from kinematic GPS measurements on three strain nets, each consisting of 3 × 3 stakes. The maximum measured velocity is 443 m a−1 and the velocity variation over short distances is large compared with studied ice streams in West Antarctica. The surface topography together with the measured velocities across the profile indicate that the bottom topography has a great influence on the flow direction, even where the ice thickness is more than 2000 m. The basal shear stresses are calculated as 180, 227 and 146 kPa in the three Strain nets, while the corresponding driving stresses are 180, 122 and 111 kPa (±5%). The heat produced by sliding and internal deformation is sufficient to keep the base at the pressure-melting point. The annual basal melting is estimated to be about 60 mm. Investigations on the effect of temperature softening show that the flow parameter’s influence on the effective strain rate is more important than the flow parameter’s direct softening in the flow low alone. The mass flow calculated by the force-balance method is between 87 and 96% of pure plug flow and total discharge is calculated to be 13.3 ± 10 km3a-1.
Tidal motion, ice velocity and melt rate of Petermann Gletscher, Greenland, measured from radar interferometry
Authors: Rignot Eric 
Published: September 2017

AbstractOver a floating glacier ice tongue or an ice shelf, the glacier motion measured by a single, repeat-pass, radar interferogram is difficult to analyze, because the long-term, steady motion of the ice is intermixed with its cyclic, downward motion induced by tidal forcing. Multiple interferograms and a quadruple-difference technique are necessary to separate the tidal signal from the long-term, steady motion of the ice. An example of application of this technique is given here using ERS-1 radar images of Petermann Gletscher, a major outlet glacier of northern Greenland. Tidal displacements are measured with < 5 mm statistical noise. The long-term ice Velocity is measured with a precision of 1 ma−1. The inferred tidal displacements agree well with model predictions from a fixed elastic beam with an elastic damping factor of 0.47 ± 0.01 km3. The hinge line is mapped with a precision of 20-80 m.Combining the interferometric ice velocities with ice thickness data, the glacier ice discharge is calculated at and below the hinge line. At the hinge line, the ice flux is 12.1 ± 1 km3 a−1. At the ice front, calf-ice production is only 0.59 km3−1 a−1, meaning that 95% of the ice that crosses the grounding line melts before it reaches the calving front. Assuming steady-state conditions, the melt rate of the glacier tongue averages 12 ± 1 m a−1, with peak values exceeding 20 ma−1 near the hinge line. This high melt rate cannot be accommodated by surface ablation alone (only about 23 ma−1) and is attributed to pronounced basal melting of the ice tongue. Basal melting, often assumed to be negligible in Greenland, is the dominant process of mass release from the floating section of Petermann Gletscher.
Thermal effects due to air flow and vapor transport in dry snow
Authors: Albert M. R. , Mcgilvary W. R. 
Published: September 2017

AbstractThe thermal effects of air flow forced through a snow sample are investigated numerically. A new method for calculating vapor transport in snow is presented which allows for the determination of the effects of sublimation. In this method, the snow is not assumed to be saturated with water vapor. Results of the model show very good agreement with analytical and experimental results. The effects of heat conduction, heat advected by the dry air and heat associated with sublimation are examined in a comprehensive theory, and then each effect is isolated to determine its overall contribution. It is demonstrated that the heat transfer associated with vapor transport is significant in the determination of the overall temperature profile of a ventilated snow sample but that the major effects are controlled by the heat carried by the dry air flow through the snow and heat conduction due to the temperatures imposed at the boundaries. The thermal effects of ventilation of snow are more likely to be observed when there is a smaller temperature gradient over the entire snowpack and a greater flow rate of air in the snow than would be observed when there is a greater overall temperature gradient and lesser air-flow rate.
Theoretical calving rates from glaciers along ice walls grounded in water of variable depths
Authors: Hughes T. 
Published: September 2017

AbstractCalving has been studied for glaciers ranging from slow polar glaciers that calve on dry land, such as on Deception Island (63.0° S, 60.6° W) in Antarctica, through temperate Alaskan tide-water glaciers, to fast outlet glaciers that float in fiords and calve in deep water, such as Jakobshavns Isbræ (69.2° N, 49.9° W) in Greenland. Calving from grounded ice walls and floating ice shelves is the main ablation mechanism for the Antarctic and Greenland ice sheets, as it was along marine and lacustrine margins of former Pleistocene ice sheets, and is for tide-water and polar glaciers. Yet, the theory of ice calving is underdeveloped because of inherent dangers in obtaining field data to test and constrain calving models. An attempt is made to develop a calving theory for ice walls grounded in water of variable depth, and to relate slab calving from ice walls to tabular calving from ice shelves. A calving law is derived in which calving rates from ice walls are controled by bending creep behind the ice wall, and depend on wall heighth, forward bending angleθcrevasse distancecbehind the ice wall and depthdof water in front of the ice wall. Reasonable agreement with calving rates reported by Brown and others (1982) for Alaskan tide-water glaciers is obtained whencdepends on wall height, wall height above water and water depth. More data are needed to determine which of these dependencies is correct. A calving ratioc/his introduced to understand the transition from slab calving to tabular calving as water deepens and the calving glacier becomes afloat.
Impurity influence on normal grain growth in the GISP2 ice core, Greenland
Authors: Alley R. B , Woods G. A. 
Published: September 2017

AbstractIntercept analysis of approximately bi-yearly vertical thin sections from the upper part of the GISP2 ice Core, central Greenland, shows that grain-size ranges increase with increasing age. This demonstrates that something in the ice affects grain-growth rates, and that grain-size cannot be used directly in paleothermometry as has been proposed. Correlation of grain-growth rates to chemical and isotopic data indicates slower growth in ice with higher impurity concentrations, and especially slow growth in “forest-fire” layers containing abundant ammonium; however, the impurity/grain-growth relations are quite noisy. Little correlation is found between growth rate and isotopic composition of ice.
Determination of timing and location of water movement and ice-layer formation by temperature measurements in sub-freezing snow
Authors: Pfeffer W. T. , Humphrey N. F. 
Published: September 2017

AbstractMeasurements of temperature in snow along a vertical profile during the onset of spring melting are used to calculate spatial and temporal temperature gradients and terms of the conduction equation with an internal energy-production term are calculated. Heat-transfer information is combined with stratigraphic observations made during melting and allow detailed determination of the timing and location of heterogeneous water movement and of refreezing. Internal energy production is interpreted as latent heat of refreezing of percolated meltwater. Times and locations of flow and refreezing of meltwater are calculated and compared to Stratigraphic observations of layering and changes in density and liquid-water content. Sequences of melt, piping, layering and refreezing seen in calculations and in stratigraphy demonstrate retarded flow at fine-to-coarse transitions, flow along such transitions and refreezing at the transitions to form ice layers. Downslope flow is also observed in the absence of an impermeable horizon to redirect flow from the vertical.
Modelling albedo and specific balance of the Greenland ice sheet: calculations for the Søndre Strømfjord transect
Authors: Zuo Z. , Oerlemans J. 
Published: September 2017

AbstractGlacio-meteorological data obtained during the Greenland Ice Margin Experiment (GIMEX) investigations in West Greenland (the Søndre Strømfjord transect) have been used to test and calibrate energy-balance/mass-balance models for the ice/snow surface. The region is characterised by the development of a wide zone of low surface albedo in the course of the melting season. This zone was simulated in one of the energy-balance models by including the effect of surficial meltwater on albedo. Observed mass-balance and albedo data were used to constrain the models. Although all the models are capable of predicting the transect balance reasonably well, only the model with the meltwater albedo coupling, is able to reproduce the observed albedo pattern and mass-balance profile along the transect. By including the feedback between surficial meltwater and albedo in the model, the sensitivity of the specific balance to changes in air temperature is found to be greatest just below the equilibrium line (in contrast to what is generally found for valley glaciers). A 1 K warming of the air temperature would increase the mean ablation along the transect by 0.5 m w.e.year −1.
Apparent Short-Term Glacier Velocity Variations
Authors: Andreasen Jørn-Ole 
Published: September 2017

AbstractIn connection with a glacier-hydrological project at a sub-polar glacier in West Greenland, short-term glacier velocity variations were measured. Both the horizontal and the vertical velocity components showed distinct diurnal variations. Close examination indicates that these variations are caused by the change in atmospheric refraction during the day, with the vertical component as the most important.
Optimal Measurement of Ice-Sheet deformation from Surface-Marker Arrays
Authors: MacAyeal D.R. 
Published: September 2017

AbstractSurface strain-rate is best observed by fitting a strain-rate ellipsoid to the measured movement of a stake network, or other collection of surface features, using a least-squares procedure. Error of the resulting fit varies as (LΔt√n)-1 where L is the stake separation, Δt is the time period between initial and final stake survey, and n is the number of stakes in the network. This relation suggests that, if n is sufficiently high, the traditional practice of re-visiting stake-network sites on successive field seasons may be replaced by a less costly single-year operation. A demonstration using Ross Ice Shelf data shows that reasonably accurate measurements can be obtained from 12 stakes after only four days of deformation. The least-squares procedure may also aid airborne photogrammetric surveys in that reducing the time interval between survey and re-survey could permit better surface-feature recognition.
The Uplift of Unteraargletscher at the Beginning of the Melt Season—A Consequence of Water Storage at the Bed?
Authors: Iken A. , Röthlisberger H. , Flotron A. , Haeberli W. 
Published: September 2017

AbstractResults of systematic movement studies carried out by means of an automatic camera on Unteraargletscher since 1969 are discussed together with supplementary 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 a few fluctuations of the vertical velocity, by an equal but slower downward movement which continued at an almost constant rate for about three months. Possible explanations of the uplift are discussed, the most satisfactory explanation being water storage at the bed. The observations then suggest that this storage system is efficiently connected with the main subglacial drainage channels only during times of very high water pressure in the channels. Detailed measurements showed that the times of maximum horizontal velocity coincided with the times of maximum upward velocity rather than with the times when the elevation of the surveyed poles had reached a maximum. On the basis of the hypothesis of water storage at the bed this finding means that the sliding velocity is influenced mainly by the subglacial water pressure and the actual, transient stage of cavity development, while the amount of stored water is of lesser influence.
Variation of Ice Velocity at Lewis Glacier, Mount Kenya, Kenya: Verification Midway Into a Forecast
Authors: Kruss Phillip , Hastenrath Stefan 
Published: September 2017

AbstractThe ice velocity slowdown occurring at Lewis Glacier, Mount Kenya, during the twentieth century has continued beyond 1978. In an earlier paper, a surface velocity decrease approaching 50% was predicted between 1978 and 1985. Measurements to January 1982, halfway through the period, reveal trends generally in line with this forecast: a velocity reduction of order 20% has taken place. The mass flux decreased by at least 25%. Intra-annual variability in velocity pattern and magnitude is apparent; comparatively rapid values occur during the January–February dry season.
Monstars on Glaciers
Authors: Nye J. F. 
Published: September 2017

AbstractIsotropic points are structurally stable features of any complicated field of stress or strain-rate, and therefore will almost always be present on the surface of a glacier. A given isotropic point for strain-rate will belong to one of six different classes, depending on the pattern (lemon, star, or monstar) of principal directions and the contours (ellipses or hyperbolas) of constant principal strain-rate values in its neighbourhood. The central isotropic point on a glacier should theoretically have a monstar pattern, but the contours around it may sometimes be elliptic and sometimes hyperbolic. Nearby, but not coincident with it there will be an isotropic point for stress. This will also have a monstar pattern but, in contrast to the strain-rate point, the contours around it must be hyperbolic. Published examples are consistent with these conclusions. In addition to isotropic points for strain-rate a glacier surface will contain isolated points of pure shear; these also can be classified into six different types. Stable features of this kind give information about the essential structure of a tensor field and form useful points of comparison between observation and numerical simulation.
On the Disintegration of Ice Shelves: The Role of Fracture
Authors: Hughes T. 
Published: September 2017

AbstractCrevasses can be ignored in studying the dynamics of most glaciers because they are only about 20 m deep, a small fraction of ice thickness. In ice shelves, however, surface crevasses 20 m deep often reach sea-level and bottom crevasses can move upward to sea-level (Clough, 1974; Weertman, 1980). The ice shelf is fractured completely through if surface and basal crevasses meet (Barrett, 1975; Hughes, 1979). This is especially likely if surface melt water fills surface crevasses (Weertman, 1973; Pfeffer, 1982; Fastook and Schmidt, 1982). Fracture may therefore play an important role in the disintegration of ice shelves. Two fracture criteria which can be evaluated experimentally and applied to ice shelves, are presented. Fracture is then examined for the general strain field of an ice shelf and for local strain fields caused by shear rupture alongside ice streams entering the ice shelf, fatigue rupture along ice shelf grounding lines, and buckling up-stream from ice rises. The effect of these fracture patterns on the stability of Antarctic ice shelves and the West Antarctic ice sheet is then discussed.
Ice Properties in the Greenland and Barents Seas During Summer
Authors: Overgaard Søren , Wadhams Peter , Leppäranta Matti 
Published: September 2017

AbstractThe analysis of sea-ice cores from three summer field operations to the European Arctic is reported, and the ice properties are related to general conditions of ice distribution, thickness, and ridging in the experimental areas. The operations were in 1978 and 1979 to the Kong Oscars Fjord area of East Greenland (about lat. 72° N.) and in 1980 to the Barents Sea, Fram Strait, and the Arctic Ocean north of Svalbard and Zemlya Frantsa Iosifa on the Swedish Ymer-80 expedition. Salinity profiles show the effect on multi-year floes of a year’s additional confinement in a fjord, the effect of a month’s desalination (July to August) on first-year and multi-year ice, and the difference between first-year and multi-year ice at the end of the melt season. The average salinity as a function of ice thickness agrees reasonably well with the results of Cox and Weeks (1974). Temperature, density, pH, and ionic composition results are also reported, and the effect of brine volume on dielectric constant discussed.
A Mechanism of Basal Ice-Layer Formation Involving Major Ice-Fabric Changes
Authors: Tison J.-L. , Lorrain R.D. 
Published: September 2017

AbstractAn opportunity to analyse the mechanism for the formation of a basal ice layer was provided by Glacier de Tsanfleuron in the Swiss Alps. This glacier has some lateral subglacial cavities in which a basal ice layer forms on the bedrock floor and is subsequently incorporated at the base of the glacier. Petrographic and crystallographic analyses of the different types of ice have provided a means of investigating the successive stages of the process. These analyses show major structural changes which provide field confirmation of the deformation mechanisms studied by several authors in laboratory experiments.
Mass Balance of Two High Arctic Plateau Ice Caps
Authors: Bradley Raymond S. , Serreze Mark C. 
Published: September 2017

AbstractMass-balance measurements have been renewed on two small ice caps on north-eastern Ellesmere Island. Original stake networks were established in 1972 and 1976. Since then, both ice caps have experienced significant mass losses averaging –70 to –140 kg m−2 a−1. They have also decreased in area. The equilibrium line in this area has averaged around 1150 m for the last decade or so. The ice caps are remnants of former climatic conditions and are out of equilibrium with contemporary climate.