bluuebunny/crossref_metadata_2025 huggingface dataset:
Teaching Psychiatry in an Integrated Medical Curriculum
Authors: Carr Vaughan J. , Hazell Philip L. , Williamson Michael
Published: November 2007

Objective: Efforts to improve the psychiatric competence of the general medical workforce must include an appraisal of how psychiatry is taught in medical schools. As a contribution to this appraisal a description is given of psychiatric education in the innovative undergraduate medical curriculum at the University of Newcastle.

Method: An outline of the features which characterise medical education at Newcastle is provided and the way in which the teaching of psychiatry is organised within this framework is presented.

Results: The characteristics of the Newcastle undergraduate program in psychiatry include its integration with teaching in other clinical and basic science disciplines, continuity throughout the entire five years of the course, and the emphasis on skills acquisition and their assessment.

Conclusions: The relative merits and disadvantages of the Newcastle approach to undergraduate psychiatry education are presented and the problem of assessing the effectiveness of this approach by outcomes measurement, particularly of integrated competencies and their application in general medical settings, is discussed.
Rooming-in: An Alternative to Involuntary Detention
Authors: Richardson Michael Ernest
Published: November 2007

Objective: To provide, via ‘rooming-in’, a local, less coercive and less frightening alternative to involuntary detention. Rooming In is the voluntary participation of so-called ‘confidants’, who may be chosen family members or trusted friends, in the management of acute, severe psychiatric disturbance by their providing a 24 hour vigil with the patient in a single, safe hospital room.

Method: There were 73 admissions to the rooming-in program at the Manning Base Hospital, Taree, New South Wales (NSW), Australia between 5 August 1986 and 21 September 1992. During the same period 78 patients were remitted from the hospital on an involuntary basis to urban detention centres: ‘scheduled’ under the NSW Mental Health Act. Demographic and diagnostic characteristics of the two populations, both of whom met identical criteria for involuntary detention, are compared in this retrospective, case report study. These two groups constituted only 6% of total psychiatric consults carried out at the hospital over the same 6 year period and those roomed-in represented only 12% of the psychiatric admissions. A quality assurance study evaluated the acceptability of the program.

Results: The scheduled patients were more likely to be single, of no fixed abode and without a local family. They were more likely to have a schizophrenic disorder, compounded by polysubstance abuse, than a mood disorder. The average inpatient stay for those roomed-in was 10 days. Seventy per cent of confidants were required for 4 days or less. The rooming-in program was valued highly by nursing staff, patients and their families.

Conclusion: A search of the world literature would suggest that rooming-in, as a model of care, is unique, at least in the developed world. It allows some seriously disturbed patients to be provided with a local and less restrictive general hospital alternative.
Fluoxetine and the Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH)
Authors: Burke David , Fanker Scott
Published: November 2007

Objective: To report three new cases of the fluoxetine-induced syndrome of inappropriate secretion of antidiuretic hormone (SIADH).

Clinical picture: All three cases occurred in elderly psychiatric inpatients treated for depression with standard doses of fluoxetine within one month of starting the medication. All three patients were clinically symptomatic of SIADH.

Treatment: In all three patients the medication was ceased and fluid restriction commenced. One patient required intravenous saline.

Outcome: All three patients recovered fully within three weeks. None were rechallenged.

Conclusions: The symptoms of hyponatraemia due to fluoxetine-induced SIADH may be difficult to distinguish from the symptoms of depression, unless appropriate laboratory investigations are made.
Australasian Psychiatry and Euthanasia
Authors: Ryan Christopher
Published: November 2007

In May 1995, the Northern Territory of Australia became the first legislative jurisdiction in the world to introduce legislation specifically sanctioning active voluntary euthanasia. Shortly after the introduction of the legislation many of Australia's political leaders announced that they would support similar legislation in their jurisdictions and there nave already been attempts to pass such legislation elsewhere in Australia and in New Zealand.
Outcome Measurement: Sharing Experiences in Australia
Authors: Walter Garry , Kffikby Ken , Marks Isaac , Whtteford Harvey , Andrews Gavin , Swinson Richard
Published: November 2007

There is growing attention to evidence-based medicine both in informing medical education and in guiding clinical practice. The result is increasing emphasis on evaluating treatment efficacy, the structure of health care delivery, the allocation of the health dollar and the application of information technology to these tasks. Implications are emerging for psychiatric care in Australia from everyday clinical practices to the political level. Collective experience in this area, as discussed at a conference forum in Sydney [1], is summarized in this paper. This information is presented to stimulate thought, foster comparisons and encourage a synthesis of clinical, administrative and political directions in this field.
Review of Australia's Capacity to Promote Mental Health
Authors: Wise Marilyn , Wood Carole , Whtteford Harvey
Published: November 2007

In 1994, Australian Health Ministers agreed that promoting mental health and preventing mental illness was one of the four priority national health goals [1], Australia's National Mental Health Strategy includes among its aims the promotion of mental health and prevention of mental illness [2]. To date, the main focus of activity under the Strategy has been on the structural reform of the mental health service delivery system.
Fritz Müller’s legacy on Axel Heiberg Island, Nunavut, Canada
Authors: Adams Peter
Published: November 2007

Fritz Müller (1926–80) was the leader of the Jacobsen-McGill Arctic Research Expeditions to Axel Heiberg Island, Nunavut, Canada. He was a faculty member at McGill University, Montreal, Canada, from 1959 to 1970. Thereafter, he was Chair of Geography at Eidgenossische Techmsche Hochschule, Zürich, Switzerland. He conducted research on Axel Heiberg Island, mainly in the vicinity of Expedition Fiord, from 1959 until his death in 1980. This paper is a personal account of Müller’s work by one of his students, with a commentary on his contributions to Arctic science. The personal account focuses on the early years of the expeditions. The commentary includes discussion of glacier mass-balance records and lake-ice break-up from 1959 to the present, glacier-terminus records from 1948 to the present and other research focused on the region.
Climate variability and glacier reaction in the Austrian eastern Alps
Authors: Schöner Wolfgang , Auer Ingeborg , Böhm Reinhard
Published: November 2007

A carefully homogenized climate dataset is used to interpret glacier behaviour in the Austrian Alps. Periods of glacier advance are generally more maritime and cooler, with reduced sunshine duration and increased precipitation sum during the ablation period. Periods of retreat are associated with a more continental, warmer climate, with increased sunshine duration and reduced precipitation sum. Three recent sub-periods of Austrian glacier behaviour are documented by direct measurement of glacier mass balance (before 1965 more negative; 1965–81 more positive; since 1982 more negative). A long-term mass-balance series in the eastern part of the Austrian Alps parameterized by snow-depth measurements indicates very clearly that periods of more negative mass balance have a higher correlation to summer air temperature and a lower correlation to winter accumulation. Periods of more positive mass balance are highly correlated to winter accumulation and only slightly correlated to summer temperature. The positive mass-balance period 1965–81 is also characterized by negative North Atlantic Oscillation index values which caused an increased meridional circulation mode, resulting in a northwesterly to northerly precipitation regime during winter.
Operational ice-model verification at the Canadian Ice Service
Authors: Carrieres Tom
Published: November 2007

An operational coupled ice-ocean forecast model is compared with observed ice features derived from daily ice charts and ice beacons. The model demonstrates significant skill in predicting ice drifts, total ice extent, total ice area and average compactness tendencies. Evaluation of ice-thickness forecasts is inconclusive. Model deficiencies may be caused by inconsistent specification of the initial ice and ocean state.
Modelling of historic variations and future scenarios of the mass balance of Svartisen ice cap, northern Norway
Authors: Engeset Rune Verpe , Elvehøy Hallgeir , Andreassen Liss Marie , Haakensen Nils , Kjøllmoen Bjarne , Roald Lars Andreas , Roland Erik
Published: November 2007

In glacier-dominated catchments, glaciers have an important effect on the water balance. It is important to understand the glacier control on inflow in order to assess historic trends and future scenarios. The mass balance of a 100 km2 glacier sub-basin of Svartisen ice cap, northern Norway, was reconstructed for 1917 to 1995. The reconstruction was carried out using three different methods, the hydrological method, the correlation between mass balance and meteorological observations and a precipitation-degree-day model. Calibration data were derived from field observations, map comparisons and correlation of observations at different glaciers. The reconstructed series showed a total loss of ∼3 × 109 m3 of water, most of which occurred between 1920 and 1950. After 1950, the net balance increased gradually and is currently near equilibrium with the present climate. Suggested climate scenarios for this region gave a loss between zero and 5 ×109 m3 of water until the year 2050.
Geotechnical centrifuge modelling of gelifluction processes: validation of a new approach to periglacial slope studies
Authors: Harris Charles , Rea Brice R. , Davies Michael C. R.
Published: November 2007

Here we compare scaled centrifuge modelling of gelifluction processes with earlier full-scale physical modelling experiments. The objective is to assess the validity of the centrifuge technique for cryogenic slope-process investigations. Centrifuge modelling allows correct self-weight stresses to be generated within a small-scale physical model by placing it in an elevated gravitational field. This paper describes an experiment in which a scaled frozen-slope model was thawed in a gravitational field equivalent to ten gravities. After four cycles of thawing, during which soil temperatures, pore pressures, thaw settlement and downslope soil displacements were continuously monitored, a series of marker columns were excavated to reveal profiles of soil movement. Comparison of these data with those from an earlier full-scale laboratory simulation experiment indicates that thaw-related gelifluction was successfully reproduced during centrifuge modelling. It is concluded that rates of soil shear strain during gelifluction were not time-dependent? since soil displacements in the centrifuge tests were of a similar magnitude to or greater than those observed in the much longer-duration full-scale simulation. This suggests that no transition occurred in soil behaviour from a frictional plastic to a true viscous fluid during the period of high moisture contents immediately following thaw.
Runoff and drainage pattern derived from digital elevation models, Finsterwalderbreen, Svalbard
Authors: Hagen Jon Ove , Etzelmüller Bernd , Nuttall Anne-Marie
Published: November 2007

Finsterwalderbreen (77°26’ N, 15° 15’ E) is a 35 km2 polythermal, surge-type glacier in southern Spitsbergen, Svalbard. Extensive field investigations have been carried out on the glacier, including mapping of bed topography by radio-echo soundings, mass-balance measurements and hydrological and meteorological registrations. In this paper we have used surface and bed topography and observations of summer ablation to estimate total runoff and subglacial drainage pattern by means of spatial map analysis in standard geographic information system software. The location and relative importance of the water-channel outlets from the glacier were estimated, as well as the change in drainage pattern over the period 1970–90. The results could be compared to direct observations of drainage pattern and discharge recordings. The analyses indicate that the location of the subglacial channels is dominated by the surface topography and thus that the channels are partly pressurized.
Modeling interdecadal variations of lake-ice thickness and sensitivity to climatic change in northernmost Alaska
Authors: Zhang T. , Jeffries M. O.
Published: November 2007

A physically based finite-element heat-transfer model with phase change is used to simulate ice growth and thickness variability on shallow, thaw lakes on the North Slope of Alaska during the period 1947–97. The basic inputs to the model are air temperature and snow depth as recorded at the U.S. National Weather Service station, Barrow, Alaska. The simulated long-term mean maximum ice thickness was 1.91 ±0.21 m with a range from 1.33 m (1962) to 2.47 m (1976). Variations in the seasonal snow cover played a much greater role than air temperatures in controlling ice-thickness variability during the 50 year simulation period. The sensitivity of lake-ice growth to extremes of snow depth, air temperature and snow bulk thermal conductivity is investigated. This study shows that lake-ice thickness has varied significantly from year to year in northern Alaska. Continued variability combined with potential climate change could affect the area of ice that freezes completely to the bottom of lakes each winter, resulting in changes in water storage and availability, permafrost thermal regime and talik dynamics beneath lakes, and methane efflux and energy fluxes to the atmosphere. It is concluded that quantification and a full understanding of these potential effects will require systematic and continuous field measurements that will provide better forcing and validation fields for improved models.
Modelling thermomechanical properties of the snowpack
Authors: Guseva-Lozinski Elena
Published: November 2007

Studying the structure inside an inhomogeneous stratified snowpack is very important for modelling of the snowpack stability on mountain slopes, and to approximate surfaces of weak zones, and boundaries with different properties These surfaces are often the sliding surfaces of avalanches. Weather conditions" windpumping, snow densification and mechanical and complex heat- and mass-transfer processes define the structural variations of snow and the strength characteristics. The main ventilation components in the snowpack during the snowstorm are the heat and mass exchange between the snow grains and bonds, vapor and heat transfer. The vapor diffusion due to windpumping through snowpack intensifies the metamorphic process We propose the current mathematical model using meteorological data to simulate the snowpack characteristics in order to clarify the changes of the structural and physical-mechanical properties in the stratified snowpack under changing weather conditions. The system of equations allows calculation of the temperature variation in the snowpack, as well as in melted or frozen soil, the snow density, the structural parameters and the snowpack strength on the mountain slope as a function of the heat- and mass-transfer parameters. A numerical finite-difference model for simulations has been used. This allows prediction of the disposition of the depth-hoar layers and the physical-mechanical snow properties. The model has potential to estimate the potential avalanche volume.
Photogrammetric reconstruction of glacier mass balance using a kinematic ice-flow model: a 20 year time series on Grubengletscher, Swiss Alps
Authors: Kääb Andreas
Published: November 2007

The kinematic boundary condition at the glacier surface can be used to provide glacier mass balance at individual points if changes in surface elevation, horizontal and vertical surface velocities and surface slope are known. Vertical ice velocity can in turn be estimated from basal slope, basal ice velocity and surface strain. This relation is applied to reconstruct a 20 year mass-balance curve of Grubengletscher, Swiss Alps, largely using repeated aerial photogrammetry, with only a minimum of fieldwork For individual years the mass-balance distribution on the glacier tongue was modelled with an accuracy of about ±0.9 m a"1. Ice-mechanical assumptions and errors in glacier bed geometry markedly affect discrete mass-balance patterns but are largely eliminated in the calculation of year-to-year mass-balance changes The resulting 1973–92 curve for the Grubengletscher tongue shows reasonable consistency with meteorological data and other glaciologically derived mass-balance series. Large changes in measured ice speed on the glacier tongue (±50%) significantly governed the long-term variability of ice thickness over the observational period.
Modelling glacier response to measured mass-balance forcing
Authors: Albrecht Olaf , Jansson Peter , Blatter Heinz
Published: November 2007

Measurements of summer and winter mass balances have been carried out over the past 53 years on Storglaciären, northern Sweden. Repeated surveys of the glacier have resulted in several maps of surface topography as well as a map of the bed topography A new time-dependent ice flow model allows us to compare the observed surface evolution of the glacier with that computed by the model using measured mass-balance maps as input. The computed volume change compares well with the measured change: the model replicates the distribution of surface elevation to within ±10 m over 30 years of integration. On the model side, these deviations can be attributed to the low-resolution discretization of the model domain as well as to the limited accuracy of the ice rheology and omitted basal sliding. On the other hand, the uncertainties of the topography and mass-balance maps match the model uncertainties. In this sense, the experiments are a validation of both model and observations.
Ice flow in the northeast Greenland ice stream
Authors: Joughin Ian R. , Fahnestock Mark A. , Bamber Jonathan L.
Published: November 2007

We have measured ice flow and detailed topography in northeastern Greenland using satellite-based synthetic-aperture radar (SAR) interferometry. The subject of this study is the large ice stream that drains this quadrant of the ice sheet. A single SAR interferogram allows the measurement of one component of motion over a several-day-long interval. We have used a set of such measurements from multiple look directions to produce a mosaic of ice-flow velocity. The resulting flow field is tied to an estimated balance-velocity distribution in slow-moving areas and assumes flow to be locally surface-parallel. The velocity field is the most detailed, consistent data-set available over a flow feature of this size. It compares with global positioning system surveyed velocity measurements at the 5 m a–1 level In the process of mapping ice-flow velocity an enhanced elevation model of the ice stream was produced. The elevation model is based on a blend of interferometrically measured short-wavelength topography and radar-altimetry-determined longer-wavelength topography. This enhanced model has improved information on local surface slope, which is useful for estimating the horizontal components of the velocity field.
Data assimilation in sea-ice monitoring
Authors: Weaver Ronald L. S. , Steffen Konrad , Heinrichs John , Maslanik James A. , Flato Gregory M.
Published: November 2007

The detection of small changes in concentration or thickness in the Arctic or Antarctic ice cover is an important topic in the current global-climate-change debate. Change detection using satellite data alone requires rigorous error analysis for their derived ice products, including inter-satellite validation for long time series. All models of physical processes are only approximations, and the best models of complicated physical processes have errors and uncertainties. A promising approach is data assimilation, combining model, in situ data and satellite remote-sensing data. Sea-ice monitoring from satellite, ice-model estimates, and the potential benefit of combining the two are discussed in some detail. In a case-study we demonstrate how the sea-ice backscatter for the Beaufort Sea region was derived using a backscattering model in combination with an ice model. We conclude that, for data assimilation, the first steps include the use of simple models, moving, with success at this level, to progressively more complex models. We also recommend reconfiguring the current remote-sensing data to include precise time tags with each pixel. For example, the current Special Sensor Microwave Imager data might be reissued in a time-tagged orbital (or gridded) format as opposed to the currently available daily averaged gridded data. Finally, error statistics and quality-control information also need to be readily available in a form useful for assimilation. The effectiveness of data-assimilation techniques is directly linked to the availability of data error statistics.
Diffusivity and vapor flow into snow during phase change
Authors: Satyawali P. K.
Published: November 2007

Large variations in values of the diffusion coefficient for snow have been reported in the literature. Some authors (Yosida and others, 1955; Yen, 1963) have claimed that the diffusion coefficient does not vary with density. Others (Colbeck, 1993; Arons and Colbeck, 1995) have reported that the diffusion coefficient decreases with an increase in mean pore length, and that it does not necessarily change with snow density. This appears to be inconsistent, since density and mean pore space are related for a given mass of snow and therefore these parameters cannot be taken independently. On the other hand, experimental results show an increase in grain-growth rate with decrease in snow density. In this paper, particulate and continuum approaches have been used to obtain the mass diffusivity Treating snow as a particulate medium, the one-dimensional model of grain growth from Satyawali (1994) has been extended. This approach has been integrated into the SNOWPACK model (Lehning and others, 1998) that predicts the rate of grain growth for a dry snowpack subject to a temperature gradient. The expression for effective vapor-diffusion coefficient resulting from the present study is

To test this equation, several experiments similar to those of Yosida and others (1955) have been conducted assuming that snow is a continuous medium. In this approach Fick’s law of diffusion is used to obtain direct experimental determinations of the diffusion coefficient. The experimental results have been compared to estimates of D∊ calculated from the above equation and it is shown that results are inconsistent at the upper and lower sample boundaries. This paper describes the features of snow metamorphism, in particular grain growth driven by an applied temperature gradient, and discusses the mass-diffusivity coefficient derived from the particle theory of Colbeck (1993).
Consequences of climate change for runoff from Alpine regions
Authors: Braun L. N. , Weber M. , Schulz M.
Published: November 2007

The water balance of Alpine regions is strongly determined by the storage of water in the form of snow and ice On the basis of long time series of daily precipitation, air temperature and discharge, the conceptual runoff model HBV3–ETH9 was applied to various basins of the eastern Alps showing a glacierization of 0–80%. Using the results of regional climate modelling under the assumption of doubling of C02 , the meteorological input data files were altered taking into account more frequent hot days and additional connective precipitation events during the summer months, and the consequences of these changes for daily discharge were evaluated. The results show that in regions with insignificant glacierization, runoff reacts primarily to changes in precipitation, and less so to rising summer air temperature. In highly glacierized basins, however, the same scenarios suggest strongly enhanced water yields in an initial phase. Higher flood peaks will result when high melt rates and heavy summer rains coincide. If glacier mass losses continue in the more distant future, the glacierized area will diminish and summer discharge will be gradually reduced, resulting in drastic water shortages in hot, dry summers once the glaciers have disappeared.
On the physical model of frozen soil
Authors: Frolov Anatoly D.
Published: November 2007

In this paper we discuss a physical model of frozen soil based on the systems approach and reflect contemporary knowledge about the constitution, structure and properties of this complicated medium. The component composition and specific spatial cryogenic coagulant-crystalline structure as well as physical subsystems of frozen soil conditioning its physical properties are considered. Examples of the use of a model for better comprehension and explanation of some electrical and mechanical property changes of sandy-clayey frozen soils are presented and discussed. The proposed model and its hierarchy is a useful tool for planning experiments and interpreting their results.
Holocene glacier fluctuations: is the current rate of retreat exceptional?
Authors: Oerlemans J.
Published: November 2007

Most glaciers in the Northern Hemisphere reached their postglacial maximum in recent times, that is, after the medieval period. During the last 100 or 150 years a significant retreat has taken place, and there is little sign that this is coming to an end. The current worldwide shrinkage of glaciers is considered to be a strong indication of global warming. However, glacier retreat should be judged against the natural variability of glacier systems. Numerical glacier models can be used to quantify this variability. I have studied the natural variability of three glaciers for which long historic records of glacier length exist: Nigardsbreen, Norway; Rhonegletscher, Switzerland; and Franz Josef Glacier, New Zealand. Integrations for a 10 000 year period, driven by random forcing of a realistic strength, show that the current retreat cannot be explained from natural variability in glacier length and must be due to external forcing.
Spatial distribution of net surface mass balance on Greenland
Authors: Zwally H. J. , Giovinetto M. B.
Published: November 2007

The spatial distribution of surface mass balance on the Greenland ice sheet is mapped on a 50 km grid using a combination of methods depending on a zonal characterization of the diagenetic snow fades. In the zones of dry snow and upper percolation fades, the accumulation rate is calculated from microwave emissivities derived from satellite measurements using a model that is calibrated with field accumulation data. In the lower percolation zone, accumulation rates are obtained from visual interpolation of previously compiled field data, with some modification so the balance is zero at the equilibrium line In the ablation zone, ablation rates are calculated as a function of ice-surface elevation and latitude. Average values of the surface balance are 263 kg m–2a–1 in the accumulation zone, (-) 1259 kg m–2 a–1 in the ablation zone and 1286 kg m–2 a–1 overall. Compared to the findings of a previous study using practically the same approach but different models, our bulk estimate of balance (216 Gt a–1) is 57% smaller, but the differences in the estimates of net accumulation and net ablation are, respectively, 30% and 172% larger. In this and other comparisons, there is evidence that the differences in estimates are primarily due to differences in the delineation of the equilibrium line and the estimate of ablation, and secondarily to the estimate of accumulation and interpolation of field data. The differences noted with six other estimates reported in the last two decades are all of a size close to the composite variation of the difference (±50Gtσ–1) . Our surface balance is smaller than three estimates, larger than one and in agreement with two. If substituted in the latest mass-budget estimate that indicates equilibrium, our surface balance estimate would suggest a negative budget of 55 Gt a–1 and thus a positive contribution to sea-level change of 0.15 mm a–1.
The mathematical modelling of salinity changes in ice and frozen soil as a result of thermal variations
Authors: Guseva-Lozinski Elena
Published: November 2007

A mathematical model makes it possible to estimate the stability of soils in permafrost, the origin of different forms of underground ice, and pingo formation in several parts of the surface in the permafrost. The cryogenic formation of pingos, which is very widespread in permafrost areas, is investigated in the paper. The velocity and height of pingo growth depend on the total moisture content in soil, the type of soil, the initial salinity and the climate conditions. This problem is addressed using equations of Stefan’s heat problem, filtration and salt diffusion and equations for water pressure, with water moving to the phase boundary under different hydrostatic and osmotic pressures.
Gridded temperature and accumulation distributions for Greenland for use in cryospheric models
Authors: Calanca Pierluigi , Gilgen Hans , Ekholm Simon , Ohmura Atsumu
Published: November 2007

Gridded distributions of the annual mean temperature and annual total accumulation for Greenland are presented. They are objectively derived by deterministic and statistical interpolation from measurements at coastal stations and at locations on the ice sheet. They can be used not only for driving cryospheric models, but also for verifying atmospheric simulations.
Spatial distribution of air molecules within individual clathrate hydrates in polar ice sheets
Authors: Ikeda Tomoko , Salamatin Andrey N. , Lipenkov Vladimir Ya. , Mae Shinji , Hondoh Takeo
Published: November 2007

We measured the N2/O2 ratios in clathrate hydrate crystals from Vostok Antarctic ice cores using Raman spectroscopy in order to investigate the spatial distribution of air molecules within a crystal. The results showed that the pattern of the spatial distribution of air molecules in clathrate hydrate depends on the crystal. Some clathrate hydrates have inhomogeneous distributions of the N2/O2 ratio within the crystals, while others are practically homogeneous. The spatial distribution of air molecules within an individual clathrate hydrate changes with time due to three processes: (1) the initial selective enclathration caused by the difference between the dissociation pressures of pure N2- and O2–clathrate hydrates, (2) the diffusive mass transfer of air molecules from surrounding air bubbles through the ice matrix, and (3) diffusion of air molecules in the clathrate hydrate crystal. The dissociation pressures and the diffusion rates of air molecules in ice and clathrate hydrate strongly depend on temperature. Therefore, it is concluded that the pattern of the spatial distribution of air molecules in clathrate hydrate is mainly determined by the depth at which they formed and the temperature in the ice sheet.
Ice-sheet modelling at different spatial resolutions: focus on the grounding zone
Authors: Pattyn Frank
Published: November 2007

A high-resolution time-dependent two-dimensional flowline model was developed, which takes into account all relevant stresses (i.e. both shear and longitudinal stresses), and which is solved on a fixed finite-difference grid. Special attention was paid to the computational efficiency. A comparison is made with a similar model that solves the velocity field according to the shallow-ice approximation. Both models were applied to an East Antarctic flowline for which the data on surface and bedrock elevation were sampled at different spatial resolutions. The numerical analysis deals with the importance of longitudinal stresses at the ice-sheet/ice-shelf interface at different grid sizes" and the importance of basal drag vs driving stress in basal sliding laws. At a grid resolution of 5–10 km the force balance indicates that all stress components are of equal importance in an area that is larger than the nominal grid size. When sliding becomes dominant, this transition zone considerably widens. Furthermore, the longitudinal stress deviator is found to vary considerably with depth due to the thermomechanical coupling.
Preliminary investigations of centrifuge modelling of polycrystalline-ice deformation
Authors: Rea Brice R. , Irving Duncan H. B. , Hubbard Bryn , Mckinley John
Published: November 2007

Glen’s flow law is a well-established general law for steady-state glacier ice deformation, and many laboratory tests and field measurements have been undertaken which have shown the generality of the law to be correct. In Nature, ice deformation is the response of the glacier/ice sheet to the applied self-weight stress of the ice mass (i.e. ice thickness, gravity and ice density) which produces a stress gradient within the ice column. Detailed experimental analyses of ice samples in the laboratory have until now only been undertaken using uniform stress fields in uniaxial or triaxial tests. Obviously the best method for investigating ice in the laboratory would be if stress gradients similar to those found in Nature could be replicated. In the following paper we describe the physical modelling of two (laboratory-prepared) isotropic, polycrystalline ice models (0.75 × 0.25 × 0.18 m) at enhanced gravity levels (80g) in a geotechnical beam centrifuge. Steel plate was placed on top of the ice model, replicating an overburden of approximately 36 m of ice (at 80g). Thus we were able to model the deformation of the lower 14 m of an ice mass approximately 50 m thick. Models are confined laterally by the Perspex strongbox walls, preventing lateral extension within the sample during testing. Models are unconfined on their downslope ends, rendering longitudinal stresses negligible. Deformation can therefore be treated as simple shear. Samples are instrumented with displacement markers and thermocouples. Values for A and n in the flow law derived from the experiments are reasonable and indicate the potential of this method for ice-deformation studies.
Analysis of ice-flow instabilities identified in the EISMINT intercomparison exercise
Authors: Payne A. J. , Baldwin D.J.
Published: November 2007

A series of ice-sheet-model intercomparison exercises have been organized as part of EISMINT. One such set of experiments investigated the implications of thermomechanical coupling on the flow of ice sheets with idealized geometry The results of these experiments are discussed by Payne and others (in press). They indicate that local concentrations of ice flow may develop as a consequence of interactions between ice flow, temperature and viscosity The nature of the intercomparison exercise meant that only a limited number of experiments could be performed by the ten contributing groups. Many of the implications arising from the results could not therefore be investigated. This paper focuses on four. They are the initiation of the patterning, its reversibility the influence of the relationship between ice temperature and viscosity and dependence on numerical time-step and horizontal grid size.
Strong single-maximum crystal fabrics developed in ice undergoing shear with unconstrained normal deformation
Authors: Jun Li , Jacka T. H. , Budd W. F.
Published: November 2007

Laboratory-ice deformation experiments are described that use an apparatus designed to apply a simple-shear stress configuration. Ice samples are deformed by applying horizontal parallel forces, with no vertical forces imposed, and with no attempt made to restrain sample dimension in the vertical direction. The vertical dimensions of the samples however are measured and, for a sample initially of rectangular vertical cross section, it is found that there is an apparent strain (compression) in this direction that increases with the shear strain. For samples initially with a 30° "back-cut" shape, a vertical (extension) strain is evident during approximately the first 20% horizontal strain until the sample has deformed to near the rectangular section shape. For a sample with length-to-height ratio of 10 the maximum vertical strain was about 1%. At this maximum vertical strain, the strain rate in the vertical direction is zero and the sample is undergoing a close approximation to plane laminar (simple shear) flow. It is then followed by a vertical (compression) strain until termination of the experiment. The greater the ratio of length-to-height for the test samples, the less the vertical stain and the greater the strain period over which approximate plane laminar flow persists. This 20% horizontal strain is sufficient to ensure, for a sample of initially isotropic ice, that tertiary steady state has been attained, and the resulting crystal fabrics indicate a strong single-maximum pattern similar to those found deep in polar ice sheets. The single-maximum pattern is however lightly elongated perpendicular to the shear direction.
Analysis of bottom morphology of the David Glacier–Drygalski Ice Tongue, East Antarctica
Authors: Tabacco I. E. , Bianchi C. , Chiappini M. , Zirizzotti A. , Zuccheretti E.
Published: November 2007

Data from radio-sounding measurements have been analysed to determine the ice thickness and the bottom morphology of Drygalski Ice Tongue, Antarctica. The morphology and the structure of the bottom surface has been studied through an electromagnetic interpretation. A function that includes the gain/loss due to the geometrical shape of the reflecting surfaces has been calculated. Such a function has been evaluated assuming some physical electromagnetic quantities (the temperature of the glacier, the complex dielectric permittivity of ice, sea ice and sea water). The ice-water interface shows both concave and convex faces toward the sounding system, producing a focusing or deocusing effect, detected as absolute (or relative) amplitude variation in the echo signal. It is shown that the calculated function follows quite well the observed bottom rippled surface of the glacier tongue estimated from the time-arrival measurements of the echo signal.
Canals under sediment-based ice sheets
Authors: Ng Felix S. L.
Published: November 2007

Classical theories of channelized subglacial drainage identify a melting vs creep balance at the channel-ice boundary that is crucial in determining its steady flow properties, but this consideration neglects the role of erodible-deformable basal sediments, especially in controlling channel morphology. Here we present a mathematical model for channel/underneath ice sheets, which incorporates the detailed mechanics of sediment transport over a mobile till-bed interface, and which allows a variable, wide channel cross section also. The resulting drainage conditions depend on the sediment flux (q) as well as the water flux (Q) through the channel - these quantities being controlled by the rates at which sediment and meltwater are captured by the flow. An approximate analytical solution indicates a "canal"-type drainage law (Walder and Fowler, 1994) of the form where N2 is thε effective channel pτessUτe, n is the exponent in Glen’s flow law for ice, and Ψ is the imposed hydraulic gradient (due to topography). By solving the downstream problem numerically, the canal characteristic has been confirmed and found to be insensitive to upstream conditions. Thus, low effective pressures can result from high basal water flux or melt rates. This supports the contention that canals may be a central component in fast ice flow over soft beds The proposed model also establishes a fundamental link between the plumbing system of a glacier and its sediment budget.
Identification of strain heterogeneities arising during deformation of ice
Authors: Mansuy Philippe , Philip Armelle , Meyssonnier Jacques
Published: November 2007

Creep tests carried out on specimens of isotropic ice containing a monocrystalline inclusion allow us to observe some strain heterogeneities that develop during the deformation of polycrystalline ice. Different kinds of heterogeneities, some of them leading to strain localization, are observed and described, and mechanisms are proposed to explain how they arise. However, when the inclusion has a very regular shape with no geometric singularity (e.g. circular shape) and is embedded in a fine-grained isotropic matrix, the observations lead us to assume homogeneous deformation of the inclusion, with no strain localization except that associated with basal glide.
Flow of anisotropic ice from the EPICA core: a new test apparatus
Authors: Sammonds Peter R. , Boon S. , Hughes N. , Rist M. A.
Published: November 2007

Our objective is to measure the mechanical properties of anisotropic ice of the EPICA ice core, from Dome Concordia, Antarctica, through the full depth of the borehole in deformation experiments under simulated ice-sheet conditions of temperature and pressure. We propose to undertake experiments on the EPICA core using both a conventional triaxial-test apparatus and a new, true, triaxial-test apparatus incorporating automated tomographic imaging of the ice-fabric evolution during deformation. We present the design of this new apparatus together with our testing methodology for EPICA ice. The new apparatus is capable of deforming an ice specimen, up to 200 mm × 100 mm × 40 mm, under servo-controlled biaxial loading with a superimposed confining pressure of 50 MPa and at temperatures down to –40°C. Highly unusual problems arising from the true triaxial nature of the apparatus and tomographic imaging are discussed.
Holocene electrical and chemical measurements from the EPICA–Dome C ice core
Authors: Udisti R. , Becagli S. , Castellano E. , Mulvaney R. , Schwander J. , Torcini S. , Wolff E.
Published: November 2007

The comparison between electric (electric-conductivity measurement (ECM) and dielectric profiling (DEP)) and chemical sulphate and chloride) depth profiles along the first 400 m of the EPICA-Dome C ice core revealed a very good fit, especially for peaks related to volcanic emissions. From the comparison between these profiles, a dominant contribution of sulphuric acid to the ionic balance of Antarctic ice for the Holocene was confirmed. A progressive increase with depth was observed for chloride concentrations, showing a change of relative contribution between sulphate and chloride. A higher increase of chloride was evident between 270 and 360 m depth, probably due to a change in source or transport processes or to an increase of the annual snow-accumulation rate. The DEP, ECM and sulphate ice signatures of Tambora (AD 1816) and El Chichon (?) (AD 1259) eruptions are described in detail. A characteristic peak series, due to HCl deposition, was identified at 103–109 m depth from the ECM, DEP and chloride profiles.
Dynamic, in situ measurement of sea-ice characteristic length
Authors: Fox Colin , Haskell Tim G. , Chung Hyuck
Published: November 2007

We present a method for measuring the characteristic length of sea ice based on fitting to a recently found solution for the flexural response of a floating ice sheet subject to localized periodic loading. Unlike previous techniques, the method enables localized measurements at single frequencies of geophysical interest, and since the measurements may be synchronously demodulated, gives excellent rejection of unwanted measurement signal (e.g. from ocean swell). The loading mechanism is described and we discuss how the effective characteristic length may be determined using a range of localized measurements. The method is used to determine the characteristic length of the sea ice in McMurdo Sound, Antarctica.
Arctic sea-ice albedo derived from RGPS-based ice-thickness estimates
Authors: Lindsay R.W.
Published: November 2007

The RADARSAT geophysical processor system (RGPS) uses sequential synthetic aperture radar images of Arctic sea ice taken every 3 days to track a large set of Lagrangian points over the winter and spring seasons. The points are the vertices of cells, which are initially square and 10 km on a side, and the changes in the area of these cells due to opening and closing of the ice are used to estimate the fractional area of a set of first-year ice categories. The thickness of each category is estimated by the RGPS from an empirical relationship between ice thickness and the freezing degree-days since the formation of the ice. With a parameterization of the albedo based on the ice thickness, the albedo may be estimated from the first-year ice distribution. We compute the albedo for the first spring processed by the RGPS, the early spring of 1997. The data include most of the Beaufort and Chukchi Seas. We find that the mean albedo is 0.79 with a standard deviation of 0.04, with lower albedo values near the edge of the perennial ice zone. The biggest source of error is likely the assumed rate of snow accumulation on new ice.
Introduction of variable drag coefficients into sea-ice models
Authors: Steiner Nadja
Published: November 2007

In order to consider the effect of different ice conditions on the momentum exchange between atmosphere and ocean, a parameterization for variable drag coefficients is introduced. A square dependence on ice concentration is combined with a linear dependence on deformation energy to account for the influence of floe edges as well as for roughness elements in regions with a more compact ice cover. The approach is not regionally specified and is applied over the whole model region. Empirical parameters are optimized via comparison with observed buoy-drift data.
Temporal evolution of Arctic sea-ice temperature
Authors: Perovich Donald K. , Elder Bruce C.
Published: November 2007

Vertical profiles of temperature from the air through the snow and ice and into the upper ocean were measured over an annual cycle, from October 1997 to October 1998, as part of a study of the Surface Heat Budget of the Arctic Ocean (SHEBA). These observations were made at nine locations, including young ice, ponded ice, undeformed ice, a hummock, a consolidated ridge and a new blocky ridge. All of the sites had similar environmental forcing, with air temperatures at the different sites typically within 1°C. In general, the seasonal evolution of ice temperature followed a pattern of (1) a cold front propagating down through the ice in the fall, (2) cold ice temperatures and ice growth in late fall, winter and early spring, and (3) warming to the freezing point in the summer. Within this general pattern, there was considerable spatial variability in the temperature profiles, particularly during winter. For example, snow/ice interface temperatures varied by as much as 30°C between sites. The coldest ice temperatures were observed in a consolidated ridge with a thin snow cover, while the warmest were in ponded ice. The warm pond temperatures were a result of two factors: the initial cooling in the fall was retarded by freezing of pond water, and the depressed surface of the pond was quickly covered by a deep layer of snow (0.6 m). In an 8 m thick unconsolidated ridge, the cold front did not penetrate to the ice bottom during winter, and a portion of the interior remained below freezing during the summer. The spatial variability in snow depth and ice conditions can result in situations where there is significant horizontal transport of heat.