Glacial dynamics (glaciology)

Recent results are reviewed from studies of ice dynamics that relate to the objectives of the West Antarctic Ice Sheet initiative. The large amount of knowledge gained is emphasized. The best evidence shows that the ice sheet in West Antarctic is the most rapidly changing ice sheet on earth today. Its rate of change is much faster than most glaciologists had expected and it is changing in a manner much more complex than foreseen. It appears that the changes have two broad causes: a delayed but ongoing response to the termination of the last glaciation about 10,000 years ago; and automatic, internally caused flow adjustments. It is not fully known why the response to the last global termination is so delayed, nor is the operation of internal instabilities understood, and certainly the position has not yet been attained to predict the future course of the evolution of the ice sheet

Proceedings of a Workshop on Antarctic Meteorite Stranding Surfaces

The discovery of large numbers of meteorites on the Antarctic Ice Sheet is one of the most exciting developments in polar science in recent years. The meteorites are found on areas of ice called stranding surfaces. Because of the sudden availability of hundreds, and then thousands, of new meteorite specimens at these sites, the significance of the discovery of meteorite stranding surfaces in Antarctica had an immediate and profound impact on planetary science, but there is also in this discovery an enormous, largely unrealized potential to glaciology for records of climatic and ice sheet changes. The glaciological interest derives from the antiquity of the ice in meteorite stranding surfaces. This exposed ice covers a range of ages, probably between zero and more than 500,000 years. The Workshop on Antarctic Meteorite Stranding Surfaces was convened to explore this potential and to devise a course of action that could be recommended to granting agencies. The workshop recognized three prime functions of meteorite stranding surfaces. They provide: (1) A proxy record of climatic change (i.e., a long record of climatic change is probably preserved in the exposed ice stratigraphy); (2) A proxy record of ice volume change; and (3) A source of unique nonterrestrial material

Equal Access (Un)equal Uptake?: A longitudinal study of cataract surgery uptake in older people in England

BACKGROUND: Uptake of cataract removal is a function of the effectiveness of the healthcare delivery services: services that are inaccessible, inappropriate, or unaffordable will not be utilised by (sub)populations, who consequently live with untreated cataracts. The aim of the study was to identify the relationship between individual wealth inequalities and uptake of cataract surgery in England, having controlled for the effects of potentially confounding variables. METHODS: The final sample comprised of 2091 respondents from the English Longitudinal Study on Ageing (ELSA) who were diagnosed with cataracts prior to or during the study, aged 50 and over at wave 1, who had not undergone cataract surgery prior to the first survey observation, and had also provided a response in the second wave of the study. The uptake of cataract surgery was measured using the question, have you ever had cataract surgery? Data from waves 1-5 were used to identify those having received treatment during the 8-year observation window of ELSA. Survival analysis techniques were used. RESULTS: Having controlled for the effects of potentially confounding variables, wealth did not make a statistically significant contribution to the overall fit of the Cox proportional hazard model nor were individual parameters statistically significant. Thus, respondents’ socioeconomic position was not found to be a significant predictor in the uptake of cataract surgery in the UK. Receiving a recommendation from a medical professional was a key driving factors in the uptake of cataract surgery. CONCLUSIONS: Study findings suggest that uptake of cataract surgery among over 50s with a cataracts diagnosis in England do not discriminate on the grounds of individuals’ material social position (wealth)

Techniques for Restoration of Disturbed Coastal Wetlands of the Great Lakes

A long history of human-induced degradation of Great Lakes wetlands has made restoration a necessity, but the practice of wetland restoration is relatively new, especially in large lake systems. Therefore, we compiled tested methods and developed additional potential methods based on scientific understanding of Great Lakes wetland ecosystems to provide an overview of approaches fur restoration. We addressed this challenge by focusing on four general fields of science: hydrology, sedimentology, chemistry, and biology. Hydrologic remediation methods include restoring hydrologic connections between diked and hydrologically altered wetlands and the lakes, restoring water tables lowered by ditching, and restoring natural variation in lake levels of regulated lakes Superior and Ontario. Sedimentological remediation methods include management of sediment input from uplands, removal or proper management of dams on tributary rivers. and restoration of protective barrier beaches and sand spits. Chemical remediation methods include reducing or eliminating inputs of contaminants from point and non-point sources, natural sediment remediation by biodegradation and chemical degradation, and active sediment remediation by removal or by in situ treatment. Biological remediation methods include control of non-target organisms, enhancing populations of target organisms, and enhancing habitat for target organisms. Some of these methods were used in three major restoration projects (Metzger Marsh on Lake Erie and Cootes Paradise and Oshawa Second Marsh on Lake Ontario). which are described as case studies to show practical applications of wetland restoration in the Great Lakes. Successful restoration techniques that do not require continued manipulation must be founded in the basic tenets of ecology and should mimic natural processes. Success is demonstrated by the sustainability, productivity, nutrient-retention ability, invasibility, and biotic interactions within a restored wetland

How to (actually) save time while working remotely

The pandemic has given many of us the opportunity to ditch the commute and work from home long-term, offering huge potential time savings. But to truly reap the benefits of remote work during the current crisis and beyond, we need to think proactively about how we restructure our workday in this new normal. The authors suggest six concrete, research-backed actions you can take today to create clearer work-life boundaries and optimize how you spend your time

Local Rates of Ice-Sheet Thickness Change in Greenland

The rate of ice-sheet thickness change is calculated for 10 sites in Greenland by comparing measured values of ice vertical velocity and snow-accumulation rate. Vertical velocities are derived from repeat surveys of markers using precision global positioning system techniques, and accumulation rates are determined from stratigraphic analysis of firn cores. The results apply to time-scales covered by the firn-core records, which in most cases are a few decades. A spectrum of thickness-change rates is obtained, ranging from substantial thinning to slow thickening. The sites where ice-sheet thinning is indicated are located near the ice-sheet margin or in outlet glacier catchments. Interior and high-elevation sites are predominantly in balance or thickening slowly. Uncertainties in the rates of thickness change are dominated by errors in the determination of accumulation rates. The results of this work are broadly comparable with regional estimates of mass balance obtained from the analysis of catchment input vs discharge

Patterns of calculated basal drag on ice streams B and C, Antarctica

This is the published version.Patterns of strain rate and slope on the ice streams are unusual. They cannot be accounted for in the usual way as due to standing waves in ice flow over a basal obstruction to flow (such as a sticky spot) . The features are studied using the force-budget technique. The conventional flow law is used, together with measurements of surface strain rate and shape of the glacier, to compute basal drag. The results for Ice Stream C are as expected, in that the drag varies from site to site but is directed inland, restraining the flow. The calculated drag at the base of Ice Stream B, on the other hand, is in places such that it acts to propel the glacier forward. This result is untenable. Either the conventional flow law is not applicable to Ice Stream B or there are large spatial variations in ice stiffness, perhaps associated with foliation, or both

The role of lateral drag in the dynamics of Ice Stream B, Antarctica

The partitioning of resistive force between the bed and sides of Ice Stream B, Antarctica , is obtained for three large areas that have bee n measured using repeat aerial photogrammetry. Problems associated with data errors and local variations in ice strength and velocity are reduced by considering the a really ave raged budget of forces for each photo block. Results indicate that the bed under Ice Stream B must be very weak and unable to provide much res instance. Mechanical l control on this ice stream emanates almost entirely from the lateral margins

Flow laws for glacier ice: comparison of numerical predictions and field measurements

This is the published version, also available here: http://dx.doi.org/10.3189/002214390793701372.Ice flow along the 20 km long strain network up-stream of the Dye 3 bore hole in Greenland is studied in detail. By solving the force—balance equations and using selected flow laws, stresses and strain-rates are calculated throughout the section of the ice sheet. The validity of the results is evaluated by comparison with the velocity profile derived from bore-hole-tilting measurements, and with observed surface strain-rates. A number of constitutive relations are tried and most predict a velocity profile at the bore-hole site that is in good agreement with that observed, if appropriate enhancement factors are used. However, there are major discrepancies between modeled and measured surface strain-rates. Use of Nye's generalization of Glen's flow law, or an anisotropic constitutive relation, requires unrealistically large along-flow variations in the enhancement factor. Inclusion of normal stress effects can lead to much better agreement, but it is possible that other processes, such as dynamic recrystallization or primary creep, should be included in the constitutive relation of polar ice

Force Budget: II. Application to Two-Dimensional Flow Along Byrd Station Strain Network, Antarctica

This is the published version, also available here: http://dx.doi.org/10.3189/002214389793701455.Resistive stresses and velocities at depth are calculated along the Byrd Station Strain Network, Antarctica, using field data. There are found to be large longitudinal variations in basal drag and this result is little affected by errors in the input data or by uncertainties in the constitutive relation for ice. Basal drag varies by a factor of about 2 along the strain network, and is usually equal to the driving stress to within 10–20%. Sites of high drag are not always correlated with basal topographic highs, indicating that some process such as basal water drainage is involved in controlling the friction at the bed. Basal sliding velocities are very sensitive to errors in measured surface velocities and the rate factor in Glen's flow law. As a result, calculated sliding velocities are much less reliable than deep stresses, and need to be interpreted with caution