bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ice Loss in the Ablation Area of a Himalayan Glacier; Studies on Miar Glacier, Karakoram Mountains, Pakistan
Authors: Young G.J. , Schmok J.P. 
Published: September 2017

One of the main aims of the Snow and Ice Hydrology Project, a joint Canada-Pakistan endeavour, is to estimate ice loss in the ablation areas of glaciers in order to predict with greater confidence stream flow in the headwaters of the Indus River. To this end, Miar Glacier, located in the central Karakoram Range, north of Gilgit, was intensively studied during the summers of 1986 and 1987.Measurements of glacier mass balance by the monitoring of accumulation and ablation at stake locations is very difficult in the Himalyan environment. It is usually almost impossible to reach elevations above the equilibrium line without major effort, and always very difficult once there to make meaningful measurements; the ablation areas are often heavily crevassed and/or debris-covered, and this poses difficult sampling problems.The method used in this study was to monitor annual surface movement on a cross-profile as near as possible to the equilibrium line. The measurements, obtained in conjunction with depth soundings made on the same profile, allow the annual ice flux through the cross-profile to be calculated. If an approximately steady-state glacier is assumed, it would be expected that this flux would be roughly equivalent to the rate of ice loss below the profile.The movements of wooden stakes drilled into the glacier were monitored throughout each of the summers and, since two of the stakes survived the intervening winter, this allowed calculation of annual movement. Distances between the crests of ogives were also surveyed, providing an independent assessment of glacier movement. Depth measurements by radio-echo sounder were successfully made in the summer of 1987, showing maximum ice depths of 550 m. The annual ice flux through the transverse profile was estimated as 5.67 × 107 m3, which corresponds to a mean annual ice loss from the glacier surface below the profile of 8.10 m of ice.
Paleogeographic Significance of Middle Pleistocene Glaciomarine Deposits on Baldwin Peninsula, Northwest Alaska
Authors: Huston Matt M. , Brigham-Grette Julie , Hopkins David M. 
Published: September 2017

Baldwin Peninsula, northwest Alaska, is a middle Pleistocene push-moraine complex composed of marine, fluvial, and glaciogenic sediments. The peninsula was formed by three ice lobes emanating from the De Long and Baird mountains and the Selawik Lowlands in the southwest Brooks Range during the Anaktuvuk River glaciation. This glaciation was nearly an order of magnitude more areally extensive than late Pleistocene glaciations in the same region and occurred c. 500 to 600 ka B.P. based on paleomagnetism, and amino-stratigraphic and morphostratigraphic correlations with other numerically-dated northwest Alaskan deposits.Extensive deposits of massive and laminated clayey silt with striated, faceted stones indicate that local sea level was high as glacial ice reached its maximum extent. Glacio-isostasy does not seem to have been important in maintaining a high relative sea level; therefore we infer that eustatic sea level remained high during ice advance. For this to occur, high latitude glaciation must have preceded the build-up of ice in lower latitudes. The source of moisture for such massive glaciation may have come from submerged Bering and Chukchi shelves, enhanced flow of North Pacific/southern Bering Sea winter storms, reduced intensity of the winter Arctic High, or a combination thereof.
Meridional Sea-Ice Transport and its Impact on Climate
Authors: Ledley Tamara Shapiro 
Published: September 2017

Sea ice is an important factor in controlling the ocean–atmosphere energy exchange in polar regions, and has an important impact on climate. This is because sea ice insulates the relatively warm ocean from the cold winter atmosphere, and has a higher surface albedo than the ocean. In this study the effect of sea-ice transport on the energy exchange between the atmosphere and ocean, and thus on climate, is examined using a coupled energy-balance climate–thermodynamic sea-ice model.Transport of sea ice produces a thinning of the zonally annually-averaged sea ice in the poleward-most zones, and an extension of the ice edge equatorward. Thinning of the poleward-most ice produces an increase in the annual sensible heat flux from the ocean to the atmosphere, which produces an increase in the mean annual atmospheric temperatures. Sensible heat flux is decreased in the zones that contain the ice edge. However, warming in the poleward-most zones produces an increased meridional energy convergence at the ice edge that offsets the decrease in the sensible heat flux to the atmosphere, resulting in a net warming.
Identification of Some Global Volcanic Horizons by Major Element Analysis of Fine Ash in Antarctic Ice
Authors: Palais Julie M. , Kirchner Severine , Delmas Robert J. 
Published: September 2017

Acid fallout from volcanic eruptions is well documented in the Greenland and Antarctic ice sheets (Hammer and others, 1980; Hammer, 1984; Legrand and Delmas, 1987). However, to date, no volcanic ash (tephra) layers have been positively identified in association with any of the high electrical conductivity layers that mark the volcanic acid deposition. In this paper we report the results of a study of the chemical composition of insoluble microparticles filtered from five intervals of a core from the South Pole. These five intervals were identified by Kirchner (1988) as being due to volcanic fallout, on the basis of electrical conductivity and sulfuric acid measurements.The major element composition of tiny (<5 µm) glass shards found in these layers was determined and compared with analyses of volcanic ash from known eruptions or from volcanic sources suspected of having produced the fallout. Glass shards from volcanic eruptions of both local (Antarctic and sub-Antarctic) and of global (Indonesian/South American) importance have been identified in this study.
A Simple Parameterization of Ice Leads In a General Circulation Model, and the Sensitivity of Climateto Change in Antarctic Ice Concentration
Authors: Simmonds Ian , Budd W.F. 
Published: September 2017

We present a simple parameterization of the effect of open leads in a general circulation model of the atmosphere. We consider only the case where the sea ice distribution is prescribed (i.e., not interactive) and the fraction of open water in the ice is also prescribed and set at the same value at all points in the Southern Hemisphere and a different value in the Northern Hemisphere. We approximate the distribution of sea ice over a model “grid box” as a part of the box being covered by solid ice of uniform thickness and the complement of the box consisting of open water at a fixed -1.8 C. Because of the nonlinearity in the flux computations, separate calculations are performed over the solid sea ice and over the open leads. The net fluxes conveyed to the atmosphere over the grid box are determined by performing the appropriate area-weighted average over the two surface types.We report on an experiment designed to assess the sensitivity of the modelled climate to the imposition of a 50% concentration in the winter Antarctic sea ice. Significant warming of up to 6°C takes place in the vicinity of and above the Antarctic sea ice and is associated with significant changes in the zonal wind structure. Pressure reductions are simulated over the sea ice, being particularly marked in the Weddell Sea region, and an anomalous east-west aligned ridge is simulated at about 60°S. Very large changes in the sensible heat flux (in excess of 200 Wm−2) are simulated near the coast of Antarctica.
Effect of Area Distribution with Altitude on Glacier Mass Balance – A Comparison of North and South Klawatti Glaciers, Washington State, U.S.A.
Authors: Tangborn Wendell V. , Fountain Andrew G. , Sikonia William G. 
Published: September 2017

The North and South Klawatti glaciers are adjacent glaciers in the North Cascade Mountains of Washington state. During 1947–61 North Klawatti Glacier lost volume, equivalent to a mean decrease in thickness of 8.3 m over the glacier area, whereas South Klawatti Glacier gained volume, equivalent to an increase in thickness of 5.8 m. Although the glaciers are in the same climate, they have different distributions of area with altitude, resulting in different responses to climatic variations.A quadratic equation is assumed to approximate the relation of mass balance to altitude for both Klawatti glaciers. The coefficients of the equation are derived by comparing the calculated mass change to the mass change for each glacier estimated from topographic maps. The resultant relation of mass balance to altitude is the mean for the time period between maps (1947–61).Steady-state longitudinal profiles of both glaciers were obtained by shifting the existing mass-balance versus altitude curve by a magnitude equal to the measured mean annual mass balance. To produce steady-state conditions, the equilibrium-line altitudes of both glaciers would need to move less than 90 m (85 m higher for South Klawatti Glacier and 88 m lower for North Klawatti Glacier).
Reaction Of The Heat Regime Of Antarctic Ice Sheet Inland Regions On Long-Term Changes Of Climate
Authors: Barbash Vitaly 
Published: September 2017

A nonstationary mathematical model of thermics and dynamics of the Antarctic ice sheet has been developed, taking into consideration the influence of long-term changes of climate.The influence of climatic variations during the last 100 000 years on the temperature field within the ice sheet has been analysed. Information about climatic changes is based on paleographic data and isotope analyses of ice samples from bore holes at Vostok and Byrd stations.The input data used include results from field surveys of accumulation, temperatures of upper surface, relief of the base and thickness of the ice sheet along the flowlines in the western and eastern parts of the ice sheet, as well as experimental data on ice rheology.The computations show that traces of the climatic minimum that took place about 18 000 years ago are found in the temperature field of the Antarctic ice sheet.The model developed has proved that warming of climate due to the “greenhouse effect” leads to significant changes in the thermal regime in the upper parts of the ice sheet, but will not lead to conditions threatening bottom layers.
Potential For Basal Melting Under The Summit Coring Site, Central Greenland
Authors: Firestone John , Waddington Ed , Cunningham Jim 
Published: September 2017

The climatic record from Greenland boreholes is likely to extend well beyond the last interglacial only if the basal ice near the drilling sites has never reached its pressure melting point (−2°C). A simplified one-dimensional analysis (Paterson and Waddington, 1986) suggested that this would be true at Crête, Greenland, if the geothermal flux was less than 48 mW m−2. In that study, the vertical velocity pattern for an isothermal ice sheet was used. We have repeated the Crête calculations using the vertical velocity pattern derived by a finite element analysis. Using this temperature-dependent velocity pattern lowered the basal temperature by about 3°C.We have carried out a similar analysis for the Summit coring site further north on the Greenland ice divide. Here we find that the basal ice does not melt if the geothermal flux is less than 54 mW m−2, using the same mass balance and surface temperature histories as the previous study. We are repeating these one-dimensional calculations with more recently compiled histories and plan to present results from a full two-dimensional temperature model that includes processes only parameterized in the one-dimensional models. Using two dimensions, we will more realistically incorporate the special ice-flow patterns found at divides (e.g. Raymond, 1983; Dahl-Jensen, 1989). In steady-state flow models these patterns lead to significant horizontal temperature gradients and a “hot spot” beneath an ice divide (Paterson and Waddington, 1986). In addition, we will more accurately determine the transient effects on basal temperature resulting from the interaction of these flow patterns and the changing climate. Our discussion will include sensitivity to geothermal heat flux, ice thickness and paleoenvironmental history.
Numerical Modelling Of Rutford Ice Stream, Antarctica
Authors: Frolich R.M , MacAyeal D.R. 
Published: September 2017

A two-dimensional finite element model has been applied to Rutford Ice Stream, Antarctica, and part of Ronne Ice Shelf into which the ice stream flows. The model is an extension of one describing ice-shelf flow, and relies on vertical shear in the ice stream being small in some mathematically defined sense. This is equivalent to requiring the vertical shear to be confined to a basal layer or a deformable substrate.Although there is no direct observational evidence for such a layer beneath Rutford Ice Stream, extensive surface surveys and estimates of the strength of the overlying ice show that some dynamically equivalent mechanism must occur. If basal shear stress is parameterised in terms of the thickness and viscosity of a linearly viscous substrate, as may be the case beneath Ice Stream Β in Antarctica, then going upstream from the grounding line, the thickness of this layer must decrease, and the viscosity increase (to retain a realistic thickness at the upstream limit), in order to reproduce the observed surface velocities. This physically reasonable picture is currently adopted as a working hypothesis.Vertical shear in the body of the ice stream appears to be negligible for approximately 70 km above the grounding line. Sensitivity tests show that, in this lower section, ice-shelf back stress is an important restraining influence. A 10% reduction in back stress would produce an immediate 15% increase in grounding line flux. Further upstream, however, higher surface slopes and slightly lower surface velocities suggest that the neglect of vertical shear may be less appropriate. The effect of a reduction in ice-shelf back stream is not felt in this region immediately, as the gravitational driving force is almost balanced by local basal shear traction.A complex surface morphology has been revealed by satellite imagery below the grounding line of Rutford Ice Stream. On the basis that this may be evidence of time dependent behaviour, the finite element model is being used to investigate the origin of the pattern. Ice-shelf back stress, basal melting, mass flux from tributary glaciers and substrate properties can all be varied in physically realistic ways to try to reproduce, qualitatively, the observed surface morphology.
Variability Of Thermohaline Circulation Under An Ice Shelf
Authors: Hellmer H.H. 
Published: September 2017

The production of Antarctic Bottom Water is mainly influenced by Ice Shelf Water, which is formed through the modification of shelf water masses under huge ice shelves. To simulate this modification a two-dimensional thermohaline circulation model has been developed for a section perpendicular to the ice-shelf edge. Hydrographic data from the Filchner Depression enter into the model as boundary conditions. In the outflow region they also serve as a verification of model results.The standard solution reveals two circulation cells. The dominant one transports shelf water near the bottom toward the grounding line, where it begins to ascend along the inclined ice shelf. The contact with the ice shelf causes melting with a maximum rate of 1.5 m a−1 at the grounding line. Freezing and therefore the accumulation of “sea ice” at the bottom of the ice shelf occurs at the end of the melting zone at a rate on the order of 0.1 ma−1. Both rates are comparable with values estimated or predicted by models concerning ice-shelf dynamics.As one example of model sensitivity to changing boundary conditions, a higher sea-ice production in the southern Weddell Sea, as might be expected for a general climatic cooling event, is assumed. The resultant decrease/ increase in temperature/salinity of the inflow (Western Shelf Water) reduces the circulation under the ice shelf and therefore the outflow of Ice Shelf Water by 40%. The maximum melting and freezing rate decreases by 0.1 ma−1 and 0.01 m a−1, respectively. and the freezing zone shifts toward the grounding line by 100 km.In general the intensity of the circulation cells, the characteristics of Ice Shelf Water, the distribution of melting and freezing zones and the melting and freezing rates differ from the standard results with changing boundary conditions. These are the temperature and salinity of the inflow, the surface temperature at the top, and the extension and morphology of the ice shelf.
On The Interannual Variability Of A Diagnostic Ice-Ocean Model
Authors: Hibler W.D , Ranelli Peter 
Published: September 2017

Sea-ice drift and dynamics can significantly affect the exchanges of heat between the atmosphere and ocean and salt fluxes into the ocean. The ice drift and dynamics, in turn, can be modified by the ocean circulation. This is especially true of the ice margin location whose seasonal characteristics are largely controlled by the substantial oceanic heat flux in the Greenland Sea due to convective overturning.A useful framework to analyze the interannual variability of ice–ocean interaction effects relevant to climatic change is the diagnostic ice–ocean model developed by Hibler and Bryan (1987). In this model, the oceanic temperature and salinity is weakly relaxed (except in the upper layer of the ocean which is essentially driven by the ice dynamic-thermodynamic sea-ice model) to climatological temperature and salinity data. This procedure allows seasonal and interannual variability to be simulated while still preventing the baroclinic characteristics of the ocean circulation from gradually drifting off into a total model defined state. However, in the work of Hibler and Bryan only the seasonal equilibrium characteristics of this model with the same forcing repeated year after year have been considered.In order to begin to examine the interannual behavior of this model, we have carried out a three-year simulation for the Arctic Greenland and Norwegian seas over the time period 1981–83. (The geographical region is essentially the same as used by Hibler and Bryan.) This three year simulation is carried out after an initial two year spin up using the 1981 atmospheric forcing data. For comparison purposes, an ice model simulation with only a fixed depth mixed layer was also carried out over this time interval.The results of these two simulations are analyzed with special attention to the ice margin characteristics in the Greenland and Norwegian seas to determine the role of ocean circulation on the variability there. The ice margin results are also compared to the variability in the northward transports of heat through the Faero-Shetland passage which in the fully-coupled model are calculated rather than specified.
The Effect Of Rheology On Seasonal Sea-Ice Simulations
Authors: Ip Bill , Hibler W.D. , Flato Greg 
Published: September 2017

On the seasonal time scales relevant to numerical investigations of climate, the rheology used in large-scale sea ice models significantly affects the ice thickness build-up and ice velocity fields. Plastic rheologies with a normal flow rule have been used to-date in seasonal dynamic thermodynamic simulations. These rheologies have proved useful in simulating discontinuous slip near the coast while still supplying relatively robust velocity fields in the central Arctic Basin. However, as indicated by limited numerical sensitivity studies with different types of elliptical yield curves, the amount of shear strength significantly affects the ice build-up and can possibly cause a stoppage of the ice outflow through Fram Strait. In addition to the shear strength issue, there is also the possibility that non-normal flow rule rheologies, such as the Mohr Coulomb failure criterion used in soil mechanics, may cause somewhat different types of flow patterns, especially in the Fram Strait region. However, to date no seasonal simulations with such non-normal flow rule rheologies have been carried out.In order to investigate the role of different rheologies on the large-scale flow patterns in the Arctic Basin, a more general numerical scheme than that of Hibler (1979) is developed, which allows the simulation of the dynamic thermodynamic behavior of sea ice with a wide variety of different non linear rheologies. Using this numerical scheme, comparative simulations are carried out to seasonal equilibrium with several variations of the Mohr Coulomb rheology and compared to the more standard Elliptical yield curve results. In particular, the main control Mohr Coulomb case is a capped rheology in which the shear strength is taken to be proportional to the compressive stress. In this capped case only shear flow is allowed until a maximum allowable compressive stress is reached. This cap strength is parameterized to be a function of the ice thickness and compactness. For comparison, a simulation with a very large cap strength is also carried out, and an experiment with a similar compressive cap but much lower shear strength. Overall the results are analyzed to determine the sensitivity of the ice build-up to flow rule and shear strength magnitude. In addition special attention is given to the character of the flow and stoppage (if any) through Fram Strait.