bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractData 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

AbstractClassical 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

AbstractCreep 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

AbstractOur 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

AbstractThe 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

AbstractWe 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

AbstractThe 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

AbstractIn 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

AbstractVertical 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.
Observations on sea-ice and surface-water geochemistry–implications for importance of sea ice in geochemical cycles in the northern Baltic Sea
Authors: Granskog M. A. , Virkanen J. 
Published: November 2007

AbstractSea-ice and surface-water samples collected in January-April 1999 in coastal areas in the northern Baltic Sea were analyzed for particle, nutrient and trace-element concentrations and salinity. Stratigraphic analyses of ice cores were also carried out. Bulk nutrient and trace-element concentrations in sea ice fluctuated widely. Nutrient concentrations in sea ice normalized to sea-water salinities showed that sea ice had, almost without exception, an excess of nutrients compared to underlying waters. For phosphorus and phosphate this can be explained by particle incorporation and snow-ice formation, whereas for nitrogen and the sum of nitrite and nitrate snow-ice formation and other mechanisms are important. The levels of Al, Cu, Fe and Ni in the ice were similar to those observed in underlying waters. Pb was observed in detectable concentrations in the ice only. This indicates that sea ice contributes lead to underlying waters during melting, and in some degree also affects the other elements. Furthermore, the observations indicate that incorporation of lead into the ice cover is governed by different processes than for the other elements studied.
Snow-ice accretion and snow-cover depletion on Antarctic first-year sea-ice floes
Authors: Jeffries Martin O. , Krouse H. Roy , Hurst-Cushing Barbara , Maksym Ted 
Published: November 2007

AbstractBetween austral late winter 1993 and austral autumn 1998, during five cruises aboard the research vessel Nathaniel B. Palmer, almost 300 m of core was obtained from first-year ice floes in the Ross, Amundsen and Bellingshausen Seas. Analysis of the texture, stratigraphy and stable-isotopic composition of the ice was used to assess the magnitude of the role of flooding and snow-ice formation at the base of the snowpack in the thickening of the ice cover and the thinning of the snow cover. Snow ice occurred in all ice-thickness categories and made a significant contribution to the total ice mass (12−36%) in both autumn and winter. Although the amount of snow ice was often exceeded by the amount of frazil ice and congelation ice, the thickness of individual layers of each ice type indicated that snow ice often made a greater contribution to the thermodynamic thickening of the ice cover than the other ice types. The larger quantities of frazil ice and congelation ice were primarily the result of dynamic thickening. Flooding and snow-ice formation reduced the snow cover to 42−70% of the total snow accumulation depending on time and location. On the basis of this information, ship-based snow-depth estimates were adjusted to estimate the total snow accumulation on different ice-thickness categories.
Indirect measurements of the mass balance of summer Arctic sea ice with an electromagnetic induction technique
Authors: Eicken H. , Tucker W. B. , Perovich D. K. 
Published: November 2007

AbstractIn the framework of the Surface Heat Budget of the Arctic (SHEBA) study, indirect, non-invasive ice mass-balance measurements were carried out at a drifting station in the northern Chukchi Sea between May and August 1998. Ice thickness was derived from electromagnetic induction (EM) measurements of apparent conductivity along 13 profiles (60−900 m long). As shown through sensitivity studies with a one-dimensional model, the apparent conductivity data from individual points can be inverted to yield estimates of ice thickness and ablation with an accuracy of approximately 0.05 m (for 2 m thick level ice). Ablation rates were 8−18 mm d−1, with total ablation amounting to roughly 0.9−1.2 m. Measurements of thickness and melt rates along different profiles in undeformed multi-year ice corresponded closely, indicating that the sampling statistics are adequate. The roughness of undeformed ice has been found to increase during the summer due to deepening of melt ponds and enhanced bottom melt. Ice under melt ponds was disproportionately thinner, most likely a result of thicker snow cover reducing winter accretion.
Interannual variability of the Storfjorden (Svalbard) ice cover and ice production observed by ERS-2 SAR
Authors: Haarpaintner Jörg , Haugan Peter M. , Gascard Jean-Claude 
Published: November 2007

AbstractThe Storfjorden (Svalbard) ice cover has been observed via European remote-sensing satellite (ERS-2) synthetic aperture radar (SAR) over two winters from 1997 to 1999 that showed a high interannual variability in atmospheric forcing. This has resulted in different scenarios in the formation of the ice cover. We reconstruct the ice-cover evolution with a simple ice-drift and polynya model consistent in parameterization for both winters and with ERS-2 SAR and ground-truth observations. The observations showed that, during the rather cold winter of 1997/98, a fast-ice cover developed over the whole northern part of Storfjorden that closed the ice advection through two sounds. A polynya of up to 6000 km2 developed persistently under northerly winds. The mild winter of 1998/99 showed a different pattern in the Storfjorden ice cover: the fast-ice extent was reduced to the coastal region, so ice motion was more important than in the previous winter. A larger thin-ice and open-water area over the whole fjord resulted in lower total ice production, but relocated the strong ice production sites to shallower waters. Thus, freezing in a large region of shallow waters in the north of Storfjorden in 1998/99 produced denser waters than freezing in a smaller polynya over the deeper centre of Storfjorden during the colder winter 1997/98.
The onset of Arctic sea-ice snowmelt as detected with passive- and active-microwave remote sensing
Authors: Forster Richard R. , Long David G. , Jezek Kenneth C. , Drobot Sheldon D. , Anderson Mark R. 
Published: November 2007

AbstractDaily acquisitions from satellite microwave sensors can be used to observe the spatial and temporal characteristics of the Arctic sea-ice snowmelt onset because the initial presence of liquid water in a dry snowpack causes a dramatic change in the active-and passive-microwave response. A daily sequence of backscatter coefficient images from the NASA scatterometer (NSCAT) clearly shows the spatially continuous progression of decreasing backscatter associated with snowmelt onset across the Arctic Ocean during spring 1997. A time series of the active NSCAT backscatter and a scattering index from the passive Special Sensor Microwave/Imager (SSM/I) show similar trends during the time of the melt onset. An NSCATsnowmelt-onset detection algorithm is developed using the derivative of the backscatter with respect to time to select a melt-onset date for each pixel, generating a melt map for the Arctic sea ice. Comparison between this melt map and one previously generated from an SSM/I scattering index shows the NSCAT algorithm predicts the onset occurs 1−10 days earlier than the SSM/I-based algorithm for most portions of multi-year ice.
Ice formation in the Mertz Glacier polynya, East Antarctica, during winter
Authors: Lytle V. I. , Worby A. P. , Massom R. , Paget M.J. , Allison I. , Wu X. , Roberts A. 
Published: November 2007

AbstractDuring August 1999, detailed data were collected in the Mertz Glacier polynya along the coast of Antarctica on the drift of newly forming ice tracked with drifting buoys and the ice thickness in the vicinity of the buoys over time. Using these measurements, we estimate the ice-growth rate and the processes which are important in the early stages of ice formation. We find that although there is rapid frazil formation in the open-water areas near the coast and Mertz Glacier Tongue, this frazil ice can take several days to consolidate. A period of warmer weather, when temperatures reached as high as 0°C, delayed the consolidation of the frazil for > 4.5 days. The undeformed new-ice growth rate averaged about 4 cm d-1 for the first 5 days of formation. Ridging and rafting doubled the total growth rate to an average of 8 cm d-1. Blowing and falling snow was incorporated into the surface of the newly forming ice, with 16 of 22 ice cores having some snow in the top few centimeters.
Evaluation of operational SSM/I ice-concentration algorithms
Authors: Meier Walter N. , Van Woert Michael L. , Bertoia Cheryl 
Published: November 2007

AbstractThe United States National Ice Center (NIC) provides weekly ice analyses of the Arctic and Antarctic using information from ice reconnaissance, ship reports and high-resolution satellite imagery. In cloud-covered areas and regions lacking imagery, the higher-resolution sources are augmented by ice concentrations derived from Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Imager (SSM/I) passive-microwave imagery. However, the SSM/I-derived ice concentrations are limited by low resolution and uncertainties in thin-ice regions. Ongoing research at NIC is attempting to improve the utility of these SSM/I products for operational sea-ice analyses. The refinements of operational algorithms may also aid future scientific studies. Here we discuss an evaluation of the standard operational ice-concentration algorithm, Cal/Val, with a possible alternative, a modified NASA Team algorithm. The modified algorithm compares favorably with Cal/Val and is a substantial improvement over the standard NASA Team algorithm in thin-ice regions that are of particular interest to operational activities.
Sensitivity of the Antarctic sea-ice distribution to oceanic heat flux in a coupled atmosphere-sea-ice model
Authors: Wu Xingren , Budd W. F. , Worby A. P. , Allison Ian 
Published: November 2007

AbstractA coupled atmosphere-sea-ice model is used to study the sensitivity of the Antarctic sea-ice distribution to oceanic heat flux (OHF). Remote sensing of sea ice from microwave radiometers provides data on ice extent and ice concentration. The ice-thickness data used are from ship-based observations. Our simulations suggest that OHF values of 0−5 W m−2 will cause sea ice to be too thick in the model. A value of 20−25 Wm−2 throughout the year causes sea ice to be too thin in the model. The model results indicate that a seasonally varying OHF is required to match the modelled thickness with observations. Values of 5−30 Wm with an annual mean of 10−15 Wm−2, give a reasonable distribution of sea-ice thickness. This agrees with the limited observations of OHF available for the Antarctic. The model results also indicate that the OHF should be varied spatially. When a seasonally and spatially variable OHF is applied to the coupled atmosphere-sea-ice model a still better simulation of the sea-ice distribution is obtained. Our results also suggest that the role of ice advection is very important in the determination of the sea-ice distribution, and it can be quantified by the model.
Behaviour of dissolved organic matter and inorganic nutrients during experimental sea-ice formation
Authors: Giannelli Virginia , Thomas David N. , Haas Christian , Kattner Gerhard , Kennedy Hilary , Dieckmann Gerhard S. 
Published: November 2007

AbstractIt is well established that during sea-ice formation, crystals aggregate into a solid matrix, and dissolved sea-water constituents, including inorganic nutrients, are rejected from the ice matrix. However, the behaviour of dissolved organic matter (DOM) during ice formation and growth has not been studied to date. DOM is the primary energetic substrate for microbial heterotrophic activity in sea water and sea ice, and therefore it is at the base of the trophic fluxes within the microbial food web. The aim of our study was to compare the behaviour of DOM and inorganic nutrients during formation and growth of sea ice. Experiments were conducted in a large indoor ice-tank facility (Hamburg Ship Model Basin, Germany) at −15°C. Three 1 m3 tanks, to which synthetic sea water, nutrients and dissolved organic compounds (diatom-extracted DOM) had been added, were sampled over a period of 5 days during sea-ice formation. Samples were collected throughout the experiment from water underlying the ice, and at the end from the ice as well. Brine was obtained from the ice by centrifuging ice cores. Inorganic nutrients (nitrate and phosphate) were substantially enriched in brine in comparison to water and ice phases, consistent with the processes of ice formation and brine rejection. Dissolved organic carbon (DOC) was also enriched in brine but was more variable and enriched in comparison to a dilution line. No difference in bacteria numbers was observed between water, ice and brine. No bacteria growth was measured, and this therefore had no influence on the measurable DOC levels. We conclude that the incorporation of dissolved organic compounds in newly forming ice is conservative. However, since the proportions of DOC in the brine were partially higher than those of the inorganic nutrients, concentrating effects of DOC in brine might be different compared to salts.