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  • 1
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    Gas inclusions in the Antarctic ice sheet and their significance (1975)
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
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    Signatur: ZSP-202-339
    In: Research report
    Beschreibung / Inhaltsverzeichnis: CONTENTS: Abstract. - Preface. - Introduction. - Analytical procedures. - Thick section analysis. - Measurements of inclusion pressure. - Gas volume measurements. - Density and porosity measurements. - Results and discussion. - Sizes, shapes and distributions of bubbles. - Sizes, shapes and distributions of cavities. - Inclusion abundances. - Gas pressures in bubbles and cavities. - Total gas content. - Case for lattice diffusion. - Literature cited.
    Beschreibung / Inhaltsverzeichnis: Cores obtained to the bottom of the Antarctic Ice Sheet at Byrd Station were used to analyze the physical properties of air bubbles trapped in the ice. These bubbles originate as pockets of air in the upper layers of snow and approximately 10 ml of air/100 cm^3 of ice; i.e., 10% by volume is retained permanently when the snow transforms into ice. Parameters measured were the sizes, shapes, abundances, spatial distributions, gas volumes and pressures of bubbles, and their variations with depth in the ice sheet. Bubbles occur abundantly in the top 800 m of ice but then gradually disappear until they can no longer be detected optically below 1100 m. This disappearance is not accompanied by any significant loss of air from the ice and all available evidence indicates that the air actually diffuses into the ice in response to increasing overburden pressure. The possibility exists that the dissolved gases are retained in the form of a gas hydrate or clathrate which, because of release of confining pressures, begins to decompose soon after ice cores are pulled to the surface. This decomposition is accompanied by the growth of gas-filled bubble-like cavities, and as much as 40% of the dissolved air has exsolved already from some cores in the space of less than three years. Bubble pressure measurements show that 1) bubbles with pressures exceeding about 16 bars begin to relax back to this value soon after in situ pressures are relieved by drilling, 2) further slow decompression occurs with time, and 3) the rate of decompression is controlled to some extent by the intrinsic structural properties of the ice and its thermal and deformational history. Only small variations were observed in the entrapped air content of the ice cores; they probably reflect variations in the temperature and/or pressure of the air at the time of its entrapment, but the data are not sufficient to draw any firm conclusions regarding past variations in ice sheet thickness. Only ice from the bottom 4.83 m was found to lack any detectable trace of air. Since this absence of air coincided precisely with the first appearance of stratified moraine in the cores, it is concluded that this ice originated from the refreezing of air-depleted water produced under pressure melting conditions at the bottom of the ice sheet.
    Materialart: Schriftenreihen ausleihbar
    Seiten: v, 18 Seiten , Illlustrationen
    Serie: Research report / Cold Regions Research and Engineering Laboratory, CRREL, US Army Material Command 339
    URL: http://www.worldcat.org/oclc/1086574366
    Sprache: Englisch
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  • 2
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    Depth-time-temperature relationships of ice crystal growth in polar glaciers (1971)
    Hanover, NH : Corps of Engineers, U.S. Army Cold Regions Research and Engineering Laboratory
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    Signatur: ZSP-202-300
    In: Research report
    Beschreibung / Inhaltsverzeichnis: CONTENTS: Introduction. - Sampling. - Byrd Station. - Plateau Station. - Camp Century. - lnge Lehmann. - Grain-crystal relations. - Analytical techniques. - Thin sections. - Crystal size measurements. - Results and discussion. - Literature cited. - Appendix A: Crystal size as a function of depth and age in the Antarctic and Greenland ice sheets. - Abstract.
    Beschreibung / Inhaltsverzeichnis: The growth of ice crystals as a function of depth and time in polar firn and glacier ice has been investigated at a number of locations in Antarctica and Greenland. Thin sections of snow and ice were used to measure crystal size variations which showed, in all cases, that crystal size increases essentially linearly with the age of samples. Crystal growth rates are strongly temperature dependent. At Camp Century, Greenland, where the firn temperature is -24°C, crystals grow approximately 23 times faster than at Plateau Station, Antarctica, where the in situ temperature is -57°C. Extrapolation of the existing data indicates that crystal growth rates in polar firn and ice could be expected to vary by about two orders of magnitude over the temperature range -60°C to -15°C. Examination of the changes in the pore-crystal structure relationships to a dpeth of 100 m at Camp Century shows that these changes closely resemble those occuring in the full-scale isothermal sintering of powder compacts.
    Materialart: Schriftenreihen ausleihbar
    Seiten: iii, 19 Seiten , Illustrationen
    Serie: Research report / Cold Regions Research and Engineering Laboratory, CRREL, US Army Material Command 300
    URL: http://www.worldcat.org/oclc/5974076
    Sprache: Englisch
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  • 3
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    Bubbles and bubble pressures in Antarctic glacier ice (1968)
    Hanover, NH : U.S. Army Materiel Command, Terrestrial Sciences Center, Cold Regions Research & Engineering Laboratory
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    Signatur: ZSP-202-249
    In: Research report
    Beschreibung / Inhaltsverzeichnis: CONTENTS: Preface. - Abstract. - Introduction. - Analytical procedures. - Results and discussion. - Bubbles in ice. - Conclusions. - Literature cited.
    Beschreibung / Inhaltsverzeichnis: Application of the gas law to fourth-place density measurements of ice samples from two deep drill holes at Byrd Station and Little America V, Antarctica, shows that virtually all density increase beyond the pore close-off density (0.830 g/cm^3) can be attributed to compression of the entrapped bubbles of air. Data from Byrd Station also indicate that the lag between overburden pressure and bubble pressure, initially 4-5 kg/cm^2 at pore close-off, diminishes to less than 1.0 kg/cm^2 at about 200-m depth. By substituting the overburden pressure for the bubble pressure in the pressure-density relationship based on the gas law, ice densities below 200 m can be calculated more accurately than they can be measured per se on cores because of the relaxation that occurs in samples recovered from high confining pressures. This relaxation, resulting in a progressive increase in the bulk volume of the ice with time, is generally attributed to decompression of the entrapped air bubbles following removal of the ice from high confining pressures. However, calculations of the stress in ice due to bubble pressure, together with measurements of bubble sizes in cores from various depths at Byrd Station, both tend to indicate that there has'been negligible decompression of the inclosed bubbles. It is suggested that most of this relaxation may be due to the formation of microcracks in the ice. Anomalous bubble pressure-density relations at Little America V tend to confirm abundant stratigraphic evidence of the existence of considerable deformation in the upper part of the Ross Ice Shelf. Studies of crystal-bubble relations at Byrd Station revealed that the concentration of bubbles in ice remains remarkably constant at approximately 220 bubbles per cm^3. Bubbles and crystals were found to be present in approximately equal numbers at pore close-off at 64-m depth, at which level the average bubble diameter was 0.95 mm, decreasing to 0.49 mm at 116 m and to 0.33 mm at 279 m. Despite a tenfold increase in the size of crystals between 64 and 279 m, the bubbles showed no tendency to migrate to grain boundaries during recrystallization of the ice. The observation that most of the bubbles had assumed substantially spherical shapes by 120-m depth points to essentially hydrostatic conditions in the upper layers of the ice sheet at Byrd Station.
    Materialart: Schriftenreihen ausleihbar
    Seiten: iv, 16 Seiten , Illustrationen
    Serie: Research report / Cold Regions Research and Engineering Laboratory, CRREL, US Army Material Command 249
    URL: https://www.worldcat.org/de/title/6023806
    Sprache: Englisch
    Standort: AWI Archiv
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  • 4
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    Electrolytic conductivity of snow and glacier ice from Antarctica and Greenland (1968)
    Hanover, NH : U.S. Army Materiel Command, Terrestrial Sciences Center, Cold Regions Research & Engineering Laboratory
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    Signatur: ZSP-202-248
    In: Research report
    Beschreibung / Inhaltsverzeichnis: CONTENTS: Preface. - Abstract. - Introduction. - Analytical procedures. - Results and discussion. - Literature cited.
    Beschreibung / Inhaltsverzeichnis: Conductivity measurements have been made on snow and ice samples from pits and deep drillholes at a number of localities in Antarctica and Greenland. Conductivities of the order 1-2 [My]mho/cm only were recorded at the inland sites. Data from deep cores representing more than 1900 years of continuous snow accumulation at Byrd Station, Antarctica, and more than 400 years deposition at Inge Lehmann, Greenland, showed no significant variations of conductivity with time. Measurements of freshly precipitated snow from a single coastal location in McMurdo Sound, Antarctica, also yielded relatively low conductivities of the order 3-4 [My]mho/cm. The substantial increase observed in the conductivity of core samples from near the surface of the Ross Ice Shelf at Little America V can be attributed most probably to windborne salts of marine origin that had accumulated on the surface after the snow was deposited. A peak conductivity of 49 [My]mho/cm was recorded in snow estimated to have been deposited within 20 km of the seaward edge of the Ross Ice Shelf and the maritime effect could still be detected in samples deposited more than 40 km from the ice front. For samples deposited at distances of greater than 200 km from the edge of the Ross Ice Shelf conductivities never exceeded 2 [My]mho/cm. The very low conductivities observed in ice cores from near the bottom of the Ross Ice Shelf confirm earlier conclusions based on detailed petrographic studies oi the cores that the 258-m-thick ice shelf at Little America V is composed entirely of glacial ice.
    Materialart: Schriftenreihen ausleihbar
    Seiten: iv, 8 Seiten , Illustrationen
    Serie: Research report / Cold Regions Research and Engineering Laboratory, CRREL, US Army Material Command 248
    URL: https://dx.doi.org/10.1029/JB073i012p03643
    Sprache: Englisch
    Standort: AWI Archiv
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  • 5
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    Isua, Greenland : glaciological investigations during 1973 (1974)
    Hanover, NH : Corps of Engineers, U.S. Army Cold Regions Research and Engineering Laboratory
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    Signatur: ZSP-202-318
    In: Research report
    Beschreibung / Inhaltsverzeichnis: CONTENTS: Introduction. - Drilling and field observations. - Interpretation. - Implications for the feasibility study. - Conclusions. - Literature cited. - Abstract.
    Beschreibung / Inhaltsverzeichnis: Two holes were drilled through the Greenland ice sheet during 1973 and temperature measurements were made in one hole drilled during 1972. These measurements show that the area of liquid water beneath the ice cap extends to ice depths as shallow as 100 m. The consequences of removing the frozen margin of glacial ice could be serious and more temperature measurements are needed to exactly locate the subglacial water. Petrographic studies of a few ice cores revealed a strongly oriented crystal fabric and an appreciable surface accumulation of superimposed ice.
    Materialart: Schriftenreihen ausleihbar
    Seiten: iii, 15 Seiten , Illustrationen, Karten
    Serie: Research report / Cold Regions Research and Engineering Laboratory, CRREL, US Army Material Command 318
    URL: http://www.worldcat.org/oclc/1035634454
    Sprache: Englisch
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  • 6
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    Flexural strength of lake ice in relation to its growth structure and thermal history (1975)
    Hanover, N.H. : U.S. Army Cold Regions Research and Engineering Laboratory
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    Signatur: ZSP-202-349
    In: Research report / Cold Regions Research and Engineering Laboratory, 349
    Beschreibung / Inhaltsverzeichnis: CONTENTS: Abstract. - Preface. - Introduction. - Test locations. - Post Pond. - Mascoma Lake. - Winter freeze-up. - Ice cover properties. - Stratigraphy. - Microstructure. - Porosity. - Impurity content. - Flexural strength. - Test sites. - Beam test procedure. - Beam dimensions. - Beam temperatures. - Beam strengths. - Results. - Post Pond, Site PB, 12 February 1974. - Post Pond, Site PC, 21 February 1974. - Mascoma Lake, Site MD, 25 February 1974. - Mascoma Lake, Site MD, 26 February 1974. - Mascoma Lake, Site MD, 1 March 1974. - Post Pond, Site PA, 4 March 1974. - Post Pond, Site PA, 7 March 1974. - Post Pond, Site PA, 8 March 1974. - Post Pond, Site PB, 12 March 1974. - Post Pond, Midway between Sites PB and PC, 15 March 1974. - Post Pond, Midway between Sites PA and PB, 26 March 1974. - Post Pond, Midway between Sites PA and PB, 29 March 1974. - Post Pond, Midway between Sites PA and PB, 3 April 1974. - Conclusions. - Literature cited.
    Beschreibung / Inhaltsverzeichnis: In-place cantilever beam tests on Post Pond and Mascoma Lake ice yielded a maximum flexural strength of 7.1 kg/cm^2. The minimum strength, unrelated to failure along pre-existing cracks in the ice, was 2.9 kg/cm^2. The majority of tests were performed in the push-down mode after it was discovered that beams tested in the pull-up mode, which places the bottom surface in tension, frequently broke prematurely along cracks in the bottom of the ice. Premature failures of this kind usually occurred at stresses of 2-3 kg/cm^2. Data further demonstrate that the intrinsic strength of lake ice decreases significantly as the surface air temperature goes to 0°C. Ice that has just become isothermal, but has not yet begun to candle, has a strength of about 4 kg/cm^2; ice that has been subjected to prolonged periods of above-freezing air temperatures generally fails at about 3 kg/cm^2. Tests also show that cold unrecrystallized snow-ice is as strong as the underlying lake ice. Tests of the effect of crystalline structure indicate that ice composed of crystals with their c-axes horizontal is measurably stronger than ice in which the crystals are oriented with their c-axes vertical.
    Materialart: Schriftenreihen ausleihbar
    Seiten: v, 28 Seiten , Illustrationen
    Serie: Research report / Cold Regions Research and Engineering Laboratory 349
    URL: https://usace.contentdm.oclc.org/digital/collection/p266001coll1/id/6226/rec/1
    Sprache: Englisch
    Standort: AWI Archiv
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  • 7
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    The internal structure of fast ice near Narwhal Island, Beaufort Sea, Alaska (1977)
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
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    Signatur: ZSP-201-77/29
    In: CRREL Report, 77-29
    Beschreibung / Inhaltsverzeichnis: Results of measurements of salinity, grain size, substructure dimensions and crystal fabrics of the undeformed 2.15-m-thick annual sea ice sheet near Narwhal Island, Alaska, are presented. A notable observation was the formation of a dominant c-axis horizontal structure in all ice below 14 cm, including transformation to a pronounced east-west alignment of the c-axes by a depth of 66 cm. This study confirms earlier reports of the occurrence of very strong horizontal c-axis alignments in arctic fast ice.
    Materialart: Schriftenreihen ausleihbar
    Seiten: iii, 8 Seiten , Illustrationen
    Serie: CRREL Report 77-29
    URL: https://hdl.handle.net/11681/9500
    Sprache: Englisch
    Anmerkung: CONTENTS Abstract Preface Introduction Sampling and analytical procedures Results Discussion Conclusions Literature cited
    Standort: AWI Archiv
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  • 8
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    Compressibility characteristics of compacted snow (1976)
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
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    Signatur: ZSP-201-76/21
    In: CRREL Report, 76-21
    Beschreibung / Inhaltsverzeichnis: The effects of snow temperature and initial density on the stress vs density and stress vs deformation relationships were investigated for shallow compacted snow in the density range of 0.28 to 0.76 g/cu m, for stress range of 0.5 to 72 bars and a temperature range of -1 to -34 C at a deformation rate of 40 cm/s. A decrease in temperature increases the resistance to stress, the effect increasing with applied stress. For any stress, an increase in the initial density results in an increase in the resulting density, the effect decreasing with an increase in stress. The approximate yield envelopes, which define the stress required to initiate any deformation of snow of a particular density and temperature, were determined. Rapid compaction of snow results in extensive recrystallization, significantly different from that of naturally compacted snow. At a stress of 72 bars, transformation to ice occurs only at temperature above -10C.
    Materialart: Schriftenreihen ausleihbar
    Seiten: vi, 47 Seiten , Illustrationen
    Serie: CRREL Report 76-21
    URL: https://cdm16021.contentdm.oclc.org/digital/collection/p266001coll1/id/6184/rec/1
    Sprache: Englisch
    Anmerkung: CONTENTS Abstract Preface Nomenclature Introduction Description of study Sample preparation Test equipment and procedure Discussion of results Stress-density relationship Stress-deformation relationship Summary and conclusions Microstructural examination of artifically compacted snow Analytical techniques Results and discussion Conclusions Literature cited Appendix: Photographs of oscilloscope traces
    Standort: AWI Archiv
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  • 9
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    Preferred crystal orientations in the fast ice along the margins of the Arctic Ocean (1978)
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
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    Signatur: ZSP-201-78/13
    In: CRREL Report, 78-13
    Beschreibung / Inhaltsverzeichnis: Field observations of the growth fabrics of the fast and near-fast ice along the coasts of the Beaufort and Chukchi Seas show that, at depths of more than 60 cm below the upper ice surface, the sea ice crystals show striking alignments within the horizontal plane. At one site this alignment was well developed at a depth of 15 cm and in all cases the degree of preferred orientation increased with depth, with the strongest orientations occurring at the bottom of the ice sheet. In general the c-axes of the crystals were aligned roughly E-W parallel to the coast. In the vicinity of islands the alignment roughly paralleled the outlines of the islands and in narrow passes between islands the alignment paralleled the channel. Our observations, as well as similar observations made in the Kara Sea by Cherepanov, can be explained if it is assumed that the c-axes of the crystals are aligned parallel to the 'long-term' current direction at the sea ice/sea water interface. The alignments are believed to be the result of geometric selection among the growing crystals, with the most favored orientation being that in which the current flows normal to the (0001) plates of ice that make up the dendritic ice/water interface characteristics of sea ice. It is hypothesized that current flow in this direction reduces the thickness of the solute boundary layer as well as the salinity in the liquid at the interface. This lowered salinity allows crystals in the favored orientation to extend farther into the melt than neighboring crystals with less favored orientations. In addition the current tends to induce a continuous flux of supercooled seawater against the sides of the crystals that extend ahead of the interface.
    Materialart: Schriftenreihen ausleihbar
    Seiten: v, 29 Seiten , Illustrationen
    Serie: CRREL Report 78-13
    URL: https://hdl.handle.net/11681/9402
    Sprache: Englisch
    Anmerkung: CONTENTS Abstract Preface Introduction Locale and techniques Observations Vertical variations in crystal orientation Regional variations in crystal orientation Summary of observations Causes Initial ice skim Earth’s magnetic field Currents Conclusions and consequences Literature cited
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  • 10
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    Islands of grounded sea ice (1976)
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
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    Signatur: ZSP-201-76/4
    In: CRREL Report, 76-4
    Beschreibung / Inhaltsverzeichnis: Large areas of grounded sea ice have been reported by early arctic explorers and more recently by the U.S. Coast Guard. The ESSA, ERTS, NOAA and DMSP satellites now provide multispectral imagery with sufficiently high resolution to allow detailed sequential observations to be made of the movement and spatial extent of arctic sea ice. This report discusses the location, formation and decay of five large (greater than 30 sq km) islands of grounded sea ice in the southern Chukchi Sea as observed for an extended period of time using satellite imagery. Measurements of the bathymetry around one grounded sea ice feature are presented along with observations made and photos taken from the ice surface. The potential use of these sea ice islands as research stations is also discussed.
    Materialart: Schriftenreihen ausleihbar
    Seiten: v, 24 Seiten , Illustrationen
    Serie: CRREL Report 76-4
    URL: https://apps.dtic.mil/docs/citations/ADA025257
    Sprache: Englisch
    Anmerkung: Contents Introduction The discovery Age of the island Island visit Other islands of grounded ice Discussion Literature cited
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