scholarly journals Isotopic Fractionation at the Base of Polar and Sub-Polar Glaciers

1986 ◽  
Vol 32 (112) ◽  
pp. 475-485 ◽  
Author(s):  
G.S. Boulton ◽  
U. Spring
Keyword(s):  
Isotopic Composition ◽  
Large Scale ◽  
Isotopic Fractionation ◽  
Strong Support ◽  
Sharp Change ◽  
West Antarctica ◽  
Tectonic Structures ◽  
Melt Water ◽  
Glacier Ice ◽  
Hydrological System

AbstractThe melting of ice and the subsequent production of regelation ice from the melt water in a large-scale closed system beneath sub-polar and polar glaciers produces progressive fractionation between the melt water and the regelation ice derived from it. A theory is developed which predicts the change of isotopic composition in regelation ice in a subglacial zone of freezing and in the water from which it is derived. The theory is tested against data from the Byrd Station bore hole in West Antarctica, and applied to explain features of the isotopic composition in several other glaciers where thick sequences of regelation ice have formed.The principal conclusions are:1. Basal isotopic profiles can be used to reconstruct important features of a glacier’s hydrological system.2. Isotopic profiles in basal regelation ice do not simply reflect isotopic characteristics of ancient atmospheres but also, by using the theory, some of the isotopic characteristics of the normal glacier ice which was destroyed by melting and subsequently produced regelation ice can be reconstructed. Basal regelation ice at Byrd Station reflects an original ice source isotopically colder than the overlying normal ice, and may have formed during the penultimate glacial period, equivalent to stage 6 of the oceanic record.3. The subglacially derived debris typically found in basal regelation ice gives a complex strain response to a changing pattern of stresses produced by flow over an irregular subjacent bed. Thus, complex tectonic structures in this ice produce highly variable isotopic profiles. However, its gross isotopic characteristics can still be used to reconstruct some of its history. A sharp change in isotopic values tends to occur at the upper limit of basal regelation ice, the nature of which depends on the style and thickness of tectonic disturbance.4. Isotopic profiles in basal ice can be used to distinguish normal glacier ice from regelation ice, and give strong support to the view that regelation is the major process by which debris is incorporated into the base of a glacier.

scholarly journals Isotopic Fractionation at the Base of Polar and Sub-Polar Glaciers

1986 ◽  
Vol 32 (112) ◽  
pp. 475-485 ◽  
Author(s):  
G.S. Boulton ◽  
U. Spring
Keyword(s):  
Isotopic Composition ◽  
Large Scale ◽  
Isotopic Fractionation ◽  
Strong Support ◽  
Sharp Change ◽  
West Antarctica ◽  
Tectonic Structures ◽  
Melt Water ◽  
Glacier Ice ◽  
Hydrological System

AbstractThe melting of ice and the subsequent production of regelation ice from the melt water in a large-scale closed system beneath sub-polar and polar glaciers produces progressive fractionation between the melt water and the regelation ice derived from it. A theory is developed which predicts the change of isotopic composition in regelation ice in a subglacial zone of freezing and in the water from which it is derived. The theory is tested against data from the Byrd Station bore hole in West Antarctica, and applied to explain features of the isotopic composition in several other glaciers where thick sequences of regelation ice have formed.The principal conclusions are:1. Basal isotopic profiles can be used to reconstruct important features of a glacier’s hydrological system.2. Isotopic profiles in basal regelation ice do not simply reflect isotopic characteristics of ancient atmospheres but also, by using the theory, some of the isotopic characteristics of the normal glacier ice which was destroyed by melting and subsequently produced regelation ice can be reconstructed. Basal regelation ice at Byrd Station reflects an original ice source isotopically colder than the overlying normal ice, and may have formed during the penultimate glacial period, equivalent to stage 6 of the oceanic record.3. The subglacially derived debris typically found in basal regelation ice gives a complex strain response to a changing pattern of stresses produced by flow over an irregular subjacent bed. Thus, complex tectonic structures in this ice produce highly variable isotopic profiles. However, its gross isotopic characteristics can still be used to reconstruct some of its history. A sharp change in isotopic values tends to occur at the upper limit of basal regelation ice, the nature of which depends on the style and thickness of tectonic disturbance.4. Isotopic profiles in basal ice can be used to distinguish normal glacier ice from regelation ice, and give strong support to the view that regelation is the major process by which debris is incorporated into the base of a glacier.

scholarly journals The Isotopic Composition of Present-Day Antarctic Snow in a Lagrangian Atmospheric Simulation*

2007 ◽  
Vol 20 (4) ◽  
pp. 739-756 ◽  
Author(s):  
M. M. Helsen ◽  
R. S. W. Van de Wal ◽  
M. R. Van den Broeke
Keyword(s):  
Isotopic Composition ◽  
General Circulation ◽  
Isotopic Fractionation ◽  
General Circulation Models ◽  
Deuterium Excess ◽  
West Antarctica ◽  
Temperature Relation ◽  
Weather Forecasts ◽  
Spatial Differences ◽  
Antarctic Snow

Abstract The isotopic composition of present-day Antarctic snow is simulated for the period September 1980–August 2002 using a Rayleigh-type isotope distillation model in combination with backward trajectory calculations with 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data as meteorological input. Observed spatial isotopic gradients are correctly reproduced, especially in West Antarctica and in the coastal areas. However, isotopic depletion of snow on the East Antarctic plateau is underestimated, a problem that is also observed in general circulation models equipped with isotope tracers. The spatial isotope–temperature relation varies strongly, which indicates that this widely used relation is not applicable to all sites and temporal scales. Spatial differences in the seasonal amplitude are identified, with maximum values in the Antarctic interior and hardly any seasonal isotope signature in Marie Byrd Land, West Antarctica. The modeled signature of deuterium excess remains largely preserved during the last phase of transport, though the simulated relation of deuterium excess with δ18O suggests that parameterizations of kinetic isotopic fractionation can be improved.

scholarly journals Some Observations on the Behavior of the Liquid and Gas Phases in Temperate Glacier Ice

1975 ◽  
Vol 14 (71) ◽  
pp. 213-233 ◽  
Author(s):  
C. F. Raymond ◽  
W. D. Harrison
Keyword(s):  
Large Scale ◽  
Water Flux ◽  
Coarse Grained ◽  
Glacier Surface ◽  
Cross Sectional ◽  
Gas Phases ◽  
Upper Limit ◽  
Melt Water ◽  
Glacier Ice ◽  
Typical Summer

Microscopic and textural observations were made on ice samples cored from Blue Glacier slightly below the equilibrium line to depths of 60 m. Observations were started within a few minutes after collection Water was found in veins along three-grain intersections, in lenses on grain boundaries and in irregular shapes. Gas was found in bubbles in the interior of crystals, in bubbles touching veins and locally in veins Vein sizes showed some spread; average cross-sectional area was about 74 × 10−4mm2with no discernible, trend with texture or depth except within 7 m of the surface. Before the samples were examined they could have experienced a complex relaxation which could have changed them significantly As a result it is not possible to determine thein situsize of veins, but an upper limit can be determined. Also it is not possible to predict intergranular water flux per unit area, but 1 × 10−1m a−1represents an upper limit. In coarse-grained ice the water flux density is likely to be even smaller, because of a low density of veins and blocking by bubbles. This indicates that only a very small fraction of the melt-water production on a typical summer day can penetrate into the glacier on an intergranular scale except possibly near the surface. The existence of conduit-like features in several cores suggests that much melt water ran nevertheless penetrate the ice locally without large-scale lateral movements along the glacier surface. The observed profile of ice temperature indicates that the intergranular water flux may be much smaller than the upper limit determined from the core samples.

scholarly journals Some Observations on the Behavior of the Liquid and Gas Phases in Temperate Glacier Ice

1975 ◽  
Vol 14 (71) ◽  
pp. 213-233 ◽  
Author(s):  
C. F. Raymond ◽  
W. D. Harrison
Keyword(s):  
Large Scale ◽  
Water Flux ◽  
Coarse Grained ◽  
Glacier Surface ◽  
Cross Sectional ◽  
Gas Phases ◽  
Upper Limit ◽  
Melt Water ◽  
Glacier Ice ◽  
Typical Summer

Microscopic and textural observations were made on ice samples cored from Blue Glacier slightly below the equilibrium line to depths of 60 m. Observations were started within a few minutes after collection. Water was found in veins along three-grain intersections, in lenses on grain boundaries and in irregular shapes. Gas was found in bubbles in the interior of crystals, in bubbles touching veins, and locally in veins. Vein sizes showed some spread; average cross-sectional area was about 7 × 10−4 mm2 with no discernible, trend with texture or depth except within 7 m of the surface. Before the samples were examined they could have experienced a complex relaxation which could have changed them significantly. As a result it is not possible to determine the in situ size of veins, but an upper limit can be determined. Also it is not possible to predict intergranular water flux per unit area, but 1 × 10−1 m a−1 represents an upper limit. In coarse-grained ice the water flux density is likely to be even smaller, because of a low density of veins, and blocking by bubbles. This indicates that only a very small fraction of the melt-water production on a typical summer day can penetrate into the glacier on an intergranular scale except possibly near the surface. The existence of conduit-like features in several cores suggests that much melt water can nevertheless penetrate the ice locally without large-scale lateral movements along the glacier surface. The observed profile of ice temperature indicates that the intergranular water flux may be much smaller than the upper limit determined from the core samples.

scholarly journals Climatic Change in a High-Altitude Alpine Area Suggested by the Isotopic Composition Of Cold Basal Glacier Ice

1990 ◽  
Vol 14 ◽  
pp. 168-171 ◽  
Author(s):  
R. Lorrain ◽  
W. Haeberli
Keyword(s):  
Isotopic Composition ◽  
High Altitude ◽  
Temperature Effect ◽  
Climatic Change ◽  
Swiss Alps ◽  
Value Differences ◽  
Water Percolation ◽  
Melt Water ◽  
Glacier Ice ◽  
First Time

For the first time, a cold ice cover of a summit in the central Swiss Alps has been sampled from the surface to the bed for determining its isotopic composition in δD and δ18O. Results of the analyses show a striking decrease of δ-values with depth. The δ-value differences are greater than those explicable by a direct temperature effect, but a substantial increase in melt water percolation through the firn since the formation of the deepest ice layer may explain the situation of this high-altitude ice.

scholarly journals Climatic Change in a High-Altitude Alpine Area Suggested by the Isotopic Composition Of Cold Basal Glacier Ice

1990 ◽  
Vol 14 ◽  
pp. 168-171 ◽  
Author(s):  
R. Lorrain ◽  
W. Haeberli
Keyword(s):  
Isotopic Composition ◽  
High Altitude ◽  
Temperature Effect ◽  
Climatic Change ◽  
Swiss Alps ◽  
Value Differences ◽  
Water Percolation ◽  
Melt Water ◽  
Glacier Ice ◽  
First Time

For the first time, a cold ice cover of a summit in the central Swiss Alps has been sampled from the surface to the bed for determining its isotopic composition in δD and δ18O. Results of the analyses show a striking decrease of δ-values with depth. The δ-value differences are greater than those explicable by a direct temperature effect, but a substantial increase in melt water percolation through the firn since the formation of the deepest ice layer may explain the situation of this high-altitude ice.

scholarly journals Large-Scale, High-Throughput Validation of Short Hairpin RNA Sequences for RNA Interference

2006 ◽  
Vol 11 (3) ◽  
pp. 236-246 ◽  
Author(s):  
Laurence H. Lamarcq ◽  
Bradley J. Scherer ◽  
Michael L. Phelan ◽  
Nikolai N. Kalnine ◽  
Yen H. Nguyen ◽  
...  
Keyword(s):  
High Throughput ◽  
Large Scale ◽  
Strong Support ◽  
Gc Content ◽  
Rapid Identification ◽  
Hairpin Rna ◽  
Rna Sequences ◽  
Short Hairpin ◽  
Short Hairpin Rnas ◽  
Interfering Rna

A method for high-throughput cloning and analysis of short hairpin RNAs (shRNAs) is described. Using this approach, 464 shRNAs against 116 different genes were screened for knockdown efficacy, enabling rapid identification of effective shRNAs against 74 genes. Statistical analysis of the effects of various criteria on the activity of the shRNAs confirmed that some of the rules thought to govern small interfering RNA (siRNA) activity also apply to shRNAs. These include moderate GC content, absence of internal hairpins, and asymmetric thermal stability. However, the authors did not find strong support for positionspecific rules. In addition, analysis of the data suggests that not all genes are equally susceptible to RNAinterference (RNAi).

scholarly journals Seasonal changes in the D  /  H ratio of fatty acids of pelagic microorganisms in the coastal North Sea

2016 ◽  
Vol 13 (19) ◽  
pp. 5527-5539 ◽  
Author(s):  
Sandra Mariam Heinzelmann ◽  
Nicole Jane Bale ◽  
Laura Villanueva ◽  
Danielle Sinke-Schoen ◽  
Catharina Johanna Maria Philippart ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Isotopic Composition ◽  
North Sea ◽  
Phytoplankton Bloom ◽  
Isotopic Fractionation ◽  
Spring Phytoplankton Bloom ◽  
Fractionation Factor ◽  
Culture Studies ◽  
Hydrogen Isotopic Composition

Abstract. Culture studies of microorganisms have shown that the hydrogen isotopic composition of fatty acids depends on their metabolism, but there are only few environmental studies available to confirm this observation. Here we studied the seasonal variability of the deuterium-to-hydrogen (D / H) ratio of fatty acids in the coastal Dutch North Sea and compared this with the diversity of the phyto- and bacterioplankton. Over the year, the stable hydrogen isotopic fractionation factor ε between fatty acids and water (εlipid/water) ranged between −172 and −237 ‰, the algal-derived polyunsaturated fatty acid nC20:5 generally being the most D-depleted (−177 to −235 ‰) and nC18:0 the least D-depleted fatty acid (−172 to −210 ‰). The in general highly D-depleted nC20:5 is in agreement with culture studies, which indicates that photoautotrophic microorganisms produce fatty acids which are significantly depleted in D relative to water. The εlipid/water of all fatty acids showed a transient shift towards increased fractionation during the spring phytoplankton bloom, indicated by increasing chlorophyll a concentrations and relative abundance of the nC20:5 polyunsaturated fatty acids, suggesting increased contributions of photoautotrophy. Time periods with decreased fractionation (less negative εlipid/water values) can potentially be explained by an increased contribution of heterotrophy to the fatty acid pool. Our results show that the hydrogen isotopic composition of fatty acids is a promising tool to assess the community metabolism of coastal plankton potentially in combination with the isotopic analysis of more specific biomarker lipids.

scholarly journals CAF and CAMM analyses on the first 10 years of national Kanta services in Finland

2020 ◽  
Vol 12 (4) ◽  
Author(s):  
Vesa Jormanainen ◽  
Jarmo Reponen
Keyword(s):  
Health Information ◽  
Large Scale ◽  
National Level ◽  
Health Information System ◽  
Strong Support ◽  
Evaluation Framework ◽  
Macro Level ◽  
State Budget ◽  
Study Results ◽  
Clinical Adoption

We report the large-scale deployment, implementation and adoption of the nationwide centralized integrated and shared Kanta health information services by using the Clinical Adoption Framework (CAF). The meso and macro level dimensions of the CAF were incorporated early into our e-health evaluation framework to assess Health Information System (HIS) implementation at the national level. We found strong support for the CAF macro level model concepts in Finland. Typically, development programs were followed by government policy commitments, appropriate legislation and state budget funding before the CAF meso level implementation activities. Our quantitative data point to the fact that implementing large-scale health information technology (HIT) systems in practice is a rather long process. For HIT systems success in particular citizens’ and professionals’ acceptance are essential. When implementation of the national health information systems was evaluated against Clinical Adoption Meta-Model (CAMM), the results show that Finland has already passed many milestones in CAMM archetypes. According to our study results, Finland seems to be a good laboratory entity to study practical execution of HIT systems, CAF and CAMM theoretical constructs can be used for national level HIS implementation evaluation.

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