scholarly journals Acoustic velocity measurements for detecting the crystal orientation fabrics of a temperate ice core

2021 ◽  
Vol 15 (7) ◽  
pp. 3507-3521
Author(s):  
Sebastian Hellmann ◽  
Melchior Grab ◽  
Johanna Kerch ◽  
Henning Löwe ◽  
Andreas Bauder ◽  
...  
Keyword(s):  
Acoustic Waves ◽  
Crystal Orientation ◽  
Ice Core ◽  
Point Contact ◽  
Ice Cores ◽  
Swiss Alps ◽  
Mechanical Anisotropy ◽  
Similar Amount ◽  
Core Samples ◽  
Ultrasonic Measurements

Abstract. The crystal orientation fabric (COF) in ice cores provides detailed information, such as grain size and distribution and the orientation of the crystals in relation to the large-scale glacier flow. These data are relevant for a profound understanding of the dynamics and deformation history of glaciers and ice sheets. The intrinsic, mechanical anisotropy of the ice crystals causes an anisotropy of the polycrystalline ice of glaciers and affects the velocity of acoustic waves propagating through the ice. Here, we employ such acoustic waves to obtain the seismic anisotropy of ice core samples and compare the results with calculated acoustic velocities derived from COF analyses. These samples originate from an ice core from Rhonegletscher (Rhone Glacier), a temperate glacier in the Swiss Alps. Point-contact transducers transmit ultrasonic P waves with a dominant frequency of 1 MHz into the ice core samples and measure variations in the travel times of these waves for a set of azimuthal angles. In addition, the elasticity tensor is obtained from laboratory-measured COF, and we calculate the associated seismic velocities. We compare these COF-derived velocity profiles with the measured ultrasonic profiles. Especially in the presence of large ice grains, these two methods show significantly different velocities since the ultrasonic measurements examine a limited volume of the ice core, whereas the COF-derived velocities are integrated over larger parts of the core. This discrepancy between the ultrasonic and COF-derived profiles decreases with an increasing number of grains that are available within the sampling volume, and both methods provide consistent results in the presence of a similar amount of grains. We also explore the limitations of ultrasonic measurements and provide suggestions for improving their results. These ultrasonic measurements could be employed continuously along the ice cores. They are suitable to support the COF analyses by bridging the gaps between discrete measurements since these ultrasonic measurements can be acquired within minutes and do not require an extensive preparation of ice samples when using point-contact transducers.

scholarly journals Acoustic velocity measurements for detecting the crystal orientation fabrics of a temperate ice core

2021 ◽  
Author(s):  
Sebastian Hellmann ◽  
Melchior Grab ◽  
Johanna Kerch ◽  
Henning Löwe ◽  
Andreas Bauder ◽  
...  
Keyword(s):  
Acoustic Waves ◽  
Crystal Orientation ◽  
Ice Core ◽  
Point Contact ◽  
Ice Cores ◽  
Swiss Alps ◽  
Mechanical Anisotropy ◽  
Similar Amount ◽  
Core Samples ◽  
Ultrasonic Measurements

Abstract. The crystal orientation fabrics (COF) in ice cores provides detailed information, such as grain size and distribution and the orientation of the crystals in relation to the large-scale glacier flow. These data are relevant for a profound understanding of the dynamics and deformation history of glaciers and ice sheets. The intrinsic, mechanical anisotropy of the ice crystals causes an anisotropy of the polycrystalline ice of glaciers and affects the velocity of acoustic waves propagating through the ice. Here, we employ such acoustic waves to obtain the seismic anisotropy of ice core samples and compare the results with calculated acoustic velocities derived from COF analyses. These samples originate from an ice core from Rhonegletscher, a temperate glacier in the Swiss Alps. Point-contact transducers transmit ultrasonic p-waves with a dominant frequency of 1 MHz into the ice core samples and measure variations of the travel times of these waves for a set of azimuthal angles. In addition, the elasticity tensor is obtained from laboratory-measured COF and calculate the associated seismic velocities. We compare these COF-derived velocity profiles with the measured ultrasonic profiles. Especially in the presence of large ice grains, these two methods show significantly different velocities since the ultrasonic measurements examine a limited volume of the ice core whereas the COF-derived velocities are integrated over larger parts of the core. This discrepancy between the ultrasonic and COF-derived profiles decreases with an increasing number of grains that is available within the sampling volume and both methods provide concise results in presence of a similar amount of grains. We also explore the limitations of ultrasonic measurements and provide suggestions for improving their results. These ultrasonic measurements could be employed continuously along the ice cores. They are suitable to support the COF analyses by bridging the gaps between discrete measurements, since these ultrasonic measurements can be acquired within minutes and do not require an extensive preparation of ice samples when using point-contact transducers.

Ultrasonic velocity experiments on ice cores to complement fabric measurements

2021 ◽  
Author(s):  
Sebastian Hellmann ◽  
Johanna Kerch ◽  
Melchior Grab ◽  
Henning Löwe ◽  
Andreas Bauder ◽  
...  
Keyword(s):  
Light Microscopy ◽  
Crystal Orientation ◽  
Ice Core ◽  
Ice Cores ◽  
Ultrasonic Waves ◽  
Thin Sections ◽  
Core Drilling ◽  
Core Samples ◽  
Ultrasonic Measurements ◽  
Polarised Light

<p>The ice crystal structure and in particular the crystal orientation fabrics (COF) provide valuable information about the deformation history of ice sheets and glaciers. Therefore, COF analysis has been among the standard measurement techniques for most deep ice core drilling projects in the last three decades. The analysis depends on carefully prepared thin sections of ice that are measured with cross-polarised light microscopy or electron backscattering and diffraction (EBSD). The preparation of thin sections is labour-intensive and therefore only a discrete number of samples along the ice core is usually analysed. Geophysical methods such as ultrasonic sounding along the ice core could be employed to complement the discrete fabric data by providing data to fill the gaps. A suitable method needs to be reasonably fast, ideally non-invasive and provides unambiguous information in combination with the established methods.</p><p>In our study, we demonstrate the feasibility of such ultrasonic experiments applied to an ice core to support the approved cross-polarised light microscopy method. Point-contact transducers transmitted ultrasonic waves into ice core samples from a temperate glacier. X-ray computer tomography measurements provide the required information to consider the effect of a two-phase medium (ice and air bubbles) in a porosity correction of the velocity. We determined the azimuthal variation of the seismic velocity. This variation is a result of seismic anisotropy due to the crystal orientation within the ice core volume. The measurements can be acquired within minutes and do not require an extensive preparation of ice samples.</p><p>In addition, the COF of adjacent ice core samples was measured with cross-polarised light spectroscopy. From this, we derived the elasticity tensor and finally calculated the associated seismic velocities for the same azimuth and inclination angle as for the ultrasonic experiments. We compare these two velocity profiles and discover a significant discrepancy in presence of large ice grains. However, with an increasing number of ice grains both methods provide similar results. Although the ultrasonic measurements reveal some ambiguities, these can be resolved when considering the information derived from the standard analysis.</p><p>We conclude that ultrasonic measurements along the ice core are suitable to support the established COF analysis for sufficiently small grains as found in polar cores. We recommend further exploration of the potential of the presented technique as it provides both the chance to obtain a continuous fabric profile and a direct link to large-scale seismic measurements in the vicinity of ice core drilling sites.</p>

scholarly journals Comparison of seismic velocities derived from crystal orientation fabrics and ultrasonic measurements on an ice core

2020 ◽  
Author(s):  
Sebastian Hellmann ◽  
Johanna Kerch ◽  
Melchior Grab ◽  
Henning Löwe ◽  
Ilka Weikusat ◽  
...  
Keyword(s):  
Seismic Data ◽  
Acoustic Waves ◽  
Crystal Orientation ◽  
Ice Core ◽  
Elasticity Tensor ◽  
Swiss Alps ◽  
Seismic Velocities ◽  
Air Bubble ◽  
Core Samples ◽  
Glacier Ice

<p>Understanding the internal structure of glacier ice is of high interest for studying ice flow mechanics and glacier dynamics. The micro-scale deformation mechanisms cause a reorientation and alignment of the ice grains resulting in a polycrystalline structure with a strong anisotropy. By studying the crystal orientation fabric (COF), details about past and ongoing ice deformation processes can be derived. Usually, obtaining COF requires a work-intensive ice core analysis, which is typically carried out only at a few ice core samples. When similar information can be obtained from geophysical, for example, seismic experiments, a more detailed and more continuous image about the ice deformation would be available. <br>For checking the suitability of seismic data for such purposes, we have analysed the COF of several ice core samples extracted from Rhone Glacier, a temperate glacier located in the Central Swiss Alps. The COF analysis yield a polycrystalline elasticity tensor for a given volume of ice, from which we predicted seismic velocities for acoustic waves originating from any azimuth and inclination. The seismic data predicted were then verified with ultrasonic experiments conducted along the ice core in the vicinity of the analysed COF. Additional X-ray tomographic measurements yield further constraints about the microstructure, especially about the air bubble content in the ice affecting the data of the ultrasonic experiments. Predicted and measured velocities generally show a good match. This is a very encouraging result, because it suggests that in-situ measurements of seismic velocities can be employed for studying ice deformation. A possible option is to perform seismic cross-hole measurements within an array of boreholes drilled into the glacier ice.</p>

scholarly journals Extraction of Dissolved Organic Carbon from Glacier Ice for Radiocarbon Analysis

Radiocarbon ◽  
2019 ◽  
Vol 61 (03) ◽  
pp. 681-694 ◽  
Author(s):  
L Fang ◽  
J Schindler ◽  
T M Jenk ◽  
C Uglietti ◽  
S Szidat ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Working Conditions ◽  
Irradiation Time ◽  
Ice Core ◽  
Ice Cores ◽  
Swiss Alps ◽  
Carbonaceous Aerosols ◽  
Core Samples ◽  
Reported Data

ABSTRACTAlpine glaciers are valuable archives for the reconstruction of human impact on the environment. Besides dating purposes, measurement of radiocarbon (14C) content provides a powerful tool for long-term source apportionment studies on the carbonaceous aerosols incorporated in ice cores. In this work, we present an extraction system for 14C analyses of dissolved organic carbon (DOC) in ice cores. The setup can process ice samples of up to 350 g mass and offers ultra-clean working conditions for all extraction steps. A photo-oxidation method is applied by means of external UV irradiation of the sample. For an irradiation time of 30 min with catalyzation by addition of Fe2+ and H2O2, we achieve an efficiency of 96 ± 6% on average. Inert gas working conditions and stringent decontamination procedures enable a low overall blank of 1.9 ± 1.6 μg C with a F14C value of 0.68 ± 0.13. This makes it possible to analyze the DOC in ice samples with a carbon content of as low as 25 μg C kg−1 ice. For a first validation, the new method was applied to ice core samples from the Swiss Alps. The average DOC concentration and F14C values for the Fiescherhorn ice core samples show good agreement with previously reported data for the investigated period of 1925–1936 AD.

scholarly journals Towards radiocarbon dating of ice cores

2009 ◽  
Vol 55 (194) ◽  
pp. 985-996 ◽  
Author(s):  
M. Sigl ◽  
T.M. Jenk ◽  
T. Kellerhals ◽  
S. Szidat ◽  
H.W. Gäggeler ◽  
...  
Keyword(s):  
Aerosol Particles ◽  
Ice Core ◽  
Ice Cores ◽  
Swiss Alps ◽  
Carbonaceous Aerosol ◽  
Polar Ice ◽  
Low Latitude ◽  
Bolivian Andes ◽  
Glacier Ice ◽  
Dating Method

AbstractA recently developed dating method for glacier ice, based on the analysis of radiocarbon in carbonaceous aerosol particles, is thoroughly investigated. We discuss the potential of this method to achieve a reliable dating using examples from a mid- and a low-latitude ice core. Two series of samples from Colle Gnifetti (4450 m a.s.l., Swiss Alps) and Nevado Illimani (6300 m a.s.l., Bolivian Andes) demonstrate that the 14C ages deduced from the water-insoluble organic carbon fraction represent the age of the ice. Sample sizes ranged between 7 and 100 μg carbon. For validation we compare our results with those from independent dating. This new method is thought to have major implications for dating non-polar ice cores in the future, as it provides complementary age information for time periods not accessible with common dating techniques.

The Anthropogenic Impact on Snow Chemistry at Colle Gnifetti, Swiss Alps

1988 ◽  
Vol 10 ◽  
pp. 183-187 ◽  
Author(s):  
D. Wagenbach ◽  
K.O. Münnich ◽  
U. Schotterer ◽  
H. Oeschger
Keyword(s):  
Chemical Analysis ◽  
Ice Core ◽  
Ice Cores ◽  
Summer Precipitation ◽  
Snow Accumulation ◽  
Swiss Alps ◽  
Saharan Dust ◽  
Water Conductivity ◽  
Air Masses ◽  
Melt Water

By chemical analysis of the upper 40 m of a 124 m ice core from a high-altitude Alpine glacier (Colle Gnifetti, Swiss Alps; 4450 m a.s.l.), records of mineral dust, pH, melt-water conductivity, nitrate and sulfate are obtained. The characteristics of the drilling site are discussed, as derived from glacio-meteorological and chemical analysis. As a consequence of high snow-erosion rates (usually during the winter months), annual snow accumulation is dominated by summer precipitation. Clean-air conditions prevail even during summer; however, they are frequently interrupted by polluted air masses or by air masses which are heavily loaded with desert dust.Absolutely dated reference horizons for Saharan dust, together with the position of the broad nuclear-weapon tritium peak, provide the time-scale for the following statements:(1) Since at least the turn of the century the background melt-water conductivity has been rising steadily, as has the mean snow acidity. The trend of increasing background conductivity at Colle Gnifetti (1.9μS/cm around the beginning of this century, and at present 3.4 μS/cm) is found to be comparable with the records of mean melt-water conductivity reported from ice cores from the Canadian High Arctic.(2) Sulfate and nitrate concentrations are higher by a factor of 4–5 than they were at the beginning of the century. This is to be compared with the two- to three-fold rise in the concentrations in south Greenland during about the same time span.

scholarly journals The Anthropogenic Impact on Snow Chemistry at Colle Gnifetti, Swiss Alps

1988 ◽  
Vol 10 ◽  
pp. 183-187 ◽  
Author(s):  
D. Wagenbach ◽  
K.O. Münnich ◽  
U. Schotterer ◽  
H. Oeschger
Keyword(s):  
Chemical Analysis ◽  
Ice Core ◽  
Ice Cores ◽  
Summer Precipitation ◽  
Snow Accumulation ◽  
Swiss Alps ◽  
Saharan Dust ◽  
Water Conductivity ◽  
Air Masses ◽  
Melt Water

By chemical analysis of the upper 40 m of a 124 m ice core from a high-altitude Alpine glacier (Colle Gnifetti, Swiss Alps; 4450 m a.s.l.), records of mineral dust, pH, melt-water conductivity, nitrate and sulfate are obtained. The characteristics of the drilling site are discussed, as derived from glacio-meteorological and chemical analysis. As a consequence of high snow-erosion rates (usually during the winter months), annual snow accumulation is dominated by summer precipitation. Clean-air conditions prevail even during summer; however, they are frequently interrupted by polluted air masses or by air masses which are heavily loaded with desert dust. Absolutely dated reference horizons for Saharan dust, together with the position of the broad nuclear-weapon tritium peak, provide the time-scale for the following statements: (1) Since at least the turn of the century the background melt-water conductivity has been rising steadily, as has the mean snow acidity. The trend of increasing background conductivity at Colle Gnifetti (1.9μS/cm around the beginning of this century, and at present 3.4 μS/cm) is found to be comparable with the records of mean melt-water conductivity reported from ice cores from the Canadian High Arctic. (2) Sulfate and nitrate concentrations are higher by a factor of 4–5 than they were at the beginning of the century. This is to be compared with the two- to three-fold rise in the concentrations in south Greenland during about the same time span.

scholarly journals The preservation of methanesulphonic acid in frozen ice-core samples

2008 ◽  
Vol 54 (187) ◽  
pp. 680-684 ◽  
Author(s):  
Nerilie J. Abram ◽  
Mark A.J. Curran ◽  
Robert Mulvaney ◽  
Tessa Vance
Keyword(s):  
Sea Ice ◽  
Ice Core ◽  
Frozen Storage ◽  
Ice Cores ◽  
Ice Storage ◽  
Core Samples ◽  
Proxy Records ◽  
Subsequent Determination ◽  
Earth’S Climate

AbstractIce-core records of methanesulphonic acid (MSA) provide a potentially powerful tool for producing proxy records of sea ice, a critical but poorly understood component of the Earth’s climate system. However, MSA is able to diffuse through solid ice, and here we examine the effect of two different methods of frozen storage on the preservation of MSA in archived ice-core samples. Re-analysis of archived ice sticks confirms that MSA diffuses out of ice cores archived in this manner. Despite MSA losses of up to 39% after 7 years storage, the ice sticks studied here preserve much of the variability of the original MSA record, suggesting that useful proxy records can be obtained from archived ice sticks. Furthermore, re-analysis of ice-core samples that had been refrozen into discrete bottled samples for storage demonstrates that it is possible to archive ice samples in a way that prevents MSA loss. In this case, accurate records of MSA variability and concentration were preserved even over storage periods of 15 years. This has important implications for the storage of ice cores and subsequent determination of MSA, and demonstrates that ice storage history needs to be considered when interpreting MSA records.

scholarly journals EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice

Solid Earth ◽  
2017 ◽  
Vol 8 (5) ◽  
pp. 883-898 ◽  
Author(s):  
Ilka Weikusat ◽  
Ernst-Jan N. Kuiper ◽  
Gill M. Pennock ◽  
Sepp Kipfstuhl ◽  
Martyn R. Drury
Keyword(s):  
Basal Slip ◽  
Plastic Anisotropy ◽  
Ice Core ◽  
Ice Cores ◽  
Dislocation Slip ◽  
Slip Systems ◽  
Polar Ice ◽  
Electron Backscattered Diffraction ◽  
Depth Level ◽  
Core Samples

Abstract. Ice has a very high plastic anisotropy with easy dislocation glide on basal planes, while glide on non-basal planes is much harder. Basal glide involves dislocations with the Burgers vector b = 〈a〉, while glide on non-basal planes can involve dislocations with b = 〈a〉, b = [c], and b = 〈c + a〉. During the natural ductile flow of polar ice sheets, most of the deformation is expected to occur by basal slip accommodated by other processes, including non-basal slip and grain boundary processes. However, the importance of different accommodating processes is controversial. The recent application of micro-diffraction analysis methods to ice, such as X-ray Laue diffraction and electron backscattered diffraction (EBSD), has demonstrated that subgrain boundaries indicative of non-basal slip are present in naturally deformed ice, although so far the available data sets are limited. In this study we present an analysis of a large number of subgrain boundaries in ice core samples from one depth level from two deep ice cores from Antarctica (EPICA-DML deep ice core at 656 m of depth) and Greenland (NEEM deep ice core at 719 m of depth). EBSD provides information for the characterization of subgrain boundary types and on the dislocations that are likely to be present along the boundary. EBSD analyses, in combination with light microscopy measurements, are presented and interpreted in terms of the dislocation slip systems. The most common subgrain boundaries are indicative of basal 〈a〉 slip with an almost equal occurrence of subgrain boundaries indicative of prism [c] or 〈c + a〉 slip on prism and/or pyramidal planes. A few subgrain boundaries are indicative of prism 〈a〉 slip or slip of 〈a〉 screw dislocations on the basal plane. In addition to these classical polygonization processes that involve the recovery of dislocations into boundaries, alternative mechanisms are discussed for the formation of subgrain boundaries that are not related to the crystallography of the host grain.The finding that subgrain boundaries indicative of non-basal slip are as frequent as those indicating basal slip is surprising. Our evidence of frequent non-basal slip in naturally deformed polar ice core samples has important implications for discussions on ice about plasticity descriptions, rate-controlling processes which accommodate basal glide, and anisotropic ice flow descriptions of large ice masses with the wider perspective of sea level evolution.

scholarly journals An improved method for delta <sup>15</sup>N measurements in ice cores

2008 ◽  
Vol 4 (1) ◽  
pp. 149-171 ◽  
Author(s):  
F. S. Mani ◽  
P. Dennis ◽  
W. T. Sturges ◽  
R. Mulvaney ◽  
M. Leuenberger
Keyword(s):  
High Precision ◽  
Climate Changes ◽  
Ice Core ◽  
Ice Cores ◽  
Atmospheric Nitrogen ◽  
Nitrogen Gas ◽  
Last Glacial Period ◽  
Temperature Changes ◽  
Core Samples ◽  
The Last Glacial

Abstract. The use of isotopic ratios of nitrogen gas (δ15N) trapped in ice cores as a paleothermometer to characterise abrupt climate changes is becoming a widespread technique. The versatility of the technique could be enhanced, for instance in quantifying small temperature changes during the last glacial period in Antarctic ice cores, by using high precision methods. In this paper, we outline a method for measuring δ15N to a precision of 0.006\\permil (1σ, n=9) from replicate ice core samples. The high precision results from removing oxygen, carbon dioxide and water vapour from the air extracted from ice cores. The advantage of the technique is that it does not involve correction for isobaric interference due to CO+ ions. We also highlight the importance of oxygen removal from the sample, and how it influences δ15N measurements. The results show that a small amount of oxygen in the sample can be detrimental to achieving an optimum precision in δ15N measurements of atmospheric nitrogen trapped ice core samples.

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