Development, principles, and applications of automated ice fabric analyzers

Wilen, Larry; Diprinzio, C.L.; Alley, Richard B.; Azuma, Nobuhiko

doi:10.1002/jemt.10380

Cited by 73 publications

(55 citation statements)

References 75 publications

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“…Data at the periphery of a pole figure (projection onto a thin section plane) are of low quality and thus partly excluded from the population in display and LPO data processing, leading to the described bias. The automatic fabric analysers used here calculate the extinction angle, where no light gets through the system, by fitting the light amplitude values for each step of the polarizers to a sinusoid curve [73,74]. The low-quality effect of c -axes in a plane normal to the observation axes is caused by the G20 instrument often being unable to resolve the quadrant pair of the azimuth of these orientations.…”

Section: Results and Datamentioning

confidence: 99%

Physical analysis of an Antarctic ice core—towards an integration of micro- and macrodynamics of polar ice

Weikusat

Jansen

Binder

et al. 2017

Phil. Trans. R. Soc. A.

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Microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail. Ice core parameters (crystal lattice-preferred orientation (LPO), grain size, grain shape), mesostructures (visual stratigraphy) as well as borehole deformation were measured in a deep ice core drilled at Kohnen Station, Dronning Maud Land (DML), Antarctica. These observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the EDML ice core drilling site (European Project for Ice Coring in Antarctica in DML). The results suggest a division of the core into five distinct sections, interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock-parallel shear. Region 1 (uppermost approx. 450 m depth) with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization. Region 2 (approx. 450–1700 m depth) shows a girdle-type LPO with the girdle plane being perpendicular to grain elongations, which indicates triaxial deformation with dominating horizontal extension. In this region (approx. 1000 m depth), the first subtle traces of shear deformation are observed in the shape-preferred orientation (SPO) by inclination of the grain elongation. Region 3 (approx. 1700–2030 m depth) represents a transitional regime between triaxial deformation and dominance of shear, which becomes apparent in the progression of the girdle to a single maximum LPO and increasing obliqueness of grain elongations. The fully developed single maximum LPO in region 4 (approx. 2030–2385 m depth) is an indicator of shear dominance. Region 5 (below approx. 2385 m depth) is marked by signs of strong shear, such as strong SPO values of grain elongation and strong kink folding of visual layers. The details of structural observations are compared with results from a numerical ice sheet model (PISM, isotropic) for comparison of strain rate trends predicted from the large-scale geometry of the ice sheet and borehole logging data. This comparison confirms the segmentation into these depth regions and in turn provides a wider view of the ice sheet.This article is part of the themed issue ‘Microdynamics of ice’.

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Section: Results and Datamentioning

confidence: 99%

Physical analysis of an Antarctic ice core—towards an integration of micro- and macrodynamics of polar ice

Weikusat

Jansen

Binder

et al. 2017

Phil. Trans. R. Soc. A.

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“…This, however, does not mean that rotation recrystallization does not occur. The most efficient way to detect rotation recrystallization is based on the correlation of c axes orientation between neighboring grains [ Wilen et al , 2003]. This analysis requires detailed crystallographic data that are not yet available for the EPICA ice core.…”

Section: Critical Review Of the Possible Mechanisms That Could Explaimentioning

confidence: 99%

Effect of impurities on grain growth in cold ice sheets

Durand¹,

Weiss²,

Lipenkov³

et al. 2006

J. Geophys. Res.

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[1] On the basis of a detailed study of the ice microstructure of the European Project for Ice Coring in Antarctica (EPICA) ice core at Dome Concordia, Antarctica, we analyze the effect of impurities (solubles, and insolubles, that is, dust particles) on the grain growth process in cold ice sheets. As a general trend, the average grain size increases with depth. This global increase, induced by the normal grain growth process, is punctuated by several sharp decreases that can be associated with glacial-interglacial climatic transitions. To explain the modifications of the microstructure with climatic changes, we discuss the role of soluble and insoluble impurities on the grain growth process, coupled with an analysis of the pinning of grain boundaries by microparticles. Our data indicate that high soluble impurity content does not necessarily imply a slowdown of grain growth kinetics, whereas the pinning of grain boundaries by dust explains all the observed modifications of the microstructure. We propose a numerical model of the evolution of the average grain size in deep ice cores that takes into account recrystallization processes such as normal grain growth and rotation recrystallization as well as the pinning effect induced by dust particles, bubbles, and clathrates on the grain boundaries. Applied to the first 2135 m of the Dome Concordia core, the model reproduces accurately the measured mean grain radius. This indicates a major role of dust in the modification of polar ice microstructure and shows that the average grain size is not a true paleothermometer, as it is correlated with climatic transitions through the dust content of the ice.

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“…In the time since these measurements were made considerable technological advances in the instruments available to measure crystal orientations have occurred (e.g. Yun and Azuma, 1999;Wilen et al, 2003;Wilson et al, 2007;Wilson and Peternell, 2011). Modern instruments provide several benefits over the universal stage including (i) higher resolution, enabling small-scale differences in crystallographic orientations within individual grains to be detected, (ii) the ability to spatially map c-axis orientations, (iii) automated operation and a significantly higher speed of determining orientations, and (iv) lower levels of uncertainty in both caxis azimuth and colatitude.…”

Section: Crystallographic C-axis Measurementsmentioning

confidence: 99%

Ice crystal <i>c</i>-axis orientation and mean grain size measurements from the Dome Summit South ice core, Law Dome, East Antarctica

Treverrow

Jacka

2016

Earth Syst. Sci. Data

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Abstract. We present measurements of crystal c-axis orientations and mean grain area from the Dome Summit South (DSS) ice core drilled on Law Dome, East Antarctica. All measurements were made on location at the borehole site during drilling operations. The data are from 185 individual thin sections obtained between a depth of 117 m below the surface and the bottom of the DSS core at a depth of 1196 m. The median number of c-axis orientations recorded in each thin section was 100, with values ranging from 5 through to 111 orientations. The data from all 185 thin sections are provided in a single comma-separated value (csv) formatted file which contains the c-axis orientations in polar coordinates, depth information for each core section from which the data were obtained, the mean grain area calculated for each thin section and other data related to the drilling site. The data set is also available as a MATLAB™ structure array. Additionally, the c-axis orientation data from each of the 185 thin sections are summarized graphically in figures containing a Schmidt diagram, histogram of c-axis colatitudes and rose plot of c-axis azimuths. All these data are referenced by doi:10.4225/15/5669050CC1B3B and are available free of charge at https://data.antarctica.gov.au.

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Development, principles, and applications of automated ice fabric analyzers

Cited by 73 publications

References 75 publications

Physical analysis of an Antarctic ice core—towards an integration of micro- and macrodynamics of polar ice

Physical analysis of an Antarctic ice core—towards an integration of micro- and macrodynamics of polar ice

Effect of impurities on grain growth in cold ice sheets

Ice crystal <i>c</i>-axis orientation and mean grain size measurements from the Dome Summit South ice core, Law Dome, East Antarctica

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Development, principles, and applications of automated ice fabric analyzers

Cited by 73 publications

References 75 publications

Physical analysis of an Antarctic ice core—towards an integration of micro- and macrodynamics of polar ice

Physical analysis of an Antarctic ice core—towards an integration of micro- and macrodynamics of polar ice

Effect of impurities on grain growth in cold ice sheets

Ice crystal &lt;i&gt;c&lt;/i&gt;-axis orientation and mean grain size measurements from the Dome Summit South ice core, Law Dome, East Antarctica

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Product

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Ice crystal <i>c</i>-axis orientation and mean grain size measurements from the Dome Summit South ice core, Law Dome, East Antarctica