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Siple Dome A (SDMA) Grain Orientation 640 - 790 Meters

This data set characterizes the microstructure in ice cores, in particular the microstructural locations of impurities, grain orientations, and strain gradients. The fabric of polycrystalline ice is typically described using only the c-axis orientation, but this is insufficient for a full description of grain orientations in this hexagonal material. Thus, both the
a-axis and c-axis are used in this data set showing pole figures for five depths of the Siple Dome (SDMA) core between 640 m and 790 m and misorientation angle distribution for the same grains.

Table of Contents

  1. Contacts and Acknowledgments
  2. Detailed Data Description
  3. Data Access and Tools
  4. Data Acquisition and Processing
  5. References and Related Publications
  6. Document Information

Citing These Data

The following example shows how to cite the use of this data set in a publication. For more information, see our Use and Copyright Web page.

Ian Baker, Obbard, Rachel W., and Sieg, Katherine. 2012. Siple Dome A (SDMA) Grain Orientation 640-790 Meters. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N53T9F5X

Overview

Sensor

FEI XL30 Environmental Scanning Electron Microscope - Field Emission Gun
(ESEM - FEG).

Spatial Coverage

Siple Dome, Antarctica
Northernmost Latitude: 81.66°S
Southernmost Latitude: 81.66°S
Westernmost Longitude: 148.82° W
Easternmost Longitude: 148.82° W

Spatial Resolution

1 mm vertical

Temporal Coverage

12.92 kyrBP to 33.39 kyrBP - (temporal coverage)
15 January 2009 to 15 June 2009 - (collection period)

Parameters

Glaciers
Ice Sheets
Electron Backscatter Diffraction (EBSD)

Data Format

Microsoft Word 2007 (.doc)
Microsoft Excel (.xls)

Metadata Access

View Metadata Record

Data Access

FTP

1. Contacts and Acknowledgments

Investigator(s) Name and Title

Dr. Ian Baker
Dartmouth College - Thayer School
Thayer School of Engineering
14 Engineering Dr.
Hanover, NH 03755

Dr. Rachel W. Obbard
Dartmouth College - Thayer School
Thayer School of Engineering
14 Engineering Dr.
Hanover, NH 03755

Katherine Sieg
Dartmouth College - Thayer School
Thayer School of Engineering
14 Engineering Dr.
Hanover, NH 03755

Technical Contact

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org

Acknowledgements

This research was supported by the Advanced Microstructural Characterization of Polar Ice Cores, grant number 0738975.

2. Detailed Data Description

This data set characterizes the microstructure in ice cores, in particular the microstructural locations of impurities, grain orientations and strain gradients. This work will complement the optical observations, electrical conductivity measurement, and the precise, detailed measurements of the soluble ion and gas contents that are performed by others. Linking the concentrations of soluble ions and gases, measured to a few parts per billion, to the optically determined annual layer structure and the stable isotope data in ice cores has enabled a great deal to be established about the concentrations and depth/age distributions of particles, trace gases, and impurities for several polar ice cores. Ice core studies carried out by several groups contribute immensely to our understanding of paleoclimate, and to our ability to predict future climate change. The work will build on previous measurements and techniques developed in this area, as well as focusing on new techniques to characterize ice cores.

Format

Data are provided in the following formats:

  • Microsoft Word 2007 (.doc)
  • Microsoft Excel (.xls).

File and Directory Structure

Data are available on the FTP site in the ftp://sidads.colorado.edu/pub/DATASETS/AGDC/nsidc0526_baker_V01/ directory. Within this directory, the SDMAGrainOrientation.doc file contains pole figures and misorientation angle distribution figures that are labeled with their nominal depths to the closest meter. The SDMAGrainSize640-790.xls file contains eight sheets. Sheet one is a summary of all seven ice core samples, and sheets two through eight are for ice core samples 640 m to 790 m.

File Size

The Microsoft Excel file is 329 KB in size, and the Microsoft Word Document is 138 KB in size.

Data Volume

The entire data set is approximately 0.138 MB

Spatial Coverage

Siple Dome, Antarctica
Northernmost Latitude: 81.66°S
Southernmost Latitude: 81.66°S
Westernmost Longitude: 148.82° W
Easternmost Longitude: 148.82° W

Spatial Resolution

1 mm vertical

Temporal Coverage

These data were collected from 15 January 2009 to 15 June 2009. The actual temporal coverage of the data is 12.92 kyrBP to 33.39 kyrBP.

Parameter or Variable

This data set contains the following parameters:
Glaciers
Ice Sheets
Electron Backscatter Diffraction (EBSD).

Sample Data Records

Figures 1 through 3 are a sample of the data records for this data set. Figure 1 is a sheet within the Microsoft Excel Spreadsheet, and Figures 2 and 3 are provided in a single Microsoft Word file and labeled with their nominal depths to the closest meter.

The Summary Sample Data Record in Figure 1 contains seven samples; however, only five of the samples are illustrated in Figures 2 and 3. Samples 640 and 790 were not used in those figures.

summary data file

Figure 1. Summary Sample Data Record for Seven Depths of the SDMA Core Between 640 m and 790 m

Figure 2 displays Pole figures for both the a-axis {0001} and c-axis {11-20} for five depths of the SDMA core between 670 m and 770 m. Pole figures shown are not oriented to True North. Exact depths of samples are as follows:

670.030 - 670.120 m (6 samples, 131 grains)
700.000 - 700.040 m (7 samples, 335 grains)
727.410 - 727.470 m (5 samples, 391 grains)
750.000 - 750.072 m (6 samples, 367 grains)
770.150 - 770.200 m (6 samples, 378 grains)

smda pole figures

Figure 2. Pole Figures for Five Depths of the SDMA Core Between 670 m and 770 m

Figure 3 shows the SDMA misorientation angle distribution for the same grains that are shown in Figure 2. The blue lines represent correlated values that are between user defined adjacent grains. The dashed red line represents uncorrelated values that are between 1000 randomly chosen pairs of measured grains. The black line represents random (theoretical) orientation for a randomly oriented hexagonal crystal.

sdma misorientation angle distribution

Figure 3. SDMA Misorientation Angle Distribution for Five Depths of the SDMA Core Between 670 m and 770 m

3. Data Access

Data are available via FTP.

4. Data Acquisition and Processing

The data set was created by using both a Scanning Electron Microscope (SEM) coupled with X-ray Energy Dispersive Spectroscopy (EDS), and Confocal Scanning Optical Microscopy (CSOM) coupled with Raman Spectroscopy (RS) to determine the microstructural locations of impurities and correlate this information with depth/age, and impurity type and concentration for several polar ice cores.

Data Acquisition Methods

A method called Electron Backscatter Diffraction (EBSD) was used with a FEI XL30 Environmental Scanning Electron Microscope - Field Emission Gun
(ESEM - FEG) to collect the samples for this data set. Accelerated electrons in the primary beam of an SEM can be diffracted by atomic layers in crystalline materials. These diffracted electrons can be detected when they impinge on a phosphor screen and generate visible lines called Kikuchi bands, or Electron Backscatter Patterns (EBSP's). These patterns are effectively projections of the geometry of the lattice planes in the crystal, and they give direct information about the crystalline structure and crystallographic orientation of the grain from which they originate. When used in conjunction with a database that includes crystallographic structure information for phases of interest and with software for processing the EPSP's and indexing the lines, the data can be used to identify phases based on crystal structure and also to perform fabric analyses on polycrystalline aggregates (Swapp). The SEM EBSD technique used in this data set is described in detail by Iliescu et al. (2004) and Obbard et al. (2006b).

Sensor or Instrument Description

The FEI XL30 ESEM-FEG offers high resolution secondary electron imaging at pressures as high as 10 Torr and sample temperatures as high as 1,000°C. This means that wet, oily, dirty, outgassing, and non-conductive samples can be examined in their natural state without significant sample modification or preparation. The XL30 ESEM-FEG employs the stable, high brightness Schottky Field Emission Source for outstanding observation performance of potentially problematic samples for conventional high vacuum Scanning Electron Microscope (SEMs). For more information about this instrument, visit the FEI Web site.

5. References and Related Publications

Iliescu, D., I. Baker, and H. Chang. 2004. Determining the Orientations of Ice Crystals Using Electron Backscatter Patterns. Microsc. Res. Techn., 63(4), 183 - 187.

Obbard, R., I. Baker, and K. Sieg. 2006b. Using Electron Backscatter Diffraction Patterns to Examine Recrystallization in Polar Ice Sheets. Journal of Glaciology, 52(179), 546 - 557.

Obbard R. W., K. E. Sieg, I. Baker, D. Meese. 2011. Microstructural Evolution in the Fine-graine Region of the Siple Dome Ice Core. Journal of Glaciology, 57(206):1046-1056.

Swapp, Susan. "Scanning Electron Microscopy (SEM)" Geochemical Instrumentation and Analysis. http://serc.carleton.edu/research_education/geochemsheets/ techniques/SEM.html [Accessed 11/15/2012]

6. Document Information

Acronyms and Abbreviations

The acronyms used in this document are listed in Table 1.

Table 1. Acronyms and Abbreviations
Acronym Description
CSOM Confocal Scanning Optical Microscopy
EBSD Electron Backscatter Diffraction
EDS X-ray Energy Dispersive Spectroscopy
ESEM Environmental Scanning Electron Microscope
kyrBP Thousands of Years Before Present
RS Raman Spectroscopy
SDMA Siple Dome A
SEM Scanning Electron Microscope

Document Creation Date

12 November 2012

Document Revision Date

.....

Document URL

http://nsidc.org/data/docs/agdc/nsidc0526-baker/index.html