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Data Set ID:

Analysis of Siple Dome Ice Core: Carbonyl Sulfide (COS), Methyl Chloride (CH3Cl), and Methyl Bromide (CH3Br), Version 1

This data set is part of the WAISCORES (West Antarctic Ice Sheet cores) project, research funded by the National Science Foundation (NSF) and designed to improve understanding of how the West Antarctic ice sheet influences climate and sea level change. WAISCORES investigators acquired and analyzed ice cores from the Siple Dome, in the Siple Coast region, West Antarctica. These data provide researchers with a record of natural climatic variability and anthropogenic influence on biogeochemical cycles. Because ice cores contain an archive of preindustrial air, a baseline can be established, and the extent of human impact on the climate can be ascertained.

This data set includes mixing ratios of carbonyl sulfide (COS), methyl chloride (CH3Cl), and methyl bromide (CH3Br). Data samples were retrieved from the Siple C ice core, which was drilled at 81.65° S, 148.81° W in December 1995. The core site sits 620 m above sea level near the edge of the Ross Ice Shelf where there is a mean annual temperature of -25.4 °C.

Data are available via FTP.

Geographic Coverage

  • Atmospheric Chemistry > Sulfur Compounds > Sulfur Oxides > Carbonyl Sulfide
  • Air Quality > Sulfur Oxides > Carbonyl Sulfide
  • Glaciers/Ice Sheets > Firn
  • Atmospheric Chemistry > Halocarbons and Halogens
  • Ice Core Records > Ice Core Air Bubbles
  • Glaciers/Ice Sheets > Ice Sheets
  • Atmospheric Chemistry > Halocarbons and Halogens > Halocarbons > Methyl Chloride
  • Methyl Bromide
  • Snow/Ice > Snow/Ice Chemistry
Spatial Coverage:
  • N: -81.65, S: -81.65, E: -148.81, W: -148.81

Spatial Resolution: Not Specified
Temporal Coverage: Not specified
Temporal Resolution: Not specified
Data Format(s):
  • Microsoft Excel
  • Microsoft Word
Version: V1
Data Contributor(s): Eric Saltzman, Murat Aydin
Data Citation

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Saltzman, E. and M. Aydin. 2005. Analysis of Siple Dome Ice Core: Carbonyl Sulfide (COS), Methyl Chloride (CH3Cl), and Methyl Bromide (CH3Br), Version 1. [Indicate subset used]. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: [Date Accessed].

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Detailed Data Description


Data files are in Microsoft Excel format viewable with spreadsheet software, and the metadata file is in Microsoft Word format viewable with a text editor.

There are 22 and 23 samples for CH3Cl and CH3Br, respectively. The COS data includes 22 samples taken in 2004 along with the results from an older data set of 11 ice core samples taken in 2002 from the same core, making up for 33 COS samples in total. The 2002 and 2004 samples for COS are listed separately in the COS data file. Each data file contains three columns:

  1. Depth of the ice core sample that the air was extracted from
  2. Mixing ratio of the relevant gas reported in units of parts per trillion by volume (pptv)
  3. Estimated error (±1 σ) reported as percent of the mixing ratio

A metadata file titled "metadata.doc" is also provided.

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File and Directory Structure

This is a list of the data files distributed on the FTP site.

  • CH3Brdata.xls (16 KB)
  • CH3Cldata.xls (17 KB)
  • COSdata.xls (19 KB)
  • metadata.doc (21 KB)

See the Format section for more details on these files.

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The entire data set is approximately 71.5 KB.

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Spatial Coverage

The ice core was retrieved from a site 620 m above sea level.

Southernmost Latitude: 81.65° S
Northernmost Latitude: 81.65° S
Westernmost Longitude: 148.81° W
Easternmost Longitude: 148.81° W

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Temporal Coverage

The Siple Dome C core was collected in December 1995. With the deepest sample taken at 90.7 m, the ice core data comprises a paleoclimate record reaching back as far as 1616 AD.

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Parameter or Variable

Parameter Description

Carbonyl sulfide (COS) is the most abundant sulfur gas in the troposphere. Because this compound is believed to contribute sulfur to the stratospheric aerosol layer, it affects stratospheric ozone and influences the radiative balance of the atmosphere (Ko, et al., 2003). It currently has an average mixing ratio of approximately 500 pptv and an atmospheric lifetime of 4.3 years (Chin and Davis, 1995). Recent measurements of COS in Antarctic firn air indicate that concentrations have increased nearly 21% in the Southern Hemisphere within the last century.

Methyl chloride (CH3Cl), which is produced primarily by natural sources, is the most abundant halocarbon in the atmosphere. It currently has an average mixing ratio of about 550 pptv (about 530 pptv over Antarctica) and accounts for more than 10% of the ozone-depleting halogen delivered to the stratosphere. The atmospheric lifetime of CH3Cl is estimated to be about 1.3 years.

Methyl bromide (CH3Br) is a stratospheric halogen and a contributor to stratospheric ozone depletion whose industrial production has been phased out by the Montreal Protocol. It has a complex biogeochemical cycle with natural sources and sinks both terrestrial and oceanic. However, the CH3Br budget is not well characterized and there appears to exist a naturally occurring "unknown source." The atmospheric lifetime of methyl bromide ranges from 0.7 years to 0.9 years. It currently has an average mixing ratio of 9.5 pptv, but its preindustrial mixing ratios have proven quite difficult to model as is shown by Saltzman et al. (2004).

Parameter Range

COS: 305.8 pptv - 448.8 pptv 
CH3Cl: 461.7 pptv - 579.5 pptv 
CH3Br: 3.2 pptv - 9.0 pptv 
Depth: 55 m - 90.7 m

See the Data Source section below for information on the depth ranges at which the samples were taken.

Sample Data Record

The data below are the first 10 data samples showing methyl chloride (CH3Cl) mixing ratios at various depths along the Siple C ice core from the file "CH3Cldata.xls".

depth (m)

CH3Cl (pptv)

% error































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Software and Tools

Quality Assessment

The pore close-off depth at Siple Dome occurs in the range of 48 m to 56 m. Above this depth, air is able to circulate within the firn because the gaps have not been fully closed. This eventually happens as the snow accumulates above and the firn continues to densify. However, until the pores close off and trap the gases, the age of the ice and the age of the gas are not the same.

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Data Acquisition and Processing

Data Acquisition Methods

The Siple C ice core was retrieved in December 1995. Using a Polar Ice Coring Office (PICO) designed electromechanical drill, the core reached a depth of 91.945 m and was 10 cm in diameter. Air trapped in ice core samples were analyzed for trace levels of carbonyl sulfide (COS), methyl chloride (CH3Cl), and methyl bromide (CH3Br). All samples are from a dry-drilled shallow core from Siple Dome (C core), Antarctica, collected as part of the WAISCORES project.

The extraction of the gas samples was performed by mechanically shredding the core in a stainless steel chamber under a vacuum. The samples were then analyzed by gas chromatography with mass spectrometric detection conducted at the National Oceanic and Atmospheric Administration's (NOAA) Climate Monitoring and Diagnostics Laboratory (CMDL) in Boulder, CO and the University of California, Irvine. For more details on the procedures for data analysis, refer to the investigators' published research papers, which are listed in the References and Related Publications section.

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Data Source

Data for the mixing ratios of the three compounds measured in this study were collected at various depths along the Siple C ice core retrieved in December 1995. The depth ranges from which chemical samples were taken are as follows:

COS: 82.3 m - 90.7 m and 56.8 m - 90.7 m (Note: The two depth ranges represent samples taken in 2002 and those taken in 2004, respectively, from the same ice core with a depth overlap.) 
CH3Cl: 57 m - 83 m 
CH3Br: 55 m - 85 m

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Calculated Variables

The percent error reflects the cumulative uncertainty (±1 σ) of the precision of the methyl bromide measurements and the error introduced due to system blanks. Precision calculation is based on calibration of the analytical system with known standards. System blank refers to methyl bromide levels observed in clean nitrogen runs through the ice core extraction system.

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References and Related Publications

Contacts and Acknowledgments

Eric Saltzman
Department of Earth System Science
University of California
3325 Croul Hall
Mail Code: 3100
Irvine, CA 92697

Murat Aydin
Department of Earth System Science
University of California
3325 Croul Hall
Mail Code: 3100
Irvine, CA 92697


This research was supported by the National Science Foundation (NSF) Office of Polar Programs (OPP) grant OPP-0338359 to E. Saltzman.

Document Information

Document Creation Date

14 December 2011

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