Methane Concentration and Chronology from the WAIS Divide Ice Core (WDC05A)

Summary

This data set provides a high-precision and high-resolution record of atmospheric methane from the West Antarctic Ice Sheet (WAIS) Divide ice core WDC05A, spanning the years 1000 to 1800 C.E. The data include methane (CH4) concentration measurements and ice age chronology. Methane concentration data include mean sample depth, gas age, mean concentration, and concentrations from individual measurements, at a temporal resolution of approximately nine years. Ice chronology data include depth and ice age.

Data are available via FTP, in Microsoft Excel (.xlsx) format.

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.

The following example shows how to cite the use of this data set in a publication. List the principal investigators, year of data set release, publisher: NSIDC, and digital media.

Mitchell, L. E., E. J. Brook, T. Sowers, J. R. McConnell, and K. Taylor. 2011. Methane Concentration and Chronology from the WAIS Divide Ice Core (WDC05A). Boulder, Colorado, USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5319SV3.

Overview Table

Category	Description
Data format	Microsoft Excel (.xlsx) tab delimited
Spatial coverage and resolution	Southernmost Latitude: 79.47°S Northernmost Latitude: 79.47°S Westernmost Longitude: 112.09°E Easternmost Longitude: 112.09°E
Temporal coverage and resolution	The WAIS Divide ice core WDC05A was drilled in 2005. Ice age data ranges from 1,000 to 1,800 C.E. Temporal resolution for concentration data is approximately nine years.
File naming convention	Methane_Concentration_WDC05A.xlsx Chronology_WDC05A.xlsx
File size	13.67 MB
Parameter(s)	Depth Gas age Individual measurements of methane concentration, in parts per billion Mean methane concentration (ppb) Ice age
Procedures for obtaining data	Data are available via FTP.

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

1. Contacts and Acknowledgments

Investigators

Dr. E. J. Brook
Department of Geosciences
Oregon State University
104 Wilkinson Hall
Corvallis, OR 97331
USA

Dr. J. R. McConnell
Desert Research Institute
Division of Hydrologic Sciences
Nevada System of Higher Education
2215 Raggio Parkway
Reno, NV 89512
USA

Logan E. Mitchell
Department of Geosciences
Oregon State University
104 Wilkinson Hall
Corvallis, OR 97331

Dr. Todd A. Sowers
Penn State University
Earth and Environment Systems Institute
Penn State University
237 Deike Building
University Park, PA 16802
USA

Dr. Kendrick Taylor
Desert Research Institute
Division of Hydrologic Sciences
Nevada System of Higher Education
2215 Raggio Parkway
Reno, NV 89512
USA

Technical Contact

Acknowledgements

This research was supported by National Science Foundation Office of Polar Programs. Methane measurements and analysis were funded by the NSF Office of Polar Programs grants 0538578, 0520523, and 0538538 as well as NASA Oregon Space Grant Consortium grant number NNG05GJ85H. Glaciochemical dating of the WDC05A and WDC06A ice cores was supported by NSF OPP grants 0538427 and 0739780 to the Desert Research Institute.

2. Detailed Data Description

This data set includes two data files in Microsoft Excel (.xlsx) format. The data set also includes eight figures from Mitchell, et. al., 2011, in Portable Document Format (pdf).

Format

Data are in Microsoft Excel (.xlsx) tab delimited format.

File and Directory Structure

Data are available on the FTP site in the ftp://sidads.colorado.edu/pub/DATASETS/AGDC/nsidc0493_mitchell_V01/ directory. Within this directory, there are two data files in Microsoft Excel (.xlsx) format, eight figure files in Portable Document Format (.pdf) and a Readme file in text (.txt) format.

File Naming Convention

Figure files are named according to their location in Mitchell, et. al., 2011. Data files are named according to the following convention and as described in Table 1.

Datatype_WDC05A.xlsx

Where:

Table 1. File Naming Convention

Variable	Description
Datatype	Methane_Concentration: Methane concentration data by ice core depth and age Chronology: Ice age data by core depth
WDC05A	WAIS Divide Ice Core 05 A
.xlsx	File extension for Microsoft Excel files.

File Size

The data files, in Microsoft Excel (.xlsx) format, are approximately 55 KB each. Figure files, in Portable Document Format (.pdf) range in size from 375 KB to 2597 KB.

Spatial Coverage

Data are from the WAIS Divide ice core WDC05A in Antarctica.

Southernmost Latitude: 79.47°S
Northernmost Latitude: 79.47°S
Westernmost Longitude: 112.09°E
Easternmost Longitude: 112.09°E

Temporal Coverage

Ice age data ranges from 1,000 to 1,800 C.E..

Temporal Resolution

Temporal resolution for the methane concentration data is nine years.

Parameter or Variable

This data set contains depth, age, and methane concentration measurements for the WDC05A ice core.

Parameter Description

Table 2. Parameter Description for Methane_Concentration_WDC05A.xlsx

Parameter	Description
Mean depth	Mean sample depth, in meters
Gas age	Gas age, in years C.E., based on the WDC05A:2 time scale described in Mitchell, et. al., 2011.
Mean Concentration	Average methane concentration for samples in parts per billiion (ppb)
Samples 1 through 4	Measured methane concentration in individual samples, in ppb

Sample Data Record

Mean depth (m)	Gas Age (Year C.E., timescale:"WDC05A:2")	Mean Concentration (ppb)	Sample 1 (ppb)	Sample 2 (ppb)	Sample 3 (ppb)	Sample 4 (ppb)
109.215	1814.2	739.3	740.0	740.3	742.7	734.1
110.490	1808.8	742.9	743.7	742.2

Note: This sample data record shows only the first two records in the data file. The file also includes rejected measurements, due to outliers, leaks, and insufficient cleaning of flasks.

Table 3. Parameter Description for Chronology_WDC05A.xlsx

Parameter	Description
Depth	Depth in meters
Ice age	Ice age, in years before 1950 C.E.

Sample Data Record

Depth (m)	Years before 1950 C.E.
0.661	-55
1.201	-54

Note: This sample data record shows only the first two records in the data file

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

The data set is a total of 14 MB.

Software and Tools

Data are accessible using Microsoft Excel spreadsheet software. Figures can be viewed using image viewing software.

Related Data Collections

• Carbon-13 Isotopic Composition of Atmospheric Methane in Firn Air, South Pole and Siple Dome, Antarctica
• Siple Dome Methane Record
• Gases in Firn Air and Shallow Ice at the WAIS Drilling Site, Antarctica

4. Data Acquisition and Processing

Theory of Measurements

This data set includes methane (CH4) concentration measurements as well as the ice age chronology from the West Antarctic Ice Sheet (WAIS) Divide ice core, WDC05A. The WDC05A ice core was a 298 m deep shallow core that was collected in the 2005 to 2006 Antarctic field season. It was drilled with a 10 cm electromechanical drill without drilling fluid and the core quality was excellent.

Methane Concentration
Samples were processed using a wet extraction technique. Methane concentration was measured using gas chromatography. Detailed methods are described in Mitchell, et. al., 2011. The mean methane concentrations have an analytical uncertainty of +/- 2.8 ppb and are reported on the NOAA04 calibration scale described in Dlugokencky et al., 2005. This data set has a temporal resolution of approximately 9 years.

Ice Chronology
Between the surface and 70 m, ice chronology was established using detailed annual layer counting of the non-sea-salt sulfur to sodium ratio (nssS/Na), as described in Banta et al., 2008. From 70 m to 298 m the chronology was established by optimizing correlations between the monthly resolved mineral acidity measurements from the main borehole (WDC06A) which is dominated by fallout from volcanic emissions and the WDC05A alternative current electric conductivity measurements (ACECM).

The uncertainty of the ice age chronology is better than +/- 1 year. The difference between the final ice chronology established in this data set, and the original ice chronology, described in Mischler et. al., 2009, is negligible between 0 and 70 m, increasing to 13 years at 148 m, and then decreasing to -36 years at 298 m.

To estimate the gas age, the researchers used a 1-D firn air diffusion model similar to Mischler et. al., 2009. The results of the firn air diffusion model indicate a delta age of 207.8 years for methane (M. Battle, personal communication, 2009). To convert the ice chronology to the gas chronology, you must subtract the delta age from the ice chronology. The estimated uncertainty of the gas chronology is +/- 10 years. Further details on the chronology are provided in Mitchell, et. al., 2011.

5. References and Related Publications

Banta, J. R., J. R. McConnell, M. M. Frey, R. C. Bales, and K. Taylor. 2008. Spatial and temporal variability in snow accumulation at the West Antarctic Ice Sheet Divide over recent centuries, J. Geophys. Res.-Atmos., 113(D23), 8.

Dlugokencky, E. J., R. C. Myers, P. M. Lang, K. A. Masarie, A. M. Crotwell, K. W. Thoning, B. D. Hall, J. W. Elkins, and L. P. Steele. 2005. Conversion of NOAA atmospheric dry air CH4 mole fractions to a gravimetrically prepared standard scale, J. Geophys. Res.-Atmos., 110(D18), 8.

Mischler, J. A., T. A. Sowers, R. B. Alley, M. Battle, J. R. McConnell, L. Mitchell, T. Popp, E. Sofen, and M. K. Spencer. 2009. Carbon and hydrogen isotopic composition of methane over the last 1000 years, Global Biogeochemical Cycles, 23, GB4024, doi:10.1029/2009GB003460.

Mitchell, L. E., E. J. Brook, T. Sowers, J. R. McConnell, and K. Taylor. 2011. Multidecadal variability of atmospheric methane, 1000-1800 C.E. Journal of Geophysical Research, Vol. 116, G02007, doi:10.1029/2010JG001441.

The following related Web sites are available :

Table 2. Related Documents

Document	Description	URL
Antarctic Glaciological Data Center (AGDC)	Data Center Web site	http://nsidc.org/agdc/
West Antarctic Ice Sheet Divide Ice Core	Project Web site	http://www.waisdivide.unh.edu/

6. Document Information

Acronyms

The following acronyms are used in this document.

Table 3. Acronyms and Abbreviations

Acronym	Description
ACECM	Alternative Current Electric Conductivity Measurements
CH4	Methane
CE	Common Era
FTP	File Transfer Protocol
NSIDC	National Snow and Ice Data Center
PPB	Parts Per Billion
URL	Uniform Resource Locator
WAIS	West Antarctic Ice Sheet
WDC05A	WAIS Divide Ice Core 05A

Document Creation Date

03 May 2011

Document URL

http://nsidc.org/data/docs/agdc/nsidc0493_mitchell/index.html