Firn Air Inert Gas and Oxygen Observations from Siple Dome, 1996, and the South Pole, 2001

Summary

This data set includes gas ratios in polar firn air: O₂/N₂, ¹⁵N/¹⁴N, ⁴⁰Ar/N₂, ⁴⁰Ar/³⁶Ar, ⁴⁰Ar/³⁸Ar, ⁸⁴Kr/³⁶Ar, ¹³²Xe/³⁶Ar, and ²²Ne/³⁶Ar. Investigators sampled air from the permeable snowpack (firn) layer at two sites: Siple Dome, Antarctica in 1996 and at the South Pole in 2001. They observed and modeled the processes of gravitational settling, thermal fractionation, and preferential exclusion of small gas molecules from closed air bubbles. The purpose of this study was to understand these physical processes, which affect the composition of bubbles trapped in ice. By measuring these gas ratios in the ancient air preserved in bubbles trapped in ice, researchers can determine past atmospheric composition and local temperature changes along with the relative timing and magnitude of such events.

The data file is available in Microsoft Excel format. The research paper is available in PDF. Data and the research paper are available via FTP.

Citing These Data

Severinghaus, J., M. Bender, and M. Battle. 2006. Firn air inert gas and oxygen observations from Siple Dome, 1996, and the South Pole, 2001. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5FJ2DQC.

Overview Table

Category	Description
Data format	Data are available in Microsoft Excel format. The supplementary research paper provided is in PDF format.
Spatial coverage and resolution	South Pole sampling: Southernmost Latitude: 90° S Northernmost Latitude: 90° S Westernmost Longitude: 0° W Easternmost Longitude: 0° W Siple Dome sampling: Southernmost Latitude: 80.667° S Northernmost Latitude: 80.667 ° S Westernmost Longitude: 148.767° W Easternmost Longitude: 148.767° W
Temporal coverage and resolution	Data were collected at Siple Dome, Antarctica from 15 December to 21 December 1996 and at the South Pole on 21 January 2001.
Tools for accessing data	Spreadsheet software
File naming convention	Data_SeveringhausBattleEPSL-2.xls Closeoff_fractionation_EPSL-1.pdf
File size	The data file is approximately 177 KB. The supplementary research paper provided is 975 KB.
Parameters	Gas ratios in polar firn air: O2/N2, 15N/14N, 40Ar/N2, 40Ar/36Ar, 40Ar/38Ar, 84Kr/36Ar, 132Xe/36Ar, and 22Ne/36Ar
Procedures for obtaining data	Data and the research paper 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

Jeff Severinghaus
Scripps Institution of Oceanography
University of California
5900 Gilman Dr.
San Diego, CA, USA 92093-0244

Michael Bender
Department of Computer Science
State University of New York at Stony Brook
Stony Brook, NY, USA 11794-4400

Mark Battle
Department of Physics and Astronomy
Bowdoin College
8800 College Station
Brunswick, ME, USA 04011-8488

Technical Contact

Acknowledgements

This research was funded by the National Science Foundation (NSF) Office of Polar Programs (OPP) grants 9725305 and 0230452 awarded to Jeff Severinghaus and 0230260 awarded to Michael Bender.

2. Detailed Data Description

Format

Data are Microsoft Excel format.

File and Directory Structure

File Name	Approximate File Size	Description
Data_SeveringhausBattleEPSL-2.xls	177 KB	Data file in Microsoft Excel format
Closeoff_fractionation_EPSL-1.pdf	975 KB	supplementary research paper: Fractionation of gases in polar ice during bubble close-off: New constraints from firn air Ne, Kr and Xe observations

Spatial Coverage

South Pole sampling:

Southernmost Latitude: 90° S
Northernmost Latitude: 90° S
Westernmost Longitude: 0° W
Easternmost Longitude: 0° W

Siple Dome sampling:

Southernmost Latitude: 80.667° S
Northernmost Latitude: 80.667 ° S
Westernmost Longitude: 148.767° W
Easternmost Longitude: 148.767° W

Temporal Coverage

Data were collected at the Siple Dome from 15 December to 21 December 1996 and at the South Pole on 21 January 2001.

Parameter or Variable

Parameter Description

Atmospheric constituents that are nearly constant in time, such as the noble gases and the isotopes of N₂, are used to infer the local histories of climate-related processes occurring within the firn layer that overlies polar ice sheets. Investigators measured gas ratios (O₂/N₂, ¹⁵N/¹⁴N, ⁴⁰Ar/N₂, ⁴⁰Ar/³⁶Ar, ⁴⁰Ar/³⁸Ar, ⁸⁴Kr/³⁶Ar, ¹³²Xe/³⁶Ar, and ²²Ne/³⁶Ar) in polar firn air to understand the processes that alter the firn and bubble air composition. The findings have implications for ice core and firn air studies that use ratios to infer paleotemperature, chronology, and past atmospheric composition.

Sample Data Record

Data are arranged by the order in which they appear in figures in the paper (Severinghaus et al., 2006). These data are the first 10 records for Figure 7.

depth	flask ID	d15N	----"shallow hole"----			depth	model d15N
m		per mil	depth	flask ID	d15N	m	gravcorr
			m		per mil		per mil
0	sdf30	0.0009	0	sdf01	0.0241	0	0
0	sdf31	-0.0024	0	sdf02	0.0205	1	0.0553
0	sdf32	0.0019	1.55	sdf03	0.0524	2	0.11
8.18	sdf33	0.0923	1.55	sdf04	0.0406	3	0.1419
8.18	sdf34	0.0973	1.55	sdf05	0.0509	4	0.1506
8.18	sdf35	0.0755	3.42	sdf06	0.1216	5	0.1452
10.35	sdf36	0.0632	3.42	sdf07	0.1331	6	0.1336
10.35	sdf37	0.0556	5.39	sdf08	0.155	7	0.1206
12.35	sdf38	0.0511	5.39	sdf09	0.1571	8	0.1081
12.35	sdf39	0.0456	5.39	sdf10	0.1473	9	0.0954

Error Sources

See Data Acquisition Methods.

Quality Assessment

Siple Dome:

The pooled standard deviations from the mean of replicate flasks are 0.004‰, 0.003‰, and 0.007‰ for O₂/N₂, ¹⁵N/¹⁴N, and ⁴⁰Ar/N₂, respectively. The pooled standard deviations from the mean of replicate aliquots (reproducibility) are 0.004‰ and 0.009‰ for ⁴⁰Ar/³⁶Ar and ⁴⁰Ar/³⁸Ar, and 0.10‰ and 0.26‰ for ⁸⁴Kr/³⁶Ar and ¹³²Xe/³⁶Ar, respectively.

South Pole:

The pooled standard deviations of the remaining 43 points was 0.006‰ and 0.007‰ for ⁴⁰Ar/³⁶Ar and ⁴⁰Ar/³⁸Ar, and 0.09‰, 0.42‰, and 0.35‰ for ⁸⁴Kr/³⁶Ar, ¹³²Xe/³⁶Ar, and ²²Ne/³⁶Ar, respectively.

3. Data Access and Tools

Data Access

Data and the research paper are available via FTP.

Volume

The volume of the data set and the corresponding research paper is 1.12 MB.

Related Data Collections

• Firn Air Isotope and Temperature Measurements from Siple Dome and South Pole
• Siple Dome Core Data from Measurements of the d18O of Paleoatmospheric O2
• Siple Dome Ice Core Chemistry and Ion Data

4. Data Acquisition and Processing

Theory of Measurements

Noble gases and the isotopes of N₂ are atmospheric constituents that have remained constant during the 10⁶ year period spanned by ice cores. These constituents can be used to investigate climate-related processes occurring within the firn layer that overlies the polar ice sheets, such as gravitational settling, thermal fractionation, and preferential exclusion. In the process of gravitational settling, heavier gas molecules are enriched toward the bottom of a column of gas in diffusive equilibrium. In the process of thermal fractionation, a gas mixture subjected to a temperature gradient will unmix and the heavier molecules will migrate toward colder regions. Investigators focused the majority of this study on the preferential exclusion of Ne, Ar, and O₂ during bubble close-off. The fact that Ar is heavier than N₂ and O₂, yet has intermediate depletion, argues against a mass-dependent fractionation process, but is consistent with the ordering of molecular sizes.

Data Acquisition Methods

Investigators drilled a borehole to the desired depth, inserted a 4 m long natural rubber packer, and inflated the packer to form a seal in the hole. They pumped air from the approximately 10 cm-high space below the packer from two openings separated by a horizontal stainless steel baffle nearly as wide as the borehole. They pumped the upper opening to waste at a flow rate of a 10 L * min^-1 eliminating any air that had leaked out of or around the packer. They flushed the lines for at least 10 minutes before sampling. From the lower opening, investigators took the sample at a rate of 2 L * min^-1 assuming that because the sample was below the baffle it should not have come in contact with the packer. They passed each sample through a P₂O₅ desiccant and stored them in 2 L flow-through glass flasks sealed with Louwers-Hapert valves and viton o-rings. They filled additional flasks after pumping approximately 1000 L of air from the firn at several depths to look for changes in composition during the course of sampling, but they observed no changes.

Investigators analyzed flasks from Siple Dome on a Finnigan MAT 251 mass spectrometer at the University of Rhode Island. They set the instrument to dual-collector mode for O₂/N₂, ¹⁵N/¹⁴N and ¹⁸O of O₂ as described in Bender et al. They analyzed the South Pole flasks on a Finnigan Delta Plus XL mass spectrometer at Princeton. They ran samples in triplicate at least for O₂/N₂, ¹⁵N/¹⁴N, and ⁴⁰Ar/N₂ as described by Bender et al. They measured the samples against a dry air standard and reported them against samples of surface air.

Investigators analyzed subsets of the Siple Dome flasks (n=13 out of 45 total) and South Pole flasks (n=20 out of 54 total) for noble gases. They selected the subset arbitrarily but voided flasks with anomalous ¹⁵N/¹⁴N. They ran the noble gases on a Finnigan MAT 252 mass spectrometer at Scripps Institution of Oceanography (SIO) for ⁴⁰Ar/³⁶Ar and ⁴⁰Ar/³⁸Ar in dual-collector mode. ⁸⁴Kr/³⁶Ar and ¹³²Xe/³⁶Ar were measured by peak-jumping with mass spectrometry as described by Severinghaus et al. Samples were prepared by exposing 40 cc standard temperature and pressure (STP) to a Zr/Al getter at 900°C for 10 minutes to destroy all the reactive gases, followed by 2 minutes at 300°C to remove H₂. This process left approximately 0.4 cc STP of residual noble gas (primarily Ar). Investigators then concentrated the residual into a vessel cryogenically at 4 K and admitted the sample into the mass spectrometer after allowing the vessel contents to mix internally for 45 minutes at room temperature, which insured homogeneity. They analyzed the South Pole flasks for ²²Ne/³⁶Ar by peak-jumping. Investigators ran the samples against aliquots of a standard gas mixture of commercially obtained Ne, Ar, Kr, and Xe. They monitored the mass/charge 44 beam to assure insignificant isobaric interference with ²²Ne from doubly charged CO₂. There is no data for Ne and the samples have been consumed.

Investigators ran the 13 Siple Dome flasks in duplicate (9 flasks) or triplicate (4 flasks) aliquots. They ran one flask a third time because of a gross procedural error and the results from the affected aliquot were rejected. The remaining flasks were run a third time because of poor reproducibility in the first two aliquots' results. From these, investigators rejected one ¹³²Xe/³⁶Ar measurement (from 30.55 m depth) on the basis of poor agreement with the other two measurements.

Investigators initially ran the South Pole flasks in duplicate but rejected and re-ran 8 aliquots because they discovered that the sample pressure was inadequate due to low pressures in the flasks. They rejected and re-ran one aliquot due to the presence of O₂ and N₂, which indicates a leak. The remaining data set consists of 17 flasks run in duplicate and 3 flasks run in triplicate. Investigators re-ran the latter 3 flasks a third time because of poor agreement between replicates; however, they rejected none.

Derivation Techniques and Algorithms

Investigators built a model describing the close-off of bubbles, the diffusion of gases within the firn and exchange with the atmosphere, and the evolution of temperature and gas composition in the open pores and bubbles in time and space as described in Severinghaus et al. (2006).

5. References and Related Publications

Bender, M. L., T. Sowers, J. -M. Barnola, and J. Chappellaz. 1994. Changes in the O2/N2 ratio of the atmosphere during recent decades reflected in the composition of air in the firn at Vostok Station, Antarctica. Geophysical Research Letters 21 189–192.

Bender, M. L., P. P. Tans, J. T. Ellis, J. Orchardo, and K. Habfast. 1994. A high-precision isotope ratio mass-spectrometry method for measuring the O2/N2 ratio of air. Geochimica et Cosmochimica Acta 58 4751–4758.

Bender, M. L., D. T. Ho, M. B. Hendricks, R. Mika, M. O. Battle, P. P. Tans, T. J. Conway, B. Sturtevant, and N. Cassar. 2005. Atmospheric O2/ N2 changes, 1993–2002: implications for the partitioning of fossil fuel CO2 sequestration. Global Biogeochemical Cycles 19 GB4017.

Severinghaus, J. P., A. Grachev, B. Luz, and N. Caillon. 2003. A method for precise measurement of argon 40/36 and krypton/argon ratios in trapped air in polar ice with applications to past firn thickness and abrupt climate change in Greenland and at Siple Dome, Antarctica. Geochimica et Cosmochimica Acta 67 325–343.

Severinghaus, J. P., and M. O. Battle. 2006. Fractionation of gases in polar ice during bubble close-off: new constraints from firn air Ne, Kr and Xe observations. Earth and Planetary Science Letters EPSL-08011.

6. Document Information

Acronyms and Abbreviations

The following acronyms and abbreviations are used in this document:

FTP	File Transfer Protocol
NSF	National Science Foundation
NSIDC	National Snow and Ice Data Center
OPP	Office of Polar Programs
PDF	Portable Document Format
SIO	Scripps Institution of Oceanography
STP	Standard temperature and pressure
URL	Uniform Resource Locator

Document Creation Date

August 2006

Document URL

http://nsidc.org/data/docs/agdc/nsidc0290_severinghaus/index.html