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Data Set ID:
NSIDC-0290

Firn Air Inert Gas and Oxygen Observations from Siple Dome, 1996, and the South Pole, 2001, Version 1

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.

Geographic Coverage

Spatial Coverage:
  • N: -90, S: -90, E: 0, W: 0

  • N: -80.667, S: -80.667, E: -148.767, W: -148.767

Spatial Resolution: Not Specified
Temporal Coverage:
  • 15 December 1996 to 21 December 1996
  • 21 January 2001
Temporal Resolution: Not specified
Parameter(s):
  • Glaciers/Ice Sheets > Firn
  • Ice Core Records > Ice Core Air Bubbles
  • Glaciers/Ice Sheets > Ice Sheets
  • Sea Ice > Isotopes
  • Snow/Ice
  • Snow/Ice > Snow/Ice Chemistry
Platform(s) GROUND-BASED OBSERVATIONS
Sensor(s): CORING DEVICES, FLASKS, MASS SPECTROMETERS
Data Format(s):
  • Microsoft Excel
  • PDF
Version: V1
Data Contributor(s): Jeffrey Severinghaus, Mark Battle, Michael Bender

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.

Severinghaus, J. P., M. Bender, and M. Battle. 2006. Firn Air Inert Gas and Oxygen Observations from Siple Dome, 1996, and the South Pole, 2001, Version 1. [Indicate subset used]. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: http://dx.doi.org/10.7265/N5FJ2DQC. [Date Accessed].

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Detailed Data Description

Format

Data are Microsoft Excel format.

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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
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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

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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.

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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/N215N/14N, 40Ar/N240Ar/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

Figure7:  Siple Dome 15N/14N provile

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Error Sources
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Quality Assessment

Siple Dome

The pooled standard deviations from the mean of replicate flasks are 0.004‰, 0.003‰, and 0.007‰ for O2/N215N/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.

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Software and Tools

Volume

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

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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.

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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/N215N/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/N215N/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.

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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).

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References and Related Publications

Contacts and Acknowledgments

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

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.

Document Information

Document Creation Date

August 2006

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