Data Set ID:
NSIDC-0598

Methyl Bromide Measurements in the Taylor Dome M3C1 Ice Core, Version 1

The data set includes methyl bromide (CH3Br) measurements made on air extracted from 70 samples from the Taylor Dome M3C1 ice core. CH3Br was measured in air from the Taylor Dome ice core to reconstruct an atmospheric record for the Holocene (11-0 kyr B.P.) and part of the last glacial period (50-30 kyr B.P.).

NSIDC does not archive these data.

Parameter(s):
  • Aerosols > Aerosol Optical Depth/Thickness > Depth
  • Atmospheric Chemistry > Halocarbons and Halogens > Methyl Bromide > METHYL BROMIDE
Data Format(s):
  • Excel
Spatial Coverage:
N: -77.44, 
S: -77.44, 
E: 157.4, 
W: 157.4
Platform(s):LABORATORY
Spatial Resolution:Not SpecifiedSensor(s):GAS CHROMATOGRAPHS, MASS SPECTROMETERS
Temporal Coverage:
  • 1 January 2008 to 31 December 2012
Version(s):V1
Temporal ResolutionNot specifiedMetadata XML:View Metadata Record
Data Contributor(s):Eric Saltzman, Murat Aydin

Geographic Coverage

Please contact the data provider for the correct Data Citation for this data set.

Literature Citation

As a condition of using these data, we request that you acknowledge the author(s) of this data set by referencing the following peer-reviewed publication.

  • Aydin, M., M. Williams, and E. Saltzman. 2007. Feasibility of reconstructing paleoatmospheric records of selected alkanes, methyl halides, and sulfur gases from Greenland ice cores, J. Geophys. Res. 112. D07312. https://doi.org/10.1029/2006JD008027

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Detailed Data Description

The data set includes methyl bromide (CH3Br) measurements made on air extracted from 70 samples from the Taylor Dome M3C1 ice core. CH3Br was measured in air from the Taylor Dome ice core to reconstruct an atmospheric record for the Holocene (11-0 kyr B.P.) and part of the last glacial period (50-30 kyr B.P.) in order to examine the behavior of these trace gases over longer time scales and a wider range of climatic conditions. The ice core samples were about 15 cm long on average. The depths represent the mid-depth for each sample. Methyl chloride levels are reported as dry-air molar mixing-ratios.

Format

Data are provided in Microsoft Excel (.xls) format.

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File and Directory Structure

Data are available on the FTP site in the ftp://sidads.colorado.edu/pub/DATASETS/AGDC/nsidc0598_saltzman/ directory. Within this directory, there is one Microsoft Excel file: UCI methyl bromide.xls.

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File Size

20 KB

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Spatial Coverage

Taylor Dome, East Antarctica: 77.40° S, 157.40° E

Spatial Resolution

105.0 meters to 467.6 meters

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Temporal Coverage

Data were collected from January 2008 to December 2012.

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Parameter or Variable

Depth (m)
Methyl Bromide (CH3Br) in parts per trillion (ppt)

Sample Data Record

Figure 1 is sample data from the UCI methyl bromide.xls data file.

sample data

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Software and Tools

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Data Acquisition and Processing

Data Acquisition Methods

The air is liberated from the ice core samples using a dry-extraction technique in which ice is mechanically shredded under vacuum (Etheridge et al. 1988Sowers and Jubenville 2000). The extraction chamber is a cylindrical electropolished stainless steel tube, which is 14.5 cm in diameter and 20 cm in length. The chamber ends are conflat flanges sealed by copper gaskets, and a bellows valve is welded to the flange on one end for transferring gas. A flat stainless steel grater is mounted lengthwise in the chamber. Since dry-extraction requires that the samples stay frozen during extraction, the chamber is mounted inside a chest freezer and connected to a motorized piston providing a linear motion of 13 cm at 1 Hz. When not in motion, the extraction chamber is connected to a stainless steel vacuum line via a flexible stainless steel bellows. All valves on the vacuum line are stainless steel bellows valves with alloy or copper valve tips (Aydin 2007).

In preparation for the extraction, the ice core sample and the extraction chamber are precooled to -40 or -50°C. We found that the extraction process worked successfully at either temperature for the gases presented here. The outer 2-3 mm are shaved off, and the sample is placed on the grater inside the chamber. After loading the sample, the chamber is pumped down to 10-2 torr and repeatedly flushed with clean N2 to remove residual air. The chamber is then disconnected from the vacuum line, and the motorized piston is operated for 15 minutes. The ice core shreds as it slides back and forth over the grater, liberating 70-80 percent of the air trapped in the sample. The GISP2 samples were 300-600 g, yielding 30-60 cm3 Standard Temperature and Pressure (STP) of air. After extraction, the chamber is reconnected to the vacuum line, and the air is condensed into a 76-cm long, 1/4'' Outside Diameter (OD) stainless steel tube immersed in liquid helium. It takes about 4 minutes to cryogenically pump >95 percent of the sample into the tube. The analysis of the extracted air starts 10 minutes after recovery (Aydin 2007).

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Data Processing Methods

The air extracted from the ice cores is analyzed using Gas Chromatography (GC) with mass spectrometric detection (HP 5890/Micromass Autospec Ultima). The sample is cryogenically focused on a 1/8'' OD glass bead trap immersed in liquid nitrogen. The size of the sample is determined by measuring the pressure change on a calibrated volume downstream of the cryotrap. An aliquot of isotope-labeled gas standard (30 cm3 STP) is added to the cryotrap to provide an internal reference for quantitation. The mixture of condensable gases from the sample and the internal standard are then transferred in a helium stream to a fused silica loop in liquid nitrogen and thermally injected onto the GC column. The GC oven is programmed to stay isothermal at -50°C for 3 minutes, ramp to -40°C at 5°C/minute, followed by a 15°C/minute ramp to 30°C and a 30°C/minute ramp to 120°C (Aydin 2007).

The mass spectrometer is operated in selected ion mode at a mass resolution of 6000 (M/DM at 5 percent), using ion fragments of deuterium (D-) labeled dodecane as the lock masses. At this mass resolution, halocarbons are fully resolved from hydrocarbons at the same mass to charge ratio [Engen et al. 1998, 1999]. D-labeled dodecane is used because its ion fragments do not interfere with fragments from undeuterated atmospheric hydrocarbons, from 13C-labeled hydrocarbons used as internal standards, or from halocarbons (Aydin 2007).

The primary standards used for the calibration of the system are prepared at University of California, Irvine (UCI), in Aculife-treated aluminum cylinders (Scott Specialty Gases) pressurized with dry N2. Each standard cylinder contains a parts per billion (ppb)- level mixture of all the unlabeled trace gases, which are added into the cylinders by volumetric injection of commercially purchased pure compounds. One exception is CS2. Since pure CS2 is in liquid phase at laboratory temperature and pressure, it is prediluted to parts per thousand levels in a separate aluminum cylinder, which is used in the preparation of the ppb-level standards. Currently, there are three of these primary standards that were prepared in 2003, 2004, and 2005 calendar years. All three cylinders are used to calibrate a fourth standard cylinder, prepared at ppb-level in the same manner as the primary standards but containing the isotope-labeled analogues of the same trace gases. The isotope-labeled gas standard contains 13C-labeled C2H6, C3H8, n-C4H10, OCS, and CS2 as well as fully deuterated CH3Cl and CH3Br. CFC-12 is also measured but not calibrated by isotope dilution. The stability of the trace gases in the pressurized cylinders is monitored by cross calibrating the standard tanks twice a year (Aydin 2007).

System calibration and routine analyses with isotope dilution are carried out, using parts per trillion (ppt)- level working standards. Both the unlabeled and labeled working standards are prepared at near ambient levels by diluting the ppb-level primary standards with humid N2 in electropolished stainless steel flasks. New working standards are prepared every 3-4 weeks to avoid compromising their stability in the flasks. The use of isotope-labeled internal standards compensates for drift in the mass spectrometer response and run-to-run variations in chromatographic peak shape (Aydin 2007).

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References and Related Publications

Contacts and Acknowledgments

Eric S. Saltzman
University of California, Irvine
Deptartment of Earth System Science
Croul Hall 1212
Irvine, CA 92697

Murat Aydin
University of California, Irvine
Deptartment of Earth System Science
Croul Hall 1212
Irvine, CA 92697

Acknowledgments: 

This research was supported by NSF Division of Polar Programs (PLR) Grant Number 0636953.

Document Information

Document Creation Date

September 2014

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