A study of carbon-14 of paleoatmospheric methane for the last glacial termination from ancient glacial ice
Ice core records from Greenland and Antarctica reveal large and rapid variations in atmospheric methane concentrations ([CH₄]) in response to abrupt climate change. Two such events occurred at the Oldest Dryas (OD) - Bølling and Younger Dryas (YD) - Preboreal (PB) climatic transitions during the las...
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ftcdlib:oai:escholarship.org/ark:/13030/qt4zd4n5f8 2023-05-15T13:58:20+02:00 A study of carbon-14 of paleoatmospheric methane for the last glacial termination from ancient glacial ice Petrenko, Vasilii Victorovich 2008-01-01 application/pdf https://escholarship.org/uc/item/4zd4n5f8 unknown eScholarship, University of California qt4zd4n5f8 https://escholarship.org/uc/item/4zd4n5f8 public UCSD Earth sciences. (Discipline) Dissertations Academic etd 2008 ftcdlib 2020-06-06T07:56:21Z Ice core records from Greenland and Antarctica reveal large and rapid variations in atmospheric methane concentrations ([CH₄]) in response to abrupt climate change. Two such events occurred at the Oldest Dryas (OD) - Bølling and Younger Dryas (YD) - Preboreal (PB) climatic transitions during the last glacial termination. A record of ¹⁴C of atmospheric CH₄ (¹⁴CH₄) through these transitions can help to identify the sources of the [CH4] increases and constrain the fossil fraction of paleo CH₄ budgets. Very large (1̃00 L STP) samples of paleoatmospheric air are needed for such ¹⁴CH₄ measurements. To obtain these samples, ancient ice outcropping at an ice-margin ablation site in West Greenland was explored. Ice sections dating to the last glacial termination were identified and found to contain high-quality gas records. A new method for large-scale air extraction from glacial ice was developed and twelve large air samples from the YD-PB and the OD-Bølling transitions were obtained. New methods were also developed for processing this air for ¹⁴CH₄. ¹⁴CH₄ procedural blanks were greatly reduced through the construction of a new CH₄ conversion line utilizing platinized quartz wool for CH₄ combustion and the use of an ultra high purity iron catalyst for graphitization. The overall ¹⁴CH₄ processing blank was 0.75 ± 0.38 pMC. Measured ¹⁴CH₄ values were too high by 14 - 38% as compared to the highest expected values based on paleoatmospheric ¹⁴CO₂. In-situ production of CH₄ and direct cosmogenic production of ¹⁴CH₄ molecules in ablating ice were identified as the two most likely mechanisms that elevated ¹⁴CH₄ . Sample ¹⁴CH₄ was then corrected for both mechanisms, however these corrections are speculative and do not allow any definite conclusions to be drawn from the results. Corrected ¹⁴CH₄ results suggest that there was a 7% increase in the fossil CH₄ fraction from the YD to the PB. The corrected ¹⁴CH₄ results also suggest no large changes in the fossil fraction between the OD and the YD. Finally, the corrected results suggest that up to 80% of the OD - Bølling [CH₄]- rise (1̃00 ppb) was due to ¹⁴C -free CH₄ Other/Unknown Material Antarc* Antarctica Greenland ice core University of California: eScholarship Greenland |
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Open Polar |
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University of California: eScholarship |
op_collection_id |
ftcdlib |
language |
unknown |
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UCSD Earth sciences. (Discipline) Dissertations Academic |
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UCSD Earth sciences. (Discipline) Dissertations Academic Petrenko, Vasilii Victorovich A study of carbon-14 of paleoatmospheric methane for the last glacial termination from ancient glacial ice |
topic_facet |
UCSD Earth sciences. (Discipline) Dissertations Academic |
description |
Ice core records from Greenland and Antarctica reveal large and rapid variations in atmospheric methane concentrations ([CH₄]) in response to abrupt climate change. Two such events occurred at the Oldest Dryas (OD) - Bølling and Younger Dryas (YD) - Preboreal (PB) climatic transitions during the last glacial termination. A record of ¹⁴C of atmospheric CH₄ (¹⁴CH₄) through these transitions can help to identify the sources of the [CH4] increases and constrain the fossil fraction of paleo CH₄ budgets. Very large (1̃00 L STP) samples of paleoatmospheric air are needed for such ¹⁴CH₄ measurements. To obtain these samples, ancient ice outcropping at an ice-margin ablation site in West Greenland was explored. Ice sections dating to the last glacial termination were identified and found to contain high-quality gas records. A new method for large-scale air extraction from glacial ice was developed and twelve large air samples from the YD-PB and the OD-Bølling transitions were obtained. New methods were also developed for processing this air for ¹⁴CH₄. ¹⁴CH₄ procedural blanks were greatly reduced through the construction of a new CH₄ conversion line utilizing platinized quartz wool for CH₄ combustion and the use of an ultra high purity iron catalyst for graphitization. The overall ¹⁴CH₄ processing blank was 0.75 ± 0.38 pMC. Measured ¹⁴CH₄ values were too high by 14 - 38% as compared to the highest expected values based on paleoatmospheric ¹⁴CO₂. In-situ production of CH₄ and direct cosmogenic production of ¹⁴CH₄ molecules in ablating ice were identified as the two most likely mechanisms that elevated ¹⁴CH₄ . Sample ¹⁴CH₄ was then corrected for both mechanisms, however these corrections are speculative and do not allow any definite conclusions to be drawn from the results. Corrected ¹⁴CH₄ results suggest that there was a 7% increase in the fossil CH₄ fraction from the YD to the PB. The corrected ¹⁴CH₄ results also suggest no large changes in the fossil fraction between the OD and the YD. Finally, the corrected results suggest that up to 80% of the OD - Bølling [CH₄]- rise (1̃00 ppb) was due to ¹⁴C -free CH₄ |
format |
Other/Unknown Material |
author |
Petrenko, Vasilii Victorovich |
author_facet |
Petrenko, Vasilii Victorovich |
author_sort |
Petrenko, Vasilii Victorovich |
title |
A study of carbon-14 of paleoatmospheric methane for the last glacial termination from ancient glacial ice |
title_short |
A study of carbon-14 of paleoatmospheric methane for the last glacial termination from ancient glacial ice |
title_full |
A study of carbon-14 of paleoatmospheric methane for the last glacial termination from ancient glacial ice |
title_fullStr |
A study of carbon-14 of paleoatmospheric methane for the last glacial termination from ancient glacial ice |
title_full_unstemmed |
A study of carbon-14 of paleoatmospheric methane for the last glacial termination from ancient glacial ice |
title_sort |
study of carbon-14 of paleoatmospheric methane for the last glacial termination from ancient glacial ice |
publisher |
eScholarship, University of California |
publishDate |
2008 |
url |
https://escholarship.org/uc/item/4zd4n5f8 |
geographic |
Greenland |
geographic_facet |
Greenland |
genre |
Antarc* Antarctica Greenland ice core |
genre_facet |
Antarc* Antarctica Greenland ice core |
op_relation |
qt4zd4n5f8 https://escholarship.org/uc/item/4zd4n5f8 |
op_rights |
public |
_version_ |
1766266573483409408 |