Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methane
<p>Air trapped in polar ice provides unique records of the past atmospheric composition ranging from key greenhouse gases such as methane (CH<span class="inline-formula"><sub>4</sub></span>) to short-lived trace gases like ethane (C<span class="inline-...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-05-01
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| Series: | Climate of the Past |
| Online Access: | https://cp.copernicus.org/articles/19/999/2023/cp-19-999-2023.pdf |
| _version_ | 1827943052469075968 |
|---|---|
| author | M. Mühl J. Schmitt B. Seth J. E. Lee J. S. Edwards E. J. Brook T. Blunier H. Fischer |
| author_facet | M. Mühl J. Schmitt B. Seth J. E. Lee J. S. Edwards E. J. Brook T. Blunier H. Fischer |
| author_sort | M. Mühl |
| collection | DOAJ |
| description | <p>Air trapped in polar ice provides unique records of the past
atmospheric composition ranging from key greenhouse gases such as methane
(CH<span class="inline-formula"><sub>4</sub></span>) to short-lived trace gases like ethane (C<span class="inline-formula"><sub>2</sub></span>H<span class="inline-formula"><sub>6</sub></span>) and
propane (C<span class="inline-formula"><sub>3</sub></span>H<span class="inline-formula"><sub>8</sub></span>). Recently, the comparison of CH<span class="inline-formula"><sub>4</sub></span> records
obtained using different extraction methods revealed disagreements in the
CH<span class="inline-formula"><sub>4</sub></span> concentration for the last glacial in Greenland ice. Elevated
methane levels were detected in dust-rich ice core sections measured
discretely, pointing to a process sensitive to the melt extraction technique. To shed light on the underlying mechanism, we performed targeted experiments and analyzed samples for methane and the short-chain alkanes ethane and propane covering the time interval from 12 to 42 kyr. Here, we report our findings of these elevated alkane concentrations, which scale linearly with the amount of mineral dust within the ice samples. The alkane production happens during the melt extraction step of the classic wet-extraction technique and reaches 14 to 91 ppb of CH<span class="inline-formula"><sub>4</sub></span> excess in dusty ice samples. We document for the first time a co-production of excess methane, ethane, and propane, with the observed concentrations for ethane and propane exceeding their past atmospheric background at least by a factor of 10. Independent of the produced amounts, excess alkanes were produced in a fixed molar ratio of approximately <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">14</mn><mo>:</mo><mn mathvariant="normal">2</mn><mo>:</mo><mn mathvariant="normal">1</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="42pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="21b5996f25aa1e5d07b05d6b9de8bc7e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-19-999-2023-ie00001.svg" width="42pt" height="10pt" src="cp-19-999-2023-ie00001.png"/></svg:svg></span></span>, indicating a shared origin. The measured carbon isotopic signature of excess methane is (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">47.0</mn><mo>±</mo><mn mathvariant="normal">2.9</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="58pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="c6173d5bf7057daaac0302665a05af1f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-19-999-2023-ie00002.svg" width="58pt" height="10pt" src="cp-19-999-2023-ie00002.png"/></svg:svg></span></span>) ‰ and its deuterium isotopic signature is (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">326</mn><mo>±</mo><mn mathvariant="normal">57</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="52pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="277b23ef94208fe1851cd38d246bdc8c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-19-999-2023-ie00003.svg" width="52pt" height="10pt" src="cp-19-999-2023-ie00003.png"/></svg:svg></span></span>) ‰. With the co-production ratios of excess alkanes
and the isotopic composition of excess methane we established a fingerprint
that allows us to constrain potential formation processes. This fingerprint
is not in line with a microbial origin. Moreover, an adsorption–desorption
process of thermogenic gas on dust particles transported to Greenland
does not appear very likely. Instead, the alkane pattern appears to be
indicative of abiotic decomposition of organic matter as found in soils and
plant leaves.</p> |
| first_indexed | 2024-03-13T10:09:38Z |
| format | Article |
| id | doaj.art-92dccacfa9524de9bf6bad049c223f44 |
| institution | Directory Open Access Journal |
| issn | 1814-9324 1814-9332 |
| language | English |
| last_indexed | 2024-03-13T10:09:38Z |
| publishDate | 2023-05-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Climate of the Past |
| spelling | doaj.art-92dccacfa9524de9bf6bad049c223f442023-05-22T07:37:10ZengCopernicus PublicationsClimate of the Past1814-93241814-93322023-05-0119999102510.5194/cp-19-999-2023Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methaneM. Mühl0J. Schmitt1B. Seth2J. E. Lee3J. S. Edwards4E. J. Brook5T. Blunier6H. Fischer7Climate and Environmental Physics and Oeschger Centre for Climate Change Research, University of Bern, 3012 Bern, SwitzerlandClimate and Environmental Physics and Oeschger Centre for Climate Change Research, University of Bern, 3012 Bern, SwitzerlandClimate and Environmental Physics and Oeschger Centre for Climate Change Research, University of Bern, 3012 Bern, SwitzerlandLos Alamos National Laboratory, Earth Systems Observation, Los Alamos, NM 87545, USACollege of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USACollege of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USACentre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, 2200, DenmarkClimate and Environmental Physics and Oeschger Centre for Climate Change Research, University of Bern, 3012 Bern, Switzerland<p>Air trapped in polar ice provides unique records of the past atmospheric composition ranging from key greenhouse gases such as methane (CH<span class="inline-formula"><sub>4</sub></span>) to short-lived trace gases like ethane (C<span class="inline-formula"><sub>2</sub></span>H<span class="inline-formula"><sub>6</sub></span>) and propane (C<span class="inline-formula"><sub>3</sub></span>H<span class="inline-formula"><sub>8</sub></span>). Recently, the comparison of CH<span class="inline-formula"><sub>4</sub></span> records obtained using different extraction methods revealed disagreements in the CH<span class="inline-formula"><sub>4</sub></span> concentration for the last glacial in Greenland ice. Elevated methane levels were detected in dust-rich ice core sections measured discretely, pointing to a process sensitive to the melt extraction technique. To shed light on the underlying mechanism, we performed targeted experiments and analyzed samples for methane and the short-chain alkanes ethane and propane covering the time interval from 12 to 42 kyr. Here, we report our findings of these elevated alkane concentrations, which scale linearly with the amount of mineral dust within the ice samples. The alkane production happens during the melt extraction step of the classic wet-extraction technique and reaches 14 to 91 ppb of CH<span class="inline-formula"><sub>4</sub></span> excess in dusty ice samples. We document for the first time a co-production of excess methane, ethane, and propane, with the observed concentrations for ethane and propane exceeding their past atmospheric background at least by a factor of 10. Independent of the produced amounts, excess alkanes were produced in a fixed molar ratio of approximately <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">14</mn><mo>:</mo><mn mathvariant="normal">2</mn><mo>:</mo><mn mathvariant="normal">1</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="42pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="21b5996f25aa1e5d07b05d6b9de8bc7e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-19-999-2023-ie00001.svg" width="42pt" height="10pt" src="cp-19-999-2023-ie00001.png"/></svg:svg></span></span>, indicating a shared origin. The measured carbon isotopic signature of excess methane is (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">47.0</mn><mo>±</mo><mn mathvariant="normal">2.9</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="58pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="c6173d5bf7057daaac0302665a05af1f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-19-999-2023-ie00002.svg" width="58pt" height="10pt" src="cp-19-999-2023-ie00002.png"/></svg:svg></span></span>) ‰ and its deuterium isotopic signature is (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">326</mn><mo>±</mo><mn mathvariant="normal">57</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="52pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="277b23ef94208fe1851cd38d246bdc8c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-19-999-2023-ie00003.svg" width="52pt" height="10pt" src="cp-19-999-2023-ie00003.png"/></svg:svg></span></span>) ‰. With the co-production ratios of excess alkanes and the isotopic composition of excess methane we established a fingerprint that allows us to constrain potential formation processes. This fingerprint is not in line with a microbial origin. Moreover, an adsorption–desorption process of thermogenic gas on dust particles transported to Greenland does not appear very likely. Instead, the alkane pattern appears to be indicative of abiotic decomposition of organic matter as found in soils and plant leaves.</p>https://cp.copernicus.org/articles/19/999/2023/cp-19-999-2023.pdf |
| spellingShingle | M. Mühl J. Schmitt B. Seth J. E. Lee J. S. Edwards E. J. Brook T. Blunier H. Fischer Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methane Climate of the Past |
| title | Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methane |
| title_full | Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methane |
| title_fullStr | Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methane |
| title_full_unstemmed | Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methane |
| title_short | Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methane |
| title_sort | methane ethane and propane production in greenland ice core samples and a first isotopic characterization of excess methane |
| url | https://cp.copernicus.org/articles/19/999/2023/cp-19-999-2023.pdf |
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