Clumped isotope measurements reveal aerobic oxidation of methane below the Greenland ice sheet

Getachew Agmuas Adnew; Thomas Röckmann; Thomas Blunier; Christian Juncher Jørgensen; Sarah Elise Sapper; Carina van der Veen; Malavika Sivan; Maria Elena Popa; Jesper Riis Christiansen

doi:10.1016/j.gca.2024.11.009

Clumped isotope measurements reveal aerobic oxidation of methane below the Greenland ice sheet

Getachew Agmuas Adnew^*, Thomas Röckmann, Thomas Blunier, Christian Juncher Jørgensen, Sarah Elise Sapper, Carina van der Veen, Malavika Sivan, Maria Elena Popa, Jesper Riis Christiansen

^*Corresponding author for this work

Research output: Contribution to journal › Journal article › Research › peer-review

Abstract

Clumped isotopes of methane (CH₄), specifically Δ¹³CH₃D and Δ¹²CH₂D₂, provide additional information to constrain its sources and sink processes. These isotopes complement interpretations of CH₄ provenance based on bulk isotopes. However, interpreting the origin of CH₄ using isotopes becomes challenging when the isotopic signature is altered by post-generation processes. In this study, we measured, for the first time, the bulk and clumped isotopic composition of sub-glacial CH₄ samples. These samples were collected from the air-filled headspace of the glacier portal (ice cave) at the edge of the Isunnguata Sermia glacier (ISG), located at the western margin of the Greenland ice sheet (GrIS). Our goal was to identify the processes underlying the sub-glacial production and potential processing of CH₄. The Δ¹³CH₃D and Δ¹²CH₂D₂ values of the samples measured in this study are 3.7 ± 0.3‰ and 39.7 ± 2.0‰, respectively (95% confidence interval). The Δ¹²CH₂D₂ values are close to those of atmospheric CH₄. The elevated Δ¹²CH₂D₂ values can be attributed to the alteration of the source's isotope signal by aerobic oxidation. This conclusion is supported by previous studies at this site, which reported the presence of methanotrophic bacteria and dissolved oxygen close to saturation in the meltwater. Our results confirm that the correlation between Δ¹³CH₃D and Δ¹²CH₂D₂ is a useful tool for deciphering oxidation pathways. Our results support the inference that aerobic CH₄ oxidation can strongly modify the Δ¹²CH₂D₂ isotope signal, which must be considered when determining the source signatures of environmental samples.

Original language	English
Journal	Geochimica et Cosmochimica Acta
Volume	389
Pages (from-to)	249-264
Number of pages	16
ISSN	0016-7037
DOIs	https://doi.org/10.1016/j.gca.2024.11.009
Publication status	Published - 2025

Bibliographical note

Funding Information:
This study was funded by the Danish Independent Research Fund (DFF), Grant No. 0135-00229B, \u2018MetICE\u2019. We thank Vasileios Gkinis from the Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen for measuring water samples. We gratefully acknowledge the support of Frank Keppler and Moritz Schroll from Heidelberg University during sampling. We appreciate the feedback and suggestions of the executive editor Jeffrey G. Catalano and associate editor Weifu Guo. We acknowledge the constructive feedback of Peter Douglas, Jiarui Liu and one anonymous reviewer which helped for accessibility of the manuscript for wider audience.

Publisher Copyright:
© 2024 The Authors

Keywords

Aerobic and anaerobic oxidation
Clumped isotopes
Ice sheet
Isotopes
Methane
Methanogenesis
Methanotrophy
Subglacial meltwater

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Cite this

Clumped isotope measurements reveal aerobic oxidation of methane below the Greenland ice sheet. / Adnew, Getachew Agmuas; Röckmann, Thomas; Blunier, Thomas; Jørgensen, Christian Juncher; Sapper, Sarah Elise; van der Veen, Carina; Sivan, Malavika; Popa, Maria Elena; Christiansen, Jesper Riis.

In: Geochimica et Cosmochimica Acta, Vol. 389, 2025, p. 249-264.

Research output: Contribution to journal › Journal article › Research › peer-review

Adnew, Getachew Agmuas ; Röckmann, Thomas ; Blunier, Thomas ; Jørgensen, Christian Juncher ; Sapper, Sarah Elise ; van der Veen, Carina ; Sivan, Malavika ; Popa, Maria Elena ; Christiansen, Jesper Riis. / Clumped isotope measurements reveal aerobic oxidation of methane below the Greenland ice sheet. In: Geochimica et Cosmochimica Acta. 2025 ; Vol. 389. pp. 249-264.

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title = "Clumped isotope measurements reveal aerobic oxidation of methane below the Greenland ice sheet",

abstract = "Clumped isotopes of methane (CH4), specifically Δ13CH3D and Δ12CH2D2, provide additional information to constrain its sources and sink processes. These isotopes complement interpretations of CH4 provenance based on bulk isotopes. However, interpreting the origin of CH4 using isotopes becomes challenging when the isotopic signature is altered by post-generation processes. In this study, we measured, for the first time, the bulk and clumped isotopic composition of sub-glacial CH4 samples. These samples were collected from the air-filled headspace of the glacier portal (ice cave) at the edge of the Isunnguata Sermia glacier (ISG), located at the western margin of the Greenland ice sheet (GrIS). Our goal was to identify the processes underlying the sub-glacial production and potential processing of CH4. The Δ13CH3D and Δ12CH2D2 values of the samples measured in this study are 3.7 ± 0.3‰ and 39.7 ± 2.0‰, respectively (95% confidence interval). The Δ12CH2D2 values are close to those of atmospheric CH4. The elevated Δ12CH2D2 values can be attributed to the alteration of the source's isotope signal by aerobic oxidation. This conclusion is supported by previous studies at this site, which reported the presence of methanotrophic bacteria and dissolved oxygen close to saturation in the meltwater. Our results confirm that the correlation between Δ13CH3D and Δ12CH2D2 is a useful tool for deciphering oxidation pathways. Our results support the inference that aerobic CH4 oxidation can strongly modify the Δ12CH2D2 isotope signal, which must be considered when determining the source signatures of environmental samples.",

keywords = "Aerobic and anaerobic oxidation, Clumped isotopes, Ice sheet, Isotopes, Methane, Methanogenesis, Methanotrophy, Subglacial meltwater",

author = "Adnew, {Getachew Agmuas} and Thomas R{\"o}ckmann and Thomas Blunier and J{\o}rgensen, {Christian Juncher} and Sapper, {Sarah Elise} and {van der Veen}, Carina and Malavika Sivan and Popa, {Maria Elena} and Christiansen, {Jesper Riis}",

note = "Funding Information: This study was funded by the Danish Independent Research Fund (DFF), Grant No. 0135-00229B, \u2018MetICE\u2019. We thank Vasileios Gkinis from the Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen for measuring water samples. We gratefully acknowledge the support of Frank Keppler and Moritz Schroll from Heidelberg University during sampling. We appreciate the feedback and suggestions of the executive editor Jeffrey G. Catalano and associate editor Weifu Guo. We acknowledge the constructive feedback of Peter Douglas, Jiarui Liu and one anonymous reviewer which helped for accessibility of the manuscript for wider audience. Publisher Copyright: {\textcopyright} 2024 The Authors",

year = "2025",

doi = "10.1016/j.gca.2024.11.009",

language = "English",

volume = "389",

pages = "249--264",

journal = "Geochimica et Cosmochimica Acta. Supplement",

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TY - JOUR

T1 - Clumped isotope measurements reveal aerobic oxidation of methane below the Greenland ice sheet

AU - Adnew, Getachew Agmuas

AU - Röckmann, Thomas

AU - Blunier, Thomas

AU - Jørgensen, Christian Juncher

AU - Sapper, Sarah Elise

AU - van der Veen, Carina

AU - Sivan, Malavika

AU - Popa, Maria Elena

AU - Christiansen, Jesper Riis

N1 - Funding Information: This study was funded by the Danish Independent Research Fund (DFF), Grant No. 0135-00229B, \u2018MetICE\u2019. We thank Vasileios Gkinis from the Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen for measuring water samples. We gratefully acknowledge the support of Frank Keppler and Moritz Schroll from Heidelberg University during sampling. We appreciate the feedback and suggestions of the executive editor Jeffrey G. Catalano and associate editor Weifu Guo. We acknowledge the constructive feedback of Peter Douglas, Jiarui Liu and one anonymous reviewer which helped for accessibility of the manuscript for wider audience. Publisher Copyright: © 2024 The Authors

PY - 2025

Y1 - 2025

N2 - Clumped isotopes of methane (CH4), specifically Δ13CH3D and Δ12CH2D2, provide additional information to constrain its sources and sink processes. These isotopes complement interpretations of CH4 provenance based on bulk isotopes. However, interpreting the origin of CH4 using isotopes becomes challenging when the isotopic signature is altered by post-generation processes. In this study, we measured, for the first time, the bulk and clumped isotopic composition of sub-glacial CH4 samples. These samples were collected from the air-filled headspace of the glacier portal (ice cave) at the edge of the Isunnguata Sermia glacier (ISG), located at the western margin of the Greenland ice sheet (GrIS). Our goal was to identify the processes underlying the sub-glacial production and potential processing of CH4. The Δ13CH3D and Δ12CH2D2 values of the samples measured in this study are 3.7 ± 0.3‰ and 39.7 ± 2.0‰, respectively (95% confidence interval). The Δ12CH2D2 values are close to those of atmospheric CH4. The elevated Δ12CH2D2 values can be attributed to the alteration of the source's isotope signal by aerobic oxidation. This conclusion is supported by previous studies at this site, which reported the presence of methanotrophic bacteria and dissolved oxygen close to saturation in the meltwater. Our results confirm that the correlation between Δ13CH3D and Δ12CH2D2 is a useful tool for deciphering oxidation pathways. Our results support the inference that aerobic CH4 oxidation can strongly modify the Δ12CH2D2 isotope signal, which must be considered when determining the source signatures of environmental samples.

AB - Clumped isotopes of methane (CH4), specifically Δ13CH3D and Δ12CH2D2, provide additional information to constrain its sources and sink processes. These isotopes complement interpretations of CH4 provenance based on bulk isotopes. However, interpreting the origin of CH4 using isotopes becomes challenging when the isotopic signature is altered by post-generation processes. In this study, we measured, for the first time, the bulk and clumped isotopic composition of sub-glacial CH4 samples. These samples were collected from the air-filled headspace of the glacier portal (ice cave) at the edge of the Isunnguata Sermia glacier (ISG), located at the western margin of the Greenland ice sheet (GrIS). Our goal was to identify the processes underlying the sub-glacial production and potential processing of CH4. The Δ13CH3D and Δ12CH2D2 values of the samples measured in this study are 3.7 ± 0.3‰ and 39.7 ± 2.0‰, respectively (95% confidence interval). The Δ12CH2D2 values are close to those of atmospheric CH4. The elevated Δ12CH2D2 values can be attributed to the alteration of the source's isotope signal by aerobic oxidation. This conclusion is supported by previous studies at this site, which reported the presence of methanotrophic bacteria and dissolved oxygen close to saturation in the meltwater. Our results confirm that the correlation between Δ13CH3D and Δ12CH2D2 is a useful tool for deciphering oxidation pathways. Our results support the inference that aerobic CH4 oxidation can strongly modify the Δ12CH2D2 isotope signal, which must be considered when determining the source signatures of environmental samples.

KW - Aerobic and anaerobic oxidation

KW - Clumped isotopes

KW - Ice sheet

KW - Isotopes

KW - Methane

KW - Methanogenesis

KW - Methanotrophy

KW - Subglacial meltwater

U2 - 10.1016/j.gca.2024.11.009

DO - 10.1016/j.gca.2024.11.009

M3 - Journal article

AN - SCOPUS:85211612277

VL - 389

SP - 249

EP - 264

JO - Geochimica et Cosmochimica Acta. Supplement

JF - Geochimica et Cosmochimica Acta. Supplement

SN - 0046-564X

ER -