The atmospheric methane (CH 4) burden is rising sharply, but the causes are still not well understood. One factor of uncertainty is the importance of tropical CH 4 emissions into the global mix. Isotopic signatures of major sources remain poorly constrained, despite their usefulness in constraining the global methane budget. Here, a collection of new δ 13 C CH 4 signatures is presented for a range of tropical wetlands and rice fields determined from air samples collected during campaigns from 2016 to 2020. Long-term monitoring of δ 13 C CH 4 in ambient air has been conducted at the Chacaltaya observatory, Bolivia and Southern Botswana. Both long-term records are dominated by biogenic CH 4 sources, with isotopic signatures expected from wetland sources. From the longer-term Bolivian record, a seasonal isotopic shift is observed corresponding to wetland extent suggesting that there is input of relatively isotopically light CH 4 to the atmosphere during periods of reduced wetland extent. This new data expands the geographical extent and range of measurements of tropical wetland and rice δ 13 C CH 4 sources and hints at significant seasonal variation in tropical wetland δ 13 C CH 4 signatures which may be important to capture in future global and regional models. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 2)'.
|Journal||Philosophical transactions. Series A, Mathematical, physical, and engineering sciences|
|State||Published - 2022|
Bibliographical noteFunding Information:
We thank the UK Natural Environment Research Council for Grants to EGN: NE/N016238/1 MOYA. The Global Methane Budget 2016–2020, NE/S00159X/1 ZWAMPS Quantifying methane emissions in remote tropical settings: a new 3D approach. NE/P019641/1, New methodologies for removal of methane from the atmosphere, NE/M005836/1 Methane at the edge: jointly developing state-of-the-art high-precision methods to understand atmospheric methane emissions and NE/K006045/1 Investigation of the Southern Methane Anomaly: causes, implications and relevance to past global events. The Vietnam sampling was carried out under the NERC Newton Fund project for DO ‘A Two City study of Air Quality in Vietnam’ (NE/P014771/1). Acknowledgements
We thank Ambassador Ross Denny for initial Seedcorn support and funding. We are very grateful to the Air Crew of the British Antarctic Survey who supported the Bolivian campaign, and Dan Beeden in securing all necessary flight permissions. We would like to thank Airtask Ltd, especially Mo Smith and David Simpson and all those involved in the operation and maintenance of the BAe-146-301 Atmospheric Research Aircraft including FAAM, UK Research and Innovation (UKRI) and the University of Leeds. Stephen Andrews and Stuart Young in York, who developed and tested the new sWAS system for the FAAM aircraft. Mark Stephens is very grateful to the University of Botswana (UB) for a research grant that funded transport, accommodation and field assistants to sample methane in Botswana. He is also thankful to the Department of Environmental Science at UB for the generous use of the departmental vehicle for the fieldwork. Kentsenao Tlalang and Innocent Ndaba (both UB) are thanked for their assistance in the field. We would also like to thank the camp owners at Ikoga for facilitating the visit and to the guides there for their help in the field. We thank Duong Huu Huy and Nguyen Doan Thien Chi for help with sample collection in Vietnam. We thank Prof. Gray Williams, Cecily Law and the staff of the Swire Institute for Marine Science at the University of Hong Kong for their very generous help and support, and Alan Wong and the Yi O rice growers and Martin Williams for their kind hospitality and collaboration. Zambian field work was in partnership with the Geological Survey of Zambia, whose generous help is much appreciated. In Uganda, we thank Solomon Mangeni and the Uganda National Meteorological Authority.
© 2021 The Authors.
- greenhouse gas
- tropical wetlands