大约5500万年前的一个全球变暖时期（即“古新世-始新世热极大”时期或称PETM时期），被归因于温室气体水平的迅速上升，而甲烷水合物的分解是人们所提出的最常见的解释。 曾有人提出，来自陆地环境的高纬度甲烷排放可能增强了这一变暖效应，但此前一直没有直接证据证明来自湿地的甲烷流量有增加。现在，对Cobham Lignite（最近定性的英格兰东南部的一个系列的沉积物，其时间跨度经过了PETM时期）所做的一次地球化学分析提供了一定的证据。这些沉积物记录了在这一温暖时期开始时hopanoids（一种细菌生物标记物）的碳同位素含量有所下降，这与甲烷微生物数量的增加是一致的。这一结果可能是对在较温暖和较潮湿气候条件下湿地甲烷产量增加的一个反应，这种反应有可能充当了对全球变暖的一个正反馈机制。
Page: 332
原始出处：
Nature 449, 332-335 (20 September 2007) | doi:10.1038/nature06012; Received 12 December 2006; Accepted 8 June 2007
Increased terrestrial methane cycling at the Palaeocene–Eocene thermal maximum
Richard D. Pancost1, David S. Steart2, Luke Handley1, Margaret E. Collinson2, Jerry J. Hooker3, Andrew C. Scott2, Nathalie V. Grassineau2 & Ian J. Glasspool4
Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK
Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
Palaeontology Department, Natural History Museum, Cromwell Road, London SW7 5BD, UK
Department of Geology, The Field Museum, 1400 S. Lake Shore Drive, Chicago, Illinois 60605, USA
Correspondence to: Richard D. Pancost1 Correspondence and requests for materials should be addressed to R.D.P. (Email: r.d.pancost@bristol.ac.uk).
The Palaeocene–Eocene thermal maximum (PETM), a period of intense, global warming about 55 million years ago1, has been attributed to a rapid rise in greenhouse gas levels, with dissociation of methane hydrates being the most commonly invoked explanation2. It has been suggested previously that high-latitude methane emissions from terrestrial environments could have enhanced the warming effect3, 4, but direct evidence for an increased methane flux from wetlands is lacking. The Cobham Lignite, a recently characterized expanded lacustrine/mire deposit in England, spans the onset of the PETM5 and therefore provides an opportunity to examine the biogeochemical response of wetland-type ecosystems at that time. Here we report the occurrence of hopanoids, biomarkers derived from bacteria, in the mire sediments from Cobham. We measure a decrease in the carbon isotope values of the hopanoids at the onset of the PETM interval, which suggests an increase in the methanotroph population. We propose that this reflects an increase in methane production potentially driven by changes to a warmer1, 6 and wetter climate7, 8. Our data suggest that the release of methane from the terrestrial biosphere increased and possibly acted as a positive feedback mechanism to global warming.
