大約5500萬年前的一個全球變暖時期（即“古新世-始新世熱極大”時期或稱PETM時期），被歸因于溫室氣體水平的迅速上升,，而甲烷水合物的分解是人們所提出的最常見的解釋,。 曾有人提出，來自陸地環(huán)境的高緯度甲烷排放可能增強了這一變暖效應(yīng)，但此前一直沒有直接證據(jù)證明來自濕地的甲烷流量有增加?，F(xiàn)在,，對Cobham Lignite（最近定性的英格蘭東南部的一個系列的沉積物，其時間跨度經(jīng)過了PETM時期）所做的一次地球化學(xué)分析提供了一定的證據(jù),。這些沉積物記錄了在這一溫暖時期開始時hopanoids（一種細菌生物標(biāo)記物）的碳同位素含量有所下降,，這與甲烷微生物數(shù)量的增加是一致的。這一結(jié)果可能是對在較溫暖和較潮濕氣候條件下濕地甲烷產(chǎn)量增加的一個反應(yīng),，這種反應(yīng)有可能充當(dāng)了對全球變暖的一個正反饋機制,。
Page: 332
原始出處：
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: [email protected]).
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.
