Lookup NU author(s): Dr Luke Handley,
Dr Helen Talbot,
Dr Martin Cooke,
Professor Thomas Wagner
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The Congo and Amazon Fan are regions of important methane (CH4) storage and gas seepage: gas hydrates abound at and just below the sediment surfaces as do large deeply-buried reservoirs of thermogenic methane linked with hydrocarbon source rocks. Although the steady methane seepage from the seafloor is well-documented in the present day, paleo-emissions from such regions remain unquantified due to the lack of an adequate tracer for reconstructing past methane emission and oxidation events. Here, we present paleo-records spanning up to 200 ka and 1,200 ka for the Amazon (ODP Site 942A) and Congo (ODP Site 1075A), respectively. We use the novel biomarker 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol), specific to aerobic methane oxidising bacteria, and related bacteriohopanepolyols (BHPs) to estimate past intervals of intense methane oxidation in the water column over glacial/interglacial transitions to compare and contrast oxidation histories at these two sites situated on opoiste sides of the Atlantic. These records are further compared to other recontructed climatic parameters. In the Congo core, methane oxidation intensity, and inferred emission, follows a distinct cyclical pattern that appears to correale with marine oxygen isotope stages over the last ca. 1 Ma. The cylclicity of these events and compound-specific carbon isotope data suggest that hydrates are the principal methane source, suggesting that intervals characterised by high aminopentol concentrations reflect periods of increased hydrate destabilisation with greater methane emission occurring during interglacials. Investigation of the Amazon core also reveals dramatic variaibility in aminopentol concentrations, possibly also linked to orbital cyclicity and the destabilisation of hydrates, although ongoing investigation will allow the testing of this hypthesis and a direct comparison between the two sites. This work highlights the uitlity of aminopentol as a potential sedimentary tracer for past methane emission events from hydrates.
Author(s): Handley L, Talbot HM, Cooke MP, Anderson K, Wagner T
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Published
Conference Name: Geochimica et Cosmochimica Acta: Conference on Goldschmidt, Earth, Energy, and the Environment
Year of Conference: 2010
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