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Lookup NU author(s): Dr Helen Talbot, Dr Luke Handley, Charlotte Spencer-Jones, Dr Rob Spencer, Professor Thomas Wagner
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
Methane (CH4) is a strong greenhouse gas known to have perturbed global climate in the past, especially when released in large quantities over short time periods from continental or marine sources. It is therefore crucial to understand and, if possible, quantify the individual and combined response of these variable methane sources to natural climate variability. However, past changes in the stability of greenhouse gas reservoirs remain uncertain and poorly constrained by geological evidence. Here, we present a record from the Congo fan of a highly specific bacteriohopanepolyol (BHP) biomarker for aerobic methane oxidation (AMO), 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol), that identifies discrete periods of increased AMO as far back as 1.2 Ma. Fluctuations in the concentration of aminopentol, and other 35-aminoBHPs, follow a pattern that correlates with late Quaternary glacial-interglacial climate cycles, with highest concentrations during warm periods. We discuss possible sources of aminopentol, and the methane consumed by the precursor methanotrophs, within the context of the Congo River setting, including supply of methane oxidation markers from terrestrial watersheds and/or marine sources (gas hydrate and/or deep subsurface gas reservoir). Compound-specific carbon isotope values of -30 ‰ to -40 ‰ for BHPs in ODP 1075 and strong similarities between the BHP signature of the core and surface sediments from the Congo estuary and floodplain wetlands from the interior of the Congo River Basin, support a methanotrophic and likely terrigenous origin of the 35-aminoBHPs found in the fan sediments. This new evidence supports a causal connection between marine sediment BHP records of tropical deep sea fans and wetland settings in the feeding river catchments, and thus tropical continental hydrology. Further research is needed to better constrain the different sources and pathways of methane emission. However, this study identifies the large potential of aminoBHPs, in particular aminopentol, to trace and, once better calibrated and understood, quantify past methane sources and fluxes from terrestrial and potentially also marine sources.
Author(s): Talbot HM, Handley L, Spencer-Jones CL, Dinga B, Schefuss E, Mann PJ, Poulsen JR, Spencer RGM, Wabakanghanzi JN, Wagner T
Publication type: Article
Publication status: Published
Journal: Geochimica et Cosmochimica Acta
Year: 2014
Volume: 133
Pages: 387-401
Print publication date: 15/05/2014
Online publication date: 11/03/2014
Acceptance date: 24/02/2014
Date deposited: 16/04/2014
ISSN (print): 0016-7037
ISSN (electronic): 1872-9533
Publisher: Pergamon
URL: http://dx.doi.org/10.1016/j.gca.2014.02.035
DOI: 10.1016/j.gca.2014.02.035
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