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Variability in aerobic methane oxidation over the past 1.2 Myrs recorded in microbial biomarker signatures from Congo fan sediments

Lookup NU author(s): Dr Helen Talbot, Dr Luke Handley, Charlotte Spencer-Jones, Dr Rob Spencer, Professor Thomas Wagner

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

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.


Publication metadata

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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