Blog: Quantifying Aerobic Methane Oxidation in the Ocean

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By Angela Sherry. 7th June 2011.

AMOprox Quantifying aerobic methane oxidation in the ocean: Calibration and palaeo application of a novel proxy
Supervised by Dr Helen Talbot in the School of Civil Engineering and Geosciences @ Newcastle University we are an inter-disciplinary team of scientists consisting of analytical chemists, bio-geochemists and molecular microbiologists who have come together to study aerobic methane oxidation in the ocean. Read on to find out a little more about our ERC-funded project.
Methane is a key greenhouse gas and its release to the atmosphere is altered by microbes by two different pathways; an aerobic and an anaerobic pathway. Research on the marine methane cycle has largely focussed on the anaerobic pathway, but recent biomarker data has provided convincing evidence that aerobic methane oxidation (AMO) may play a much more significant role in reducing the amount of methane emitted from sediments than previously considered. Aerobic methane oxidation in these settings is poorly understood and a more complete understanding of present and past methane fluxes requires novel proxies that can be applied to present day samples and subsequently linked to the sedimentary record. This study fills this gap by targeting bacterial lipids, which are made by aerobic methanotrophs (methane oxidising bacteria), known as aminobacteriohopanepolyols (BHPs).  Recently BHPs have been identified in a wide range of modern and recent environments including a continuous record from the Congo deep sea fan spanning the last 1.2 million years.
The way in which BHPs are regulated and expressed within methanotrophs will be investigated and calibrated against environmental variables including temperature, pH, salinity and, most importantly, methane concentrations and fluxes to identify markers that correlate BHP concentration and composition with environmental conditions. These will then be used to evaluate palaeo-environmental conditions in relation to methane cycling in the sedimentary record.
This 5-year study has three complementary strands:
(1) The microbiologists and analytical chemists will work in unison to analyse BHPs systematically in pure cultures of methanotrophs and sediment microcosm experiments providing an approximation to natural conditions
(2) We will calibrate BHP signatures in natural marine settings (e.g. cold seeps, mud volcanoes, pockmarks) against measured methane gradients
(3) We will apply this approach to the marine sedimentary record to approximate methane fluxes in the past, explore the age and bathymetric limits of this novel molecular proxy, and identify and 14C date palaeo-pockmarks structures.
Accurate and sensitive quantitative analysis of BHPs is vital to these goals and development of methods with a new triple-quadrupole mass spectrometer will be an essential component of the project.
For further information on this project and other projects currently running in Geoscience@Newcastle, please follow the link below: http://www.ncl.ac.uk/ceg/
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