AMOPROX · Quantifying Aerobic Methane Oxidation in the Ocean: Calibration and palaeo application of a novel proxy

Methane, a key greenhouse gas, is cycled by microorganisms via two pathways, aerobically and anaerobically. Research on themarine methane cycle has mainly concentrated on anaerobic processes. Recent biomarker work has provided compellingevidence that aerobic methane oxidation (AMO) can play a more significant role in cycling methane emitted from sediments thanpreviously considered. AMO, however, is not well studied requiring novel proxies that can be applied to the sedimentary record. Agroup of complex lipids biosynthesised by aerobic methanotrophs known as aminobacteriohopanepolyols represent an ideal targetfor developing such poxies. Recently BHPs have been identified in a wide range of modern and recent environments including acontinuous record from the Congo deep sea fan spanning the last 1.2 million years.In this integrated study, the regulation and expression of BHP will be investigated and calibrated against environmental variablesincluding temperature, pH, salinity and, most importantly, methane concentrations. The work program has three complementarystrands. (1) Pure culture and sedimentary microcosm experiments providing an approximation to natural conditions. (2) Calibrationof BHP signatures in natural marine settings (e.g. cold seeps, mud volcanoes, pockmarks) against measured methane gradients.(3) Application of this novel approach to the marine sedimentary record to approximate methane fluxes in the past, explore the ageand bathymetric limits of this novel molecular proxy, and identify and potentially 14C date palaeo-pockmarks structures. Crucial tothe success is also the refinement of the analytical protocols to improve both accuracy and sensitivity, using a more sensitiveanalytical instrument (triple-quadrupole mass spectrometer).