MERIR · Methane related iron reduction processes in sediments: Hidden couplings and their significance for carbon and iron cycles

About one-third of annual methane (CH4) emissions to the atmosphere originate from natural, nonanthropogenicsources. However, if all the naturally produced methane actually did reach the atmosphere, itslevels would increase by an order of magnitude, dwarfing anthropogenic CO2 emissions. Fortunately, naturalscavengers of this methane near its production zone limit its release. One of these scavengers, iron (Fe) oxide,can become a major sink for methane when sulfate concentrations are low. Methane-iron couplings inestablished sediments, however, are poorly understood. Specifically, significant iron oxide reduction has beenobserved in many aquatic sediments at depths well below its expected redox zone, where methane is producedby methanogenesis, often accompanied by decreases in methane concentrations. These observations challengeour understandings of iron-methane couplings and microbial players in the deep methanogenic zone and theirimpacts on the carbon, iron and other cycles. I aim in the proposed research to elucidate the unexploredmechanisms of methane-related iron reduction (MERIR) in the methanogenic zone of establishedsedimentary profiles under various environmental conditions and their impact on global biogeochemicalcycles. I will resolve two striking yet unexplained phenomena: (1) the active involvement of aerobicmethanotrophs in iron-coupled anaerobic oxidation of methane (AOM), and (2) the unusual reactivityof iron minerals toward reduction that is accompanied by intensive authigenic magnetite precipitation, andthe effects of this mineralogy change on sedimentary magnetism. My expertise will enable me to achieve theobjectives of this interdisciplinary proposed work using novel approaches from different fields. The projectwill likely lead to breakthroughs in our understanding of microbial survival strategies, reveal novel pathwaysfor aerobic methanotrophs, and change our perspectives on iron mineral reactivities and sedimentarymagnetism.