Collaborative Research: Controls on Aerobic Methane Oxidation in the Deep Sea

Gas seeps on the sea floor inject huge amounts of methane into the ocean along the coasts. Most of this is eaten by tiny organisms who rely on oxygen to consume the methane, a process called 'methane oxidation'. Oxygen levels vary naturally throughout the world’s oceans, so it is not known whether the ability of these organisms to consume methane is disrupted in some places. Custom one-of-a-kind instruments to measure methane consumption rates and monitor what organisms are present have been built by the investigators. The instruments will be sent to the bottom of the ocean for weeks and in different locations. The goal is to see how methane oxidation and the types of organisms present adjust to different oxygen concentrations and other environmental conditions. Natural gas seeps along the continental margins inject huge amounts of dissolved methane into overlying waters. This methane is largely oxidized by microbes. Although microbial methanotrophs are largely microaerophilic, it is not known how differences in oxygen concentrations enhance or hinder their ability to respond nor whether methane consumption rates are controlled by deep-sea oxygen concentrations. Recent work has shown that microbial aerobic methane oxidation (MOx) in the deep sea occurs with widely varying rate constants. The project is to explore factors that drive this variation by making in situ measurements of MOx and microbial community dynamics at known seep sites offshore Louisiana, an area with frequent episodic methane releases, and on the Cascadia Margin offshore Oregon where highly variable bottom water dissolved oxygen (DO) will provide vital evidence for how oxygen limitation affects MOx in situ. The in situ measurements are possible due to newly-developed benthic landers that can make MOx rate measurements on timescales of hours to weeks using advanced laser methane and optode DO sensors. An in situ collection and incubation scheme allows collection of microbial time-series, tracking the relative abundance of methanotrophs (through 16S rRNA surveys and metagenomes) and their activity (through metatranscriptomes) to study methanotrophic responses to varying ambient conditions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.