ACCELERATED METHANE OXIDATION RATES IN GULF OF CALIFORNIA HYDROTHERMAL PLUMES PROVIDE A WINDOW TO THE PAST AND INSIGHT FOR THE FUTURE
In the Gulf of California, deposition of organic-rich sediments atop volcanic sills enables thermocatalytic cracking of sedimentary organic matter, generating copious amounts of methane in the sediment column. The Gulf of California is a modern analogue for large igneous provinces (LIP), areas where volcanic intrusions into organic-rich sediments led to hydrocarbon release that drove rapid warming in Earth’s geologic past. In the modern day, discharge of hot, methane-rich fluids generates hydrothermal plumes that rise and spread laterally in the overlying water column. Here, we report methane concentrations and methane oxidation rates in the rising plume from several hydrothermal point sources in Guaymas Basin and one in Pescadero Basin as well as cold seeps along Sonora Margin. Methane concentrations were 1-5 micromoles per liter in dilute plume samples but were over 400 micromoles per liter in elevated temperature samples. Plume methane oxidation rates were the highest measured in the marine environment, up to 21 micromoles per liter per day. The high turnover rates in Guaymas Basin rising plumes reflect a methanotroph community primed for rapid response due to frequent injection of reduced substrates into water that is recirculated locally within the basin. LIP-generated injections of greenhouse gases in Earth’s geologic past occasionally overwhelmed the capacity for oceanic microbial consumption and caused the dramatic warming events recorded by paleoclimate proxies. These data show that consistent localized intense injections of methane can be captured effectively by the microbial community, shedding light on the conditions necessary for overwhelming the capacity of the biological methane filter in the ocean.