“…In the ocean, the two major sources of methane are ongoing biogenic production by microbes in anoxic sediment (Formolo, 2010;Reeburgh, 2007;Whiticar, 1999) and release of fossil methane from geological storage (summarized by Kvenvolden and Rogers, 2005;Saunois et al, 2016). Other sources include release from permafrost, river runoff, submarine groundwater discharge (Lecher et al, 2016;Overduin et al, 2012), and production from methylated substrates under aerobic conditions (Damm et al, 2010;Karl et al, 2008;Repeta et al, 2016). More than 90 % of the methane sourced in the seabed is oxidized within the sediment by anaerobic and aerobic oxidation (Barnes and Goldberg, 1976;Boetius and Wenzhöfer, 2013;Knittel and Boetius, 2009;Reeburgh, 1976).…”