Deep Biosphere: Source of Methane for Oceanic Hydrate

Abstract

Methane is an important product of anaerobic bacterial metabolism. Bacterial methane makes a substantial contribution to global methane reserves. Methanogenesis is the final step in the anaerobic degradation of organic matter, and can continue in deeply buried sediments. Methane can also be produced abiologically at elevated temperatures and pressures e. g., thermal breakdown of organic matter, crustal and hydrothermal processes. The boundary between biological and abiological processes is not always clear. Bacteria can be active at temperatures up to 113°C and pressures in excess of 1000 atm, and abiological processes can produce energy sources for bacterial methanogenesis. In addition, deep sourced thermogenic methane can diffuse to the surface, and under certain conditions, biogenic methane can have a chemical and stable isotope signature indicating an abiological origin.