Methane Carbon and Deuterium Isotopic Composition

Methane in the clam colonies is likely produced by non-clam symbionic bacteria via the carbonate reduction pathway:

CO₂ + 8H⁺ + 8e^- <<-->> CH₄ + 2 H₂O

A small amount of amount of thermogenic methane from depth may account for some methane near carbonate crust site #2 (6/27/94).