Methanogenesis methane carbon source

There is another, very important and large repository of methane methane hydrates (also known as gas hydrates or clathrates Kvenvolden 1988).They comprise ice in which the interstices of the lattice house small molecules, such as methane, ethane, carbon dioxide and hydrogen sulphide. In fact, enough gas needs to be present to fill 90% of the interstices in order for the hydrate to form, and it has a different crystal structure from normal ice (Sloan 1990). If fully saturated, the most common crystalline structure can hold one molecule of methane for every 5.75 molecules of water, so lm3 of hydrate can contain 164 m3 of methane at STP (see Box 4.8).The solubility of methane in water is insufficient to account for hydrate formation, and a major nearby source is required, typically methanogenesis, based on the dominance of methane (99%) and its very light isotopic composition (813C generally <—60%o see Section 5.8.2). 

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