GEOLOGY: Taking Inventory

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Science  12 Nov 2004:
Vol. 306, Issue 5699, pp. 1103c
DOI: 10.1126/science.306.5699.1103c

An enormous amount of methane, an important greenhouse gas, is stored in sediments in the ocean basins as icy methane clathrate and as gas trapped by this ice and by sediments. Catastrophic release of methane from this warehouse has been suggested to have caused abrupt climate change (warming) in the past, and there are concerns that a warmer future climate may destabilize this reservoir, which would enhance warming further.

To assess the amount of clathrate stored and to evaluate its stability, Buffett and Archer developed a mechanistic model for clathrate dynamics based on experimental and theoretical data on its stability and on factors affecting its formation and release, such as the supply of carbon to sediments and its diagenesis, storage, and oxygen content. Application to the current ocean basin implies that the global inventory is on the order of 1018 g of carbon stored as methane gas and clathrate. The modeling results imply that increasing temperature would likely deplete this inventory considerably; rebuilding would take several million years. The model also reveals that unless the oxygen content of the deep oceans was lower than at present, not enough methane would have been stored to account for the carbon isotope shift and the abrupt warming at the Paleocene-Eocene boundary, about 55 million years ago. — BH

Earth Planet. Sci. Lett. 227, 185 (2004).

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