Stability of thermogenic gas hydrate in the gulf of mexico: Constraints on models of climate change

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Thermogenic (structure II) gas hydrate is abundant on the Gulf of Mexico continental slope because hydrocarbon gases from a deep, hot subsurface petroleum system vent prolifically to the sea floor in regions of low temperatures and high pressures that are within the gas hydrate stability zone (GHSZ). The distribution of gas hydrate is controlled by geologic structure. Molecular distributions of gases venting from hydrate-bearing sediments show that gas hydrate decomposition is not significant in comparison to flux from the subsurface petroleum system. Structure II gas hydrate is commonly encountered, and contains C – C hydrocarbons that crystallize from relatively unaltered vent gases. Most surficial structure II gas hydrate sites (0-6 m) studied from the ∼540 - 1930 m water depth range are stable, and gas hydrate is thought to be accumulating to considerable depth in sediment because of the prolific, ongoing venting of gas. Bacterial methane hydrate is also abundant in the Gulf of Mexico. A leaky petroleum system is the larger contributor of thermogenic greenhouse gases to the ocean and atmosphere from the Gulf of Mexico, not gas hydrate decomposition. Gas hydrate crystallization in the Gulf of Mexico sequesters large volumes of greenhouse gases in sediments, deforming soft sediments, and is proposed as an agent that stabilizes or dampens climatic change under the present climatic regime. 1 5

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Geophysical Monograph Series

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