Role of Gas Hydrate in Global Change Appears Overestimated: Results of Modeling in the Northwestern Gulf of Mexico

It has been suggested that the release of hydrate-bound greenhouse gases (mainly methane) and their subsequent oxidation to carbon dioxide may lead to appreciable climate change at global scale. It also may impact the global carbon cycle by affecting the volume and average isotopic composition of carbon reservoirs. Two-dimensional modeling of gas hydrate decomposition in response to bottom water temperature increases and sea level drops in the NW Gulf of Mexico was carried out to test this hypothesis. A sea level fall of 100 m is unlikely to significantly influence the stability of gas hydrate especially when coupled with a decrease in water temperature. A bottom water temperature increase around 4 degrees C may lead to appreciable (around 30 %) thinning of the gas hydrate stability zone (GHSZ). Neither a 100 m sea level drop nor a 4 degrees C bottom water temperature increase can initiate meaningful gas flux from decomposition of gas hydrate. This is because the volume of hydrate-bound gas in the NW Gulf is not so great. The minimum late Pleistocene - Holocene gas flux from a leaky petroleum system in the Gulf is suggested to significantly exceed the maximum rate at which gas might have been released from gas hydrate decomposition attributed to 100 m sea level drops and 4 degrees C bottom water temperature increases. In addition, recrystallization of gas hydrate in the GHSZ, trapping of free gas below the GHSZ, and aerobic and anaerobic oxidation of hydrocarbons in sediments contribute to sequestration of gas released from gas hydrate. These processes keep hydrate-derived gas in sediments and significantly diminish the role of the gas in global change. The results of this study imply that the role of gas hydrate in global change is likely to be overestimated.