The occurrence of gas hydrates in Eastern Mediterranean mud dome structures as indicated by pore-water composition

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Abstract
During ODP Leg 160 to the Eastern Mediterranean, two mud dome structures have been sampled. The massive presence of gas hydrates at relatively shallow depths in the sediment of one of these, Milano Dome, contrasts to that of the other, Napoli Dome, where gas hydrates are unlikely to be present at depths greater than 1 m below the sea floor (mbsf). Some observations from very shallow pore-waters at Napoli Dome, however, suggest that some gas hydrates must be present above 1 mbsf. In the case of Milano Dome, it is likely that a massive cap of gas hydrates is overlying natural gas that cannot escape due to this cap and its shape. In this report, some of the mud dome pore-water results of Ocean Drilling Program Leg 160 to the Eastern Mediterranean are discussed in relation to the inferred presence of gas hydrates. In addition, the total quantity of methane, including gas hydrates and ‘free gas’, has been estimated for Milano Dome (∼5 × 10 9 m 3 CH 4 ) and for the Eastern Mediterranean Ridge mud dome structures (∼1 × 10 14 m 3 CH 4 ).