Journal
BIOGEOSCIENCES
Volume 8, Issue 12, Pages 3555-3565Publisher
COPERNICUS GESELLSCHAFT MBH
DOI: 10.5194/bg-8-3555-2011
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Funding
- German Research Foundation
- German Ministry of Education and Research [03G0604A]
- German Ministry of Economy Technology [03SX250]
- German Ministry of Education and Research (BMBF)
- German Research Foundation (DFG)
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In the eastern Black Sea, we determined methane (CH4) concentrations, gas hydrate volumes, and their vertical distribution from combined gas and chloride (Cl-) measurements within pressurized sediment cores. The total gas volume collected from the cores corresponded to concentrations of 1.2-1.4 mol CH4 kg(-1) porewater at in-situ pressure, which is equivalent to a gas hydrate saturation of 15-18% of pore volume and amongst the highest values detected in shallow seep sediments. At the central seep site, a high-resolution Cl- profile resolved the upper boundary of gas hydrate occurrence and a continuous layer of hydrates in a sediment column of 120 cm thickness. Including this information, a more precise gas hydrate saturation of 22-24% pore volume could be calculated. This volume was higher in comparison to a saturation calculated from the Cl- profile alone, resulting in only 14.4 %. The likely explanation is an active gas hydrate formation from CH4 gas ebullition. The hydrocarbons at Batumi Seep are of shallow biogenic origin (CH4 > 99.6 %), at Pechori Mound they originate from deeper thermocatalytic processes as indicated by the lower ratios of C-1 to C-2-C-3 and the presence of C-5.
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