Quantifying in-situ gas hydrates at active seep sites in the eastern Black Sea using pressure coring technique.

Heeschen, K. U., Haeckel, Matthias , Klaucke, Ingo , Ivanov, M. K. and Bohrmann, Gerhard (2011) Quantifying in-situ gas hydrates at active seep sites in the eastern Black Sea using pressure coring technique. Open Access Biogeosciences (BG), 8 (12). pp. 3555-3565. DOI 10.5194/bg-8-3555-2011.

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Abstract

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 C1 to C2–C3 and the presence of C5.

Document Type: Article
Keywords: Biogeochemistry; Gas hydrates, methane, AOM, cold vents
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.5194/bg-8-3555-2011
ISSN: 1726-4170
Projects: Future Ocean
Date Deposited: 12 Dec 2011 09:53
Last Modified: 28 Nov 2017 17:47
URI: http://oceanrep.geomar.de/id/eprint/12908

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