HR: 1340h
AN: B43B-0154    [Abstracts]
TI: Compared chemistry of natural gas hydrates from different oceanic environments
AU: * Charlou, J
EM: charlou@ifremer.fr
AF: J. L. Charlou, J. P. Donval, H. Ondreas, J. P. Foucher, M. Voisset, IFREMER, Centre de Brest, Departement Geosciences Marines, Plouzane, 29280 France
AU: Donval, J
AF: J. L. Charlou, J. P. Donval, H. Ondreas, J. P. Foucher, M. Voisset, IFREMER, Centre de Brest, Departement Geosciences Marines, Plouzane, 29280 France
AU: Ondreas, H
AF: J. L. Charlou, J. P. Donval, H. Ondreas, J. P. Foucher, M. Voisset, IFREMER, Centre de Brest, Departement Geosciences Marines, Plouzane, 29280 France
AU: Foucher, J
AF: J. L. Charlou, J. P. Donval, H. Ondreas, J. P. Foucher, M. Voisset, IFREMER, Centre de Brest, Departement Geosciences Marines, Plouzane, 29280 France
AU: Voisset, M
AF: J. L. Charlou, J. P. Donval, H. Ondreas, J. P. Foucher, M. Voisset, IFREMER, Centre de Brest, Departement Geosciences Marines, Plouzane, 29280 France
AU: Chazallon, B
AF: B. Chazallon, Lab. Physique des Lasers Atomes Molecules, Universite des Sciences et Techniques, Villeneuve d'Ascq, 69655 France
AU: Jean-Baptiste, P
AF: P. Jean-Baptiste, LSCE, CEA-CNRS UMR 1572, Centre Etudes de Saclay, Gif sur Yvette, 91191 France
AU: Sauter, E
AF: E. Sauter, Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, Bremerhaven, 27570 Germany
AU: Levache, D
AF: D. Levache, Total, CSTJF, Avenue Larribau, Pau, 64018 France
AB: Natural gas hydrates are generally associated with pockmarks or mud volcanoes on margins. They occurred both in deep sedimentary structures, and sometimes as outcrops on the seafloor. The gas hydrates studied here were collected from gravity sediment cores and occur as small fragments and massive crystal aggregates, mostly disseminated irregularly in the sediment. In most cases, they escape in the overlying deep seawater creating CH4-rich plumes which extend 100-150 m above the seafloor. These plumes are also enriched in particles, manganese, iron related to discharges of high turbid fluids issued from sediments and in all cases methane is rejected from sediment as free gas or as a consequence of the decomposition of gas hydrates. Specific equipments are necessary for collecting, and storing these gas hydrates in good conditions to avoid decomposition. The crystalline structure of solid gas hydrates is studied by Raman Spectrometry and Synchrotron techniques and show mainly methane gas hydrate of cubic Structure I. Analyses of hydrate water show variations (depletions or enrichments) of mineral elements compared to ambient deep seawater. Gas analysis shows that CH4 is the major component but CO2 and heavier gases (C2H4, C2H6, H2S) are also present as traces. In addition, many families of organic compounds detected by chromatography-mass spectrometry are present as traces. In most cases, the carbon and hydrogen isotopic data indicate a primarily microbial origin for the CH4 which is generated through bacterial CO2 reduction. All these chemical data contribute to understand the origin, formation and stability of gas hydrates trapped in sediments on oceanic margins. Specimens of natural gas hydrates recently collected on the African and Norvegian margins will be discussed.
DE: 4825 Geochemistry
DE: 1050 Marine geochemistry (4835, 4850)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting