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Shallow gas off the Rhone prodelta, Gulf of Lions

Shallow gas off the Rhone prodelta, Gulf of Lions
Shallow gas off the Rhone prodelta, Gulf of Lions
Sediment cores acquired in 2004 off the Rhône prodelta show consistent anomalous methane concentrations of up to 87,440 ppm. Methane compositional and isotopic data support a biogenic origin, although there are a few sites that show strongly depleted ?13C values (? 53‰ PDB) suggesting a mixed source for the gas (biogenic and thermogenic). Anomalous methane concentrations (samples with more than 90 ppm) are discussed and integrated with organic carbon data, sedimentary rates and ADCP profiles. Highest gas concentrations were found directly off the river mouth (20–40 m water depth) and where the IFREMER models point to the thickest accumulation (> 2 m) in response to the Rhône flood event.

In areas unaffected by the high flux of organic matter and rapid/thick flood deposition, or in between flood events, the conditions for methanogenesis and gas accumulation have not been met; in these areas, the physical and biological reworking of the surficial sediment may effectively oxidize and mineralize organic matter and limit bacterial methanogenesis in the sub-surface. We propose that in the Rhône prodelta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried, effectively removing this organic matter from aerobic oxidation and biological uptake and leading to the potential for methanogenesis with burial.

shallow gas, biogenic methane, flood deposits, Rhone prodelta, Gulf of Lions
0025-3227
215-231
Garcia-Garcia, A.
6023a77d-f94e-44a7-85f3-122e519f95c3
Orange, D.
9a973f5c-a6d2-4ef5-85c5-f9504adec9e8
Lorenson, T.
8bc5e809-531d-48e6-9bda-8e254dbcd867
Radakovitch, O.
183b74ea-d8f4-4704-aea7-ceca7f45f920
Tesi, T.
acfae1a5-0e18-4639-8e72-f575a9d0e856
Miserocchi, S.
8aa41834-a63f-4f37-b9b7-9b2807ed095d
Berne, S.
e03ffd6b-50e9-4c20-a710-435212c69571
Friend, P.L.
600afae0-5185-4e55-8322-34bb8e0ae1f4
Nittrouer, C.
21f6cc55-21d8-4835-a3b5-5d602aa91913
Normand, A.
05dc4d02-5cb4-4a7f-b44b-de899e182253
Garcia-Garcia, A.
6023a77d-f94e-44a7-85f3-122e519f95c3
Orange, D.
9a973f5c-a6d2-4ef5-85c5-f9504adec9e8
Lorenson, T.
8bc5e809-531d-48e6-9bda-8e254dbcd867
Radakovitch, O.
183b74ea-d8f4-4704-aea7-ceca7f45f920
Tesi, T.
acfae1a5-0e18-4639-8e72-f575a9d0e856
Miserocchi, S.
8aa41834-a63f-4f37-b9b7-9b2807ed095d
Berne, S.
e03ffd6b-50e9-4c20-a710-435212c69571
Friend, P.L.
600afae0-5185-4e55-8322-34bb8e0ae1f4
Nittrouer, C.
21f6cc55-21d8-4835-a3b5-5d602aa91913
Normand, A.
05dc4d02-5cb4-4a7f-b44b-de899e182253

Garcia-Garcia, A., Orange, D., Lorenson, T., Radakovitch, O., Tesi, T., Miserocchi, S., Berne, S., Friend, P.L., Nittrouer, C. and Normand, A. (2006) Shallow gas off the Rhone prodelta, Gulf of Lions Marine Geology, 234, (1-4), pp. 215-231. (doi:10.1016/j.margeo.2006.09.005).

Record type: Article

Abstract

Sediment cores acquired in 2004 off the Rhône prodelta show consistent anomalous methane concentrations of up to 87,440 ppm. Methane compositional and isotopic data support a biogenic origin, although there are a few sites that show strongly depleted ?13C values (? 53‰ PDB) suggesting a mixed source for the gas (biogenic and thermogenic). Anomalous methane concentrations (samples with more than 90 ppm) are discussed and integrated with organic carbon data, sedimentary rates and ADCP profiles. Highest gas concentrations were found directly off the river mouth (20–40 m water depth) and where the IFREMER models point to the thickest accumulation (> 2 m) in response to the Rhône flood event.

In areas unaffected by the high flux of organic matter and rapid/thick flood deposition, or in between flood events, the conditions for methanogenesis and gas accumulation have not been met; in these areas, the physical and biological reworking of the surficial sediment may effectively oxidize and mineralize organic matter and limit bacterial methanogenesis in the sub-surface. We propose that in the Rhône prodelta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried, effectively removing this organic matter from aerobic oxidation and biological uptake and leading to the potential for methanogenesis with burial.

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More information

Published date: 2006
Keywords: shallow gas, biogenic methane, flood deposits, Rhone prodelta, Gulf of Lions

Identifiers

Local EPrints ID: 42954
URI: http://eprints.soton.ac.uk/id/eprint/42954
ISSN: 0025-3227
PURE UUID: b773984b-6b68-4f5a-85e3-4c3557a333af

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Date deposited: 04 Jan 2007
Last modified: 17 Jul 2017 15:20

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Contributors

Author: A. Garcia-Garcia
Author: D. Orange
Author: T. Lorenson
Author: O. Radakovitch
Author: T. Tesi
Author: S. Miserocchi
Author: S. Berne
Author: P.L. Friend
Author: C. Nittrouer
Author: A. Normand

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