Resistivity image beneath an area of active methane seeps in the west Svalbard continental slope
Resistivity image beneath an area of active methane seeps in the west Svalbard continental slope
The Arctic continental margin contains large amounts of methane in the form of methane hydrates. The west Svalbard continental slope is an area where active methane seeps have been reported near the landward limit of the hydrate stability zone. The presence of bottom simulating reflectors (BSRs) on seismic reflection data in water depths greater than 600 m suggests the presence of free gas beneath gas hydrates in the area. Resistivity obtained from marine controlled source electromagnetic (CSEM) data provides a useful complement to seismic methods for detecting shallow hydrate and gas as they are more resistive than surrounding water saturated sediments. We acquired two CSEM lines in the west Svalbard continental slope, extending from the edge of the continental shelf (250 m water depth) to water depths of around 800 m. High resistivities (5-12 Ωm) observed above the BSR support the presence of gas hydrate in water depths greater than 600 m. High resistivities (3-4 Ωm) at 390-600 m water depth also suggest possible hydrate occurrence within the gas hydrate stability zone (GHSZ) of the continental slope. In addition, high resistivities (4-8 Ωm) landward of the GHSZ are coincident with high-amplitude reflectors and low velocities reported in seismic data that indicate the likely presence of free gas. Pore space saturation estimates using a connectivity equation suggest 20-50 per cent hydrate within the lower slope sediments and less than 12 per cent within the upper slope sediments. A free gas zone beneath the GHSZ (10-20 per cent gas saturation) is connected to the high free gas saturated (10-45 per cent) area at the edge of the continental shelf, where most of the seeps are observed. This evidence supports the presence of lateral free gas migration beneath the GHSZ towards the continental shelf.
Electrical properties, Marine electromagnetics, Gas and hydrate systems, Arctic region
1286-1302
Goswami, Bedanta K.
c2e137f2-fe5d-4814-9df0-e956fe8075a8
Weitemeyer, Karen A.
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Minshull, Timothy A.
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Sinha, Martin C.
794c3012-d0e8-4d2f-b328-c8cfd56c5976
Westbrook, Graham K.
ccd95de7-a1a1-4fc9-be37-f1a487bb65ca
Marín-Moreno, Héctor
e466cafd-bd5c-47a1-8522-e6938e7086a4
Goswami, Bedanta K.
c2e137f2-fe5d-4814-9df0-e956fe8075a8
Weitemeyer, Karen A.
22c524f6-b24d-4d2a-a46d-16b06c70a5d1
Minshull, Timothy A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Sinha, Martin C.
794c3012-d0e8-4d2f-b328-c8cfd56c5976
Westbrook, Graham K.
ccd95de7-a1a1-4fc9-be37-f1a487bb65ca
Marín-Moreno, Héctor
e466cafd-bd5c-47a1-8522-e6938e7086a4
Goswami, Bedanta K., Weitemeyer, Karen A., Minshull, Timothy A., Sinha, Martin C., Westbrook, Graham K. and Marín-Moreno, Héctor
(2016)
Resistivity image beneath an area of active methane seeps in the west Svalbard continental slope.
Geophysical Journal International, 207 (2), .
(doi:10.1093/gji/ggw330).
Abstract
The Arctic continental margin contains large amounts of methane in the form of methane hydrates. The west Svalbard continental slope is an area where active methane seeps have been reported near the landward limit of the hydrate stability zone. The presence of bottom simulating reflectors (BSRs) on seismic reflection data in water depths greater than 600 m suggests the presence of free gas beneath gas hydrates in the area. Resistivity obtained from marine controlled source electromagnetic (CSEM) data provides a useful complement to seismic methods for detecting shallow hydrate and gas as they are more resistive than surrounding water saturated sediments. We acquired two CSEM lines in the west Svalbard continental slope, extending from the edge of the continental shelf (250 m water depth) to water depths of around 800 m. High resistivities (5-12 Ωm) observed above the BSR support the presence of gas hydrate in water depths greater than 600 m. High resistivities (3-4 Ωm) at 390-600 m water depth also suggest possible hydrate occurrence within the gas hydrate stability zone (GHSZ) of the continental slope. In addition, high resistivities (4-8 Ωm) landward of the GHSZ are coincident with high-amplitude reflectors and low velocities reported in seismic data that indicate the likely presence of free gas. Pore space saturation estimates using a connectivity equation suggest 20-50 per cent hydrate within the lower slope sediments and less than 12 per cent within the upper slope sediments. A free gas zone beneath the GHSZ (10-20 per cent gas saturation) is connected to the high free gas saturated (10-45 per cent) area at the edge of the continental shelf, where most of the seeps are observed. This evidence supports the presence of lateral free gas migration beneath the GHSZ towards the continental shelf.
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Geophys. J. Int.-2016-Goswami-1286-302.pdf
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Accepted/In Press date: 1 September 2016
e-pub ahead of print date: 4 September 2016
Additional Information:
Funding Information:
We are grateful to the Captain, crew and shipboard scientific party of the RRS James Clark Ross cruise JCR269B for their hard work at sea. We are also thankful to Veit Huehnerbach for operating Hy-BIS, Laurence North and Yee Yuan Tan for their time during DASI operation and former PhD students, Amelia Astley, Anupama Rajan, Carolyn Graves, Helen Miller and Joan Campanya i Llovet for their hard work during the cruise. We would also like to thank Natural Environment Research Council's Ocean Bottom Instrumentation Facility and especially Ben Pitcairn and Robert Kirk for their onboard technical support. This research would not have been possible without the funding of the National Environment Research Council (NERC), UK (grant NE/H002732/1 and NE/H022260/1). TAMis supported by aWolfson Research Merit award. Seismic and CSEM data are archived at the British Oceanographic Data Centre. We thank Kerry Key for developing the MARE2DEM code and making it publicly available and David Myer for the CSEM processing codes and valuable discussions. We thank reviewers Katrin Schwalenberg and Ann Cook for their suggestions to improve the manuscript.
Keywords:
Electrical properties, Marine electromagnetics, Gas and hydrate systems, Arctic region
Organisations:
Geology & Geophysics, Marine Geoscience
Identifiers
Local EPrints ID: 399952
URI: http://eprints.soton.ac.uk/id/eprint/399952
ISSN: 0956-540X
PURE UUID: 7b33ba95-3c0f-497c-aef6-124114d9e30e
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Date deposited: 05 Sep 2016 15:29
Last modified: 15 Mar 2024 04:14
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Contributors
Author:
Bedanta K. Goswami
Author:
Karen A. Weitemeyer
Author:
Martin C. Sinha
Author:
Héctor Marín-Moreno
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