Broadband acoustic inversion for gas flux quantification - application to a methane plume at Scanner Pockmark, central North Sea
Broadband acoustic inversion for gas flux quantification - application to a methane plume at Scanner Pockmark, central North Sea
The release of greenhouse gases from both natural and man-made sites has been identified as a major cause of global climate change. Extensive work has addressed quantifying gas seeps in the terrestrial setting while little has been done to refine accurate methods for determining gas flux emerging through the seabed into the water column. This paper investigates large-scale methane seepage from the Scanner Pockmark in the North Sea with a new methodology that integrates data from both multibeam and single-beam acoustics, with single-beam data covering a bandwidth (3.5 to 200 kHz) far wider than that used in previous studies, to quantify the rate of gas release from the seabed into the water column. The multibeam data imaged a distinct fork-shaped methane plume in the water column, the upper arm of which was consistently visible in the single-beam data, while the lower arm was only intermittently visible. Using a novel acoustic inversion method, we determine the depth-dependent gas bubble size distribution and the gas flux for each plume arm. Our results show that the upper plume arm comprises bubbles with radii ranging from 1 to 15 mm, while the lower arm consists of smaller bubbles with radii ranging from 0.01 to 0.15 mm. We extrapolate from these estimates to calculate the gas flux from the Scanner Pockmark as between 1.6 and 2.7 × 10
6 kg/year (272 to 456 L/min). This range was calculated by considering uncertainties together with Monte Carlo simulation. Our improved methodology allows more accurate quantification of natural and anthropogenic gas plumes in the water column.
broadband, bubble, gas, methane, sonar, underwater acoustics
Li, Jianghui
9c589194-00fa-4d42-abaf-53a32789cc5e
Roche, Ben
08938cb1-4901-4f45-ba9a-aba53ed4ef7f
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
White, Paul
2dd2477b-5aa9-42e2-9d19-0806d994eaba
Leighton, Timothy
3e5262ce-1d7d-42eb-b013-fcc5c286bbae
Provenzano, Giuseppe
076fb0cd-74db-4b62-bc0b-afffbe442cc4
Dewar, Marus
92a8672d-4cf9-4c6c-aaa8-071a70f59505
Henstock, Timothy
27c450a4-3e6b-41f8-97f9-4e0e181400bb
September 2020
Li, Jianghui
9c589194-00fa-4d42-abaf-53a32789cc5e
Roche, Ben
08938cb1-4901-4f45-ba9a-aba53ed4ef7f
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
White, Paul
2dd2477b-5aa9-42e2-9d19-0806d994eaba
Leighton, Timothy
3e5262ce-1d7d-42eb-b013-fcc5c286bbae
Provenzano, Giuseppe
076fb0cd-74db-4b62-bc0b-afffbe442cc4
Dewar, Marus
92a8672d-4cf9-4c6c-aaa8-071a70f59505
Henstock, Timothy
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Li, Jianghui, Roche, Ben, Bull, Jonathan, White, Paul, Leighton, Timothy, Provenzano, Giuseppe, Dewar, Marus and Henstock, Timothy
(2020)
Broadband acoustic inversion for gas flux quantification - application to a methane plume at Scanner Pockmark, central North Sea.
Journal of Geophysical Research: Oceans, 125 (9), [e2020JC016360].
(doi:10.1029/2020JC016360).
Abstract
The release of greenhouse gases from both natural and man-made sites has been identified as a major cause of global climate change. Extensive work has addressed quantifying gas seeps in the terrestrial setting while little has been done to refine accurate methods for determining gas flux emerging through the seabed into the water column. This paper investigates large-scale methane seepage from the Scanner Pockmark in the North Sea with a new methodology that integrates data from both multibeam and single-beam acoustics, with single-beam data covering a bandwidth (3.5 to 200 kHz) far wider than that used in previous studies, to quantify the rate of gas release from the seabed into the water column. The multibeam data imaged a distinct fork-shaped methane plume in the water column, the upper arm of which was consistently visible in the single-beam data, while the lower arm was only intermittently visible. Using a novel acoustic inversion method, we determine the depth-dependent gas bubble size distribution and the gas flux for each plume arm. Our results show that the upper plume arm comprises bubbles with radii ranging from 1 to 15 mm, while the lower arm consists of smaller bubbles with radii ranging from 0.01 to 0.15 mm. We extrapolate from these estimates to calculate the gas flux from the Scanner Pockmark as between 1.6 and 2.7 × 10
6 kg/year (272 to 456 L/min). This range was calculated by considering uncertainties together with Monte Carlo simulation. Our improved methodology allows more accurate quantification of natural and anthropogenic gas plumes in the water column.
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2020JC016360R
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Accepted/In Press date: 29 July 2020
e-pub ahead of print date: 3 August 2020
Published date: September 2020
Keywords:
broadband, bubble, gas, methane, sonar, underwater acoustics
Identifiers
Local EPrints ID: 443106
URI: http://eprints.soton.ac.uk/id/eprint/443106
ISSN: 2169-9275
PURE UUID: 4b69fdfa-027e-464b-ad04-f70d0fbd9eed
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Date deposited: 11 Aug 2020 16:30
Last modified: 12 Jul 2024 01:39
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Author:
Ben Roche
Author:
Giuseppe Provenzano
Author:
Marus Dewar
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