A wideband acoustic method for direct assessment of bubble-mediated methane flux

Elizabeth Weidner, Thomas C. Weber, Larry Mayer, Martin Jakobsson, Denis Chernykh, Igor Semiletov

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

The bubble-mediated transport and eventual fate of methane escaping from the seafloor is of great interest to researchers in many fields. Acoustic systems are frequently used to study gas seep sites, as they provide broad synoptic observations of processes in the water column. However, the visualization and characterization of individual gas bubbles needed for quantitative studies has routinely required the use of optical sensors which offer a limited field of view and require extended amounts of time for deployment and data collection. In this paper, we present an innovative method for studying individual bubbles and estimating gas flux using a calibrated wideband from the Bolin Centre for Climate Research database: http://bolin.su.se/data/.and split-beam echosounder. The extended bandwidth (16 – 26 kHz) affords vertical range resolution of approximately 7.5 cm, allowing for the differentiation of individual bubbles in acoustic data. Split-aperture processing provides phase-angle data used to compensate for transducer beam-pattern effects and to precisely locate bubbles in the transducer field of view. The target strength of individual bubbles is measured and compared to an analytical scattering model to estimate bubble radius, and bubbles are tracked through the water column to estimate rise velocity. The resulting range of bubble radii (0.68–8.40 mm in radius) agrees with those found in other investigations with optical measurements, and the rise velocities trends are consistent with published models. Together, the observations of bubble radius and rise velocity offer a measure of gas flux, requiring nothing more than vessel transit over a seep site, bypassing the need to deploy time-consuming and expensive optical systems.

Original languageEnglish
Pages (from-to)104-115
Number of pages12
JournalContinental Shelf Research
Volume173
DOIs
Publication statusPublished - 1 Feb 2019

Fingerprint

acoustic method
bubbles
methane production
bubble
acoustics
methane
gases
methodology
transducer
field of view
gas
water column
target strength
acoustic data
visualization
vessel
seafloor
researchers
water
scattering

Keywords

  • Broadband acoustics
  • Bubble fate
  • East Siberian Arctic Ocean
  • Ebullition
  • Gas flux
  • Methane gas bubbles
  • SWERUS-C3

ASJC Scopus subject areas

  • Oceanography
  • Aquatic Science
  • Geology

Cite this

A wideband acoustic method for direct assessment of bubble-mediated methane flux. / Weidner, Elizabeth; Weber, Thomas C.; Mayer, Larry; Jakobsson, Martin; Chernykh, Denis; Semiletov, Igor.

In: Continental Shelf Research, Vol. 173, 01.02.2019, p. 104-115.

Research output: Contribution to journalArticle

Weidner, Elizabeth ; Weber, Thomas C. ; Mayer, Larry ; Jakobsson, Martin ; Chernykh, Denis ; Semiletov, Igor. / A wideband acoustic method for direct assessment of bubble-mediated methane flux. In: Continental Shelf Research. 2019 ; Vol. 173. pp. 104-115.
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