Implementation of an Acoustic-based Methane Flux Estimation Methodology in the Eastern Siberian Arctic Sea

TitleImplementation of an Acoustic-based Methane Flux Estimation Methodology in the Eastern Siberian Arctic Sea
Publication TypeConference Abstract
AuthorsWeidner, E, Weber, TC, Mayer, LA
Conference Name2017 Fall Meeting, American Geophysical Union (AGU)
Conference LocationNew Orleans, LA
Conference DatesDecember 11-15

Quantifying methane flux originating from marine seep systems in climatically sensitive regions is of critically importance for current and future climate studies. Yet, the methane contribution from these systems has been difficult to estimate given the broad spatial scale of the ocean and the heterogeneity of seep activity. One such region is the Eastern Siberian Arctic Sea (ESAS), where bubble release into the shallow water column (<40 meters average depth) facilitates transport of methane to the atmosphere without oxidation. Quantifying the current seep methane flux from the ESAS is necessary to understand not only the total ocean methane budget, but also to provide baseline estimates against which future climate-induced changes can be measured.

At the 2016 AGU fall meeting, we presented a new acoustic-based flux methodology using a calibrated broadband split-beam echosounder. The broad (14-24 kHz) bandwidth provides a vertical resolution of 10 cm, making possible the identification of single bubbles. After calibration using 64 mm copper sphere of known backscatter, the acoustic backscatter of individual bubbles is measured and compared to analytical models to estimate bubble radius. Additionally, bubbles are precisely located and traced upwards through the water column to estimate rise velocity. The combination of radius and rise velocity allows for gas flux estimation.

Here, we follow up with the completed implementation of this methodology applied to the Herald Canyon region of the western ESAS. From the 68 recognized seeps, bubble radii and rise velocity were computed for more than 550 individual bubbles. The range of bubble radii, 1-6 mm, is comparable to those published by other investigators, while the radius dependent rise velocities are consistent with published models. Methane flux for the Herald Canyon region was estimated by extrapolation from individual seep flux values.