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M³ - Acoustic monitoring of natural release of methane gas from the seafloor

Objective

The objective of the M³ project (Jan 2017- Dec 2019) is to quantify the amount of emitted methane gas at the Southern Hydrate Ridge (SHR) and to monitor in real time the future changes using sonar systems connected to the underwater cabled observatory of the Ocean Observatory Initiative (OOI). The M³ project is funded by the Federal Ministry of Education and Research (BMBF).

Methane acts as a strong greenhouse gas when it enters the atmosphere. While methane emissions on land are comparably easy to estimate, it is challenging to estimate submarine gas emissions in the oceans. Continuous measurements are needed to evaluate if methane release in response to ocean warming, e.g. from dissociating gas hydrate reservoirs in the sediments, provides a positive feedback mechanism. In recent years, state-of-the-art sonar systems have been developed to quantify the emissions of methane emitting as gas bubbles from the seafloor. Up to now, sonar systems have only been deployed during short time periods due to limited power availability. However, supply of power and high bandwidth data transmission is now available through the NSF-financed deep-sea network installed within the frame of the Ocean Observatory Initiative (OOI). With this, it is finally possible to continuously measure the methane gas emissions at Hydrate Ridge.

 

OOI Control Center
Control Center of the OOI Regional Cabled Array at the University of Washington, Seattle (Photo: Yann Marcon, MARUM, Bremen).

 

The M³ project aims at monitoring the natural release of methane from the seabed over the long-term (> 2 years), continuously and in real time. To achieve this, it is planned to install two sonar systems at the seafloor in order to monitor gas bubble emissions at the southern summit of Hydrate Ridge. One rotating multibeam sonar will provide the overview of the entire gas and gas-hydrate influenced area. A second high-resolution sonar will be used for quantifying the amount of individual gas streams. 

 

Operation of the Overview sonar
Schematic showing the operation of the overview sonar. The multibeam rotates 360° to scan the water column for gas emissions in all directions. The swath of the multibeam is oriented vertically and uses an opening angle of 90°. (Credit: Yann Marcon)

 

The ultimate objective is to combine the results of both sonar systems for an overall estimation of the bubble flux at southern Hydrate Ridge. A camera system and a hydrographic CTD probe will also be connected to the OOI infrastructure to complement the hydro-acoustic monitoring. The camera system will provide ground-truthing data for validating sonar observations and facilitate the determination of the bubble size distribution. The CTD probe will record environmental parameters (temperature, salinity, pressure and concentration of dissolved oxygen) in order to study how the bubble flux varies with the hydrographic conditions and to measure the bottom water sound velocity (for the sonar calibration). Finally, a dedicated software for the processing and visualization of the sonar data (MCubedViewer) is under development through a cooperation with the Fraunhofer MEVIS Institute for Medical Image Computing.

 

Screenshot of the MCubedViewer program
Extraction and visualization of gas emissions from the acoustic data using the dedicated visualization software (MCubedViewer).

 

The technological innovations of the M³ project open new fields in marine environmental sciences and have the potential of being deployed in other regions of the ocean for the future monitoring of changing environments.

 

Design of the Overview sonar
Design of the Overview sonar (Credit: Till von Wahl)


Design of the Quantification sonar
Design of the Quantification sonar. The sonar head can be detached during deployment and recovery of the tripod (Credit: Till von Wahl)

The overview sonar during tests
Testing of the overview sonar at the MARUM (Photo: Volker Diekamp, MARUM, Bre­men)
Handling of the overview sonar with the ROV MARUM-SQUID
Handling of the overview sonar with the ROV MARUM-SQUID during tests in the MARUM saltwater tank (Photo: Volker Diekamp, MARUM, Bremen).

 

Related links:

OOI Cabled Array

Fraunhofer MEVIS

 

TEAM

Yann Marcon

Project Management / Coordination

Ulli Spiesecke

Engineering (Instrument design)

Till von Wahl

Engineering (Instrument design)

Vincent Vittori

Engineering (Instrument control)

Eberhard Kopiske

Engineering (Instrument design)

Tom Leymann

Engineering (Instrument construction)

Gerhard Bohrmann

Project Management

Manipulation of the Overview Sonar in the test tank with the ROV MARUM-SQUID (Original footage: courtesy of MARUM and ROV SQUID team)

ROV Jason control van during deployment of the Overview Sonar
ROV Jason control van during deployment of the Overview Sonar (Photo: Yann Marcon)
Deployment of the MJ01B Junction Box
Deployment of the MJ01B Junction Box during the VISIONS'18 expedition on RV Roger Revelle (Photo: Yann Marcon)

Deployment of the Overview Sonar at the southern Hydrate Ridge with ROV JASON, VISIONS'18 (Credits: UW / NSF-OOI / WHOI / MARUM)

 

Contact

Funding

The M³ project is funded by the Federal Ministry of Education and Research (BMBF). Period of the pro­ject: 01.01.2017 - 31.12.2019. It is co-or­din­ated by the University of Bremen (Department of Geosciences and MARUM Centre for Marine Environmental Sciences).