Characterizing Variability in Pacific Northwest Methane Seeps Using a Fleet of Small AUVs (RC 101)

Dates

August 11-13, 2023

Vessel

Research Vessel Rachel Carson

Location

Off the Coast of Washington

Primary Goal

Develop and demonstrate an approach to efficiently and effectively map and characterize methane seeps over wide areas

Primary Technologies

Autonomous underwater vehicles, sonar, CTD

Expedition Summary

From August 11 to 13, 2023, a team of researchers visited known methane seeps off the coast of Washington to test their new approach to mapping and characterizing methane seeps over wide areas. With easily deployable and relatively inexpensive autonomous underwater vehicles (AUVs) equipped with imaging sonars and custom sensors, they successfully located and mapped seeps and measured associated bubbles and dissolved methane right at their source and up through the water column.

On the deck of Research Vessel <i>Rachel Carson</i>
On the deck of Research Vessel Rachel Carson: Two REMUS 100 autonomous underwater vehicles (AUVs) (right), two VT690 AUVs, and a CTD (conductivity, temperature, depth) rosette (left). Image courtesy of Characterizing Variability in Pacific Northwest Methane Seeps Using a Fleet of Small AUVs. Download largest version (jpg, 868 KB).
Map showing the westward track line of Research Vessel <i>Rachel Carson</i> from Westport, Washington, to the study area. The ship's track line is color-coded by bathymetry collected with the pole-mounted multibeam sonar.
Map showing the westward track line of Research Vessel Rachel Carson from Westport, Washington, to the study area. The ship's track line is color-coded by bathymetry collected with the pole-mounted multibeam sonar. Map courtesy of Characterizing Variability in Pacific Northwest Methane Seeps Using a Fleet of Small AUVs. Download largest version (jpg, 202 KB).

Why Explore Methane Seeps?

Methane is a potent greenhouse gas, and it's released into the ocean from the seafloor as gas bubbles via methane seeps. Despite the prevalence of seeps along continental margins, data is limited, and their impacts on the ocean and atmosphere, both positive and negative, are largely unknown. To improve our understanding of these emissions, how they influence life on the seafloor and in the water column as well as their role in the global carbon cycle, high-resolution, close-up acoustic data focused at the seafloor source and co-located physical and chemical data from a variety of seeps, at a variety of depths, are needed.

Searching for and Sampling Methane Seeps

To collect these data, this research team is developing new robotic sampling techniques using AUVs with advanced capabilities that eventually will be able to search for and intensively sample seeps without human involvement.

During this expedition, they used a combination of traditional (shipboard) and novel (AUVs) sampling tools to achieve their goals. Among the most important tools were the acoustic sonars. To make sure the data collected by the shipboard and AUV sonars were accurate in relation to each other, the team calibrated them with an artificial bubble source (a dive tank) in the controlled environment of Seattle’s Lake Washington before heading out to deeper waters.

A REMUS 100 autonomous underwater vehicle being deployed from Research Vessel <i>Jack Robertson</i> during calibration in Seattle's Lake Washington.
A REMUS 100 autonomous underwater vehicle being deployed from Research Vessel Jack Robertson during calibration in Seattle's Lake Washington. Image courtesy of Characterizing Variability in Pacific Northwest Methane Seeps Using a Fleet of Small AUVs. Download largest version (jpg, 3.78 MB).

Once at sea, with a storm on its way, the team went right to work, targeting an area with previously reported seeps. At night, researchers surveyed the area for seeps using a shipboard pole-mounted multibeam sonar and a CTD (conductivity, temperature, depth) rosette. Their survey showed a surprisingly large and intense seep that they nicknamed "Mondo."

The project team deploying an autonomous underwater vehicle from the deck of Research Vessel <i>Rachel Carson</i>.
The project team deploying an autonomous underwater vehicle from the deck of Research Vessel Rachel Carson. Image courtesy of Characterizing Variability in Pacific Northwest Methane Seeps Using a Fleet of Small AUVs. Download largest version (jpg, 3.78 MB).

Information about Mondo was shared with the dayshift, who then deployed the small-class AUVs to study it more closely. They used Virginia Tech 690 AUVs with 3D side-scan sonar to locate the seep and commercially available REMUS 100 AUVs with a high-resolution forward-looking sonar and custom sensors to perform more intensive in situ sampling (e.g., measure bubbles and dissolved methane). Together, the AUVs were able to locate the bubble plume and then sample the water in and around it. It's much easier to sample a seep in situ with an AUV than with a CTD rosette dangling from a ship. And, the close-up acoustic data collected by the AUVs is more accurate than those data collected by shipboard sonars, which may be hundreds of feet from a seep's source.

A project team member collecting high-resolution coastal elevation data using a Trimble SX10 scanning total station.
Screenshot of a seep flare captured with the pole-mounted multibeam sonar. Image courtesy of Characterizing Variability in Pacific Northwest Methane Seeps Using a Fleet of Small AUVs. Download largest version (png, 4 MB).
Preliminary point cloud data from a Trimble SX10 scanning total station set up on boulders on the shoreline of Agat facing inland to measure bank erosion at the shoreline in February 2023.
Sidescan sonar imagery from a VT690 autonomous underwater vehicle showing distinct acoustic scattering features, including rising bubble plumes at methane seeps (bubble curtains) and a school of fish (round ball near the seafloor). Data is colored by depth; blue is deeper and red is shallower. Image courtesy of Characterizing Variability in Pacific Northwest Methane Seeps Using a Fleet of Small AUVs. Download largest version (png, 917 KB).

Mondo wasn't the only seep in the area, or the only one visited, but it had the strongest signal, which made it a good target for testing of the AUVs.

Next Steps

Back on shore, the team will synthesize the data and estimate seep emissions and analyze water samples collected with the shipboard CTD rosette. Outcomes from this expedition will inform ongoing development of the AUVs and their suite of tools, which will be further tested during additional lake tests and a second expedition planned for 2024 targeting deeper seeps.

Exploration Team

View all
Craig McNeil

Craig McNeil

 Principal Investigator
Tamara Baumberger

Tamara Baumberger

 Co-Principal Investigator
Jeff Beeson

Jeff Beeson

 Co-Principal Investigator
Dan Stilwell

Dan Stilwell

 Co-Principal Investigator

Education Content

Education theme pages provide the best of what the NOAA Ocean Exploration website has to offer to help educators in the classroom incorporate this project into their curriculum. Each theme page includes expedition features, lessons, multimedia, career information, and associated past projects and expeditions.

Cold Seeps

Cold Seeps
Underwater Robots

Underwater Robots
Seafloor Mapping

Seafloor Mapping

Related Links

Partners

Media Contact

Emily Crum

Communications Specialist
NOAA Ocean Exploration
ocean-explore-comms@noaa.gov

Funding for this expedition was provided by NOAA Ocean Exploration via its Ocean Exploration Fiscal Year 2022 Funding Opportunity.

Published November 2, 2023