After three weeks of scanning and sampling for methane seeping out along the Cascadia Subduction Zone, researchers aboard the Nautilus pulled into the Port of Astoria on Friday with their findings.
The Nautilus, a converted 1960s East German research ship, is operated by the Ocean Exploration Trust. The exploration and research nonprofit was started by Robert Ballard, a professor known for discovering the wreck of the RMS Titanic and the German battleship Bismarck.
On its way north from San Francisco, the Nautilus scanned more than 1,300 square miles along the subduction zone, a tectonic plate boundary running from Vancouver Island to Northern California. Researchers with Oregon State University and the National Oceanic and Atmospheric Administration have documented more than 1,000 methane seep sites in the zone caused by tectonic activity releasing hydrocarbon-rich fluids such as hydrogen sulfide and methane, a main component in natural gas.
Deep in the ocean, the methane often crystallizes into methane hydrate, an opaque or translucent ice.
“The most important thing right now is to get to know what is out there,” said Tamara Baumberger, a researcher with the Cooperative Institute for Marine Resources Studies operated by Oregon State and NOAA at the Hatfield Marine Science Center in Newport. “Three years ago, we almost knew nothing. Now we’re starting to get an idea of how many seeps we have. How much hydrate is still a big question.”
At night, the Nautilus used a multibeam sonar to scan the zone for more vents, and a sub-bottom profiler that can pierce more than 160 feet into the seafloor to look at soil composition and for pockets of gas.
During the day, researchers used an onboard submersible, the Hercules, to collect samples of the gas, hydrates, seepwater, plants, animals, sediments and rocks around the seeps. The robot is connected via a tether to Argus, a smaller submersible that buffers the Hercules from movement in the line, and can descend 2.5 miles underwater.
The Hercules includes two arms for sampling and an array of cameras and acoustic sensors, but is designed to be outfitted with different tools for each expedition. For the methane seep study, it was fitted to take airtight samples of both gas and hydrate crystals.
Studying the ratio of noble gases inside the methane can inform Baumberger whether they were once hydrates, and in turn what causes hydrates to turn into gases that contribute to global warming and ocean acidification, she said.
Hercules was also used to deploy a hydrophone — an underwater microphone that detects ocean sounds from all directions — to record the methane bubbles coming out of the earth’s crust.
Robert Dziak, an acoustics scientist with NOAA, recently authored a study about how the pitch of methane bubbles can help scientists estimate the amount of methane in an underwater reservoir.
“Our ultimate goal is to use sound to estimate the volume and rate of methane gas exiting these seafloor fields,” Dziak said in a recent news release about the study.
The samples collected during the expedition were shipped back to the Hatfield Marine Science Center for analysis. The Nautilus left Sunday for the coast off the Olympic Peninsula, where it searched this week for fragments of a meteor that crashed down in March in the Olympic Coast National Marine Sanctuary.
Nicole Raineault, an expedition leader with the Ocean Exploration Trust, said the group was approached by Marc Fries, a research scientist at the Planetary Science Institute in Arizona, about looking for remnants of the meteor.
“Nobody’s ever found a meteorite in the ocean, but this is just offshore of Washington,” she said. “It’s in just about 100 meters water depth, and he thinks that the fragments were fairly large and in a small enough area that we might be able to find it.”
Afterward, the Nautilus will head for Canada to map northern sea mounts and help maintain the underwater cables connecting a network of observatories overseen by the University of Victoria, British Columbia. Several other mapping expeditions are planned around the Pacific Ocean through September.
• Live feed: The Ocean Exploration Trust provides a live feed of the ship and expeditions at nautiluslive.org