Observing Seafloor Methane Seeps at the Edge of Hydrate Stability

Spinning a Food Web Nearly Three Thousand Feet Underwater

ROV SuBastian / Schmidt Ocean Institute
Jun. 14 2019
.Shelton Du Preez / Schmidt Ocean Institute

The black of the mud makes for a stark contrast against the brilliant purple of USGS scientist Jennie McClain-Count’s gloves as she passes the sample from its tube to three freshly prepared bottles. The samples in her hands have just had a rather precipitous journey, rising from a depth of 850 meters (a little less than 2800 feet) to the wet lab of the R/V Falkor. Now, these sediments and other samples will be analyzed by Jennie’s capable hands.

USGS scientist Jennie McClain-Courts prepares to collect samples from ROV SuBastian onboard R/V Falkor. These samples have just come up from the seafloor of Astoria Canyon off the coast of Oregon.Shelton Du Preez / Schmidt Ocean Institute

Our focus on this cruise is the methane seeps, but they are inextricably linked to many other aspects of the ocean floor. The deep-sea food web, which is the intricate network of living things that rely on each other for food, is very often anchored by the methane that comes from the seeps.

“Food webs are almost always defined by where they get their carbon. For most communities, they rely on sunlight. Sunlight fuels photosynthesis in plants, which then serve as the primary food source for animals,” Jennie explained. “But these guys, they live so far underwater that sunlight doesn’t get to them. So they have to find an alternate source of carbon.”

Methane bubbles up from a cold seep in the Astoria Canyon.

Enter the Methane Seeps
Carbon in the methane is eaten by a variety of creatures, from one-celled organisms to larger creatures. They in turn serve as food for other creatures, like shrimp-like amphipods and polychaetes, which are segmented worms. Jennie has seen ecosystems like this before, on other deep-sea cruises that looked at methane seeps in the Atlantic and northern Gulf of Mexico.

USGS scientist Jennie McClain-Courts and Coastal Carolina University student Charlotte Kollman collect sediment samples from ROV SuBastian on board the R/V Falkor.Shelton Du Preez / Schmidt Ocean Institute

“I think it’s really interesting how these food webs have developed around this chemosynthetic, or methane-based habitats,” said Jennie. “But what I also find most fascinating is how similar each community is. I’m always looking forward to studying the biodiversity at these seeps.”

Jennie points out some white mats that coat the sediment samples. They stand out quite a bit from the black mud. “These are white Beggiatoa, a kind of bacteria. I’ve seen them at the methane seeps in the Atlantic and the Gulf of Mexico too. Even though each of these places and the US Pacific margin are different in some ways, we see these same Beggiatoa near seeps in each location.” When asked what else we can expect to see near these seeps, she begs off. “It’s too soon to tell, but check back in a week after we’ve made a few more dives.”

White beggiatoa mats cover the seafloor of Astoria Canyon off the coast of Oregon. These mats appear to be more widespread than when a previous sampling cruise came through in 2016.ROV SuBastian / Schmidt Ocean Institute

Shaped by Their Environment
Moving to the rest of what ROV SuBastian brought up, Jennie takes out several strikingly orange starfish as well as a dozen or so white snails. The starfish prey on the amphipods and other creatures living in the seafloor, forming another connection in the methane-based food web.

USGS scientist Amanda Demopoulos holds recently collected starfish and sediment samples collected by ROV SuBastian from the Astoria Canyon seafloor off the coast of Oregon.Shelton Du Preez / Schmidt Ocean Institute

These collections also have valuable information about their habitat, like what kinds of chemicals are in the sediments, in the waters, and in their food. It is this information about the ecosystem surrounding the deep-sea food web that our lead scientist and fellow USGS researcher Amanda Demopoulos hopes this cruise will shed some light on.

“Living things don’t just affect their environment, they’re shaped by it too,” said Amanda. “If we want to understand why these animals live here and are able to thrive here, then we need to understand the physical and chemical parts of these seeps.”

USGS scientists Jennie McClain-Courts and Penny McCowen process sediment samples onboard R/V Falkor.Shelton Du Preez / Schmidt Ocean Institute

Amanda would know – like Jennie, she is the veteran of many research cruises and has studied the same methane seeps in the Atlantic and northern Gulf of Mexico. “In the Atlantic, Jennie and I worked on understanding how the submarine canyons affected the ways that benthic, or seafloor communities got their food,” recalled Amanda. “We want to build on that research here in the Pacific.”

Here on R/V Falkor, she will have that opportunity with the advanced methane-studying equipment and expertise available. Next, we will check in with the scientists who run some of that equipment. So make sure to come back to the cruise log each day!

R/V Falkor crew, UNC scientist Howard Mendlovitz, and UNC student Adam Rok prepare a lander. This lander will measure methane oxidation rates near seeps on the seafloor of Astoria Canyon off the coast of Oregon.Shelton Du Preez / Schmidt Ocean Institute

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