Investigating Methane Seeps

Located off of North America’s Pacific coast lies the Cascadia Subduction Zone. Here, The E/V Nautilus conducted the first comprehensive study of the region, studying methane seep habitats. Methane (CH4) is a hydrocarbon that is a primary component of the natural gas we burn for energy. With 23 times the global warming potential of carbon dioxide, it is also a powerful greenhouse gas. The E/V Nautilus used its hull-mounted Kongsberg multibeam sonar to search for methane bubble plumes in the water column and used remotely-operated vehicles (ROVs) to further investigate the seep ecosystems. The bubble plumes are given off by methane deposits and methane hydrate, a solid, ice-like form of methane that fuels these unique ecosystems.

Hercules prepares to take a sediment core sample, at a newly discovered methane seep around 850 meters. These sediment cores help scientists understand the biological and chemical makeup of the seafloor. Image courtesy of Ocean Exploration Trust.
Hercules prepares to take a sediment core sample, at a newly discovered methane seep around 850 meters. These sediment cores help scientists understand the biological and chemical makeup of the seafloor. Image courtesy of Ocean Exploration Trust.
Methane seep with bubbles and hydrate. Image courtesy of the Ocean Exploration Trust.
Methane seep with bubbles and hydrate. Image courtesy of the Ocean Exploration Trust.

During the 2015 expedition, The E/V Nautilus discovered extensive white, orange, and gray chemosynthetic bacterial mats within the Cascadia Subduction Zone. Chemosynthesis is similar to photosynthesis in that the microbes use methane, sulfide, and/or other compounds (instead of sunlight) to generate energy. The bacteria consume about 80% of the methane given off by the seeps, and produce carbon as a byproduct. By making carbon readily available, these microbes make the seep sites habitable to other organisms such as tube worms, shrimp, mussels, and clams, which use carbon as an energy source.

Methane ice worms inhabiting a white methane hydrate seen in the Gulf of Mexico, 2102. Studies suggest that these worms eat chemoautotrophic bacteria that are living off of chemicals in the hydrate. Image courtesy of NOAA Okeanos Explorer Program.
Methane ice worms inhabiting a white methane hydrate seen in the Gulf of Mexico, 2102. Studies suggest that these worms eat chemoautotrophic bacteria that are living off of chemicals in the hydrate. Image courtesy of NOAA Okeanos Explorer Program.
This site had a fantastic “amphitheater of chemosynthetic life.” Here we saw bathymodiolus mussels, methane hydrate or ice, and ice worms. There were also a number of sea urchins, sea stars, and fish in this area. Most impressive about this ledge was large accumulation of hydrates under the ledge as well as the large collection of mussels hanging upside down and a group of mussels that hung down off the ledge. Image courtesy of NOAA Okeanos Explorer Program, Gulf of Mexico 2014 Expedition.
This site had a fantastic “amphitheater of chemosynthetic life.” Here we saw bathymodiolus mussels, methane hydrate or ice, and ice worms. There were also a number of sea urchins, sea stars, and fish in this area. Most impressive about this ledge was large accumulation of hydrates under the ledge as well as the large collection of mussels hanging upside down and a group of mussels that hung down off the ledge. Image courtesy of NOAA Okeanos Explorer Program, Gulf of Mexico 2014 Expedition.
Overview of extensive chemosynthetic mussel communities colonizing carbonate and sedimented mounds at a seep site south of Norfolk Canyon. Image courtesy of NOAA Okeanos Explorer 2013 ROV Shakedown and Field Trials in the U.S. Atlantic Canyons.
Overview of extensive chemosynthetic mussel communities colonizing carbonate and sedimented mounds at a seep site south of Norfolk Canyon. Image courtesy of NOAA Okeanos Explorer 2013 ROV Shakedown and Field Trials in the U.S. Atlantic Canyons.
An aggregation of vestimentiferan tubeworms (Lamellibrachia sp.). Such aggregations provide habitat for many smaller animals such as the small white anemones covering the tubeworm tubes and the shrimps Alvinocaris muricola. The tiny white spots all around the tubeworms are copepods, tiny swimming crustaceans. These tiny, mobile animals could be an important link between primary productivity in the sediment and the sessile (unable to leave their location, permanently attached) anemones on the tubes. Image courtesy of the NOAA Okeanos Explorer Program.
An aggregation of vestimentiferan tubeworms (Lamellibrachia sp.). Such aggregations provide habitat for many smaller animals such as the small white anemones covering the tubeworm tubes and the shrimps Alvinocaris muricola. The tiny white spots all around the tubeworms are copepods, tiny swimming crustaceans. These tiny, mobile animals could be an important link between primary productivity in the sediment and the sessile (unable to leave their location, permanently attached) anemones on the tubes. Image courtesy of the NOAA Okeanos Explorer Program.

Recent studies suggest that ocean warming could change the stability of seep sites by overwhelming microbial communities. The seeps could emit methane at a rate faster than the bacteria can consume it. The result is increased methane emissions into the atmosphere, leading to an increased rate of global warming. By studying the seepage sites of the Cascadia Subduction Zone, The  E/V Nautilus Corp of Exploration hopes to gather baseline data on methane seep ecosystems. A better understanding of these unique ecosystems will help us to monitor and manage potential community changes as global temperatures continue to increase.


Check out the links below for some awesome footage of the life surrounding these underwater seeps!

E/V Nautilus, “Expedition Overview: Cold Seeps in 60 Seconds”

https://youtu.be/iY-9HBhxO7A

E/V Nautilus, “Life at Extremes: Biology of Brine Pools and Methane Seeps”

https://youtu.be/0HNjZApi_fs

 

Featured image courtesy of Ocean Exploration Trust.

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