2021 Expedition
sampler collecting methane seep bubbles

Cascadia Margin Seep Exploration

July 22 – August 5, 2021
NA128
Lead Scientist
Expedition Leader

For two weeks, E/V Nautilus will return to the Cascadia Margin, a geologically active region located offshore of Washington, Oregon, and northern California, where we have mapped and explored many methane seeps and cold seeps. Since the 2016 expedition season, E/V Nautilus and other vessel’s multibeam sonar surveys have located over 3,500 previously unknown bubble streams rising from the Cascadia Margin between the Strait of Juan de Fuca in Washington and California’s Cape Mendocino at depths between 200-3,200 meters (Merle et al., 2021).

Our 2021 dives will focus on several previously unexplored regions along the margin to sample at methane seep sites on the shelf and along the slope. Most of these seep sites were discovered during mid-water surveys on previous expeditions in 2016, 2017, and 2018, but have never been visited by an ROV. Just a small number of the previous ROV dive sites will be revisited to shed light on a helium anomaly observed in 2016 and 2018, as well as for a second field test of the new hydrate sampler. During nighttime mapping efforts, we will focus on exploring for more methane seeps in currently unsurveyed areas. 

As we continue deep-sea documentation in this extensive coastal region from California to Washington, we acknowledge that the land and waters are within the traditional and modern territories of the Tolowa Dee-ni’, Chit-dee-ni, Tututni, Miluk Coos, Coos, Lower Umpqua, Siuslaw, Confederated Tribes of Grande Ronde, Älsé, Yakina, Tillamook, Siletz, Salmon River, Nestucca, Nehalem, Chinook, Clatsop, Willapa, Coast Salish, Chehalis, Quinault, Queets, ChalAt’i’lo t’sikAti, Quileute, Makah, and S’Klallum peoples. 

This expedition is sponsored by NOAA Ocean Exploration through the Ocean Exploration Cooperative Institute. 

Expedition Partners

Meet the Team

Expedition Posts

Downward facing view friom the multibeam mapping software showing a rising bubble plume with white bubbles on a dark background

While mapping the seafloor, the team detects methane seeps in the water column data by looking for 'flares' or vertical plumes of rising bubbles. The density difference between gas and water reflects sound back to the ship's multibeam transceiver sensors. 

Credit
Ocean Exploration Trust
View from the Chimaera software of the seafloor showing a diffuse white patch with a fish emoji next to it and a vertical stream indicative of a bubble plume

Multibeam mapping is an excellent tool for detecting bubble plumes rising from the seafloor because the water/air density difference bounces sound clearly back to the ship. Beyond bubbles, this also means the system detects fishy interference as schools' swim bladders reflect back our pings. The mapping team watches the system for amorphous fish schools versus tall narrow bubble flares. 

Credit
Ocean Exploration Trust
Image of crane lifting plastic totes off a raised concete harbor pier onto a ship deck.  Team members are wearing hard hats and a UHaul truck is parted off to the side of the picture unloading totes.

Hoisting science gear aboard in Astoria, our team is looking forward to two weeks of ROV dives visiting the methane seep-fueled communities of Cascadia Margin from Southern Oregon to Northern Washington. Read more about the upcoming mission ahead of our morning departure: https://nautiluslive.org/cruise/na128

Credit
Ocean Exploration Trust