What a Past Few Weeks: Legs 2 and 3 Successfully Completed

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A new Osmotic fluid sampler (left) is installed in adjacent to one deployed in 2020 at an active methane seep site at Southern Hydrate Ridge. White bacterial mats and clams thrive here, supported by the diffuse flow of fluids. Credit: UW/NSF-OOI/WHOI; V21.

It has been an exceptionally busy past few weeks onboard the R/V Thomas G. Thompson since the ship depart for Leg 2 of the Regional Cabled Array cruise on August 10 to head out to the Primary Node PN1B site to provide support to the International Telecom (IT) cable ship Integrity in its operations to recover the Primary Node for repair.

On Leg 2, during the six days at sea, the PN1B, Slope Base, Endurance Oregon Offshore and Shelf, Southern Hydrate Ridge, and Pythias Oasis sites were visited. The ROV Jason completed 13 dives (J2-1354 to J2-1366) during this leg that resulted in the:

  • Deployment of 23 OOI core instruments and recovery of 7 instruments
  • Deployment of 3 PI instruments and recovery of 2 instruments at the methane seep site – Southern Hydrate Ridge
  • Recovery and Deployment of Benthic Experiment Platforms at both the Oregon Offshore and Shelf sites
  • Turning of 1 low voltage node (LV01A) at Slope Base at the base of the continental margin, and
  • Turning of 1 medium-power junction box (MJ01C) at Endurance Oregon Shelf site. MJ01C is fondly called the sheep as it was completely encased in 100’s of sea anemones that called this node home since its installation in 2014. It was quite the cleaning event by the six VISIONS students once it was brought onboard the Thompson.
An overview of the junction box fondly called the “sheep.” Credit: UW/NSF-OOI/WHOI; Dive J2-1360; V21.

In addition, the ROV Jason successfully hooked up the recovery line to Primary Node PN1B, which allowed the Primary Node to be recovered onboard the IT Integrity cable ship. Finally, during Leg 2, EM302 multibeam sonar surveys, by the hull mounted system on the R/V Thompson, were conducted at both the Southern Hydrate Ridge and novel Pythias Oasis sites. Once again, the sonar imaged active bubble plumes emanating from both of these methane seep sites. The onboard VISIONS’21 students, working in the Jason ROV control van,  got to experience some of the diverse environments (spanning water depth of 9500 ft to 260 ft) along the Cascadia Margin, and the amazing biological communities that they host.

The Slope Base Deep Profiler Mooring comes aboard the R/V Thompson. Credit: M. Elend, University of Washington, V21.

The transition from Leg 2 to 3, involved an intense demobilization and mobilization in preparation for the main objective of Leg 3, which was to turn the Deep Profiler Mooring. This included mobilization of an 18,000 lb Medium Power Winch used to bring the heavy mooring onboard the Thompson, and over 9000 ft of new cable to be installed, which allows the instrumented Deep Profiler vehicle to make nearly full water column profiles of environmental parameters impacted by the California Current that flows along the Cascadia Margin. Of note, the ship was joined by Cathe Gill, who will be the resident artist onboard the Thompson during Legs 3 and 4, sharing “new eyes” on the sea and shipboard operations.

The Thompson exits the Yaquina channel into the Pacific at the start of Leg 3. Credit: M. Elend, University of Washington, V.21

The R/V Thompson left Newport and headed out thought the Yaquina channel on August 19th to begin leg 3. It was immediately met by rough seas, which were a bit daunting for those new comers who had not yet achieved their "sea legs". Weather delayed immediate work on the moorings, but the recovery of the Deep Profiler mooring was completed on August 21. This was followed by installation of the replacement mooring on August 22. The APL engineering team and ship crew worked long hours to complete this operation, which involved intense deck work and significant planning. The ROV Jason connected the mooring to the seafloor cabled array also on the 24th, which will once again allow live transmission of ocean environmental data to shore.

Near Pythias Oasis, a large, and very old crab, encrusted by anemones, wanders a garden of Neptunea snails and their egg casings, with the seafloor littered by orange anemones. Credit: D. Kelley, UW/NSF/ WHOI, V21.

With the OOI work completed, the Thompson transited to the novel Pythias Oasis methane seep site, which has been actively venting since its discovery in 2014. This site is like no other in the worlds’ ocean, venting low salinity, 12°C fluids that are saturated in methane and with chemistries unlike any other seep yet observed. This dive was funded by the National Science Foundation Marine Geology and Geophysics Division o Ocean Sciences to extend a site characterization survey of this area that was initially conducted in 2019. The main venting site, is still highly active with an intense plume rising hundreds of meters above the seafloor. The area hosts an incredible deep-sea animal community, including large clams supported by symbiotic microbes and a vast “garden”of beautiful Neptunea snails, anemones, and crabs.

With all scheduled work completed successfully, on Leg 3, the R/V Thompson headed 5 hours back into port at Newport, in preparation of the final Leg of the Regional Cabled Array Operations and Maintenance cruise, which will largely focus efforts at the summit of Axial Seamount – stay tuned for visitation of the ROV Jason to some of the most extreme environments on Earth, active underwater hot springs venting boiling fluids at temperatures over 600°F. A new group of VISIONS’21 students will share their experiences, witnessing for the first time the amazing life forms that thrive within these novel ecosystems.