Leg 3 Ends With a First Of Its Kind Experiment Installed

The fantail of the R/V Thompson at the start of Leg 3. Onboard is the low power junction box LJ03A, three instrumented Deep Profiler vehicles, a CTD tripod, and four FETCH tripods. Credit: M. Elend, University of Washington, V22.

Leg 3 was another exceptional Leg for the OOI-RCA VISIONS’22 expedition with all OOI and PI-funded work completed and more. A total of 31 core OOI instruments were deployed, 49 core OOI instruments were recovered, eleven externally-funded PI instruments were deployed, five PI instruments were recovered, four CTD casts and two sets of ROV-mounted Niskin bottle water samples were collected. The success of this leg was in large part due to the exceptional ROPOS team, with the ROV completing 26 dives (R2229 – R2254) during the 11 days at sea.

The eleven VISIONS’22 students and RCA team members at the start of Leg 3. Photo Credit: M. Elend, University of Washington, V22.

This Leg included a diverse cohort of 11 undergraduate and graduate students as part of the VISIONS’22 at-sea experiential learning program. Through the “eyes” of ROPOS, the students got to witness one of the most extreme environments on Earth – the underwater hot spring systems on the summit of Axial Seamount where boiling fluids are issuing from the seafloor. Eight separate sites were investigated providing an opportunity to see young, glass-covered lava flows, the steep walls of the caldera, and a diverse array of hydrothermal vent communities thriving on the outer walls of black smoker chimneys and at diffuse flow sites.  The students also got to experience coastal and blue water environments, while the ROV worked at the Endurance Oregon Offshore, Slope Base, and Axial Base Sites.

OOI-RCA Dive Operations included:

An aggressive blue shark approaches ROPOS at the Oregon Offfshore Site. Credit: UW/NSF-OOI/CSSF, R2231, V22.
  • Turning of the three instrumented Deep Profiler vehicles at the Oregon Offshore (600 m), Slope Base (2900 m), and Axial Base (2600 m) sites. At the Oregon Offshore site, some unexpected blue shark aggression towards the ROV resulted in a damaged light that required a vehicle recovery! For follow-on instrument verification, one deep, post-deployment CTD vertical cast and subsequent water sampling for oxygen, carbon, nutrient, salinity, and chlorophyll analyses was completed at each Deep Profiler locations.
  • At Axial Base, a Horizontal Electrometer Pressure-Inverted Echosounder instrument, seafloor pressure sensor, a low-power junction box (LJ03A) and the attached CTD-dissolved oxygen, and optical attenuation and absorption instruments/platforms were turned.
The high definition camera images the active hydrothermal vent ‘Mushroom’ every three hours, sending video to your living room live from nearly a mile beneath the ocean and 300 miles offshore. Credit: UW/NSF-OOI/CSSF, V22.
  • At the ASHES hydrothermal field at the summit of Axial Seamount (~1500 m) the HD video camera and digital still camera (CAMDS) lens and lamps were cleaned to remove bacteria and other biofouling, and the uncabled osmotic fluid sampler within a diffuse flow site was turned.
  • In preparation for the recovery of the Shallow Profiler Mooring at Slope Base, and its replacement on Legs 4 and 5, respectively, the instrumented platform interface assembly and profiler science pod was recovered. The winched science pod was then used to replace a faulted science pod that had been installed on Leg 1 at the Oregon Offshore Shallow Profiler Mooring.  A shallow CTD vertical cast and water sampling was completed following the science pod swap.

In addition to the core OOI efforts, there was a substantial amount of work completed for externally funded NSF projects.

ROPOS carries a FETCH tripod to the seafloor. Credit. J. Tilley, APL, University of Washington, V22 .

A major highlight of the externally funded programs was the successful installation of a first-of-its kind cabled and uncabled acoustic network spanning the central caldera and bounding walls of Axial Seamount. This work, funded by NSF as part of an award (An Acoustic Array At Axial Seamount for Geodesy and Autonomous Vehicle Support) to UW geophysicist Dr. W. Wilcock and APL Engineer D. Manalang included the deployment of four FETCH tripods across Axial Caldera that created an acoustic array that can precisely measure horizontal stresses and seafloor motion that might presage an eruption at Axial Seamount. A cabled FETCH tripod at the Central Caldera site interrogates the three other FETCH Tripods, streaming acoustic information in real-time to shore. Data from this network is particularly valuable as it provides information key to examine the shallowing of the seafloor at the summit of the volcano as it rises due to inflation of the underlying magma chamber. The data will also allow investigation of the impacts that this has on buried outward dipping faults beneath the east and west caldera walls. The network, in the future, could also provide navigational beacons for an autonomous vehicle.

Other NSF-funded work included the annual turns of a CTD (Dr. W. Chadwick, OSU) at Central Caldera, the recovery of two thermistor arrays in the ASHES hydrothermal field in support of heaflow study by Dr. K. Bemis (Rutgers University), and the recovery of two in-situ temperature probes (HOBOS) and installation of six others in high temperature anhydrite and metal sulfide rich hydrothermal chimneys (Trevi, Virgin, Hell, Inferno, El Guapo, and Castle), in support of another program to Dr. W. Chadwick.

The efficiency of the ROPOS operations, allowed opportunistic collection of macrofauna samples for use in UW senior thesis research projects on the population structure of scale worms and how they interact with tube worm populations, and sampling of protists for follow-on genetic studies.

Another highlight of Leg 3 was a 45-minute telepresence outreach event organized by ‘Exploring by the Seat of Your Pants’ which brings live events into K12 classrooms. During this event, which took place above Axial Seamount, 79 groups from 8 countries participated live. Chief Scientist, Mike Vardaro, and UW student worker Andrew Paley introduced the OOI-RCA, the purpose of this expedition, and then answered student questions via video and the chat feature. Feedback from the event organizers included “What a fun and fantastic program to kick off our school year!

With the successful completion of all work, the R/V Thompson returned to the NOAA Marine Operations Center – Pacific at 0821 local on September 4th. Demobilization of Leg 3 equipment, lead by RCA Logistics Manager Larry Nielson, began shortly after 0900 the same day and was complete by 1200. Mobilization for Leg 4, including onboarding of medium- and heavy-lift winches to support the Slope Base Shallow Profiler mooring turn, began at ~0800 on September 5th and was complete by 1130.

The Thompson departed the morning of September 6 to Slope Base to begin the recovery of the Shallow Profiler Mooring — away we go.