Regional Cable Array - Ocean Observatories Initiative

RCA Embarks on a 41-day Operations and Maintenance Expedition

By Darlene Trew crist | August 12, 2023 |

Watch live video here.

The numbers are remarkable for the Regional Cabled Array’s (RCA) Operations and Maintenance Expedition that left Newport, Oregon aboard the R/V Thomas G. Thompson on Sunday August 13. Because of its complexity and the need to move 100 different instruments, the expedition consists of four legs over 41-days. The legs are separated by ~2-3 days port call at NOAA Marine Operation Center in Newport, Oregon. A science team of 12 is conducting the scientific operations, with their work supported by an engineering team of 20 (not all onboard). The Remotely Operated Vehicle (ROV) Jason, operated by a team of 12 from the Woods Hole Oceanographic Institution, is recovering and deploying instrumentation on the RCA for the duration of the expedition.

Finally, 25 students in the University of Washington’s VISIONS Program are onboard during various legs to gain real sea-going experience and work side by side with the scientific team. Additionally, six other guest participants will be onboard, including a children’s author, engineers, and scientists.

The RCA annual expedition is always an exciting opportunity to watch real-life operations at sea. Operations will be live-streamed here. Details about the expedition, who’s involved, and what’s happening and planned can be found here. Daily updates can be found here.

[video width="608" height="1080" mp4="https://oceanobservatories.org/wp-content/uploads/2023/08/Thompson-loading.mp4"][/video] Read More

Pythias Oasis: The First-of-Its-Kind Seep in the Oceans

By ooistaff | January 26, 2023 |

Adapted and condensed by OOI from Philip, et al., 2023, doi: 10.1126/sciadv.add6688.

[media-caption path="/wp-content/uploads/2023/01/Screen-Shot-2023-01-26-at-10.21.55-AM.png" link="#"] a) A multibeam sonar image of the methane bubble plumes at Pythias Oasis in 2015. b) Pythias orifice in 2015 showing the fluid-dominated, sediment-rich plume, as first visualized on the discovery dive by the ROV ROPOS. The main orifice has been continuously active since 2015. c) Pythias’ orifice in 2021 with increased biological communities and a small Fe-rich chimney. d) The edge of a large collapse-blowout zone – coring across this area in 2019 recovered substantial methane hydrate. e) A Neptunea snail nursery between the orifice site and the blowout zone.[/media-caption]

Pythias Oasis is the first-of-its-kind seep in the oceans, providing a window into controls on megathrust events along the Cascadia Margin. Pythias Oasis, discovered during the 2015 Regional Cabled Array (RCA) Operations and Maintenance Cruise, utilizing the hull-mounted sonar on the R/V Thompson, is unlike any seep site yet described along active margins with unprecedented fluid chemistries (Figure above). It hosts an intense fluid-dominated venting system issuing low-salinity, hydrocarbon-bearing fluids carrying low concentrations of suspended particles from a discrete orifice that has been continuously active since 2015. Detailed sampling, as part of an NSF OCE-funded expedition in 2019 (OCE 16582901), and another dive in 2021 (added onto the RCA 2021 cruise) show that the fresh, warm fluids (four times background temperatures) are venting at the highest discharge rates yet measured within the Cascadia Subduction Zone (CSZ) and that the fluids are extremely enriched in boron lithium and iron.

Pythias Oasis provides a rare window into processes acting deep in the margin with fluid chemistries indicating that the fluids are sourced near the plate boundary in the Central CSZ at minimum temperatures of 150-250°C. The high discharge rates are thought to reflect draining of fluids along an over-pressurized reservoir associated with the subduction zone-perpendicular Alvin Canyon strike slip fault, suggesting that the faults regulate pore fluid pressure and megathrust slip behavior along the Central CSZ.

Results from this work are presented in Philip, B.T., E.A. Solomon, D.S. Kelley, A.M. Tréhu, T.L. Whorley, E. Roland, M. Tominaga, and R.W. Collier (2023) Fluid sources and overpressures within the central Cascadia Subduction Zone revealed by a warm, high-flux seafloor seep. Science Advances (9), doi: 10.1126/sciadv.add6688.