RCA’s Ninth Expedition: Best Laid Plans
Written by Deborah Kelley, PI of the Regional Cabled Array, September 17, 2023
The Regional Cabled Array, spanning the Cascadia Margin and Juan de Fuca tectonic plate and water depths of ~260 ft to 9500 ft, is an engineering marvel. It is the most advanced underwater observatory in the oceans comprised of >900 km of high power- and -bandwidth submarine fiber optic cables, a highly diverse suite of >150 instruments, and state-of-the-art moorings with instrumented profilers, which since 2014 have traversed >50 million meters of ocean water! The underwater substations and instruments are installed in some of the most extreme environments on Earth, including the most active submarine volcano off the Oregon-Washington coast ‘Axial Seamount’. Here, extension cables traverse glass covered lava flows and instruments are inserted into underwater, acidic hot springs, hot enough to rapidly dissolve aluminum and melt lead. Profiling science pods on moorings that traverse ocean depths from ~650 ft to 16 ft nine times a day, must be ‘smart’ enough to keep “their heads down” when storms, common in the waters of the NE Pacific Ocean, create waves reaching 30 feet in height or more. Yet, it is within these environments that the cabled observatory has thrived, largely due to its design, rigorous testing, and the hard work of the RCA Team, and Jason and Thompson crews during the annual operations and maintenance expeditions, such as the one nearing its end now: VISIONS’23.
Planning for the RCA 2023 cruise began over a year ago as there is a high demand for NSF’s global class ships that operate throughout the worlds’ oceans. Scheduling is a complex process with lots of moving parts involving minimization of transit lengths, awareness of optimum weather windows, and researchers’ schedules. As soon as lasts year’s cruise ended, RCA instruments recovered in the Fall of 2022, were sent back to vendors for calibration and refurbishment, parts and cables were ordered, and the RCA teams’ eyes were already looking to this year. By late Spring, most of the refurbishment and integration testing of platforms and instruments was complete, the four Legs were planned out in detail, and the nearly 144 berthing assignments were finished. The careful layout of equipment on the aft deck of the Thompson was of critical importance, with nearly 200,000 lbs of gear on the fantail and the need for deck space free of gear to allow for mooring cables to be recovered and redeployed.
So that brings us to now, nearing the end of Leg 4, which will end on September 18 when the Thompson arrives back to Newport, Oregon. Working at sea is just tough, no way around it, and best laid plans are often adjusted before even leaving port (such as happened at the start of Legs 1 and 3) as the weather gods do not care about our schedule. The prior three Legs experienced numerous perturbations due to the loss of a week of operational days when the ROV Jason could not dive due to bad weather and additional loss of time due to ROV issues. Plans were adjusted on the ‘fly’ over and over again to best accomplish all of our goals, including the recovery and re-installation of >100 instruments. Because of this, some work was pushed out into Leg 4, an already complicated Leg because it was especially dependent on having good sea state conditions due to the planned installation and recovery of two deep profiler moorings, the largest of which rises >8000 ft above the seafloor at the base of Axial Seamount.
Almost immediately, Leg 4 plans were adjusted following the first operation – the recovery and reinstallation of the Deep Profiler Mooring at the Oregon Offshore site. The communications and power ‘dock’ at the base of the mooring would not respond after plugging in the seafloor extension cable that connects it to a small substation (junction box) on the seafloor. While the engineers tested various aspects of the cable, and puzzled over the cause, the RCA team continued their work at the Slope Base site. There, the Deep Profiler mooring cable was cleaned, and the instrumented profiling vehicle deployed in 2022 was replaced. Following this operation, the Thompson transited ~ 18 hrs to the base of Axial Seamount, where, instead of turning the mooring, it was decided to just swap out the vehicle, similar to Slope Base.
With this work complete, a series of dives was planned to support researchers’ projects funded by the National Science Foundation outside of the Ocean Observatories Initiative. These dives were to include sampling of hydrothermal vent fluids to investigate viruses and microbes in these extreme environments, the recovery and installation of cabled CTD instruments to test the hypothesis that highly saline fluids are flushed from beneath the seafloor shortly following an eruption, and the recovery of a cabled multibeam sonar (COVIS) focused on making unique fluid flux measurements in the ASHES hydrothermal field. Time allowing, equipment on the Thompson would be used to “talk” to an acoustic array (FETCH) installed in the volcanoes’ caldera for investigation of deformation within this highly active volcano.
There was, however, a small window to complete this work. After investigation of the Deep Profiler Mooring at the Oregon Offshore site, it was determined that the Thompson would need to transit nearly 300 miles back to this area, to install a new extension cable, and/or recover and redeploy the mooring with the one just recovered at the beginning of Leg 4 – an exercise that could take 2-3 days. Indeed, Jason had other ideas because while working at the summit of Axial, there was an issue with the specialized hydrothermal vent sampler on the vehicle, followed by a failure of the power system, preventing more dives. The Jason team worked very hard overnight to fix the power supply, but with ever decreasing time to get the Deep Profiler work done back on the margin, it was decided to abandon remaining work at Axial (a very tough decision as this would impact researchers work over the entire next year) and head to the Offshore site. This also allowed optimal use of the transit time to thoroughly test the repaired power system for Jason. It also provided time for the APL engineers to ready a new extension cable for the Deep Profiler mooring, hoping that this simple fix would solve the problem, and to catch up on much needed sleep. With huge relief, the replacement of the extension cable did the trick on the first dive at the Offshore site. The docking station powered up and the vehicle completed its test profiling run — opening up a three-day window for additional work.
With a sigh of relief and desperately wanting to support the external researchers work, Chief Scientist, Katie Bigham, asked Captain Eric to turn the ship around and head back out to Axial Seamount. So away they went, following the same track line they had completed less than 24 hrs before. During the next 34 hrs, Jason pounded out the dives and completed all but the FETCH work, before it was time to once again head back to Slope Base to complete two final tasks.
The above description is only part of what goes on during the various legs of these RCA expeditions. It is hard to convey what it is like to be a Chief Scientist on an RCA cruise. As with this cruise, decisions must be made rapidly, but also strategically, with an eye towards the end of a leg and cruise – “Will this decision prevent other work from happening? What is the weather going to be like in 2-3 days? What is the status of equipment? How are the students doing and how are their projects going? Do they need help? Is the team getting enough sleep? Should we transit to another site to help with this? On and on it goes…Awareness of these questions and outcomes are always in a Chief Scientists’ thoughts and are combined with the everyday tasks of writing plans for the next day and operational reports.
This was Katie’s first time being a Chief Scientist. She has done an exceptional job making adjustments to our “best laid plans” on a cruise that has been one for the books in the near decade of RCA operations and maintenance expeditions.
For more information on the RCA’s ninth operations and maintenance expedition, visit here.
