The Regional Cabled Array, ROV Jason and R/V Thomas G. Thompson ship crew have had a very busy start to Leg 2 on the NSF-fund RCA Operations and Maintenance cruise and they have kept an intense eye on the weather forecast. Prior to departure, several tons of gear were offloaded and on loaded onto the fantail of the Thompson in preparation for Leg 2. With the help of a shore crane, the mobilization was extremely efficient, and the ship left the Newport dock at 1111 local on August 15th. Dr.
Even after a very busy port call, the crew had little time for rest, however, as the first worksite – the Oregon Shelf site – was only an hour steam away. Here, good visibility allowed for the zooplankton sonar to be installed during Dive J2-1274: the vehicle was visited by curious sablefish, one of which was content to rest atop the sonar platform. The ROV again visited the medium power junction box ‘MJ01C’, fondly called the “sheep” due to its complete encasement by beautiful anemones.
Although beautiful, the anemones show no regard for the wet-mate connectors that Jason must access with its manipulators to disconnect/reconnect cables for the zooplankton, digital still camera, and Benthic Experiment Package at this site. Hence, a toilet brush meets the anemones to clear the ports. Based on real-time weather look-aheads provided by the APL Dive Index application, as predicted, the swells at the Oregon Shelf site were too large to deploy the >3000 lb Benthic Experiment Package from the underbelly of Jason, so the R/V Thompson headed ~ 22 hrs out to Axial Seamount where better weather was predicted – the ship arrived onsite at 1448 on August 15th.
The first task within the caldera of Axial Seamount was to turn the Eastern Caldera medium powered junction box (MJ03E – small seafloor substations that provide power, bandwidth, two-way communications to instruments at this site and others) and to install a new CTD funded through an NSF award to Dr. Bill Chadwick (Oregon State University). Three cabled CTDs funded for addition onto the cabled network in anticipation of the upcoming next eruption. Based on temperature and water column data from the April 2015 eruption, salty fluids, generated by the boiling hydrothermal vents at Axial, are thought to have been emitted from the subsurface during-shortly after the eruption1. Two of the CTD’s are now installed at the ASHES hydrothermal field and at Eastern Caldera – the final CTD will be installed at the Central Caldera site next summer on VISIONS’21. The installation went very well and highlights the remarkable work that the APL engineering team has done in designing, building, testing, and installing the junction boxes. As delineated by James Tilley, the lead APL engineer for the junction boxes and lead now out on the ship, the MJ03E junction box was initially installed July 22, 2013 – it spent the last 2,583 days 1516 m (4874 feet) beneath the oceans’ surface and has worked flawlessly.
The R/V Thompson transited to the ASHES and International District hydrothermal fields following work at Eastern Caldera. Here again, weather was a concern as a strong front was predicted to come through. At ASHES, a new osmotic fluid sampler was installed to take time-series samples of diffuse vent fluid for the year, with follow-on chemical analyses once it is recovered in 2021. At the International field, the ROV visited the temperature-pH-H2S instrument in Diva, which is now venting temperatures >250°C, the temperature- resistivity probe in Escargot (320°C), and the vent cap at the Tiny Towers site that feeds the remote access fluid sampler and microbial DNA sampler. Operations, again went well and work is now completed for the year at Axial Caldera.
Jason is now conducting a several hour dive at Axial Base to clean the cable that the Deep Profiler vehicles transits on daily from ~ 2600 m to ~ 127 m water depth. Once work is complete at this site, the R/V Thompson will head back across the Juan de Fuca plate to work at the margin again, including Southern Hydrate Ridge. Onward we go….
1Xu, G., Chadwick, W.W., Jr., Wilcock, W.S.D., Bemis, K.G., and Delaney, J.R. (2018) Observation and modeling of hydrothermal response to the 2015 eruption at Axial Seamount, Northeast Pacific. Geochemistry, Geophysics, Geosystems, 19(8) https://doi.org/10.1029/2018GC007607.