Farther and Deeper We Go

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Leg 4 has gotten off to a good start. The R/V Revelle left Newport the evening of July 20th for the last time this cruise.  The primary goal of this last leg is to repair or replace the three (3) Deep Profiler (DP) moorings that are part of the Cabled Array (CA). When that work is finished, the CA Team will cap off a successful summer of work by returning to the caldera of Axial Volcano, where we spent most of Leg 2, and deploy the fourth and final new instrument for this year, a sonar which will monitor the outflow of volcanic hot springs in the caldera.


The DP moorings consist of a long cable extending from the seafloor up through the water column and overlapping with the 200 m platforms of the Shallow Profilers deployed on the earlier legs.  A battery-powered wire crawler moves up and down the cable and is charged by a docking station positioned near the seafloor. These Deep Profiler Moorings are located at three (3) sites that extend across the Juan de Fuca tectonic plate, a region characterized by significant earthquakes and volcanism at its boundaries.  The shallowest mooring location is Oregon Offshore at 48 miles from Newport, Oregon and positioned on the Continental Slope in 575 m (0.36 miles) of water. This highly dynamic location is characterized by upwelling of cold and nutrient rich water and increased primary productivity.  Slightly further west at 67 miles from land is the second and much deeper Slope Base location in 2900 m (1.8 miles) of water.  This area represents the transition to the deeper outer reaches of the continental margin.  The furthest from shore at 292 miles is Axial Base in 8500 m (1.6 miles) of water.  This location is near the plate’s western boundary where the seafloor rises to the caldera of Axial Volcano. The combinations of Deep Profilers and Shallow Profilers at these same sites provide complete profiles of the water column across this tectonic plate.  The profiles are sent back to scientists on shore in near real-time and deliver critical data on the currents, chemistry, biology, and energy budgets of this active continental margin.


Deployments of these DP moorings set the ship on a very different schedule as compared with the breakneck pace of the first two legs. Though the CA Team on the ship is no less busy and is still carefully watching the weather, the work is now more tied to the rising of the sun. Mooring deployments involve an intricate dance of deck work and ship positioning that is made easier with plenty of daylight. At the Oregon Offshore site, work started the morning of July 21st with the ROV JASON diving to unplug the mooring and attaching a recovery line to the top float. A successful hand off of the line from the ROV to the team on deck kicks off a busy day for the Applied Physics Lab (APL) Ocean Engineering Team led by Tim McGinnis and Eric Boget that culminates with the entire mooring on deck over 6 hours later. This does not signal the end of the day’s work. For the rest of the day, and well into the evening, the engineers troubleshoot the recovered instruments in preparation for deploying and/or making adjustments to the replacement wire crawlers and/or charging stations, sometimes even swapping electronics that allow communications with and/or power the profilers.  All these late-night activities are designed to ensure that the mooring and all its components are ready to be deployed at dawn the next day.  Deployment of a deep profiler mooring looks much like the reverse of recovering one – a long day on deck that finishes with an ROV dive to connect the mooring to the CA network.


While the APL engineers prepare for the next morning’s activity, and get a good night’s rest, the rest of the CA Team and VISIONS’18 students continue activities to verify that the mooring and other CA instruments are operating properly. APL Research Associate Wu-Jung Lee led two plankton net tows with a Tucker Trawl at the Oregon Offshore site the evening of June 22nd and mid-day on July 23rd. The plankton collected in these tows will be identified at UW and used to provide ground-truth or calibration information for the zooplankton sonar that is on the Shallow Profiler Mooring at the site. Grays Harbor College Professor Julie Nelson led CTD casts and collected water samples at Oregon Offshore on June 23rd to compare to the data from the newly installed Deep Profiler and to cap off the summer’s work at this site. With all of the work completed at this first Offshore site, the team will now repeat these actions two more times as we transit further from shore to replace the two remaining mooring.