Nodes Are Primary

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The doors on Primary Node PN1B are open and the crabs do not appreciate the presence of the ROV Jason. Credit: UW/NSF-OOI/WHOI, V21.

After finishing up our work at the base of Axial Seamount, we moved farther inshore to the location of one of the Regional Cabled Array’s Primary Node: PN1B.

The importance of the Primary Nodes is in the name: “node,” as in a central hub with multiple connections, and “primary” as in they are the first point of connection for the 900 km of high-power, high-bandwidth backbone fiber optic cables on the array. The Primary Nodes are large seafloor substations where 8,000 volts of power gets stepped down and provided to medium- and low-power junction boxes through a series of extension cables. The junction boxes, with additional extension cables, connect to the seafloor instruments and water column moorings in a form that their electronics can use. Industry wetmate connectors allow plugging in and unplugging of extension cables underwater – similar to plugging in an electrical chord to your house outlet, but in this case the node is >3000 feet beneath the oceans surface. The nodes also provide 10 Gb bandwidth for communication to and from the infrastructure in the water – bringing the Internet directly into the ocean.

Wetmate connectors in PN1B. Credit: UW/NSF-OOI/WHOI, V21.

The Primary Nodes have performed nearly flawlessly since they were deployed by an industrial cable ship in 2014. However, if they malfunction, then everything farther down the line will lose power and be unable to communicate scientific data to shore.

This is why we are at PN1B: to prepare the node for repair work to correct a power failure that occurred in August 2020. The length of the cable was inspected last year, and the fault was isolated to PN1B, necessitating repair work. This is the first time that anyone on the ship (scientists, engineers, and ROV crew) has conducted this type of repair, and it requires coordination between the UW research vessel  the R/V Thomas G. Thompson, and an industrial cable ship, the IT International Telecom Inc. cable ship Integrity.

Crabs investigate Jason attaching an arm of the bridle to the PN1B frame. Credit: UW/NSF-OOI/WHOI, V21.

We completed two dives at the node site, which is in 1242 meters (about 3600 feet) of water. One Jason dive disconnected all the cables and attached a docking frame that allowed Jason to latch into the node and bring the Science Interface Assembly (the part that plugs into the lower-power secondary nodes) back to the surface.

On the second dive, Jason attached a harness to the node frame so that the cable ship can haul it back to the surface, when it arrives on site next week.

All operations went very smoothly, despite them being new to the engineering team and the Jason team. We also inspected the site to see how it has changed since the node was first deployed in 2014 – it was surprisingly clean of biofouling (animals and microbes that grow on any hard surface deployed in the ocean), but it was colonized by a few crabs who seemed a little upset that their house was being moved.

A rockfish rests on the top of Primary Node PN1B. Credit: UW/NSF-OOI/WHOI, V21.

Now that the initial steps are complete, we’re ready to meet the cable ship and finish the primary node maintenance, so we can power up the rest of the array and start delivering data again!