NPEO Mooring Deployment and Recovery

The third NPEO mooring is currently anchored to the ocean floor in 4120 meters (2.6) miles) of water and reaches up to within 50 meters of the underside of the ice. The scientific instruments shackled to the mooring line must be recovered to acquire their internally-recorded data. A major purpose of the logistical effort each spring of the program is the recovery of the previous year's mooring, and installation, or "deployment", of the next.

Typically working from the temporary Russian ice station "Borneo", the University of Washington mooring team flies out with a helicopter to the GPS position of the previous year's deployment. After landing, two 8- x 12-foot tents, mounted on sleds, are installed at the mooring site for five days as living and work space for the two scientists and three divers responsible for the mooring work. They auger a hole through the ice and lower the hydrophone from the acoustic command gear. This enables them to communicate with the transponders at the top of the mooring. Using transponders at the top of a mooring allows them to get more accurate range and bearing than using the releases that are located down at 2500 meters depth.

Once the position is accurately located, they wait until a large flat pan of refrozen ice passes over the mooring, the flatter and thinner the better. Once they have the ice of choice over the site, the release code is sent to one of the lower two Acoustic Releases.
Fifty seconds after the code is transmitted, the mooring team expects the float and instrument at the top of the mooring to hit the ice below their feet. Forty minutes later, they expect floats farther down the cable to finally bring the tail end of the mooring up against the ice. Located at the top of the mooring is an avalanche beacon that that can be located within a meter beneath the ice. If all goes well, the released mooring is situated something like ...

—— drawing by Jim Johnson

With the top located, the SCUBA divers begin melting two 4-foot diameter holes through the ice, one for the recovery and one for the divers. A 10-foot high A-frame is erected over the recovery hole, and the divers will go in and attach a haul line to the top of the mooring. Then begins what is typically a 16-to-24-hour job of hauling miles of cable up through the hole in the ice, stopping to remove floats and instruments as they emerge. At any point, if part of the mooring should get hung up on ice keels, which are steep, sharp edges jutting down into the ocean, the divers will have to go in and move instruments and floats around the obstruction.

Redeployment of the new mooring is accomplished within two days at the same location. The new mooring is lowered anchor-first. Deployed in the ocean for another year, the instruments on NPEO mooring patiently monitor the changing state of the water column at the North Pole.