Dispatch 6: The First Mooring Recovery     Print

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Joey Wenig

September 26, 2014

If, over the first five days of the cruise, anyone managed to fall into a routine, they were probably shaken out of it today when the group from WHOI—Rick Krishfield, John Kemp, Jeff O’Brien, and Meghan Donohue, along with Cory Beatty of the University of Montana—took over the ship to recover a several-thousand-meter-long array of oceanographic instruments called a ‘mooring’. This particular mooring had been sitting out here at station BGOS-D, anchored to the bottom of the central Beaufort Sea, since it was deployed last August. Needless to say, it seemed glad to have us stop by and haul it up for a bit of fresh air.

When it’s on the job, the mooring extends vertically through the water column, with a 3800-pound anchor at the bottom end, and a gigantic yellow sphere providing 2500 lbs of buoyancy (flotation) at the top. The sphere sits about 30 meters below the sea surface and has three instruments mounted on it. These instruments are constantly monitoring the thickness of the overlying sea ice (if there is any), the velocity of currents flowing past, and the properties of waves traveling over or around the top of the mooring. Moving downwards along the mooring recovered today, we find in succession two ‘MMPs’, instruments that climb up and down a 2000 m and 1000 m stretch of wire rope (respectively), over and over and over, taking a set of measurements (including temperature and salinity) as they go. Next, at a depth of around 3000 m, is a sediment trap, which, as you would expect, collects sediment raining down through the ocean. Whatever’s collected gets funneled into bottles that rotate on a battery-operated track over the course of the deployment, providing a time-series of sediment in the water column. Below the sediment trap are forty-eight glass balls, seventeen inches in diameter, aligned vertically and mounted in groups of four on trawler chain to provide backup buoyancy should the top sphere part from the mooring. And below all of those are the all-important release units, for when the mooring is to be recovered. These communicate acoustically with a "deck unit" on the ship, and when commanded will let go of the anchor and, buoyed by the top sphere and glass balls float towards the surface. With all that water in the way, talking to these units can be difficult. As a safeguard, the two release units are redundant—only one of them needs to get the message for the mooring to be released from the anchor. As we saw today, when the acoustic transducer in one of the release units turned out to have leaked and shut down the unit so that only one was functional, this redundancy can be vital.

Since we were in fairly thick ice cover, the Louis needed to clear a patch of overtop the mooring so that it could be spotted when it was released and floated to the surface. Once it was found, we maneuvered over to the giant yellow sphere, and John Kemp was lowered over the side of the ship to attach a line to it. Then the long process of hauling in the lengthy array began, made more difficult by the constantly encroaching ice, which managed to mangle several instruments on their way up. While this is frustrating, its not the end of the world—as long as data from the previous year, encased in the instruments, is safely recovered.

For the most part, today’s recovery went smoothly. A bit of a hitch was encountered when a big portion of the array came up tangled. Fortunately, this didn’t cause any real problems, and all data is now safely on board. But the work’s not over: we are redeploying the mooring in the same location tomorrow, and so along with other preparations, any instruments that are going back down for another stint underwater need to have data downloaded, batteries changed, and repairs completed. Including today’s, three moorings will be recovered and redeployed during the cruise, and two other moorings will be deployed at new locations.

This evening was the much-anticipated Arctic Greenhorns Talent show. Highlights included a juggling act by 3^rd Engineer Don MacLeod, an apple eaten at extremely high speed and in very few bites by cadet Raphael Lapointe, a rendition of the Dixie Chick’s Travelin’ Soldier by yours truly, a strange skit by Alek Petty and Sam Thomas involving blindfolded egg-tossing intended to demonstrate their telepathic connection but merely resulting in Sam and the floor being covered in egg yolk, an enactment of a scene from Romeo and Juliet by Melissa Schwab, some banjo tunes by Wes Halfacre, and a complete ‘air band’ version of  Bohemian Rhapsody. There is some serious talent on board this ship.