Dispatch 15: More Moorings     Print

Alex Kain

October 1, 2009

Moorings fasten to anchors at the bottom of the sea. They are held taut by a large buoy, suspended from the bottom roughly 50 meters (164 feet) from the ocean's surface. At depths along the vertical line, instruments monitor the conditions of the sea. Over the past three days, WHOI technicians and CCGS Louis S. St.-Laurent crew have completed two mooring recoveries and one deployment. Each recovery and deployment requires several hours of carefully planned labor in the frigid cold.

Though conceptually simple, subzero temperatures, winds, and heavy ice cover present mooring recoveries with numerous challenges. All moorings, however, follow a similar course to get from the bottom of the Beaufort Sea to the deck of the Louis.

Step 1: Find the general location of the mooring
The mooring remains anchored to the same place on the sea floor all year, making its location easy to track. The mooring's enormous underwater buoy also shows up on the ship's radar. Even with these numerical markers, sea ice complicates the search.

Morning on the Beaufort Sea. Frost on deck railings indicates a cold morning, and a chilly environment for the recovery ahead.		Coast Guard Cadets Ryan Gurr and Kristina Kean stayed smiling despite the cold weather.

Step 2: Mow the lawn
"Mowing the lawn" is the technical term for breaking up the ice around the mooring site so that when the line floats to the surface, it can be easily spotted and retrieved. The process gets its name from the ship's paths through the ice, which resemble the ribbons of texture a mower leaves in a grassy yard.

The ship first "mows the lawn" by triangulating the mooring site. Based on radar images, the ship plows through the ice to enclose the site in a triangle shape. Then, once distances are calculated to the mooring from the vertices of the triangle, the ship can accurately break up ice throughout the site, allowing for an efficient recovery that reduces the risk of the mooring's getting stuck under a floe.

Mow, mow, mow your boat.		The Arctic mooring recovery's equivalent of grass clippings.

Step 3: Detachment
A two-ton anchor connects the line to the ocean floor. A sound wave of a specified frequency zaps the acoustic release of the mooring, causing the line to detach. The two main buoyancy implements—the huge top buoy, and yellow floats on the bottom—then carry the ends of the line to the surface of the water.

If all goes as planned, the huge top float will be visible on the surface of the water, or among small ice chunks that can be pushed aside with compressed air that spews from the side of the ship.

Buoy in the Beaufort Sea. Notice the ship's mowing path in the background. The 64-inch buoy looks like a fishing line's bobber amid the enormous ice fragments.

Step 4: Link the float
Now that the mooring is floating on the surface of the water, it needs to be brought to the surface of the boat.

This isn't as easy as it sounds. Like all other recoveries, this process resembles one of those stuffed animal crane games you find in the entryways of supermarkets. Technicians must insert a two inch-wide hook into a metal loop at the top of the buoy, a linkage that requires a platform to be lowered from the deck of the ship to the surface of the water.

WHOI's Kris Newhall and Coast Guard Winchman Al Jarvis lower to the sea to retrieve the mooring.

Step 5: Start reeling
Once the buoy is linked, the mooring line is fed into the enormous winch system on the deck, which reels in the 3,800 meters (12,467 feet) of line, chain, and profilers. This process becomes complicated because crewmen must detach all scientific gear without loosening the line from the winch. To accomplish this, the portion of line below the instrument being removed is attached to a crane, where it remains suspended until it can be fed once again into the winch system.

The buoy, fully removed, resembles a rejected Sputnik prototype. Its top was coated in the lone plant species of the Arctic Ocean, algae.

Step 6: Collect samples
Any samples collected by devices on the line must be quickly removed and stored to avoid contamination.

A sediment trap reels to the deck of the ship, splashing water as it ascends. The bottles in the sediment trap carousel rotate one notch twice a month, giving 24 bottles of sediment data at the end of a year. Scientists at WHOI will analyze the sediment to determine the species of phytoplankton and zooplankton that exist in the column of water being studied.

Step 7: Figure out how to deal with an infestation of yellow balls
No, these aren't exotic aquatic Arctic grapes. They're floatation devices known as glass balls, which get their name from the fact that they're actually hollow glass spheres covered in plastic "hard hats". The floats bring the bottom of the line to the surface of the water to aid in retrieval. They also take up a ton of space on deck, necessitating a quick transport to below deck.

Bacchus has no interest in these grape-shaped buoys.

And lastly, by far the most important step in a mooring recovery.