Dive and Discover : Exp 7 : New England Seamounts : Daily Updates

After a bit of delicate ship maneuvering, the sled was freed, with barely a scratch for its trouble. When it surfaced, it brought up a special treat in addition to its customary 1,800 or so photographs: coral. Lots of coral. Instead of the hundreds of individual Desmophyllum cristagalli that we'd gotten used to, however, this D. cris was in large chunks, which had been ripped from the seamount when the sled came up.

Tim Shank, a biologist and veteran of these cruises, said the odds of something like this happening are "not even one in a million...more like one in a billion." Thank you, Poseidon.

Along with the day's haul from Alvin, today was very productive indeed. Tomorrow will be the last dive on Muir Seamount. After that, we'll head back to Manning Seamount, where the weather seems to have finally calmed down enough for our purposes.

The episode with the towed camera encouraged us to investigate further what that important tool is all about. It's a relatively simple technology when compared to some of the equipment around here, but it greatly improves our efficiency with Alvin dives.

The tow-cam was actually built to be a camera/rock-corer—a device that can break off small chips of rock on the sea floor and bring samples up for testing.

On this cruise, however, rocks aren't what we're after. So the tow-cam functions primarily as a moveable digital camera. There's a Nikon Coolpix attached to a sturdy sled, capable of taking a picture every 10-15 seconds over a time span of 5 hours. To store all that data (roughly 1,800 photographs, depending on which resolution the camera is set at), there's a 2-gigabyte memory card installed.

"It's a way of surveying the sea floor without near the expense of Alvin or an ROV (remotely operated vehicle)," says scientist Rhian Waller. "We can use it as a tool to look at an area before we trawl or really study an area in more depth."

Waller is a tow-cam veteran, along with scientist Bob Green, whose role it is to look after the WHOI tow-cam. Waller works out of Southampton Oceanography Centre in the United Kingdom, and she says that towed cameras at that institution are often used for environmental surveys, to count animals or ocean flora.

Operating the tow-cam takes a good deal of human effort and attention. Attached to a cable, it is lowered on a cable from the side of the ship using a hydrowinch, until it approaches the ocean floor. At about 100 meters above the floor, an altimeter kicks in, so that the operator can keep the sled at its optimum distance from the seafloor: 6 meters.

This entire time, the tow-cam operator aboard the ship is watching computer monitors that relay water information as well the tow-cam's position. How often does she or he need to adjust the tow-cam's position? It depends entirely on the terrain. If the seafloor is flat, you've got a relatively easy time. Last night, moving it up a steep slope, Bob Green was continually making adjustments.

Every once in a while, the tow-cam gets stuck. When that happens, you stop the ship, which until then has been traveling at a speed of a quarter-knot, and back up. The goal is to get the cable back to a vertical position.

Sometimes re-positioning the cable and freeing the camera sled takes quite a while. Last night it took just under two hours. We were happy to have it back, coral on board or not, just so it can keep on diving, and keep on helping.