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Submersibles Give Scientists View of Life on the Ocean Floor


On VOA we often tell you about the latest developments in scientific research. What we don't mention very often are the extraordinary tools researchers use to do their work. Small submarines called submersibles, like the one on board the Research Vessel Seward Johnson, have changed the way scientists study life on the ocean floor.

I originally planned to visit the ship out at sea, but as Hurricane Wilma barreled up the Atlantic Coast, the captain decided to put in to the historic port of Charleston, South Carolina.

Instead of the crash of storm-driven ocean waves, the waters of the Cooper River gently lap up against the pier, where the Seward Johnson is tied up.

Sitting on her deck is the Johnson-Sea-Link, the bubble-domed submersible that takes scientists down as deep as 900 meters to study the life on the ocean floor. And it's been doing it for three decades.

"This submersible was built in 1973. So this boat, just in fact yesterday, did its 4,901st dive," explains Craig Caddigan, who pilots the submersible. He works for the Harbor Branch Oceanographic Institution, which owns the research ship and its submarine. The Johnson-Sea-Link submersible moves up and down with ballast tanks, like other submarines, but for fine maneuvering it's equipped with an array of small, enclosed propellers.

"There's nine thrusters," continued Mr. Caddigan. "There's three verticals, there's two horizontals, and on the side there's a pair that are four fore-and-aft and each thruster is two-directional, so if I want to go up, I flip it up; if I want to go down, I can go down. If I want to spin her -- She'll do basically anything but stand on her head."

Compared to military submarines, the Johnson-Sea-Link is tiny. It's eight meters long and three meters high, and weighs 12,000 kilos. It carries four people and has powerful lights and video cameras to record the scene outside the dome, plus gear for retrieving samples from the deep.

"The main features of this sub are the large manipulator arm," says expedition member J. Murray Roberts of the Scottish Association for Marine Science, as he stands on the deck of the Seward Johnson, next to the sub. "This has jaws that open and close wide to take samples very precisely. Next to it is a suction tube. Water is sucked through that, rather like a vacuum cleaner, say, and that allows the pilot to suck up small samples, to suck up sediments. They're then transferred via this flexible pipe into a rotating series of buckets, so you can say 'in bucket number one we're placing such-and-such a sample.' More simply, on the front here we have buckets into which you can place rocks or coral samples."

Although the sub is an expensive, high-tech piece of equipment, there are some surprisingly low-tech parts of it, such as the collection buckets on the front that look like ordinary paint buckets, sitting in plastic crates from a dairy.

"Yeah, you're exactly right," confirms Dr. Roberts, "and those crates are sitting on what looks like a mat from a swimming pool, a rigid mat. Well, they do the job. They work. You simply need a container that's gonna hold the samples. Now you could spend a few thousand dollars on that, or you could take something -- a plastic bucket, paint it black so it doesn't reflect in the light, and it'll work just as well."

Although the submersible can hover in one place, because of ocean currents it's better to set it down on the bottom for maximum stability. But the coral they're studying on this trip is very fragile, so I asked Dr. Roberts if that doesn't risk damaging the very objects they're investigating. He said it's actually a lot more gentle than the old way -- dredging the bottom.

Chief scientist Steve Ross added that today's submersibles allow researchers to do a much better job of collecting specimens. "Most of the deep sea animals collected in the past, if you ever have the opportunity to look in a museum behind the scenes, you'll see mangled bodies in jars that were the only samples we got from the deep sea work. Now we're able to collect specimens in very good condition, even alive. In our cold room here we have five or six animals that we brought up that are alive. That doesn't happen when you trawl the bottom."

And being down on the ocean floor, with the panoramic view through the 1.5 meter acrylic bubble dome, says Dr. Ross, gives the scientists a much better idea of the environment than they could get by using, say, a less-expensive remotely-operated submersible. Documentation is a key part of the work. Like scientists in any discipline, Murray Roberts says keeping complete and accurate records is a key part of his work under water.

"We log everything with Dictaphones, voice recorders, so that as the dive's proceeding, everything is logged and recorded. Position fixes can be taken very accurately with differential GPS, so we're going to know where on the sea floor the submersible was surveying. And the samples are logged very carefully on paper records and also on the audio log in the stern compartment, so you have multiple backups as you're going through a dive."

It's actually a bit of a trick, using the Global Positioning System underwater.

"What happens is that there's an acoustic link between the submersible and the ship, so they're able to fix the sub's position relative to the ship, the ship knows its position to the GPS satellites," he said.

Dr. Roberts is one of a number of scientists studying coral at the edge of the continental shelf, hence the name of their expedition, "Life on the Edge." It's sponsored by NOAA, the U.S. agency that includes our weather service as well as ocean science.