How do scientists cope under pressure in the depths of the ocean, in a place where the only natural light is the product of bioluminescence?

Plumbing of the ocean depths began in earnest in the 1930s with the invention of the bathysphere. Built by New York explorers William Beebe and Otis Barton, the device was little more than a two-ton steel ball dangling from cables attached to a ship. In 1934, Beebe and Barton dived to almost a kilometer below the sea surface off the coast of Bermuda and piped details of their findings through a telephone to the crew up top. They reported sightings of fish and invertebrates whose like science had never seen before, which have inspired generations of scientists to explore deeper.

Paul Tyler of the Oceanography Centre at Southampton University in England is a marine biologist who dives regularly and has tried out all the deep-sea submersibles except the Japanese Shinkai. "It's like sitting in a refrigerated VW Beetle without the seats," he says. "There are normally three of you in a two-meter sphere with three portals to look out of; as you get deeper, you put more and more clothes on, but it's fantastic, priceless." But a 4,000-meter dive can take three hours to reach the seabed, "so you sleep, read, or chat. But once you reach the bottom, time flies past because you don't want to waste a second, you're so busy - you're either collecting, photographing, or setting up experiments," Tyler adds.

Even graduate students can go deep. Coral biologist Scott France of the College of Charleston in South Carolina made an early start in diving. "My Ph.D. studies included research on dispersal of crustaceans between hydrothermal vents," he explains. "Within eight months of arriving at the Scripps Institution of Oceanography, I made a dive in Alvin to 3,800 meters." Alvin is a submersible operating out of Woods Hole Oceanographic Institution. France realized that no amount of reading would have prepared him for the experience. "I was ecstatic," he exclaims. "I was an explorer venturing to a place on Earth that virtually no other human had seen before, witness to an environment completely alien to most people."

For some, the experience can be quite out of this world. "It takes a few hours to descend to the bottom and is very eerie," says Emma Jones, a fish behaviorist at the FRS Marine Laboratory in Aberdeen, Scotland. "The sub tends to creak as it sinks, which can be a bit disconcerting." She revisited a dead whale that had been "planted" on the sea floor 18 months previously. "The skeleton was a very spooky sight," she says. "We were collecting bone samples to see what had colonized them, [taking] sediment samples, sucking up amphipods, and filming."

Submersibles are certainly not the most luxurious way to travel, notes geologist Paul Aharon of the University of Alabama in Tuscaloosa, who has just returned from diving in the Atlantic in Alvin. "It is an uncomfortable ride inside the submersible with three people crammed in among the oxygen tanks, carbon dioxide scrubbers, and electronic consoles," he explains. "Last dive I almost got hypothermia because I forgot to take long pants with me," he confesses. "I worked at 3 degrees Celsius with no possibility of moving my legs for over 8 hours!"

He and Tyler also point out that there are some rather personal problems that face anyone on a submersible. "There is always the question of vital body functions such as urinating," Aharon muses. "In addition, the air we breathe has less oxygen and more CO₂ than the atmosphere, to prevent sudden ignitions. The results are headaches, memory lapses, and slowdowns in brain functions."

Alvin is a titanium-hulled submersible that can remain submerged for 10 hours under normal conditions, although its life-support system will allow the sub and its occupants to remain underwater for 72 hours. It makes about 150 dives every year. There are several other equally adept submersibles, including the Clelia and the Johnson Sea-Links I and II, which are run by the Harbor Branch Oceanographic Institution (HBOI). There is also the Japanese craft Shinkai 6500, which weighs almost 26 tons and can descend, as its name suggests, to a depth of 6,500 meters. Shinkai, like the others, carries the requisite TV cameras, temperature and depth sensors, still cameras, and navigational devices. But riding Shinkai can be a lonely experience, because there is room for just one diver.

Discomfort aside, it is the wonder that keeps the scientists going back for more. "You don't realize what a unique experience entering 'inner space' is," says Tyler. "I went to Axial Seamount on the Juan de Fuca Ridge, which is actually the shallowest of my study sites, at about 1,550 meters," says Maia Tsurumi, who recently finished her Ph.D. on hot-vent ecology with Verena Tunnicliffe at the University of Victoria in British Columbia, Canada. "Getting to go down to the bottom in a sub was amazing - definitely one of the highlights of my grad career." The sites can be almost beyond belief, it seems. "The most fantastic biological site I have seen in my life is a tube worm pillar," Tyler adds. "It is just unbelievable, 14 meters high and 5 meters in diameter - it's just enormous, covered in these tube worms."

Visual ecologist Tamara Frank of HBOI made her first dive in 1992, and is now studying the effects of light on the daytime depth distributions of organisms with colleague Edie Widder. At the moment, their dives need go no deeper than 1,000 meters, but Frank is hoping also to collect benthic animals, which would mean much deeper dives. "Most dives in the submersible are fascinating; seeing these spectacular organisms in their natural habitat is just the most amazing experience in the world," she says. "Once you pass through the air-water interface, you're surrounded by seawater, and don't even realize that you're looking through a Plexiglas sphere because the refractive index of Plexiglas is the same as that of seawater. . . . there's none of this 'looking out of little tiny portals' if you're lucky enough to be in the front of the JSL [Johnson Sea-Links]. And the seats are very comfortable."

Aharon is also enthusiastic. "There are too many rewards to count. First, we descend for hours without lights, to conserve electricity, and we'll see all kinds of eerie bioluminescence with psychedelic colors. It is a wonderful experience!" "I wish I had more time to just sit and observe," laments Frank, "but on most of our dives in the Gulf of Maine, we immediately have to start transects, which are exhausting, because you're straining to identify organisms that pass through the transect area as the sub goes through the water." She confesses that science sometimes obstructs the view. "Both Edie and I have seen beautiful, gelatinous organisms during these transects, but couldn't stop to film or observe them because data collection always has priority, and that's sometimes frustrating."

Takeshi Matsumoto of the Japan Marine Science and Technology Center (JAMSTEC), which operates the Shinkai submersible, agrees that underwater observation is a busy game. "The most serious problem during a dive is the restriction of diving survey time," he explains. "Observers have to accomplish everything within a few hours during the dive. Planning and preparation are essential." Jones agrees: "Because research vessels cost so much to run, and weather can change so quickly, you do feel you have to make use of every minute available to do your science."

So what is the motivation for cramming yourself into a tiny capsule and diving to the bottom of the sea? "I was always fascinated by the abyss and grabbed the opportunity when it came my way," Aharon says. "I guess my initial attraction started in childhood when I read about [Jules Verne's] Captain Nemo." Tsurumi agrees that the deep can affect you profoundly: "There is nothing so romantic and exciting as going somewhere seemingly totally inaccessible," she says. Aharon is totally hooked. "It's an addiction, once you start going down (and hopefully, coming up again)," he says.

It is not always so dreamy, though. One of the more frustrating aspects of deep-sea science is not diving, as Southampton University oceanographer Mark Varney explains: "I went on an expedition to the central Indian Ocean in June, and found the entire trip something of an ordeal. The weather was bad for most of the period, and the science wasn't terribly successful."

Indeed, extremely rough conditions are perhaps the worst aspect of doing research at sea. "On our Indian Ocean trip we were blown out on two occasions, to Indonesia and then towards Australia; both [times it] took several days to get back on to station," says Varney. Tyler points out that "bad weather and, very occasionally, malfunctions are the only things that stop us diving." But, Frank notes, the hazards of diving are overrated. "I find it much more terrifying driving in Boston than diving in a submersible," she asserts, "At least in a submersible, you're being 'driven' by a professional, there's no 'traffic' to worry about, and you know the vehicle has been through an enormous number of safety checks."

France, too, is not perturbed by the potential dangers. "My desire to see the deep sea and its organisms first hand represses rational consideration of the dangers involved," he says. "Of course there are dangers involved in traveling to such great depths. One can't simply call for a tow-truck if the sub is stuck."

"The longest cruise I have been on was slightly over five weeks," says France, "and this was as a graduate student. At that time everything was an adventure and so the time passed quickly. Now that I am married, being away for that length of time would be an emotional hardship." However, at the end of a trip, the coming home can be a problem for some. "I often get 'post-cruise blues' after a cruise," admits Frank, "as do many of my colleagues, because you go from this exciting, noisy, 'happening' environment, where there's always someone to talk to, to a very quiet home."

But one question remains…how do they cope with those "personal" problems during a dive? Jones had her own method: "I found out I was diving in Alvin at 4 pm the day before, so I deliberately stopped drinking any fluids from then on, as I didn't want to be squirming and crossing my legs for 10 hours," she says. Aharon, however, explains the standard approach: "We take capped bottles fitted specially for men and women. Not a pretty sight, but we are all human."