EACH year, hundreds of enthralled sightseers pay good money for scenic boat trips on Yellowstone Lake, which at 7,740 feet elevation is the largest high-altitude lake in North America. When Val Klump and Charles Remsen head out onto the water, though, they sit in their research boat's bobbing cabin, its windows shrouded with aluminum foil, and watch television. The two scientists gaze at crystalline pictures of one of the most unusual lake environments in the world, one so convoluted that they call its study ``bio-geo-chemistry.'' Their unprecedented views of this strange realm come from the video camera housed in a small robotic submarine that cruises along the lake floor 300 feet below.
``This is terrific,'' Dr. Remsen says, staring at the video screen. ``Can you turn left a little? Look at those rocks, those miniature grottoes. See the bubbles coming out?''
As the submarine, known as MiniRover and piloted from the command boat, combs the murky lake floor, it comes across vast fields of gurgling thermal vents bubbling and belching hot water and gases. Around these hot spots cluster colorful red-orange sponges that gobble up strange bacteria, which manufacture their energy out of the chemical soup pumped into the icy lake from deep within the earth.
``Everybody knows about Old Faithful and the terrestrial geysers and hot springs here,'' Dr. Klump says. ``But this is a whole new world that no one ever sees; and it's even more incredible and active than what you can see on land.''
During the last seven summers, geochemist Klump and biologist Remsen, funded by the National Undersea Research Program, have been leading scientific teams to probe Yellowstone Lake's surreal depths. The scientists are from the University of Wisconsin's Center for Great Lakes Studies. They want to discover just what contributions the rich hot-water flows make to the lake's unusually high productivity.
For an alpine lake frozen over almost six months of the year, Yellowstone Lake is unexpectedly prolific, supporting a myriad of bacteria and algae diatoms, shrimp-like zooplankton, and native cutthroat trout. Scientists know that the lake is more productive when fertilized with ash from forest fires and during warmer years, but they figure changes in thermal flows could also play a role.
``It's one piece of an incredibly complex puzzle,'' Remsen says. ``Just how big it is and where it fits in, we don't know yet.''
MUCH of Yellowstone National Park with its well-known geysers and boiling springs sits within the rim of a tremendous volcanic crater about 30 miles across that last erupted about 600,000 years ago.
Like the Hawaiian Islands, Yellowstone overlies a hot spot in the earth's crust. Groundwater percolating down through cracks in the rock is heated to above boiling as it nears vast underground reservoirs of molten rock; it then resurfaces to create the park's famous thermal features.
Yellowstone Lake straddles the caldera rim. Outside the crater, the lake floor is unexpectedly flat and boring. Inside, it is topsy-turvy.
Giant cracks and crevices slice across the lake bottom, while shimmering curtains of carbon dioxide bubbles stream up from deep rifts, past tall red cliffs that are criss-crossed with cracks in a brick-like pattern.
Many rocks are unusually bare of mud; and odd depressions that should normally become filled with sediment lead the researchers to think that aquatic geysers periodically rip through the lake bottom, clearing some deposits away.
These features also hint, the scientists say, that the lake may cover one of Yellowstone's most turbulent regions. National Park Service geologist Wayne Hamilton notes that the lake floor plunges to depths of almost 400 feet, closer to the magma boilers buried beneath the park. The floor may also be frequently shifted and cracked by the flurries of tiny earthquakes that constantly rock the region.
Such earth movements result from the magma chambers actively bulging beneath the old caldera. In periods of three to four weeks, two major bulges, or ``resurgent domes,'' have risen by up to 8 inches, quickly altering Yellowstone's topography. One of these domes borders the lake's most active thermal regions and is actually tilting its north end up, flooding its southern arms and killing trees there.
That, in turn, tempers the hot-water plumbing under the lake, as shifts in a house foundation might crack and bend pipes, opening and closing various conduits. On one occasion, for instance, the team found what Remsen has dubbed ``tube gardens'': Wide arrays of inactive mineral tubes sticking out of the lake-bottom muck like bony white fingers.
These, they now surmise, are the result of heated flows that once streamed into the lake there. Just as crusty minerals are deposited on a leaky faucet, silica in the hot water solidified on contact with the icy lake water, gradually building the tubes. While the streams have since been cut off, their tubes remain as natural artifacts.
Yellowstone Lake's thermal plumbing is vital not only for the monuments it constructs, but also for the curious biological communities it feeds.
These food chains - some thriving far deeper than light can penetrate - are not founded by the usual means of photosynthesis, in which plants generate carbohydrates from sunlight. Instead, they are powered by chemosynthesis, where energy is manufactured from chemicals dissolved in the hot flows.
Simple but intriguing bacteria form the base of these rare chemosynthetic systems, digesting sulfur, methane, and other molecules carried from deep within the earth into new forms and taking energy from that process. One species of bacteria, for example, uses the energy it gains from the chemical reaction of converting iron into iron oxide (rust) to form its tiny single-celled bodies.
These basic creatures are similar to what many scientists theorize were among the first life forms to develop on earth, when raw chemicals were the only nutrients available. Their abilities may also help solve modern dilemmas: Chemical-consuming bacteria are important in the developing technology of bioremediation, where they are used to convert hazardous wastes like oil into less-damaging elements.
`BACTERIA like these may well be more than just amusing little bugs working away down there,'' says research team member Jim Maki, a microbiologist from Harvard University in Cambridge, Mass. ``They could have many lessons to teach us.''
These dynamic bacteria are prolific around hot water and gas vents, multiplying into colorful, billowy mats that flutter in the gentle flows. They, in turn, provide food for bright filter-feeding sponges that creep over rocks and rolling mounds of mud, and for zooplankton and other tiny organisms that are themselves a prime food source for fish, a favorite food of bears.
The research team has also found groups of a strange breed of freshwater worm that has no mouth, clustered on and around the bacterial mats. Scientists suspect these worms' small bodies house symbiotic bacteria that generate enough energy from absorbed chemicals to support both themselves and the worms.
Next year, Klump, Remsen, and their team will travel to the Soviet Union to probe Lake Baikal, a 5,000-foot-deep lake holding about a quarter of all the world's fresh water. That massive lake also has geothermal inputs, but has existed for 20 million years, and may thus hold even more fascinating biological treasures.
Just how vital Yellowstone Lake's chemical-dependent systems are to the health of the entire lake remains a vague mystery. But it seems certain that with each change Yellowstone's uneasy terrain wreaks on the thermal plumbing, at least some creatures - from low to high in the food chain - will likely be affected.
``What we have seen here is an incredible world, but it's very fragile and very rare too; temperature changes of just a few degrees can shut these bacteria down,'' Remsen says, standing in the team's field laboratory. ``It shows just how creative nature can be to allow life in such a crazy environment.''