Science / Medicine : Shedding Light on Mysterious Depths : Exploration: Scientists are scouring the bottom of Yellowstone Lake and discovering a unique ecosystem.
Hunched in the darkened cabin of a research boat, geochemist Val Klump and biologist Charles Remsen stare intently at a small television screen. Upon it flicker surreal images of the bottom of North America’s largest high-altitude lake, a place no person has ever seen before.
“There’s a bubbler there,” Klump says, watching a picture of tiny gas bubbles emerging from a hole on Yellowstone Lake’s floor, almost 200 feet below. “See the water flowing out?”
“Look at all these sponges!” Remsen blurts. “It’s sponge heaven! Look at the detail of that one. Isn’t it gorgeous?”
The two researchers from the University of Wisconsin’s Center for Great Lakes Studies are leading a team scouring the dark depths of Yellowstone Lake, a unique ecosystem. Yellowstone National Park’s renowned thermal springs bubble and burble not only on land but also deep beneath the lake’s icy blue surface, adding an intriguing dimension to its uncommonly rich environment.
While most lake bottoms are murky and flat, this one is distinguished by towering cliffs and abyssal crevices, oozing mounds of warm mud and the same fantastic underwater geysers, hot springs and fumaroles that have made terrestrial, forested Yellowstone famous.
Around the hot spots grow curious bacteria, the foundation for an unusual freshwater food chain that gets its basic energy not from the sun and plant-based photosynthesis, as most do, but from the rich chemical soup flowing from hot-water vents.
“It’s an incredible place down there,” Remsen says. “Nobody realizes that one of the most amazing and active places is way down at the bottom of this lake.”
Remsen and other researchers from around the country are trying to piece together the growing number of clues to the nature of this famous but mysterious body of water.
Many scientists, for example, believe that the simple life forms found around the deep vents are similar to those from which all life evolved and could provide clues to the early creation of natural systems.
“What we’re seeing is a window on the world 2 billion years ago,” Remsen says. “This is how it began.”
For now, they are busy accumulating tantalizing findings, including evidence of hundreds of tiny earthquakes every day, of fissures that extend far deeper than had been thought and of eerie silica tubes protruding from the lake bottom.
The team’s clear television image of the lake bottom is broadcast from a three-foot-long yellow robotic submarine--dubbed MiniRover--attached to the command boat by a 500-foot electronic umbilical cord. It is equipped with floodlights, video and still cameras, a compass, a sophisticated thermometer, a depth meter, and a scoop to collect specimens from the bottom.
Watching the video image from MiniRover’s big bubble eye, pilot David Lovalvo directs its electric thrusters and appurtenances with a video-game-like joy stick and push-button controls. On encountering a “bubbler,” as the team has named them, he can drop MiniRover’s mechanized arm, which holds a tube, to suck up water samples.
But since MiniRover often operates in the lake’s dark depths with lights that penetrate only a few feet, maneuvering can be difficult. Like searching a dark room with a small flashlight, it is sometimes hard to tell where it has been and where it is going.
“It’s like driving in a snowstorm,” Lovalvo says as MiniRover’s thrusters stir up a billowy cloud of sediment.
A manned submarine is out of the question in Yellowstone Lake because of the narrow cracks and crevices that the research team has been probing in its research, ongoing since 1983. Even MiniRover once got stuck in a deep fissure narrower than it appeared. Sending humans into the lake’s obscure depths would also be unsafe because of roiling turbulence around the hot springs and vents.
In some places on the lake floor, shimmering curtains of hot water and gas bubbles stream out of the ground and create a trail as they pop on the water’s surface. In other spots, sediment is pocked by strange depressions that would normally become filled.
That and sheer, brick-like cliffs oddly bare of sediment lead the scientists to surmise that periodic underwater geyser eruptions wash away accumulations.
It may also be an indication, says National Park Service geologist Wayne Hamilton, that the lake bottom is one of the most active geological regions in the park and is being constantly shifted and cracked bare by earth movements. Yellowstone is one of the most seismically active regions of the world, shaken each day by hundreds of small earthquakes known as microquakes.
Much of Yellowstone Park, in fact, lies in the depression formed by a giant volcanic crater about 30 miles across. All the thermal areas found in the lake so far are within it, an area with much more rugged topography than that outside the crater.
Each thermal zone also matches the rocky topography in the lake. Deep fissures east of narrow Stevenson Island, the research team has found, extend nearly 80 feet below the previously known maximum lake depth of 320 feet. These seem to be kept clear by constant floods of water and gas from thermal vents lining their depths.
Such thermal features are created by chambers of molten rock close under the north end of the lake. These heat ground water, which then circulates back up to the lake floor at temperatures up to boiling (water does not boil, though, because of intense pressure at those depths).
The underground magma chambers have bulged on occasion by up to eight inches in three to four weeks, creating what are know as resurgent domes within the old crater, raising the lake’s northern end and flooding its southern arms.
Such dramatic flexing can alter the earthen plumbing beneath the lake by opening up new water conduits and closing old ones. In proving this, the researchers have found fields of awkward silica tubes (Remsen calls these “tube gardens”) sticking up from the lake floor like pallid, bony fingers.
At first, they thought these were pieces of pipe that had been jettisoned from a boat. Now, though, they believe the tubes, some up to 10 inches long and an inch or so across, are relic channels of heated water. Just as minerals in water crystallize on water faucets, dissolved silica in the heated water has apparently solidified on contact with the cold (just above freezing) lake water. That silica built the tubes, which may then have been further exposed when sediment washed away.
With its hidden magma furnaces, Yellowstone Lake has some of the sharpest underground temperature differences known. Scientists from Southern Methodist University recently plunged a harpoon-like thermometer into the lake floor and found that temperatures rose by 100 degrees Celsius just three feet below. In a matter of feet, too, lake water turns from boiling temperatures to nearly freezing.
It is in these narrow gradients that some of the lake’s most fascinating life forms appear. In at least some ways, these are directly dependent on the chemicals pumped from the thermal vents; it is such an unusual set of interrelationships that the research team calls their field of study “bio-geo-chemistry.”
Stringy beds of bacteria, for one, flutter in the warm water flowing from the aquatic springs. Instead of obtaining their energy from the plants, these bacteria essentially “eat” concentrated chemicals rising from the bottom vents in a process called chemosynthesis. One type of bacteria, for instance, oxidizes iron into iron oxide (rust) and uses energy from that chemical reaction to build its cells. Others eat sulfur, methane or other molecules.
These dynamic bacteria, some of which also are dependent on lake-bottom warmth to function, may be valuable even outside their lake context. Harvard University microbiologist Jim Maki, part of the research team, says some could possibly be applied to new bioremediation processes, in which bacteria are used to clean up spilled oil or dangerous chemical waste by digesting it into simpler elements.
Scientists suspect that the lake bacteria have given rise to a community of life that includes filter-feeding sponges, leeches, shrimp-shaped zooplankton and small freshwater worms in especially large numbers. These are probably present only because of the bacteria and chemicals that feed them. The worms, which have no mouths, appear to live off chemical energy generated by bacteria within the worms’ bodies.
Yellowstone Lake’s thermal zones are not as biologically well-developed as the few regions in the world’s oceans where giant, chemical-dependent clams and tube worms live.
But those have been evolving for millions of years; Yellowstone Lake is only about 30,000 years old, just a geologic moment, although scientists believe the life forms there are similar to those that existed 2 billion years ago. Another team has found bacterial mats growing around warm spots on Oregon’s 7,000-year-old younger Crater Lake.
Next summer, Klump, Remsen and their team will be part of a multinational effort to explore in the Soviet Union’s huge Lake Baikal, which holds about 25% of the world’s fresh water. Since the 20-million-year-old lake also has geothermal inputs, it may contain even more advanced chemosynthetic communities than Yellowstone Lake.
It is a complex question--and the one the team most wants to answer--just what role thermal systems play in the overall health of Yellowstone Lake. They know its productivity is generally higher than similar lakes without hot springs, and that it is more prolific during warmer years and when its water is doused with fertilizing ash from forest fires. Natural or human-caused fluxes in the thermal inputs could surely produce similar changes.
There are threats of drilling near Yellowstone for geothermal heat to warm homes and run power plants. In other regions, such activity has sapped energy from nearby geysers and hot springs; that would only be compounded in Yellowstone by the potential damage to the rare and unusual creatures that depend on thermal vents for their survival.
Exactly how all the pieces fit together remains a mystery. “It’s a real puzzle to try to figure it all out,” says Remsen, who will return with his team to Yellowstone for more prospecting in future years, perhaps in winter when the lake freezes over and its thermal inputs may become even more vital. “But each piece we’ve been able to add only gives us more reason to keep looking for more.”
UNDERWATER EXPLORER The ‘MiniRover’ is a three-foot-long robotic submarine being used to explore the 300-foot depths of Yellowstone Lake. A pilot aboard the command boat maneuvers the submarine and its instruments by remote control, taking photographs and samples from the mineral-rich springs. 500-foot cable and electronic wiring. Electric thruster motor. 35-mm still camera. Floodlight for video camera. Video camera inside of main pressure housing. Compass appears in the bottom of the video picture to help pilot navigate. Motor for moving the sampling arm. Sampling arm with temperature probe for finding hot water vents and tube for sucking up water samples. Strobe light for 35-mm camera. Floodlight for video camera. Plexiglass housing for pressure and temperature sensors. Ice-cold water; Beds of bacteria live in the hot spring water, dependent on the minerals from the vents. Lake bottom; Deep fissures in the lake bottom are kept clear by the flow of hot water and gases from thermal vents. Magma chambers heat ground water to over 200 degrees. Temperatures rise by 180 degrees just three feet below the surface of the lake bottom. Silica tubes, up to 10 inches long, are formed when minerals from the hot vents crystalize on contact with the cold lake water.
