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By Trent Stockton
The feeling that you're sinking in deep, dark, cold water hundreds of miles from dry land is not a pleasant one. Neither is the feeling of being confined, cold and wet, for over eight hours in a metal sphere the size of a bathtub. Yet this is the only playing field for scientists exploring deep-sea ecosystems.
 William H. Smith, Ph.D., professor of earth and planetary sciences in Arts & Sciences, emerges after an eight-hour journey inside the fame submersible Alvin. Smith recently took an expedition inside the tiny craft to study deep-sea ecosystems and take measurements with a sophisticated imaging device he designed. He hoped the imager would reveal if and how microorganisms at the ocean floor might be using available light for photosynthesis. |
William H. Smith, Ph.D., professor of earth and planetary sciences in the Arts & Sciences, recently was one of 25 scientists from many universities and research institutes on an expedition to explore several aspects of the sea floor associated with the Juan de Fuca Ridge, about 240 miles off the coast of Oregon. Smith was aboard one of the descents made in the submersible Alvin, a famous craft in which scientists 23 years ago discovered a unique ecosystem that broadened "origins of life" theories. Smith rode the cramped container to test his sophisticated imager for clues on whether and how microorganisms at the ocean floor might be using available light for photosynthesis. The depth in which Smith did the majority of his work was 7,220 feet.
The ecosystem scientists found while aboard Alvin in 1977 comprises myriad life forms that exist at deep-sea vents. Deep-sea vents are hydrothermal geysers found in areas of tectonic activity, where the movement of continental plates along mid-ocean ridges creates zones of fissures in the Earth's crust as it is pulled apart. Cold seawater percolates down through the fissures, is heated as it nears the molten lava of the magma layer, and then expands and rises rapidly. The mineral-rich water is then either expelled in plumes from geysers that can be as hot as 375 degrees Celsius, or is gently released from lower-temperature springs.
The deep-sea vents support "vibrant oases of life," Smith said. "At this depth there is not much life; a few fish, some sponges," Smith said. "Then, as you approach the vent, life blooms. Fauna is everywhere, all kinds, including fish, crabs, slugs, snails, octopuses, sea spiders and many others. Many organisms, like tube worms and several species of bacteria, are unique to the vents and were seen for the first time in 1977."
On the recent expedition, Smith used a microscopy hyper-spectral image that he invented to observe the living bacteria surrounding the vents and their interactions with other organisms. Smith's sensor records digital images like a camera but resolves image data into more than 100 spectral bands, as opposed to the three broad, overlapping bands resolved by a typical color camera and the human eye. Microscopy hyperspectral data provide highly detailed color information about objects and organisms that would otherwise remain indiscernible to the human eye.
Smith has used hyperspectral imaging technology in collaborations with NASA and others in remote sensing of a variety of objects, including planets and meteors, the Earth's atmosphere, agricultural crops, ocean reefs and diverse geochemical features.
Smith, in Alvin's tiny cockpit, was accompanied by an experienced pilot and another biologist in addition to a host of monitors, switches, gauges, and other equipment, including the hyperspectral imager. After the long, spiraling descent to the ocean floor, Smith and the others had five hours in total darkness to locate the vents and to conduct a variety of experiments, many of them for scientists anxiously waiting on the surface. Because the battery-powered Alvin has a dive duration of six to 10 hours, Smith had only about an hour to conduct his own experiments, which included obtaining spectra of the unique biological communities at the vents.
The bacteria found at the vents are remarkable in that their main energy source is hydrogen sulfide, a compound toxic to humans and other animals. The bacteria thrive in sulfur-rich water surrounding the vents --which ranges from 375 degrees C at the vent itself to just above freezing (2 or 3 degrees C) only a few inches away --by transforming the abundant sulfur there into a usable energy source, a process known as chemosynthesis. The bacteria don't need solar energy, unlike nearly all other biological communities, which use the sun for photosynthesis.
There is some evidence of chlorophyll, the pigment used with solar radiation in photosynthesis, in the vent bacteria. This raised the question of whether the chlorophyll is from the surface or are vent organisms incorporating photosynthetic material in a useful way.
Smith conducted three experiments to see how organisms were using photosynthetic material. He used the hyperspectral imager to record the amount of ambient light released from the thermal energy at the vent and to see how much of this light is in the right wavelength for photosynthesis (500-700 nanometers). He then illuminated the area with blue light and recorded the protein fluorescence characteristics of the organisms present. Finally, he illuminated the area with white light and recorded spectral characteristics over a broad spectral band. Results of these experiments will be presented in April in a symposium titled "Biology in Extreme Environments" at the spring meetings of the American Chemical Society.
Future research involves very detailed investigations of deep-sea vent biological communities, a challenging proposition because this requires fine-scale observations that require more time than the sub can remain on the sea floor. To meet this challenge, Smith is developing external sensors that could be placed directly on the sea floor near a vent and left for long-term observations, up to a year or even longer.
"These vents are very dynamic geological features," Smith said. "We need to collect data over a period of time to see what is really going on."
As for coping with the chummy confines of Alvin, Smith remains undaunted.
"I'm not claustrophobic, so the tight quarters didn't bother me in the least," he said. "On your way down and back up you see incredible fauna, and once we got near the vents I was so busy conducting the experiments that the time flew. The only part of the expedition that was uncomfortable was the boat ride out to where we were going to make our descent. The waters were rough and I got a bit seasick. I'm really looking forward to going on Alvin again."
