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 Volume 9, No. 3, 46-49.
Sampling and performing analyses at the ocean floor gives a better picture of “extremophiles”.
At the surface of our planet, almost all life relies on photosynthesis—the process of using sunlight for energy to create biochemical building blocks—in one way or another. But there are places on earth that never receive sunlight, and yet life flourishes there too. Organisms that live near hydrothermal vents at depths of more than 2500 m rely not on photosynthesis, but on a totally different process called chemosynthesis. Instead of sunlight, these extremophiles use the energy released from the oxidation of inorganic compounds to build biological molecules necessary for life. Chemicals such as methane, carbon dioxide, sulfur species (such as hydrogen sulfide), iron, manganese, and other trace elements affect the balance of life in this unique ecosystem. Life has evolved at these volcanically active sites, and it is the center of great interest from biological and biotechnological points of view. Enzymes known as biocatalysts that have been isolated from hydrothermal vent bacteria can be used in the pharmaceutical and biotechnology areas instead of costly synthesized catalysts, which may be less efficient than the true biocatalysts. The vent sites are also thought to be major contributors of inorganic elements to our oceans. Near these hot vent sites are cooler areas where diffuse vent fluids flow and in which metal sulfides accumulate to form chimney-like structures that can reach tens of meters in height. At these sites, hot hydrothermal vent fluids, 180–400+ °C, are being eluted and mixed into the colder seawater, 2–4 °C. Sampling the Deep Although these techniques have aided the understanding of hydrothermal vents, the reduced pressure at the surface can cause outgassing of the samples, which can change their chemistry. Having an in situ analyzer that can perform analyses on samples in their respective environments allows for a true representation of their complex chemistry. The lab that can work in this hostile yet beautiful environment is the DSV Alvin, the research deep-submergence vehicle (DSV) operated out of Woods Hole (MA) Oceanographic Institution. This spaceship of the deep allows scientists to perform experiments and collect samples from the floor of the ocean down to 4500 m. Alvin was put into commission in 1963 and has completed more than 3500 dives. It carries all types of testing equipment; the most recent addition is an instrument for real-time, in situ measurements of chemicals eluting from hydrothermal vent areas.
In Situ Voltammetry To analyze what is eluting from these hydrothermal vents, the researcher must first place electrodes in the area of interest for analysis. This task is accomplished by using the two manipulator arms on the front of Alvin; these are like human arms except with only 5 of rotation. Alvin can pick up small and large objects, from delicate biological specimens to large chunks of hydrothermal vents. A special probe assembly allows the placement of several electrodes in and around the hydrothermal vents as well as in the areas of diffuse water flow where many of the biological species are living. This probe assembly also allows the researcher to take a small water sample where the in situ voltammetry is being performed. The temperature of the area where both electrochemistry and water samples are taken is also recorded. In our recent investigations, the oxygen concentrations in the water column and in the areas of biological activity are monitored using linear sweep voltammetry. The normal concentration ranges seen with this system extend from approximately 3 µM (lower detection limit) to >400 µM in cold waters. The voltammogram (Figure 1) shows a typical linear sweep voltammogram of oxygen. The most interesting electrochemistry performed at 2500 m was the cyclic voltammetry done at various biological sites. These sites have been and continue to be extensively studied to aid understanding of the relationship of biology to the geochemistry at diffuse flow venting areas. These voltammograms show free sulfide and iron sulfide at various Riftia and vent formations, as well as in some areas where both oxygen and sulfide are present.
The voltammograms show the presence of sulfide, oxygen, iron, manganese, and possibly iron sulfide. Researchers are now beginning to understand what compounds are necessary for the survival of the organisms at these hydrothermal vents. For example, it is felt that sulfide is required for a healthy Riftia colony to thrive; however, mussels do not move into these areas until sulfide levels are low. Riftia have symbiotic organisms within them that require both oxygen and sulfide. These materials are transported to symbiotic organisms by diffusion across the gills of the animal. The symbiotic organisms use these compounds in a chemosynthetic cycle to produce the necessary organic compounds directly used by the Riftia. Benefits of Deep Sampling
Copyright © 2000 American Chemical Society.
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on the types of analyses that would be used, such as atomic absorption, ICP, and ion chemistry. Large water samples are taken from Niskin water samplers—nonmetallic bottles that can be opened and closed remotely and can hold up to 2 L of water. Samples for gas analysis are taken in gas-tight syringes and sent back to the lab on land for analysis. Smaller sample collection devices are available for other types of analyses.
