Feature ArticleUsing Manned Submersibles to Explore The Oldest and Deepest Lake in the World
By Dr. Anatoly M. Sagalevich
Deep Manned Submersibles Laboratory
P. P. Shirshov Institute of Oceanology
In May 2008, two deep-diving manned submersibles, MIR-1 and MIR-2, were transported from Kaliningrad, Russia, to Lake Baikal by the largest mass-produced airplane in the world, the Ruslan (also known as the An-124). In winter, Lake Baikal is covered by the ice, meaning dives with the submersibles are only possible in the summer. The MIRs’ dives in Lake Baikal were originally scheduled for only the summer of 2008, but they continued over three summers with 176 dives.
The MIRs made dives at 52 sites, covering practically the whole lake. The most important discoveries from the dives occurred during the project’s first two years: The submersibles found areas on the lake bottom with oil and gas discharges and also discovered a site with gas hydrates hills (Sea Technology, December 2009).
Gas Hydrate Discovery
The expeditions’ scientists were most interested in the discovery of gas hydrates, which have potential as a long-term energy source. These hydrates were studied in detail, and special instruments were designed for the sampling and lifting up gas hydrate pieces. One such instrument, designed by MIR submersible technicians, was a transparent gas trap based on a concept developed by P. P. Shirshov Institute scientist Dr. Alexander Egorov. The gas trap provided visual observations of experiments conducted in-situ and allowed the expedition team to conduct unique tests with gas hydrates.
During the first leg of 2010 expedition, researchers searched the methane hills using a special membrane sensor. Bottom structures on the bed of Lake Baikal, where gas hydrate hills are located, are covered by sediments, making it practically impossible to determine the hills’ material composition from visuals alone.
The research team established there were high concentrations of methane dissolved in the water near the gas hydrate hills. The mapping of this area showed that six hills of different sizes are located within an area of 10,000 square meters. Testing the hills’ surface with the MIRs’ manipulators and attempting to break pieces of gas hydrate showed that the hill is a monolith constructed by crystal combination of methane with water. Based on the hills’ height and diameter, the team made estimations of the amount of hard gas hydrates deposits within the structures.
Gas hydrates are a very capacious source of energy. One cubic meter of gas hydrate transfers to 164 cubic meters of methane gas, meaning hydrates are an easy way to store and transport methane. However, it is necessary to develop new technology for the mining and storage of this unique material. According to preliminary estimates, the amount of methane in oceanic gas hydrate deposits are greater than all hydrocarbon resources on the land.
Measuring Phase Transformation of Gas Hydrates
By using manned submersibles, researchers were able to conduct unique experiments and make in-situ visual observations of the phase transfers of gas hydrates to methane and back. During these experiments, the barothermic conditions of these transfers were established.
One such experiment was conducted at the St. Petersburg site, where gas hydrate hills are located at 1,400 meters’ depth. Visual observations showed that the transfer from hydrate conditions to methane gas occurs at a water depth of 380 to 400 meters at a water temperature of about 3° C.
Other experiments were carried out at the Goloustnoe site, where an active methane discharge was found at the lake bottom with bubbles of gas streaming up from a cleft between big rocks. Methane was gathered inside a specially designed gas trap at 420 meters’ depth. After the trap filled with methane, the MIR began its descent. At 550 meters’ depth, the crew observed white crystals on the walls and upper-bottom of the trap. As depth increased, the methane converted to a gas hydrate inside of the trap. These experiments are very important for understanding how gas hydrates form and for determining how to develop technology to mine gas hydrates in the future.
Another interesting discovery on the gas hydrate fields was the observation and collection of bacterial mats, large areas of the lake bottom sometimes several hundreds of square meters covered entirely by bacteria. Isotopic analyses of these bacteria, which cover the surfaces of the gas hydrates, in the laboratory showed they are methanothrophic, or live by metabolizing methane.
In the northern part of the lake in Frolikha Bay at 400 meters’ depth, the crew discovered a wide field where the lake bottom is covered by these bacterial mats. The crew established that this field extends two kilometers up to a slope to the east. The measurements showed a high geothermic gradient throughout the whole square of the field. This gradient can be as high as 2° C to 4° C per meter, which is 100 times higher than the average geothermic gradient of other areas in Lake Baikal.
Researchers found the density of bacterial mats is connected directly with the area’s geothermic gradient value. A high density of bacterial mats means a high value of the gradient. Other indicators of a high gradient value are wide fields covered by various sponges and amphipods. To continue this article please click here.
Dr. Anatoly M. Sagalevich, one of the principle designers of the MIR submersibles, is the head of the Deep Manned Submersibles Laboratory at the Russian Academy of Sciences’ P. P. Shirshov Institute of Oceanology. He directs the deep-dive submersibles program and has led more than 30 worldwide expeditions, logging more than 3,000 hours as a submersible pilot.