Lake Vostok’s Potential for a Diverse, Undisturbed Microbial Ecosystem
Lake Vostok Introduction
For over 40 years, the scientific community-specifically that exhibiting interest in the Antarctic region-has shown keen interest in the potential for subglacial lentic ecosystems. Seismic soundings have showed that there is in fact, a subglacial lake located beneath Vostok Station-as well as in many other areas of Antarctica. The discovery of Lake Vostok has fueled the excitement that these subglacial reservoirs may be capable of supporting a completely undisturbed microbial ecosystem. The discovery of life thriving at Lake Vostok would not only potentially challenge science’s current paradigms concerning microbiology, but would also precipitate furthered understanding of life that may exist beyond Earth on Jovian satellites. The implications of finding life at Lake Vostok would assist not only biologists, but would also facilitate astrobiologist’s ability to comprehend-or at least attempt to comprehend-how life may develop on other planets or planetary satellites. Having such broad implications, the importance of researching Lake Vostok’s potential for organic habitability is accentuated.
In the late-1950’s, Russian scientists began exploring the possibility of freshwater lakes existing beneath Antarctica’s massive ice sheets. It was hypothesized that due to the intense pressure being exerted on the ground beneath the ice sheet, sufficient heat would be generated to actually melt a portion of the subglacial structure and subsequently allow a subglacial lake to form. Seismic soundings later evidenced that there is in fact a subglacial lake residing beneath Vostok Station (Siegert 1999). A follow-up survey led by U.S., U.K., and Denmark researchers utilized radar soundings sent into the ice sheet to determine whether or not subglacial lakes existed. Such soundings reflected anomalies above Vostok Station, which earned the lake the name Lake Vostok (Siegert 1999). This evidence undoubtedly excited scientists and further fueled the desire to explore Lake Vostok in search of microbial life beneath the ice sheet.
Given its dry, ice-covered, and relatively desolate environment, it is difficult to believe that the Antarctic continent is seismically active. The continent, however, boasts active volcanoes as well as an active rift valley. Just west of Lake Vostok’s location is a very active rift valley known as the West Antarctic Rift [valley]. Lake Vostok’s location is proximate to this geologically-active area and the activity found therein may contribute to a potentially critical source of energy for any life forms living in the lake: hydrothermal vents. These vent systems are generally located at or near areas of tectonic spreading and divergence. The West Antarctic Rift is an example of such a spreading center. Hydrothermal vents have been studied as benthic vanguards for bathypelagic life. However, much like the researching of Lake Vostok, science’s understanding of hydrothermal vent communities is fairly new (Oreskes 2003). While only within the past 40 years has attention been paid to hydrothermal vents, these vents and their associated microbial communities have been studied extensively. Researchers have found habitability patterns in benthic hydrothermal vent communities. Their findings may provide and enhance understanding of Lake Vostok’s potential for microbial habitability.
However, because of Lake Vostok’s remote and somewhat unreachable location, the hydrothermal vent communities found at the lake may harbor microbial communities that differ significantly from those that have previously been studied. Christner et al. (2006) showed that there exist certain thermophile and chemolithotrophic organisms at these sites. Kelly et al. (2006) showed that Hydrogen Sulfide, or H2S, is an abundant compound found being ejected from hydrothermal vents. They also found that microbial colonization concentration correlated with H2S ejection abundance. Only a certain type of heterotrophic organism can synthesize this compound. These organisms have likewise been found in the accreted ice above Lake Vostok. Such organisms being present may be indicative of geothermal activity. Unlike their marine counterparts that, through a complex food chain, derive energy from the sun-either directly or indirectly- microbes at Lake Vostok would have to rely on a secondary source of energy: sediments. Christner et al. (2006) showed that Vostok’s unique, sunless ecosystem would likely harbor a secondary, inorganic-based food web; one that is reliant on minerals and one that is chemolithotrophic in nature. Lithotrophs are capable of synthesizing inorganic material such as minerals found in lakebed sediments. These mineral-abundant sediments would absolutely be found near the lake floor of Lake Vostok. Considering that Vostok’s environment is bereft of sunlight, other, more peculiar microbial systems may be found inhabiting the Vostok ecosystem. Priscu et al. (1999) used a partitioning coefficient to derive a Dissolved Organic Carbon (DOC) content estimation from an ice core retrieved from the accreted ice above Lake Vostok. Their findings show that the ice above Vostok contains, “… 1.2 mg C litre-1 when the ice in core 3590 was accreted” (Priscu et al. 1999). They likewise performed a similar partitioning coefficient to a core retrieved from Greenland and found that the DOC content was negligible even after compensating for anthropogenic interference (Priscu et al. 1999). Given the high DOC content found in core 3590, Priscu et al. (1999) speculate that this is indicative of heterotrophic activity in the lake. If, in fact, heterotrophic organisms are present, the scientific community can expect a much more complex microbial community to be situated at Lake Vostok.
The discovery of microbial life at Lake Vostok would have broad scientific implications. Those implications, however, are too many and too robust to articulate herein. One body of scientific research that would benefit greatly from this discovery is that known as Astrobiology. Astrobiology is the study of the origin, evolution of, and distribution of extraterrestrial life. The term “life” in this section will henceforth refer to life that is of a microbial nature. The onset of the “space age” brought about a intensified interest in the potential for advanced, sentient extraterrestrial life residing on planets other than Earth. With the advancement of space technology, human knowledge pertaining to the solar system’s planetary neighborhood likewise advanced. The continued advancement of space-related knowledge precipitated the nullification of the idea that any advanced life forms could exist beyond Earth (at least in this particular solar system). At this point, research and exploration became fixated on microbial life. One potential microbial life-harboring candidate is not a planet but a planetary satellite. The Jovian satellite of Europa has garnered-and continues to do so-significant interest due to the information gathered from observational equipment. It has been discovered that Europa’s surface is one of ice and many scientists have theorized that beneath that ice is a massive ocean. The maintenance of this ocean is due to the tidal flexing inflicted on the satellite by Jupiter’s massive gravitational pull. Europa literally flexes due to this pull. The pull, in turn, creates a heating effect on the ice. In a similar fashion, geothermal heating and the pressure generated by the massive ice sheet above Lake Vostok, both contribute to Lake Vostok’s continued existence. Life at Lake Vostok would facilitate Astrobiologists’ ability to hypothesize what microbial life may exist on Europa. In both cases, neither Lake Vostok nor Europa is expected to harbor any producers, consumers, or vertebrates. At most, both may be able to provide an adequate habitat for microbial life that is of the order of chemotrophic and/or heterotrophic. Given Vostok’s lack of sunlight and Europa’s distance from the Sun, neither is capable of supporting autotrophic organisms.
Given the current knowledge from seismic and radio soundings, research of benthic hydrothermal communities, and a variety of bacterial analyses of ice cores above Lake Vostok, it is within reason to presume that Lake Vostok does harbor a microbial ecosystem. The official discovery of such life will be an exciting day for the science community. While Lake Vostok has just recently been reached, many are concerned about its fragile nature. This concern is valid in that the microbial community residing in Lake Vostok has remained undisturbed for several hundred thousand years. Being as such, assessing the microbial concentration and content will prove difficult for researchers. However, science has already provided examples off of which assumptions regarding Lake Vostok’s nature can be made. Current knowledge of rift valleys (divergent plate zones) tells us that hydrothermal vents are commonly found near such spreading centers and given Lake Vostok’s proximity to the West Antarctic Rift, it can be speculated that there is a likelihood of such vents being found on the lakebed. In addition, current knowledge of the microbial communities that proliferate near these sites is suggestive as to what type of microbes may be found. Ice core analyses showing bacterial content in accreted ice above the lake is highly suggestive of a thriving microbial community. This knowledge, along with the additional plethora of available information, paints a picture of what Lake Vostok’s unique environment may be like. This information additionally illustrates what life-supporting environments may be like on the Jovian satellite of Europa. Discoveries at Lake Vostok will have broad implications for the limnological and astrobiological science communities alike.
References Cited
Christner, Brent J., Royston-Bishop, George, Foreman, Christine M., Arnold, Brianna R., Tranter, Martyn, Welch, Kathleen A., Lyons, Berry W… (2006). Limnological Conditions in Subglacial Lake Vostok, Antarctica, Limnology and Oceanography, 51(6), 2485-2501.
Karl, D.M., Bird, D.F., Bjorkman, K., Houlihan, T., Shackelford, R., Tupas, L. (1999). Microorganisms in the Accreted Ice of Lake Vostok, Antarctica, American Association for the Advancement of Science, 286(5447), 2144-2147.
Kelly, N., Metaxas, A., Butterfield, David. (2007). Spatial and temporal patterns of colonization by deep-sea hydeothermal vent invertebrates on the Juan de Fuca Ridge, NE Pacific, Aquatic Biology, 1(1-16), 1-16.
Oreskes, Naomi. (2003). A Context of Motivation: US Navy Oceanographic Research and the Discovery of Sea-Floor Hydrothermal Vents, Social Studies of Science, 33(5), 697-742.
Priscu, John C., Adams, Edward E., Lyons, Berry W., Voytek, Mary A., Mogk, David W., Brown, Robert L., McKay, Christopher P… (1999). Geomircrobiology of Subglacial Ice Above Lake Vostok, Antarctica, American Association for the Advancement of Science, 286(5447), 2141-2144.
Siegert, Martin, J. (1999). Antarctica's Lake Vostok: Specialists in disciplines ranging from glaciology to engineering are preparing to explore the world's largest subglacial lake, American Scientist, 87(6), 510-517.