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Under the Ice
by Devon Hamilton PhD - Senior Scientist / Physics
11/05/01
Even by Canadian standards, it's cold.
Frozen desolation - lifeless and frigid, the environs of Lake Vostok are probably the last place in the world you would describe as a "hot spot". But Lake Vostok and its glacier are hot, in the figurative if not the literal sense. Lake Vostok, with an area of 10,000 square kilometres, is one of the largest freshwater lakes in the world (about the same size as Lake Ontario), and it's buried under four kilometres of glacial ice in Antarctica.
 Lake Vostok is just one of some 76 large freshwater lakes hidden under the forbidding glacial layers of Earth's coldest continent. These lakes are only detectable using radar and satellite imagery, usually from orbit, and are arguably one of the most important discoveries made in our studies of the Antarctic. Lake Vostok is the largest and deepest of these lakes, with a water depth of 484 metres, approximately twice that of Lake Ontario.
In 1957, the Soviet Union established a research station at what can be considered the most remote and frozen part of our globe. It was here that they recorded the coldest temperature ever, an astonishing minus 89 degrees Celsius on July 21st, 1983. The station is 1000 kilometres from the coast, and is usually accessed by tractor. The lake there was discovered in 1974, when a British research team were mapping the sub–glacial mountains of Antarctica using airborne radar. The radar signal penetrated the ice, and encountered a huge flat, smooth region, 4 kilometres below the surface. That type of radar signal is only produced by liquid water.
 Over the past 27 years, more than 70 other large sub–glacial lakes have been found using satellite imagery and radar. These discoveries have prompted a number of burning questions: why are the lakes there? Is there life swimming in their dark waters? What kind of life? How has this ecosystem changed over time? What does this tell us about evolution and living organisms? How can we explore the lake without contaminating it? Why do we care? It is this last question that is both the most obvious and the hardest to answer. Aside from the novelty of having a freshwater lake at this most unlikely of locations, the average person would probably greet its discovery with indifference. Some may even question the need to explore these pristine waters - we have contaminated and ventured into all the corners of the globe. Mercury and toxic heavy–metal by–products are found in the bodies of arctic marine animals, rampant deforestation is visible even from orbit - can we not leave this one corner alone?
This is a valid point. Does humanity's insatiable curiosity justify probing every mystery and corner, no matter what the consequences are? Fortunately, this is a question that the scientists who study Lake Vostok are asking themselves. They, perhaps more than anyone else, wish to preserve the pristine nature of these sub–glacial lakes. The motivation to preserve the purity of these lakes stems both from environmental concerns, and also for scientific reasons. The lake remains liquid because the overlying layer of ice acts as an insulating blanket over the water, trapping the heat radiated from the Earth's surface, which melts the glacial ice. There is even some discussion as to whether hot springs are present within the lake. Paleo–geologists and climatologists are uncertain, but estimate that Lake Vostok could have first formed as long as 15 million years ago. If this is the case, then these waters provide humanity with a window into our past. Microbial organisms that have been isolated from the rest of the Earth's environment will have followed a different evolutionary path. The differences between these organisms and their more prolific cousins in our biosphere will shed some light on how evolution operates Š how divergent have the branches been? How similar to one another are the organisms?
Before these questions can be properly addressed, scientists need to establish a way of penetrating the ice without any contamination. The introduction of non–native microbial life could be disastrous for the isolated ecosystem. Whether or not life exists in Lake Vostok, is an unanswered question, although the indications are positive. Core samples of glacial ice have been obtained from regions near the liquid lake (at a distance of approximately 100 metres above the lake). Scientists have concluded that these core samples are actually frozen lake water, and not just part of the glacier. As temperatures fluctuate, the edge portions of the lake will freeze onto the glacier, and portions of the glacier will melt and join with the lake. This process means that some of the potential microbial life should have been deposited into the ice near the lake. It is possible to distinguish the lake–water ice from glacial ice because of the conditions under which they froze - lake ice will be fairly clear, while glacial ice is granular in texture.
 The core samples obtained by a team of scientists led by Dr. John Priscu at Montana State University are clear, and resemble winter icicles. Inside these ice cores, scientists have found bacteria similar to Patagonian soil microbes. The number of different bacterial families is much smaller than that seen in our own biosphere - indicating that the extreme environment limits the diversity of life substantially. Ice is actually a fairly good home for microbes, the cold slows down their metabolism and they consume far less energy. However, they still need some energy - which is one of the reasons why the Lake Vostok investigations are so interesting. It has been perhaps as long as 15 million years since the surface of the lake was last exposed to solar energy. While a complicated cycling process is believed to transfer surface ice down to the lake (carrying microbes with it), this process is estimated to take between 200 000 to 500 000 years. The microbe images seen here are of bacteria found in core samples taken throughout the glacier.
For many scientists it is the question of energy that presents itself as the burning issue. All living organisms from the eurakocyte to the elephant require energy. Our ecology is dependent upon turning solar radiation into chemical energy via photosynthesis. Until recently, this was the only known energy source for life. The requirement of solar energy necessarily restrict where we could expect life to be found - on a planet relatively close (but not too close) to a star somewhat like our Sun, a district referred to as "the Habitable Zone". Our own solar system's "Habitable Zone" extends from just inside the Earth's orbit to around the orbit of Mars. There are several criteria used to define this zone, but one of the primary ones was the presence of an energy source with suitable intensity.
 Microbes trapped in ice can remain viable for huge periods of time, however the ecosystem still requires the input of energy. The most likely energy input for the Lake Vostok microbes (if they actually exist - remember, we have not actually penetrated the lake itself) is a result of geothermal energy. Because of radioactive decay, the Earth generates energy. It is this energy which drives the convective motions in the Earth's mantle, shoving and pushing the crustal plates about - building mountains, widening oceans and driving earthquakes and volcanic eruptions. The ice over Lake Vostok traps this heat like a blanket, retaining the energy. Perhaps local hot springs provide "hot spots" within the lake, regions of elevated temperature which provide extra energy and provide potential locations for ecological communities to thrive - just as vents do upon the ocean floor (more on this in a later column). The results from Lake Vostok - the discovery of thermophile ecosystems near ocean floor vents and even microbial ecosystems buried in isolated subterranean caves - change this perspective somewhat. All of these ecosystems are independent of photosynthesis, relying instead upon the Earth's own heat flux to provide the needed energy to drive the metabolic functions of the organisms.
Suddenly, we are no longer restricted to narrow habitable zones such as our own. We can now expand our view of where to look for life, even in our own solar system - three of JupiterÕs Galilean moons are believed to have liquid water lurking under their icy crusts, heated by tidal interactions with the giant world. The resemblance to the Lake Vostok conditions is striking and compelling. There are many who feel that an exploration of Lake Vostok and its fragile ecology will simply be a practice run, a warm–up, for a rendezvous with Europa, Ganymede and Callisto. In the end, this cold sub–glacial lake may help answer one of the most important questions we have ever asked - and in that light Vostok Station may physically be the end of the world, but metaphorically it could be the start of a whole new one.
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