Antartic Subglacial Aquatic Environments

Eos, Vol. 93, No. 1, 3 January 2012

AGU Bookshelf Antarctic Subglacial Aquatic Environments PAGES 8–9 From microbes on deep-sea hydrothermal vents, with temperatures pushing 500°C, to bacteria in the highly alkaline Mono Lake in California, the link between water and life on Earth has so far been infallible. Yet one frontier in terrestrial biology remains untested. First discovered in 1968, Antarctic subglacial lakes have the potential to validate or overthrow scientific perceptions of the hardiness of life. In the AGU monograph Antarctic Subglacial Aquatic Environments, editors Martin J. Siegert, Mahlon C. Kennicutt II, and Robert A. Bindschadler recount how the discovery of water beneath 3 kilometers of ice at the (now retired) Russian Sovetskaya research station led, over 4 decades, to our appreciation of 387 such lakes distributed widely about the Antarctic continent. They also explore the details of future missions under the ice. In this interview, Siegert talks to Eos. Eos: Lake Sovetskaya and the larger Lake Vostok were first detected in 1968 and 1970, respectively, but the field of Antarctic subglacial aquatic research did not begin in earnest until the mid-1990s. What was the reason for this delay, and what changed to make scientists take notice? Siegert: That’s a really good question. When we first knew about subglacial lakes, no one—not even glaciologists—seemed to care. The lakes are now a curiosity, but back then no one seemed curious about them! The geophysical data defining both Lake Sovetskaya and Lake Vostok were published in the late 1960s and mid-1970s, but then they were sort of lost to the literature— people’s research just didn’t follow them up. The first inventory of subglacial lakes, published in 1973, showed there to be 17 lakes, but it still didn’t get wider scientific traction and interest. The paper published in 1996 on Lake Vostok showed that the water was about 500 meters deep. Now, this is only my opinion, but what I think happened is that between the 1970s and the 1990s there was a great deal of development in our understanding of life in extreme environments. I don’t think that idea was mature enough in the 1970s for microbiologists to take an interest in subglacial lakes. But in the 1990s, when the new information on the depth of Lake Vostok was announced, microbiologists began to take notice, believing that trapped within these ­ice-​­covered lakes were bacteria that hadn’t been exposed to air for millions of years, adapted to withstand the extreme conditions. So glaciologists presented information on subglacial lakes in the 1970s, and glaciologists still presented information on subglacial lakes in the 1990s. It’s just that there was a different audience available: In the 1990s the audience suddenly became not just glaciologists but microbiologists too. Eos: In the book, you describe how subglacial lakes are formed. What mechanism explains the existence of liquid water trapped under kilometers of ice? Siegert: Ice is a good insulator of heat. In Earth’s mantle, there is radioactive decay,

which causes a heat flux through the crust to the surface. The average level of this geothermal heating is around 50 milliwatts per meter square. So while the surface of the Antarctic ice sheet is of course very cold, the ice in places is very thick. When you have surface temperatures about –50°C but ice that is 4 kilometers thick, having 50 milliwatts per meter square is enough heat for the base of the ice sheet to be warm. As you go down the ice column, from the ice surface all the way down to the bed, it gets warmer and warmer, and if the ice is thick enough it can melt. Once the water forms, it flows under gravity and under the pressure of the ice before it collects in topographic basins and sinks and hollows, just like how lakes collect on the surface of the planet. Eos: Antarctica is home to the coldest recorded temperature on Earth (–89.2°C), yet biologists are confident that microbial life exists in subglacial lakes. How do researchers expect that these microbes survive? Siegert: In these lakes, there is no sunlight, and the lakes are under a lot of pressure. However, temperatures are only around –1°C or –2°C, so it’s not really that cold. But how would these microbes survive? They need chemicals to power their biological processes because they don’t get sunlight, and there are two places from which chemicals might be delivered into the lake. From the overriding ice that melts into the lake, there will be dissolved gases and dust. These were trapped in the ice sheet surface and over time have found their way down to the bed of the ice sheet. There will also be minerals on the floor of the subglacial lake. We think microbes might find it easier to exist and cluster between the ice bed and the lake surface and between the lake bed and the sediment surface, rather than within the whole length of the water column. The main reason people connect subglacial lakes to the potential for life is because they are water, and wherever we find water on our planet there is an association with life. We’ve yet to find a natural aquatic environment on Earth that doesn’t contain microbial life. So we want to know things like, Are

these viable habitats? Are they places where life actually can thrive? Because if not, it would define the edge of the envelope in which life can exist on our planet. These are fundamental questions to which we don’t have answers. To find answers, we need to get into a subglacial lake to make measurements and take samples. Eos: What has been your main area of research in this nascent field? Siegert: I’m a glaciologist, and I use radio echo soundings to understand the basal conditions and landscape under the Antarctic ice sheet. I’ve put together collections of inventories of subglacial lakes, and from these I try to understand the potential storage of water underneath the Antarctic ice sheet and the flow of glacial water. One of the big things that drives glaciers and ice sheet flow is the presence or absence of subglacial water. Subglacial hydrology is known to be very important in Alpine glaciology, yet we know virtually nothing about it in Antarctic glaciology. The work that I and others have been doing to understand the locations of subglacial lakes and the flow of water is fundamental to our appreciation of how the ice sheet works and how it might respond to future changes. Eos: In the 2012–2013 austral summer you will lead a U.K.-based team in an attempt to penetrate into Lake Ellsworth, Western Antarctica. How do you plan to achieve this feat, and what are your main goals? Siegert: I am in charge of the Lake Ellsworth program, and it has taken us 10 years to get to where we are now. We plan to get down through 3 kilometers of ice into Lake Ellsworth, deploy a probe to get sediment and water samples, and then deploy a sediment corer to get a ­3 -meter-​­long section of the lake bed. We then need to bring these back to the surface and get them to laboratories to understand whether or not there is life in Lake Ellsworth. We also want to find out whether there are climate records in the sediments and then sort out what they tell us about the ice sheet’s history. The big challenge, of course, is to get down into the lake, and to do that we’re using a technique called ­hot-​­water drilling. In ­hot-​­water drilling you heat some of the glacier’s ice to around 90°C and then push it through a h ­ igh-​­pressure hose downward into the ice. The ice below melts, the drill goes farther downward, and then you draw the new meltwater into a boiler, recycling it. It’s a simple technique, one that’s used often in glaciology, but the problem is that it has never been used down to the depths to which we’re going. The drilling power isn’t linear with depth, which means we need a very big hot-water drill, the like of which has not previously been built. Eos: By some estimates these subglacial environments have been cut off from the surface atmosphere for millions of years. What steps are being taken to protect these pristine environments? Siegert: Well, ­hot-​­water drilling is a clean technique to start with because we are using

Eos, Vol. 93, No. 1, 3 January 2012 only clean glacier ice in the system. But we will take steps to make it even cleaner by first ensuring that all of the instrumentation is good and clean before we start. Second, we will filter the hot water to take out any viruses or microbes, and then we will treat the water with ultraviolet radiation to kill anything that remains. So the good news is, it’s clean. The bad news is that once we get into the lake, there will be a column full of quite cold water that will begin to freeze above the drill. This means we will have only about 24 hours in which to undertake the experiments, or else we won’t be able to get the drill back to the surface. So that gives us a little challenge. The good news again is that when the experiment is over, the ice will freeze up over the hole, and it will be as if we had never been there. So there is no long-term impact of this experiment on the lake. Eos: Your team isn’t the only one seeking to get under the ice. What other missions, detailed in the book, are currently in development? Siegert: There is a Russian team that has an opportunity to do a type of experiment different from our work at Lake Ellsworth. The opportunity arises because the Vostok ice core, a roughly ­3.7-​­kilometer sample taken during previous research, is located directly over Lake Vostok. That hole is kept open, and it’s filled with drilling fluid. Before the ice corer punches into the top of the lake, several hundred meters of drilling fluid will be taken out of the borehole. The base of the borehole will then be under less pressure than the base of the ice sheet, and therefore under less pressure than that in the lake. After this is done, the lake water will flow up into the borehole, where it will freeze. That team can then reactivate the ice corer and get a sample of lake water. With this sample, tests for lake biology can also be performed. So while the U.K. mission will obtain direct measurements and samples all the way down the water column, the Lake Vostok experiment will recover samples of the surface water. There is also a U.S. program to explore Whillans Subglacial Lake, which is on the edge of the West Antarctic Ice Sheet. This program is interesting because rather than exploring a small ecosystem that would exist in a single subglacial lake, the Whillans program allows the opportunity to sample downstream from a very wide upstream

A topographic map of subglacial Antarctica shows the peaks (warm colors) and valleys (cool colors) that guide lake formation, including Lake Vostok (inside the black box), the site of a 2012–2013 mission to sample the water under the ice. Image from British Antarctic ­Survey/​ ­BEDMAP Consortium.

hydrological catchment. So there are three very different types of programs that are going to be conducted in the next few years, and coupling the information together will be very valuable. One thing I’d like to add is that people often ask, “Is it a race to go into subglacial lakes?” I would argue that it really isn’t a race. As this book demonstrates, there is a lot of collaboration and discussion between the groups of those three programs. Science is our driver, not exploration. It’s not to be the first to penetrate into the subglacial lakes; it’s about doing science. The three

programs are very different, so really there is very little competition between them. They are all doing different things, but when you add them up we will learn an awful lot about subglacial lake systems and subglacial water systems in a few years’ time. AGU Geophysical Monograph Series, Volume 192, 2011, vii + 246 pp., ISBN 978-0-87590482-5, AGU Code GM1924825. List Price $110.00, AGU Member Price $70. —Colin Schultz