The Antarctic continent has always been a place of surprises. In the eighteenth century, Captain James Cook expected to find a land of forests and pastures ripe for colonization; instead he discovered a vast, frozen, and seemingly useless continent that turned out to be one of the most difficult places on Earth to explore. Far from being useless, Antarctica has proven to play a critical role in many aspects of the Earth system as well as being an important platform for exploring the universe and a place of unique ecosystems. Given this history, perhaps it is not surprising that our expectations about the ice sheet sitting firmly on its underlying rock also have proven to be wrong.
From geophysical surveys, we now know that beneath the Antarctic ice sheet, water has accumulated over millennia forming watery subglacial environments ranging in size and form from Lake Vostok, a large water body similar in surface area to Lake Ontario, to shallow frozen swamp-like features the size of several city blocks. The discovery of subglacial aquatic environments has opened an entirely new area of science in a short period of time. We continue to make discoveries that constantly change our understanding of these environments. Our speculation that Lake Vostok was a unique feature has been changed by our discovery of more than 145 of these “subglacial aquatic environments.” These environments are first beginning to be characterized with remote sensing. Because they have never been sampled, very little is known about the physicochemical and biological processes within them. Lakes and other aquatic habitats now appear to be common and widespread beneath the ice sheet, and recent evidence shows that many of the subglacial aquatic environments comprise vast watersheds connected by rivers and streams that flow beneath the ice sheet.
These environments may have formed in response to a complex interplay of tectonics, topography, climate, and ice sheet flow over millions of years. They may have been sealed from free exchange with the atmosphere for millions of years and are analogous to the icy domains of Mars and Europa. Evidence from studies of the overlying ice indicates that microbial life may exist in these subglacial aquatic environments, although this remains a subject of controversy (Chapter 3). The region of highest density of these environments surrounds what is likely to have been one of the nucleation points for the East Antarctic ice sheet; the
lakes potentially contain sediments within their lake beds that may provide a record of major changes in the Antarctic ice sheet.
On the basis of the limited data we have so far, however, there seem to be several exciting scientific discoveries to be made from the study of these unique systems, especially the potential for unique microbial communities, a general understanding of the physiochemical processes of this extreme environment, and a history of environmental conditions from the sediment record. The discovery of subglacial aquatic environments, especially lakes, and the intriguing questions posed about these extreme environments have caught the attention of the public.
There is great value in setting the exploration of these environments in motion. From a scientific perspective, they may hold critical information needed to answer many questions about microbiological life, evolution, and adaptations; Antarctic and global climate over the past 65 million years; ice sheet dynamics; and evolution of subglacial aquatic environments and their associated hydrological and biogeochemical processes. Scientific interest in the subglacial hydrology of ice sheets has never been higher, because we need to learn as much as possible about how the subglacial water systems operate beneath ice sheets. The question of whether ice sheets can have a large dynamic response to changes at their margins (e.g., the breakup of ice shelves) partly involves the question of whether or not fast flow processes will be activated by changes in subglacial conditions. Thus, there are conceivable links to the important question of sea level rise. It is important for us to acquire this information in the next 5 to 10 years—not several decades from now.
During the Lake Vostok investigation (Box 1.1), data will be gathered that may help determine whether microbial life is present or absent from this environment. Chemical analyses of water samples will help settle speculative discussions about partition coefficients, which will improve geochemical modeling of these environments. The exploration plans for Lake Ellsworth (Box 1.2) call for a concentrated radio-echo sounding (RES) campaign followed by physicochemical and biological measurements and water and sediment sample recovery. With results of both of these investigations, we will only begin to develop an initial understanding of these environments, but these first samples will provide all-important evidence about how conservative we should be in moving forward. The data and lessons learned from these endeavors should be used to guide future environmental stewardship, scientific investigations, and technological developments.
The pursuit of scientific knowledge, however, needs to be balanced against environmental stewardship and cleanliness. Responsible stewardship during the exploration of subglacial aquatic environments requires that investigators proceed in a manner that minimizes the possible damage to these remarkable habitats and protects their value for future generations, not only in terms of their scientific value but also in terms of conserving and protecting a pristine, unique environment. This is particularly important because it now appears that these environments are hydrologically and potentially biologically connected and that activities at one site may affect other sites within the system.
No lake has yet been entered, thus no lake has been directly altered, chemically or biologically, by scientific study. It is to minimize the possible damage to these remarkable habitats from scientific investigations and protect their value for future generations that this National Research Council (NRC) study has been undertaken.
THE DISCOVERY OF SUBGLACIAL LAKES
The continent of Antarctica is formed from a fragment of the Gondwana super-continent, which included the continental masses of Africa, South America, Australia, Antarctica, and India. This supercontinent began to break apart in Early Cretaceous time (around 130 million years), and full isolation of Antarctica from other Gondwana fragments, and the associated possibility of circum-Antarctic ocean circulation, was achieved by 30 million years (Early Oligocene). Although there is evidence for alpine glaciation in Antarctica from Cretaceous time, it seems that a large ice sheet did not come into existence until around 35 million years (Anderson 1999). Since its formation the ice sheet has not entirely disappeared, although its eastern and western parts have experienced substantial fluctuations in volume.
The earliest attempts to measure ice depth in Antarctica used seismic sounding from the surface of the ice sheet where the reflection of shock waves generated by explosives was measured. Admiral Byrd’s expedition to the Antarctic in 1939-1941 conducted trials of such a system, but the Norwegian-British-Swedish expedition in 1951-1952 pioneered the scientific use of this technique in the Antarctic. Although the technique proved cumbersome and slow, it was the best technique available at the time and was used during the International Geophysical Year (IGY) in 1957-1968 by several countries to provide important data about the underlying topography. The IGY data provided many interesting insights into the subglacial structures in the interior of the Antarctic, but the technique was too unwieldy to be extended across the whole continent.
The recognition that radio waves at very high frequencies could penetrate ice but were reflected by rock changed this approach and lead to the development of Antarctic airborne radio-echo sounding by the Scott Polar Research Institute in the 1960s. Use of this technique across the Antarctic ice sheet provided, for the first time, the possibility of mapping the whole of the underlying continental rock (Robin 1972). The principal intention was to enable glaciologists to calculate more accurately the total mass of the ice sheet by measuring its thickness; however, the data collected provided valuable information to a wide range of scientists with many interests. By 1980, RES had been collected from more than 400,000 km of flight track, covering approximately 50 percent of the 13.5 × 106 km2 Antarctic ice sheet. This coverage, however, was concentrated in only few areas, and despite continued survey work there are still many areas of the Antarctic continent for which no RES data exist (Figure 1.1). In some areas of the continent, flight lines are so widely spaced that subglacial features cannot be adequately mapped.
Compilation of all available data by the Scientific Committee on Antarctic Research (SCAR), however, resulted in the publication of the first detailed sub-ice topographic map (Lythe et al. 2001), which was critical in the developing search for subglacial water.
The possibility of the existence of subglacial water was first identified by Robin and others in 1968. They noted that in places the RES signal changed from one characteristic of an ice-rock interface to one indicative of an ice-water interface, which suggested that there could be water trapped between the bedrock and the bottom of the ice sheet. The first subglacial lake reported was located beneath Sovetskaya Station; water was also indicated under Vostok Station (Robin et al. 1970).
Exploration of Subglacial Lake Vostok: Brief History and Future Plans
Since 1990, the Russian Antarctic Expedition Program has drilled more than 3600 m of ice with additional support from the French and U.S. Antarctic programs between 1993 and 1998. The present borehole, 5G-1, was started in 1992 from a deviation along the previous borehole (5G) at depths of 2232-2246 m. By 1993 the coring had reached 2755 m in borehole 5G-1. After a one-year hiatus, drilling reached a depth of 3100 m in September 1995. Drilling continued during the 1995−1996 field season and was intended to continue through the 1996 winter to reach 25 m above the surface of the subglacial lake beneath Vostok (at ~3,650 m depth in accordance with the guidelines recommended by SCAR during the Lake Vostok Workshop, Cambridge 1995). However, when the station closed for the 1996 winter, drilling had reached 3350 m depth. A seismic survey was undertaken during the 1995−1996 field season in an area about 2 km2 around the borehole. A depth of 3623 m was reached in hole 5G-1 in 1998. After an eight-year hiatus, drilling resumed in 2005-2006, reaching a depth of 3650 m.
At present, the bottom of hole 5G-1 is less than 100 m above the surface of Lake Vostok and the Russian Antarctic Program plans to continue drilling and eventually sample the waters of Lake Vostok. The next step proposed is to drill an additional 75 m to obtain new scientific data on the origin, properties, and structure of the ice near the “ice cover-subglacial lake” boundary. The proposed method to access Lake Vostok will exploit the physical peculiarities of the lake-ice sheet system. The ice sheet basically floats on the lake, and the pressure at the “ice-water” boundary corresponds to the weight of the overlying ice sheet. During drilling, the pressure exerted by the drilling fluids within the borehole compensates the pressure of the overlying ice and keeps the hole open. By decreasing the quantity of drilling fluids, the water pressure in the lake will be greater than that of the drilling fluids. When the drill reaches the lake, the drilling fluids will be forced up the borehole by lake water.
The borehole fluids comprise mainly aviation fuel (TS-1) and Freon (CFC-141b). These drilling fluids will not dissolve in water and will be displaced by the water rising in the borehole. Also, a sterile drilling fluid will be introduced into the lowermost 200 m of the hole, approximately 100 m above the lake surface, which will act as a plug between the top and clean bottom sections of the borehole. The density of this fluid is intermediate between the lake water and aviation drilling fluids.
It is planned that during the last stage of penetration, the drill will be extracted from the hole immediately after reaching the water surface. Lake water will rise in the borehole and freeze. Later, this newly frozen ice will be drilled to recover samples of the lake water. The newly formed ice remaining below the sampled lake ice will form a plug and thereby prevent a possible connection between the drilling fluids and the lake water. Thus, the proposed method will allow the sampling of lake water without the drill and sampling instruments entering the lake.
SOURCE:Robin Bell, Lamont-Doherty Earth Observatory of Columbia University.
An Eight-Year Plan for the Exploration of Subglacial Lake Ellsworth
The comprehensive geophysical survey of Lake Ellsworth is planned to occur in two seasons during IPY 2007-2009 and will include RES, seismic surveying, and a variety of surface measurements. Discussion of the feasibility of a U.K.-led subglacial lake exploration program began at the British Antarctic Survey in April 2004. Currently, a consortium of more than 30 scientists from seven countries and 14 institutions is planning to access Lake Ellsworth using hot-water drilling. The project will involve a geophysical survey; instrument development; hot-water drilling and fieldwork; biological and geochemical analysis of water samples; and sedimentological analysis of lake floor deposits.
Phase 1—Geophysical Exploration (3 years): The size and shape of Lake Ellsworth, flow of the ice sheet over the lake, and subglacial topography surrounding the lake will be measured. Objectives include measuring water depth, sediment thickness across the lake floor, and dimensions of the lake’s drainage basin.
Phase 2—Instrument and Logistic Development (2 years): Equipment will be assembled and logistics for physical exploration will be planned. Probes will be built and tested to measure the physical and chemical properties of the lake’s water and to sample lake water and sediment. Objectives include developing a means of communication between the probe and the ice surface; building and testing a hot-water drill; and acquiring and testing a sediment corer capable of extracting a 2- to 3-m core from the floor of Lake Ellsworth to recover climate records.
Phase 3—Fieldwork (1 year): A hot-water drill will be used to bore a 30-cm-wide hole to gain access to the lake from the ice sheet surface. It is anticipated that the borehole will be held open for 24-36 hours. Just before the drill enters the lake, the water generated during drilling will be removed to ensure that the borehole water does not enter the lake. Once the lake is reached and lake water floods into the borehole, a probe capable of measuring the lake’s biology, chemistry, and physical environment will be deployed through the water column to the lake floor and subsequently retrieved. A sediment corer will be used to retrieve a 2- to 3-m sediment core.
Phase 4—Data Analysis and Interpretation (2 years): Data, sediment, and samples acquired by the probe will be analyzed to comprehend the physical and chemical structure of the lake; ascertain the form, level, and distribution of microbial life in the water column and water-sediment interface; undertake geochemical analysis; and if a sediment core is acquired, analyze sedimentary records.
SOURCE: Michael Studinger, Lamont-Doherty Earth Observatory of Columbia University.
In 1974-1975, an airborne radio-echo survey of ice depths over central East Antarctica near the Vostok Subglacial Highlands led to the discovery of a subglacial lake with an area of about 10,000 km2, lying underneath almost 4 km of ice and apparently close to Vostok Station. Subsequent surveys indicated a large flat area in the bedrock, lying in what appeared to be a large valley, with a water surface above it. The image was seen on the RES records as a distinctive, mirror-like reflection (Figure 1.2). It is now known that some of the lake surface is covered with accretion ice, formed from lake water, that is attached to the bottom of the glacial ice (Figure 1.2). The Russian drilling operation, which has recovered ~3600 m of ice, has entered this accretion ice but has not yet penetrated the waters of Lake Vostok itself.
The advent of satellites with radar altimeter sensors able to measure the height of the ice sheet surface to within a few centimeters has provided a complementary approach to locating such lakes, because the flat lake surface is apparently reflected in the ice surface topography kilometers above it. In 1993, altimetric data from satellite
measurements provided independent evidence of the areal extent of the Vostok lake, thus confirming it to be the largest known subglacial lake. Using RES and satellite altimetry together, the location and extent of this subglacial lake, now named Lake Vostok, was described by Kapitsa et al. (1996).
The surface area of Lake Vostok is 14,000 km2 (comparable to Lake Ontario), but early estimates of its volume have proved to be conservative. Recent geophysical interpretations (Studinger et al. 2004) yield an estimated volume of 5400 km3, more than three times the volume of Lake Ontario, and an average water depth of 360 m (Figure 1.3). Kapitsa et al. (1996) estimated that the residence time of the water in the lake is likely to be of the order of tens of thousands of years and that the mean age of water in the lake, since deposition as surface snow, is about 1 million years.
The snow and glacial ice overlying Lake Vostok contain microorganisms such as bacteria, yeasts, fungi, and microalgae (Abyzov 1993; Abyzov et al. 1998), although questions remain about the introduction of microbial contaminants during the sampling required to generate such records. Microbes may be concentrated in the liquid-water veins between ice crystals and under such conditions could metabolize at temperatures well below the freezing point (Price and Sowers 2004; Price 2007).
More recently, drilling at Vostok Station recovered 3623 m of ice core but halted in 1998, when the drill was 120 m above Lake Vostok. As summarized by Christner et al. (2006), the last 84 m of the ice core has a chemistry and crystallography distinctly different from the overlying glacial ice. This 204 m of ice, called accretion ice, is Lake Vostok water frozen onto the bottom of the glacial ice. The accretion ice contains measurable dissolved organic carbon as well as low but detectable numbers of prokaryotic (bacterial) cells. A portion of the assemblage of microbes is capable of metabolic activity, as was demonstrated when ice metabolized added 14C-organic compounds (Karl et al. 1999). Molecular identification of microbes within the accretion ice show close similarity to Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes.
Microorganisms are continually deposited from the atmosphere onto the surface of the ice sheet (Vincent 1988) and some may survive the lengthy transport to subglacial aquatic environments, thereby providing a potential source of microbial life to these environments. Spore-forming bacteria (including many Gram-positive species) are likely to be especially resistant to the severe conditions imposed by long-range transport in the atmosphere and during residence within and at the surface of the Antarctic ice sheet.
Subglacial aquatic environments have been seen by many as an analogue of ice-bound worlds elsewhere in our solar system (e.g., Europa) and a potential testing ground for how we might investigate them (Priscu et al. 1999).
Not surprisingly the discovery of Lake Vostok has stimulated others to search the RES database and satellite data to determine if other subglacial lakes exist. More than 145 lakes have now been identified by characteristically strong, mirror-like, and very flat RES reflections (Figure 1.2C) (Siegert et al. 2005a). Most of the subglacial aquatic environments are located in the ice sheet interior, and 33 percent are within 100 km of the ice crest. Mean ice thickness above the lakes is about 3000 m. About 75 percent of lakes have radio-echo lengths of <10 km, and only 5 percent are >30 km although all are smaller than Lake Vostok. Some near-flat surface regions that usually occur over lakes have also been observed where it appears that no lakes exist. Such features may be caused by water-saturated basal sediments rather than subglacial lakes (Carter et al. 2007). In areas where the RES coverage is very dense, it is possible that all but the smallest subglacial aquatic environments have been identified. However, the distribution of flight lines (Figure 1.1) is not uniform over the continent and more subglacial aquatic environments may exist in regions for which no data currently exist. Siegert et al. (2005a) used a minimum length limit of 500 m to identify and locate the 145 lakes listed in the inventory. In the future, it may be possible to improve the discrimination in the signal analysis to lower the minimum length to 100 m.
Until recently, each subglacial lake was considered to be an isolated unit. Continuing analysis has revealed that several of the lakes are clearly connected to each other; Wingham et al. (2006) used satellite altimeter data to show a 2- to 3-m change in the surface height of the ice sheet in locations above subglacial lakes, which is suggestive of water draining subglacially from one lake into another (see recent data for many lakes in Fricker et al. 2007). Although there might be other explanations, the evidence is strong enough that subglacial lakes should be considered part of a discontinuous hydrological system rather than isolated entities. This raises a caution to researchers: if one aquatic environment is contaminated during drilling or sampling, there is a possibility of the contamination spreading to other subglacial aquatic environments. An attempt to map the likely subglacial water paths and identify sub-ice catchments is under way (Siegert et al. 2006).
This changing appreciation of the extent and importance of subglacial hydrology has fundamental implications for many areas of science but seems especially critical for those investigations that intend to drill to the bottom of the ice sheet because these activities may potentially affect subglacial aquatic environments that are located down the hydrologic gradient (Carter et al. 2007). Figure 1.4 shows the location of all the holes that have already been drilled to bedrock or nearly through the ice sheet. Many of these sites are located within suspected drainage basins of identified subglacial aquatic environments.
Liquid water is able to accumulate at the bottom of the ice sheets, including the Greenland ice sheet, because of the presence of geothermal heat, the lowering of the freezing temperature of water from the pressure of the overlying ice, and the insulation provided by the ice sheet (Siegert et al. 2003). This was illustrated dramatically when “pink-colored” water unexpectedly entered the bottom 45 m of the NGRIP (North Greenland Ice Core Project) borehole in Greenland and froze (Anderson et al. 2004). The color was caused by minerals such as sulfides and iron compounds.
The region with the highest spatial density of subglacial water bodies surrounds what is likely to have been one of the nucleation points for the East Antarctic ice sheet. Subglacial aquatic environments located in these regions may contain sediments that accumulated prior to ice sheet formation and may potentially contain paleo-records of major shifts in climate.
Streams—that is, moving water beneath the Antarctic ice sheet—are inferred but have not actually been measured. Streams could form in meltwater channels that occur irregularly at the bottom of the ice sheet or could flow within layers of rocks or fractured bedrock that resemble the hyporheic flow paths beneath the beds of most rivers and streams (e.g., Wondzell 2006).
Investigation of lakes and other aquatic environments buried under kilometers of ice has attracted a great deal of scientific interest over the last decade. Although much
can be learned about these systems from remote sensing, many of the key questions require direct sampling. To sample the water, the microbial communities, the sediments, and the underlying rock under the lakes requires drilling through the ice and the insertion of sampling and monitoring equipment into the lake. All of these processes pose both technical problems and problems of potential contamination with microbes from the surface.
SCAR AND INTERNATIONAL EXPLORATION OF SUBGLACIAL AQUATIC ENVIRONMENTS
In just over a decade, subglacial lake environments have begun to emerge as the newest frontier in Antarctic science and exploration. Many nations are moving ahead with their own investigations (Boxes 1.1 and 1.2), and there has been much international debate over how to proceed in the effort to understand these unique environments. In response, the international scientific community participated in two workshops (19981 and 19992) to establish the rationale for the study and exploration of subglacial lake environments, assess technological needs for these endeavors and develop a 10-year time line for study and exploration.
During the Cambridge workshop (1999), the scope of investigation was expanded beyond just Lake Vostok to include all subglacial lakes under thick ice sheets. A set of guiding principles was established for future activities. These principles clearly stated that the program must be international and interdisciplinary in nature; noncontaminating technologies and minimum disturbance must be fundamental considerations in program design and execution; the ultimate goal should be lake entry and sample return to ensure the greatest scientific benefit; and the best opportunity to attain interdisciplinary scientific goals is by study of larger lakes, therefore Lake Vostok must the ultimate target of study.
Following a recommendation from the Cambridge workshop (1999), the Scientific Committee on Antarctic Research constituted a Subglacial Antarctic Lake Exploration Group of Specialists (SALEGOS) in 2000, composed of scientists from SCAR member nations and charged the group to begin a process of discussion and collaborative planning. This group met six times over the next four years and made great progress in developing a science and technology plan for an ambitious program of interdisciplinary exploration and study.
A final recommendation of the SALEGOS was that Subglacial Antarctic Lake Exploration (SALE) progress to a SCAR Scientific Research Program. A SALE proposal and an implementation plan were prepared and submitted to SCAR. In October 2004, SALE was named one of five SCAR major science programs. SCAR SALE3 met for the first time in April 2005, and a second meeting was held in April 2006. The SCAR SALE terms of reference are listed in Box 1.3. To focus certain activities, SCAR SALE has developed a data management policy and established Subcommittees on Data, Technology, and Education, and on Outreach and Communication.
Subglacial Lakes: A Curiosity or a Focus for Interdisciplinary Research, Washington, D.C., sponsored by the U.S. National Science Foundation.
Subglacial Lake Exploration: Workshop Report and Recommendations, Cambridge, U.K., sponsored by the Scientific Committee on Antarctic Research and the Council of Managers of Antarctic Programs.
SCAR SALE activities are chronicled on its web site: http://salepo.tamu.edu/scar_sale.
SALE Terms of Reference
SALE is charged with the following:
The main scientific goals of SCAR SALE are to understand the formation and evolution of subglacial lake processes and environments; determine the origins, evolution, and maintenance of life in subglacial lake environments; and understand the limnology and paleoclimate history recorded in subglacial lake environments. While there are numerous interesting scientific questions posed in the SCAR SALE program, one of the most important is concerned with the origins, evolution, and maintenance of life in subglacial aquatic environments. The SCAR SALE group speculated that if the residence time of the water in any subglacial aquatic environment is very long, and if the lake is ultra-oligotrophic as well as dark and under pressure, then the life it contains could be unique, possibly providing hitherto unknown species with unusual biochemical or physiological capabilities. Thus any attempt to sample the water, the sediment, or the organisms directly should ensure that the subglacial aquatic environment is not contaminated, especially by carbon substrates that might allow the aquatic system to fundamentally change.
Echoing the guiding principles from the Cambridge workshop (1999), the SCAR SALE group recommended that an integrated science plan for the future be developed to ensure that one type of investigation does not accidentally impact other investigations adversely; that sampling regimes plan for the maximum interdisciplinary use of the samples; and that the sharing of all information promotes greater understanding. SCAR continues to serve as the international focal point of activities to facilitate cooperation in the exploration and study of subglacial lake environments in Antarctica, advising the international community on issues related to exploration, research, data management, and other matters.
In addition, members of the U.S. scientific community have formed the U.S. Subglacial Antarctic Lake Environments (SALE) Program, which is a long-term exploration and research program formed by a group of scientists and technologists who share the goal of a comprehensive and environmentally safe investigation of subglacial environments with a special focus on subglacial lakes (http://salepo.tamu.edu/us_sale/saleexcom). The U.S. SALE Program seeks to support and facilitate opportunities for U.S. participation in the international collaborative teams that will be addressing common scientific and technological objectives. The U.S. SALE Program includes a series of science, technology, education, and communications or public relations committees. The committees operate relatively autonomously, responding to requests for advice and, organizing workshops or meeting as appropriate to set the SALE agenda in each focus area. U.S. SALE seeks to liaise with other SALE committees and organizations to develop cross-disciplinary connections and promote venues to consider common issues.
The exploration of subglacial aquatic environments will also be a focus for the International Polar Year (IPY),4 which began on March 1, 2007. Various parties participating in SALE projects have joined together as the SALE Unified Team for Exploration and Discovery (UNITED). Closely coupled with the SCAR SALE, these programs will join together to promote and advance common scientific, technological, and logistical issues. The ambitious interdisciplinary objectives of SALE can be realized only by multiple exploration programs that will investigate exemplars of the diverse subglacial environments over the next decade or more. The IPY provides an opportunity for an intensive period of initial exploration that will advance scientific discoveries to a new level that could not otherwise be achieved by a single nation or program. Each program is an independently managed campaign with specific scientific objectives, logistical requirements, and management structure that will contribute to, and accrue added value from, a common international research agenda. Synergy is provided by the pooling of resources where appropriate, the sharing of experiences and expertise, the coordination of logistics and technological developments, and a shared vision (more details are provided at http://salepo.tamu.edu/sale_united).
DETERMINING THE SUITABILITY OF SUBGLACIAL AQUATIC ENVIRONMENTS FOR EXPLORATION
Recommendations from a SALEGOS workshop (SALEGOS 2001) identified six questions to guide selection of suitable subglacial lake environments for exploration:
Does the lake provide the greatest likelihood for attaining the scientific goals?
Can the lake be characterized in a meaningful way—for example, size, postulated structure?
Is the lake representative of other lakes and settings?
Is the geological or glaciological setting understood?
Is the lake accessible (near existing infrastructure)?
Is the program feasible within cost and logistical constraints?
Siegert (2002) applied the first five questions to the inventory of known subglacial lakes to identify which were the most suitable subglacial aquatic environments for exploration. While the current inventory has greatly expanded since 2002, the overall approach to assess which lakes are most suitable for exploration is still valid. As Siegert (2002) points out, all subglacial aquatic environments have the potential to achieve the scientific goals of SCAR SALE, discussion earlier, in that these lakes are ice covered, and contain water and most likely sediments. The question then becomes, Which of these lakes are most suitable to attain these goals? At present, Lake Vostok is the only subglacial lake that has been characterized beyond just a broad RES survey. A concentrated RES campaign (Bell et al. 2002), coupled with seismic, interferometric synthetic aperture radar (SAR) (Siegert et al. 2001) and ice coring (Petit et al. 1999) studies, has revealed more information about this lake than any other environment. However, to fully characterize the lake floor morphology and lake sediments requires time-consuming, ground-based seismic sounding. The size of Lake Vostok makes this endeavor much more challenging and time intensive. Siegert (2002) suggested that a detailed survey of a smaller lake may provide more information in a more timely and economical manner.
In addition to size considerations, topographic setting will strongly influence how easily these environments can be characterized. Environments with relatively flat topography are more easily characterized than basins with complex topography and steep sides (Siegert 2002). Although small basins with relatively flat topography are potentially better candidates for exploration, the trade-off is that basins with steep sides are likely to be deeper and may contain longer, better-preserved sediment records.
As the inventory of subglacial aquatic environments has grown, several classification schemes have been proposed (Chapter 2). Regardless of which classification system is employed, it is clear that several different types of environments exist in different glaciological and topographic settings and that no one lake is representative of all other environments. In fact, Lake Vostok is unique in that it is the largest known subglacial lake and it occupies an entire subglacial valley (Siegert 2002). Although the physical constraints imposed by the ice sheet (Chapter 2) may cause many of the physical processes within all subglacial aquatic environments (Chapter 2) to be similar, the underlying geology and geothermal setting may influence the biogeochemical processes of these environments. At present, it is unknown whether the biogeochemical processes in different types of environments from different settings are similar. This
lack of data is a challenge for determining which environments are representative. At present, we can only choose representative environments based on physiography or geophysical characteristics.
For most subglacial aquatic environments, the glaciological setting has been rudimentarily described through RES surveys. However, there are very few detailed geological data from beneath the Antarctic ice sheet, and this lack of data inhibits our ability to characterize the geological setting in which these environments are contained and to understand the geological history of these environments. In addition the glacial history of East Antarctica is markedly different from the history of West Antarctica. The paleoenvironmental records obtained from similar types of aquatic environments from central West Antarctica or Dome C will be relevant only to their respective region of the continent (Siegert 2002). This geographical divide is another consideration in choosing exemplar environments.
Accessibility of potential sites may be the deciding factor in choosing between equally suitable environments for exploration. Logistical needs for exploration are not trivial and the proximity of sites to existing support, such as research stations or runways, is a compelling argument in selecting a site. For example, the southern end of Lake Vostok is located directly beneath Vostok Station, but the northern end is approximately 200 km from the station (Siegert 2002). Aquatic environments in the Dome C area are near where the European Project for Ice Coring in Antarctica (EPICA) ice core was recovered, and environments in the South Pole region are close to South Pole Station. Lake Ellsworth is located along a crevasse-free path to the Patriot Hills, where a blue ice runway exists enabling personnel and supplies to be directly airlifted from Punta Arenas, Chile.
After weighing all the criteria, is there one subglacial aquatic environment that is best suited for exploration? Siegert (2002) concluded that no one single environment could be studied to achieve all of the scientific objectives set forth by SCAR SALE. In terms of assessing the existence of endemic ancient life, Lake Vostok provided the most viable location because it is substantially older and deeper. However, Lake Vostok is not necessarily representative of other subglacial aquatic environments in terms of physiography and its size makes a complete characterization by ground-based methods extremely challenging. These drawbacks suggest that other lakes, such as a small lake from Dome C, may be viable candidates (Siegert 2002).
The varied glacial history of East and West Antarctica requires that more than one lake be explored to establish robust paleoenvironmental records. In addition, Siegert (2002) suggested that records from several sites would place the glacial history in a spatial context and therefore improve the details of ice sheet changes. Siegert (2002) advocated that a subglacial lake exploration strategy need not require that all scientific objectives be accomplished through sampling of a single lake. Different sites may be more appropriate to answer specific questions. For example, if the search for life is the sole objective, then any subglacial aquatic environment may be selected. If the goal is to establish paleoenvironmental records, then it would be wise to sample multiple sites in areas that are sensitive to such changes.
Since Siegert (2002) undertook this assessment, more environments have been discovered and compelling evidence for a subglacial drainage system has developed (e.g., Wingham et al. 2006; Fricker et al. 2007). Consequently, the suitability of specific subglacial aquatic environments for exploration must depend on the position of the potential site within the subglacial hydrological system. At present, our knowl-
edge of this system is rudimentary (Siegert et al. 2007) and more detailed analysis is needed to appreciate the implications of this system for any exploration strategy that is developed.
ANTARCTIC PRESERVATION VALUES
Stewardship for Science, Aesthetics, and Wilderness
The Antarctic is more highly protected, in terms of environmental legislation, than any other continent. Since the Antarctic Treaty was signed in 1959 there has been a growing international accord on providing protection for its species and ecosystems; on ensuring peace in the region; and on utilizing the unique features of the Antarctic to advance science, often by international collaboration.
The Antarctic constitutes the world’s largest remaining wilderness area, a place of great beauty and challenge, the least polluted place on Earth and one that many nations have already committed themselves to protect. Such stewardship underlies the Antarctic Treaty, and although the nations that signed the treaty constitute only 25 percent of the United Nations, they more than represent 70 percent of the global population, making such a commitment globally significant.
The lack of industry and an indigenous human population makes Antarctica unique among all the continents. The international system of governance through the Antarctic Treaty System (NRC 1986) works by consensus, providing perhaps the best global forum in which to agree and implement the concept of stewardship.
The idea of stewardship is not new but has only recently come to the fore in the Antarctic as a more coherent framework for conservation and environmental management has been implemented through the Protocol on Environmental Protection to the Antarctic Treaty. Indeed, recognition of the Earth as a connected system and the development of Earth system science have given added impetus to the need for conservation and sustainable management on a global scale.
Maintaining the present environmental state of Antarctica has assumed increasing importance as its relevance to science has become clear. The Antarctic ice sheets are a critical part of the Earth’s hydrological balance, as well as the most important heat sink. The continent provides an opportunity to measure baseline global pollution levels, and the measurements of greenhouse gases at the South Pole have been a key feature of research into global climate change. As was made clear in an earlier NRC study (NRC 1993), the twin objectives of environmental stewardship and scientific research are intimately connected through a feedback loop, with increasing knowledge allowing better regulation of research. This use of scientific results to formulate policy and regulation is at the heart of the present philosophy of Antarctic governance.
Recognition of the values that needed to be protected was clearly spelled out in the Antarctic Treaty protocol, which in turn had been derived from the many earlier resolutions agreed to by the Consultative Parties. There had been an early recognition of the importance of protecting examples of a wide range of habitats and of providing special protection to species thought to be under threat. At the habitat level, most of the Antarctic Specially Protected Areas have been established to protect the vegetation or the fauna. However, in at least two cases the importance of protecting the unique microbial communities of a site has been the basis of designation. In both of these cases the sites were associated with geothermal activity, and the regulations for access
take account of the need to avoid the inadvertent introduction of new microbes during a visit by requiring participants to wear “clean-room” clothing. The designation of the McMurdo Dry Valleys as an Antarctic Specially Managed Area (ASMA No. 2: http://www.cep.aq/apa/asma/sites/ASMA2.html) similarly recognized the importance of preserving microbial habitats and biota, and one of the stated objectives of its management plan is to minimize the introduction of alien species, including microbes.
Life in a subglacial lake under 4 km of ice is expected to be microbial. While it is not yet certain either how ancient the flora is or what connectivity may exist between lakes, it is clear that good stewardship not only would require extreme care in sampling such environments but also would require that examples of the major types of lakes, once established, should be afforded the same level of legal protection already provided for sites and habitats at the surface.
PURPOSE OF THIS REPORT
SCAR has to date led the effort to organize international planning for the exploration of subglacial aquatic environments and will continue to foster international coordination and collaboration. SCAR, however, has not done a critical analysis of stewardship issues. In particular, the issues of how to minimize contamination of subglacial lake environments during study and provide responsible stewardship of these unique and possibly connected environments would benefit from an external and objective review.
Potential contamination that might occur during the exploration and study of subglacial lake environments includes introductions of naturally occurring environmental microorganisms, anthropogenic microorganisms, and chemicals derived from exploration tools and equipment. There are two key issues: how to collect the best possible samples for scientific study while minimizing contamination of the sites and ensuring preservation for future scientific inquiry, and how to ensure wise stewardship of these unique environments, including strict observance of environmental protection responsibilities under domestic and international laws and treaties. These two issues are likely to have different requirements. Because research objectives include detecting the presence of life at very low concentrations, the collection of samples will require stringent protocols. In addition, public perception and general stewardship issues will be important for acquiring the resources and permissions needed to undertake these studies.
Before proceeding with further exploration of these unique subglacial lakes, clearer guidance is needed on how to conduct the work in an environmentally and scientifically responsible manner. To meet this need, the National Science Foundation (NSF) has requested guidance from the National Academies to address the environmental and scientific protection standards necessary to responsibly explore the subglacial lake environments found under continental-scale ice sheets. In response, the National Research Council of the National Academies created the Committee on the Principles of Environmental and Scientific Stewardship for the Exploration and Study of Subglacial Environments.
Specifically, the committee was asked to do the following:
Define levels of “cleanliness” for equipment or devices entering subglacial lake environments necessary to ensure that the environments are subject to minimal,
reversible, or acceptable change caused by the introduction of either naturally occurring Earth surface materials and life forms or anthropogenic substances.
Develop a sound scientific basis for contamination standards considering a number of steps. These steps include delineation of the most likely sources of contamination, description of methods that might be used to reduce these introductions (e.g., physical cleaning, sterilization, coating of surfaces with antifouling materials), and discussion of methodologies that might be used to demonstrate that the acceptable levels of “cleanliness” have been achieved. This analysis should recognize that different stages of exploration may be subject to differing levels of environmental concern and that some activities have been reviewed and approved for use elsewhere. The committee was asked to consider the protocols developed for planetary protection over the past 40 years by National Aeronautics and Space Administration (NASA) and assess their utility, applicability, transferability, and adaptability to subglacial lake environment exploration and research.
Recommend next steps needed to define an overall exploration strategy. The committee was asked to use existing planning documents and lessons learned from previous activities that have penetrated and potentially contaminated subglacial environments as a starting point, to consider:
The merits and disadvantages of existing technology with respect to contamination, highlighting additional technological development that is needed;
Procedures and additional scientific studies to ensure that the best available environmentally and scientifically sound practices are adhered to and contamination risks are reduced to acceptable levels during the entry and sampling of subglacial lake environments;
Costs and benefits in terms of scientific outcomes of exploring now versus later; and
Potential targets among the many Antarctic lakes.
The committee appreciates the presentations and supplementary materials provided by the scientific community and members of the SCAR SALE group. The NRC committee’s findings and recommendations are based on its analysis of the materials and briefings received and the committee’s expert judgment. Committee members were drawn from four countries and have expertise in environmental protection and stewardship, Antarctic Treaty policy, planetary protection, astrobiology, microbial ecology in extreme environments, genomics, glaciology, subglacial processes, geochemistry, polar contamination prevention, and drilling and sampling technologies.
This report addresses the environmental and scientific protection standards needed to responsibly explore the subglacial aquatic environments. The motivations for this study are to ensure wise stewardship of these unique environments, including strict observance of environmental protection responsibilities under domestic and international laws and treaties, and to determine how to collect the best possible samples for scientific study while minimizing site contamination and ensuring preservation for future scientific inquiry. The issue of environmental stewardship for the exploration of subglacial aquatic environments is important to many stakeholders and interested parties, including those from the international community. The committee sought to develop the scientific rationale for setting standards in a manner credible to this wide range of stakeholders and interested parties. The summary, introduction, and conclusion chapters address the issues in a general manner intended for a wide-ranging
In preparing this report, the committee recognized that the responsibility of all parties subject to the Antarctic Treaty is to maintain good environmental stewardship for all activities, while appreciating that some impacts are acceptable in pursuit of scientific understanding and that these should be mitigated as far as possible. The committee acknowledged that the scientific investigation of subglacial aquatic environments has previously been vetted internationally through the Antarctic Treaty Protocol and exploration has been accepted as a legitimate activity. The charge to the committee was concerned with how to undertake such an activity while maximizing the overall protection of this particular environmental resource. In managing any future activities it is assumed that parties will recognize, as did the committee that limiting the science to a few sites, maximizing the expertise, organizing a stepwise approach, and using the cleanest available technology will all maximize the scientific outputs and minimize the impacts. The committee hopes this rationale will provide important guidance for developing, testing, and verifying sensor deployment and sampling protocols to balance the value of the scientific information to be gained against the potential for alteration and/or contamination of the sites being studied.