(4) Lake Vostok: Background Information


Robin E. Bell
Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964,
p (914) 365-8827; f (914) 365-8179, robinb@ldeo.columbia.edu

The identification of Lake Vostok in 1996 by Russian and British scientists (Kapitsa et al., 1996) represented the culmination of decades of data acquisition with a broad range of techniques including ground based seismics, star observations, and airborne ice penetrating radar supplemented by spaceborne altimetric observations.


These measurements were the result of a long history of investment in Antarctic research by the international science community.


The initial discovery was subsequently complemented by results from the Russian-French-American Vostok ice coring program and the Russian Antarctic program. This review outlines the general characteristics of the Lake, beginning with a description of the overlying ice sheet, continuing to the lake itself and on into the sedimentary deposits (Figure 3).

The horizontal extent of the Lake is estimated from the flat surface (0.01 degrees) observed in the ERS-1 ice surface altimetry. The 4 km thick ice sheet floats as it crosses the lake, just as ice sheets become floating ice shelves at the grounding line. The flat ice surface associated with Lake Vostok extends 280 km in the north-south direction and 50-60 km in the east-west direction. Over the lake the ice surface slopes from 3550 m above sea level in the north to 3480 m above sea level in the south. The ice surface is ten times flatter over Lake Vostok than in the surrounding regions.


The regional ice flows in from an elevated feature known as Ridge B-C to the west down the slope to the east. The presence of water may significantly alter this flow (Robin, 1998). The flow rates across Lake Vostok have been estimated from star sights at Vostok Station in 1964 and 1972 (Kapitsa et al., 1996) and synthetic aperture radar (SAR) interferonmetric methods (Kwok et al., 1998).


The star sights at Vostok Station suggest primarily an easterly ice flow (142 degrees) at 3.7 m/yr . The SAR results indicate a significant component of flow (2.22 m/yr) along the lake axis (Kwok et al., 1998). As the overlying ice sheet is probably the major source of sediments, microbes and gas hydrates in the lake, understanding the trajectory of the ice across the lake will be critical to understanding the lake as a system.

The present understanding of the 3750-4100 m of ice sealing Lake Vostok comes from limited airborne ice penetrating radar data acquired by a joint U.S.-British program in the 1970’s, and from the deep ice core drilling at the Russian Vostok Station by an international team of scientists from 1989 - 1998. The radar data, collected as part of a reconnaissance survey of Antarctica, provides cross-sectional images of the bedrock surrounding the lake, the internal layering within the ice, and the base of the ice over the lake for six flight lines.


Across the lake the reflection from the base of the ice sheet is strong and very flat. In contrast, reflections from portions of the ice sheet over bedrock are characterized by rugged reflections of varying strength that are dominated by reflection hyperbolas. Radar data indicate that water within the northern half of the lake may be very shallow (~10-30 m) and that several bedrock islands protrude through the lake into the ice sheet.


The ice thickness is 4150 m in the north thinning to 3750 m in the south beneath Vostok Station.

The ice core at Vostok Station was drilled to recover a record of global climate changes over the past 400,000 years which is preserved in distinct ice layers. Near the bottom of the core, beginning at a core depth of 3311 m, the ice first shows signs of disruption of the layering by ice dynamics. Generally ice layers become tilted and geochemical climatic signals become difficult to interpret (Petit et al., 1998, Duval et al., 1998).


This layer between 3311 m and 3538 m has been interpreted as ice which was part of the continuous ice column but has been disrupted by deformation processes as the ice sheet moves over the underlying bedrock. The randomly distributed moraine particles in the base of this section are interpreted as an active shear layer. Below this layer, changes in ice character are significant with a dramatic increase in crystal size (to 10-100 cm), a decrease by two orders of magnitude in the electric conductivity, the stable isotopic content of the ice and the gas content.


These physical and chemical changes continue through the base of the Vostok ice core at 3623 m and is interpreted to represent ice accreted to the base of the ice sheet as it passed over Lake Vostok. The upper 70 m of this large crystal ice includes numerous mud inclusions approximately 1 mm in diameter. These 70 m of “muddy” ice are interpreted to be ice accreted during a repeated melting and freezing cycle along the lake’s margin.


Below the 70 m of ice containing mud (i.e. below 3608 m) the ice is very clear and is believed to have been formed as accreted ice as the ice sheet floated over Lake Vostok. In this interpretation, the base of the ice sheet consists of a layer of 227 m of disrupted ice, 70 m of ice with mud inclusions and approximately 150 m of clear accreted ice.


A freezing rate of several mm per year is required to generate these layers of accreted ice.


Figure 3:

Cartoon of Lake Vostok indicating the ice flow over the Lake near Vostok Station.

The melting and accreting processes are indicated at the base of the ice sheet.

Arrows also indicate the potential circulation within the lake.

The accretion ice is the light blue layered material at the base of the ice sheet.

The sediments (orange lined pattern) and hypothesized gas hydrates (pebble pattern) on the lake floor are shown.



The Russian seismic experiments, led by Kapitsa in the 1960’s and by Popkov in the 1990’s (Popkov et al., 1998), provided insights into the depth of the lake at the southern end of the Lake and the presence of sediments. Interpretation of Kapitsa’s 1960’s data is that 500 m of water exist between the base of the ice sheet and the underlying rock (Figure 3).


These seismic experiments show the base of the lake is 710 m below sea level.


This level is close to the estimated level of 600 m below sea level for the northern portion of the lake. Recent seismic experiments have confirmed the early measurement of ~500 m of water beneath Vostok Station and deeper water (670 m) several kilometers to the north.


These new experiments also identified 90-300 m sediment layers close to Vostok Station. Sediments were absent 15 km to the southwest. Leichenkov used very limited gravity data to infer as much as 4-5 km of sediments in the central portion of the lake (Leichenkov et al., 1998).


Russian scientists (Kapitsa et al., 1996) have suggested that Lake Vostok results from extensional tectonics, inferring that the Lake has an origin similar to Lakes Malawi (Africa) and Baikal (Russia) (Figure 4).


Figure 4:

Satellite images of several large lakes shown at the same scale.

(a) An ERS-1 image of Lake Vostok (R. Kwok, JPL).

Lake Vostok shows as the flat featureless region. In this image north is to the right,

and Vostok Station is on the left of the image.

Both (b) and (c) are AVHRR false color composite images.

Red indicates regions of high thermal emittance, either bare soil or urban areas.

Green represents vegetation, Blue primarily indicates clouds and black is water.

(b) An AVHRR image of Lake Ontario, a glacially scoured lake in North America.

Toronto is the red area at the western end of the lake (left side of image).

An AVHRR image of Lake Malawi, an active rift lake from the East African Rift system.

North is to the right in this image.


This interpretation is based on the long narrow nature of the lake and the bounding topography in some profiles. If the extensional origin is correct, the lake may have thick sequences of sediment, elevated heat flow, and hot springs.

Conceptual models of circulation within the lake have been advanced by Zotikov (1998) and Salamatin (1998). These models are based on the density differentials associated with variable ice thickness across the lake. The poor understanding of the size of the lake, the distribution of the melting and freezing regions and the geothermal flux, limits the applicability of these models.

Finally, in terms of understanding microbes within the lake, the overlying Vostok ice core contains a diverse range of microbes including algae, diatoms, bacteria, fungi, yeasts and actiomycetes (Ellis-Evans and Wynn-Williams, 1996). These organisms have been demonstrated to be viable to depths as deep as 2400 m (Abyzov, 1993).

In summary, these data provide us with a general sense of the horizontal scale of the lake and hints of the nature of the Lake’s structure and origin, but many questions remain unanswered.  



Martin J. Siegert
Bristol Glaciology Centre, School of Geographical Sciences,
University of Bristol, Bristol BS8 1SS, UK,
p. 44-117-928-7875; f. 44-117-928-7878, m.j.siegert@bristol.ac.uk

The location and extent of Lake Vostok have been determined from ERS-1 altimetry and radar sounding (Kapitsa et al., 1996).


The ice thickness over the lake is 3740 m at Vostok Station and 4150 m at the northern extreme of the lake. The ice-sheet surface elevation decreases by ~40 m from north to south, whilst the base of the ice sheet increases by ~400 m. The water depth is about 500 m at Vostok Station (from seismic information) and a few tens of meters at the northern end (from VHF radio-wave penetration through water).

The basal ice-sheet conditions that prevail over the lake have not been previously identified. However, this information is required in order to establish the environment within the lake and, from this, the likelihood of life in the water.


A new interpretation of internal ice-sheet layering from existing airborne 60 and 300 MHz radar indicates that as ice flows across the subglacial lake, distinct melting and freezing zones occur at the ice-water interface. These events suggest a major transfer of water between the ice sheet and lake, inducing circulation in the lake and the deposition of gaseous hydrates and sediments into the lake.

The position of one airborne radar line (Fig. 5) is approximately parallel to the direction of ice flow as derived from InSAR interferometry and steady-state ice flow considerations (Siegert and Ridley, 1998). Three individual radar layers, extracted from the raw 60 MHz radar data, were continuously traced across the lake.


The change in ice thickness between the top two internal layers, and the change in ice thickness between the lowest layer and the ice-sheet base, were then calculated (Fig. 6).


Figure 5:

The position of one airborne radar line is approximately parallel

to the direction of ice flow as derived from InSAR interferometry and steady-state ice flow considerations.



Generally, over grounded sections of ice sheets, internal layers are observed to converge and diverge in vertical sections as ice gets thinner and thicker, respectively.


In contrast, if the grounded ice-sheet base is flat, the internal layers tend to be flat in response. Along a W-E transect across the middle of Lake Vostok, the ice thickness is relatively constant and the ice-sheet base is very flat (Fig. 6).


However, along this line, internal radar layers from 60 Mhz radar are (1) approximately parallel to each other and (2) non-parallel to the ice base (Fig. 6). Any loss or gain in thickness between the ice base and the lowest internal layer along the flow-parallel transect probably reflects accumulation or ablation of ice at the ice-water interface. In contrast, 300 MHz radar indicates that compression of layering occurs in the top layers of the ice sheet, where ice density changes cause internal reflections.

Other possible explanations for the pattern of internal radar layering observed in the transect can be discounted. For example, decoupling within the ice sheet (so that ice flow above the internal layers is different from that below) is unlikely because of negligible basal shear stress between ice and water.


Further, convergent and divergent flow around the bedrock island (Fig. 6) is not observed in the ice-surface velocity field derived from InSAR interferometry.


Figure 6:

Calculation of the change in ice thickness between the top two internal layers,

and the change in ice thickness between the lowest layer and the ice-sheet base.


Divergent flow around the island in lower ice layers would only cause ice thickening in adjacent regions.


However, thickening of the ice sheet on either side of the island is not observed in radar data. Furthermore, the internal layers do not reflect ice flow around bedrock upstream of the lake because radar data show that such ice structure involves deeper internal layers diverging with increasing ice depth, whereas the layering in our transect maintains a steady separation of internal layers across the lake.

Assuming that ice does not accelerate across the lake (e.g. Mayer and Siegert, submitted), the ice velocity will be steady at around 2 m yr-1 across the transect from west to east (left to right in Fig. 6).


The processed 60 MHz radar data can then be used to determine rates of change of ice thickness between the lowest layer and the subglacial interface. Assuming that there is neither lateral flow nor compression of ice in the lower layers, these rates of change of ice thickness may be related directly to rates of subglacial melting or freezing (Fig.6).

Using this method, melting of up to 15 cm yr-1 occurs across the first ten kilometers of the ice-water interface (Fig. 6d).

This zone is followed by a thirty kilometer-long region of net freezing with an accumulation rate of up to 8 cm yr-1 (Fig. 6d). These data, therefore, indicate significant release of water from the ice sheet to the lake over the first 10 km of the transect, which is followed by net refreezing of lake water to the ice base.
Using these estimates approximately 400 m of basal ice will be accreted to the base of the ice sheet as it traverses the central portion of Lake Vostok. This compares to the 200 m of refrozen ice observed 100 km to the south at Vostok Station in the narrow portion of the lake (Fig. 5).


The melting of the ice sheet as it first encounters the lake provides a supply of water, gas hydrates, biological debris and sediments to the lake. The sediments and gas hydrates will be deposited at the base of the lake, while the water will be refrozen in the base of the ice sheet in the accretion zone. The refrozen or accreted ice appears to be derived from freshwater (J. R. Petit, pers. comm.).

This investigation indicates how basal ice-sheet conditions may be identified from analysis of airborne radar data. However, the present radar dataset is too sparse to provide a detailed analysis of ice-sheet basal melting and freezing for the entire 14000 km2 area of the lake.


New radar data are therefore required to extend this investigation over the full extent of Lake Vostok. Analysis of new surveys will quantify the total volume of water involved in the exchange between the ice sheet and the lake, and allow calculation of the input of non-ice material to the lake.


This volume estimate will supplement the glaciological parameters that radar measurements will provide.




J. R. Petit
LGGE-CNRS, BP 96, 38402 St. Martin d’Hčres Cedex, France,
p. +33 (0)4 76 82 42 44, fax +33 (0)4 76 82 42 01, petit@glaciog.ujf-grenoble.fr


As part of the long term Russian-American-French collaboration on Vostok ice cores, started in 1989, the drilling of hole number 5G was completed during the 97-98 field season. Ice coring reached 3623 m depth, the deepest ice core ever obtained.


The drilling operations stopped 120 m from the ice/water interface to prevent contamination of the underlying lake by kerosene based drilling fluid.

The ice core continuously sampled for paleoclimate studies and discontinuous sections have been sent to selected laboratories in three countries. Below 3350 m depth, one half of the main core was cut as a continuous archive for future studies, and stored at -55°C in an ice cave at Vostok station.


The very good quality and transparency of the retrieved deep ice allowed for continuous visual inspection of the ice inclusions, studies of ice crystals, and measurements of electrical conductivity. Preliminary isotopic measurements of the ice, (deuterium, dD), and analyses of the gas and dust content have be performed on selected deep ice samples.

The upper 3000 m of the ice core (88% of the total ice thickness) provides a continuous paleoclimatic record of the last 400,000 years. The preservation of this paleoclimatic record is due to the slow velocities of the glacier ice and the low accumulation rates at Vostok Station (presently 2 cm water equivalent per year).


Preliminary studies of the ice have yielded information on;

a) the local temperature and precipitation rates (from isotopic composition studies)

b) aerosol fluxes of marine volcanic, and terrestrial origin (from chemical, ECM and dust content analyses)

c) atmospheric trace gases (in particular the greenhouse gas content [CO2 and CH4] and the isotopic composition of this “fossil” air)

d) the physical properties of the ice, including air hydrates, ice crystals

The preliminary results of these studies indicate that the main patterns of the Vostok temperature are well correlated to global ice volume from deep sea sediments, back to the marine stage 11 (circa 400,000 BP) (Petit et al., 1999).


The record shows four complete climatic cycles, including four ice age or glacial periods associated with the development of large ice sheets over the Northern Hemisphere, and four transitional warmer interglacial periods (Petit et al., 1998).

Between depths of 3300 m and 3538 m, the layering is disturbed by ice sheet dynamics. For example, at 3311 m depth, three volcanic ash layers 10 cm apart are tilted in opposite directions. Moreover, 10 m deeper, at 3321 m, stable isotope content, gas composition and dust concentrations of the ice, display very sharp and significant variations which cannot be of climatic origin.


In these deep layers, the geochemical parameters interpreted as climatic proxies can no longer be interpreted as the glacial-interglacial cycles.


The observed values are intermediate between glacial and interglacial levels, suggesting the layers have been mixed. At the base of this ice there is evidence of disruption due to ice sheet dynamics (3460 - 3538 m). The ice contains randomly distributed moraine particles with particle sizes up to a few millimeters in diameter, indicative of an active shear layer.

Beneath these disturbed and apparently mixed layers, (below 3538 m) the ice character changes dramatically: ice crystals are very large (10-100 cm), electrical conductivity drops by two orders of magnitude, stable isotope content of ice shifts, and gas content becomes two orders of magnitude lower. These drastic and related changes, indicate that the basal ice at this location is re-frozen lake water. The accreted ice at the base of the Vostok core is about 220 m thick, or 6% of the total ice thickness.

The ice from the Vostok basin originates from the Ridge B area and flows over the lake in a manner similar to an ice shelf. Temperature in the ice sheet and melting or freezing events at the base are linked to ice sheet dynamics and lake and bedrock heat fluxes.


Whilst Lake Vostok exhibits evidence of large scale melting, the flow line passing through Vostok site indicates a significant refreezing event. This provides a constraint that must be taken into account when modeling the ice paths and dating the climatic record.

Sampling the lake and underlying sediments is necessary, but will require the development of “clean” sampling techniques.


A continuation of geophysical measurements in the existing bore hole, and complementary studies of deep ice from Vostok, may provide important insights into the ice sheet, regional geology and the lake.




Ian Dalziel
Institute for Geophysics, University of Texas, Austin, 4412 Spicewood Springs Rd., Bldg. 600, Austin TX 78759-8500,
p (512) 471.0431, f (512) 471-8844, ian@ig.utexas.edu

Lake Vostok is located at 77°S, 105°E within the East Antarctic Precambrian craton, remote (>500 km) from both the Neoproterozoic rifted Transantarctic margin and the Mesozoic rifted margin south of Australia and India. Its specific geologic setting is completely unknown.

It has been suggested on the basis of limited geophysical data that the Lake occupies a structural depression such as a rift (Kapitsa et al., 1996).


Assuming this to be correct, several plausible scenarios can be developed that would explain the tectonic setting of such a depression in central East Antarctica:

Intracratonic Rift associated with Extensional Processes:

Given the presence of the extensive Lambert-Amery aulacogen along the Indian Ocean margin of the craton at 69°45’S, 71°00’E, Lake Vostok could occupy an intracratonic rift valley comparable to the lakes of the East African rift.


An aulacogen is a rift system penetrating a craton from its margin. This could be either an active rift system, as suggested by Leitchenkov et al. (1998) or an ancient and tectonically inactive rift.

Despite the presence of a young volcanic edifice at Gaussberg, also on the Indian Ocean margin at 66°48’S, 89°11’E, there is nothing to directly indicate present tectonic activity in the Lake Vostok area. Gaussberg is >1000 km distant and located at the termination of the Kerguelen oceanic plateau.


The Antarctic continent is anomalously aseismic, and only proximity to the Gamburtsev Subglacial Mountains with their unusual 4 km of relief at 80°30’S, 76°00’E might be taken to indicate any local tectonic or magmatic activity. These mountains, which do not crop out, could be like the Cenozoic Tibetsi or Hoggar volcanic massifs of North Africa.


Again, however, there is no direct evidence of recent, let alone active, volcanism or tectonism in central East Antarctica.


Evidence from sedimentary strata within the Lambert-Amery system suggests that this aulacogen is of Paleozoic age, and may be the southern limb of a rift in India that predates Mesozoic opening of the Indian Ocean basin (Veevers et al., 1994).

Rift Resulting From a Continental Collision: A depression containing Lake Vostok and the Gamburtzev Subglacial Mountains could be in a setting similar to Lake Baikal and the Tien Shan Mountains or Mongolian Plateau, i.e. a rift and intracratonic uplift associated with transmission of compressive stress thousands of kilometers into a continental interior as a result of collision with another continent.


Unlike Lake Baikal, however, Lake Vostok is not situated within a craton that has undergone Cenozoic collision like that of Asia with India. Veevers (1994) has suggested that the Gamburtzevs may have resulted from far-field compressive stresses associated with the amalgamation of Pangea at the end of Paleozic times along the Ouachita-Alleghanian-Hercynian-Uralian suture.


Alternatively, uplift and rifting within the East Antarctic craton could have been generated in the latest Precambrian “Pan African” continent-continent collision of East and West Gondwanaland along the East African orogen (Dalziel, 1997).


The early Paleozoic Ross orogen along the Transantarctic Mountain margin was a subduction related event which is not likely to have transmitted compressive stress far into the cratonic interior. Consideration of subduction-generated Andean uplifts, however well to the east of the present Pacific margin of South America, demands that this possibility also be kept open.

Hot Spot or Mantle Plume Driven Depression: Plate tectonic reconstructions maintaining the present day positions of the Atlantic and Indian ocean basin “hot spots” such as Tristan da Cunha and Reunion islands, indicate that several of these (notably Crozet-Heard and Kerguelen) could have been beneath East Antarctica prior to the opening of the Southern Ocean basins.


The Gamburtzev Subglacial Mountains and an associated Lake Vostok depression could owe their origin to such activity.

Glacial Scour possibly Eroding an Older Feature: An erosional origin for the Lake Vostok depression, i.e. a Lake Ontario-type scenario, is possible, but could also have its origin in tectonism. For example, several of the Great Lakes occupy depressions formed during the development of the North American mid-continent rift system at 1100 Ma that was excavated by the Laurentide ice sheet during Cenozoic glaciation of that continent.

Meteor Impact: Circular depressions in the interior of cratons can form as a result of meteor impact. Even the elongate depression indicated by the shape of Lake Vostok could result from a bolide impact scar modified by subsequent tectonism, as in the case of the elliptical Sudbury basin in Ontario, Canada.

Hence the age of the depression that Lake Vostok appears to occupy could have resulted from a variety of tectonic causes, and could range in age from Precambrian to Recent. At present, there is no evidence to indicate that the setting is tectonically or magmatically active.


Several lines of investigation should be undertaken to clarify the tectonic setting, and hence the likely history and possible present activity of the feature:

1. Airborne geophysical survey of the region surrounding the lake
2. Seismic refraction profiling to ascertain the deep crustal structure beneath the lake
3. Seismic reflection profiling to determine the shallower structural setting, nature of the sedimentary fill, and relation to overlying present ice sheet and its base 3 Comparable geophysical studies of the Gamburtzev Subglacial Mountains

4. Sampling of the Gamburtzev Subglacial Mountains by drilling - evidence of a young volcanic construct locally would dramatically change the geologic picture.




James M. Tiedje
Center for Microbial Ecology, Michigan State University, 540 Plant and Soil Science Building, East Lansing, MI 48824-1325,
p (517)-353-9021, f (517)-353-2917, tiedjej@pilot.msu.edu

Microorganisms have been on Earth at least 3.7 billion years and during this evolutionary history have developed incredible biochemical, physiological and morphological diversity.


Members of the microbial world encompass the three domains of life, the Bacteria, the Archaea, and the lower Eukarya.


This diversity encompasses organisms with novel redox couples for production of energy; adaptations to extremes of temperature, salt, and pH; novel energy acquisition mechanisms as well as strategies for withstanding starvation. About 4,200 prokaryotic species have been described out of an estimated 105 to 106 prokaryotic species on Earth. Many of the extant microorganisms have not been cultured in the laboratory and hence remain unknown because we apparently cannot reproduce their environment in the laboratory.

Conditions in Lake Vostok are not so severe as to make microbial life impossible. Hence, at least some forms of microorganisms should exist in Lake Vostok water and sediment.


The founding populations (original inoculum) could come either from the rock or sediment prior to ice cover, or from microbes trapped in the ice that are slowly transported through the ice to the water. In either case, Lake Vostok microbes would have been isolated from their global relatives for at least 1 million years.


Some changes in genotype and even phenotype could have occurred during this time, presumably making the organisms more adapted to this cold, dark, oligotrophic environment. The time scale of 1 million years, however, is not long in terms of prokaryotic evolution when compared to their 3.7 x 109 year history. As points of reference, the E. coli-Salmonella enterica genospecies, which are closely related organisms but differentiated because of their health importance, are considered to have diverged only in the last 100 million years (Lawrence and Ochman, 1998).


Hence, species level differentiation may take at least 10-100 million years. Secondly, changes due to mutation (silent mutants) occur at the rate of approximately 5 x 10-10 per base pair (bp) per replication (Drake et al., 1998). Assuming an average gene size of 103 bp and 10 generations per year, one would expect on average a change in only one base pair per gene in the 1 million years since Lake Vostok microbes have been isolated from their relatives.


Other mechanisms of genetic change, especially recombination and mutator genes, could have altered organism phenotype more rapidly allowing for adaptation to Lake Vostok conditions.


The above discussion is based on the conservative estimate of biological isolation by the ice cover of 1 million years. If the original inoculum were derived from rocks or sediments that had been sealed from surface microbial contamination pre-Lake Vostok, their age of isolation would have been longer, probably 35-40 million years. It should be noted that this form of isolation is not unique to Lake Vostok rocks.

The major biological questions to be addressed in Lake Vostok would appear to be the following:

  1. Who (what taxonomic groups) lives there?

  2. How different are the Lake Vostok organisms from what we already know?

  3. Who are the Lake Vostok organisms related to and from what habitats do these related organisms arise?

  4. Which of the Lake Vostok organisms are metabolically active?

  5. How do these organisms live in this unique environment?

  6. Where do they get their energy (geothermal?, clathrates [gas hydrates]?, other?), and do Lake Vostok natives have special adaptive strategies for this environment?

Microbial exploration of a new ecosystem such as Lake Vostok should include three complementary approaches since each gives unique and vital information: nucleic acid-based methods, microscopy, and the isolation-cultivation approach.


The nucleic acid-based methods provide much more comprehensive information on the community than culture-based methods and, through sequencing of small subunit ribosomal RNA genes (SSU rRNA), provide information on the organism’s identity.


rRNA-based methods such as sequencing of clone libraries, fluorescent terminal restriction fragment length polymorphism (T-RFLP) analysis, denaturing gradient gel electrophoresis/temperature gradient gel electrophoresis (DGGE/TGGE), fluorescent in situ hybridization (FISH), and quantitative hybridization by phylogenetic group probes, are well proven methods for exploring the microbial community of new habitats such as Lake Vostok.


Other phylogenetically important genes such as 23S rRNA, intergeneric spacer regions and gyrB may also be useful. Once pure culture isolates are obtained, reverse sample genome probing (RSGP) can be used to quantify the importance of isolated organisms in the total community.

Microscopy remains a powerful exploratory approach because it is the best method for comprehensive observation and quantification of the microbial community.


New forms of microscopy such as confocal laser scanning and environmental scanning electron microscopy, as well as coupling microscopy with the use of fluorescent probes of various types can reveal key information both on organism’s identity as well as on their activity.

Isolation and cultivation of pure cultures remains the primary means to fully characterize a microorganism, including its metabolic capacity, unique physiology, confirming its taxonomy and for studies at the molecular level. An example of the latter could be to identify genes responsible for adaptation to cold, genes potentially useful to making plants more winter hardy.


Strategies that might be useful for cultivating Lake Vostok organisms would be to minimize the shock of warming, matching the ion composition of the medium to the lake water, maintaining oligotrophic nutritional conditions yet stimulating growth, and planning for a long incubation period.

Special challenges for the study of Lake Vostok microbes would likely include the following. Very low densities of microbes, which is probably the case in Lake Vostok, always requires special methodologies to concentrate cells. Furthermore, risk from contamination from outside microbes is more problematic.


Determination of the metabolically active cells versus resting or dead forms, is especially difficult at low temperatures because of the low metabolic rate. Isolation and cultivation of oligotrophic microbes is always difficult. The more interesting microbes are likely to be the ones most difficult to cultivate and isolate. It may be difficult to determine whether what is found is really new and unique since so many of the world’s microbes remain unknown. To answer this question one may have to seek “Lake Vostok-like” relatives outside of Lake Vostok once the former are characterized.

Abyzov and colleagues have studied microbes in the Vostok ice core by microscopy and cultivation (Abyzov et al., 1998).


They find low densities (103 cells/ml) of microbes in the ice core extending to ages of 240,000 years, the oldest period on which they have reported. Microbial density fluctuated with ice core age, being higher when the dust particle density is high, which also corresponds to periods of greater atmospheric turbulence.


Bacteria were the most prevalent microbial cells, but yeast, fungi, microalgae, including diatoms, were also seen. Thawed ice samples assimilated 14C-amino acids establishing that some of the cells were alive.

Most of the organisms that were isolated from the ice core are spore-formers, e.g. Bacillus. Attempts to isolate more oligotrophic types apparently have not been made. Organisms from the ice core could be one source of inoculum to Vostok Lake.
Studies on the microorganisms of Antarctica and buried Arctic permafrost soils have relevance to Lake Vostok questions. Culturable strains from 1 million year old buried arctic permafrost soil belong to the Planococcus, Psychrobacterium, Arthrobacter, and Exigobacterium groups. It is interesting that the closest relatives of some of these strains are found in Antarctica.


Some of the ancient arctic isolates grow relatively rapidly at -4.5°C. Hence, growth rate at the Vostok temperature of -3.2°C would not appear to be a limitation. The major limitation to microbial density in Lake Vostok would be a renewable supply of energy.


If clathrates (gas hydrates) were present, the potential microbial use of this energy source would be particularly intriguing.




Frank Carsey
California Institute of Technology Jet Propulsion Laboratory
JPL ms 300-323, 4800 Oak Grove Dr., Pasadena CA 91109,
p (818) 354-8163, f (818) 393-6720, Frank.D.Carsey@jpl.nasa.gov

About the time that the true scale of Lake Vostok was generating excitement in the Earth Science community, spacecraft images and other data of the Galilean satellites of Jupiter similarly electrified the Planetary Science community, and for a similar reason:

in both cases strong evidence was suddenly provided for large, previously unknown bodies of water which might well be home to unique life forms.

As of this writing, large, old, subsurface oceans are suspected on both Europa and Callisto, and water ice is known or speculated to occur in a great number of other sites, including Earth’s moon.


Meanwhile, the microbiologists are revolutionizing the picture of biodiversity of life on Earth and repeatedly astounding the scientific community and the public with information on microbes thriving in sites long considered untenable for life.


These developments are obviously interrelated; it is clear that explorations of Lake Vostok and Europa/ Callisto have much in common, including the scientific excitement of exploring a new place.

The chief similarity is in the primary scientific goals at Lake Vostok and the Jovian satellite oceans, the search for life. In the Jovian system, this search must be carried out robotically, and the robotic approach has much to offer in various sites on Earth where such issues as contamination prevention and remoteness make sample removal challenging.


Lake Vostok, in particular, is a site in which low temperatures, high pressures, low salinity, isolation, and great age indicate an oligotrophic environment.


This suggests that life could occur in highly specialized microbial communities with low populations.


This situation may not be representative of Europa or Callisto, as these sites may be prebiotic. However, the exercise of locating and examining life in small numbers is clearly excellent preparation for sites which may have no life forms at all. The scientist will be testing a system trying to establish a negative, which is demanding. Similarly, at both Earth and planetary sites, the issue of evaluating habitat and bioenergy sources will be crucial.

In addition to the physical and scientific similarities, the technologies required for accessing and studying the liquid water domains at Lake Vostok and Europa/Callisto have numerous elements in common, many of them quite challenging.


Both sites require vehicles that can move through great distances of ice, 4 to 10 km vertically; both sites require communication of data through the ice and water; both sites require sophisticated instrumentation to locate and describe life and evaluate habitats; and both sites call for exploration with little basic data on site characterization as they are unknown places.


In addition, it is worth noting that when a NASA mission goes to a planetary site it can take only the smallest quantity of equipment, yet it must do a sophisticated job. These kinds of capabilities could greatly benefit Earth-bound science, especially in polar regions, as the investment in on-site support could be dramatically reduced, and more of the agency resources could go into science.


Additional sites exist on Earth with key similarities to both the deep ice sheet and the oceans of Europa/Callisto, e.g., the deep ocean. Timely and interesting projects that promise multi-use developments for all three sites include observations of clathrates, high pressure habitat characteristics, and microbiological studies.

There is clear benefit in collaborative efforts of U.S. and foreign agencies concerned with cold-region science and operations, aqueous instrumentation and robotics, high pressure/low temperature processes in water and sediment, and extremophile biology. There are programmatic vehicles in place to initiate and coordinate these collaborations, NSF, NASA, the Polar Research Board and the Scientific Committee for Antarctic Research.


Communications with and among these agencies should be encouraged.




David C. White
University of Tennessee, ORNL, JPL, 10515 Research Dr., Suite 300Knoxville TN 37932-2575,
p (423) 974-8001, f (423)974-8027, Milipids@aol.com

Lake Vostok as a pristine, cold, dark, high-pressure, and large lake provides a new extreme environment in which to search for indigenous microorganisms that have been isolated from the rest of the biosphere for a long time.


Thus it is of paramount importance to prevent contamination of the lake by organisms from the overlying ice or contaminants introduced by the sampling device during the assessment process.


The parallels to the detection of life on the Jovian moon Europa with a thick ice layer provide an excellent venue for monitoring the Planetary Protection technologies’ life detection through a thick ice cover. The technologies discussed below were derived for use within the space program, but are applicable to the Lake Vostok exploration project.

The cleaning, sterilization, and validation technologies for extraterrestrial life detection require extraordinary “instrument” protection.


Since the life forms that might be encountered may not conform to the rules of life as currently understood, the JPL Astrobiology team under Ken Nealson has defined the criteria for life as having some essential characteristics that form the basis for life detection:

1. Life detection technology will require mapping those localized areas of heterogeneities in the distribution of biomarkers between the putative life forms and the background matrices. These localized areas of putative life forms must also show concentrations of biomarkers and state conditions far from chemical equilibrium in the components of cells, macromolecules, smaller molecules, and/or elements. The system requires mapping in space and time to demonstrate localization of these heterogeneities and their metabolic activities.


2. The system must have an exploitable energy source and this source for extraterrestrial life may be non-traditional. Non-traditional energy sources could be tidal, radiation, heat, wind, or magnetic, not typical of the visible solar or chemosynthetic redox driven energy systems currently understood.

3. Whatever the system, the basic chemistry must be thermodynamically feasible.

These broad constraints indicate that these missions will require much more comprehensive “instrument” cleaning than the Viking standard of 300 viable spores/m2.


This was considered adequate twenty years ago when the entire spacecraft was held at 112° C for a long period so that no cells known on Earth were known to survive the treatment. This was prior to the discovery of the hyperthermophilic Archaea from the deep oceanic hydrothermal vents.

The sterilization technologies currently under examination at JPL utilize hydrogen peroxide under pressure (oxidative sterilization) and low temperature non-oxidative use of supercritical fluid or other solvents that result in cell lysis, leaving no organic residues. The hydrogen peroxide yields water and oxygen.


Not only must the critical areas of the spacecraft be sterile they must be cleaned of biomarkers that could interfere with the detection of life. Life detection will be based in part on detection spatial heterogeneities in concentrations of biomarkers.

The JPL efforts in “instrument” cleaning are currently exploring in situ destruction techniques utilizing ultra-violet with photodynamic activation and deep ultra-violet delivered in a vacuum.


This is used in combination with various types and recovery techniques more effective than the previously employed cotton swab with 70% aqueous alcohol at room temperature and pressure. Whatever the technology utilized for cleaning, the residue left on the “instrument” after cleaning must be analyzed quantitatively, structurally identified, and mapped.


Validation of the cleaning will require detection of biomarkers in cells, macromolecules, and small molecules. Cells will be detected and mapped microscopically and live/dead determinations made. These are currently compared to traditional viable culture methods that are required for flight. Nucleic acid macromolecules will be determined by polymerase chain reaction (PCR) of various nucleic acid polymers and enzymes that detect their activity.


Small molecule detection will exploit diagnostic lipids. Lipids can quantitatively indicate viable biomass by differentiating the polar phospholipids, which are lysed by endogenous phospholipases during cell stress forming diglycerides.


The nutritional/physiological status, as well as the community composition, can be determined by analysis of specific lipid components, which with HPLC/electrospray ionization/tandem mass spectrometry can be detected at the subfemtomolar levels (approaching detection limits of a single bacterial cell).


Spores can be detected in this system by their dipicolinic acid content. Lipid analysis has the potential for automation and speed by the application of enhanced solvent extraction at high pressure saved temperatures. Components like amino acids, carbohydrates, nucleotides can be detected at subfemtomolar concentrations by capillary electrophoresis which has great potential for miniaturization.


There is a possibility of using tracer biomolecules labeled with several isotopes at unusual concentrations that can be clearly identified. These techniques would provide a direct estimate of the degree of contamination after the cleaning procedures have been completed.

The JPL program currently utilizes modifications of extant analytical detection methods and equipment to analyze “coupons” exposed on the “instrument”. (Coupons or “witness plates” are recoverable surfaces on or around the spacecraft that are exposed and then removed for analysis; they can also be used to test various cleaning methods by putting a known contaminant mixture on them and then analyzing the biomarkers after treatment.)


Alternative recovery methods of solvent or adhesive polymers like the Scotch tape 5414 used in forensic investigations are being explored. A proposed second level of analysis would involve direct detection from the “instrument” using soft X-rays, Raman, infrared, or fluorescent detectors that could be mapped on a virtual “instrument” and successively cleaned.


The next level would be on-line reporting of in situ biosensors built into the “instrument”. These would be developed into the in situ life detection systems that monitor the extraterrestrial site and validate planetary protection.

Significant research remains to be done and adequate methods need to be in place by 2000 if the new methods are to be used during sample return missions.


International collaboration with industries, academia and the government will be required to fulfill the responsibility to protect Lake Vostok from contamination.

Roger G. Kern
Technical Group Lead/Planetary Protection Technologies
Mail Stop: 89-2, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109
p (818) 354-2233, f (818) 393-4176, Roger.G.Kern@jpl.nasa.gov

The Jet Propulsion Laboratory’s Planetary Protection Technologies Group is currently assessing the feasibility of entering Lake Vostok without introducing new types of microorganisms into the lake.


Since the inception of robotic missions to the Mars surface, Viking Landers 1 and 2 in the mid 1970’s, JPL has had an interest in this specialized type of microbial contamination control.


The objective of the Vostok microbial contamination protection research is to prevent contamination of Lake Vostok with viable microbes from the Earth’s surface while enabling the robotic exploration of the lake.

The Vostok contamination control challenge is composed of three parts:

1) delivery of a clean and sterile probe to the ice surface 4 km above the lake

2) preventing contamination of the probe as it is lowered down a warm water drilled bore hole to within a few hundred meters of the lake surface

3) performing a sterilization event upon entering the ice at the base of the bore hole to enable the melter probe to proceed without introducing viable surface microorganisms into the lake

Microorganisms present in the ice immediately above the lake are constantly raining into the lake as the ice melts, at an estimated rate of 1 to 2 mm per year, and are therefore not considered contamination in this approach.


An environmentally benign chemical sterilization is being tested that could take place at the base of the bore hole and would permit entry into the ice above the lake without entraining viable microbes from the surface.

JPL is currently adapting methods under development by the Mars Exploration Technology Program for application to aqueous environments such as Lake Vostok and the suspected Europan ocean. For future exploration of the surface of Mars, JPL is currently evaluating basic decontamination approaches for the efficacy against microbial cells and molecular cell remnants; proteins, nucleic acids, lipids, and carbohydrates.


These initial studies have focused on hardware surface cleaning to remove materials of biological origin from all surfaces both inside and outside the probe. Cleaning techniques being evaluated at JPL include: hydrogen peroxide plasma sterilization; 70% sterile ethanol wash; and existing precision cleaning methods.


Sterilization techniques being evaluated at JPL include: hydrogen peroxide plasma; gamma irradiation; and a dry heat procedure developed for the Viking mission to Mars.

At present four methods for characterizing biological contamination are being evaluated for use in verifying the level of cleanliness of hardware. The first of these is a viable count assessment based on the ability to remove and culture a single viable organism on tryptic soy agar.


The second method does not require microbial growth since it is widely recognized that less than 1% of the total microbial world is currently culturable. Epifluorescent microscopy is being adapted for validating microbial cleanliness. Microbes sampled are transferred to a 0.2 micron filter where cells are suitably stained to enumerate the total population as well as confirm the absence of viability. This allows the assessment of the microbial population independent of ability to culture in the laboratory.


PCR techniques are being employed to detect the presence of trace amounts of DNA associated with the sampled surfaces. Recently capillary electrophoresis has been added to JPL’s list of approaches for determining the presence or absence of trace biological molecules associated with hardware. This research into cleaning and sterilization methods, as well as techniques to validate cleanliness is ongoing, and new approaches are constantly being evaluated to achieve and assure a level of cleanliness and the absence of viable microbes.
These ongoing planetary protection efforts can be applied to the NASA Vostok Probe (consisting of a cryobot and hydrobot) and instrumentation, and the overall mission design.


The current planetary protection technologies research effort will influence the selection of materials compatible with cleaning and sterilization procedures. Recommendations are awaiting results that are expected in 1999. Materials compatibility studies could lead to the co-location of components with similar cleaning and sterilization constraints (i.e. electronics, optics, chemical sensors).

The protection of Lake Vostok presents challenges new to NASA, since the probe does not transverse sterile space, but rather a water column containing viable surface organisms and ice containing a very low level of viable spore forming microbes.


The mission sequence will be determined by unique forward biological contamination constraints.


The current mission approach calls for a sterile biobarrier capable of permitting pressure equalization, to deliver the probe to the base of a warm water drilled bore hole. Prior to further descent of the probe by ice melting, an antimicrobial oxidizing agent would be employed to kill organisms present at the base of the bore hole.

At present, experiments are underway to assess the application of 30% concentrated hydrogen peroxide (H2O2) to sterilize both the water at the base of the borehole as well as the ice surfaces around the probe. Freezing point suppression caused by the release of H2O2, results in the melting of ice at the bore hole base and formation of a sterile slush as the H2O2self dilutes to a concentration permitting the solution to freeze.


Using this approach it may be possible to execute a surface sterilization event at the base of the bore hole in the ice, hundreds of meters above the lake. A straight forward experimental design to test the efficacy of ice formation in situ with respect to H2O22 concentration, temperature and time, is planned to evaluate this approach.

The ability to enter the Lake without contamination that could impact either the environment or the scientific goals of the mission, will require stringent cleaning, sterilization and verification methods.


The proposed mission sequence for the Vostok melter probe calls for a sterilization event to occur at the base of the bore hole that will enable the already sterile probe to leave its biobarrier, pass through sterilized ice, and proceed to the lake’s surface entraining only those living microorganisms that naturally rain into the lake as the glacial ice melts.


The only organisms recovered by culture to date from deep drill cores at Vostok station are spore-forming bacteria and actinomycetes although others may be present and as yet not detected.

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