(1) Executive Summary
Life continues to appear in the unusual and extreme locations from
hot vents on the seafloor to ice covered hypersaline lakes in
Antarctica (Priscu et al., 1998). The subglacial environment
represents one of the most oligotrophic environments on earth, an
environment with low nutrient levels and low standing stocks of
viable organisms. It is also one of the least accessible habitats.
Recently the significance of understanding subglacial communities
has been highlighted by discoveries including the thriving bacterial
communities beneath alpine glaciers (Sharp et al., 1999), to the
evidence from African stratigraphy for a Neoproterozoic snowball
earth (Hoffman et al., 1998a, Kirschvink, 1992) to the compelling
ice images from
Europa, the icy moon of Jupiter. If life thrives in
these environments it may have to depend on alternative energy
sources and survival strategies. Identifying these strategies will
provide new insights into the energy balance of life.
The identification of significant subglacial bacterial action (Sharp
et al., 1999) as well the work on permafrost communities (i.e.
Gilichinsky et al., 1995) suggests that life can survive and
possibly thrive at low temperatures. Neither the alpine subglacial
environment nor the permafrost environment is as extreme as the
environment found beneath a continent-wide ice sheet as Antarctica
today.
The alpine subglacial environment has a continual high level
of flux of nutrients from surface crevasses. The Antarctic
subglacial environment lacks a rapid flux of surface meltwater and
subsequently is more isolated. In addition to being more isolated,
the Antarctic subglacial environment is a high pressure region due
to the overburden of ice.
The Antarctic subglacial environment may be similar to the
environment beneath the
widespread ice sheets in the Neoproterozoic, a time period from
about 750 to 543 million years
ago. It has been suggested that during this period the earth
experienced a number of massive
glaciations - covering much of the planet for approximately 10
million years at a time. The
evidence for an ancient ice covered planet comes from thick
widespread sedimentary sequences
deposited at the base of large ice bodies.
These glacial units
alternate with thick carbonates units-warm shallow water sedimentary deposits. These paired sequences have
been interpreted as representing a long period when the earth
alternated between from an extremely cold, completely ice covered
planet (the snowball earth) and a hothouse planet (Hoffman et al,
1998b). Some speculate that the extremes of these climates
introduced an intense “environmental filter”, possibly linked to a
metazoan radiation prior to the final glaciation and an Ediacaran
radiation (Hofmann et al., 1990; Knoll, 1992).
Portions of the
Antarctic continental subglacial environment today, which have been
isolated from free exchange with the atmosphere for at least 10
million years, are similar to the environment in this ancient global
environment. Understanding the environmental stresses and the
response of the microbes in a modern extreme subglacial environment
will help us decipher the processes which lead to the post-glacial
evolutionary radiation over 500 million years ago.
The third important analogue for modern Antarctic subglacial
environments is from the outer reaches of the solar system, the ice
moon of Jupiter, Europa. Recent images resembling sea ice, combined
with the very high albedo of this moon has lead to the
interpretation that this moon is ice covered. Beneath the ice
covering Europa is believed to be an ocean. The thick cover of ice
over a liquid ocean may be a fertile site for life (Chyba, 1996;
Williams et al., 1997). The Antarctica subglacial lakes have similar
basic boundary conditions to Europa.
An investigation of Antarctic subglacial environments should target
the unique role these lakes may have in terms of the triggers for
rapid evolutionary radiation, for understanding the global carbon
cycle through major glaciations and as an analogue for major
planetary bodies.
Lake Vostok is a large (10,000 km2) water body located beneath ~4 km
of glacial ice at 77oS, 105oE within the East Antarctica Precambrian craton (Kapitsa et al., 1996). Based on limited geophysical data, it
has been suggested that the Lake occupies a structural depression,
perhaps a tectonically active rift.
The water depth varies from
approximately 500 m beneath Vostok Station to a few 10’s of meters
at the northern end of the Lake; the ice sheet thickness also varies
by nearly 400 m and is thickest in the north (4,150 m). Ice motion
across the lake, freezing and melting at the base of the ice sheet
and geothermal heating could establish density-driven flows, large
scale circulation and geochemical gradients in Lake Vostok.
Figure 1:
ERS-1 Surface Altimetry indicating location of Lake Vostok
The existence of this lake, and at least 76 others like it, has been
documented by extensive airborne 60 MHz radio-echo sounding records
that provide coarse sampling coverage of approximately half of the
Antarctic ice sheet (Siegert et al., 1996). The majority of
sub-glacial lakes are near ice divides at Dome C and Ridge B, East
Antarctica.
More recently, the European Research Satellite-1 (ERS-1,
Figure 1) has provided radar altimeter data which provide
unprecedented detail of ice surface elevations. These data have been
used to define the physical dimensions of the lake, its drainage
basin, and predict lake water density (Kapitsa et al., 1996).
The water body appears to be fresh. Based on considerations of
temperature and pressure fields, most of the dissolved gases in the
lake would be present as hydrates, which may be segregated in
density layers. The unique geochemical setting of Lake Vostok may
present an opportunity and a challenge for the development of novel
life forms.
Lake Vostok, due to its size, is the lake which is most
likely to have remained liquid during changes in the Antarctic ice
sheet volume and therefore most likely to provide new insights into
these subglacial environments. We understand much more about the subglacial processes such as accretion and melting within Lake
Vostok than any other lake, and we have a solid local climate record
for the last 400,000 years from the overlying ice core (Petit et
al., 1999).
Figure 2:
Location of subglacial lakes in Antarctica determined from
the NSF/SPRI airborne radar program.
The radar flight lines are
shown in the inset on the lower left. (adapted from Siegert et al.,
1996)
An international team of scientists and engineers has been drilling
the ice sheet above Lake Vostok to obtain a detailed record of the
past climate on earth. This ice-core program, started in 1989,
recently terminated drilling at a 3,623 m depth (approximately 120 m
above the ice-water interface at this location). This is the deepest
ice core ever recovered.
The ice core corresponds to an
approximately 400,000 year environmental record, including four
complete ice age climate cycles. Below 3,538 m there is
morphological and physical evidence that basal ice is comprised of
re-frozen Lake Vostok water.
Throughout most of the ice core, even to depths of 2,400 m, viable
microorganisms are
present (Abyzov, 1993). Previous sampling of ice in the interior of
the Antarctic continent has
repeatedly demonstrated that microorganisms characteristic of
atmospheric microflora are
present. Air-to-land deposition and accumulation is indicated,
rather than in situ growth in the
ice (Lacy et al., 1970; Cameron et al., 1972).
Cameron and Morelli
(1974) also studied 1 million
year old Antarctic permafrost and recovered viable microorganisms.
Prolonged preservation of viable microorganisms may be prevalent in
Antarctic ice-bound habitats. Consequently, it is possible that
microorganisms may be present in Lake Vostok and other Antarctic
subglacial lakes. However, isolation from exogenous sources of
carbon and solar energy, and the known or suspected extreme physical
and geochemical characteristics, may have precluded the development
of a functional ecosystem in Lake Vostok.
In fact, subglacial lakes
may be among the most oligotrophic (low nutrient and low standing
stocks of viable organisms) habitats on earth. Although “hotspots”
of geothermal activity could provide local sources of energy and
growth-favorable temperatures, in a manner that is analogous to
environmental conditions surrounding deep sea hydrothermal vents
(Karl, 1995), it is important to emphasize that without direct
measurements, the possible presence of fossil or living
microorganisms in these habitats isolated from external input for
nearly 500,000 years is speculation.
Lake Vostok may represent an unique region for detailed scientific
investigation for the following reasons:
-
it may be an active tectonic rift
which would alter our understanding of the East Antarctic
geologic terrains
-
it may contain a sedimentary record of earth’s climate, especially
critical information about the initiation of Antarctic glaciation
-
it may be an undescribed extreme
earth habitat with unique geochemical characteristics
-
it may contain novel, previously undescribed, relic or fossil
microorganisms with unique adaptive strategies for life
-
it may be a useful earth-based analogue and technology “test-bed” to
guide the design of unmanned, planetary missions to recently
discovered ice-covered seas on the Jovian moon, Europa.
These diverse characteristics and potential opportunities have
captivated the public and motivated an interdisciplinary group of
scientists to begin planning a more comprehensive investigation of
these unusual subglacial habitats. As part of this overall planning
effort, a NSF-sponsored workshop was held in Washington, D.C. (7-8
Nov. 1998) to evaluate whether Lake Vostok is a curiosity or a focal
point for sustained, interdisciplinary scientific investigation.
Because Lake Vostok is located in one of the most remote locations
on earth and is covered by a thick blanket of ice, study of the lake
itself that includes in situ measurements and sample return would
require a substantive investment in logistical support, and, hence
financial resources.
Over a period of two days, a spirited debate was held on the
relative merits of such an investment of intellectual and fiscal
resources in the study of Lake Vostok. The major recommendations of
this workshop were:
-
To broaden the scientific community knowledgeable of Lake Vostok by
publicizing the scientific findings highlighted at this workshop.
-
To initiate work on sampling, measurement and contamination control
technologies so that the Lake can be realistically and safely
sampled.
-
Both NASA and NSF should prepare separate, or a joint, announcement
of opportunity for the study of Lake Vostok, possibly through the
LExEn program.
Back to Contents
(2) Introduction
The goal of the workshop was to stimulate discussion within the U.S.
science community on Lake Vostok, specifically addressing the
question:
“Is Lake Vostok a natural curiosity or an opportunity for
uniquely posed interdisciplinary scientific programs?”
The workshop
was designed to outline an interdisciplinary science plan for
studies of the lake.
The structure of the workshop was a series of background talks on
subjects including:
-
Review of Lake Vostok Studies - Robin E. Bell
-
The Overlying Ice: Melting and Freezing
- Martin Siegert
-
Evidence from the Vostok Ice Core Studies
- Jean Robert Petit
-
Tectonic Setting of Lake Vostok
- Ian Dalziel
-
Biodiversity and Extreme Niches for Life
- Jim Tiedje
-
Lake Vostok Planetary Analogs - Frank Carsey
-
Identification of Life - David White
-
Mircrobial Contamination Control
- Roger Kern
A summary of each of these background talks is presented in this
report Section (4) entitled:
“Lake Vostok: Background Information.”
Following these talks each workshop participant presented a 3
minute, one overhead presentation of why, from their perspective,
Lake Vostok was more than a curiosity, and warranted significant
effort to study. These presentations ranged from discussion of
helium emerging from the mantle, to the unique temperature and
density structure which might develop in such an isolated high
pressure, fresh water environment as Lake Vostok. Written summaries
of these presentations and key illustrations are included in
Appendix 1 entitled “Why Lake Vostok?”.
Next, the workshop participants as a large group, identified the
fundamental aspects of a research program across Lake Vostok with
each participant presenting five key ideas. These ideas were
synthesized into 6 major themes which became the subject of working
groups.
The working groups and their members were:
-
Geochemistry-Mahlon C. Kennicutt II, Berry Lyons, Jean Robert
Petit, Todd Sowers
-
Biodiversity-Dave Emerson, Cynan Ellis-Evans, Roger Kern, José de
la Torre, Diane
McKnight, Roger Olsen
-
Sediment Characterization - Luanne Becker, Peter Doran, David
Karl, Kate Moran,
Kim Tiedje, Mary Voytek
-
Modeling - David Holland, Christina Hulbe
-
Site Survey - Robin Bell, Ron Kwok, Martin Siegert, Brent Turrin
-
Technology Development - Eddy Carmack, Frank Carsey, Mark
Lupisella, Steve Platt,
Frank Rack, David White
Each group was tasked with developing: a) justification for a Lake
Vostok effort; b) the goals of a research effort; c) a strategy to
meet the goals; and d) a time-frame for the effort. In addition, the
groups were tasked with presenting the single most compelling
scientific justification for studying Lake Vostok.
The groups worked
through the morning of the second day preparing draft presentations.
The draft reports were presented in plenary at the conclusion of the
workshop. The reports from the working groups are found in Section
6, “Group Reports”. The workshop participants debated the
justifications and the major obstacles to studying Lake Vostok.
The discussion of the major obstacle to advancing a well developed
scientific justification and plan to study Lake Vostok hinged on
several major factors including:
-
the exploratory nature of the
program coupled with the paucity of data about this unknown
region making development of a detailed scientific justification
difficult
-
the need for technological
developments to ensure contamination control and sample
retrieval, recognizing that Lake Vostok is a unique system whose
pristine nature must be preserved
-
the need for a strong consensus within the U.S. science community
that Lake Vostok
represents an important system to study, and recognition that
international collaboration is a necessary component of any study
-
the recognition that the logistical impact of a Lake Vostok program
will be significant
and that the scientific justification must compete solidly with
other ongoing and emerging programs
-
that the lack of understanding of the present state of knowledge of
the Lake as a system within the U.S. science community remains a
difficulty in building community support and momentum for such a
large program.
These obstacles were addressed in workshop discussions and are
specifically addressed in the
report recommendations, the draft science plan and the proposed
timeline. The preliminary
science plan and timeline was based on working group reports and is
presented below in Section (3) "Preliminary Science Plan and
Timeline ".
Back to Contents
(3) Preliminary
Science Plan and Timeline
This preliminary science plan is based on a synthesis of working
group reports. The overarching goal of the science plan is to
understand the history and dynamics of the Lake Vostok as the
culmination of a unique suite of geological and glaciological
factors. These factors may have produced an unusual ecological niche
isolated from major external inputs. The system structure may be
uniquely developed due to stratification of gas hydrates.
Specific
scientific targets to accomplish this goal include:
-
determine the geologic origin of
Lake Vostok within the framework of an improved understanding of
the East Antarctic continent as related to boundary conditions
for a Lake Vostok ecosystem
-
develop an improved understanding of
the glaciological history of the lake including the flux of
water, sediment, nutrients and microbes into a Lake Vostok
ecosystem
-
characterize the structure of the
lake’s water column, to evaluate the possibility of density
driven circulation associated with melting/freezing processes or
geothermal heat, the potential presence of stratified gas
hydrates, and the origin and cycling of organic carbon
-
establish the structure and
functional diversity of any Lake Vostok biota, an isolated
ecosystem which may be an analogue for planetary environments
-
recover and identify extant microbial communities and a
paleoenvironmental record
extending beyond the available ice core record by sampling the
stratigraphic record of gas hydrates and sediments deposited within
the Lake
-
ensure the development of appropriate technologies to support the
proposed experiments without contaminating the Lake.
Timeline
1999 (99-00)
Planning Year
Modeling studies Develop international collaboration
SCAR Lake Vostok workshop Begin technology development
2000 (00-01)
Site Survey Year I Joint NSF/NASA LExEn Call for Lake Vostok Proposals
Airborne site survey Preliminary ground based measurements
Preliminary identification of observatory sites
2001 (01-02)
Site Identification and Site Survey Year II
Ground based site surveys Complete airborne survey if necessary
Test access/contamination control technology at a site on the Ross
Ice Shelf Finalize selection of observatory sites
2002 (02-03)
In Situ Measurement Year Drill access hole for in situ measurements
Attempt in situ detection systems to demonstrate presence of
microbial life Install long term observatory Acquire vertical profile of water column
Acquire microscale profiles within surface sediments Conduct interface survey (ice/water and water/sediment)
International planning workshop (including exchange workshop)
2003 (03-04)
Sample Retrieval Year Acquire samples of basal ice
Acquire samples of water and gas hydrates Acquire samples of surface sediments
Stage logistics for second observatory International planning workshop (including data exchange)
2004 (04-05)
Installation of Second Long Term Observatory
Installation of second long term observatory Analysis of data
Build new models International planning workshop (including data exchange)
2005 (05-06)
Core Acquisition Year Begin acquisition of long core
International planning workshop (including data exchange)
In order for this science plan and timetable to be realized, several
coordination issues must be addressed including inter-agency and
international collaboration, refinement of the scientific
objectives, rigorous selection of the observatory and sample
locations, and identification of the critical observations.
The
development of three major groups is envisioned including,
(1) an
interagency working group to identify the relative interests and
potential roles in a Lake Vostok program
(2) an international
working group focused on scientific and logistical coordination for
studies of Lake Vostok
(3) a Lake Vostok Science Working group
to address refinement of science objectives, site selection and
determination of primary objectives
Inter-agency Working Group:
The study of the Lake Vostok system is
relevant to the mandate of several agencies, most notably NASA,
NSF
and the USGS. Active coordination between these agencies will be key
to a successful science program focused on Lake Vostok. Other
agencies or industrial partners might be sought as well. Due to
their role as stewards of Antarctica and providers of logistical
support, NSF would be the preferred lead U.S. agency for any Lake
Vostok mission.
International Working Group:
To date, our understanding of Lake
Vostok is the result of integration of diverse data sets from the
international research community. A successful exploration of Lake
Vostok will require ongoing international collaboration with
significant contributions from all participants. International
collaboration will broaden the scope of the Lake Vostok studies. The
SCAR workshop in 1999 is an excellent venue for developing an
international Lake Vostok Working Group. Science Working Group:
Before implementation of the science plan can
begin, scientific objectives must be refined, the site selection
process defined, and the critical observations defined. Careful
review of these issues would best be accomplished by a small team of
scientists, engineers, and logistics experts. The creation of this
group is a key first step. This group will be tasked with addressing
issues such as site selection and development of an observation and
sampling strategy.
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