Geomicrobiology of Vostok Ice: Implications for Life in Lake Vostok


Vostok ice crystal.jpg (88063 bytes)Recent studies have revealed a number of subglacial lakes beneath the Antarctic ice sheet. Lake Vostok, lying 4 km beneath the ice surface is the largest of these lakes with a surface area near 10,000 km2 and a depth exceeding 600 m. A permanent ice sheet covered the lake about 15 million years ago isolating it from the atmosphere. Geochemical and crystallographic measurements, in concert with airborne radar studies, indicate regions of frozen lakewater accreted to the bottom of the permanent ice sheet. There is evidence that the accretion ice from Lake Vostok contains microbes, implying that a microbial assemblage exists within the lake itself. This collaborative (5 institutions, 9 investigators), multidisciplinary effort will be the first to examine (i) physical stresses in deep glacial and accretion ice, (ii) the role of clathrates on gas dynamics within the lake, (iii) the origin of microbes in accretion ice, (iv) the physiological state of ice-bound microbes, (v) the geochemistry of the ice column (bulk and within veins), and (vi) living microbes in ice veins that form at triple junctions in the ice crystal matrix. Collectively, results from this study will provide new information on the deepest ice yet collected and allow boundaries to be placed on conditions within Lake Vostok. Considering the enormous financial and logistic effort that will be required to obtain uncontaminated samples from Lake Vostok, it is imperative that conditions within the overlying ice, which presumably supplies the nutrients and biological seed to the lake, be understood before any attempt is made to sample the actual lakewater. Such information will allow meaningful and hypotheses to be drawn regarding the physical, chemical and biological properties of the lake, and will provide critical background for the development and implementation of a sterile sample recovery system.

Hypotheses

 1.       Accretion ice does not exist under hydrostatic conditions. After freezing onto the ice sheet, it undergoes gradual but significant increases in shear resulting in substantial development of dislocations within the lattice structure, reorientation of the crystallographic texture, and stress-induced effects on triple junctions.
 2.      Clathrates exist at the ice/water interface, sequestering biologically and geochemically important gases (e.g., O2, CO2) from the water column.
 3.      The microbes in accretion ice did not originate from the Lake Vostok environment. The original biological seed was aeolian deposition onto the surface of the ice sheet rather than remnant microbes associated with pre-glacial periods or contemporary thermal vents.
 4.      Liquid veins that form at triple junctions in the ice crystal matrix exist in deep-accretion ice providing a habitat that supports extant microbial growth and movement.
 5.      Microbes in accretion ice are physiologically acclimated or adapted to the temperature, pressure, pH, salinity and gas regimes in Lake Vostok, and posses stress proteins that allow them to cope with the environment.
 6.      Non-cellular particles in accretion ice consist of both particulate organic matter derived from overlying glacial ice and from the Earth’s crust.
 7.      The geochemistry (DOC, nutrients, ions) of accretion ice is different from overlying glacial ice. The geochemical profile from accretion ice can be used together with water/ice partitioning coefficients to construct the geochemical history on Lake Vostok over the past 100,000 years (approx. age of the oldest accretion ice).


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