Lac sous glaciaire de Vostok (Antarctique) : caractérisation biologique, géochimique glaciologique d'un environnement sous-glacaire unique – LAC VOSTOK

Subglacial lakes are focus of scientific curiosity which captured the interest of a wide public. Their exploration rise scientific and technological challenges promoted by SCAR as one of its Scientific Program for the coming decade, the International Polar Year representing a start point and framework for concerted actions (http://salepo.tamu.edu/saleworkshop2006). The availability of frozen samples extracted from the Vostok subglacial Lake, offers opportunity to conduct a comprehensive research on a unique subglacial environment. The Vostok subglacial lake, located 4km under ice sheet and the Russian station, is so far the largest water body in Antarctica, as large as lake Ontario (14000 km2) and rather deep (more than 1200m). A 3658m deep ice core drilling stopped 100m before the water interface penetrated into an ice massif of frozen water from the lake which is attached under the glacier. The extracted ice samples of 'accretion ice' open an astonishing window over this 'unique' subglacial environment. Subglacial lakes have been isolated from the surface environment since millions years and microorganisms possibly having similarities by physiology to those from the original biotope may be present. From the recent studies, the biological content appears dramatically low and only a few taxons have been identified. The 16S rDNA signature of a thermophilic bacterial phylotype Hydrogenophilus thermoluteolus, was identified suggesting a hydrothermal contribution. Hydrothermal fluids activated by local tectonic may sustain some niches within deep faults from surrounding bedrock and supplying the lake. The project aims to develop a series of complementary approaches to improve robustness of the suggested scenario. The objective is to estimate for the sub-glacial biosphere from Vostok, the magnitude and the way of survival, to understand the physical, chemical, geochemical interactions between the lake, the glacier and the bedrock. The biological, geochemical, physicochemical assessments imply investigations which can be expressed within six themes and interdependent questions: 1-Is life present in the sub glacial lake Vostok? Can we confirm presence of H. thermoluteolus, detection of genes coding rubisco, or hydrogenase associated to physiology using CO2 as carbon source and H2 as energy sources, allowing survival in extreme conditions ? What is the microbial diversity, can we detect viruses? Can subglacial lakes be seeded by microbes transiting through the overlying glacier? 2-What are indices for hydrothermal contribution? Is isotopic composition of the accretion ice (2H, 18O) enriched with respect to the glacier? Is there mantellic contribution (3He), heavy metal enrichment, reduced form of sulphurs, elements with redox potential useful for micro-organisms? 3-Is there evidence of sismo-tectonic activity? What about the ice concentration of 4He (from rocks degassing) of hydrogen gas (from water reduction at very high temperature and electron-donor), of the soluble salt inclusions (associated to rapid processes of integration triggered by seismic events)? Can we set the mass balance of geochemical tracers? 4-Why and how accretion ice forms? What is the accretion rate, the ice lattice defect concentration? What are the partitioning coefficients for salts, organic carbon, gases, DNA, during the expected very low freezing process? 5- Are biogenic gases present in the lake (N2O, CH4, CO2)? What is the fate of air and gases from the glacier ice which melt and supply the lake? What is the mass balance for gases, does lake saturated with gases? 6-What is the chemical composition of the lake? What are origin and concentration of dissolved organic carbon, minerals and sulphates salt found in excess in accretion ice? The analysis will be performed on available samples from the subglacial lake Vostok along with samples from glacier ice (Antarctica, Mt Blanc, Svalbard) for biological investigation as references. The experiments will include: -Biology and genomic: the cell concentration, cultivation assays, DNA amplification, contaminations controls, sequencing and cloning, searching for gene coding of enzymes. -Geochemistry: ice analysis of ionic species, organic acids, organic carbon, heavy metals, gases, isotope composition of ice, helium, sulphur, -Physical- chemistry: geophysics, freezing experiments, localization and in-situ composition of impurities, of defects within ice lattice. The four partners involved in this interdisciplinary project requested for 36 months duration gather along with their collaborations the necessary equipment and expertise in glaciology, molecular biology, ancient DNA, microbial ecology, geochemistry, modeling.