Microbiology and Molecular Ecology studies in Antarctica
Our collaborators: John Priscu, Berry Lyons and Todd Sowers
LAKE VOSTOK, in the East Antarctic Precambrian craton, is the largest (~14,000 km2) and deepest (maximum depth ~650 m) of about 77 lakes that have been identified beneath Antarctic glacial ice. The upper 3,500 m represents a 420,000 year environmental record covering four complete ice age climate cycles. Ice below 3,500 m is thought to represent refrozen lakewater accreted to the bottom of the glacial ice.
Lake VostokCOLLABORATIVE RESEARCH - Mary Voytek (Microbial Ecologist, USGS) has been working with university collaborators on two projects involving both glacial and accretion ice core samples. With collaborators Dr John Priscu (Montana State University) and Dr Berry Lyons (Ohio State University) we are examining the geochemical and microbiological conditions within accretion ice in order to predict the chemical and biological environment in Lake Vostok.
Using epifluorescence and electron microscopy we were able to visualize intact cells and detrital matter. Molecular analysis of extracted DNA revealed that the microbial community present contains only bacterial phylotypes related to extant species found in both soil and aquatic communities. Science News® Article
Our work in glacial ice is with Dr.Todd Sowers (Pennsylvania State University). Dr. Sowers's research involves reconstructing records of the isotopic composition of paleoatmospheric methane (CH4) and nitrous oxide (N2O) from polar ice cores covering the last 200,000 years. The primary objective of this work is to further our understanding of the biogeochemical cycles of these two greenhouse gases throughout the anthropogenic period as well as over glacial/interglacial timescales. The stable isotopic signatures(18O and 15N) observed suggest that nitrous oxide, as well as CO2 and CH4, may be affected by microbial activity in the ice. Both nitrification and denitrification are microbially mediated processes that produce N2O as an intermediate. In situ production of N2O could explain some of the unusual concentration fluctuations observed during this period and would have serious implications for existing interpretations and reconstructions of paleoclimate and environment based on these gases.
THE FINAL FRONTIER - Our study of microbes in deep ice will advance knowledge of life in icy environments, and allow us to draw meaningful hypotheses for the future exploration of Lake Vostok, which has been identified as one of the last unexplored frontiers on Earth.
Moreover, the
microorganisms in the
Vostok ice can serve as a model for what may have happened to life
forms on Mars when it became dry and cold, and provides the closest
Earthly analog for possible life on Europa.
THE MICROBES OF VOSTOK ICE - Airborne radar mapping has identified about 77 lakes beneath Antarctic glacial ice. These lakes remain liquid as a result of adiabatic melting point depression, insulating ice cover, and heat flux from the Earth. Lake Vostok is the largest (10,000 km2) and deepest (>600 m) of these lakes, located under about 4 km of ice within the East Antarctic Precambrian craton. A permanent ice sheet covered the lake about 15 million years ago isolating it from direct contact with the atmosphere. The residence time of the water in the lake has been estimated to be about 10,000 years and the mean age of the water, since deposition as surface ice, is > 500,000 years. The ice above the lake has been cored to a record depth of 3,623 m, stopping ~120 m above the surface of the lake. The upper 3,500 m of glacial ice represents a 420,000 year environmental record covering four complete ice age climate cycles; ice below 3,500 m is thought to represent refrozen lake water accreted to the bottom of the glacial ice. Abyzov et al. (1998) provided evidence that a wide range of microbes (bacteria, yeasts, fungi and microalgae) exist in the Vostok glacial ice at depths ranging from 1500-2750 m. The concentration of microbes, some viable, was correlated with the density of mineral particles in the ice, implying that they were deposited in the snow mainly during glacial periods when the flux of dust and the wind speed were greatest.
Recent studies of accretion ice from 3590 m and 3603 m have shown the presence of microbes at densities of 102 to 104 cells ml-1, and the development of metabolic activity in the presence of liquid water. Bacterial 16S rDNA revealed low diversity in the gene population. The phylotypes were closely related to extant members of the alpha- and beta-Proteobacteria and the Actinomycetes. Actinomycetes were also observed in overlying glacial ice implying that the biological seed for the accretion ice (and presumably for Lake Vostok) may have arisen from airborne particulates deposited on the surface of the ice sheet ~500,000 years. The microbes were released into the lake and subsequently refrozen to the overlying glacial ice following downward migration and melt at the glacial grounding point. Alternatively, the microbes could be remnants from an ancient Lake Vostok that existed before permanent glacial ice cover (~15 million years ago).
Links:
Science
News® Article
Ice
and Climate, Dr. Todd Sowers of Pennsylvania State University
Lake
Vostok
Astrobiology
Study funded by NASA
Pictures
  |
 |
|
||||
|
|
||||||
 |
|
