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Antarctic microorganism
Antarctica is one of the most physically and chemically extreme terrestrial environments to be inhabited by microorganisms.〔Cary, S.C., et al. "On the rocks: the microbiology of Antarctic Dry Valley soils." ''Nature Reviews'' 8 (2010): 129-138.〕 Nonetheless, on February 6, 2013, scientists reported that bacteria were found living in the cold and dark in a lake buried a half-mile deep under the ice in Antarctica. This finding was later confirmed by scientists on August 20, 2014.
== Climate and habitat ==
Although most of the continent is covered by glacial ice sheets, ice-free areas comprising approximately 0.4% of the continental land mass are discontinuously distributed around the coastal margins.〔 The McMurdo Dry Valleys region of Antarctica is a polar desert characterized by extremely low annual precipitation (<100 mm) and an absence of vascular plants and vertebrates; microbial activity dominates biological functioning.〔Zeglin, L.H., et al. "Landscape distribution of microbial activity in the McMurdo Dry Valleys: linked biotic processes, hydrology, and geochemistry in a cold desert ecosystem." ''Ecosystems'' 12 (2009): 562-573.〕 Mean summer high and winter low temperatures in the dry valleys are -5 and -30 °C.〔 Because precipitation is both infrequent and low, seasonal water availability in hydrologically connected soils make areas adjacent to water bodies more hospitable relative to dry upland soils.〔 Polar ecosystems are particularly sensitive to climate change, where small changes in temperature result in greater changes in local hydrology, dramatically affecting ecosystem processes.〔Simmons, B.L., et al. "Long-term experimental warming reduces soil nematode populations in the McMurdo Dry Valleys, Antarctica." ''Soil Biology & Biochemistry'' 41.10 (2009): 2052-2060.〕
Soils in Antarctica are nearly two-dimensional habitats, with most biological activity limited to the top four or five inches by the permanently frozen ground below.〔Baskin, Yvonne. ''Under Ground: How Creatures of Mud and Dirt Shape Our World.'' Washington, DC: Island Press, 2005. 14-37.〕 Environments can be limiting due to soil properties such as unfavorable mineralogy, texture, structure, salts, pH, or moisture relationships.〔Cameron, R.E. "Cold desert characteristics and problems relevant to other arid lands." ''Arid Lands In Perspective'' (1969): 169-205.〕 Visible sources of organic matter are absent for most of continental Antarctica.〔 Dry Valley soil ecosystems are characterized by large variations in temperature and light regimes, steep chemical gradients and a high incidence of solar radiation with an elevated ultraviolet B (UVB) light component.〔 Dry Valley soils originate from weathering of bedrock and glacial tills that consist of granites, sandstones, basalts and metamorphic rocks.〔 Space within these rocks provide protection for microorganisms against some (but not all) of these conditions: i.e., protection from wind scouring and surface mobility, a reduction in UV exposure, reduced desiccation and enhanced water availability, and thermal buffering.〔Cowan, D.A. "Cryptic microbial communities in Antarctic deserts." ''Proceedings of the National Academy of Sciences of the United States of America'' 106.47 (2009): 19749-19750〕 Half of the soils in the Dry Valleys have subsurface ice, either as buried massive ice or as ice-cemented soil (permafrost).〔 The permafrost layer is typically within 30 cm of the soil surface.〔
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