Biogeochemistry of basal ice from Taylor Glacier, Antarctica.

摘要

The thesis addresses a topical and exciting question in cryospheric biology: are microorganisms capable of metabolism in debris-rich basal ice of a polar glacier? The research was carried out on debris-rich basal ice from a cold-based glacier, Taylor Glacier, McMurdo Dry Valleys, Antarctica. A key component of the research was the collection and analysis of large parallel samples of basal ice for analysis of sediment concentration and mineralogy, nutrient and ion chemistry, gas composition, isotopic gas composition, cell density and metabolic activity on individual ∼1-2cm thick layers. The primary material for the thesis was from a 4 m high section of basal ice collected from a vertical shaft at the end of a 15m tunnel chainsawed into the northern margin of the Taylor Glacier. Some data was derived from ice samples collected from tunnels 500m upglacier and downglacier from the 2007 tunnel, excavated in 1999 and 2009 respectively. The main research findings presented in this dissertation are that (a) debris-rich basal ice is a viable habitat for microbial life, (b) in situ microbial heterotrophic respiration is a source of CO2 in debris-rich basal ice, and (c) microbially-mediated weathering of entrained mineral debris is a source of solute in the ice. Geologic debris in basal ice is the key component for microbial activity since it leads to a higher fraction of liquid water in the ice and provides both organic and inorganic substrates to organisms in the ice. Microbial activity in the ice produces isotopic and geochemical signatures that could be used as biomarkers for exploration of other icy systems. The results of the thesis enforce the notion that the debris-rich basal ice environment is a viable microbial habitat that supports life at temperatures below 0°C. This has broader implications at the ice sheet scale since recent discoveries in East Antarctica, indicate significant basal ice up to 1100 m thick with approximately the same volume as the world’s fourth largest freshwater lake, Lake Michigan-Huron.