9419413 Priscu The permanent ice cover of antarctic lakes within the McMurdo dry valleys provides a habitat for viable microbial consortia consisting of cyanobacteria and eubacteria. This microbial assemblage, which is concentrated in a liquid water lens associate with a layer of rock debris at mid-ice depth, presumably grows only during a period when the ice cover in not completely frozen ( 190 d y-1). Despite the potential importance this assemblage may have with regards to overall ecosystem dynamics, it has never been studied with respect to its origin, distribution and ecological significance. It is hypothesized that (1) viable microbial consortia exist in the ice covers of all dry valley lakes, (2) the microorganisms originate from terrestrial mat communities, (3) the rock debris and associated microbial layer persists at mid-ice depths owing to a balance between solar energy absorption and upward advection from surface ablation and bottom ice freezing, (4) primary production by ice cyanobacteria contributes a significant amount of new production to the lake ecosystem, (5) microbial growth rates are low but are higher than rates of ice turnover, (6) the nitrogen pool associated with the microbial assemblage results from N2 fixation and (7) bacterial and cyanobacterial interactions within the assemblage are commensualistic. These hypotheses will be addressed through a combination of geographical sampling, physical ice modeling, molecular identification using probes for 16S rRNA and nitrogenase, and physiological assays. A majority of this work will focus on the assemblage found in the east lobe of Lake Bonney which has been tentatively characterized. This project, which will be the first to examine the antarctic lake ice microbial assemblage, will yield important new information on carbon and nitrogen dynamics within the McMurdo dry valleys and will complement numerous studies of sea ice microbial communities.
