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Project Progress

Our studies of photosynthetic microbial ecosystems has focused increasingly on the role of sulfate as (i) a key arbiter of the distribution and of photosynthetic energy across several possible biosignature classes (e.g., volatile vs. solid phase) and (ii) a critical influence on mechanisms of organic preservation in sulfate evaporite sedimentary systems that serve as analogs for sulfate-rich evaporates on Mars.
We have imaged at micron resolution the lateral and vertical distributions of 34S/32S (an indicator of biological sulfur cycling and an important biosignature for interpreting Earth’s rock record), in the surface layer of an actively photosynthesizing microbial mat. We have developed a technique that links genetic identity to consumption of isotopically labeled substrates through micron-scale imagery. These imaging techniques will be combined with classical geochemical approaches to characterize extensively the oxidative sulfur cycle in microbial mats subjected to >1-year incubation (to be completed in the Fall of 2007) under sulfate concentrations similar to those in Archean seawater.
We have documented the occurrence of approximately seven sulfate evaporite mineral microfacies that appear to be uniquely associated with biological mediators, based on lipid and microbial diversity assays conducted in parallel with the microfacies analysis.

Our studies of chemosynthetic systems focused on understanding (i) the physical and chemical determinants of habitability in reference to rock-hosted chemosynthetic systems, and (ii) the possible biological templating of alteration minerals and cements associated with serpentinizing systems.
We have developed a conceptual framework to quantify and link the various physical and chemical constraints on habitability, through their common effect on biological energy demand (in press, for publication as part of a “Follow the Energy” special issue of Astrobiology)

We have documented the occurrence of finely-laminated dolomite (high-Mg carbonate) cements in the outflow of springs influenced by serpentizing host-rocks and are currently investigating the possible biological mediation accompanying their formation.