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Project Progress

Photosynthetic systems: Work has focused on characterizing the role of sulfate concentration, sulfur cycling, and sulfate mineralization in production and preservation of volatile and non-volatile biosignatures in microbial mat ecosystems. We are presently analyzing the results of a just-completed year-long incubation experiment to examine the effects of variable sulfate levels (including Archaean ocean levels) on sulfide isotopes as signatures of biological sulfur-cycling activity. This work will characterize a broader range of sulfur isotopes and sulfur species at considerably finer spatial resolution than has thus far been achieved in comparable systems. Further work has examined the templating, by biofilms, of unique morphology during sulfate mineral formation (as may have characterized the last stages of surface water availability on Mars). More specifically, biofilms have been found to impart distinctive textures and induce unique crystallographic aspect ratios, such as enlarged {110} prisms and shortening on the [001] axis, during gypsum mineral formation. Additionally, biologically-induced accessory phases (native sulfur, Ca-carbonate and celestite) have been found in syngenetic and replacive relationships with gypsum phases.

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Chemosynthetic systems: Work has focused on characterizing the energetic dimension of habitability as specifically applicable to water-rock reactions in the terrestrial and Martian subsurface. Theoretical work in this area has served to develop an energy balance concept of habitability, which provides a framework for quantifying habitability (as volumetrically or areally normalized biomass density) as a function of physical and chemical environment. This work was published in the journal Astrobiology during the past year. We have worked to apply this concept with the goal of characterizing and quantifying habitability in the context of robotic exploration of Mars surface deposits. Specifically, we are working as part of the Carnegie-led AMASE expedition to assess habitability using MSL flight instrumentation in Mars-analog settings. Our work will define habitability through application of the energy balance criterion to mineralogical indicators of past physical and chemical conditions. Results of this work are in press at Astrobiology. We are further applying the energy balance approach to consider the habitability of the present-day Martian subsurface, through development of cell-scale numerical reaction-transport models that calculate energy balance and habitability in fluid conditions that would develop via serpentinization processes. Results were recently presented at the 2008 Goldschmidt Conference.

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