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Project Progress

• To better understand the preservation of microbial biosignatures in hydrothermal settings, I have traced the fate of epiphytic diatoms entombed in travertine spherulites. These structures are pervasively formed in distal, low temperature environments around modern hot spring outflows at Angel Terrace (Mammoth Springs, Yellowstone) and Thermopolis (southern Wyoming). The diatoms in these modern systems consist of pennate skeletons (frustrules) of opaline silica. Qualitative electron microprobe analysis of the diatoms entombed in modern speherulites showed them to contain concentrations of molybdenum, compared to the entombing carbonate matrix. For comparison, similar Pleistocene-aged spherulitic travertines were collected from quarries at Gardiner, Montana, and in the Cuatro Cienegas Basin (Central Mexico). These travertines had undergone substantial post-burial recrystallization and cementation. Small silica grains discovered by electron microprobe mapping were easily missed in a precursor thin section analysis, but electron microprobe mapping of polished thin sections revealed the presence of small patchy domains of silica within spherulites. Silica patches retained the basic size and shape of diatoms, but were composed of quartz, the stable low-temperature silica phase. Electron microprobe mapping failed to reveal evidence for carbon or trace metal signatures. However, the electron microprobe is typically not sensitive enough for quantitative trace element analysis. Therefore, the next steps in this study are to 1) examine silica patches for evidence of trace element enrichments using more sensitive methods of X-ray (Synchotron) tomography and 2) use ion microprobe analysis to look for evidence of biological fractionation in silicon isotopes.
• In collaboration with the Ecogenomics Focus Group, I continued my previous studies of laminated fabrics in submerged, cyanobacterial mats of shallow saltern environments of Guerrero Negro, Baja Sur, Mexico. This involved the collection and field fixation of mat materials from the newly designated Ecogenomics Focus Group study sites, followed by a lab characterization of preserved mat materials by electron, dual interference contrast and flourescence microscopy of large format thin sections. Section preparation required perfecting a new embedding method for exopolymer-rich mats using low viscosity resins. Microfabric studies have now been completed and a draft manuscript is in preparation.
• This past year, as part of the Ecogenomics Focus Group project, we also began a systematic study of meiofaunal grazers (primarily nematode species) associated with the Microcoeleus mats at Guerrero Negro. The meiofauna of laminated mats provides a potential ecological analog for early metazoan evolution. We have been documenting the patterns of meiofaunal migration during a diel experiment where we also monitored changes in oxygen, sulfide, and pH during a daily cycle of photosynthesis. This year we also began documenting the trophic interactions of meiofaunal species using dual interference microscopy to identify gut contents. Next we will isolate meiofaunal species from Microcoeleus mats to identify morphospecies using a scanning electron micrograph (SEM). Isolates of living nematode species will be cultured to obtain pure isolates of morphospecies for molecular sequencing and phylogenetic analysis.