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Are carbonate structures common in lakes in this area, or do you only find them in Pavilion lake and Kelly Lake?
The carbonate structures in Pavilion & Kelly lake are known as "microbialites," as we hypothesize that they are formed by the trapping, binding, and then the sedimentation of calcium carbonate particles by the biofilm/mats of microorganisms (mainly bacteria). Microbialites and stromatolites are found all over the globe from the high Yukon in northern Canada, to Cuatro Cienegas Basin in Mexico, the largest microbialites of Lake Van in Turkey, to marine systems of Shark Bay in Western Australia and the Highborne Cay in the Bahamas. However, the large structures found in Kelly & Pavilion are unique in their morphological diversity and that in comparison to some of the sites mentioned above, which are relatively shallow, they are found at reasonably deep depths within the lakes. --Rick White
I wonder which methodologies you use to characterize the microbial communities in these structures. Have you been doing large scale sequencing of the communities over the past several years? Do you know if there are any major differences in the community composition between the rough carbonate structures versus the smoother ones? I wonder about the production of carbonate structures, too. Are microbes involved in the precipitation of carbonate, or is that a physical process which is simply creating a surface which the microbes can adhere to? Also, for those of us interested, have you published any major papers that would be a good read for catching up with where you are at? Thank you!

Thanks for the questions. I'm already in the field, so my apologies for this short response. Steve Pointing, Jennifer Biddle, Curtis Suttle, Jim Nienow, Dawn Sumner, Greg Slater, Allyson Brady and I have been using various methods to discern both community structure and biosignature preservation. This includes sequencing techniques, light and SEM work, thin sectioning, and isotopic methods. There are indeed community composition differences, but primarily by location in Pavilion Lake rather than by depth, which is what we were initially expecting based on the fact that there are clear morphological distinctions by depth. In the shallower structures, the rough nodules are primarily composed of filamentous cyanobacteria, and the coccoidal species lay flat, almost in an endolithic manner, along the primary carbonate substrate. However, deeper in the lake the structures loose this nodular texture and the surface communities shift to predominantly coccoidal species. We can see isotopically that there is a biosignature commensurate with photosynthetically driven carbonate precipitation in the nodules (~1cm in diameter), however that isotopic enrichment is not preserved within the carbonate structures. See Brady et al 2010, and Brady et al 2009. Lim et al gives you an overview of the limnology. Laval et al is an overview of Pavilion Lake. The first set of papers focused on the sequencing/molecular work from Steve Pointing's lab will be out this year. In the mean time, please see the papers posted on http://www.pavilionlake.com/publications.php. There are a set of physical limnology and exploration research papers that I have not included, as I think you are more interested in the geobiological/geochem aspects of the program? Please feel free to contact any of us again for more details. --Darlene Lim

 
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