Diffusion Modeling of Microbial Metabolism

Microbes eat carbon to live; it can be in the form of organic carbon, carbon dioxide, or methane. Their metabolic processes fractionate 12C from 13C to varying degrees. These signatures can be preserved in the rock record when carbonate precipitates contemporaneously with microbial activity. However, numerous processes make these signatures difficult to preserve and measure. By using computer modeling to predict the size and distribution of isotopic shifts, insights into where and when microbial shifts can be expected to be preserved in rocks. I have started a modeling project to make these predictions, and am using the results to guide sampling of ancient microbialites to identify these signatures.

The figure on the left shows the isotopic composition of total dissolved inorganic carbon above a 100 micron-thick photosynthetic mat located at 0 cm. Photosynthesis started at 0 hours. There is no convection in the overlying water, and the isotopic effects of the mat extend significantly into the water column. For a more complete explanation see my Microbial Influences... paper at the Astrobiology web site.

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Dawn Y. Sumner
Department of Geology
University of California
Davis, CA 95616