Isotopic Fingerprints of Microbial Respiration in Aragonite from Modern Bahamian Stromatolites Dawn Sumner , Geology Department, University of California, Davis In honor of Prof. Ginsburg and the numerous insightful conversations we have had with him, we present new results on processes causing lithification in modern Bahamian stromatolites. As Ginsburg has argued for longer than we have been scientists, understanding how modern stromatolites or “strombolites” form and lithify is critical to properly interpreting the origins of ancient stromatolites. Microbial roles in stromatolite lithification can be traced in carbonates because microbial communities produce carbon isotopic shifts when they cycle local DIC (dissolved inorganic carbon). Thus, the isotopic composition of carbonates can record ancient microbial CO 2 cycling, providing insights into the processes of stromatolite growth and microbial influences on carbonate chemistry. In shallow subtidal modern stromatolites from Highborne Cay, Bahamas, authigenic aragonite
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