13C-contents of sedimentary bacterial lipids in a shallow sulfidic monomictic lake (Lake Cisó, Spain)

Stable carbon isotopic analysis was performed on sedimentary biomarkers of a shallow sulfide-rich monomictic lake, Lake Cisó (NE Spain). Specific biomarkers derived from phototrophic sulfur bacteria in Lake Cisó were considerably depleted in 13C, most likely due to the depleted 13C-content of the dissolved inorganic carbon that was photosynthetically fixed. Recycling of respired CO2, a well-known phenomenon in monomictic lakes, probably caused this depletion. The stable carbon isotopic composition of terrestrial markers, such as C25–33 odd-carbon-numbered n-alkanes and C22–30 even-carbon-numbered n-alkan-1-ols and fatty acids, were rather similar to each other and their 13C depleted values (c. −31 to −35‰) indicated that they were derived from the surrounding vegetation. Phytol was predominantly derived from the bacteriochlorophylls of phototrophic purple sulfur bacteria as were specific fatty acids.