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

Stable carbon isotopic analysis was performed on sedimentary biomarkers of a shallow sulfide-rich monomictic lake, Lake Ciso (NE Spain). Specific biom arkers derived from phototrophic sulfur bacteria in Lake Ciso were consider ably depleted in C-13, most likely due to the depleted C-13-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 marke rs, such as C25-33 odd-carbon-numbered n-alkanes and C22-30 even-carbon-num bered n-alkan-1-ols and fatty acids, were rather similar to each other and their C-13 depleted values (c. -31 to -35 parts per thousand) indicated tha t they were derived from the surrounding vegetation. Phytol was predominant ly derived from the bacteriochlorophylls of phototrophic purple sulfur bact eria as were specific fatty acids. (C) 2000 Elsevier Science Ltd. All right s reserved.