Reconstruction of delta C-13 of chemocline CO2 (aq) in past oceans and lakes using the delta C-13 of fossil isorenieratene

摘要

High abundances of the diaromatic carotenoid isorenieratene derived from photosynthetic green sulfur bacteria (Chlorobiaceae) were found just below the chemocline in an anoxic fjord in Norway, throughout the annual cycle. The stable carbon isotope composition of this carotenoid co-varied with the delta(13)C of CO2 (aq) and is independent of the CO2 and isorenieratene concentration. This constant isotopic fractionation epsilon(p) of isorenieratene versus CO2, 4 +/- 1 parts per thousand, was subsequently used in the reconstruction of delta(13)C Of CO2 at the chemocline in ancient oceans and lakes. These reconstructions indicate that delta(13)C of CO2 at the chemocline is often influenced by isotopically light CO2, formed by remineralization of organic matter. This process can, depending on the depth and stability of the chemocline, also effect the isotopic composition of the phytoplankton and, thus, isotopic records of sedimentary inorganic and organic carbon. (c) 2005 Elsevier B.V. All rights reserved.