2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 7
Presentation Time: 9:30 AM


KENIG, Fabien, Earth and Environmental Sciences, Univ of Illinois at Chicago, 845 W. Taylor St. (MC 186), Chicago, IL 60607-7059, SIMONS, Dirk-Jan, EAES, Univ of Illinois at Chicago, m/c 186, 845 West Taylor Street, Chicago, IL 60607, GONZALEZ-MELER, Miquel, Biological Sciences, Univ of Illinois at Chicago, m/c 066, 845 W. Taylor street, Chicago, IL 60607-7059 and SINNINGHE DAMSTÉ, Jaap S., Marine Biogeochemistry and Toxicology, Netherlands Institute for Sea Rsch, PO BOX 59, Den Burg, Texel, 1790 AB, Netherlands, FKenig@uic.edu

The evolution of C4 plants is thought to have occurred several times during the Miocene when atmospheric carbon dioxide levels were low. Transition from C3 to C4 dominated communities during the Miocene are inferred from the 13C enrichment of paleosols and fossils. Earlier appearance of C4-like CO2 concentrating mechanisms have only been found in CAM plants which are confined to aquatic areas. A positive 13C excursion measured in land plant biomarkers at 10ºN paleolatitude from sediments deposited during the Cenomanian-Turonian (Late Cretaceous) ocean anoxic event (OAE II) may be evidence of early expression of C4 metabolism (Kyupers et al., 1999; Nature 399, p342). We have confirmed these observations at 35ºN but not at 55ºN in the Western Interior Seaway (USA). However, at 35ºN, this positive excursion occurs significantly later than the excursion recorded at 10ºN. In a period of angiosperm expansion, burial of OM during OAE II resulted in pCO2 draw-down and pO2 increase. These conditions may have prompted the expression of C4-type photosynthetic pathways that momentarily dominated the ecosystem in Late Cretaceous intertropical regions. However, C4 metabolism is not confined to Kranz anatomy (Vosznesenskaya et al., 2001; Nature 414, p543) which likely evolved in the Miocene. Additionally, C4 metabolism has been identified in cells of stems and petioles of a C3 plant, suggesting that genes for expression of C4 photosynthesis are present in C3 plants, possibly explaining why C4 photosynthesis has evolved independently many times (Hibberd and Quick, 2002; Nature 415, p451) and might have evolved as early at the Late Cretaceous.