HR: 0800h
AN: PP51B-0588    [Abstracts]
TI: Miocene Global Carbon Isotope Shifts and Marine Biological Productivity.
AU: * Diester-Haass, L
EM: l.haass@mx.uni-saarland.de
AF: Universitaet des Saarlandes Zentrum fuer Umweltforschung, Am Markt, Zeile 2, Saarbruecken, 66041 Germany
AU: Billups, K
EM: kbillups@udel.edu
AF: University of Delaware College of MArine Studies, 700 Pilottown Road, Lewes, DE 19958 United States
AB: The Miocene contains two major global carbon isotope shifts: a negative shift during the late Miocene (~8-6 Ma) and a positive shift during the mid-Miocene (16-14 Ma). We aim at deciphering possible changes in marine biological export productivity during these shifts by calculating paleoproductivity in gC/cm*ky from benthic foraminiferal numbers and accumulation rates at a number of sites spanning the world oceans. Our previous work has illustrated that the onset of the late Miocene negative d 13C shift, which has been attributed to enhanced erosion of terrestrial biomass and expansion of C4 plants, is also accompanied by an increase in marine export productivity from lower than present day values up to 2-3 times modern values at six sites (982, 1088, 721, 846, 1146, 1172; Diester-Haass et al, in press; Diester-Haass et al., in preparation). The Mid-Miocene 'Monterey Event', on the other hand, has been attributed to sequestration of organic material in circum-Pacific basins (Vincent and Berger, 1985) or wide spread deposition of brown coal and drowning of carbonate platforms (Föllmi et al., 2005) . For this particular time interval, our initial results from Site 608 (Atlantic Ocean) reveal relatively constant paleoproductivity values similar to modern ones ( about 10 gC/cm*ky) until 16.5 Ma, after which time paleoproductivity begins to increase until the end of our record at 11 Ma. Superimposed on the trend of generally increasing productivity, there are a number of productivity minima spaced roughly 0.5 million years apart. The long term trend in the paleoproductivity finds some similarities in the global composite benthic foraminiferal d 13C record as both proxies show an overall increase until ~14 Ma. Thereafter, however, paleoproductivity continues to increase while d 13C values decrease marking the end of the Monterey excursion. Stable isotope analyses from these same intervals will show to what extend the smaller scale fluctuations in paleoproductivity can be related to changes in the d13C of the oceanic reservoir or regional water masses. Diester-Haass, L., Billups, K., Emeis, K-C., 2005, Paleoceanography, in press. Vincent, E. and Berger, W., 1985, In: The carbon cycle and atmospheric CO2: Natural variations Archaen to present, edited by Sunquist, E.T. and Broecker, W.S., Am.Geophys. Union Monogr. 32,455-468 Föllmi, K.B. et al., 2005, Geol.Soc.Am.Bull., 117/5, 589-619.
DE: 3030 Micropaleontology (0459, 4944)
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4944 Micropaleontology (0459, 3030)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005