HR: 0830h
AN: PP51B-0923    [PDF]
TI: A Closer Look at the Late Miocene-Early Pliocene,Biogenic Bloom".
AU: * Diester-Haass, L
EM: l.haass@mx.uni-saarland.de
AF: Universitaet des Saarlandes, Zentrum fuer Umweltforschung, Am Markt, zeile 2, 66041 Saarbruecken, Saa 66041 Germany
AU: Billups, K
EM: kbillups@UDel.edu
AF: College of Marine Studies, University of Delaware, 700 Pilottown Road, Lewes, DE 19958 United States
AB: A late Miocene-early Pliocene increase in marine biological productivity has been recorded in equatorial upwelling areas of the Indo-Pacific Ocean as well as in the Benguela coastal upwelling area. Before proposing possible causes of the biogenic bloom, we ask two questions: 1) was the biogenic bloom a global event? 2) was the onset of the biogenic bloom simultaneous in different areas? Here we present productivity reconstructions from 3 Atlantic Ocean ODP sites that lie outside of upwelling influence: Site 982 (subpolar North Atlantic); Site 925 (western tropical Atlantic), and Site 1088 (subantarctic South Atlantic). To reconstruct paleoproductivity we use a multiproxy approach based on benthic foraminiferal accumulation rates (and thus derived paleoproductivity after Herguera, 2000), Uvigerina counts, and mass accumulation rates of bulk carbonate and planktic foraminifera. Our results indicate a three-fold increase in paleoproductivity during the late Miocene/early Pliocene climate transition. The timing, however, of productivity maxima differs among the sites. At subantarctic site 1088 productivity increases rapidly at ~7.5 Ma reaches a maximum between 7.5 and 6.6 Ma and decreases again 6.6 Ma. At tropical Atlantic site 925 our reconstructions indicate an increase at 7 Ma, a peak at 6.8-6.5 Ma and a decrease toward 6 Ma. At subpolar site 982, productivity increases gradually from 9 Ma to 5.4 Ma, rapidly at 5.4 Ma, and then decreases gradually again between 5 and 4 Ma. Only at sites 1088 and 925 can we observe an association between paleoproductivity maxima and decreasing benthic foraminiferal \d13C values during the late Miocene \d13C shift. These results suggest that placing the paleoproductivity events into a context of oceanic nutrient levels linked to changes in external (e.g., weathering and gateways) boundary conditions and internal (e.g., ocean circulation) boundary conditions will be complex.
DE: 3030 Micropaleontology
DE: 4267 Paleoceanography
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting