HR: 15:10h
AN: PP23C-07    [Abstracts]
TI: Tectonic Gateways, Circumglobal Currents, and the Stepwise Development of the Great Ocean Conveyor: Inferences From Basinal Benthic Foraminiferal Isotope Syntheses
AU: * Cramer, B S
EM: bscramer@uoregon.edu
AF: Department of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403-1272, United States
AU: Katz, M E
EM: katzm@rpi.edu
AF: Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180, United States
AU: Wright, J D
EM: jdwright@rci.rutgers.edu
AF: Department of Geological Sciences, Rutgers University, Piscataway, NJ 088, NJ 08854, United States
AU: Miller, K G
EM: kgm@rci.rutgers.edu
AF: Department of Geological Sciences, Rutgers University, Piscataway, NJ 088, NJ 08854, United States
AB: We have compiled a database of published benthic foraminiferal stable isotope (δ¹³C, δ¹⁸O) records from ODP and DSDP cores. Comparison of separate trends for the Pacific, North Atlantic, South Atlantic/Subantarctic, and high-latitude Southern Oceans provides insight into the development of the strong nutrient (δ¹³C) and density (δ¹⁸O) gradients that characterize the late Neogene conveyor circulation. The transition occurred in a series of four steps: 1) middle Eocene development of a Southern Ocean- to-Pacific/Atlantic density gradient; 2) early Oligocene development of a density gradient between sub-Antarctic and high-latitude Southern Ocean deep water; 3) early Miocene increase in the Southern Ocean-to-Pacific nutrient gradient; 4) middle--late Miocene development of a strong North Atlantic-to-Pacific nutrient gradient. The middle-- late Miocene development of North Atlantic-to-Pacific nutrient gradients has previously been linked to the near- modern influence of North Atlantic deep water and the development of modern conveyor circulation. We link the middle Eocene--Oligocene development of density gradients to the formation of the Antarctic circumpolar current (ACC), initially as a shallow current allowing substantial outflow of Antarctic bottom water (AABW) and subsequently as a deep current and barrier to lateral flow of AABW. The timing of the changes in density gradients is consistent with recent evidence indicating a middle Eocene opening of the Drake passage to shallow flow and deepening of the passage in the early Oligocene. We interpret weak nutrient and density gradients in the pre- middle Eocene Cenozoic as reflecting deep ocean circulation dominated by diffusive transport with insignificant advective currents, and speculate that strong gradients in the Late Cretaceous reflect a Tethyan circumglobal current that, analogous to the ACC, stabilized bipolar deepwater source regions with distinct density characteristics.
DE: 1620 Climate dynamics (0429, 3309)
DE: 1635 Oceans (1616, 3305, 4215, 4513)
DE: 3036 Ocean drilling
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting