HR: 0830h
AN: PP41C-0850    [PDF]
TI: A 9 Million Year Long High-Resolution Benthic $\delta$$^{13}$C and $\delta$$^{18}$O Record: Implications for Late Oligocene to Middle Miocene Paleoceanography
AU: * Frazier, J M
EM: jfrazier@es.ucsc.edu
AF: Univ. of California, Santa Cruz, Earth Sciences Dept., Santa Cruz, CA 95064 United States
AU: Zachos, J C
EM: jzachos@es.ucsc.edu
AF: Univ. of California, Santa Cruz, Earth Sciences Dept., Santa Cruz, CA 95064 United States
AU: Sluijs, A
EM: a.sluijs@students.uu.nl
AF: Utrecht Univ., Geobiology Dept., Utrecht, 3584 CD Netherlands
AU: Shackleton, N J
EM: njs5@cam.ac.uk
AF: Cambridge Univ., Godwin Laboratory for Quaternary Research, Cambridge, CB2 3RS United Kingdom
AB: We present a high-resolution (~3 ky) stable isotope time series based on benthic foraminifera data collected from ODP site 926 on Ceara Rise in the western equatorial Atlantic. With data from a second Site 929, the combined record continuously spans a period of almost 9 million years (17.8-26.7 Ma). The age model is based on tuning to a new orbital solution (Laskar 2002). This work extends previously published records deeper into the Oligocene and further into the Miocene in an attempt to create a continuous time-series with the resolution to resolve paleoclimatic change on orbital to tectonic time-scales. As observed previously, the long-term $\delta$$^{13}$C and $\delta$$^{18}$O records collected from benthic foraminifera {\it C. mundulus} display pervasive cyclic responses at all Milankovitch frequencies with power largely concentrated in the obliquity and 400 kyr eccentricity bands. Cross-spectral analysis of these records and orbital curves indicates a high degree of correlation at all primary Milankovitch periods. The extended, spliced record reveals several new features. Over the long-term, the $\delta$$^{18}$O record now captures the structure of the late Oligocene warming which initiates at roughly 26.5 Ma, and through a series of steps, peaks by 24.5 Ma, before the initiation of cooling at 23.5 Ma. Over the short-term, high frequency $\delta$$^{13}$C cycles with amplitudes in excess of 0.5$\permil$ are evident throughout the record. However, the amplitudes are noticeably higher during two periods, 25.9 to 26.7 Ma in the late Oligocene, and 17.9 to 19.5 Ma in the early Miocene, with minimum falling as low as -1.0$\permil$ during the former. The extreme amplitudes of these $\delta$$^{13}$C cycles suggest vertical migration of a mixing line between two water masses, Northern and Southern Component water, implying changes in deep water circulation. Carbonate dissolution proxies support this inference.
DE: 3030 Micropaleontology
DE: 4283 Water masses
DE: 4870 Stable isotopes
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting