HR: 0830h
AN: PP21C-1184    [PDF]
TI: Middle Miocene Climate Change and Carbon Cycle: Milankovitch Forcing and Deep Ocean circulation in the Western Pacific and Eastern Indian Ocean
AU: * Holbourn, A
EM: ah@gpi.uni-kiel.de
AF: Dept. of Geosciences, Christian-Albrechts-Universitaet, Olshausenstr. 40, Kiel, 24118 Germany
AU: Kuhnt, W
EM: wk@gpi.uni-kiel.de
AF: Dept. of Geosciences, Christian-Albrechts-Universitaet, Olshausenstr. 40, Kiel, 24118 Germany
AU: Schulz, M
EM: mschulz@geo.palmod.uni-bremen.de
AF: Dept. of Geosciences, Universitaet Bremen, Postfach 330 440, Bremen, 28334 Germany
AB: The relation of enhanced carbon burial, carbon isotope excursions and global cooling remains an unsolved problem in the Mesozoic and early Neogene climate history of the Earth. The enigmatic long-term positive carbon isotope excursion between 16.4 and 13.6 Ma ("Monterey excursion") coincided initially with a period of extreme warmth and high sea level (mid-Miocene climate optimum) and a subsequent increase in deep-water oxygen isotopic values, related to the cooling of deep water masses and growth of the East Antarctic ice sheet. High resolution reconstruction of the succession of events reveals a complex relationship between orbital forcing, carbon burial and climate cooling, mediated by a major re-organization of ocean circulation patterns. We used high resolution benthic deep water oxygen and carbon isotopes in combination with new age models at critical locations in a West Pacific marginal basin (South China Sea, ODP Site 1146), in the eastern Indian Ocean (NW Australian margin, ODP Site 761) and in the tropical Pacific (Ontong Java Plateau, ODP Site 806) to investigate the frequency and amplitude of deep water isotope fluctuations during the middle Miocene. Benthic stable isotope records document complete recovery of the six main $\delta$$^{13}$C maxima of the,Monterey Excursion" between 16.4 and 13.6 Ma and the characteristic stepped increase in $\delta$$^{18}$O between 14.5 and 13.1 Ma. At Site 761, the $\delta$$^{18}$O curve shows an excellent match with the global sea level curve between 11.5 and 15.1 Ma, and thus closely reflects changes in global ice volume. Prior to 15.1 Ma, the $\delta$$^{18}$O curve is mainly driven by bottom water temperature. At Site 1146, a major increase in $\delta$$^{18}$O and $\delta$$^{13}$C values (1\permil) at 14.0 Ma, indicates a radical change in the deep water circulation of this marginal West Pacific basin. Spectral analysis of benthic isotopes time series, combined with magnetic susceptibility and color reflectance records, indicate Milankovitch forcing on virtually all proxies and a change from eccentricity to precession driven cyclicity at approximately 14.8 Ma. The $\delta$$^{13}$C curve closely reflects the eccentricity forcing of Laskar's astronomical solution. Strikingly, a period of anomalous eccentricity forcing between approximately 14.8 and 14.1 Ma coincides with the fifth carbon maximum and initiation of major global cooling. Variations in the global carbon cycle modulated by eccentricity probably played a major role in controlling mid Miocene climate evolution.
DE: 3030 Micropaleontology
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 4806 Carbon cycling
DE: 4870 Stable isotopes
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting