HR: 0800h
AN: PP11A-0550    [Abstracts]
TI: Orbitally Paced Climate Variability During the Middle Miocene: High Resolution Stable Isotopes and Fe Records From the Western and Southeastern Pacific
AU: * Holbourn, A
EM: ah@gpi.uni-kiel.de
AF: Department of Geosciences, Christian-Albrechts-University, Olshausenstr. 40, Kiel, 24118 Germany
AU: Kuhnt, W
EM: wk@gpi.uni-kiel.de
AF: Department of Geosciences, Christian-Albrechts-University, Olshausenstr. 40, Kiel, 24118 Germany
AU: Schulz, M
EM: mschulz@palmod.uni-bremen.de
AF: Department of Geosciences, Bremen University, Postfach 330 440, Bremen, 28334 Germany
AU: Erlenkeuser, H
EM: HErlenkeuser@leibniz.uni-kiel.de
AF: Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Christian-Albrechts-University, Max-Eyth-Str. 11-13, Kiel, 24118 Germany
AB: We present continuous high resolution middle Miocene benthic foraminiferal isotope ($\sim$ 4-ky) and XRF scanner Fe ($<$ 1-ky) records from two deep-sea cores in the western and southeastern Pacific (ODP Sites 1146 and 1237). These records provide new insights into the pacing of climatic variability across the middle Miocene climate transition. Spectral analyses of the $\delta$$^{13}$C records from Sites 1146 and 1237 and the Fe record from Site 1237 reveal spectral power concentrated in the eccentricity band (400-ky, 100-ky) over the time interval from 13 to 17 Ma. In the $\delta$$^{18}$O records, a switch occurs at $\sim$ 14.9 Ma from predominant 100-ky eccentricity to 41-ky obliquity periodicity, suggesting a shift in the ocean-climate response to orbital forcing from the low to the high latitudes. The $\delta$$^{18}$O obliquity signal, mainly attributed to the waxing and waning of an expanded southern polar ice sheet, is pervasive in the $\delta$$^{18}$O records until $\sim$ 13.9 Ma, when a sharp increase in $\delta$$^{18}$O values indicates a further climatic transition (major expansion of East Antarctic Ice Sheet). This critical step into the "icehouse-world" coincided with a further switch in the $\delta$$^{18}$O records from the obliquity (41-ky) to the eccentricity (100-ky) band.
DE: 9355 Pacific Ocean
DE: 9604 Cenozoic
DE: 4870 Stable isotopes
DE: 4267 Paleoceanography
DE: 1620 Climate dynamics (3309)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting