HR: 15:25h
AN: PP23C-08    [Abstracts]
TI: Pacific circulation during the middle Miocene climate transition (12-17 Ma)
AU: * Holbourn, A
EM: ah@gpi.uni-kiel.de
AF: Institute of Geosciences, Christian-Albrechts-University, Olshausenstr. 40, Kiel, D-24118, Germany
AU: Kuhnt, W
EM: wk@gpi.uni-kiel.de
AF: Institute of Geosciences, Christian-Albrechts-University, Olshausenstr. 40, Kiel, D-24118, Germany
AU: Haley, B
EM: bhaley@ifm-geomar.de
AF: Leibniz Institute of Marine Sciences, Wischhofstr. 1-3, Kiel, D-24148, Germany
AU: Mix, A
EM: mix@coas.oregonstate.edu
AF: COAS, Oregon State University, 104 COAS Admin Bldg, Corvallis, OR 97331-5, United States
AU: Andersen, N
EM: nandersen@leibniz.uni-kiel.de
AF: Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Christian- Albrechts-University, Max-Eyth-Str. 11-13, Kiel, D-24118, Germany
AB: We present planktonic and benthic foraminiferal Mg/Ca, δ¹³C and δ¹⁸O as well as census counts and carbonate dissolution proxy data in four ODP cores from the northwestern, central and southeastern Pacific to monitor SST/salinity gradients, thermocline evolution and deep-water ventilation during the middle Miocene climate transition (17-12 Ma). We additionally use Nd isotopes as water mass tracers to track the origins of intermediate and deep water masses during intervals of major climate and circulation change. Our results indicate three main Pacific circulation modes exhibiting different imprints of orbital variations: (1) "Climate Optimum" mode prior to 14.7 Ma characterized by poorly ventilated deep water with prominent 100 kyr variability; (2) transitional mode from 14.7 to 13.9 Ma, principally driven by obliquity and marked by transient improvement in deep-water ventilation as well as surface warming in the subtropical West Pacific; (3) "Icehouse" mode after 13.9 Ma, paced by short eccentricity (100 kyr) and characterized by CCD deepening and increased influence of well ventilated southern sourced deep water. The onset of the transitional and "Icehouse" modes coincided with prominent global positive δ¹³C excursions and increasing stratification in the subtropical West Pacific (higher δ¹⁸O gradients between surface and intermediate/deep waters). Therefore, our results suggest that Antarctic glaciation events were synchronous with the development or expansion of a West Pacific Warm Pool and the establishment of a more vigorous deep water circulation.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 9355 Pacific Ocean
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting