HR: 1340h
AN: PP33A-1557    [Abstracts]
TI: Middle Miocene Antarctic Ice Sheet Dynamics, Deep-Sea Temperatures, and Global Carbon Cycling: A Southern Ocean Perspective
AU: * Shevenell, A E
EM: ashevenell@ocean.washington.edu
AF: University of California Santa Barbara, Department of Geological Sciences, Santa Barbara, CA 93106-9630 United States
AU: Kennett, J
EM: kennett@geol.ucsb.edu
AF: University of California Santa Barbara, Department of Geological Sciences, Santa Barbara, CA 93106-9630 United States
AU: Lea, D
EM: lea@geol.ucsb.edu
AF: University of California Santa Barbara, Department of Geological Sciences, Santa Barbara, CA 93106-9630 United States
AB: Benthic foraminifer ( Cibicidoides mundulus) magnesium/calcium data from the Southern Ocean reveal a ~2°C cooling of regional bottom waters during the middle Miocene climate transition (14.2-13.8 Ma), which indicates that the globally recognized ~1‰ δ¹⁸O increase (~14 Ma) describes a major expansion of the Antarctic cryosphere. A record of seawater δ¹⁸O, calculated using paired C. mundulus Mg/Ca and δ¹⁸O records, suggests that Antarctic ice sheets entered an interval of eccentricity-modulated glacial advance and retreat at ~15 Ma, approximately one million years before the ~1‰ middle Miocene δ¹⁸O increase. Glacial episodes increased in intensity between ~15 and 13.8 Ma, revealing a central role for internal climate feedbacks in this major Cenozoic climate transition. Comparison of ice volume, paleotemperature, and paleo-pCO₂ records indicates that middle Miocene expansion of the Antarctic cryosphere coincided with an interval of relatively warm Southern Ocean waters and inferred low atmospheric pCO₂. This relationship confirms that changes in heat and moisture transport were important in the development of the Antarctic cryosphere and that atmospheric pCO₂ concentrations may dictate the sensitivity of the Antarctic system to low-latitude-derived heat and moisture.
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1065 Major and trace element geochemistry
DE: 4910 Astronomical forcing
DE: 4924 Geochemical tracers
DE: 4930 Greenhouse gases
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005