HR: 0800h
AN: PP11A-0541    [Abstracts]
TI: Middle Eocene to early Oligocene paleoceanography of the Southern Ocean from foraminiferal stable isotope and Mg/Ca records
AU: * Bohaty, S M
EM: sbohaty@es.ucsc.edu
AF: Earth Sciences Department/ Institute of Marine Sciences, 1156 High Street University of California, Santa Cruz, Santa Cruz, CA 95064 United States
AU: Zachos, J C
EM: jzachos@es.ucsc.edu
AF: Earth Sciences Department/ Institute of Marine Sciences, 1156 High Street University of California, Santa Cruz, Santa Cruz, CA 95064 United States
AU: Delaney, M L
EM: delaney@ucsc.edu
AF: Ocean Sciences Department/ Institute of Marine Sciences, 1156 High Street University of California, Santa Cruz, Santa Cruz, CA 95064 United States
AB: The middle Eocene to early Oligocene is a critical phase of Cenozoic climatic evolution, characterized by long-term cooling of deep waters and the first appearance of large Antarctic ice sheets. The Southern Ocean is a key area for monitoring Eocene-Oligocene climatic variability, and development of high-resolution paleoceanographic records from this region is crucial to evaluating possible mechanisms of long-term climate change. These records will ultimately help constrain the timing and nature of middle-to-late Eocene cooling and ice buildup on Antarctica in relation to the timing of major paleogeographic changes, especially the opening of Southern Ocean gateways, and independent records of {\it p}CO2 variability. We have generated high-resolution stable isotope records from ODP Sites 689, 702, 738, and 748 in the Atlantic and Indian sectors of the Southern Ocean. These sites are separated by considerable distances, but the records display coherent trends with several unique features. These features enable detailed site-to-site correlation and indicate that a common paleoceanographic history is shared by all study sites. The late middle Eocene records are punctuated by a strong, transient warming event at $\sim$41 Ma. This event is followed by an increase in $\delta$$^{18}$O values that culminates at $\sim$37 Ma, indicative of long-term cooling and/or growth of small ice sheets. This is followed by an inferred brief warming in the early late Eocene ($\sim$36.5-36.0 Ma), and a slight cooling step at ($\sim$35.5 Ma). A period of relative stability in the latest Eocene precedes the well-documented $\sim$1.4$\permil$ increase in $\delta$$^{18}$O (the Oi-1 event) in the earliest Oligocene. In addition to the stable isotope records, we are developing high-resolution planktonic foraminiferal Mg/Ca records. The primary goal of this work is to separate the ice-volume and temperature contributions to the Eocene-Oligocene $\delta$$^{18}$O signal. Our initial focus is on the early Oligocene Oi-1 event, which is thought to represent the first major Cenozoic buildup of large ice sheets in East Antarctica. At Site 748, Mg/Ca data from the thermocline-dweller Subbotina angiporoides indicate a significant decrease in temperature in the earliest Oligocene. These data are interpreted to represent a 2-3$\deg$C cooling at the Oi-1 transition. Removal of this temperature component from the oxygen isotope signal retains a significant ice volume signature. A minimum of 60% modern ice volume is estimated during peak Oi-1 glaciation.
DE: 4870 Stable isotopes
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting