HR: 0800h
AN: OS11A-0182    [Abstracts]
TI: Organic Walled Dinoflagellate Cysts and the Middle Eocene Climatic Optimum (MECO): Preliminary results from ODP leg 120, Kerguelen Plateau.
AU: * Houben, S
EM: a.j.p.houben@students.uu.nl
AF: Palaeoecology, Institute of Environmental Biology, Utrecht University, Budapestlaan 4, Utrecht, NL-3584CD, Netherlands
AU: Brinkhuis, H
EM: h.brinkhuis@uu.nl
AF: Palaeoecology, Institute of Environmental Biology, Utrecht University, Budapestlaan 4, Utrecht, NL-3584CD, Netherlands
AU: Bohaty, S
EM: s.bohaty@noc.soton.ac.uk
AF: School of Ocean and Earth Science, National Oceanography Centre, Southampton, University of Southampton, European Way SO14 3ZH, Southampton, SO14 3ZH, United Kingdom
AU: Reichart, G
EM: reichart@geo.uu.nl
AF: Department of Earth Sciences - Geochemistry, Faculty Geosciences, Utrecht University, Budapestlaan 4, Utrecht, NL-3584CD, Netherlands
AU: Sluijs, A
EM: a.sluijs@uu.nl
AF: Palaeoecology, Institute of Environmental Biology, Utrecht University, Budapestlaan 4, Utrecht, NL-3584CD, Netherlands
AU: Zachos, J C
EM: jzachos@pmc.ucsc.edu
AF: Department of Earth Sciences, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA CA-95064, United States
AB: The Middle Eocene (~ 50-35 Ma) is generally considered as a period of gradual cooling in Earth's transition from the greenhouse into the icehouse. Recently however, oxygen-isotope based studies showed a ~ 600 kyr episode of warming in the Southern Ocean at ~ 41.5 Ma, termed the Middle Eocene Climatic Optimum (MECO). Documentation of potential biotic change during the MECO is very limited. To evaluate if the MECO exhibited a response in algal communities we are currently studying remains of dinoflagellates, i.e. their cysts. Here we present preliminary results from a pelagic ooze from the Indian sector of the Southern Ocean (ODP leg 120 site 748B, Kerguelen Plateau), which comprise the first Eocene well-preserved open ocean dinocyst assemblages ever encountered. Preceding the MECO event, a typical Southern Oceanic offshore community flourished. In contrast, during the MECO, an increasingly cosmopolitan assemblage persisted. Furthermore, low-salinity tolerant species were present in a number of pulses. Remarkably, two huge abundance peaks (acmes) of the cosmopolitan marker Thalassiphora pelagica occurred. According to benthic oxygen isotopes, the first acme occurred during a phase of initial cooling just prior to the MECO. The second acme occurred just after rapid cooling that apparently terminated the MECO. Such acmes are generally considered to reflect strongly stratified water masses. After the MECO, the endemic open oceanic community reappeared. Our preliminary results strongly suggest that, at least in the Southern Ocean, major oceanographic and biotic reorganizations took place during this period of climate change. In order to elucidate the further constraints of the MECO-event, dinocyst-specific stable carbon isotopes and TEX paleo-thermometry will be applied.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1630 Impacts of global change (1225)
DE: 4855 Phytoplankton
DE: 4950 Paleoecology
DE: 4952 Palynology
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting