Early Paleogene deep-water overturning in the South Atlantic - implications from the ODP Leg 208 Walvis Ridge depth transect

• Applicant: Dr. Dirk Christopher Leuschner
• Subject Area: Palaeontology
• Term: from 2005 to 2010
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 13000175

• Final Report Year: 2010

Final Report Abstract

We analysed a large number of sediment samples recovered from a depth transect along the northern flank of the Walvis Ridge (ODP Leg 208) for their grain size distribution and clay mineral composition. The clay mineral assemblages indicate that environmental conditions in the eastern South Atlantic underwent significant changes during the late Paleogene. These changes were in particular associated with the Early Eocene Climatic Optimum and the Eocene/Oligocene boundary. Differences in the relative abundances of smectite , illite, kaolinite and chlorite, as well as in the illite crystallinity, reflect temporal changes in the sediment provenance and transport mechanisms. The late Paleocene and early Eocene sediments underwent a significant diagenetic overprint, as indicated by the occurrence of clinoptilolite. This overprint, however, does not obliterate the paleoclimatic information of the clay mineral assemblages. In the late Paleogene, abrupt climatic events like the Paleocene-Eocene Thermal Maximum (PETM) at about 55.5 Ma ago and other hyperthermals, with the most pronounced is the Eocene Thermal Maximum 2 (ETM2 or "ELMO"-event) at about 53.5 Ma ago, are of highest interest in recent climate research, in particular, because of their strong impact on oceanic and atmospheric temperature, oceanic chemistry and environment and therefore on the biosphere. It is interesting that these events are documented in the clay mineral assemblages at Walvis Ridge, but that they do not exceed significantly the overall variations. This has major implications. We have no indication for a major change in the oceanic circulation and/or the provenance of the clay minerals deposited at the Walvis Ridge associated with these short events, despite of the intense changes in temperature and ocean water chemistry, that are resulting in a shoaling of the CCD of more than 2000 m in the South Atlantic. The most striking feature in the late Eocene and Neogene record is the occurrence of strong carbonate dissolution phases, as indicated by the increase of the terrigenous silt and clay fraction of the bulk sediment. The dissolution is stronger in the deeper basin and contemporaneous with ephemeral Antarctic ice sheets, implying that the variability of the ice sheets result in major perturbations of the carbon cycle and the shoaling of at least the South Atlantic CCD.

Publications

• 2004. Cenozoic deep-water circulation at the Leg 208 Walvis Ridge depth transect, eastern South Atlantic. ICDP/IODP Euroforum, Bremen, Germany
  Leuschner, D.C., Ehrmann, W.
  
• 2005. Late Quaternary Variability in the Deep Water Exchange Between South Atlantic, Southern and Indian Oceans. AGU Fall Meeting, San Francisco, USA
  Leuschner, D.C. & Ehrmann, W.
  
• 2005. Towards the reconstruction of the Cenozoic deepwater flow at the northern flank of the Walvis Ridge - preliminary clay mineral and grain size data from Site 1265. ODP Leg 208 Post Cruise Meeting, Padova, Italy
  Leuschner, D.C. & Ehrmann, W.
  
• 2007. Early Paleogene deep-water overturning in the South Atlantic (EPASA) - A progress report. ICDP/IODP Kolloquium, Potsdam, Germany
  Leuschner, D.C.
  
• 2007. Indian Ocean SST modulation of past Indian Summer Monsoon. 17th International Congress of the Union of Quaternary Research (INQUA), Cairns, Australia
  Kiefer, T. & Leuschner, D.C.
  
• 2007. Influence of Indian Ocean sea surface temperatures on past Indian Summer Monsoon variations. 3rd Alexander von Humboldt International Conference: The EAST ASIAN MONSOON, Past, Present and Future, Beijing, China
  Leuschner, D.C. & Kiefer, T.
  
• 2007. Late Quaternary variability in the oceanic circulation South of Africa and associated environmental changes on the adjacent continent. 17th International Congress of the Union of Quaternary Research (INQUA), Cairns, Australia
  Leuschner, D.C., Krueger, S., Ehrmann, W., Schmiedl, G., Morgenstern, P., Zarrieß, M., Mackensen, A. & Diekmann, B.
  
• 2007. Paleogene changes in the South Atlantic circulation – Clay mineralogical evidence from the ODP Leg 208 Walvis Ridge transect. ICP 9, Shanghai, China
  Leuschner, D.C.
  
• 2008. Early Paleogene deep-water overturning in the South Atlantic (EPASA) - implications from ODP Leg 208 at Walvis Ridge. ICDP/IODP Kolloquium, Hannover, Germany
  Leuschner, D.C.