HR: 0800h
AN: PP11A-0557    [Abstracts]
TI: Cenozoic variations in the South Atlantic carbonate saturation profile: Insights from the Walvis depth-transect (ODP Leg 208)
AU: * Schellenberg, S A
EM: schellenberg@geology.sdsu.edu
AF: Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, Ca 92182-1020 United States
AU: Nielsen, J L
EM: jnielsen@rohan.sdsu.edu
AF: Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, Ca 92182-1020 United States
AB: Ocean Drilling Program Leg 208 Science Party (D. Kroon, J. C. Zachos, P. Blum, J. Bowles, P. Gaillot, T. Hasegawa, E. C. Hawthorne, D. A. Hodell, D. C. Kelly, J. Jung, S. M. Keller, Y. Lee, D. C. Leuschner, Z. Liu, K. C. Lohmann, L. Lourens, S. Monechi, M. Nicolo, I. Raffi, C. Riesselman, U. R”hl, D. Schmidt, A. Sluijs, D. Thomas, E. Thomas, H. Vallius) Carbonate saturation profiles are complex and dynamic products of processes operating on temporospatial scales from the "short-term local" (e.g. carbonate export production) to the "long-term global" (e.g. carbonate-silicate weathering, shelf:basin carbonate partitioning). Established, if admittedly crude, proxies for reconstructing carbonate saturation from sediments include wt% carbonate, where values of 0-20% are typically attributed to deposition below the carbonate compensation depth (CCD), and planktonic foraminifer fragmentation, where enhanced fragmentation is typically attributed to deposition below the lysocline. Ocean Drilling Program Leg 208 successfully drilled a six-site Walvis Ridge depth-transect spanning modern water depths from 2,717 to 4,755 m. Exceptional core recovery, well-constrained biomagnetostratigraphy, and standard crustal subsidence corrections provide a working age-depth framework for contouring ship-board wt% carbonate determinations and identifying the following first-order features of the regional CCD: (1) $>$3.5 km position from 60-48 Ma punctuated by a major transient shoaling to $<$2 km during the Paleocene-Eocene Thermal Maximum at $\sim$55 Ma; (2) shoaling to $\sim$2.75 km from 48 to 44 Ma; (3) subsequent deepening to $>$4.25 km from 37 to 28 Ma; (4) marked high amplitude fluctuations from 28 to 20 Ma followed by deepening to $>$4.75 km; (5) transient shoaling to $\sim$4 km around 15 Ma followed by deepening to $>$4.75 km by $\sim$12 Ma. These first-order features are broadly congruent with classic Atlantic CCD reconstructions by van Andel (1975) and Berger and Roth (1975). A wealth of higher frequency variation in carbonate saturation is clearly preserved within the Leg 208 depth-transect. Ongoing shore-based analyses aim to transform cm-scale variations in core physical properties (i.e. magnetic susceptibility, color reflectance) into synthetic records of wt% carbonate. These data, combined with other proxies (e.g., planktonic foraminifer fragmentation, stable isotopes) and placed within the evolving post-cruise biomagnetostratigraphic and cyclostratigraphic age-model, will provide valuable constraints on cyclic and secular fluctuations in the South Atlantic carbonate saturation profile and their relation to other major components of the earth system (e.g. pCO$_{2}$, eustacy).
DE: 9325 Atlantic Ocean
DE: 9604 Cenozoic
DE: 4806 Carbon cycling
DE: 4863 Sedimentation
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting