HR: 0800h
AN: PP51B-0587    [Abstracts]
TI: New Constraints on Evolutionary Changes in Coccolithophorid Cell Geometry: Implications for Past pCO₂ Reconstructions
AU: * Henderiks, J
EM: jorijntje.henderiks@geo.su.se
AF: Dept. of Geology and Geochemistry, Stockholm University, Svante Arrheniusväg 8C, Stockholm, SE 106 91 Sweden
AU: Pagani, M
EM: mark.pagani@yale.edu
AF: Dept. of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520 United States
AU: Hall, J
EM: jenney.hall@yale.edu
AF: Dept. of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520 United States
AB: Reconstructions of atmospheric pCO₂, based on δ¹³C values of diunsaturated alkenones and estimates of the total carbon isotopic fractionation during photosynthetic carbon fixation (ε_p37:2), show a distinct decline in pCO₂ during the Oligocene, as well as regionally confined, short-term fluctuations in ε_p37:2 during the Miocene. Additional to surface water [CO₂ (aq)], ε_p37:2 values are controlled by algal growth rates and cell geometry; specifically the ratio of the cell volume to surface area of the cell. Here, we confirm for the first time that substantial evolutionary changes in coccolithophorid cell geometry, based on coccolith morphology, warrant a re-evaluation of pCO₂ reconstructions and interpretations of ε_p37:2 trends. A portion of the ε_p37:2 signal during specific events in the Miocene can be strongly explained by changes in cell geometry, resolving apparent contradictions between ε_p37:2 values and independent nutrient-proxy data from the Miocene record. However, the long term signal cannot be explained by the observed size variability, which in fact implies a steeper slope of change in ε_p37:2 during the Oligocene and possibly higher pCO₂ estimates during the late-middle Eocene.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1055 Organic and biogenic geochemistry
DE: 4930 Greenhouse gases
DE: 4944 Micropaleontology (0459, 3030)
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005