HR: 14:25h
AN: PP53D-04 INVITED     [Abstracts]
TI: How Reliable are Plants as CO$_{2}$ Proxies: Lessons From the Late Cenozoic
AU: * Kuerschner, W
EM: w.m.kuerschner@bio.uu.nl
AF: Utrecht University, Dept. of Palaeoecology, Lab. of Palaeobotany and Palynology,, Budapestlaan 4, Utrecht, 3584CD Netherlands
AU: Wagner, F
EM: f.wagner@bio.uu.nl
AF: Utrecht University, Dept. of Palaeoecology, Lab. of Palaeobotany and Palynology,, Budapestlaan 4, Utrecht, 3584CD Netherlands
AU: van Hoof, T
EM: T.B.vanHoof@bio.uu.nl
AF: Utrecht University, Dept. of Palaeoecology, Lab. of Palaeobotany and Palynology,, Budapestlaan 4, Utrecht, 3584CD Netherlands
AU: Kouwenberg, L
EM: L.L.R.Kouwenberg@bio.uu.nl
AF: Utrecht University, Dept. of Palaeoecology, Lab. of Palaeobotany and Palynology,, Budapestlaan 4, Utrecht, 3584CD Netherlands
AU: Visscher, H
EM: h.visscher@bio.uu.nl
AF: Utrecht University, Dept. of Palaeoecology, Lab. of Palaeobotany and Palynology,, Budapestlaan 4, Utrecht, 3584CD Netherlands
AB: Stomatal frequency analysis is a biological proxy for palaeo-atmospheric CO$_{2}$ reconstructions. As a biological proxy it depends on the careful calibration of the plant response by growth experiments, field observations and comparative studies with other independent CO$_{2}$ archives (ice core and geochemical proxy records). The present contribution summarizes recent advancements in the development and validation of the method. Quantification techniques, the reproducibility of Holocene stomatal frequency records and the comparison with available ice core records are evaluated: (1) In order to address the potential influence of local environmental changes or methodological insufficiencies on the CO$_{2}$ reconstructions, multiple stomatal frequency records are compared for three climatic key periods during the Holocene. It appears that stomatal frequency records from different continents and plant species using different calibration techniques are reproducible. (2) Differences with Holocene ice-based CO$_{2}$ records are evaluated by applying a firn gas diffusion model to a stomatal frequency based CO$_{2}$ record. It allows to test the potential influence of smoothing during gas enclosure on the temporal resolution as well as the amplitude of CO$_{2}$ fluctuations. Apparently, the large discrepancies between ice core and stomatal frequency records diminish when the effect of natural smoothing of the ice core CO$_{2}$ record is simulated with the raw data obtained from stomatal frequency record. These results indicate that the differences derived by the two methods may be less significant than previously thought. (3) Having discussed some critical issues of the Holocene stomatal frequency records we will move to the Middle Miocene, a key period of Neogene climate evolution. In the marine record a marked positive \delta$^{13}$C shift between about 17.5 Ma and 13.5 Ma indicates enhanced biological productivity and burial of organic carbon, which in turn may have resulted into a drastic depletion in atmospheric CO$_{2}$ concentration and finally into global cooling (Monterey hypothesis). Multiple stomatal frequency records from Europe and N-America corroborate the predicted CO$_{2}$ drawdown during the period of the Monterey C isotope excursion.
DE: 1610 Atmosphere (0315, 0325)
DE: 1615 Biogeochemical processes (4805)
DE: 1620 Climate dynamics (3309)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting