Elevated CO2 levels in the Peri-Tethys during the Middle Eocene Climatic Optimum

Abstract

The Middle Eocene Climatic Optimum (MECO) is a phase of climate warming that occurred ∼40 Ma, encountered globally as a negative δ18O excursion. To examine its cause and exceptional duration of 500,000 years, more knowledge on the carbon cycle during the MECO is required. Therefore, this thesis presents a CO2 reconstruction based on carbon fractionation of bulk organic matter from Eocene shelf sediments deposited in the Peri-Tethys. To test if bulk organic matter primarily represents a marine signal, the BIT index and C:N were applied. A TEX86 temperature reconstruction was performed as sea-surface temperatures must be accounted for when reconstructing CO2. Finally, carbonate content and total organic carbon were calculated to study environmental effects of the MECO and test if carbonate deposition shifted from the deep ocean to the shelves, as is hypothesized to explain the remarkable duration of the MECO. The position of the MECO was successfully determined using δ18O. It coincides with a distinctive TOC increase and carbonate decrease, possibly due to changes in productivity, oxygen conditions and/or carbonate production. BIT index and C:N indicate negligible to low terrestrial input throughout the section and reconstructed temperatures suprisingly indicate no warming during the MECO. Finally, a CO2-level increase of at least 50-350 ppmv during the MECO is inferred.