Branched glycerol dialkyl glycerol tetraethers (brGDGTs) from maar sediments were analyzed in order to reconstruct continental air temperatures across a middle Eocene (47.2 Ma) hyperthermal event. Additionally, carbon isotopes of total organic carbon (δ13C TOC) were measured from the same samples to reconstruct changes in global and local carbon cycle. Measurements for both, brGDGTs and carbon isotopes, were carried out between beginning of 2021 and end of 2022. Based on the current age model the temporal resolution of the samples is millennial to sub-millennial. Sediment samples (organic-rich pelites) are from the FB2001 drill core, recovered from the Messel Fossil Site located in the vicinity of Frankfurt, Germany. The brGDGTs were solvent extracted by Soxhlet apparatus and further analyzed by high-performance liquid chromatography (HPLC-) - atmospheric pressure chemical ionization (APLCI-) - mass spectrometry (MS). Aliquots for total organic carbon isotope measurements were decalcified with HCl (10%) prior analyses on a Flash Elemental Analyzer.
The greenhouse to icehouse climate transition from the Eocene into the Oligocene is well-documented by sea surface temperature records from the southwest Pacific and Antarctic margin that show evidence of pronounced long-term cooling. However, identification of a driving mechanism depends on a better understanding of whether this cooling was also present in terrestrial settings. Here, we present a semi-continuous terrestrial temperature record spanning from the middle Eocene to the early Oligocene (~41-33 Ma), using bacterial molecular fossils (biomarkers) preserved in a sequence of SE Australian lignites from two locations. We reconstruct terrestrial temperatures and compare them to existing sea-surface temperature records from the Southern Hemisphere from the middle Eocene to Early Oligocene.