SHALLOW WATER TEMPERATURE OSCILLATIONS IN THE CENTRAL EUROPEAN EPICONTINENTAL SEAWAY (MAINZ BASIN) DURING THE OLIGOCENE - A SHELL-BASED RECONSTRUCTION

According to future climate projections continuously rising global temperatures will have dramatic effects on global ice budget and circulation patterns which, in turn, will alter seasonality and decadal variability. Such changes will jeopardize economic hotspots and ecosystems alike and enhance the threat of natural hazards. However, the mode and tempo of these environmental changes are yet poorly constrained and controversially debated, because the validity of numerical climate models is difficult to test.

In this context, the investigation of short-term climate variability in time intervals of the past during which similar boundary conditions were present as the ones predicted for the forthcoming millennia, represent a promising avenue to understand the possible evolution of the future climate. The last time a unipolar glaciation occurred in earth history was during the Early Oligocene. During this time interval, atmospheric CO₂ levels were slightly higher than today, nevertheless, the overall paleogeographic configuration of Europe was comparable to today. Thus, the Oligocene world can be exploited as a fossil testing ground to study the possible consequences of anthropogenic climate forcing.

Here, we present the result of the sclerochronological investigation of three fossil Glycymeris spp. shells collected from the Lower Oligocene (~30 Ma) coastal deposits of the Alzey Formation (Mainz Basin, Germany). Particularly, we analyzed the seasonal δ¹⁸O_shell variations over several consecutive annual increments. Shells were sequentially sampled by milling and yielded three highly resolved (up to few weeks) time-series. The Glycymeris spp. shells recorded both the winter and the summer extremes. Seasonal temperatures oscillated between 12° and 22°C (confidence interval σ = ±0.3°C) and showed significant inter-annual changes. Our results provide more detailed information than ever before on the climate that prevailed in Central Europe during the Oligocene.