Increased hydroclimate variability in midlatitude Europe during the middle Eocene greenhouse

The extent of continental mid-latitude hydroclimate variability during Eocene warm periods is still poorly understood due to the lack of temporal resolution, coherence of preserved records or lack of proxies capable of accurately quantifying changes in the hydrological cycle. Here, we utilize the hydrogen and carbon isotopic composition of plant waxes preserved within varved maar sediments of the UNESCO World Heritage Site ‘Messel Fossil Pit’ (Germany) to reconstruct a high-resolution hydroclimate record between 47.7 and 47.2 Ma. Biomarker hydrogen isotopic ( δ 2 H) variability of up to 45‰ is only little affected by contemporaneous temperature change and thus suggests that the hydrological cycle was partly decoupled from the mid-latitude temperature history. Instead, the δ 2 H variability indicates that Central Europe received moisture from different source areas characterized by distinct isotopic signatures due the fragmented paleogeography of Europe during the Eocene. In our analysis, we reconstructed changes in relative humidity by coupling biomarker δ 2 H and temperature data obtained from identical stratigraphic levels. Relative humidity varied by up to 60% during the time period investigated here. Crucially, the amplitude of relative humidity changes decreased from 47.7 to 47.2 Ma. This observation coincides with changes in plant fossil assemblages and follows the long-term transition from a high to low 400 kyr eccentricity orbital configuration. We therefore suggest, that orbitally-driven changes in Northern Hemisphere insolation drove the hydroclimatic trends at Messel. • Time-continuous ~500 kyr Eocene n -alkane-derived hydroclimate record from Germany. • Hydroclimate partly decoupled from temperature history in Eocene Central Europe. • Strong hydroclimate variability likely driven by changes in Earth orbital cycles.