How dry was the Younger Dryas? Evidence from a coupled δ 2 H-δ 18 O biomarker paleohygrometer, applied to the Lake Gemündener Maar sediments, Western Eifel, Germany

Abstract. The Late Glacial to Early Holocene transition phase and particularly the Younger Dryasperiod, i.e. the major last cold spell in Central Europe during the Late Glacial, are considered crucial for understanding rapid natural climate change in the past. The sediments from Maar lakes in the Eifel, Germany, have turned out to be valuable archives for recording such paleoenvironmental changes. For this study, we investigated a Late Glacial to Early Holocene sediment core that was retrieved from Lake Gemundener Maar in the Western Eifel, Germany. We analysed the hydrogen (δ 2 H) and oxygen (δ 18 O) stable isotope composition of leaf wax-derived lipid biomarkers ( n -alkanes C 27 and C 29 ) and hemicellulose-derived sugar biomarkers (arabinose), respectively. Both δ 2 H and δ 18 O are suggested to reflect mainly leaf water of vegetation growing in the catchment of the Gemundener Maar. This enables the coupling of the results via a δ 2 H-δ 18 O biomarker paleohygrometer approach and allows calculating past relative air humidity values, which is the major advantage of the applied approach. Fundamental was the finding that the isotopic enrichment of leaf water due to evapotranspiration depends mainly on relative humidity. We hence use the coupled δ 2 H-δ 18 O biomarker approach to reconstruct the deuterium-excess of leaf water and in turn relative air humidity values corresponding to the vegetation period and daytime (RH dv ). Most importantly, the results of the coupled δ 2 H-δ 18 O biomarker paleohygrometer approach (i) support a two-phasing of the Younger Dryas, i.e. a relative wet phase (on Allerod level) followed by a drier Younger Dryasending, (ii) do not corroborate overall drier climatic conditions characterising the Younger Dryasor a two-phasing with regard to a first dry and cold Younger Dryasphase followed by a warmer period along with increasing precipitation amounts, and (iii) suggest that the amplitude of RH dv changes during the Early Holocene was more pronounced compared to the Younger Dryas. One possible driver for the unexpected Lake Gemundener Maar RH dv variations could be the solar activity.