How dry was the Younger Dryas? Evidence from a coupled <i>δ</i><sup>2</sup>H–<i>δ</i><sup>18</sup>O biomarker paleohygrometer applied to the Gemündener Maar sediments, Western Eifel, Germany

Abstract

Abstract. Causes of the Late Glacial to Early Holocene transition phase and particularly the Younger Dryas period, i.e. the major last cold spell in central Europe during the Late Glacial, are considered to be keys 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 the Gemündener Maar in the Western Eifel, Germany. We analysed the hydrogen (δ2H) and oxygen (δ18O) stable isotope composition of leaf-wax-derived lipid biomarkers (n-alkanes C27 and C29) and a hemicellulose-derived sugar biomarker (arabinose), respectively. Both δ2Hn-alkane and δ18Osugar are suggested to reflect mainly leaf water of vegetation growing in the catchment of the Gemündener Maar. Leaf water reflects δ2H and δ18O of precipitation (primarily temperature-dependent) modified by evapotranspirative enrichment of leaf water due to transpiration. Based on the notion that the evapotranspirative enrichment depends primarily on relative humidity (RH), we apply a previously introduced “coupled δ2Hn-alkane–δ18Osugar paleohygrometer approach” to reconstruct the deuterium excess of leaf water and in turn Late Glacial–Early Holocene RH changes from our Gemündener Maar record. Our results do not provide evidence for overall markedly dry climatic conditions having prevailed during the Younger Dryas. Rather, a two-phasing of the Younger Dryas is supported, with moderate wet conditions at the Allerød level during the first half and drier conditions during the second half of the Younger Dryas. Moreover, our results suggest that the amplitude of RH changes during the Early Holocene was more pronounced than during the Younger Dryas. This included the occurrence of a “Preboreal Humid Phase”. One possible explanation for this unexpected finding could be that solar activity is a hitherto underestimated driver of central European RH changes in the past.

Cryogenic cave carbonates in the Dolomites (northern Italy): insights into Younger Dryas cooling and seasonal precipitation

“…MAAT Modern-Allerød = −2 • C), consistent with regional proxy data (e.g. Ilyashuk et al, 2009). As stalagmite Cioc1 was actively growing in the Bølling interstadial (see the Results section), we assume that no permafrost was present at the site at the start of the interstadial.…”

“…Lotter et al, 2000), consistent with a 3.5 • C drop in July air temperatures reported from the Maloja Pass (Fig. 6) in eastern Switzerland (Ilyashuk et al, 2009). We therefore consider 0.3 and 4 • C as minimum and maximum estimates of YD summer cooling, respectively, relative to the Bølling-Allerød.…”

“…(a) NGRIP δ 18 O data(Rasmussen et al, 2014) and (b) lacustrine benthic ostracod δ 18 O data from Ammersee(von Grafenstein et al, 1999). YD palaeotemperature reconstructions are shown by (c) chironomid-inferred July air temperatures from the Maloja Pass(Ilyashuk et al, 2009) and by (d) MAAT inferred from fluid inclusion stable isotope data on stalagmites and speleothem δ 18 O data from Milandre Cave(Affolter et al, 2019). CCC ages are compared to (e) speleothem δ 18 O data from Hölloch Cave(Li et al, 2021) and (f) the extent of central and southern Alpine palaeoglaciers(Heiri et al, 2014b).…”

Leaf Waxes and Hemicelluloses in Topsoils Reflect the δ2H and δ18O Isotopic Composition of Precipitation in Mongolia

“…These compounds and their compound-specific stable hydrogen (δ 2 H n-alkane ) and oxygen (δ 18 O sugar ) isotopic composition get incorporated into soils through above-ground and root litter, abrasion, as well as grazing (dung), and they have a mean residence time of ∼40 years (leaf wax n-alkanes), while pentoses (including the hemicellulose-derived sugar arabinose) average over ∼20 years (Schmidt et al, 2011). Since δ 2 H n-alkane and δ 18 O sugar are not strongly affected by degradation effects (Zech et al, 2011(Zech et al, , 2012, they are increasingly used for paleohydrological reconstructions (Aichner et al, 2015;Hepp et al, 2015Hepp et al, , 2019Thomas et al, 2016;Rach et al, 2017;Schäfer et al, 2018;Bliedtner et al, 2020). Usually, they are interpreted to record the isotopic composition of precipitation (Sachse et al, 2006(Sachse et al, , 2012Tuthorn et al, 2015;Hou et al, 2018;Hepp et al, 2020), which in turn is long acknowledged as a valuable proxy for paleoclimate reconstructions and controlled by e.g., the temperature and amount effect, continentality, and altitude (Dansgaard, 1964).…”

Evaluation of bacterial glycerol dialkyl glycerol tetraether and <sup>2</sup>H–<sup>18</sup>O biomarker proxies along a central European topsoil transect

“…Deep-rooting species most likely use the water from deeper soil horizons and/or shallow groundwater, which is equal to the (weighted) mean annual precipitation (e.g. Herrmann et al, 1987). Shallowrooting plants take up water from upper soil horizons, which is influenced by seasonal variations in δ 2 H precipiation and δ 18 O precipiation and by soil water enrichment (Dubbert et al, 2013).…”