Limnological response to the Laacher See eruption (LSE) in an annually laminated Allerød sediment sequence from the Nahe palaeolake, northern Germany

Abstract

This paper presents evidence for a limnological response to the Laacher See eruption (LSE) as detected in lake sediments from Nahe, northern Germany. The sediment section of the Allerød period dating to between 13 422 and 12 708 cal. a BP is preserved in annual laminations. Within this section, the LSE was identified as a cryptotephra layer (12 944±44 cal. a BP). Microfacies analysis, continuous high‐resolution geochemical measurements and pollen analyses enabled a high‐resolution reconstruction of environmental change. The older part of the Allerød (c. 13 422 to 12 943 cal. a BP) was characterized by relatively stable sedimentation conditions. Evidence for windier conditions dating to c. 13 160 to 13 080 cal. a BP probably reflects the Gerzensee oscillation. Pronounced changes of the lake sedimentation followed the LSE. Four unusually thick varves with increased amounts of allochthonous material indicate serious disturbance of the local environment immediately after the LSE, related to increased storminess and/or the occurrence of high intensity rainfall events. A pronounced reduction of biogenic silica accumulation for c. 60 years after the LSE could reflect a period of acidification. Indications of a simultaneous lake level increase until c. 60 years after the LSE are in line with the supposed reduced evapotranspiration associated with cooler conditions. About 120 years after the LSE, increased oxygen access at the lake bottom, allochthonous input and Cl fluxes point to an onset of increasingly stronger westerly winds, probably as a long‐term response to the LSE. This supports the idea of a southward shift of the mid‐latitude westerlies wind system within the interval between the LSE and the beginning of the Younger Dryas. The pace of the southwards shift of this wind system decreased from 10 km a−1 in the initial phase (40–120 years after LSE) to 6 km a−1 in the later phase (120–200 years after LSE).

Small shards and long distances — three cryptotephra layers from the Nahe palaeolake including the first discovery of Laacher See Tephra in Schleswig‐Holstein (Germany)

“…Firstly, only minor and expectable rearrangements of shards can be observed. This is in line with previous results from other approaches (Dreibrodt et al 2020;Krüger et al 2020). Therefore, large-scale rearrangements can be excluded.…”

“…The shift from the Lateglacial to Holocene is reflected in a gradual shift from clayish to calcareous and finally detrital gyttja. Lateglacial mainly organic depositions of 1.6 m thickness contain a 50 cm sequence of very fine annual lamination (Dreibrodt et al 2020;Krüger et al 2020). The sediment cores reached glacial sand at 15.8 m. The chronology is based on AMS radiocarbon dates, pollen events, varve counting and additionally on the identified tephra layers (Dreibrodt et al 2020).…”

“…2). The high resolution of the pollen record allowed a clear distinction between the termination of the (palynologically defined) Gerzensee Oscillation and the timing of cryptotephra deposition (Dreibrodt et al 2020;Krüger et al 2020). It correlates to decreasing Pinus pollen values as well as increasing concentration values of pollen from grasses and herbaceous plants towards the end of the Allerød period.…”

“…Despite numerous palaeo-environmental investigations (Krüger et al 2020 and literature cited therein), a correlation of the individual records is difficult because age modelling is mainly missing, or because of hiatuses (Usinger 1981). The analyses of sediment cores from the Nahe palaeolake (NAH; Dreibrodt et al 2020;Krüger et al 2020) fill a gap in Lateglacial/Early Holocene palaeo-environmental research in Schleswig-Holstein. For the first time a complete Lateglacial to Early Holocene sequence is described without being affected by the Allerød-Younger Dryas hiatus that had been documented for numerous lake sediments in northern Germany and Denmark (Krüger and Damrath 2019;Bennike et al 2004;Usinger 1981).…”

“…For the first time a complete Lateglacial to Early Holocene sequence is described without being affected by the Allerød-Younger Dryas hiatus that had been documented for numerous lake sediments in northern Germany and Denmark (Krüger and Damrath 2019;Bennike et al 2004;Usinger 1981). Furthermore, a sequence of the sediment is annually laminated, allowing for a high resolution of the temporal scale (Dreibrodt et al 2020). Therefore, an attempt was made to identify tephra layers as additional chronological horizons to supplement radiocarbon dating of macrofossils, as volcanic ash layers mainly represent single events.…”