Limnological response to the Laacher See eruption (LSE) in an annually laminated Allerød sediment sequence from the Nahe palaeolake, northern Germany. (21st September 2020) - Dreibrodt, Stefan
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).