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

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 Aller ø d period dating to between 13 422 and 12 708 cal.aBPis preserved inannuallaminations. Withinthissection,the LSEwasidentifiedasa cryptotephralayer (12 944 44 cal. a BP). Microfacies analysis, continuous high-resolution geochemical measurements and pollen analysesenabledahigh-resolutionreconstructionofenvironmentalchange.TheolderpartoftheAller ø d(c. 13 422to 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 associatedwith cooler conditions. About120 yearsafterthe LSE,increasedoxygenaccessat thelakebottom,allochthonous inputandClfluxespointto anonsetofincreasinglystrongerwesterlywinds,probablyasalong-termresponsetotheLSE.Thissupportstheideaof a southward shift of the mid-latitude westerlieswind system within the interval between the LSE and the beginning of the YoungerDryas. Thepaceofthe southwards shiftof thiswind systemdecreased from 10 km a 1 inthe initialphase (40 – 120 years after LSE) to 6 km a 1 in the later phase (120 – 200 years after LSE)



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