A high-resolution late-glacial and early Holocene environmental history of Rotmeer, southern Black Forest (Germany)

Abstract

The late-glacial and early Holocene environmental history of Rotmeer (960m s.m.l.), a mire in the southern Black Forest (Germany) was investigated by analysing 96 contiguous 1 cm samples of lacustrine sediments. Pollen concentrations and geochemical erosion indicators (e.g. Al, Ti, K) suggest that the reforestation of the catchment by pine and birch occurred at the onset of the Allerød. Moreover, geochemistry and pollen indicate three phases of climatic deterioration, each characterized by the occurrence of allochthonous minerogenic sediment with increased values of NAP. The first fluctuation occurred shortly before the pine expansion and was correlated with the Aegelsee oscillation of the Alps. The second and major event was identified as the Younger Dryas. It resulted in a substantial lowering of the timberline in the Black Forrest. The third oscillation occurred during the Preboreal and is very inconspicuous in the terrestrial pollen record, whereas the geochemical analysis shows a short increase in elements indicative of soil erosion. The diatom assemblages of the Oldest Dryas and Bølling biozones are dominated by epiphytic alkaliphilous and circumneutral species. Progressing pedogenesis in the catchment connected with decreased inwash of basic cations into the former lake may then have favoured the expansion of acidophilous diatoms, mainly Aulacoseira species. The climatically induced changes evidenced in vegetation and in soil erosion are well reflected as changes in the pH spectra of the diatoms, indicating more neutral to basic pH conditions.