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ABSTRACT A new record from the heart of the Moroccan Middle Atlas cedar forests spans the last 18 000 years and provides valuable insight into our understanding of the natural vegetation and environmental changes. The approach is based on the study of pollen content, geochemical elements and grain size analysis. The pollen data indicate that the vegetation was dominated by herbaceous plants until 9000 BP. Such open landscape allowed greater soil erosion and an input of chemical elements from the watershed. After 9000 BP, tree cover, mainly oak, increased slightly and was accompanied by a higher taxonomic diversity. However, several steppe elements remain well represented in the area until 5000 BP, which suggests that the climate was rather dry during the first part of the Holocene. After 6000 BP, the climate became more favourable to expansion of the forest ecosystems, including Cedrus atlantica, thereby reducing erosion. A strong reduction of the tree pollen percentages is recorded after 2000 BP, which may be related to increasing human activities during the Roman period. These forest changes are concomitant with an increase of lead and copper concentrations in the record, probably related to Roman metalworking activities. [ABSTRACT FROM AUTHOR]

This paper presents a reconstruction of the climatic changes at the Pleistocene/Holocene transition, recorded in the annually laminated sediments of Lake Gos´cia¸z˙, Poland. This reconstruction is based on pollen, stable isotope, mineralogical and chemical analyses of sediments, made with a time resolution of 1–4 yr. It reveals a sequence of abrupt climatic changes which preceded and followed the major warming around 11 500 cal BP. Our data show that the warming period was preceded by a 30-yr-long phase of increased winter and decreased summer precipitation (11 550–11 520 cal BP). About 11 520 cal BP, a very brief period of wetter conditions occurred, simultaneously with the beginning of the major warming. However, most of the first phase of the major warming (11 520–11 500 cal BP) was characterised by a generally dry climate, presumably due to lowered winter precipitation. Our records suggest that in this phase the warming concerned winter seasons mostly. In the second phase (11 500–11 460 cal BP) the warming also concerned summer seasons. Also, a distinct increase of humidity is noted in this period, which caused moistening of soils and, despite enhanced evaporation and evapotranspiration, inhibited the process of lake-level drop. The following 70 years (11 460–11 390 cal BP) were rather dry, which caused a distinct lowering of the lake (and probably also of groundwater) level. In this period, maximum biological productivity (per unit area) in the lake is noted. The whole sequence of phases of rather different climates was completed within a time interval (160 years) spanning two human lifes only. One should stress that the transitions between the consecutive phases were rather abrupt, lasting no longer than 10 years. [Copyright &y& Elsevier]