Very fast environmental changes at the Pleistocene/Holocene boundary, recorded in laminated sediments of Lake Gosciaz, Poland

This paper presents a reconstruction of the climatic changes at the Pleistocene/Holocene transition, recorded in the annually laminated sediments of Lake Go 642, 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 11500 cal BP. Our data show that the warming period was preceded by a 30-yr-long phase of increased winter and decreased summer precipitation (11550-11520 cal BP). About 11520 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 (11520-11500 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 (11500-11460 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 (11460-11390 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. (C) 2003 Elsevier Science B.V. All rights reserved.