Faculty of Geology, Geophysics and Environmental Protection

This paper presents an array of analyses of the laminated sediments of Lake Perespilno, eastern Poland, covering the period between Older Dryas and Preboreal. Using the varve chronologies, pollen and 14C data, the laminated sequence of Lake Perespilno has been synchronised with that of Lake Gościa̧ż. The length of the Alleröd and Younger Dryas periods, derived from Lake Perespilno sediments,

The daily rainfall data for the twentieth century, from three stations across the region, constitute the basis for statistical analysis. However, the low signal-to-noise ratio makes it difficult to find any significant departure from the simplest null hypothesis of the stability of the rain record at individual stations in northeast India. Only the coarsest possible view, i.e. comparing the two halves of the century, provided strongly significant results in the numbers of days with extreme rain. Using a more general approach, the number of Fourier transform extreme amplitudes also differed significantly. Increasingly heavy events during the summer monsoon season, and partly in the pre- and post-monsoon seasons, are offset by a weakening in the winter monsoon season, so that the annual mean rainfall does not show a significant trend over the Meghalaya Hills. Apart from a greater number of years with noticeable extreme rainfall events in the second half of the twentieth century, we can also observe a more pronounced quasi-periodicity of 10–20 and 30–60 days during the same period. The detection of the latter periodicity indicates that the Madden–Julian oscillation plays an important role in the formation of extreme rainfall events over the Meghalaya Hills during extreme monsoon years.

In modern lakes different associations of submerged and fl oating macrophytes, as well as mire plants, may develop at the same time in various places of one basin, depending on the substrate, bottom relief, availability of plant propagules, and several other factors (Kępczyński & Noryśkiewicz 1998). Similar situations may have occurred in the past, and for palaeoecological investigations it is impor-tant to recognize if the analysis of one sedi-ment core (the usual procedure) may provide reliable information about plant palaeo-succes-sions over the entire lake. The studies carried out on Lake Zeribar sediments may contribute to an understanding of this problem. Lake Zeribar (Fig. 1), situated in an inter-montane valley in the Zagros Mountains, SW Iran (35°32′N, 46°07′E), contains sediments over 40 m thick, dating back to about 42 000 radiocarbon years BP at the bottom. The age of the sediments, as well as the location of the lake in an area of crucial signifi cance for the reconstru...