Response of terrestrial and lake environments in NE Poland to Preboreal cold oscillations (PBO)

The multi-proxy data (pollen, diatoms, Cladocera, 14C) from the sediments of Lake Suchar Wielki representing the period ca. 11,600-9800 cal. BP have allowed the reconstruction of the influence of Preboreal cold oscillations on terrestrial and aquatic environments in NE Poland. The reconstructed changes in plant, cladoceran and diatom communities indicated an occurrence of four short-lasting negative climate events during the Preboreal period. The first three of them occurred in the early Preboreal (ca. 11,300-11,150, 11,100-11,000 and 10,900-10,850 cal. BP) and they were separated by short, warmer intervals. The obtained palynological data indicated that these events did not result in the transformations of the pine-birch forests strongly dominant in that period, but were only manifested by changes in the pollen production by the trees forming woodstands. In the lake during these coolings, cold-water Cladocera species developed, and the abundance of aquatic organisms decreased. Water level in the lake during two older early-Preboreal cold events increased significantly, and remained low during the last event. In the late Preboreal a fourth cooling took place. The cold peak was relatively short (ca. 10,300-10,200 cal. BP), but was preceded by a ca. 300-year-long period when conditions for plants were unfavourable. The drop in temperature was accompanied by a decrease in the humidity of the climate and a decrease in the water level in the lake. Again, the abundance of cold-water species increased. The acreage covered by pine decreased, and a temporary spreading of birch occurred. This last cold event in the Preboreal was followed by a relatively stable warm phase at the end of this chronozone. The recorded climate changes in NE Poland during the Preboreal correspond fairly well with those reported for other regions of Europe and the whole Northern Hemisphere.