Late-Weichselian (Vistulian) environmental changes in NE Poland - Evidence from Lake Suchar Wielki

By applying pollen and subfossil Cladocera analyses to the Late-Weichselian section of the sediment profile from Lake Suchar Wielki, we aimed to track paleoenvironmental changes in NE Poland, locally (lake formation and its early development) and regionally (terrestrial plant succession).The article aims to indicate how not only stadial-interstadial changes were noticeable in the study area, but above all even short-term climatic fluctuations. The obtained record covers the period of ca. 13,400-11,500 cal. BP, i.e. the part of the Allerod interstadial (GI 1c1 to GI-1a), the Younger Dryas stadial (GS-1), and the very beginning of the Holocene. During the Allerod, a short-lasting cooling was recognized (the Gerzensee oscillation, GI-1b). It is the first study for this part of Poland evidencing the inter-Allerod cooling by the Cladocera-based mean July temperature reconstruction. In the palynological record it was reflected in an increased temporary share of Betula alba t. pollen, while in the Cladocera record in the appearance of cold-water taxa and low total abundance. At the transition to the Younger Dryas further cooling took place that was evidenced by the increase in the proportion of herbaceous plants together with a distinct decrease of tree pollen concentration in sediments as well as by important changes in Cladocera communities including reduced species diversity, disappearance of more demanding temperate taxa and the expansion of cold-tolerant species. The palaeobotanical record revealed that the proportion of juniper pollen in the studied area was lower than in other regions of NE Poland. A case study demonstrated this was mainly due to local conditions. Moreover, it is noteworthy that, at the end of the Younger Dryas, spruce appeared temporarily in local forest stands. The results of the study suggest climate change, which has also been recorded in ice cores from Greenland as cooling ca. 11,800-11,600 cal. BP.