Search

Lake Gosciąz is located in the zone of the maximum extent of the last ice sheet. Distinct lake terraces and deposits related to the lateglacial transgression do not exist. Detailed examination of annually laminated sediments and landforms revealed three phases of higher water level and storage, represented by shore features, by littoral, deltaic and bog deposits, and by higher rates of lacustrine deposition in the pelagic zone. Holocene lake transgressions at c. 8.4-7.7 ka, 2.5-2.3 ka, and less distinct at 5-4 ka BP coincide with phases of higher flood frequency in Poland and glacial advances in the Alps. Because of sedimentation, isolation from groundwaters, encroachment by peatland and drainage of the lake, lake volume during the last 12 ka diminished by as much as 70%, and current water-level fluctuations of about 1-2 m can change water storage by 20-25%.

Laminated sediments of Gościaż Lake can be used as an independent source of material for calibrating the radiocarbon time scale. The varve chronology is based on three long cores from the deepest part of the lake, with one additional core from the second deepest part. From pollen and Cladocera spectra and stable isotope and chemical content sequences, we have determined the Allerød(AL)/Younger Dryas(YD) and Younger Dryas/Preboreal(PB) boundaries in the three long cores with relatively good accuracy, and have tentatively defined the AL/YD boundary in the fourth core. The Younger Dryas period contains at least 1520 varves, with 980 varves in fragments well replicated in all four cores. The duration of the Younger Dryas as recorded in sediments of Gościaż Lake corresponds well to the duration derived from 230Th/234U and 14C dates on Barbados corals, but disagrees with estimates from Soppensee, Lake Holzmaar and Swedish varves. Two AMS dates of terrestrial macrofossils from the PB and YD periods seem to fit both the data obtained for Swiss lake sediments and Barbados corals.