Climate change, vegetation development, and lake level fluctuations in Lake Purwin (NE Poland) during the last 8600 cal. BP based on a high-resolution plant macrofossil record and stable isotope data (δ~(13)C and δ~(18)O)

摘要

This paper presents a history of the vegetation in Lake Purwin (NE Poland) and its catchment along with water level changes for the last 8600 cal. BP. The reconstructions are based on a high-resolution plant macroremains analysis and the stable isotope record in authigenic carbonates, a fine fraction that is precipitated within the epilimnion of the lake. The stable isotope records suggest that the lake had throughflow during the Holocene and that isotope data can therefore be used in palaeoclimatic reconstructions. The δ~(18)O values record the thermal maximum of the Holocene and the subsequent cooling of the upper Holocene. Water level changes and the history of the lake's productivity are both recorded in the δ~(13)C values. A chronology is established using radiocarbon dating of terrestrial plant macrofossils. The vegetation and water levels in Lake Purwin reflect regional climate changes. The combination of the lithology along the sedimentary sequence, the results of the plant macroremains analysis and the isotope data allowed several alternating periods of high (8600-7300, 6500-5200, 4400-3500, and 3000 -950 cal. BP) and low (7300-6500, 5200-4400,3500-3000 and 950 to -59 cal. BP) water stands to be distinguished in Lake Purwin. Low water levels are indicated by sediments that are enriched in coarse plant detritus, seeds of Rubus ideaus, fruits of Uritca dioica and more macroremains of Alnus glutinosa and rushes.