Two generations of Late Glacial palaeolakes: insights from multiproxy analyses (Suwałki Lake District, Poland)

Two generations of palaeolakes (Lipowo I, Lipowo II), associated with the termination of the Last Glacial, were documented in the Suwałki Lake District, northeastern Poland. Multiproxy analyses and radiocarbon (14C) and OSL dating were performed on lacustrine sediments. The older generation of basins developed among gradually melting dead-ice blocks and was eventually buried under mineral deposits at the end of the Allerød. The younger generation formed after the complete melting of dead-ice blocks and reflects environmental changes from the late Allerød to the Holocene. Observed changes in sedimentation style during the Late Glacial and early Holocene were linked to significant climatic shifts and their consequences. These changes were also recorded in palynological analyses, fossil Cladocera, geochemical data, and stable isotope results.

The vegetation composition during the Younger Dryas shows distinct regional features, including the strong development of Juniperus shrubs and herbaceous and grassy plants at the beginning of this stage, as well as the appearance of Picea abies in its later part. Northeastern Poland was more similar to northeastern Europe than to the rest of the Polish Lowlands, reflecting the paleoclimatic gradient that occurred in Poland during the Younger Dryas. The Holocene section of the Lipowo II profile also documents the first cold Holocene event at 11.4 ka.

Cladocera analysis for the studied lakes revealed remains of only 10 species in Lake “Lipowo I,” belonging to three families: Chydoridae, Bosminidae, and Daphniidae, with most remains attributed to Chydoridae. These species were mainly cold-water tolerant, and their frequency was low (max. 2200 ind./cm³). In Lipowo II, 25 Cladocera species were identified, representing various ecological zones, including open-water taxa requiring higher water temperatures. The number of individuals increased to a maximum of 6000 ind./cm³, indicating more favorable conditions for Cladocera development. Environmental changes recorded in vegetation and zooplankton are further supported by stable isotope analyses. Total organic carbon (TOC) and total nitrogen (TN) increased from approximately 2% to 53% and from 0% to 3.8%, respectively. Multiproxy analyses enabled the reconstruction of significant environmental changes associated with the transition from glacial to interglacial conditions in northeastern Poland.