Environmental conditions in northwestern Russia during MIS 5 inferred from the pollen stratigraphy in a sediment core from Lake Ladoga

Abstract

© 2019 Collegium Boreas. Published by John Wiley & Sons Ltd Lake Ladoga hosts preglacial sediments, although the Eurasian ice sheet overrode the area during the LGM. These sediments were first discovered by a seismic survey and are investigated using a 22.75-m-long core. Its upper 13.30 m comprise Holocene and Lateglacial sediments separated from the lower 11.45 m of preglacial sediments by a hiatus. They consist of highly terrigenous lacustrine sediments, which according to OSL dating, were deposited during an early stage of the last ice age (MIS 5). The palynological data allow a first reconstruction of the Early Weichselian environmental history for northwestern Russia. Birch and alder forests with broad-leaved taxa dominated during MIS 5d (c. 118–113 ka), suggesting a climate more favourable than in the Holocene. A high content of well-sorted sands and poorly preserved palynomorphs indicates a shallow-water environment at least temporarily. More fine-grained sediments and better preserved organic remains suggest deeper water environments at the core location during MIS 5c (c. 113–88 ka). Pine and spruce became dominant, while broad-leaved taxa started to disappear, especially after c. 90 ka, pointing to a gradual climate cooling. An increase in open herb-dominated habitats at the beginning of MIS 5b (c. 88–86 ka) reflects a colder and dryer climate. However, later (c. 86–82 ka) pine and spruce again became more common. Birch and alder forests dominated in the area c. 82–80 ka (beginning of MIS 5a). Although open treeless habitats also became more common at this time, a slight increase in hazel may point to somewhat warmer climate conditions coinciding with the beginning of MIS 5a. The studied sediments also contain numerous remains of freshwater algae and cysts of marine and brackish-water dinoflagellates and acritarchs documenting that the present lake basin was part of a brackish-water basin during the Early Weichselian, probably as a gulf of the Pre-Baltic Sea.