Reconstruction of the Holocene palaeoenvironmental conditions accordingly to the multiproxy sedimentary records from Lake Pilvelis, Latvia

Reconstruction of the Holocene palaeoenvironment conditions in Southeastern Latvia is based on multiproxy records from Lake Pilvelis: pollen, plant macrofossil and microfossil analysis; loss-on-ignition (LOI) measurements; 14C dating; humic substances content; humification index; and elemental composition of gyttja organic mass. The data complex obtained in the result of multiproxy studies of sediments in Lake Pilvelis indicates significant changes in the depositional environment during the lake development. Data from Lake Pilvelis show that the start of organic-rich sediments formation before approximately 9750 cal BP, when birch–pine forest dominated in the surrounding landscape. Diagrams and data sets show six remarkable comparatively short cooling periods during the Holocene, which are related to changes in temperature and water level and influenced values and variability of remains. The investigation recognized the 8.4 ka BP and 4.6 ka BP cold events, while other cooling events can be recognised conditionally. During the events of 4.0 ka BP, the water level decreased extremely and the climate was probably drier, indicated by the comparison of records from Lake Pilvelis, Mazais Svetinu Bog and Lake Razna. A comparison of pollen data from Lake Pilvelis with Lake Kurjanovas, Mazais Svetinu Bog and Lake Razna shows some similarities, revealing features of cooler climatic conditions approximately at the time characterised by an increase of Betula and herb pollen.