Environmental Changes on Kunashir Island (Kuril Archipelago) during the Middle and Late Holocene

Sea level rise during the Pleistocene-Holocene transition period caused the formation of lagoon lakes along the western and eastern coasts of the Kuril Islands. These lakes include Lake Serebryanoye, located in the northern part of the South Kuril Isthmus near the Pacific coast of Kunashir Island (44°03'21" N; 145°49'46" E). The total thickness of sediments in the lake was 367 cm. They are characterized by diatom flora (334 species), representing various ecological groups: freshwater, brackish water, marine, marsh, lacustrine, rheophilic, planktonic, benthic. The analysis of diatoms made it possible to distinguish two complexes. As shown by radiocarbon dating, in the Middle Holocene (100.5-367 cm interval) the sediments corresponded to the lagoon stage, which changed in the Late Holocene (100.5-0 cm interval) to the freshwater lake stage. Palynological analysis showed a successive change of biocenoses, reflecting the development in the Middle Holocene of birch-broadleaved forests with the participation of Pinus koraiensis, Picea sp. The most abrupt change in biocenoses is observed at the boundary of the Middle and Late Holocene. This change of biocenoses is expressed by the dominance of conifers in the vegetation cover, represented by various species of Picea, Pinus, Abies, Larix. It also shows the relative cooling of the climate in the Late Holocene.