New data on the palynostratigraphy of the Mikulinian (Eemian) deposits in the lower reaches of the Pyoza River (northeastern White Sea region)

The palynological method was used to study a 455 cm thick marine sediment sequence, which overlies the Moscovian moraine in the Bychye-2 section on the Pyoza River (Arkhangel’sk region). The pollen records obtained allowed us to make a palynozonal subdivision of the section and to trace the plant cover transformations that occurred in the northeastern White Sea region during the Boreal transgression. When comparing the established local palynozones with the regional subdivisions of the reference sections Bychye-1, located 5 km upstream on the Pyoza River from the Bychye-2 site, and Peski on the Karelian Isthmus, we also employed the methods of correlation and event palynostratigraphy. It has been found that the marine sediments in the Bychye-2 section accumulated from the end of the Moscovian glaciation (~ 131 ka BP) until ~ 119,5 ka BP. The seven local palynozones established in the Bychye-2 section indicate a consistent change in climatic conditions and vegetational feedbacks. The main trend is the rapid displacement of Arctic-type shrub-herbaceous communities by pine-birch forests at the very beginning of the Mikulinian (Eemian) interglacial and the subsequent rise in the proportion of dark coniferous elements in the forests due to the growing humidity of the climate in the course of the transgression. A significant warming of the climate led to the emergence of thermophilic deciduous plants (oak, elm, hazel, and possibly even hornbeam) in the forests of the region. The predominance of pine-birch forests and the disappearance of all thermo- and hygrophilic elements of the vegetation followed the deterioration of climatic conditions during the final stage of the Mikulinian interglacial.