—The paper presents new lithological, geochronological, and biostratigraphic data on the studied sections of the Middle Valdai interstadial sediments in the sections of two terraces in the basin of the Severnaya Dvina River and on the southern coast of the Kola Region and in its southwestern part. The obtained data are correlated with the data available for other regions of northeastern Europe. The Severnaya Dvina River was found to have flowed into a marine reservoir existed in the White Sea basin throughout the Middle Valdai time corresponding to Marine Isotopic Stage 3 (MIS 3). The alluvial sedimentation in the river catchment area occurred in the environment of base level instability and permanently changing climate. In northeastern Europe, the warmest (optimum) intervals are related to the time spans of 47–43 and 31.3–29.2 cal. ka BP. In general, the available data point to 12 warming and cooling episodes in northeastern Europe.