This work examines the geological and geomorphological structure of the depression of Lake Ladoga, the largest European freshwater basin. The history of the development of Lake Ladoga from the time of the last Eemian (Mikulino) Interglacial to the final deglaciation and the formation of the present-day waterbody is discussed. All modern data on the formation of the lake and its basin are brought together.

We present the results of study sediment core, taken in the southern part of Lake Ladoga at the depth of 44 m. The sediments are gray silt with total thickness of 0.8 m. Diatom and loss-on-ignition and grain-size analyzes and radiocarbon dating were carried out. The retrieved sediments formed during the Holocene starting from the regression of the Ancylus Lake at the Baltic ca. 10,200 cal. BP. Changes in the composition of diatom assemblages and the dynamics of organic accumulation correspond to the typical scenarios that we recorded in the Holocene sediments in the central part of Lake Ladoga. No sedimentary hiatuses were recorded. Thus, it has been established that aquatic, relatively deep-water conditions existed in this part of the Ladoga basin starting from the Early Holocene with the accumulation of fine-grained sediments.

The study is focused on the litho- and biostratigraphic record of Lake Lavijarvi, presently a small lake in the closest vicinity from the Ladoga coast, and formerly a sheltered bay of Lake Ladoga. Several stages of its evolution were revealed that are characterized with different organic matter content in the sediments, diatom assemblages composition and abundances of siliceous microalgae remains. It has been demonstrated that at the earlier stages, the environments in the basin of Lake Lavijarvi were similar to those in Lake Ladoga. Later in the Holocene, local factors became more pronounced, and the conditions different from those in the open-water part of Lake Ladoga established in the basin of Lake Lavijarvi. The regression of Lake Ladoga resulted in the isolation of Lake Lavijarvi and the beginning of its small-lake stage after ca. 3900 cal. BP.

Paleolimnological studies of the Lososinskiy Reservoir (Karelia) have made it possible to reconstruct the history of its development from the Ice Lake to the artificial waterbasin. Five stages of sedimentogenesis were identified. It was based on lithostratigraphy, diatom and geochemical analysis of bottom sediments. The detailing of the anthropogenic period of the Lososinskiy Reservoir was carried out on the study of the landscape structure of the catchment area using the mass-balance production model of the ecosystem.

A 23.5 m deep borehole was drilled on the dried bed of the Aral Sea 9 km south of the former Barsakelmes Island. At a depth of 21.3 m, the borehole penetrated Paleogene bedrock. In the interval 21.3 - 15.2 m the conditions of a shallow freshwater reservoir at a considerable distance from the flowing rivers (deltaic channels of the Syr Darya River) - the first phase of filling of the Aral Basin with river water - were reconstructed. It has been preliminary attributed by three 14C AMS dates to the time about 23-25 thousand years BP. Above 15.2 m of the section the conditions become even more shallow, starting from 12.0 m of the section - brackish-water. The upper 10.5 m of the section correlates with the sediments of the modern geological phase of the Aral Sea development studied in detail in the same area by Burr et al. (2019), the beginning of which was estimated at 17.6 thousand BP. The new data obtained indicate an earlier appearance of the modern Aral Sea, which originated as a shallow freshwater body.

Some results of the study of bottom sediments of Lake Pertozero (Onega Coast of the White Sea) are presented – section stratigraphy, loss on ignition, diatom and chironomid analyses. At the initial stage of its development, the lake basin was part of a periglacial basin. Since its isolation around 11000 years ago, the lake has experienced several changes in sedimentary conditions that have affected the amount of organic matter contained in the sediments. These changes are noted throughout the lake. Brackish-water diatom complexes were not noted in the Holocene sediments, which indicates that in this area the sea level did not rise above 11 m.

The diatom study of the sediment sections of low terraces located at the top of the Purnema Bay (the Onega Bay, White Sea) was carried out to infer the influence of sea-level changes on the evolution of coastal marine ecosystems. Changes in the composition of diatom assemblages and abundances of siliceous microfossils revealed the transformation of ecological conditions associated with the gradual shallowing of these areas of the seabed, their emergence from the tidal zone and establishing subaerial environments characterized by moisture deficiency.

The first study of the composition and structure of the diatom assemblages from sediment traps installed in different parts of Lake Onega is presented. A total of 171 species and intraspecific diatom taxa belonging to 59 genera have been identified. The predominance of planktonic diatoms is favored by large depths of the lake and a small area of the littoral zone. Aulacoseiraislandica and A. subarctica, the most abundant species in spring phytoplankton in Lake Onega, dominate in the sediment-trap diatom assemblages. In the sites subjected to anthropogenic eutrophication, Aulacoseira ambigua is numerous as well. Lindavia radiosa and Pantocsekiella tripartita are among the subdominating species in a number of sites, while P. schumannii,Stephanodiscus neoastraea, and Stephanodiscus sp. are less common. Higher proportions of periphytic Tabellaria fenestrata are recorded at the sites with the largest areas colonized by macrophytes. Neutrophilous oligo-mesotrophic and oligo-hypereutrophic taxa prevail in the diatom assemblages in all sampling sites. The predominance of two or three species in the diatom assemblage results in low values of the floristic diversity index. More diverse diatom assemblages are found in rather isolated bays. Concentrations of diatom valves and chrysophyte cysts in sediment traps material are also calculated.

We studied sedimentary archives on the Karelian coast of the White Sea (area of the White Sea Biological Station, Moscow State University) from various objects-filling of the paleoseismic fault trench, marine terraces, and buried shell lenses-to obtain new data on the relative sea level dynamics in the Holocene in the areas where block tectonic movements took place. The specific features of the formation of subfossil malacofauna taphocenoses in Kandalaksha Gulf, changes in the sedimentation environment under the conditions of uplifting coast, and traces of strong seismicity in the late glacial and postglacial periods are also revealed.

The multi-proxy study of the lowermost part of the sediment sequence of Lake Kanozero (south-western part of the Kola Peninsula, ca. 53 m a.s.l.) revealed the evidences for marine waters penetration into the basin during the earliest stage of its evolution. The diatom analysis inferred the conditions of a large brackish-water basin. Sediments composition and very low organic content also supported large-basin and low-productivity environments. Based on the pollen study, this stage covers a cooling period preceding the Allerød (tentatively assigned to the Older Dryas) and the onset of the Allerød. Periglacial vegetation typical of the cold and dry climate prevailed in the area for the most of the period. The subsequent transition to the freshwater conditions inferred from the diatom study took place in the Allerød, according to the pollen data. Except for a minor decrease in the fine sand fraction, no other corresponding changes were observed in the sediment record suggesting no major shifts in sedimentary environments. In the late Allerød and throughout the Younger Dryas, Lake Kanozero remained a large, low-productive freshwater basin. Our results indicate that ice-free conditions with aquatic sedimentation in the Kanozero depression had already existed in the Older Dryas. This assumes earlier deglaciation of the study area than it was previously thought. The study also suggests that brackish conditions in the White Sea basin established earlier than reported before. While the previous studies found no signals of marine transgression above ca. 41 m a.s.l., our results indicate that the local marine limit in the study area exceeds ca. 53 m a.s.l.

For the first time for saline lakes of the Crimean Peninsula, the results of a comprehensive study of lacustrine sediments using litho-, bio- and chronological methods were obtained. For the first time, radiocarbon dating of the Crimean lake sediments was performed. In lakes Saki and Dzharylgach, sediment sequences of closed highly mineralized reservoirs, which overlay marine deposits, were retrieved. The surface of marine sediments is dated to 5610–5340 cal BP for Lake Saki and 5590–5350 cal BP for Lake Dzharylgach. By this time, sand barriers began to form, which subsequently completely separated the lagoons from the sea and led to the formation of closed reservoirs. Full isolation of Lake Dzharylgach occurred about 4600 cal BP. The vegetation change at the first stage of the lakes’ existence was controlled by changes in the sea level, as well as by fluctuations of salinity, later changes being mainly influenced by changes in climate humidity. The first Cerealia-type pollen occurs in the Subboreal period. Human settlements in the area of Lake Dzharylgach represent the Eneolithic, Bronze Age, as well as the Greco-Roman and medieval periods. A notable demographic change is observed in the period from the early first millennium to the end of the 5th century BC. The majority of archaeological sites in the vicinity of Lake Saki belongs to the Greco-Roman period.

Comprehensive investigations of the northern coast of the Sambian (Kaliningrad) Peninsula, that included geomorphological survey, lithostratigraphic description of the section logs, diatom, botanical and LOI analyses, radiocarbon dating, and GNSS survey relating lithological boundaries and sampling levels to the sea level and determining terrace elevations, were performed. New data on the regional palaeogeographic settings of the Late Glacial period and the stages of development of the large proglacial basin, the Baltic Ice Lake (BIL) were obtained. It has been established that after the degradation of the last glaciation, erosional (subaquatic) processes prevailed in the coastal area, while in the interval of 14–13 cal kyr BP subaerial conditions established at the study site, and tree-moss phytocenoses formed during the Allerød warming. At the end of the warming period there was a shallow, isolated lake, with decreasing depth. During the Younger Dryas oscillation, ca. 12 000 cal kyr BP, the area was flooded by waters of a vast freshwater, ultra-oligotrophic basin with high content of suspended fine mineral particles. The conditions of a shallow bay of the BIL sheltered from the main basin by a moraine ridge at least 4–5 m high, are suggested for this period. The lake drainage took place around 11 660 cal kyr BP. Since then, no accumulation or alternating accumulation and erosion conditions prevailed in the study site until the late Holocene. The obtained results allow us to speak about two stages of flooding of the northern coast of the Sambia Peninsula during the Late Glacial, possibly caused by the BIL transgressions. The occurrence of BIL deposits in the northern part of the Sambia Peninsula above sea level suggests that the Late Glacial basin level in the study area may have exceeded the present sea level.

This paper discusses the results of siliceous microfossils studies performed in a "staircase" of four isolation basins (33.7 m-2.9 m a.s.l.) on Big Solovetskiy Island (Solovki Archipelago, the White Sea). Diatoms were used as a primary group for paleoinferences, while chrysophyte cysts and sponge spicules also demonstrated high indicative potential. In all study lakes, the siliceous microfossils stratigraphy revealed three main stages of their evolution, i.e. large-basin, transitional and small-lake stages, each characterized by certain composition of the diatom assemblages and floristic diversity, relative abundances of chrysophyte cysts and sponge spicules, and siliceous microfossils concentrations. In the uppermost lake, glaciolacustrine environments unfavorable for aquatic biota existed during the large-basin stage. The proglacial lake stage terminated prior to ca. 10.4 cal ka BP, followed by a (semi)terrestrial episode before the transition to small-lake environments. In the other three lakes, marine environments were inferred at the earlier stage, characterized by the predominance of marine and brackish-marine diatoms, increased proportions of sponge spicules and low "cysts to diatoms" ratio. At the transitional marine-freshwater stage, mass growth of small fragilarioid diatoms and decreased abundances of spicules indicated unstable environments, while increased proportions of cysts pointed to progressive freshening of the basins. The duration of the marine-freshwater transition expectedly prolonged from ca. 200 yr in the upper basin (16.6 m a.s.l) to ca. 500 yr in the lowermost lake (2.9 m a.s.l.). The isolation from the sea took place between ca. 6.3 and 1.4 cal ka BP. At the small-lake stage, siliceous microfossils stratigraphies reflected local specifics of the basins and their catchments. We argue that besides traditionally used diatom data, relative and absolute abundances of siliceous microfossils also possess high indicative value for isolation basin studies. Our study demonstrated that marine waters on Big Solovetskiy Island never reached ca. 34 m a.s.l. during the Holocene, unlike the western coast of the Onega Bay where the Preboreal marine intrusion was recorded even at higher elevated localities. Different rates and amplitudes of shoreline displacement are thus suggested for the inner and outer parts of the Onega Bay. During the mid-Holocene Tapes transgression, before ca. 6.3 cal ka BP, the relative sea level on Big Solovetskiy Island exceeded 17 m a.s.l. The average estimated rates of the shoreline retreat during the second half of the Holocene gradually decreased from 0.28 cm year  1 to 0.2 cm year  1, indicating slowed isostatic uplift.

For the first time for saline lakes of the Crimean Peninsula, the results of a comprehensive study of lacustrine sediments using litho-, bio- and chronological methods were obtained. For the first time, radiocarbon dating of the Crimean lake sediments was performed. In lakes Saki and Dzharylgach, sediment sequences of closed highly mineralized reservoirs, which overlay marine deposits, were retrieved. The surface of marine sediments is dated to 5610–5340 cal BP for Lake Saki and 5590–5350 cal BP for Lake Dzharylgach. By this time, sand barriers began to form, which subsequently completely separated the lagoons from the sea and led to the formation of closed reservoirs. Full isolation of Lake Dzharylgach occurred about 4600 cal BP. The vegetation change at the first stage of the lakes’ existence was controlled by changes in the sea level, as well as by fluctuations of salinity, later changes being mainly influenced by changes in climate humidity. The first Cerealia-type pollen occurs in the Subboreal period. Human settlements in the area of Lake Dzharylgach represent the Eneolithic, Bronze Age, as well as the Greco-Roman and medieval periods. A notable demographic change is observed in the period from the early first millennium to the end of the 5th century BC. The majority of archaeological sites in the vicinity of Lake Saki belongs to the Greco-Roman period.

The macrophyte pollen is a valuable source of information about lake level changes. Continuing our previous studies on the use of the macrophytes pollen analysis in the paleolimnology we studied the Lake Vitalievskoye sediments sequence of on the Valaam Island (the northern part of Lake Ladoga). To confirm the results of pollen analysis we conducted lithological and diatom analyzes. The macrophytes distribution of the island lakes at the present time has been established with the help of geobotanical and pollen analyzes of the lacustrine surface sediments. As a result, a comprehensive study made it possible to establish the stages of the Lake Vitalievskoye development during the Late Holocene: The Lake Ladoga Bay stage with a slight overgrowth of aquatic vegetation; the lake isolation stage of the from Lake Ladoga, when macrophytes disappeared from the lake, and the lake independent development stage, when their maximum distribution occurred and later began to decline as a result of the human impact. According to our research of the Valaam Island lakes we have received new data about the modern distribution of macrophytes in the island lakes, their dynamics in the Late Holocene. We also conducted a methodological study establishing the macrophytes pollen role in studying the small island lakes history and the Lake Ladoga level.

Abstract. The study examines the issues of changes in the level of the Baltic Sea over the past 10 thousand years. According to the data of domestic and foreign authors on time, there is no unambiguous data on the duration and level of littorina transgression, which is considered the largest during the Holocene period. By the research, with the financial support of the RFBR grant-graduate students No. 20-35-90089, studies of bottom sediments of lakes Goluboye, Bolshoye Molochnoye and Zaychikhinskoye are being carried out. The report presents the results of the diatom analysis of Lake Zaychikhinskoye. The main stages of the lake s development are determined, it is established that in the early Holocene its development was determined by the transgressive-regressive stages of the Baltic. At the initial stage, the reservoir was part of a deep oligotrophic Ancylus lake. During the littorina transgression, the Baltic Sea level most likely did not rise to lake level in this area.

Abstract. We present the new data concerning the traces of the Baltic Ice Lake in the northern coast of the Sambian Peninsula, Kaliningrad region, Russia, based upon the studies of the Aleika section (lithostratigraphy, radiocarbon dating, plant macrofossil, diatom and LOI analyses).

Результаты комплексных исследований двух небольших озер на о. Хачин, расположенном в северной части оз. Селигер, позволили провести реконструкцию этапов развития озер в течение голоценового периода. Исследования включали в себя литологический, палинологический, диатомовый анализы, анализ динамики фосфора и металлов, расчеты вероятности влияния антропогенных факторов на развитие озерных экосистем. Изученные озера отличаются от остальных многочисленных озер острова значительной глубиной, воронкообразными котловинами, условиями осадконакопления, что подтверждает карстовое происхождение озер. Морфометрические модели распределения глубин и уклонов позволили изучить рельеф дна озер, установить точные морфометрические характеристики. Установлены максимальные глубины озер 33,7 и 15,2 м. Подробное комплексное изучение поверхностных проб донных отложений озер позволили адекватно интерпретировать результаты проведенных реконструкций голоценовой истории озер. The results of studies of two small lakes on the Khachin Island, located in the northern part of the Lake Seliger, made it possible to reconstruct the lakes development stages during the Holocene period. The studies included lithological, pollen, diatom analyzes, analysis of the phosphorus and metals dynamics, calculations of the probability of the influence of anthropogenic factors on the lake ecosystems development. The studied lakes differ from the other numerous lakes of the Khachin Island in considerable depth, funnel-shaped hollows and sedimentation conditions, which confirms the karst origin of the lakes. The morphometric models of the depths and slopes distribution made it possible to study the relief of the lakes bottom, to establish the exact morphometric characteristics. The maximum depths of the lakes were determined to be 33,7 and 15,2 m. A detailed study of surface lake sediments samples made it possible to adequately interpret the results of the Holocene history reconstructions of the lakes.

Abstract. The study of the siliceous microalgae (diatoms and chrysophytes) enabled reconstructing the evolution of the ecosystem of the Unitskaya Bay, the northern bay of Lake Onega. Changes in the composition of diatom assemblages, floristic diversity and abundances of siliceous microalgae indicated past productivity changes, as well as shifts in duration of hydrological and biological seasons.

Abstract. Despite of a long period study of the sediments sequences of Lake Ladoga there are currently only two cores with a series of radiocarbon dates. Now the radiocarbon dates for one more core have been received. The results of new multi-proxy studies have been obtained. The new series of radiocarbon dates allows the obtained data to be correlated with other dated cores. Our studies show different sedimentation conditions in different parts of Lake Ladoga in the same time periods. In this regard, for a correct reconstruction of the history of Lake Ladoga, it is necessary to continue multi-proxy studying of the cores with a series of radiocarbon dates.