Dmitry A Subetto

Palaeoenvironment of the Karelian Isthmus, the easternmost part of the Gulf of Finland, during the Litorina Sea stage of the Baltic Sea history

The palaeoenvironment of the Karelian Isthmus area during the Litorina Sea stage of the Baltic Sea history, between 8.0 and 4.5 kyr BP (8.8-5.2 cal. kyr BP), was reconstructed by studying four sites located on the Karelian Isthmus in Russia. Methods included diatom and pollen analyses, sediment lithostratigraphical interpretation and 14C dating. The brackish-water (Litorina) transgression began c. 7.7 kyr BP (8.45 cal. kyr BP) in the Karelian Isthmus area. The transgression maximum occurred between 6.7 and 5.7 kyr BP (7.6-6.5 cal. kyr BP), depending on the glacio-isostatic land uplift rate. Regarding the vegetation, the maximum occurrence of temperate deciduous trees took place at the same time. The transgression was interrupted by a short-lived sea-level standstill during the middle phase of the main transgression, c. 6.3 kyr BP (7.2 cal. kyr BP), on the eastern part of the isthmus. The highest Litorina shoreline is located between 8 and 13 m above present sea-level and the amplitude of the Litorina transgression has varied between 5 and 7 m. The 8.2-kyr cold event is not evident, but the sea-level standstill around 6.3 kyr BP (7.2 cal. kyr BP) could reflect a cool episode at that time in the Karelian Isthmus area.

Mid-Holocene Littorina Sea transgressions based on stratigraphic studies in coastal lakes of NW Russia

Abstract The mid-Holocene Littorina Sea transgression has been studied in sediment cores from four coastal lakes in NW Russia. The basins are situated in the same drainage system at elevations from 6.9 to 9.2 m a.s.l. Complementary parameters have been applied to identify water-level changes. Chronological models are based on AMS radiocarbon dating of bulk sediments but also wood remains and moss sedge peat has been dated in a few cases. All radiocarbon ages have been calibrated to calendar years BP (cal. BP). Between 8000 and 6000 cal. BP the present-day lakes were in contact with the Littorina Sea and brackish conditions prevailed. The water level was higher than 6 m a.s.l. clearly documented in all four basins. A peak reaching above the level of the uppermost lake (9.2 m a.s.l.) has been dated to ca. 7500 cal. BP. During the high level phase a short lived regression/transgression is recognized in all but the uppermost basin. This minor water level fluctuation lasted for a few hundred years around 7000 cal. BP. It is reflected in various parameters in the different basins. Correlations are made with recent studies from Blekinge in southeastern Sweden situated at the 10 m Littorina isobase as the present investigation area. The parallel Littorina Sea history in these two areas seems to confirm a multi-transgression pattern across the southern Baltic Sea.

New data on chronology of landscape-paleoclimatic stages in northwestern Russia during the late glacial and Holocene.

Two lake and bog sediments have been thoroughly studied using palynological and radiocarbon dating methods. These are the Lembolovskoye Lake section located in the southern part of the Karelian Ithmus and the Mshinskoye bog section located in the southwestern part of the Leningrad province. The data obtained allow us to reconstruct the main features of the vegetation cover evolution, the chronology for the appearance and a real distribution of the main arboreal species from the south of the Leningrad province to the north, and to construct curves of the paleoclimate parameter changes for the area under study. Thirty-six (super 14) C dates were obtained for the Lembolovskoye Lake section (7 m thick). According to those dates, the organic gyttja formation in the lake began 9870+ or -170 BP. Spore-pollen spectra with high percentage of herbs, arborescent, and shrub-birch dated back to the Younger Dryas were found out in clay layers at a depth of 6.5 m. An appearance of spruce and alder pollen is dated at 6860+ or -120 and 7510+ or -150 BP, respectively. The maximal percentage of broad-leaved species falls on the first half of the Atlantic (AT-1). Thirty-two dates were obtained for the Mshinskoye bog section (6 m thick): from 60+ or -70 to 9520+ or -170 BP (the last date fixed the beginning of peat formation); 12 palinozones from the Preboreal to the Subatlantic were recognized there. The spruce and alder pollen began to appear 7520+ or -110 and 7670+ or -130 BP, respectively. The maximal amount of broad-leaved species is observed at 4690+ or -80 BP. The detailed reconstruction of changes in vegetation communities during the Late Glacial and Holocene was correlated with paleoclimatic characteristics, which have been reconstructed for the section under study by using the information from a statistical method of spore-pollen data processing.

Late- and postglacial history of lakes of the Karelian Isthmus

The Late Pleistocene and Holocene history of five lakes in the central part of Karelian Isthmus, south of the present Vuoksi River, are described on the basis of sediment stratigraphical investigations. Two of the Lakes, Michurinskoe (94 m a.s.l.) and Uzornoe (55 m a.s.l.) are situated in an upland area that remained dry land after the deglaciation even during the early high water stages of the Baltic Sea (Baltic Ice Lake until c. 10000 yr BP and Ancylus Lake 9500–8800 BP). The low-lying central parts of the Isthmus were flooded by the outflow of Lake Ladoga that took place across this area until the formation of Neva River, c. 3100 yr BP, and further by the waters of River Vuoksi that started flowing into the area from the NW c. 5000 yr BP as a new outlet of Lake Saimaa. The basins of the lakes Krasnoe and Vishnevskoe (both 16 m a.s.l.) became isolated when River Neva was formed and Lake Ladoga sank to its present level. Lake Rakovoe (12 m a.s.l.) was on the level of River Vuoksi up until the mid-19th century, when water level in the central stretch of the river was artificially lowered. Each of the lakes has been variously affected by hydrological and climatic changes and consequences of human activities, e.g. eutrophication due to intensified land use. As a consequence to artificial lowering, done in order to gain field and meadowland, the large, shallow Lake Rakovoe has been largely overgrown by macrophytic vegetation.

The first case study of 230Th/U and 14C dating of mid-valdai organic deposits

From the viewpoint of precision and reliability of radioisotopic dating, deposits whose quantitative age can be determined through several methods of geochronometry are of special interest. The mutually conforming finite 14C and 230Th/U dates of buried Neopleistocene organic deposits, taken from the Tolokonka section by the North Dvina River (100 km downstream from the city of Kotlas), have been obtained for the first time in Russia. The stratigraphical reference of these results to those obtained via the optically induced luminescence for upper and lower bedding layers has been established. The presented geochronometric data have allowed us to consider the age of oxbow lake organic deposits completely reliable and refer the time of their formation to the Tyrbei warming within the MIS-3. The applicability of the new version of the 230Th/U method for dating of interglacial and interstadial deposits, for the purpose of solving the Middle and Late Neopleistocene chronostratigraphy issues, is confirmed.

Foreword to the Special Issue: Arctic Palaeoclimate and Its Extremes (APEX)

The recent mass loss of the Greenland ice sheet (Chen et al. 2006), the observed increases in the velocity of its fast-flowing outlets (Luthcke et al. 2006) and the melting of the permafrost demonstrate the profound changes occurring in the Arctic region as a result of global warming (ACIA 2005). This is corroborated by systematic satellite monitoring that shows there has been a progressive decrease in the extent of sea ice over the last 30 years, with a record low in 2007 (Comiso et al. 2008). Forward modelling predicts accelerated rates of sea-ice disintegration and the almost complete disappearance of Arctic Ocean summer sea-ice cover within this century. It is clear that the environment in the Arctic is changing at a pace not previously monitored by humankind. It is equally clear, however, that to place the current changes in a millennial time perspective, we need to know more about the Pleistocene natural variability and amplitude of, for example, the Greenland ice sheet, Arctic Ocean sea ice and permafrost. Such a longer time perspective can only be established through international collaborative and multidisciplinary studies of nature’s own archives, such as marine and terrestrial stratigraphic records, sediment distribution and landforms.

Geochronology of vegetation stages of south-east Baltic coast (Kaliningrad region) during the middle and Late Holocene

The raised bog sediments that have been continuously accumulated over time represent the most suitable natural object which enables us to reconstruct Late Glacial and Holocene vegetation and palaeoclimates. Bog peat consists of organic carbon formed in situ. It contains moss, plant fragments and microfossils that are necessary for the study of palaeovegetation and palaeoclimate. However, a successful study of palaeoenvironment can be carried out on the basis of investigation of a great quantity of samples along the whole peatbog thickness. In the present paper, the authors present the results of palynological, botanical investigations and radiocarbon dating of 31 peat samples taken from the raised bog Velikoye, located in the eastern part of Kaliningrad Region. The data obtained have enabled us to reconstruct the palaeovegetation, reveal the evolution of the bog and determine rate of peat formation at different evolutional stages over the last 7500 cal BP.

New Data on the Ladoga Transgression, the Neva River Formation, and Agricultural Development of Northwestern Russia

The geological history of Lake Ladoga, its connection with the Baltic basin, the formation of the Neva River, and the development of the whole region by people have been studied by Russian and Finnish scholars for a long time. Investigations carried out over the last fifteen years [1‐4] have made it possible to obtain new data on the problem; nevertheless, many problems still remain to be solved. To fill the existing gaps as well as to reveal the effect of hydrological changes on the early human settlements, international complex studies were carried out within an INTAS project and a project of the Russian Foundation for Basic Research. As subjects of investigation there were chosen peat bogs and lakes located in the central part of the Karelian Isthmus, in the region of the Vetokalio Rapids, the lowest area of the Ladoga‐Baltic watershed (the absolute height is 15.4 m above sea level) situated near the settlement of Veshcheevo, Vyborg raion, Leningrad oblast. Moreover, sections in the Neva River valley and in the southern part of the Ladoga region at the Volkhov and Oyat’ rivers (Fig. 1) were also studied. In the region of Veshcheevo (Karelian Isthmus), deposits of the Nizhneosinovskoe bog and Lamskoe and Makarovskoe lakes located west and east of the Vetokalio Rapids respectively were studied (Fig. 2). The section of the Nizhneosinovskoe bog located 23 m above sea level (masl) exposed the sequence of lacustrine and mire lake‐bog deposits reflecting early stages of the existence of the so-called Hejnijoki Strait: a Baltic Ice lake (BIL), the Yoldia Sea, the later stage of which was dated at 9580 ± 100 years (9200‐8600 cal BC, LY-5306), and Ancylus Lake. Judging from the data obtained, the level of the Yoldia Sea in the central part of the Karelian Isthmus (25 masl) was reached 9400 ± 130 years (9150‐8250 cal BC, LU-5309). Overlying deposits comprise the diatom assemblage characteristic of the Ancylus freshwater lake. Between 8250 and 7100 cal BC, following the regressive lowering of the Ancylus Lake level, the basin in Nizhnesinovskoe peatbog area became isolated, existed for some time as a small lake and consequently became transformed into a bog. The study of bottom deposits of Makarovskoe (11.4 masl), Lamskoe (14.5 masl), and Uzlovoe (13.0 masl) lakes revealed final episodes of the existence of the Hejnijoki Strait. Deposits represented by lake mud were formed under conditions of shallowwater, slightly running-water, and stagnant lakes. The disappearance of “Ladoga elements” from the diatom flora and a change of the sedimentary environment from the strong-flow (sandy deposits), to slow-flow and stagnant ones (organogenic deposits) perceptible after 1980 cal BC, are indicative of isolation of lakes in the course of recession of the Lake Ladoga water level.

EVOLUTION OF WATERWAYS AND EARLY HUMAN SETTLEMENTS IN THE EASTERN BALTIC AREA: RADIOCARBON-BASED CHRONOLOGY

Newly obtained radiocarbon measurements are used to suggest that the initial settlement of the northeastern Baltic area was largely controlled by the Ladoga-Baltic waterway in the north of the Karelian Isthmus, which emerged ~11,500 cal BP and remained in action for ~7000 yr. The transgression of Ladoga Lake started ~5000 cal BP and reached its maximum at ~3000 cal BP (~11001000 cal BC). The formation of a new outlet via the Neva River led to a rapid regression of the lake that stimulated the spread of farming populations.

Late Pleistocene-Holocene paleolimnology of three north-western Russian lakes

The vegetation history and development of three different types of lakes, lakes Valday, Kubenskoye and Vishnevskoye (northwest of the East European Plain) were reconstructed using paleolimnological techniques. Watershed vegetation demonstrates a close connection with climate fluctuations: gradual expansion of the southern broad-leaved trees to the North during the Holocene with the maximum extent during the climate optimum (8000–5000 BP); and their subsequent retreat afterwards; followed by the extension of spruce during the cold and dry Subboreal time; and dominance of pine-spruce-birch forests in the Subatlantic time. The Late Pleistocene and Holocene climate changes resulted in lake-level fluctuations and other ecosystem changes. Valday Lake was formed ca. 12,500 BP as an oligotrophic, deep water basin. The lake level decreased during the dry Boreal, then increased again during the humid Atlantic period. The large shallow Kubenskoye Lake was formerly a part of an ice margin lake, which was then separated (ca. 13,000 BP) and developed into the Sukhona Basin with an outflow to the northwest. During the Atlantic, the outflow direction changed to the east. As a result, the ancient Sukhona Lake disappeared and Kubenskoye Lake formed in its modern size and shape. Vishnevskoye Lake, on the Karelian Isthmus, was formed at the beginning of the Preboreal after the disappearance of the Baltic Ice Lake. It was flooded by waters of the Boreal Ancylus transgression of the Baltic Basin and had become a small eutrophic lake by the time.