Yelena I. Polyakova

Diatom-inferred salinity records from the Arctic Siberian Margin: Implications for fluvial runoff patterns during the Holocene

Diatom assemblages were employed to study temporal changes of Siberian river runoff on the Laptev Sea shelf. Using a correlation between freshwater diatoms (%) in core-top sediments and summer surface water salinities from the inner Kara Sea, salinity conditions were reconstructed for a site northeast of the Lena River Delta (present water depth 32 m) since 9 calendar years (cal) ka. The reconstruction indicate a strong, near-coastal, and river-influenced environment at the site until about 8.6 cal ka. Corroborated by comparison with other proxy records from further to the east, surface salinities increased from 9 to 14 until about 7.4 cal ka, owing to ongoing global sea level rise and synchronous southward shift of the coastline. Although riverine water became less influential at the site since then, salinities still varied between 12.5 and 15, particularly during the last 3.5 kyr. These more recent salinity fluctuations agree well with reconstructions from just north of the Lena Delta, emphasizing the strong linkage between shelf hydrography and riverine discharge patterns in Arctic Siberia.

Changes in the Lena River runoff during the Holocene

The spatial and temporal changes in the Lena River runoff over the last 9 thousand years are reconstructed through studying the freshwater microfossils in sediment cores obtained from the Laptev Sea inner shelf immediately adjacent to the Lena delta and subject to the freshening effect of river water inflowing the sea through the main arms of the delta (the Trofimovskaya, Bykovskaya, and Tumatskaya arms), the sediments having been thoroughly AMS 14C dated. The freshwater species of diatoms (predominantly the river ones) and green algae that enter the shelf with river water served as indicators of river runoff. The reconstruction of paleosalinity of the sea surface water in the regions under study is based on the relationships (established earlier) between the distribution of freshwater diatoms in the surface layers of sediments in the Arctic seas and the gradients of water salinity in summer. Data on variations in the composition of aquatic microfossil associations in sediments and the reconstructed paleosalinity in the regions of the eastern and western paleovalleys of the Lena River are used to determine the main paleohydrologic events that controlled the variations in the Lena runoff into the shelf zone of the Laptev Sea during the Holocene.

Diatoms and Aquatic Palynomorphs in the White Sea Sediments as Indicators of Sedimentation Processes and Paleoceanography

Comprehensive studies of diatoms and palynomorphs from the White Sea sediments revealed the following features of the composition of their assemblages. The species composition of the marine plankton diatoms and dinoflagellate cysts in the sediments reflects the features of the high-latitude position of the sea and the impact of the Arctic and North Atlantic water masses on hydrological regime of the White Sea. The spatial distribution of plankton species in the surface sediments (both diatoms and dinoflagellate cysts) matches the distribution of the main types of water masses in the White Sea. The characteristic property of the diatom and dinoflagellate cyst assemblages is the presence, in high concentrations, of relatively warmwater species typical for the Atlantic water masses. Diatom algae, aquatic palynomorphs, and the grain size of surface sediments from bays of the White Sea were investigated in a program dedicated to the study of marginal filters (MF) in the Northern Dvina, the Onega, and the Kem’ Rivers.

Russian-German collaboration in the arctic environmental research

The overview of the 20-years joint Russian-German multidisciplinary researches in the Arctic are represented in this article. Data were obtained during numerous marine and terrestrial expeditions, all-year-round measurements and observations. On the basis of modern research methods including satellite observation, radiocarbon (AMS 14C) dating of the Arctic sea sediments, isotope, biochemical and other methods, the new unique records were obtained. Special emphasis devoted to the latest data concerning modern sea-ice, ocean and sedimentation processes, evolution of the permafrost and paleoenvironments in the Laptev Sea System.