Anatoly A Bobrov

Paleoenvironmental and paleoclimatic records from permafrost deposits in the Arctic region of Northern Siberia

Ice Complexes, extremely ice-rich permafrost deposits with large ice wedges, are widely distributed in the Arctic region of northeast Siberia. They present excellent archives for the reconstruction of Late Quaternary paleoenvironmental conditions in nonglaciated areas. In 1998, 1999, and 2000 Russian and German scientists worked together on the Bykovsky Peninsula southeast of the Lena Delta in order to investigate the Ice Complex and its associated sediments. Intensive cryolithological and sedimentological studies, Radiocarbon age determinations, paleobotanical studies, micropaleontological investigations, studies of mammal and insect fossils, and stable isotope analyses of ground ice were performed. Radiocarbon data have been obtained from the entire exposed sequence coveringapproximately the last 60,000 years. The results indicate that compared with modern time the investig ated Ice Complex sequence was formed duringtwo cooler and more arid stages of the Late Pleistocene with relatively uniform environmental conditions, separated by a stage with environmental variations and more intensive soil formation caused by climate amelioration. The Late Pleistocene environmental changes were not as strong as those occurring during the Pleistocene/Holocene transition where a sharp break is evident. r 2002 Elsevier Science Ltd and INQUA. All rights reserved.

Ecology of Testate Amoebae (Protozoa: Rhizopoda) on Peatlands in Western Russia with Special Attention to Niche Separation in Closely Related Taxa

Testate amoebae (Protozoa: Rhizopoda) are frequently used as indicators of past environmental changes, and the interpretation of fossil assemblages depends upon our knowledge of ecological affinities of taxa in modern environments. A variety of taxonomic approaches have been used in fossil studies, mostly involving grouping of closely related taxa. This paper presents data from peatlands in western Russia relating surface wetness parameters to species occurrence. Relationships between species abundance, water table depth and soil moisture are modelled using weighted averaging, and species niches are calculated as optima and tolerance for these parameters. Niche separation of closely related taxa is examined in detail and it is shown that there is often a gradient of hydrological preference within each group of taxa. Wet to dry gradients include those found in the Trigonopyxis arcula group (T. arcula var. major > T. arcula > T. minuta), the Assulina-Valkanovia group (A. seminulum > A. muscorum > V. elegans), and the Trinema lineare group (T. lineare var. truncatum/ T. lineare > T. lineare var. terricola), all of which are associated with a large to small size gradient. In addition, spined forms within the Euglypha and Placocista genera are shown to consistently occur in wetter habitats than glabrous forms or those with shorter spines. It is concluded that palaeoecological studies should attempt the lowest taxonomic divisions possible within these groups, to maximise the ecological indicator value of the assemblages recorded.

Late Quaternary History of the Accumulation Plain North of the Chekanovsky Ridge (Lena Delta, Russia): A Multidisciplinary Approach

Permafrost deposits were studied along the Olenyeksky and the Arinsky distributaries in the western Lena delta using a multidisciplinary approach that included sedimentological, mineralogical, stable-isotope, and paleoecological analyses in order to reconstruct the Late Quaternary landscape and environmental history of this Northeast

Taxonomic and Ecological Implications of Shell Morphology of Three Testaceans (Protozoa: Rhizopoda) in Russia and Canada

Summary: Morphological comparisons of shells of three testaceans, Trigonopyxis arcula, Nebela militaris , and Hyalosphenia papilio were made between a population in Russia and in Canada. Morphological differences were noted in the shells of T. arcula sensu lato , while no major differences in shell morphology were found in the latter two species. We suggest that the degree of variability, found in the two geographically isolated populations of T. arcula sensu lato indicates shell polymorphism. Shell polymorphism may complicate traditional taxonomic treatments which depend solely on morphological features of the shell.

Vegetation history of central Chukotka deduced from permafrost paleoenvironmental records of the El'gygytgyn Impact Crater

Introduction Conclusions References

Findings of the Tropical Group Testate Amoebae (Protozoa: Testacea) at the Far East (Sikhote Alin Reserve)

Testate amoebae species Hoogenraadia humicola, Planhoogenraadia media, and Distomatopyxis couillardiof the Gondwana–tropical and tropical groups have been found for the first time in the territory of Russia. Brown and dark-colored soil of oak forest in Primorskii Krai (Sikhote Alin Reserve, northeast part of the East Asian Holarctic) are the northernmost range of these tropical species. The morphometric data are presented, and the specific composition of the communities and geographical distribution of the tropical group species are discussed. A new species, Planhoogenraadia dauricaBobrov, has been described.

[Ecology of testate amoebae from oligotrophic peatlands: specific features of polytypic and polymorphic species].

Relationships between species abundance and water table depth and soil moisture have been modeled using weighted averaging and species niches have been calculated as optima and tolerance for these parameters. Niche separation of closely related taxa has been examined in detail and it has been shown that there is often a gradient of hydrological preference within each taxon. Wet to dry gradients include those found in the Trigonopyxis arcula group (T. arcula var. major > T. arcula > T. minuta), Assulina–Valkanovia group (A. seminulum > A. muscorum > V. elegans), and Trinema lineare group (T. lineare var. truncatum > T. lineare > T. lineare var. terricola), all of which are associated with a large to small size gradient. In addition, spined forms within the Euglypha and Placocista genera have been shown to consistently occur in wetter habitats than glabrous forms of those with shorter spines. A conclusion has been drawn that palaeoecological studies should cover the lowest taxa possible within these groups to maximize the ecological indicator value of the assemblages recorded.

Testate amoebae and environmental features of polygon tundra in the Indigirka lowland (East Siberia)

Polygon tundra characterizes large areas of arctic lowlands. The micro-relief pattern within polygons offers differentiated habitats for testate amoeba (testacean) communities. The objective of this study was to relate testacean species distribution within a polygon to the environmental setting. Therefore, testaceans from four cryosol pits dug at different locations within a low-centered polygon were studied in the context of pedological and pedochemical data, while ground temperature and ground moisture were measured over one summer season. The study site is located on the Berelekh River floodplain (Indigirka lowland, East Siberia). The environmental data sets reflect variations along the rim-to-center transect of the polygon and in different horizons of each pit. The testacean species distribution is mainly controlled by the soil moisture regime and pH. Most of the identified testaceans are cosmopolitans; eight species are described from an arctic environment for the first time. Differences in environmental conditions are controlled by the micro-relief of polygon tundra and must be considered in arctic lowland testacean research because they bias species composition and any further (paleo-)ecological interpretation.

Testate amoebae communities from some freshwater and soil habitats in China (Hubei and Shandong Provinces)

Seventy-eight species and forms of testate amoebae were identified from 29 freshwater and soil habitats in three territories of China (Shandong and Hubei Provinces). Most abundant species from the genera Plagiopyxis, Centropyxis and Trinema represent the globally-distributed and eurybiont group of testate amoebae. The species richness was observed to be the lowest (7–12 species per biotope) in sandy sediments of the Yangtze River, but considerably higher (20–30 taxa) in soil environment. In the range of terrestrial habitats, the most remote communities from Laoshan Mountain in Shandong Province, China manifested the highest difference from others. On the other hand, communities originated in the most distant from industrial center places (Guifeng Mountain in Hubei Province, China) possess the most peculiar species composition including specific Gondwanian taxa (e.g. Nebela bigibbosa). In sum, the results obtained provide the evidence that the community complexity and specificity reduce in the places located within areas that are highly populated and intensively visited by humans.

[Testaceans (Protozoa: Testacea) in quaternary permafrost sediments of Bykovsky Peninsula, arctic Yakutia].

The results of the first protozoological study in terms of paleoecology of long-term sediments and buried soils formed in the cryolite zone of northeastern Siberia are discussed. The data on testaceans (Protozoa: Testacea) inhabiting various sites of Bykovsky Peninsula, Laptev Sea coast near estuary of Lena, within the last 53 000 years (Late Pleistocene and Holocene) are presented.