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Doklady Earth Sciences - 相似文献
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Larisa Frolova Larisa Nazarova Ludmila Pestryakova Ulrike Herzschuh 《Journal of Paleolimnology》2014,52(1-2):107-119
Subfossil Cladocera were sampled and examined from the surface sediments of 35 thermokarst lakes along a temperature gradient crossing the tree line in the Anabar-river basin in northwestern Yakutia, northeastern Siberia. The lakes were distributed through three environmental zones: typical tundra, southern tundra and forest tundra. All lakes were situated within the continuous permafrost zone. Our investigation showed that the cladoceran communities in the lakes of the Anabar region are diverse and abundant, as reflected by taxonomic richness, and high diversity and evenness indices (H = 1.89 ± 0.51; I = 0.8 ± 0.18). CONISS cluster analysis indicated that the cladoceran communities in the three ecological zones (typical tundra, southern tundra and forest-tundra) differed in their taxonomic composition and structure. Differences in the cladoceran assemblages were related to limnological features and geographical position, vegetation type, climate and water chemistry. The constrained redundancy analysis indicated that TJuly, water depth and both sulphate (SO4 2?) and silica (Si4+) concentrations significantly (p ≤ 0.05) explained variance in the cladoceran assemblage. TJuly featured the highest percentage (17.4 %) of explained variance in the distribution of subfossil Cladocera. One of the most significant changes in the structure of the cladoceran communities in the investigated transect was the replacement of closely related species along the latitudinal and vegetation gradient. The results demonstrate the potential for a regional cladoceran-based temperature model for the Arctic regions of Russia, and for and Yakutia in particular. 相似文献
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Koshlyakova N. N. Pekov I. V. Vigasina M. F. Agakhanov A. A. Nazarova M. A. 《Doklady Earth Sciences》2022,507(1):900-903
Doklady Earth Sciences - A novel solid solution between isostructural Mg arsenate and phosphate of the wagnerite group and a new As5+-rich variety of wagnerite were discovered in sublimates of the... 相似文献
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Katherine A. Nazarova 《Marine Geophysical Researches》1994,16(6):455-462
New data acquired on the slow spreading Mid-Atlantic Ridge during several Legs of the Ocean Drilling Programme (ODP) give evidence that, in many places, serpentinized peridotites constitute the upper oceanic crust in the vicinity of rift valley. This discovery contradicts the classical view on the formation of oceanic crust at the ridge axis, which postulates that only basalts constitute the upper oceanic crust.The magnetic properties of 57 samples of such serpentinized peridotites, collected at five ODP sites in the Atlantic Ocean, have been analyzed in order to examine the origin and evolution of their natural remanent magnetization (NRM). All samples are characterized by NRM (average value about 3.5 A/M) comparable with NRM of altered oceanic basalts. Average Q-ratio (NRM to induced magnetization ratio) was about 2.The results reported here give evidence that serpentinization is a complex and irregular process. The local concentration of magnetite is determined by magnetostatic interaction between magnetic grains rather than volume concentration of magnetite. This local concentration, which represents the degree of serpentinization, affects the NRM value. The domain structure of magnetite grains developed during serpentinization is controlled by the degree of serpentinization.Experimental data show that original remanence of serpentinites exposed in the upper oceanic crust may contribute to the oceanic magnetic anomalies. In particular, serpentinites with magnetite of pseudodomain size represent a very probable source for magnetic anomalies. It is however unlikely that such ODP serpentinites systematically contribute to the oceanic magnetic lineations. 相似文献
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On the basis of Sobolev's method, the population of 30 levels of hydrogen atom is determined allowing for the radiative and collision processes of the heating and ionization of the medium with velocity gradient gradv=10–9–10–11s–1, electron temperatureT
e=104 K-2×104 K and electron densityN
e=1010 cm–3–1011 cm–3. The central source radiation is characterized by a power spectrum with spectral indices varying from 0 to 2. A region of possible physical conditions is found where the thermal diffuse radiation of the envelope exceeds the emission in the Balmer H line. 相似文献
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I. N. Yeltsov L. A. Nazarov L. A. Nazarova G. V. Nesterova M. I. Epov 《Doklady Earth Sciences》2012,445(2):1021-1024
The problem of interpretation of geophysical data taking into account hydrodynamical and geo-mechanical processes in oil-drilling wells is considered. The effects emerging due to change of porosity and permeability are studied, and the influence of such effects on the geophysical measurements in a borehole is analyzed on the basis of characteristic parameters of the Kogalym oilfield reservoirs. 相似文献
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Larisa Nazarova Ulrike Herzschuh Sebastian Wetterich Thomas Kumke Ludmila Pestryakova 《Journal of Paleolimnology》2011,45(1):57-71
We investigated the subfossil chironomid fauna of 150 lakes situated in Yakutia, northeastern Russia. The objective of this
study was to assess the relationship between chironomid assemblage composition and the environment and to develop chironomid
inference models for quantifying past regional climate and environmental changes in this poorly investigated area of northern
Russia. The environmental data and sediment samples for chironomid analysis were collected in 5 consecutive years, 2003–2007,
from several regions of Yakutia. The lakes spanned wide latitudinal and longitudinal ranges and were distributed through several
environmental zones (arctic tundra, typical tundra, steppe-tundra, boreal coniferous forest), but all were situated within
the zone of continuous permafrost. Mean July temperature (TJuly) varied from 3.4°C in the Laptev Sea region to 18.8°C in central Yakutia near Yakutsk. Water depth (WD) varied from 0.1 to
17.1 m. TJuly and WD were identified as the strongest predictor variables explaining the chironomid communitiy composition and distribution
of the taxa in our data set. Quantitative transfer functions were developed using two unimodal regression calibration techniques:
simple weighted averaging (WA) and weighted averaging partial least squares (WA-PLS). The two-component TJuly WA-PLS model had the best performance. It produced a strong coefficient of determination (r
2
boot = 0.87), root mean square error of prediction (RMSEP = 1.93), and max bias (max biasboot = 2.17). For WD, the one-component WA-PLS model had the best performance (r
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boot = 0.62, RMSEP = 0.35, max biasboot = 0.47). 相似文献
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L. B. Nazarova D. A. Subetto L. S. Syrykh I. M. Grekov P. A. Leontev 《Doklady Earth Sciences》2018,480(2):710-714
The use of chironomids (Diptera: Chironomidae) as indicators of changes in natural and climatic settings allows one to reconstruct paleoclimatic and paleoenvironmental conditions. Based on the results of lithological and chironomid analyses, the loss on ignition (LOI) values, as well as the results of radiocarbon dating (14C AMS), new data on the paleoclimate in the Karelian Isthmus, in particular the quantitative reconstruction of the mean July temperature (TJuly, °C) in the Late Pleistocene and Holocene and the evolution of the ecosystem of Medvedevskoe Lake have been obtained. 相似文献
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Nadia Solovieva Vivienne J. Jones Larisa Nazarova Stephen J. Brooks H. J. B. Birks John-Arvid Grytnes Peter G. Appleby Tommi Kauppila Boris Kondratenok Ingemar Renberg Vasily Ponomarev 《Journal of Paleolimnology》2005,33(4):463-482
The recent sediments from two deep arctic lakes, Mitrofanovskoe and Vanuk-ty, situated in the permafrost belt within the Bolshezemelskaya Tundra in the northern Ural region, were studied for diatoms, chironomids, spheroidal carbonaceous particles and stable lead isotopes. The magnitudes and rates-of-change in diatom and chironomid assemblages were numerically estimated. Instrumental climate records were used to assess statistically the amount of variance in diatom and chironomid data explained by temperature. August and September air temperatures have a statistically significant effect on diatom composition at both lakes. At Mitrofanovskoe Lake, major compositional changes in diatom and chironomid assemblages occurred at the turn of the 20th century and might be related to the regional increase in temperature. Chironomid-inferred air temperature also increased by approximately 1 °C since the early 1900s. At both lakes diatom compositional changes, coincident with the increase in June and September temperatures, also occurred in the late 1960s. These compositional changes are correlated with the increase in diatom production, sediment organic content and diatom species richness, and are likely to be a diatom response to the lengthening of the growing season. These changes are also correlated with the circum-Arctic temperature increase from the 1960s. A chironomid response to the late 1960s temperature increase was less pronounced at both lakes. Pollution levels are relatively low and pollution history is unrelated to ecological changes. Both lead isotopes and spheroidal carbonaceous particles show a clear atmospheric pollution signal, peaking in the 1980s. 相似文献