Search

The lithological and mineralogical characteristics of sea surface sediments, composition of microfossils, contribution of organic matter, and element composition have been studied in a core from the northern part of East Novaya Zemlya Trough. Sedimentation rates were calculated based on the radioisotopes 210Pb and 137Cs. Lithological, biogeochemical, and geochemical studies showed a low variability of the sedimentation conditions over the last 250 years. However, even small changes in microfossils, as well as lithological and geochemical parameters, make it possible to trace some short-term climate changes in this area, probably controlled by atmospheric circulation. The core shows a clear binomial structure, reflecting changes in sedimentation at the end of the Little Ice Age (LIA) and afterward. For the northern part of the East Novaya Zemlya Trough, low sea surface temperatures and an increase in the duration of ice cover at the end of the LIA in the 1780s−1810s have been reconstructed. Since the 1810s, the hydrodynamic activity of water masses intensified sharply due to glacier melting (especially after the 1840s). In addition, an increase in sea surface temperatures can be assumed, except for the cooling of the 1910s. Later, circulation of water masses increased, contributing to the supply of terrigenous material to the deep parts of the trough.

The White Sea being connected with the Arctic Ocean via the Barents Sea has an influence on its water temperature/salinity structures and biological processes and thus has an indirect impact on the Eurasian climate system. In this work, we have managed to find a correspondence between the climate fluctuation in the Holocene and changes in the geochemical and microfossil properties in the sediment core of the White Sea. For the first time, the element speciation in the sediment core covering about 10,000 cal yr BP period was investigated. The cooling periods (the early Holocene and the Subboreal stage) were characterized by a trend of increase in Si, Al, and Ti contents and Ti/Al ratios, which reflect lithogenous contribution, and decrease in geochemically labile forms of trace elements. A significant increase in the content of organic-bound trace elements and biogenic components (Сorg, BSi, and chlorin) was observed during periods of Holocene climatic optimums. The evident relationship between the metal speciation and indicators of the sedimentation paleoenvironment is observed at the stage of the active phase of early diagenesis after the slowing down of the biogeochemical processes. Down-core decrease in the Mn oxyhydroxide content exhibited a weakening of diagenesis processes at the ~130–150 cm depth.

Marine sediments and samples of suspended particulate matter from the North Atlantic were studied. It is shown that modern sedimentation in this area is controlled mainly by the efficiency of autochthonous marine phytoplankton and sediment supply by the system of near-bottom currents, as well as by means of the ice-rafting. The studied sediment sections were formed in the North Atlantic during the Middle Pleistocene to Holocene. The highest sedimentation rate, up to 58.3 cm/kyr, is established for AI-3359 core, collected in the area of the Gardar and Björn Drifts. This makes the core very interesting for detailed paleoreconstructions. AI-3378 and AI-3415 cores are characterized by low sedimentation rates. Nevertheless, they are of interest for spatial paleoreconstructions on a continuous timeline. The general pattern is established for the first time for the sediments from the central North Atlantic: biogeochemically significant processes are detected only in the thin surface layer (0–2 cm) and almost completely cease at depths of 90–180 cm. The processes are probably controlled by the position of the sampling stations and the composition of organic matter (OM) but not related to the age of the sedimentary layer. The low microbial activity in the sediments is most likely the result of a lack of OM.

The distribution of natural radionuclides and organic matter in bottom sediments of the active biosedimentation zone on the section drawn through the arctic front of the North Atlantic was studied. The ratios of the amounts of 226Ra, 238U, and 232Th, both deposited in the surface layer of bottom sediments from seawater and supplied with the terrigenic material, were estimated. Direct deposition of radium from water to marine sediments correlates with the organic matter content. The concentration of radium that is not in equilibrium with uranium varies in the range 95–99% of the total content and increases with an increase in the content of chloroform-soluble bitominoid (CB) (R = 0.95). The deposition of nonequilibrium 238U from water to bottom deposits is also significant and ranges from 42 to 69% of the total 238U content. The concentration ratio of nonequilibrium uranium and nonequilibrium radium in the sediments decreases with increasing depth and increases with an increase in the CB content of the deposit. Positive correlation is observed between the content of thorium and total uranium (R = 0.93) and of its nonequilibrium and terrigenic fractions (R = 0.93 and 0.94, respectively).

Marine sediments and samples of suspended particulate matter from the North Atlantic were studied. It is shown that modern sedimentation in this area is controlled mainly by the efficiency of autochthonous marine phytoplankton and sediment supply by the system of near-bottom currents, as well as by means of the ice-rafting. The studied sediment sections were formed in the North Atlantic during the Middle Pleistocene to Holocene. The highest sedimentation rate, up to 58.3 cm/kyr, is established for AI-3359 core, collected in the area of the Gardar and Bjorn Drifts. This makes the core very interesting for detailed paleoreconstructions. AI-3378 and AI-3415 cores are characterized by low sedimentation rates. Nevertheless, they are of interest for spatial paleoreconstructions on a continuous timeline. The general pattern is established for the first time for the sediments from the central North Atlantic: biogeochemically significant processes are detected only in the thin surface layer (0–2 cm) and almost completely cease at depths of 90–180 cm. The processes are probably controlled by the position of the sampling stations and the composition of organic matter (OM) but not related to the age of the sedimentary layer. The low microbial activity in the sediments is most likely the result of a lack of OM.

A combination of physicochemical and radiotracer analysis, high-throughput sequencing of the 16S rRNA, and particulate methane monooxygenase subunit A (pmoA) genes was used to link a microbial community profile with methane, sulfur, and nitrogen cycling processes. The objects of study were surface sediments sampled at five stations in the northern part of the Barents Sea. The methane content in the upper layers (0–5 cm) ranged from 0.2 to 2.4 µM and increased with depth (16–19 cm) to 9.5 µM. The rate of methane oxidation in the oxic upper layers varied from 2 to 23 nmol CH4 L−1 day−1 and decreased to 0.3 nmol L−1 day−1 in the anoxic zone at a depth of 16–19 cm. Sulfate reduction rates were much higher, from 0.3 to 2.8 µmol L −1 day −1. In the surface sediments, ammonia-oxidizing Nitrosopumilaceae were abundant, the subsequent oxidation of nitrite to nitrate can be carried out by Nitrospira sp. Aerobic methane oxidation could be performed by uncultured deep-sea cluster 3 of gamma-proteobacterial methanotrophs. Undetectable low levels of methanogenesis were consistent with a near complete absence of methanogens. Anaerobic methane oxidation in the deeper sediments was likely performed by ANME-2a-2b and ANME-2c archaea in consortium with sulfate-reducing Desulfobacterota. Sulfide can be oxidized by nitrate-reducing Sulfurovum sp. Thus, the sulfur cycle was linked with the anaerobic oxidation of methane and the nitrogen cycle, which included the oxidation of ammonium to nitrate in the oxic zone and denitrification coupled to the oxidation of sulfide in the deeper sediments. Methane concentrations and rates of microbial biogeochemical processes in sediments in the northern part of the Barents Sea were noticeably higher than in oligotrophic areas of the Arctic Ocean, indicating that an increase in methane concentration significantly activates microbial processes.

A comprehensive examination of the elemental (including radionuclides and heavy metals), mineral, and grain-size composition of sediments from different areas of the Barents Sea was performed. Sediment cores were sampled in the Central Deep, Cambridge Strait (Franz Josef Land Archipelago), Russkaya Gavan&rsquo, Bay (Novaya Zemlya Archipelago), and Bear Island Trough. We aim to evaluate how the modern and more ancient environmental conditions are reflected in the elemental and mineral composition, as well as to test indicative elemental ratios. The applied methods include elemental analysis using gamma-ray spectroscopy, X-ray fluorescence (XRF), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), and X-Ray Difractometry XRD analysis of minerals. Difference in sedimentation rates, grain-size composition, and sources of material, are reflected in downcore variation of Si/Al, Mn/Fe, P/Al, Ti/K, and quartz-feldspar ratios. At boundary Early Holocene/Late Deglaciation, intensive bottom currents from the West-Southern shelf areas contributed to increase of Si/Al and Zr/Ca ratios. Distinct growth of the Si/Fe ratio within the sediments deposited over Late Pleistocene to Mid Holocene may be caused by increased contents of the coarse sand material, as well as by abundant fluxes of clay-mineral-loaded glacial meltwater during the main deglaciation phase. The Mn/Fe ratio used as redox proxy, displayed peaks at different depths related to oxygen concentration growth in bottom water.

Data file presents information on the variation in sea surface temperatures (SST), as well as geochemical (e.g. stable isotope, calcium carbonate), micropaleontological and grain size data from the Gloria Drift (Northwest Atlantic). The data are obtained from the three marine sediment gravity core sections (AMK-4493, AI-3646 and AI-3415) which were formed during Quaternary period. Dataset contains SST values (winter and summer: 0–50 water layer) and ice-rafted debris (IRD) counts, each in 308 samples; stable isotope data (δ18O and δ13C) from 235 samples; calcium carbonate content from 351 samples; relative abundance of polar species of planktonic foraminifera Neogloboquadrina pachyderma (sinistral) (Ehrenberg) in 51 samples, data of grain size analysis in bulk sediments (123 samples) and carbonate-free sediments (664). These data provide information about conditions of sedimentation at the Gloria Drift area. Keywords: Sea surface temperature, Ice-rafted debris, Stable isotope data, Sediment grain size, Quaternary sediments, North Atlantic, Gloria Drift

A multiproxy study of the sediment cores taken from the Snorri Drift, formed under the influence of the Iceland&ndash, Scotland bottom contour current, and from the Gloria Drift, located southward Greenland at the boundary of Irminger and Labrador Seas, was performed. This area undergoes a variable mixing of polar waters with the warm North Atlantic current, whose intensity and direction seemed to change dramatically with the alteration of warming and cooling periods during the six marine isotope stages MIS 1-6. The relative age of this core does not exceed 190,000 cal yr BP, the average sedimentation rate was 1.94 and 2.45 cm/kyr in the Gloria and Snorri Drifts core respectively. In both the cores, the sediment records showed the downcore co-variation of ice-rafted debris (IRD), and terrigenous elements, such as Si, Al, Ti, Cr, and Zr, were revealed, their values were clearly higher in the glacial periods (MIS 2, 4, and 6) compared to interglacials (MIS 1, 3, and 5). The downcore rhythmic distributions of these elements, as well as Al/Si, Ti/Al, Fe/Al ratios exhibit an opposite trend with that of &delta, 18O values, biogenic components (CaCO3, BioSiO2), and Si/Fe and Mn/Fe ratios.

Herein we report the first decadal to centennial–scale resolution data on foraminiferal and dinocyst assemblages from core AMK-5454 collected in the hard-to-reach Cambridge Strait, Franz Josef Land, and on corresponding paleoenvironments over the last 9.2 ka. The dinocyst and foraminiferal assemblages from the core are rather diverse through the Holocene and represented by 24 and 33 taxa, respectively. The most active hydrodynamics and probably Atlantic Water (AW) inflow are suggested by the enhanced values of autotrophic dinocysts and epibenthic species, as well as Melonis barleeanus, from 9.2 to 6.3 cal ka BP. Specific benthic assemblages indicate high-productivity frontal conditions at site location from 6.3 to 4.1 cal ka BP. AW influx from the Franz Victoria Trough to the Cambridge Strait in subsurface to bottom layer, below the very cold Arctic Water and dense sea ice, is documented by enhanced % Cassidulina teretis over the last 4.5 ka.

The descent of a large quantity of dust responsible for bright colors of atmospheric precipitation in the temperate, subpolar, and polar zones of the northern hemisphere is rarely observed [1–5]. In the twentieth century and in the beginning of the twenty-first century in the northern part of European Russia, such events had not been registered right up to March 25–26, 2008. At that time in some parts of the Arkhangelsk region, Komi Republic, and Nenets Autonomous Area, atmospheric precipitation as moist snow and rain responsible for sand and saffron colors of ice crust formation on the snow surface was observed. Thus, due to detailed mineralogical, geochemical, pollen, diatom, and meteorological investigations, it was established that the main source of the yellow dust is the semidesert and steppe regions of the Northwest Kazakhstan, and the Volgograd and Astrakhan regions, Kalmykia.

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 (14)C 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.

Dinoflagellate cysts were studied in 42 samples from the surface sediments of the White Sea. The total concentration of dinocysts varies from single cysts to 25 000 cyst/g of dry sediments, which reflects the biological productivity in the White Sea waters and the regional particular features of the sedimentation processes. The highest concentrations are observed in silts; they are related to the regions of propagation of the highly productive Barents Sea waters in the White Sea. Generally, the spatial distribution of dinocysts species in the surface sediments corresponds to the distribution of the major types of water masses in the White Sea. The cysts of the relatively warm-water species (Operculodinium centrocarpum, Spiniferites sp.) of North Atlantic origin that dominate in the sediments indicate an intensive intrusion of the Barents Sea water masses to the White Sea along with hydrological dwelling conditions in the White Sea favorable for the development of these species during their vegetation period. The cold-water dinocyst assemblage (Islandinium minutum, Polykrikos sp.) is rather strictly confined to the inner parts of shallow-water bays, firstly, those adjacent to the Onega and Severnaya Dvina river mouths.

According to available historical evidence, colonization of the White Sea region began in the 9th–8th centuries B.C. [2]. This unique region with ancient residence sites experiences progressively increasing anthropogenic load against the background of natural climatic changes. The intense economic development of the region requires complex ecological and paleogeographic studies aimed at detailed reconstruction of past sedimentation settings. The analysis of dinocysts, which makes it possible to reconstruct various parameters of water masses washing the Arctic shelf, has become a promising method in paleohydrological studies, widely used in recent years [10, 11]. Dinoflagellates, which represent one of the main phytoplankton groups in the Arctic Seas, the White Sea included, form cysts with biopolymer envelopes, which are preserved in sediments. Thus, information on glacial–hydrological conditions is recorded in marine sediments. In the White Sea, this method was first used for the study of bottom sediments only in 2003 [3, 15]. In this communication, we present the first results obtained during the thorough study of dinocysts in bottom sediment cores from the White Sea, which cover the last 250 years. The study of this microfossil group made it possible to reconstruct in detail changes in glacial–hydrological settings in the sea and reveal their relations with known climatic–hydrological events that occurred in neighboring regions during the historical period.

Immediate and long term results of 2 methods of coronary angioplasty (balloon dilatation and stenting) were analyzed retrospectively. During 10 years proportion of stent implantations increased 30-fold reaching 95-97% of coronary interventions. This was associated with improvement of immediate results of angioplasty: lowered rates of myocardial infarctions, urgent coronary artery bypass graftings and acute coronary artery occlusions (from 2.7% after balloon angioplasty to 0.6% after stenting). Improved long-term prognosis after stenting manifested in lower frequency of cardiovascular events. Five year survival was 98,8 and 92.7% after stenting and balloon angioplasty, respectively (p=0.004). However effect of stenting on rates of angiographic restenosis and repeat revascularizations was less pronounced (27.1 and 30.4%, respectively, after stenting vs. 30.1 and 34.5%, respectively, after balloon angioplasty).