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Multidisciplinary studies of the bottom sediments–water column–atmospheric water layer system in the Barents and Pechora seas and Baydaratskaya Bay of the Kara Sea were carried out on the expedition European Arctic–2023: Geological Record of Environmental and Climate Change during the season of polar night and active development of autumn–winter thermal convection. Fundamentally new data on a number of areas of oceanology were obtained in the cruise. [ABSTRACT FROM AUTHOR]

Analysis of the lithological, isotope-geochemical, and micropaleontological parameters of the surface layer of bottom sediments in the North Atlantic was carried out at 26 stations on the profile along 59.5° N. The distribution of moisture content and grain size of sediments reflects vertical/circumcontinental zoning, since fine-grained and water-saturated material accumulates in the deepest parts of the Iceland Basin and the Labrador and Irminger seas, which are farthest from land. Larger masses of calcium carbonate also form there, but organic carbon is unevenly distributed. Both vertical/circumcontinental and climatic (circulation of warm North Atlantic water) zoning affect the mineral composition of the >0.063 mm sediment fraction. Accumulation of diatoms, radiolarians, and planktic foraminifers in sediments reflects both vertical/circumcontinental and, to a greater extent, climatic zoning. Variations in the oxygen and carbon isotopic ratios in the tests of benthic and planktic foraminifers require comprehensive interpretation involving data on the parameters of various surface and bottom water masses. The distribution of planktic microfossil assemblages according to cluster analysis shows distribution areas of different water masses with a distinct boundary along the eastern margin of the Subpolar Gyre. The distribution of cluster assemblages of benthic foraminifers does not correspond much to that of planktic microfossils, reflecting division of the study region into abyssal and shallow areas. [ABSTRACT FROM AUTHOR]

Research regarding the conditions and processes of paleo- and modern sedimentation with an assessment of particles and pollution fluxes, with determination of the rates of biogeochemical processes and regional paleoclimatic reconstructions in the contact area of cold Polar and warm Atlantic water masses under the influence of cold (seep) and hot (hydrothermal) fluids were carried out during the expedition in the Norwegian-Greenland Sea Area and the Barents Sea. The consequences of atlantification are recorded in all components of the geosystems of the Barents Sea and the high-latitude Arctic as well as the reverse effect of the Arctic amplification on the geosystems of the northern North Atlantic occurring both at the present time and in the Pleistocene and Holocene. [ABSTRACT FROM AUTHOR]

The article is devoted to research of warm-water planktonic foraminifera species in the Arctic. The fauna of planktonic and benthic foraminifera in the surface and subsurface layer of Kara Sea sediments were studied. It was found that benthic foraminifera complexes were characteristic of this region. In planktonic foraminifera complexes obtained near Novaya Zemlya, a significant amount of warm-water species from equatorial, tropical, and subtropical regions not native to this region were present. We suggested that these species were brought to the Arctic by waters from low latitudes. The results were compared with published data, demonstrating the presence of warm-water planktonic foraminifera species in sediments around Novaya Zemlya and the Arctic. It was shown that living warm-water planktonic foraminifera were noted in the water column of the Laptev Sea and their tests were observed in modern sediments of its marginal part. [ABSTRACT FROM AUTHOR]

Geological, hydrological, hydrochemical, and biological research has been carried out in the eastern tropical Atlantic. Based on the multibeam echo-sounding and seismic profiling north of the Kane Gap (Sierra Leone Rise), an extensive sedimentary body (contourite fan) has been identified. Data of hydrophysical sounding allows assuming the existence of an overflow of the Antarctic Bottom Water (AABW) through the Kane Gap and its northward penetration. In the sediment cores (Middle Pleistocene to Holocene age), an influence of the AABW is reflected in the alternation of the high and medium carbonate dissolution rates. [ABSTRACT FROM AUTHOR]

Here we present the results of lithological and microfossil (Ostracoda and Foraminifera) analyses and reconstruct the transgressive-regressive changes on the Northern Caspian Sea shelf during the Holocene. Modern and Novocaspian faunas consist of abundant Ostracoda (Cyprideis torosa) and Foraminifera (Ammonia beccarii), which are characteristic of dynamic shallow water conditions. Novocaspian sediments in core profiles GS 194-08-01 and GS 194-08-14 obtained at water depths of 7.5 and 10.3 m, respectively, were deposited in shallower and fresher water environments compared to modern ones. We distinguished Mangyshlak, Novocaspian, and modern sediments in the studied cores from the Northern Caspian shelf. The age of the boundary between Mangyshlak and Novocaspian sediments in the study area correspond to approximately 10550 years BP. [ABSTRACT FROM AUTHOR]

The article summarizes and analyzes published data on the distribution of sea-ice and open-ocean diatoms in 42 cores of bottom sediments from the northwestern part of the Subarctic Pacific that accumulated during the last glacial maximum (LGM). Based on micropaleontological records, the extent of winter sea ice during the LGM could be limited to the Okhotsk and Bering seas. During the warm season, the surface water masses from the open Subarctic Pacific spread widely in the marginal seas. [ABSTRACT FROM AUTHOR]

Planktonic foraminiferal and ice-rafted debris count data, as well as the mean size of mineral particles of the 10-63 μm fraction (sortable silt, $$\overline {SS} $$ ) were used as a proxy for surface and near-bottom paleocurrent intensity variations. The data obtained support our hypothesis about turbiditic origin of the lower (80-370 cm) section of the studied AMK-4515 core. Stratigraphic subdivision of the upper section (0-80 cm) makes it possible to allocate two marine isotope stages (MIS) covering the last 27 ka. The main intervals of the North Atlantic Polar Front (PF) migrations were recorded: south of the modern PF position during early MIS 2 (24-27 ka) with PF presence in the study area during MIS 2 (20-24 ka); south of the study area during the last glacial maximum (18-20 ka). Influence of the near-bottom currents within the investigated interval led to beginning of the channel-related drift formation on the northern slope of the southern channel of the Charlie-Gibbs Fracture Zone. There is a weak relationship between intensity of near-bottom contour currents and long-term climatic cyclicity. However, intervals corresponding to Heinrich events coincide with decrease in bottom currents activity. [ABSTRACT FROM AUTHOR]

The micropaleontological study of two sediment cores taken from the continental slope of the Eastern Kamchatka Peninsula and from the northern Shirshov Ridge in the Bering Sea in the scope of the international KALMAR project reveals regional environmental changes over the last 20 kyr: the end of the last glaciation 20-15 ka, Bølling-Allerød warming 15.0-13.3 ka, the Younger Dryas cooling 13.3-11.9 ka, and the Early Holocene 11.9-5.0 ka. The most drastic paleoclimatic changes occurred at the transition from the last glacial period to the Holocene, which had different consequences in these two neighboring areas of the northwestern Pacific. The Bølling-Allerød warming episode resulted in the formation of a high- productivity marginal ice zone over the Shirshov Ridge and open-ocean conditions near eastern Kamchatka with the dominant influence of Alaskan water masses. The Younger Dryas cooling event in the continental slope area of Kamchatka was likely the most significant over the last 20 kyr: the neritic environments with a winter ice cover were dominant in this area at that time. The onset of the Holocene was probably marked by the formation of seasonally contrasting surface conditions in the northwestern corner of the open subarctic Pacific, which is evident from features indicating winter sea ice development and penetration of south-boreal water masses. [ABSTRACT FROM AUTHOR]

A comparison of micropaleontological data on the distribution of the Cycladophora davisiana radiolarian species in the surface sediment layer and the Late Quaternary sediments from the Subarctic Pacific and Far East marginal seas allowed conclusions concerning the possible conditions and occurrence of intermediate waters during the last glacial maximum. We used the modern data on the C. davisiana species, which is a micro-paleontological indicator of the cold oxygen-rich upper intermediate water mass, which is now forming only in the Sea of Okhotsk. The high amount of C. davisiana in sediments of the last glacial maximum may point to the possible formation and expansion of the ventilated intermediate water in the most part of the Subarctic paleo-Pacific: the Bering Sea, the Sea of Okhotsk, within the NW Gyre, and in the Gulf of Alaska. [ABSTRACT FROM AUTHOR]

Analysis of the ostracod assemblages and the distribution of benthic foraminifera Ammonia beccarii in the core section GS 194-08-1 recovered at a depth of 7.5 m near the Volga delta front showed changes in environmental conditions in response to sea-level fluctuations. The pre-Novocaspian ostracod assemblage reflects the conditions that were dominant during the Late Khvalynian transgression, with a depth of about 20-30 m, and a salinity range of 12-13‰. The Early Novocaspian sediments contain an ostracod assemblage that represents a deeper water environment compared to the present, with an inferred depth of 12-16 m. The faunas from the younger Novocaspian sediments with abundant monospecific populations of Cyprideis torosa and co-occurring benthic foraminifera Ammonia beccarii represent modern-like environmental conditions. [ABSTRACT FROM AUTHOR]

The data on the distribution of the radiolarian species Cycladophora davisiana in the present-day ocean and its Quaternary sediments are summarized. The distribution of this species is influenced by the formation of the cold ventilated intermediate water mass enriched in suspended organic matter. The maximal abundance of the species is recorded above the continental slopes. The long-term Quaternary variations in the relative abundance of C. davisiana are inconsistent with the cyclic glacial-interglacial fluctuations and are of limited significance for the regional stratigraphy. [ABSTRACT FROM AUTHOR]

The study of foraminifers from sediments accumulated during the last 30 ky revealed their similar distribution in the central and marginal parts of the Deryugin Basin, which implies similar environmental changes throughout this morphological structure. The lack or extreme taxonomical impoverishment of the benthic foraminiferal assemblages during the Last Glacial Maximum indicates a combination of several factors: the significant deterioration of the parameters controlling their bioproductivity in response to the general cooling; the development of anoxic bottom conditions; and, probably, the unfavorable influence of cold barite-methane seeps on the geochemical parameters of the bottom waters. The weaker activity of these seeps in the central part of the basin during the Holocene is evident from some deviations in the structure of the benthic foraminiferal assemblages against the background of their general taxonomic similarity. [ABSTRACT FROM AUTHOR]

Diatoms were studied in the KOMEX LV28-34-2 sediment core from the northwestern Sea of Okhotsk. The interval from the penultimate glacial to the Holocene was subdivided into stratigraphic units based on the distribution of biogeographic groups and individual index species. The analysis of the diatom assemblages indicated that, during the Last Glacial Maximum, of the Deryugin Basin was regularly covered with extensive seasonal ice of at least 70% concentration for a minimum of 6–7 months per year. Cold subarctic water from the adjacent open Pacific could have reached as far as the northwestern sea area. [ABSTRACT FROM AUTHOR]

The radiolarian distribution is studied in Core IMAGES MD01-2415 (46-m-long) from the central Sea of Okhotsk. The obtained data made it possible to refine the regional biostratigraphy and document the major paleoenvironmental changes in the basin in the last million years. In total, 17 radiolarian datum planes are defined with 12 of them being new. Their number exceeds that previously established for different fossil groups in the Subarctic Pacific for this period. Radiolarian datum planes are usually confined to the main boundaries and Quaternary climatic events. The analysis of the radiolaria distribution reveals several major paleoenvironmental shifts in the sea that occurred 950, 700, and 420–280 ka ago and are correlative with regional and global phases of the Middle Pleistocene climatic revolution. [ABSTRACT FROM AUTHOR]

Benthic foraminifera are investigated in sediment core LV28-34-2 (53°51.971′N, 146°47.499′E, sea depth 1431 m, core length 965 cm). The distribution of foraminifera is studied in coarse-grained (>0.125 mm) sediment fractions of 191 samples taken with a step of 5 cm. The core covers the interval from oxygen isotope stage (OIS) 6 up to the Holocene. The foraminiferal assemblages of the penultimate (OIS 6) and last (OIS 5d-2) glaciations are characterized by low abundances and prevalence of Uvigerina auberiana. The specific structure of the OIS 6 assemblages differs from the last glaciation ones by the mass presence of Cassidulina teretis, which characterizes low temperatures and a high influx of organic matter to the sea floor. The major factor responsible for the weak development of benthic foraminifers during the glacial time is the deficiency of food resources. The foraminiferal assemblage of the interglacial optimum (OIS 5e) is composed of both calcareous and agglutinated species ( Martinottiella communis).The inflow of Pacific waters was probably more intensive, the bioproductivity was higher, and the critical carbonate compensation depth was shallower at that time than during the glaciations. During the deglaciation, the quantity and structure of the foraminiferal assemblages reflected two pulses of warming (terminations 1B and 1A) with an intervenient cooling event (Younger Dryassic). The assemblages of warm periods were characterized by exclusively high foraminiferal abundances, which sharply decreased during the Younger Dryassic cooling. The specific structure of the foraminiferal assemblage during deglaciation was relatively uniform, being composed of only calcareous taxa typical of highly productive areas of the ocean. The paleoenvironmental conditions were similar to the conditions of the interglacial optimum (OIS 5e), although the preservation of calcareous tests is better. In the Holocene sediments, the concentration of benthic foraminifera is substantially lower than during the deglaciation, which is explainable by their dilution in the sediments by diatoms; the composition of the foraminiferal assemblages is similar to that of their glacial counterparts. [ABSTRACT FROM AUTHOR]

The distribution of diatoms, radiolarians, planktonic and benthic foraminifers, and sediment components in the fraction >0.125 mm was analyzed in the core obtained from the central Sea of Okhotsk within the frameworks of the Russian-German KOMEX project. The core section characterizes the period 190–350 ka, which corresponds to marine-isotopic stages (MIS) 7 to 10. During glacial MIS 10 and MIS 8, the basin accumulated terrigenous material lacking microfossils or containing them in low abundance, which reflects, along with their composition, heavy sea-ice conditions, suppressed bioproductivity, and bottom environments aggressive toward calcium carbonate. Interglacial MIS 9 was characterized by elevated bioproductivity with accumulation of diatomaceous ooze during the climatic optimum (328 to 320 ka). The water exchange with the Pacific was maximal from 328 to 324 ka ago. Environments became moderate and close to the present-day ones at the end of the optimum exhibiting the possible existence of a dichothermal layer with substantial amounts of the surface Pacific water still flowing into the basin. Similar to interglacial MIS 5e and MIS 1, the “old” Pacific water determined near-bottom environments in the central Sea of Okhotsk during that period, although the influx of terrigenous material was higher, probably reflecting a more humid climate of the region. Slight warming marked the terminal MIS 8 (approximately 260 ka ago). The paleoceanographic situation during interglacial MIS 7 was highly variable: from warm-water to almost glacial. The main climatic optimum of MIS 7 occurred within 220–210 ka, when the subsurface stratification increased and the dichothermal layer developed. Bottom environments during the studied time interval, except for the optimum of interglacial MIS 9, resembled those characteristic of glacial periods: the actively formed “young” Okhotsk water displaced the “old” Pacific deep water. [ABSTRACT FROM AUTHOR]