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The species composition, distribution and preservation of carbonate shells of nanno and microfossils of biogenic bottom sediments within the hydrothermal cluster Pobeda (1707.451708.7 n) were studied on the basis of materials obtained in flight No. 37 of NIS Professor Logachev in the Russian exploration area (Mid-Atlantic ridge). Physical-chemical parameters and the total carbonate content of sediments were measured, their changes in column sections were revealed. For complexes of coccoliths studied precipitation is attributed to the top (acme) biostratigraphic zone of Emiliania huxleyi. It is established that within the zone of hydrothermal activity (ore cluster Pobeda) the total number of microorganisms decreases and their species diversity decreases, as a rule, in the lower part of the columns. Down the column section also decreases the Eh, pH and carbonate precipitation. These changes are explained by the influence of diffuse hydrothermal fluids.

Nannofossils were studied, recovered from Late Pliocene–Pleistocene sediments at station 3316 on cruise 46 of the R/V Akademik Ioffe north of the Rio Grande Rise in the Southwest Atlantic. The presence of irregular discoasters in a narrow horizon at the end of the Discoaster brouweri zone of the Upper Pliocene indicates dramatic changes in the living conditions of these organisms, which led to deviations in the regular structure of their skeletons and subsequent extinction at the end of the Pliocene.

Trawling of the bottom in the northeastern Kara Sea during cruise 125 of the R/V Professor Shtokman in 2013 recovered a block of cavernous, partly phosphatized carbonate rock consisting of biogenic carbonate material and partly crystallized diagenetic calcite. The fauna remains are mainly Oligocene–Pliocene planktonic and benthic foraminifers, with less common Oligocene–Miocene coccoliths and single wormlike organisms. Part of the phosphatized material in caverns is impregnated by manganese and iron oxides and enriched in heavy and trace metals. According to the oxygen isotopic composition, this rock formed under moderate temperature conditions. In terms of morphology, mineralogy, and the abundance of organic remains, the block is comparable to methanogenic carbonates found in other parts of the ocean, but shows no isotopically light carbon signatures typical of methane activity. This indicates the diversity of the carbon isotope composition of the Arctic carbonates.

The analysis of calcareous nannoplankton assemblages in bottom sediments sampled during Cruise 21 of the R/V Akademik Mstislav Keldysh in three areas located in back-arc basins of the southwestern Pacific (western Woodlark in the Solomon Sea, Manus in the Bismarck Sea, Central Lau) reveal that they belong to the Emiliania huxleyi Acme Zone, the most detailed one in the Gartner’s scale of 1977. The content of coccoliths and their taxonomic composition indicate warm subtropical-tropical conditions. Long cores demonstrate a decrease in species diversity reflecting the transition from the cold late Pleistocene to the Holocene. The changes in species diversity and presence/absence of thermophilic representatives indicate transformation of depositional environments with unstable conditions in the water column and bottom layer, seismic activity, and widely developed processes of sediment redistribution and reworking.

The chemical and mineral composition of the bottom sediments, as well as the assemblages of carbonate planktonic and benthic fossils (nannoplankton, foraminifers), were analyzed in two cores obtained in the North Atlantic within the Peterburgskoe hydrothermal ore field and beyond its limits. Their sections include the Upper Pleistocene and Holocene sediments with the boundary between them located at the depth of 20 cm. It is established that planktonic fossils (foraminifers and nannoplankton) reflect the replacement of subtropical conditions in the Late Pleistocene by tropical environments in the Holocene. It is shown that hydrothermal fluids significantly affect biogenic carbonate sediments in the ore formation zone of the Peterburgskoe field (core 33L159) resulting in dissolution of microfossils and their replacement by hydrothermal material. Their transformation patterns and vertical distribution indicate the influx of diffuse acid solutions to sediments from below. In background sediments constituting the core 33L148 section located 5 km away from the ore field, microfossils exhibit good preservation through its entire length. The sediments from the basal part of the section demonstrate the slight influence of the aggressive acid medium reflected in the disappearance of pteropod remains and changes in the abundance and taxonomic composition of benthic foraminifers and nannofossils. These data may be used as a criterion for defining potential nearby active hydrothermal sources.

Reference cores of sediments from the Angola and Cape basins were subjected to lithological, geochemical, and micropaleontological investigations. Based on nannofossil and diatom assemblages, the examined sediments represented by oxidized miopelagic clays, calcareous (nannofossil-foraminiferal, foraminiferal-nannofossil), calcareous-clayey, and clayey-calcareous mud are estimated to be the Pleistocene-Holocene in age. The Cape Basin section includes surface and buried ferromanganese nodules. There are indications of sedimentary material redeposition by the Antarctic Bottom Water and turbidity currents. The South Polar Front zone changed repeatedly its geographic position and migrated northward from the presentday one. As a whole, the Pleistocene-Holocene sedimentation in the Angola and Cape basins corresponds to the incomplete pelagic (miopelagic) type of oceanic lithogenesis.

The study of the upper part of the section of borehole 362 DSDP (southeastern Atlantic) allowed the recognition of five zonal units in the Quaternary based on nannofossils and refinement of the UpperLower Pleistocene boundary based on benthic foraminifers. The study of planktonic and benthic foraminifers in sediments display the history of the Benguela upwelling. The temperature of the surface water layer reconstructed based on Upper Pleistocene planktonic foraminifers reaches 17°–19°C and decreases downward in the section to 2°–3°C, suggesting that, in the Early Pleistocene, the upwelling was more extensive in area. The increasing proportion of benthic foraminifers and large nannofossils downward in the section is evidence of more active dissolution of carbonates in the Early Pleistocene and the high content of terrigenous matter suggests that the Benguela Current occupied a westerly position. The existence of the Benguela upwelling throughout the Late Pliocene-Pleistocene was accompanied by a decrease in its activity.

The foraminiferal (planktonic and benthic) and nannofosssil assemblages have been analyzed in the sediments of Core ACB-17-1447 taken from the South America continental slope north of the Rio Grande Rise piedmont during Cruise 17 of the R/V Akademik Sergey Vavilov. The core section is largely composed of carbonate and marly hemipelagic mud. The Quaternary age of the host sediments is evident from the occurrence of the planktonic foraminiferal index species Globorotalia truncatulinoides. Based on the nannofossil assemblages, the core sediments are attributed to the upper Pleistocene-Holocene. They contain abundant reworked Pliocene, Miocene, and Paleogene taxa transported from the slopes of the underwater Rio Grande Rise. The paleotemperature analysis of the planktonic foraminifers provided data for constructing the temperature curve that demonstrates two warm peaks. During the first warm period (Interval of 7–9 cm), the surface water temperature was as high as 26°C (Holocene optimum), which exceeds by 3–4°C its presentday values and implies the more intense warm Brazil Current. The earlier warm peak with temperatures up to 24°C recorded in the upper Pleistocene sediments (Interval of 69–71 cm) most likely reflects the 3rd oxygenisotope stage (MIS 3), which corresponds to the interstadial phase of the last glaciation (30–40 ka ago). Based on the abundances, taxonomic diversity, and proportions of the characteristic species of benthic foraminifers, the Core ASV-17-1447 section is divided into six intervals correlated with the marine isotopic stages defined by both the planktonic foraminifers and climatic changes evident from the variations in the bottom water circulation along the southwestern slope of the Brazilian Basin during the Late Quaternary.

The nannofosssil assemblages have been analyzed in five cores taken from the Titanic area of the northwestern Atlantic (∼41°–42° N, ∼47°–50° W, water depths >3500 m) during cruises 41 and 43 of the R/V Akademik Mstislav Keldysh in 1998 and 2000. They correlate the host sediments with the upper Pleistocene-Holocene Emiliania huxleyi zone. The changes in the structure of the nannofossil assemblages and the lithological characteristics such as the content of biogenic CaCO3, the abundance of ice-rafted debris, and the grain-size composition were used for the high-resolution stratigraphy of sections with defining marine isotopic stages 1–3 of the last 24 kyr. A characteristic feature of the nannofossil assemblages from this area is their enrichment with the cold-resistant species Coccolthus pelagicus during the warm climatic stages and the lack of allochthonous coccolitophorid remains.

Analysis of carbonate microfossils (planktonic foraminifers and nannoplankton) in the DSDP Hole 362 Quaternary section made it possible to specify its zonal subdivision (almost all zones of Gartner’s high-resolution nannofossil scale are recognized), establish depositional environments, and restore past surface water temperatures. The latter appeared to be several degrees lower than their present-day values, which is evident from the anomalously high share of the subpolar species Neogloboquadrina pachyderma sin. that constitutes 97% of the fossil assemblage in Lower Pleistocene sediments. It is shown that the Benguela upwelling existed throughout the entire Pleistocene, being less intense in the Late Pleistocene and Holocene.

The first thorough analysis of microfossils from ore-bearing sediments of the Ashadze-1 hydrothermal field in the Mid-Atlantic Ridge sampled during cruise 26 of the R/V Professor Logachev in 2005 revealed the substantial influence of hydrothermal processes on the preservation of planktonic calcareous organisms, as well as on the preservation and composition of the benthic foraminifers. From the lateral and vertical distribution patterns and the secondary alterations of the microfossils, it is inferred that the main phase of the hydrothermal mineralization occurred in the Holocene. Heavy metals (Cu, Co, Cr, and Ag) were accumulated by foraminiferal tests and in their enveloping Fe-Mn crusts. The distribution of authigenic minerals replacing foraminiferal tests demonstrates local zoning related to the hydrothermal activity. There are three mineral-geochemical zones defined: the sulfide zone, the zone with an elevated Mg content, and zone of Fe-Mn crusts.

A complex of lithological and micropaleontological methods were used for the study of sediments from the central North Atlantic (50–60°N). The data on the lithology, carbonate content, and occurrence of ash interbeds and ice-rafted material, combined with the nannofossil zonal biostratigraphy, allowed detailed subdivision of five core sections obtained during Cruise 48 of R/V Akademik Mstislav Keldysh. MIS 1–MIS 9 are established in the sections. In some of them, climatic changes related to migrations of the Subarctic Front are established based on the lithology and the characteristic coccolithophorid species: for example, a higher latitudinal position of the front is revealed for the Eemian interglacial (Substage 5e) as compared with that in the Holocene.

Diatom and nannoplankton microfossils in the samples of the surface bottom sediments and cores from the western part of the Norwegian Sea (64°–79°N) were studied. The abundance, distribution, taxonomic composition, and structure of the assemblages are determined by the productivity and temperature of the surface waters, by the distance from the shore, by the hydrological setting, and by the intensity of the supply of the Atlantic (from the south) and Arctic (from the north) waters to the Norwegian Sea. The repeated changes in the ecological structure of the diatom assemblages with time allowed us to distinguish five different ages and to estimate the changes in the paleoenvironment in the region under study during the past ∼19–21 ky. The nannofossil distribution is not universal over the entire area studied owing to the extreme northern location of the stations and low water temperatures. All the sediments examined refer to the Emiliania huxleyi zone of the Late Pleistocene-Holocene; in selected cases, narrower temperate and cold-water intervals were also recognized. The low species diversity and the poor preservation of nannofossils prove the dominating influence of the Arctic water masses.

Calcareous nannoplankton from sediment trap samples collected at six sites in the Atlantic Ocean from 23° S to 73° N (cruise 20 of R/V Vityaz’ and cruise 33 and 34 of R/V Akademik Mstislav Keldysh). Those samples were studied with a scanning electron microscope. In the coastal and open-sea regions of the North and South Atlantic and in the subarctic region of the Norwegian Sea, the conditions are significantly different. In the shelf area of the Benguela upwelling, 11 species were recognized; some of them were agglutinated by diatoms and tintinnides or covered the surface of pellets. The Broken Spur and TAG pelagic areas of the North Atlantic contained up to 43 coccolith species. They included holococcoliths, large pelagic, and delicate easily soluble species distributed over the entire water column. The presence of coccoliths in the high-latitude area of the Norwegian Sea is related to their supply with the warmer North Atlantic waters. These assemblages are distinguished by a low species diversity and an enhancement of the coccolith solubility with the depth increase.