Planktonic foraminifers in the southern Bering Sea: Changes in composition and productivity during the Late Pleistocene-Holocene

Taxonomic composition and distribution of planktonic foraminifers are studied in section of Core GC-11 that penetrated through Upper Quaternary sediments of the Bowers Ridge western slope, the southern Bering Sea. As is shown, structure of foraminiferal assemblage and productivity have varied substantially during the last 32000 calendar years in response to changes in surface water temperatures and water mass circulation in the northern part of the Pacific, the Bering Sea included. The productivity was maximal during deglaciation epoch, being notably lower in the Holocene and minimal at the glaciation time.     

Recent and Late Holocene environments on the southeastern shelf of the Laptev Sea as inferred from microfossil data

The study of diatoms and benthic foraminifers from the southeastern shelf of the Laptev Sea shows that their most diverse and abundant recent assemblages populate the peripheral underwater part of the Lena River delta representing the marginal filter of the sea. This area is characterized by an intense interaction between the fresh waters of the Siberian rivers and the basin seawater, the Atlantic one included. Local Late Holocene (～last 2300 years) environments reflect the main regional and global paleoclimatic changes, the Medieval Warm Period (～600–1100 years B.P.) and the Little Ice Age (～100–600 years B.P.) inclusive. In addition, the composition and distribution of planktonic foraminifers implies a strong influence of the Atlantic water during the Holocene optimum ～5100–6200 years B.P.     

Benthic and Plankton Foraminifers in Hydrothermally Active Zones of the Mid-Atlantic Ridge (MAR)

Comparison of benthic foraminiferal assemblages from the core obtained within the Peterburgskoe ore field (Mid-Atlantic Ridge) and from the core taken five kilometers away from the ore field revealed evident differences in their composition, in the appearance of their shells, and also in the benthic–plankton species ratio. It was noted that the foraminiferal assemblage from the ore-bearing sediments of the Petersburg field was characterized by a higher relative content of benthic species and a large number of chemically altered and broken shells. The first occurrence of the species Osangularia umbonifera, which is able to exist in lowoxygen and CaCO₃-undersaturated bottom waters at the boundary of biogenic sediments surrounding the ore field and in the ore-bearing sediments, was established. In the core section sampled beyond the ore field, the composition of foraminiferal assemblages differs insignificantly from typical oceanic ones.     

Paleoenvironment changes in the NW Okhotsk Sea for the last 18 kyr determined with micropaleontological,geochemical, and lithological data

Lithological, geochemical, and micropaleontological data indicate that the Late Glacial of the northwestern Okhotsk Sea (OS) is characterised by severe climatic and environmental conditions with mainly perennial sea ice coverage and low productivity accompanied by weak deep-water ventilation and a temperate formation of the upper Sea of Okhotsk Intermediate Water (SOIW). The age model of the studied core sediments was constructed by AMS ¹⁴C dating. The most severe environmental conditions occurred during the period 15.8–14.8 kyr, synchronous with cold Heinrich event 1. Insignificant regional environmental amelioration accompanied by an increase of productivity and ice weakening during summer occurred almost simultaneously with the Bølling–Allerøed (BA) warming. The obtained results distinguished both the Bølling and Allerøed warmings as having different environmental conditions. Oxygen content in the surface sediment was low, as seen from the production of the benthic foraminifera (BF) species. During 12.6–11.1 kyr, synchronous with the Younger Dryas (YD) cold event, the regional environment conditions were cold, but not as severe as the glacial ones. Some climatic warming since the Preboreal has stimulated sea ice melting and surface amelioration during the summer season, which in turn led to a productivity rise and changes in the water column and bottom environment. Some increase in the surface water stratification and the intensified oceanic diatom and surface radiolarian production is parallel with the development of a mesopelagic regime of productivity. The surface sediment condition favours BF abundance and domination by BF species tolerant to oxygen deficiencies. During the Boreal period more stable surface conditions were accompanied by continuously high productivity and an intensifying of its mesopelagic regime.Significant regional climate warming since the Atlantic (9 kyr ago) strongly intensified the summer sea ice melting in the OS, and this created considerable surface environment amelioration with the preferential transport of bacteria and phytodetritus into the SOIW. Further considerable warming of the regional climate from 6 kyr ago contributed to slight sea ice changes, surface water warming, and the enhancement of its stratification; all typical for most of the OS. Along with a high nutrient supply from the Amur River, the NW OS experienced a strong diatom production increase with the maximum amount occurring during the last 3.6 kyr. This changed the productivity type and organic matter export into the water column while increasing the feeding of the “productive” Plagoniidae spp. group and decreasing the microbial biomass supply into the upper SOIW. Some sea surface water cooling or saltier conditions at the beginning of the Subatlantic (2.4–1.8 kyr) was followed by its warming or freshening 1.5–1.0 kyr ago, which likely correlated with the Medieval Warm Period. In turn, that probably led to strong surface water stratification, productivity deterioration and considerable changes in the overall NW OS environment. The established sequence of the northwestern OS environmental changes during the Late Glacial–Holocene is related to the Northern Hemispheric climate changes and was likely forced by atmospheric teleconnection in line with the polar circulation index variability.     

Warm-Water Planktonic Foraminifera in Kara Sea Sediments

Oceanology - 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...     

Systems Research of Sedimentation in the European Arctic during the 84th Cruise of the Research Vessel Akademik Mstislav Keldysh

Oceanology - 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...     

Paleocurrents in the Charlie-Gibbs Fracture Zone during the Late Quaternary

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.     

Late Quaternary polycystine radiolarian datum events in the Sea of Okhotsk

Five radiolarian datum events have been recorded in the Late Quaternary sediment section from the Sea of Okhotsk, using age assignments based on oxygen-isotope stratigraphy: the last occurrence datum (LOD) of Stylacontarium acquilonium (at about 329 ka), the LOD of Spongodiscus sp. (at about 287 ka), the LOD of Amphimelissa setosa (at about 72 ka), the LOD of Lychnocanoma nipponica sakaii (at about 28 ka), and the L. nipponica sakaii acme event (at about 72 ka). The LODs of S. acquilonium, Spongodiscus sp. and A. setosa appear to be synchronous in comparison with those in the Subarctic North Pacific, but the LOD and the acme event of L. nipponica sakaii show an apparent diachroneity with the corresponding North Pacific events.     

Late pleistocene-holocene ostracod assemblages of the Northern Caspian Sea shelf

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.     

Late quaternary diatom stratigraphy and paleoceanology of the Deryugin Basin (Sea of Okhotsk) during the Last Glacial Maximum

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.