I. O. Murdmaa

Quaternary seismic facies of the atlantic continental rise

High-resolution seismic profiles collected by Parasound and SES-2000 deep profilers during Cruise 26 of the R/V Akademik Sergei Vavilov (2009) along the continental slope base of South America, NW Africa, and West Europe are correlated with the deep-sea drilling boreholes. Lithofacies interpretation of the Quaternary deep-water seismic facies of hemipelagites, bottom current deposits (contourites), and gravitites (turbidites, mud flow deposits) is presented. The data obtained reveal the domination of contourites in the accumulation of continental rise apron under conditions of relatively scarce terrigenous material supply. It is shown that acoustically stratified seismic facies under these conditions commonly reflect interbedding of the terrigenous clay and biogenic calcareous ooze related to the Pleistocene glacial/interglacial cycles.

Upper quaternary laminated sapropelic sediments from the continental slope of Baja California

Core MD02-2508 retrieved from the plateau of the continental slope off Baja California recovered a 40-m-thick section of sapropel (up to 15% Corg), calcareous clay, and diatom ooze with the age of 120 ka at the core bottom. The section is subdivided into three units: Unit I (Holocene) consists of the laminated sapropel; Unit II comprising oxygen isotope stages (MIS) 2, 3, and 4 is represented by homogeneous calcareous clay with interbeds of slightly siliceous sapropelic mud; and Unit III (MIS-5) is composed of laminated sapropelic diatom ooze. Laminated intervals are characterized by the intercalation of two lamina types: (1) dark-colored organic-rich laminae containing multi-species “oceanic” diatom assemblages, as well as radiolarians, coccoliths, planktonic and benthic foraminifera; (2) lighter-colored laminae consisting of diatom ooze with the neritic colonial diatom assemblages commonly composed of one to three species of a single genera. The dark laminae are assumed to be generated within a high productivity zone over the slope, whereas light ones likely represent diatom mats produced by short-term boisterous phytoplankton blooms, possibly in the coastal upwelling.

Chemical composition of surface sediments of the White Sea

Contents of major elements in surface sediments of the White Sea were determined by the X-ray fluorescence method. Application of the statistical analysis (principal component method and cluster analysis) made it possible to divide the sediments into more or less homogeneous seven groups with different chemical and grain size compositions. In general, the groups corresponded to sediment lithotypes based on the classification elaborated at the Shirshov Institute of Oceanology, Russian Academy of Sciences. Contents of Si and Al are controlled by the ratio of sand-silt and pelite fractions, while variations in the content of Mn (and Fe in part) are governed by the redistribution of elements in the course of redox processes of early diagenesis.

Postglacial paleoceanographic environments in the Barents and Baltic seas

This paper presents reconstructions of ice sheet boundaries, lacustrine and marine paleobasins, as well as the connections of the Barents and Baltic seas with the North Atlantic from the Last Glacial Maximum to the Holocene. The reconstructions are based on original and published data obtained from the northern and western parts of the Barents Sea and Baltic depressions with account for the available regional schematic maps of deglaciation. The early deglaciation of the Scandinavian–Barents ice sheet culminated with the Bølling-Allerød interstadial (14.5–12.9 cal ka BP), which was characterized by a more vigorous Atlantic meridional overturning circulation (AMOC) and a corresponding increase in surface Atlantic water inflow into the Barents Sea through deep troughs. The Baltic Ice Lake (BIL) remained a dammed-up isolated basin during deglaciation from 16.0 to 11.7 cal ka BP. In the Younger Dryas (YD), the lake drained into the North Sea and was replaced by a brackish Yoldia Sea (YS) at the beginning of the Holocene (Preboreal, 11.7–10.7 cal ka BP), due to a limited connection between two basins through the Närke Strait. In the Barents Sea, the next increase in the Atlantic water influx into the deep basins corresponded to terminal YD and Preboreal events with a culmination in the Early Holocene. The Yoldia Sea became a lake again during the next stage, the Ancylus (~10.7–8.8 cal ka BP). Atlantic water inflow both into the Barents and Baltic seas varied during the Holocene, with a maximum contribution in the Early Holocene, when the Littorina Sea (LS, 8–4 cal ka BP) connection with the North Sea via the Danish Straits was formed to replace the Ancylus Lake. The recent, post-Littorina stage (PS, the last 4 cal ka) of the Baltic Sea evolution began in the Late Holocene.

Extraterrestrial native iron in deep-water sediments of the NW Atlantic: Evidence from thermomagnetic analyses

Thermomagnetic determination of the content and composition of native iron was accomplished in Miocene-Late Jurassic sediments and sedimentary rocks of the NW Atlantic recovered by DSDP holes 386, 387, 391A, and 391C. Native iron particles are ubiquitous therein. Presence of a zero group in the bar chart of native iron concentrations is a global feature of the cosmic particle distribution caused by small values of cosmic dust fluxes relative to sedimentation fluxes. Based on the Ni content, native iron is divided into two groups: (1) pure iron; (2) iron with Ni admixture from 3 to 17% (mode 4 to 5% Ni). The global pattern of Ni distribution in the native iron is emphasized by similarity of bar charts for the Atlantic and Eurasian sediments. Similarity of bar charts of the Ni distribution in the metallic portion of meteorites testifies to a common (extraterrestrial) origin of native iron in bottom sediments and meteorites. Concentrations of native iron lack any correlation with the rock composition and age, but high contents of native iron (up to 10−3%) are recorded in deposits related to pulsatory sedimentation (turbidites, laminites), where this element was likely accumulated intensely during slow (or zero) sedimentation intervals between the geologically instantaneous episodes of accumulation.

Sedimentation in the submarine Shirshov Ridge area (Bering Sea) during the last 180–185 ka (Penultimate glaciation-Holocene)

The lithological analysis of sediments from Core SO201-2-85KL (18 m long) taken from the Shirshov Ridge in the western part of the Bering Sea (57°30.30′ N, 170°24.79′ E, water depth 968 m), which recovered the section spanning from the penultimate glaciation till Holocene, revealed their mostly terrigenous composition with several intercalations of diatomaceous ooze. The latter was accumulated mainly during relatively warm epochs (last interglacial and Holocene) with elevated bioproductivity of surface waters. Sedimentation during the penultimate glaciation was strongly influenced by bottom currents. Ice rafting of detrital material was intensified during cold marine isotope stages (MIS 6, MIS 4, MIS 2). Glaciations were accompanied by increased sedimentation rates probably due to the glacioeustatic sea level falls, desiccation of the Bering Sea shelf, and enhanced influx of sedimentary material transported by large rivers immediately to the deepwater basin.

Sedimentary infill in the equatorial Mid-Oceanic Canyon, Atlantic Ocean

Facts confirming the hypothesis of contourite sediment infill of the Equatorial Mid-Ocean Canyon (EMOC) are presented. We examined two cores recovered in Cruises 37 and 43 of the R/V Akademik Ioffe (2012, 2013). The cores recovered upper Quaternary miopelagic clays on the EMOC floor (AI-3149) and the adjacent abyssal plain (AI-2620). The study of these cores unraveled significant differences in their composition. In contrast to the lithologically homogeneous Core AI-2620, Core AI-3149 includes interlayers enriched in the biogenic CaCO3, terrigenous silt, and authigenic ferromanganese micronodules. These peculiarities are attributed to activity of the Antarctic Bottom Water (AABW) contour currents along the EMOC.

Response of the bering sea to Heinrich Event 11

The present paper addresses the issue of the existence of inferred hiatus on the Shirshov Ridge in the western Bering Sea, which is represented by a sand layer allegedly produced by intensification of the bottom current at the penultimate glacial/last interglacial boundary. Intensification of current velocity near the ocean floor likely provoked washout of the light fine fraction and enrichment of the sediment with heavy coarse particles. Comparison of our and published data on the western Bering Sea and North Atlantic revealed that the sand layer in sediments of the western Bering Sea at the penultimate glacial/last interglacial boundary is related to ice rafting and serves to some extent an analog of Heinrich Event 11 in the North Atlantic.