(Table 2) Chemical composition of phosphates from the Namibian and Chilean shelves

This study on phosphorites of different compositions and ages from shelf sediments and seamounts of the Pacific Ocean by means of analytical electron microscopy showed that these phosphorites contain ultra-microscopic inclusions of authigenic minerals and, more rarely, of rare earth element (REE) minerals. In some of phosphorite samples of Pleistocene-Pliocene age from the Namibian shelf both kinds of minerals were found. Uranium minerals were represented by uraninite, coffinite, and ningioite; those of REE - by monazite, xenotime, and bastnesite, which points to their potential accumulation not only as isomorphous admixtures in calcium phosphate but also as independent mineral phases. Coexistence of the minerals noted in shelf phosphorites is caused by repeated changes in redox conditions during formation and then redeposition of phosphate concretions. Presence of uranium minerals in phosphorites from seamounts shows that during an initial step of formation of these phosphorites environment was rather suboxic or reductive than oxic.

Chemical composition of basalts and basaltic glasses from the Sierra Leone Fracture Zone region

Major and trace element (including REE) geochemistry of basalts and chilled basaltic glasses from the MAR axial zone in the vicinity of the Sierra Leone FZ (5-7°10'N) has been studied. Associations of basalts of various compositions with particular ocean-floor geological structural features have been analyzed as well. Three basaltic varieties have been discriminated. Almost ubiquitous are high-Mg basalts (Variety 1) that are derivatives of N-MORB tholeiitic melts and that are produced in the axial zone of spreading. Variety 2 is alkaline basalts widespread on the southwestern flank of the MAR crest zone in the Sierra Leone region, likely generated through deep mantle melting under plume impact. Variety 3 is basalts derivative from T- and P-MORB-like tholeiitic melts and originating through addition of deeper mantle material to depleted upper mantle melts. Magma generation parameters, as calculated from chilled glass compositions, are different for depleted tholeiites (44-55 km, 1320-1370°C) and enriched tholeiites (45-78 km, 1330-1450°C). Mantle plume impact is shown to affect not only tholeiitic basalt compositions but also magma generation conditions in the axial spreading zone, resulting in higher Ti and Na concentrations in melts parental to rift-related basalts occurring near the plume. T- and P-MORBs are also developed near areas where mantle plumes are localized. High-Mg basalts are shown to come in several types with distinctive Ti and Na contents. Nearly every single MAR segment (bounded by sinistral strike slips and the Bogdanov Fracture Zone) is featured by its own basalt type suggesting that it has formed above an asthenospheric diapir with its unique magma generation conditions. These conditions are time variable. Likely causes of temporal and spatial instability of the mantle upwelling beneath this portion of the MAR are singular tectonic processes and plume activity. In sulfide-bearing rift morphostructures (so-called "Ore area'' and the Markov Basin), basalts make up highly evolved suites generated through olivine and plagioclase fractionation, which is suggestive of relatively long-lived magma chambers beneath the sulfide-bearing rift morphostructures. Functioning of these chambers is a combined effect of singular geodynamic regime and plume activity. In these chambers melts undergo deep differentiation leading to progressively increasing concentration of sulfide phase, eventually to be supplied to the hydrothermal plumbing system.

Oxygen isotopic and species composition of planktonic foraminiferas in sediment cores from the North Atlantic

Paleotemperature curves were drawn from oxygen-isotope ratios in CaCO3 of planktonic foraminiferal tests and by the micropaleontological method using quantitative relationships of their species. Two series of curves yield similar results. These data confirm that isotope composition of oxygen reflects primarily temperature, and not isotope composition in ocean water. Temperature of the upper layer of ocean water increased from north to south both during the last two glaciations and in the interglacials. All three sediment cores collected from different latitudes show approximately the same amplitudes of fluctuation of mean annual temperature during times of their accumulation, as determined independently by different methods; these amplitudes are estimated as 5-7°C.

(Table 2) Oxygen, carbon, and strontium isotopic composition of carbonate-brucite material from the Lost City hydrothermal field

The isotopic (dD, d18O, d13C, and 87Sr/86Sr) and geochemical characteristics of hydrothermal solutions from the Mid-Atlantic Ridge and the material of brucite-carbonate chimneys at the Lost City hydrothermal field at 30°N, MAR, were examined to assay the role of the major factors controlling the genesis of the fluid and hydrothermal chimneys of the Lost City field. The values of dD and d18O in fluid samples indicates that solutions at the Lost City field were produced during the serpentinization of basement ultramafic rocks at temperatures higher than 200°C and at relatively low fluid/rock ratios (<1). The active role of serpentinization processes in the genesis of the Lost City fluid also follows from the results of the electron-microscopic studying of the material of hydrothermal chimneys at this field. The isotopic (d18O, d13C, and 87Sr/86Sr) and geochemical (Sr/Ca and REE) signatures indicate that, before its submarine discharging at the Lost City field, the fluid filtered through already cold altered outer zones of the Atlantis Massif and cooled via conductive heat loss. During this stage, the fluid could partly dissolve previously deposited carbonates in veins cutting serpentinite at the upper levels of the Atlantis Massif and the carbonate cement of sedimentary breccias underlying the hydrothermal chimneys. Because of this, the age of modern hydrothermal activity at the Lost City field can be much younger than 25 ka.

Aerosols over the East Atlantic in spring and summer 2001

Data on the concentration and mineral composition of aerosols collected by nets in Cruise 18 of R/V Akadernik Fedorov on a submeridional section in the East Atlantic are presented. An empirical curve for calculating efficiency factor of a net is given for different concentrations of mineral part of aerosols. Fluxes of lithogenic part of aerosols to the sea surface are calculated. A comparison of lithogenic fluxes from the atmosphere and in the water column of the ocean showed that values of fluxes practically coincide in areas with dominating supply of dry atmospheric material. These fluxes strongly differ in the intratropical convergence zone, where deposition of aerosols depends on atmospheric precipitation, or in regions, where sedimentary material is supplied to the ocean mainly by river run-off. Residence time of aerosol lithogenic matter in the euphotic layer is calculated.

Radiocarbon age of bottom sediments from the Atlantic and Pacific Oceans

Procedures for radiocarbon dating of ocean sediments on board the ship using the benzene variant of the method are described. The main features of the benzene synthesis scheme, together with its differences from the method usually used onshore laboratories, are discussed briefly. Parameters of radiometric installation, in which activity of synthesized benzenes is determined are cited. The method was used successfully during Cruise 14 of R/V Dmitry Mendeleev (45 datings) and Cruise 24 of R/V Akademik Kurchatov (81 datings).

Planktonic foraminiferas in bottom sediments and paleotemperatures in the areas of the Benguela and Canary upwellings

Distribution of planktonic foraminiferal tests was studied in four drill cores of Upper Quaternary sediments from the zone of influence of the Canary upwelling and in nine sediment cores from the zone of the Benguela upwelling. Paleotemperatures were reconstructed from these data. It was established that under conditions during stadials, interstadials, and interglacials of Quaternary time, the upwelling existed continuously, intensifying and expanding during colder epochs and weakening and contracting in the warmer intervals. During the last stadial (about 18000 yrs ago), relative cooling of sea waters as compared to central regions of the ocean in the zone of the Canary upwelling was not lower than 9°C (4.5°C higher than at present time), and in the zone of the Benguela upwelling it was not lower than 15°C (8.5°C higher than at present time).