(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.

(Table 1) Concentrations of dissolved organic carbon and phosphates in southern tropical waters of the Indian Ocean

Determinations of dissolved organic carbon and salinity were made in a region of the subtropical convergence of southern tropical waters of the Indian Ocean. It is shown that nature of vertical distribution of dissolved organic carbon together with salinity reflects water subsiding.

Concentrations of phosphates and silicon in near-bottom and interstitial waters of the Baltic Sea

Fine structure of vertical distributions of phosphorus and silicon in near-bottom layers and interstitial waters is studied in different regions of the Baltic Sea (Gulf of Finland, Bornholm area, Gotland trench). Data obtained are used to calculate fluxes of mineral forms of phosphorus and silicon in exchange processes between sediments and the near-bottom water layer. Depending on sediment types, values of nutrient fluxes vary from 9.8 to 632.6 µg-at/m**2/day for phosphorus and from 232.4 to 1881.1 µg-at/m**2/day for silicon. Fluxes calculated for different regions are compared.

Concentration of dissolved phosphates and total phosphorus in seawater near the Cape Utrish, Black Sea

Dynamics of growth of natural phytoplankton and bacterioplankton in deep seawater upwelled to the upper sea layer were studied. Seawater from the lower part of the aerobic zone of the Black Sea was shown to have high bio-productive potential and can be used as an environment for algae and bacteria cultivation.

Isotope compositions of oxygen and carbon from phosphates and Fe-Mn crusts and nodules sampled at Pacific seamounts

Results of a study of phosphates collected on Pacific Ocean seamounts using some physicochemical methods are described. Particular attention is paid to isotopic studies of both phosphates and their accompanying features. Oxygen isotopic compositions in phosphates of different genetic types were compared. Possible hydrothermal origin of phosphates is considered, and probable conditions of their formation are determined.

(Table 1) Chemical composition of oceanic phosphates and their selenium content

Selenium content of phosphate material from the ocean bottom ranges from 0.2 to 4.7 mg/kg. Phosphorites of various ages from the Atlantic and Pacific Oceans contain 1.0-2.4 mg/kg of selenium, phosphatized coproliths 0.7-1.2 mg/kg, fish bones 0.2-1,4 mg/kg, and bones of marine mammals 0.5-4.7 mg/kg. Recent diatom muds on the shelf of Namibia are considerably enriched in selenium (12.2-13.8 mg/kg) than phosphorites that form within them. Accumulation of selenium in phosphate material on the ocean bottom results from diagenetic reduction, causing it to be precipitated from liquid phase and to concentrate in organic components and sulfides.

(Table 2) Oxygen isotope composition of authigenic and detrital phosphates from ODL Leg 201 sites

Many (bio)geochemical processes that bring about changes in sediment chemistry normally begin at the sediment-water interface, continue at depth within the sediment column and may persist throughout the lifetime of sediments. Because of the differential reactivity of sedimentary phosphate phases in response to diagenesis, dissolution/precipitation and biological cycling, the oxygen isotope ratios of phosphate (d18OP) can carry a distinct signature of these processes, as well as inform on the origin of specific P phases. Here, we present results of sequential sediment extraction (SEDEX) analyses combined with d18OP measurements, aimed at characterizing authigenic and detrital phosphate phases in continental margin sediments from three sites (Sites 1227, 1228 and 1229) along the Peru Margin collected during ODP Leg 201. Our results show that the amount of P in different reservoirs varies significantly in the upper 50 m of the sediment column, but with a consistent pattern, for example, detrital P is highest in siliciclastic-rich layers. The d18OP values of authigenic phosphate vary between 20.2 per mil and 24.8 per mil and can be classified into at least two major groups: authigenic phosphate precipitated at/near the sediment-water interface in equilibrium with paleo-water oxygen isotope ratios (d18Ow) and temperature, and phosphate derived from hydrolysis of organic matter (Porg) with subsequent incomplete to complete re-equlibration and precipitated deeper in the sediments column. The d18OP values of detrital phosphate, which vary from 7.7-15.4 per mil, suggest two possible terrigenous sources and their mixtures in different proportions: phosphate from igneous/metamorphic rocks and phosphate precipitated in source regions in equilibrium with d18Ow of meteoric water. More importantly, original isotopic compositions of at least one phase of authigenic phosphates and all detrital phosphates are not altered by diagenesis and other biogeochemical changes within the sediment column. These findings help to understand the origin and provenance of P phases and paleoenvironmental conditions at/near the sediment-water interface, and to infer post-depositional activities within the sediment column.

Sand geochemistry on sediment core CRP-3 from the Ross Sea, Antarctica

A total of 167 samples distubuted throughout the CRP-3 drillhole from 5.77 to 787.68 mbsf and representing fine to coarse sandstones have been analysed by X-ray fluorescence spectrometry (XRF) Bulk sample geochemistry (major and trace elements) indicates a dominant provenance of detritus from the Ferrar Supergroup in the uppermost 200 mbsf of the core. A markedly increased contribution from the Beacon sandstones is recognized below 200 mbsf and down to 600 mbsf. In the lower part of CRP-3, down to 787.68 mbsf, geochemical evidence for influxes of Ferrar materials is again recorded. On the basis of preliminary magnetostratigraphic data reported for the lower 447 mbsf of the drillhole, we tentatively evaluated the main periodicities modulating the geochemical records. Our results identify a possible influence of the precession, obliquity and long-eccentricity astronomical components (21, 41, and 400 ky frequency bands) on the deposition mechanisms of the studied glaciomarine sediments.

Geochemistry of bulk samples and various minerals of sediment core CRP-1 from the Ross Sea, Antarctica

Thirty-nine medium and fine grained sandstones from between 19,26 and 147,23 mbsf in the Cape Roberts-l core (CRP-1) were analysed for 10 major and 16 trace elements. Using whole-lock compositions, 9 samples were selected for analyses of mineral and glass grains by energy dispersive electron microscope. Laser-Ablation Mass-Spectrometry was used to determine rare earth elements and 14 additional trace elements in glass shards, pyroxenes and feldspars in order to examine their contribution to the bulk rock chemistry. Geochemical data reveal the major contribution played by the Granite Harbour Intrusives to the whole rock composition, even if a significant input is supplied by McMurdo volcanics and Ferrar dolerite pyroxenes McMurdo volcanics were studied in detail; they appeal to derive from a variety of litologies, and a dominant role of wind transpoitation from exposures of volcanic rocks may be inferred from the contemporary occurrence of different compositions at all depths. Only at 116.55 mbsf was a thin layer of tephra found, linked to an explosive eruption McMurdo volcanic rocks exhibit larger abundances at depths above 62 mbsf, in correspondence with the onset of volcanic activity in the McMurdo Sound area. From 62 mbsf to the bottom of the core, McMurdo volcanics are less abundant and probably issued from some centres in the McMurdo Sound region. However, available data do not allow the exclusion of wind transport from some eruptive centres active in north Victoria Land at the beginning of the Miocene Epoch.