Phytoplankton of the southwest Kara Sea on August 9-12, 2007

A research was carried out along a transect from the Yamal Peninsula coast towards the outer shelf of the southwestern the Kara Sea in September 2007. 130 phytoplankton species were identified, among which 63 were found in the area for the first time. Total phytoplankton abundance varied from of 0.2 x10**9 to 11.3x10**9 cells/m**2, while biomass from 43 to 1057 mgC/m**2. A well pronounced cross-shelf zoning in phytoplankton communities was ascertained. The inner shelf zone about 30 km wide with depths down to 30 meters was characterized by predominance of diatoms (up to 80% of total algal abundance and biomass). The second group by value was dinoflagellates. Seaward in the area of depth increase from 30 to 140 m, the zone of the Yamal Current was located, which was 40 km wide and notable for its active water dynamics. Total abundance in the zone was maximal for the entire investigated area: up to 11.3x10**9 cells/m**2. Autotrophic flagellates were the leading group in phytoplankton, their share in total abundance reached 56-82%. Further than 70 km from the shore, the outer shelf zone was found with the water column rigidly stratified. The highest for the whole area phytoplankton biomass was identified here (up to 1.06 gC/m**2), 80% of which concentrated above the halocline. Diatoms dominated in phytoplankton abundance (up to 92%) and biomass (up to 90%) that resulted from mass development of two species: Chaetoceros diadema and Leptocylindrus danicus.

Chemical and mineral composition of rocks and sediments from the Amirante Arc

New geological and geophysical data on the Amirante Arc, which locates to the south of the Seychelles Islands, are presented. These data were obtained by Pacific Oceanological Institute during the 33-rd cruise of R/V Professor Bogorov in 1990. The Amirante Arc represents a seamount chain, which has submeridional strike and total length about 400 km. To the west of the Amirante Arc there are a deep sea trench and a back-arc basin, i.e. this area is characterized by structural elements associated with the subduction zone of Western Pacific type. According to our data the Amirante Arc is composed by tholeiites of ocean plateau type. This facts are evidences that the Amirante Arc differs from typical Pacific island arcs. This gives an opportunity to distinguish a special type of oceanic structures, i.e. non-volcanic (amagmatic) ridges. The Amirante Ridge has been probably formed as a result of oceanic crust heaping due to horizontal displacements of its blocks in the process of spreding ridge formation in the Indian Ocean during Cretaceous-Paleogene.

Chemical composition of ferromanganese nodules from the Black Sea

Ferruginate shells and tubular worm burrows from the oxygenated zone of the Black Sea (Kalamit Bay and Danube River mouth) are studied by transmission and scanning electron microscopy combined with analyses of elemental composition. Iron and manganese oxyhydroxide nodules considered here are enriched in phosphorus. They contain variable amounts of terrigenous and biogenic material derived from host sediments. Oxyhydroxides are mainly characterized by colloform structure, whereas globular and crystalline structures are less common. The dominating iron phase is represented by ferroxyhite and protoferroxyhite, whereas the manganese phase is composed of Fe-free vernadite. Concentrations of Mn, As, and Mo are 12-18 times higher relative to sediments, while concentrations of Fe, P, Ni, and Co increase 5-7 times during nodule formation.

Biogeochemistry (speciation and isotopes of S and C) in bottom sediments, water and bacterial mats from the White Sea

This publication presents results of microbiological and biogeochemical studies in the White Sea. Material was obtained during a series of expeditions in 1999-2002. The studies were carried out in the open part of the White Sea, in the Onega, Dvina and Kandalaksha Bays, as well as in the intertidal zone of the Kandalaksha Bay. Quantitative characteristics of activity of microbial processes in waters and bottom sediments of the White Sea were obtained. The total number of bacteria was equal to 150000-800000 cells/ml, and intensity of dark CO2 assimilation was equal to 0.9-17 µg C/l/day. Bacterial sulfate reduction was equal to 3-150 mg S/m**2/day, and methane formation and oxidation was equal to 13-6840 and 20-14650 µl CH4/m**2/day, respectively. Extremely high values of intensity of all principal microbial processes were found in intertidal sediments rich in organic matter: under decomposing macrophytes, in local pits at the lower intertidal boundary, and in the mouth of a freshwater brook. Average hydrogen sulfide production in highly productive intertidal sediments was 1950-4300 mg S/m**2/day, methane production was 0.5-8.7 ml CH4/m**2/day, and intensity of methane oxidation was up to 17.5 ml CH4/m**2/day. Calculations performed with account for areas occupied by microlandscapes of increased productivity showed that diurnal production of H2S and CH4 per 1 km**2 of the intertidal zone (August) was estimated as 60.8-202 kg S/km**2/day and 192-300 l CH4/km**2/day, respectively.

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).

Biological, physical and chemical characteristics of water and sediment samples from the Volga River delta, northern Caspian

Based on the data of synchronous observations of hydrophysical and biogeochemical parameters in the near-mouth and shallow-water areas of the northern Caspian in 2000-2001, the scale of spatiotemporal variability in the following characteristics of the water-bottom system was estimated (1) flow velocity and direction within vortex structures formed by the combined effect of wind, discharge current, and the presence of higher aquatic plants; (2) dependence of the spatial distribution of the content and composition of suspended particulate matter on the hydrodynamic regime of waters and development of phytoplankton; (3) variations in the grain-size, petrographic, mineralogical, and chemical compositions of the upper layer of bottom sediments at several sites in the northern Caspian related to the particular local combination of dominant natural processes; and (4) limits of variability in the group composition of humus compounds in bottom sediments. The acquired data are helpful in estimating the geochemical consequences of a sea level rise and during the planning of preventive environmental protection measures in view of future oil and gas recovery in this region.

Sulfur isotope composition of pore fluids at ODP Sites 128-798 and 128-799

Micro-crystalline barites recovered by deep-sea drilling from Site 684 on the Peru margin and Site 799 in the Japan Sea are highly enriched in the heavy sulfur isotope relative to seawater ( d34S up to +84?). This isotopic composition is consistent with remobilization of biogenic barite triggered by sulfate reduction, and subsequent reprecipitation as a diagenetic barite front. The high levels of barium sulfate in these deposits (10-50%) cannot be explained by a diffusive transport model in sediments experiencing a constant rate of sedimentation. When sedimentation rates change radically, the barite front will remain at a given depth interval leading to large accumulations of barium sulfate. Such conditions may have generated the barite deposits at Site 799. At Site 684, on the other hand, there is evidence that the barite deposits are a result of the tectonically-driven advection of sulfate-bearing fluids through the sediment column.

Estimatin of roughness lengths with a ship-mounted ADCP from Knudedyb, Denmark in October 2009

The hydraulic effect of asymmetric compound bedforms on tidal currents was assessed from field measurements of flow velocity in the Knudedyb tidal inlet, Denmark. Large asymmetric bedforms with smaller superimposed ones are a common feature of sandy shallow water environments and are known to act as hydraulic roughness elements in dependence with flow direction. The presence of a flow separation zone on the bedform lee was estimated through analysis of the measured velocity directions and the calculation of the flow separation line. The Law of the Wall was used to calculate roughness lengths and shear velocities from log-linear segments sought on transect-averaged and single-location velocity profiles. During the ebb tide a permanent flow separation zone was established over the steep (10-20°) lee sides of the ebb-oriented primary bedforms, which generated a consequent drag on the flow. During the flood, no flow separation was induced by the gentle (2°) lee side of the primary bedforms except over the steepest (10°) part of the lee side where a small separation zone was sometimes observed. As a result, hydraulic roughness was only due to the superimposed bedforms. The parameterized flow separation line was found to underestimate the length of the flow separation zone of the primary bedforms. A better estimation of the presence and shape of the flow separation zone over complex bedforms in a tidal environment still needs to be determined; in particular the relationship between flow separation zone and bedform geometry (asymmetry, relative height or slope of the lee side) is unclear. This would improve the prediction of complex bedform roughness in tidal flows.

Chemical and amino acid compositions of bottom sediments from the Canary upwelling

Amino acid composition of bottom sediments on the northwestern continental slope of Africa is determined. Correlation similar to that found earlier in Caspian sediments between type of amino acid spectra of Atlantic sediments and distribution of reduced forms of sulfur in them is found. These correlations result from geochemical activity of benthic biocoenosis, which transforms sulfur compounds.

Pore-water chemistry of ODP Sites 124-767 and 124-768

The combination of multiple sediment sources and varying rates of sediment accumulation in the Celebes and Sulu seas have had significant impact on the processes of diagenesis, mineralization, and pore-fluid flow. Isotopic and mass-balance calculations help elucidate the various reactions taking place in these western Pacific basins, where ash alteration and basalt-seawater interactions are superimposed on the effects of sulfate oxidation of organic carbon and biogenic methane and of dolomitization of biogenic carbonates. Based on the shape of the calcium and magnesium depth profiles, two major reactive zones have been identified. The first is located near the zone of sulfate depletion and is characterized by carbonate recrystallization, dolomitization and ash alteration reactions at both Ocean Drilling Program Sites 767 and 768. The second reactive zone corresponds to the bottom of the sedimentary sequence and is characterized by alteration reactions in the basement (Site 767) and in the pyroclastic deposits beneath the sediment column (Site 768).

Ba, Al and SO4 concentrations in sediments and pore fluid of ODP Leg 127/128 samples

The barium distribution in sediments and pore fluids from five sites drilled in the Japan Sea have been used to illustrate the geochemical behavior of this element as it pertains paleoproductivity reconstructions, diagenetic remobilization, and barite precipitation in authigenic fronts. Sites where sulfate is depleted in the pore fluids also show high concentrations of dissolved barium, reflecting dissolution of biogenic barite. The high rate of sedimentation at Sites 798 and 799 results in a rapid sulfate depletion, which in turn leads to barite dissolution and reprecipitation in diagenetic fronts. The dissolved barium distribution at these sites has been used to quantify the rate of barite dissolution; we estimate a first-order rate constant for barite dissolution to be 2*10**-6/s at Site 799 and 2*10**-7/s at Site 798. Authigenic barite has been documented in sediments from Site 799 at 323 meters below seafloor by scanning electron microscopy and X-ray fluorescence analysis. These results indicate barite precipitation in a diagenetic front near the zone of sulfate depletion by upward migration of dissolved barium and downward diffusion of sulfate. Barite precipitation has also been inferred at Sites 796 and 798 based on sedimentary and dissolved barium distributions. Sulfate is not depleted in the pore fluids of Site 794. The lack of diagenetic remobilization of biogenic barium at this site preserves the high barium signal associated with the high-productivity sequences deposited during the late Miocene to Pliocene. Significantly, the organic carbon distribution does not indicate high accumulation rates during the periods of high opal and barium deposition. Instead, higher organic carbon accumulations are recorded in the Quaternary and middle Miocene sequences; intervals that are also characterized by deposition of siliciclastic turbidites. The presence of a terrestrial component in the organic carbon record renders barium a more useful indicator than organic carbon for paleoproductivity reconstructions in this marginal sea.

Geochemistry of abyssal peridotites from ODP Hole 209-1274A

Aqueous dihydrogen (H2,aq) is produced in copious amounts when seawater interacts with peridotite and H2O oxidizes ferrous iron in olivine to ferric iron in secondary magnetite and serpentine. Poorly understood in this process is the partitioning of iron and its oxidation state in serpentine, although both impose an important control on dihydrogen production. We present results of detailed petrographic, mineral chemical, magnetic and Mößbauer analyses of partially to fully serpentinized peridotites from the Ocean Drilling Program (ODP) Leg 209, Mid-Atlantic Ridge (MAR) 15°N area. These results are used to constrain the fate of iron during serpentinization and are compared with phase equilibria considerations and peridotite-seawater reaction path models. In samples from Hole 1274A, mesh-rims reveal a distinct in-to-out zoning from brucite at the interface with primary olivine, followed by a zone of serpentine + brucite ± magnetite and finally serpentine + magnetite in the outermost mesh-rim. The compositions of coexisting serpentine (Mg# 95) and brucite (Mg# 80) vary little throughout the core. About 30-50% of the iron in serpentine/brucite mesh-rims is trivalent, irrespective of subbasement depth and protolith (harzburgite versus dunite). Model calculations suggest that both partitioning and oxidation state of iron are very sensitive to temperature and water-to-rock ratio during serpentinization. At temperatures above 330 °C the dissolution of olivine and coeval formation of serpentine, magnetite and dihydrogen depends on the availability of an external silica source. At these temperatures the extent of olivine serpentinization is insufficient to produce much hydrogen, hence conditions are not reducing enough to form awaruite. At T < 330 °C, hydrogen generation is facilitated by the formation of brucite, as dissolution of olivine to form serpentine, magnetite and brucite requires no addition of silica. The model calculations suggest that the iron distribution observed in serpentine and brucite is consistent with formation temperatures ranging from <150 to 250 °C and bulk water-to-rock ratios between 0.1 and 5. These conditions coincide with peak hydrogen fugacities during serpentinization and are conducive to awaruite formation during main stage serpentinization. The development of the common brucite rims around olivine is either due to an arrested reaction olivine -> brucite -> serpentine + brucite, or reflects metastable olivine-brucite equilibria developing in the strong gradient in silica activity between orthopyroxene (talc-serpentine) and olivine (serpentine-brucite).

Planktonic foraminiferas in bottom sediments and Late Quaternary paleotemperatures of surface waters in the North Tropical Atlantic

Distribution of planktonic foraminiferal tests was studied in 15 Upper Quaternary sediment cores from the continental slope of Africa, the Canary and Cape Verde basins, and slopes of the Mid-Atlantic Ridge. In all the cores substantial variations were found in relationship between foraminiferal planktonic species reflecting fluctuations of mean annual temperatures of surface waters. Temperature difference in temperatures between present time and that of the maximum of the stadial of the last continental glaciation glacial stadial (about 18,000 yrs ago) ranges from 8.5°C in the Canary upwelling region to minimum values of 2.0°C in the central part of the ocean, i.e. the southern part of the subtropical gyre. Temperature difference the Holocene optimum and 18,000 yrs ago ranges from 10°C to 3°C. Age estimates are supported by radiocarbon dates.