Distribution, fluxes and balance of particulate organic carbon in the Arctic ocean

Particulate organic carbon (POC) is one of main component of carbon cycle in the Ocean. In this study an attempt to construct a picture of the distribution and fluxes of POC in the Arctic Ocean adjusting for interchange with the Pacific and Atlantic Oceans has been made. The specificity of this construction is associated with an irregular distribution of POC measurements and complicated structure and hydrodynamics of the waters masses. To overcome these difficulties, Multiple Linear Regression technic (MLR) was performed to test the significant relation between POC, temperature, salinity, as well depth, horizon, latitude and offshore distance. The mapping of POC distribution and its fluxes was carrying out at 38 horizons from 5 to 4150 m (resolution 1°×1°). Data on temperature, salinity, meridional and zonal components of current velocities were obtained from ORA S4 database (Integrated Climate Data Center, http://icdc.cen.uni-hamburg.de/las). The import-export of POC between the Arctic, Atlantic and Pacific Oceans as well as between Arctic Seas was precomputed by summer fluxes. The import of POC in the Arctic Ocean is estimated to be 38±8Tg Cyr-1, and the export is -9.5±4.4Tg Cyr-1.

Caractéristiques Morphopédologiques et Géochimiques des Sols Brunifiés de Anikro et de Kahankro (Centre-Sud de la Côte d’Ivoire)

In an ecosystem where ferrallitization is the dominant pedogenetic process, brown soils of a particular character are observed. They are dominant clay texture, very often spotted, and heavily loaded in coarse elements consisting of ferromanganic nodules and concretions. This paper focuses on highlighting the morphopedological and geochemical characteristics, determining the originality of the brown soils observed at Anikro and Kahankro, in the region of Toumodi, in Côte d’Ivoire. In the field, the toposquencial approach has been adopted. Soil pits have been opened and described. The samples taken were then analyzed by the triacid method in view of the determination of the content of total elements horizon by horizon. The results obtained show that the brown soils observed at Anikro and Kahankro are generally regosols and cambisols. They are subject to phenomena of reworking and rejuvenation and were affected by a phenomenon of hydromorphy at the bottom of the slope. The oxidation-reduction spots that occur in soil profiles and which predispose them to concretion are more abundant in topographic top and bottom position. Chemical analysis shows that at Anikro, the silica content decreases as the depth increases. Also, iron (Fe2O3) and aluminum (Al2O3) have an antagonistic character on the midslope. While at the bottom of slope, the MgO, MnO, Al2O3 and Fe2O3 contents increase in the BfeC depth horizon, with respective values of 3.6%, 2% and 20% for each of the last two. In Kahankro soils, the antagonism exists between silica and iron. Magnesium and manganese accumulate only in the surface horizons. At the lower slopes, the highest levels of iron (30%), aluminum (20%), magnesium (1.2%) and manganese (0.4%) in the Bg horizons begin with horizon A3. These high grades are obtained due to pseudogleyic to gleyic characters of soils located at this topographic position. The various oxides measured sometimes show a dispersed character according to the locality in relation to the nature of the rock formations whose alteration has been given to the soil. The various characteristics of the soils described reveal their particular characteristics. These soils deserve to be referred to as browned soils.

Vertical migration of Siphonophora (Cnidaria) and their productivity in the Croker Passage, the Antarctic

The population structure, seasonal and diel changes in vertical distribution of two siphonophore species, Dimophyes arctica and Pyrostephos vanhoeffeni, in Croker Passage (Antarctic Peninsula) are examined, and compared with the results obtained by other au− thors in various oceanic areas. Zooplankton samples were taken at discrete depth intervals between 0 and 1200 m during day and night shifts, in both summer and winter seasons. Dimophyes arctica was present both in polygastric and eudoxid forms, with the latter being dominant throughout the entire study period. The results obtained demonstrate that Antarc− tic waters clearly enhance the reproductive ability of this species when compared with spec− imens from other oceanic regions. Maximum densities of Dimophyes arctica were recorded in December in the 200-400 m depth horizon. However, high concentrations of eudoxids were also recorded at deeper parts of the water column. Pyrostephos vanhoeffeni was, in contrast, most abundant in autumn and winter, and both species were found to proliferate and disperse or sink further down the water column during autumn and winter. Daily verti− cal migration was observed only during the summer period.

Fundamental Aspects of Stray Current Corrosion on Buried Pipeline

Stray current is one of the main reasons in pipeline failure. In pipeline design and maintenance, it is important to know the fundamentals influencing stray current corrosion. However, it is difficult to control stray currents because many factors can affect its inflow points, outflow points and current densities. Several fundamental aspects, such as soil resistivity, coating worn rate, buried depth and horizon distance have been studied in order to find useful information in pipeline design. The results show stray current can be influenced by soil resistivity, coating worn rate and buried depth. It is suitable to control stray current corrosion by increasing soil resistivity, buried depth, horizon distance and decreasing coating worn rate. However, there are boundary values in controlling stray current corrosion by increasing soil resistivity, buried depth and horizon distance. For example, in this laboratory study, the boundary horizon distance is 200mm.

Seismic tomography and mixing in the deep earth

Recently constructed tomographic models of the lateral heterogeneity of elastic properties in the Earth's mantle are contrasted in terms of their implications concerning the extent to which the endothermic phase transformation at 660 km depth is influencing the radial style of mixing. Previously published whole mantle and split mantle tomographic reconstructions, SH8/WMI3 and SH8/U4L8 respectively, fit the seismic observations equally well but disagree on the extent to which radial mixing may be impeded across this depth horizon. We show that inferences from seismic tomographic images based on the application of diagnostic functions (global and regional variance spectra and the radial correlation function) lead to the conclusion that the mantle circulation is whole mantle in style if model SH8/WM13 is employed. The split mantle tomographic inversion SHS/U4L8 leads to the contradictory conclusion that the mantle circulation is significantly impeded across the 660 km depth horizon. This latter interpretation is reinforced when we employ the new higher resolution split mantle model SH12/U7L5 in our calculations. We demonstrate that the depth-dependent radial heat flow delivered by both of the split models implies the existence of a thermal boundary layer at 660 km depth, and therefore significant layering, whereas that delivered by the whole mantle model does not. By insisting that the depth-dependent viscosity profile of the mantle be compatible with the thermal structure if the flow were layered, we argue that the split mantle tomographic inversions lead to a self-consistent description of geodynamic constraints (geoid and postglacial rebound data).

PROPRIETES PHYSICO-CHIMIQUES ET MINERALOGIQUES DES SOLS DES FORETS DE CHENES DE L’OUEST DE L’IRAN

Most of the soils studied are non-evolved. The other soils of the area that can be distinguished are calcareous brown soils, sierozems and erosion soils. The soils are low in organic matter. The carbonate, varying from 0.4 to 46.3%, tends to increase with depth. Horizon of accumulation of carbonate (in the sierozems) is found between 30 and 100 cm from the soil surface. Sulfate exceeds chlorine ions in the soil extract. The salinity does not exist in these soils. The exchange capacity varies from 4.7 to 29.4 meq/100 g of soil. The dominant clay mineral in some of these soils is vermiculite. In the forests of western Iran, Quercus persica and Quercus saii generally occupy calcareous, poor and rather deep soils, whereas Quercus infectoria is usually grown on the less calcareous, rich and deep soils.