Dusty Plasma of a Wind-Sand Flux in Desertified Areas

Izvestiya, Atmospheric and Oceanic Physics - Measurements of electric currents of saltation in the wind-sand flux and currents caused by the wind transport of dust aerosol particles have been...     

Effect of slowly varying drift forces on the motion characteristics of truss spar platforms

Spar platform has been regarded as a competitive floating structure for deep and ultra deep water oil and gas production. In this paper, an efficient methodology has been developed to determine the slow motion responses of slender floating offshore structures due to wave forces. Based on this methodology, a MATLAB program named ‘TRSPAR’ was developed to predict the dynamic responses in time domain and it was used in this study to obtain the numerical results of a typical truss spar platform connected to sea bed using nine taut mooring lines. The difference frequency forces were calculated using the principles of the extension of Morison equation for an inclined cylinder and the wave kinematics were predicted using hyperbolic extrapolation. Mooring lines were modelled as nonlinear springs and their stiffness was obtained by conducting the static offset simulation. Because of the lack of detailed calculations in literature, most of the equations used were derived and presented in this paper. The effects of the different sources of the second order difference frequency forces were compared for inertia and drag forces in terms of response spectra. To validate the TRSPAR code, its results were compared to results of a typical truss spar model test.     

Composition and secondary alterations of microfossils in sediments of the Ashadze-1 hydrothermal field (tropical Mid-Atlantic Ridge)

The first thorough analysis of microfossils from ore-bearing sediments of the Ashadze-1 hydrothermal field in the Mid-Atlantic Ridge sampled during cruise 26 of the R/V Professor Logachev in 2005 revealed the substantial influence of hydrothermal processes on the preservation of planktonic calcareous organisms, as well as on the preservation and composition of the benthic foraminifers. From the lateral and vertical distribution patterns and the secondary alterations of the microfossils, it is inferred that the main phase of the hydrothermal mineralization occurred in the Holocene. Heavy metals (Cu, Co, Cr, and Ag) were accumulated by foraminiferal tests and in their enveloping Fe-Mn crusts. The distribution of authigenic minerals replacing foraminiferal tests demonstrates local zoning related to the hydrothermal activity. There are three mineral-geochemical zones defined: the sulfide zone, the zone with an elevated Mg content, and zone of Fe-Mn crusts.     

Interannual variability in vertical export in the Ross Sea: Magnitude, composition, and environmental correlates

The vertical flux of particulate matter from the surface of the Ross Sea, Antarctica, has been suggested as being large, with substantial seasonal and spatial variations. We conducted a study in which vertical flux was quantified using sediment traps deployed at 200 m and compared to estimates calculated from one-dimensional budgets of nutrients (nitrogen and silicon). Estimates of flux were collected at two locations in the southern Ross Sea from late December to early February during four years: 2001-2002, 2003-2004, 2004-2005, and 2005-2006. Phytoplankton biomass and vertical flux varied substantially seasonally and spatially between the two sites, and among years. The greatest flux was observed in 2001-2002, with a short-term maximum organic carbon flux of 3.13 mmol m⁻² d⁻¹, and the summer mean organic carbon flux equal to 0.93 mmol m⁻² d⁻¹. In contrast, the mean carbon flux at the same site in 2003-2004 was over an order of magnitude less, averaging 0.19 mmol m⁻² d⁻¹, despite the fact that productivity in that year was substantially greater. In 2005-206 the contribution of fecal pellets to flux was smallest among all years, and the pellet contribution ranged from <1 to more than 50% of organic flux. As the moorings also had surface layer fluorometers, the relationship between surface biomass and sediment trap flux was compared. Temporal lags between surface fluorescence and flux at 200 m maxima in 2003-2004 and 2004-2005 ranged from two to six days; however, in 2005-2006 the temporal offset between biomass and flux was much longer, ranging from 11 to 27 days, suggesting that fecal pellet production appeared to increase the coupling between flux and surface production. Estimates of export from the upper 200 m based on one-dimensional nutrient budgets were greater than those recorded by the sediment traps. Nutrient budgets also indicated that siliceous production averaged ca. 40% of the total annual production. The variations observed in the flux of biogenic matter to depth in the Ross Sea are large, appear to reflect different forcing among years, and at present are not adequately understood. However, such variability needs to be both understood and represented in biogeochemical models to accurately assess and predict the effects of climate change on biogeochemical cycles.     

Airborne imagery of a disintegrating Sargassum drift line

Airborne hyperspectral and thermal infrared imagery collected over the Florida Current provide a view of the disintegration of a Sargassum drift line in 5 m s⁻¹ winds. The drift line consists mostly of rafts 20-80 m² in size, though aggregations larger than 1000 m² also occur. Rafts tend to be elongated, curved in the upwind direction, and 0.1-0.5 °C warmer than the surrounding ocean surface. Long weed ‘trails’ extending upwind from the rafts are evidence of plants dropping out and being left behind more rapidly drifting rafts. The raft line may be a remnant of an earlier Sargassum frontal band, which is detectible as an upwind thermal front and areas of submerged weed. Issues are identified that require future field measurements.     

Variations in the elemental composition of ferromanganese structures from Lake Baikal

The elemental composition of ferromanganese sedimentary structures from the bottom of Lake Baikal represented by nodules and crusts, as well as the enclosing sediments, have been studied by the atomic absorption, chemical, and ICP-MS methods. It is established that the contents of the rock-forming and accompanying elements in them are highly variable. In this connection, the examined samples are divided in two groups differing by their Mn/Fe values. In most of the samples, they range from 0.01 to 0.1, although some of the ferromanganese structures or their parts are substantially enriched in manganese. The contents of most of the rare and dispersed elements in the ferromanganese structures are usually at the background level, although the samples maximally enriched in iron or manganese are characterized by relatively high copper, nickel, cobalt, vanadium, zinc, and molybdenum concentrations.     

Effect of wave amplitude on turbulent flow in a wavy channel by direct numerical simulation

The present study numerically investigates the characteristics of three-dimensional turbulent flow in a wavy channel. For the purpose of a careful observation of the effect of the wave amplitude on the turbulent flow, numerical simulations are performed at a various range of the wave amplitude to wavelength ratio (0.01?α/λ?0.05), where the wavelength is fixed with the same value of the mean channel height (H). The immersed boundary method is used to handle the wavy surface in a rectangular grid system, using the finite volume method. The Reynolds number (Re=U_bH/ν) based on the bulk velocity (U_b) is fixed at 6760. The present computational results for a wavy surface are well compared with those of references. When α/λ=0.02, the small recirculating flow occurs near the trough at the instant, but the mean reverse flow is not observed. In the mean flow field, the reverse flow appears from α/λ=0.03 among the wave amplitude considered in this study. The domain of the mean reverse flow defined by the locations of separation and reattachment depends strongly on the wave amplitude. The pressure drag coefficient augments with increasing the wave amplitude. The friction drag coefficient shows the increase and decrease behavior according to the wave amplitude. The quantitative information about the flow variables such as the distribution of pressure and shear stress on the wavy surface is highlighted.     

Two-dimensional,two-phase granular sediment transport model with applications to scouring downstream of an apron

We present a two-dimensional, two-phase model for non-cohesive sediment transport. This model solves concentration-weighted averaged equations of motion for both fluid and sediment phases. The model accounts for the interphase momentum transfer by considering drag forces. A collisional theory is used to compute the sediment stresses, while a two-equation (k–ε) fluid turbulence closure is implemented. A benchmark sediment transport problem concerning the scouring downstream of an apron is carried out as an example and numerical results agree with existing experimental data.     

Metals,arsenic, and sulfur in the Aue and Eibenstock granites,Erzgebirge

Average concentrations of Pb, Zn, Cu, and other metals, as well as S and As, were calculated for the Aue granitic cupola, the contact aureole of which hosts the large vein-type uranium deposit of Schlema-Alberoda and the Schneeberg uranium-base metal deposit (Erzgebirge, Germany). The cupola was exposed by mine workings and boreholes, which provided an opportunity to evaluate variations in the abundances of metals in the granites over a vertical interval of more than 2.5 km and estimate their losses in the upper oxidized part of the investigated volume of the cupola (coefficient of iron oxidation, KO _Fe, increases in the granites from bottom to top from 7 to 70%) compared with the lower unaltered and unoxidized part (with a KO _Fe plateau at about 5%). The average concentrations of metals in the upper part of the cupola are lower than those in the lower part by a factor of 2.5 for Pb, 1.56 for Zn, 1.45 for Cu, 1.3 for Co, etc. A similar decrease in the abundances of ore elements along the vertical section associating with the relative epigenetic alteration and oxidation of the granite was previously described by us for U and Th and for the components of high-temperature ores, W, Sn, and Mo. The removal of ore elements from the granite was accompanied by a decrease in the bulk contents of sulfur and arsenic by a factor of 1.35 and 1.65, respectively. The leaching of trace metals from the granites of the upper part of the Aue cupola was followed by their partial redeposition above the cupola in the ore veins of the Schlema and Schneeberg deposits. Original Russian Text ? Vikt. L. Barsukov, N.T. Sokolova, O.M. Ivanitskii, 2006, published in Geokhimiya, 2006, No. 9, pp. 967–982.     

Using Hydrogeochemical Methods To Evaluate Complex Quaternary Subsurface Stratigraphy Block Island,Rhode Island,USA

One of the major problems in hydrogeologic investigations of glaciated regions is the determination of complex stratigraphic relationships in the subsurface where insufficient information is available from drilling and geophysical records. In this paper, chemical characteristics of groundwater were used to identify stratigraphic changes in glacial deposits that were previously inferred on Block Island, Rhode Island, USA, an emergent remnant of the late Wisconsinan terminal moraine, located approximately 16 km south of the Rhode Island mainland. Two chemically distinct water types are recognized on the island: 1) high-iron, characterized by dissolved silica levels in excess of 20 mg/L, bicarbonate greater than 30 mg/L and dissolved iron ranging from 1-20 mg/L; and 2) low-iron, characterized by dissolved silica levels below 16 mg/L, bicarbonate less than 30 mg/L, and less than 0.3 mg/L dissolved iron. The spatial distribution of iron-bearing minerals and organic matter and the resulting redox conditions are believed to control the occurrence of high-iron groundwater. The high-iron waters occur almost exclusively in the eastern half of the island and appear to coincidence with the presence of allochthonous blocks of Cretaceous-age coastal-plain sediments that were incorporated into Pleistocene-age deposits derived from the Narragansett Bay-Buzzard's Bay lobe of the Late Wisconsinan Laurentide ice sheet. The low-iron waters occur in the western half of the island, where the occurrence of these Cretaceous-age blocks is rare and the sediments are attributed to a sublobe of the Hudson-Champlain lobe of the Late Wisconsinan ice-sheet. RÉSUMÉ: L'un des principaux problèmes dans les études hydrogeologiques des régions qui ont été englacées est la définition des relations stratigraphiques complexes sous la surface, lá où les informations fournies par les forages et par la géophysique sont insuffisantes. Dans l'exemple traité, les caractéristiques chimiques de l'eau souterraine sont utilisées pour identifier les variations stratigraphiques dans les dépôts glaciaires qui avaient auparavant été supposées, sur l'île de Block (Rhode Island), restes émergeant d'une moraine terminale du Wisconsinien récent, situé à environ 16 km au sud de Rhode Island. Deux types d'eau chimiquement distincts ont été reconnus dans l'île: 1) à fortes teneurs en fer, caractérisées par des concentrations en silice supérieures à 20 mg/L, en bicarbonates supérieures à 30 mg/L et en fer comprises entre 1 et 20 mg/L; et 2) à faibles teneurs en fer, marquées par des concentrations en silice inférieures à 16 mg/L, en bicarbonate inférieures à 30 mg/L et en fer dissous inférieures à 0.3 mg/L. La distribution spatiale des minéraux riches en fer et de la matière organique et les conditions redox résultantes contrôlent probablement la présence de fer dans les eaux souterraines à fortes concentrations. Les eaux à fortes teneurs en fer sont connues presque exclusivement dans la moitié orientale de l'île et semblent coïncider avec la présence de blocs allochtones provenant des sédiments côtiers crétacés, introduits dans les formations pléistocènes liées au lobe glaciaire des baies de Narragansett et du Busard de la calotte glaciaire laurentide du Wisconsinien récent. Les eaux à faibles teneurs en fer apparaissent dans la moitié occidentale de l'île, là où ces blocs de Crétacé sont rares et où les sédiments sont attrbués à une digitation du lobe de l'Hudson-Champlain de la calotte glaciaire du Wisconsinien récent. RESUMEN: Uno de los mayores problemas en la investigación hidrogeológica en regiones glaciares es la determinación de las complejas relaciones estratigráficas en el subsuelo, donde la información procedente de registros de perforaciones y de geofísica no es suficiente. En este artículo, se han usado las características químicas del agua subterránea para identificar unos cambios estratigráficos que se habían predicho previamente en unos depósitos glaciares en Block Island, Rhode Island (Estados Unidos), un remanente emergente de la morrena terminal del Winsconsiniense tardío, situada unos 16 km al sur de la Rhode Island continental. En la isla se encuentran dos tipos de agua distintos: 1) de alto contenido en hierro, caracterizada por niveles de sílice disuelto superando los 20 mg/L, bicarbonatos por encima de 30 mg/L y hierro disuelto oscilando entre 1-20 mg/L; y 2) de bajo contenido en hierro, caracterizada por niveles de sílice disuelto inferiores a 16 mg/L, bicarbonatos por debajo de 30 mg/L y menos de 0.3 mg/L de hierro disuelto. La distribución espacial de los minerales ricos en hierro y de la materia orgánica, así como las condiciones redox resultantes se supone que condicionan la presencia de aguas de alto contenido en hierro. Estas aguas aparecen casi exclusivamente en la mitad oriental de la isla y parecen coincidir con la presencia de bloques alóctonos de sedimentos costeros, de edad cretácica, que se incorporaron a los depósitos de edad pleistocena procedentes del lóbulo de la Bahía de Narragansett-Bahía de Buzzard, correspondiente a la capa glaciar del Winsconsiniense-Lauréntido tardío. Las aguas de bajo contenido en hierro aparecen en la mitad occidental de la isla, donde la presencia de estos sedimentos de edad cretácica es rara y los sedimentos se suponen procedentes de un sublóbulo del lóbulo de Hudson-Camplain, correspondiente a la capa glaciar del Winsconsiniense tardío.