Reproduction of Pechora runoff hydrographs with the help of a model of heat and water exchange between the land surface and the atmosphere (SWAP)

The potentialities of a procedure for calculating the Pechora River runoff from the pan-Arctic river basin are studied. The procedure is based on the use of a model describing heat and water exchange between the land surface and the atmosphere and two variants of input data sets relying on global databases on meteorological characteristics and land surface parameters and data of standard measurements of meteorological characteristics in combination with parameters of the land surface of the basin, taken from global databases. In both cases, use was made of the method for optimizing part of the most important model parameters, including both land surface parameters and correction factors for some meteorological elements.     

Turbulent structure of the subsurface layer of the sea according to the data of the <Emphasis Type="Italic">Sigma-1</Emphasis> measuring complex

We present the results of experimental investigations of the characteristics of turbulence in the layer of wave-induced mixing. The data on the fluctuations of velocity, temperature, and conductivity are obtained with the help of a Sigma-1 measuring complex. The computed values of the dissipation rate of turbulent energy are compared with different models proposed for the subsurface layer. It is shown that the available models fail to guarantee satisfactory agreement of the numerical results with the experimental data for the layer of active wave action and, in particular, in the presence of swell. This leads us to the conclusion concerning the necessity of parametrization and assimilation of more complete data on the state of the sea surface, the structure of currents, and the surface layer of the atmosphere in the models. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 15–28, March–April, 2007.     

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.     

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.     

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.     

Retrowedge-related Carboniferous units and coeval magmatism in the northwestern Neuquén province, Argentina

The studied Carboniferous units comprise metasedimentary (Guaraco Norte Formation), pyroclastic (Arroyo del Torreón Formation), and sedimentary (Huaraco Formation) rocks that crop out in the northwestern Neuquén province, Argentina. They form part of the basement of the Neuquén Basin and are mostly coeval with the Late Paleozoic accretionary prism complex of the Coastal Cordillera, south-central Chile. U–Pb SHRIMP dating of detrital zircon yielded a maximum depositional age of 374?Ma (Upper Devonian) for the Guaraco Norte Formation and 389?Ma for the Arroyo del Torreón Formation. Detrital magmatic zircon from the Guaraco Norte Formation are grouped into two main populations of Devonian and Ordovician (Famatinian) ages. In the Arroyo del Torreón Formation, zircon populations are also of Devonian and Ordovician (Famatinian), as well as of Late Neoproterozoic and Mesoproterozoic ages. In both units, there is a conspicuous population of Devonian magmatic zircon grains (from 406?±?4?Ma to 369?±?5?Ma), indicative of active magmatism at that time range. The ε_Hf values of this population range between ?2.84 and ?0.7, and the TDM-(Hf) are mostly Mesoproterozoic, suggesting that the primary sources of the Devonian magmatism contained small amounts of Mesoproterozoic recycled crustal components. The chemical composition of the Guaraco Norte Formation corresponds to recycled, mature polycyclic sediment of mature continental provenance, pointing to a passive margin with minor inputs from continental margin magmatic rocks. The chemical signature of the Huaraco Formation indicates that a magmatic arc was the main provenance for sediments of this unit, which is consistent with the occurrence of tuff—mostly in the Arroyo del Torreón Formation and very scarcely in the Huaraco Formation—with a volcanic-arc signature, jointly indicating the occurrence of a Carboniferous active arc magmatism during the deposition of the two units. The Guaraco Norte Formation is interpreted to represent passive margin deposits of mostly Lower Carboniferous age (younger than 374?Ma and older than 326?Ma) that precede the onset of the accretionary prism in Chile and extend into the earliest stage of the accretion, in a retrowedge position. The Arroyo del Torreón and Huaraco formations are considered to be retrowedge basin deposits to the early frontal accretionary prism (Eastern Series) of Chile. The presence of volcanism with arc signature in the units provides evidence of a Mississippian magmatic arc that can be correlated with limited exposures of the same age in the Frontal Cordillera (Argentina). The arc would have migrated to the West (Coastal Batholith) during Pennsylvanian–Permian times (coevally with the later basal accretionary prism/Western Series). The source of a conspicuous population of Devonian detrital zircon interpreted to be of magmatic origin in the studied units is discussed in various possible geotectonic scenarios, the preferred model being a magmatic arc developed in the Chilenia block, related to a west-dipping subduction beneath Chilenia before and shortly after its collision against Cuyania/Gondwana, at around 390?Ma and not linked to the independent, Devonian–Mississippian arc, developed to the south, in Patagonia.     

Biogeochemical impacts due to mesoscale eddy activity in the Sargasso Sea as measured at the Bermuda Atlantic Time-series Study (BATS)

A comparison of monthly biogeochemical measurements made from 1993 to 1995, combined with hydrography and satellite altimetry, was used to assess the impacts of nine eddy events on primary productivity and particle flux in the Sargasso Sea. Measurements of primary production, thorium-234 flux, nitrate+nitrite, and photosynthetic pigments made at the US JGOFS Bermuda Atlantic Time-series Study (BATS) site were used. During the 3 years of this study, four out of six high thorium-234 flux events occurred during the passage of an eddy. Primary production nearly as high as the spring bloom maximum was observed in two mode-water eddies (May 1993 and July 1995). The 1994 spring bloom at BATS was suppressed by the passage of an anticyclone. Distinct phytoplankton community shifts were observed in mode-water eddies, which had an increased percentage of diatoms and dinoflagellates, and in cyclones, which had an increased percentage of Synechococcus. These variations in species composition within mode-water eddies and cyclones may be associated with the ages of the sampled eddies, and/or differences in physical, chemical, and biological factors in these two distinct eddy types. In general, eddies that were 1–2 months old elicited a large biological response; eddies that were 3 months old may show a biological response and were accompanied by high thorium flux; eddies that were 4 months old or older did not show a biological response or high thorium flux. A conceptual model depicting temporal changes during eddy upwelling, maturation, and decay can explain the observations in all seven upwelling eddies present in the time-series investigated herein.