Seasonal and event-controlled export of organic matter from the shelf towards the Gulf of Lions continental slope

To investigate the role of coastal canyons in the transfer of organic matter from the shelf to the slope and basin, we deployed sediment trap/current meter pairs at the head of five canyons in the Gulf of Lions (GoL) between November 2003 and May 2004. Analysis of organic carbon, biogenic silica, Corg isotopic composition, Corg/total nitrogen, chloropigments, and amino acids clearly shows the seasonal influence and effect of extreme meteorological events on the composition of collected particles. The sampling period was divided into three “scenarios”. The first corresponded to a large easterly storm and flood of the Rhone river during stratified water column conditions; the composition of material collected during this event was influenced by increased transfer of riverine and coastal particulate matter, with a lower Corg content. During the second “fall-winter” scenario, northern and northwestern winds blowing over the shelf caused cooling and homogenization of the shelf water column; particles collected at this time reflected the homogeneous source of particulate matter transported through canyons; particles sitting in the vicinity of canyon heads are most likely swept downslope by the general south-westward circulation. Organic tracers indicate a degraded origin for organic matter transported during this period. A third “spring” scenario corresponded to northern winds alternating with eastward windstorms that triggered and/or enhanced the cascading of dense waters accumulated on the bottom of the shelf due to previous cooling. These conditions occurred in conjunction with increased phytoplankton productivity in shelf surface waters. Organic matter advected mainly by dense shelf water cascading was fresher due to the transport of newly produced particles and a variable terrestrial fraction; this fraction depended on the proportion of resuspended material accumulated during previous high discharge periods that was involved in each transport pulse. The tight link shown between meteorological conditions and organic matter transport is important for continental margin geochemical studies as future changes in climatic conditions may lead to dramatic changes in carbon sequestration capability and in the ecosystems of deep margin environments.     

Studying the errors in the estimation of the variation of energy by the “patched-conics” model in the three-dimensional swing-by

The swing-by maneuver is a technique used to change the energy of a spacecraft by using a close approach in a celestial body. This procedure was used many times in real missions. Usually, the first approach to design this type of mission is based on the “patched-conics” model, which splits the maneuver into three “two-body dynamics.” This approach causes an error in the estimation of the energy variations, which depends on the geometry of the maneuver and the system of primaries considered. Therefore, the goal of the present paper is to study the errors caused by this approximation. The comparison of the results are made with the trajectories obtained using the more realistic restricted three-body problem, assumed here to be the “real values” for the maneuver. The results shown here describe the effects of each parameter involved in the swing-by. Some examples using bodies in the solar system are used in this part of the paper. The study is then generalized to cover different mass parameters, and its influence is analyzed to give an idea of the amount of the error expected for a given system of primaries. The results presented here may help in estimating errors in the preliminary mission analysis using the “patched-conics” approach.     

“Amount effect” of water isotopes and quantitative analysis of post‐condensation processes

A numerical model is proposed that describes the interaction between raindrops and water vapour near the planetary boundary layer to explain the “amount effect”. This model relates the intensity to the isotopic composition of precipitation. The model resolves raindrop sizes, and explicitly includes: (1) the isotopic equilibration time of raindrops that is drop‐size dependent; (2) raindrop transit times through the atmosphere; and (3) the evolution of the isotopic composition of vapour at various rain rates. At high rain rate, the precipitation through a layer is less equilibrated with the vapour because the isotopic equilibration time is long compared to the fast transit time, and there is a preponderance of large drops, which take longer to equilibrate. The δ¹⁸O of vapour in the lower atmosphere becomes lower as a result of the interaction with these raindrops of low δ¹⁸O, and the degree of depletion of ¹⁸O is higher when precipitation rates are high. The model reproduces time‐series observations of isotopic composition of precipitation in Japan, and a vapour replenishment rate is inferred by either advection or evaporation of about 5% of the precipitation rate. The results could be the basis for a new parameterization of the isotopic equilibration for different precipitation types and rates in General Circulation Models (GCMs). When the model is applied to a GCM, this parameterization is important for places where precipitation occurs at cold temperatures (<15 °C). Copyright © 2007 John Wiley & Sons, Ltd.     

Correlations between OH,NaD and OI 5577 Å emissions in the airglow

Simultaneous measurements of the night airglow OI 5577 Å and OH (8,3) band have been carried out at Cachoeira Paulista (23°S, 45°W), Brazil since 1976. Cross correlation analyses between the nocturnal variations of these emissions and also with the OH rotational temperature (ROT) for various time shifts are presented. It is found that OH (8,3) is well correlated with ROT but with a time lag of about 1 h. The variations of OI 5577 Å lead OH (8,3) by about 2–3 h and ROT covaries with 5577 Å with a time lag less than 1 h. For the sake of comparison, OI 5577 Å, OH and NaD data from a number of IQSY stations have been analysed. It is noted that (1) OI 5577 Å leads OH by about 2 h at mid-latitude stations and (2) OH is well correlated with Na 5893 Å with a time lag of less than 1 h. The presence of the phase lagged correlation patterns between OH/5577 Å, OH/ROT and OH/NaD indicates vertical propagation of a wavelike perturbation of the upper atmosphere.     

Sediment hosted lead–zinc deposits of the Neoproterozoic Bambuí Group and correlative sequences, São Francisco Craton, Brazil: A review and a possible metallogenic evolution model

The Proterozoic sediment-hosted Zn–(Pb) sulfide and non-sulfide deposits of the São Francisco Craton, Brazil, are partially syn-diagenetic and epigenetic and were probably formed during extensional events. The majority of the deposits occur within shallow water dolomites. The Pb isotopic data of sulfides are relatively homogeneous for individual deposits and plot above the upper crust evolution curve of the Plumbotectonic model. Some of the deposits are characterized by highly radiogenic lead (²⁰⁶Pb/²⁰⁴Pb ≥ 21) originating from the highly radioactive crust of the São Francisco Craton. Pb and S isotopic data suggest the sources of metal and sulfur for the deposits to be the basement rocks and seawater sulfates in the sediments, respectively. The relatively high temperatures of formation (100 to 250 °C) and moderate salinity (3% to 20% NaCl equiv.) of the primary fluid inclusions in the sphalerite crystals suggest the participation of basinal mineralizing fluids in ore formation. The steep paleo-geothermal gradient generated by the radioactively enriched basement rocks probably assisted in heating up the circulating mineralizing fluids.     

A 14-year monthly climatology and trend in the 35–65 km altitude range from Rayleigh Lidar temperature measurements at a low latitude station

A sodium resonance lidar at 589 nm has been operated in São José dos Campos, Brazil (23°S, 46°W) since 1972 mainly for studies related to the origin, chemistry and dynamics of the mesospheric sodium layer. Beginning in 1993, the improved laser capability has also enabled the processing of the Rayleigh signal from which the temperatures from 35 to 65 km are retrieved on a nightly mean basis. We used these nightly profiles to determine the monthly temperature profiles from 1993 to 2006. The mean temperature characteristics for each year and for the whole period are obtained. Seasonal thermal amplitude is small (6 K peak to peak at 40 and 60 km). Compared with the MSISE-90 model, a large difference is noted, with temperature lower than the model below the stratopause and higher above. Also the seasonal variation has a large difference with better agreement occurring around local winter, but with temperatures higher by 8–10 K at the equinoxes. The semiannual component is dominant over the annual at all altitudes. Linear trends with decreasing temperature of 1.09, 2.29 and 1.42 K/decade are observed at 40, 50 and 60 km, respectively.     

Photochemistry of Cu complexed with chromophoric dissolved organic matter: implications for Cu speciation in rainwater

Significant quenching of fluorescence by Cu in rainwater samples from southeastern North Carolina demonstrates that chromophoric dissolved organic matter (CDOM) is an effective ligand for Cu in rainwater. A strong inverse correlation between the decrease in fluorescence upon Cu addition and CDOM abundance suggests the presence of excess binding sites for Cu in high CDOM samples. Electroanalytical studies indicate that CDOM extracted from C₁₈ cartridges formed Cu complexes with concentrations and conditional stability constants similar to ligands found in ambient rainwater. When authentic rainwater samples were photolyzed with simulated sunlight both photoproduction and photodestruction of ligands were observed, suggesting the photochemical response of Cu-complexing ligands in rainwater is the result of two competing reactions. The rate of CDOM photobleaching was directly related to changes in strong ligands (K_CuL ∼ 10¹⁵) whereas weaker ligands (K_CuL < 10¹³) were not correlated, suggesting the photolabile CDOM resides in the strong ligand class. A photolysis study comparing filtered and unfiltered rainwater samples indicated that Cu-complexing ligands adsorbed onto or otherwise associated with particles are photodegraded much more rapidly than dissolved ligands. Photolysis with UV radiation appears to be most effective at engendering changes in Cu ligands, however a significant photochemical response was also observed when samples were exposed to photosynthetically active radiation with wavelengths greater than 400 nm. Results from this study demonstrate that complexation of Cu by CDOM has important ramifications for controlling both the speciation of the metal and the reactivity of CDOM in rainwater.     

The Effect of Heavy Tamping on Structured Residual Clay Site

This paper examines the effect of heavy tamping (dynamic compaction) on highly porous structured residual clayey soil. The aim of this study is to analyse the feasibility of this technique when applied on lightly bonded residual soil sites, which are commonly found in tropical and subtropical regions. This soil has some interesting characteristics, such as high fine grain soil percentages (56% clay and 22% silt), a plastic index of 11%, high porosity (initial void ratio of 1.21), high hydraulic conductivity (about 10^?5 m/s) and a high stiffness at small strains (E?=?49.2-MPa). The research involves field [Cone Penetration Test (CPT) and the dynamic compaction] and laboratory (triaxial tests, characterization and hydraulic conductivity) investigation. According to laboratory tests, the void ratio decreased to 0.96, hydraulic conductivity decreased to 2.8?×?10^?7 m/s, the effective peak friction angle (?′) increased from 30.5° (in natural conditions) to about 35.5°, and the triaxial stiffness at small strains decreased to E?=?20-MPa due to dynamic compaction. CPT results have shown an improved depth in which CPT tip strength (q_t) increased from nearly 650-kPa to an average of 1700-kPa and CPT sleeve friction (f_s) increased from approximately 50-kPa to about 130-kPa. Horizontal displacements were observed up to about 4.0 m of depth (approximately the same depth at which CPT results showed soil improvement). It was concluded that heavy tamping reduces soil voids and substantially increases soil strength, but also breaks soil structure and decreases soil stiffness. It is thus not a suitable ground improvement solution for highly porous structured residual clayey soil.

     

Changes in physicochemical properties of biodiesel after degradation and remediation

Biodiesel is the main substitute for petrodiesel being constituted by several alkyl esters including unsaturated compounds. It can undergo partial oxidation when stored for long periods and transported over long distances. The aims of this study were to analyze the impact of the oxidation process on the physicochemical properties of biodiesel and its remediation through distillation and esterification. Due to its high susceptibility to oxidation, sunflower biodiesel was used as a model. Specific mass, cloud point, cold filter plugging point, oxidation stability and iodine value were the properties analyzed. The results revealed that the treatments affected each sample differently, and in some cases the product after remediation had properties close to or even better than the initial biodiesel. The results reported here indicate that although biodiesel undergoes degradation during storage and transport, this does not mean the affected fuel cannot be marketed. Some important properties can be recovered with simple treatment.