Dispersal of natural and anthropogenic lead through submarine canyons at the Portuguese margin

Submarine canyons represent natural conduits for preferential transport of particulate material, including anthropogenic contaminants, from coastal zones directly to the deep sea. To assess related dispersal of natural and anthropogenic lead (Pb), we analyzed Pb concentrations and stable isotope ratios in surface sediments and sediment trap particulate material from the Portuguese margin Nazaré and Setúbal/Lisbon canyons. Geochemical data are integrated with previously obtained data on near-bottom hydrodynamics and processes and pathways of sediment transport. The two canyon systems are located in close geographic proximity to each other, but represent contrasting settings in terms of sediment input and down-canyon sediment transport processes.Concentration–isotope diagrams and three-isotope plots (²⁰⁶Pb/²⁰⁷Pb vs. ²⁰⁸Pb/²⁰⁶Pb) suggest binary mixing between natural and anthropogenic end members. The inferred isotopic signature of pollutant Pb (²⁰⁶Pb/²⁰⁷Pb=1.143 [1.134–1.149, 95% confidence interval]) is most consistent with industrial Pb; ongoing influence from gasoline Pb additives is at most of minor importance. Two proposed natural end members most likely bracket the isotopic signature of natural Pb. Accordingly, binary mixing calculations indicate that on average 20–45% vs. 35–55% of total Pb is derived from anthropogenic sources in the Nazaré and Setúbal–Lisbon canyon systems, respectively. Enhanced anthropogenic influence in the latter area is consistent with its proximity to heavily populated and industrialized areas and with sediment input from the Tagus and Sado rivers, potential major carriers of pollutant particles. In both canyon systems, the anthropogenic component generally decreases with increasing water depth.Isotopic signatures of sediment trap particulate material are generally consistent with surface sediment data at similar water depth, but show large variability in the upper Nazaré canyon and major deviations from surface sediments in the lower canyon. In the lower canyon, Pb isotopic ratios of sediment trap particulate material mostly reflect low pelagic fluxes from the overlying water column, whereas surface sediment signatures are dominated by episodic down-canyon mass transport events. Such gravity flows appear to incorporate older (pre-industrial) material masking the isotopic signature of pollutant Pb. Large variability in the upper canyon reflects continuous sediment resuspension by bottom currents. Stronger average bottom currents are associated with higher ²⁰⁶Pb/²⁰⁷Pb ratios of sediment trap particulate material and hence decreased influence of pollutant Pb. This may reflect preferential resuspension of natural Pb at the canyon floor and/or additional remobilization of older, less-polluted sediment in adjacent areas such as the canyon walls.     

Mortality by cause of death in Colombia: a local analysis using spatial econometrics

Journal of Geographical Systems - Colombia is undergoing major changes in mortality patterns. National- and department-level cause-specific analyses have previously been carried out, but very...     

Building a 3D geomodel for water resources management: case study in the Regional Park of the lower courses of Manzanares and Jarama Rivers (Madrid, Spain)

Water resources management of protected sites requires a powerful tool to analyze the process and changes that are occurring in the environment. This paper describes a 3D geomodel design of the Jarama River Detrital Aquifer located in Madrid (Spain). That hydrogeological unit is included in the “Parque Regional de los Cursos Bajos de los Ríos Manzanares y Jarama” (Regional Park of the Lower Courses of Manzanares and Jarama Rivers). The goal of this work is to define a method by which a three-dimensional (3D) model can be created with hydrogeologic geometry real of main aquifer, to accomplish an adequate management of the groundwater resources. All data used in this study were integrated in a geographic database: geological and hydrogeological information, geological map (1:25,000), eleven cross-sections, piezometric maps and a digital elevation model. The constructed 3D model of the Jarama Aquifer shows geometric features and spatial distribution and variations of geologic units. Thus, the 3D model allows the assessment of volumes of each unit, the depth and thickness variations of the main aquifer, and the spatial and temporal variations of water tables. From the 3D model, the most suitable areas (in terms of groundwater protection) for managed recharge and mining works have been identified.     

Underestimation of Snow Accumulation Rate in Central Antarctica (Vostok Station) Derived from Stake Measurements

Russian Meteorology and Hydrology - It is shown that the snow stake measurements in central Antarctica systematically underestimate the value of the snow build-up. Two methods for the calculation...     

Sutter's Mill dicarboxylic acids as possible tracers of parent‐body alteration processes

Dicarboxylic acids were searched for in three Sutter's Mill (SM) fragments (SM2 collected prerain, SM12, and SM41) and found to occur almost exclusively as linear species of 3‐ to 14‐carbon long. Between these, concentrations were low, with measured quantities typically less than 10 nmole g^?1 of meteorite and a maximum of 6.8 nmole g^?1 of meteorite for suberic acid in SM12. The SM acids' molecular distribution is consistent with a nonbiological origin and differs from those of CMs, such as Murchison or Murray, and of some stones of the C2‐ungrouped Tagish Lake meteorite, where they are abundant and varied. Powder X‐ray diffraction of SM12 and SM41 show them to be dominated by clays/amorphous material, with lesser amounts of Fe‐sulfides, magnetite, and calcite. Thermal gravimetric (TG) analysis shows mass losses up to 1000 °C of 11.4% (SM12) and 9.4% (SM41). These losses are low compared with other clay‐rich carbonaceous chondrites, such as Murchison (14.5%) and Orgueil (21.1%). The TG data are indicative of partially dehydrated clays, in accordance with published work on SM2, for which mineralogical studies suggest asteroidal heating to around 500 °C. In view of these compositional traits and mineralogical features, it is suggested that the dicarboxylic acids observed in the SM fragments we analyzed likely represent a combination of molecular species original to the meteorite as well as secondary products formed during parent‐body alteration processes, such as asteroidal heating.     

H2 in molecular shocks: observations from 2 to 12 microns

We present spectroscopy of the molecular shock in the supernova remnant IC 443. The H₂ level populations in IC 443 are nearly identical to Orion Peak 1 (Brand et al. 1988; Parmar et al. 1994) and are consistent with a partially dissociative J-shock. The similarity with Orion suggests the shock processes which dominate the emission in both regions are essentially identical.