Urbanizaciones cerradas polderizadas en la cuenca baja del río Luján : Aproximaciones al dimensionamiento del fenómeno

El trabajo parte de la reflexión sobre los vínculos entre capitalismo global y urbanización, específicamente de las transformaciones producidas en los territorios metropolitanos en las últimas dos décadas. En particular, se observa la difusión de urbanizaciones cerradas de tipo polderizado -UCP-, nuevas formas de producción de ámbitos residenciales en los bordes del aglomerado metropolitano de Buenos Aires, cuyo despliegue supone una demanda extensiva de suelo sobre áreas de gran valor patrimonial y fragilidad ambiental, como los humedales de la cuenca baja del Río Luján. Desde esta perspectiva, el trabajo aporta elementos que permiten realizar una caracterización y dimensionamiento del fenómeno, sobre la base de un relevamiento exhaustivo de variables consideradas esenciales por el estudio a partir del cruce de bases de datos de organismos públicos, información periodística y sitios web de desarrolladores inmobiliarios del sector.

Physical and chemical oceanography in the Arctic Ocean

Data from sections across the Eurasian Basin of the Arctic Ocean occupied by the German Research Vessel Polarstern in 1987 and by the Swedish icebreaker Oden in 1991 are used to derive information on the freshwater balance of the Arctic Ocean halocline and on the sources of the deep waters of the Nansen, Amundsen and Makarov basins. Salinity, d18O and mass balances allow separation of the river-runoff and the sea-ice meltwater fractions contained in the Arctic halocline. This provides the basis for tracking the river-runoff signal from the shelf seas across the central Arctic Ocean to Fram Strait. The halocline has to be divided into at least three lateral regimes: the southern Nansen Basin with net sea-ice melting, the northern Nansen Basin and Amundsen Basin with net sea-ice formation and increasing river-runoff fractions, and the Canadian Basin with minimum sea-ice meltwater and maximum river-runoff fractions and water of Pacific origin. In the Canadian Basin, silicate is used as a tracer to identify Pacific water entering through Bering Strait and an attempt is made to quantify its influence on the halocline waters of the Canadian Basin. For this purpose literature data from the CESAR and LOREX ice camps are used. Based on mass balances and depending on the value of precipitation over the area of the Arctic Ocean the average mean residence time of the river-runoff fraction contained in the Arctic Ocean halocline is determined to be about 14 or 11 years. Water column inventories of river-runoff and sea-ice meltwater are calculated for a section just north of Fram Strait and implications for the ice export rate through Fram Strait are discussed. Salinity, tritium, 3He and the d18O ratio of halocline waters sampled during the 1987 Polarstern cruise to the Nansen Basin are used to estimate the mean residence time of the river-runoff component in the halocline and on the shelves of the Arctic Ocean. These estimates are done by comparing ages of the halocline waters based on a combination of tracers yielding different time information: the tritium 'vintage' age which records the time that has passed since the river-runoff entered the shelf and the tritium/3He age which reflects the time since the shelf waters left the shelf. The difference between the ages determined by these two methods is about 3 to 6 years. Correction for the initial tritium/3He age of the shelf waters (about 0.5 to 1.5 years) yields a mean residence time of the river-runoff on the shelves of about 3.5 ± 2 years. Comparison of the 18O/16O ratios of shelf water, Atlantic water and the deep waters of the Arctic Ocean indicate that the sources of the deep and bottom waters of the Eurasian Basin are located in the Barents and Kara seas.

Los extranjeros de Buenos Aires en los albores del siglo XIX : Algunos rasgos de su composición

Para el período colonial tardío, Buenos Aires era una ciudad diferente del resto de Hispanoamérica, tanto en términos de su cultura como en sus manifestaciones sociales y en su crecimiento poco común. Bastaron poco más de tres décadas para que la pequeña aldea se transformara en una pujante ciudad hispanoamericana. La clave de esta transformación estuvo dada a lo largo de todo el siglo XVIII, dado que éste fue un período de profundos cambios político-sociales y Buenos Aires no fue la excepción. La ciudad comenzó a cambiar en todos sus aspectos. En primer lugar el conflicto de la España Borbónica con Inglaterra y Portugal llevó a introducir cambios profundos en la política española para el control estricto de las colonias en los bordes del imperio. La creación del Virreinato del Río de la Plata en 1776 y la extensión de la ordenanza de libre comercio dos años más tarde otorgaron un gran empuje a la ciudad. De este modo, Buenos Aires pasó a ser un activo polo de atracción tanto para los migrantes internos como para los externos del imperio español. Estos motivos provocaron mutaciones a nivel político, social y arquitectónico, dando lugar a un crecimiento único para una ciudad hispanoamericana entre 1750 y 1810

Evaluación espacial de procesos geodinámicos en el ambiente montañoso de la cuenca del río Cachapoal, Chile central. Impacto geodinámico sobre el potencial corredor de comercio Las Leñas, VI Región del Libertador Gral. Bernardo O'Higgins

En el contexto de la posible habilitación de una ruta entre Chile y Argentina a través del paso fronterizo Las Leñas en Chile central, alternativo al Cristo Redentor, se procedió a analizar las vulnerabilidades y los impactos provocados por la geodinámica en áreas montañosas. Se evaluaron procesos erosivos en los ambientes de baja, media y alta montaña en el valle del río Cachapoal. La alta energía de estos paisajes es causante de la generación y el aporte de sedimentos mediante erosión, la que es activada por las precipitaciones intensas y la acción periglacial. Las diferencias erosivas se entienden por la presencia de distintas formas del paisaje; así, los depósitos basales en alta montaña están asociados a movimientos del terreno en masa, y la erosión lineal se desarrolla sobre las terrazas fluviales ubicadas en fondo de valle, las que se encuentran estabilizadas por la mayor cobertura vegetal.

Urbanizaciones cerradas polderizadas en la cuenca baja del río Luján : Aproximaciones al dimensionamiento del fenómeno

El trabajo parte de la reflexión sobre los vínculos entre capitalismo global y urbanización, específicamente de las transformaciones producidas en los territorios metropolitanos en las últimas dos décadas. En particular, se observa la difusión de urbanizaciones cerradas de tipo polderizado -UCP-, nuevas formas de producción de ámbitos residenciales en los bordes del aglomerado metropolitano de Buenos Aires, cuyo despliegue supone una demanda extensiva de suelo sobre áreas de gran valor patrimonial y fragilidad ambiental, como los humedales de la cuenca baja del Río Luján. Desde esta perspectiva, el trabajo aporta elementos que permiten realizar una caracterización y dimensionamiento del fenómeno, sobre la base de un relevamiento exhaustivo de variables consideradas esenciales por el estudio a partir del cruce de bases de datos de organismos públicos, información periodística y sitios web de desarrolladores inmobiliarios del sector.

Las misiones jesuitas en la región del Guayrá en las primeras décadas del siglo XVII

Las misiones jesuitas en el espacio de la cuenca del Plata son bastante conocidas en la historiográfica nacional. Desde la relación geográfica de Azara hasta los últimos aportes de Di Stefano y Zanatta en su "Historia de la Iglesia Argentina ", la historia de los "30 pueblos" en la provincia argentina de Misiones ha dado mucho que hablar -y escribir- a lo largo de la historia nacional. Esto es perceptible tanto en las imágenes idílicas de comunión entre jesuitas y guaraníes hasta los trabajos que develan los complejos sistemas de alianzas que posibilitaban la aparente sumisión guaraní al dominio español. Pero todas estas imágenes deben considerarse como el estado final de un proceso que -con sus marchas y contramarchas- se inicia a principios del siglo XVII, cuando los jesuitas comienzan su tarea evangelizadora con los indígenas. Será nuestra intención trabajar las dos primeras décadas de la fundación y funcionamiento de las misiones jesuitas en el Guayrá (1609-1629), momento en el cual van tomando forma las estrategias y estructuras de dominación, cuando la metodología de la prueba y error es moneda corriente, y los enfrentamientos entre indígenas, jesuitas, españoles y portugueses tienen lugar en el marco de una frontera tan inestable como era en ese momento la región guayrense.

Análisis de usos normativos y su vinculación con áreas en riesgo de inundación. El caso de 23 partidos del litoral bonaerense

El presente trabajo se basa en un análisis de la normativa dispuesta en materia de ordenamiento territorial y usos de suelo de los 23 partidos de la cuenca Parano- Platense que conforman el área de estudio del proyecto en el cual se encuadra el mismo1, considerando el tratamiento específico de áreas afectadas y prevención de las inundaciones. Para ello se ha tenido en cuenta: a) el análisis de la evolución de la regulación del Estado en la ocupación del suelo para el Gran Buenos Aires; b) el registro actualizado de ordenanzas en materia de ordenamiento territorial y Usos del Suelo convalidadas por Poder Ejecutivo (PE) (Nº de ordenanza y el Nº de Decreto del Poder Ejecutivo de convalidación; c) la norma específica (Nº de ordenanza / Nº de decreto del PE) por municipio / por contenido. Los datos para llevar a cabo el estudio de usos de suelo normativos se obtuvieron del nuevo Mapa Interactivo de Ordenamiento Territorial de la Provincia de Buenos Aires, que fue generado por el Ministerio de Gobierno de la Provincia de Buenos Aires, Subsecretaría de Asuntos Municipales. El análisis de la normativa vigente de cada uno de los 23 partidos que abarcan el ámbito de estudio nos permitirá definir estrategias futuras de intervención, las cuales actuarán como instrumento en materia de ordenamiento territorial desde la gestión de cada municipio.

Actores, argumentación y agenda en la gestión del territorio de la cuenca baja del río Luján

En el marco conceptual del análisis de políticas públicas, se identifican los actores del subsistema de gestión del suelo, sus lógicas, sus intereses y sus relaciones conflictivas en el proceso de transformación urbana y conformación del patrón de uso actual de la baja cuenca del río Lujan de los últimos diez años. Los discursos y argumentos de estos grupos de interés inciden en la formación de la agenda, entendida como proceso de agregación de intereses que refleja tanto el orden de prioridad de los problemas sociales como la visión que el gobierno tiene de la situación. El presente trabajo1 rastrea en las manifestaciones escritas y orales asociadas a los distintos actores del área de estudio, como factor que contribuye a explicar por qué ciertos temas se adoptan como problemas públicos y se incorporan a la agenda gubernamental.

Geothermal measurements in the Tyrrhenian Sea

Geothermal data obtained during Cruise 12 of the R/V Vityaz-II and published data on heat flux of the Tyrrhenian Sea are analyzed. The thermal field is related to principal tectonic structures of the basin. Distribution of heat flux indicates that the initial stage of rifting occurs in the central basin of the Tyrrhenian Sea.

Carbonate properties and oxygen concentrations at time series station DYFAMED

Monthly measurements of pH, alkalinity and oxygen over two years (February 1998-February 2000) at the Dyfamed site in the central zone of the Ligurian-Provençal Basin of the Mediterranean made it possible to assess the vertical distributions (5-2000 m) and the seasonal variations of these properties. Alkalinity varies linearly with salinity between surface water and the Levantine Intermediate Water (marked by a maximum of temperature and salinity). In deep water, total alkalinity is also correlated linearly to salinity, but the slope of the regression line is 15% less. In surface water, the pH at 25°C varies between 7.91 and 8.06 on the total proton scale depending upon the season. The lowest values are observed in winter, the highest in spring and in summer. These variations are primarily due to biological production. The pH goes through a minimum around 150-200 m and a small maximum below the intermediate water. The total dissolved inorganic carbon content (deduced from pH and alkalinity) is variable in surface water (2205-2310 ?mol/kg) and has a maximum in intermediate water, which is related to the salinity maximum. Normalized total inorganic carbon at a constant salinity is strongly negatively correlated with pH at 25°C. The fugacity of CO2, (fCO2) varies between 320 and 430 ?atm in surface water, according to the season. Below the seasonal thermocline, the maximum fCO2 (about 410 ?atm) is located around 150-200 m. The presence of a minimum of oxygen in the intermediate water of this area has been observed for several years, but our measurements made it possible to specify the relationship between oxygen and salinity in deep water. Data from the intense vertical mixing during the winters of 1999 and 2000 were used to calculate the oxygen quantity exchanged with the atmosphere during these periods. The estimated quantity of oxygen entering the Mediterranean Sea exceeds that deduced from exchange coefficients calculated with the formula of Wanninkhof and McGillis. During the vertical mixing in the 1999 winter, fCO2 in surface water was on average below equilibrium with atmospheric fCO2, thus implying that CO2 was entering the sea. However, on this time scale, even with high exchange coefficients, the estimated CO2 uptake had no significant influence on the inorganic carbon content in the water column.

Os and Re concentrations and Os isotope ratios for DSDP and ODP metalliferous sediments from the Pacific Ocean (Table 1)

We report new 187Os/186Os data and Re and Os concentrations in metalliferous sediments from the Pacific to construct a composite Os isotope seawater evolution curve over the past 80 m.y. Analyses of four samples of upper Cretaceous age yield 187Os/186Os values of between 3 and 6.5 and 187Re/186Os values below 55. Mass balance calculations indicate that the pronounced minimum of about 2 in the Os isotope ratio of seawater at the K-T boundary probably reflects the enormous input of cosmogenic material into the oceans by the K-T impactor(s). Following a rapid recovery to 187Os/186Os of 3.5 at 63 Ma, data for the early and middle part of the Cenozoic show an increase in 187Os/186Os to about 6 at 15 Ma. Variations in the isotopic composition of leachable Os from slowly accumulating metalliferous sediments show large fluctuations over short time spans. In contrast, analyses of rapidly accumulating metalliferous carbonates do not exhibit the large oscillations observed in the pelagic clay leach data. These results together with sediment leaching experiments indicate that dissolution of non-hydrogenous Os can occur during the hydrogen peroxide leach and demonstrate that Os data from pelagic clay leachates do not always reflect the Os isotopic composition of seawater. New data for the late Cenozoic further substantiate the rapid increase in the 187Os/186Os of seawater during the past 15 Ma. We interpret the correlation between the marine Sr and Os isotope records during this time period as evidence that weathering within the drainage basin of the Ganges-Brahmaputra river system is responsible for driving seawater Sr and Os toward more radiogenic isotopic compositions. The positive correlation between 87Sr/86Sr and U concentration, the covariation of U and Re concentrations, and the high dissolved Re, U and Sr concentrations found in the Ganges-Brahmaputra river waters supports this interpretation. Accelerating uplift of many orogens worldwide over the past 15 Ma, especially during the last 5 Ma, could have contributed to the rapid increase in 187Os/186Os from 6 to 8.5 over the past 15 Ma. Prior to 15 Ma the marine Sr and Os record are not tightly coupled. The heterogeneous distribution of different lithologies within eroding terrains may play an important role in decoupling the supplies of radiogenic Os and Sr to the oceans and account for the periods of decoupling of the marine Sr and Os isotope records.

(Tabls S1) Bulk geochemistry for sediment samples collected from the Cenomanian-Turonian boundary section at Pont d'Issole

Oceanic Anoxic Event 2 (OAE2), spanning the Cenomanian-Turonian boundary (CTB), represents one of the largest perturbations in the global carbon cycle in the last 100 Myr. The d13Ccarb, d13Corg, and d18O chemostratigraphy of a black shale-bearing CTB succession in the Vocontian Basin of France is described and correlated at high resolution to the European CTB reference section at Eastbourne, England, and to successions in Germany, the equatorial and midlatitude proto-North Atlantic, and the U.S. Western Interior Seaway (WIS). Delta13C (offset between d13Ccarb and d13Corg) is shown to be a good pCO2 proxy that is consistent with pCO2 records obtained using biomarker d13C data from Atlantic black shales and leaf stomata data from WIS sections. Boreal chalk d18O records show sea surface temperature (SST) changes that closely follow the Delta13C pCO2 proxy and confirm TEX86 results from deep ocean sites. Rising pCO2 and SST during the Late Cenomanian is attributed to volcanic degassing; pCO2 and SST maxima occurred at the onset of black shale deposition, followed by falling pCO2 and cooling due to carbon sequestration by marine organic productivity and preservation, and increased silicate weathering. A marked pCO2 minimum (~25% fall) occurred with a SST minimum (Plenus Cold Event) showing >4°C of cooling in ~40 kyr. Renewed increases in pCO2, SST, and d13C during latest Cenomanian black shale deposition suggest that a continuing volcanogenic CO2 flux overrode further drawdown effects. Maximum pCO2 and SST followed the end of OAE2, associated with a falling nutrient supply during the Early Turonian eustatic highstand.

Heavy metal and petroleum product concentrations in waters at the Obskaya 1 drill site

During recent years, the basins of the Kara Sea (Kamennomysskaya, Obskaya, and Chugor'yakhinskaya structures) in the Russian Federation have been considered as promising regions for oil and gas exploration and, simultaneously, as possible paths of relatively cheap pipeline and tanker transportation of hydrocarbons projected for recovery. On the other hand, exploration operations, recovery, and transportation of gas pose a considerable risk of accidents and environmental pollution, which causes a justified concern about the future state of the ecological system of the Gulf of Ob and the adjoining parts of the Kara Sea. Therefore, regular combined environmental investigations (monitoring) are the most important factor for estimating the current state and forecasting the dynamics of the development of estuary systems. The program of investigations (schedule, station network, and measured parameters) is standardized in accordance with the international practice of such work and accounts for the experience of monitoring studies of Russian and foreign researchers. Two measurement sessions were performed during ecological investigations in the region of exploration drilling: at the beginning at final stage of drilling operations and borehole testing; in addition, natural parameters were determined in various parts of the Ob estuary before the beginning of investigations. Hydrophysical and hydrochemical characteristics of the water medium were determined and bottom sediments and water were analyzed for various pollutants (petroleum products, heavy metals, and radionuclides). The forms of heavy-metal occurrence in river and sea waters were determined by the method of continuous multistep filtration, which is based on water component fractionation on membrane filters of various pore sizes. These investigations revealed environmental pollution by chemical substances during the initial stage of drilling operations, when remains of fuels, oils, and solutions could be spilled, and part of the chemical pollutants could enter the environment. Owing to horizontal and vertical turbulent diffusion, wave mixing, and the effect of the general direction of currents in the Ob estuary from south to north, areas are formed with elevated concentrations of the analyzed elements and compounds. However, the concentration levels of chemical pollutants are practically no higher than the maximum admissible concentrations, and their substantial dissipation to the average regional background contents can be expected in the near future. Our investigations allowed us to determine in detail the parameters of anthropogenic pollution in the regions affected by hydrocarbon exploration drilling in the Obskii and Kamennomysskii prospects in the Gulf of Ob and estimate their influence on the ecological state of the basin of the Ob River and the Kara Sea on the whole.

Strontium isotope ratios and concentrations in fossil fish teeth

We analyzed 87Sr/86Sr ratios in foraminifera, pore fluids, and fish teeth for samples ranging in age from Eocene to Pleistocene from four Ocean Drilling Program sites distributed around the globe: Site 1090 in the Cape Basin of the Southern Ocean, Site 757 on the Ninetyeast Ridge in the Indian Ocean, Site 807 on the Ontong-Java Plateau in the western equatorial Pacific, and Site 689 on the Maud Rise in the Southern Ocean. Sr isotopic ratios for dated foraminifera consistently plot on the global seawater Sr isotope curve. For Sites 1090, 757, and 807 Sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values, as are values for fossil fish teeth. In contrast, pore fluid 87Sr/86Sr values at Site 689 are more radiogenic than contemporaneous seawater, and the corresponding fish teeth also record more radiogenic values. Thus, Sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values; furthermore, there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve, and the associated offset between the fish teeth and the seawater curve. These data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange Sr with its surroundings during burial and diagenesis. Therefore, Sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores, but cannot be used to fine-tune age models. In contrast to the Sr isotopic system, our Nd concentration data, combined with published isotopic and rare earth element data, suggest that fish teeth acquire Nd during early diagenesis while they are still in direct contact with seawater. The concentrations of Nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids. As a result, Nd isotopes are not altered during burial and later diagenesis. Therefore, fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater Nd isotopic compositions from the time of deposition.

Major components and major and trace elements from ODP Site 175-1085

We have analyzed 33 Pliocene bulk sediment samples from Ocean Drilling Program Site 1085 in the Cape Basin, located offshore of western Africa in the Angola-Benguela Current system, for 17 major and trace elements, and interpreted their associations and temporal variations in the context of an allied data set of CaCO3, opal, and Corg. We base our interpretations on elemental ratios, accumulation rates, inter-element correlations, and several multi-element statistical techniques. On the basis of qualitative assessment of downhole changes in the distributions of P and Ba, utilized as proxies of export production, we conclude that highs in bulk and biogenic accumulation that occur at 3.2 Ma, 3.0 Ma, 2.4 Ma, and 2.25 Ma were caused by increases in export production as well as terrigenous flux, and record a greater sequestering of organic matter during these time periods. Studies of refractory elements and other indicator proxies (SiO2, Al2O3, TiO2, Fe2O3, MgO, V, Cr, Sr, and Zr) strongly suggest that the terrigenous component of the bulk sediment is composed of two compositional end-members, one being 'basaltic' in composition and the other similar to an 'average shale'. The basaltic end-member comprises approximately 10-15% of the total bulk sediment and its presence is consistent with the local geology of source material in the drainage basin of the nearby Orange River. The increase in bulk accumulation at 2.4 Ma appears to reflect a greater relative increase in basaltic input than the relative increase in shale-type input. Although studies such as this cannot precisely identify the transport mechanisms of the different terrigenous components, these results are most consistent with variations in sea level (and associated changes in shelf geometry and fluvial input) being responsible for the changing depositional conditions along the Angolan Margin during this time period.