Composition and stable isotope record of bulk sediment and belemnite rostra from ODP Hole 122-761C

A sedimentary sequence documenting the early history of the proto-Indian Ocean was drilled at Site 761 on the Wombat Plateau, northwest Australia. Directly above the post-rift unconformity, two lithologic units were recovered which reflect deposition in incipient oceanic environments. The lower unit, composed of sandstone, contains abundant belemnites and a few lenses composed of low-diversity coccolith assemblages. The second unit, composed of chalk, contains abundant calcispheres, thoracospheres, low-diversity coccolith assemblages, and a few radiolarians. Belemnites and organisms that produced calcispheres and thoracospheres are thought to be opportunistic. Their abundance, and the absence of a normal marine fauna and flora, reflects an unstable early ocean environment. Stable oxygen and carbon isotopic data for the two units fall into almost separate fields. Heavy delta18O values for the belemnites indicate that they have not been affected by recrystallization. Instead, these isotopic values are thought to indicate either the deep, cool habitat of the belemnites or strong vital effects. A bulk chalk delta18O value from the belemnite sand is 3 to 4 parts per mil lighter than the belemnite delta18O values, possibly because it is largely composed of coccoliths which inhabited warmer surface waters. Light delta13C values for bulk calcisphere-bearing nannofossil chalk samples are thought to be a direct result of upwelling or of vital effects. Heavy delta18O values for the chalk unit are interpreted as resulting from upwelling of cool waters. Assemblage and isotopic data are consistent with this incipient ocean basin being highly productive, either as a result of upwelling or runoff of nutrient-rich waters from nearby land areas. However, it is not possible to rule out the control of vital effects on the isotopic signature of any of the fossil groups.

Chemical composition of zoobenthos and bottom sediments from the gas-hydrate seep area near the Paramushir Island, Kuril Island arc

Bioaccumulation of metals by zoobenthos was investigated during cruise 11A of R/V Akademik Mstislav Keldysh in the vicinity of a gas-hydrate seep off Paramushir Island in the Sea of Okhotsk. Atomic absorption studies of concentrations of Al, Fe, Mn, Ni, Cu and Zn in zoobenthos (polychaetes, bivalves, ophiurans and echinoderms) collected from depths of 700-800 m indicated that their concentrations in individuals near the seep were not significantly different from those in individuals from other communities. Obtained results indicate that sea urchins and holothurians (non-sorting bottom-feeders) can separate mineral fraction of ingested bottom material.

Geochemistry on Holocene sediments from the Mediterranean

The enhanced accumulation of organic matter in Eastern Mediterranean sapropels and their unusually low d15N values have been attributed to either enhanced nutrient availability which led to elevated primary production and carbon sequestration or to enhanced organic matter preservation under anoxic conditions. In order to evaluate these two hypothesis we have determined Ba/Al ratios, amino acid composition, N and organic C concentrations and d15N in sinking particles, surface sediments, eight spatially distributed core records of the youngest sapropel S1 (10-6 ka) and older sapropels (S5, S6) from two locations. These data suggest that (i) temporal and spatial variations in d15N of sedimentary N are driven by different degrees of diagenesis at different sites rather than by changes in N-sources or primary productivity and (ii) present day TOC export production would suffice to create a sapropel like S1 under conditions of deep-water anoxia. This implies that both enhanced TOC accumulation and d15N depletion in sapropels were due to the absence of oxygen in deep waters. Thus preservation plays a major role for the accumulation of organic-rich sediments casting doubt on the need of enhanced primary production for sapropel formation.

Políticas sociales, cooperativas y capital social : Estudio sobre la promoción de cooperativas de trabajo en la ciudad de Río Gallegos

El presente trabajo profunda la relación establecida entre las Cooperativas de Trabajo de la ciudad de Río Gallegos promovidas por el gobierno provincial y el desarrollo de capital social de sus asociados. Se optó por este eje conductor porque se consideró que la organización cooperativa tiende a favorecer el desarrollo de este activo. Frente a las transformaciones del mercado laboral sufridas en la década del ?90, cuyos efectos persisten hasta la actualidad, las cooperativas de trabajo aparecen como una opción para la progresiva inserción en el mercado laboral formal, hecho que se refleja en el incremento sostenido de la cantidad de cooperativas de trabajo a lo largo de todo el país a partir de mediados de los 90?. En este contexto, describir la relación establecida entre estas cooperativas y el desarrollo de capital social de sus miembros, se vincula con la inclusión de esta estrategia, cuyos contenidos no siempre se explicitan, en las líneas de acción de las políticas sociales. En vista del objetivo antes mencionado y a la luz del análisis bibliográfico sobre dicho concepto, se realizaron entrevistas en profundidad orientadas a identificar los precursores de capital social puestos en juego y a examinar la distribución del stock de capital social (individual, grupal y externo) en los cooperativistas

Los cardos y las tareas rurales en la provincia de Buenos Aires durante el siglo XIX

En estos comentarios nos ocupamos de los cardos y su influencia en el desarrollo de las tareas rurales durante el siglo XIX, a partir de los siguientes puntos de discusión: La localización de los cardos en el ámbito de la provincia de Buenos Aires; su forma de reproducción; cual es la relación existente entre la presencia de cardos y la presencia de hombres y animales; el manejo y la organización del trabajo en la estancia primitiva en función de los cardos, la influencia del cardo en la yerra y su papel de condicionante temporal. Contrariamente a lo que la historiografía había supuesto, consideramos que los cardos no determinaron el ritmo de las tareas rurales, sino que esto estuvo más relacionado con la escasez de mano de obra.