Carbon and Lead chemistry of sediments from the Middle Atlantic Bight

A mass budget was constructed for organic carbon on the upper slope of the Middle Atlantic Bight, a region thought to serve as a depocenter for fine-grained material exported from the adjacent shelf. Various components of the budget are internally consistent, and observed differences can be attributed to natural spatial variability or to the different time scales over which measurements were made. The flux of organic carbon to the sediments in the core of the depocenter zone, at a water depth of 1000 m, was measured with sediment traps to be 65 mg C m**-2 day**-1, of which 6-24 mg C m**-2 day**-1 is buried. Oxygen fluxes into the sediments, measured with incubation chambers attached to a free vehicle lander, correspond to total carbon remineralization rates of 49-70 mg C m**-2 day**-1. Carbon remineralization rates estimated from gradients of Corg within the mixed layer, and from gradients of dissolved ammonia and phosphate in pore waters, sum to only 4-6 mg C m**-2 day**-1. Most of the Corg remineralization in slope sediments is mediated by bacteria and takes place within a few mm of the sediment-water interface. Most of the Corg deposited on the upper slope sediments is supplied by lateral transport from other regions, but even if all of this material were derived from the adjacent shelf, it represents <2% of the mean annual shelf productivity. This value is further lowered by recognizing that as much as half of the Corg deposited on the slope is refractory, having originated by reworking from older deposits. Refractory Corg arrives at the sea bed with an average 14C age 600-900 years older than the pre-bomb 14C age of DIC in seawater, and has a mean life in the sediments with respect to biological remineralization of at least 1000 years. Labile carbon supplied to the slope, on the other hand, is rapidly and (virtually) completely remineralized, with a mean life of < 1 year. Carbon-14 ages of fine-grained carbonate and organic carbon present within the interstices of shelf sands are consistent with this material acting as a source for the old carbon supplied to the slope. Winnowing and export of reworked carbon may contribute to the often-described relationship between organic carbon preservation and accumulation rate of marine sediments.

Incidencia de la radicación urbana de los productores sobre las características de las explotaciones agropecuarias de la provincia de Buenos Aires, 1988

Fil: Balsa, Juan Javier. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

De chacareros a rentistas : Trayectorias de abandono de la actividad agropecuaria en el SO bonaerense (Puán y Adolfo Alsina, 1988-2012)

En este artículo se analizan las experiencias de un grupo de familias de los partidos de Puán y Adolfo Alsina (ubicados en el sudoeste de la provincia de Buenos Aires), que hacia fines de los los años 1980 organizaban su actividad en torno al trabajo de lo miembros de la familia y que, en diferentes puntos de los últimos treinta años, abandonaron la producción y se transformaron en rentistas. A partir de un abordaje cualitativo se indaga en las razones que llevaron a esa situación, teniendo en cuenta aspectos objetivos y subjetivos de los procesos. En esa línea, se analizan los factores involucrados en las trayectorias de retiro de la actividad y los efectos que estos procesos han tenido sobre las identidades y perspectivas de los entrevistados

Consolidación y desvanecimiento del mundo chacarero : Transformaciones de la estructura agraria, las formas sociales de producción y los modos de vida en la agricultura bonaerense, 1937-1988

Fil: Balsa, Juan Javier. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.