Mineralogical and grain size analysis of ODP Hole 119-745B from the Southern Ocean

The upper Miocene to Pleistocene sediments recovered at ODP Sites 745 and 746 in the Australian-Antarctic Basin are characterized by cyclic facies changes. Sedimentological investigations of a detailed Quaternary section reveal that facies A is dominated by a high content of siliceous microfossils, a relatively low terrigenous sediment content, an ice-rafted component, low concentrations of fine sediment particles, and a relatively high smectite content. This facies corresponds to interglacial sedimentary conditions. Facies B, in contrast, is characteristic of glacial conditions and is dominated by a large amount of terrigenous material and a smaller opaline component. There is also a prominent ice-rafted component. The microfossils commonly are reworked and broken. The clay mineral assemblages show higher proportions of glacially derived illite and chlorite. A combination of four different processes, attributed to glacial-interglacial cycles, was responsible for the cyclic facies changes during Quaternary time: transport by gravity, ice, and current and changes in primary productivity. Of great importance was the movement of the grounding line of the ice shelves, which directly influenced the intensity of ice rafting and of gravitational sediment transport to the deep sea. The extension of the ice shelves was also responsible for the generation of cold and erosive Antarctic Bottom Water, which controlled the grain-size distribution, particularly of the fine fraction, in the investigated area.

Territorialidades, espacios vividos y sentidos de lugar en tiempos de avance de la frontera productiva

En pleno proceso de corrimiento de la frontera productiva y emergente disputa por el uso y apropiación de los recursos, la intervención de distintos sujetos sociales en el oeste de La Pampa está redefiniendo las prácticas productivas-reproductivas de los crianceros campesinos y, en consecuencia, la construcción social del espacio. Desde la finalización de las campañas militares contra las sociedades indígenas diferentes agentes, mediante el ejercicio de poder, construyeron determinadas representaciones territoriales y pusieron en acción prácticas tendientes a articular el oeste pampeano con la economía nacional. Sin embargo la escasa valorización de este espacio posibilitó el desarrollo de cierta autonomía en las formas de organización socio-productivas y simbólicas. Ante la expansión de la frontera ganadera, el impuso hidrocarburífero en la región y creciente presencia de nuevas lógicas territoriales crecen las confrontaciones por el desigual acceso a los recursos naturales, por la apropiación del espacio y la construcción de territorialidades. En este marco, el artículo focaliza la mirada en la organización interna de los asentamientos rurales y en los usos sociales de los espacios a través del tiempo, en dos áreas del "extremo" oeste: La Humada y Chos Malal. De este modo se pretende establecer cómo se organizaron diacrónicamente los espacios doméstico, peridoméstico y monte y qué sentidos expresan los sujetos en torno a los espacios de vida y lugares en tiempos de expansión de la frontera productiva. El nuevo campo social generado producto del avance del capitalismo sobre las unidades campesinas se expresa, no sólo en las modificaciones en las formas de manejo del ganado, organización de la producción y construcción social del espacio, sino también en las formas de sociabilidad y estrategias de resistencia colectivas. Este proceso, que se está gestando en la región, tiene un desarrollo similar en otros espacios donde el avance productivo se ha generado con anterioridad o a un ritmo más acelerado. Para la realización de la investigación se articulan diferentes estrategias de metodología cualitativa que combinan el estudio de caso con historias de vida, entrevistas en profundidad y análisis de fuentes documentales.

A reconstruction of atmospheric carbon dioxide and its stable carbon isotopic composition from the penultimate glacial maximum to the glacial inception

The reconstruction of the stable carbon isotope evolution in atmospheric CO2 (d13Catm ), as archived in Antarctic ice cores, bears the potential to disentangle the contributions of the different carbon cycle fluxes causing past CO2 variations. Here we present a new record of d13Catm before, during and after the Marine Isotope Stage 5.5 (155 000 to 105 000 years BP). The record was derived with a well established sublimation method using ice from the EPICA Dome C (EDC) and the Talos Dome ice cores in East Antarctica. We find a 0.4 permil shift to heavier values between the mean d13Catm level in the Penultimate (~ 140 000 years BP) and Last Glacial Maximum (~ 22 000 years BP), which can be explained by either (i) changes in the isotopic composition or (ii) intensity of the carbon input fluxes to the combined ocean/atmosphere carbon reservoir or (iii) by long-term peat buildup. Our isotopic data suggest that the carbon cycle evolution along Termination II and the subsequent interglacial was controlled by essentially the same processes as during the last 24 000 years, but with different phasing and magnitudes. Furthermore, a 5000 years lag in the CO2 decline relative to EDC temperatures is confirmed during the glacial inception at the end of MIS 5.5 (120 000 years BP). Based on our isotopic data this lag can be explained by terrestrial carbon release and carbonate compensation.

Territorialidades, espacios vividos y sentidos de lugar en tiempos de avance de la frontera productiva

En pleno proceso de corrimiento de la frontera productiva y emergente disputa por el uso y apropiación de los recursos, la intervención de distintos sujetos sociales en el oeste de La Pampa está redefiniendo las prácticas productivas-reproductivas de los crianceros campesinos y, en consecuencia, la construcción social del espacio. Desde la finalización de las campañas militares contra las sociedades indígenas diferentes agentes, mediante el ejercicio de poder, construyeron determinadas representaciones territoriales y pusieron en acción prácticas tendientes a articular el oeste pampeano con la economía nacional. Sin embargo la escasa valorización de este espacio posibilitó el desarrollo de cierta autonomía en las formas de organización socio-productivas y simbólicas. Ante la expansión de la frontera ganadera, el impuso hidrocarburífero en la región y creciente presencia de nuevas lógicas territoriales crecen las confrontaciones por el desigual acceso a los recursos naturales, por la apropiación del espacio y la construcción de territorialidades. En este marco, el artículo focaliza la mirada en la organización interna de los asentamientos rurales y en los usos sociales de los espacios a través del tiempo, en dos áreas del "extremo" oeste: La Humada y Chos Malal. De este modo se pretende establecer cómo se organizaron diacrónicamente los espacios doméstico, peridoméstico y monte y qué sentidos expresan los sujetos en torno a los espacios de vida y lugares en tiempos de expansión de la frontera productiva. El nuevo campo social generado producto del avance del capitalismo sobre las unidades campesinas se expresa, no sólo en las modificaciones en las formas de manejo del ganado, organización de la producción y construcción social del espacio, sino también en las formas de sociabilidad y estrategias de resistencia colectivas. Este proceso, que se está gestando en la región, tiene un desarrollo similar en otros espacios donde el avance productivo se ha generado con anterioridad o a un ritmo más acelerado. Para la realización de la investigación se articulan diferentes estrategias de metodología cualitativa que combinan el estudio de caso con historias de vida, entrevistas en profundidad y análisis de fuentes documentales.

(Table 1) Results of geothermal measurements in the Black Sea 2000 and 2001 expeditions

According to the World Ocean Program in the northeastern part of the continental slope of the Black Sea geothermal, seismologic and seismic studies were carried out. An analysis of heat flow distribution allowed to distinguish a negative geothermal anomaly near the Dzhubga area, where the Russia-Turkey pipeline was being constructed. During seismological observations (August-September 1999, September 2001) more than 1200 seismic events were recorded. They proved high tectonic activity of the region under study, which stimulates gravitational sediment transport on the continental slope. The seismo-acoustic survey carried out in the area of the geothermal anomaly revealed no reflecting horizons within the sedimentary cover. This may be related to turbidite-landsliding processes. Results of modeling of the heat flow anomaly showed that it had originated approximately 1000 years ago due to a powerful landslide. This also suggests a possibility of an avalanche displacement of sedimentary masses in the area of the pipeline at present.

Territorialidades, espacios vividos y sentidos de lugar en tiempos de avance de la frontera productiva

En pleno proceso de corrimiento de la frontera productiva y emergente disputa por el uso y apropiación de los recursos, la intervención de distintos sujetos sociales en el oeste de La Pampa está redefiniendo las prácticas productivas-reproductivas de los crianceros campesinos y, en consecuencia, la construcción social del espacio. Desde la finalización de las campañas militares contra las sociedades indígenas diferentes agentes, mediante el ejercicio de poder, construyeron determinadas representaciones territoriales y pusieron en acción prácticas tendientes a articular el oeste pampeano con la economía nacional. Sin embargo la escasa valorización de este espacio posibilitó el desarrollo de cierta autonomía en las formas de organización socio-productivas y simbólicas. Ante la expansión de la frontera ganadera, el impuso hidrocarburífero en la región y creciente presencia de nuevas lógicas territoriales crecen las confrontaciones por el desigual acceso a los recursos naturales, por la apropiación del espacio y la construcción de territorialidades. En este marco, el artículo focaliza la mirada en la organización interna de los asentamientos rurales y en los usos sociales de los espacios a través del tiempo, en dos áreas del "extremo" oeste: La Humada y Chos Malal. De este modo se pretende establecer cómo se organizaron diacrónicamente los espacios doméstico, peridoméstico y monte y qué sentidos expresan los sujetos en torno a los espacios de vida y lugares en tiempos de expansión de la frontera productiva. El nuevo campo social generado producto del avance del capitalismo sobre las unidades campesinas se expresa, no sólo en las modificaciones en las formas de manejo del ganado, organización de la producción y construcción social del espacio, sino también en las formas de sociabilidad y estrategias de resistencia colectivas. Este proceso, que se está gestando en la región, tiene un desarrollo similar en otros espacios donde el avance productivo se ha generado con anterioridad o a un ritmo más acelerado. Para la realización de la investigación se articulan diferentes estrategias de metodología cualitativa que combinan el estudio de caso con historias de vida, entrevistas en profundidad y análisis de fuentes documentales.

Measurements of stable carbon isotope ratios of CO2 over the last 24000 years and CO2 concentration measurements on Antarctic ice cores using three different methods

The stable carbon isotope ratio of atmospheric CO2 (d13Catm) is a key parameter in deciphering past carbon cycle changes. Here we present d13Catm data for the past 24,000 years derived from three independent records from two Antarctic ice cores. We conclude that a pronounced 0.3 per mil decrease in d13Catm during the early deglaciation can be best explained by upwelling of old, carbon-enriched waters in the Southern Ocean. Later in the deglaciation, regrowth of the terrestrial biosphere, changes in sea surface temperature, and ocean circulation governed the d13Catm evolution. During the Last Glacial Maximum, d13Catm and atmospheric CO2 concentration were essentially constant, which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then.

Geochemistry of oceanic flood basalts from the Caribbean plate

The thick oceanic crust of the Caribbean plate appears to be the tectonized remnant of an eastern Pacific oceanic plateau that has been inserted between North and South America. The emplacement of the plateau into its present position has resulted in the obduction and exposure of its margins, providing an opportunity to study the age relations, internal structure and compositional features of the plateau. We present the results of 40Ar-39Ar radiometric dating, major-, trace-element, and isotopic compositions of basalts from some of the exposed sections as well as drill core basalt samples from Leg 15 of the Deep Sea Drilling Project. Five widely spaced, margin sections yielded ages ranging from 91 to 88 Ma. Less well-constrained radiometric ages from the drill cores, combined with the biostratigraphic age of surrounding sediments indicate a minimum crystallization age of ~90 Ma in the Venezuelan Basin. The synchroneity of ages across the region is consistent with a flood basalt origin for the bulk of the Caribbean plateau i.e., large volume, rapidly erupted, regionally extensive volcanism.. The ages and compositions are also consistent with plate reconstructions that place the Caribbean plateau in the vicinity of the Galápagos hotspot at its inception. The trace-element and isotopic compositions of the ~90 Ma rocks indicate a depleted mantle and an enriched, plume-like mantle were involved in melting to varying degrees across the plateau. Within the same region, a volumetrically secondary, but widespread magmatic event occurred at 76 Ma, as is evident in Curacao, western Colombia, Haiti, and at DSDP Site 152/ODP Site 1001 near the Hess Escarpment. Limited trace-element data indicate that this phase of magmatism was generally more depleted than the first. We speculate that magmatism may have resulted from upwelling of mantle, still hot from the 90 Ma event, during lithospheric extension attending gravitational collapse of the plateau, andror tectonic emplacement of the plateau between North and South America. Still younger volcanics are found in the Dominican Republic (69 Ma) and the Quepos Peninsula of Costa Rica (63 Ma). The latter occurrence conceivably formed over the Galápagos hotspot and subsequently accreted to the western edge of the plateau during subduction of the Farallon plate.

Layer-by-layer correlation of ODP Leg 117 sites

One hundred thirty-one marker horizons relating to the distinct and traceable layers were described for the Owen Ridge and Oman Margin sites. The correlations incorporated the calculations of true depth, corrected for coring disturbance and gas expansion. Intersite correlation of marker horizons has been improved based on color density data, measured with video densitometer, and oxygen isotope stratigraphic data. Distinct hiatuses were detected by the intersite correlation of the marker horizons in the Owen Ridge. The hiatuses are related to submarine slides induced by increasing gravitational instability for the accumulation of the pelagic sediments on the top of the Owen Ridge. The large amount of sediment supply with variable lithofacies during the glacial stages is represented by layer-bylayer correlation in the Oman Margin. The color density patterns with glacial-interglacial cycles are controlled by the balance of organic carbon content, increasing in the interglacial stages with strong upwelling induced by the southwest monsoon, and flux of terrigenous matter, increasing in the glacial stages. The present distinct climatic cycle relating to the southwest monsoon has been developed since Stage 8, 250 ka. The large amount of sediment supply in the glacial stages can be assumed as fluvial in origin from the humid Arabian Peninsula, relating to the weakened Tropical Easterly Jet, which is induced by the counter-current of the southwest monsoon and maintains the present arid climate in the north Africa and Arabian Peninsula.

Physical properties, grain size distribution and clay mineralogy of ODP Leg 117 sites

The fabric of sediments recovered at sites drilled on the Indus Fan, Owen Ridge, and Oman margin during Ocean Drilling Program Leg 117 was examined by scanning electron microscopy to document changes that accompany sediment burial. Two sediment types were studied: (1) biogenic sediments consisting of a variety of marly nannofossil and nannofossil oozes and chalks and (2) terrigenous sediments consisting of fine-grained turbidites deposited in association with the Indus Fan. Biogenic sediments were examined with samples from the seafloor to depths of 306 m below seafloor (mbsf) on the Owen Ridge (Site 722) and 368 mbsf on the Oman margin (Sites 723 and 728). Over these depth ranges the biogenic sediments are characterized by a random arrangement of microfossils and display little chemical diagenetic alteration. The microfossils are dispersed within a fine-grained matrix that is predominantly microcrystalline carbonate particles on the Owen Ridge and clay and organic matter on the Oman margin. Sediments with abundant siliceous microfossils display distinct, open fabrics with high porosity. Porosity reduction resulting from gravitational compaction appears to be the primary process affecting fabric change in the biogenic sediment sections. Fabric of illite-rich clayey silts and silty claystones from the Indus Fan (Site 720) and Owen Ridge (Sites 722 and 731) was examined for a composite section extending from 45 to 985 mbsf. In this section fabric of the fine-grained turbidites changes from one with small flocculated clay domains, random particle arrangement, and high porosity to a fabric with larger domains, strong preferred particle orientation roughly parallel to bedding, and lower porosity. These changes are accomplished by a growth in domain size, primarily through increasing face-to-face contacts, and by particle reorientation which is characterized by a sharp increase in alignment with bedding between 200 and 400 mbsf. Despite extensive particle reorientation, flocculated clay fabric persists in the deepest samples examined, particularly adjacent to silt grains, and the sediments lack fissility. Fabric changes over the 45-985 mbsf interval occur in response to gravitational compaction. Porosity reduction and development of preferred particle orientation in the Indus Fan and Owen Ridge sections occur at greater depths than outlined in previous fabric models for terrigenous sediments as a consequence of a greater abundance of silt and a greater abundance of illite and chlorite clays.

Composition of bottom sediments and rocks from the Philippine Trough

New data on bottom sediments and igneous rocks of the Philippine Trench are under consideration. They show differences in geological structures of the island slope and the ocean slope of the trench. The island slope is comparable to the accretionary prism formations on the Philippines; there processes of gravitational re-deposition of sediments occur. The ocean slope is an edge of the Philippine Plate sinking into the trough, where basalts of the oceanic crust are exposed.

(Table 2) Age interval and accumulation rates of organic and inorganic carbon from ODP Sites 175-1082, 175-1084, 175-1085 and 175-1087

The Ocean Drilling Program Leg 175 recovered a unique series of stratigraphically continuous sedimentary sections along the SW African margin, an area which is presently affected by active coastal upwelling. The accumulation rates of organic and inorganic carbon are a major component of this record. Four Leg 175 sites (1082, 1084, 1085, 1087) are chosen as part of a latitudinal transect from the present northern to southern boundaries of the Benguela Current upwelling system, to decipher the Pliocene-Pleistocene history of biogenic production and its relationship with global and local changes in oceanic circulation and climate. The pattern of CaCO3 and Corg mass accumulation rates (MARs) over 0.25-Myr intervals indicates that the evolution of carbon burial is highly variable between the northern and the southern Benguela regions, as well as between sites that have similar hydrological conditions. This, as well as the presence over most locations of high-amplitude, rapid changes of carbon burial, reflect the partitioning of biogenic production and patterns of sedimentation into local compartments over the Benguela margin. The combined mapping of CaCO3 and Corg MARs at the study locations suggests four distinct evolutionary periods, which are essentially linked with major steps in global climate change: the early Pliocene, the mid-Pliocene warm event, a late Pliocene intensification of northern hemisphere glaciation and the Pleistocene. The early Pliocene spatially heterogeneous patterns of carbon burial are thought to reflect the occurrence of mass-gravitational movements over the Benguela slope which resulted in disruption of the recorded biogenic production. This was followed (3.5-3 Ma) by an episode of peak carbonate accumulation over the whole margin and, subsequently, by the onset of Benguela provincialism into a northern and a southern sedimentary regime near 2 Ma. This mid and late Pliocene evolution is interpreted as a direct response to changes in the ventilation of bottom and intermediate waters, as well as to dynamics of the subtropical gyral circulation and associated wind stress.