896 resultados para Marciniak, Gerald
Resumo:
Accelerator mass spectrometry (AMS) radiocarbon dating of ostracod and gastropod shells from the southwestern Black Sea cores combined with tephrochronology provides the basis for studying reservoir age changes in the lateglacial Black Sea. The comparison of our data with records from the northwestern Black Sea shows that an apparent reservoir age of ~1450 14C yr found in the glacial is characteristic of a homogenized water column. This apparent reservoir age is most likely due to the hardwater effect. Though data indicate that a reservoir age of ~1450 14C yr may have persisted until the Bølling-Allerød warm period, a comparison with the GISP2 ice-core record suggests a gradual reduction of the reservoir age to ~1000 14C yr, which might have been caused by dilution effects of inflowing meltwater. During the Bølling-Allerød warm period, soil development and increased vegetation cover in the catchment area of the Black Sea could have hampered erosion of carbonate bedrock, and hence diminished contamination by "old" carbon brought to the Black Sea basin by rivers. A further reduction of the reservoir age most probably occurred contemporary to the precipitation of inorganic carbonates triggered by increased phytoplankton activity, and was confined to the upper water column. Intensified deep water formation subsequently enhanced the mixing/convection and renewal of intermediate water. During the Younger Dryas, the age of the upper water column was close to 0 yr, while the intermediate water was ~900 14C yr older. The first inflow of saline Mediterranean water, at ~8300 14C yr BP, shifted the surface water age towards the recent value of ~400 14C yr.
Resumo:
The coccolithophore Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler was cultured in natural seawater with the addition of either the microtubule-inhibitor colchicine, the actin-inhibitor cytochalasin B, or the photosynthesis inhibitor 3-(3,4 dichlorophenyl)-1,1-dimethyl-urea (DCMU). Additionally, E. huxleyi was cultured at different light intensities and temperatures. Growth rate was monitored, and coccolith morphology analyzed. While every treatment affected growth rate, the percentage of malformed coccoliths increased with colchicine, cytochalasin B, and at higher than optimal temperature. These results represent the first experimental evidence for the role of microtubules and actin microfilaments in coccolith morphogenesis.
Resumo:
Southern Ocean sediments reveal a spike in authigenic uranium 127,000 years ago, within the last interglacial, reflecting decreased oxygenation of deep water by Antarctic Bottom Water (AABW). Unlike ice age reductions in AABW, the interglacial stagnation event appears decoupled from open ocean conditions and may have resulted from coastal freshening due to mass loss from the Antarctic ice sheet. AABW reduction coincided with increased North Atlantic Deep Water (NADW) formation, and the subsequent reinvigoration in AABW coincided with reduced NADW formation. Thus, alternation of deep water formation between the Antarctic and the North Atlantic, believed to characterize ice ages, apparently also occurs in warm climates.
Resumo:
Este texto es una réplica al artículo de Julián Verardi "Forma y contenido en la concepción materialista de la historia". Contiene una respuesta a las críticas que Verardi formulara a Materialismo histórico: interpretaciones y controversias, y una clarificación de algunos conceptos centrales del materialismo histórico
Resumo:
The effects of changing ice and atmospheric conditions on the upwelling of deep nutrient-laden waters and biological productivity in the coastal Beaufort Sea were quantified using a unique combination of in situ and remote-sensing approaches. Repeated instances of ice ablation and upwelling during fall 2007 and summer 2008 multiplied the production of ice algae, phytoplankton, zooplankton and benthos by 2 to 6 fold. Strong wind forcing failed to induce upward shifts in the biological productivity of stratified waters off the shelf.
Resumo:
En este trabajo se analiza si es apropiado evaluar acciones individuales con los principios de justicia aplicables a las instituciones. Para lograr este objetivo, el artículo examina la teoría de la justicia rawlsiana y algunas de las principales objeciones en su contra. Los críticos niegan que los principios de justicia de esta teoría estén configurados para evaluar exclusivamente las instituciones sociales básicas. Es más: afirman que la justicia no sólo exige instituciones justas sino que además exige acciones individuales justas. La hipótesis de este trabajo afirma que principios aptos para ciertos contextos sociales no son adecuados para evaluar otro tipo de interacciones sociales. El argumento apela a una interpretación normativa de la noción de estructura básica, elemento clave para defender el carácter institucional de la justicia rawlsiana
Resumo:
En este trabajo se analiza si es apropiado evaluar acciones individuales con los principios de justicia aplicables a las instituciones. Para lograr este objetivo, el artículo examina la teoría de la justicia rawlsiana y algunas de las principales objeciones en su contra. Los críticos niegan que los principios de justicia de esta teoría estén configurados para evaluar exclusivamente las instituciones sociales básicas. Es más: afirman que la justicia no sólo exige instituciones justas sino que además exige acciones individuales justas. La hipótesis de este trabajo afirma que principios aptos para ciertos contextos sociales no son adecuados para evaluar otro tipo de interacciones sociales. El argumento apela a una interpretación normativa de la noción de estructura básica, elemento clave para defender el carácter institucional de la justicia rawlsiana
Resumo:
Este texto es una réplica al artículo de Julián Verardi "Forma y contenido en la concepción materialista de la historia". Contiene una respuesta a las críticas que Verardi formulara a Materialismo histórico: interpretaciones y controversias, y una clarificación de algunos conceptos centrales del materialismo histórico
