Radiocarbon ages and 230Th data of five sediment cores from the Björn and Gardar Drift, North Atlantic

In locations of rapid sediment accumulation receiving substantial amounts of laterally transported material the timescales of transport and accurate quantification of the transported material are at the focus of intense research. Here we present radiocarbon data obtained on co-occurring planktic foraminifera, marine haptophyte biomarkers (alkenones) and total organic carbon (TOC) coupled with excess Thorium-230 (230Thxs) measurements on four sediment cores retrieved in 1649-2879 m water depth from two such high accumulation drift deposits in the Northeast Atlantic, Björn and Gardar Drifts. While 230Thxs inventories imply strong sediment focussing, no age offsets are observed between planktic foraminifera and alkenones, suggesting that redistribution of sediments is rapid and occurs soon after formation of marine organic matter, or that transported material contains negligible amounts of alkenones. An isotopic mass balance calculation based on radiocarbon concentrations of co-occurring sediment components leads us to estimate that transported sediment components contain up to 12% of fossil organic matter that is free of or very poor in alkenones, but nevertheless appears to consist of a mixture of fresh and eroded fossil material. Considering all available constraints to characterize transported material, our results show that although focussing factors calculated from bulk sediment 230Thxs inventories may allow useful approximations of bulk redeposition, they do not provide a unique estimate of the amount of each laterally transported sediment component. Furthermore, our findings provide evidence that the occurrence of lateral sediment redistribution alone does not always hinder the use of multiple proxies but that individual sediment fractions are affected to variable extents by sediment focussing.

Clearence rates by Calanus finmarchicus and Calanus helgolandicus determined experimentally

We studied the response in development times of Calanus finmarchicus and Calanus helgolandicus to changes in temperature and food conditions. The ingestion response to temperature was determined in the laboratory, where the copepods C. finmarchicus and C. helgolandicus were fed the diatom Thalassiosira weissflogii (cultivated at 18°C-20°; 12 : 12 light :dark cycle; exponential growth). C. finmarchicus was obtained for experiments from the Gullmar fjord. C. finmarchicus was incubated at in situ temperature (5°C) until the experiments were performed. First-generation cultures were grown in the laboratory at 15°C from the eggs from the Sta. L4 females. During growth both C. finmarchicus and C. helgolandicus cultures were fed a mixture of the cryptophyte Rhodomonas salina, the diatom Thalassiosira weissflogii, and the dinoflagellate Prorocentrum minimum. Five 600-mL glass bottles containing 1400 cells mL**-1 or 5 mg chlorophyll a (Chl a) L**-1 of T. weissflogii (200 mg C) and 1-2 C. finmarchicus or C. helgolandicus copepodite stage 5 (CV) or females were incubated in darkness at series of temperatures between 1°C and 21 ± 0.5°C. Three bottles without copepods served as control. In the C. helgolandicus experiment, T. weissflogii cells were counted at the beginning and end of the experiment in the grazing bottles and controls using a Coulter CounterH (MultisizerTM 3, Beckman Coulter). In the C. finmarchicus experiment, phytoplankton reduction was determined by Chl a measurements. The reduction in phytoplankton during any of the experiments was generally below 20% and never more than 32%. Clearance rates were calculated following Harris et al. (2000).

Northwards and eastwards velocities extracted from a historical run (for the year 2000) of the UVic Earth System Climate Model of Weaver et al. (2001)

This study provides a theoretical assessment of the potential bias due to differential lateral transport on multi-proxy studies based on a range of marine microfossils. Microfossils preserved in marine sediments are at the centre of numerous proxies for paleoenvironmental reconstructions. The precision of proxies is based on the assumption that they accurately represent the overlying watercolumn properties and faunas. Here we assess the possibility of a syn-depositional bias in sediment assemblages caused by horizontal drift in the water column, due to differential settling velocities of sedimenting particles based on their shape, size and density, and due to differences in current velocities. Specifically we calculate the post-mortem lateral transport undergone by planktic foraminifera and a range of other biological proxy carriers (diatoms, radiolaria and fecal pellets transporting coccolithophores) in several regions with high current velocities. We find that lateral transport of different planktic foraminiferal species is minimal due to high settling velocities. No significant shape- or size-dependent sorting occurs before reaching the sediment, making planktic foraminiferal ideal proxy carriers. In contrast, diatoms, radiolaria and fecal pellets can be transported up to 500km in some areas. For example in the Agulhas current, transport can lead to differences of up to 2°C in temperature reconstructions between different proxies in response to settling velocities. Therefore, sediment samples are likely to contain different proportions of local and imported particles, decreasing the precision of proxies based on these groups and the accuracy of the temperature reconstruction.

Klett, Estela et al. (2005) Didáctica de las lenguas extranjeras: una agenda actual. Buenos Aires: Araucaria Editora, 120p. ; 21 x 16 cm. ISBN 987-9443-15-2

Fil: Lozada, María Helena.

Detección de Xanthomonas cucurbitae (Bryan) Vauterin et al. afectando frutos de zapallo coreano en Mendoza y San Juan, Argentina

Durante las campañas 2007/08 y 2008/09, en explotaciones comerciales de zapallo coreano (Cucurbita moschata Duch) de las zonas hortícolas de Mendoza y San Juan, se observaron sobre los frutos numerosas lesiones circulares, de 3 a 6 mm de diámetro, de aspecto húmedo, algo deprimidas hacia el centro, con un exudado gomoso color ámbar. Cuando las lesiones superficiales se unían, se desarrollaba una podredumbre gelatinosa hacia el interior de los tejidos, que podía profundizar hasta la cavidad seminal. El resultado final de la afección era una podredumbre seca y costrosa, que abarcaba gran parte del fruto, inutilizándolo para ser comercializado. En follaje también se observaron síntomas de la enfermedad, como manchas cloróticas angulares de 2 a 3 mm de lado, que en ocasiones se fusionaban. El objetivo del presente trabajo fue determinar la etiología de la enfermedad. Para ello, se tomaron y analizaron muestras de frutos y hojas afectadas, durante ambas temporadas. Se concluyó que la sintomatología es causada por una bacteria, que de acuerdo con los estudios morfobioquímicos y patogénicos es Xanthomonas cucurbitae (Bryan) Vauterin et al. Esta investigación constituye la primera cita de este patógeno afectando frutos en Argentina.

Sbatella, José et al. Origen, apropiación y destinos del excedente económico en la Argentina de la posconvertibilidad, Buenos Aires, Colihue, 2012, 163 págs., ISBN 978-987-684-304-1.

Fil: García, Marcos. Universidad Nacional de Cuyo. Facultad de Filosofía y Letras. Instituto Multidisciplinario de Estudios Sociales Contemporáneos

Revisión de un estudio por Koch et al. sobre el impacto de las restricciones al aborto en la mortalidad materna en Chile

En este comunicado se describen las fallas conceptuales y metodológicas graves que invalidan algunas de sus conclusiones concernientes al aborto y a la mortalidad materna del estudio de Koch y otros. Por lo cuál no altera el acervo de evidencia existente sobre el impacto de las restricciones al aborto sobre la mortalidad materna. En particular, dado que las leyes de aborto en Chile ya eran altamente restrictivas antes de 1989, el estudio no demuestra que el restringir significativamente las leyes de aborto no produzca un impacto negativo en la salud de las mujeres.

Plio-Pleistocene Mg/Ca and TEX86 sea surface temperature records of ODP Sites 184-1143 and 165-999,

The western warm pools of the Atlantic and Pacific oceans are a critical source of heat and moisture for the tropical climate system. Over the past five million years, global mean temperatures have cooled by 3-4 °C. Yet, current reconstructions of sea surface temperatures indicate that temperature in the warm pools has remained stable during this time. This stability has been used to suggest that tropical sea-surface temperatures are controlled by some sort of thermostat-like regulation. Here we reconstruct sea surface temperatures in the South China Sea, Caribbean Sea and western equatorial Pacific Ocean for the past five million years, using a combination of the Mg/Ca, TEXH86-and Uk'37 surface temperature proxies. Our data indicate that during the period of Pliocene warmth from about 5 to 2.6 million years ago, the western Pacific and western Atlantic warm pools were about 2 °C warmer than today. We suggest that the apparent lack of warming seen in the previous reconstructions was an artefact of low seawater Mg/Ca ratios in the Pliocene oceans. Taking this bias into account, our data indicate that tropical sea surface temperatures did change in conjunction with global mean temperatures. We therefore conclude that the temperature of the warm pools of the equatorial oceans during the Pliocene was not limited by a thermostat-like mechanism.

Accumulation rates of ODP Site 177-1090

Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean (Martin et al., 1990, doi:10.1038/345156a0; Martin, 1990, doi:10.1029/PA005i001p00001). Indeed, dust supply to the Southern Ocean increases during ice ages, and 'iron fertilization' of the subantarctic zone may have contributed up to 40 parts per million by volume (p.p.m.v.) of the decrease (80-100 p.p.m.v.) in atmospheric carbon dioxide observed during late Pleistocene glacial cycles (Watson et al., 2000, doi:10.1038/35037561; Kohfeld et al., 2005, doi:10.1126/science.1105375; Martínez-Garcia et al., 2009, doi:10.1029/2008PA001657; Sigman et al., 2010, doi:10.1038/nature09149; Hain et al., 2010, doi:10.1029/2010gb003790). So far, however, the magnitude of Southern Ocean dust deposition in earlier times and its role in the development and evolution of Pleistocene glacial cycles have remained unclear. Here we report a high-resolution record of dust and iron supply to the Southern Ocean over the past four million years, derived from the analysis of marine sediments from ODP Site 1090, located in the Atlantic sector of the subantarctic zone. The close correspondence of our dust and iron deposition records with Antarctic ice core reconstructions of dust flux covering the past 800,000 years (Lambert et al., 2008, doi:10.1038/nature06763; Wolf et al., 2006, doi:10.1038/nature04614) indicates that both of these archives record large-scale deposition changes that should apply to most of the Southern Ocean, validating previous interpretations of the ice core data. The extension of the record beyond the interval covered by the Antarctic ice cores reveals that, in contrast to the relatively gradual intensification of glacial cycles over the past three million years, Southern Ocean dust and iron flux rose sharply at the Mid-Pleistocene climatic transition around 1.25 million years ago. This finding complements previous observations over late Pleistocene glacial cycles (Martínez-Garcia et al., 2009; Lambert et al., 2008; Wolff et al., 2006), providing new evidence of a tight connection between high dust input to the Southern Ocean and the emergence of the deep glaciations that characterize the past one million years of Earth history.

Reconstruction of dust flux of ODP Hole 198-1209C

Eolian dust in pelagic deep sea sediments can be used to reconstruct ancient wind patterns and paleoenvironmental response to climate change. Traditional methods to determine dust accumulation involve isolating the non-dissolvable aluminosilicate minerals from deep sea sediments through a series of chemical leaches, but cannot differentiate between minerals from eolian, authigenic and volcanogenic sources. Other geochemical proxies, such as sedimentary 232Th and crustal 4He content, have been used to construct high-resolution records of atmospheric dust fluxes to the deep sea during the Quaternary. Here we use sedimentary Th content as a proxy for terrigenous material (eolian dust) in ~58 Myr-old sediments from the Shatsky Rise (ODP Site 1209) and compare our results with previous dust estimates generated using the traditional chemical extraction method and sedimentary 4He(crustal) concentrations. We find excellent agreement between Th-based dust estimates and those generated using the traditional method. In addition our results show a correlation between sedimentary Th and 4He(crustal) content, which suggests a source older than present day Asian loess supplied dust to the central subtropical Pacific Ocean during the early Paleogene.

Investigations on sediments from Lake Nam Co (Tibetan Plateau)

This study focuses on the analysis of lake sediments retrieved from the deepest part of Lake Nam Co (Tibetan Plateau). One gravity core of 115 cm length, covering the last ~ 4000 cal BP, was analyzed for geochemical and biological parameters. High organic content at ~ 4000 cal BP and the coinciding presence of pyrite framboids until ~ 2000 cal BP point to hampered decomposition of organic material due to anoxic conditions within the lake sediments. At the same time sedimentological and biological proxies suggest a rather high lake level, but still ~ 5 m below the recent one, with less saline lake water due to enhanced monsoonal activity. During this time a change in the source of organic matter to lowered input of terrestrial components is observed. A rather quick shift to a dry environment with less monsoonal influence and a lake level ~ 15 m lower than today at ~ 2000 cal BP lead to the oxygenation of sediment, the degradation of organic matter and the absence of pyrite. Oscillations of the lake level thereafter were of minor amplitude and not able to establish anoxia at the lake bottom again. A wet spell between ~ 1500 cal BP and ~ 1150 cal BP is visible in proxies referring to catchment hydrology and the ostracod-based water depth transfer function gives only a slightly elevated lake level. The last ~ 300 years are characterized by low TOC and rising TN values reflecting enhanced nutrient supply and hence an advancing influence of human activity in the catchment. Decreasing TOC/TN values point to a complete shift to almost solely aquatic biomass production. These results show that hydrological variations in terms of lake level change based on monsoonal strength can be linked to redox conditions at the lake bottom of Nam Co. Comparison with other archives over larger parts of the Tibetan Plateau and beyond exhibits a rather homogeneous climatic pattern throughout the late Holocene.

La formación docente en Educación Física : Estudio sobre las elecciones de los docentes de escuelas secundarias de La Plata ante la oferta de capacitación, durante el 2007 al 2009

La pregunta que orienta la propuesta de investigación es ¿Qué lugar ocupa la participación de los docentes en el diseño las políticas de capacitación? ¿Cuáles son los aspectos que inciden en la elección de la oferta de capacitación? La intención es analizar los factores que inciden en la elección de la oferta de capacitación estatal y/o privada, que realizan los docentes del área Educación Física pertenecientes al sector estatal, que se desempeñan en escuelas medias del distrito de La Plata. Son considerados los aportes de los estudios sobre saber docente, el proceso de análisis de las políticas públicas, las regulaciones del trabajo docente y la institucionalización de ciertas modalidades de capacitación. Desde un enfoque cualitativo, la estrategia metodológica utilizará fuentes de datos orales y documentales, a través de entrevistas en profundidad y análisis de documentos que regulan la capacitación en la provincia

Reseña del libro: Filo (en) rompecabezas. Búsqueda colectiva de la memoria histórica institucional (1966-1983) de Graciela Daleo et al (comp.)

Fil: Abbattista, Lucía. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación. Instituto de Investigaciones en Humanidades y Ciencias Sociales (UNLP-CONICET); Argentina.

Franco Cardini et al. L'Europa del pellegrinaggio, Rimini: II Cerchio, 1998, 123 páginas

Fil: Disalvo, Santiago Aníbal. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.