Paleoceanography of sediment cores SO202-27-6 during MIS 3

The modern subarctic Pacific is characterized by a steep salinity-driven surface water stratification, which hampers the supply of saline and nutrient-rich deeper waters into the euphotic zone, limiting productivity. However, the strength of the halocline might have varied in the past. Here, we present diatom oxygen (d18Odiat) and silicon (d30Sidiat) stable isotope data from the open subarctic North-East (NE) Pacific (SO202-27-6; Gulf of Alaska), in combination with other proxy data (Neogloboquadrina pachydermasin d18O, biogenic opal, Ca and Fe intensities, IRD), to evaluate changes in surface water hydrography and productivity during Marine Isotope Stage (MIS) 3, characterized by millennial-scale temperature changes (Dansgaard-Oeschger (D-O) cycles) documented in Greenland ice cores.

Los desafíos del uso combinado de un cuestionario estructurado y un calendario de historia de vida para el estudio de trayectorias laborales

El presente artículo se enmarca en un proyecto de investigación más amplio, realizado en la localidad de Ministro Rivadavia en el Partido de Alte. Brown. La investigación tiene como objetivo evaluar los procesos de movilidad, estancamiento y marginalización social en el período 1994-2008, para una población con elevados índices de pobreza e inserciones laborales precarias e informales. En este estudio nos proponemos reflexionar sobre los desafíos que implicó la articulación entre un cuestionario estructurado y un calendario de historia de vida para el análisis de trayectorias laborales. El trabajo presenta las características de la metodología empleada, discute sus antecedentes teórico-metodológicos y especifica dónde se inscribe la articulación metodológica propuesta en el mapa posible de estrategias de investigación sociológica. A lo largo del artículo, retomamos los debates y propuestas en torno al manejo de la dimensión temporal y presentamos distintos esquemas de análisis centrados en la consideración del tiempo en sus múltiples manifestaciones micro y macrosociales. El artículo contribuye al debate sobre la integración de estrategias de investigación cualitativas y cuantitativas, y evidencia las potencialidades del instrumento propuesto para captar la temporalidad en su carácter plural y multidimensional

La flexibilidad del obispo : Gregorio Magno, los judíos y la Regula pastoralis

El episcopado de Gregorio Magno (590-604) representa un hito al momento de analizar el derrotero del cristianismo entre la Antigüedad Tardía y el Alto Medioevo. Hombre de enorme flexibilidad política y discursiva, construyó -a lo largo de su vida- un repertorio textual de incalculable valor para el historiador moderno. En una de sus obras de mayor impacto en los siglos posteriores -la Regula pastoralis- el obispo de Roma analiza minuciosamente el rol del hombre de Iglesia en todas sus facetas, realizando especial hincapié en la parénesis. El objetivo de este trabajo será comparar algunas de las directivas allí vertidas con el accionar efectivo de Gregorio, observable en el Registrum epistularum. Para lograr tal fin, nos concentraremos en las epístolas referidas al judaísmo en general y a los judíos en particular. Observaremos, de tal modo, la concordancia entre algunos de los lineamientos gregorianos establecidos en la Regula y su aplicación en el caso judío

Climate proxies in sediment core MD95-2010

High-amplitude, rapid climate fluctuations are common features of glacial times. The prominent changes in air temperature recorded in the Greenland ice cores (Dansgaard et al., 1993, doi:10.1038/339532a0; Grootes et al., 1993 doi:10.1038/366552a0) are coherent with shifts in the magnitude of the northward heat flux carried by the North Atlantic surface ocean (Bond et al., 1993, doi:10.1038/365143a0; Bond and Lotti, 1995, doi:10.1126/science.267.5200.1005); changes in the ocean's thermohaline circulation are a key component in many explanations of this climate flickering (Broecker, 1997, doi:10.1126/science.278.5343.1582). Here we use stable-isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate-change events. Deep water was generated more or less continuously in the Nordic Seas during the latter part of the last glacial period (60 to 10 thousand years ago), but by two different mechanisms. The deep-water formation occurred by convection in the open ocean during warmer periods (interstadials). But during colder phases (stadials), a freshening of the surface ocean reduced or stopped open-ocean convection, and deep-water formation was instead driven by brine-release during sea-ice freezing. These shifting magnitudes and modes nested within the overall continuity of deep-water formation were probably important for the structuring and rapidity of the prevailing climate changes.

Las iglesias locales, los señores feudales y la comunidad : Dinámicas de consolidación del episcopado castellano-leonés, 1150-1250

El presente trabajo analiza el proceso de incorporación de diezmos e iglesias al episcopado a partir de mediados del siglo XII. Éste constituye el punto de partida de la organización de los señoríos episcopales de la Extremadura castellano-leonesa. Se demuestra que la reorganización eclesiástica promovida desde la reforma gregoriana no se produjo sin conflictos y no puede comprenderse cabalmente si no se consideran las condiciones de base sobre las que se desarrolló. Los casos de Zamora, Salamanca y Ávila permitirán establecer observaciones comparativas entre áreas de feudalización más temprana, similar a las del norte peninsular, y otras posteriores, pertenecientes a la Extremadura histórica

La extensión universitaria en el pensamiento pedagógico de Ricardo Nassif

Este ensayo se propone realizar una lectura particular de diferentes trabajos de Ricardo Nassif. Si bien la profusa obra de este pedagogo no focaliza en la extensión universitaria, se pretende encontrar distintas alusiones y emergentes que aporten elementos para reflexionar sobre esta función, en tanto hoy puesta en la agenda de discusión en el marco del Centenario de su institucionalización y de la actualidad y potencialidad que conlleva para la Universidad y para la formación y transformación de la Sociedad. Su obra se presenta como una clara manifestación de un lazo con la Sociedad que la pedagogía no debe perder en su camino como disciplina científica. Este pedagogo falleció el 30 de Noviembre de 1984 y, en el vigésimo aniversario de su muerte, estas líneas se constituyen en un humilde homenaje.

Coordenadas marianas : Tiempos y espacios de devoción a la Virgen a través de las cofradías porteñas coloniales

En el presente trabajo intentamos aproximarnos al estudio de la devoción a la Virgen en la ciudad de Buenos Aires durante la colonia a través de la identificación de las conmemoraciones del calendario y de los lugares de culto. Para ello se rastrearon las asociaciones de laicos con fines religiosos, cofradías y hermandades. Las fuentes utilizadas son libros de constituciones y actas de diferentes cofradías, un almanaque del siglo XVIII y documentación emitida por la corona española sobre la organización de las festividades religiosas y las reuniones de las cofradías. También se ha usado bibliografía editada para rastrear información sobre asociaciones y espacios de culto. Este trabajo se propone construir una base empírica para poder analizar la construcción de escenarios religiosos que desbordan los límites de la devoción privada constituyendo un espacio público, hacia finales del período colonial.

Radiocarbon ages and diatom abundance in cores GA306-BC4 and GA306-GC4 obtained during Galathea 3 cruise, West Greenland

Diatom assemblages from Holsteinsborg Dyb on the West Greenland shelf were analysed with high temporal resolution for the last 1200 years. A high degree of consistency between changes in frequency of selected diatom species and instrumental data from the same area during the last 70 years confirms the reliability of diatoms (particularly sea-ice species and warm-water species) for the study of palaeoceanographic changes in this area. A general cooling trend with some fluctuations is marked by an increase in sea-ice species throughout the last 1200 years. A relatively warm period with increased influence of Atlantic water masses of the Irminger Current (IC) is found at AD 750-1330, although with some oceanographic variability after AD 1000. A pronounced oceanographic shift occurred at AD 1330, corresponding in time to the transition from the so-called 'Medieval Warm Period' (MWP) to the 'Little Ice Age' (LIA). The LIA cold episode is characterized by three intervals with particularly cold sea-surface conditions at AD 1330-1350, AD 1400-1575 and AD 1660-1710 as a result of variable influence of Polar waters in the area. During the last 70 years, two relatively warm periods and one cold period (the early 1960s to mid-1990s) are indicated by changes in the diatom components. Our study demonstrates that sedimentary records on the West Greenland shelf provide valuable palaeoenvironment data that confirm a linkage between local and large-scale North Atlantic oceanographic and atmospheric oscillations.

Age determination of corals from the North Atlantic and the Tasman Sea

During the past 40,000 years, global climate has moved into and out of a full glacial period, with the deglaciation marked by several millennial-scale rapid climate change events. Here we investigate the ecological response of deep-sea coral communities to both glaciation and these rapid climate change events. We find that the deep-sea coral populations of Desmophyllum dianthus in both the North Atlantic and the Tasmanian seamounts expand at times of rapid climate change. However, during the more stable Last Glacial Maximum, the coral population globally retreats to a more restricted depth range. Holocene populations show regional patterns that provide some insight into what causes these dramatic changes in population structure. The most important factors are likely responses to climatically driven changes in productivity, [O2] and [CO3]2-.

Gotland Deep (Baltic Sea) independent age model based on Palaeomagnetic Secular Variation (PSV) and lead (Pb) deposition profiles

Dating of sediment cores from the Baltic Sea has proven to be difficult due to uncertainties surrounding the 14C reservoir age and a scarcity of macrofossils suitable for dating. Here we present the results of multiple dating methods carried out on cores in the Gotland Deep area of the Baltic Sea. Particular emphasis is placed on the Littorina stage (8 ka ago to the present) of the Baltic Sea and possible changes in the 14C reservoir age of our dated samples. Three geochronological methods are used. Firstly, palaeomagnetic secular variations (PSV) are reconstructed, whereby ages are transferred to PSV features through comparison with varved lake sediment based PSV records. Secondly, lead (Pb) content and stable isotope analysis are used to identify past peaks in anthropogenic atmospheric Pb pollution. Lastly, 14C determinations were carried out on benthic foraminifera (Elphidium spec.) samples from the brackish Littorina stage of the Baltic Sea. Determinations carried out on smaller samples (as low as 4 µg C) employed an experimental, state-of-the-art method involving the direct measurement of CO2 from samples by a gas ion source without the need for a graphitisation step - the first time this method has been performed on foraminifera in an applied study. The PSV chronology, based on the uppermost Littorina stage sediments, produced ten age constraints between 6.29 and 1.29 cal ka BP, and the Pb depositional analysis produced two age constraints associated with the Medieval pollution peak. Analysis of PSV data shows that adequate directional data can be derived from both the present Littorina saline phase muds and Baltic Ice Lake stage varved glacial sediments. Ferrimagnetic iron sulphides, most likely authigenic greigite (Fe3S4), present in the intermediate Ancylus Lake freshwater stage sediments acquire a gyroremanent magnetisation during static alternating field (AF) demagnetisation, preventing the identification of a primary natural remanent magnetisation for these sediments. An inferred marine reservoir age offset (deltaR) is calculated by comparing the foraminifera 14C determinations to a PSV & Pb age model. This deltaR is found to trend towards younger values upwards in the core, possibly due to a gradual change in hydrographic conditions brought about by a reduction in marine water exchange from the open sea due to continued isostatic rebound.

Age determination of sediments and biomarkers of ODP Hole 169-1034C

The radiocarbon contents of various biomarkers extracted from the varve-counted sediments of Saanich Inlet, Canada, were determined to assess their applicability for dating purposes. Calibrated ages obtained from the marine planktonic archaeal biomarker crenarchaeol compared favorably with varve-count ages. The same conclusion could be drawn for a more general archaeal biomarker (GDGT-0), although this biomarker proved to be less reliable due to its less-specific origin. The results also lend support to earlier indications that marine crenarchaeota use dissolved inorganic carbon (DIC) as their carbon source. The average reservoir age offset DR of 430 years, determined using the crenarchaeol radiocarbon ages, varied by ±110 years. This may be caused by natural variations in ocean-atmosphere mixing or upwelling at the NE Pacific coast but variability may also be due to an inconsistency in the marine calibration curve when used at sites with high reservoir ages.