Sea-surface tempertaure reconstruction of sediment cores from the Southeast Pacific

Applying the alkenone method, we estimated sea-surface temperatures (SSTs) for the past 33 kyr in two marine sediment cores recovered from the continental slope off mid-latitude Chile. The SST record shows an increase of 6.7°C from the last ice age (LIA) to the Holocene climatic optimum, while the temperature contrast between LIA and modern temperatures is only about 3.4°C. The timing and magnitude of the last deglacial warming in the ocean correspond to those observed in South American continental records. According to our SST record, the existence of a Younger Dryas equivalent cooling in the Southeast Pacific is much more uncertain than for the continental climate changes. A warming step of about 2.5°C observed between 8 and 7.5 cal kyr BP may have been linked to the early to mid-Holocene climatic transition (8.2-7.8 cal kyr BP), also described from equatorial Africa and Antarctica. In principal, variations in the latitudinal position of the Southern Pacific Westerlies are considered to be responsible for SST changes in the Peru-Chile current off mid-latitude Chile.

Alkenone-derived sea surface temperature records of three sediment cores from the southern Benguela upwelling system

We present alkenone-derived Sea Surface Temperature (SST) records from three marine cores collected within the southern Benguela Upwelling System (BUS) spanning the last 3 ka. The SST evolution over the last 3 millennia is marked by aperiodic millennial-scale oscillations that broadly correspond to climatic anomalies identified over the North Atlantic region. The BUS SST data further suggest cooling and warming trends opposite to the temperature evolution in the Moroccan upwelling region and in Antarctica. In contrast, the last decades are marked by a cooling of unprecedented magnitude in both the Benguela and Moroccan upwelling systems, which is not observed in the Antarctic record. These contrasted responses in Atlantic upwelling systems triggered by natural and anthropogenic forcings shed light on how different climatic mechanisms are mediated by ocean-atmosphere interactions and transmitted to the geological records of past and present climate changes.

Morphology and size of Neogloboquadrina pachyderma in the North Atlantic

The variability in size and shape of shells of the polar planktonic foraminifer Neogloboquadrina pachyderma have been quantified in 33 recent surface sediment samples throughout the northern Atlantic Ocean and correlated with the properties of the ambient surface waters. The aim of the study was to determine whether any of the morphological features could be used to reconstruct sea surface properties in the polar realm of the North Atlantic, where most paleotemperature proxies appear to fail. The analyses revealed that shell morphology is only weakly controlled by habitat properties, whereas shell size showed a strong correlation with sea surface temperature. The regression of mean shell size on sea surface temperature revealed the presence of two trends among the sinistrally coiled shells: a continuous increase in shell size with decreasing SST in sediments deposited under polar water masses and a continuous increase in shell size with increasing SST in samples from transitional waters. The second trend mirrors the trend observed for dextrally coiled shells, which are frequent in the same samples and signal the presence of N. incompta. The identical mean shell size trends among the sinistral and dextral specimens in the temperate samples confirms the results of earlier genetic studies which indicated the existence of a small but distinct proportion of opposite coiling in N. incompta, to which the sinistral shells in the temperate samples could be attributed. The linear correlation between mean shell size and sea surface temperature in the polar domain (summer SST < 9 °C) has been used to develop an empirical formula for the reconstruction of past sea surface temperatures from shell sizes in fossil samples. The standard error of the residuals of the linear regression is 2.36 °C (1 sigma), which implies a much larger error than for most paleothermometers, but enough precision to allow resolution between results by individual paleothermometers in the polar domain. The resulting regression model has been applied on two sediment cores spanning the interval from the Last Glacial Maximum (LGM) to the present day. The results from core PS1906-1 are consistent with ice-free conditions during the LGM in the Norwegian Sea. The SST estimates for the LGM inferred from N. pachyderma shell size are similar or slightly higher than those for the latest Holocene. The results do not indicate anomalously high SST during the glacial and the LGM reconstructions thus appear more consistent with the results from foraminiferal transfer functions and geochemical proxies. Both sediment cores show the highest reconstructed SST during the early Holocene insolation optimum.

La política exterior argentina durante la guerra fría : Interpretaciones y debates

El artículo se propone ver cuáles han sido los usos del pasado en los trabajos de política exterior desde las distintas perspectivas teóricas. Para hacerlo, presentaremos un brevísimo racconto del desarrollo disciplinar y señalaremos cuales son sus principales enfoques sobre el periodo, tanto en términos generales, como específicos, cuando terminó esta fase, para finalmente realizar una conclusión sobre la misma.

Element concentrations, and Sr and Os isotope ratios of DSDP Leg 92 metalliferous carbonates

The Os concentration and isotopic composition of metalliferous carbonates deposited on the East Pacific Rise over the past 28 Ma are reported with complimentary Sr isotope data. Variations in the Os isotopic composition of these samples are interpreted as a record of past changes in the Os isotopic composition of seawater. These results are consistent with isotopic analyses of leachable Os in pelagic clays which have also been interpreted as a record of the 187Os/186Os ratio of seawater through time (Pegram et al., 1992, doi:10.1016/0012-821X(92)90132-F). The metalliferous carbonate record clearly shows that seawater Os and Sr isotope systems are partially decoupled from one another over the past 28 Ma. Accelerated weathering of ancient organic-rich sediments is suggested as a possible mechanism to account for this decoupling and the rapid increase in the 187Os//186Os ratio of seawater over the past 15 Ma. This rapid increase suggests that the seawater Os record can potentially be used as a stratigraphic tool in some Neogene marine deposits.

Memoria rota, tensión y armonía en crónicas mestizas novohispanas

Las crónicas de la conquista de México ponen en escena una peculiar tensión entre experiencia y saber como formas de acreditación del relato acerca del pasado. En estas polémicas, la apelación a la memoria (propia y de los antepasados) se convierte en un tópico, enunciado primero por el cronista y retomado, siglos después, por el analista. Aquí, se trata de poner en escena algunos de los usos de la memoria en crónicas de tradición mestiza, para responder a la pregunta acerca de la configuración textual del argumento memorialista. Así, al interrogar estas crónicas a partir del funcionamiento de la memoria, volvemos a asistir al cruce de concepciones y cosmovisiones: a las nociones de "memorial", "recuerdo" y "monumento" en la tradición occidental debemos sumarle las acepciones del término "memoria" en el mundo nahua. A analizar brevemente estas modulaciones dedicaremos estas páginas

Implicancias territoriales de los nuevos usos del suelo agrario en el partido de Monte

Los territorios rurales muestran importantes transformaciones en las últimas décadas, en el marco del modelo de desarrollo implementado en el país. Los espacios rurales próximos a las ciudades se van integrando al ámbito urbano a través de nuevos hábitos de vida y consumo. Los territorios son cada vez más interdependientes pero también cada vez más diversificados, lo que da lugar a distintas formas de apropiación, situación que muchas veces genera conflictos debido a la coexistencia de diversas lógicas productivas y sociales. En este contexto, el trabajo analiza los cambios territoriales que se manifiestanen las áreas rurales y los conflictos que surgen a raíz de las distintas formas de utilizar el territorio. Centramos nuestra atención en el partido de Monte, provincia de Buenos Aires, y en las implicancias territoriales generadasentre la avicultura y la expansión de actividades no agroproductivas. El análisis realizado permite visualizar la situación de los actores intervinientes, los intereses en juego y sus consecuencias en el uso y apropiación del territorio.

Age models of five ice cores from the Dronning Maud Land, Antarctica

For the first time, annually resolved accumulation rates have been determined in central Antarctica by means of counting seasonal signals of ammonium, calcium, and sodium. All records, obtained from three intermediate depth ice cores from Dronning Maud Land, East Antarctica, show rather constant accumulation rates throughout the last 9 centuries with mean values of 63, 61, and 44 mm H2O yr**-1 and a typical year-to-year variation of about 30%. For the last few decades, no trend was detected accounting for the high natural variability of all records. A significant weak intersite correlation is apparent only between two cores when the high-frequency part with periods less than 30 years is removed. By analyzing the records in the frequency domain, no persistent periods were found. This suggests that the snow accumulation in this area is mainly influenced by local deposition patterns and may be additionally masked by redistribution of snow due to wind. By comparing accumulation rates over the last 2 millennia a distinct change in the layer thickness in one of the three cores was found, which might be attributed either to an area upstream of the drilling site with lower accumulation rates, or to deposition processes influenced by surface undulations. The missing of a clear correlation between the accumulation rate histories at the three locations is also important for the interpretation of small, short time variations of past precipitation records obtained from deep ice cores.

Memoria rota, tensión y armonía en crónicas mestizas novohispanas

Las crónicas de la conquista de México ponen en escena una peculiar tensión entre experiencia y saber como formas de acreditación del relato acerca del pasado. En estas polémicas, la apelación a la memoria (propia y de los antepasados) se convierte en un tópico, enunciado primero por el cronista y retomado, siglos después, por el analista. Aquí, se trata de poner en escena algunos de los usos de la memoria en crónicas de tradición mestiza, para responder a la pregunta acerca de la configuración textual del argumento memorialista. Así, al interrogar estas crónicas a partir del funcionamiento de la memoria, volvemos a asistir al cruce de concepciones y cosmovisiones: a las nociones de "memorial", "recuerdo" y "monumento" en la tradición occidental debemos sumarle las acepciones del término "memoria" en el mundo nahua. A analizar brevemente estas modulaciones dedicaremos estas páginas

Isotopic composition of terrestrial plant waxes (dD and d13C of n-alkanes) of sediment core SO188_342 from the Northern Bay of Bengal for the last 18 ka

The Indian Summer Monsoon (ISM) is a major global climatic phenomenon. Long-term precipitation proxy records of the ISM, however, are often fragmented and discontinuous, impeding an estimation of the magnitude of precipitation variability from the Last Glacial to the present. To improve our understanding of past ISM variability, we provide a continuous reconstructed record of precipitation and continental vegetation changes from the lower Ganges-Brahmaputra-Meghna catchment and the Indo-Burman ranges over the last 18,000 years (18 ka). The records derive from a marine sediment core from the northern Bay of Bengal (NBoB), and are complemented by numerical model results of spatial moisture transport and precipitation distribution over the Bengal region. The isotopic composition of terrestrial plant waxes (dD and d13C of n-alkanes) are compared to results from an isotope-enabled general atmospheric circulation model (IsoCAM) for selected time slices (pre-industrial, mid-Holocene and Heinrich Stadial 1). Comparison of proxy and model results indicate that past changes in the dD of precipitation and plant waxes were mainly driven by the amount effect, and strongly influenced by ISM rainfall. Maximum precipitation is detected for the Early Holocene Climatic Optimum (EHCO; 10.5-6 ka BP), whereas minimum precipitation occurred during the Heinrich Stadial 1 (HS1; 16.9-15.4 ka BP). The IsoCAM model results support the hypothesis of a constant moisture source (i.e. the NBoB) throughout the study period. Relative to the pre-industrial period the model reconstructions show 20% more rain during the mid-Holocene (6 ka BP) and 20% less rain during the Heinrich Stadial 1 (HS1), respectively. A shift from C4-plant dominated ecosystems during the glacial to subsequent C3/C4-mixed ones during the interglacial took place. Vegetation changes were predominantly driven by precipitation variability, as evidenced by the significant correlation between the dD and d13C alkane records. When compared to other records across the ISM domain, precipitation and vegetation changes inferred from our records and the numerical model results provide evidence for a coherent regional variability of the ISM from the Last Glacial to the present.

Implicancias territoriales de los nuevos usos del suelo agrario en el partido de Monte

Los territorios rurales muestran importantes transformaciones en las últimas décadas, en el marco del modelo de desarrollo implementado en el país. Los espacios rurales próximos a las ciudades se van integrando al ámbito urbano a través de nuevos hábitos de vida y consumo. Los territorios son cada vez más interdependientes pero también cada vez más diversificados, lo que da lugar a distintas formas de apropiación, situación que muchas veces genera conflictos debido a la coexistencia de diversas lógicas productivas y sociales. En este contexto, el trabajo analiza los cambios territoriales que se manifiestanen las áreas rurales y los conflictos que surgen a raíz de las distintas formas de utilizar el territorio. Centramos nuestra atención en el partido de Monte, provincia de Buenos Aires, y en las implicancias territoriales generadasentre la avicultura y la expansión de actividades no agroproductivas. El análisis realizado permite visualizar la situación de los actores intervinientes, los intereses en juego y sus consecuencias en el uso y apropiación del territorio.

La política exterior argentina durante la guerra fría : Interpretaciones y debates

El artículo se propone ver cuáles han sido los usos del pasado en los trabajos de política exterior desde las distintas perspectivas teóricas. Para hacerlo, presentaremos un brevísimo racconto del desarrollo disciplinar y señalaremos cuales son sus principales enfoques sobre el periodo, tanto en términos generales, como específicos, cuando terminó esta fase, para finalmente realizar una conclusión sobre la misma.