A time-slice study in Heinrich Stadial 1 and Mid Holocene sediment cores off northern Senegal

Sediment dynamics in limnic, fluvial and marine environments can be assessed by granulometric and rock-magnetic methodologies. While classical grain-size analysis by sieving or settling mainly bears information on composition and transport, the magnetic mineral assemblages reflect to a larger extent the petrology and weathering conditions in the sediment source areas. Here, we combine both methods to investigate Late Quaternary marine sediments from five cores along a transect across the continental slope off Senegal. This region near the modern summer Intertropical Convergence Zone is particularly sensitive to climate change and receives sediments from several aeolian, fluvial and marine sources. From each of the investigated five GeoB sediment cores (494-2956 m water depth) two time slices were processed which represent contrasting climatic conditions: the arid Heinrich Stadial 1 (~ 15 kyr BP) and the humid Mid Holocene (~ 6 kyr BP). Each sediment sample was split into 16 grain-size fractions ranging from 1.6 to 500 µm. Concentration and grain-size indicative magnetic parameters (susceptibility, SIRM, HIRM, ARM and ARM/IRM) were determined at room temperature for each of these fractions. The joint consideration of whole sediment and magnetic mineral grain-size distributions allows to address several important issues: (i) distinction of two aeolian sediment fractions, one carried by the north-easterly trade winds (40-63 µm) and the other by the overlying easterly Harmattan wind (10-20 µm) as well as a fluvial fraction assigned to the Senegal River (< 10 µm); (ii) identification of three terrigenous sediment source areas: southern Sahara and Sahel dust (low fine-grained magnetite amounts and a comparatively high haematite content), dust from Senegalese coastal dunes (intermediate fine-grained magnetite and haematite contents) and soils from the upper reaches of the Senegal River (high fine-grained magnetite content); (iii) detection of partial diagenetic dissolution of fine magnetite particles as a function of organic input and shore distance; (iv) analysis of magnetic properties of marine carbonates dominating the grain-size fractions 63-500 µm.

Physico-chemical parameters of sediment core PG1972-1 (09-Tik-03) from a Tundra Lake, Northeastern Siberia

Thermokarst lakes in the Siberian Arctic contain sediment archives that can be used for paleoenvironmental inference. Until now, however, there has been no study from the inner Lena River Delta with a focus on diatoms. The objective of this study was to investigate how the diatom community in a thermokarst lake responded to past limnogeological changes and what specific factors drove variations in the diatom assemblage. We analysed fossil diatom species, organic content, grain-size distribution and elemental composition in a sediment core retrieved in 2009 from a shallow thermokarst lake in the Arga Complex, western Lena River Delta. The core contains a 3,000-year record of sediment accumulation. Shifts in the predominantly benthic and epiphytic diatom species composition parallel changes in sediment characteristics. Paleoenvironmental and limnogeological development, inferred from multiple biological and sedimentological variables, are discussed in the context of four diatom zones, and indicate a strong relation between changes in the diatom assemblage and thermokarst processes. We conclude that limnogeological and thermokarst processes such as lake drainage, rather than direct climate forcing, were the main factors that altered the aquatic ecosystem by influencing, for example, habitat availability, hydrochemistry, and water level.

(Table 1) Bioclimatic subzones and soil characteristics along the Yamal Arctic Transect, northwestern Siberia

Sustainability of tundra vegetation under changing climate on the Yamal Peninsula, northwestern Siberia, home to the world's largest area of reindeer husbandry, is of crucial importance to the local native community. An integrated investigation is needed for better understanding of the effects of soils, climate change and grazing on tundra vegetation in the Yamal region. In this study we applied a nutrient-based plant community model - ArcVeg - to evaluate how two factors (soil organic nitrogen (SON) levels and grazing) interact to affect tundra responses to climate warming across a latitudinal climatic gradient on the Yamal Peninsula. Model simulations were driven by field-collected soil data and expected grazing patterns along the Yamal Arctic Transect (YAT), within bioclimate subzones C (high arctic), D (northern low arctic) and E (southern low arctic). Plant biomass and NPP (net primary productivity) were significantly increased with warmer bioclimate subzones, greater soil nutrient levels and temporal climate warming, while they declined with higher grazing frequency. Temporal climate warming of 2 °C caused an increase of 665 g/m**2 in total biomass at the high SON site in subzone E, but only 298 g/m**2 at the low SON site. When grazing frequency was also increased, total biomass increased by only 369 g/m**2 at the high SON site in contrast to 184 g/m**2 at the low SON site in subzone E. Our results suggest that high SON can support greater plant biomass and plant responses to climate warming, while low SON and grazing may limit plant response to climate change. In addition to the first order factors (SON, bioclimate subzones, grazing and temporal climate warming), interactions among these significantly affect plant biomass and productivity in the arctic tundra and should not be ignored in regional scale studies.

Myers, K.S. (ed.), Ovid Metamorphoses, Book XIV (Cambridge Greek and Latin Classics), Nueva York, Cambridge University Press, 2009, IX + 237 pp. ISBN 978-0-521-00793-1

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

Estructura organizativa del Sistema de Gestión Integral de Documentos de archivo (SiGeID 1.0)

El nuevo contexto impone a las organizaciones la necesidad vital de disponer de adecuadas infraestructuras de comunicación, que les permitan conseguir un conocimiento real y suficiente del entorno. El presente artículo pretende mostrar la estructura organizativa del Sistema de Gestión Integral de Documentos de archivo SiGeID (1.0), como una herramienta informática que ayuda a las organizaciones empresariales al perfeccionamiento de la gestión de documentos. Dividido en tres módulos: Gestión y Seguridad Documental, Gestión de Archivo y Administración y Configuración, se tienen en cuenta además sus requerimientos funcionales y no funcionales

Age determination, sedimentological, biogeochemical, and plant macrofossils analyses of outcrop PG2038-1

Thermokarst lakes are a widespread feature of the Arctic tundra, in which highly dynamic processes are closely connected with current and past climate changes. We investigated late Quaternary sediment dynamics, basin and shoreline evolution, and environmental interrelations of Lake El'gene-Kyuele in the NE Siberian Arctic (latitude 71°17'N, longitude 125°34'E). The water-body displays thaw-lake characteristics cutting into both Pleistocene Ice Complex and Holocene alas sediments. Our methods are based on grain size distribution, mineralogical composition, TOC/N ratio, stable carbon isotopes and the analysis of plant macrofossils from a 3.5-m sediment profile at the modern eastern lake shore. Our results show two main sources for sediments in the lake basin: terrigenous diamicton supplied from thermokarst slopes and the lake shore, and lacustrine detritus that has mainly settled in the deep lake basin. The lake and its adjacent thermokarst basin rapidly expanded during the early Holocene. This climatically warmer than today period was characterized by forest or forest tundra vegetation composed of larches, birch trees and shrubs. Woodlands of both the HTM and the Late Pleistocene were affected by fire, which potentially triggered the initiation of thermokarst processes resulting later in lake formation and expansion. The maximum lake depth at the study site and the lowest limnic bioproductivity occurred during the longest time interval of ~7 ka starting in the Holocene Thermal Maximum and lasting throughout the progressively cooler Neoglacial, whereas partial drainage and an extensive shift of the lake shoreline occurred ~0.9 cal. ka BP. Correspondingly, this study discusses different climatic and environmental drivers for the dynamics of a thermokarst basin.

Myers, K.S. (ed.), Ovid Metamorphoses, Book XIV (Cambridge Greek and Latin Classics), Nueva York, Cambridge University Press, 2009, IX + 237 pp. ISBN 978-0-521-00793-1

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

Estructura organizativa del Sistema de Gestión Integral de Documentos de archivo (SiGeID 1.0)

El nuevo contexto impone a las organizaciones la necesidad vital de disponer de adecuadas infraestructuras de comunicación, que les permitan conseguir un conocimiento real y suficiente del entorno. El presente artículo pretende mostrar la estructura organizativa del Sistema de Gestión Integral de Documentos de archivo SiGeID (1.0), como una herramienta informática que ayuda a las organizaciones empresariales al perfeccionamiento de la gestión de documentos. Dividido en tres módulos: Gestión y Seguridad Documental, Gestión de Archivo y Administración y Configuración, se tienen en cuenta además sus requerimientos funcionales y no funcionales

Myers, K.S. (ed.), Ovid Metamorphoses, Book XIV (Cambridge Greek and Latin Classics), Nueva York, Cambridge University Press, 2009, IX + 237 pp. ISBN 978-0-521-00793-1

Fil: Martínez Astorino, Pablo Leandro. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Estructura organizativa del Sistema de Gestión Integral de Documentos de archivo (SiGeID 1.0)

El nuevo contexto impone a las organizaciones la necesidad vital de disponer de adecuadas infraestructuras de comunicación, que les permitan conseguir un conocimiento real y suficiente del entorno. El presente artículo pretende mostrar la estructura organizativa del Sistema de Gestión Integral de Documentos de archivo SiGeID (1.0), como una herramienta informática que ayuda a las organizaciones empresariales al perfeccionamiento de la gestión de documentos. Dividido en tres módulos: Gestión y Seguridad Documental, Gestión de Archivo y Administración y Configuración, se tienen en cuenta además sus requerimientos funcionales y no funcionales