Climate change in southern South America during the last 51 ka based on geochemical analyses of Laguna Potrok Aike sediments

The climate archive Laguna Potrok Aike is located in a scarcely studied yet key area of the southern hemisphere. Recent studies on the role of the Southern Hemispheric Westerlies and the Southern Ocean circulation patterns in the global climate system stress the importance of this area. The Laguna Potrok Aike lacustrine sediment record covers the past 51 ka of environmental change. In order to capture the high variability in the climate system, high resolution analysis is particularly important. Therefore, aside from conventional methods and X-ray fluorescence scanning, infrared spectrometry, a relatively new method for analyzing sediment biogeochemistry, was applied. The Diffuse Reflectance Fourier Transform Infrared Spectrometry technique has proven to provide the most reliable calibration models for the analysis of the organic and carbonaceous fraction of the Laguna Potrok Aike sediments. For glacial sediments, paleoenvironmental reconstructions for Laguna Potrok Aike rely on proxies recording variations in organic versus clastic input to the lacustrine system. Increases in organic productivity (mainly aquatic moss growth and diatom blooms) may have been caused by ameliorations of the climatic conditions in the Laguna Potrok Aike area. At the same time, sediment availability for erosional processes would have been limited by the development of soils and vegetation cover. Intervals with more organic sediment compositions are often associated with periods of Antarctic warming (Antarctic A-events, the postglacial warming and the Younger Dryas chronozone). During intervals of highly clastic, coarse grained sediment we assume that lacking vegetation and erosion related to high waves and flash flood events increased sediment availability in the catchment and on the lake shore. The transport of this material to the lake center would have been facilitated by strong winds. The sediment is especially clastic and coarse grained during the presumably cold, arid and windy Oxygen Isotope Stage 2. Despite these conditions, the lake level must have remained relatively high during glacial conditions as inorganic carbonate is not precipitated until the end of the Late Glacial. Glacial high lake levels may be attributed to increased runoff over permafrost grounds, reduced evaporation due to colder temperatures and lacking influence of the Southern Hemispheric Westerlies. The southward shift of the Southern Hemispheric Westerlies over the latitudes of Laguna Potrok Aike is not assumed to have occurred prior to ca. 9.4 cal. ka BP; the onset of continuous inorganic carbonate precipitation. Throughout the Holocene the variability in the total inorganic carbon record shows the frequent lake level fluctuation probably related to shifts in the position of the Southern Hemispheric Westerlies

Guitar Studio

Music of the Renaissanc

elexiko – das elektronische, lexikografisch-lexikologische korpusbasierte Wortschatzinformationssystem : zur Neukonzeption, Erweiterung und Revision einzelner Angabebereiche

In diesem Beitrag werden wichtige Neukonzeptionen und umfangreiche Nachbearbeitungen einzelner Angabebereiche in elexiko erläutert. Die linguistische Konzeption dieser Angaben stellt eine Weiterentwicklung gegenüber der Konzeption dar, wie sie im Band „Grundfragen der elektronischen Lexikographie. elexiko – das Online-Informationssystem zum deutschen Wortschatz“ (2005) vorgelegt wurde. Betroffen sind z.B. die Angabebereiche der typischen Verwendungen, der sinn- und sachverwandten Wörter und der Besonderheiten des Gebrauchs.This paper presents extensive amendments to the original concept of elexiko, which has been published in the volume „Grundfragen der elektronischen Lexikographie. elexiko – das Online-Informationssystem zum deutschen Wortschatz“ (2005). These complement, for example, information on habitual syntagmatic patterns, sense-related terms, and pragmatics

Congo River sand and the equatorial quartz factory

A never solved problem in sedimentary petrology is the origin of sandstone consisting exclusively of quartz and most durable heavy minerals. The Congo River offers an excellent test case to investigate under which tectonic, geomorphological, climatic, and geochemical conditions pure quartzose sand is generated today. In both upper and lowermost parts of the catchment, tributaries contain significant amounts of feldspars, rock fragments, or moderately stable heavy minerals pointing at the central basin as the main location of the "quartz factory". In Congo sand, quartz is enriched relatively to all other minerals including zircon, as indicated by Si/Zr ratios much higher than in the upper continental crust. Selective elimination of old zircons that accumulated radiation damage through time is suggested by low percentages of grains yielding Archean U-Pb ages despite the basin being surrounded by Archean cratonic blocks. Intense weathering is documented by the lack of carbonate grains in sand and by dominant kaolinite and geochemical signatures in mud. In sand, composed almost entirely of SiO2, the weathering effect is masked by massive addition of quartz grains recycled during multiple events of basin inversion since the Proterozoic. Changes in mineralogical, geochemical, and geochronological signatures across Bas-Congo concur to suggest that approximately 10% of the sand supplied to the Atlantic Ocean is generated by rapid fluvial incision into the recently uplifted Atlantic Rise. The Congo River connects with a huge canyon similar to 30 km upstream of the mouth, and pure quartzose sand is thus funnelled directly toward the deep-sea to feed a huge turbidite fan. Offshore sediments on both sides of the canyon are not derived from the Congo River. They reflect mixed provenance, including illite-rich dust wind-blown from the arid Sahel and augite, hypersthene, and smectite ejected from volcanic centres probably situated along the Cameroon Line in the north. Because mixing of detritus from diverse sources and supply of polycyclic grains almost invariably occurs in the terminal lowland tract of a sediment-routing-system, no ancient sandstone can be safely considered as entirely first-cycle. Moreover, the abundance of pure quartzarenite in the rock record can hardly be explained by chemical weathering or physical recycling alone. The final cleansing of minerals other than quartz, zircon, tourmaline, and rutile requires one or more cycles of chemical dissolution during diagenesis, which operates at higher temperatures and over longer periods than weathering at the Earth's surface

Viscoelastic Behavior of Embroidered Scaffolds for ACL Tissue Engineering Made of PLA and P(LA-CL) After In Vitro Degradation

A rupture of the anterior cruciate ligament (ACL) is the most common knee ligament injury. Current applied reconstruction methods have limitations in terms of graft availability and mechanical properties. A new approach could be the use of a tissue engineering construct that temporarily reflects the mechanical properties of native ligament tissues and acts as a carrier structure for cell seeding. In this study, embroidered scaffolds composed of polylactic acid (PLA) and poly(lactic-co-"-caprolactone) (P(LA-CL)) threads were tested mechanically for their viscoelastic behavior under in vitro degradation. The relaxation behavior of both scaffold types (moco: mono-component scaffold made of PLA threads, bico: bi-component scaffold made of PLA and P(LA-CL) threads) was comparable to native lapine ACL. Most of the lapine ACL cells survived 32 days of cell culture and grew along the fibers. Cell vitality was comparable for moco and bico scaffolds. Lapine ACL cells were able to adhere to the polymer surfaces and spread along the threads throughout the scaffold. The mechanical behavior of degrading matrices with and without cells showed no significant differences. These results demonstrate the potential of embroidered scaffolds as an ACL tissue engineering approach. © 2019 by the authors. Licensee MDPI, Basel, Switzerland