Search results for "550 Geowissenschaften"

The effects of environment on Arctica islandica shell formation and architecture

2017

Mollusks record valuable information in their hard parts that reflect ambient environmental conditions. For this reason, shells can serve as excellent archives to reconstruct past climate and environmental variability. However, animal physiology and biomineralization, which are often poorly un- derstood, can make the decoding of environmental signals a challenging task. Many of the routinely used shell-based proxies are sensitive to multiple different environmental and physiological variables. Therefore, the identification and in- terpretation of individual environmental signals (e.g., water temperature) often is particularly difficult. Additional prox- ies not influenced by multiple enviro…

Multi-phase classification by a least-squares support vector machine approach in tomography images of geological samples

2016

Abstract. Image processing of X-ray-computed polychromatic cone-beam micro-tomography (μXCT) data of geological samples mainly involves artefact reduction and phase segmentation. For the former, the main beam-hardening (BH) artefact is removed by applying a best-fit quadratic surface algorithm to a given image data set (reconstructed slice), which minimizes the BH offsets of the attenuation data points from that surface. A Matlab code for this approach is provided in the Appendix. The final BH-corrected image is extracted from the residual data or from the difference between the surface elevation values and the original grey-scale values. For the segmentation, we propose a novel least-squar…

Microwear textures associated with experimental near-natural diets suggest that seeds and hard insect body parts cause high enamel surface complexity…

2022

In mammals, complex dental microwear textures (DMT) representing differently sized and shaped enamel lesions overlaying each other have traditionally been associated with the seeds and kernels in frugivorous diets, as well as with sclerotized insect cuticles. Recently, this notion has been challenged by field observations as well as in vitro experimental data. It remains unclear to what extent each food item contributes to the complexity level and is reflected by the surface texture of the respective tooth position along the molar tooth row. To clarify the potential of seeds and other abrasive dietary items to cause complex microwear textures, we conducted a controlled feeding experiment wi…

Halogen activation in the plume of Masaya volcano: field observations and box model investigations

2020

Volcanic emissions are a source of halogens in the atmosphere. Rapid reactions convert the initially emitted hydrogen halides (HCl, HBr, and HI) into reactive species such as BrO, Br2, BrCl, ClO, OClO, and IO. The activation reaction mechanisms in the plume consume ozone (O3), which is entrained by ambient air that is mixed into the plume. In this study, we present observations of the oxidation of bromine, chlorine, and iodine during the first 11 min following emission, examining the plume from Santiago crater of the Masaya volcano in Nicaragua. Two field campaigns were conducted: one in July 2016 and one in September 2016. The sum of the reactive species of each halogen was determined by g…

Development of a Method for Anodic Degradation of Lignin for the Analysis of Paleo‐Vegetation Proxies in Speleothems

2022

From omniscient narrator to involved participants: Places and spaces “activated” in the EHEC O104:H4 crisis 2011

2020

Crisis management is often conceived from the position of an omniscient narrator, albeit the general consensus that crises are subjectively interpreted and experienced. The paper makes an analytical attempt to de-homogenize the notion of crisis. We argue that the perception of crises differs and present a spatial perspective on crisis to foreground the positionality of different actor groups. By referring to the EHEC outbreak 2011 in Germany, we explore two spatial configurations that seem to be of particular relevance: territories embedded in a nested hierarchy and topologies of interconnected places. State authorities think and act strongly in terms of territorial borders and along sector…

Opposite trends in Holocene speleothem proxy records from two neighboring caves in Germany : a multi-proxy evaluation

2021

Chemistry-climate interactions of aerosol nitrate from lightning

2016

Abstract. Lightning represents one of the dominant emission source for NOx in the troposphere. The direct release of oxidised nitrogen in the upper troposphere does not only affect ozone formation, but also chemical and microphysical properties of aerosol particles in this region. This study investigates the direct impact of LNOx emissions on upper tropospheric nitrate using a global chemistry climate model. The simulation results show a substantial influence of the lightning emissions on the mixing ratios of nitrate aerosol in the upper troposphere of more than 50%. In addition to the impact on nitrate, lightning substantially affects the oxidising capacity of the atmosphere with substanti…

Dynamic pressure variations in the lower crust caused by localized fluid-induced weakening

2022

When continents collide, the Earth’s crust experiences structural and metamorphic transformations that control the geodynamic evolution of the orogen. Metamorphism of dry, lower crust requires fluid supply and produce mechanically weaker rocks. Metamorphism is often localized in shear-zones, which provide the available fluid pathways. Several field-based studies show that shear zone development is preceded by brittle faults, frequently portraying evidence for seismic slip rates and introduction of externally derived fluids. However, despite the extensive documentation of lower crustal metamorphism and associated deformation features, a unifying model coupling deformation to fluid …

Combining inorganic and organic carbon stable isotope signatures in the Schwalbenberg Loess-Palaeosol-Sequence near Remagen (Middle Rhine valley, Ger…

2020

Western Central European Loess-Palaeosol-Sequences (LPS) provide valuable terrestrial records of palaeoenvironmental conditions, which formed in response to variability in the North Atlantic climate systems. Over the last full glacial cycle (∼130 ka), climate oscillations within these systems are best documented in deep sea- and ice cores; the responses of terrestrial systems are not yet fully understood. A better understanding of metabolism governing input and output variables of organic- and inorganic C pools is, however, crucial for investigating landscape-atmospheric feedback processes and in particularly, for understanding the formation of calcareous LPS as environmental archives. Here…