The city of Chemnitz in Saxony (Germany) building its new economic profile     

Andreas Bochmann  Achim Dresler  Wolf Tietze 《GeoJournal》1995,37(4):539-556

  相似文献   

Balance of tectonically accreted and subducted sediment at the Chile Triple Junction     

Jan H. Behrmann  Achim Kopf 《International Journal of Earth Sciences》2001,90(4):753-768

An active oceanic spreading ridge is being subducted beneath the South American continent at the Chile Triple Junction. Mass balance estimations to characterize temporal and spatial variations in the frontal accretion, or underplating and subduction of sediments since the Late Miocene, were made using seismic and drill-hole data. At 200 km north of the triple junction, almost 80% of the sediment on the downgoing Nazca plate are subducted. Sediment subduction rate decreases towards the triple junction because of a low in sedimentation rates as the flank of the spreading ridge approaches the trench. At the triple junction, the forearc is almost completely destroyed by spreading ridge collision and subduction erosion. Less than 12% of the available sedimentary input is accreted. South of the triple junction, where the spreading ridge passed 6 Ma ago, a large fraction (>60%) of the sediment on the incoming Antarctic plate has been scraped off and was frontally accreted to the Chile forearc. Spreading ridge subduction leaves a distinctive geological fingerprint, and has a large impact on the mass balance of the subduction zone. However, the high rates of change in the process may make this fingerprint hard to detect in fossil convergent orogens. In the ridge collision zone the sediment supplied to the trench, and the amount of sediment subducted, show strong and distinctive variations on a 1- to 5-million-year time scale. On a 10-million-year time scale, sediment subduction to the Earth's mantle is reduced by spreading ridge collision, caused by the need of the overriding forearc to regain a low angle of taper by frontal accretion.  相似文献   

A biogeochemical study of sediments from the eutrophic Lake Lugano and the oligotrophic Lake Brienz,Switzerland     

Achim Bechtel  Carsten J. Schubert 《Organic Geochemistry》2009,40(10):1100-1114

The biomarker composition and stable isotope (C, O) ratio values of organic matter (OM) and carbonate from sediment cores from the oligotrophic Lake Brienz and the eutrophic Lake Lugano (both in Switzerland) are compared, in order to obtain information about OM sources and transformation processes. Eutrophic conditions at Lake Lugano are reflected in elevated total organic carbon (TOC) content and hydrogen index (HI) values, as well as higher lipid concentrations. Parallel down core trends in δ¹³C values of TOC and calcite in the Lake Lugano sediments reflect bioproductivity cycles. Variations in δ¹⁸O values of calcite are consistent with changes in mean summer temperature over the time interval covered by the core. In contrast, such a correlation does not exist for Lake Brienz and there the stable isotope composition of calcite reflects its allochthonous origin. In the sediments of both lakes, fatty acid (FA) distributions and the composition of n-alkanols and n-alkanes indicate highly variable proportions of autochthonous OM sources (algae, zooplankton, bacteria) and OM from land plants. Enhanced in situ microbial synthesis during sediment deposition in Lake Lugano is suggested by the higher TOC-normalised concentrations of branched chain FAs (C₁₅–C₁₇), hopanoic acids and triterpenoid alcohols (i.e. tetrahymanol, diplopterol). Variations in the concentrations of cholesterol are related to contributions from zooplankton and/or green algae, while sitosterol concentrations reflect the input of vascular plants. Periods of increased input of OM from diatoms are evidenced by high 24-methylcholesta-5,22-dien-3β-ol (either epibrassicasterol or brassicasterol) and/or highly branched isoprenoid (HBI) alkenes concentrations. High relative concentrations of diplopterol in Lake Lugano sediments are consistent with the predominance of cyanobacteria commonly observed in eutrophic lakes. The presence of archeol and hydroxyarcheol in very low concentrations in the Lugano sediments argues for the activity of methanogens and/or anaerobic methanotrophs.Differences in OM degradation processes are reflected in higher chlorin index values in the Brienz sediments but higher saturated vs. unsaturated n-FAs in the core from Lugano. Higher concentrations of branched chain FAs and 16:1ω7 n-FA, as well as enhanced 18:1ω7/18:1ω9 n-FA, are consistent with enhanced bacterial biomass in the Lugano water column or sediments. The preservation of phytol seems to be enhanced in sediments with a high relative contribution of land plant OM. Major factors affecting OM accumulation in the lakes are differences in OM sources (i.e. terrestrial OM vs. autochthonous production), extent of bacterial activity and most likely oxygen availability in the water column.  相似文献   

GARSTEC—the Garching Stellar Evolution Code     

Achim Weiss  Helmut Schlattl 《Astrophysics and Space Science》2008,316(1-4):99-106

We describe the Garching Stellar Evolution Code. General features, treatment of the microphysics, details of the numerical solution, handling and particularities are discussed. The standard solar model serves as the most basic benchmark to test the accurateness of the code and is presented, too.  相似文献   

A large skull of Ichthyosaurus (Reptilia: Ichthyosauria) from the Lower Sinemurian (Lower Jurassic) of Frick (NW Switzerland)     

Michael W. Maisch  Achim G. Reisdorf  Rudolf Schlatter  Andreas Wetzel 《Swiss Journal of Geoscience》2008,101(3):617-627

  相似文献   

Recent ecological responses to climate variability and human impacts in the Nianbaoyeze Mountains (eastern Tibetan Plateau) inferred from pollen,diatom and tree-ring data   总被引：1，自引：0，他引：1  

Juliane Wischnewski  Ulrike Herzschuh  Kathleen M. Rühland  Achim Bräuning  Steffen Mischke  John P. Smol  Lily Wang 《Journal of Paleolimnology》2014,51(2):287-302

The Tibetan Plateau is a region that is highly sensitive to recent global warming, but the complexity and heterogeneity of its mountainous landscape can result in variable responses. In addition, the scarcity and brevity of regional instrumental and palaeoecological records still hamper our understanding of past and present patterns of environmental change. To investigate how the remote, high-alpine environments of the Nianbaoyeze Mountains, eastern Tibetan Plateau, are affected by climate change and human activity over the last ~600 years, we compared regional tree-ring studies with pollen and diatom remains archived in the dated sediments of Dongerwuka Lake (33.22°N, 101.12°E, 4,307 m a.s.l.). In agreement with previous studies from the eastern Tibetan Plateau, a strong coherence between our two juniper-based tree-ring chronologies from the Nianbaoyeze and the Anemaqin Mountains was observed, with pronounced cyclical variations in summer temperature reconstructions. A positive directional trend to warmer summer temperatures in the most recent decades, was, however, not observed in the tree-ring record. Likewise, our pollen and diatom spectra showed minimal change over the investigated time period. Although modest, the most notable change in the diatom relative abundances was a subtle decrease in the dominant planktonic Cyclotella ocellata and a concurrent increase in small, benthic fragilarioid taxa in the ~1820s, suggesting higher ecosystem variability. The pollen record subtly indicates three periods of increased cattle grazing activity (~1400–1480 AD, ~1630–1760 AD, after 1850 AD), but shows generally no significant vegetation changes during past ~600 years. The minimal changes observed in the tree-ring, diatom and pollen records are consistent with the presence of localised cooling centres that are evident in instrumental and tree-ring data within the southeastern and eastern Tibetan Plateau. Given the minor changes in regional temperature records, our complacent palaeoecological profiles suggest that climatically induced ecological thresholds have not yet been crossed in the Nianbaoyeze Mountains region.  相似文献   

Insights into Holocene relative sea-level changes in the southern North Sea using an improved microfauna-based transfer function     

Juliane Scheder  Friederike Bungenstock  Kristin Haynert  Anna Pint  Frank Schlütz  Peter Frenzel  Achim Wehrmann  Helmut Brückner  Max Engel 《第四纪科学杂志》2022,37(1):71-85

In light of global warming and rising relative sea level (RSL), detailed reconstructions of RSL histories and their controlling processes are essential in order to manage coastal-protection challenges. This study contributes to unravelling Holocene RSL change on the East Frisian North Sea coast in high resolution and with a new approach for the German Bight. For the first time, a transfer function (vertical error: 29.7 cm ? ~11% of the mean tidal range) for RSL change based on a combined training set of benthic foraminifers and ostracods from the back-barrier tidal basin of Spiekeroog is applied to the Holocene record of the back-barrier tidal basin of Norderney. The resulting RSL curve for the Norderney tidal basin is corrected for decompaction and shows a deceleration in RSL rise between 6000 and 5000 cal bp. The smallest possible error envelope (~1 m) results from the good suitability of salt-marsh layers between 5000 and 4000 cal bp. The RSL curve provides an approach towards the closure of the common data gap of peat-based curves for the southern North Sea related to a lack of basal peats in the youngest age range, and verifies regional differences in glacial isostatic adjustment.  相似文献