Korallen,Fischer und Touristen

Ocean Dynamics - Als Folge von natürlichen und anthropogenen Störungen sind Korallenriffe weltweit gefährdet. Im vorliegenden Vortrag wird von zwei sehr wesentlichen menschlichen...     

Isotopic fingerprints on lacustrine organic matter from Laguna Potrok Aike (southern Patagonia, Argentina) reflect environmental changes during the last 16,000 years

A combination of carbon-to-nitrogen ratios (TOC/TN), Rock Eval-analyses, and stable isotope values of bulk nitrogen (δ¹⁵N) and organic carbon (δ¹³C_org) was used to characterize bulk organic matter (OM) of a piston core from the Patagonian maar lake Laguna Potrok Aike (Argentina) for the purpose of palaeoenvironmental reconstruction. Sedimentary data were compared with geochemical signatures of potential OM sources from Laguna Potrok Aike and its catchment area to identify the sources of sedimentary OM. Correlation patterns between isotopic data and TOC/TN ratios allowed differentiation of five distinct phases with different OM composition. Before 8470 calibrated ¹⁴C years before present (cal. yrs BP) and after 7400 cal. yrs BP, isotopic and organo-geochemical fingerprints indicate that the sediments of Laguna Potrok Aike consist predominantly of soil and diatom OM with varying admixtures of cyanobacterial and aquatic macrophyte OM. For a short phase of the early Holocene (ca. 8470–7400 cal. yrs BP), however, extremely high input of soil OM is implied by isotopic fingerprints. Previous seismic and geochronological results indicate a severe lake-level drop of 33 m below present-day shortly before 6590 cal. yrs BP. It is suggested that this lake level drop was accompanied by increased erosion of shore banks and channel incision enhancing soil OM deposition in the lake basin. Thus, isotopic data can be linked to hydrological variations at Laguna Potrok Aike and allow a more precise dating of this extremely low lake level. An isotopic mixing model was used including four different sources (soil, cyanobacteria, diatom and aquatic macrophyte OM) to model OM variations and the model results were compared with quantitative microfossil data.     

Evaluation of seismic response of bridges under asynchronous excitation and comparisons with Eurocode 8-2 provisions

The paper aims to evaluate the way Eurocode 8 treats the consideration of asynchronous earthquake ground motion during the seismic design of bridges, and to discuss alternative solutions for cases wherein existing provisions do not lead to satisfactory results. The evaluation of EC8-2 new provisions and simplified methods is performed through comparison with a more refined approach whereas an effort is made to quantitatively assess the relative importance of various design and analysis assumptions that have to be made when spatial variability of ground motion is taken into consideration, based on the study of the dynamic response of 27 different bridges. It is concluded that, despite the complexity of the problem, there are specific cases where EC8 provisions can be safely and easily applied in practice, while in other cases ignoring the effect of asynchronous excitation or performing simplified calculations can significantly underestimate the actual seismic demand.     

Spatio-temporal dynamics of suspended matter properties and bacterial communities in the back-barrier tidal flat system of Spiekeroog Island

Back-barrier tidal flat systems are characterized by basins and inlets through which water is exchanged with the coastal sea by tidal water movements. The hydrographic and morphometric properties at the inlets and in the basins vary considerably, but there is little information available how biogeochemical properties in the water column at these different sites respond to these differences. Therefore, we investigated tidal dynamics of suspended particulate matter (SPM), particulate and dissolved organic carbon (DOC), chlorophyll a, phaeopigments, numbers of particle-associated (PA) and free-living bacteria (FL), bacterial biomass production, and concentrations of dissolved manganese (Mn). Samples were taken at the surface, a mid-depth and 1 m above the bottom at a fixed station at the inlet and in the basin of the Spiekeroog back-barrier tidal flat system in the German Wadden Sea. Five tidal cycles representative for typical seasonal situations, January (winter), April and May (late spring bloom), July (summer), and November (late fall) were studied in 2005 and 2006. In July, processes related to phytoplankton dynamics and bacterial decomposition were much more enhanced in the basin, whereas in April, these processes were enhanced at the inlet but were particularly low within the basin itself. The low values within the basin were a result of the settled phytoplankton spring bloom and represent a rather short period at the decline of this bloom. In November and January, differences were much less pronounced than during the growing season and restricted mainly to SPM and PA bacteria, exhibiting higher values in the basin. FL bacteria, DOC, and dissolved Mn exhibited different patterns and much less differences between the two stations, indicating that biogeochemical processes in the dissolved phase were controlled by different factors than PA biogeochemical processes. These differences reflect the retentive properties of the basin for particles and PA biogeochemical processes, particularly during the growing season, and in general emphasize the high productivity of back-barrier tidal flat systems.     

First results on determination of cosmogenic 36Cl in limestone from the Yenicekale Complex in the Hittite capital of Hattusha (Turkey)

We have measured ³⁶Cl in three rock surfaces of the Yenicekale building complex in Hattusha (Bo?azköy, Turkey). Hattusha was the capital of Hittite Empire which lasted from about 1650/1600 to 1200 BC. At Yenicekale, Hittite masons flattened the summit of an outcropping limestone knoll to form an artificial platform as the foundation for a building. Next they built a circuit wall along the lateral precipices of the flattened bedrock platform. We took one sample from the limestone bedrock platform and two samples from limestone building blocks of the circuit wall for cosmogenic ³⁶Cl analysis. Calculated exposure ages are 20 ± 1 ka for the sample from the bedrock platform and 24 ± 1 ka and 52 ± 2 ka for the circuit wall blocks. These exposure ages are significantly older than the age expected based on the estimated time of construction between 3.2 ka and 3.7 ka. We conclude that the sampled surfaces contain significant inherited cosmogenic ³⁶Cl. We cannot directly determine exposure ages for the building complex based on these three samples. On the other hand we may use the measured concentrations to determine how much of the rock was removed from the platform during flattening. To this end we modeled the variation of ³⁶Cl production with depth at Yenicekale using the results from the bedrock sample. We conclude that the Hittite masons removed only around 3 m from top of the limestone block. This means that the volume of rock removed from the bedrock platform is significantly less than the volume in the circuit wall atop the platform. They did not gain enough rock from this flattening to make the building. In agreement with this, the first results of our detailed microfacies analysis indicate that many of the building blocks are not of the same facies as the underlying limestone and must have been quarried elsewhere. Although we were not able to exposure date the Yenicekale complex due to the presence of inherited ³⁶Cl, our data suggest that Hittite masons excavated (most of) the building stones not at Yenicekale, but in quarries outside of Hattusha and then transported them to the construction site. These quarries have not yet been identified.     

Late Pleistocene dust deposition in the Patagonian steppe - extending and refining the paleoenvironmental and tephrochronological record from Laguna Potrok Aike back to 55 ka

Paleoenvironmental records extending well into the last glacial period are scarce in the steppe regions of southern South America. Here, we present a continuous record for the past 55 ka from the maar lake Laguna Potrok Aike (51°58′ S, 70°23′ W, southern Patagonia, Argentina). Previous studies on a sedimentary core from a lake level terrace near the northern margin of the lake covered parts of Oxygen Isotope Stage (OIS) 3 (59–29 ka) whereas a second core from the centre of the basin comprised the last 16 ka. Tephrostratigraphical constraints and OSL ages from a third core located below the lake level terrace provide the crucial piece to close the gap between the previous coring sites. High-resolution XRF and magnetic susceptibility as well as grain size data indicate a positive hydrological balance alongside with relatively high aeolian activity during the glacial which is contemporaneous with increased dust fluxes in Antarctica. This is therefore the first evidence for contemporaneity of aeolian deposition in both the target area (Antarctica) and in the major source area of Patagonia. During the Holocene climatic conditions driving sediment deposition seem to have been more variable and less dominated by wind compared to glacial times. The identification of a minor lake level lowering at approximately 4 cal ka BP allows to refine earlier paleoenvironmental reconstructions for the Holocene. Within error margins the OSL ages are consistent with published radiocarbon-dated records offering hence a valuable tool for further studies of the sediments from Laguna Potrok Aike. The new chronology confirms the age of three tephra layers up to now only found in Laguna Potrok Aike sediments and ascribed to OIS 3.     

Why do people not learn from flood disasters? Evidence from Vietnam’s northwestern mountains

This article explores how the causes and impacts of a flood event as perceived by local people shape immediate responses and future mitigation efforts in mountainous northwest Vietnam. Local flood perception is contrasted with scientific perspectives to determine whether a singular flood event will trigger adjustments in mitigation strategies in an otherwise rarely flood-affected area. We present findings from interdisciplinary research drawing on both socioeconomic and biophysical data. Evidence suggests that individual farmers?? willingness to engage in flood mitigation is curbed by the common perception that flooding is caused by the interplay of a bundle of external factors, with climatic factors and water management failures being the most prominent ones. Most farmers did not link the severity of flooding to existing land use systems, thus underlining the lack of a sense of personal responsibility among farmers for flood mitigation measures. We conclude that local governments cannot depend on there being a sufficient degree of intrinsic motivation among farmers to make them implement soil conservation techniques to mitigate future flooding. Policy makers will need to design measures to raise farmers?? awareness of the complex interplay between land use and hydrology and to enhance collective action in soil conservation by providing appropriate incentives and implementing coherent long-term strategies.