Impact lithologies and their emplacement in the Chicxulub impact crater: Initial results from the Chicxulub Scientific Drilling Project,Yaxcopoil, Mexico

Abstract— The Chicxulub Scientific Drilling Project (CSDP), Mexico, produced a continuous core of material from depths of 404 to 1511 m in the Yaxcopoil‐1 (Yax‐1) borehole, revealing (top to bottom) Tertiary marine sediments, polymict breccias, an impact melt unit, and one or more blocks of Cretaceous target sediments that are crosscut with impact‐generated dikes, in a region that lies between the peak ring and final crater rim. The impact melt and breccias in the Yax‐1 borehole are 100 m thick, which is approximately 1/5 the thickness of breccias and melts exposed in the Yucatán‐6 exploration hole, which is also thought to be located between the peak ring and final rim of the Chicxulub crater. The sequence and composition of impact melts and breccias are grossly similar to those in the Yucatán‐6 hole. Compared to breccias in other impact craters, the Chicxulub breccias are incredibly rich in silicate melt fragments (up to 84% versus 30 to 50%, for example, in the Ries). The melt in the Yax‐1 hole was produced largely from the silicate basement lithologies that lie beneath a 3 km‐ thick carbonate platform in the target area. Small amounts of immiscible molten carbonate were ejected with the silicate melt, and clastic carbonate often forms the matrix of the polymict breccias. The melt unit appears to have been deposited while molten but brecciated after solidification. The melt fragments in the polymict breccias appear to have solidified in flight, before deposition, and fractured during transport and deposition.     

Secondary dispersion patterns of fluoride in the osor area,Province of Gerona,Spain

The distribution of fluoride in spring and stream waters, stream sediments and soils of the Osor district, Province of Gerona, northeastern Spain, has been studied. Fluoride was determined by use of a fluoride-sensitive electrode. This potentiometric method has been found useful for geochemical exploration for fluorite because of its simplicity and high sensitivity.Investigations of the fluoride contents of natural waters and stream sediments resulted in the discovery of new fluorite mineralizations.Secondary dispersion patterns of soils have been studied. Different analytical procedures to extract the fluoride have been used. The application of the methods in geochemical exploration surveys is discussed.     

Effect of enhanced water exchange on ecosystem functions in backwaters of an urban floodplain

This study evaluated the effects of a controlled surface water connectivity scheme on several backwaters in an urban floodplain within the city limits of Vienna, the Upper Lobau. A phosphorus budget and ecosystem metabolism measurements were used to assess the reaction of two trophically distinct floodplain backwater sections on changed connectivity conditions. The surface water connection led to a reduction of the retention times in the backwater system. The water column nutrient concentrations in the individual backwater sections approached those of the source water body. The significance of these effects, however, depends on the historical and current trophic situation of the respective water bodies. Generally, the surface water connectivity introduced particulate phosphorus export up to 30% increase over the influent loading and dissolved phosphorus up to 14% increase over the influent loading. However, in sections with submersed macrophyte development, which provided enhanced filtering capacities for particulate matter, sediment and phosphorus accumulation rates were increased. At the same time, water transparency increased resulting in a positive feedback supporting further macrophyte development. Based on these findings, the evaluation of restoration measures in urban floodplains needs to consider the spatial and temporal dynamics of nutrients and ecosystem processes such as gross primary production and community respiration to predict long-term development.     

Measurements of meteor smoke particles during the ECOMA-2006 campaign: 2. Results

The first sounding rocket of the European ECOMA-project (ECOMA, Existence and Charge state Of Meteoric smoke particles in the middle Atmosphere) was launched on 8 September 2006. Measurements with a new particle detector described in the companion paper by Rapp and Strelnikova [2008. Measurements of meteor smoke particles during the ECOMA-2006 campaign: 1. Particle detection by active photoionization. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.06.002] clearly showed meteor smoke particle (MSP) signatures in both data channels. The data channels measure particles directly impacting on the detector electrode and photoelectrons from the particles actively created using ionization by the UV-photons of a xenon-flashlamp. Measured photoelectron currents resemble model expectations of the shape of the MSP layer almost perfectly, whereas derived number densities in the altitude range 60–90 km are larger than model results by about a factor of 5. Given the large uncertainties inherent to both model and the analysis of our measurements (e.g., the composition of the particles is not known and must be assumed) we consider this a satisfactory agreement and proof that MSPs do extend throughout the entire mesosphere as predicted by models. The measurements of direct particle impacts revealed a confined layer of negative charge between 80 and 90 km. This limited altitude range, however, is quantitatively shown to be the consequence of the aerodynamics of the rocket flight and does not have any geophysical origin. Measured charge signatures are consistent with expectations of particle charging given our own measurements of the background ionization. Unfortunately, however, a contamination of these measurements from triboelectric charging cannot be excluded at this stage.     

Feed forward neural network and interpolation function models to predict the soil and subsurface sediments distribution in Bam,Iran

An application of the artificial neural network (ANN) approach for predicting mean grain size using electric resistivity data from Bam city is presented. A feed forward back propagation network was developed employing 45 sets of input data. The input variables in the ANN model are the electrical resistivity, water table as a Boolean value and depth; the output is the mean grain size. To demonstrate the authenticity of this approach, the network predictions are compared with those from interpolation methods and the same data. This comparison shows that the ANN approach performs better results. The predicted and observed mean grain size values were compared and show high correlation coefficients. The ANN approach maps show a high degree of correlation with well data based grain size maps and can therefore be used conservatively to better understand the influence of input parameters on sedimentological predictions.     

The Ecology of a Novel Symbiosis Between a Marine Peritrich Ciliate and Chemoautotrophic Bacteria

Abstract. A symbiosis between a sessile colonial ciliate, Zoothamnium niveum HEMPRICH & EHRENBERG. 1831. and chemolithoautotrophic bacteria oxidizing reduced sulfur compounds is described. The ciliates and their ectosymbionts occur on mangrove peat in the Caribbean. The feather-shaped ciliate colonies expand and contract, thus exposing the microbes alternately to oxygenated water above and sulfidic water within the boundary layer developed on the surface of the highly sulfidic peat. The symbioticciliates colonize sites with high sulfide flux where the microbial surface mat has been disturbed and grow there until the microbe mat re-establishes itself.     

Labrador Sea convection and subpolar North Atlantic Deep Water export in the SODA assimilation model

Labrador Sea convection was most intense and reached the greatest depths in the early 1990s, followed by weaker, shallower, and more variable convection after 1995. The Simple Ocean Data Assimilation (SODA) version 2.0.2/2.0.4 assimilation model is used to explore convective activity in the North Atlantic Ocean for the period from 1992 to 2007. Hydrographic conditions, which are relatively well observed during this period, are used to compare modeled and observed winter mixed-layer depths and water mass anomalies in relation to Deep Western Boundary Current transports and meridional overturning circulation (MOC) changes at the exit of the subpolar basin. The assimilation differs markedly from local observations in the March mixed-layer depth, which represents deep convection and water mass transformation. However, mean MOC rates at the exit of the subpolar gyre, forced by stratification in the mid-latitudes, are similar to estimates based on observations and show no significant decrease during the 1992–2007 period. SODA reproduces the deep Labrador Sea Water formation in the western North Atlantic without any clear indication of significant formation in the Irminger Sea while the lighter upper Labrador Sea Water density range is reached in the Irminger Sea in the 1990s, in agreement with existing assumptions of deep convection in the Irminger Sea and also supported by computed lag correlations with the Labrador Sea. Deep Water transformation mainly takes place in the eastern North Atlantic. The introduction of CFC-11 into the SODA model as a tracer reproduces the mean and multiyear variations of observed distributions.