Dewatering of an unvegetated muddy tidal flat during exposure—Desiccation or drainage?

An unvegetated muddy tidal flat was sampled to determine the changes in surface pore water content and salinity during exposure. Local evaporation accounted for 61% of the upper intertidal surface salinity, with evaporation rates increasing salinity as high as 2.2‰ per hour. In contrast, only 37% of the decrease in pore water content was attributed to evaporative processes. This suggests that drainage (a combination of porosity and permeability) controlled the water content rather than local evaporative conditions.     

Ca isotopes in refractory inclusions

We report measurements of the absolute isotope abundance of Ca in Ca-Al-rich inclusions from the Allende and Leoville meteorites. Improved high precision measurements are reported also for ⁴⁶Ca. We find that nonlinear isotope effects in Ca are extremely rare in these inclusions. The absence of nonlinear effects in Ca, except for the effects in FUN inclusions, is in sharp contrast to the endemic effects in Ti. One fine-grained inclusion shows an excess of ⁴⁶Ca of (7 ± 1)%., which is consistent with addition of only ⁴⁶Ca or of an exotic (1) component with ⁴⁶Ca¹ ~ ⁴⁸Ca¹. FUN inclusion EK-1-4-1 shows a small ⁴⁶Ca excess of (3.3 ± 1.0)%.; this confirms that the exotic Ca components in EK-1-4-1 were even more deficient in ⁴⁶Ca relative to ⁴⁸Ca than is the case for normal Ca. The Ca in the Ca-Al-rich inclusions shows mass dependent isotope fractionation effects (as deduced from the absolute ${}^{40}\text{Ca}{}^{44}\text{Ca}$) which have a range from ?3.8 to +6.7%. per mass unit difference. This range is a factor of 20 wider than the range previously established for bulk meteorites and for terrestrial and lunar samples. Ca and Mg isotope fractionation effects in the Ca-Al-rich inclusions are common and attributed to kinetic isotope effects which imply the production of the inclusions by complex sequences of condensation, vaporization and recondensation. A correlation was found between Ca and Mg isotope fractionation effects and inclusion type. A possible correlation between isotope fractionation and rare earth element abundance patterns is discussed.     

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Estuaries and Coasts -     

Use of biological traits for interpreting functional relationships in large rivers

Altogether 64 predominantly biological traits were coded for more than 600 macroinvertebrate species from European rivers. The main question was: Are biological traits able to reflect “biological functionality” in large rivers and if so, is it possible to deduce an assessment system based on functionality? Analysis of the raw trait structure of all species indicates that these traits are not completely independent from their higher systematic units. To avoid mis-interpretations when judging from mixtures of habitats (β-biocoenosis) we used for our investigations only sample series from -biocoenosis, pre-tested by a mathematical criterion of homogeneity. Within -biocoenosis, traits are shown to be able to compensate for drastic changes with respect to species number and species composition along a river continuum, demonstrating their functional quality. Long-term changes in the trait and species structures of German waterways were studied using multivariate methods, based on an analysis of 142 sampling series. A shift from traits typical for K-strategists to traits typical for r-strategists was detected to be the main background variable. The rK-strategy is regarded as a true functional character of species. We calculated the relative positions of all trait-coded species on this rK-scale, and plotted the functional diversity of our samples against the structural diversity of the species from several river systems. Rivers extremely dominated by r-strategists show a deficit in functional diversity. Rivers dominated by K-strategists also show deficits, possibly in concordance with modern ecological theories such as the intermediate disturbance theory. The quantitative proportions of extreme r- to K-Strategists in -biocoenosis can be used as a general disturbance measure.     

Saturn: UBV photoelectric pinhole scans of the disk

UBV pinhole scans of the Saturn disk have been made with a photoelectric area-scanning photometer. Limb profiles, spaced parallel to the equator, were obtained over the entire southern hemisphere of the planet. Saturn was found to exhibit strong limb brightening in the ultraviolet, moderate limb brightening at blue wavelengths, and strong limb darkening in the visual region of the spectrum. Latitudinal variations in the disk profiles were found. In general, the degree of limb brightening decreases towards the polar region. Pronounced asymmetry is apparent in the disk profiles in each color. The sunward limb is significantly brighter than the opposite limb. This asymmetry depends on phase angle; approaching zero at opposition, it reaches a maximum near quadrature. Our observations are interpreted using an elementary radiative transfer model. The Saturn atmosphere is approximated by a finite homogeneous layer of isotropically scattering particles overlying a Lambert scattering haze or cloud layer. The reflectivity of the haze or clouds is a strongly dependent function of wavelength. Our best-fitting model consists of a clear H₂ layer of column density ～31 km-am above the haze or clouds; the maximum permitted H₂ column density is ～46 km-am. The H₂ column density above the equatorial region appears to be less than at temperate latitudes. The phase-dependent asymmetry in the disk profiles is a natural consequence of the scattering geometry. Our results are consistent with current knowledge of the Saturn atmosphere.     

Turbulence Structure in the Wake Region of a Meteorological Tower

A meteorological tower significantly modifies the air flow, the mean windspeed and wind direction as well as the turbulencestructure of the air. Suchchanges can be noticed in particular in the wake region of the tower.Measurementson the 200 m tower ofForschungszentrum Karlsruhewere carried outusing Solent sonic anemometers in the lee of the towerand cup anemometers on both sides.In the wake region, spectral energydensity is increased in the high-frequency range. Superposition of this disturbance spectrum on the undisturbedspectrum yields a `knee' in the resulting spectrum. In the case of low turbulence intensity with stable stratification,a plateau with a constant energy content is observed in front of the knee.This effect is caused by the new production of turbulence energy from the mean flow as well as by an energy transfer fromlarger to smaller vortices. Power spectra in strongly stable conditionsshow a more rapid decrease of intensity in the region where the inertialsubrange is expected.The relevant scales of wake turbulence are derived from the maximum of the disturbance spectrum.Locations of the high-frequency peak do not depend on atmospheric stability,but are controlled mainly by mean wind speed.Apart from the reduction of the mean wind speed, the spectra and cospectra exhibit a strong anisotropy for such cases.The results demonstrate the significant influence of a tower on turbulence spectra in the wake region.     

Cathodoluminescence, electron microscopy, and Raman spectroscopy of experimentally shock-metamorphosed zircon

Thorough understanding of the shock metamorphic signatures of zircon could be the basis for the use of this mineral as a powerful tool for the study of old, deeply eroded, and metamorphically overprinted impact structures and formations. This study of the cathodoluminescence (CL) and Raman spectroscopic signatures of experimentally (20-60 GPa) shock-metamorphosed zircon single crystals contributes to the understanding of high-pressure microdeformation in zircon. For all samples, an inverse relationship between the brightness of the backscattered electron (BSE) signal and the corresponding cathodoluminescence intensity was observed. The unshocked sample shows crosscutting, irregular fractures. The 20 GPa sample displays some kind of mosaic texture of CL brighter and darker domains, but does not exhibit any shock metamorphic features in BSE or CL images. The 40 GPa sample shows a high density of lamellar features, which might be explained by the phase transformation between zircon- and scheelite-structure phases of zircon and resulting differences in the energy levels of the activator elements. The CL spectra of unshocked and shocked (20, 40, and 60 GPa) zircon samples are dominated by narrow emission lines and broad bands in the region of visible light and in the near-UV range. The emission lines result from rare earth element activators and the broad bands might be associated with lattice defects. Raman spectra revealed that the unshocked and 20 GPa samples represent zircon-structure material, whereas the 40 GPa sample yielded additional peaks with relatively high peak intensities, which are indicative of the presence of the scheelite-type high-pressure phase. The 60 GPa sample has a Raman signature that is similar to that of an amorphous phase, in contrast to the observations of an earlier TEM study that the crystalline scheelite-structure phase is stable at this shock pressure. The 60 GPa Raman signature cannot be explained at this stage. The results show a clear dependence of the CL and Raman properties of zircon on shock pressure, which confirm the possible usage of these methods as shock indicators.     

Interstitial flow through preferential flow paths in the hyporheic zone of the Oberer Seebach,Austria

We investigated interstitial flow velocities in the Oberer Seebach, Austria, with NaCl tracer injections at a sediment depth of 30 cm to estimate the hydraulic conditions experienced by invertebrates inhabiting the hyporheic zone. Flow velocity measured with tracers is taken as travel time of the water along a straight line between injection and sampling points, although the water flows around sediment particles, and thus travels a somewhat longer distance. From sections of stream sediment in which the interstitial spaces were replaced by concrete, we estimated that this difference amounts, on average, to 27% and used this factor to correct the results of our velocity measurements. Corrected interstitial water velocities ranged from 0.01 to 1.32 cm s^-1 and were independent of surface discharge. We also studied spatial flow patterns in the bed sediments with long-term tracer injections. The three-dimensional distribution of tracer concentrations 24 hours after the start of the injection indicated that interstitial water preferentially flows in a complex network of areas of high hydraulic connectivity. Reynolds numbers for flow in the hyporheic pore space ranged from 0.1 to 489, implying that the flow environment varies from laminar up to the zone of transition to turbulent flow. Therefore, invertebrates may have a size-related active choice of areas where either friction drag or pressure drag predominates. The consequence of flow patterns, such as those observed in our study, is that small-scale variability of hydraulic conditions may be an important determinant of the patchy invertebrate distribution in bed sediments.     

A new model order reduction strategy adapted to nonlinear problems in earthquake engineering

Earthquake dynamic response analysis of large complex structures, especially in the presence of nonlinearities, usually turns out to be computationally expensive. In this paper, the methodical developments of a new model order reduction strategy (MOR) based on the proper orthogonal decomposition (POD) method as well as its practical applicability to a realistic building structure are presented. The seismic performance of the building structure, a medical complex, is to be improved by means of base isolation realized by frictional pendulum bearings. According to the new introduced MOR strategy, a set of deterministic POD modes (transformation matrix) is assembled, which is derived based on the information of parts of the response history, so‐called snapshots, of the structure under a representative earthquake excitation. Subsequently, this transformation matrix is utilized to create reduced‐order models of the structure subjected to different earthquake excitations. These sets of nonlinear low‐order representations are now solved in a fractional amount of time in comparison with the computations of the full (non‐reduced) systems. The results demonstrate accurate approximations of the physical (full) responses by means of this new MOR strategy if the probable behavior of the structure has already been captured in the POD snapshots. Copyright © 2016 The Authors. Earthquake Engineering & Structural Dynamics Published by John Wiley & Sons Ltd.