Conspicuous sediment structures in fossil beach deposits (southern Tenerife, Canary Islands, Spain): paleoliquefaction features versus biogenic origin

Tubular-shaped concretions and concretionary dykes occur in Holocene fossil beach deposits between the township of El Médano and Punta Roja in southern Tenerife, Canary Islands. These sediment structures have been interpreted either as the result of (a) the interaction between hot ignimbrites that overflowed wet beaches; (b) fast accumulation of beach sands on hot and degassing ignimbrites; (c) paleoliquefaction caused by an earthquake (seismites). Based on the interpretation as seismites, an intense paleoearthquake with a moment magnitude of M = 6.8 was proposed to be responsible for the generation of the paleoliquefaction structures. However, we here reinterpret the sedimentary structures in question using the general criteria diagnostic for rhizocretions and root tubules with respect to their orientation, size, branching system, and style of cementation and, thus, consider them, to be of biogenic origin.     

Protein carbonyls and antioxidant defenses in corkwing wrasse (Symphodus melops) from a heavy metal polluted and a PAH polluted site

The use of fish in environmental monitoring has become increasingly important in recent years as anthropogenic substances, many of which function as prooxidants, are accumulating in aquatic environments. We have measured a battery of antioxidant defenses as a measure of oxidative status, as well as protein carbonylation as a measure of oxidative damage, in corkwing wrasse (Symphodus melops) captured near a disused copper mine, where water and sediment are contaminated with heavy metals, and an aluminum smelter, a site contaminated with PAHs. Results were compared to two different reference sites. Fish at the heavy metal site had lower glucose-6-phosphate dehydrogenase activity and elevated protein carbonyls (1.8 times) compared to fish from the reference site. At the PAH site, EROD was increased 2-fold, while total glutathione and methemoglobin reductase concentration, were decreased. No differences were seen in protein carbonyl levels at the PAH site. Measures of both antioxidant defenses and oxidative damage should be used when assessing effects of xenobiotics on oxidative stress in fish species.     

The curse of physiology—challenges and opportunities in the interpretation of geochemical data from mollusk shells

Physiology corrupts geochemical records of mollusk shells in many ways, e.g., by actively controlling the incorporation of trace elements in the skeleton. However, the effects of variable biomineralization rates and growth cessation have largely remained unconsidered. Mediated by endogenous timekeeping mechanisms, mollusks stop growing skeletal material on a regular basis ranging from ultradian to annual timescales. During growth cessation, the shells do not record environmental conditions. Shell growth also stops when environmental conditions are beyond the physiological tolerance of the organism, e.g., above and below genetically determined, species-specific thermal extremes where shell growth slows and eventually ceases. Such growth disruptions can occur at non-periodic time intervals. Due to growth retardations and halts, proxy records of mollusk shells are thus incomplete, and reconstructed environmental amplitudes prone to truncation. Furthermore, environmental records are biased toward the physiological optimum of the animal. Favorable environmental conditions increase shell growth, whereas adverse environmental conditions result in reduced shell production and lowered overall metabolism. Not least, the duration of the growing season and overall growth rate decrease as the mollusk grows older. Mathematical modeling approaches can significantly improve proxy records obtained from mollusk shells. For example, if the duration of growth cessation is known, it may be possible to model the missing environmental record. It is also fairly easy to account for age-related growth trends, or variable time-averaging in different portions of the shell. However, a major premise for a reliable interpretation of proxy records from a mollusk shell or other organisms secreting biogenic hard parts is a proper understanding of the physiology, and of course, a high-resolution record of the many different environmental factors that may influence physiology and shell growth. The present paper reviews examples from the literature, and unpublished data on how physiology influences geochemical proxy records from mollusk shells, and presents methods how to eliminate such adverse effects.     

Organized bacterial assemblies in manganese nodules: evidence for a role of S-layers in metal deposition

Polymetallic/ferro-manganese nodules (Mn-nodules) reach sizes of up to 10 cm in diameter and are abundantly found on the seabed. To date, the origin of Mn-nodules remains unclear, and both abiogenic and biogenic origins have been proposed. In search of evidence for a contribution of microbial processes to the formation of Mn-nodules, we analyzed those spherical nodules which contain a concentrically banded texture in their interior. The Mn-nodules were collected at a depth of 5,152 m from the Clarion-Clipperton Zone. Our high-resolution scanning electron microscopy analyses reveal first published evidence that endolithic microorganisms exist and are arranged in a highly organized manner on plane mineral surfaces within the nodules. These microorganisms are adorned on their surfaces with S-layers, which are indicative for bacteria. Moreover, the data suggest that these S-layers are the crystallization seeds for the mineralization process. We conclude that the mineral material of the Mn-nodule has a biogenic origin, and hope that these data will contribute to the development of biotechnological approaches to concentrate metals from seawater using bacteria in bioreactors.     

小气候、雪盖及土壤湿度对高山生态系统功能的影响

1 Introduction High mountain landscapes above the tree-line are often regarded as close to nature, although human impact has obviously changed the environment, partly exceeding its carrying capac- ity (L?ffler, 2000). Due to their fragility regarding expected environmental changes and an increasing land use pressure in many regions, high mountain landscapes recently became a major focus within the discussion on a sustainable development in a worldwide (Messerli and Ives, 1997), and regional p…     

Statistical Properties of Ribbon Evolution and Reconnection Electric Fields in Eruptive and Confined Flares

A statistical study of the chromospheric ribbon evolution in H\(\alpha\) two-ribbon flares was performed. The data set consists of 50 confined (62%) and eruptive (38%) flares that occurred from June 2000 to June 2015. The flares were selected homogeneously over the H\(\alpha\) and Geostationary Operational Environmental Satellite (GOES) classes, with an emphasis on including powerful confined flares and weak eruptive flares. H\(\alpha\) filtergrams from the Kanzelhöhe Observatory in combination with Michelson Doppler Imager (MDI) and Helioseismic and Magnetic Imager (HMI) magnetograms were used to derive the ribbon separation, the ribbon-separation velocity, the magnetic-field strength, and the reconnection electric field. We find that eruptive flares reveal statistically larger ribbon separation and higher ribbon-separation velocities than confined flares. In addition, the ribbon separation of eruptive flares correlates with the GOES SXR flux, whereas no clear dependence was found for confined flares. The maximum ribbon-separation velocity is not correlated with the GOES flux, but eruptive flares reveal on average a higher ribbon-separation velocity (by ≈?10 km?s^?1). The local reconnection electric field of confined (\(cc=0.50 \pm0.02\)) and eruptive (\(cc=0.77 \pm0.03\)) flares correlates with the GOES flux, indicating that more powerful flares involve stronger reconnection electric fields. In addition, eruptive flares with higher electric-field strengths tend to be accompanied by faster coronal mass ejections.     

An Event-Based Verification Scheme for the Real-Time Flare Detection System at Kanzelhöhe Observatory

In the framework of the Space Situational Awareness program of the European Space Agency (ESA/SSA), an automatic flare detection system was developed at Kanzelhöhe Observatory (KSO). The system has been in operation since mid-2013. The event detection algorithm was upgraded in September 2017. All data back to 2014 was reprocessed using the new algorithm. In order to evaluate both algorithms, we apply verification measures that are commonly used for forecast validation. In order to overcome the problem of rare events, which biases the verification measures, we introduce a new event-based method. We divide the timeline of the H\(\upalpha\) observations into positive events (flaring period) and negative events (quiet period), independent of the length of each event. In total, 329 positive and negative events were detected between 2014 and 2016. The hit rate for the new algorithm reached 96% (just five events were missed) and a false-alarm ratio of 17%. This is a significant improvement of the algorithm, as the original system had a hit rate of 85% and a false-alarm ratio of 33%. The true skill score and the Heidke skill score both reach values of 0.8 for the new algorithm; originally, they were at 0.5. The mean flare positions are accurate within \({\pm}\,1\) heliographic degree for both algorithms, and the peak times improve from a mean difference of \(1.7\pm 2.9~\mbox{minutes}\) to \(1.3\pm 2.3~\mbox{minutes}\). The flare start times that had been systematically late by about 3 minutes as determined by the original algorithm, now match the visual inspection within \(-0.47\pm 4.10~\mbox{minutes}\).     

Extreme Climatic Events in the Altai-Sayan Region as an Indicator of Powerful Volcanic Eruptions

Izvestiya, Atmospheric and Oceanic Physics - Analytic data on anomalies of the tree-ring structure of Siberian larch on the transect, passing through the Russian part of the Altai-Sayan Mountain...     

Experimental impact cratering: A summary of the major results of the MEMIN research unit

This paper reviews major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two-stage light-gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta. In addition, explosive setups, membrane-driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high-temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise (1) projectile–target interaction, (2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, (3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, (4) in situ target damage, (5) ejecta dynamics, and (6) geophysical survey of experimental craters.     

Mullite in Libyan Desert Glass: Evidence for high-temperature/low-pressure formation

Libyan Desert Glass (LDG) is a SiO₂-rich natural glass whose origin, formation mechanism, and target material are highly debated. We here report on the finding of a lens-shaped whitish inclusion within LDG. The object is dominantly composed of siliceous glass and separated from the surrounding LDG by numerous cristobalite grains. Within cristobalite, several regions rich in mullite often associated with ilmenite were detected. Mineral assemblage, chemical composition, and grain morphologies suggest that mullite was formed by thermal decomposition of kaolinitic clay at atmospheric pressure and T ≥ 1600 °C and also attested to high cooling rates under nonequilibrium conditions. Cristobalite contains concentric and irregular internal cracks and is intensely twinned, indicating that first crystallized β-cristobalite inverted to α-cristobalite during cooling of the SiO₂-rich melt. The accompanied volume reduction of 4% induced the high density of defects. The whitish inclusion also contains several partly molten rutile grains evidencing that at least locally the LDG melt was at T ≥ 1800 °C. Based on these observations, it is concluded that LDG was formed by high-temperature melting of kaolinitic clay-, rutile-, and ilmenite-bearing Cenozoic sandstone or sand very likely during an asteroid or comet impact onto Earth. While melting and ejection occurred at high pressures, the melt solidified quickly at atmospheric pressure.