World space observatory-ultraviolet among UV missions of the coming years

Continuous access to the UV domain has been considered of importance to astrophysicists and planetary scientists since the mid-sixties. However, the future of UV missions for the post-HST era is believed by a significant part of astronomical community to be less encouraging. We argue that key science problems of the coming years will require further development of UV observational technologies. Among these hot astrophysical issues are: the search for missing baryons, revealing the nature of astronomical engines, properties of atmospheres of exoplanets as well as of the planets of the Solar System etc. We give a brief review of UV-missions both in the past and in the future. We conclude that UV astronomy has a great future but the epoch of very large and efficient space UV facilities seems to be a prospect for the next decades. As to the current state of the UV instrumentation we think that this decade will be dominated by the HST and coming World Space Observatory-Ultraviolet (WSO-UV) with a 1.7 m UV-telescope onboard. The international WSO-UV mission is briefly described. It will allow high resolution/high sensitivity imaging and high/low resolution spectroscopy from the middle of the decade.     

First Late Triassic Record of a Paleoentomofauna from South America(Malargüe Basin,Mendoza Province,Argentina)

<正>Late Middle Triassic to early Late Triassic insects from Argentina have been previously described from the Bermejo and Cuyana Basins where they have been recovered from the Ischichuca-Los Rastros and Potrerillos-Cacheuta Formations,respectively.The insect fauna discussed herein was collected during field studies in 1986/1987 from the Llantenes section(Norian to Rhaetian? Late Triassic),which is situated in the Malargue Basin in southern Mendoza province.The insect remains were found in the upper part of the Llantenes section (Llantenes Formation),which is built up of two coarsening-upwards cycles reflecting a deltaic progradation of a fluvial into a lacustrine environment(lower part),succeeded by repeated progradations into a floodplain-dominated environment(upper part;with finds of insects,conchostracans,fish remains,plant fragments,and drifted logs).The new finds represent the youngest Triassic insect records described from Argentina and even from South America in its entirety.There is only one contemporaneous fossil assemblage in Gondwana:in the Clarence/Moreton Basin(Aberdare Conglomerate;Late Norian)in Australia.The new Triassic insects include an impression of an isolated Mecopterida-like wing(Mendozachorista volkheimeri gen.et sp.nov.; Mendozachoristidae fam.nov.),coleopteran elytra of the Permosynidae(Ademosyne rosenfeldi sp.nov.and Ademosyne llantenesensis sp.nov.)and other isolated body fragments.This new Late Triassic entomofauna from Argentina is of considerable importance in the reconstruction of the biotic recovery of continental environments in Gondwana after the catastrophic mass extinction at the P/T boundary.     

The biogeochemistry of sorbed methane in marine sediments

Sorption of volatile hydrocarbon gases (VHCs) to marine sediments is a recognized phenomenon that has been investigated in the context of petroleum exploration. However, little is known about the biogeochemistry of sorbed methane and higher VHCs in environments that are not influenced by thermogenic processes. This study evaluated two different extraction protocols for sorbed VHCs, used high pressure equipment to investigate the sorption of methane to pure clay mineral phases, and conducted a geochemical and mineralogical survey of sediment samples from different oceanographic settings and geochemical regimes that are not significantly influenced by thermogenic gas. Extraction of sediments under alkaline conditions yielded higher concentrations of sorbed methane than the established protocol for acidic extraction. Application of alkaline extraction in the environmental survey revealed the presence of substantial amounts of sorbed methane in 374 out of 411 samples (91%). Particularly high amounts, up to 2.1 mmol kg⁻¹ dry sediment, were recovered from methanogenic sediments. Carbon isotopic compositions of sorbed methane suggested substantial contributions from biogenic sources, both in sulfate-depleted and sulfate-reducing sediments. Carbon isotopic relationships between sorbed and dissolved methane indicate a coupling of the two pools. While our sorption experiments and extraction conditions point to an important role for clay minerals as sorbents, mineralogical analyses of marine sediments suggest that variations in mineral composition are not controlling variations in quantities of sorbed methane. We conclude that the distribution of sorbed methane in sediments is strongly influenced by in situ production.     

Sedimentological evidence for environmental changes since 34,000 years BP from Lago di Mezzano, central Italy

Sediment cores recovered from Lago di Mezzano, central Italy, were petrographically and geochemically (dry densitity, total organic carbon) investigated. A floating chronology was established with sedimentation rates derived from varve thickness measurements, and this chronology was both supported and extrapolated with calibrated AMS-14C-datings. The profile has a length of 29.7 m and comprises a total of 34,000 years.Late Pleistocene sediments consist of minerogenic-organic mud with few benthic diatoms and an organic carbon content of 2%, thus suggesting a high allochthonous input. The onset of the Late Glacial at 14,580 cal BP is documented by a lithologic change to more organic-dominated sedimentation. The Younger Dryas cold event is recorded between 12,650 and 11,400 cal BP and exhibits higher dry densities and minerogenic input. These dates agree with records from other lacustrine archives in Europe and the Greenland ice cores.The early Holocene comprises a laminated organic diatom gyttja deposited at a time of climatic amelioration and increased primary productivity. The establishment of an anoxic hypolimnion enhanced the varve and organic matter preservation. Since 3700 varve years BP the sedimentation pattern has been strongly influenced by human impact, as documented by the increase in minerogenic sediments and turbidites as well as higher sedimention rates. The onset of this influence coincides with a Bronze Age settlement at the lake shore.     

Arctic margin gravity highs: Deeper meaning for sediment depocenters?

Morphologic, gravity, and seismic reflection/refraction data from ca. 10,000 km of Arctic passive continental margins suggest that the numerous oval free-air gravity anomalies, their +50–150 mGal extrema typically located just landward of shelf breaks, are caused by combinations of rapidly deposited Plio-Pleistocene glacial marine sediment loads, older post-breakup sediments, and perhaps causally related density anomalies (mascons) in the underlying oceanic crust. Dispersed seismicity associated with some gravity highs may reflect ongoing brittle, flexural adjustment to the loads. Multi-channel-seismic-controlled depocenter models for several prominent highs (including the Hornsund gravity high re-examined here) suggest that sediments alone do not suffice to explain the gravity highs, unless depocenter seismic velocities have been significantly underestimated. A flexural backstripping model for the Hornsund anomaly only roughly replicates observed gravity. Subjacent 'mascons', if present below some depocenters, may be caused by (1) anomalous subsidence of initially formed dense/thin crust; (2) depocenter blanketing of early-formed crust, mitigating hydrothermal fracturing and related density reduction; or (3) metastable phase transitions, converting basalt/gabbro to denser phases (Neugebauer–Spohn hypothesis), while cracks close or fill under the increased pressures and temperatures.     

Numerical studies of gas hydrate systems: sensitivity to porosity-permeability models

The formation of sub-seafloor gas hydrates in marine environments can be described as a coupled transport and thermodynamic process inside a host sediment matrix undergoing structural evolution. The transport processes are driven by the sedimentary load and induced overpressure gradients, controlled by sediment permeability. In order to accurately model the resulting fluid flow profile, the decrease of sediment permeability during hydrate precipitation has to be taken into account, which affects both the transport of solutes and sediment compaction. In this paper, we investigate how total hydrate abundance is affected by regions of low permeability which deflect the flow field in their vicinity. For this purpose, a two-dimensional numerical hydrate system model was set up which permits to quantify this effect in scenarios where changes in water depth cause lateral variations of the thickness of the hydrate stability field, as well as of hydrate saturation and sediment permeability. The microscopic structure of gas hydrate crystals in the host sediment matrix defines the evolution of the permeability reduction during hydrate formation. Grain-coating precipitates have a stronger tendency to clog flow paths through pore throats than do pore-filling precipitates. Our results clearly show that these pore-scale processes affect the large-scale flow field and hydrate abundance. The sensitivity depends on the model geometry and, for a 5° slope of the seafloor, 4.1% relative difference is predicted for the hydrate saturation according to different porosity-permeability relationships.