Fast X-ray and IR variability of A 0535+262

X-ray bursts of the source A 0535+262 with a characteristic time-scale 5 min have been discovered using the observational data of the Soviet Astron satellite obtained on 7 April, 1983. Similar temporal variations were observed in the IR range on 26 September, 1981, 26–27 October and 16–17 December, 1983. The presence of such bursts gives evidence of strong inhomogeneity in the electron shell around the optical component and an accreting flow of matter in the vicinity of the neutron star. The parameters of the inhomogeneities are estimated.     

Evidence for prolonged acceleration based on a detailed analysis of the long-duration solar gamma-ray flare of June 15, 1991

Gamma-ray emission extending to energies greater than 2 GeV and lasting at least for two hours as well as 0.8–8.1 MeV nuclear line emission lasting 40 min were observed with very sensitive telescopes aboard the GAMMA and CGRO satellites for the well-developed post-flare loop formation phase of the 3B/X12 flare on June 15, 1991. We undertook an analysis of optical, radio, cosmic-ray, and other data in order to identify the origin of the energetic particles producing these unusual gamma-ray emissions. The analysis yields evidence that the gamma-rays and other emissions, observed well after the impulsive phase of the flare, appear to be initiated by prolonged nonstationary particle acceleration directly during the late phase of the flare rather than by a long-term trapping of energetic electrons and protons accelerated at the onset of the flare. We argue that such an acceleration, including the acceleration of protons up to GeV energies, can be caused by a prolonged post-eruptive energy release following a coronal mass ejection (CME), when the magnetic field above the active region, strongly disturbed by the CME eruption, relaxes to its initial state through magnetic reconnection in the coronal vertical current sheet.     

Fluid controlled eclogitization of granulites in deep crustal shear zones,Bergen arcs,Western Norway

During the Caledonian orogeny large parts of the western margin of the Baltic shield were disrupted, sliced and stacked. Caledonian deformation resulted in a massif thickening of the continental crust. Mafic granulites and granulite facies meta-anorthosites build up a large portion of the Bergen Arcs terrane in southwestern Norway. The rocks represent typical Precambrian continental lower crust. These rocks experienced extensive eclogitization in response to stacking and crustal thickening during the Caledonian orogenic cycle. Eclogite formation resulted from shear deformation and associated infiltration of H₂O-rich fluids (X _H2O0.75). During an early stage, eclogite facies mineralogy formed in extension fractures (veins). The veins are probably related to hydraulic fracture systems which transported the inferred fluid phase. During the main stage, eclogitization occurred along shear zones ranging from centimeters to tens of meters in thickness. Eclogite forming reactions are shown to consume H₂O, alkalies and to release SiO₂. Much of the SiO₂ released by the eclogitization process can be found in late quartz vein systems. The eclogitization took place at a temperature of about 700°C and a pressure between 18 and 21 kbar. Fluid infiltration was supported by a decrease in rock volume during reaction (V _solids<0). The negative volume change of reaction occurs despite that the process of eclogitization involves hydration reactions. The formation of eclogite from granulite produces approximately 15 KJ heat per 100 cm³ original granulite. Numerical modeling of the regional temperature effects associated with partial hydration of the lower crust suggests that these processes may not cause large perturbations on the geotherm. Both, transport of heat and matter by advection of the fluid phase is negligible on a regional scale.     

Plankton: Its chemical composition and its significance as a source of pelagic sediments

The absolute concentrations of minor and trace elements vary considerably in plankton. However, normalization of elemental abundances versus the minor elements Fe, Al and Zn (instead of the commonly used normalization versus seawater concentrations) demonstrates that these elements show remarkably constant proportions vis à vis each other. Thus, Ti, Fe, Al, Mn, V, and Zr occur in marine lower organisms in the same proportions as in the average shale, whereas Ba, Cr, Cu, Ni, Cd, Pb, Zn and B are enriched relative to the shale abundances, as are also Ca, Mg, Na, K, and Sr. These patterns appear to suggest that marine plankton are rich in lithogenic matter, but this is probably not the normal case.Contrary to the uniformity of plankton, sediments from the Pacific vary considerably in composition. Under the Equatorial high-productivity region the sediments show striking similarities with a mixture of average shale and average plankton mass, as could be expected, whereas sediments from the East Pacific Rise differ considerably from such mixtures. An iron—manganese phase (of deep-seated origin?), mixed with biological matter, on the other hand, yields model sediments with remarkable similarities to the East Pacific Rise deposits. It is therefore likely that biological processes account for a considerable fraction of some elements such as Cu, Ni, Zn and Ba also in the East Pacific Rise metalliferous sediments.     

A New Video and Digital Camera System for Studies of the Dynamics of Microtopographic Features on Tidal Flats

A newly developed video and camera system for tidal flat microtopographic studies is presented. It consists of a SONY handy cam placed in an underwater housing mounted on a frame about 70 cm above the sediment surface. A rectangular surface area of 30 ×40 cm is imaged by the camera. The camera records video sequences and/or digital images at predetermined time lapses. The total number of images is about 540, and a similar number of 10-second long video sequences can be recorded. The camera is programmed with a PC before deployment, and the total deployment time depends on the time lapse between recordings. The camera is connected to an external power supply (12 volt), and a halogen projector pointing towards the sediment surface ensures that the system is operable on a 24-hours scale. The system has been tested in the Danish Wadden Sea. It has proved to be a very useful tool in studies of topographic effects of erosion and deposition sequences, and for studies of benthic organisms-sediment interactions. The test site was further equipped with sensors for water and seabed measurements, which proved to be indispensable regarding the interpretation of recorded image time-series.     

Effects of Direct Ocean CO<Subscript>2</Subscript> Injection on Deep-Sea Meiofauna

Purposeful deep-sea carbon dioxide sequestration by direct injection of liquid CO₂ into the deep waters of the ocean has the potential to mitigate the rapid rise in atmospheric levels of greenhouse gases. One issue of concern for this carbon sequestration option is the impact of changes in seawater chemistry caused by CO₂ injection on deep-sea ecosystems. The effects of deep-sea carbon dioxide injection on infaunal deep-sea organisms were evaluated during a field experiment in 3600 m depth off California, in which liquid CO₂ was released on the seafloor. Exposure to the dissolution plume emanating from the liquid CO₂ resulted in high rates of mortality for flagellates, amoebae, and nematodes inhabiting sediments in close proximity to sites of CO₂ release. Results from this study indicate that large changes in seawater chemistry (i.e. pH reductions of ∼0.5–1.0 pH units) near CO₂ release sites will cause high mortality rates for nearby infaunal deep-sea communities. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sedimentationsverhältnisse im Mesozoikum der nördlichen Kalkalpen

Ohne Zusammenfassung     

Last glacial maximum climate inferences from cosmogenic dating and glacier modeling of the western Uinta ice field, Uinta Mountains, Utah

During the last glacial maximum (LGM), the western Uinta Mountains of northeastern Utah were occupied by the Western Uinta Ice Field. Cosmogenic ¹⁰Be surface-exposure ages from the terminal moraine in the North Fork Provo Valley and paired ²⁶Al and ¹⁰Be ages from striated bedrock at Bald Mountain Pass set limits on the timing of the local LGM. Moraine boulder ages suggest that ice reached its maximum extent by 17.4 ± 0.5 ka (± 2σ). ¹⁰Be and ²⁶Al measurements on striated bedrock from Bald Mountain Pass, situated near the former center of the ice field, yield a mean ²⁶Al/¹⁰Be ratio of 5.7 ± 0.8 and a mean exposure age of 14.0 ± 0.5 ka, which places a minimum-limiting age on when the ice field melted completely. We also applied a mass/energy-balance and ice-flow model to investigate the LGM climate of the western Uinta Mountains. Results suggest that temperatures were likely 5 to 7°C cooler than present and precipitation was 2 to 3.5 times greater than modern, and the western-most glaciers in the range generally received more precipitation when expanding to their maximum extent than glaciers farther east. This scenario is consistent with the hypothesis that precipitation in the western Uintas was enhanced by pluvial Lake Bonneville during the last glaciation.