Stratospheric Photolysis Frequencies: Impact of an Improved Numerical Solution of the Radiative Transfer Equation

Numerical schemes for the calculation of photolysis rates are usually employed in simulations of stratospheric chemistry. Here, we present an improvement of the treatment of the diffuse actinic flux in a widely used stratospheric photolysis scheme (Lary and Pyle, 1991). We discuss both the consequences of this improvement and the correction of an error present in earlier applications of this scheme on the calculation of stratospheric photolysis frequencies. The strongest impact of both changes to the scheme is for small solar zenith angles. The effect of the improved treatment of the diffuse flux is most pronounced in the lower stratosphere and in the troposphere. Overall, the change in the calculated photolysis frequencies in the region of interest in the stratosphere is below about 20%, although larger deviations are found for H₂O, O₂, NO, N₂O, and HCl.     

Black Sea chemocline oscillations during the Holocene: molecular and isotopic studies of marginal sediments

We measured δ¹³C values of free and sulfur-bound lipids and framboidal pyrite-size distributions in three sediment cores from the southern margins of the Black Sea. The margin cores show a marked difference in the occurrence of biomarkers from green sulfur bacteria compared with the deep-basin cores, as a result of deepening of the chemocline resulting from enhanced mixing and/or decreased light-penetration as a consequence of high turbidity and productivity in shelf waters. Quantitation of biomarkers suggests that photic-zone anoxia along the shelf margin was generally absent during the deposition of unit I, although occurred during the deposition of Unit IIb at two sites.     

Provenance of sandstones from the Wakino Subgroup of the Lower Cretaceous Kanmon Group, northern Kyushu, Japan

Abstract The Wakino Subgroup is a lower stratigraphic unit of the Lower Cretaceous Kanmon Group. Previous studies on provenance of Wakino sediments have mainly concentrated on either petrography of major framework grains or bulk rock geochemistry of shales. This study addresses the provenance of the Wakino sandstones by integrating the petrographic, bulk rock geochemistry, and mineral chemistry approaches. The proportions of framework grains of the Wakino sandstones suggest derivation from either a single geologically heterogeneous source terrane or multiple source areas. Major source lithologies are granitic rocks and high‐grade metamorphic rocks but notable amounts of detritus were also derived from felsic, intermediate and mafic volcanic rocks, older sedimentary rocks, and ophiolitic rocks. The heavy mineral assemblage include, in order of decreasing abundance: opaque minerals (ilmenite and magnetite with minor rutile), zircon, garnet, chromian spinel, aluminum silicate mineral (probably andalusite), rutile, epidote, tourmaline and pyroxene. Zircon morphology suggests its derivation from granitic rocks. Chemistry of chromian spinel indicates that the chromian spinel grains were derived from the ultramafic cumulate member of an ophiolite suite. Garnet and ilmenite chemistry suggests their derivation from metamorphic rocks of the epidote‐amphibolite to upper amphibolite facies though other source rocks cannot be discounted entirely. Major and trace element data for the Wakino sediments suggest their derivation from igneous and/or metamorphic rocks of felsic composition. The major element compositions suggest that the type of tectonic environment was of an active continental margin. The trace element data indicate that the sediments were derived from crustal rocks with a minor contribution from mantle‐derived rocks. The trace element data further suggest that recycled sedimentary rocks are not major contributors of detritus. It appears that the granitic and metamorphic rocks of the Precambrian Ryongnam Massif in South Korea were the major contributors of detritus to the Wakino basin. A minor but significant amount of detritus was derived from the basement rocks of the Akiyoshi and Sangun Terrane. The chromian spinel appears to have been derived from a missing terrane though the ultramafic rocks in the Ogcheon Belt cannot be discounted.     

Composition and provenance of the Upper Cretaceous to Eocene sandstones in Central Palawan, Philippines: Constraints on the tectonic development of Palawan

Abstract Sandstones from the Upper Cretaceous to Eocene succession of Central Palawan are rich in quartz grains and acidic volcanic rock fragments. Potassium feldspar grains and granitic rock fragments are commonly observed. The moderate to high SiO₂ and low FeO plus MgO contents of the sandstones support the proposal that clasts were derived from a continental source region. Southern China (Kwangtung and Fukien regions) is inferred to be the source area of the sandstones. The sedimentary facies of the Upper Cretaceous to Eocene succession consist of turbidite and sandstones, suggesting that they were deposited in the deep sea portions of submarine-fans and basin plains situated along a continental margin. These features indicate that the Upper Cretaceous to Eocene succession of the Central Palawan were derived and drifted from the southern margin of China. The tectonic history related to the formation of Palawan Island is also discussed.     

A soil acidification study using the PROFILE model on two contrasting regions in Switzerland

The steady-state soil chemistry model PROFILE was used to calculate the chemical status of forest soils under present deposition loads for two areas with dissimilar ecosystem properties. Two regions in Switzerland, with contrasting bedrock geology were selected to be investigated in detail: 88 locations in the Jura Mountains, representative for carbonate bedrock and 91 locations in the Ticino Area dominated by metamorphic crystalline host rocks. Weathering rates calculated for the key regions cover the tremendous range between 0.013 and 25 keq ha⁻¹ yr⁻¹. In the Ticino Area, the effect of increased abundance of relatively fast weathering silicates (epidote, hornblende and plagioclase) on the weathering rate is apparently masked by the total effects of the physical conditions applied and by the variation in the deposition load. In the Jura Mountains, generally high weathering rates occur with about 50% of the sites yielding rates above 1 keq ha⁻¹ yr⁻¹. In many of the sites investigated, however, carbonates have already been dissolved completely in the soil horizons of interest resulting in very low weathering rates. The critical load of actual acidity was calculated according to: CL_Acidity=R_Weathering−ANC_Leaching, where alkalinity leaching is estimated by keeping the base cation to aluminum molar ratio at the critical limit of 1 at steady-state. The minimum critical load calculated was 0.2 keq ha⁻¹ yr⁻¹ and the maximum was 6.2 keq ha⁻¹ yr⁻¹. Comparing the cumulative frequency distributions of critical loads of actual acidity for forest soils in the individual areas it can be seen that the differences between the key regions are less substantial than with the weathering rates. Critical loads of acidity for the Ticino Area range from 1 to 3.9 keq ha⁻¹ yr⁻¹. Sites yielding the lowest critical loads of acidity are observed in the Jura Mountains. Among these apparent sensitive soils are soils with intermediate or high weathering rates, although it has depleted topsoil layers. Within the context of this model application, it becomes apparent that the sensitivity of these soils with respect to acidification is also governed by the alkalinity leaching term and not only by the susceptibility of its minerals to weathering.     

Effect of temperature and illumination on pyrite oxidation between pH 2 and 6

The effect of heat and illumination with visible light on the oxidation of pyrite with dissolved molecular oxygen in solutions between pH 2 and 6 has been investigated using a combination of surface science experiments and batch oxidation experiments. The rate of the oxidation of pyrite is strongly dependent on temperature. It is, however, not possible to cast the temperature dependence in a simple Arrhenius equation because the magnitude of the activation energy depends on the progress variable chosen. Activation energies based on proton release rate, sulfate release rate, and total iron release rate vary by as much as 40 kJ mol^-1, suggesting that the oxidation mechanism of the sulfur and iron component of pyrite are largely independent of each other. This difference in mechanism can also explain why the reaction rates on the basis of these three different progress variables do not show the same pH dependence. Exposed to visible light, the rate of pyrite oxidation is under most conditions accelerated by less than a factor of two. Some of this acceleration may be accounted for by a light-induced heating of the pyrite surface. Surface science experiments employing photoelectron spectroscopy show no evidence for significant changes in the chemical composition of the surface as a function of exposure to visible light. The batch sorption experiments show, however, that the reaction stoichiometry changes somewhat, which indicates that there might be a change in reaction mechanism as a result of exposure to visible light.     

Slab pull effects from a flexural analysis of the Tonga and Kermadec trenches (Pacific Plate)

Thin-plate flexure models have been frequently used to explain the mechanical behaviour of the lithosphere at oceanic trenches, but little attention has been paid to using them as a way to check the relative importance of different plate-driving mechanisms. A 2-D numerical algorithm accounting for the flexural deflection of the lithosphere controlled by multilayered elastic–plastic rheology (brittle–elastic–ductile) has been applied to the seaward side of the Tonga and Kermadec trenches. This approach gives a better fit to the bathymetry on both trenches than assuming classical homogeneous plate models, and allows the interplate coupling forces and the lithospheric strength profile to be constrained. Our results show that, in order to fit the observed deflection of the lithosphere, a regional tensile horizontal force must act in both regions. This tensile force and its flexural effects are discussed in terms of slab pull as a main plate-driving mechanism. The predicted stress and yielding distributions partially match the outer-rise earthquake hypocentres within the subducting plate, and thus do not invalidate the model.     

Gravitational lensing by elliptical galaxies

The fraction of high-redshift sources which are multiply imaged by intervening galaxies is strongly dependent on the cosmological constant, and so can be a useful probe of the cosmological model. However its power is limited by various systematic (and random) uncertainties in the calculation of lensing probabilities, one of the most important of which is the dynamical normalization of elliptical galaxies. Assuming ellipticals' mass distributions can be modelled as isothermal spheres, the mass normalization depends on the velocity anisotropy, the luminosity density, the core radius and the area over which the velocity dispersion is measured. The differences in the lensing probability and optical depth produced by using the correct normalization can be comparable to the differences between even the most extreme cosmological models. The existing data are not sufficient to determine the correct normalization with enough certainty to allow lensing statistics to be used to their full potential. However, as the correct lensing probability is almost certainly higher than is usually assumed, upper bounds on the cosmological constant are not weakened by these possibilities.     

Superhumps in V348 Pup

The eclipsing nova-like cataclysmic variable star V348 Pup exhibits a persistent luminosity modulation with a period 6 per cent longer than its 2.44-h orbital period ( P _orb). This has been interpreted as a 'positive superhump' resulting from a slowly precessing non-axisymmetric accretion disc gravitationally interacting with the secondary. We find a clear modulation of mid-eclipse times on the superhump period, which agrees well with the predictions of a simple precessing eccentric disc model. Our modelling shows that the disc light centre is on the far side of the disc from the donor star when the superhump reaches maximum light. This phasing suggests a link between superhumps in V348 Pup and late superhumps in SU UMa systems. Modelling of the full light curve and maximum entropy eclipse mapping both show that the disc emission is concentrated closer to the white dwarf at superhump maximum than at superhump minimum. We detect additional signals consistent with the beat periods between the implied disc precession period and both and