Noble gas systematics of the Réunion mantle plume source and the origin of primordial noble gases in Earth’s mantle

New noble gas data of ultramafic xenoliths from Réunion Island, Indian Ocean, further constrain the characteristics of primordial and radiogenic noble gases in Earth’s mantle plume reservoirs. The mantle source excess of nucleogenic ²¹Ne is significantly higher than for the Hawaiian and Icelandic plume reservoirs, similar to excess of radiogenic ⁴He. ⁴⁰Ar/³⁶Ar of the Réunion mantle source can be constrained to range between 8000 and 12 000, significant ¹²⁹Xe and fission Xe excess are present. Regarding the relative contribution of primordial and radiogenic rare gas nuclides, the Réunion mantle source is intermediate between Loihi- and MORB-type reservoirs. This confirms the compositional diversity of plume sources recognized in other radioisotope systematics. Another major result of this study is the identification of the same basic primordial component previously found for the Hawaiian and Icelandic mantle plumes and the MORB reservoir. It is a hybrid of solar-type He and Ne, and ‘atmosphere-like’ or ‘planetary’ Ar, Kr, Xe (Science 288 (2000) 1036). ²⁰Ne/²²Ne ratios extend to maximum values close to 12.5 (Ne-B), which is the typical signature of solar neon implanted as solar corpuscular radiation. This suggests that Earth’s solar-type noble gas inventory was acquired by small (less than km-sized) precursor planetesimals that were irradiated by an active early sun in the accretion disk after nebular gas dissipation, or, alternatively, that planetesimals incorporated constituents irradiated in transparent regions of the solar nebula. Previously, such an early irradiation scenario was suggested for carbonaceous chondrites which follow common volatile depletion trends in the sequence CI–CM–CV–Earth. In turn, CV chondrites closely match Earth’s mantle composition in ²⁰Ne/²²Ne, ³⁶Ar/²²Ne and ³⁶Ar/³⁸Ar. This indicates that mantle Ar could well be a planetary component inherited from precursor planetesimals. However, a corresponding conclusion for mantle Kr and Xe is less convincing yet, but this may be just due to the lack of appropriate ‘meteoritic’ building blocks matching terrestrial composition. Alternatively, heavy noble gases in Earth’s mantle could be due to admixing of severely fractionated air, but this effect must have affected all mantle sources to a very similar extent, e.g. by global subduction before the last homogenization of the mantle reservoirs.     

煤系岩石物理力学参数与声波速度之间的关系

通过超声-时间动态测试方法系统地分析了煤系沉积岩石纵波和横波速度,计算了煤系岩石动弹性力学参数,同步测试了煤系岩石的静态力学参数,建立了煤系沉积岩石动弹性力学参数与静弹性力学参数之间和煤系岩石物理力学参数与其声波速度之间的定性定量关系.研究结果表明,煤系岩石的动弹性模量与岩石的纵波或横波速度具有很好的正相关关系,而与泊松比不具有这种正相关关系.煤系岩石的动弹性模量要大于其静弹性模量,而动泊松比要小于其静泊松比,它们之间呈线性相关关系.煤系岩石密度、单轴抗压和抗拉强度与其纵波或横波速度之间也呈正相关关系,它们分别服从二次函数、指数函数和线性函数分布.     

Influence of wind turbines on seismic stations in the upper rhine graben,SW Germany

By analysing long- and short-term seismological measurements at wind farms close to the town of Landau, SW Germany, we present new insights into ground motion signals from wind turbines (WTs) at local seismic stations. Because of their need to be located in similar regions with sparsely anthropogenic activities, wind turbines impact seismic stations and their recordings in a way that is not yet fully understood by researchers. To ensure the undisturbed recording tasks of a regional seismic array or a single station by a protected area around those endangered stations, it is very important to investigate the behavior of WTs as a seismic source. For that reason, we calculate averaged one-hour long spectra of the power spectral density (PSD) before and after the installation of a new wind farm within the investigated area. These PSD are ordered according to the rotation speed. We observe a clear increase of the PSD level after the WT installation in a frequency range of 0.5 to 10 Hz up to a distance of 5.5 km away from the WT. By analysing seismic borehole data, we also observe a decrease of the PSD of wind dependent signals with depth. The impact of wind-dependent signals is found to be much more pronounced for the shallower station (150 m depth) than for the deeper one (305 m depth). Using short-term profile measurements, we fit a power-law decay proportional to 1/r ^b to the main WT-induced PSD peaks and differentiate between near-field and far-field effects of ground motions. For low frequencies in the range from 1 to 4 Hz, we determine a b value of 0.78 to 0.85 for the far field, which is consistent with surface waves. The b value increases (up to 1.59) with increasing frequencies (up to 5.5 Hz), which is obviously due to attenuating effects like scattering or anelasticity. These results give a better understanding of the seismic wavefield interactions between wind turbines (or wind farms) with nearby seismic stations, including borehole installations, in a sedimentary setting.     

A Fresh Look at Dickinsonia： Removing It from Vendobionta

The Ediacaran Dickinsonia is well-known for being the only fossil to be assigned to many phyla, ranging from lichens, Cnidaria, Piatyheiminthes, Annelida, and a phylum of its own to a nonmetazoan kingdom. A new specimen from the Ediacaran fine-grained sandstone on the Winter Coast of the White Sea in northern Russia, which has an age of -555 million years ago, preserved convincing internal anatomies of definite animals, comparable with meridionai canals of extant ctenophores （comb jellies）. Additionally, we reconsidered Dickinsonia as a biradiaily symmetrical animal rather than a bilateral one as previously thought. The animal nature of Dickinsonia is, thus, well established and its affinities are most probably allied to ctenophores. This research is not only removing Dickinsonia from Vendobionta, but also bringing the fossil record of ctenophores forward to 20 million years before the Cambrian ＂explosion＂.     

Methane in the southern North Sea: Sources, spatial distribution and budgets

Measurements of methane (CH₄) so far have always shown supersaturation in the entire North Sea relative to the atmospheric partial pressure and the distribution of surface CH₄ reveals a distinct increase towards the shore. Since North Sea sediments presumably are an insignificant source for CH₄ the coastal contribution via rivers and tidal flats gains in importance.In this work, CH₄ data from the River Weser, the back barrier tidal flats of Spiekeroog Island (NW Germany), and the German Bight are presented. Results from the River Weser are compared to other rivers draining into the German Bight. Measurements in the tidal flat area of Spiekeroog Island highlight this ecosystem as an additional contributor to the overall CH₄ budget of the southern North Sea. A tidally driven CH₄ pattern is observed for the water column with maximum values during low tide. Tidal flat sediments turn out to be the dominating source because pore waters discharged during low tide are highly enriched in CH₄. In contrast, the freshwater contribution to the tidal flats by small coastal tributaries has almost no impact on water column CH₄ concentrations. The CH₄ level seems to be disturbed irregularly by wind forcing due to elevated degassing and prevention of advective flow when tidal flats remain covered by water.Based on our data, two model calculations were used to estimate the impact of tidal flats on the CH₄ budget in the German Bight. Our results demonstrate that the back barrier tidal flats of the east Frisian Wadden Sea contribute CH₄ in an order of magnitude between the Wash estuary and River Elbe and thus have to be considered in budget calculations.     

Oxidative damage in rainbow trout caged in a polluted river

Sewage treatment works (STWs) are a common source of chemicals entering into the aquatic environment. In order to assess effects of these effluents on oxidative stress parameters in aquatic organisms, we caged rainbow trout at five sites: upstream, near an STW effluent, and three sites downstream in the river Viskan in western Sweden for 14 days during autumn, 2006. We then measured protein carbonyls in plasma as well as 20S proteosome activity and lipid peroxidation products, i.e. MDA and 4-HNE, in liver samples. Levels of both lipid and protein oxidative damage products were elevated in fish caged near the STW effluent while 20S activity showed no differences. This argues that complex mixtures of chemicals entering into the aquatic environment do have deleterious effects on fish. Additionally, oxidative stress parameters can serve as a biomarker in aquatic organisms.     

The effect of the 19F(α, p)22Ne reaction rate uncertainty on the yield of fluorine from Wolf–Rayet stars

In the light of recent recalculations of the  ¹⁹F(α, p)²²Ne  reaction rate, we present results of the expected yield of ¹⁹F from Wolf–Rayet (WR) stars. In addition to using the recommended rate, we have computed models using the upper and lower limits for the rate, and hence we constrain the uncertainty in the yield with respect to this reaction. We find a yield of  3.1 × 10⁻⁴ M_⊙  of ¹⁹F with our recommended rate, and a difference of a factor of 2 between the yields computed with the upper and lower limits. In comparison with previous work we find a difference in the yield of a factor of approximately 4, connected with a different choice of mass loss. Model uncertainties must be carefully evaluated in order to obtain a reliable estimate of the yield, together with its uncertainties, of fluorine from WR stars.     

Relativistic effects in the motion of artificial satellites: The oblateness of the central body II

The motion of artificial satellites in the gravitational field of an oblate body is discussed in the post — Newtonian framework using the technique of canonical Lie transformations. Two Lie transformations are used to derive explicit results for the longperiodic and secular perturbations for satellite orbits in the Einstein case.