Mineralogy and composition of concentric layers within a manganese nodule from the North Pacific Ocean

The minor-element composition of concentric layers within a single ferromanganese nodule from the eastern North Pacific exhibits strong correlations with Fe and Mn contents but appears to be independent of pronounced mineralogic variations. On the basis of these correlations, the elemental composition of individual layers apparently is controlled by the relative contribution of two sources: seawater, and interstitial water of associated sediment. In contrast, the mineralogy of the nodule, consisting of birnessite in the outer few layers and todorokite in the inner layers, is considered to be a function of nodule diagenesis.     

The drying up of Britain? A national estimate of changes in seasonal river flows from 11 Regional Climate Model simulations

As climate change may modify the hydrological cycle significantly, understanding the impact on river flow is important because it affects long‐term water resources planning. Here, we describe a high‐resolution British assessment of changes in river flows in the 2050s under 11 different realisations of HadRM3. In winter, river flows may either increase or decrease, with a wide range of possible decreases in summer flow. These results should encourage adaptation that copes with a broad range of future hydrological conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Starspots and relativity: Applied Doppler imaging for the Gravity Probe B mission

We present Doppler images and surface differential rotation measurements for the primary of the RS CVn binary IM Pegasi, the guide star for the Gravity Probe B experiment. The data used is a subset of that taken during optical support of the mission and was obtained almost nightly over a near three year period from the Automatic Spectroscopic Telescope operated by Tennessee State University. Using the technique of least-squares deconvolution to increase the signal-to-noise ratio of the data, we have reconstructed 31 maximum entropy Doppler images of the star. The images show that the spot features are relatively stable for over a year (and possibly longer) with both a polar spot and lower latitude features. The most intense features are located on the side facing the secondary. In addition, we have incorporated a solar-like differential rotation law into the imaging process to determine the level of surface differential rotation for IM Peg for 22 epochs. A weighted least-squares average of the measurements gives a surface shear of 0.0142 ± 0.0007 rad/d, meaning that the equator takes ∼440 ± 20 days to lap the poles. Although the level of surface differential rotation was shown to vary over the period of the observations, this may indicate an underestimate in the errors of the method rather than any temporal evolution in the differential rotation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phytolith indices as proxies of grass subfamilies on East African tropical mountains

The main objective of this paper is to provide researchers that investigate fossil phytolith assemblages and model/data comparisons a new tool for estimating C₃/C₄ grass composition over time. We tested the reliability of modern soil phytolith assemblages and phytolith indices for tracing the dominance of different grass subfamilies and tree cover density. We analyzed modern soil phytolith assemblages from sites over elevation gradients on Mount Kenya (Kenya), Mount Rungwe and around Lake Masoko (southern Tanzania). These data were compared with available botanical data. A phytolith index named Ic, proved to be an effective proxy of the proportions of Pooideae, Arundinoideae and Bambusoideae grasses (mainly C₃ grasses) versus Panicoideae grasses (mainly C₄ grasses), increasing with elevation in East-Africa. When tropical mountains are covered by open habitats (e.g. grasses and shrublands), Ic should be a reliable proxy of the C₃/C₄ grass composition. These results highlight the value of the phytolith index Ic, when interpreting paleo-environmental records from tropical mountains, to: 1) better understand past local and regional C₃/C₄ grass distributions and associated climatic changes and 2) increase the set of C₃/C₄ data available for model/data comparisons.     

High-levels of microplastic pollution in a large,remote, mountain lake

Despite the large and growing literature on microplastics in the ocean, little information exists on microplastics in freshwater systems. This study is the first to evaluate the abundance, distribution, and composition of pelagic microplastic pollution in a large, remote, mountain lake. We quantified pelagic microplastics and shoreline anthropogenic debris in Lake Hovsgol, Mongolia. With an average microplastic density of 20,264 particles km⁻², Lake Hovsgol is more heavily polluted with microplastics than the more developed Lakes Huron and Superior in the Laurentian Great Lakes. Fragments and films were the most abundant microplastic types; no plastic microbeads and few pellets were observed. Household plastics dominated the shoreline debris and were comprised largely of plastic bottles, fishing gear, and bags. Microplastic density decreased with distance from the southwestern shore, the most populated and accessible section of the park, and was distributed by the prevailing winds. These results demonstrate that without proper waste management, low-density populations can heavily pollute freshwater systems with consumer plastics.     

Characterization of respirable volcanic ash from the Soufrière Hills volcano,Montserrat, with implications for human health hazards

Volcanic ash, generated in the long-lived eruption of the Soufrière Hills volcano, Montserrat, is shown to contain respirable (sub-4 μm) particles and cristobalite, a crystalline silica polymorph. Respirable particles of cristobalite can cause silicosis, raising the possibility that volcanic ash is a respiratory health hazard. This study considers some of the main factors which affect human exposure to respirable volcanic ash, namely, the composition and proportions of respirable ash, and the composition and concentrations of airborne suspended particulates. The composition, size distribution and proportion (by weight) of respirable particles in representative samples of the Soufrière Hills tephra (dome-collapse ash-fall deposits, dome-collapse pyroclastic-flow matrix, Vulcanian explosion ash and mixed ash) have been characterized. Dome-collapse ash-fall deposits are significantly richer in respirable particles (12 wt%) than the other tephra samples, in particular the matrices of dome-collapse pyroclastic-flow deposits (3 wt%). Within the respirable fraction, dome-collapse ash contains the highest proportion of crystalline silica particles (20–27 number%, of which 97 wt% is cristobalite), compared with other primary tephra types (0.4–5.6 number%). This enrichment of crystalline silica in the dome-collapse ash is most pronounced in the very fine particle fraction (sub-2 μm). The results are explained as being due to significant size fractionation during fragmentation of pyroclastic flows, resulting in a fines-depleted dome-collapse matrix and a fines-rich dome-collapse ash deposit. For all sample types, the sub-4 μm fraction comprises 45–55 wt% of the sub-10 μm fraction. Aeolian deposit, lahar deposit and airborne samples of suspended ash, collected on filters, were characterized. These samples show enrichment of crystalline silica in the respirable fraction (10–18 number%). The results are consistent with ash in the environment having a mixed origin but originating predominantly from dome-collapse eruptions. The reworked ash, however, contains low proportions of respirable ash (～3 wt%) compared to primary ash samples. The concentration of ash particles re-suspended by road vehicles on Montserrat is found to decrease exponentially with height above the ground, indicating higher exposure for children compared with adults: PM₄ concentration at 0.9 m (height of two-year-old child) is 3 times that at 1.8 m (adult height). The composition of the re-suspended road particles is similar to that re-suspended by the wind.     

Cross-section for the dissociative photoionization of hydrogen by 584 Å radiation: The formation of protons in the Jovian ionosphere

The cross-section for dissociative photoionization of hydrogen by 584 Å radiation has been measured, yielding a value of 5 × 10^?20 cm². The process can be explained as a transition from the $\text{X}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ ground state to a continuum level of the $\text{X}{}^2\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ ionized state of H₂ The branching ratio for proton (H⁺) vs molecular ion (H₂⁺) production at this energy is 8 × 10^?3. This process is quite likely an important source of protons in the Jovian ionosphere near altitudes where peak ionization rates are found.