Search results for "Geophysics"

Weakening of annual temperature cycle over the Tibetan Plateau since the 1870s

2017

The annual cycle of extra-tropical surface air temperature is an important component of the Earth's climate system. Over the past decades, a reduced amplitude of this mode has been observed in some regions. Although attributed to anthropogenic forcing, it remains unclear when dampening of the annual cycle started. Here we use a residual series of tree-ring width and maximum latewood density from the Tibetan Plateau >4,000 m asl to reconstruct changes in temperature seasonality over the past three centuries. The new proxy evidence suggests that the onset of a decrease in summer-to-winter temperature difference over the Tibetan Plateau occurred in the 1870s. Our results imply that the influen…

2019

Here we explore the carbon and oxygen isotope compositions of the co-existing carbonate and phosphate fractions of fish tooth enameloid as a tool to reconstruct past aquatic fish environments and harvesting grounds. The enameloid oxygen isotope compositions of the phosphate fraction (δ18OPO4) vary by as much as ~4‰ for migratory marine fish such as gilthead seabream (Sparus aurata), predominantly reflecting the different saline habitats it occupies during its life cycle. The offset in enameloid Δ18OCO3-PO4 values of modern marine Sparidae and freshwater Cyprinidae from the Southeast Mediterranean region vary between 8.1 and 11.0‰, similar to values reported for modern sharks. The mean δ13C …

Lithium isotope evidence for enhanced weathering and erosion during the Paleocene-Eocene Thermal Maximum.

2021

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Enzymatic Hydrolysis of Lignocellulose for Bioethanol Production

2017

Abstract The effect of temperature, time and amount of enzyme on hydrolysis of wheat straw lignocellulose remaining after furfural production was studied. The residual substrate was subjected to enzymatic hydrolysis at different temperatures — 45 °C, 50 °C and 55 °C. Hydrolysis time was 72 hours, and samples were taken every 24 hours. The maximum glucose yield (76.5% of the theoretically possible) was reached when hydrolysis temperature 50 °C was used. The production rate of glucose increased with a hydrolysis period of time. The yield of glucose significantly depended on the ratio of enzyme to substrate.

Volcano seismicity and ground deformation unveil the gravity-driven magma discharge dynamics of a volcanic eruption.

2015

Effusive eruptions are explained as the mechanism by which volcanoes restore the equilibrium perturbed by magma rising in a chamber deep in the crust. Seismic, ground deformation and topographic measurements are compared with effusion rate during the 2007 Stromboli eruption, drawing an eruptive scenario that shifts our attention from the interior of the crust to the surface. The eruption is modelled as a gravity-driven drainage of magma stored in the volcanic edifice with a minor contribution of magma supplied at a steady rate from a deep reservoir. Here we show that the discharge rate can be predicted by the contraction of the volcano edifice and that the very-long-period seismicity migrat…

Exploring the effect of absence selection on landslide susceptibility models: A case study in Sicily, Italy

2016

Abstract A statistical approach was employed to model the spatial distribution of rainfall-triggered landslides in two areas in Sicily (Italy) that occurred during the winter of 2004–2005. The investigated areas are located within the Belice River basin and extend for 38.5 and 10.3 km 2 , respectively. A landslide inventory was established for both areas using two Google Earth images taken on October 25th 2004 and on March 18th 2005, to map slope failures activated or reactivated during this interval. Geographic Information Systems (GIS) were used to prepare 5 m grids of the dependent variables (absence/presence of landslide) and independent variables (lithology and 13 DEM-derivatives). Mul…

Prediction of debris-avalanches and -flows triggered by a tropical storm by using a stochastic approach: An application to the events occurred in Moc…

2019

Abstract Landslides are among the most dangerous natural processes. Debris avalanches and debris flows in particular have often caused casualties and severe damage to infrastructures in a wide range of environments. The assessment of susceptibility to these phenomena may help policy makers in mitigating the associated risk and thus it has attracted special attention in the last decades. In this experiment, we assessed susceptibility to debris-avalanche and -flow landslides by using a stochastic approach. Two different modeling techniques were employed: i) Multivariate Adaptive Regression Splines (MARS) and ii) Logistic Regression (LR). Both MARS and LR allow for calculating the probability …

Composition and clues to the origin of refractory metal nuggets extracted from chondritic meteorites

2014

Refractory metal nuggets (RMNs) contain elements, such as Os, Ir, Mo, and Ru, which are predicted to condense from a cooling gas of solar composition simultaneously with CAI-minerals. Berg et al. (2009) identified a large number of RMNs in acid-resistant residues of the Murchison meteorite and suggested that they are pristine condensates. In extending the work of these authors, we have improved the chemical extraction process to enrich the concentration of RMNs in the residue sample and prepared three additional RMN-rich residues from the chondritic meteorites Murchison, Allende, and Leoville. The results show that, while their origin is clearly solar, the compositions in detail of RMNs fro…

Understanding melt generation beneath the slow-spreading Kolbeinsey Ridge using 238U, 230Th, and 231Pa excesses

2011

International audience; To examine the petrogenesis and sources of basalts from the Kolbeinsey Ridge, one of the shallowest locations along the global ridge system, we present new measurements of Nd, Sr, Hf, and Pb isotopes and U-series disequilibria on 32 axial basalts. Young Kolbeinsey basalts (full-spreading rate = 1.8 cm/yr; 67 degrees 05'-70 degrees 26'N) display ((230)Th/(238)U) 1 with ((230)Th/(238)U) from 0.95 to 1.30 and have low U (11.3-65.6 ppb) and Th (33.0 ppb-2.40 ppm) concentrations. Except for characteristic isotopic enrichment near the Jan Mayen region, the otherwise depleted Kolbeinsey basalts (e. g. (87)Sr/(86)Sr = 0.70272-0.70301, epsilon(Nd) = 8.4-10.5, epsilon(Hf) = 15…

Conservation Status of Some Peatbogs in Maramureş County

2016

AbstractPeat bogs and specially raised bogs are vulnerable ecosystems all over the world and they create refuges for some rare plant species. The aim of this paper is to provide information regarding the conservation status of five oligotrophic peat bogs situated in the volcanic mountains in the Oriental Chain of Carpathians, in Maramureș County. The studied peat bogs are: Tăul lui Dumitru (Dumitru Pond), Mlaștina Vlășinescu (Vlășinescu Peat bog), Iezeru Mare (Big Tarn), Tăul Chendroaiei (Chendroaiei Pond) and Tăul Negru (Black Pond), all of them have the status of nature reserve and under the IUCN categories they are included in category IV Habitat/Species Management Area (www.iucn.org, 20…