Effect of Pinus radiata plantations on water balance in Chile

The effect of Pinus radiata (D. Don) plantations on water resources at different Chilean sites located between 33 and 40 south was determined. Incoming precipitation, canopy interception loss, evapotranspiration, net evapotranspiration (transpiration and evaporation from the soil), percolation and soil water content were measured in each site, where Pinus radiata plantations were 12 to 17 years old and between 700 and 830 trees ha^?1 dense. The results were compared with those obtained from areas covered with perennial grasses and shrubs at the same sites. The pine canopies intercepted on average 36–40% of the annual rainfall at all sites where rainfall was less then 1200 mm, while only 15% of the mean rainfall was intercepted in the southernmost and rainy (2081 mm year^?1) site. Annual net evapotranspiration increased from south to north from 32% of the incoming precipitation for the southernmost site to 55% for the one located at the lower latitude. In this northernmost site almost the entire incoming precipitation was evapotranspired. Annual percolation registered its minimum value in the northern site (5% of incoming precipitation) and its maxima in the southern one (53%). The values of net evapotranspiration and percolation were regulated by the pluviometric regime and the soil moisture retention capacity in each site. Compared with the shrub or grass covers, sites under Pinus radiata plantations registered higher water consumption by evapotranspiration and reduced percolation. Copyright © 2007 John Wiley & Sons, Ltd.     

Runoff and peak flow responses to timber harvest and forest age in southern Chile

Runoff and peak flows in three experimental catchments with different forest conditions were analysed in a rainy temperate climate in southern Chile. The hydrological effects of clearcutting a Pinus radiata plantation covering 79·4% of the La Reina catchment were studied by analysing runoff and peak flows in the pre‐ and post‐harvesting periods. Mean annual runoff increased 110% after timber harvesting. Clearcutting generated a 32% mean increase in peak flows. Peak flow and runoff were examined in two adjacent catchments with different forest conditions. The older plantation in Los Ulmos 1 increasingly consumed more water than the younger plantation established at Los Ulmos 2, whereas differences in peak flows between these two catchments were not significant. Runoff and peak flows comparisons not only reflected changes in forest cover, but also the effect of rainfall characteristics during the study periods and the basins' morphologies. Comparisons between pre‐ and post‐harvesting peak discharges must be undertaken with caution, because a previous analysis at La Reina using a partial set of data overestimated changes in peak flows after timber harvesting. Copyright © 2005 John Wiley & Sons, Ltd.     

Interaction of peridotite with Ca-rich carbonatite melt at 3.1 and 6.5 GPa: Implication for merwinite formation in upper mantle,and for the metasomatic origin of sublithospheric diamonds with Ca-rich suite of inclusions

We performed an experimental study, designed to reproduce the formation of an unusual merwinite?+?olivine-bearing mantle assemblage recently described as a part of a Ca-rich suite of inclusions in sublithospheric diamonds, through the interaction of peridotite with an alkali-rich Ca-carbonatite melt, derived from deeply subducted oceanic crust. In the first set of experiments, we studied the reaction between powdered Mg-silicates, olivine and orthopyroxene, and a model Ca-carbonate melt (molar Na:K:Ca?=?1:1:2), in a homogeneous mixture, at 3.1 and 6.5 GPa. In these equilibration experiments, we observed the formation of a merwinite?+?olivine-bearing assemblage at 3.1 GPa and 1200 °C and at 6.5 GPa and 1300–1400 °C. The melts coexisting with this assemblage have a low Si and high Ca content (Ca#?=?molar 100?×?Ca/(Ca?+?Mg)?>?0.57). In the second set of experiments, we investigated reaction rims produced by interaction of the same Ca-carbonate melt (molar Na:K:Ca?=?1:1:2) with Mg-silicate, olivine and orthopyroxene, single crystals at 3.1 GPa and 1300 °C and at 6.5 GPa and 1400 °C. The interaction of the Ca-carbonate melt with olivine leads to merwinite formation through the expected reaction: 2Mg₂SiO₄ (olivine)?+?6CaCO₃ (liquid)?=?Ca₃MgSi₂O₈ (merwinite)?+?3CaMg(CO₃)₂ (liquid). Thus, our experiments confirm the idea that merwinite in the upper mantle may originate via interaction of peridotite with Ca-rich carbonatite melt, and that diamonds hosting merwinite may have a metasomatic origin. It is remarkable that the interaction of the Ca-carbonate melt with orthopyroxene crystals does not produce merwinite both at 3.1 and 6.5 GPa. This indicates that olivine grain boundaries are preferable for merwinite formation in the upper mantle.     

Cache-efficient parallel eikonal solver for multicore CPUs

Numerical solution of the eikonal equation is frequently used to compute first-arrival travel times for a given velocity model in seismic applications. Computations for large three-dimensional models become expensive requiring the use of efficient parallel solvers. We present new parallel implementations of the fast sweeping and locking sweeping methods optimized for shared memory systems such as multicore CPUs; we call them block fast sweeping method (BFSM) and block locking sweeping method (BLSM). Proposed methods are based on the domain decomposition approach with a special attention paid to high efficiency of the cache utilization and task execution synchronization. Performance tests on realistic models show high parallel efficiency of 85–95% on modern multicore CPUs and require the same number of iterations to converge as do the serial sweeping methods. We also highlight the importance of properly selecting the stopping criterion in the iterative sweeping methods aiming for a balance between computational time and accuracy of the result required by an application. In particular, we show that in seismic applications one can reach reasonable accuracy of computed travel times while dramatically reducing the number of iterations compared to the case of using the full convergence stopping criterion.     

The spatio-temporal development of Copenhagen’s bicycle infrastructure 1912–2013

Cycling plays an important role in low-carbon transitions. Around the globe, cities are constructing bicycle infrastructure. The city of Copenhagen has a bicycle-friendly infrastructure celebrated for its fine-meshed network. This study documents the spatio-temporal development of Copenhagen’s bicycle infrastructure and explores how the development corresponds to other processes of urban transformation. The study builds on historical maps of bicycle infrastructure that are digitised into geographical information, which allows for a comprehensive analysis of the formation of the network. In search for identifying drivers, the study analyses the city’s spatial growth pattern, migration pattern, development of road network and changes in the transport culture. Analyses reveal that the bicycle infrastructure expanded at a relatively constant pace during distinct periods of urban transformation, including periods when the city suffered from spatial, economic and demographic decline, and dominance of car traffic. By discussing reasons and demands for constructing bicycle infrastructure, the study identifies four distinct periods in which bicycle infrastructure was constructed to enhance comfort and safety (first cycling city); the flow for cars (car city); urban liveability for soft transport (liveable city); and, finally, to improve the flow for cyclists as part a strategic re-design of urban space (liveable cycling city).     

Southern East Siberia Pliocene–Quaternary faults: Database, analysis and inference

This paper presents the first release of an Informational System（IS）devoted to the systematic collection of all available data relating to Pliocene-Quaternary faults in southern East Siberia,their critical analysis and their seismotectonic parameterization.The final goal of this project is to form a new base for improving the assessment of seismic hazard and other natural processes associated with crustal deformation.The presented IS has been exploited to create a relational database of active and conditionally active faults in southern East Siberia（between 100°-114° E and 50°-57° N）whose central sector is characterized by the highly seismic Baikal rift zone.The information within the database for each fault segment is organized as distinct but intercorrelated sections（tables,texts and pictures,etc.）and can be easily visualized as HTML pages in offline browsing.The preliminary version of the database distributed free on disk already highlights the general fault pattern showing that the Holocene and historical activity is quite uniform and dominated by NE-SW and nearly E-W trending faults;the former with a prevailing dip-slip normal kinematics,while the latter structures are left-lateral strike-slip and oblique-slip（with different proportion of left-lateral and normal fault slip components）.These faults are mainly concentrated along the borders of the rift basins and are the main sources of moderate-to-strong（M≥5.5）earthquakes on the southern sectors of East Siberia in recent times.As a whole,based on analyzing the diverse fault kinematics and their variable spatial distribution with respect to the overall pattern of the tectonic structures formed and/or activated during the late Pliocene-Quaternary,we conclude they were generated under a regional stress field mainly characterized by a relatively uniform NW-SE tension,but strongly influenced by the irregular hard boundary of the old Siberian craton.The obtained inferences are in an agreement with the existing models of the development of     

Metasomatism of the Pan-African lithospheric mantle beneath the Damara Belt,Namibia, by the Tristan mantle plume: geochemical evidence from mantle xenoliths

In situ trace element analyses of constituent minerals in mantle xenoliths occurring in an alnöite diatreme and in nephelinite plugs emplaced within the central zone of the Damara Belt have been determined by laser ablation ICP-MS. Primitive mantle-normalized trace element patterns of clinopyroxene and amphibole indicate the presence of both depleted MORB-like mantle and variably enriched mantle beneath this region. Clinopyroxenes showing geochemical depletion have low La/Sm_n ratios (0.02–0.2), whereas those showing variable enrichment have La/Sm_n ranging up to 3.8 and La/Yb_n to 9.1. The most enriched clinopyroxenes coexist with amphibole showing similar REE patterns (La/Sm_n = 1.3–4.1; La/Yb_n = 4.5–9). Primitive mantle-normalized trace element patterns allow further groups to be distinguished amongst the variably enriched clinopyroxenes: one having strong relative depletion in Rb–Ba, Ta–Nb and relative enrichment in Th–U; another with similar characteristics but with additional strong relative depletion in Zr–Hf; and one showing no significant anomalies. Amphiboles show similar normalized trace element patterns to co-existing clinopyroxene. Clinopyroxene and amphiboles showing LREE_N enrichment have high Sr and low Nd isotope ratios compared to clinopyroxene with LREE-depleted patterns. Numerical simulation of melt percolation through the mantle via reactive porous flow is used to show that the chromatographic affect associated with such a melt migration process is able to account for the fractionation seen in La–Ce–Nd in cryptically metasomatized clinopyroxenes in Type 1 xenoliths, where melt–matrix interactions occur near the percolation front, whereas REE patterns in clinopyroxenes proximal to the source of metasomatic melt/fluid match those found in modally metasomatized Type 2 xenoliths. The strong fractionation between Rb–Ba, Th–U and Ta–Nb shown by some cryptically metasomatized xenoliths can be also accounted for by reactive porous flow, provided amphibole crystallizes from the percolating melt/fluid close to its source. The presence of amphibole in vein-like structures in some xenoliths is consistent with this interpretation. The strong depletion in Zr–Hf in clinopyroxene and amphibole in some xenoliths cannot be accounted for by melt migration processes and requires metasomatism by a separate carbonate-rich melt/fluid. When taken together with published isotope data on these same xenoliths, the source of metasomatic enrichment of the previously depleted (MORB-like) sub-Damaran lithospheric mantle is attributed to the upwelling Tristan plume head at the time of continental breakup.     

Deep incision in an Aptian carbonate succession indicates major sea‐level fall in the Cretaceous

Long‐term relative sea‐level cycles (0·5 to 6 Myr) have yet to be fully understood for the Cretaceous. During the Aptian, in the northern Maestrat Basin (Eastern Iberian Peninsula), fault‐controlled subsidence created depositional space, but eustasy governed changes in depositional trends. Relative sea‐level history was reconstructed by sequence stratigraphic analysis. Two forced regressive stages of relative sea‐level were recognized within three depositional sequences. The first stage is late Early Aptian age (intra Dufrenoyia furcata Zone) and is characterized by foreshore to upper shoreface sedimentary wedges, which occur detached from a highstand carbonate platform, and were deposited above basin marls. The amplitude of relative sea‐level drop was in the order of tens of metres, with a duration of <1 Myr. The second stage of relative sea‐level fall occurred within the Late Aptian and is recorded by an incised valley that, when restored to its pre‐contractional attitude, was >2 km wide and cut ≥115 m down into the underlying Aptian succession. With the subsequent transgression, the incision was backfilled with peritidal to shallow subtidal deposits. The changes in depositional trends, lithofacies evolution and geometric relation of the stratigraphic units characterized are similar to those observed in coeval rocks within the Maestrat Basin, as well as in other correlative basins elsewhere. The pace and magnitude of the two relative sea‐level drops identified fall within the glacio‐eustatic domain. In the Maestrat Basin, terrestrial palynological studies provide evidence that the late Early and Late Aptian climate was cooler than the earliest part of the Early Aptian and the Albian Stage, which were characterized by warmer environmental conditions. The outcrops documented here are significant because they preserve the results of Aptian long‐term sea‐level trends that are often only recognizable on larger scales (i.e. seismic), such as for the Arabian Plate.     

The origin of crystalline residues in Stardust Al foils: Surviving cometary dust or crystallized impact melts?

Abstract– Samples returned by the Stardust mission from comet 81P/Wild 2 provide an unequaled opportunity to investigate cometary formation and evolution. Crystalline silicates have been identified in impact craters in Stardust Al foil, yet their origin is ambiguous. They may be original cometary components, or they may have grown from melt generated by impact. We have now studied experimental impacts of the calcium silicate mineral wollastonite, using scanning and transmission electron microscopy to document the relationship between impact feature shape and crystal lattice orientation in impact residue. Wollastonite can have a characteristic acicular habit, forming crater shapes that indicate crystal orientation upon impact. From extracted impact residue, we determined the lattice orientation of crystalline material for comparison with the whole particle orientation. We assume that crystallization from melt, without surviving seed nuclei, should result in randomly oriented crystallite growth, with no preferred direction for individual crystals. However, we find that the majority of crystalline material in the residue retains b‐axis orientation parallel to the long axis of the crater form. This, together with impact parameter calculations and lack of Al incorporation by the residue (suggesting melting did not occur), indicates that these crystals and, by analogy, the majority of Al‐free crystalline silicates in Stardust foil, are surviving remnants of the impactor. Furthermore, amorphous wollastonite residue probably did not form via melting and subsequent quenching, but instead by high‐pressure amorphization or degradation of unquenchable phases. Finally, one crystal studied appears to be a new high‐pressure/temperature polymorph of CaSiO₃, indicating that such polymorphs may be observed in Stardust residues in craters.