Effect of hysteretic smoothness on inelastic response spectra with constant‐ductility

This paper presents an efficient methodology for computing constant‐ductility inelastic response spectra. The computation of constant‐ductility spectra involves numerical root‐finding algorithms to find the strongest structure providing a desired ductility response. Smooth inelastic structural behavior is modeled using a first‐order nonlinear differential equation and the transient structural response is solved using an implicit algorithm requiring Newton iterations at each time step. For structural models with smooth hysteretic behavior (not piece‐wise linear), a simple root‐finding method involving a combination of hyperbolic fits, linear interpolation, and Newton's method converges upon the highest strength (conservative) solution with a small number of iterations. The effect of the hysteretic smoothness on the occurrence of multiple roots is examined for two near‐fault and two far‐fault earthquake records, and for two measures of ductility and for normalized hysteretic energy. The results indicate how the smoothness of the hysteretic behavior affects ductility demand and constant‐ductility response spectra. Copyright © 2010 John Wiley & Sons, Ltd.     

Export and degassing of terrestrial carbon through watercourses draining a temperate podzolized catchment

We measured spatial and temporal variations in carbon concentrations, isotopic compositions and exports during a complete hydrological cycle in nine watercourses draining a lowland forested podzolized catchment, flowing into the Arcachon lagoon (France). In addition, integrated fluxes of CO₂ across the water-atmosphere interface were estimated to assess the relative importance of CO₂ evasion versus lateral carbon transport at the catchment scale. Watercourse similarities and specificities linked to the local catchment characteristics are discussed and compared with other riverine systems. Low concentrations of suspended particulate matter and particulate organic carbon (POC) were generally measured in all the watercourses (8.4 ± 3.4 and 1.6 ± 0.6 mg L^?1, respectively), reflecting limited mechanical soil erosion. The generally high POC content in the suspended matter (20 %), low Chl a concentrations (1.3 ± 1.4 μg L^?1) and the relatively constant δ¹³C-POC value (near ?28 ‰) throughout the year reveal this POC originates from terrestrial C₃ plant and soil detritus. The presence of podzols leads to high levels of dissolved organic carbon (DOC; 6.6 ± 2.2 mg L^?1). Similarly, high dissolved inorganic carbon (DIC) concentrations were measured in the Arcachon lagoon catchment (5.9 ± 2.2 mg L^?1). The δ¹³C-DIC value around ?20 ‰ throughout the year in many small watercourses reveals the predominance of terrestrial carbon mineralisation and silicate rock weathering in soils as the major DIC source. With pCO₂ between 1,000 and 10,000 ppmv, all watercourses were a source of CO₂ to the atmosphere, particularly during the low river stage. Organic carbon parameters remained relatively stable throughout the year, whereas DIC parameters showed strong seasonal contrasts closely linked to the hydrological regime and hyporheic flows. In total, the carbon export from the Arcachon watershed was estimated at 15,870 t C year^?1 or 6 t C km^?2 year^?1, mostly exported to the lagoon as DOC (35 %), DIC (24 %) and lost as CO₂ degassing to the atmosphere (34 %).     

Environmental hypoxia as a metabolic constraint on fish: the case of Atlantic cod, Gadus morhua

Hypoxia is known to provoke a wide range of effects on aquatic animals. Here we use laboratory and field data on Atlantic cod, Gadus morhua, to illustrate that many of these responses can be explained within the metabolic scope (MS) framework, i.e. taking into account the directive and limiting effects of dissolved oxygen (DO) on the ability of animals to acquire energy for growth and activity. A MS model for cod shows that scope for activity (swimming, feeding, etc.) is proportional to DO and becomes nil, jeopardising survival, when DO is < approximately 20% air saturation. Laboratory studies have confirmed this lethal threshold and demonstrated that growth and food ingestion were significantly reduced below 70% sat. This loss of appetite has been linked to a reduction of the peak value and an increase in duration of postprandial metabolism, in agreement with the MS model. Dwindling MS during hypoxia imposes an upper limit to swimming performance. Cod may also opt to reduce spontaneous swimming activity to spare oxygen for other activities such as digestion. In the Kattegat, the Baltic Sea, and the Gulf of St. Lawrence, eastern Canada, cod completely avoid waters where their MS is near zero. Furthermore, cod density increases exponentially with DO up to approximately 70% sat in the Gulf of St. Lawrence. Although hypoxia results in other direct and indirect effects as well, the MS framework allows modelling of many of the responses to hypoxia for individual cod that ought to be reflected at the population and community levels. The MS framework is also useful to compare species responses. We show that the impact of hypoxia on MS is similar, when expressed as a proportion of MS in normoxia, in cod, European sea bass (Dicentrarchus labrax), the common sole (Solea solea) and turbot (Psetta maxima). Data are required for other species to evaluate how general these findings are.     

SrNdPb geochemical morphology between 10° and 17°N on the Mid-Atlantic Ridge: A new MORB isotope signature

Basalts dredged along the Mid-Atlantic Ridge axis between 10°N and 17°N have been studied for their trace element characteristics [1]. To give complementary information on mantle source history and magma genesis, these samples have been analysed for their SrNdPb isotopic compositions. There is a good correlation between the structure of the ridge axis which shows a topographic anomaly centered around 14°N and hygromagmaphile element ratios such as Rb/Sr, (Nb/Zr)_N or Sm/Nd as well as isotopic ratios plotted as a function of latitude. The samples coming from the 14°N topographic high show new MORB SrNd isotopic characteristics which pictured in a classical mantle array diagram, put their representative points close to HIMU sources of ocean islands such as St. Helena, Tubuaïand Mangaia. The 14°N mantle source presents geochemical characteristics which indicate mantle differentiation processes and a mantle history that are more distinct than so far envisaged from typical MORB data. Pb data indicates that the 14°N mantle source cannot be the result of binary mixing between a depleted mantle and a HIMU-type source. Rather, the enriched endmember could itself be a mixture of Walvis-like and HIMU-like materials. The geochimical observations presented favour the model of an incipient ridge-centered plume, in agreement with [1].     

The economics of decarbonizing the energy system—results and insights from the RECIPE model intercomparison

This paper synthesizes the results from the model intercomparison exercise among regionalized global energy-economy models conducted in the context of the RECIPE project. The economic adjustment effects of long-term climate policy are investigated based on the cross-comparison of the intertemporal optimization models ReMIND-R and WITCH as well as the recursive dynamic computable general equilibrium model IMACLIM-R. A number of robust findings emerge. If the international community takes immediate action to mitigate climate change, the costs of stabilizing atmospheric CO₂ concentrations at 450?ppm (roughly 530?C550?ppm-e) discounted at 3% are estimated to be 1.4% or lower of global consumption over the twenty-first century. Second best settings with either a delay in climate policy or restrictions to the deployment of low-carbon technologies can result in substantial increases of mitigation costs. A delay of global climate policy until 2030 would render the 450?ppm target unachievable. Renewables and CCS are found to be the most critical mitigation technologies, and all models project a rapid switch of investments away from freely emitting energy conversion technologies towards renewables, CCS and nuclear. Concerning end use sectors, the models consistently show an almost full scale decarbonization of the electricity sector by the middle of the twenty-first century, while the decarbonization of non-electric energy demand, in particular in the transport sector remains incomplete in all mitigation scenarios. The results suggest that assumptions about low-carbon alternatives for non-electric energy demand are of key importance for the costs and achievability of very low stabilization scenarios.     

The provenance of Australian uranium ore concentrates by elemental and isotopic analysis

Elemental and isotopic ratio analyses of U ore concentrate samples, from the 3 operating U mining facilities in Australia, were carried out to determine if significant variations exist between their products, thereby allowing the U ore concentrate’s origin to be identified. Elemental analyses were conducted using inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence spectrometry (XRF). Lead isotope ratios were measured using ICP-MS and U isotope analyses were conducted using thermal ionisation mass spectrometry (TIMS). Minute quantities of sample, such as that obtained from a swipe, were also examined for elemental concentrations using secondary ion mass spectrometry (SIMS). The results of multivariate statistical analysis show clear patterns in the trace elemental composition of the processed U ores, indicating that it is possible to use this feature as a unique identifier of an Australian U ore concentrate’s source. Secondary ion mass spectrometry analyses also allow individual particles to be differentiated using this ‘fingerprinting’ technique. Isotope ratios determined using TIMS reveal that there is a significant difference in the n(²³⁴U)/n(²³⁸U) isotope ratio between the U ore concentrate from each mine.     

Facies sequences in large-volume debris- and turbidity-flow deposits from the Pyrenees (Cretaceous; France,Spain)

Facies types and depositional models for thick gravity-flow deposits are inferred from Cretaceous Pyrenean examples occurring in different sedimentary settings: basin-plain during relative low sea level stand; slope-apron or deep valleys during relative sea level rise; and slope during relative sea level rise. The depositional units are interpreted as debrites, debrite-turbidite couplets, and megaturbidites. They are a function of transport distance and hydraulic jump by liquefaction and phase separation in large subaqueous flows.     

Sedimentary record of redox-sensitive elements (U, Mn, Mo) in a transitory anoxic basin (the Thau lagoon, France)

In order to further document the relation between redox conditions and the sedimentary record of Mn, U and Mo in a transitory anoxic water basin, their distribution has been studied along two profiles in the Thau lagoon (France). Sediments and pore-water have been sampled at two contrasting sites located, respectively, in the shellfish-farming area and in the centre of the lagoon. In the shellfish-farming area, the particulate organic carbon (POC) data indicate a more rapid organic matter mineralisation compared to the centre of the lagoon. This results in a sharper redox gradient characterized by the appearance of H₂S in pore-water a few millimetres below the sediment–water interface. In the centre of the lagoon, H₂S appears at a depth of 35 cm.In both cores, sedimentary Mn is relatively depleted through out the whole sedimentary column and varies with the proportion of clay minerals. After an initial release into solution at the sediment–water interface in relation to Mn-oxide reductive dissolution, authigenic U is immobilized when sulphides appear. Despite the occurrence of anoxic conditions at the sediment–water interface at the site influenced by shellfish farming, the burial of U is reduced by bioturbation, which raises reducing sediments to the surface. In the centre of the lagoon, Mo profiles reflect continuous diffusion into pore water and immobilization at 15 cm probably in anoxic microenvironments. At shellfish farms, dissolved Mo undergoes removal with sulphides but contrary to U, sedimentary Mo does not appear to be strongly affected by bioturbation. The profile indicates an increase in the frequency of anoxia crises during the second half of the 20th century.     

Radiometric age constraints on mineral growth,metamorphism, and tectonism of the Gummfluh Klippe,Briançonnais domain of the Préalpes,Switzerland

A combined ⁴⁰Ar/³⁹Ar, K/Ar, Rb/Sr and stable isotope study has been made of white micas from the Gummfluh klippe (Briançonnais domain of the Préalpes), Switzerland. The klippe consists mainly of Mesozoic to early Tertiary carbonate rocks metamorphosed from anchizonal to epizonal conditions. At the base of the klippe is a 10–50 m thick, ductilely deformed marble mylonite containing deformed authigenic quartz segregations. Stable isotope measurements of the coexisting calcite (¹⁸O_SMOW=24.5) and quartz (¹⁸O_SMOW=28.4) from the mylonite indicate relatively low temperatures (<300°C) during mylonitization. Analyses of white mica separates of varying size fractions from the mylonitic rocks by K/Ar and Rb/Sr techniques yield ages between 57 and 103 Ma. This variation is correlated with two parameters, the size of the mineral fraction, and the proportion of 2M₁ (more phengitic) to 1M (more muscovitic) polytype in the sample. The K/Ar and Rb/Sr ages are generally younger in the smaller size fractions, which also containless 2M₁ phengite. High precision ⁴⁰Ar/³⁹Ar age spectra from different size fractions of these micas record three distinct components, a small Hercynian component (ca. 200–300 Ma), a significant Eoalpine component (64–80 Ma) forming ⁴⁰Ar/³⁹Ar age plateaus, and a very minor Tertiary component (ca. 20–40 Ma). Characterization of the samples by SEM indicates the presence of two white mica populations, a coarser grained, deformed, detrital mica that probably corresponds to the 2M₁ phengite and a finer grained neoformed 1M mica. Collectively these observations suggest that the Gummfluh samples contain a mixture of detrital phengites of Hercynian age together with neocrystallized muscovites grown during the late Eoalpine metamorphic event followed by minor argon loss during the Tertiary. The main geologic episode recorded in the ⁴⁰Ar/³⁹Ar age spectra of white micas in the mylonite is of Late Cretaceous/Early Tertiary age (64–80 Ma), representing the first reliable Eoalpine ages ever to be reported from the Préalpes. Contrary to tectonic models, the marble mylonite at the base of the Gummfluh klippe appears to be a Cretaceous thrust plane and not the thrust surface formed during transport of the klippe into its present position from the Penninic Alps during the Tertiary. The late Cretaceous thrust developed during marine sedimentation at a depth of 800 m below the seafloor at temperatures of 280°C, facilitated by warm fluids along the tectonic discontinuity.