Coupled atmospheric and marine palaeoclimatic reconstruction for the last 35 ka in the Sele Plain–Gulf of Salerno area (southern Italy)

Planktonic foraminifera and pollen data from core GNS84-C106 (Gulf of Salerno, Tyrrhenian Sea) were analysed through the Modern Analogue Technique, Constrained Cluster Analysis and relative variation biplots. A long period of mild climate, centred around 25 ka BP, is evident in both marine and continental reconstructions. The cooling phase from 17 to 14.7 ka BP, correlated to the H1 Heinrich event, is indicated by a sea surface temperature (SST) decrease, which roughly coincides with the cold-arid phase identified by annual and January temperatures. A rapid increase in atmospheric temperatures and precipitation, culminating at 13.8 ka BP, marks the BA cronozone. The corresponding increase in summer and winter SSTs, of 11 and 6.5 °C, respectively, occurred over 600 years. The beginning of the YD, centred around 12.5 ka BP, is marked by a decrease in summer and winter SSTs of, respectively, 4.5 and 3.5 °C in one century. The atmospheric evidence of the YD is primarily reflected in low January temperatures, reaching −6 °C, the lowest values ever experienced in the analysed time interval. The Late Glacial–Holocene transition is clearly recorded in both the continental and marine realms. From 11.5 to 9 ka BP, atmospheric temperatures record a period of substantial stability followed by a drop at 8.9 ka BP, which chronologically fall within the first RCC event (9–8 ka BP) of Mayewski et al. [2004. Holocene climate variability. Quaternary Research 62, 243–255], in correspondence with a phase of relatively high seasonality, indicated by foraminifera.     

Gold–palladium mineralization at Bleïda Far West, Bou Azzer–El Graara Inlier, Anti-Atlas, Morocco

The structurally controlled Au–Pd mineralization at Bleïda Far West occurs in a volcano-sedimentary rock sequence in altered amphibolites and chlorite schists of the Neoproterozoic Bou Azzer–El Graara inlier. The Au–Pd mineralization is virtually sulfide-free; instead, gold is associated with hematite, barite, quartz, and calcite. The gold grains are silver- and palladium-bearing (up to 19 wt% Ag and 6.3 wt% Pd) and are intergrown with a distinct suite of mainly Pd-dominated platinum group minerals, namely mertieite-I/isomertieite, merenskyite, keithconnite, kotulskite, palladseite, and sperrylite, defining a Au–Pd–As–Sb–Se–Te chemical signature. Stable isotope and fluid inclusion studies indicate a wide range of fluid compositions with a prominent saline component. In conjunction with the mineral association, oxidizing fluids are indicated, and Au and PGE transport and deposition likely took place by chloride complexes in the epithermal range, at elevated f O₂ and/or low pH. It is still speculative whether the mineralization is late Pan-African (～600–550 Ma) in age, or connected with the Variscan orogeny (～330–300 Ma), or related to some other hydrothermal event. Common to all Au–Pd mineralizations worldwide (Brazil, Australia, UK), including Bleïda Far West, is their formation in the epithermal (<300°C) range; deposition mainly in brittle structures; sulfide-poor mineral assemblages comprising hematite, sulfate minerals, and selenides; and metal transport by, and deposition from, oxidized, chloride-rich fluids. These deposits are further characterized by noble metal abundances in the order Au>Pd>Pt and the chemical signature Au–Pd–Se–Te (±As, Sb, Bi). As such, the Au–Pd association represents a discrete style of gold mineralization distinct from other classes of gold deposits.     

Comparison of climatic threshold of geographical distribution between dominant plants and surface pollen in China

The geographical distribution of dominant plant species in China was georeferenced and climatic variables were interpolated into all grids.Accordingly,the percentage distributions of principal pollen taxa based on 1860 surface pollen sites in China were selected and the related climate values were interpolated with the same method. The geographical and climatic comparison between the two data-sets indicated that the climate threshold of most pollen taxa from surface pollen is coherent with plant distributions. The climatic envelopes of dominant plant are mostly accordant with those of pollen taxa at certain levels. However, some distinct offsets of the climate ranges exist between the two datasets for most pollen taxa identified at family level, such as Ericaceae,Asteraceae, Poaceae and Chenopodiaceae. The present study provides for the first time rich information on temperature and precipitation in relation to pollen and plant distribution based on the datasets on a continental scale useful for global ecological modeling and Quaternary palaeoclimate reconstruction.     

Spectral band decomposition combined with nonlinear models: application to indoor formaldehyde concentration forecasting

This paper proposes a new approach for forecasting continuous indoor air quality time series and in particular the concentration of a common air pollutant in offices like formaldehyde. Forecasting is achieved through the combination of the spectral band decomposition using fast Fourier transform and nonlinear time series modeling. Two nonlinear models have been tested: a threshold autoregressive (TAR) model and a Chaos dynamics-based modeling. This study shows the benefit of the Fourier decomposition coupled with nonlinear modeling of each extracted component, compared to forecasting applied directly on the raw data. Both TAR and Chaos dynamics models are able to reproduce nonlinearities, with slightly better performance in the case of the second model. These hybrid models provide good performance on forecast time horizon up to 12 h ahead.     

Unsteady convective atmospheric vortices

The convective atmospheric vortex models of Kuo (1966) and Kendall (1978) are extended to allow the formulation of similarity equations for the unsteady vortex arising from an ambient flow with unstable stratification and rotation. In particular, a new analytical solution is found which allows flow at large radius that is more physically realistic than in any earlier solutions. Additional unsteady solutions are obtained numerically but at large radius these are subject to the limitations of earlier solutions.     

Spatial and morphometric relationships of submarine landslides offshore west and southwest Iberia

Landslides - Submarine landslides are a ubiquitous geohazard in the marine environment and occur at multiple scales. Increasing efforts have been made during the last decade to catalogue and...     

Three-Dimensional Simulations of Jets from Keplerian Disks: Stability Issues

Three-dimensional simulations of the time-dependent evolution of non-relativistic outflows from the surface of Keplerian accretion disks are presented. We investigate the outflow that arises from a magnetized accretion disk that is initially in hydrostatic balance with its surrounding cold corona. Our simulations show that jets maintain their long-term stability through a self-limiting process wherein the average Alfvénic Mach number within the jet is maintained to order unity. This is accomplished in at least two ways. First, poloidal magnetic field is concentrated along the central axis of the jet forming a `backbone' in which the Alfvén speed is sufficiently high to reduce the average jet Alfvénic Mach number to unity. Second, the onset of higher order Kelvin-Helmholtz `flute' modes (m ≥ 2) reduce the efficiency with which the jet material is accelerated, and transfer kinetic energy of the out flow into the stretched, poloidal field lines of the distorted jet. This too has the effect of increasing the Alfvén speed and thereby reducing the Alfvénic Mach number. The jet is able to survive the onset of the more destructive m=1 mode in this way.     

Analyse multirésolution croisée de pluies et débits de sources karstiquesMultiresolution cross-analysis of rainfall rates and karstic spring runoffs

In order to quantify the quality of the rainfall/discharge relationship across time-scales, we propose the use of both orthogonal wavelet multiresolution analysis and cross-correlation analysis. By using the two techniques together, it is possible to show, scale-by-scale, the influence of the input to the system (rainfall) on the response (discharge) of the aquifer and also to relate these results to the internal structure of the aquifer and to the degree of organisation of the karst drainage. An application of this method to three Pyrenean karsts is also shown. To cite this article: D. Labat et al., C. R. Geoscience 334 (2002) 551–556.     

Boulder deposition during major tsunami events

A remarkable accumulation of marine boulders located above the present spring tide level has occurred in two coastal lowlands of the Algarve (Portugal). The size‐interval of the particles studied here is seldom reported in the literature in association with extreme events of coastal inundation, thus making this study of relevance to many other coasts worldwide. The spreads of boulders extend several hundred meters inland and well beyond the present landward limit of storm activity. The marine origin of the boulders is demonstrated by well‐developed macro‐bioerosion sculpturing and in situ skeletal remains of endolithic shallow marine bivalves. The good state preservation of the fossils within the boulders indicates that abrasion during transport and redeposition was not significant. We envisage boulder deposition as having taken place during the Lisbon tsunami of ad 1755 through the simultaneous landward entrainment of coarse particles from nearshore followed by rapid shoreward suspended‐dominated transport and non‐graded redeposition that excluded significant sorting by weight or boulder dimensions. We use numerical hydrodynamic modeling of tsunami (and storm) waves to test the observational data on boulder dimensions (density, size, distribution) on the most likely processes of sediment deposition. This work demonstrates the effectiveness of the study of boulder deposits in tsunami reconstruction. Copyright © 2011 John Wiley & Sons, Ltd.