Field investigation on rilling in the experimental Sparacia area,South Italy

In this paper the results of a field investigation on rilling carried out in the experimental Sparacia area are reported. The measurements were made on a plot 6 m wide and 22 m long subjected to natural rainfalls. For ten rainfalls the total soil loss (interrill and rill erosion) was collected in a storage system consisting of two tanks arranged in series at the base of the plot. Rill morphology (rill length and cross‐sections) was measured for five rainfall events, while the rill profile was surveyed for three events. First the contribution of each component (rill and interrill erosion) to total soil loss was established. Then the analysis allowed establishment of a power relationship between the rill length and the rill volume. Finally, for three events detailed information on rill erosion and rill morphology allowed verification of the applicability of WEPP and estimation of the rill erodibility constant. Copyright © 2007 John Wiley & Sons, Ltd.     

Triploporella ? edgelli n. sp., a new Dasycladalean alga from the Lower Cretaceous of Lebanon

The Dasycladalean assemblage of the Jezzinian strata (uppermost Barremian–lowermost Aptian) of Lebanon consists of two organo‐genera and eight genera with eleven species, including eight Triploporellaceae. Although Triploporella marsicana (Praturlon, 1964) was reported by Saint‐Marc from the same interval, it is not found in our material. However, a lookalike, which is herein described as Triploporella ? edgelli n. sp., is identified. This new species has cyst‐containers within the primary segments of its laterals but, because it lacks calcified secondary segments, it is left in open nomenclature.     

Influence du Bani sur la variabilité saisonnière et interannuelle de la crue du fleuve Niger dans le delta intérieur au Mali

Le delta intérieur du fleuve Niger est une zone humide sahélienne dont l’inondation dépend de la pluviométrie des bassins supérieurs du fleuve Niger et de son principal affluent, le Bani. La crise climatique qui a débuté en 1970 a très peu influencé les dates de passage des maximums de crue sur le Niger amont et son principal défluent, le Diaka. L’influence par contre est très forte sur le Bani, à la confluence avec le Niger à Mopti et sur le delta aval avec des dates de passages des maximums plus précoces qu’auparavant. Cela est dû à la faiblesse des superficies inondées au cours des années sèches. Pendant les années humides, l’importance des débordements latéraux ralentit la propagation de la crue avec pour conséquence des dates de passages plus tardives des maximums. Par ailleurs pendant les années humides antérieures à 1970 l’importance des débordements latéraux conférait au delta amont un caractère d’autorégulation par écrêtage des crues au niveau de certaines station.     

Eddy properties in the Southern California Current System

The California Current System (CCS) is an eastern boundary upwelling system characterized by strong eddies that are often generated at the coast. These eddies contribute to intense, long-distance cross-shelf transport of upwelled water with enhanced biological activity. However, the mechanisms of formation of such coastal eddies, and more importantly their capacity to trap and transport tracers, are poorly understood. Their unpredictability and strong dynamics leave us with an incomplete picture of the physical and biological processes at work, their effects on coastal export, lateral water exchange among eddies and their surrounding waters, and how long and how far these eddies remain coherent structures. Focusing our analysis on the southern part of the CCS, we find a predominance of cyclonic eddies, with a 25-km radius and a SSH amplitude of 6 cm. They are formed near shore and travel slightly northwest offshore for ~?190 days at ~?2 km day^?1. We then study one particular, representative cyclonic eddy using a combined Lagrangian and Eulerian numerical approach to characterize its kinematics. Formed near shore, this eddy trapped a core made up of ~?67% California Current waters and ~?33% California Undercurrent waters. This core was surrounded by other waters while the eddy detached from the coast, leaving the oldest waters at the eddy’s core and the younger waters toward the edge. The eddy traveled several months as a coherent structure, with only limited lateral exchange within the eddy.     

Coupling of tectonic factors and precipitation variability as a driver of Late Quaternary aggradation in Northeast Brazil

The coupling between tectonic factors and climate processes is a key element in understanding landscape evolution. However, few studies address this issue in the context of unglaciated tropical areas in passive continental margins. Thus, this research aimed to understand the origins and evolution of the geomorphological landscape in the eastern sector of Northeast Brazil along the Late Quaternary, between the Last Interstadial (Marine Isotopic State 3) and the Upper Holocene. The morphostratigraphic approach, coupled with sedimentological analyses and optically stimulated luminescence dating of sediments, showed that the depositional record stored in the landscape ranges from at least 60 000 years BP until the Upper Holocene. Depositional intervals suggest that there were moments of climatic instability followed by moments of relative geomorphological quiescence. Such active moments coincide chronologically with Heinrich and Dansgaard-Oeschger events, which are likely linked to changes in paleo-pluviosity that might respond to the dismantling of elluvial covers and colluvial deposition in the area. Likewise, reworking of hillslope materials led to increased deposition in the fluvial realm. In addition, such deposits might have been affected by the neotectonic complexity of the area, responsible for the creation of non-concatenated accommodation spaces, indicating a dynamics of uplifting and subsidence of blocks typical of passive margin taphrogenic environments. Therefore, the formative processes that led to the Late Quaternary deposition of sediments in a platform margin context reflect a coupling between tectonic and climatic factors. The former, driven by precipitation variability on a regional scale, triggered fluvial and high-energy hillslope processes that resulted in ubiquitous valley floor and piedmont aggradation, whereas the latter led to the dismantling of local base levels, transforming depositional units into new denudational landforms subject to the current climate dynamics. © 2020 John Wiley & Sons, Ltd.     

A SEM-based method to determine the mineralogical composition and the particle size distribution of suspended sediment

A robust method for characterizing the mineralogy of suspended sediment in continental rivers is introduced. It encompasses 3 steps: the filtration of a few milliliters of water, measurements of X-ray energy dispersive spectra using Scanning Electron Microscopy (SEM), and robust machine learning tools of classification. The method is applied to suspended particles collected from various Amazonian rivers. A total of more than 204,000 particles were analyzed by SEM-EDXS (Energy Dispersive X-ray Spectroscopy), i.e. about 15,700 particles per sampling station, which lead to the identification of 15 distinct groups of mineralogical phases. The size distribution of particles collected on the filters was derived from the SEM micrographs taken in the backscattered electron imaging mode and analyzed with ImageJ freeware. The determination of the main mineralogical groups composing the bulk sediment associated with physical parameters such as particle size distribution or aspect ratio allows a precise characterization of the load of the terrigenous particles in rivers or lakes. In the case of the Amazonian rivers investigated, the results show that the identified mineralogies are consistent with previous studies as well as between the different samples collected. The method enabled the evolution of grain size distribution from fine to coarse material to be described in the water column. Implications about hydrodynamic sorting of mineral particles in the water column are also briefly discussed. The proposed method appears well suited for intensive routine monitoring of suspended sediment in river systems.     

Assessment of the geometry and volumes of small surface water reservoirs by remote sensing in a semi-arid region with high reservoir density

Water fluxes in highly impounded regions are heavily dependent on reservoir properties. However, for large and remote areas, this information is often unavailable. In this study, the geometry and volume of small surface reservoirs in the semi-arid region of Brazil were estimated using terrain and shape attributes extracted by remote sensing. Regression models and data classification were used to predict the volumes, at different water stages, of 312 reservoirs for which topographic information is available. The power function used to describe the reservoir shapes tends to overestimate the volumes; therefore, a modified shape equation was proposed. Among the methods tested, four were recommended based on performance and simplicity, for which the mean absolute percentage errors varied from 24 to 39%, in contrast to the 94% error achieved with the traditional method. Despite the challenge of precisely deriving the flooded areas of reservoirs, water management in highly reservoir-dense environments should benefit from volume prediction based on remote sensing.     

Peat layer accumulation and post‐burial deformation during the mid‐late Holocene in the Po coastal plain (Northern Italy)

Peat horizons are characteristic features of delta plains worldwide. In this study, we tested the use of peat‐based correlations to assess the deformation of Holocene strata in the Po coastal plain (Northern Italy). The Holocene stratigraphy, about 30 km inland from the modern coastline consists of a peat‐bearing, estuarine and deltaic succession, up to 23 m thick. Through the analysis of 31 core data and 100 piezocone penetration tests, we identified and mapped three 10–40 cm‐thick peat layers (T1–T3) dated to 6.6–5.8, 5.5–5.0 and 3.3–2.7 cal kyr BP respectively. These peat horizons were found to be suitable stratigraphic markers within the Holocene succession over an area of about 200 km². The mid‐late Holocene palaeogeography, reconstructed through high‐resolution peat correlation, supported by 72 radiocarbon dates, highlights a typical upper delta plain environment, with ribbon‐shaped distributary channels and swamp interdistributary areas. Peat layers are inclined towards E‐NE with gradients that increase downsection from ~0.016% (T3) to 0.021% (T1). The gradient of the oldest peat horizon is one order of magnitude larger than the slope of the modern delta plain (~0.0025%). We infer that peat horizons accumulated during periods of low sediment supply mainly controlled by autogenic processes and were deformed after deposition. Differential compaction of underlying sedimentary strata and recent tectonic activity of the buried Apenninic thrust systems are the most likely drivers of strata deformation. Based on isochore maps, we document that higher sedimentation rates in topographically depressed areas compensated, in part at least, the ongoing deformation, keeping unaltered the topographic gradient and the depositional environment. This study demonstrates that peat‐based correlation and mapping can shed lights on the mechanisms of strata accumulation and deformation in deltaic settings, constituting a robust basis for reconstructing delta evolution.     

Type Ia Supernovae

Summary. Type Ia Supernovae are in many aspects still enigmatic objects. Their observational and theoretical exploration is in full swing, but we still have plenty to learn about these explosions. Recent years have already witnessed a bonanza of supernova observations. The increased samples from dedicated searches have allowed the statistical investigation of Type Ia Supernovae as a class. The observational data on Type Ia Supernovae are very rich, but the uniform picture of a decade ago has been replaced by several correlations which connect the maximum luminosity with light curve shape, color evolution, spectral appearance, and host galaxy morphology. These correlations hold across almost the complete spectrum of Type Ia Supernovae, with a number of notable exceptions. After 150 days past maximum, however, all observed objects show the same decline rate and spectrum. The observational constraints on explosion models are still rather sparse. Global parameters like synthesized nickel mass, total ejecta mass and explosion energetics are within reach in the next few years. These parameters bypass the complicated calculations of explosion models and radiation transport. The bolometric light curves are a handy tool to investigate the overall appearance of Type Ia Supernovae. The nickel masses derived this way show large variations, which combined with the dynamics from line widths, indicate that the brighter events are also coming from more massive objects. The lack of accurate distances and the uncertainty in the correction for absorption are hampering further progress. Improvements in these areas are vital for the detailed comparison of luminosities and the determination of nickel masses. Coverage at near-infrared wavelengths for a statistical sample of Type Ia Supernovae will at least decrease the dependence on the absorption. Some of the most intriguing features of Type Ia Supernovae are best observed at these wavelengths, like the second peak in the light curve, the depression in the J band, and the unblended [Feii] lines in the ashes. Received 24 January 2000 / Published online 8 May 2000