Ephemeral rollover points and clinothem evolution in the modern Po Delta based on repeated bathymetric surveys

Reconstructions of ancient delta systems rely typically on a two-dimensional (2D) view of prograding clinothems but may miss their three-dimensional (3D) stratigraphic complexity which can, instead, be best documented on modern delta systems by integrating high-resolution geophysical data, historical cartography, core data and geomorphological reconstructions offshore. We quantitatively compare three precisely positioned, high-resolution multi-beam bathymetry maps in the delta front and pro delta sectors (0.3 to 10 m water depth) of Po di Pila, the most active of the modern Po Delta five branches. By investigating the detailed morphology of the prograding modern Po Delta, we shed new light on the mechanisms that control the topset to foreset transition in clinothems and show the temporal and spatial complexity of a delta and its pro delta slope, under the impact of oceanographic processes. This study documents the ephemeral nature of the rollover point at the transition between sandy topset (fluvial, delta plain to mouth-bar) and muddy seaward-dipping foreset deposits advancing, in this case, in >20 m of water depth. Three multibeam surveys, acquired between 2013 and 2016, document the complexity in space and time of the topset and foreset regions and their related morphology, a diagnostic feature that could not be appreciated using solely 2D, even very high-resolution, seismic profiles. In addition, the comparison of bathymetric surveys gathered with one-year lapses shows the migration of subaqueous sand dunes on the clinothem topset, the formation of ephemeral cut-and-fill features at the rollover point (few m below mean sea level), the presence of collapse depressions derived by sagging of sediments and fluid expulsion (possibly induced by storm waves) on the foreset, and splays of sand likely reflecting gravity flows on the lower foreset. Though the modern Po Delta is anthropogenic in many respects, its subaqueous clinothem can be studied as a scale model for ancient clinothems that are less resolved geometrically and far less constrained chronologically.     

A review of undulated sediment features on Mediterranean prodeltas: distinguishing sediment transport structures from sediment deformation

Most Mediterranean prodeltas show undulated sediment features on the foresets of their Holocene wedges. These features have been described all along the Mediterranean for the last 30 years and interpreted as either soft sediment deformation and incipient landsliding, and more recently, as sediment transport structures. We perform a review and detailed analysis of these undulated sediment features using ultrahigh-resolution seismic and bathymetric data as well as geotechnical information and hydrodynamic time series and hydrographic transects. In this study we show that the characteristics of the sediment undulations (configuration of the reflections down section and between adjacent undulations and overall morphologic characteristics) are incompatible with a genesis by sediment deformation alone and do not show evidence of sediment deformation in most cases. Various processes in the benthic boundary layer can be invoked to explain the variety of features observed in the numerous areas displaying sediment undulations.     

Parallel finite element algorithm with domain decomposition for three-dimensional magnetotelluric modelling

We present a new finite element (FE) method for magnetotelluric modelling of three-dimensional conductivity structures. Maxwell's equations are treated as a system of first-order partial differential equations for the secondary fields. Absorbing boundary conditions are introduced, minimizing undesired boundary effects and allowing the use of small computational domains. The numerical algorithm presented here is an iterative, domain decomposition procedure employing a nonconforming FE space. It does not use global matrices, therefore allowing the modellization of large and complicated structures. The algorithm is naturally parallellizable, and we show results obtained in the IBM SP2 parallel supercomputer at Purdue University. The accuracy of the numerical method is verified by checking the computed solutions with the results of COMMEMI, the international project on the comparison of modelling methods for electromagnetic induction.     

Integral-field high spatial resolution spectroscopy of the giant Hii region NGC5461

We present preliminary results obtained from integral-field (IFU) data of the giant extragalactic Hii region NGC5461, located in a spiral arm (RA=14^h03^m41.4^s, dec=+54°19′05″) of M101. The spatial and spectral information obtained with IFUs allows us to decompose the Hii region and analyze it at high resolution.     

Inclination of large coronal loops observed by TRACE

A TRACE field of view well inside the solar disk shows very well defined large loops, likely to be very inclined to the solar surface. On the other hand there is little evidence of large loops perpendicular to the solar surface. We show that this does not mean that most large loops have such large inclination but that perpendicular loops are much less visible to TRACE, because of density stratification. We quantitatively evaluate this effect by modeling in detail loops with different inclinations.     

Midlittoral polychaete communities in the Eastern Mediterranean Sea: new information from the implementation of the Natural Geography in Shore Areas (NaGISA) protocol and comparisons at local and regional scales

The aim of this study was to attempt to fill current knowledge gaps on midlittoral Mediterranean biodiversity at local and regional scales, by using benthic polychaetes as a model taxon. Two different data sets were analysed: (i) a quantitative data set from the two Natural Geography in Shore Areas (NaGISA) study sites in Crete and (ii) a qualitative data set from multiple sites across the Mediterranean. At the local scale, the results provide evidence that (i) discrete species communities are formed in midlittoral Mediterranean habitats, which vary by geographical location and year, depending on the scale of observation; (ii) macrophyte coverage and Chl‐a are the only environmental variables associated, albeit weakly, with the above pattern; (iii) although naturally disturbed, the Cretan NaGISA sites do not seem to experience any anthropogenic stress; (iv) environmental heterogeneity and history seem to be much less important in shaping the polychaete communities than inter‐specific interactions; however, it is not possible to specify at this stage whether local or regional processes or even their interactions may shape the polychaete communities. At the regional scale, the results indicate that (i) the only factor that seems to be involved in the regional pattern is the identity of the study providing the data sets, which implies variability and bias in how research projects are carried out, from the sampling design through to data collection and analysis; (ii) the Cretan NaGISA sites may be considered as representative of the habitat in the Mediterranean, under certain conditions.     

Brazil’s Financial Centers in the Twenty-first Century: Hierarchy,Specialization, and Concentration

The purpose of this article is to examine how the geography of Brazil’s financial centers changed since 2000 in terms of financial center hierarchy, specialization, and spatial concentration. To address these questions, we use data on employment and mergers and acquisitions in financial and business services, complemented with data on remuneration and bank assets. Our results show that São Paulo has consolidated its dominance as Brazil’s primary financial center, with market for corporate control as an important channel of this process. Rio’s decline as a financial center, which started more than fifty years ago, has continued into this century. At the same time, Brasília has emerged as the third most important financial center of Brazil. We document the recent dynamic of this territorial division of labor, with Rio’s specialization in insurance and Brasília’s dependence on government-owned banks. Finally, we show signs that Brazil’s financial center activities might be following an inverse U-shaped pattern whereby increasing geographical concentration is followed by its slow decline. Key Words: Brazil, concentration, financial centers, São Paulo, territorial division of labor.     

Evolution of the mass function of dark matter haloes

We use a high-resolution ΛCDM numerical simulation to calculate the mass function of dark matter haloes down to the scale of dwarf galaxies, back to a redshift of 15, in a  50 h ⁻¹ Mpc  volume containing 80 million particles. Our low-redshift results allow us to probe low-σ density fluctuations significantly beyond the range of previous cosmological simulations. The Sheth & Tormen mass function provides an excellent match to all of our data except for redshifts of 10 and higher, where it overpredicts halo numbers increasingly with redshift, reaching roughly 50 per cent for the  10¹⁰–10¹¹ M_⊙  haloes sampled at redshift 15. Our results confirm previous findings that the simulated halo mass function can be described solely by the variance of the mass distribution, and thus has no explicit redshift dependence. We provide an empirical fit to our data that corrects for the overprediction of extremely rare objects by the Sheth & Tormen mass function. This overprediction has implications for studies that use the number densities of similarly rare objects as cosmological probes. For example, the number density of high-redshift  ( z ≃ 6) QSOs  , which are thought to be hosted by haloes at 5σ peaks in the fluctuation field, are likely to be overpredicted by at least a factor of 50 per cent. We test the sensitivity of our results to force accuracy, starting redshift and halo-finding algorithm.