Resting Stages of Plankton in Recent North Adriatic Sediments

Abstract. Plankton-derived resting stages were found in 26 sediment cores collected in the North Adriatic Sea; 46 morphotypes were identified, 38 were attributed to taxa according to their morphology and, in some hatching cases, also according to the morphology of the derived active forms. Six species of Dinophyta were recorded for the first time from the North Adriatic Sea. Each morphotype was described in detail. Twenty-nine resting stages were Dinophyta; one was a Chrysophyta; two were Tintinnina; and six were metazoans. At every site Dinophyta cysts were more abundant than Metazoa cysts. Cyst bank densities were variable, with empty forms generally more abundant than full ones; cyst concentrations were highest at the mouth of the Po River delta.     

The crystal chemistry of lithium and Fe3+ in synthetic orthopyroxene

Lithian ferrian enstatite with Li₂O = 1.39 wt% and Fe₂O₃ 7.54 wt% was synthesised in the (MgO–Li₂O–FeO–SiO₂–H₂O) system at P = 0.3 GPa, T = 1,000°C, fO₂ = +2 Pbca, and a = 18.2113(7), b = 8.8172(3), c = 5.2050(2) Å, V = 835.79(9) Å³. The composition of the orthopyroxene was determined combining EMP, LA-ICP-MS and single-crystal XRD analysis, yielding the unit formula ^M2(Mg_0.59Fe _0.21 ²⁺ Li_0.20) ^M1(Mg_0.74Fe _0.20 ³⁺ Fe _0.06 ²⁺ ) Si₂O₆. Structure refinements done on crystals obtained from synthesis runs with variable Mg-content show that the orthopyroxene is virtually constant in composition and hence in structure, whereas coexisting clinopyroxenes occurring both as individual grains or thin rims around the orthopyroxene crystals have variable amounts of Li, Fe³⁺ and Mg contents. Structure refinement shows that Li is ordered at the M2 site and Fe³⁺ is ordered at the M1 site of the orthopyroxene, whereas Mg (and Fe²⁺) distributes over both octahedral sites. The main geometrical variations observed for Li-rich samples are actually due to the presence of Fe³⁺, which affects significantly the geometry of the M1 site; changes in the geometry of the M2 site due to the lower coordination of Li are likely to affect both the degree and the kinetics of the non-convergent Fe²⁺-Mg ordering process in octahedral sites.     

Burial and scour around short cylinder under progressive shoaling waves

The results of a laboratory experimental program aimed at better understanding the scour around and burial of heavy cylindrical objects under oscillating flow on a sandy bed are described. This study was motivated by its application to the dynamics of isolated cobbles/mines on a sandy floor under nonlinear progressive waves, such as that occur in shallow coastal waters beyond the wave-breaking region. In the experiments, nonlinear progressive waves were generated in a long wave tank of rectangular cross-section with a bottom slope. Model mines (short cylinders) were placed on the sandy bottom and the temporal evolution of the bed profile and the velocity field in the near field of the object were observed. Experiments were conducted at relatively high Reynolds numbers for a range of flow conditions, which can be characterized by the Keulegan–Carpenter number and Shields parameter. Depending on the values of these parameters, four different scour regimes around the cylinder including periodical burial of cylinder under migrating sand ripples were observed; they were classified as: (i) no scour/burial, (ii) initial scour, (iii) expanded scour, and (iv) periodic burial cases. A scour regime diagram was developed and the demarcation criteria between different regimes were deduced. Semi-empirical formulae that permit estimation of the scour depth with time, the equilibrium maximum scour depth and length, and conditions necessary for the burial of the cylinder as a function of main external parameters are also proposed.     

Putative Meteoritic Craters in Río Cuarto (Central Argentina) Interpreted as Eolian Structures

Ten oblong aligned depressions in the Río Cuarto area (provincia de Córdoba, Argentina) were supposed to be the result of very-low-angle Holocene meteoroid impacts. However, we consider that authors that studied the structures did not demonstrated their extraterrestrial origin. We suggest that an eolian origin for the structures of Río Cuarto is more likely. Actually, these landforms integrate large systems of similar deflation/accumulation geoforms aligned according to predominant winds during different periods.     

Computer simulation studies of Crystallization under confinement conditions

Crystallization under confinement conditions is a very important process in geochemistry and geophysics. Computer simulations of fluids in nanometer scale pore spaces can provide a unique microscopic insight into the structure, dynamics and forces arising from the crystallization process. We discuss in this paper molecular dynamics computer simulations of crystallization in pores of nanometer dimensions. The crystallization pressure due to the freezing of a model of Argon in a nanopore is computed using molecular dynamics simulations. We also investigate the influence of pore geometry in determining the dynamics of confined fluids, as well as mass separation in binary mixtures. It turns out that the pore geometry reveals itself as an important variable, leading to 1) new mechanisms for fast diffusion in confined spaces, and 2) accumulation of solute in specific regions inside the pore.     

Vulnerability assessment in a volcanic risk evaluation in Central Mexico through a multi-criteria-GIS approach

The Valley of Toluca is a major industrial and agricultural area in Central Mexico, especially the City of Toluca, the capital of The State of Mexico. The Nevado de Toluca volcano is located to the southwest of The Toluca Basin. Results obtained from the vulnerability assessment phase of the study area (5,040 km² and 42 municipalities) are presented here as a part of a comprehensive volcanic risk assessment of The Toluca Basin. Information has been gathered and processed at a municipal level including thematic maps at 1:250,000 scale. A database has been built, classified and analyzed within a GIS environment; additionally, a Multi-Criteria Evaluation (MCE) approach was applied as an aid for the decision-making process. Cartographic results were five vulnerability maps: (1) Total Population, (2) Land Use/Cover, (3) Infrastructure, (4) Economic Units and (5) Total Vulnerability. Our main results suggest that the Toluca and Tianguistenco urban and industrial areas, to the north and northeast of The Valley of Toluca, are the most vulnerable areas, for their high concentration of population, infrastructure, economic activity, and exposure to volcanic events.     

Tides and mixing in the northwestern East China Sea Part I: Rotating and reversing tidal flows

Bottom-mounted ADV and ADCP instruments in combination with CTD profiling measurements taken along the Chinese coast of the East China Sea were used to study the vertical structure of temperature, salinity, and velocity in reversing tidal currents on a shallow inner shelf and in rotating tidal flows over a deeper sloping bottom of the outer shelf. These two regimes of barotropic tide affect small-scale dynamics in the lower part of the water column differently. The reversing flow was superimposed by seiches of ∼2.3 h period generated in semienclosed Jiaozhou Bay located nearby. As the tidal vector rotates over the sloping bottom, the height of the near-bottom logarithmic layer is subjected to tidal-induced variations. A maximum of horizontal velocity U_max appears at the upper boundary of the log layer during the first half of the current vector rotation from the minor to the major axis of tidal ellipse. In rotating tidal flow, vertical shear generated at the seafloor, propagated slowly to the water interior up to the height of U_max, with a phase speed of ∼5 m/h. The time-shifted shear inside the water column, relative to the shear at the bottom, was associated with periodically changing increases and decreases of the tidal velocity above the log layer toward the sea surface. In reversing flows, the shear generated near the bottom and the shear at the upper levels were almost in phase.     

Distribuzione geografica dell'attivita' magnetica terrestre

Riassunto Richiamate le caratteristiche secondo cui le perturbazioni regolari ed irregolari del campo terrestre concorrono a definire l'attività geomagnetica, se ne analizza la distribuzione geografica mediante le grandezze:HR _H ,ZR _Z , e (10^–4.²). Di queste sono illustrati e discussi gli andamenti in funzione della latitudine geomagnetica, dedotti dai valori medi calcolati per quasi tutte le stazioni funzionanti durante l'Anno Polare 1932–33 ed il triennio successivo 1933–36. Si rileva particolarmente il massimo assoluto di attività della zone anulare delle aurore, e quello relativo delle regioni equatoriali. Segue un'indagine, a carattere piuttosto indicativo, sulla ripartizione geografica del grado di variazione dell'attività nel tempo, introducendo a tale scopo opportuni indici ed esponendone il comportamento. Conclude la Nota un cenno sugli andamenti stagionali dell'attività e della variabilità geomagnetica.