Nursery use patterns of commercially important marine fish species in estuarine systems along the Portuguese coast

Analysing the estuarine use patterns of juveniles of marine migrant fish species is vital for identifying important sites for juveniles as well as the basic environmental features that characterize these sites for different species. This is a key aspect towards understanding nursery function. Various estuarine systems along the Portuguese coast (Minho, Douro, Ria de Aveiro, Mondego, Tejo, Sado, Mira, Ria Formosa and Guadiana) were sampled during Spring and Summer 2005 and 2006. Juveniles of commercially important marine fish species Solea solea, Solea senegalensis, Platichthys flesus, Diplodus vulgaris and Dicentrarchus labrax, predominantly 0-group individuals, were amongst the most abundant species and had distinct patterns of estuarine use as well as conspicuous associations with several environmental features. Juvenile occurrence and density varied amongst estuaries and sites within them, and differed with species. Sites with consistently high juvenile densities were identified as important juvenile sites (i.e. putative nursery grounds). Through generalized linear models (GLM), intra-estuarine variation in occurrence and density of each of the individual species was largely explained by environmental variables (temperature; salinity; depth; percentage of mud in the sediment; presence of seagrass; importance of intertidal areas; relative distance to estuary mouth; macrozoobenthos densities; and latitude). Decisive environmental factors defining important sites for juveniles varied depending on the system as a result of different environmental gradients, though there were common dominant features for each species regardless of the estuary considered. Analysed environmental variables in the GLM also accounted for inter-estuarine variation in species' occurrence and density. In several estuaries, the identified important juvenile sites were used by many of these species simultaneously and may be of increased value to both management and conservation. Overall, the variability in site features amongst estuaries highlighted the tolerance of these species to different available environmental conditions and provided fundamental information for future spatially explicit modelling of their distribution. This should ultimately enable the prediction of species response to habitat alterations.     

The role of fault reactivation in the development of tropical montane lakes

This work details the role of fault reactivation in the development of tropical montane lakes by using basin morpho-structural analysis and seismostratigraphic studies. The upland lakes are severely faulted sinkholes, whose faults penetrate the Quaternary sedimentary units. Four main stages are related to the lake formation: (i) an Early Proterozoic tectonic deformation of the rocks along the southern border of the Carajás Structure, where the lake is placed; (ii) differential erosion by – and building of – the formation of the South Carajás Hill; (iii) Fe-rich crust formation by weathering and gravitational collapse faults following the E–W plateau border and the start of Violão Lake formation during the Pliocene–Pleistocene; and (iv) episodic fault-fracture reactivation by gravitational collapse causing pulses of subsidence in the lake and outlining its faulted borders. Dissolution of the lateritic crust and erosion by runoff drainage under wet climate conditions were coeval with fault activities, which allowed the deposition of relatively thick clastic deposits organized in three main seismostratigraphic units associated with major lake-level fluctuations. Initial fault reactivation under low-level water started lacustrine basin development with deposition of prograding fan deltas related to the main drainage. A second fault reactivation by gravitational collapse increased the lake accommodation space and resulted in the deposition of fine-grained sediments from dilute interflows or overflows until 36 000 cal year BP. At about 31 000 cal year BP, rapid decreases in the lake water level under redox conditions at the sediment/water interface allowed widespread siderite formation. A third gravitational collapse episode was responsible for the increase in the lake area and depth and the returning of clastic/organic deposition up to the present. This tropical montane lake can be seen as a representative example for understanding the formation of other upland lakes controlled by fault reactivation. © 2020 John Wiley & Sons, Ltd.     

Observations of near-inertial oscillations along the Brazilian continental shelf break

Ocean Dynamics - Near-inertial oscillations (NIO) are intermittent motions with a frequency close to the inertial frequency and represent an important fraction of the energy to the currents in the...     

Centrifugal Forces and Optical Geometry in Neutron Stars

In this paper centrifugal forces and the geometry of light ray trajectories in neutron stars are discussed. The general behavior of centrifugal forces and angular momentum transfer is closely linked to the geometry of photon trajectories, such a behavior is here graphically depicted for realistic neutron stars, shown to be quite different from the non-relativistic case and to depend on the particular form of the equation of state. This revised version was published online in July 2006 with corrections to the Cover Date.     

Correlated fast time structures at millimeter waves and hard X-rays during a solar burst

We present an analysis of the time profiles detected during a solar impulsive flare, observed at one-millimeter radio frequency (48 GHz) and in three hard X-ray energy bands (25–62, 62–111, and 111–325 keV) with high sensitivity and time resolution. The time profiles of all emissions exhibit fast time structures of 200–300 ms half power duration which appear in excess of a slower component varying on a typical time scale of 10 s. The amplitudes of both the slow and fast variations observed at 48 GHz are not proportional to those measured in the three hard X-ray energy bands. However, the fast time structures detected in both domains are well correlated and occur simultaneously within 64 ms, the time resolution of the hard X-ray data. In the context of a time-of-flight flare model, our results put strong constraints on the acceleration time scales of electrons to MeV energies.     

Multiple frequency analysis of the large-amplitude SX Phoenicis star BL Camelopardalis

A multifrequency analysis of the SX Phoenicis star BL Camelopardalis is presented on the basis of new high-speed photometry, along with fitting a total of 136 maxima. BL Cam is a multiple periodic pulsator. We find f ₀=25.5768, f ₁=25.2982, f ₂=25.8622, f ₃=31.5912, f ₄=25.1065, f ₅=25.5147 and f ₆=25.6188 cycle d⁻¹ together with the harmonics 51.1513 and 76.7268 cycle d⁻¹ and combination frequencies f ₀+ f ₁, f ₀+ f ₂ and f ₀+ f ₃. The new frequency solution represents the light curves of BL Cam quite well. The observed minus calculated (O-C) analysis indicates that the fundamental frequency is in good agreement with the results of Fourier analysis.     

Application of the CN Intermediate-term Earthquake Prediction Algorithm to the Area of the Southern External Dinarides

—The paper presents the results of application of the CN algorithm to the area of the Southern External Dinarides. Two cases are considered—one for the knowledge gained throughout the considered period of time (1936–1996), and the other when learning ceased in 1986. In the first case 8 out of 9 strong earthquakes could have been predicted, three false alarms are declared (covering 7% of the total time considered) and TIPs occupy 32% of the total time. There is no clear relation between the TIPs duration and the size of the related earthquake. The second case (when the CN functions are defined on the basis of a shorter learning period) produces even slightly better results: only two false alarms are declared. In both cases current alarm exists in the region. All attempts to reduce the area of the regional polygon resulted in poorer prediction results.     

Inhomogeneous distribution of REE in scheelite and dynamics of Archaean hydrothermal systems (Mt. Charlotte and Drysdale gold deposits, Western Australia)

Scheelite is a widespread accessory mineral in hydrothermal gold deposits, and its rare earth element (REE) patterns and Nd and Sr isotopic compositions can be used to constrain the path and origin of the mineralising fluids and the age of the hydrothermal activity. Micro-analyses by laser ablation high resolution inductively coupled mass spectroscopy and cathodoluminescence imaging reveal a very inhomogeneous distribution of the REE in single scheelite grains from the Mt. Charlotte and Drysdale Archaean gold deposits in Western Australia. Two end-member REE patterns are distinguished: type I is middle REE (MREE)-enriched, with no or minor positive Eu-anomaly, whereas type II is flat or MREE-depleted with a strong positive Eu-anomaly. The chemical inhomogeneity of these scheelites is related to oscillatory zoning involving type I and type II patterns, with zone widths varying from below 1 to 200 μm. Intra-sectorial growth discontinuities, syn-crystallisation brittle deformation, and variations in the relative growth velocities of crystallographically equivalent faces suggest a complex crystallisation history under dynamic hydraulic conditions. The co-existence of MREE-enriched and MREE-depleted patterns within single scheelite crystals can be explained by the precipitation of a mineral which strongly partitions MREE relative to light and heavy REE. Scheelite itself has such characteristics, as does fluorapatite, which is locally abundant and has REE contents similar to that of scheelite. In this context, the systematic increase of the Eu-anomaly between type I and type II patterns is produced by the difference between the partition coefficients of Eu²⁺ and Eu³⁺, and not by fluid mixing or redox reactions. Consequently, the high positive Eu-anomaly typical of scheelite from gold ores may not necessarily be inherited from the hydrothermal fluid, but may reflect processes occurring during ore deposition. This case study demonstrates that in hydrothermal systems characterised by low REE concentrations in the fluid, and by the precipitation of a REE-rich mineral which strongly fractionates the REE, the REE patterns of such a mineral will be highly sensitive to the dynamics of the hydrothermal system. Received: 1 November 1999 / Accepted: 4 February 2000