The structure of the benthic macrofaunal assemblages and sediments characteristics of the Paraguaçu estuarine system, NE, Brazil

The structure of the benthic macrofaunal assemblages of the estuarine portion of Paraguaçu River, NE, Brazil, and its relationship with surface sediment characteristics (trace metals, PAHs, nutrients and grain size) and physical variables were investigated at ten stations on two contrasting occasions, summer (dry season) and winter (rainy season). A total of 1258 individuals (632 in winter and 626 in summer) and 62 taxa representing polychaetes, crustaceans, bivalves, echinoderms, bryozoans, sponges, cnidarians and cephalochordates were collected. Benthic assemblages in the upper estuary were unlike those in the lower estuary and a clear substitution of benthic taxa along the estuary was observed. Macrofaunal invertebrates in the low salinity region, composed of coarse sediments, were dominated by tellinids, venerids (bivalves), cirolanids (isopods), cyclopoids (copepods), and nereidids (polychaetes). While the high salinity region, composed of fine sediments, were dominated by nuculids (bivalves), cirratulids (polychaetes), and by amphiurids (ophiuroids). The Paraguaçu estuarine system is not severely affected by anthropogenic activities. In the great majority of the study sites, concentrations of trace metals and PAHs in the sediments were near background values. Nutrients values were also low. We formulated new models of taxon distribution and suggested detailed studies on the effects of salinity variation and studies using functional approaches to better understand the processes causing the spatial patterns in tropical estuarine benthic assemblages.     

Plate convergence measured by GPS across the Sundaland/Philippine Sea Plate deformed boundary: the Philippines and eastern Indonesia

The western boundary of the Philippine Sea (PH) Plate in the Philippines and eastern Indonesia corresponds to a wide deformation zone that includes the stretched continental margin of Sundaland, the Philippine Mobile Belt (PMB), extending from Luzon to the Molucca Sea, and a mosaic of continental blocks around the PH/Australia/Sunda triple junction. The GPS GEODYSSEA data are used to decipher the present kinematics of this complex area. In the Philippines, the overall scheme is quite simple: two opposing rotations on either side of the left-lateral Philippine Fault, clockwise to the southwest and counterclockwise to the northeast, transfer 55 per cent of the PH/Sundaland convergence from the Manila Trench to the northwest to the Philippine Trench to the southeast. Further south, 80 per cent of the PH/Sunda convergence is absorbed in the double subduction system of the Molucca Sea and less than 20 per cent along both continental margins of northern Borneo. Finally, within the triple junction area between the Sundaland, PH and Australia plates, from Sulawesi to Irian Jaya, preferential subduction of the Celebes Sea induces clockwise rotation of the Sulu block, which is escaping toward the diminishing Celebes Sea oceanic space from the eastward-advancing PH Plate. To the south, we identify an undeformed Banda block that rotates counterclockwise with respect to Australia and clockwise with respect to Sundaland. The kinematics of this block can be defined and enable us to compute the rates of southward subduction of the Banda block within the Flores Trench and of eastward convergence of the Makassar Straits with the Banda block. The analysis made in this paper confirms that this deformation is compatible with the eastward motion of Sundaland with respect to Eurasia determined by the GEODYSSEA programme but is not compatible with the assumption that Sundaland belongs to Eurasia, as was often assumed prior to this study.     

Population III stars: hidden or disappeared?

A Population III/Population II transition from massive to normal stars is predicted to occur when the metallicity of the star-forming gas crosses the critical range   Z _cr= 10^−5±1 Z_⊙  . To investigate the cosmic implications of such a process, we use numerical simulations which follow the evolution, metal enrichment and energy deposition of both Population II and Population III stars. We find that: (i) due to inefficient heavy element transport by outflows and slow 'genetic' transmission during hierarchical growth, large fluctuations around the average metallicity arise; as a result, Population III star formation continues down to   z = 2.5  , but at a low peak rate of  10⁻⁵ M_⊙ yr⁻¹ Mpc⁻³  occurring at   z ≈ 6  (about 10⁻⁴ of the Population II one); and (ii) Population III star formation proceeds in an 'inside–out' mode in which formation sites are progressively confined to the periphery of collapsed structures, where the low gas density and correspondingly long free-fall time-scales result in a very inefficient astration. These conclusions strongly encourage deep searches for pristine star formation sites at moderate  (2 < z < 5)  redshifts where metal-free stars are likely to be hidden.     

BeppoSAX observations of 1-Jy BL Lacertae objects – I

We present new BeppoSAX observations of seven BL Lacertae objects selected from the 1-Jy sample plus one additional source. The collected data cover the energy range     (observer's frame), reaching ∼50 keV for one source (BL Lac). All sources characterized by a peak in their multifrequency spectra at infrared/optical energies (i.e., of the low-energy peaked BL Lac type, LBL) display a relatively flat     X-ray spectrum, which we interpret as inverse Compton emission. Four objects (two-thirds of the LBLs) show some evidence for a low-energy steepening, which is probably due to the synchrotron tail merging into the inverse Compton component around ∼     . If this were generally the case with LBLs, it would explain why the     ROSAT spectra of our sources are systematically steeper than the BeppoSAX ones     . The broad-band spectral energy distributions fully confirm this picture, and a synchrotron inverse Compton model allows us to derive the physical parameters (intrinsic power, magnetic field, etc.) of our sources. Combining our results with those obtained by BeppoSAX on BL Lacs covering a wide range of synchrotron peak frequency, ν _peak, we confirm and clarify the dependence of the X-ray spectral index on ν _peak originally found in ROSAT data.     

Dust formation in primordial Type II supernovae

We have investigated the formation of dust in the ejecta of Type II supernovae (SNe), mostly of primordial composition, to answer the question of where the first solid particles are formed in the Universe. However, we have also considered non-zero progenitor metallicity values up to Z = Z_⊙ . The calculations are based on standard nucleation theory, and the scheme has been tested for the first time on the well-studied case of SN1987A, yielding results that are in agreement with the available data. We find that: (i) the first dust grains are predominantly made of silicates, amorphous carbon (AC), magnetite and corundum; and (ii) the largest grains are the AC ones, with sizes around 300 Å, whereas the other grain types have smaller radii, around 10–20 Å . The grain size distribution depends somewhat on the thermodynamics of the ejecta expansion, and variations in the results by a factor ≈2 might occur within reasonable estimates of the relevant parameters. Also, and for the same reason, the grain size distribution is essentially unaffected by metallicity changes. The predictions on the amount of dust formed are very robust: for Z =0 , we find that SNe with masses in the range (12–35) M_⊙ produce about 0.08 M_⊙≲ M _d≲0.3 M_⊙ of dust per supernova. The above range increases by roughly three times as the metallicity is increased to solar values. We discuss the implications and the cosmological consequences of the results.     

Large-scale velocity field and strain tensor in Iran inferred from GPS measurements: new insight for the present-day deformation pattern within NE Iran

A network of 26 GPS sites was implemented in Iran and Northern Oman to measure displacements in this part of the Arabia–Eurasia collision zone. We present the GPS velocity field obtained from three surveys performed in 1999 September, 2001 October and 2005 September and the deduced strain tensor. This study refines previous studies inferred from only the two first surveys. Improvements are significant in NE Iran. The present-day shortening rate across the mountain belts of NE Iran is estimated to 5 ± 1 mm yr⁻¹ at about N11°, 2 ± 1 mm yr⁻¹ of NS shortening across the eastern Kopet Dag and 3 ± 1 mm yr⁻¹ of NS shortening across Binalud and Kuh-e-Sorkh. Our GPS measurements emphasize the varying character of the Kopet Dag deformation between its southeastern part with prevailing thrusting at low rates and its northwestern part with dominant strike-slip activity at increasing rates. The principal axes of the horizontal strain tensor appears very homogeneous from the Zagros to the Alborz and the Kopet-Dag (N20°) and in eastern Iran (Makran and Lut block: N30°). Only NW Iran suffers a variable strain pattern which seems to wrap the Caspian basin. The strain tensor map underlines the existence of large homogeneous tectonic provinces in terms of style and amplitude of the deformation.