Metals from star-forming dwarfs: retention or ejection?

We show evidences that gas outflows occur in starburst galaxies as superbubbles evolve. We then question whether hot gas will be expelled and enrich the IGM with metals or be retained within the host galaxy. For this purpose we construct three extreme scenarios of the star formation histories for a sample of dwarf galaxies using either their present metallicity or their luminosity. The three scenarios imply different mechanical energy input rates, those are compared with theoretical lower limits for the ejection of processed matter out of host galaxies. The comparison strongly points at the existence of extended gaseous haloes acting as a barrier that allows these galaxies to retain their metals and enhance their abundance. Our findings strongly point that continuous star-forming processes, rather than coeval bursts, must contribute to the overall metallicity in our galaxy sample. This revised version was published online in September 2006 with corrections to the Cover Date.     

Ecosystem metabolism and carbon fluxes of a tidally-dominated coastal lagoon

The metabolism and carbon flux in the western sector of the highly dynamic coastal lagoon Ria Formosa (south Portugal) were assessed to elucidate the relative importance of the contribution of the main communities, the treated sewage inputs from the adjacent city of Faro, and the exchange with the adjacent coastal waters to the ecosystem metabolism. The results depict the Ria Formosa as being a highly productive ecosystem dominated by the seagrassZostera noltii. The community dominated by the seagrassCymodocea nodosa had half of the gross production ofZ. noltii, followed by bare sediments and phytoplankton. The net contribution of seagrasses to community metabolism was negligible, as bothZ. noltii andC. nodosa showed a production: respiration ratio close to 1. Benthic microalgae emerge as the most important components of the net metabolism. The western sector of Ria Formosa was in metabolic balance during the summer when the study was done. Even though the total net ecosystem production was 7.22 Kmol C d⁻¹, the error associated with this estimate was 8.38 Kmol C d⁻¹, so ecosystem net production was not significantly different from zero. The Ria Formosa ecosystem is shallow and rapidly flushed by the tides, which force an important exchange of dissolved organic carbon (DOC) and particulate organic carbon (POC) with the adjacent coastal waters. The daily net export rate to the adjacent coastal waters, 0.98 Kmol d⁻¹, represented 7.6% of the net ecosystem production, suggesting that the bulk of the net ecosystem production accumulates within the ecosystem. The organic carbon retention in the western sector of the Ria Formosa is higher than net production, because the allochthonous carbon inputs from urban sewage enter the carbon mass balance with about 40% of the autochthonous processes, at about 1.6 Kmol d⁻¹ of DOC and 2.8 Kmol d⁻¹ of POC. The western sector of Ria Formosa has an organic carbon sink of about 46.4 tons per year. Most of this is harvested in the form of molluscs (clams, cuttlefish, etc.) and fish (sea bream, sea bass, etc.). The total carbon harvested every year in the form of bivalves is about 40 tons, rendering the Ria Formosa the most productive seafood area in Portugal.     

Low-Mass Young Stars in Cep OB2: Ages, Distribution and Accretion Disks

We are studying the young clusters Tr37 and NGC7160 in the Cep OB2 region as part of a program to understand the evolution of accretion disks at the ages of disk dissipation and planet formation. Here, we present the first identifications of low mass (spectral types K-M) members of the clusters and study the presence and characteristics of their accretion disks, finding evidences of disk evolution. Using optical photometry and spectroscopy, we have identified ～70 members in Tr37 and ～20 in NGC7160, confirming age estimates of 3 and 10 Myr respectively. Accretion rates are ～10^?8 M _⊙yr^?1 in Tr37. We have not found any accreting members in NGC7160, suggesting that disk accretion generally ends before the age of 10 Myr, which is consistent with the results from other populations.     

Amphibolite to granulite transition in aluminous greywackes from the Sierra de Comechingones, Córdoba, Argentina

We discuss upper-amphibolite to granulite facies, early Palaeozoic metamorphism and partial melting of aluminous greywackes from the Sierra de Comechingones, SE Sierras Pampeanas of Central Argentina. Consistent P–T estimates, obtained from equilibria involving Al and Ti exchange components in biotite and from more traditional thermobarometric equilibria, suggest that peak metamorphism of the exposed section took place at an essentially constant pressure of 7–8 kbar, and at temperatures ranging from 650 to 950 °C. Mineral compositions record an initial decompression, after peak metamorphism, of c. 1.5 kbar, which was accompanied by a cooling of c. 100 °C. Upper-amphibolite facies gneisses consist of the assemblage Qtz+Pl+Bt+Grt+Rt/Ilm. The transition to the granulite facies is marked by the simultaneous appearance of the assemblage Kfs+Sil and of migmatitic structures, suggesting that the amphibolite to granulite transition in the Sierra de Comechingones corresponds to the beginning of melting. Rocks with structural and/or chemical manifestations of partial melting range from metatexites, to diatexites, to melt-depleted granulites, consisting of the assemblage Grt+Crd+Pl+Qtz+Ilm±Ath. The melting stage overlapped at least partially with decompression, as suggested by the occurrence of cordierite, in both the migmatites and the residual granulites, of two distinct textural types: idiomorphic porphyroblasts (probably representing peritectic cordierite) and garnet-rimming coronas. Metapelitic rocks are unknown in the Sierra de Comechingones. Therefore, it appears most likely that the Al-rich residual assemblages found in the migmatites and residual granulites were formed by partial melting of muscovite- and sillimanite-undersaturated metagreywackes. We propose a mechanism for this that relies on the sub-solidus stabilization of garnet and the ensuing changes in the octahedral Al content of biotite with pressure and temperature.     

A method of downscaling temperature maps based on analytical hillshading for use in species distribution modelling

Climate maps have been widely used for the construction of species distribution models. These maps derive from interpolation of data collected by meteorological stations. The sparse distribution of stations generates maps with coarse spatial resolution that are unable to detect microclimates or areas that can serve as plant or animal refuges. This work proposes a method for downscaling temperature maps using the solar radiation falling upon hillsides as predictor for the influence of relief on local variability. Solar irradiance is estimated from a digital elevation model of the study area using a routine based on analytical hillshading. Some examples of downscaling from 1 km to 25 m spatial resolution are shown. The results are compared with the surface temperature maps from Landsat 8 satellite imagery.     

Pedo‐Geochemical Signatures of Archeological Sites in the Tapirapé‐Aquiri National Forest in Marabá, Amazonia,Brazil

The present study aims to interpret the occupation of terra firme (nonflooded uplands) archeological sites located at Tapirapé‐Aquiri National Forest in the Brazilian state of Pará, through an integrated analysis of pedological, archeological, and geochemical data. We focus on seven archaeological sites, selected among 22 identified in the region. Radiocarbon and thermoluminescence dating indicate distinct periods of occupation over the past ∼6000 years, and the pedo‐geochemical data identify intra‐ and inter‐site differences in soil. Archaeological, chronometric, and pedo‐geochemical data provide a basis for the functional classification of archeological sites found in the region and help to identify specific human activity areas. The results lead us to infer that many of the archeological sites were the result of multiple occupations that left a persistent pedological signature on the landscape.     

Environmental change in the Ría de Vigo,NW Iberia,since the mid‐Holocene: new palaeoecological and seismic evidence

Pollen analyses (pollen, dinocysts and others) were combined with high‐resolution seismic‐stratigraphy sequences to reconstruct environmental dynamics and regional sea‐level (RSL) changes in a ria in NW Iberia. The chronological framework was established using radiocarbon dating and pollen markers that are related to a number of historical events. Major intensifications of the regional upwelling regime occurred during predominant NAO positive stages, dated to c. 4600–4300, 3800–3600, 3200–2700 and 2600–2400 cal. a BP. The regional Early Highstand System Tract spans from before 4500 to c. 3200 cal. a BP. During this period RSL was still rising, but several short episodes of higher terrestrial influence were detected between c. 4300–3800 and 3600–3200 cal. a BP. A readjustment occurred between 3200 and 2300 cal. a BP, including the first stage of relative sea‐level drop (2.8 ka event) dated to 3200–2800 cal. a BP, with the RSL recovering between 2800 and 2300 cal. a BP. The subsequent Later Highstand System Tract, after 2300 cal. a BP, corresponds to a final period of rising sea level that caused the final inundation of San Simón Bay. Since then, only minor changes in relative sea level can be postulated (e.g. towards the end of the Roman Period, in the Middle Ages and during the Little Ice Age). This new evidence is consistent with most of the available palaeoecological and historical information, but it provides a more detailed, near‐complete succession of simultaneous changes occurring in both the terrestrial and the marine ecosystems.     

Environmental issues in urban groundwater systems: a multidisciplinary study of the Paranhos and Salgueiros spring waters,Porto (NW Portugal)

This study presents the results of a multidisciplinary approach, using hydrogeochemical, isotopic and ecotoxicological analyses, performed to assess the nature and suitability for use of Paranhos and Salgueiros spring waters (Porto city, NW Portugal). Based on the surface activities located along the course of the springs, 23 water samples were collected. All the samples were analysed for major element concentrations. The isotopic techniques employed included δ²H, δ¹⁸O and ³H. Standard acute bioassays with Daphnia magna were also performed. The hydrogeochemical analyses showed a nitrate and sulphate-enriched composition for these groundwaters, resulting mainly from urban drainage and sewer leakage. In the ecotoxicological analyses, no significant mortality was observed in any of the tests performed. The results obtained in this study suggest that Porto urban groundwater could be suitable for irrigation uses.