Linking thermodynamic modelling,Lu–Hf geochronology and trace elements in garnet: new P–T–t paths from the Sevier hinterland

Major element, trace element and Lu–Hf geochronological data from amphibolite facies pelitic schist in the Raft River and Albion Mountains of northwest Utah and southern Idaho indicate that garnet grew during increasing pressure, interpreted to be the result of tectonic burial and crustal thickening during Sevier orogenesis. Garnet growth was interrupted by hiatuses interpreted from discontinuities in major element zonation. Pressure–temperature paths were determined from the pre‐hiatus portions of the garnet chemical zoning profiles and indicate an increase of ~2 kbar and ~50 °C in the western Raft River Mountains. Garnet Lu–Hf dates of 150 ± 1 Ma in the western Raft River Mountains and 138.7 ± 0.7 Ma and 132 ± 5 Ma in the southern Albion Mountains indicate the timing of garnet growth. Lutetium garnet zoning profiles indicate that the Lu–Hf ages are biased towards the post‐hiatus or outer pre‐hiatus segments, indicating that the determined ages likely post‐date the recorded P–T path history or date the tail end of the paths. Crustal thickening associated with Sevier orogenesis in the western Raft River Mountains thus began slightly before 150 ± 1 Ma, in the Late Jurassic. This study shows that integrating P–T paths determined from garnet growth zoning with Lu–Hf garnet geochronology and in situ garnet trace element analyses is an effective approach for interpreting and dating deformation events in orogenic belts.     

DDT in endangered Galapagos sea lions (Zalophus wollebaeki)

We characterize for the first time the presence of DDT and its metabolites in tropical Galapagos sea lions (Zalophus wolleabeki). ∑DDT concentrations in Galapagos sea lion pups sampled in 2005 and 2008 ranged from 16 to 3070 μg/kg lipid. Concentrations of ∑DDT in pups in 2008 averaged 525 μg/kg lipid and were 1.9 times higher than that (281 μg/kg lipid) detected in pups in 2005. These concentrations are lower than those reported in many pinnipeds elsewhere, comparable to those in Hawaiian monk seals, and higher than those in southern elephant seals. The health risk characterization showed that 1% of the male pups exceeded the p,p′-DDE toxic effect concentration associated with anti-androgenic effects reported in rats. The findings provide preliminary guidance on the relationship between DDT use and ecological impacts, serving as a reference point against which possible future impact of tropical DDT use can be assessed.     

Consistent scale-dependency of future increases in hourly extreme precipitation in two convection-permitting climate models

Climate Dynamics - Convection-permitting models (CPMs) have been proven successful in simulating extreme precipitation statistics. However, when such models are used to study climate change,...     

Effects of Elevated Atmospheric CO(2) on Rhizosphere Soil Microbial Communities in a Mojave Desert Ecosystem

The effects of elevated atmospheric carbon dioxide [CO₂] on microbial communities in arid rhizosphere soils beneath Larrea tridentata were examined. Roots of Larrea were harvested from plots fumigated with elevated or ambient levels of [CO₂] using Free-Air CO₂ Enrichment (FACE) technology. Twelve bacterial and fungal rRNA gene libraries were constructed, sequenced and categorized into operational taxonomical units (OTUs). There was a significant decrease in OTUs within the Firmicutes (bacteria) in elevated [CO₂], and increase in Basiomycota (fungi) in rhizosphere soils of plots exposed to ambient [CO₂]. Phylogenetic analyses indicated that OTUs belonged to a wide range of bacterial and fungal taxa. To further study changes in bacterial communities, Quantitative Polymerase Chain Reaction (QPCR) was used to quantify populations of bacteria in rhizosphere soil. The concentration of total bacteria 16S rDNA was similar in conditions of enriched and ambient [CO₂]. However, QPCR of Gram-positive microorganisms showed a 43% decrease in the population in elevated [CO₂]. The decrease in representation of Gram positives and the similar values for total bacterial DNA suggest that the representation of other bacterial taxa was promoted by elevated [CO₂]. These results indicate that elevated [CO₂] changes structure and representation of microorganisms associated with roots of desert plants.     

The non-Gaussian cold spot in WMAP

We review the properties of the non-Gaussian cold spot found in the WMAP data. The spot, which was first found in the WMAP 1-year data at position (b = −57°, l = 209°) and subtending ≈10° in the sky, has been now confirmed with the WMAP 3-year data. It is clearly detected with several different statistical methods acting on wavelet coefficients. The probability of finding such a spot in Gaussian simulations is around 1%. The frequency dependence of the spot is flat at a very high precision, rejecting the possibility of being due to the Sunyaev–Zeldovich effect or Galactic foregrounds. Finally, we discuss different possibilities which can help to explain its origin.     

The 6C** sample of steep-spectrum radio sources – II. Redshift distribution and the space density of high-redshift radio galaxies

We use the 6C** sample to investigate the comoving space density of powerful, steep-spectrum radio sources. This sample, consisting of 68 objects, has virtually complete K -band photometry and spectroscopic redshifts for 32 per cent of the sources. In order to find its complete redshift distribution, we develop a method of redshift estimation based on the K – z diagram of the 3CRR, 6CE, 6C* and 7CRS radio galaxies. Based on this method, we derive redshift probability density functions for all the optically identified sources in the 6C** sample. Using a combination of spectroscopic and estimated redshifts, we select the most radio luminous sources in the sample. Their redshift distribution is then compared with the predictions of the radio luminosity function of Jarvis et al. We find that, within the uncertainties associated with the estimation method, the data are consistent with a constant comoving space density of steep-spectrum radio sources beyond z ≳ 2.5, and rule out a steep decline.     

Stock Evaluation of Three Littoral Echinoid Species on the Catalan Coast North-Western Mediterranean

Abstract. We estimated the abundances of the three common littoral echinoid species Paracentrotus lividus, Arbacia lixula and Sphaerechinus granularis in a littoral zone between 0 and 10m depth on the Catalan shores NE Spain. Densities of each species were estimated from a total number of 11 571× 1 m² sampling units deployed at 152 sites along the 13 zones into which the coast was divided. The surface area available in each of these zones was estimated at the scale of the sampling unit 1 m² taking into account the fractal dimension of the shore. The stocks individuals > 2cm test diameter of these species for the whole Catalan shore ≅ 300 km, straight-line distance were estimated to be about 279.1 × 10⁶ individuals for P. lividus , 28.9 × 10⁶ individuals for A. lixula and 10.9 × 10⁶ individuals for S. granularis. These sea-urchins are key species in the regulation of algal communities and some of them P. lividus. S. granularis are of commercial interest. This information will provide a tool for the future monitoring and management of this resource, which now faces diverse pressures of human origin.