The Varre-Sai chondrite,a Brazilian fall: petrology and geochemistry

The Varre-Sai meteorite fell along the border of the states of Espirito Santo and Rio de Janeiro, Brazil; on 19 June 2010 at 5:40 pm. Petrography and X-ray powder diffraction (XRD) indicate that the rock is an L5 S4 chondrite, with blastoporphyritic texture that has not been previously described. Geochemical data based on major and rare-earth elements (REEs) show that Varre-Sai is highly similar to the other L chondrites. In Harker diagrams, Varre-Sai, L, and LL chondrites form a single group, suggesting no significant chemical differences between them and contributing to the long-standing debate of whether LL chondrites form a distinct group or whether they are a subset of the L group. Harker diagrams also define a trend from E to H and L/LL chondrites, similar to the cosmochemical trends suggested by other authors. The behaviour of Fe₂O_3t and NiO indicates a relationship with Fe-Ni alloys, and their trend in the diagram suggests some chemical differentiation in the ordinary chondrite parental bodies. The REE content in Varre-Sai, normalized to C chondrites, falls in the field of L chondrites and others, but with slight REE enrichment. The chemical differences in chondrites, mainly in REEs, Fe₂O_3t and NiO could be alternatively interpreted as variations in the inherited agglutinated materials as chondrules, Ca–Al-rich inclusions and Fe–Ni nodules.     

Multi-model calibration and combination of tropical seasonal sea surface temperature forecasts

Different combination methods based on multiple linear regression are explored to identify the conditions that lead to an improvement of seasonal forecast quality when individual operational dynamical systems and a statistical–empirical system are combined. A calibration of the post-processed output is included. The combination methods have been used to merge the ECMWF System 4, the NCEP CFSv2, the Météo-France System 3, and a simple statistical model based on SST lagged regression. The forecast quality was assessed from a deterministic and probabilistic point of view. SSTs averaged over three different tropical regions have been considered: the Niño3.4, the Subtropical Northern Atlantic and Western Tropical Indian SST indices. The forecast quality of these combinations is compared to the forecast quality of a simple multi-model (SMM) where all single models are equally weighted. The results show a large range of behaviours depending on the start date, target month and the index considered. Outperforming the SMM predictions is a difficult task for linear combination methods with the samples currently available in an operational context. The difficulty in the robust estimation of the weights due to the small samples available is one of the reasons that limit the potential benefit of the combination methods that assign unequal weights. However, these combination methods showed the capability to improve the forecast reliability and accuracy in a large proportion of cases. For example, the Forecast Assimilation method proved to be competitive against the SMM while the other combination methods outperformed the SMM when only a small number of forecast systems have skill. Therefore, the weighting does not outperform the SMM when the SMM is very skilful, but it reduces the risk of low skill situations that are found when several single forecast systems have a low skill.     

Mercury in the ecosystem of Admiralty Bay,King George Island,Antarctica: Occurrence and trophic distribution

Mercury (Hg) can reach the environment through natural and human-related sources, threatening ecosystems all over the planet due to its well known deleterious effects. Therefore, Antarctic trophic webs, despite being relatively isolated, are not exempt of its influence. To evaluate Hg concentrations in an Antarctic ecosystem, different tissues from 2 species of invertebrates, 2 of fish, 8 of birds, 4 of pinnipeds and at least 5 of vegetation were investigated (n = 176). For animals, values ranged from 0.018 to 48.7 μg g^? 1 dw (whole Antarctic krill and Antarctic Fur Seal liver). They were generally correlated to trophic position (assessed by δ¹⁵N and δ¹³C) but also to cephalopods and myctophids consumption. For vegetation, values ranged from 0.014 to 0.227 μg g^? 1 dw (Colobanthus quitensis and an unidentified lichen), with lichens presenting significantly higher values than mosses, likely due to year-round exposure and absorption of animal derived organic matter, as hypothesized by literature.     

Persistent organic pollutants in marine biota of São Pedro and São Paulo Archipelago,Brazil

Remote islands, such as the São Pedro and São Paulo Archipelago (SPSPA), Brazil, are pristine areas. However, these locations are not exempt from the arrival of anthropogenic agents, such as persistent organic pollutants (POPs). The present study aimed to determine the occurrence and distribution of POPs in the marine biota of the SPSPA. Sample extractions were performed using a microwave-assisted method. The predominant compounds were PCBs and DDTs, which respectively had mean wet weight concentrations of 62.23 and 9.23 ng g⁻¹ in the tropical two-wing flying fish (Exocoetus volitans), 78.66 and 6.81 ng g⁻¹ in the brown booby (Sula leucogaster) and 43.40 and 3.03 ng g⁻¹ in the red rock crab (Grapsus grapsus). Low levels of contaminants suggest a relative degree of isolation. Occurrence and distribution profiles of PCBs support long-range atmospheric transport as the main source of contamination and demonstrate the ubiquity of these pollutants in the marine environment.     

Trophic relationships in tidepool fish assemblages of the tropical Southwestern Atlantic

Trophic studies are fundamental to understanding the dynamics of assemblages and functional roles of species within ecosystems, contributing to the identification of factors responsible for the organization and structure of communities. This study aimed to analyse the trophic organization of tidepool fish assemblages in the tropical Southwestern Atlantic, based on the underlying idea that food resources are not limiting and that trophic guild formation is not driven by food competition. Diets were based on feeding index values of food categories for 12 representative species collected in six tidepools (20º49′ S, 40º36′ W) at quarterly intervals (2005 to 2007). The main food categories were small crustaceans, polychaetes and macroalgae. Multivariate techniques evidenced two multispecific trophic guilds: small‐prey carnivores, including Bathygobius soporator, Bathygobius geminatus, Malacoctenus delalandii and Halichoeres poeyi, and herbivores, including Sparisoma axillare and Acanthurus bahianus. Other species presented significantly different diets and were classified into the following guilds: omnivores feeding on filamentous algae and copepods (Abudefduf saxatilis); large‐prey carnivores (Labrisomus nuchipinnis); omnivores feeding on polychaetes and filamentous algae (Stegastes fuscus); and polychaete feeders (Ahlia egmontis). Gymnothorax funebris and Gymnothorax moringa were classified as carcinophagores and piscivores, respectively. Trophic organization appears related to species convergence toward the use of abundant food resources, driven by a combination of factors allowing some resource partitioning through inter‐specific differences in consumer size, microhabitat, behavior, and trophic specialization.     

Late Holocene mangrove dynamics dominated by autogenic processes

Generally, palaeoenvironmental interpretations consider only allogenic processes, when autogenic factors may have a strong influence on proxies of stratigraphic sequences. For instance, the Holocene history of the vegetation along the southern littoral of the State of Bahia in north‐eastern Brazil is characterized by mangrove dynamics controlled by allogenic processes. However, over smaller timescales (~700 years), autogenic processes may have controlled vegetation dynamics and hence observed pollen distribution. This work proposes tidal channel dynamics as one of the main cause for changes in pollen assemblage along the studied stratigraphic profiles during the last centuries, based on sedimentology, pollen and elemental analysis (δ¹³C, δ¹⁵N and C/N) and radiocarbon dating of sedimentary organic matter from two cores sampled from an abandoned meander and a tidal flat at the mouth of the Jucuruçu River. One core was sampled from a mangrove formed during the past ~550 cal yr bp . Another core recorded sediments in a várzea forest (swamp seasonally and permanently inundated by freshwater) located ~2.7 km from the current shoreline, which displayed a maximum age of ~680 cal yr bp . Two facies associations were identified: tidal channel (A) and tidal flat/oxbow lake (B). This work proposes allogenic processes as the main driving forces controlling the wetlands dynamics at the studied site during the Holocene. However, our data also reveal that part of the changes in vegetation over the last ~700 years reflect tidal channels and tidal flats development, which represent autogenic processes. The change in timescale analysis from the Holocene to recent centuries may have weakened the influence of allogenic factors. However, this needs interpretation with reference to the spatial scale of the depositional environment as the larger the depositional system analyzed, the stronger the influence of autogenic processes on stratigraphic sequences over longer timescales. Copyright © 2017 John Wiley & Sons, Ltd.