The northern Patagonia Somuncura plateau basalts: a product of slab‐induced,shallow asthenospheric upwelling?

The Meseta de Somuncura forms the largest basaltic plateau (20 000 km²) of southern Argentina (extra-Andean domain). Most of these tholeiitic to alkaline rocks were extruded at ˜ 25 Ma (late Oligocene). The absence of rifting–thinning processes, plume activity, or slab-window phenomena leaves only one major possibility for the generation of Somuncura: asthenospheric ('OIB-like') corner flow leading to a transient thermal anomaly above the subducting plate. It is suggested herein that the intake of hot asthenosphere was forced into a favourable topography (concave-up) of the subducting plate, when a major plate reorganization event (Farallon to Nazca) was taking place in late Oligocene to early Miocene time. The fast and vigorous intake of asthenosphere would have been induced by slab roll-back, leading to decoupling of the subducting plate. The Somuncura volcanic episode can be regarded as a marker of the passage from the extremely oblique subduction of Farallon, to the birth of the Nazca plate and roughly perpendicular convergence between South America and Nazca.     

Long‐term temporal and spatial patterns in bioeroding sponge distribution at the Abrolhos Bank,Brazil, Southwestern Atlantic

Bioeroding sponges belong to the most dominant bioeroders, significantly contributing to the erosion of coral reefs. Some species are tolerant or even benefit from environmental conditions such as ocean warming, acidification, and eutrophication. In consequence, increases in sponge bioerosion have been observed on some coral reefs over the last decades. The Abrolhos Bank is the largest coral reef system in the South Atlantic. It has been affected by sedimentation, eutrophication, overfishing, and climate change, mainly affecting coastal reefs, and at lesser intensity outer ones as well. This study aimed to describe spatial and temporal patterns in bioeroding sponge distribution in carbonate substrates in the Abrolhos Bank. Photo‐quadrats were used to compare bioeroding sponge abundance between two shallow reefs: a coastal, Pedra de Leste (PL), and an outer reef, Parcel dos Abrolhos (PAB). Each individual was delimitated over the substrate by determining the sponge surface through a line connecting the outermost papillae. The study was conducted over 6 years in 2008–2009 and 2013–2016. Four species of bioeroding sponges were identified: Cliona carteri Ridley, 1881, C. delitrix Pang, 1973, C. cf. schmidtii Ridley, 1881, and Siphonodictyon coralliphagum Rützler, 1971. The distribution and abundance of species varied between the inner and outer reefs and across the years, and displayed certain selectivity for the calcareous substrates recorded. Crustose coralline algae (CCA) were the main substrate excavated by the most abundant bioeroding species, C. carteri, and represented 70% of the substrate types occupied by this sponge (CCA, coral overgrown by CCA and plain coral). The highest abundance of bioeroding sponges observed in photo‐quadrats was 21.3 individuals/m² at the outer reefs (PAB) in 2014. The abundances or areal extents of bioeroding sponges were up to 10 times greater on the outer reefs than on the coastal ones, where sedimentation is higher and more strongly influenced by siliciclastic material. Moreover, a higher herbivorous fish biomass has been reported on outer reefs which could also influence the higher abundance of bioeroding sponges in outer reefs. During the study period of 6 years, an increase in bioeroding sponge abundance was observed at the outer reefs (PAB), with the sea surface temperature increase. As CCA have an important role in reefal cementation and carbonate production in the Abrolhos reefs, a bioerosion impact might be expected, in particular, on the outer reefs.     

An algorithm to resolve γ-rays from charged cosmic rays with DAMPE

The DArk Matter Particle Explorer(DAMPE),also known as Wukong in China,which was launched on 2015 December 17,is a new high energy cosmic ray and γ-ray satellite-borne observatory.One of the main scientific goals of DAMPE is to observe Ge V-Te V high energy γ-rays with accurate energy,angular and time resolution,to indirectly search for dark matter particles and for the study of high energy astrophysics. Due to the comparatively higher fluxes of charged cosmic rays with respect to γ-rays,it is challenging to identify γ-rays with sufficiently high efficiency,minimizing the amount of charged cosmic ray contamination. In this work we present a method to identify γ-rays in DAMPE data based on Monte Carlo simulations,using the powerful electromagnetic/hadronic shower discrimination provided by the calorimeter and the veto detection of charged particles provided by the plastic scintillation detector. Monte Carlo simulations show that after this selection the number of electrons and protons that contaminate the selected γ-ray events at～10 Ge V amounts to less than 1% of the selected sample.Finally,we use flight data to verify the effectiveness of the method by highlighting known γ-ray sources in the sky and by reconstructing preliminary light curves of the Geminga pulsar.     

Release the iron: does the infection of magnetotactic bacteria by phages play a role in making iron available in aquatic environments?

Journal of Oceanology and Limnology - Magnetotactic bacteria(MTB) are ubiquitous prokaryotes that orient along magnetic field lines due to magnetosomes’ biomineralization within the cell....     

Regional climate change experiments over southern South America. I: present climate

We present an analysis of a regional simulation of present-day climate (1981–1990) over southern South America. The regional model MM5 was nested within time-slice global atmospheric model experiments conducted by the HadAM3H model. We evaluate the capability of the model in simulating the observed climate with emphasis on low-level circulation patterns and surface variables, such as precipitation and surface air mean, maximum and minimum temperatures. The regional model performance was evaluated in terms of seasonal means, seasonal cycles, interannual variability and extreme events. Overall, the regional model is able to capture the main features of the observed mean surface climate over South America, its seasonal evolution and the regional detail due to topographic forcing. The observed regional patterns of surface air temperatures (mean, maxima and minima) are well reproduced. Biases are mostly within 3°C, temperature being overestimated over central Argentina and underestimated in mountainous regions during all seasons. Biases in northeastern Argentina and southeastern Brazil are positive during austral spring season and negative in other seasons. In general, maximum temperatures are better represented than minimum temperatures. Warm bias is larger during austral summer for maximum temperature and during austral winter for minimum temperature, mainly over central Argentina. The broad spatial pattern of precipitation and its seasonal evolution are well captured; however, the regional model overestimates the precipitation over the Andes region in all seasons and in southern Brazil during summer. Precipitation amounts are underestimated over the La Plata basin from fall to spring. Extremes of precipitation are better reproduced by the regional model compared with the driving model. Interannual variability is well reproduced too, but strongly regulated by boundary conditions, particularly during summer months. Overall, taking into account the quality of the simulation, we can conclude that the regional model is capable in reproducing the main regional patterns and seasonal cycle of surface variables. The present reference simulation constitutes the basis to examine the climate change simulations resulting from the A2 and B2 forcing scenarios which are being reported in a separate study.     

Macroseepage of methane and light alkanes at the La Brea tar pits in Los Angeles

Geologic seepage of methane and light (C₂-C₅) alkanes was measured at the La Brea Tar Pits in Los Angeles. Samples were collected using flux chambers with stainless steel canisters and analyzed using gas chromatography. Average seepage rates from individual seepage sites were 970 ± 330 mg/h of methane, 14.0 ± 5.5 mg/h of ethane, 9.1 ± 3.7 mg/h of propane, 3.7 ± 1.6 mg/h of i-butane, 0.33 ± 0.16 mg/h of n-butane, 260 ± 120 μg/h of i-pentane, and 5.3 ± 1.9 μg/h of n-pentane, while maximum seepage rates exceeded 17 g/h of methane, 270 mg/h of ethane, 190 mg/h of propane, 95 mg/h of i-butane, 10 mg/h of n-butane, 7 mg/h of i-pentane, and 0.1 mg/h of n-pentane. These absolute fluxes have an additional unknown amount of error associated with them due to sampling methodology, and should be taken as the lower limit of emissions. Samples collected revealed generally dry gas, with high methane emissions relative to the light alkanes. Overall emissions from the tar pits were found to come not only from the active geologic seepage, but also from the outgassing of the standing asphalt at the site. Using the gas ratios, which are negligibly affected by errors introduced by sampling methodology, observed in this study, daily emissions of C₂ – C₅ alkanes from the La Brea area were estimated to be 4.7 ± 1.6 Mg, which represents 2–3 % of total emissions in the entire Los Angeles region.     

The Almadén mercury mining district, Spain

The Almadén district is the largest mercury concentration in the world, with a total content of about 250 000 t of mercury, nearly one third of the known total mercury resources of the Earth. Mercury has been exploited since the Celtic and Roman times, with peak production during the Renaissance and between 1939–1945. The district is hosted by a Paleozoic synclinorium overlying Precambrian rocks. The Paleozoic sequence comprises epicontinental quartz arenite rocks, including black shales and quartzites. Diatremes, alkaline lavas of different composition, and late tholeiitic diabases account for the Ordovician to Devonian magmatism. The tectonic setting of this complex suite corresponds to the intraplate type. The mercury deposits of Almadén can be classified into two main types: type 1, early stratiform type ores characterized by cinnabar deposition on the lower Silurian quartzites (Criadero quartzite; e.g. the Almadén and El Entredicho deposits), and type 2, late discordant orebodies (e.g. Las Cuevas), largely hosted or related to diatremes (the `frailesca rocks') of alkaline basaltic composition. In type 1 cinnabar was deposited during diagenesis, in relation to hydrothermal circulation driven by magmatic activity. Type 2 include a variety of deposits having in common the discordant character of the orebodies (e.g. veins, stockworks, massive replacements), and their wide dispersion along the stratigraphic column, i.e. from Lower Silurian (e.g. Nueva Concepción) to Upper Devonian (e.g. Corchuelo). Received: 23 October 1998 / Accepted: 4 January 1999     

Large-Scale and Mesoscale Distribution of Plankton Biomass and Metabolic Activity in the Northeastern Central Atlantic

Plankton biomass and indices of metabolism and growth [electron transport system (ETS), glutamate dehydrogenase (GDH) and aspartate transcarbamylase (ATC) activities] were studied over a 2,800 km east-west section of the tropical North Atlantic Ocean (21°N) in <200, 200–500 and >;500 µm size classes. On the large-scale, zooplankton (>;200 µm) enzymatic activities increased westward in the study section, where large cyanobacteria chains (Trichodesmium spp.) were observed. Parallel to it, an increase in medium calanoids (1–2 mm length) was observed towards the western part of the transect, whereas small calanoids (<1 mm) were dominant throughout the boundary area of the subtropical gyre. Microplankton ETS and mesoplankton ETS and ATC activities seemed to match the wave length of low frequency waves. Our results suggest that such waves are related to the observed enhancement of metabolic activity of micro- and mesoplankton. The large-scale and mesoscale variability observed give evidence of the inadequacy of assuming a steady-state picture of the euphotic zone of tropical and subtropical waters.     

Water and nutrient fluxes in a cool temperate rainforest at the Cordillera de la Costa in southern Chile

Water and nutrient fluxes were studied during a 12-month period in an alerce (Fitzroya cupressoides) forest, located in a remote site at the Cordillera de la Costa (40°05′S) in southern Chile. Measurements of precipitation, throughfall, stemflow, effective precipitation, soil infiltration and stream flow were carried out in an experimental, small watershed. Simultaneously, monthly water samples were collected to determine the concentrations and transport of organic-N, NO₃-N, total-P, K⁺, Ca²⁺, Na⁺ and Mg²⁺ in all levels of forest. Concentration of organic-N, NO₃-N, total-P and K⁺ showed a clear pattern of enrichment in the throughfall, stemflow, effective precipitation and soil infiltration. For Ca²⁺ and Mg²⁺, enrichment was observed in the effective precipitation, soil infiltration and stream flow. Annual transport of K⁺, Na⁺, Ca²⁺ and Mg²⁺ showed that the amounts exported from the forest via stream flow (K⁺=0·95, Na⁺=32·44, Ca²⁺=8·76 and Mg²⁺=7·16 kg ha⁻¹ yr⁻¹) are less than the inputs via precipitation (K⁺=6·39, Na⁺=40·99, Ca²⁺=15·13 and Mg²⁺=7·61 kg ha⁻¹ yr⁻¹). The amounts of organic-N and NO₃-N exported via stream flow (organic-N=1·04 and No₃-N=3·06 kg ha⁻¹ yr⁻¹) were relatively small; however, they represented greater amounts than the inputs via precipitation (organic-N=0·74 and NO₃-N=0·97 kg ha⁻¹ yr⁻¹), because of the great contribution of this element in the superficial soil horizon, where the processes of decomposition of organic material, mineralization and immobilization of the nutrients occurs. © 1998 John Wiley & Sons, Ltd.     

Assessment of evaporation and water fluxes in a column of dry saline soil subject to different water table levels

Dry saline soils are common in the arid and hyper‐arid basins located in the Chilean Altiplano, where evaporation from shallow groundwater is typically the major component of the water balance. Thus, a good understanding of evaporation processes is necessary for improving water resource planning and management in these regions. In this study, we conducted laboratory experiments with a natural saline soil column to estimate evaporation rates and assess the liquid and water vapor fluxes under different water table levels. Water content, electrical conductivity and temperature at different depths were utilized to assess the liquid and water vapor fluxes in the soil column. We observed movement of water that dissolves salts from the soil and transports them to areas in the column where they accumulate. Isothermal liquid flux was predominant, while thermal and isothermal liquid and thermal water vapor fluxes were negligible, except for deep water table levels where isothermal and thermal water vapor fluxes had similar magnitude but opposite directions. Differences observed in total fluxes for all water table levels were due to different upward and downward fluxes, which depend on changes in water content and temperature within the soil profile. Both the vapor flux magnitude and direction were found to be very sensitive to the choice of empirical parameters used in flux quantification, such as tortuosity and the enhancement factor for local temperature gradients in the air phase within the column. Copyright © 2013 John Wiley & Sons, Ltd.