Development of a foraminifera-based transfer function in the Basque marshes, N. Spain: Implications for sea-level studies in the Bay of Biscay

In order to reconstruct former sea level we have developed a foraminifera-based transfer function using three models based on a modern dataset of 59 samples and 23 species obtained from four Basque marshes in Northern Spain. The relationship between observed and foraminifera-predicted elevation illustrated the strong performance of the transfer function (r²_jack ranges from 0.74 to 0.81). These results indicated that precise reconstructions of former sea levels are possible (error ranges from 0.11 to 0.19 m). The transfer function was used to calibrate the foraminiferal assemblages collected from a 50 cm salt marsh core. We placed the foraminifera-based reconstructions into a temporal framework using ¹³⁷Cs, Pb concentrations, and ²¹⁰Pb-derived sediment accumulation rates. The resulting relative sea-level curve is in good agreement with regional tide-gauge data. Both instrumental data and microfossil records suggest a rate of relative sea-level rise of approximately 2 mm yr^− 1 for the 20th century.     

Season‐based rainfall–runoff modelling using the probability‐distributed model (PDM) for large basins in southeastern Brazil

Southeastern Brazil is characterized by seasonal rainfall variability. This can have a great social, economic, and environmental impact due to both excessive and deficient water availability. During 2014 and 2015, the region experienced one of the most severe droughts since 1960. The resulting water crisis has seriously affected water supply to the metropolitan region of São Paulo and hydroelectric power generation throughout the entire country. This research considered the upstream basins of the southeastern Brazilian reservoirs Cantareira (2,279 km²; water supply) and Emborcação (29,076 km²), Três Marias (51,576 km²), Furnas (52,197 km²), and Mascarenhas (71,649 km²; hydropower) for hydrological modelling. It made the first attempt at configuring a season‐based probability‐distributed model (PDM‐CEMADEN) for simulating different hydrological processes during wet and dry seasons. The model successfully reproduced the intra‐annual and interannual variability of the upstream inflows during 1985–2015. The performance of the model was very satisfactory not only during the wet, dry, and transitional seasons separately but also during the whole period. The best performance was obtained for the upstream basin of Furnas, as it had the highest quality daily precipitation and potential evapotranspiration data. The Nash–Sutcliffe efficiency and logarithmic Nash–Sutcliffe efficiency were 0.92 and 0.93 for the calibration period 1984–2001, 0.87 and 0.88 for the validation period 2001–2010, and 0.93 and 0.90 for the validation period 2010–2015, respectively. Results indicated that during the wet season, the upstream basins have a larger capacity and variation of soil water storage, a larger soil water conductivity, and quicker surface water flow than during the dry season. The added complexity of configuring a season‐based PDM‐CEMADEN relative to the traditional model is well justified by its capacity to better reproduce initial conditions for hydrological forecasting and prediction. The PDM‐CEMADEN is a simple, efficient, and easy‐to‐use model, and it will facilitate early decision making and implement adaptation measures relating to disaster prevention for reservoirs with large‐sized upstream basins.     

Object-based image analysis supported by data mining to discriminate large areas of soybean

This research aimed to analyze the possibility to estimate and automatically map large areas of soybean cultivation through the use of MODIS (Moderate-Resolution Imaging Spectroradiometer) images. Two major techniques were used: GEOgraphic-Object-Based Image Analysis (GEOBIA) and Data Mining (DM). In order to obtain the images, the segmentation algorithm implemented by Definiens Developer was used. A decision tree (DT) was created from a training set previously prepared. Time-series of images from the MODIS sensor aboard the Terra satellite were acquired in order to represent the wide variation of the vegetation pattern along the soybean crop cycle. The time-series data were used only for the CEI index. Furthermore, to compare the results obtained from GEOBIA, the slicing technique was used at the CEI level. After the training, the DT was applied to the vegetation indices generating the thematic map of the spatial distribution of soybean. In accordance with the error matrix and kappa parameter analysis, tests for statistical significance were created. Results indicate that the classification achieved by Kappa coefficients is 0.76. In short, the obtained results proved that combining vegetation indices and time-series data using GEOBIA return promising results for mapping soybean plantation on a regional scale.     

Ionic exchange in groundwater hydrochemical evolution. Study case: the drainage basin of El Pescado creek (Buenos Aires province,Argentina)

The phreatic aquifer beneath the Pampean plain, in eastern central Argentina, constitutes a relevant source of water supply in the area. The objective of this work was to assess the significance of the cation exchange processes in the hydrochemical evolution of this aquifer, based on a study case located in the middle and upper basin of the El Pescado creek. Results indicate that Ca²⁺/Na⁺ exchange is the main process determining the evolution of groundwater from the recharge areas (Ca–HCO₃) towards the local discharge areas (Na–HCO₃), as well as representing a source of Na⁺ contribution to the water in the aquifer. This hydrochemical characteristic is central to the identification of local discharge areas within a plain environment which extends regionally. The ion exchange capacity of these discharge areas has environmental importance, due to its influence on groundwater quality and potential groundwater uses. These results may be applied to any aquifer sharing similar hydrogeological characteristics.     

Daily hydrological modeling in the Amazon basin using TRMM rainfall estimates

Rainfall measurements by conventional raingauges provide relatively accurate estimates at a few points of a region. The actual rainfield can be approximated by interpolating the available raingauge data to the remaining of the area of interest. In places with relatively low gauge density such interpolated rainfields will be very rough estimates of the actual events. This is especially true for tropical regions where most rainfall has a convective origin with high spatial variability at the daily level. Estimates of rainfall by remote sensing can be very useful in regions such as the Amazon basin, where raingauge density is very low and rainfall highly variable. This paper evaluates the rainfall estimates of the Tropical Rainfall Measuring Mission (TRMM) satellite over the Tapajós river basin, a major tributary of the Amazon. Three-hour TRMM rainfall estimates were aggregated to daily values and were compared with catch of ground-level precipitation gauges on a daily basis after interpolating both data to a regular grid. Both daily TRMM and raingauge-interpolated rainfields were then used as input to a large-scale hydrological model for the whole basin; the calculated hydrographs were then compared to observations at several streamgauges along the river Tapajos and its main tributaries. Results of the rainfield comparisons showed that satellite estimates can be a practical tool for identifying damaged or aberrant raingauges at a basin-wide scale. Results of the hydrological modeling showed that TRMM-based calculated hydrographs are comparable with those obtained using raingauge data.     

Upper Cretaceous trench deposits of the Neo-Tethyan subduction zone: Jiachala Formation from Yarlung Zangbo suture zone in Tibet,China

The history of convergence between the India and the Asia plates, and of their subsequent collision which triggered the Himalayan orogeny is recorded in the Yarlung Zangbo suture zone. Exposed along the southern side of the suture, turbidites of the the Jiachala Formation fed largely from the Gangdese arc have long been considered as post-collisional foreland-basin deposits based on the reported occurrence of Paleocene-early Eocene dinoflagellate cysts and pollen assemblages. Because magmatic activity in the Gangdese arc continued through the Late Cretaceous and Paleogene, this scenario is incompatible with U-Pb ages of detrital zircons invariably older than the latest Cretaceous. To solve this conundrum, we carried out detailed stratigraphic, sedimentological, paleontological, and provenance analyses in the Gyangze and Sajia areas of southern Tibet,China. The Jiachala Formation consists of submarine fan deposits that lie in fault contact with the Zongzhuo Formation.Sandstone petrography together with U-Pb ages and Hf isotope ratios of detrital zircons indicate provenance from the Gangdese arc and central Lhasa terrane. Well preserved pollen or dinoflagellate cysts microfossils were not found in spite of careful research, and the youngest age obtained from zircon grain was ～84 Ma. Based on sedimentary facies, provenance analysis and tectonic position, we suggest that the Jiachala Formation was deposited during the Late Cretaceous(~88–84 Ma) in the trench formed along the southern edge of Asia during subduction of Neo-Tethyan oceanic lithosphere.     

Simulated X-ray emission from a single-explosion model for a supernova remnant 3C 400.2

We present a single-explosion model study of the 3C 400.2 supernova remnant (SNR), made with two-dimensional axisymmetric simulations. The numerical simulations were made with the adaptive grid code yguazú-a . Several initial scenarios have been tested in order to reproduce the centrally peaked X-ray emission observed for this remnant. This study reveals that the explosion of the SN inside a pre-existing stellar wind bubble successfully generates the observed morphology, when thermal conduction is included in the model. The best morphological fit is obtained at an evolution time of 21 000 yr, when the total luminosity is  1.2 × 10³⁴ erg s⁻¹  .     

Evaluation of the possible presence of clathrate hydrates in Europa's icy shell or seafloor

Several substances besides water ice have been detected on the surface of Europa by spectroscopic sensors, including CO₂, SO₂, and H₂S. These substances might occur as pure crystalline ices, as vitreous mixtures, or as clathrate hydrate phases, depending on the system conditions and the history of the material. Clathrate hydrates are crystalline compounds in which an expanded water ice lattice forms cages that contain gas molecules. The molecular gases that may constitute Europan clathrate hydrates may have two possible ultimate origins: they might be primordial condensates from the interstellar medium, solar nebula, or jovian subnebula, or they might be secondary products generated as a consequence of the geological evolution and complex chemical processing of the satellite. Primordial ices and volatile-bearing compounds would be difficult to preserve in pristine form in Europa without further processing because of its active geological history. But dissociated volatiles derived from differentiation of a chondritic rock or cometary precursor may have produced secondary clathrates that may be present now. We have evaluated the current stability of several types of clathrate hydrates in the crust and the ocean of Europa. The depth at which the clathrates of SO₂, CO₂, H₂S, and CH₄ are stable have been obtained using both the temperatures observed in the surface [Spencer, J.R., Tamppari, L.K., Martin, T.Z., Travis, L.D., 1999. Temperatures on Europa from Galileo photopolarimeter-radiometer: Nighttime thermal anomalies. Science 284, 1514-1516] and thermal models for the crust. In addition, their densities have been calculated in order to determine their buoyancy in the ocean, obtaining different results depending upon the salinity of the ocean and type of clathrate. For instance, assuming a eutectic composition of the system MgSO₄H₂O for the ocean, CO₂, H₂S, and CH₄ clathrates would float but SO₂ clathrate would sink to the seafloor; an ocean of much lower salinity would allow all these clathrates to sink, except that CH₄ clathrate would still float. Many geological processes may be driven or affected by the formation, presence, and destruction of clathrates in Europa such as explosive cryomagmatic activity [Stevenson, D.J., 1982. Volcanism and igneous processes in small icy satellites. Nature 298, 142-144], partial differentiation of the crust driven by its clathration, or the local retention of heat within or beneath clathrate-rich layers because of the low thermal conductivity of clathrate hydrates [Ross, R.G., Kargel, J.S., 1998. Thermal conductivity of Solar System ices, with special reference to martian polar caps. In: Schmitt, B., De Berg, C., Festou, M. (Eds.), Solar System Ices. Kluwer Academic, Dordrecht, pp. 33-62]. On the surface, destabilization of these minerals and compounds, triggered by fracture decompression or heating could result in formation of chaotic terrain morphologies, a mechanism that also has been proposed for some martian chaotic terrains [Tanaka, K.L., Kargel, J.S., MacKinnon, D.J., Hare, T.M., Hoffman, N., 2002. Catastrophic erosion of Hellas basin rim on Mars induced by magmatic intrusion into volatile-rich rocks. Geophys. Res. Lett. 29 (8); Kargel, J.S., Prieto-Ballesteros, O., Tanaka K.L., 2003. Is clathrate hydrate dissociation responsible for chaotic terrains on Earth, Mars, Europa, and Triton? Geophys. Res. 5. Abstract 14252]. Models of the evolution of the ice shell of Europa might take into account the presence of clathrate hydrates because if gases are vented from the silicate interior to the water ocean, they first would dissolve in the ocean and then, if the gas concentrations are sufficient, may crystallize. If any methane releases occur in Europa by hydrothermal or biological activity, they also might form clathrates. Then, from both geological and astrobiological perspectives, future missions to Europa should carry instrumentation capable of clathrate hydrate detection.     

Evidence for a temperature rise in the outer layers of α Lyrae,fromCopernicus observations of lyman-α

The wings of Lα in α Lyr (A0 V), observed by theCopernicus satellite, cannot be interpreted if one assumes a classical LTE model photosphere. We argue that the electron temperature must increase outwards over the surface value reached in radiative equilibrium.