The Role of Multi-Mission ERS Altimetry in the Determination of the Marine Geoid in the Azores

This study concerns the determination of a regional geoid model in the North Atlantic area surrounding the Azores islands by combining multi-mission altimetry from the ERS (European Remote Sensing) satellites and surface gravity data. A high resolution mean sea surface, named AZOMSS99, has been derived using altimeter data from ERS-1 and ERS-2 35-day cycles, spanning a period of about four years, and from ERS-1 geodetic mission. Special attention has been paid to data processing of points around the islands due to land contamination on some of the geophysical corrections. A gravimetric geoid has been computed from all available surface gravity, including land and sea observations acquired during an observation campaign that took place in the Azores in October 1997 in the scope of a European and a Portuguese project. Free air gravity anomalies were derived by altimetric inversion of the mean sea surface heights. These were used to fill the large gaps in the surface gravity and combined solutions were computed using both types of data. The gravimetric and combined solutions have been compared with the mean sea surface and GPS (Global Positioning System)-levelling derived geoid undulations in five islands. It is shown that the inclusion of altimeter data improves geoid accuracy by about one order of magnitude. Combined geoid solutions have been obtained with an accuracy of better than one decimetre.     

Geoarchaeology of Pleistocene open-air sites in the Vila Nova da Barquinha-Santa Cita area (Lower Tejo River basin, central Portugal)

This paper aims to provide insight into human occupation and landscape change during the Pleistocene in a central area of the Lower Tejo basin (Portugal). Detailed geomorphological mapping, coupled with lithostratigraphy, sedimentology and luminescence dating, supports the identification of a complete terrace staircase sequence. It consists of six gravely terraces located below the culminant (Pliocene) basin unit. A chronological framework for the sedimentary sequences and associated human industries is proposed and correlated with marine oxygen isotope stages (MIS): T1 terrace, not dated; T2, not dated; T3, >300 ka; T4, ∼300-160 ka (MIS8, MIS7 and MIS6); T5, ∼136-75 ka (MIS5); T6, ∼62-30 ka (MIS3); colluvium and aeolian sands, ∼30-14 ka (MIS2); valley fill deposits, ∼14 ka to present (MIS1). The oldest artefacts were found at the base of the T4 terrace, with the local stratigraphic level dated to ≥175 ± 6 ka (Middle Pleistocene). The lithic assemblages collected from distinct stratigraphic levels (T4, T5 top, T6 terraces and colluvium) are characterized by the predominance of opportunistic technological choices, a feature that can be attributed partly to the preferential exploitation of the available raw material, dominated by local-sourced quartzites and quartz pebbles. The adaptation to local raw material (texture and volume), together with subsistence patterns and behaviours, could explain the rarity of Acheulian types (handaxes and cleavers) and picks in the T4 terraces of the Tejo tributaries; this is in contrast to the same terrace of the Tejo valley, in which these types are found. Interpretation of the environmental conditions (controlled by climate and glacio-eustatic sea-level changes) affecting the hunter-gatherer human groups is also presented.     

Management of non-structural measures in the prevention of flash floods: a case study in the city of Duque de Caxias,state of Rio de Janeiro,Brazil

In the last years, natural hazards related to flash floods have caused serious damage and losses to the population of the state of Rio de Janeiro. This research discusses the importance of implementing a methodology for the prevention of flash floods, by comparing the methods applied since 2013 in the city of Duque de Caxias, in the Baixada Fluminense region of the state of Rio de Janeiro, Brazil, and the major prevention actions suggested by the Flash Flood Early Warning System Reference Guide from the National Oceanic and Atmospheric Administration, questioning civil defense professionals about the importance of each method to vulnerable communities. Even without the occurrence of an extreme event that proves the effectiveness of the method between 2014 and 2016, the population will certainly be better prepared to face the risks of disasters in the city in the future. In addition, the study also underscores an approach of approximation between academic studies and operational activities, which is still very incipient in Brazil.     

Lead isotope constraints on the genesis of Pb–Zn deposits in the Neoproterozoic Vazante Group, Minas Gerais, Brazil

The Neoproterozoic Vazante Group at the western border of the São Francisco Craton, Brazil, hosts the largest Zn–Pb district in South America. Several authors have classified this mineral district as Mississippi Valley-type (MVT), based on the intimate association with carbonates and the epigenetic character of most ore bodies. In this paper, we present 47 new lead isotope data from four deposits located along the 300 km N–S Vazante–Paracatu–Unai linear trend. Pb isotope ratios indicate sources with relatively high U/Pb and Th/Pb ratios. Considering the ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios as indicative parameters for the source, we suggest an upper crustal source for the metals. The small variation on the Pb isotope ratios compared to those observed in the classical MVT deposits, and other geological, fluid inclusion and sulphur isotopic data indicates a metallogenic event of long duration. It was characterized by focused circulation of hydrothermal fluids carrying metals from the basement rocks and from the sedimentary pile. The data obtained are more compatible with an evolution model similar to that of IRISH-type deposits. The existence of three Pb isotopic populations could be the result of regional differences in composition of the source rocks and in the fluid–rock interaction since the mineralization is a long-term process.     

Prospective scenarios for water quality and ecological status in Lake Sete Cidades (Portugal): The integration of mathematical modelling in decision processes

The design of alternative strategies for water and ecological quality protection at the Lake Verde of Sete Cidades should be coupled with the assessment of future trophic states. Therefore, a mathematical model was developed to make prospective scenarios to reduce the risk of environmental degradation of the lake, and a modified Psenner scheme was used to characterize P distribution in the sediments. The model was able to describe thermal stratification, nutrient cycling (P, NH₄ and NO₃), dissolved O₂, and phytoplankton dynamics in the water column and adjacent sediment layers. Internal P recycling, resulting from thermal stratification and sediment anoxia, was identified as the main cause for the increase of P concentration in the hypolimnion followed by slow transfer to the epilimnion (about 20 μg/L annual average). Cyanobacteria blooms during spring were explained by the availability of P and increased water temperature verified during this season. The most sensitive model parameter was sediment porosity. This parameter has a direct effect in dissolved O₂ and P profiles and also in phytoplankton biomass. Finally, different water quality restoration scenarios were identified and their effectiveness assessed. Without the adoption of remediation measures (scenario control), Lake Verde water quality would deteriorate with annual average concentrations of total P and phytoplankton biomass (dry matter) reaching 34 μg/L and 2 mg/L, respectively, after 10 years of simulation. The reduction of P loads (scenario PORAL) into the lake would improve water quality comparatively to the scenario control, reducing the annual average concentrations of total P from 34 μg/L to 26 μg/L and of phytoplankton from 2 mg/L down to 1.4 mg/L after 10 years of simulation. In scenario sediments, corresponding to a decrease in the organic content of the sediments, a reduction in the concentrations of total P and phytoplankton is expected in the first two years of simulation, but this effect, would be attenuated throughout the years due to organic matter sedimentation. The best strategy is obtained by combining external and internal measures for P remediation. Finally, it is recommended that the model be used to integrate the results of water quality monitoring and watershed management plans.     

The influence of geological, geochemical, and biogenic habitat heterogeneity on seep biodiversity

Cold seeps are among the most heterogeneous of all continental margin habitats. Abiotic sources of heterogeneity in these systems include local variability in fluid flow, geochemistry, and substrate type, which give rise to different sets of microbial communities, microbial symbiont-bearing foundation species, and associated heterotrophic species. Biogenic habitats created by microbial mats and the symbiotic species including vesicomyid clams, bathymodiolin mussels, and siboglinid tubeworms add an additional layer of complexity to seep habitats. These forms of habitat heterogeneity result in a variety of macrofaunal and meiofaunal communities that respond to changes in structural complexity, habitat geochemistry, nutrient sources, and interspecific interactions in different ways and at different scales. These responses are predicted by a set of theoretical metacommunity models, the most appropriate of which for seep systems appears to be the 'species sorting' concept, an extension of niche theory. This concept is demonstrated through predictable patterns of community assembly, succession, and beta-level diversity. These processes are described using a newly developed analytical technique examining the change in the slope of the species accumulation curve with the number of habitats examined. The diversity response to heterogeneity has a consistent form, but quantitatively changes at different seep sites around the world as the types of habitats present and the size-classes of fauna analyzed change. The increase in beta diversity across seep habitat types demonstrates that cold seeps and associated biogenic habitats are significant sources of heterogeneity on continental margins globally.     

The influence of seasonal signals on the estimation of the tectonic motion in short continuous GPS time-series

Most GPS time-series exhibit a seasonal signal that can have an amplitude of a few millimetres. This seasonal signal can be removed by fitting an extra sinusoidal signal with a period of one year to the GPS data during the estimation of the linear trend.However, Blewitt and Lavallée (2002) showed that including an annual signal in the estimation process still can give a larger linear trend error than the trend error estimated from data from which the annual signal has been removed by other means. They assumed that the GPS data only contained white noise and we extend their result to the case of power-law plus white noise which is known to exist in most GPS observations. For the GPS stations CASC, LAGO, PDEL and TETN the difference in trend error between having or not having an annual signal in the data is around ten times larger when a power-law plus white noise model is used instead of a pure white noise model. Next, our methodology can be used to estimate for any station how much the accuracy of the linear trend will improve when one tries to subtract the annual signal from the GPS time-series by using a physical model.Finally, we demonstrate that for short time-series the trend error is more influenced by the fact that the noise properties also need to be estimated from the data. This causes on average an underestimation of the trend error.     

Visual analytics for diagnosing spatial interpolation models

The development and widespread use of statistical learning models have brought the need for tools that help analysts diagnose, build, and refine those models. In this work, in particular, we focus on interpolation models, which spatially predict the value of a variable based on the values of its neighborhood. Investigating these results spatially or comparing them with other models at different levels of granularity is still a challenge for the analysts trying to understand and refine their models. To deal with that, we propose a visual analytics model-agnostic tool for facilitating the comparison and refinement of spatial models at different levels of granularity using interactive visualization techniques. The tool was built in collaboration with specialists who used it to diagnose and improve a spatial model for predicting residential real estate prices.