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- The continental shelf off the Guadiana estuaryPublication . Mendes, Isabel; Rosa, Francisca; Moura, Delminda; Mendes, I.; Gomes, Ana; Aníbal, JaimeThe Continental shelf is the seafloor area around a large land mass where the sea is relatively shallow compared with the open ocean.This major physiographic domain is comprised between the shoreline and the shelf break located at variable water depths (generally, around 200 m water depth) and variable extensions (average width of about 80 km). The continental shelf off the Guadiana estuary is the area in front of the Guadiana River mouth,which is influenced by the discharges of the Guadiana River Basin.This area is located in the southern border between Portugal and Spain, in the middle part of the northern Gulf of Cadiz continental shelf, southwestern Iberian Peninsula.
- Distribution of living benthic foraminifera on the northern Gulf of Cadiz continental shelfPublication . Mendes, Isabel; Dias, J. A.; Schonfeld, J.; Ferreira, ÓscarLiving (stained) benthic foraminiferal faunas were analyzed in 51 surficial sediment samples taken from the northern Gulf of Cadiz continental shelf between the mouths of the Guadiana and Guadalquivir rivers. The distribution and abundance of 26 species with relative abundance .5% were related to water depth, sediment type, river discharge, water temperature, salinity, turbidity, and primary productivity. Hierarchical classification using R- and Q-mode cluster analyses, and individual distributions, allowed these taxa to be categorized into four general groups. Group 1 is represented by Bolivina ordinaria and Hopkinsina atlantica. These species are linked to river discharge, and are associated with muddy sediments. They are considered the most opportunistic species in the assemblage, and are associated with the limits of productivity. Group 2, contains Ammonia beccarii, Eggerelloides scaber, Elphidium gerthi, Quinqueloculina laevigata, and Q. stelligera, and is characteristic of shallow water depths. Its species are associated with different sediment types and their distribution is influenced by river discharge. Group 3 is dominated by Bulimina aculeata, B. elongata, Elphidium excavatum, E. cuvillieri, Epistominella vitrea, and Rectuvigerina phlegeri. These species display the highest abundances between 30–100 m water depths. They prevail in muds associated with weak hydrodynamics, low oxygenation, and high organic matter. Group 4 includes species that are more abundant in deep stations and is divided into two subgroups. Subgroup 4A includes Bolivina catanensis, B. italica, B. striatula, Cassidulina laevigata, Stainforthia sp., Nouria polymorphinoides, and Nouria sp., with higher abundances in one or two samples. Subgroup 4B, with Brizalina dilatata, B. spathulata, Bulimina marginata, Nonionella iridea, N. stella, and N. turgida, has patchy distribution. Higher abundances of Nonionella species off the Guadiana River are related to low temperature and salinity.
- The record of a high-energy event in a mud entrapment on the inner shelf off the Guadiana riverPublication . Mendes, Isabel; Lobo, F. J.; Schönfeld, J.; Lebreiro, S. L.; Hanebuth, T.; Lantzsch, H.; Reguera, M. I.; Antón, L.; Ferreira, ÓscarRecent environmental changes associated with high-energy events and human impacts were investigated in a mud entrapment confined in the paleo-Guadiana incised valley. Those changes were recorded in a gravity core during the last 2500 years. An erosional event seems to have occurred at ca. 500 cal yr BP but it is not clear how much sediment was removed. This event was followed by an increase in river discharges until ca. 465 cal yr BP while the benthic foraminiferal faunas were dominated by species associated with shallow-water sandy sediments. Upward, sedimentological and benthic foraminiferal variations indicated environmental changes, promoted by variable sediment supplies to the shelf.
- Last ca. 250 years shifts of benthic foraminiferal assemblages in response to natural and anthropogenic impacts, northern Alboran SeaPublication . Mendes, Isabel; Lobo, F. J.; Ferreira, Óscar; Schönfeld, J.; Rosa, F.; Bárcenas, P.; Fernandez-Salas, L. M.; López-González, N.; Dias, J. A.Benthic foraminifera have a wide distribution in space and time and also respond rapidly to environmental changes. The northern Alboran Sea is influenced by a torrential regime with sporadic, intense rainfalls and extended periods of aridity. In addition, anthropogenic activities such as river channel deviation have taken place during the last ca. 150 years. In order to understand the interaction between natural and anthropogenic impacts through time, shifts of most abundant benthic foraminiferal species, species richness and diversity indices were combined with sedimentological analyses and radiocarbon dating of sediment cores collected from the Adra shelf prodeltaic deposit, in the northern Alboran Sea. The strong variations of benthic foraminiferal assemblages involving significant population density changes occurred until ca. 1870 AD, and are interpreted as response to natural processes. Low population densities correlate with rainfall-driven periods of increased sediment supply to the shelf. In contrast, intervals with increased population densities, followed by a raise of successful colonizers and opportunistic species, indicate the establishment of an environment with new ecological constraints. After ca. 1870 AD, the impact of anthropogenic activities with the deviation of the main river course to the east, are responsible for a drastic reduction of sedimentation rates in the study area.
- Benthic foraminifera and pore water carbonate chemistry on a tidal flat and salt marsh at Ria Formosa, Algarve, PortugalPublication . Schönfeld, Joachim; Mendes, IsabelBenthic foraminifera showed a vertical zonation in tidally influenced salt marshes, which has been used for sea level reconstructions. Growing evidence suggested that freshwater influx, salinity, or the pH of interstitial waters has also an impact on the foraminiferal distribution. A tidal flat and salt marsh transect was investigated in the north-western Ria Formosa coastal lagoon, Algarve, Portugal, to constrain the relationship of benthic foraminifera, halophytes, and pore water properties. The dominance of saltworts from the subfamily Salicornioideae and landward increasing soil salinities depicted evaporation as governing environmental factor. The carbonate chemistry from lagoonal and pore waters identified anoxic tidal flat sediments of as main source of total alkalinity. The alkalinity was lower in the salt marsh, where the pCO(2) was extremely high. Salt marsh pore waters showed a high variability of carbonate system parameters, which mirrored small-scale spatial heterogeneities in the soil. The distribution of textulariid salt marsh foraminifera was confined to the vegetated zones, where their abundance increased with elevation. Calcareous species were frequent on the tidal flat and in the highest salt marsh. Many of them were specialised to high salinities or to extreme and variable environmental conditions. Two levels of faunal change in the salt marsh coincide with vegetation zonal boundaries, mean tide or mean high water levels. The two other faunal changes were related to changes in calcite saturation state or organic carbon concentrations. The proportion of textulariids showed a negative correlation with submergence time or eleva-tion, and a significant correlation with pore water pCO(2). The faunal distribution, pore water calcite saturation, and Ammonia dissolution patterns indicated that calcareous species specialised to tolerate carbonate-corrosive conditions prevailed even at lowest saturation levels.
- Factors influencing recent benthic foraminifera distribution on the Guadiana shelf (Southwestern Iberia)Publication . Mendes, Isabel; Gonzalez, R.; Dias, João M. A.; Lobo, F.J.; Martins, V.Benthic foraminiferal assemblages in 24 sediment surface samples collected at water depths ranging from 9 to 103 m on the continental shelf off Guadiana River were analysed, leading to the identification of a total of 270 species. Cluster analyses performed on species with a relative abundance higher than 5% led to the identification of four assemblages. The shallowest assemblage, down to 12 m water depth, is represented by Ammonia beccarii, Asterigerinata mamila, Eggerelloides scaber, Mississipina concentrica, Planorbulina mediterranensis, Elphidium crispum and Quinqueloculina laevigata. A second assemblage between 12 and 40 m water depth is characterised by Bulimina elongata, Cribrononion gerthi and Nonion fabum. The assemblage between 40 and 95 m water depth is characterised by Bolivina dilatata, Epistominella vitrea, Bulimina aculeata, Bolivina ordinaria, Spiroloxostoma croarae and Nonionella iridea. Finally, below a depth of 95 m on the upper outer shelf, an assemblage exists characterised by Brizalina spathulata, Bulimina marginata, Cassidulina minuta, Brizalina subaenariensis, Cassidulina laevigata and Uvigerina peregrina. The spatial distribution of assemblages is closely associated with sea-bottom sedimentary environments and bathymetry. The number of benthic foraminiferal tests, and the distribution of several nearshore species within the two shallowest assemblages are clearly influenced by the outflow of the Guadiana Estuary and by local hydrodynamic conditions. The deeper water assemblages, on the other hand, were found to be more related to low levels of tidal energy, low oxygen environments associated to fine-grained sediments, and cold-water filaments related to seasonal upwelling.
- Relatório setor segurança de pessoas e bens: vulnerabilidades atuais e futurasPublication . Ferreira, Andreia; Oliveira, André; Dias, Luís Filipe; Fernandes, Luís; Brito, David; Braunschweig, Frank; Sampath, Ruwan; Moura, Delminda; Mendes, Isabel; Carrasco, A. Rita; Costas, Susana; C. Veiga-Pires, C.As alterações no clima constituem um fator a ter em conta no setor da segurança de pessoas e bens. Muitos dos impactos associados às alterações climáticas exacerbam ou alteram ameaças já existentes, como aquelas associadas a eventos extremos, inundações e secas (Sperling e Szekely, 2005). Os cenários de alterações climáticas projetados para Portugal tornam necessário um esforço de adaptação do Sistema de Proteção Civil face à probabilidade do aumento da ocorrência de eventos meteorológicos extremos, na medida em que poderá ocorrer um aumento de fenómenos em que a segurança de pessoas e bens seja colocada em causa. A este nível, a Estratégia Nacional de Adaptação às Alterações Climáticas (ENAAC) indica que as medidas de adaptação face às alterações climáticas, no contexto da segurança de pessoas e bens, se devem desenrolar em duas principais linhas de atuação.
- Incised valleys on the Algarve inner shelf, northern Gulf of Cadiz margin: stratigraphic architecture and controlling factors in a low fluvial supply settingPublication . Carrión-Torrente, Álvaro; Lobo, Francisco José; Puga-Bernabéu, Ángel; Luján, María; Mendes, Isabel; Hanebuth, Till J. J.; Lebreiro, Susana; García, Marga; Reguera, María Isabel; Antón, Laura; Van Rooij, David; Cerrillo-Escoriza, JavierA network of cross-shelf paleovalleys has been recognized over the paleo-inner shelf off the Gila & SIM;o-Almargem Estuary, a small fluvial drainage system that presently receives minor sediment supply in the eastern Algarve shelf, northern margin of the Gulf of Cadiz (SW Iberian Peninsula). This study is aimed at determining the driving controls that triggered substantially different paleohydrological conditions and sedimentary dynamics of ancient fluvial systems in this margin. We focus on evidences of secondary controls on valley genesis and evolution, superimposed to primary glacio-eustatic control such as antecedent geology, low fluvial supply and changing hydrodynamic regimes. The architecture and spatial distribution of these paleovalleys were interpreted based on a grid of seismic profiles with different resolutions. Likewise, a sediment core obtained in a distal position of the paleovalley system provided information about sedimentary processes during the most recent stage of valley infilling. The chronostratigraphic framework was constructed based on regional seismic horizons defined in previous studies and complemented with two AMS 14C dates obtained from bivalve shells.The inner shelf paleovalley system is composed of several incised valley features which exhibit a remarkable similar internal architecture. These inner valley features exhibit two major incision phases (from oldest to youngest; IP 2 and IP 1) that are thought to constitute a simple paleovalley system formed during the last glacial cycle. The origins of the incision are considered to be different. The older one is related to fluvial incision during the sea-level fall leading into the Last Glacial Maximum, whereas the recent one is interpreted as the result of tidal scour during the postglacial transgression. Their corresponding infillings are interpreted, respectively, as estuarine bay-fill deposits and estuary-mouth sands. Overlying the paleovalley infilling, a distinctive reflective unit is in agreement with the generation of coastal barriers and related depositional systems.The formation of the paleo-inner-shelf paleovalley system was strongly conditioned by antecedent geology, which strongly limited the generation of wide incised valleys and determined the amount of incision landward of a well-defined break of slope. Its postglacial infilling was mainly estuarine in nature, likely involving the development of a dendritic system, with numerous barriers interrupted by tidal inlets and channels in a mixed estuarine system with low fluvial supply.
- Guadalfeo and Adra submarine deltas evolution in response to sediment supply variationsPublication . Mendes, Isabel; Lobo, F. J.; Ferreira, Óscar; López-González, N.; Bárcenas, P.; Fernandez-Salas, L. M.The Guadalfeo and the Adra submarine deltas off the northern coast of the Alboran Sea have been built up under the direct influence of short and mountainous rivers. The area is subjected to strong climatic seasonality, with sporadic winter torrential floods and high summer aridity. In addition numerous anthropogenic activities have affected these systems, mostly during the last two centuries. In order to decode the influence of climatic variability and anthropogenic impacts on sediment supplies during the recent past, five sediment cores were collected from the Guadalfeo and Adra submarine deltas. Benthic foraminiferal and sedimentological analyses, combined with radiocarbon dating, were performed. The impact of torrential floods alternating with periods of low rainfall or dry periods were recorded in the Adra and Guadalfeo prodeltas. Periods with low abundance of benthic foraminifera and high amounts of coarse-grained sediments, were interpreted as the result of enhanced sediment supply to the shelf triggered by major flood events. On the other hand, periods with high amounts of fine-grained sediments and high abundances of colonizers and opportunistic foraminiferal species indicate the establishment of new environments with distinct ecological constraints. These environments were driven by lower sediment supplies during low rainfall or dry periods. The most recent sedimentation seems to reflect the human interventions in the rivers basins, such as deviation of the main river courses and dams construction, which reduced the sediment input and promoted the deposition of shallow-water submarine deltas.
- Benthic foraminiferal and sedimentological response to the evolution of the Adra submarine delta, northern Alboran SeaPublication . Mendes, Isabel; Lobo, F. J.; Ferreira, Óscar; Schönfeld, J.; Rosa, F.; Bárcenas, P.; Fernandez-Salas, L. M.; López-González, N.; Dias, J. A.The Adra submarine delta is located on the northern Alboran Sea shelf in the western Mediterranean Sea. The genesis of this deltaic system is associated with the discharges of the short and mountainous Adra River. The area is under the influence of a Mediterranean climate with sporadic winter torrential flows and increased summer aridity. Major anthropogenic activities in the river system occurred in 1872 AD, with the deviation of the main fluvial course to the east. The channel was silted up in 1910 AD as result of a flood event and relocated further west, at its present position. These artificial changes are reflected in the submarine morpho‐stratigraphy of the delta that is composed of two main lobes. In order to understand the interaction between river discharges and the evolution of the submarine delta at different timescales, two sediment cores were collected from both lobes. A chronological framework was performed and combined with sedimentological and benthic foraminiferal analyses. Radiocarbon dating of plant debris from the base of the cores indicates that the sedimentary record goes back 250 years BP. The correlation of sediment cores with seismic records indicate that both cores penetrated the same seismic unit, deposited between ca. 1070 to ca. 1872 AD, under the direct influence of the ancient river course. The predominant sedimentary facies is sandy silt with intercalated sand layers. The uppermost core sections are pure sand. The number of benthic foraminifera is generally below 100 specimens per gram. The most abundant species in both cores are Ammonia tepida, Bolivina ordinaria, Nonionella stella, Reophax arctica and Textularia earlandi. The increases of sand and the low faunal density, followed by increased abundance of successful colonizers and opportunistic species, is interpreted as result of periods of high precipitation, and sediment supply to the shelf, and the subsequent establishment of an environment with new ecological constrains.
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