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- Chronology of the sedimentary processes during the postglacial sea level rise in two estuaries of the Algarve coast, Southern PortugalPublication . Boski, T.; Camacho, Sarita; Moura, Delminda; Fletcher, William; Wilamowski, A.; Veiga-Pires, C.; Correia, Victor; Loureiro, C.; Santana, PauloFour profiles of estuarine sediments obtained from boreholes drilled in the Algarve, Southern Portugal were studied in order to reconstruct the process of sediment accumulation driven by the postglacial sea level rise. In addition to the sedimentological analysis, the Foraminifera Index of Marine Influence (FIMI) permitted assessment of the nature and organization of sedimentary facies in the BelicheeGuadiana and Gilão-Almargem estuaries. The Beliche- Guadiana CM5 and Almargem G2 profiles accumulated in a sheltered environment, with the former presenting an almost continuous record of the sea level rise since ca 13 000 cal yr BP. The G1 and G3 profiles from the Gilão-Almargem area represent a more discontinuous record of the last 8000 years, which accumulated in the more dynamic environment of an outer estuary. The integration of all radiocarbon ages of dated levels, led to an estimate of sediment accumulation rates. Assuming a constant position of the sediment surface with respect to the tidal range and a negligible compaction of sediment, the sea level rose at the rate of 7 mm yr ^-1 in the period from 13 000 to 7500 cal yr BP. This process slowed down to ca 0.9 mm yr 1 from 7500 cal yr BP until the present. The marked historical change in the rate of sediment accumulation in these estuaries also occurred with the accumulation of organic matter and is, therefore, important data for global biogeochemical models of carbon. The main obstacle to obtain higher temporal resolution of the sedimentary processes was the intense anaerobic respiration of organic matter via sulphate reduction, which did not allow any accumulation of peat and, furthermore, led to erasure of the palaeontological record by acid formed from the subsequent oxidation of sulphides.
- Evolução paleoambiental holocénica dos estuários dos rios Guadiana e Arade com base nas associações fósseis de foraminíferos bentónicosPublication . Camacho, Sarita; Boski, T.A análise das variações no conteúdo em espécies de foraminíferos bentónicos ao longo de um testemunho de sondagem recolhido no Estuário do Rio Guadiana e de três testemunhos no Estuário do Rio Arade permitiram identificar cinco paleoambientes com diferentes GIM (Graus de Influência Marinha) que ocorreram ao longo do Holocénico. O GIM 1 foi atribuído às amostras indefinidas pela ausência de foraminíferos, traduzindo um ambiente terrestre sem qualquer influência marinha ou um ambiente de deposição não ideal à preservação post-mortem das carapaças. O ambiente sujeito a um GIM 2 foi denominado de intermareal superior e é colonizado exclusivamente por formas aglutinadas (Trochammina macrescens, Trochammina inflata, Trochammina spp., Ammobaculites sp., Eggerella sp.) e forros internos, indicando forte confinamento, típico de médio a alto sapal. O ambiente sujeito a um GIM 3 foi denominado de intermareal médio e é colonizado predominantemente por formas aglutinadas e/ou forros internos e carapaças carbonatas em elevado estado de dissolução, caracterizando um ambiente confinado, típico de médio a baixo sapal. O ambiente sujeito a um GIM 4 foi denominado de intermareal inferior é dominado (mais de 65% dos indivíduos) pela associação das espécies estuarinas Ammonia beccarii e Haynesina germanica associada a Elphidium spp. e aos miliolídeos, caracterizando um ambiente moderadamente confinado, abrangendo o baixo sapal e toda a planície lodosa exposta em baixa mar de marés vivas. O ambiente sujeito ao GIM 5 foi denominado de intermareal aberto e é definido pela associação das espécies estuarinas A. beccarii e H. germanica a formas de maior influência marinha, nomeadamente, os géneros Brizalina, Fissurina, Discorbis, Rosalina e Cibicides, verificando-se ainda um aumento no índice de Diversidade e no número de carapaças indeterminadas e pequenas. De acordo com as sequências paleoambientais, em todas as sondagens se reconheceu a existência de uma fase transitiva fluvio-marinha imediatamente antes de um episódio transgressivo. No estuário do Guadiana, entre um episódio pré-holocénico e o auge de transgressão marinha, foi possível identificar uma sequência paleoambiental de pré-invasão marinha, caracterizada por uma substituição de dominância de espécies de sapal por espécies de baixo sapal e de estuário. No estuário do Arade, os primeiros vestígios de influência marinha coincidem com o período de maior oceanidade, sugerindo a concomitância deste fenómeno com o início da formação do estuário. A inexistência de registo de uma fase de pré-invasão marinha na base dos testemunhos sedimentares deste sistema estuarino sugere que a invasão marinha ocorreu de forma mais abrupta e menos premonitória que no caso do estuário do Guadiana. Em todas a sondagens reconhece-se um abrandamento na incursão marinha logo após o auge transgressivo. A ocorrência de um ambiente de sapal em todos os biohorizontes mais recentes das quatro sondagens sugere um recente equilíbrio entre as taxas de acreção e as taxas actuais de subida do Nível Médio do Mar.
- Guadiana EstuaryPublication . Boski, T.; Camacho, Sarita; Moura, DelmindaThe Hercynian Serra in the North which belongs to the Hesperic Massif is essentially composed of shales and greywackes.
- Postglacial sea-level rise and sedimentar response in the Guadiana Estuary, Portugal/Spain borderPublication . Boski, T.; Moura, Delminda; Veiga-Pires, C.; Camacho, Sarita; Duarte, Duarte; Scott, David; Fernandes, SandroThe study of sedimentological features, foraminifera and molluscan fauna in samples recovered from four rotary boreholes permitted, after 14C dating, the first assessment of the post-glacial transgression in Guadiana River Estuary. The Holocene sequence is underlain by coarse sediments from delta fan enclosing continental swamp deposits dated 16980 year BP. The Holocene sedimentary sequence was deposited either directly on this delta fan gravels or on top of fluvial sands deposited probably between 11000 and 10000 yr BP. An accelerated phase of the estuary infilling by clayey sediments containing the saltmarsh foraminifer Trochammina, began ca. 9800 year BP, when sea level was about 39 m below present. Between 7500 and 7000 year BP, the central part of the estuary started to accommodate coarser sediments, partially introduced from the continental shelf. The first phase of Holocene sea-level rise at a rate of 0.85 m/century terminated ca. 6500 year BP. Since then, lagoonal sediments in the vicinity of the estuary have been enclosed behind sand spits and predominantly sandy sedimentation was initiated within the estuary. After a second phase of slower rise at the rate of 0.3 m/century, which lasted until ca. 5000 year BP, the sea approached the present level.
- Palaeosurface reconstruction based on sedimentary record and in sea level evolution in the Guadiana Estuary (Southern Iberia)Publication . Loureiro, C.; Boski, T.; Albardeiro, L.; Moura, Delminda; Terefenko, P.; Camacho, Sarita; Veiga-Pires, C.The sedimentary infilling of the Guadiana estuary, in the Southern Iberian Peninsula, has been extensively studied using a variety of laboratory methods, namely geochemical and sedimentological analyses, foraminifera assemblages and palynological profiles, supported by 14C dating [1-3](...)
- Paleoenvironmental evolution of the Guadiana Estuary, Portugal, during the Holocene: a modern foraminifera analog approachPublication . Camacho, Sarita; Boski, T.; Moura, Delminda; Scott, David; Connor, Simon; Pereira, LauraIn this paper, we reconstruct the Holocene paleoenvironmental evolution of the Guadiana Estuary, southwestern Iberian Peninsula. Two previously studied boreholes (CM3 and CM5) were revisited and analyzed in the light of a foraminifera modern analog approach. Cluster analyses define four assemblages with different biocenotic, taphonomic, elevation and distance-to-sea settings, which serve as a baseline for paleoassemblages interpretation. Faunal changes along the sedimentary sequences, together with previous sedimentological and chronological data, redefine the different phases of environmental evolution in the Guadiana Estuary since ca. 13 kyr cal. BP, with special emphasis on the Holocene marine highstand. Estuarine flooding began synchronously in both locations (ca. 9 kyr cal. BP) but manifested differently in each sedimentary sequence. The most seaward borehole records a more evident and longer highstand (ca. 8.8–3.8 kyr cal. BP), characterized by the occurrence of subtidal environments and by the presence of open marine species (Pararotalia cf. spinigera, planktic forms and a significant number of exotic/allochthonous tests), indicating warmer and more marine conditions than today. In the most landward borehole, the highstand is shorter (ca. 8–7.6 kyr cal. BP) and less intense, characterized by the presence of a diverse, mainly autochthonous, open estuary assemblage, dominated by Ammonia aberdoveyensis and Haynesina germanica. At 4.4 kyr cal. BP, during a long deceleration phase of regional sea-level rise, a short but well-defined pulse of marine influence is recorded in CM5, when open estuarine assemblages reappear and replace marsh agglutinated assemblages, suggesting a new submergence phase. This short event is not identified in the previous works carried out in the same area, thus further data are needed to understand whether it is consequent from a global, warming period or whether it resulted only from local and ephemeral forcing effects.
- Geochemical characteristics of sediments along the margins of an atlantic-mediterranean estuary (the Guadiana, Southeast Portugal): spatial and seasonal variationsPublication . Camacho, Sarita; Moura, Delminda; Connor, Simon; Boski, T.; Gomes, AnaThe present work describes spatial and seasonal variability in grain-size, pH and elemental characteristics (TOC, TIC, TN and C/N) in superficial sediments, as well as salinity, temperature and oxygen in the water, within the intertidal range of the Guadiana Estuary, SW Iberian Peninsula, during the year 2010. The results indicate that environmental parameters in the estuary are strongly dependent on spatial patterns, which reflect seasonal oscillations in freshwater discharge. The sediment is generally poorly sorted, with a symmetrical to very finely skewed distribution, in accordance with the low-energy conditions typical of the deposition areas. During winter, heavy rains forced the continuous discharge of Europe’s largest reservoir, the Alqueva dam, creating exceptional hydrodynamic conditions and causing coarser sediment deposition in the estuary. High marsh areas are controlled by flood tides, promoting vertical accretion of muddy sediments, especially silts. The lower areas of the saltmarsh and-mud flat areas are controlled by the ebb, with more efficient export of fines toward the platform and retention of sands, sometimes with significant amounts of bioclasts. In winter (average Q = 654 m3 s -1), salinity remained low throughout the estuary with the highest values (< 3) recorded up to 3 km inland from the river mouth, except in the most confined environments subject to greater evaporation. In summer (average Q = 52 m3 s -1), the estuarine waters are better mixed and significant saltwater intrusion extends approximately 8 km inland. The seasonal variation in surface water temperature was very high, with a difference of ca 14 º C in the maximum temperature recorded in winter and summer. A clear relationship between elevation (in relation to mean sea level) and organic matter, pH and particle size was observed. In the higher areas of the marsh, where the hydrodynamics is attenuated, differential deposition of fine sediments promotes organic matter entrapment and low pH. Sedimentary organic matter derives from a mixture of native aquatic and terrestrial sources. The mid-upper estuary areas and higher zones of the saltmarsh in the lower estuary incorporate a greater terrestrial component, whereas the low-middle marsh areas of the lower estuary experience a substantial contribution from indigenous aquatic sources. The present data help to understand the present environmental condition of the Guadiana Estuary and contribute baseline data for future climatic and environmental management studies based on sediment-dependent proxies
- Testate amoebae and tintinnids as spatial and seasonal indicators in the intertidal margins of Guadiana Estuary (southeastern Portugal)Publication . Camacho, Sarita; Connor, Simon; Asioli, Alessandra; Boski, T.; Scott, DavidThe present study gathers pioneering taxonomical and community data on testate amoebae and agglutinated tintinnids, analyzing their seasonal and spatial distribution patterns in the mesotidal system of the Guadiana Estuary, southeastern Portugal. To evaluate both groups’ potential as bioindicators in climate monitoring and paleoenvironmental reconstructions, their abundance, diversity and living proportions were compared to elevation in relation to mean sea-level, marine influence and to periods of elevated water levels. The distributions of testate amoebae and tintinnid total assemblages were also related to major physicochemical variables by means of multivariate analysis. From 49 surface sediment samples collected in winter and summer 2010, 17 species (25 strains) of testate amoebae were identified (in the 63 m fraction). The Centropyxidae, mainly represented by Centropyxis aculeata, Centropyxis arcula and Centropyxis constricta, had the greatest density (71% of total individuals), while the Difflugidae represented the most species (82% of total species). Higher diversities and densities were observed in winter in the upper estuary, where salinity is negligible, and in the middle estuary where they are concentrated at the lower levels of the intertidal zone. Few or no individuals were observed in the highest marsh zones. In winter, dead testate amoebae were dominant, with empty tests accumulating in the sediments from post-mortem transport by high river discharge. In summer, an increase in the living fraction is observed, with living testate amoebae along the entire estuary, which could indicate that some species are able to live in the lower reaches of the estuary. Along with the testate amoebae, two species of agglutinated tintinnids (>63 m), Stenosemella ventricosa and Tintinnopsis cf. lata, were abundant in the sediments. Their highest abundances were observed in summer. Living individuals were only recorded in summer, mainly in the vicinities of freshwater and sewage outflows, where elevated nutrient concentrations may be expected. The present study demonstrates that both testate amoebae and tintinnids have well defined patterns in their temporal and spatial distribution, offering high bioindicator potential in environmental/climate monitoring studies as well as in paleoenvironmental reconstructions.
- Taxonomy, ecology and biogeographical trends of dominant benthic foraminifera species from an Atlantic-Mediterranean estuary (the Guadiana, southeast Portugal)Publication . Camacho, Sarita; Moura, Delminda; Connor, Simon; Scott, David; Boski, T.This study analyses the taxonomy, ecology and biogeography of the species of benthic foraminifera living on the intertidal margins of the Guadiana Estuary (SE Portugal, SW Spain). Of the 54 taxa identified during sampling campaigns in winter and summer, 49 are systematically listed and illustrated by scanning electron microscope (SEM) photographs. Ammonia spp. were the most ubiquitous calcareous taxa in both seasons. Morphological analysis and SEM images suggested three distinct morphotypes of the genus Ammonia, two of which proved to be Ammonia aberdoveyensis on the basis of partial rRNA analyses. Jadammina macrescens and Miliammina fusca were the most ubiquitous agglutinated taxa in the estuary. Jadammina macrescens dominates the upper-marsh zones almost exclusively, occurring at very high densities. Ammonia spp. are the most abundant in the low-marsh and tidal-flats of the lower reaches of the Guadiana Estuary, but are widespread throughout the estuary, especially during summer when environmental conditions favor their proliferation. Miliammina fusca dominates the sparsely vegetated low-marsh and tidal-flat zones of the upper reaches, where it is associated with calcareous species. Due to its geographical position, the Guadiana system shares characteristics of both Atlantic and Mediterranean estuaries. This is reflected in the foraminiferal assemblages, with a dominance of thermophilous species and an ecological zonation typical of the Mediterranean climatic zone.
- Ecologic zonation model of the benthic foraminifera and thecamoebians of Guadiana river estuary and application in paleoenvironmental reconstructionPublication . Camacho, Sarita; Moura, Delminda; Boski, T.; Scott, David B.This thesis explores the potential of benthic foraminifera as environmental indicators in the Guadiana River estuary according to an actual perspective, where we study the species distribution patterns and their responses to seasonal environmental changes and a paleoenvironmental perspective, in which the previous information in combination with the knowledge of diagenetic processes is applied in interpreting analogues environments that formed in the estuary during the Holocene. The variation of environmental parameters in the estuary showed strong dependence on spatial and seasonal gradients, exhibiting prevailing river conditions in winter and marine conditions in summer. The distribution of foraminifera in the Guadiana estuary mirrored the seasonal variation of environmental factors, whose relative importance depended on the proximity the tolerance limits of the species. The elevation proved to be the most important parameter in the distribution of foraminifera by combining the effect of a series of other variables. Based on the dominant species of living foraminifera and seasonal variations in their relations was possible to define a model of ecological zonation for the Guadiana estuary. Four biocenoses were identified and compared with the fraction of dead and fossil foraminifera. The total assemblage that combines the seasonal and taphonomic effects on modern microfaunas proved to represent reliably the estuary indigenous microfauna. Its application in the interpretation of paleoenvironments recorded over two sedimentary sequences (CM3 and CM5) allowed refining the knowledge on how the estuary has evolved over the past 13 000 cal yr BP. The pioneering study of communities of thecamoebian and tintinnids suggests that both groups are an asset in studies of environmental monitoring and paleoenvironmental reconstruction. The present work demonstrated that the three indicators analyzed, when integrated in a multi-proxy perspective, increase the potential interpretive which can be applied in paleoenvironmental reconstructions.