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- Foraminifera as tsunami tracers in Holocene sequences of Southwestern SpainPublication . Guerra, Liliana; Ruiz, F.; Abad, Manuel; Veiga-Pires, C.El objetivo de este trabajo es la identificación de eventos de alta energia (tsunamis?) em el P.N. de Doñana a partir del análisis de asociaciones de foraminíferos, llevando a cabo en un testigo corto, y comparar estos datos con el registro del Tsunami de 1755 que tuvo lugar en el SO de la Península Ibérica, donde los foraminíferos se han mostrado como indicadores muy útiles para caracterizar los paleoambientes pre- y postsunami y delimitar capas tsunamigénicas. The southwestern Spanish coast is a low-probability tsunamigenic area (e.g., Reichester, 2001), although sixteen tsunami have been documented for the time-period between 218 BC and 1900 AD (Campos, 1991). These high-energy events have tremendous morphological effects and drastic ecological impacts in coastal areas (Borrero, 2005) and cause the deposition of sedimentary beds with characteristic textural and mineralogical features (e.g. Babu et al., 2007).
- 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.
- Holocene sea level fluctuations and coastal evolution in the central Algarve (southern Portugal)Publication . Moura, Delminda; Veiga-Pires, C.; Albardeiro, L.; Boski, T.; Rodrigues, Ana; Tareco, HelderIn Armação de Pêra Bay, southern Portugal, environmental changes during the Holocene can be interpreted based on the morphological and sedimentological similarities between older geomorphic features (cemented beach and dune rocks) and present coastal features. Using knowledge of the present beach and dune processes, we propose a two-step model for the evolution of Armação de Pêra Bay. First, during the rapid sea level rise between about 8800 and 6600 yr cal BP, the bay changed from a positive to a negative budget littoral cell and transgressive dunes formed, favoured by drought conditions. At about 5000 yr cal BP, during a sea level maximum, beach width was less than the critical fetch and dunes stabilized and underwent cementation during the wetter Atlantic climatic event. The second phase of dune accumulation started at about 3200 yr cal BP, due to a regression of sea level during which the bay changed back to a positive budget littoral cell in which beach width was greater than the critical fetch. Currently, the beach width is less than the critical fetch, dunes are inactive, and the sedimentary budget is negative due to sediment storage in local river systems.
- Postglacial sea-level rise in South Portugal as recorded in Guadiana EstuaryPublication . Boski, T.; Moura, Delminda; Camacho, Sarita; Duarte, Duarte; Scott, David; Veiga-Pires, C.; Pedro, Paulo; Santana, PauloThe Guadiana River Estuary is located in the terminal part of a deeply incised river valley, which accumulated several tens of meters of sediments during the Holocenic transgression. Five cored boreholes (see Fig.1 for localisation) that reached the pre-Holocenic substratum were drilled recently in order to recognize the architecture of sedimentary facies and to quantify the accumulation of organic carbon trapped in sediments during the valley infilling by marine waters. It was assumed that due to structural constraints imposed by Palaeozoic and Mezozoic substratum, the main estuarine channel did not change its position significantly. Consequently borehole locations were chosen in order to represent different sedimentary environments in the estuary: proximity to the main channel (CM1 and CM3), external sea facing (CM4) and lagoonal (CM2 and CM5) environments.
- Organic carbon accumulation in coastal zones since the last glacial maximum? A clue for varying atmospheric CO2 levels?Publication . Boski, T.; Veiga-Pires, C.; Moura, DelmindaIt is a generally accepted concept that the carbon storage within the principal earth surface reservoirs varies in a multitude of time scales. The shallow water continental margins belong to the most fertile areas in terms of organic carbon (OC) production and are also very effective carbon traps.
- Algarve: a study case for global vs regional climatic changes in mid latitude estuaries during the HolocenePublication . Veiga-Pires, C.; Mestre, Nélia; Moura, Delminda; Luis, Joaquim; Boski, T.Located at the extreme southwestern end of the Iberian Peninsula, in the South of Portugal, the Algarve province is bordered to the north by the Alentejo province, to the east by the Guadiana River, and to the west and south by the Atlantic Ocean. Its coastal region can be divided into two different sectors: the eastern sector, which is mainly made of barrier island and lagoon system named the Ria Formosa, and the western sector mainly represented by clastic and carbonated cliffs. In each sector, we sampled long and short sedimentary cores (ca. 30m and 3m, respectively) in two different estuaries. Therefore, the different sedimentary records obtained from the four estuaries should permit to identify global vs. west-eastern regional climatic changes through the observation of several proxies. Two of these proxies are sediment color and magnetic susceptibility, which have been acquired every five centimeters along core depth, using the Colortron II spectrophotometer and SM-20 magneto-susceptometer, respectively. Sediment surfaces of short cores were also digitized using the Mustek 1200 A3 PRO Scanner. Furthermore, short cores have been sampled every five centimeters along depth in order to analyze the sediment for its major and minor elements content, its organic carbon content, and its granulometry and mineralogy. Some shell fragments have also been sampled and sent for radiocarbon radiometry or AMS dating, allowing therefore constructing some absolute chronologies for the several cores. Some relative chronologies based on digital color profiles are also being used in order to correlate sedimentary sequences between cores. All the cores are mainly composed of clay, with the existence of soil horizons at the top of the cores and frequent sand layers towards their base. Several element profiles along depths are compared, namely those regarding Sr, Ca, F, Ba, Al and Ti, as well as their ratios. First results indicate that geochemical and color data allow to identify similar sequences from west to east probably related to major climate episodes. Although, pronounced differences in mineralogy and accumulation rates from on site to another are probably due to differences, respectively, in the geochemistry of the drainage basin substratum and in the flow rate of the rivers, and therefore to local precipitation. We acknowledge FEDER and OE that financed this study through the Portuguese Foundation for Science and Technology (FCT) (POCTI/CTA/39733/2001).
- Postglacial organic carbon accumulation in coastal zones-A possible cause for varying atmospheric CO2 levels: preliminary data from SW PortugalPublication . Boski, T.; Moura, Delminda; Correia, Victor; Martins, H.; Veiga-Pires, C.; Camacho, Sarita; Wilamowski, A.We report the preliminary data on organic carbon accumulation rates which are being determined in the infill sequences of several estuaries, in the coastal fringe of Algarve (S Portugal). The so far analysed sedimentary sequences of Guadiana River estuary represent the time span from ca 10000 yr. cal BP to present. The obtained data indicate that until ca 7000 yr. cal BP, i.e. during the period of fast sea level rise, organic carbon accumulated at an average rate ranging from 160 to 320 gm yr . In the Middle and Upper Holocene, when the sea level rise was not exceeding 25cm/century the organic carbon accumulation rate dropped to an average value of ca 50 gm yr . The analysis of gas bubble content from ice cores indicates that the atmospheric CO concentration evolved during the last glacial/interglacial transition, from 180 ppv minimum during the LGM to the 270 ppmV preindustrial level. Considering that the terrestrial particulate organic matter is an essential fertiliser of the ocean, it is postulated that enhanced burial of POM in the coastal areas during the period of fast postglacial sea level rise is responsible for decrease of primary productivity in the open ocean and consequent transfer of 200 Gt. ofCto the atmosphere.