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- 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.
- 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.
- 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.