GMC - Artigos em revistas internacionais
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- Atlantic circulation changes across a stadial-interstadial transitionPublication . Waelbroeck, Claire; Tjiputra, Jerry; Guo, Chuncheng; Nisancioglu, Kerim H.; Jansen, Eystein; Riveiros, Natalia Vazquez; Toucanne, Samuel; Eynaud, Frédérique; Rossignol, Linda; Dewilde, Fabien; Marches, Elodie; Lebreiro, Susana; Nave, SilviaABSTRACT: We combine consistently dated benthic carbon isotopic records distributed over the entire Atlantic Ocean with numerical simulations performed by a glacial configuration of the Norwegian Earth System Model with active ocean biogeochemistry in order to interpret the observed Cibicides delta C-13 changes at the stadial-interstadial transition corresponding to the end of Heinrich Stadial 4 (HS4) in terms of ocean circulation and remineralization changes. We show that the marked increase in Cibicides delta C-13 observed at the end of HS4 between similar to 2000 and 4200 m in the Atlantic can be explained by changes in nutrient concentrations as simulated by the model in response to the halting of freshwater input in the high-latitude glacial North Atlantic. Our model results show that this Cibicides delta C-13 signal is associated with changes in the ratio of southern-sourced (SSW) versus northern-sourced (NSW) water masses at the core sites, whereby SSW is replaced by NSW as a consequence of the resumption of deep-water formation in the northern North Atlantic and Nordic Seas after the freshwater input is halted. Our results further suggest that the contribution of ocean circulation changes to this signal increases from similar to 40 % at 2000 m to similar to 80 % at 4000 m. Below similar to 4200 m, the model shows little ocean circulation change but an increase in remineralization across the transition marking the end of HS4. The simulated lower remineralization during stadials compared to during interstadials is particularly pronounced in deep subantarctic sites, in agreement with the decrease in the export production of carbon to the deep Southern Ocean during stadials found in previous studies.
- Long-term coastline evolution of Figueira da Foz - Nazaré sector (Portugal)Publication . Nave, Silvia; Rebêlo, LuísABSTRACT: ome sectors of the west Portuguese coast are particularly endangered by erosion and flooding. Regional to local scale information, on coastline evolutionary trend, is particularly valuable in sectors that includes areas with relevant erosion. A continuous, high-resolution, dataset on coastal evolution, from 1947 and 2015, between Figueira da Foz and Nazaré, was achieved within the Programme “Geological and Coastal Hazard Mapping at a 1:3000 resolution scale” at the National Laboratory of Energy and Geology (LNEG). This work, due to the detailed scale of analysis in a wide geographic context, allows to have both, a general overview of the coastal evolution and, at the same time, when zooming in up to 1:3000 scale, to observe the local behaviour and to quantify the occurred changes. Also, the well time-spaced aerial photograph dataset allows to compare the resultant coastline movement between the oldest and the youngest coastline (NSM index), with the total coastline oscillation (SCE index), bringing new insights on the coastline stability at a local scale. The evolution trend shows an overall erosional behaviour, if considering the entire sector. Erosion occurs predominantly in the north, as the south shows more stability and progradation. Quantification of the land-lost and land-gain due to the coastline shift in a 68-year period shows that 1 164 888 m2 of land were lost along 30 470 m of the coastal fringe, and 462 330 m2 were gained along an extension of 21 010 m.
- Coastline evolution of the Portuguese south eastern coast: a high-resolution approach in a 65 years’ time-windowPublication . Nave, Silvia; Rebêlo, LuísAbstract. The coast, as the interface between land and sea, is a highly dynamic area, endangered by erosion and flooding, particularly at times of sea-level rise. At the present context of climate change, the use of scientific knowledge to understand coastal dynamics and coastal evolution assessment through time is essential to find a suitable management response for a successful adaptive coastal governance. It is proposed that the obtained high-resolution and long-term coastline change dataset is of crucial impor tance to improve the knowledge on mesoscale evolution of the Portuguese south-eastern coast, from Ancão to Vila Real de Santo António (VRSA), a 55 km long coastal stretch. The evolutionary trend, from 1950 to 2015, points to a general seaward progradation at the western (Barreta island) and eastern (Cacela peninsula – VRSA) sectors, and mostly an erosional trend at the central barrier island system (Culatra, Tavira and Cabanas islands). Moreover, a considerable average landward displacement of approximately 130 m is observed at Cabanas island. Regarding overall coastline movement, seaward displacement prevails, with a prograding coastline occupying approximately 54% of the studied sector even though this is mostly associated with human intervention on the coast. The exception is the Manta Rota - Monte Gordo sector where accumulation is likely related to natural processes. Considering the significant influence man-made interventions have had on the coastline evolution, it is believed that the natural evolutionary pattern would point to an overall erosional trend in the islands sector and a progradational trend from Manta Rota to VRSA beach.
- Paleoenvironmental evolution of estuarine systems during the last 14000 years - the case of Douro Estuary (NW Portugal)Publication . Drago, Teresa; Freitas, Maria da Conceição; Rocha, Fernando; Moreno, João; Cachão, Mário; Naughton, Filipa; Fradique, Catarina; Araújo, Fátima; Silveira, T.; Oliveira, A.; Cascalho, João Pedro; Fatela, Francisco
- Benchmarks and sediment source(s) of the 1755 Lisbon tsunami deposit at Boca do Rio EstuaryPublication . Font, Eric; Pires, Cristina Veiga; Pozo, Manuel; Nave, Silvia; Costas, Susana; Ruiz Muñoz, Francisco; Abad, Manuel; Simões, Nuno; Duarte, Sílvia; Rodríguez-Vidal, JoaquínStandardizing the signature of tsunami deposits has been identified as a major limitation for the identification of paleo-tsunami deposits. This limitation mostly arises from the strongly source-dependent nature of these deposits, which in turn determines their composition and depositional architecture, and from the effect of the local morphology of the corresponding depositional environment. Here, we provide new high-resolution mineralogical, geochemical and micro/macrofauna data of the 1755 tsunami layer of Boca do Rio estuary (Algarve, Portugal) with the aim of unraveling the signatures of estuarine tsunami deposits and linking them to possible sediment sources. We also apply for the first time diffuse reflectance spectrophotometry (DRS) analysis. Our results show that the 1755 tsunami deposit of the Boca do Rio estuary is featured by an enhancement in Sr and Ca, which are linked to the input of biogenic and detrital carbonates (shell fragments and limestone clasts) from the beach foreshore and a strong depletion in most terrestrial- and marine-sensitive indicators. The latter is interpreted as resulting from the reworking of the estuarine clays and subsequent dilution within a huge volume of sand eroded from the coastal barrier. It confirms that in the case of the Boca do Rio estuary, the sediment source is essentially proximal and coastal. Textural and mineralogical features between the base and the top of the tsunami layer suggest the imprint of run-up and backwash currents derived from a unique wave. Micro and macrofauna analysis and DRS data of the siliciclastic fraction show slight but significant environmental changes occurring just after the tsunami, which could be provoked by an eventual closure of the estuary mouth.
- Impact of atmospheric circulation patterns on coastal dune dynamics, NW SpainPublication . González-Villanueva, Rita; Costas, Susana; Pérez-Arlucea, Marta; Jerez, Sonia; Trigo, Ricardo MachadoDunes in temperate latitudes have experienced a significant stabilization in recent times, essentially as a consequence of the expansion of dense vegetation cover. Yet, the causes for this gradual stabilization as well as the causes promoting antecedent aeolian mobilization remain poorly understood. The Traba coastal dune field, located in NW Spain, was examined to explore the causes inducing aeolian activity and subsequent stabilization since 1940. Morphological changes were identified through the combination of aerial photographs and geophysical techniques. Local wind field regimes were simulated using a regional climate model to obtain the variability of the most relevant modes of atmospheric circulation in the North Atlantic and European regions; North Atlantic Oscillation (NAO), Eastern Atlantic (EA) and Scandinavian (SCAND). This allows us to identify the impact of these circulation modes over dune dynamics. Results document an episode of aeolian activity during the 1950s followed by a gradual stabilization and fixation of the dune coincident with a decrease on storm and wind intensity. Yet, aeolian sand movement remained active in small areas (blowouts), occurring mainly during the summer. NE winds associated with a negative phase of the EA explain the movement of sand within the dune field under favorable conditions of sand supply. On the other hand, sand supply to the dune field from the beach was promoted by NW winds coincident with the summer negative phase of NAO. During winter, the negative NAO favored frequent SW winds associated with the passage of intense storms, which in turn explain sand remobilization from the beach making sediment available for the NW winds to blow inland. With this work, it is proven that to understand past and future aeolian activity requires critical consideration of the variability and impact of the two principal modes of atmospheric circulation in the North Atlantic (NAO and EA). The SCAND mode explaining a lower percentage of the local wind field variability was also included to achieve higher significance levels of explained variance.
- Geographical variation in shell shape of the pod razor shell Ensis siliqua (Bivalvia: Pharidae)Publication . Rufino, Marta M.; Vasconcelos, Paulo; Pereira, Fábio; Fernández-Tajes, Juan; Darriba, Susana; Méndez, Josefina; Gaspar, Miguel B.
- The influence of coastal processes on inner shelf sediment distribution : the Eastern Algarve Shelf (Southern Portugal)Publication . Rosa, F.; Rufino, Marta M.; Ferreira, Ó.; Matias, A.; Brito, A. C.; Gaspar, M. B.
- Millennial-scale climate change and intermediate water circulation in the Bering Sea from 90 ka : A high-resolution record from IODP Site U1340Publication . Schlung, Shiloh Anne; Ravelo, A. Christina; Aiello, Ivano W.; Andreasen, Dyke H.; Cook, Mea S.; Drake, Michelle; Dyez, Kelsey A.; Guilderson, Thomas P.; LaRiviere, Jonathan P.; Stroynowski, Zuzanna; Takahashi, Kazo
- ECORD-IODP sessions and reception in LisbonPublication . Barriga, Fernando; Dias, Olga; Pinheiro, Luís; Voelker, Antje H. L.
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