title: Characterization of bottom hydrodynamic conditions on the central western Portuguese continental shelf based on benthic foraminifera and sedimentary parameters.
abstract: Dead benthic foraminiferal assemblages from the central western Portuguese continental shelf have been studied to identify the prevalent oceanographic processes in the study area. Sediment samples collected at 46 stations along transepts perpendicular to the coastal line, between the latitudes of 38-40 °N and 17-190 m water depth, in April/May 2008, were analysed for selected physicochemical parameters (temperature, redox potential), grain size, organic matter content, and benthic foraminifera. Statistical analysis identified two main groups of stations, the Inshore/Offshore groups, which are not only defined by their geographical positions, but easily distinguishable by different hydrodynamic conditions. The Offshore Group is mainly represented by deeper stations characterized by a higher percentage of fines and TOM, negative values of redox potential and by the higher foraminiferal density and species diversity than the Inshore one. Foraminiferal assemblages of the Offshore Group are dominated/represented by species (such as Cassidulina laevigata/Cassidulina carinata, Bolivina spathulata, Bolivina ordinaria, Globocassidulina minuta, Bulimina elongata/Bulimina gibba and Bulimina marginata) common in areas with significant concentrations of organic matter. The benthic foraminiferal assemblages of the Inshore Group are instead characterized by epifaunal species such as Lobatula lobatula, Cibicides ungerianus, Planorbulina mediterranensis, Gavelinopsis praegeri and Quinqueloculina seminula. Both the sedimentary and foraminiferal results suggest that this group of stations is subjected to stronger bottom hydrodynamic conditions, caused by waves and swell activity and coastal currents, than the Offshore Group. Bray-Curtis similarity comparison between the stations of both groups reveals that the Offshore Group has a higher internal similarity than the Inshore Group. These differences seem to stem from topographic forcing, from the presence of rocky outcrops, from canyons and capes, from the distribution of rivers and from the magnitude of their discharges, which determine specific hydrodynamic features and differences in the sedimentary deposits and biological productivity. The influence of the Tagus river (supply of fresh water, detritus and organic matter from continental sources), the presence of canyons and capes, which leave the most important imprint on the study area, are marked by changes in the foraminiferal assemblages both in the Inshore and Offshore groups.
authors.affiliation: Department of Stratigraphy and Paleontology, Faculty of Geology, University of State of Rio de Janeiro (UERJ), Av. San Francisco Xavier, 524, 4037F, Maracanã, 20550-013 Rio de Janeiro, RJ, Brazil; University of State of Amazonas (UEA), Av. Djalma Batista, 3578, Flores, CEP 69050-010 Manaus, Brazil; Department of Geosciences and GeoBioTec, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: virginia.martins@ua.pt.
authors.forename: Maria Virgínia Alves
authors.initials: MV
authors.lastname: Martins
authors.affiliation: Department of Biology and CESAM, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: victor.quintino@ua.pt.
authors.forename: Victor
authors.initials: V
authors.lastname: Quintino
authors.affiliation: Department of Geosciences and GeoBioTec, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: ritatentugal@ua.pt.
authors.forename: Rita Marques
authors.initials: RM
authors.lastname: Tentúgal
authors.affiliation: University of Urbino "Carlo Bo", DiSTeVA, 61029 Urbino, Italy. Electronic address: fabrizio.frontalini@uniurb.it.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Frontalini
authors.affiliation: Department of Geosciences and GeoBioTec, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: pfnmiranda@gmail.com.
authors.forename: Paulo
authors.initials: P
authors.lastname: Miranda
authors.affiliation: Micropaleontology Laboratory, LabMicro, University Federal of State of Rio de Janeiro - UNIRIO, Av. Pasteur, 436, Urca, 22290-240 Rio de Janeiro, Brazil. Electronic address: lazarolaut@hotmail.com.
authors.forename: Lazaro Luiz
authors.initials: LL
authors.lastname: Mattos Laut
authors.affiliation: Department of Biology and CESAM, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: roberto@ua.pt.
authors.forename: Roberto
authors.initials: R
authors.lastname: Martins
authors.affiliation: Department of Biology and CESAM, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: anarod@ua.pt.
authors.forename: Ana Maria
authors.initials: AM
authors.lastname: Rodrigues
mesh_terms: D001267:Atlantic Ocean; D044822:Biodiversity; D004784:Environmental Monitoring; D056908:Foraminifera / Q000145:classification / Q000502:physiology*; D019015:Geologic Sediments / Q000032:analysis*; D057446:Hydrodynamics; D011174:Portugal
keywords: Benthic foraminifera; Continental shelf; Hydrodynamic; Sediment grain size; Tagus and Sado rivers; Upwelling