Browsing by Author "Cardeira, Sara"
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- Influence of an upwelling filament on the distribution of labile fraction of dissolved Zn, Cd and Pb off Cape Sao Vicente, SW IberiaPublication . Monteiro, Carlos Eduardo; Cardeira, Sara; Cravo, Alexandra; Bebianno, Maria João; Sanchez, Ricardo F.; Relvas, PauloUnder northerly winds upwelling is recurrent at the Cape Sao Vicente, SW Iberia, and plays a major role on the distribution of dissolved nutrients and metals. The aim of this work was to characterize the dissolved metals distribution of zinc (Zn), cadmium (Cd) and lead (Pb), associated with a filament of upwelled water that stretches seaward from the Cape. Additionally, the relationships between labile metals and other oceanographic parameters, such as current velocity and wind field patterns, temperature and salinity, nutrients, chlorophyll a and suspended solids were evaluated. The mass transport of the dissolved metals exported offshore was estimated, after a period of relatively strong and persistent upwelling. At the end of October 2004 a total of 42 CID Rosette casts up to 400 dbar were sampled, distributed on an almost regular grid, together with along-track Acoustic Doppler Current Profile (ADCP) velocities. Seawater samples from two transects across the filament were analysed: one closest to the shore, where upwelling was intense and phytoplankton noticeably grew; and another further offshore where the filament was still well defined, but narrower and less marked despite with the maximum velocity currents. Labile dissolved metals were determined using anodic stripping voltammetry (ASV). The range of the metals recorded at the transect closest to the coast recorded was 0.26-3.8 nM (mean: 0.8 nM) for Zn, 2-11 pM (mean: 3 pM) for Cd and 8-60 pM (mean: 13 pM) while for the offshore transect was: 0.26-5.1 nM (mean: 1.2 nM) for Zn, 2-26 pM (mean 4 pM) for Cd and 8-74 pM (mean: 15 pM). Zinc recorded the highest concentrations, similar at both transects, and like Cd the lowest concentrations were found at near-surface depths. In opposition, the highest Pb concentrations were found at the near-surface depths at the northern stations in both transects. The filament exported more material in the offshore transect than in the transect closest to the coast, corresponding to a maximum export of 135 kmol d(-1) of Zn, 276 mol d(-1) of Cd and 1365 mol d(-1) of Pb. The quantification of the cross-shelf fluxes imposed by the filament did show that metals fluxes are strong enough to play a key role in the oceanographic behaviour of the transition zone between the coastal and offshore waters in the region. Considering the periods of strong upwelling events and the extent of their duration along the year, the amounts of exported water mass which include nutrients, metals and particles must be hugely increased and responsible for the high productivity of the waters. (C) 2015 Elsevier Ltd. All rights reserved.
- Nutrients and chlorophyll-a exchanges through an inlet of the Ria Formosa Lagoon, SW Iberia during the productive season - Unravelling the role of the driving forcesPublication . Cravo, Alexandra; Cardeira, Sara; Pereira, Catarina; Rosa, Monica; Alcantara, Pedro; Madureira, Miguel; Rita, Filomena; Correia, Cátia; Rosa, Alexandra; Jacob, J.Despite the advances and increase of observations of physical and chemical processes to better understand thefunctioning of coastal environments, a large gap still exists in quantifying exchanges and interactions betweenadjacent coastal systems. It is important to bear in mind that the dynamics and mass exchanges depend on thevariability of the driving mechanisms and respond to several time scales (tidal, seasonal and inter-annual). Thegeneral objective of this work was to unravel the role of the driving forces on the nutrients and chlorophyll-aexchanges at the Ancão inlet of Ria Formosa lagoon during the most productive season - spring. This is thesmallest inlet of the western system, the closest to continental interface and the one where migratory patterns areevident. So, the changes along time could be more evident there than at the other two inlets of the westernsector. Ancão inlet will serve as a reference to compare the mass budgets exchanged with the ocean with theother two inlets. Specifically, this work intends to: i) better understand the behaviour of this inlet; ii) its role inthe mass exchanges; and iii) its interplay with phytoplankton productivity during the peak season. In thiscontext, the transport of water, nutrients and chlorophyll-a(proxy of phytoplankton density) were estimatedacross the Ancão inlet section during the spring season. Surveys were conducted under extreme fortnightly tidalconditions during 2007, 2009 and 2012, covering different hydrodynamic, meteorological and environmentalconditions. To estimate the mass transport,field velocities, nutrients and chlorophyll-aconcentrations weremeasured concurrently along its cross section. Results show that although the hydrodynamic and morphologicchanges recorded at this inlet provoked a loss of hydraulic efficiency apparently these did not markedly affectthe mass exchanges during the spring productive season. Globally, the contribution and intensity of the me-teorological/physical, chemical and biological drivers superimposed those affected by tides, reflected in thedifferences between thefive surveys conducted. Upwelling was frequent during the spring season and played akey role on the exchanges and mass transport through the Ancão inlet. Data also show that nutrients behaveddissimilarly; silicate was consistently exported, nitrate mostly imported, dependent on the intensity of upwellingand biological consumption, while phosphate generally followed the direction of residual circulation.Chlorophyll-ashowed a general import except in both 2012 campaigns, when it was exported in small amounts(< 1 kg). Data support that during spring season, particularly in periods when upwelling is relevant, theavailability of nutrients on the coast will promote afterwards the growth of phytoplankton that enters andfertilizes the Ria Formosa, increasing its productivity. The estimated amounts are relative to the smallest inlet ofthe western sector of Ria Formosa. In consequence, it may be anticipated that through the other main inlets fromthis sector the exchanges are intensified and may enhance their contribution to the Ria Formosa fertilization.
- Temporal variability of the mass exchanges between the main inlet of Ria Formosa lagoon (southwestern Iberia) and the Atlantic OceanPublication . Rosa, Alexandra; Cardeira, Sara; Pereira, Catarina; Rosa, Monica; Madureira, Pedro Miguel; Rita, Filomena; Jacob, J.; Cravo, AlexandraUnderstanding the mass exchange patterns between coastal lagoons and ocean plays a key role to explain their impact upon the water quality and biological productivity of these systems. Ria Formosa is a temperate lagoon on the southwestern coast of Iberia, one of the most important coastal system in this region in terms of biological productivity, ecological and economic values. Given its relevance and strong interconnectivity with the adjoining ocean, the quantification of these exchanges is a key issue that had not yet been thoroughly addressed. In this context, this study is focused on understanding the role of Ria Formosa's main inlet in terms of mass budgets dynamics of water, nutrients, suspended solids and chlorophyll a with the Atlantic Ocean and to identify its seasonal variability. In order to attain this purpose, the influence of the forcing mechanisms at different time scales, including tides, oceanographic/meteorological synoptic conditions and seasons, was assessed. To accomplish this, six semidiurnal tidal cycles surveys were conducted at Faro-Olhao inlet, comprising hourly water samples collection and in situ measurements at a selected cross-section of the inlet channel. Results revealed that mass exchanges variability through Faro-Olhao inlet was mainly due to oceanographic processes (upwelling and coastal countercurrent events) and, secondly, to phytoplankton activity within the lagoon. Seasonally, regardless the direction of the residual current through the inlet, Ria Formosa acted as a source of material during Spring and Summer seasons, which contributed to increase the biological productivity of the coastal ocean. Upwelling events that occurred more evidently during the Autumn survey drove an import amount of nutrients into the lagoon, enhancing its biological productivity. Furthermore, the rainfall period that prevailed before the Winter survey contributed to export material and nutrients to the adjacent ocean, confirming that Ria Formosa fertilizes the coastal ocean, even during a period of low productivity.