Anabela Oliveira

Winter dynamics on the northern Portuguese shelf. Part 1: physical processes

Results of a program of observations carried out on the northern Portuguese shelf and slope, between July 1996 and June 1999 are used to characterise the main physical processes of the winter regime. The data set includes time series of waves and currents at mid-shelf (86 m depth) and of winds, atmospheric pressure and sea level at the coast, as well as hydrographic and suspended particle matter (SPM) observations carried during three multidisciplinary surveys. The wave regime was found to be characterised by highly energetic conditions during the winter, with storm events leading to waves of significant heights exceeding 5 m with mean periods of over 10 s. Prevailing southerly winds force a downwelling regime over the shelf with poleward flow at mid-shelf (~10–20 cm/s) and offshore transport in the bottom Ekman layer. Episodic strong upwelling events can occur during this period, leading to important changes in the near bottom stratification at mid-shelf. Tidal currents at mid-shelf are dominated by the contribution of the M2 tide (~3 cm/s) and are polarised in the cross-shelf direction, reflecting the guiding effect of the Porto Canyon.

Present day sedimentary processes on the northern Iberian shelf

Abstract The Galicia-Minho Shelf features two large mud patches, the Douro and the Galicia Mud patches. These are recent sediment bodies that have accumulated under a combination of conditions including: (1) abundant supplies of sediment; (2) morphological barriers that act as sediment traps; and (3) hydrographic conditions that favour the accumulation of fine sediment in these sinks. This paper describes the mechanisms controlling the deposition of the fine-grained sediment depositions and the processes that result in resuspension processes on the Galicia-Minho Shelf. Fine-grained sediments are provided from discharges from the river basins on the southern sector of the shelf, mainly the Douro and Minho rivers. Sediments are exported from river estuaries onto the shelf during episodic flood events. In contrast, most of the sediments originating from the Galician hinterland fail to contribute significantly to sedimentation on the shelf, because they are retained in the Galician Rias, which function as sediment traps. Sediments deposited on the shelf are frequently remobilized, particularly during southwesterly storms that coincide with downwelling conditions. Once in suspension the fine-grained sediments are transported northwards by the poleward flowing bottom currents and are eventually deposited on the Douro and Galicia Mud patches after a series of resuspension events. The locations of the two mud patches are strongly influenced by the shelf morphology. Fines already deposited on the mud patches are occasionally reintroduced into the system by large storm events. Some material from the Douro Mud patch and adjacent areas is re-deposited in the Galicia Mud patch. It is probable that sediments re-suspended from the Galicia Mud patch are carried off the shelf when storm events coincide with downwelling conditions.

Europe’s Grand Canyon: Nazaré submarine canyon

The Nazare submarine canyon extends similar to 210 km westward from the coast of Portugal, down to a water depth of > 4300 m. The considerable habitat heterogeneity found throughout the canyon is affected by strong currents and high turbidity, especially in the upper parts of the canyon. The canyon morphology comprises steep slopes, scarps, terraces, and overhangs, and a deeply incised thalweg is found in the lower part of the canyon. The seabed within the canyon is composed of varying proportions of rock and sediments that range from sand to fine mud. This great variation in physical environment is reflected by the varied fauna inhabiting the canyon. Diversity tends to decrease with depth, but there is also continual replacement of species with increasing water depth. Certain groups, such as the gorgonians and sea lilies, tend to be found on rocky surfaces, while large protozoans dominate the sediments at 3400-m depth. In addition to describing the fauna of Nazare Canyon, we discuss experiments undertaken as part of the HERMES project to elucidate the ecosystem function processes operating in the deeper parts of the canyon.

Recent sedimentation and sedimentary budgets on the western Iberian shelf

Abstract Thus study is based on 31 box-core samples collected mainly from the mud-patches of the Galician and North-Portuguese shelf. Each of these cores, some decimetres in length, have been described, radiographied and sampled each centimetre for grain-size analysis and measurement of the particulate organic carbon (Corg) content. 210Pb excess profiles have been measured using gamma spectrometry, which, combined with the analysis of the vertical variations of the sedimentary facies, have allowed estimates of sedimentation rates. These rates were found to vary between 0.05 and 0.40 cm yr−1. Considering the latitudinal variation of sedimentation rates around the 100m contour, we note that the maximum rates occurred off the Douro estuary in the southern sector and also near the Galician rias to the north. The organic content (Corg) of sediments varied between 0.4 and 2%. Latitudinally Corg showed a decrease from the South to the North. These results coupled with the sedimentary map (see Dias, Gonzalez, Garcia & Diaz del Rio, 2001 ) have permitted us to establish the detrital mass budget and an inventory of Corg burial.

Geochemical tracers of northern Portuguese estuarine sediments on the shelf

The northern Portuguese coastal zone is drained by large Iberian rivers, along which there is intensive industrial, agricultural and urban activity. Offshore of the two main river basins of the Douro and Minho, two fine-grained sedimentary formations can be characterised. A geochemical study of this sediment cover has been performed focussing in particular on the fine deposits and the adjacent estuaries. The chemical composition of superficial sediments collected from the northern Portuguese shelf and from the river basins of the Minho and Douro rivers was determined for major, minor and trace elements; the rare earth elements (REE) composition was also determined in selected samples. Statistical analyses of these data for the shelf sediments allow us to identify elements with similar behaviours and the different sediment types along the shelf, and to evaluate of their origins. Downcore profiles of the chemical composition of the fine sediments reveal no evidence for changes induced by recent human activities. To assess the influence of the rivers on the fine sedimentary formations, the elemental distribution patterns of selected sediments have been compared with the estuarine sediments. Lithogenic elements composition normalised to Al and the shale normalised REE distributions showed there are similarities between the Douro River sediments and the sediment composition of the Douro and Galicia mud patches. However, the Galicia mud field showed no relationship in its chemical composition to sediments derived from the Minho River. Nor was any evidence for heavy metal contamination originating from the Douro estuary detected in anthropogenic element/Al ratios in the shelf sediments. This may be because of processes associated with resuspension, complexation and bioturbation that occur during sediment transport and deposition. Nevertheless, the Douro River seems to be the main continental source of fine sediments being deposited on the northern Portuguese shelf.

Porphyrin derivatives as photosensitizers for the inactivation of Bacillus cereus endospores.

Aims:  In this study, we propose (i) to study the photodynamic inactivation (PDI) efficiency of neutral and cationic porphyrin derivatives, (ii) to characterize the kinetics of the inactivation process using Bacillus cereus as a model endospore‐producing bacterium and (iii) to conclude on the applicability of porphyrin derivatives in the inactivation of bacterial endospores.

Antimicrobial photodynamic activity of porphyrin derivatives: potential application on medical and water disinfection

In this highlight an overview of the advances performed by the Aveiro group on the design and synthesis of tetrapyrrolic photosensitizers with potential photodynamic antimicrobial activity is presented.

Some evidences of northward fine sediment transport in the northern portuguese continental shelf

Abstract On the basis of sedimentological and oceanographical data, a transport scheme for fine-grained material is proposed in order to explain the location of a muddy deposit present in the northern Portuguese continental shelf, north-west off the Douro River mouth. This mid-shelf deposit is recent, active and its main source is apparently the Douro River. The sediment supply can be related with the oceanographic conditions in winter regime, characterised by a poleward along-shelf current with a bottom westward component, as a consequence of a south-west wind. The resulting fine sediment transport, essentially made in the bottom nepheloid layer, is believed to have a north-west direction.

A cross-scale numerical modeling system for management support of oil spill accidents

A flexible 2D/3D oil spill modeling system addressing the distinct nature of the surface and water column fluids, major oil weathering and improved retention/reposition processes in coastal zones is presented. The system integrates hydrodynamic, transport and oil weathering modules, which can be combined to offer different-complexity descriptions as required by applications across the river-to-ocean continuum. Features include accounting for different composition and reology in the surface and water column mixtures, as well as spreading, evaporation, water-in-oil emulsification, shoreline retention, dispersion and dissolution. The use of unstructured grids provides flexibility and efficiency in handling spills in complex geometries and across scales. The use of high-order Eulerian-Lagrangian methods allows for computational efficiency and for handling key processes in ways consistent with their distinct mathematical nature and time scales. The modeling system is tested through a suite of synthetic, laboratory and realistic-domain benchmarks, which demonstrate robust handling of key processes and of 2D/3D couplings. The application of the modeling system to a spill scenario at the entrance of a port in a coastal lagoon illustrates the power of the approach to represent spills that occur in coastal regions with complex boundaries and bathymetry.

NUMERICAL MODELING OF THE AVEIRO INLET DYNAMICS

The dynamics of the Aveiro lagoon is assessed through a combination of field data and numerical modeling. An unstructured grid hydrodynamic model is set-up for this system for the first time and its results compare well with data and with a wellestablished model. The model and the data are then used to analyze the propagation of the tide in the lagoon and the variability of tidal asymmetry in the upper and lower lagoon. The lagoon shifts from mild ebb-dominance at the inlet to strong flooddominance in the upper lagoon. This variability may be responsible for the importing capacity suggested by the sediment particle model, estimated at 10% of the littoral drift. On the contrary, a preliminary application of the morphodynamics modeling system MORSYS2D suggests a net export capacity. These opposite results maybe due to the tidal excursion of sediments in the system, which is much larger than the scale of variability of the hydrodynamics.