Federica Pessini

The Western Mediterranean basin (WMED) is characterized by the presence of energetic and dynamic mesoscale cyclonic and anticyclonic eddies. They mainly originate along the Algerian and the Northern currents and have a large influence on the basin circulation. Eddies can last for months, with longer lifetimes associated with the anticyclones, which can move far from their areas of origin. As they partially isolate and transfer water masses, they also have an impact on water properties (physical, chemical and biological), pollutant’s dispersion and transport of eggs, larvae and planktonic organisms. In this study, a connectivity analysis method is applied to the anticyclonic eddies (AEs) identified by an automated hybrid detection and tracking algorithm south of 42° N in the WMED. The same methodology is also applied to the trajectories of Lagrangian surface drifters available in the study area. The purpose is to highlight the connections between different areas of the basin linked to eddy activities in addition to the connectivity due to the mean surface circulation. Drifter data analysis showed that all the WMED sub-basins are strongly interconnected, with the mean surface circulation allowing a shortcut connection among many areas of the basin. The connectivity analysis of the AEs tracks shows that although AEs are ubiquitous in the WMED, their connectivity is limited to well-defined regions, depending on their origin location. Three main regions: the south-western, the south-eastern and the northern parts of the basin are characterized by AEs recirculation, with sporadic export of eddies to the other WMED zones.

Since 2000, and for the following 20 years, hydrological data of the Mediterranean Sea, with a particular focus on the western and central Mediterranean sub-basins, have been acquired to study the hydrodynamics at both coastal and open sea scales. In total, 1468 hydrological casts were realized in 29 oceanographic cruises planned due to scientific purposes linked with funding research projects but were also sometimes driven by sea conditions and type of vessel. After accurate quality assurance and control, following standard procedures, all hydrological data were included in four online public open-access repositories in SEANOE (SEA scieNtific Open data Edition), available from https://doi.org/10.17882/87567 (Ribotti et al., 2022). Hydrological and dissolved oxygen data are always present in all of the datasets, whereas pH, fluorescence, turbidity, and chromophoric dissolved organic matter (CDOM) are available just for some cruises. Samplings were carried out mainly along transects, with some repetition over the years. The results of two data analyses, i.e., staircase systems in the Tyrrhenian Sea and in the Algero-Provençal sub-basin and spreading of the Western Mediterranean Transient, are mentioned.

Since 2000 and for the following 20 years hydrological data of the Mediterranean Sea, with a particular focus on the western and central Mediterranean sub-basins, have been acquired to study the hydrodynamics at both coastal and open sea scales. Totally 1468 hydrological casts were realized in 29 oceanographic cruises planned due to scientific purposes linked with funding research projects but sometimes driven by sea conditions and type of vessel. After an accurate quality assurance and control, following standard procedures, all hydrological data were included in four online public open access repositories in SEANOE available from https://doi.org/10.17882/87567 (Ribotti et al., 2022). Hydrological and dissolved oxygen data are always present in all the datasets whereas pH, fluorescence, turbidity and CDOM are available just for some cruises. Samplings were carried out mainly along transects with some repetitions in the years. Then the results of two data analyses, staircase systems in the Tyrrhenian Sea and in the Algero-Provencal sub-basin and spreading of the Western Mediterranean Transient, are mentioned.

The Western Mediterranean basin (WMED) is characterized by the presence of energetic and dynamic mesoscale cyclonic and anticyclonic eddies. They mainly originate along the Algerian and the Northern currents and have a large influence on the basin circulation. Eddies can last for months, with longer lifetimes associated with the anticyclones, which can move far from their areas of origin. As they partially isolate and transfer water masses, they also have an impact on water properties (physical, chemical and biological), pollutant’s dispersion and transport of eggs, larvae and planktonic organisms. In this study, a connectivity analysis method is applied to the anticyclonic eddies (AEs) identified by an automated hybrid detection and tracking algorithm south of 42°N in the WMED. The same methodology is also applied to the trajectories of Lagrangian surface drifters available in the study area. The purpose is to highlight the connections between different areas of the basin linked to eddy activities in addition to the connectivity due to the mean surface circulation. Drifter data analysis showed that all the WMED sub-basins are strongly interconnected, with the mean surface circulation allowing a shortcut connection among many areas of the basin. The connectivity analysis of the AEs tracks shows that although AEs are ubiquitous in the WMED, their connectivity is limited to well-defined regions, depending on their origin location. Three main regions: the south-western, the south-eastern and the northern parts of the basin are characterized by AEs recirculation, with sporadic export of eddies to the other WMED zones.

Oil spill models are used to simulate the evolution of an oil slick that occurs after an accidental ship collision, malfunctioning of oil extraction platforms, or illegal discharges intentionally released by ships into the marine environment. We present an integrated operational oil spill prediction system that improves capacities in preventing and mitigating maritime risks from oil spills. The objective is to provide forecast information about the transport and the fate of a hypothetical oil spill under Nearly-Real Time hydrodynamic conditions in the western and central Mediterranean Sea. This complex forecast system is developed in the framework of the project SOS-Piattaforme & Impatti Off-Shore to the needs of Italian Coast Guard and other institutions, such as the Ministry of the Environment. This service has been operational since July 2020. The innovative aspect of this work is a graphical user interface (the GUI), which allows to select properties, time, and location of a potential oil spill and show the evolution of oil slick concentration and oil fate parameters. This platform represents the first component of a future Decision Support System aimed to identify the risk assessment of oil spills in order to better manage emergencies and minimize economic damages.

The circulation of the western Mediterranean Sea (WMED) is dominated by highly variable and heterogeneous mesoscale circulation that is strongly driven by the formation and propagation of eddies (cyclonic and anticyclonic) mainly acting in the Algerian Basin. In order to investigate the spatial and temporal distribution of eddy generation and their respective paths in the Algerian Basin, the most energetic WMED portion, we use an automated detection and tracking hybrid method applied to 24 years of sea level anomaly (SLA) data. The algorithm is based on the computation of the Okubo–Weiss parameter in SLA closed loops and has been modified in order to fill the gaps in single eddy tracks. In this work we analysed both cyclonic and anticyclonic structures, but the conclusions will be focused mainly on anticyclones with a lifespan longer than 3 months, as they are characterized by higher kinetic energy, thereby potentially contributing to a large extent to the mesoscale characterization of the basin. In particular, we find that anticyclonic short-life eddies mostly occur in the northern portion of the domain, north of 39 ^∘ N along the North Balearic Front (NBF). Such short-life eddies, labelled frontal eddies (FEs), are characterized by low translational velocity and a highly variable direction of propagation. We found a weak seasonality in their formation, with maxima in fall and winter. By contrast, anticyclonic longer-life eddies tend to arise in the southern part of the basin along the Algerian Current, with a clear maximum in spring. All the structures (both cyclonic and anticyclonic) originating along the Algerian Current are known as Algerian eddies (AEs). According to previous studies, we observe that these anticyclonic eddies mainly form east of 6.5 ^∘ E and move eastward along the African coast to the Sardinia Channel, where they detach from the coast, continuing offshore and following the cyclonic intermediate circulation. We detect a region between 4.5 and 6.5 ^∘ E where such eddies tend to converge and terminate their life. Finally, the analysis suggests that eddies formed in the northern and in the southern part of the Algerian Basin present some physical differences such as lifetime, kinetic energy and vorticity. Furthermore, the connection between the two parts in terms of eddy tracks is limited to a very small number of southbound (FEs) or northbound (AEs) structures crossing 39 ^∘ N.

The circulation of the Western Mediterranean Sea (WMED) is dominated by highly variable and heterogeneous mesoscale circulation, strongly driven by the formation and propagation of eddies (cyclonic and anticyclonic) mainly acting in the Algerian Basin. Anticyclones are characterized by longer life, so potentially contributing to a large extent to the mesoscale characterization of the basin. Hereafter we will take into account only anticyclonic structures. In order to investigate the spatial and temporal distribution of eddy generation and their respective paths in the Algerian Basin, the most energetic WMED portion, we use an automated detection and tracking hybrid method (modified to fill the gaps in single eddy tracks) applied to 22 years of Sea Level Anomaly (SLA) data. The method is based on the computation of the Okubo–Weiss parameter in SLA closed loops. We find that anticyclonic short-life eddies mostly occur in the northern portion of the domain, north of 39° N, along the North Balearic Front (NBF). We refer to all the structures formed in that area as Frontal Anticyclonic Eddies (FAEs). Such short-life eddies are characterized by low translational velocity and a highly variable direction of propagation. We found a weak seasonality in their formation, with maxima in fall and winter. By contrast, anticyclonic longer-life eddies tend to arise in the southern part of the basin, along the Algerian Current, with a clear maximum in spring. All the structures originating along the Algerian Current are known as Algerian Eddies (AEs). According to previous studies, we observe that AEs mainly form east of 6.5° E and move eastward along the African coast to the Sardinia Channel, where they detach from the coast, continuing offshore and following the cyclonic intermediate circulation. We detect a region where such eddies tend to converge and terminate their life. Finally, the analysis suggests that the Algerian Basin can be separated in two parts, southern and northern one as function of the eddy properties like formation site, path, number, energy and lifetime. The only connection in terms of eddy tracks between the two areas is represented by a few FAEs moving southward and being entrapped in the southern cyclonic circulation.

A twin numerical experiment was conducted in the seas around the island of Sardinia (Western Mediterranean) to assess the impact, at regional and coastal scales, of the use of relative winds (i.e., taking into account ocean surface currents) in the computation of heat and momentum fluxes through standard (Fairall et al., 2003) bulk formulas. The Regional Ocean Modelling System (ROMS) was implemented at 3 km resolution in order to well resolve mesoscale processes, which are known to have a large influence in the dynamics of the area. Small changes (few percent points) in terms of spatially averaged fluxes correspond to quite large differences of such quantities (about 15 %) in spatial terms and in terms of kinetics (more than 20 %). As a consequence, wind power input P is also reduced by ~ 14 % on average. Quantitative validation with satellite SST suggests that such a modification of the fluxes improves the model solution especially in the western side of the domain, where mesoscale activity (as suggested by eddy kinetic energy) is stronger. Surface currents change both in their stable and fluctuating part. In particular, the path and intensity of the Algerian Current and of the Western Sardinia Current (WSC) are impacted by the modification in fluxes. Both total and eddy kinetic energies of the surface current field are reduced in the experiment where fluxes took into account the surface currents. The main dynamical correction is observed in the SW area, where the different location and strength of the eddies influence the path and intensity of the WSC. Our results suggest that, even at local scales and in temperate regions, it would be preferable to take into account such a contribution in flux computations. The modification of the original code, substantially cost-less in terms of numerical computation, improves the model response in terms of surface fluxes (SST validated) and it also likely improves the dynamics as suggested by qualitative comparison with satellite data.

The photoinduced optical retardation in mesostructured polymeric materials containing photo-orientable dyes has been investigated as a function of time and pump irradiance by an imaging pump-probe technique. The mesostructured samples show higher maximum retardation and lower residual anisotropy than amorphous ones. Several hypotheses are made to explain both results, taking into account the influence of the mesostructures on the chromophores. The retardation-irradiance curves measured in different samples are fitted against current available models.