Marine and Coastal Hazard Assessment for Three Coastal Oil Rigs

A forecasting and hazard assessment system for oil dispersion from Italian oil rigs was set up within the framework of a national research project. The system is based on 3D hydrodynamic, mesoscale resolving models providing forcing fields for a Lagrangian module of oil dispersion and slick evolution (oil transport and transformation). The tool provides,daily, the outputs of numerical simulations of possible oil spills from extraction platform sites. In this work we present the results for the 3 platforms closest to the Italian coast. Aside the operational usage, the numerical outputs are also stored and adopted to compute statistics of the slick distributions in the coastal and marine areas of interest. The hazard was assessed by means of two different indices (Hazard Index and Occurrence Index) based on the operational system outputs, for the estimation of the hazard at sea (marine hazard or aerial hazard). As short forecasts (2 days long) often do not allow the oil to reach the coast, an extra set of long-period simulations has been performed in order to compute a third Hazard Index (Coastal Hazard Index) suitable to estimate the hazard along the shorelines. The adopted methodology allowed, as a whole, to assess both coastal and marine oil spill hazard due to oil spill extraction activities. The indices constitute a basic informative layer on which the environmental risk could be also evaluated, once opportunely combined with coastal vulnerability and sensitivity layers

Interannual variability of the hydrology on the Sardinia shelf

The interannual variability of the physical properties of the shelf waters in Sardinia, western Mediterranean Sea, is studied by using hydrological data gathered during three oceanographic cruises: two in late summer of 2019 and 2021 respectively and another one in early autumn of 2020. The data consist of vertical profiles of salinity and potential temperature acquired by a multiparametric probe for a total of 171 casts performed along a set of transects extending from the nearshore to the continental slope, up to the depth of 200 m. Satellite remote sensing and numerical modelling oceanographic products support the phenomenological analysis. Atlantic Water, characterised by low salinity signatures (S<37.0), is detected in the surface waters of the southwestern shelf areas, induced by the Algerian Eddies, and with differences between years. It is also observed on the southern-eastern and north-eastern shelf areas of Sardinia, mainly driven by the interaction with large-scale circulation features like the southeast Sardinia Gyre and the Bonifacio Gyre. An upwelling phenomenology is identified as one of the major features of the coastal circulation on the western shelf area. The study provides the first assessment of the thermohaline features on the Sardinian shelf; an enhanced contribution to the current knowledge of the coastal sea phenomena, and contributes to numerical modelling applications and implementations for ecosystem services

Mesoscale eddies in the Algerian Basin: do they differ as a function of their formation site?

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

Mesoscale eddies in the Algerian Basin: formation, translational and energetic characteristics as obtained from 22 years of altimetric satellite data

The formation and propagation of mesoscale structures in the Algerian Basin strongly influence the circulation of the Western Mediterranean Sea and have been subject to several studies in the past. In order to investigate the spatial and temporal distribution of the anticyclones and their pathways within the basin, we applied an automated detection and tracking method to 22 years of Sea Level Anomaly (SLA) data. The algorithm is based on the computation of the Okubo-Weiss parameter in SLA closed loops. The results show two different types of anticyclonic eddies depending of the area of formation. Most of the eddies occurring above 39 ◦ N and along the North Balearic Front (NBF), have lifespans shorter than 3 months. They are supposed to be caused by the instabilities of the thermal front and are thus labelled Frontal Anticyclonic Eddies (FAEs). These short-life structures form mainly in fall and winter and are characterized by low translational velocity and a highly variable direction of propagation. By contrast, the eddies in the southern part of the basin (the Algerian Eddies - AEs), originate along the Algerian Current as a consequence of baroclinic instabilities and on the whole have lifetimes greater than 3 months. They are also the largest and the most energetic structures of the area. The peak of formation is observed in spring, when the transport of the Algerian Current is maximum. These features form mainly east of 6.5 ◦ E and move eastward along the African slope to the Sardinia Channel, where they detach from the coast and continue offshore following a cyclonic closed pathway corresponding to the intermediate circulation. In the southern part of the basin we also detect a convergence area where the eddies tend to merge. Lastly, the analysis suggests that the Algerian Basin can be separated into a southern and a northern part as a function of the properties of the eddies, such as formation site, path, number, energy and lifetime. The only connection in terms of eddy tracks between the two areas is represented by a few long-life FAEs moving southward and becoming entrapped by the southern cyclonic circulation

Caratterizzazione idrodinamica del Golfo di Cagliari mediante misure lagrangiane

In data 9 settembre 2014 il gruppo di oceanografia dell’Istituto per l’Ambiente Marino Costiero (IAMC) di Torregrande (Oristano), del Consiglio Nazionale delle Ricerche (CNR), ha partecipato alla esercitazione di Search and Rescue (SAR) denominata “Squalo 2014”. L’esercitazione è stata organizzata e coordinata dalla Direzione Marittima della Guardia Costiera di Cagliari e ha visto la partecipazione di numerosi enti (civili e militari) preposti alle operazioni di salvataggio e/o di supporto logistico. La partecipazione del CNR ha visto come obiettivo specifico la caratterizzazione idrodinamica dell’area di studio utilizzando osservazioni Lagrangiane e modelli numerici di simulazione. L’obiettivo a lungo termine è la ideazione e la realizzazione di un sistema di supporto alle decisioni (Decisional Support System) capace di determinare l'area di ricerca ottimale (area di probabilità). Questo sarà possibile unendo tecniche di simulazione numerica di tipo deterministico (modelli idrodinamici costieri e moduli di dispersione Lagrangiana) con metodi statistici per la stima dell’errore ed il calcolo delle probabilità. Compatibilmente con le risorse disponibili (finanziarie, computazionali ed umane), l’intenzione è di proseguire la ricerca iniziata nel corso della esercitazione, testando un modello SAR denominato “Leeway” che ha le potenzialità per consentire lo sviluppo del suddetto DSS Questa attività è stata finanziata nell’ambito del progetto bandiera RITMARE (SP3-WP4-AZ6 e SP5-WP4-AZ3)

An Operational Supporting System for Oil Spill Emergencies Addressed to the the Italian Coast Guard

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