Knowledge about marine circulation and its variability is a basic requirement for the correct management of activities aimed at exploiting marine resources and for the prevention and eventual mitigation of the risks involved. The activities of the Marine Hazard Project, to which this special number of Sustainability is dedicated, focus on geothermal resources connected with some submerged volcanic systems located in the Tyrrhenian Sea. This sea hosts delicate coastal and marine ecosystems, and is characterized by rich dynamics, both driven by the interaction of the local forcing with the complex morphology and bathymetry of the basin, and by exchanges with adjacent sub-basins which take place at all depths. The main purpose of the present review is to summarize the present understanding of the Tyrrhenian Sea circulation and its variability, with special emphasis on the results of experimental and modelling works of the last decade.

The Mediterranean Sea has experienced pronounced warming over the past few decades, but since 2022 this trend has accelerated markedly, culminating in 2024, the hottest and most dynamically energetic year of the last four decades. Record-high sea surface temperatures (SSTs) were observed across both the Western and Eastern subbasins. This study examines the spatio-temporal variability of the 2024 temperature anomaly and its driving mechanisms using satellite observations of SST and sea level, surface fluxes from atmospheric reanalysis, Citizen Science in-situ coastal data, and ocean reanalysis products from the Copernicus Marine Service. Following the strong ocean heat uptake during summer 2023, a prolonged phase of reduced ocean-to-atmosphere heat loss maintained SSTs well above climatology through autumn 2023 and winter–spring 2024. In February 2024, SSTs exceeded 15°C in the Western Mediterranean and nearly 18°C in the Eastern basin. During summer 2024, the Eastern Mediterranean underwent an exceptional marine heatwave, with surface temperatures reaching about 29°C by late August. This anomaly was mainly driven by intense air–sea heat fluxes acting on an unusually shallow mixed layer, which amplified upper-ocean heat storage and persistence. Altimeter and model data reveal that 2024 also marked a sharp increase in mean and eddy kinetic energy (EKE), particularly in the Algerian, Northwestern, and Levantine basins, where the strongest SST anomalies were observed. We found that basin-scale geostrophic kinetic energy has increased markedly from 1993 to 2024, with 2024 standing out as an exceptionally energetic year that deviates from the long-term linear trend. Overall, 2024 represents a year of exceptional oceanic conditions in the Mediterranean, with a strong link between the surface warming and enhanced oceanic kinetic energy.

Over the last 15 years, five operational systems for the forecasting of the circulation of the Italian seas have been developed, which provide products of use for the management and safety of marine activities and for the protection of the marine environment. The first systems which focused on the Adriatic Sea and the Sicily Strait, have been added to over the years, to cover the Tyrrhenian Sea, the seas around Sardinia, and, finally, the region around the Bonifacio Strait, a small area interested by an intense marine traffic. In this work, the main features of the five regional systems are described and examples are given of their capabilities and their use for revealing new features of marine circulation.

Availability of detailed short-term forecasts of the ocean main characteristics (circulation and waves) is essential for a correct management of the human activities insisting on coastal areas. These activities include the extraction of renewable energy, which has developed in recent years, and will play an important role in the context of future blue growth. The present work describes the implementation of a new ocean operational system, named MITO, that provides daily 5 days forecasts of the Mediterranean Sea circulation. Distinctive features of this system are the inclusion of the main effects of the tidal forcing, both local and propagating from the Atlantic, and the high spatial detail. The horizontal resolution is of 1/48° (about 2 km) in most of the computational domain, and is smoothly increased (down to few hundred meters) in key passages, such as the Gibraltar Strait and the Turkish Straits, to correctly resolve the complex local dynamics. Initial and boundary conditions for MITO are taken from the reference European operation model of Copernicus, which covers the Mediterranean Sea with a uniform resolution of 1/24°. A thorough validation of the new system is performed, analyzing the forecasts of the year 2020, whose results are compared with in situ and remote observational data (sea surface temperature, altimeter data, temperature and salinity profiles by floats, tide-gauge measurements, available through the Copernicus portal) using the same large-scale metrics applied in the validation of the Copernicus operational model. MITO results are generally found in very good agreement with the observations, despite the fact that the model does not make explicit use of data assimilation. We also give examples of the capability of the model to correctly describe complex local mesoscale dynamics, and point out aspects that need to be improved, which will be addressed in a future upgrade of the operational implementation.

The Ionian Sea is a crucial intersection for various water masses in the Mediterranean. Its hydrography and dynamics play a significant role in the seawater budgets and biogeochemistry of the neighboring sub-basins. Multiple theories have been formulated to gain a better understanding of the Ionian dynamics. These theories primarily attribute the variability of the near-surface Ionian circulation to internal processes. Here, we utilize horizontal currents and temperature–salinity profiles from the Copernicus reanalysis to examine the contribution of baroclinic modes to the variability of the basin horizontal circulation. Our findings demonstrate that, although the basin vertical structure is characterized by three layers, the primary patterns of the Ionian circulation can be attributed to the first baroclinic mode. This mode, along with the barotropic mode, accounts for over 85% of the overall variability in the Ionian circulation, suggesting that only one of the three interfaces separating the different water masses in the basin is dynamically active. We estimate the depth of this interface to be about 490 m. Additionally, our analysis shows that more than 90% of the kinetic energy over the water column is localized above this interface, indicating that the deep layer of the Ionian is dynamically nearly inert.

The Ionian Sea is a crucial intersection for various water masses in the Mediterranean. Its hydrography and dynamics play a significant role in the seawater budgets and biogeochemistry of the neighboring sub-basins. Multiple theories have been formulated to gain a better understanding of the Ionian dynamics. These theories primarily attribute the variability of the near-surface Ionian circulation to internal processes. Here, we utilize horizontal currents and temperature-salinity profiles from the Copernicus reanalysis to examine the contribution of baroclinic modes to the variability of the basin horizontal circulation. Our findings demonstrate that, although the basin vertical structure is characterized by three layers, the primary patterns of the Ionian circulation can be attributed to the first baroclinic mode. This mode, along with the barotropic mode, accounts for over 85% of the overall variability in the Ionian circulation, suggesting that only one of the three interfaces separating the different water masses in the basin is dynamically active. We estimate the depth of this interface to be about 490 m. Additionally, our analysis shows that more than 90% of the kinetic energy over the water column is localized above this interface, indicating that the deep layer of the Ionian is dynamically nearly inert.