Abstract. A 2-year dataset of a stand-alone mooring, deployed in November 2020 down the Levante Canyon in the eastern Ligurian Sea, is presented. The Levante Canyon Mooring (LCM) is a deep submarine multidisciplinary observatory positioned at 608 m depth in a key ecosystem area. The Levante Canyon hosts a valuable and vulnerable ecosystem of deep-living cold-water corals (CWCs), studied and monitored since 2013 through integrated mapping of the seabed and water column. The 2-year dataset, acquired on the mooring and presented here (data from November 2020 to October 2022), includes measurements conducted with both current meters and conductivity–temperature–depth (CTD) probes and provides information about the hydrodynamics and thermohaline properties across almost the entire water column. The observatory is still ongoing, and the dataset is regularly updated. All the described data are publicly available from https://doi.org/10.17882/92236 (Borghini et al., 2022). They must therefore be preserved and are of considerable scientific interest.

Climate change investigation, protection of marine ecosystems and mitigation of natural risks are the main research objectives of the Levante Canyon Mooring (LCM), a deep submarine multidisciplinary observatory, installed in September 2019 in the Eastern Ligurian Sea (Lat 44°05.443'N, Long 009°29.900'E at 608 m depth), inside the Pelagos Sanctuary. The observatory consists of a stand-alone station, with an instrumented mooring line ending with a submerged buoy. It operates in delayed-mode and is equipped with sensors that measure physical and biogeochemical parameters continuously and it is expected to provide data in the long-term. Temperature and salinity monitoring is carried out at three depth levels (about 80, 335 and 580 m depth), while turbidity is recorded at 580 m depth. LCM is also equipped with a sediment trap and two acoustic current profilers, able to measure direction and speed of currents in nearly the entire water column.Data will be used to measure flux of sediments, nutrients and organic matter and to better understand the hydrodynamic and physical conditions of the Levante Canyon, which hosts valuable and vulnerable ecosystems, such as the deep-living cold-water corals, identified by IIM and ENEA in 2014, near the LCM mooring site. The LCM site is also located in an area where surface currents are monitored in near-real time by the CNR’s High Frequency Radar network, allowing data integration from multiplatform observations.The project, co-financed by the Liguria Region, is coordinated by the DLTM in strict collaboration, in terms of human resources, infrastructures and instruments with the associated public research bodies (CNR, ENEA, INGV) and with the IIM. The project also includes the next deployment of a cabled station in the Gulf of La Spezia (10 m depth, less than 100 m far from the coast) that will monitor the gravimetric field, temperature and marine current. The main objective of the coastal station is to provide a test site for new instruments and sensors.

Flow reversals within the Corsica Channel, a strait East of Corsica, are investigated with a realistic, high-resolution (∼1.5km) numerical setup simulating the year 2004. The simulations compare well with available water mass transport estimates resulting in an annual mean of 0.49±0.49Sv. Similarly, the model agrees with hydrographic observations in the area, and current velocity measurements showing a flow in the Corsica Channel predominantly directed northward from the Tyrrhenian to the Ligurian Sea. On top of the well-documented Corsica Channel seasonal variability, a higher-frequency variability can be found throughout the year but more frequently during the summer season. This temporal variability, highest close to the western flank of the Channel, is of the order of a few days to a week and associated with reversals of the currents. We find that this variability is ascribed to periodic intrusions of the West Corsica Current on the Eastern side of the Island. Moreover, our findings suggest the importance, of a so-far neglected, across-channel variability of the meridional velocity throughout the entire 2004. This result potentially questions the single-mooring assumption that has always been at the center of the observational scheme. This assumption holds while looking at low-frequency/seasonal variability but fails when focusing on higher-frequency variability.

The variability and evolution of the Northern Current (NC) in the area off Toulon is studied for 2 weeks in December 2011 using data from a glider, a high-frequency (HF) radar network, vessel surveys, a weather station, and an atmospheric model. The NC variability is dominated by a synoptic response to wind events, even though the dataset also evidences early stages of transition from late summer to fall-winter conditions. With weak winds, the current is mostly zonal and in geostrophic balance even at the surface, with a zonal transport associated with the NC of approximate to 1 Sv. Strong westerly wind events (longer than 2-3 days) induce an interplay between the direct-wind-induced ageostrophic response and the geostrophic component: upwelling is observed, with offshore surface transport, surface cooling, flattening of the isopycnals, and reduced zonal geostrophic transport (0.50.7 Sv). The sea surface response to wind events, as observed by the HF radar, shows total currents rotated at approximate to 55 to 90 degrees to the right of the wind. Performing a decomposition between geostrophic and ageostrophic components of the surface currents, the wind-driven ageostrophic component is found to rotate by approximate to -25 to -30 degrees to the right of the wind. The ageostrophic component magnitude corresponds to approximate to 2% of the wind speed.

In June 2013 the Institute of Marine Sciences of the National Research Council of Italy (CNR-ISMAR) started the test phase of one of the few Mediterranean autonomous profiling systems, produced by NiGK Corporation, installed in a mooring configuration, transmitting daily hydrological vertical profiles in real time through satellite communication. The selected site is the Corsica Channel, a narrow passage between the Corsica and Capraia islands connecting the two main regions of the western Mediterranean: the Tyrrhenian and the Liguro-Provencal basins. During the test phase of this new instrument a continuous monitoring of the upper 181m of the water column was performed, with more than 90% of successful satellite transmissions. The high-quality data received have been processed and analysed. The data collected confirmed our previous hydrological knowledge of the Corsica Channel, allowing us to observe in real time the variable and significant behaviour of the channel.

The Italian Fixed-Point Observatory Network (IFON) integrates well-established coastal and ocean infrastructures (buoys, platforms, moorings, mast platforms, etc.), most of them providing real-time multidisciplinary monitoring for a number of marine and atmospheric variables. Here, we describe the network characteristics and then discuss an example of its operation during the cold spell of winter 2012. One of the goals of the Italian Flagship Project Ricerca Italiana per il mare (RITMARE) is to create a common, validated IFON database able to fulfil both public and private demands, including validation of remotely sensed data and numerical models, environmental planning and management, and time-series analysis of climate and oceanographic data.

Hydrological and current measurements collected in the Tyrrhenian Sea during May-June 2004 are analyzed with an inverse boxmodel (IBM) to establish the mean spring circulation patterns of the basin. These patterns are compared with those provided by a high resolution, primitive equation model (POM) implemented over the area to simulate the mean basin circulation during the survey. The good agreement between the two circulation fields represents a solid evidence for the reliability of the estimated dynamical structures. Moreover, the POM reveals the short spatial variability of the basin not always resolved by IBM because of the low spatial resolution of the in-situ measurements. The comparative study indicates the Tyrrhenian basin as a highly dynamically active region of the Mediterranean Sea, characterized by a rich mesoscale dynamics.

The overall objective of this proposal is to build an advanced and original prototype specifically devoted to seafloor and water-column monitoring as starting Italian contribution to the further development of the EMSO Ligurian Sea node. In detail the aim of the observatory is to ensure realtime continuous acquisition of geophysical, oceanographic and biological data by a cable system from a marine depth of about 500 m to the shore station.

High-frequency (HF) coastal radars measure current velocity at the ocean surface with a 30-100 km range and 1-3 km resolution, every 0.25-1 h. HF radars are well suited to many applications, such as search and rescue (SaR), oil-spill mitigation and ecosystem management. Here we present a first organized core of 12 HF radars installed in five sites in four countries (Greece, Italy, France and Spain) within the European MED project, the Tracking Oil Spill and Coastal Awareness (TOSCA) network. Dedicated experiments tested radar capabilities to estimate transport driven by currents, which is the key feature for all the above applications. Experiments involved the deployment of drifters, i.e., floating buoys, acting as proxies for substances passively advected by currents. Using HF radars the search range is reduced by a factor of 1.6 to 5.3 after 24 h. The paper also underlines the importance of sharing common tools for HF radar data processing and the need to mitigate radio frequency interference. The effort can be regarded as an initial step toward the creation of a Mediterranean or European HF radar network, crucial for any European integrated ocean observing system (IOOS).

The deep waters of the western Mediterranean Sea have become saltier and warmer for at least the past 40 years at rates of about 0.015 and 0.04 °C per decade. Here we show that two processes contribute to these increases in temperature and salinity. On interannual timescales, deep water formation events in severe winters transmit increasingly salty intermediate waters into the deep water. The second process is a steady downward flux of heat and salt associated with salt finger mixing down through the halocline–thermocline that connects the Levantine Intermediate Water with the deep water. We illustrate these two processes with observations from repeat surveys of the western Mediterranean basin we have made over the past 10 years.

The general aim of this paper is to present a possible multidisciplinary approach to the problem of connectivity among marine protected areas (MPAs) describing some of the mechanisms and vectors that control the dispersal of propagules among spatially distributed marine communities of MPAs in the Southern Adriatic Sea. A joint approach is described that focuses on (a) measurements of surface water current and model data integrated with a dedicated software (LAVA, LAgrangian Variational Analysis), (b) measurements of rafting objects and their evaluation as an alternative way to species dispersal, and (c) a tool to automatically monitor propagules and plankton species in the water column. Studies on the dynamics of water currents demonstrated that the Gargano area has the potential to supply dispersal propagules to the Southern Adriatic both along the Italian coastline and offshore across the basin, thus providing important services to the dispersal processes and the connectivity routes among MPAs. The natural dispersion is however enhanced by floating objects, on which entire marine communities are living and travelling. The number of these objects has greatly increased with the introduction of human litter: in the Adriatic, man-made litter composes nowadays the majority (79 %) of all floating objects, with this corresponding to an almost fourfold increase in the abundance of floating objects since pre-industrial times. Such enhanced dispersion may benefit transmission of propagules from MPAs along biodiversity corridors, but may also enhance the arrival of invasive species. The direct observation of organisms can provide information on the species distribution and mobility. New technology (GUARD-1 system) has been developed to automatically identify spatial or temporal distributions of selected species in the water column by image analysis. The system has so far successfully detected blooms of ctenophores in the water column and is now being tested for identification of other zooplankton groups, such as copepods, as well as marine litter. This low-cost, long-lasting imaging system can be hosted on mobile devices such as drifters, which makes it very suitable for biological dispersal studies.

In terms of the overall mixing environment, the Mediterranean Sea has relatively small tides and relatively weak winds compared with the greater ocean environment, so vertical diffusion due to mechanical mixing is likely to be generally smaller than in the open ocean. As the western Mediterranean deep water (WMDW) is naturally fresher and colder than the Levantine intermediate water (LIW), salinity and temperature both decrease downward below the LIW core toward the deep water. In the halocline-thermocline between the core of LIW and the deep water, warmer saltier waters overlie colder fresher waters and in such a region salt finger mixing processes can be effective mixing agents transporting salt, heat, and density downward. For the deep western Mediterranean, vertical diffusion due to mechanical mixing is expected to be small; and downward mixing of heat salt and density is expected to be substantial in the halocline-thermocline 400–1500-m depth.

Thermohaline staircase structures are commonly observed in the western Mediterranean Sea within the halocline-thermocline connecting the Levantine Intermediate Water at about 400 m depth with the western Mediterranean deep waters below 1,500 m. In this halocline-thermocline where warmer, saltier waters overlie colder, fresher deep waters, salt finger mixing processes are thought to be active and produce staircases with layers of order 75 m thickness containing nearly constant properties separated by sharp steps of order 6 m thickness with jumps in properties between the layers. While the layers have nearly constant salinity, potential temperature, and potential density, each property decreases very slightly downward through the layer so that it appears that salinity, heat, and density are being put into the top of each layer and then convectively mixing downward through the layer. Such observations are consistent with salt finger processes that transport salinity, heat and density downward through the halocline-thermocline.Using repeat occupations of stations across the southern western Mediterranean Sea in 2006, 2008, and 2010, we have calculated downward salt transport, F-S, of 5.35 x 10(-8) psu m s(-1), and downward heat transport, F-T, of 12.4 x 10(-8) degrees C m s(-1). After multiplying these fluxes by haline contraction (beta) and thermal expansion (alpha) coefficients respectively, the buoyancy flux ratio, alpha F-T/beta F-S, is found to be 0.74 and there is a downward density flux of 1.0 x 10(-10) W kg(-1). The halocline-thermocline in this region between 600 and 1,400 dbar has a background vertical salinity gradient of 0.95 x 10(-4) m(-1) and a vertical temperature gradient of 4.1 x 10(-4) degrees C m(-1) so the background density ratio is R-p = (alpha d theta/dz)/(beta dS/dz) is 1.28. Dividing the downward fluxes by the background vertical gradients yields vertical diffusivities k(S) = 5.6 x 10(-4) m(2) s(-1) and k(T) = 3.0 x 10(-4) m(2) s(-1). These downward fluxes of salt and heat are compared with estimates based on salt finger experiments and theory and with the long-term increases in salinity and temperature in the deep western Mediterranean Sea over the past 40 years.

Previous studies have demonstrated that the salinity in the Levantine basin depends on the intensity of the Atlantic water (AW) inflow. Moreover, its spreading eastward (to the Levantine basin) or northward (to the Ionian Sea) is determined by the Ionian circulation pattern, i.e. by the Adriatic–Ionian Bimodal Oscillating System (BiOS) mechanism. The aim of this paper is to relate salinity variations in the Levantine basin to the salt content variability in the core of the Levantine Intermediate Water (LIW) passing through the Sicily Channel (SC) and its possible impact on the Western Mediterranean Transition – WMT (i.e. the sudden salinity and temperature increase in the deep layer of the Algero-Provençal subbasin occurring since 2004). From the historical data set MEDAR/MEDATLAS in the Levantine and northern Ionian, we present evidence of decadal occurrences of extreme salinities associated with the varying influx of AW over the last 60 yr. Furthermore, we show that the salinity variations in the two subbasins are out of phase. High-salinity episodes in the Levantine are a pre-conditioning for the potential occurrence of the events like the Eastern Mediterranean Transient (EMT). Cross-correlation between the salinity time series in the Levantine basin and in the SC suggests that the travel time of the LIW is between 10 and 13 yr. Comparing the timing of the salinity increase associated with the WMT and the salinity in the LIW core in the SC, we estimate that the total time interval needed for the signal propagating from the Levantine to reach the deep mixed layers of the Algero-Provençal subbasin is about 25 yr. We also showed that the extra salt input from the eastern Mediterranean contribute up to about 60% to the salt content increase in the bottom layer of the western Mediterranean.

New insights into the structure and variability of the Tyrrhenian Sea's surface circulation are obtained through the analysis of a very long series of altimetric observations (1993-2010). In late winter and part of spring, a consistent mean flow is individuated in the eastern Tyrrhenian Sea, formed by a stream of Atlantic water that meanders around four anticyclonic structures located along the Italian coast, which have smaller cyclonic companions offshore. The signatures of these vortices are also found in images of chlorophyll and sea surface temperature, as well as in modeling results, both from a high-resolution operational model of the Tyrrhenian Sea's circulation and from a dedicated numerical simulation. Analysis of the energy exchange between eddies and mean flow, together with numerical evidence, suggests that this winter-spring circulation pattern may result from basin-scale instability of the Atlantic stream. In summer, the dynamic is dominated by a well-known dipole located to the east of the Bonifacio Strait. However, in the eastern part of the basin, an anticyclonic cell is also found, probably driven by the negative wind stress curl present in summer in this region. The cell encompasses two anticyclonic vortices located in the areas of the Vavilov and Marsili Seamounts. A multichannel singular spectral analysis of the altimetric time series reveals that, besides the expected, dominant seasonal mode, a significant low-frequency mode of variability is also present. This mode has a period of about six years and is mostly localized in the western part of the basin.