Vincenzo Artale

The abyssal Ionian Sea is a deep region of interest for the entire ocean circulation of the Mediterranean Sea, since it plays an important role in the ventilation processes of the whole basin. Here we investigate spatial patterns of internal wave climate over the bottom of the Ionian sub-basin. To identify regional features of the internal wave field in terms of vertical shear and strain, we analyze LADCP and CTD profiles, measured across the basin in 2007, covering various seafloor morphologies (shelf, shelf break, and abyssal plain). By introducing broadband statistical quantities derived from the shear–strain variance partition, our results show that increasing seafloor roughness reduces the absolute values of shear-to-strain ratio, a pattern also influenced by correlations between slope and roughness. Roughness appears to constrain waves toward higher frequencies, with high shear-to-strain ratios associated with lower frequencies and flatter propagation angles, and low ratios linked to higher frequencies and steeper beams. Spectral analyses indicate that rougher regions enhance strain variance at small vertical scales while reducing shear variance at larger scales, leading to flatter shear spectra in the low-wavenumber band. Together, these findings suggest that roughness redistributes energy from large-scale (low-mode, low-vertical-wavenumber internal waves with vertical scales O(10 ² –10 ³ m)) toward small-scale (high-vertical-wavenumber internal waves with vertical scales O(10–10 ¹ m)), fundamentally altering the balance of internal wave energy across scales. These results provide useful knowledge for ad hoc finescale parameterization based on seafloor topography.

The abyssal Ionian Sea is a deep region of interest for the entire ocean circulation of the Mediterranean Sea, since it plays an important role in the ventilation processes of the whole basin. Here we investigate spatial patterns of diapycnal mixing due to internal waves, over the bottom of the Ionian sub-basin. To identify regional features of the internal wave field in terms of vertical shear and strain, we analyze LADCP and CTD profiles, measured across the basin in 2007, covering various seafloor morphologies (shelf, shelf break, and abyssal plain). Our results show that increasing seafloor roughness reduces the variability of the shear-to-strain ratio, a pattern also influenced by correlations between slope and roughness. Roughness appears to constrain waves toward higher frequencies, with high shear-to-strain ratios associated with lower frequencies and flatter propagation angles, and low ratios linked to higher frequencies and steeper beams. Spectral analyses indicate that rougher regions enhance strain variance at small vertical scales while reducing shear variance at larger scales, leading to flatter shear spectra in the low-wavenumber band. Together, these findings suggest that roughness redistributes energy from large-scale toward small-scale, fundamentally altering the balance of internal wave energy across scales. These results expand our insights for 3D ocean circulation models, providing useful knowledge for ad hoc parameterization of mixing that should capture abyssal, internal wave–driven processes in the Mediterranean Sea.

The abyssal Ionian Sea is a deep region of interest for the entire ocean circulation of the Mediterranean Sea, since it plays an important role in the ventilation processes of the whole basin. Here we investigate spatial patterns of diapycnal mixing due to internal waves, over the bottom of the Ionian sub-basin. To identify regional features of the internal wave field in terms of vertical shear and strain, we analyze LADCP and CTD profiles, measured across the basin in 2007, covering various seafloor morphologies (shelf, shelf break, and abyssal plain). Our results show that increasing seafloor roughness reduces the variability of the shear-to-strain ratio, a pattern also influenced by correlations between slope and roughness. Roughness appears to constrain waves toward higher frequencies, with high shear-to-strain ratios associated with lower frequencies and flatter propagation angles, and low ratios linked to higher frequencies and steeper beams. Spectral analyses indicate that rougher regions enhance strain variance at small vertical scales while reducing shear variance at larger scales, leading to flatter shear spectra in the low-wavenumber band. Together, these findings suggest that roughness redistributes energy from large-scale toward small-scale, fundamentally altering the balance of internal wave energy across scales. These results expand our insights for 3D ocean circulation models, providing useful knowledge for ad hoc parameterization of mixing that should capture abyssal, internal wave–driven processes in the Mediterranean Sea.

The abyssal Ionian Sea is a deep region of interest for the entire ocean circulation of the Mediterranean Sea, since it plays an important role in the ventilation processes of the whole basin. Here we investigate spatial patterns of diapycnal mixing due to internal waves, over the bottom of the Ionian sub-basin. To identify regional features of the internal wave field in terms of vertical shear and strain, we analyze LADCP and CTD profiles, measured across the basin in 2007, covering various seafloor morphologies (shelf, shelf break, and abyssal plain). Our results show that increasing seafloor roughness reduces the variability of the shear-to-strain ratio, a pattern also influenced by correlations between slope and roughness. Roughness appears to constrain waves toward higher frequencies, with high shear-to-strain ratios associated with lower frequencies and flatter propagation angles, and low ratios linked to higher frequencies and steeper beams. Spectral analyses indicate that rougher regions enhance strain variance at small vertical scales while reducing shear variance at larger scales, leading to flatter shear spectra in the low-wavenumber band. Together, these findings suggest that roughness redistributes energy from large-scale toward small-scale, fundamentally altering the balance of internal wave energy across scales. These results expand our insights for 3D ocean circulation models, providing useful knowledge for ad hoc parameterization of mixing that should capture abyssal, internal wave–driven processes in the Mediterranean Sea.

The processes involved in abyssal variability, their connections to the water column above, and their vulnerability to climate change are still unknown. This is due to a dearth of long-term observations below 2 km of depth. To fill these gaps, our approach leverages existing datasets using different methodologies. The Ionian Sea in the eastern Mediterranean is a unique location to investigate abyssal dynamics considering that it serves as a gateway between two major deep-water formation zones i.e., the Adriatic and Aegean seas. Moreover, the observed severe thermohaline variations experienced by the bottom layers of the Ionian Sea during the last decades, had dramatic effects on the deep circulation, leaving their signature on the whole Mediterranean Sea. The variation of the deep stratification, the causes that generate it, and the impact it produces are still under debate. The mechanisms involved in such variability, as well as the connection with the abyss and the above layers of the water column, are not fully understood. Through tidal and fine-scale mixing analysis, seafloor observations, and a tailored semi-analytical model we depicted the critical role of stratification, morphology, and tides in enhancing local diffusivity in the abyssal layer. Stratification, in particular, influences stability and the rotation of vorticity among different density layers, linking deep-sea variability to the entire water column. We achieved these results by combining different indirect methodologies exploiting all available resources at best with a synergic approach, getting a possible representation of what happens at depths.

Observations of abyssal variability performed in the Ionian Sea (Mediterranean Sea) have revealed the presence of a dense, stable abyssal layer, whose thermohaline and dynamical properties changed drastically over a decade. Building upon these available observations, we aim to investigate the role that stratification can play in the transmission of vorticity throughout the water column to the abyss and, in turn, in the redistribution of energy stored in the deep sea, with a set of stationary states. A quasi-geostrophic level model equipped with four coupled layers, a free surface, and a mathematical artifice for parameterizing decadal time evolution has been considered, proving that the relative-thickness and relative-density differences among the layers are the two critical factors that determine the dynamical characteristics of this rearrangement. The variability in ocean stratification is a relevant aspect that can activate deep and intermediate dynamics, engaging in the propagation and stabilization of signals throughout the water column. This demonstrates the non-negligible active connection between the dynamics of the bottom layers and the surface. The theoretical framework and parameterization used are based on specific observations made in the Ionian Sea over the last decades but retain general applicability to all ocean basins that are characterized by the presence of a stratified, dense water mass in their deep and intermediate layers.

The warming trend of the Mediterranean region is already well known, but there is still a lack of information on its seasonal/annual to multidecadal time scales and its distribution in all water masses, including deep water. New temporal and spatial evidence of this thermal variability has been presented in the Tyrrhenian Sea, thanks to twenty-year continuous monitoring by eXpendable BathyThermographs (XBTs) along a fixed route from Genoa to Palermo. The Tyrrhenian Sea is one of the deepest Mediterranean sub-basins (with a maximum depth of about 4000 m), but its interaction with neighbouring basins is controlled by topographical factors, such as the Sardinian Channel to the south and the Corsican Channel to the north. The way in which the warm signal, originating from the Levantine sub-basin, and entering from the south, affects the entire Tyrrhenian Basin spreading rapidly northwards is studied, considering its peculiarities, such as topography, surface circulation, and strong stratification, as well as its climate variability. The warming trend observed for the Tyrrhenian Sea is consistent with the trend for the Mediterranean Sea as a whole. However, the Tyrrhenian Sea shows some peculiar features: around 2014, a shift to a new equilibrium (warmer) state was detected, with mean values along the monitored route that were significantly higher than the previous period (from 1999 to 2013), especially for the subsurface level, from 100 to 450 m depth.

Observations of abyssal variability performed in the Ionian Sea (Mediterranean Sea) revealed the presence of a dense stable abyssal layer, whose thermohaline and dynamical properties changed drastically over a decade. Building upon these available observations, we aim to investigate the role that stratification can have on the propagation of vorticity throughout the water column to the abyss, and in turn on the redistribution of the energy stored in the deep sea, with a set of stationary states. A quasi-geostrophic equation with four coupled layers, a free surface, and a mathematical artifice for parametrizing decadal time evolution has been considered, proving that the relative layer thicknesses and the density difference among the layers are the two critical factors that determine the dynamical characteristics of this propagation. The variability of the ocean stratification is a relevant aspect that can activate the deep and intermediate dynamics engaging in the propagation and stabilization of signals throughout the water column. This demonstrates the non-negligible active connection of the dynamics of the bottom layers with the surface. The theoretical framework and the parametrization used were based on specific observations made in the Ionian Sea in the last decades, but without losing general applicability in all ocean basins that are characterized by the presence of a stratified dense water mass in the deep and intermediate layers.

Observations of abyssal variability performed in the Ionian Sea (Mediterranean Sea) revealed the presence of a dense stable abyssal layer, whose thermohaline and dynamical properties changed drastically over a decade. Building upon these available observations, we aim to investigate the role that stratification can have on the propagation of vorticity throughout the water column to the abyss, and in turn on the redistribution of the energy stored in the deep sea, with a set of stationary states. A quasi-geostrophic equation with four coupled layers, a free surface, and a mathematical artifice for parametrizing decadal time evolution has been considered, proving that the relative layer thicknesses and the density difference among the layers are the two critical factors that determine the dynamical characteristics of this propagation. The variability of the ocean stratification is a relevant aspect that can activate the deep and intermediate dynamics engaging in the propagation and stabilization of signals throughout the water column. This demonstrates the non-negligible active connection of the dynamics of the bottom layers with the surface. The theoretical framework and the parametrization used were based on specific observations made in the Ionian Sea in the last decades, but without losing general applicability in all ocean basins that are characterized by the presence of a stratified dense water mass in the deep and intermediate layers.