Analysis of the effects of barotropic and internal tides on the Mediterranean Sea dynamics through numerical experiments

Tides in the Mediterranean Sea are low in amplitude compared to many regions of the global ocean, but they have impacts beyond their own temporal and spatial scales, affecting temperature, salinity, currents, and mixing. Additionally, due to the complex geometry of this semi-enclosed basin, they can generate intense and complex internal waves. A numerical modelling approach can be used to investigate these impacts and understand the scales at which tides affect the Mediterranean Sea dynamics. Twin experiments using a high-resolution general circulation model of the Mediterranean Sea, with and without tides, were used for this initial investigation. It was found that tides amplify several basin and sub-basin modes (seiches) of the Mediterranean Sea, and their effects on kinetic energy are nonlinear, including interactions between baroclinic tides and near-inertial internal waves. Tides increase the mixed layer depth of the Mediterranean Sea and the western Mediterranean deep water formation rates. Further experiments were carried out to map the generation sites and regions of propagation of internal tides at the Mediterranean Sea basin level. Implementations of two numerical models were used, unveiling the effects of internal tides in the Mediterranean Sea in more detail. Internal tides are primarily generated in the Gibraltar Strait, the Sicily Strait/Malta Bank, and the Hellenic Arc regions. Long-distance propagation of semidiurnal internal tides up to hundreds of kilometres was discovered, affecting mainly the Algerian Sea, Tyrrhenian Sea, and Ionian Sea. Additionally, bottom-trapped diurnal internal tides are found in several regions. The models depict two modes of the M2 internal tide and three modes of the K1 internal tide, as revealed by wavenumber spectra. The two models show similar regions of internal tide generation and propagation, but are not identical, which is attributed to differences in modelling set-up, stratification, bathymetry, and the tidal forcing implemented in the models.