Abstract

Internal tides, generated by the interaction of tidal currents with underwater topography, are critical to ocean dynamics, significantly influencing ocean mixing, nutrient transport, and the thermal structure of marine environments. These processes are vital for sustaining marine ecosystems, particularly in regions such as the Arabian Sea, where complex topographical features and climatic conditions contribute to intense internal tide activity. This thesis aims to reveal the characteristics of internal tides in the Arabian Sea, examine their seasonal variability, and explore their potential role in mitigating coral bleaching under changing climatic conditions. Additional insights into the internal tides of the Red Sea and Arabian Gulf are also provided to broaden the understanding of their regional impact. To achieve this, this thesis utilized a combination of satellite altimeter data and high-resolution general ocean circulation models. Satellite data from eight different altimeters were employed to extract internal tides from sea surface height signals, enabling the identification of key source regions and an analysis of their propagation patterns and energy distribution. Additionally, two models were implemented to simulate the internal tide dynamics in the Arabian Sea under tidal forcing alone, as well as under a comprehensive set of environmental forces.

The thesis identified four primary source regions for internal tides in the Arabian Sea: the Socotra Island, the Carlsberg Ridge, the northeastern Arabian Sea, and the Maldives. It revealed that internal tides are most active during the winter months when enhanced stratification leads to stronger and more widespread tidal activity compared to the summer. A 17-year analysis from simulations uncovered a roughly six-year cycle in internal tide energy, with significant reductions observed during strong ENSO events, suggesting a link between large-scale climatic phenomena and internal tide variability. Furthermore, the research established a connection between internal tide dynamics and coral bleaching, particularly in the Maldives, where stronger internal tides correlated with reduced bleaching severity. This finding suggests that internal tides may provide thermal refugia by transporting cooler waters to the surface, thereby alleviating thermal stress on coral reefs.