Simon Barbot

La marée interne est générée lorsque les courants de la marée barotrope interceptent frontalement une pente bathymétrique importante dans un contexte d'océan stratifié, créant un déplacement périodique des couches océaniques. Les anomalies de pression baroclines générées ainsi se propagent sous la forme d'ondes internes sur des distances pouvant atteindre 2000 km, impactent la totalité de la colonne d'eau. La composante stationnaire du signal de surface de la marée interne est observée grâce aux longues séries temporelles de mesures altimétriques disponibles en continu depuis 1993. La composante non-stationnaire de la marée interne, principalement due à la variabilité de la circulation océanique et de la stratification, doit être abordée par des méthodologies différentes afin de décrire la variabilité de la marée interne. Cette dernière thématique a pris un essor particulier avec la préparation de la nouvelle mission large-fauchée SWOT, pour laquelle il devient indispensable de fournir des corrections précises de la marée interne pour pouvoir accéder à la mesure des signaux océaniques de sub-mésoéchelles notamment. La modélisation est un outil puissant permettant d'obtenir le signal complet de la marée interne, autrement difficilement accessible. Cette thèse fait le choix d'aborder la complexité de la marée interne de façon séquentielle, en analysant séparément chaque mécanisme pour en apporter une compréhension détaillée. Elle s'appuie sur des approches de modélisation idéalisées et semi-réalistes produisent un signal simplifié de la marée interne, pour examiner la contribution de la variabilité de la stratification océanique à la variabilité de la marée interne. Le signal de la marée interne est produit en utilisant des approches spectrales de modélisation et ces solutions sont détaillés en utilisant la décomposition en modes verticaux. L'analyse se focalise sur deux zones caractérisées par des dynamiques océaniques différentes : le Golfe de Gascogne et l'Atlantique équatorial-ouest. Tout d'abord, plusieurs conditions caractéristiques de stratification sont définies en utilisant une classification innovante des profils de densité in situ, et permettant de représenter la variabilité de la stratification à partir d'un nombre réduits de profils types. À partir de ces profils, la marée interne est simulée dans un cas idéalisé en utilisant le modèle T-UGOm, puis dans un cas semi-réaliste du Golfe de Gascogne en utilisant le modèle SYMPHONIE. Le cas idéalisé permet de mettre en évidence et de quantifier l'influence de la stratification sur l'amplitude et la longueur d'onde de la marée interne pour chaque mode, et d'étudier précisément les bilans d'énergie associés. Le cas semi-réaliste permet d'étendre cette étude à contexte réaliste, présentant plusieurs sites de génération et d'aborder la complexité des interactions entre ondes internes issues de ces sites. Afin de comparer ces simulations semi-réalistes aux données altimétriques, celles-ci sont analysées selon un découpage saisonnier, cohérent avec le contexte de stratification défini pour les simulations. Ce découpage mettant à l'épreuve la robustesse des méthodes d'analyse harmoniques traditionnellement utilisées pour la marée, cette thèse explore une méthode numérique et ses limitations. Ces travaux permettent de mieux comprendre la marée interne et les mécanismes qui la contrôlent et de mieux cerner la variabilité associée à la stratification seule en proposant de nouvelles approches. Cette compréhension de la marée interne et les simulations réalisées permettent également d'évaluer l'impact de la marée interne sur la remise en suspension profonde des sédiments dans le but d'affiner l'interprétation de mesures géochimiques.

Off the Amazon shelf, internal solitary waves (ISWs) generated by internal tides interact with mesoscale eddies, leading to significant modifications in their propagation and structure. For the first time, these interactions are directly observed from repeated high-resolution satellite measurements, notably those provided by the newly launched SWOT (Surface Water and Ocean Topography) mission. The study investigates ISWs detection and the modifications in ISW's characteristics resulting from interactions with eddies across three contrasting scenarios: ISW propagation in the absence of mesoscale eddies, ISW refraction by a cyclonic eddy, and ISW diffraction by an anticyclonic eddy. ISW crests are extracted using a band-pass filtering approach, enabling precise tracking of essential geometric and dynamical features, including propagation direction, crest-to-crest spacing, and wavefront shape. Prior to any interaction with eddies, three mode-1 ISW packets propagate in a steady and coherent manner, exhibiting planar wavefronts and consistent direction, with Absolute Dynamic Topography (ADT) amplitudes ranging from 8 to 14 cm. The results highlight the diversity of ISW responses depending on eddy conditions. In the absence of eddies, interaction with a seamount induces energy transfer from mode-1 to mode-3 ISWswaves (13 crests detected), while propagation direction is maintained and the ADT signature weakens to below 8 cm. In the presence of a cyclonic eddy above the seamount, ISW trajectories are refracted westward by roughly 50 degrees (7 crests detected), with increased wavecrest curvature and intensification of mode-3 generation, while ADT amplitudes decrease below 6 cm. Conversely, near the western boundary of an anticyclonic eddy, ISWs split into two distinct pathways: a western branch is refracted with flatter wavefronts, reduced crest spacing, and ADT amplitudes below 0.2 cm (9 crests detected), while an eastern branch follows the eddy's edge, displaying enhanced curvature, recognizable surface signatures of wave packets, and ADT values exceeding 9 cm (6 crests detected). Together, these findings demonstrate the ability of SWOT-based monitoring to capture the complexity of ISW dynamics and provide new insight into their nonlinear response to interactions with mesoscale and submesoscale oceanic structures.

The northern Brazilian region constitutes one of the most energetic tidal environments of the tropical Atlantic, where distinct mixing regimes coexist over short spatial scales. While barotropic tidal motions exert a dominant control on turbulent mixing across the shallow continental shelf, energy dissipation associated with internal tides (ITs) governs the intensity and distribution of mixing at the shelf-break and in offshore waters. As demonstrated in the Part 1 companion study (Assene et al., 2024), these contrasting processes strongly influence upper-ocean thermal structure. Yet, the expression of tidal forcing in temperature variability at tidal timescales—particularly at semidiurnal (principal solar: M₂ and principal lunar: S₂) and fortnightly (lunisolar synodic: MSf) frequencies—remains poorly documented in this region. In this study, we investigate the role of tides, with a focus on ITs, in shaping temperature variability throughout the NBR by combining long-term satellite sea surface temperature (SST) records with high-resolution three-dimensional numerical simulations operated with and without tidal forcing. The main findings are as follows: At semidiurnal frequencies, temperature variability at the sea surface is very weak offshore and remains modest over the continental shelf, consistent with the prevalence of barotropic mixing that acts largely as a depth-integrated process in shallow waters. In contrast, pronounced temperature variability emerges at thermocline depths, with mean amplitudes reaching approximately 0.6 °C for S₂ and exceeding 2 °C for M₂. The spatial structure of these subsurface signals aligns closely with simulated mode-1 and mode-2 IT wavelengths, propagation pathways, and dissipation hot-spots, underscoring the central role of ITs in driving semidiurnal thermal variability below the surface mixed layer; Fortnightly (MSf) variability contrasts sharply with the semidiurnal response. Both satellite observations (MUR, TMI) and tidal simulations reveal low amplitudes on the order of 0.15 °C, with maximums confined to the northwestern shelf where Spring–Neap modulation of barotropic tidal currents is the dominant tidal process. Composite analyzes contrasting Spring versus Neap conditions further suggest that this MSf variability manifests primarily as a net cooling with the same amplitude. At the surface, neither model nor satellite observations exhibit a significant SST expression at MSf frequency along internal tide propagation pathways. This may reflect a rapid atmospheric heat flux adjustment that counteracts internal tide–induced cooling and/or the inherently incoherent nature of internal tide dynamics that disperses energy across frequencies, preventing harmonic methods from capturing a clear MSf signature. At subsurface depths (~120 m), MSf temperature variability becomes more pronounced along IT pathways, particularly near the shelf break and downstream of generation sites where dissipation is strongest. The vertical penetration depth of tidally driven temperature variability decreases systematically with increasing tidal period, from penetration depths approaching 2500 m for M₂, to 800–1000 m for S₂ and 600–800 m for MSf. These contrasts indicate that the capacity of tidal motions to influence the water column depends strongly on the available energy at each frequency and points to a frequency-dependent control of deep-ocean mixing and heat redistribution. Together, these findings provide the first regional quantification of temperature variability at tidal frequencies in the northern Brazilian region and demonstrate that internal tides constitute a major driver of subsurface thermal structure across this dynamically energetic margin. This improved characterization is essential for understanding heat redistribution, interpreting coastal and open-ocean temperature variability, and ultimately constraining the representation of tidal processes in ocean and climate models.

Off the Amazon shelf, mesoscale eddies interact with internal solitary waves (ISWs), modifying their characteristics. For the first time, such interactions are directly observed through repeated measurements from a set of high-resolution satellite data, including the recently launched SWOT (Surface Water and Ocean Topography) mission. This study investigates ISWs detectable in SWOT Absolute Dynamic Topography (ADT) and characterizes the changes in their properties induced by interactions with mesoscale eddies. The analysis focuses on three scenarios: ISW propagation in the absence of eddies, ISW refraction by a cyclonic eddy, and ISW diffraction by an anticyclonic eddy. ISW crests were identified and extracted using a band-pass filtering technique, allowing accurate tracking of key features such as propagation direction, spacing between individual crests, and wavecrest geometry. Before any interaction with eddies, mode-1 ISWs propagate steadily, with consistent direction and planar wavefronts. A key finding is the variety of ISW responses depending on eddy conditions. In the first case, in the absence of eddy, the interaction of ISWs with a seamount induced energy transfer from mode-1 to mode-3 ISWs, while the propagation direction remains unchanged. In the second case, a cyclonic eddy overlaying the seamount refracted ISW trajectories westward by approximately 50°, while also increasing wavecrest curvature and enhancing the generation of mode-3 waves. In the third case, at the western edge of an anticyclonic eddy near the seamount, the ISWs are split into two distinct paths: one branch refracted westward, exhibiting flatter wave crests and reduced spacing between them; the other branch followed the eastern edge of the eddy, displaying surface signatures of wave packets and enhanced wavecrest curvature. These results demonstrate the effectiveness of the proposed approach in capturing the complex dynamics of ISWs. They offer novel insights into the nonlinear behavior of ISWs and their interactions with mesoscale and submesoscale oceanic features.

Off the Amazon shelf, mesoscale eddies interact with internal solitary waves (ISWs), modifying their characteristics. For the first time, such interactions are directly observed through repeated measurements from a set of high-resolution satellite data, including the recently launched SWOT (Surface Water and Ocean Topography) mission. This study investigates ISWs detectable in SWOT Absolute Dynamic Topography (ADT) and characterizes the changes in their properties induced by interactions with mesoscale eddies. The analysis focuses on three scenarios: ISW propagation in the absence of eddies, ISW refraction by a cyclonic eddy, and ISW diffraction by an anticyclonic eddy. ISW crests were identified and extracted using a band-pass filtering technique, allowing accurate tracking of key features such as propagation direction, spacing between individual crests, and wavecrest geometry. Before any interaction with eddies, mode-1 ISWs propagate steadily, with consistent direction and planar wavefronts. A key finding is the variety of ISW responses depending on eddy conditions. In the first case, in the absence of eddy, the interaction of ISWs with a seamount induced energy transfer from mode-1 to mode-3 ISWs, while the propagation direction remains unchanged. In the second case, a cyclonic eddy overlaying the seamount refracted ISW trajectories westward by approximately 50°, while also increasing wavecrest curvature and enhancing the generation of mode-3 waves. In the third case, at the western edge of an anticyclonic eddy near the seamount, the ISWs are split into two distinct paths: one branch refracted westward, exhibiting flatter wave crests and reduced spacing between them; the other branch followed the eastern edge of the eddy, displaying surface signatures of wave packets and enhanced wavecrest curvature. These results demonstrate the effectiveness of the proposed approach in capturing the complex dynamics of ISWs. They offer novel insights into the nonlinear behavior of ISWs and their interactions with mesoscale and submesoscale oceanic features.

Off the Amazon shelf, mesoscale eddies interact with internal solitary waves (ISWs), modifying their characteristics. For the first time, such interactions are directly observed through repeated measurements from a set of high-resolution satellite data, including the recently launched SWOT (Surface Water and Ocean Topography) mission. This study investigates ISWs detectable in SWOT Absolute Dynamic Topography (ADT) and characterizes the changes in their properties induced by interactions with mesoscale eddies. The analysis focuses on three scenarios: ISW propagation in the absence of eddies, ISW refraction by a cyclonic eddy, and ISW diffraction by an anticyclonic eddy. ISW crests were identified and extracted using a band-pass filtering technique, allowing accurate tracking of key features such as propagation direction, spacing between individual crests, and wavecrest geometry. Before any interaction with eddies, mode-1 ISWs propagate steadily, with consistent direction and planar wavefronts. A key finding is the variety of ISW responses depending on eddy conditions. In the first case, in the absence of eddy, the interaction of ISWs with a seamount induced energy transfer from mode-1 to mode-3 ISWs, while the propagation direction remains unchanged. In the second case, a cyclonic eddy overlaying the seamount refracted ISW trajectories westward by approximately 50°, while also increasing wavecrest curvature and enhancing the generation of mode-3 waves. In the third case, at the western edge of an anticyclonic eddy near the seamount, the ISWs are split into two distinct paths: one branch refracted westward, exhibiting flatter wave crests and reduced spacing between them; the other branch followed the eastern edge of the eddy, displaying surface signatures of wave packets and enhanced wavecrest curvature. These results demonstrate the effectiveness of the proposed approach in capturing the complex dynamics of ISWs. They offer novel insights into the nonlinear behavior of ISWs and their interactions with mesoscale and submesoscale oceanic features.

Off the Amazon shelf, mesoscale eddies interact with internal solitary waves (ISWs), modifying their characteristics. For the first time, such interactions are directly observed through repeated measurements from a set of high-resolution satellite data, including the recently launched SWOT (Surface Water and Ocean Topography) mission. This study investigates ISWs detectable in SWOT Absolute Dynamic Topography (ADT) and characterizes the changes in their properties induced by interactions with mesoscale eddies. The analysis focuses on three scenarios: ISW propagation in the absence of eddies, ISW refraction by a cyclonic eddy, and ISW diffraction by an anticyclonic eddy. ISW crests were identified and extracted using a band-pass filtering technique, allowing accurate tracking of key features such as propagation direction, spacing between individual crests, and wavecrest geometry. Before any interaction with eddies, mode-1 ISWs propagate steadily, with consistent direction and planar wavefronts. A key finding is the variety of ISW responses depending on eddy conditions. In the first case, in the absence of eddy, the interaction of ISWs with a seamount induced energy transfer from mode-1 to mode-3 ISWs, while the propagation direction remains unchanged. In the second case, a cyclonic eddy overlaying the seamount refracted ISW trajectories westward by approximately 50°, while also increasing wavecrest curvature and enhancing the generation of mode-3 waves. In the third case, at the western edge of an anticyclonic eddy near the seamount, the ISWs are split into two distinct paths: one branch refracted westward, exhibiting flatter wave crests and reduced spacing between them; the other branch followed the eastern edge of the eddy, displaying surface signatures of wave packets and enhanced wavecrest curvature. These results demonstrate the effectiveness of the proposed approach in capturing the complex dynamics of ISWs. They offer novel insights into the nonlinear behavior of ISWs and their interactions with mesoscale and submesoscale oceanic features.

Off the Amazon shelf, mesoscale eddies interact with internal solitary waves (ISWs), modifying their characteristics. For the first time, such interactions are directly observed through repeated measurements from a set of high-resolution satellite data, including the recently launched SWOT (Surface Water and Ocean Topography) mission. This study investigates ISWs detectable in SWOT Absolute Dynamic Topography (ADT) and characterizes the changes in their properties induced by interactions with mesoscale eddies. The analysis focuses on three scenarios: ISW propagation in the absence of eddies, ISW refraction by a cyclonic eddy, and ISW diffraction by an anticyclonic eddy. ISW crests were identified and extracted using a band-pass filtering technique, allowing accurate tracking of key features such as propagation direction, spacing between individual crests, and wavecrest geometry. Before any interaction with eddies, mode-1 ISWs propagate steadily, with consistent direction and planar wavefronts. A key finding is the variety of ISW responses depending on eddy conditions. In the first case, in the absence of eddy, the interaction of ISWs with a seamount induced energy transfer from mode-1 to mode-3 ISWs, while the propagation direction remains unchanged. In the second case, a cyclonic eddy overlaying the seamount refracted ISW trajectories westward by approximately 50°, while also increasing wavecrest curvature and enhancing the generation of mode-3 waves. In the third case, at the western edge of an anticyclonic eddy near the seamount, the ISWs are split into two distinct paths: one branch refracted westward, exhibiting flatter wave crests and reduced spacing between them; the other branch followed the eastern edge of the eddy, displaying surface signatures of wave packets and enhanced wavecrest curvature. These results demonstrate the effectiveness of the proposed approach in capturing the complex dynamics of ISWs. They offer novel insights into the nonlinear behavior of ISWs and their interactions with mesoscale and submesoscale oceanic features.

The M2 MIOST24 (Multivariate Inversion of Ocean Surface Topography 2024) internal tide atlases described in this study are available in annual (MIOST24a) and monthly (MIOST24m) regional versions for modes 1 and 2 in the Indo-Philippine archipelago and the region off the Amazon shelf. They are derived from 25 years (1993–2017, period 1) of sea level anomalies (SLAs) from altimetry observations. Compared to the MIOST22 (Multivariate Inversion of Ocean Surface Topography 2022) internal tide atlases, MIOST24 incorporates M2 mode-1 and mode-2 wavelengths based on monthly stratification profiles from GLORYS12v1 (1993–2020). The differences between MIOST24a and MIOST22a lead to a RMSD (root mean square difference) of up to 3 cm, reflecting amplitude changes, while the RMSD between MIOST24a and the internal tide atlas HRET (High-Resolution Empirical Tide) indicates both amplitude and phase differences. MIOST24m highlights significant monthly variability of M2 internal tides in the Indo-Philippine archipelago and off the Amazon shelf. In the Amazon region, the internal tide propagates far offshore from March to June but is blocked closer to the coast from August to December. In both regions, the RMSDs between the MIOST24a annual and MIOST24m monthly mode-1 atlases are mainly governed by the phase contribution term. This suggests that the monthly variability of the mode-1 internal tide is more affected by changes in its propagation direction than by fluctuations in amplitude. In contrast, for mode 2, the monthly variability is predominantly associated with amplitude variations, particularly near internal tide generation sites. Variance reductions of SLAs show that MIOST24m outperforms MIOST24a, MIOST22a, and HRET in period 1 in the two regions of interest and in the Amazon region in period 2 (2018–2023). Monthly atlases are therefore recommended to correct the internal tides of the SLAs used to derive them. All these results support the development of MIOST24 global atlases.