Verónica Morales Márquez

Understanding the transport pathways of floating material at the ocean surface is important to improve our knowledge on surface circulation and assessing its environmental impacts. Numerical experiments through Lagrangian particle simulations are widely used to investigate the dispersion of floating material, typically relying on velocity fields from ocean circulation models. However, the contribution of different ocean dynamics (at different temporal and spatial scales) to the net Lagrangian transport remains unclear. Here we focus on tidal forcing, only included in recent ocean models, to explore its effect on particle dispersion at the ocean surface. By comparing a twin simulation with and without tidal forcing, we conclude that tide‐induced dynamics play an important role in horizontal Lagrangian pathways. We focus on the Azores Islands region and find that surface particles travel a longer cumulative distance and a lower total distance with than without tidal forcing. Additionally, tidal forcing leads to higher variability in surface particle accumulation patterns. The differences found in the surface particle accumulation patterns can be greater than 40%. These findings have important implications for virtual particle simulations, suggesting that considering tidal currents alone may not capture the full range of tide‐induced effects. A deeper understanding of the underlying dynamics is essential for accurately analyzing transport properties. Our outcomes can already help improve Lagrangian simulations made to understand the connectivity of marine species and for marine pollution applications, for example, ocean clean‐up strategies for plastics or oil spills, in the Azores Islands and regions with similar dynamics.

Understanding the oceanic surface dispersion has important applications in ocean pollution scenarios. Of the different ocean pollution events, some of which have the most impact both on the marine environment and, on society and economy are: marine plastics, oil spills and Sargassum inundation events. Understanding the ocean dynamics that affect their trajectories is vital to simulate their pathways, and thus know their sources and sinks. This can then be used to implement clean-up strategies and to better manage MPAs. It can also help reduce the impact of ocean pollution on the marine environment and some major economic sectors like tourism. High frequency motions have an important impact on the surface dynamics, but high temporal resolution data is necessary to study their effects. New datasets and methodologies have allowed to obtain better representations of high frequency motions. Here, we specifically focus on the high frequency motions due to tides (like for example internal waves), as well as inertial oscillations. We simulate surface trajectories of plastic, oil and Sargassum using the OceanParcels Lagrangian simulator. We focus on three regions in the Atlantic Ocean: Açores Islands, North Atlantic and Tropical Atlantic, respectively. For the plastic simulations we look at the effect of tides by using velocity outputs from a high-resolution model which is a twin simulation without and with tidal forcing. For the oil spills and Sargassum outputs we use a new surface currents product generated by combining velocity data from drifters, high-frequency winds and altimetry to reconstruct high-frequency surface currents. We find that considering high-frequency motions is key to correctly simulate their surface trajectories, but that further work is necessary to understand the ocean dynamics at the fine-scales that can drive the variability in these Lagrangian trajectories.

Understanding the pathways of floating material at the surface ocean is important to improve our knowledge on surface circulation and for its ecological and environmental impacts. Virtual particle simulations are a common method to simulate the dispersion of floating material. To advect the particles, velocities from ocean models are often used. Yet, the contribution of different ocean dynamics (at different temporal and spatial scales) to the net Lagrangian transport remains unclear. Here we focus on tidal forcing, only included in recent models, and so our research question is: What is the effect of tidal forcing on virtual particle dispersion at the ocean surface? By comparing a twin simulation with and without tidal forcing, we conclude that tides play an important role in horizontal Lagrangian dynamics. We focus on the Açores Islands region, and we find that surface particles travel a longer cumulative distance and a lower total distance with than without tidal forcing and a higher variability in surface particle accumulation patterns is present with tidal forcing. The differences found in the surface particle accumulation patterns can be more than a 40\% increase/decrease. This has important implications for virtual particle simulations, showing that more than tidal currents need to be considered. A deeper understanding of the dynamics behind these tidal forcing impacts is necessary, but our outcomes can already help improve Lagrangian simulations. This is particularly relevant for simulations done to understand the connectivity of marine species and for marine pollution applications.

Understanding the pathways of floating material at the surface ocean is important to improve our knowledge on surface circulation and for its ecological and environmental impacts. Virtual particle simulations are a common method to simulate the disper

The Mediterranean Institute of Oceanography (MIO) has been operating for one decade a network of high-frequency radars for the monitoring of coastal surface currents on the French Mediterranean coast. More recently, ONERA has been developing an original over-the-horizon radar system for the detection and tracking of ships in the coastal zone. The two institutions have joined their efforts to provide dual civil and environmental applications of surface wave radars in theframework of the ROSMED project. We present preliminary results of the unique capabilities of the ONERA radar for the mapping of surface currents at very long range in the Gulf of Lion. We also present new results of the MIO high-frequencyradar for the measurement of surface currents and waves and the automatic detection of ships.

The wave–current–seabed interaction problem is studied by using a coupled-mode system developed for modeling wave scattering by non-homogeneous, sheared currents in variable bathymetry regions. The model is based on a modal series expansion of wave velocity based on vertical eigenfunctions, dependent on local depth and flow parameters, including propagating and evanescent modes. The latter representation is able to accurately satisfy the wave flow continuity condition and the no-entrance boundary condition on the sloping parts of the seabed. A new derivation of a simplified nonlinear system is introduced using decomposition to a mean flow and a perturbative wave field. To force the system to consider incoming waves at the inlet, boundary knowledge of periodic, travelling nonlinear water waves over a flat bottom is required. For this purpose, specific solutions are derived using the semi-analytical method based on the stream function formulation, for cases of water waves propagating above linearly and exponentially sheared currents. Results obtained by the application of the CMS concerning the propagation of waves and currents—in particular, examples characterized by depth inhomogeneities—are presented and discussed, illustrating the applicability and performance of the method.

Understanding the pathways of floating material at the surface ocean is important to improve our knowledge on surface circulation and for its ecological and environmental impacts. Virtual particle simulations are a common method to simulate the dispersion of floating material. To advect the particles, ocean models’ velocities are usually used, but only recent ones include tidal forcing. Our research question is: What is the effect of tidal forcing on virtual particle dispersion and accumulation at the ocean surface? As inputs we use velocity outputs from eNATL60, a twin simulation with and without tidal forcing. We focus on the Açores Islands region and we find: 1) Surface particles have a larger displacement, but a lower distance travelled with than without tidal forcing 2) Surface accumulation seasonal differences depend on the spatial scale of the ocean structures 3) A greater variability in surface accumulation is present with tidal forcing.

We study the impact of the Ekman currents and Stokes drift on the surface horizontal transport and mixing properties of the Mediterranean Sea. Finite Size Lyapunov Exponents (FSLE) at the ocean surface are computed over the whole basin using 25 years of satellite altimetry derived geostrophic currents, 10‐m wind velocity and wave fields. We find that the transport pathways unveiled by the geostrophic Lagrangian Coherent Structures (LCS) are significantly modified by the ageostrophic currents (i.e., Ekman and Stokes induced velocities), often leading to a decrease of the retention capacity of the eddies. An exhaustive assessment of the regional and temporal variability of the FSLE shows an increase of the horizontal mixing processes, due to the ageostrophic component, up to 37% in regions such as the Gulf of Lion or the Aegean Sea, during the seasons where wind and waves are intense and persistent. Positive trends in the total FSLE (up to 1.2% of the value of FSLE per year in some regions) suggest that Mediterranean Sea has experienced a significant increase in the intensity of the mixing processes over the last decades. Ageostrophic features are considered to play a role in determining the properties of the relative dispersion. Through the analysis of the Lagrangian Anisotropy Index (LAI) using virtual and real pair of drifters, we observe that the particle dispersion is mainly dominated by the zonal flow, and that the ageostrophic currents induce meridional dispersion, particularly in regions where wind and wave are intensified.

Understanding the pathways of floating material at the surface ocean is important to improve our knowledge on surface circulation and for its ecological and environmental impacts. Virtual particle simulations are a common method to simulate the dispersion of floating material. To advect the particles, ocean models’ velocities are usually used, but only recent ones include tidal forcing. Our research question is: What is the effect of tidal forcing on virtual particle dispersion and accumulation at the ocean surface? As inputs we use velocity outputs from eNATL60, a twin simulation with and without tidal forcing. We focus on the Açores Islands region and we find: 1) Surface particles have a larger displacement, but a lower distance travelled with than without tidal forcing 2) Surface accumulation seasonal differences depend on the spatial scale of the ocean structures 3) A greater variability in surface accumulation is present with tidal forcing.