Aurelie Albert

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.

Characterization of coherent eddies is often based on gridded satellite altimetry products. In subpolar regions, these products face limitations due to their low spatial resolution and the decreasing Rossby radius of deformation at higher latitudes, making in situ observations indispensable for eddy characterization. Here, we present a census of mesoscale-to-submesoscale eddy characteristics in the Labrador Sea—a region where eddies play an important role in winter deep convection and subsequent restratification. Using ship-based observations, we fit an idealized eddy solution to horizontal velocity measurements acquired along ship tracks, determining an optimal eddy center and other key eddy properties. Based on three research cruises, we reconstructed 40 eddies ranging from 3 to 39 km in radius (mean 15 km) and azimuthal velocity between 7 and 58 cm s ⁻¹ (mean 26 cm s ⁻¹ ). The azimuthal velocity structure implies to a large extent solid-body rotation in the eddy’s inner core, while opposite signs of vorticity in the outer ring suggest strong vorticity shields. When compared to ship-based observations, the eddy field representation in gridded altimetry products is significantly distorted, with many eddies being underrepresented or undetected. This is even the case for larger-scale features despite having an eddy signature in the along-track altimetry product, which appears to be suppressed in the subsequent mapping methodology. Finally, comparisons with submesoscale-permitting numerical simulation output show favorable agreement giving confidence in both the ship-based reconstruction and the numerical model’s realism in representing high-latitude eddy dynamics. Significance Statement: Oceanic eddies in the Labrador Sea play an important role in advecting heat, salt, and other properties to the interior basin with implications for winter deep convection and subsequent restratification of the homogenized water column. Using ship-based observations, our research provides a basinwide eddy characterization, capturing a broad range of spatial scales with radii from 3 to 39 km. We show that conventional satellite altimetry distorts eddy properties at high latitudes, where eddies are smaller in size and often remain undetected. By expanding the census of eddy characteristics in the Labrador Sea, our study offers a valuable dataset for assessing eddy dynamics in high-resolution numerical models, which often lack direct validation.

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

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.

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.

Ocean circulation is dominated by turbulent geostrophic eddy fields with typical scales ranging from 10 to 300 km. At mesoscales (>50 km), the size of eddy structures varies regionally following the Rossby radius of deformation. The variability of the scale of smaller eddies is not well known due to the limitations in existing numerical simulations and satellite capability. Nevertheless, it is well established that oceanic flows (<50 km) generally exhibit strong seasonality. In this study, we present a basin‐scale analysis of coherent structures down to 10 km in the North Atlantic Ocean using two submesoscale‐permitting ocean models, a NEMO‐based North Atlantic simulation with a horizontal resolution of 1/60 (NATL60) and an HYCOM‐based Atlantic simulation with a horizontal resolution of 1/50 (HYCOM50). We investigate the spatial and temporal variability of the scale of eddy structures with a particular focus on eddies with scales of 10 to 100 km, and examine the impact of the seasonality of submesoscale energy on the seasonality and distribution of coherent structures in the North Atlantic. Our results show an overall good agreement between the two models in terms of surface wave number spectra and seasonal variability. The key findings of the paper are that (i) the mean size of ocean eddies show strong seasonality; (ii) this seasonality is associated with an increased population of submesoscale eddies (10–50 km) in winter; and (iii) the net release of available potential energy associated with mixed layer instability is responsible for the emergence of the increased population of submesoscale eddies in wintertime.

Ocean circulation is dominated by turbulent geostrophic eddy fields with typical scales ranging from 10 km to 300 km. At mesoscales (> 50 km), the size of eddy structures varies regionally following the Rossby radius of deformation. The variability of the scale of smaller eddies is not well known due to the limitations in existing numerical simulations and satellite capability. But it is well established that oceanic flows (< 50km) generally exhibit strong seasonality. In this study, we present a basin-scale analysis of coherent structures down to 10\,km in the North Atlantic Ocean using two submesoscale-permitting ocean models, a NEMO-based North Atlantic simulation with a horizontal resolution of 1/60 (NATL60) and an HYCOM-based Atlantic simulation with a horizontal resolution of 1/50 (HYCOM50). We investigate the spatial and temporal variability of the scale of eddy structures with a particular focus on eddies with scales of 10 to 100\,km, and examine the impact of the seasonality of submesoscale energy on the seasonality and distribution of coherent structures in the North Atlantic. Our results show an overall good agreement between the two models in terms of surface wavenumber spectra and seasonal variability. The key findings of the paper are that (i) the mean size of ocean eddies show strong seasonality; (ii) this seasonality is associated with an increased population of submesoscale eddies (10\,–\,50\,km) in winter; and (iii) the net release of available potential energy associated with mixed layer instability is responsible for the emergence of the increased population of submesoscale eddies in wintertime.