Coherent Lagrangian Pathways Near an East Alboran Front

In the eastern Alboran Sea, frontogenesis (FG) is a dominant process for fronts extending from the Spanish coast toward the basin interior, promoting large vertical displacements that connect the surface mixed layer with the oceanic interior. Using a realistic, high‐resolution model simulation for this region, we conduct the offline advection of virtual water parcels released near the surface during a 2‐day episode of intense FG. Three‐dimensional trajectories exhibit high variability depending on the release location, and some large, rapid vertical displacements are induced by different coherent submesoscale flow patterns and by interactions among them: Ageostrophic secondary circulation associated with strain‐ and mixing‐induced FG and internal waves generated by currents over topography. These deep displacements mostly are irreversible, at least on a short time scale, because of the rapidly changing flow patterns. Significant diapycnal mixing and density changes occur along trajectories as they pass through the surface and bottom boundary layers. While we expect these processes to be typical for this region, the computational expense of such a Lagrangian analysis and the complexity of its outcome present a considerable challenge for more comprehensive assessments. Plain Language Summary An ocean front is the boundary between two different water masses (e.g., with different densities). In the Alboran Sea, strong surface fronts develop due to the clash between the incoming fresh strong current from the Atlantic Ocean and the resident salty Mediterranean waters. A “secondary circulation” can develop along the front driving the confluent waters (and suspended nutrients and other tracers) toward the interior of the ocean. Ocean circulation in this region is also highly conditioned by the complex shape of the basin. In this work, we use a realistic model simulation to reproduce the development of an intense front in the East Alboran Sea. Virtual water parcels are released near the surface around the front to simulate the trajectories of the water as it flows toward the front and the possible mixing between neighboring water masses. Our results show that deep vertical displacements occur in different locations, driven by the frontal secondary circulation and by other processes generated through the interaction of the currents with bottom topography. Some mixing is experienced by the water trapped in the frontal secondary circulation, and also within the upper