Scale-dependency of vertical velocities in the Alboran Sea through high-resolution simulations and glider observations

Abstract

Vertical velocities associated with meso- and sub-mesoscale eddies, fronts and filaments generate important fluxes of carbon and biogeochemical tracers between the surface layer and depths below the mixed layer. Vertical velocities are very weak (approximately hundreds of times smaller than horizontal velocities) and often characterized by small spatio-temporal scales. As a result, they are very difficult to properly observe and monitor. In this context, numerical modelling provides an essential complementary tool to study the variability of vertical transports. High-resolution simulations have been completed in the Alboran Sea (Western Mediterranean) in the framework of the CALYPSO project (Coherent Lagrangian Pathways from the Surface Ocean to Interior, Office of Naval Research Departmental Research Initiative), in conjunction with a large observational effort. The Alboran Sea is marked by a very dynamic frontal activity associated with the intense density gradients between the relatively fresh water of Atlantic origin and the more saline water of the Mediterranean Sea. Several modeling systems are used both to provide real-time predictions during sea trial experiments and to analyze model dynamics in free-run experiments. The numerical approach is based on a multiple refinement subgrid strategy with two-way nested grids from 2000 m to 200 m of horizontal resolution, and ensembles of simulations downscaled from varied larger-scale ocean modelling systems.

In this presentation we analyze these high spatial resolution numerical simulations (a) to better understand the spatial and temporal variability of vertical velocities and dynamic 3D pathways in relation to the governing ocean processes, and (b) to help interpreting the observations from the repetitive sampling of the highly variable Almeria-Oran front by slow-moving gliders. Model sensitivity studies to the horizontal and vertical resolutions, bathymetry smoothing and data assimilation will be presented.