3D reconstruction of horizontal and vertical quasi-geostrophiccurrents in the North Atlantic Ocean

Direct in situ measurements of ocean currents are still quite limited and, due to its small magnitude, measurements of the vertical velocity remain one of the biggest challenges in oceanography. Vertical velocities are therefore generally inferred indirectly, and a common approach to diagnose them is to use the quasi-geostrophic omega equation. In the framework of the European Space Agency World Ocean Circulation project, a new high-resolution (1/10°) data-driven dataset of 3D ocean currents, including the vertical component, has been developed: the WOC-NATL3D dataset. The product domain extends over a wide portion of the North Atlantic Ocean from the surface down to 1500 m depth, and the dataset covers the period between 2010 and 2019. This entire domain holds immense importance for fishery activities and is identified as a key area within international conventions for the conservation of fishing resources, such as tuna and tuna-like fishes under ICCAT (International Commission for the Conservation of Atlantic Tunas). To generate this product, a diabatic quasi-geostrophic diagnostic model is applied to data-driven 3D temperature and salinity fields obtained through a deep learning technique, along with ERA5 fluxes and empirical estimates of the horizontal Ekman currents based on input provided by the European Copernicus Marine Service. The assessment of WOC-NATL3D currents is performed by direct validation of the total horizontal velocities with independent drifter estimates at various depths (0, 15 and 1000 m) and by comparing them with existing reanalyses that are obtained through the assimilation of observations into ocean general circulation numerical models. Our estimates of the ageostrophic components of the flow improve the total horizontal velocity reconstruction, being more accurate and closer-to-observations than model reanalyses in the upper layers, also providing an indirect proof of the reliability of the resulting vertical velocities.