The ocean's role in transporting heat and carbon from the surface to depth is crucial to regulate Earth's climate. Although deep convection and mixed-layer deepening dominate the vertical transport on seasonal timescales, vertical flows associated with mesoscale (10-100 km) and submesoscale (1-10 km) processes play a key role in the exchange of physical (temperature and salinity) and biogeochemical (nutrients, organic carbon, dissolved gasses, and pollutants) properties between the ocean surface and interior on shorter timescales. Previous studies that focused on vertical motion associated with mesoscale variability (characterized by a small Rossby number (R o = ζ/f < 1, where ζ is the relative and f the planetary vorticity) have reported vertical velocities of (10-50 m day −1 ) (

An Algerian Eddy, anticyclonic vortex generated by the instability of the Algerian Current in the southwestern Mediterranean Sea, is studied using data provided by drifters (surface currents), Argo floats (temperature and salinity profiles), environmental satellites (absolute dynamic topography maps and ocean color images) and operational oceanography products. The eddy was generated in May 2018 and lasted as an isolated vortex until November 2018. Its morphology and kinematics are described in June–July 2018 when drifters were trapped in its core. During that period, the eddy was slowly moving to the NE (~2 km/day), with an overall diameter of about 200 km (slowly growing with time) and maximal surface swirl velocity of ~50 cm/s at a radius of ~50 km. Geostrophic currents derived from satellite altimetry data compare well with low-pass filtered drifter velocities, with only a slight overestimation, which is expected as its maximum vorticity corresponds to a small Rossby number of ~0.6. Satellite ocean color images and some drifters show that the eddy has an elliptical spiral structure. The looping tracks of the drifters trapped in the eddy were analyzed using two statistical methods: least-squares ellipse fitting and wavelet ridge analysis, revealing a typical eccentricity of about 0.5, a wide range of inclination and a rotation period between 3 and 10 days. Clusters of drifters on the northeastern limb of the eddy were also considered to estimate divergence and vorticity. The results indicate convergence (divergence) and downwelling (upwelling) at scales of 20–50 km near the northeastern (northwestern) edge of the eddy, in agreement with the quasi-geostrophic theory. Vertically, the eddy extends mostly down to 250 m depth, with a warm, low-salinity and low-density signature and with geostrophic currents near 50 cm/s in the top layer (down to ~80 m) reducing to less than 10 cm/s near 250 m. Near the surface, colder water is advected into it.

Measuring vertical motions represent a challenge as they are typically 3–4 orders of magnitude smaller than the horizontal velocities. Here, we show that surface vertical velocities are intensified at submesoscales and are dominated by high frequency variability. We use drifter observations to calculate divergence and vertical velocities in the upper 15 m of the water column at two different horizontal scales. The drifters, deployed at the edge of a mesoscale eddy in the Alboran Sea, show an area of strong convergence (scriptO $\mathcal{O}$(f)) associated with vertical velocities of −100 m day−1. This study shows that a multilayered‐drifter array can be an effective tool for estimating vertical velocity near the ocean surface.

The cruise was organized into 2 legs, the first without the equipment in the container and the second, with the equipment after the container was picked up in Almería.