An Annual Cycle of Submesoscale Vertical Flow and Restratification in the Upper Ocean

AbstractNumerical simulations suggest that submesoscale turbulence may transform lateral buoyancy gradients into vertical stratification, and thus restratify the upper ocean via vertical flow. However, the observational evidence for this restratifying process has been lacking due to the difficulty in measuring such ephemeral phenomena, particularly over periods of months to years. This study presents an annual cycle of the vertical velocity and associated restratification estimated from two nested clusters of meso- and submesoscale-resolving moorings, deployed in a typical mid-ocean area of the Northeast Atlantic. Vertical velocities inferred using the non-diffusive density equation are substantially stronger at submesoscales (horizontal scales of 1-10 km) than at mesoscales (horizontal scales of 10-100 km), with respective root mean square values of 38.0 ± 6.9 m/day and 22.5 ± 3.3 m/day. The largest submesoscale vertical velocities and rates of restratification occur in events of a few days’ duration in ...