Raffaele Ferrari Massachusetts Institute of Technology The sea-surface temperature field often exhibits fronts, regions characterized by strong temperature gradients that are 1km to 100km wide. They are associated with strong horizontal currents and rapid vertical exchanges, which take atmospheric gases such as carbon and oxygen down into the interior ocean, accelerating the air-sea fluxes, and deep nutrients up into the sun-lit surface layer, enabling primary production. We will illustrate the dynamics that generate upper ocean fronts using a combination of idealized models, realistic numerical simulations, and recent observations from the North Atlantic.