Direct observational evidence of an oceanic dual kinetic energy cascade and its seasonality

The ocean's turbulent energy cycle has a paradox; large-scale eddies under the control of Earth's rotation transfer kinetic energy (KE) to larger scales via an inverse cascade, while a transfer to smaller scales is needed for dissipa-tion. It has been hypothesized, using simulations, that fronts, waves, and other turbulent structures can produce a forward cascade of KE toward dissipation scales. However, this forward cascade and its coexistence with the in-verse cascade have never been observed. Here, we present the first evidence of a dual KE cascade in the ocean by analyzing in situ velocity measurements from surface drifters. Our results show that KE is injected at two domi-nant scales and transferred to both large and small scales, with the downscale flux dominating at scales smaller than similar to 1 to 10 km. The cascade rates are modulated seasonally, with stronger KE injection and downscale transfer during winter.