Filamentogenesis and Filamentolysis of a Low-Density Filament: Dynamic Processes in the Near-Surface Ocean Under Tidal Forcing

This study investigates the dynamics and alteration of a low-density filament driven by freshwater-induced buoyancy embedded within a tidal mixing front, focusing on its spatial and temporal evolution in the near-surface layer (0.1–10 m) of the water column. A high-resolution, multi-sensor dataset, consisting of surface drifters, a drifting sensor chain, and an autonomous surface vehicle equipped with an Acoustic Doppler Current Profiler, temperature, and conductivity sensors, was used to observe patterns of divergence, vorticity, and vertical velocities. The measurements resolved three phases of the filament occurring on length scales of O(0.1–2 km) and time scales of minutes to one hour: (I) establishment of the filament in the overlying first meter and filamentolysis <1 m, (II) the ongoing filamentolysis in the lower NSL induced filamentogenesis above 0.6 m, (III) restratification of the upper 0.6 m. Vertical velocities ranged between ±20md-1 with pronounced asymmetric responses on the filament boundaries due to the coupling of local filamentary kinematics and tide-induced vertical motions. In phase III, stratification allowed for increased heat uptake within the filament. These investigations highlight the role of the overlooked top surface layer in potentially altering the energy, heat, and gas budget of the ocean, which is critical for understanding the air–sea interface in the context of climate change.