Characterizing turbulence at the Fåvne hydrothermal vent field with Acoustic Doppler Velocimetry

Understanding hydrothermal systems and their influence on the surrounding environment is essential for characterizing oceanographic processes. High-resolution measurements of ocean currents are particularly important for investigating transport and mixing in such dynamic environments.

The Acoustic Doppler Velocimeter (ADV) provides detailed measurements of small-scale velocity fluctuations, offering insight into both local flow dynamics and broader current structures. In this study, currents at the Fåvne vent field on the North Atlantic Mid-Atlantic Ridge are investigated using a short-term mooring equipped with multiple instruments sampling at different depths. Small-scale flow variability is examined using two ADVs deployed at approximately 40m above the seafloor, and their time series are compared to assess consistency and spatial variability.

Kalman filtering, combined with despiking via the phase-space method, was applied to improve data quality and enable reliable turbulence estimates. Turbulence energy estimates, in addition to length scales and cross-correlations, were estimated. These estimates are used to infer the general current structure and to evaluate whether the mooring was sampled within a hydrothermal plume. For most of the deployment, current directions indicate that the measurements captured background ocean turbulence. On the final day of observations, the current turned 180◦ from the vents toward the mooring, and the measurements may reflect plume-influenced conditions. The flow during the measurement period was characterized by elevated turbulence levels and strong mechanical mixing, with dissipation rates on the order of 10−8 m2 s−3, indicating a well-developed turbulent energy cascade. However, the extent of plume-induced turbulence remains uncertain, and measurement limitations introduce additional uncertainty.