Hydrothermal Plume Near‐Field Dynamics From LES and Observations

Hydrothermal plumes play a crucial role in vent fields by injecting significant buoyancy flux from centimeter‐scale vents and rising hundreds of meters. This is a multiscale process, yet only the large scales have been well studied. Near‐vent dynamics remain a challenge in plume modeling, despite their importance for understanding deep‐sea environments. Thus, this work addresses this gap by characterizing the near‐field hydrodynamics and comparing it with plume theory and observations. We use a large‐eddy simulation (LES) approach with adaptive mesh refinement, achieving centimeter‐scale resolution within a 6‐m domain above the vent. We first study a typical black smoker to quantify the mean flow and spatial variability, investigating the link between turbulent structures and the entrainment rate of surrounding water. Significant vertical and temporal variability in is observed, limiting the applicability of the theoretical model. The LES reproduces in situ data well. Next, we investigate the sensitivity of the flow to source parameters, from forced to lazy plumes. The results reveal a transition region between vent conditions to the pure plume regime, where flow self‐similarity breaks down. This transition region is key to interpreting observations. Above this region, plumes achieve self‐similarity, and the flow field becomes consistent with theoretical plume scaling, showing dependence on source buoyancy flux. Finally, we show that extreme temperatures above 100C occur within the first two m of the plume, but exposure times for a proxy tracer are short. This suggests that hydrothermal plumes could serve as viable transport vectors for biological materials.