Fig. 2

Vertical profiles of hydrothermal plume tracers from two vent fields along the Central Indian Ridge. (a) Profiles from the Cheoeum Vent Field (CVF), and (b) profiles from the MIRAE2 Vent Field (M2VF). Each panel shows the depth distribution of 3He/4He (both R/Ra and Δ3He, blue), CH4 concentration (nmol/kg, green), δ13C of CH4 (‰ vs vPDB, orange), and 222Rn activity (dpm/L, red). Samples collected by ROV are indicated by diamond symbols. Black lines connect samples from sequential depths to illustrate plume structures. Error bars represent analytical uncertainties. See Methods 5.1–5.3 for detailed sampling and measurement procedures.