Near-field variability of the TAG non-buoyant plume, 26°N, Mid-Atlantic Ridge

We report the initial results of a nine hour monitoring of the non-buoyant plume above the TAG hydrothermal vent field at 26°N on the Mid-Atlantic Ridge. A CTD (conductivity, temperature and pressure) and nephelometer (particle sensor) were continuously raised and lowered through the non-buoyant plume for nine hours at a site situated ∼ 100 m south of the hydrothermal mound. This method permits a detailed record of the variability of the non-buoyant plume close to the vent field to be made. Our results show that the particulate maximum of the non-buoyant plume appears ∼ 150 m lower in the water column at the start and end of the record, compared with profiles recorded towards the middle of the record. A corresponding structure also appears in the temperature and salinity records, with the result that the plume particle maximum resides on the σθ ≈ 27.8035 isopycnal throughout. Modelling of the rise height of an axisymmetric plume can only account for ∼ 95 m of the variability in the final level of neutral buoyancy. Plume bending due to currents is a likely explanation for the recorded temporal variability.