Temporal variability of the hydrothermal plume above the Kairei vent field, 25°S, Central Indian Ridge

Abstract

Continuous profiling of the nonbuoyant plume above a hydrothermal vent site can be used to determine the interaction between the plume formed by venting high‐temperature fluids and changing background temperature, salinity, and current fields over a tidal cycle. We have conducted a 12‐hour monitoring of the nonbuoyant plume above the Kairei vent field, 25°S, Central Indian Ridge. The depth of the plume particle maximum varies significantly in the water column, from 2150 m to >2350 m, but remains strongly associated with the σ 2 = 36.987 potential density isopycnal. We have used the interaction between two unrelated physical oceanographic phenomena to isolate the section of the time series record most suitable for determining the heat flux of the Kairei source on the basis of the rise height of the plume to neutral buoyancy. At the start of the time series, internal waves are observed with a period similar to the calculated buoyancy period N −1 , about 3 hours; no consistent relationship is observed between the rise height of the plume and the calculated heat flux. For the last 6 hours of the time series, isopycnal surfaces are compressed above a strongly developed nonbuoyant plume such that the calculated buoyancy period is less than that of the internal waves. A more constant heat flux can be calculated, on the basis of the plume rise height, from this part of the record.