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  • Print publication year: 1999
  • Online publication date: August 2010

Thermocline penetration by buoyant plumes


Plumes of buoyant fluid rise in a stratified environment until their buoyancy with respect to the environment reverses, they become heavier than their surroundings and gravitational forces bring them to a halt. Obstacles to turbulent plume rise, occur in the form of external stratification and two-component mixing, which changes the buoyancy of the plume. Volcanic eruptions introduce large amounts of heat to the water column, and the question arises as to whether or not such eruptions can drive plumes up to the sea surface, and create a significant sea surface temperature anomaly.

A turbulent plume model is used to estimate the magnitude of an eruption which might be capable of driving a plume across the ocean's thermocline, which poses a substantial barrier to vertical motion—more so, for instance, than the tropopause with respect to atmospheric plumes. The confining effect of Earth's rotation helps to maintain stronger anomalies in the horizontal spreading phase of the motion at the sea surface. Plumes which cannot attain the surface may also have substantial temperature and salinity anomalies if these quantities vary in the the source or water column through which the plume rises and entrains water.


The effect of marine geothermal sources is mostly hidden from view, occuring for the most part on deep mid-ocean ridges where new crust is formed, or in basins where old crust is sinking into the Earth. Often the sources are thousands of metres deep, and require large institutional efforts merely to access them.