A High-resolution Numerical Study of a Hydrothermal Plume
A High-resolution Numerical Study of a Hydrothermal Plume
Abstract:
Hydrothermal vents discharge high-temperature fluid laden with minerals, among which iron that is critical for marine life. The associated heat flux drives overturning instabilities which provide locally enhanced diapycnal mixing in the deep ocean.
In this work, we use a 3D non-hydrostatic PE code (CROCO-NH) to reproduce the dynamics of an idealized buoyant plume model in a stratified, rotating environment, inspired from the Lucky Strike volcano on the Medio-Atlantic Ridge. We investigate the sensitivity to horizontal resolution, with grid sizes of dx=80m, 40m and down to 10m. The large heat flux associated with the vents generate turbulent upward motion that entrains the surrounding fluid. This motion is strongly affected by the earth's rotation. The statistical steady state is characterized by an anticyclone on top of a cyclone, respectively in gradient wind and cyclostrophic balance. The anticyclone formed at the neutral buoyancy level is subjected to geostrophic adjustment that confine the lateral extent of the anticyclone such that the ratio of Rossby deformation radius to the horizontal scale of the anticyclone (R) is an order of 1 (NH/fR ~ O(1)).
We investigate the plume in terms of its potential vorticity dynamics (PV), in which the vents act as a source of negative PV. Even though the plume has a moderate horizontal extension of a few kilometers, it is continuously transported away by the mean larger scale currents. We carefully quantify the overall diapycnal mixing induced by the plume and estimate its long-term contribution to deep ocean mixing.
In this work, we use a 3D non-hydrostatic PE code (CROCO-NH) to reproduce the dynamics of an idealized buoyant plume model in a stratified, rotating environment, inspired from the Lucky Strike volcano on the Medio-Atlantic Ridge. We investigate the sensitivity to horizontal resolution, with grid sizes of dx=80m, 40m and down to 10m. The large heat flux associated with the vents generate turbulent upward motion that entrains the surrounding fluid. This motion is strongly affected by the earth's rotation. The statistical steady state is characterized by an anticyclone on top of a cyclone, respectively in gradient wind and cyclostrophic balance. The anticyclone formed at the neutral buoyancy level is subjected to geostrophic adjustment that confine the lateral extent of the anticyclone such that the ratio of Rossby deformation radius to the horizontal scale of the anticyclone (R) is an order of 1 (NH/fR ~ O(1)).
We investigate the plume in terms of its potential vorticity dynamics (PV), in which the vents act as a source of negative PV. Even though the plume has a moderate horizontal extension of a few kilometers, it is continuously transported away by the mean larger scale currents. We carefully quantify the overall diapycnal mixing induced by the plume and estimate its long-term contribution to deep ocean mixing.