  The amplification and equilibration of three-dimensional salt fingers in
unbounded uniform vertical gradients of temperature and salinity is modeled
with a Direct Numerical Simulation in a triply periodic computational domain. A
fluid dynamics video of the simulation shows that the secondary instability of
the fastest growing square-planform finger mode is a combination of the
well-known vertical shear instability of two-dimensional fingers [Holyer, 1984]
and a new horizontal shear mode.
