  We observe the emergence of strong vertical drafts in direct numerical
simulations of the Boussinesq equations in a range of parameters of geophysical
interest. These structures, which appear intermittently in space and time,
generate turbulence and enhance kinetic and potential energy dissipation,
providing a possible explanation for the observed variability of the local
energy dissipation in the bulk of oceanic flows, and the modulation of its
probability distribution function. We show how, due to the extreme drafts, in
runs with Froude numbers observable in geophysical scenarios, roughly 10% of
the domain flow can account for up to 50% of the global volume dissipation,
reminiscent of estimates based on oceanic models.
