  We study the dynamics of an initially flat interface between two immiscible
fluids, with a vortex situated on it. We show how surface tension causes
vorticity generation at a general curved interface. This creates a velocity
jump across the interface which increases quadratically in time, and causes the
Kelvin-Helmholtz instability. Surface tension thus acts as a destabiliser by
vorticity creation, winning over its own tendency to stabilize by smoothing out
interfacial perturbations to reduce surface energy. We further show that this
instability is manifested within the vortex core at times larger than $\sim (k
We)^{1/4}$ for a Weber number $We$ and perturbation wavenumber $k$, destroying
the flow structure. The vorticity peels off into small-scale structures away
from the interface. Using energy balance we provide the growth with time in
total interface length. A density difference between the fluids produces
additional instabilities outside the vortex core due to centrifugal effects. We
demonstrate the importance of this mechanism in two-dimensional turbulence
simulations with a prescribed initial interface. We show an increase in kinetic
energy at large wave numbers due to the creation of small-scale vortices by the
action of surface tension.
