We study the dynamics of massive black hole pairs in clumpy gaseous circumnuclear disks .
We track the orbital decay of the light , secondary black hole M _ { \bullet 2 } orbiting around the more massive primary at the center of the disk , using N -body/smoothed particle hydrodynamic simulations .
We find that the gravitational interaction of M _ { \bullet 2 } with massive clumps M _ { cl } erratically perturbs the otherwise smooth orbital decay .
In close encounters with massive clumps , gravitational slingshots can kick the secondary black hole out of the disk plane .
The black hole moving on an inclined orbit then experiences the weaker dynamical friction of the stellar background , resulting in a longer orbital decay timescale .
Interactions between clumps can also favor orbital decay when the black hole is captured by a massive clump which is segregating toward the center of the disk .
The stochastic behavior of the black hole orbit emerges mainly when the ratio M _ { \bullet 2 } / M _ { cl } falls below unity , with decay timescales ranging from \sim 1 to \sim 50 Myr .
This suggests that describing the cold clumpy phase of the inter-stellar medium in self-consistent simulations of galaxy mergers , albeit so far neglected , is important to predict the black hole dynamics in galaxy merger remnants .