The sinking of biogenic particles in a realistic flow, with major energetic structures in the mesoscale, is a fundamental process of the biological carbon pump, which plays a key role in the global carbon cycle. This talk focus on the assessment of the theoretical results of finite-size particle dynamics in their applications to the oceanographic context. In particular, by using a simplified equation of motion in a mesoscale ocean flow simulation, we observe that three-dimensional density inhomogeneities due to inertial effects are extremely low. Instead, two-dimensional projections of the three-dimensional density display inhomogeneities. We identify the two processes that produce these inhomegeneities which in some cases can develop extreme values, caustics.