Soft Matter and Complex Systems Seminar

Oceans are vital carbon sinks, absorbing approximately 30% of anthropogenic carbon emissions. A portion of this carbon settles to the seafloor, reducing its presence in the short-term global cycle. The primary drivers of this vertical transport are sinking aggregates of dead phytoplankton, known as marine snow. To predict sedimentation dynamics, it is essential to understand encounters between sinking particles. Collisions between these particles promote aggregation, increasing their sedimentation velocity, while interactions with free-floating bacteria enhance dissolution, potentially slowing their descent. Models for encounter rates involve two dominant mechanisms of particle interception: advection and diffusion. The relative importance of these mechanisms depends on the sizes of the colliding particles. However, many existing studies either neglect one of these processes or simply superimpose them, raising concerns about their accuracy. Here, we present a systematic approach to modeling collision rates as a function of particle size and Peclet number.