Data From: Active sinking particles: Flow and transport dynamics due to sessile suspension feeders on sinking aggregates

Sinking or sedimentation of biological aggregates plays a critical role in
carbon sequestration in the ocean and in vertical material fluxes in
waste-water treatment plants. In both these contexts, the sinking
aggregates are “active,” since they are biological hot-spots and are
densely colonized by microorganisms including bacteria and sessile
protists, some of which generate feeding currents. However, the effect of
these feeding currents on the sinking rates, trajectories, and mass
transfer to these "active sinking particles," has not previously
been studied. Here we use a novel scale-free vertical-tracking microscope
(a.k.a. Gravity Machine, Krishnamurthy et al. "Scale-free vertical
tracking microscopy." Nature Methods (2020)) to follow model sinking
aggregates (agar spheres) with attached protists (Vorticella convallaria),
sinking over long distances while simultaneously measuring local flows. We
find that activity due to attached \vortc causes significant changes to
the flow around aggregates in a dynamic manner and reshapes mass transport
boundary layers. Furthermore, we find that activity-mediated local flows
along with sinking modify the encounter and plume cross-sections of the
aggregate and induce sustained aggregate rotations. Overall our work shows
the important role of biological activity in shaping the near-field flows
around aggregates with potentially important effects on aggregate fate and
material fluxes.