Mucus Comet tails in Marine Snow

Phytoplankton in the upper layers of the ocean agglomerate and sink in the form of aggregates called marine snow. This transport mechanism is a dominant carbon sequestration pathway that regulates atmospheric CO₂ and global climate. Although sedimentation physics dates back to the late nineteenth century, a predictive understanding of marine snow remains a puzzling fluid-structure interaction problem, which can be attributed to the lack of a dynamical underpinning of the various ecophysiological parameters that are central to the sinking behavior. In this work we experimentally study marine snow using vertical tracking microscopy in a field setting, in the Gulf of Maine on R/V Endeavor. We discover hitherto unexplored invisible degrees of freedom coming from mucus, which significantly modifies the geometry and sinking dynamics of marine snow. The microscopically resolved in-situ PIV of marine snow reveals a comet tail like flow morphology that is universal across a range of hydrodynamic fingerprints of marine snow, which renders porosity unimportant in the sedimentation dynamics. We construct a minimal model based on Stokesian sedimentation and viscoelastic distortions of mucus to understand the scaling behavior of both sinking speeds and tail lengths of these mucus comets. Our theoretical framework is in good agreement with our field observations and paves the way towards more detailed in-situ observations and predictive understanding of this crucial transport phenomena.