Marine snow

Marine snow are composed mainly of organic aggregates formed by dead organisms, plankton and bacteria. These particles slowly sink and in this manner transport carbon to the deep ocean. Since marine snow has a critical role in the carbon cycle, studying the rates at which it settles towards the seafloor is crucial in the present context of climate change. We have performed several theoretical studies to understand the physical aspects of formation and settling of marine snow particles. To that extent they were modeled using an individual based approach: considering each one of them as an inertial particle advected by a fluid flow. The advection dynamics was described with the use of Maxey-Riley equations.

The research work primarily followed two main lines:

• The first one consisted in analysing the relevance of the so-called Basset force — an integral over a particle’s history for and in turbulent flows (performed by means of direct numerical simulations, DNS).

• The second research line consisted in the study of aggregation-fragmentation processes of small inertial particles advected by a synthetic turbulent flow. As a result of forces that act on these inertial particles, their distribution in space is strongly non-homogeneous. Within this project we have numerically studied the aggregate’s break-up dynamics and analysed the applicability or failure of scaling relations derived from the mean-field theory for the aggregation-fragmentation process.

Publications:

• A snapshot attractor view of the advection of inertial particles in the presence of history force Guseva, Ksenia, Daitche, Anton, and Tél, Tamás The European Physical Journal Special Topics Jun 2017

• History effects in the sedimentation of light aerosols in turbulence: The case of marine snow Guseva, Ksenia, Daitche, Anton, Feudel, Ulrike, and Tél, Tamás Physical Review Fluids Nov 2016

• Influence of the history force on inertial particle advection: Gravitational effects and horizontal diffusion Guseva, Ksenia, Feudel, Ulrike, and Tél, Tamás Physical Review E Oct 2013

• Aggregation and fragmentation dynamics in random flows: From tracers to inertial aggregates Guseva, Ksenia, and Feudel, Ulrike Physical Review E Jun 2017

• Numerical simulations of aggregate breakup in bounded and unbounded turbulent flows Babler, Matthaus U., Biferale, Luca, Brandt, Luca, Feudel, Ulrike, Guseva, Ksenia, Lanotte, Alessandra S., Marchioli, Cristian, Picano, Francesco, Sardina, Gaetano, Soldati, Alfredo, and Toschi, Federico Journal of Fluid Mechanics Mar 2015