Dr. Elisa Romanelli, postdoctoral researcher in the Stocker Lab, Institute of Environmental Engineering, Department of Civil, Environmental and Geomatic Engineering, ETH Zurich, Zurich, Switzerland (email: eromanelli@ethz.ch), will give a seminar in the OCEANOMED Amphitheatre, Méditerranée Building, Luminy Campus, on Monday, 21 September 2026, at 1.30 pm on the topic: Microscale controls on the degradation of marine particulate organic carbon.
Abstract
Microorganisms play a key role in determining the fate of marine particulate organic carbon (POC), controlling how much is remineralised in the surface ocean as opposed to being exported to the deep ocean. Much of this activity takes place on sinking particles, where microscale processes govern how bacteria encounter, colonise and access organic matter.
Yet how these physical and biochemical processes regulate POC degradation remains poorly understood. In this talk, I will present recent work combining microfluidics, microscopy and mathematical modelling to uncover how physical forces and microbial traits control particle degradation.
First, I will demonstrate how shear affects bacterial colonisation of model marine particles. Using a controlled shear-flow microfluidic platform, we have found that increasing shear enhances bacterial colonisation and accelerates particle degradation.
A population dynamics model also shows that the effect of enhanced degradation depends on the bacteria’s lifestyle, with increased attachment significantly accelerating degradation by transient degraders.
I will then demonstrate how bacterial extracellular enzymatic strategies determine particle degradation rates. By combining microfluidics, Raman microspectroscopy and reaction–diffusion modelling, we find that diffusible enzymes drive more extensive degradation throughout the particle’s interior than enzymes that are predominantly cell-associated.
Laminar sinking flow (i.e. the flow produced by a particle as it sinks) further modifies solute transport and enhances particle degradation for both enzymatic strategies. Taken together, these findings reveal how microscale physical and biological processes jointly regulate particle degradation and, ultimately, the fate of sinking POC.
