Porous media, such as marine aggregates and sandy sediments, are densely colonized by microorganisms, making them hotspots of microbial activity and key players in ocean biogeochemistry. Marine aggregates drive the export and transformation of organic material in the water column, regulating the biological carbon pump, while sandy sediments on the coastal seafloor are crucial for removing anthropogenic nutrient inputs. Together, these porous media play a central role in carbon sequestration and nutrient cycling.

In my talk, I will examine how the heterogeneous physical, chemical and biological properties of marine aggregates and sandy sediments shape biogeochemical processes and how mathematical methods can be applied to enhance predictions of these processes. By introducing innovative techniques to visualize microscale solute gradients and flow fields, I will illustrate the intricate interplay between advective and diffusive fluxes and microbially catalyzed reactions. Taking a microscale perspective, my talk aims to provide a mechanistic understanding of how transport processes and microbial activity drive ocean biogeochemistry at the ecosystem scale.