The ocean is a major global carbon sink, estimated to have absorbed ~30% of anthropogenic carbon dioxide over the past two decades. The ocean sequesters carbon via the “biological pump”: carbon, fixed by photosynthesis at the surface, sinks to the deep ocean where it is trapped over climatically relevant timescales.
"When I think of the floor of the deep sea, the single, overwhelming fact that possesses my imagination is the accumulation of sediments. I see always the steady, unremitting, downward drift of materials from above, flake upon flake, layer upon layer - a drift that has continued for hundreds of millions of years, that will go on as long as there are seas and continents.
For the sediments are the materials of the most stupendous snowfall the earth has ever seen."
- Rachael Carson
The Sea Around Us
The goals of our projects in this area are to examine active microbial communities on sinking marine particles and investigate how their microscale ecology influences the fate of carbon at the ecosystem scale.
We aim to characterize the genomic diversity, spatial organization, and population dynamics of these communities; and to quantify their metabolic activity and identify key cross-feeding interactions between species.
This work will inform collaborative efforts to improve predictive models for oceanic carbon sequestration.
A major route for this carbon export is via sinking particles formed by aggregation of phytoplankton cells, fecal pellets and detritus (large particles are known as “marine snow”). From the microbial perspective, the water column is not a well-mixed solution, but instead a jungle of complex features, from microscopic colloids to macroscopic particles. When microbes digest these particles, they short-circuit the biological pump with respiration that releases carbon back into the atmosphere.
Image credit: EXPORTS Science Plan; Siegel et al. 2014