Marine snow under pressure: Implications for carbon sequestration in the deep ocean

The HADAL Center in Odense (Denmark) studies the biogeochemistry and microbial ecology of deep-sea (hadal) trenches both in situ and in simulation experiments using pressure tanks. One of the major findings is that trenches represent globally important deposition sites for organic and inorganic matter. Trench-focused deposition generates microbially and chemically reactive sediments that harbor anaerobic microbial processes at relatively shallow sediment depth, such as anammox and sulfate reduction. Additionally, surprisingly large inventories of anthropogenic pollutants accumulate in trench sediments.

Organic and inorganic matter deposition in hadal trenches may be due to both seismic-driven sediment slides and sinking marine snow. We simulate the descent of marine snow into hadal trenches by incubating model diatom aggregates in rotating pressure tanks. Hydrostatic pressure emerges as a key environmental factor that induces hitherto unknown transformations in marine snow. High pressure levels inhibit the microbial degradation of sinking particles, which may enrich trench sediments with relatively undegraded particulate organic matter. Additionally, pressure-exposed sinking particles leak dissolved organic matter (DOM) that enters the persistent DOM pool in the ocean. Taken together, pressure effects on marine snow likely increase carbon sequestration in the deep ocean.