Microbial Dynamics in Oceanic Carbon Cycling

Marine microorganisms are central agents in the transformation and transport of carbon throughout the ocean. Photosynthetic plankton in the sunlit surface layer fix atmospheric CO₂ into organic matter, much of which aggregates into sinking particles. As these particles descend, heterotrophic bacteria and archaea colonise and degrade them, determining the fraction of carbon that reaches the deep sea for long‐term sequestration. Microbial activity on sinking particles drives the attenuation of particulate organic carbon (POC) with depth, influencing the efficiency of the biological carbon pump. In addition to the physical sinking of particles, dissolved organic matter released by phytoplankton and microbial remineralisation constitutes the microbial carbon pump, converting labile compounds into more refractory forms that persist in the ocean interior. Depth‐stratified shifts in community composition—from copiotrophic bacteria at the surface to pressure‐ and cold‐adapted assemblages in the mesopelagic—reflect changing substrate availability and environmental conditions. Understanding these microbial dynamics is pivotal for predicting responses of the ocean carbon cycle to climate change and for quantifying the ocean’s role in global carbon budgets.

Research from Nature Portfolio

Recent studies have elucidated the microbial signatures associated with sinking particle export in the open ocean. Analyses of particle‐entrained prokaryotes revealed depth‐dependent patterns of colonisation, with a decline in suspended prokaryote abundance from 75 to 250 m followed by an unexpected increase at meso- and bathypelagic depths, highlighting active microbial entrainment and transformation of POC during descent. Another investigation simulating hadal pressure conditions demonstrated that increasing hydrostatic pressure markedly reduces microbial respiration and diatom degradation on sinking aggregates, while altering both organic matter composition and microbial community structure. These findings underscore the role of pressure as a regulator of deep‐sea carbon processing and suggest that pressure‐tolerant taxa may contribute to the seeding of benthic ecosystems with relatively fresh organic matter.

Microbial Dynamics in Oceanic Carbon Cycling publication trend

The graph below shows the total number of articles in microbial dynamics in oceanic carbon cycling across all publications each year (not limited to Nature Index journals).

Technical terms

Particulate Organic Carbon (POC): Solid organic particles produced by phytoplankton and other organisms that sink through the water column.

Biological Carbon Pump (BCP): The suite of processes by which marine life transports carbon from the surface ocean to depth, aiding long‐term sequestration.

Mesopelagic Zone: Ocean layer between approximately 200 m and 1,000 m depth, where sunlight wanes and microbial remineralisation intensifies.

Microbial Succession: Sequential shifts in community composition and function as microbes colonise, degrade and alter sinking particles.

Dissolved Organic Matter (DOM): Organic molecules released into seawater by phytoplankton and microbial activity, serving as substrates for heterotrophic microorganisms.

References

1. Planktonic microbial signatures of sinking particle export in the open ocean’s interior. Nature Communications (2023).
2. Direct observations of microbial community succession on sinking marine particles. The ISME Journal: Multidisciplinary Journal of Microbial Ecology (2024).
3. Pronounced Diel Cycling of Dissolved Carbohydrates and Amino Acids in the Surface Ocean and across Diverse Regimes. Environmental Science and Technology (2024).
4. Hydrostatic pressure induces transformations in the organic matter and microbial community composition of marine snow particles. Communications Earth & Environment (2023).