Carbon Flux Dynamics in Oceanic Ecosystems

Carbon flux in oceanic ecosystems encompasses the movement of carbon from atmospheric CO₂ into marine biota, its transformation into organic matter, and its eventual sequestration in the deep sea or return to the surface. Phytoplankton in the euphotic zone fix CO₂ through photosynthesis, forming the basis of the biological carbon pump. Sinking particles, active transport by migratory zooplankton and physical processes such as mixing and subduction together transfer organic and inorganic carbon below the mixed layer. Microbial and zooplanktonic remineralisation in mesopelagic waters dictate how much carbon is respired back to CO₂ or stored on timescales ranging from months to millennia. Variations in temperature, nutrient availability and ocean circulation modulate export efficiency and sequestration time, thereby influencing atmospheric CO₂ levels and climate feedbacks. Improved understanding of vertical flux profiles, particle dynamics and model uncertainties is essential for projecting the ocean’s capacity to buffer anthropogenic emissions and for evaluating marine carbon removal strategies.

Research from Nature Portfolio

Recent studies have leveraged decades of hydrographic observations to refine top-down estimates of organic carbon export from the euphotic zone, revealing that approximately 15 Pg C year⁻¹ is produced, of which only two-thirds reach 100 m due to rapid upper-ocean remineralisation. Investigations in coastal upwelling systems have quantified the relative contributions of sinking particles, diel vertical migration and the physical pump, demonstrating that while sinking particles dominate export, active transport by zooplankton extends sequestration depths and enhances long-term storage. Complementary model intercomparison work has partitioned uncertainty in biological pump simulations, showing that export uncertainty prevails above 900 m but transfer efficiency dominates deeper, and that single-parameter metrics underestimate the true variability of vertical flux profiles. Together, these advances improve predictive capacity for carbon cycling under future climate scenarios and guide the refinement of biogeochemical models.

Carbon Flux Dynamics in Oceanic Ecosystems publication trend

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

Technical terms

Euphotic zone: The upper ocean layer where light penetration supports photosynthesis.

Biological carbon pump: The suite of biological processes that fix CO₂ in surface waters and transport organic carbon to depth.

Export flux: The rate at which organic carbon leaves the euphotic zone towards deeper layers.

Remineralisation: The microbial or zooplanktonic conversion of organic carbon back to inorganic forms, primarily CO₂.

Sequestration efficiency: A measure of how long and how much fixed carbon remains stored below the surface before returning to contact with the atmosphere.

Diel vertical migration: Daily movement of organisms between surface and deeper waters, actively transporting carbon vertically.

References

1. Biological carbon pump estimate based on multidecadal hydrographic data. Nature (2023).
2. Carbon sequestration by multiple biological pump pathways in a coastal upwelling biome. Nature Communications (2023).
3. Distinct sources of uncertainty in simulations of the ocean biological carbon pump at different depths. Communications Earth & Environment (2024).
4. Misconceptions of the marine biological carbon pump in a changing climate: Thinking outside the “export” box. Global Change Biology (2024).
5. Knowledge Gaps in Quantifying the Climate Change Response of Biological Storage of Carbon in the Ocean. Earth's Future (2024).
6. Sinking Organic Particles in the Ocean—Flux Estimates From in situ Optical Devices. Frontiers in Marine Science (2020).