Biological carbon-pump efficiency

Tiny ocean organisms capture carbon. Why does carbon from some survive the journey to deep water while much of the rest is recycled?[1] [2]

A particle made from microscopic ocean organisms can sink, join other particles or be consumed by microbes before reaching deep water. What determines the fraction of carbon from each group that survives this journey? These organisms, phytoplankton, capture carbon near the sunlit surface. Below it, microbial consumption converts organic material back into forms such as carbon dioxide, a process called remineralization.

South China Sea isotope tracing distinguishes carbon from cyanobacteria and larger microalgae in sinking particles. The observations support contrasting losses and compensating contributions, with aggregation helping small cells sink. They do not establish that the same compensation occurs throughout the ocean.[1] [2]

Sinking material can clump together or be consumed along the way. Regional observations reveal contrasting fates for different groups of organisms, but these results do not yet establish how the balance changes across the oceans.[1] [2]

South China Sea data support compensating taxon-specific pathways; their global applicability and response to changing conditions remain unestablished.[1]

Capturing carbon near the surface and keeping it deep in the ocean are different outcomes. The depth at which the material is consumed affects carbon storage and the food reaching deep-water organisms, connecting small ocean life to the wider carbon cycle.[1] [2]

The carbon reaching depth supplies deep-water microbes and can remain away from the surface for a time shaped by ocean circulation. Consumption at shallower depths has a different storage consequence from delivery farther down. Connecting community composition, particle loss and water movement is therefore necessary to interpret how ecosystem changes affect the marine carbon cycle.[1] [2]