4.1.9 (HL)—Ocean carbon sequestration

Ocean carbon can move into dissolved chemistry, biomass, carbonate or buried sediment, and each pathway has a different residence time.

Dissolved CO₂ can lower pH quickly; biology transfers carbon through food webs, but most biomass is respired or decomposed. A small fraction reaches the seabed as organic matter or inorganic carbonate, may be buried in sediment and, over millions of years, can contribute to fossil-fuel formation.

Phytoplankton fix CO₂ this season, but most carbon is respired or decomposed; a small sinking fraction may be buried for much longer.

Long-term sequestration requires carbon to reach and remain in buried seabed sediment; temporary biological uptake alone does not provide the same residence time.

‘Biological’ does not mean permanent; distinguish flux, pool and residence time.