The Southern Ocean could temporarily become a carbon source during rapid emissions cuts
Two reports describe coupled climate simulations in which the Southern Ocean could temporarily switch from a carbon sink to a net source under rapid atmospheric decarbonization pathways. The proposed mechanism is outgassing of natural dissolved carbon brought up from depth as atmospheric carbon-dioxide pressure falls. This is a model projection under specified emissions-reduction assumptions, not a direct observation of a reversal.
Science··Midday
A possible switch from sink to source
Phys.org and SciTech Pulse report from the same study that the Southern Ocean could temporarily become a net carbon source during rapid emissions reductions. The ocean currently absorbs an important share of human-produced carbon dioxide. The reported result does not say that this function has permanently disappeared. It projects that, along a specified rapid decarbonization pathway, the direction of carbon exchange between ocean and atmosphere could reverse for a period.[1], [2]
Natural carbon from deep water reaches the surface
In the mechanism described by the reports, upwelling driven by westerly winds brings natural dissolved inorganic carbon from deep water to the surface. When atmospheric carbon-dioxide pressure falls rapidly, the gradient between ocean and air changes, allowing some of that surfaced carbon to escape into the atmosphere. SciTech Pulse also describes warmer surface water and declining alkalinity as parts of the balance. These are processes used to explain the modeled switch, rather than measurements of a reversal already occurring.[2]
The boundary of the projection
The result does not show that cutting emissions would be ineffective. Phys.org reports that carbon released from the ocean could damp the near-term rate of atmospheric decline. Whether the switch occurs depends on assumptions including how quickly emissions fall and how the ocean-atmosphere system responds. The finding should therefore be read as a conditional simulation result that highlights the need to include the Southern Ocean's response when calculating future carbon budgets.[1]
