Ocean acidification

Assembled from 15 blocks · 2 evidence · 5 related

1. Story
2. The change in seawater carbonate chemistry caused by the ocean absorbing a large share of the carbon dioxide emitted to the atmosphere — roughly a quarter to a third of anthropogenic emissions. Dissolved carbon dioxide forms carbonic acid, which dissociates and releases hydrogen ions; those ions react with carbonate ions to form bicarbonate. Two things therefore happen at once: pH falls, and the concentration of the carbonate ion that corals need to build aragonite falls with it. Surface ocean pH has declined by roughly 0.1 units since the pre-industrial period, which on a logarithmic scale is an increase in hydrogen ion concentration of about thirty per cent. For a reef the operative quantity is the aragonite saturation state: as it drops, calcification costs the coral more energy and net reef accretion slows even where no coral has died. Acidification and bleaching share a cause and share nothing else — different timescale, different mechanism, different tissue. A reef can be entirely unbleached and still be losing its carbonate budget.
3. Knowledge
4. Reef carbonate budget
5. Ocean acidification
6. Connections
7. Coral calcification
8. Reef carbonate budget
9. A measured decline in Great Barrier Reef coral calcification is published
10. Coral calcification
11. Ocean acidification
12. Parrotfish (Scarinae)
13. Evidence
14. The ocean has absorbed a large share of anthropogenic carbon dioxide emissions and surface ocean pH has declined by roughly 0.1 units since the pre-industrial period, corresponding to an increase in hydrogen ion concentration of around thirty per cent. V55 verification basis: not consulted in this session; these are standard assessed figures stated from the producing model's knowledge of the assessment, not read from the chapter, and no confidence language from the report is reproduced.
15. Calcification in massive Porites on the Great Barrier Reef declined by about fourteen per cent from 1990, a change the authors described as without precedent in the preceding four centuries of the skeletal record. V55 verification basis: not consulted; the figure is stated from the producing model's knowledge. This result has been the subject of subsequent methodological debate that could not be reviewed here.