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GRID-Arendal has published a new spatial analysis of seafloor environments to assess the impact of anthropogenic global climate change and ocean acidification. We found that the estimated ~100 m shoaling of the carbonate compensation depth (CCD) since the industrial revolution has submerged an additional 12,432,100 km2 of the ocean floor, a 3.60% increase. Life below the CCD is limited to animals that do not produce carbonate shells (like molluscs) because their shells will dissolve in the deepest ocean waters with a lower pH.

Due to the burning of fossil fuels, carbon dioxide is being absorbed by the ocean, where its chemical conversion to carbonic acid has already caused the surface ocean to become more acidic than it has been for at least the last 2 million years. Global ocean modelling suggests that the CCD has risen by nearly 100 m on average since pre-industrial times and will likely rise further by several hundred meters this century.

We carried out a relative risk assessment for future submergence of the ocean floor below the CCD in 17 ocean regions if the CCD rose by another 300 m. We found that the western equatorial Atlantic is at high risk, and nine other ocean regions are at moderate risk of greater seafloor area submerging below the CCD. Uniform hypothetical 300 m shoaling of the CCD across all ocean regions illustrates that the area of seafloor submerged below the CCD rises by 14% relative to pre-industrial revolution times (a total of 51% of the ocean floor below the CCD). Overall, the Atlantic Ocean and southern Indian Ocean appear to be at greater risk of impact from a rising CCD than the Pacific and other Indian Ocean regions.

We also estimated the area of national Exclusive Economic Zones submerged below the rising CCD and found that the results exhibit extreme variability; with 300 m of CCD shoaling, we find >12% increase in area submerged below the CCD for 23 national EEZs, mainly of developing countries. The five most impacted EEZs are Bermuda (UK), El Salvador, Nauru, Guatemala and Sri Lanka, which will see more than 28% of their EEZs submerged below a rising CCD. By comparison, for the US EEZ (lower 48 states), the area of seabed projected to be submerged below the CCD rises from 0.09% to 6.09%

Release date: 15 Aug 2023


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