https://ceramics.org/ceramic-tech-today/environment/explorin...
In contrast, if we wanted to get the same metals from the land, it would release 0.065 gigatons of CO2.
While there's a good bit of uncertainty in these estimates. Regardless, the impact is dwarfed by the savings from more efficient smelting processes enabled by deep sea nodules, which could save about 1 gigaton of carbon.
[^0]: https://www.theatlantic.com/science/archive/2021/07/soil-rev...
Meanwhile, I'm not aware of any proposals to sequester carbon in seabed ecosystems.
I'm certainly not qualified to analyze the accuracy of a soil science study or the field as a whole. As someone not in that specialty, the figure that jumps out at me is the 40x difference between the impact from ecosystem damage vs. other impacts. Generally that tells me that the potential for ecosystem impacts to nix the climate benefits of deep sea mining is low - it would require that soil science be so wrong that they missed over 90% of the carbon content of the seabed.