Just found this article with some research from earlier polymetallic nodule mining finding significantly decreased carbon sequestration in the mined areas. Won't be great news if mining the "Planet’s Largest Deposit of Battery Metals" winds up worsening global warming.
This study (https://www.sciencedirect.com/science/article/pii/S095965262...) looked at what the actual impact of that carbon release would be. Even if deep sea mining completely destroyed the ability of the sea floor to sequester carbon and it took 100 years to recover, it would only release 0.025 gigatons of CO2.
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.
That's releasing, but what about the impact of the ability to sequester more CO2? Most of soil sequestration estimates are based on some really shaky soil science,[^0] but the oceans are known to be a much more effective means of sequestering carbon
Oceans are great at sequestering carbon, but that's via dissolved CO2 and ecosystems near the surface (which are not impacted by deep sea mining). The seabed ecosystem plays an ancillary role.
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.
Near the surface? My understanding is that absorption happens at the surface but actual sequestration only happens when the carbon drops below some depth (1000m?) and never comes back.
I’m far from an expert in this - but I thought the paper I linked did a good job explaining it. Suffice it to say that it has nothing to do with the seabed itself.
https://ceramics.org/ceramic-tech-today/environment/explorin...