It's "easier" to capture from water in chemical terms but harder to actually move the water. I think the economy of moving the weight of water makes this a nonstarter.
Also yes, ocean acidification is likely to be the bigger immediate problem. People depend heavily on fish protein and other sealife. That plus poor farming yields will be bad.
I imagine any CO2 capture system that uses ocean water would be placed in the ocean, not have the water pumped into it.
CO2 is easier to chemically react when dissolved into water, and its mobility is about the same as on air. So the decision is about engineering something that can survive being immersed on the ocean vs. engineering something that can use atmospheric CO2. I believe there's no general answer, we can only answer that question for specific designs.
Mechanical and electrical engineering aren’t going to do you enough good quickly enough.
But can you think of any forms of life on the bottom of the food chain that depend on carbon inputs as part of its own metabolic processes in order to reproduce itself? Because if you want a self-sustaining ocean-based carbon capture solution, that’s where I would look.
e.g, instigate some large bloom of plant matter or algae, and engineer/find the right conditions for the matter to sink to the bottom of the ocean without decomposing.
At least the first part. There’s an easy profit motive: increasing the base of the food chain feeds the rest of it, and some of those are products we like to eat.
The second part, if you can find a profit motive to compost the ocean floor and actually do it in a profitable way, then it will get done. Else we’re stuck relying on natural processes.
The problem with GMO life is an organism trying to reproduce plus your goal is inherently less fit than an organism merely trying to reproduce. This really only works at accelerating a reset after a mass die off.
Also yes, ocean acidification is likely to be the bigger immediate problem. People depend heavily on fish protein and other sealife. That plus poor farming yields will be bad.