Question: if we take CO2 out of the oceans, will the oceans take it out of the air? And is it easier to take it out of the oceans than it is to take it out of the air/can we take out stuff out of ocean water at the same time (lithium, gold, etc.) that would make processing all that water worth it?
It looks like a group at the University of Exeter is working on that exact plan.
"SeaCURE harnesses two natural properties of the ocean that can circumvent this problem. (1) The amount of carbon dissolved in a seawater is approximately 150 times higher than its concentration in air, making extraction significantly easier and quicker, (2) we can utilise the ocean’s vast surface area to remove CO2 from the enormous volume of air sitting above it, rather than having to push all of that air through air-based CO2 capture facilities."
"SeaCURE will combine and refine existing approaches to develop a new system that removes CO2 from seawater and releases the CO2-depleted water back to the ocean, where it will naturally re-absorb an equivalent amount of CO2 from the atmosphere. Specifically, at the University of Exeter and Plymouth Marine Laboratory we will benchmark established approaches to prepare seawater for CO2 extraction, strip that CO2 from the seawater, and collaborating with Brunel University concentrate the CO2 to high purity. TP Group, a UK based technology and engineering firm with world leading expertise in gas extraction from seawater, will then develop and upscale the most cost effective approach from this toolkit. The SeaCURE team will design a portable pilot plant to remove at least 100 tonnes of CO2 a year. Future testing using the pilot plant would generate the data required to develop commercially viable CO2 removal at the megaton scale, aimed at public and private sector offsetting and the carbon trading market."
Energy costs of carbon sequestration from seawater is far lower than from the atmosphere directly, carbon does cycle fairly rapidly to the oceans, and increased ocean acidification is itself a major concern. I think the question is well-worth exploring. I'm mostly familiar with it in the context of synfuel production, one possible application (though of course burning such fuels re-introduces an captured carbon to the atmosphere).
A set of papers, several of which address energy costs of carbon sequestration from seawater:
Biomass that falls into the deep ocean doesn't quickly cycle back into the carbon cycle, so some companies are look at the opposite, with the deep ocean as a sink. https://www.phykos.co/
But your idea is somewhat correct, and it has to do with desalinization tailings. There are companies like Heimdal which can take the high mineral runoff from desalinization and use it to make concrete. https://www.ycombinator.com/companies/heimdal
