These companies are trying to make the oceans a better carbon sink

The company’s plan is to electrochemically strip carbon dioxide out of the ocean, store or use the CO2, and then return the water to the sea, where it will naturally absorb more CO2from the air. What’s not easy to quantify is what happens after the CO2-depleted effluent is returned to the sea. Theoretically, if 1,000 tonnes of CO2 is artificially pulled out of the ocean’s upper layer, the ocean will eventually draw down 1,000 tonnes of CO2 from the air. How fast that happens depends on ocean currents, temperatures, and wind.

https://spectrum.ieee.org/ocean-carbon-removal