Comment by version_five

Had to read most of the way through to get to what I was most interested in:

  The process could be more efficient than air-capture systems, Hatton says, because the concentration of carbon dioxide in seawater is more than 100 times greater than it is in air. In direct air-capture systems it is first necessary to capture and concentrate the gas before recovering it. 

Sounds like a promising area to explore. I wonder how long it takes water to absorb CO2 in the first place. I picture eventually engineering some kind of big ponds that pull CO2 out of the air and leave limestone sediment behind