The water just dilutes back into the rest of the ocean, lowering its average carbon content a minuscule amount. It’ll take a year or less for it to reabsorb as much atmospheric CO2 as was removed. This isn’t a big deal unless it’s done at massive scale in concentrated areas.

An “easy” way to handle this is to return the water to the deep ocean, where it’s less impactful to ocean life and has a much larger area in which to dilute.