That article I read also said the average depth of the ocean is...

That article I read also said the average depth of the ocean is 3.700m. To my way of thinking waves would agitate a very thin layer on the top of that. Convection not a lot more, so like you I wonder about the mechanism whereby the heat [and dissolved CO2] gets to the depths. If it were reasonably quickly, why are the depths so bloody cold?

This would be a V slow process which dovetails into the theory that atmospheric CO2 lags surface temp rises by upwards of 200 years. That of course is the exact opposite of the alarmists' theory that CO2 precedes [causes] surface temp. rises.