[EngManagerIsMe]

Wood in the ocean will float for a long time, eventually sinking and storing that carbon. It will be broken down over a very long span, and the CO2 will enter the hydrocycle and eventually be released as a gas. Probably on the order of millennia.

That said, it's not clear what impact smothering the ocean floor would have in the habitats there, nor how we would get the wood to sink reasonably rapidly and stay sunk -- we don't want massive logs floating back up and hitting ships.

I (personally) believe we are better served by heating the wood in an oxygen free environment (pyrolysis). This produces a charcoal like substance and energy, we can bury the biochar or use it as a soil amendment to achieve the same result (hundreds to thousands of years of sequestration) and get energy out of the process.