Out of curiosity, what happens when you dump wood in the deep ocean? Does the wood breakdown and does the carbon come back up as CO2 in the atmosphere?
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.
After the logs become fully submerged and settle, I do not believe that they decompose rapidly, but (again) cannot find reliable sources. The state of Florida has a licensed program for "Deadhead Logging"[0], but much of the content I've found about that program is specific to river ecosystems, not oceans.
A 2020 article entitled "First evidence of microbial wood degradation in the coastal waters of the Antarctic"[1] offers a few nice quotes:
> Wood submerged in saline and oxygenated marine waters worldwide is efficiently degraded by crustaceans and molluscs.
> Our results establish that there is ongoing wood degradation also in the Antarctic, albeit at a vastly reduced rate compared to warmer environments. Historical shipwrecks resting on the seafloor are most likely still in good condition, although surface details such as wood carvings, tool marks, and paint slowly disintegrate due to microbial decay.
[0] https://floridadep.gov/water/submerged-lands-environmental-r...