Why are the oceans considered a large carbon sink?

I've tried looking through the book but I only found that the ocean is a large carbon sink, but I never saw as to why.
The answers could be:
- Phytoplankton takes in carbon through cellular respiration.
- Decomposition rates in the water are far greater than on land.
- Water absorbs carbon directly from the atmosphere by diffusion.
- Carbon gets transferred among all the organisms of every food chain

1 answer

in the ocean.