Well it depends too on how long things take to settle out. Salt is easily suspended in water, but silt is not, so the water would be salty but not muddy. The water would also probably have lots of photosynthetic bacteria/algae in it, so you would probably have blooms of green, blue, red, and brown all over. Those blooms would uptake light and carbon through that process then as they died drop the content down the long water column. All sorts of feeding below that would create a full eecological web. If there were deep sea vents, volcanic activity breaking through the sea floor, you would have a second source of energy and chemistry at the bottom. That said, the over level of life at the surface would be limited by things like iron, phosphorus, copper, and so on. Any heavier ions would be less available at the surface because there is no surface erosion bringing them in at the top so as they are bound up in dead algae they will drop to the floor.

The rate limiting at the sea floor will be based on energy but not too bad, you would likely see a lot of diverse life around vents and it would have a fairly large complexity over time. That said, the depth would make for less complex life due to the lack of light and associated vision. Some things would make light but it would be dangerous to make and would not be super common.

Another interesting consideration is the geography of the sea floor. Would there be fault lines? If there are continental plates but way under the ocean they would still have movement, so subduction and so on would play out, so you would probably have chains of vents along the diverging or merging plate boundaries. Life would spread along these lines, so life would be closely related at nearby vents but distant over the surface of the planet. I would anticipate a fairly heterogeneous population over the surface of the planet in the deep, but far less so at the surface.