[nf3]

Earth worms provide a similar service in mixing clay and organic material to create clay-humus aggregate.

In oceans, whales also mix different layers of sea water with their vertical movements.

[quercusa]

Earthworms are a mixed bag: https://en.wikipedia.org/wiki/Invasive_earthworms_of_North_A...

[BurningFrog]

I think the whale population is still at least 90% below pre whaling levels.

So the sea water layers are probably less mixed than natural. No idea what effects that might have.