If there is a sudden change in the thermocline and thermohaline circulations in the ocean waters, the organisms that live in the ocean waters would suffer badly, and there's a even a high chance of a mass extinction occurring. The reason for such a devastating effect will be that the water temperature will change, the salinity levels will change, and the amount of nutrients and at which depth they will be will change. Since every living organism is adapted to be able to survive in a particular environment, sudden changes in it will put the organisms in a situation where they are not suited to survive in such conditions, so t=they will most probably die out.
