Yes, it is generally pitch black in the ocean at night, especially in deeper parts of the ocean. The absence of natural light sources, such as the sun or moon, combined with the scattering and absorption of light by water, creates a dark environment.
In the upper layers of the ocean, there may be some residual light from the stars and the moon if it is present and not obscured by clouds. This dim light is often not sufficient to illuminate the depths of the ocean significantly.
However, it's worth mentioning that some marine organisms possess bioluminescent abilities, meaning they can produce light through chemical reactions within their bodies. These organisms, including certain species of plankton, jellyfish, and deep-sea fish, can create their own light, resulting in faint glows or flashes in the dark ocean. These bioluminescent displays can sometimes be seen as glowing trails, sparks, or even whole patches of light, adding some illumination to the otherwise dark environment.
Overall, though, the deep ocean is predominantly characterized by darkness during the nighttime hours.