The bathyal zone or bathypelagic – from Greek βαθύς (bathýs), deep – (also known as midnight zone) is that part of the pelagic zone

Pelagic zone

Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...

 that extends from a depth of 1000 to 4000 metres (3300 to 13000 feet) below the ocean surface

Sea level

Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

. It lies between the mesopelagic

Mesopelagic

The mesopelagic is that part of the pelagic zone that extends from a depth of 200 to 1000 metres below the ocean surface. It lies between the photic epipelagic above and the aphotic bathypelagic below, where there is no light at all...

 above, and the abyssopelagic below. The average temperature hovers at about 39°F (4°C). Although larger by volume than the euphotic zone, the bathyal zone is less densely populated.