Bathyal Zone

The bathyal zone, also called the bathypelagic zone, is the layer of open ocean spanning roughly one thousand to four thousand meters in depth, lying between the sunlit mesopelagic zone above and the abyssal zone below. It is sometimes called the midnight zone because no sunlight penetrates this far, which rules out photosynthesis and the plant life that depends on it. Temperature stays almost constant near four degrees Celsius, salinity holds steady between thirty three and thirty five grams per kilogram, and pressure ranges from about one hundred to four hundred atmospheres. Bioluminescence provides the only light most organisms here ever encounter. Conditions in this zone have stayed largely unchanged for thousands of years, and its sheer volume, larger than all the sunlit ocean layers above it combined, remains poorly explored because of the difficulty of studying water this deep.