The bathypelagic zone or bathyal zone is the part of the open ocean that extends from a depth of 1,000 to 4,000 m below the ocean surface. It lies between the mesopelagic above and the abyssopelagic below. The bathypelagic is also known as the midnight zone because of the lack of sunlight; this feature does not allow for photosynthesis-driven primary production, preventing growth of phytoplankton or aquatic plants. Although larger by volume than the photic zone, human knowledge of the bathypelagic zone remains limited by ability to explore the deep ocean.
Champagne vent, a hydrothermal vent on the Northwest Eifuku seamount.
Particulate organic matter (marine snow) traveling through the water column.
A type of archaea, Crenarchaeaota are linked to dissolved inorganic carbon fixation.
ROV Jason
The mesopelagic zone, also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins at the depth where only 1% of incident light reaches and ends where there is no light; the depths of this zone are between approximately 200 to 1,000 meters below the ocean surface.
Sediment trap sample, Thermaikos Gulf, Greece, 2000. Stereoscopic image of the collected material above 63-μm pore size net. Calcareous shells and skeletons of planktonic organisms can be identified.
Sonar data. The green layer in the water column is the deep scattering layer of diel vertically migrating mesopelagic zooplankton and fish.
Illustration by Charles Frederick Holder of various bioluminescent fish that live in the mesopelagic zone
Helmet jellyfish, Periphylla periphylla