Mesopelagic

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The mesopelagic (Greek μέσον, middle) (also known as the middle pelagic or twilight zone) is a pelagic zone extending from 200 m down to around 1000 m below sea level. It is located between the photic epipelagic and the aphotic bathypelagic, where where there is no light at all. Although some light penetrates this deep, it is insufficient for photosynthesis. Though the temperature varies less at any one height than the epipelagic, the mesopelagic is the location of the thermocline, with temperatures varying from over 20°C at the top to around 4°C at the boundary with the bathyal zone.