 The dysphotic zone, where light intensity is considerably less than 1% of surface irradiance, extends from the base of the euphotic zone to about 1000 meters.Extending from the bottom of the photic zone down to the seabed is the aphotic zone, a region of perpetual darkness.Since the average depth of the ocean is about 4300 meters, the photic zone represents only a tiny fraction of the ocean’s total volume.