The euphotic zone
is the surface layer of the ocean
where sufficient light is available for photosynthesis
. It extends from the atmosphere-ocean interface downwards to a depth where light intensity falls to 1% of that at the surface (the euphotic depth
), so its thickness depends on the extent of light attenuation
in the water column. Typical euphotic depths vary from only several metres in turbid estuaries
to around 200 metres in the open ocean.