What is the deepest any amount of sunlight can reach in the ocean?
In 1975, I was at 115 meters under to North Sea in a two-men mini-submarine. It was for the company Intersub of Marseilles, where the Condeep oil production platform Statfjord B was to rest on the seabed.
I was the navigator on board. One day, the pilot told me: "Should we try to switch off the lights? After we did, we could see the contour of the huge porthole we had in front of us. After a few minutes, the contour of the frame of the submarine and its instruments. The light goes this deep but then ... not much of it.
Here is the submarine we used:
It is usually accepted that 200 metres is the extent of how far sunlight can travel below the surface.
At this level everything lives in the dark. Some creatures down there have adapted to life in these low level light and some even produce there own headlamps. These creatures not only have to contend with the lack of light, but also the massive pressures exerted upon their bodies, which perhaps explains there very angular body shapes?
Deep sea fish
Depends on the turbidity of the water. The more particles (algae, sediment or marine snow) there are in the water column, the less far light can penetrate.
So in the coast of the North Sea, light is already very limited at 30 meters deep as there is high turbidity. But in less turbid areas light can reach further than 200m.
Also, it depends on what light you measure. Waves of blue light penetrate way deeper than red light.