B2. Solar radiation through water

Solar radiation is the primary source of energy on Earth and affects all the layers of water. When sunlight reaches the water surface:

• part is reflected back to the atmosphere. How much penetrates depends on the angle at which the rays strike the surface: maximum penetration when the rays fall perpendicularly (angle 90° to the surface), and less when they strike at a slant (low sun, near poles or early morning/evening, when much is reflected). Calm water reflects less than choppy water at a glancing angle;
• part is absorbed by the water, by suspended particles and by aquatic plants;
• part is scattered, and so penetrates deeper in many directions.

As the depth increases, the light intensity gradually decreases, so the ocean is divided into zones:

Marine organisms live in each zone according to their ability to adapt to the amount of available light.