What is the euphotic zone?

The euphotic zone refers to the upper layer of a body of water where there is enough sunlight penetration to allow photosynthesis to occur. Specifically, it is defined as the area where at least 1% of the incoming sunlight penetrates, enabling aquatic plants and phytoplankton to carry out photosynthesis effectively. This zone typically extends to depths of about 200 meters in the open ocean, but can be shallower in coastal areas or in waters with a high concentration of dissolved organic matter or sediments.

The other options describe characteristics that do not apply to the euphotic zone. The first option mentions a zone with no light penetration, which would refer to deeper water layers like the aphotic zone where photosynthesis cannot occur. The description of high cloud cover does not adequately represent the conditions of the euphotic zone, as this zone's definition specifically relates to light availability rather than atmospheric conditions. Lastly, a zone where temperature is constant is misleading because the euphotic zone typically exhibits variations in temperature related to factors like sunlight and environmental conditions, rather than a consistent temperature profile.