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How does the euphotic zone support photosynthesis in the ocean?

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Diagram showing ocean zonation by depth and region, with labeled layers: littoral, sublittoral, bathyal, abyssal, and hadal along the seafloor, and epipelagic, mesopelagic, bathypelagic, and abyssalpelagic in open water. The littoral zone is at the high-tide mark. Vertical scale marks photic and aphotic zones from surface to 10,000 meters. — Marine ecosystem Zonation of the ocean. Note that in the littoral zone the water is at the high-tide mark.

The euphotic zone is the uppermost layer of the ocean, typically extending to depths of 80 to 100 meters, where sunlight penetration is sufficient to support photosynthesis. This zone provides the necessary light energy that phytoplankton and other phototrophs require to convert carbon dioxide and dissolved nutrients into energy-rich organic compounds.12345

The ability of this zone to sustain such productivity depends on several factors:

Light Availability: The intensity and quality of solar radiation decrease with depth due to absorption and scattering by water molecules and suspended particulates. Only the euphotic zone receives enough light for the rate of photosynthesis to exceed the rate of respiration.652
Environmental Conditions: The actual depth of the zone varies based on water turbidity, cloud cover, and the angle of the Sun.12
Biological Contribution: While benthic algae contribute to primary production, the vast majority—approximately 98 percent—is carried out by free-floating phytoplankton within this illuminated surface layer.45

Beneath the euphotic zone lies the disphotic zone, where light is present but insufficient for photosynthesis to be the dominant biological process.12