What is the euphotic zone?
Light must be present for photosynthesis to occur, but the amount of sunlight able to penetrate the water column decreases with depth. The body of water with enough light for photosynthesis to occur is called the euphotic zone and ends at a depth where there is approximately one percent of the light intensity found at the ocean surface. This depth changes with a number of factors. The length of day, cloudiness, and turbidity all affect the depth of the euphotic zone. Turbidity is a measure of how much suspended matter is in the water and it helps define the depth sunlight can reach. Seasonal winds and storms can increase turbidity, thereby decreasing the euphotic zone. The euphotic zone is much shallower in coastal waters (20-35m) than in the open ocean (100-200m). The depth of the euphotic zone tends to correlate well with the level of primary productivity since light availability is a major limiting factor of photosynthesis in the ocean.
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