What is the term for the portion of the ocean where sunlight can penetrate?

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Light availability defines ocean depth zones. The portion where sunlight can penetrate enough to support photosynthesis is the euphotic zone. In this upper layer, light is strong enough for photosynthesis, fueling the growth of phytoplankton and supporting most of the ocean’s primary production. Below this layer, light fades and photosynthesis becomes limited or impossible, which is the aphotic zone. The bathyal and hadopelagic zones are deeper regions with little to no light. So, the sunlit, photosynthesis-supporting part of the ocean is the euphotic zone.