The Aphotic Zone: Where Sunlight Never Reaches in the Ocean

Sunlight penetrates only the top ~200 meters (the epipelagic). Below that lies the aphotic zone—extending from the base of the mesopelagic (~1,000 m) to the ocean floor. Here, perpetual darkness reigns. No photosynthesis occurs; life depends on marine snow (organic detritus), chemosynthesis at hydrothermal vents, or predation. Temperatures hover near freezing, pressure is crushing, yet bizarre creatures thrive: anglerfish, giant squid, vampire squid, and countless microbial communities. The aphotic zone comprises over 90% of the ocean's volume—Earth's largest habitat.