Abyssal Zone

The abyssal zone is the layer of open ocean lying at extreme depth, generally between about 4,000 and 6,000 meters, between the shallower bathyal zone above and the hadal zone of ocean trenches below. It covers a large share of the planet, spanning most of the ocean floor and roughly sixty percent of Earth's surface. The zone sits in permanent darkness, so no sunlight reaches it and no photosynthesis can occur there. The little oxygen present largely traces back to cold water that sank from the polar surface long ago, leaving much of the seafloor short of dissolved oxygen. Water temperature stays close to freezing, around two to three degrees Celsius, while pressure builds to roughly seven hundred fifty atmospheres. Nutrients such as nitrogen, phosphorus and silica collect here from organic matter drifting down from the productive waters far above, feeding the sparse, specialized life that survives the cold, dark, high pressure conditions.