Deep Sea

This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.

The deep sea does not begin at the seafloor. NOAA marks its start at about 200 meters down, the point at which sunlight has thinned too far to run photosynthesis. Below that line the water is, in NOAA's own words, dark, cold, food poor and subject to intense pressure. The agency gives an average temperature there of only 4 degrees Celsius and a pressure running from roughly 40 to over 110 times what the atmosphere presses on the surface. Push another 800 meters down, past 1,000 meters total, and the water is completely without light of any kind, and photosynthesis stops being possible at all rather than merely difficult. NOAA calls this stretch of ocean one of the largest, but least understood, living places on the planet, a description worth taking seriously: without sunlight to grow plants, almost nothing here survives the way a sunlit ecosystem does. Life in the deep sea either scavenges what sinks down from the lit water above or draws its energy from chemistry rather than light. This atlas keeps the Deep Sea as its own ecosystem inside the Marine biome rather than treating it as more of the same ocean, because past 200 meters the conditions, permanent dark, near freezing cold, crushing pressure, are the same from the Arctic to the equator in a way no coastal or surface marine setting shares.

This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.

Between 200 and 1,000 meters down, in what oceanographers call the twilight zone, light from the surface is fading out and darkness is closing in. NOAA states that 80 percent of the animals living at that depth are bioluminescent, meaning they generate their own light through a chemical reaction inside their bodies. That is not a rare adaptation restricted to a few strange fish. It is closer to the default condition of life at this depth, uncommon on land and yet ordinary here. NOAA notes the exact purpose is not always clear, but documents bioluminescence being put to work for finding food, for reproduction and for defense, a single trait doing several different jobs depending on the species carrying it. The scale of the number is worth pausing on: at a depth where a human eye finds almost nothing but blackness, the overwhelming majority of the animals sharing that water are quietly generating their own light, all the time, for reasons science is still working out. It reframes what an unlit ocean actually looks like from the inside. To a human observer sinking through it with no equipment, the twilight zone reads as darkness. To the animals living there, by NOAA's own figure, it is anything but dark.