The sliver of ocean less than 200 meters (650 feet) deep near land accounts for just 7 percent of the sea surface, but is among the most productive parts of the ocean. Human activity in coastal regions on land and in the ocean accounts for nearly two-thirds of global GDP, but runoff, pollution, and overfishing put many of these resources at risk, while sea level rise and storm surges threaten cities and other infrastructure near the ocean.
The surface ocean extends from 0 to roughly 100 meters (330 feet) depth across the entire ocean. This is where the ocean meets the atmosphere and absorbs carbon dioxide from the aira key link in the planetary carbon cycle and primary cause of ocean acidification.
The mid-water stretches from the bottom of the surface ocean to about 1,000 meters (3,000 feet) depth. The darkness that pervades this region hides many of the organisms that inhabit it, but recent studies have found that it may hold the largest mass of fish on the planet. Currents here connect the surface to the deep ocean, an important part of Earth's carbon cycle and climate system.
The deep ocean extends from 1,000 to 6,000 meters (20,000 feet) and constitutes most of the ocean's volume as well as the largest living space on Earth. The crushing pressure, permanent darkness, and vast expanse of the deep ocean combine to make it one of the least explored parts of the planet. From 6,000 meters to nearly 11,000 meters (nearly 7 miles)50 percent of the ocean's depth?is a patchwork of extremely deep Hadal Zone regions, which are even less understood.
Whether it's made of rock, mud, coral or sand, the seafloor is just as much a part of the ocean as the water above it. Water that percolates down through cracks often comes back to the surface of the seafloor, heated and chemically altered, at hydrothermal vents or cold seeps, where it helps support unique life forms that survive on the chemicals in the water.
Humans are leaving a large and growing imprint on Earth's largest feature, the ocean. Carbon dioxide emissions are warming and acidifying ocean waters, runoff and fishing are decimating coral reefs, and warming waters are threatening critical species with extinction. Even far from the surface and far from land, evidence of human activity is often close at hand?synthetic chemicals have been found in many fish and trash can be found even in the deepest parts of the ocean. The good news is that we humans can make a difference by working to conserve the ocean.