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The deep sea seems almost to belong to another planet. Bizarre, little understood creatures live there in perpetual darkness and under mountainous pressures — vampire squids, sawtooth eels, sea spiders. They and many others have largely eluded science or appear for a tantalizing moment before the headlamps of submersibles only to vanish again.
Despite decades of exploration, less than a tenth of the deep ocean realm has been explored, despite it being the largest habitat for life on Earth. There are a lot of sea monsters yet to be discovered.
The deep sea is invisible to anyone on a ship, of course. It's just the open ocean. But there are subtle signs even on the surface that great depths lie below. Creatures like great whales, albatrosses, tuna and sharks may be seen. But no sea gulls, harbor seals or otters are found in these expanses. To live in this part of the ocean, an animal has to swim all the time. There is no place to rest or hide from natural enemies.
The Abyss
Technically speaking, the deep sea is any place away from coasts and beyond the continental shelves where the seafloor drops away to extreme depths — miles deep. These vast regions were once considered lifeless or perhaps inhabited by monstrous squids and little else.
Explorers using remotely operated submersible vehicles have begun to penetrate these dark depths, and they have discovered bizarre gardens rife with life around smoking hydrothermal vents. The gardens host entire communities of life that never see the sun and have no need of it. Giant tube worms, clams and shrimp live all around these "black smoker" vents, surviving off the exotic primitive "archaea," bacteria-like organisms that extract a living from the chemicals dissolved in the hot mineral-rich waters spewing from the seafloor.
The minerals that come out of the smoker vents are not only of interest to sea life. Humans are preparing to mine the thick crusts created by the vents for their gold, silver and copper. Some geologists suspect that all the major copper deposits now found on land are actually the fossilized remains of deep sea smoker vents. Already mineral rights have been granted to a company to look for metal-rich lodes over 1,500 square miles (4,000 square kilometers) of the Bismarck Sea, north of New Guinea, according to a report by the American Association for the Advancement of Science.
But even far from these extraordinary gardens, also under more than 10,000 feet of water, the muddy expanses of the seafloor can still harbor animals — like sea urchins and shrimp that live off the debris that slowly descends from the more productive waters high above. There have even been discoveries of deep-sea corals growing on ledges of rock 650 to 5,000 feet deep off the Atlantic coast of Canada in cold waters — a far cry from what most people think of when they hear the words "coral reef."
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Poison Zones
Unfortunately, the old idea that the deep sea is lifeless has led to a long history of dumping some of the most toxic waste into the seas. Though now illegal, not long ago everything from sewage sludge to drums of radioactive waste were dumped into the deep sea. Hydrocarbons from ocean drilling operations are still a source of deep-sea pollution.
According to the United Nations Environment Program (UNEP), dumping accounts for about 10 percent of all pollution to the deep sea. The top source of pollution is runoff from land (44 percent), followed by air pollution (33 percent) and losses from shipping (12 percent). Offshore oil and gas exploration and production adds about 1 percent more of toxic chemicals — usually concentrated in areas like the Gulf of Mexico and the North Sea, where they cause a far greater proportion of the deep-sea pollution.
Global Storehouse
The deep sea also plays another role often overlooked in the operation of Earth: storing heat. Seawater that is warmed at the surface eventually becomes dense with salts and sinks into the deep sea. There it retains heat that can take centuries to come again to the surface. This is a critical concern regarding global warming, since the only way to truly cool down Earth is to expel the heat trapped by the greenhouse effect into space. That's harder to do when the heat is trapped in the deep sea and taking its time coming up again.
Finally, there's the matter of carbon dioxide, the most notorious greenhouse gas. Microscopic ocean plants account for about half of all the carbon dioxide-absorbing photosynthesis on the planet. A lot of the carbon trapped by sea life near the surface eventually drops to the seafloor and is buried there — sequestered away from the atmosphere and out of the global warming equation for a long time. Without this giant carbon dioxide sink, the gas would increase faster in the atmosphere and global warming would accelerate even more quickly than it already is.
So no matter how otherworldly the deep sea may seem, it is actually an essential part of life everywhere on planet Earth.