0 FEET: EPIPELAGIC ZONE
Ample sunlight penetrates down to 650 feet, making photosynthesis possible. With abundant plant life (read: food), this zone is the most densely populated with fish.
220 feet: Depth at which compressed air becomes toxic and can cause seizures in divers.
558 feet: Only two people have held their breath to this depth: Audrey Mestre, who died in 2002 when her equipment failed; and her husband, Pipin Ferreras, who tied her unofficial dive record one year later.
656 FEET: MESOPELAGIC ZONE
Too deep to support photosynthesis: The fish that survive here are sit-and-wait predators that tend to have large mouths and specialized retinas to increase light reception.
660 feet: Maximum diving depth of the Pacific white-sided dolphin.
1,010 feet: Scuba-diving record set by Brit diver John Bennett in 2001.
1,640 feet: Maximum diving depth of the blue whale.
1,969 feet: The Deep Sound Channel, a layer in which acoustic signals travel far and fast.
1,969 feet: Maximum diving depth of nuclear-powered attack subs.
3281 FEET: BATHYPELAGIC ZONE
The ocean is dark at this level; the only glow is from bioluminescent animals. There are no living plants, and creatures subsist by eating the debris that falls from the levels above, including dead or dying fish and plankton.
3,281 feet: Maximum diving depth of the sperm whale. To navigate in the darkness, these whales emit high pitched sounds and use echoes to determine the location of prey.
3,937 feet: Maximum diving depth of the leatherback sea turtle.
4,000 feet: The domain of the Pacific sleeper shark, the largest toothed shark ever photographed. It can reach lengths of 28 feet.
5,000 feet: A new species of jellyfish, about the size of a thumbnail, was caught at this depth during Emory Kristof's 2002 Arctic expedition.
5,187 feet: Maximum diving depth of the elephant seal.
6,562 feet: Maximum operating depth of the research submersibles Pisces IV and Pisces V.
8,038 feet: Depth of the hydrothermal vents at the Galápagos Rift, discovered in 1977.
8,500 feet: Kristof discovered a new species of octopus living at this depth, 500 miles west of Acapulco, Mexico.
10,500 feet: The largest cusk eel, at a mammoth 7 feet long, was observed at this depth.
12,434 feet: Average ocean depth.
12,500 feet: Depth of the wreck of the Titanic discovered by a US-French team headed by Woods Hole researcher Robert Ballard in 1985.
13,123 FEET: ABYSSOPELAGIC ZONE
In the pitch-dark of the abyss, there is no light at all, the water temperature is near freezing. Of the few creatures found at these crushing depths, most are blind and have long tentacles - tiny invertebrates such as shrimp, basket stars, and small squids.
13,123 feet: Depth of the first transatlantic cable, laid in August 1858. The 2,500-mile cable connected Ireland and Newfoundland.
13,123 feet: Maximum operating depth of the ROV Tiburon.
14,000 feet: A lone 8-inch-long shrimp spotted at this depth in 1979 may be all we know about the deep-sea biology of the North Pole.
14,764 feet: Maximum operating depth of the research submersible Alvin. In use since 1964, Alvin was the first deep-sea sub to successfully carry passengers.
15,420 feet: Some of the deepest photos Kristof has taken are of anemones on the wreck of the Bismarck in the Atlantic Ocean.
19,685 FEET: HADOLPELAGIC ZONE
Despite the intense pressure and frigid temperature in the deepwater trenches and canyons, life still exists here, especially near hydrothermal vents on the ocean floor. Invertebrates such as starfish actually thrive.
19,685 feet: Maximum operating depth of the three-person Russian submersibles Mir I and Mir II.
26,850 feet: Deepest depth reading taken by HMS Challenger at the Mariana Trench in 1875 during the world's first oceanographic expedition. The measurement was made by lowering a weighted line to the seafloor. The Challenger stocked 144 miles of rope for this purpose.
27,460 feet: Depth of deepest-living fish ever recorded. The 8-inch-long Abyssobrotula galatheae, a species of cusk eel, was collected from the Puerto Rico Trench.
35,800 feet: Depth of the deepest manned dive. Jacques Piccard and US Navy lieutenant Don Walsh visited the Mariana Trench in the submersible Trieste on January 23, 1960. Through their porthole, Piccard and Walsh reportedly observed an animal resembling a type of flatfish that was about a foot long. The Japan Marine Science and Technology Center revisited the site with an ROV in 1995, setting a new official unmanned submersible depth record.
36,201 feet: Deepest recorded ocean depth, taken by the Soviet submersible Vityaz in 1957.
Issue 12, December 2004