factsheethead_blue.GIF (8610 bytes)

THE ABYSS

Prentice K. Stout
P 858

What's it like at the bottom of the ocean? That depends on what ocean you're talking about and exactly where on that ocean you happen to be located.

If you are over:

the Mariana Trench in the North Pacific, the depth will be 35,800 feet.
the TongaKermadec Trench in the South Pacific, the depth will be 34,876 feet.
the Puerto Rico Trench in the North Atlantic, the depth will be 27,500 feet.
the Sandwich Trench in the South Atlantic, the depth will be 27,144 feet.

These statistics are impressive if you consider that Mount Everest, the tallest mountain in the world, is 29,028 feet high.

Let's establish some basic concepts. The ocean contour is divided into three domains: the continental shelf, the continental slope, and the deep ocean basins. The average depth of the sea floor is 4,000 meters Cone meter + 3.28 feet).

The abyss of the oceans is characterized by intense cold, 0.6 C to 3.5 C (water freezes at O C), no light, and lots of pressure. The tremendous pressure is due to the weight of the water column at the particular depth you happen to be measuring. As you proceed down, the pressure increases 15 pounds per square inch for every 30 feet. Spend a few minutes with your pocket calculator estimating the pressure at each of the great depths of the oceans mentioned above.

At these great depths, the pressure can equal about 8 tons per square inch and that pressure, because of the liquid nature of water, is exerted in all directions. One would think that nothing could live in this extremely hostile environment. But research has proven this to be untrue. Creatures with names such as the whip tail gulper eel, sea cucumber, grenadier or rattail fish, a host of marine isopods, and the glass sponge, Eupleetella asperfillum, live down there. There is an intriguing story connected with this species of glass sponge. An abyssal shrimp enters into the sponge's hollow interior and, after feeding on the food the sponge takes in, grows too large to escape. The shrimp is doomed to a life of captivity within the sponge. In Japan, these sponges, with their imprisoned shrimp, were once given as wedding presents—symbols of everlasting matrimonial union.

What is the bottom of these depths really like? The answer is ooze! Not the kind you associate with the muddy bottom of a pond or saltwater marsh. It's a grayish, yellowish, tarnish ooze. A handful soon makes it apparent that it is butterlike, slippery, and mighty cold. With such attractive qualities, what use can it have for mankind? Ooze is composed of particles of sediments, the dead bodies of microscopic plankton which, year after year, eon after eon, fall to the bottom. These age-old sediments are a help to scientists. Over the millions of years that these sediments have been falling, the "snowfall" has deposited a biological history of life in the ocean. There are several kinds of ooze, each with its "index fossils." Certain fossils are keys to geological periods in the earth's history, thus, their presence offers the scientist an index of life that existed during a certain time. This fossil record also tells much about the age of the abyssal deposits.

Briefly, there are four types of ooze: red clay, globigerina ooze, radiolarian ooze, and pteropod ooze. Each kind of ooze is made of different substances and seems to be specific, to a certain degree, to various parts of the earth's oceans. Petroleum industry scientists are most interested in reading geologic history in these oozes, for certain types are more apt to be oilbearing than others, while other types may be harder or softer to drill through. Scientists who study these fossils are called micro paleontologists (micro, "small"; pale, from the Greek "palai," meaning "ancient, old in years").

In 1977, some very interesting discoveries were made on the deep ocean floor 500 miles off the coast of Ecuador and 215 miles east of the Galapagos Islands. Drs. Robert Ballard and Fred Grassle, of the Woods Hole Oceanographic Institution, descended to the Galapagos Rift, a rugged split in the ocean floor. There, in the minisub Alvin, 2,500 meters beneath the surface and subjected to pressures of more than 3,650 pounds per square inch, these men discovered new forms of life. On this rough, dark seascape they found that warm water, heated from the earth's core, was erupting to the earth's crust. The warm springs, called "hydrothermal vents," changed the surrounding water (at 2C) to temperatures that approached 10 to 15C. On and near these vents they found worms, footlong clams, mussels, and crabs. Perhaps most fascinating was a lovely orange creature with long filamentsthey called it "dandelion" for its strong resemblance to the flower. How could these animals exist at that depth, with no sun, and therefore no plant life on which to feed? Research found the answer chemosynthesis (chemo, "chemical"; synthesis, "making from") held the clue. The deep ocean bacteria, always present and a potential food source, were being nourished by a chemical synthesis of hydrogen sulfide (the gas that smells like rotten eggs) and other substances in the heated water that issued from these vents. Thus, the bacteria grew and became food for the mussels and clams. The "dandelion" upon further study proved to be a colony of organisms related to the Portuguese manofwar and belonging to the family Rhodaliidae (from the Greek "rhodon," "a rose"; hence, red). Perhaps of equal interest were the large red tube worms belonging to the family Vertimentiferan (vert, from the Latin "vertex," meaning "twining, whirling"). These worms had attained lengths of up to three metersabout 9.8 feet long.

The oceanic world gives up its secrets reluctantly and not without much effort on the part of man. There is still a great deal to be learned from the abyss. Such study will exact a great deal of research and planning on the part of those who will venture into this world of cold, pressure, and eternal darkness.

Return to Rhode Island Sea Grant Fact Sheets