swuklink.com: The Abyssal Plain

Because of the great pressures exerted by the water in the depths of the ocean, there are only five manned craft in the world which are able to descend to depths such as that of the abyssal plain. The number of people who have descended to these ocean depths is comparable to the number who have travelled into space. Because of its inacessability, this vast volume of the planet, and the life it contains in particular, has been studied very little.

One such submersible is the "Alvin" of the US Navy's Submarine Development Squadron 5 (formerly Submarine Development Group 1) which can descend to depths of 4,500 metres (three miles). Its two-metre titanium sphere with tiny portholes can just hold the pilot and two observers.

see also: Oceans

In the middle of the abyssal plains are the mid-ocean ridges which rise almost two miles from the ocean floor and extend for almost 24,000 miles. This submerged mountain range is the largest geological feature on the planet Earth. These are formed by the upwelling of molten lava from beneath the earth's crust and are still active.

Superheated water is pushed from the crust through vents at temperatures of over three hundred degrees centigrade. As the mineral-laden water cools rapidly, the minerals are depositted around the vents to form huge chimneys. The mid-ocean ridges have only been explored since the 1970s but the little exploration which has been done here has produced remarkable results. Among the cocktail dissolved in the water of the submarine spouts is hydrogen sulfide (H₂S) which is lethal to most living organisms on the surface. The hydrogen sulfide can be brocken down to release energy. In the utter blackness of the ocean deeps, the only energy which can be derived from the sunlight is in the form of the detritus from living organisms which drifts slowly into the deeps. Around the vents, the hydrogen sulfide has been found to support communities of living organisms which were first discovered in 1979. Colonies of a species of polychaete worm in their white tubes have been found attached the the walls of some of the chimneys themselves in water at a scalding teperature of 80°C.

Whole communities of creatures have been found around the deep ocean vents. Large mussels, white crabs devoid of pigment and colonies of giant red tube worms 4cm across and two metres in length. The apex predators in these communities are fish. Investigation of the bodies of these tubeworms and mussels showed that they live in symbiosis with bacteria which can extract energy from the solution of sulfides in which the animals are constantly bathed. In the absence of the energy of the sun, these bacteria support communities numbering over five hundred species.

Until the discovery of the profuse communities supported by the sulfide processing bacteria of the ocean's deep volcanic vents, all life on Earth was thought to be dependant on the conversion of the energy of the sun by photosynthesis. Since the first discovery of these submerged communities in 1979, a new species has been discovered about every ten days. This ability of complex organisms to survive in the ocean depths utilising the chemistry of geothermal vents has had a profound influence on thought about life on the outer planets of the solar system and beyond. These communities have also caused biologists to reconsider how life evolved in the harsh conditions of the Earth's oceans before the benign bioshpere which we know developed.

Although the vents are ever present along the mid-ocean ridges, individual vents have a life measured in decades and as they become inactive, the living communities which they support have to migrate to new vents.

The number of large animals found here are only about a thousandth of those found on the continental shelf. Fish have been found throughout the depths of the oceans and most of those on the bed belong to the "rat-tail" family. The skins of these are equipped with numerous sensory pits allowing them to smell the rotting carcasses which have sunk down to the ocean bed.

This time-line has been generated for this page from our general time-line
which you can view by clicking here or on the dates in the left-hand column.

To view links to related pages, click here

Links to Other Pages on This Site

FISH
OCEANS

Links to Other Sites
. . . . . the inclusion of these links to other sites is for the interest and convenience of visitors to this site only and does not imply any endorsement of the products or services offered by the individuals or organisations involved nor the accuracy of the information contained therein . . . . .

Wikipedia