The abyss

abysses The abyss refers to the deep ocean floor beyond 2,000 metres, where complete darkness prevails.

The deepest point on the Earth is the Mariana Trench in the Pacific Ocean, which reaches 10,916 metres. The great ocean trenches represent only 2% of the ocean’s floor.
The deep ocean floor of the abyss is mostly made up of abyssal plains, which range over vast areas and are covered with a layer of sediment. They can be between 4,000 and 6,000 metres deep.

These plains have geological features caused by the movements of tectonic plates (the Earth’s crust):

where the plates are moving apart, magma has erupted from the ocean floor to form ocean ridges (e.g. the Mid-Atlantic Ridge).
where the plates are colliding, one can dive under the other to form a trench (e.g. the Mariana, Puerto Rico or de Bird trenches, etc.)

In the ocean, pressure increases with depth. On the surface of the sea, the pressure is on average a fraction over 1 bar. In the abyss, the pressure reaches 600 bars (and over 1,000 bars in the great ocean trenches below 10,000 m). In other terms this represents more than one tonne/cm².

The exploration of the abyss

To this day, less that 2% of the deep ocean floor has been explored. Man first began his exploration of the abyss in the 19th century. Between 1839 and 1843, James Clark ROSS’ vessels brought up seastars and worms from a depth of 7 km beneath the ocean. Between 1872 and 1876, a large-scale marine research expedition was carried out by scientists aboard the British Royal Navy ship H.M.S. Challenger: a large number of soundings were made and innumerable samples were brought up from the deep. In 1951 the ship Challenger II detected the deepest point in the ocean using echo sounding, 11 km below the surface. This point thus became known as "Challenger Deep".

The first manned descent (in a bathysphere suspended from a cable) was carried out by the zoologist William BEEBE and the enginer Otis BARTON in 1934. Twenty-six years later Don WALSH and Jacques PICCARD, onboard the bathyscape Trieste, which was designed by PICCARD’s father, reached a depth of 10,912 metres in the Mariana trench (Pacific Ocean). No-one has gone so deep since. However, the Japanese ROV (Remote operated vehicle) KAIKO recorded a trough extending to 11,034 metres at the edge of the Mariana trench.

While these deep ocean trenches are only rarely visited, the abyssal plains between 3,000 and 6,000 metres are explored and studied using various diving vehicles, both manned and unmanned. And these abyssal plains have provided us with plenty of surprises...

Life in the abyss

Despite the extreme conditions (total darkness making plant life impossible, colossal pressure, lack of food, extreme temperature, etc.), explorers of the abyss have discovered numerous forms of life.

Practically the only food available on the deep ocean floor is the "snow" of organic matter falling from above. This marine snow is organic matter from the surface which supplies the ocean nutrient cycles (especially upwellings).

The deep ocean floor is home to a range of invertebrates and fish while bioluminescent fish, molluscs, gelatinous organisms such as jellyfish and microrganisms swim in the open water.

At the end of the 1970s, in the vicinity of the Galapagos Islands, 2,500 metres below sea level close to the mid-ocean ridge, the submarine Alvin discovered a wealth of life and new species, including giant tube worms, shellfish of 20 cm and white shelled crabs. Biologists dubbed these concentrations of life ‘ocean oases’ because of their contrast with the sparsely populated abyssal plains.Scientists recorded that these oases of animal life flourished near hydrothermal vents, suggesting a link between hydrothermal fluid and animal life. Such oases can be found around hot or cold fluid vents.

The abyss and the themes of the Citizen of the Ocean

Abyssal ecosytems are very important for the biosphere’s carbon, nitrogen and phosporous cycles.

This ecosystem, which we barely understand, produces goods: biodiversity, chemicals with promising therapeutic or engineering qualities (molecular biology, biotransformation), oil, potential new energy sources such as methane clathrate, minerals and precious metals, fishing resources and so on.

But the abyss is sensitive to pollution or habitat changes. In addition, species interdependance is even more marked.The ocean floor also provides us with insights into the history of our planet, how its geology and conditions for life have evolved.

The deep ocean floor has an important strategic role. However, since it is mostly located in international waters, its exploitation is subject to few regulatory constraints. Only a small number of countries have the exploration capability and the intention to exploit it. The fair and sustainable exploitation of deep ocean resources has therefore become an important ocean management issue.

The preservation of the Global Ocean includes the preservation of the deep ocean floor

Sources

The references in the section "A Nausicaa, l'extraordinaire richesse des abysses", as well as the following:

ARTICLES

Hervé MORIN. Les Abysses sont très sensibles aux atteintes de la biodiversité. Monde Of January, 2nd, 2008.
Gaëtane de LANSALUT. L'Entrepreneur des abysses. Le Monde 2 of August 27th, 2007.
Franck ZAL. Les Sources abyssales, berceau de la vie ? Recherche, # 355,July-August, 2002

BOOKS

B. ARNAUD et IFREMER. Explorons les grands fonds sous-marins. Ed. Rouge et Or, 1991
T. DAY. adapt. S. WEINBERG. Planétoscope Océans. Nathan, 2000
P. KOHLER. Les Abysses. Ed. Fleurus, coll. Encyclopédie Fleurus, 1995
C. CAUSSE. Grande Encyclopédie Fleurus de la Mer, 2003
L. LAUBIER. Des oasis au fond des mers. Ed. Rocher,1986
L. LAUBIER. Ténèbres océanes. Le triomphe de la vie dans les abysses. Ed.Buchet/Castel,2008
D. REYSS. Dans la nuit des abysses : au fond des océans.Ed. Gallimard, coll. Découverte-Nature, 1990
C. NOUVIAN. Abysses. Ed. Fayard, 2006
R. HEKINIAN et N. BINARD. Le Feu des abysses. Ed.Quae, 2008
M. GROSS. La Vie excentrique : Voyage dans les mondes extrêmes. Ed. Belin/Pour la Science, 2003
K. FUJIOKA, A. TAIRA, K. KOBAYASHI. A moins 6 000 m : l'exploration des fosses japonaises, photographies des plongées du submersible Nautile dans les fosses de subduction du Japon. Ed. University of Tokyo Press/IFREMER/CNRS, 1988