Deep-water organisms depend on thesurface not only for food, but also for oxy-gen (O2). If the ocean were stagnant, theoxygen below the surface would bequickly used up by respirationhowever, there is gradual thermohalinecirculation
to even the deepest parts of the sea, bringing life-giving oxygen. Tosink all the way to the deep sea, oxygen-rich surface water must become very dense, that is, cold and relatively salty (see“Vertical Motion and the Three-LayeredOcean,” p.63). This takes place at only afew locations and only occasionally. Themain places where this surface overturnreaches the bottom are in the Atlantic,south of Greenland and just north of Antarctica (Fig. 16.2). After sinking, the water spreads through the Atlantic andinto the other ocean basins. The watereventually rises to the surface and flowsback to the Atlantic, where the cycle be-gins again (Fig. 16.3). This global circula-tion pattern, called the
great oceanconveyor,
is thought to play a central role
and animallife would be impossible. Fortunately,
Castro−Huber: Marine Biology, Fourth EditionIII. Structure and Function of Marine Ecosystems16. The Ocean Depths
© The McGraw−Hill Companies, 2003
however, there is gradual
thermohalinecirculation
to even the deepest parts of the sea, bringing life-giving oxygen. Tosink all the way to the deep sea, oxygen-rich surface water must become very dense, that is, cold and relatively salty (see“Vertical Motion and the Three-LayeredOcean,” p.63). This takes place at only afew locations and only occasionally. Themain places where this surface
overturn
reaches the bottom are in the Atlantic,south of Greenland and just north of Antarctica (Fig. 16.2). After sinking, the water spreads through the Atlantic andinto the other ocean basins. The watereventually rises to the surface and flowsback to the Atlantic, where the cycle be-gins again (Fig. 16.3). This global circula-tion pattern, called the
great oceanconveyor,
is thought to play a central rolein regulating the earth’s climate. Further-more, it constantly replenishes the supply of oxygen to the deep sea. Oxygen may become depleted in some places, but by and large the ocean depths have plenty of oxygen to support life.