The Deep Sea

Abstract

The deep sea, or abyssal zone, is the largest single environmental zone in the world. The enormity of this zone is illustrated by the following comparative figures: 70% of the earth’s surface is covered by oceanic waters while approximately 94% of the ocean bottom and 86% of the ocean's area is in excess of depths of 2,000 meters (Bruun, 1957). In general, the physical parameters are constant at depths below 2,000 meters. The temperature variation in the principal oceans is small; from latitude of 50°N to 58°S the maximum range is only 3.6°C to 0.6°C (Sverdrup et al., 1942). At any one geographical location little seasonal variation is observed; however, there is some thermal variation with depth below 2,000 meters, since the waters immediately above the sea floor are slightly warmer (Bruun, 1957). Salinities average 34.8 ± 0.2 0/00 and vary little with the seasons either at one location or between oceans with the exception of smaller accessory seas (Bruun, 1957). The concentration of oxygen is both constant and high. Between 2,000–4,000 meters, oxygen content ranges from 6.30 to 6.34 ml/liter. Twenty to 50 meters above the bottom, down to approximately 1 meter from the bottom, oxygen concentration values range downward from 4.1 to 3.6 ml/liter (Koczy, 1954). The only light present in this region is produced by bioluminescent organisms, since light striking the ocean’s surface penetrates only a relatively short distance.