Photosynthesis does not occur in bathyal waters as a rule, the zone being characteris.... bathyal condit

Salinities typically range between 34 and 36 parts per thousand in the bathyal zone, varying with local conditions of water-mass formation. Bathyal fauna reflect the generally narrow ranges of temperature and salinity that occur. At bathyal depths, currents are exceedingly slow, and in many areas bathyal waters deeper than 1,000 m (3,280 feet) are essentially stagnant, resulting in low oxygen concentrations and impoverished faunal levels. Although upwelling and countercurrents may create favourable conditions for fish and other aquatic life in some middle- to high-latitude areas, the number of individuals in a bathyal faunal assemblage is generally only about half as large as in shallow-water fauna. It has been suggested that this condition is caused by the constancy of the bathyal environmental conditions, especially its temperature. Coarser terrigenous sediments are also brought to the bathyal seafloor by sporadic turbidity currents originating in shallower areas.