The relationships of sediments, life and water in a marine basin

Benthic animals are essentially absent at the deepest part of Santa Barbara Basin where the oxygen content of the bottom water is very low and where hydrogen sulphide is present in surface layers of the sediments. Past periods of similarly barren seafloor in the area are recorded by the presence of laminated sediments in cores. These periods are alternated with others when benthic megafauna was sufficiently abundant to mix and homogenize the sediments. The presence or absence of benthic megafauna in the basin appears to be controlled by small differences in the content of oxygen in bottom waters. It is inferred that periodically oxygen contents greater than 0·1 ml/l result from the inflow of larger than ordinary quantities of new basin water, which in turn is permitted by greater than normal mixing of basin waters by standing internal waves.