Mean mixed depth of sediments: The wherefore and the why

The activities and consequently the bioturbational effects of deposit-feeding organisms are largely restricted to a narrow surficial zone of marine sediments with a worldwide, environmentally invariant mean of 9.8 cm with a standard deviation of 4.5 cm. Currently available theories of infaunal behavior cannot predict quantitatively this observation. A new simple model that accounts for the feedback between resource (food) abundance, its reactivity, and the intensity of bioturbation leads to a quantitative estimate of 9.7 cm. This model constitutes a fundamental advance in our understanding bioturbation.