8 
water television has greatly increased the discovery of manganese 
nodule deposits. As more deposits have been found, more information 
has become available concerning the nature of the ocean floor where 
high concentrations are most likely to be found. In general, the nodules 
are found predominantly in areas of oxygen-rich water and low sedi- 
mentation. Areas of low sedimentation are generally in deep regions of 
the ocean, farthest from land and volcanic or high biological activity. 
Manganese nodules have also been discovered in Lake Michigan.* 
Since nodules are found mainly on the sediment surface, or partially 
buried, and form much more slowly than sediment accumulates, there 
is some uncertainty as to what prevents their burial. Some investigators 
suggest that deep sea predators feed on microorganisms living on the 
nodules and nudge the nodules, keeping them on the surface. Others 
suggest that the microorganisms themselves keep the nodules buoyed 
up. The decrease of nodules with depth in the sediment (Fig. 2) may be 
explained by dissolution of the metal oxides after burial due to the 
different geochemical environment of the seafloor. 
8 Rossman, R., and H. Callander. Manganese nodules in Lake Michigan. Science, y. 162, 
1968, pp. 1123-1124. 
