Origin of deep-ocean polymetallic nodules

Determine whether the formation of deep-ocean polymetallic (Fe–Mn) nodules is predominantly abiotic (hydrogenetic, diagenetic, or mixed) or biogenic, and quantify the relative contributions of microbial catalysis versus purely chemical precipitation in their growth.

Background

Polymetallic nodules are widespread Fe–Mn concretions that form on abyssal plains under very low sedimentation rates. Abiotic models include hydrogenetic precipitation from seawater and diagenetic growth within sediments; biogenic models invoke microbial oxidation of Mn(II) and Fe(II) and bacterial structuring of micronodules.

The review notes extensive study and economic interest, yet emphasizes ongoing debate over whether nodules are primarily abiotic or biogenic, motivating further high-resolution analyses to resolve their origin.