Latitudinal manganese gradient dynamics associated with Earth's major ice ages.

Distinct sedimentary deposits of manganese are known to be associated with extreme glaciations in ancient environments. The redox-sensitive nature of manganese led scientists to propose theories about how oxygen and climate collaborated to cause major perturbations in the global geochemical cycle of this important metal. Temporal analyses of a large sedimentary dataset demonstrate high manganese concentrations in marine sediments were commonly associated with oxygenation events and glaciations in deep time. Here we show spatial analyses of those intervals that reveal a common pattern of relative enrichment of manganese in sediments at high latitudes during the six greatest glaciations of Earth's history. The pattern of relatively lower manganese concentrations in tropical sediments was most likely driven by ocean oxygen gradients. This manganese gradient increasingly flattened as the oxygen level rose in the atmosphere and ocean over the geological time scale. Our analyses suggest that anoxia frequently occurred during icehouse conditions, challenging the conventional wisdom of warming-driven ocean deoxygenation.