Figure 7. Schematic diagram indicating the proposed chemical conditions experienced by each of the Ca/Mn groups identified in Figure 2. The irregular- shaped particles represent solids, the circles enclosing the Mn⁺⁺ indicate dissolved Mn species, and the dashed line around the Mn oxides in Ca/Mn groups III and IV indicates that some Mn oxides would be dissolving in the water column. The Mn intercepts in Figure 3 suggest that at least some Mn species, not correlated with Ca, are sufficiently refractory that they remain even under strongly reducing conditions, possibly even at relatively low pH.