ON THE FORMATION OF THE MANGANESE MAXIMUM IN THE OXYGEN MINIMUM

A simple model that accounts for the formation of the Mn maximum in th e oxygen minimum is presented here. In this model, Mn is proposed to c ycle in a constant proportion to carbon, as do nitrogen and phosphorou s. Superimposed on the Mn-carbon cycle is the removal of Mn(II) via sc avenging onto sinking particles and transport by vertical diffusion. S cavenging is assumed to follow the rate law observed in the laboratory for Mn(II) oxidation. Manganese(II) concentrations were calculated wi th the model at stations in the Pacific and Atlantic Oceans and compar ed with measurements of dissolved Mn. All parameters in the model were based on laboratory measurements or field observations. The model rep roduced Mn(II) maxima of the correct concentration and at the correct depth. This agreement was observed at a range of oxygen concentrations . The calculations demonstrate that the Mn maximum can form because of a reduction in the pseudo-first order scavenging rate constant (k') w ithin the oxygen minimum. The value of k' will decrease in regions of the water column with low oxygen and pH (k' = k(0) [O-2] {OH-}(2)). Th ese regions will accumulate higher dissolved Mn(II) concentrations bef ore the rate of Mn(II) removal, k' [Mn(II)], equals the input from rem ineralization of POC and a steady state is reached. An additional sour ce of Mn, such as flux from continental margin sediments or dissolutio n of Mn oxides, is not necessary to account for formation of the Mn ma ximum.