Mechanisms of formation of deep-sea ferromanganese nodules: Mathematical modeling and experimental results

Our study attempts to provide insight into the physicochemical processes operating in bottom seawater and to develop mathematical models for the formation of marine nodules owing to the diffusive transport of the major elements from ambient water to the nodule. A comparison of the model results with experimental data on the growth rates and the age of nodules provided an argument in favor of a rapid-growth concept (millimeters per thousand years). The distribution of trace elements in the nodules was derived from the limited source model and appeared to be related to the process of nodule formation; therefore, it is largely identical for many of the trace elements. These results are in line with the experimental data. Both stable and radioactive isotopes show an exponential concentration profile measured in the outer layers of the nodule, which has no bearing on radioactive decay. Given these results, the earlier conclusions on the slow growth of the nodules (millimeters per million years), which were based on the interpretation of the observed isotope distribution as a result of radioactive decay, appear questionable.