MANGANESE NODULES FROM THE PACIFIC OCEAN: MIXTURES OF OXIC-HYDROGENETIC AND SUBOXIC-DIAGENETIC PRECIPITATES – WHY OXIC DIAGENESIS IS NEGLIGIBLE
Here we present results of high-resolution investigations of nodules from these three different Pacific regions using electron microprobes, laser-ablation ICPMS and X-ray photoelectron analysis as well as mineralogical and crystallographic methods. Our study indicates that the Peru Basin nodules were indeed formed under suboxic conditions with only a minor hydrogenetic fraction whereas the Cook Island nodules are generally hydrogenetic precipitates. In contrast to former studies, we propose that the CCZ nodules are only a mixture of oxic-hydrogenetic and suboxic-diagenetic layers, albeit with a higher hydrogenetic fraction than the Peru Basin nodules. The diagenetic layers of the CCZ nodules have mainly been formed under suboxic conditions similar to the environmental conditions currently prevailing in the Peru Basin. Furthermore, these results suggest that in the deep Pacific Ocean suboxic and oxic bottom waters alternated, probably due to recurrent shifts of surface water productivity and deep-ocean ventilation, on glacial-interglacial time scales.