Variation of the Fe/Mn ratio of ferromanganese crusts from the Central North Pacific: implication for paleoclimate changes

Abstract Contentsn of Fe, Mn and other elements in four ferromaganese crusts recovered from the ceteral. North Pacific are analyzed at high depth-resolution by electron microprobe for reconstruting factors controlling their deposition. Maganese (Iv) in hydrogenetic ferromaganese crusts is mainly supplied as collidal precipitates from the Oxygen Minimum zone (OMZ), which consentrates high amounts of disolved Mn (II). The iron is derived from carbonate dissolution and silcate particles of eolian dust. An increase in paleoprodutivety during cooler climate would potentially lead to adecrease in Mn despostion and due to enlargement of the OMZ which has a “temporary storage” effect for Mn. On the other hand, not affected by the OMZ, the iron enering the Fe-Mn crust would likely increase with the eolian dust input and surface productivity at glacial stages. As a result, the increasing FE/Mn ratio shoud indicate a cooling climate. This is a sopported by the following opservations. In the profile of the past 1 Ma,...