Current situation and perspectives of paleoceanography based on ages and isotopic compositions of ferromanganese crusts

Abstract

Ferromanganese crusts have been used as archives for monitoring long-term evolution of seawater chemistry throughout the Cenozoic. Because of their high metal concentrations, ferromanganese crusts are logical targets for analyzing both radiogenic and stable metal isotopes. An extensive dataset of metal isotopes is now available from ferromanganese crusts. However, further work is needed to validate age models of ferromanganese crusts and to develop frameworks to interpret the isotope signatures. This paper is intended to provide an overview of paleoceanographic study using ferromanganese crusts with special attention to their isotope records. We begin by reviewing age-dating methods of ferromanganese crusts using beryllium and osmium isotopes. Subsequent section summarizes strontium, neodymium, lead, and stable metal (such as molybdenum and thallium) isotope records of ferromanganese crusts which have been used to understand the timing of phosphatization, changes in ocean circulation patterns, and evolution of oceanic elemental cycles. Finally, we will discuss possible directions for future paleoceanographic studies using isotopic compositions of ferromanganese crusts.