Sediment Accumulation and Diagenesis in the Late Quaternary Equatorial Atlantic Ocean: An Environmental Magnetic and Geochemical Perspective

Abstract

This thesis investigates 25 Late Quaternary sediment records from the central Equatorial Atlantic by rock magnetic, geochemical and stratigraphical methods. The work was performed in the framework of the Collaborative Research Center 261 The South Atlantic in the Late Quaternary: Reconstruction of Material Budgets and Current Systems funded by the Deutsche Forschungsgemeinschaft. The main objective was to analyze and distinguish terrigenous and diagenetic proxysignatures, in particular of rock magnetic parameters. All cores were correlated and dated on basis of their carbonate, iron and rock magnetic records. Magnetite coarsening and partial depletion was observed in glacial organic-rich layers, most intensely during oxygen isotope stages 6, 10 and 12. Non-magnetic and magnetic iron mineral enrichments were found below and at former and active Fe(II) / Fe(III) redox boundaries. Various new proxies quantifying magnetite reduction (ratio of Fe to magnetic susceptibility, ratio of non-ferrimagnetic to total magnetic susceptibility) and authigenesis (ratio of Fe to magnetic susceptibility) were established and found to be highly sensitive indicators of past redox conditions. Comparing these signals with the organic carbon records, it was shown, that rock magnetic, carbon and carbonate records in most parts of the Equatorial Atlantic are merely preservation signals. Suboxic reductive magnetite loss can be used to identify burn-down of organic carbon. The depth of the active iron redox boundary correlates with the last preserved productivity pulse (stages 2 or 6) and not with modern productivity. Two composite core profiles span the full WE and NS extension of the Equatorial Atlantic and mark zones and sources of enhanced continental and marine particle fluxes. These and more conclusions of this thesis are discussed in detail within the enclosed four published manuscripts.