caa a22 4500 475827732 CHVBK 20180406123833.0 cr unu---uuuuu 170329e20000301xx s 000 0 eng 10.1007/s005310050293 doi (NATIONALLICENCE)springer-10.1007/s005310050293 Hilgenfeldt K. Fachbereich Geowissenschaften, Universität Bremen, Postfach 33 0440, D-28334 Bremen, Germany e-mail: khilgenfeldt@uni-bremen.de Fax: +49-421-2187008, DE aut Diagenetic Dissolution of Biogenic Magnetite in Surface Sediments of the Benguela Upwelling System [Elektronische Daten] [K. Hilgenfeldt] Intense primary biologic productivity in the surface waters of the Benguela upwelling system provides a high supply of organic matter to the sea floor at the continental slope off Namibia and sustains extreme concentrations of magnetite producing bacteria in the top sediment layers. Biogenic magnetite is thus by far the dominant carrier of the magnetic signal in these deposits also because of a very minor input of terrigenous ferrimagnetic minerals. Reducing conditions in the sediment column cause a selective dissolution of the bacterial magnetite fraction just a few centimeters below the main mineralization horizon. This diagenetic process is documented in detail by high-resolution rock magnetic analyses and transmission electron microscopy. Concentration dependent and grain-size sensitive magnetic parameters, such as susceptibility, laboratory imparted remanences, and hysteresis data, reveal a significant drop in ferrimagnetic mineral content within the upper 10 cm of the sediments accompanied by a gradual downward coarsening of the ferrimagnetic mineral assemblage from primarily magnetic single-domain particles in the top centimeters to multi-domain grains in deeper strata. Electron microscope observations enable both an unequivocal identification of bacterial magnetite on the basis of shape and grain-size and to trace dissolution effects on the biogenic magnetic mineral component to depth. Springer-Verlag Berlin Heidelberg, 2000 Key words Marine sediments nationallicence Biogenic magnetite nationallicence Early diagenesis nationallicence Magnetite dissolution nationallicence Rock magnetic properties nationallicence https://doi.org/10.1007/s005310050293 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s005310050293 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Hilgenfeldt K. Fachbereich Geowissenschaften, Universität Bremen, Postfach 33 0440, D-28334 Bremen, Germany e-mail: khilgenfeldt@uni-bremen.de Fax: +49-421-2187008, DE aut Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer