Magnetic Measurements of Bacterial Activity in Mid Oceanic Ridge Basalt Samples.

HR: 09:15h
AN: GP21C-06 [Abstracts]
TI: Magnetic Measurements of Bacterial Activity in Mid Oceanic Ridge Basalt Samples.
AU: * Carlut, J
EM: jcarlut@geologie.ens.fr
AF: Ecole normale SupＳieure, UMR 8538, 24 rue Lhomond, PARIS, 75005 France
AU: Horen, H
EM: horen@geologie.ens.fr
AF: Ecole normale SupＳieure, UMR 8538, 24 rue Lhomond, PARIS, 75005 France
AU: Brunet, F
EM: brunet@geologie.ens.fr
AF: Ecole normale SupＳieure, UMR 8538, 24 rue Lhomond, PARIS, 75005 France
AU: Janots, D
EM: janots@geologie.ens.fr
AF: Ecole normale SupＳieure, UMR 8538, 24 rue Lhomond, PARIS, 75005 France
AU: Pozzi, J
EM: pozzi@geologie.ens.fr
AF: Ecole normale SupＳieure, UMR 8538, 24 rue Lhomond, PARIS, 75005 France
AB: Magnetic properties of the young oceanic crust gives insights on the 3D structure at ridges axis and on variations of the Earth's magnetic field. Accurate interpretations depend on our understanding of the magnetic stability of titanomagnetite crystals carrying the magnetic signal. The mean remanent intensity of young ocean basalts shows significant variations with age and it has been suggested that rapid chemical alteration of titanomagnetite could be responsible. Ubiquitous presence of bacteria in deep marine environment and their ability to interact with iron oxides suggest a possible important impact of these life forms on the stability of titanomagnetites. In vivo experiments have been conducted on more than 15 fresh lava macro samples with a batch of selected sulfate reducing bacteria of the desulfovibrio genus, relevant to the deep biosphere. Remanent magnetization of samples was measured at regular time interval, in addition to more complete magnetic and chemical characterization at beginning and end of experiments. After a few months results show a significant contribution of bacterial activity on magnetic properties of samples, in particular a well defined drop in remanence. Our results suggest a strong impact of bacteria on the alteration rate of iron oxides carrying the magnetic signal within the oceanic crust.
DE: 1505 Biomagnetism
DE: 1540 Rock and mineral magnetism
DE: 0400 Biogeosciences
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting