HR: 0800h
AN: GP31B-0835    [Abstracts]
TI: Volcanic Influence on the Susceptibility Signal: a Case Study in Indian Ocean
AU: * Salome, A
EM: salome@ipgp.jussieu.fr
AF: IPG Paris, 4 place Jussieu, Paris, 75252 France
AU: Meynadier, L
EM: meynad@ipgp.jussieu.fr
AF: IPG Paris, 4 place Jussieu, Paris, 75252 France
AU: Allegre, C
EM: allegre@ipgp.jussieu.fr
AF: IPG Paris, 4 place Jussieu, Paris, 75252 France
AB: Magnetic susceptibility of sediments is now widely used as a climate proxy in paleoclimatic and paleoceanographic studies. The correlation between the susceptibility and the oxygen isotopic variations is either positive or negative and thus cannot be only caused by carbonate dilution. So far no convincing model has been proposed to entirely explain the dependency of the two signals. Many studies used the fact that the weathering products, which are transported by rivers or by winds to the sea, keep the signature of their source. In order to evaluate the contribution of magnetic particles from different origins to the budget of susceptibility signal, we measured mass normalized susceptibilities for sands and suspended load from the world major rivers and from rivers draining volcanic lithologies. We found that weathering products transported by rivers which drain volcanic terrains have a susceptibility signal which is 10 to 100 fold higher than for granites. Taking into account the size of river basins, their lithology and the fact that the weathering rates of basalts are much higher than that of continental silicates, the contribution of volcanic particles to the susceptibility of oceanic sediments is estimated to be 100 to 1000 fold stronger than the contribution of particles eroded from granites. Thus we infer that the susceptibility signal of oceanic sediments is mostly dominated by basaltic inputs to the sea. With this assumption in mind, we can compare the carbonate-free susceptibility signals of several cores collected in the Arabian Sea [1,2], the Somali Basin [3] and from the Ninety East Ridge (ODP Leg 121). The time-depth calibration was based on the oxygen isotopic variations measured in the same cores. In addition we measured the susceptibility of individual samples to improve and validate the calibration between different cores with different material. Comparison of absolute values from carbonate-free sediments to our river sands data should allow us to estimate the contribution of the volcanic input for each area. Ultimately this approach should lead us to retrace the amount of alteration of volcanic terrains through time. 1 P. DeMenocal, J. Bloemendal and J. King, 1991, Proc. Ocean Drilling Program Sci. Results 117, 389-401. 2 M.W. Hounslow and B.A. Maher, 1999, J. Geophys. Res. 104, 5047-5061. 3 L. Meynadier, J.P. Valet and F.E. Grousset, 1995, Paleoceanography 10(3), 459-472.
DE: 3022 Marine sediments--processes and transport
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting