A high resolution authigenic 10Be/9Be record of geomagnetic moment variations over the last 300 ka from sedimentary cores of the Portuguese margin.

Julien Carcaillet (1) , Didier Bourlès (2) , Nicolas Thouveny (2) , Maurice Arnold

1 LGCA - Laboratoire de Géodynamique des Chaines Alpines
2 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement

A high resolution study of authigenic Be isotopes (10Be and 9Be) combined with continuous relative paleointensity records has been performed along the same marine sedimentary sequences from the Portuguese margin (N.E. Atlantic) covering the past 300 ka in order to assess relationships between geomagnetic moment variations and 10Be production rate variations. A carefull examination of the various ways of taking into account environmental disturbing effects on the authigenic 10Be concentration leads to the conclusion that the most reliable proxy of cosmonuclide production rates is presently the authigenic 10Be/9Be ratio. Eight intervals of significant authigenic 10Be/9Be enhancement evidence geomagnetic moment drops related to global paleomagnetic excursions, some being already admitted, others being proposed as new geomagnetic features. Since, contrarily to sedimentary magnetic remanence, the authigenic 10Be/9Be records dipole moment variations without significant acquisition delay, it provides better constraints on their timing. Comparison of 10Be/9Be and benthic δ18O records from the same cores suggests that dipole moment lows preferentially occured during or at the end of interglacial episodes, with a quasi-period of 100 ka.

Mots clés: authigenic Be isotopes; cosmonuclides; geomagnetic dipole lows; geomagnetic excursions

Domaines: Tectonique; Géochimie

Julien Carcaillet, Didier Bourlès, Nicolas Thouveny, Maurice Arnold. A high resolution authigenic 10Be/9Be record of geomagnetic moment variations over the last 300 ka from sedimentary cores of the Portuguese margin.. Earth and Planetary Science Letters, 2004, 219, pp.397-412. ⟨hal-00099482⟩