HR: 1340h
AN: GP43B-0850    [Abstracts]
TI: Was the Regime of Geomagnetic Dipole Lows and Excursions Influenced by the Pleistocene Climate?
AU: * THOUVENY, N
EM: thouveny@cerege.fr
AF: CEREGE, BP80 Europole de l'Arbois, Aix en Provence, 13545 France
AU: CARCAILLET, J T
EM: carcaillet@cerege.fr
AF: CEREGE, BP80 Europole de l'Arbois, Aix en Provence, 13545 France
AU: BOURLES, D L
EM: bourles@cerege.fr
AF: CEREGE, BP80 Europole de l'Arbois, Aix en Provence, 13545 France
AU: SARACCO, G
EM: saracco@cerege.fr
AF: CEREGE, BP80 Europole de l'Arbois, Aix en Provence, 13545 France
AB: Paleomagnetic directions and relative paleointensities (NRM/ARM) as well as cosmogenic nuclide concentration (authigenic Be-10/Be-9 ratio, i.e. cosmogenic vs lithogenic isotopes adsorbed on the sedimentary particles) were measured along clayey-carbonate sequences deposited through the last 1300 kyr in high accumulation rate area of the North-East Atlantic (0-400 kyr BP) and West-Equatorial Pacific (600-1300 kyr BP). The Low Dipole Moment phases (LDM) generally match with large amplitude or even excursional deviations of paleomagnetic vector directions, at the time of excursions [Laschamp, Blake, Icelandic basin, Jama‹ca, Portuguese margin, Levantine .] or reversals [Brunhes/Matuyama, Jaramillo boundaries, Cobb Mountain]. Peaks of the Be-10/Be-9 ratio occur at the level of each LDM, or slighlty above (pDRM lock-in depth may reach ~15-20 cm, which has significant consequences for the use of LDM phases and/or excursions as global correlation markers at least at the submillennial scale). Over the last 400 kyr, paleomagnetic and geochemical evidences of the LDM very often coincide with the end of integlacial stages. Although such relationship generally cast doubts about the reliability and significance of sedimentary RPI records, this observation can be supported and extended to the last 800 kyr using other archives of the dipole moment variation: first the SINT 800 (Guyodo and Valet, 1999) but more importantly the S.E. Pacific near Sea Floor magnetization record (Gee et al. 2000). However this relationship (LDM - interglacials) can not be confirmed prior to 800 kyr BP. Complex Wavelet Analyses identify a modulation of RPI variations between periods of 80 and 120 kyr, and in few time windows, near a period of 40 kyr. A modulation between 40 and 100 kyr appears in the S.E. Pacific sea floor record and in the 600-1300 kyr window of the cosmogenic isotope records of theWest-Equatorial Pacific. Such coupling "geomagnetic field /climate" limited to the last 800 kyr, might be explained by a VDM regime triggered by variations of polar ice caps (dominated by the ~100 kyr eccentricity period), at the time of their maximum amplitude. Variations of the speed rotation due to strong polar load/unload alternation may have provoked variations of the geodynamo regime: Ice volume minimum = slower rotation = weakened geodynamo (low dipole moment) Ice volume maximum = faster rotation = enhanced geodynamo (high dipole moment).
DE: 1513 Geomagnetic excursions
DE: 1521 Paleointensity
DE: 1522 Paleomagnetic secular variation
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting