HR: 15:25h
AN: U42A-07    [PDF]
TI: Field Behavior During the {\it Next} Geomagnetic Event: Clues From Paleomagnetic and Geomagnetic Data
AU: * Hoffman, K A
EM: khoffman@calpoly.edu
AF: Cal Poly State University, Physics Department, San Luis Obispo, CA 93407 United States
AB: Although it is unclear whether the present weakening of the axial dipole will ultimately result in a geomagnetic event or complete reversal of polarity, particular subsets of paleomagnetic transition data suggest that the pattern of flux emanating from the core today is not so unlike that which dominated transitional fields over the past few million years. We focus first on the Plio-Pleistocene records obtained from lavas erupted at the Society Island hotspot. With the newly-reported record of the 600 ka Big Lost Event exposed on Tahiti, there now exist five reasonably detailed transition records spanning 2.3 myr between 2.9 Ma and 0.6 Ma from the islands of Tahiti and Huahine. All five of these records contain a sequential clustering of virtual geomagnetic poles (VGPs) found near western Australia. The same is the case for several records of the Matuyama-Brunhes transition, the last reversal, from sites about the globe. In order to compare these findings with the modern-day and historic fields, first, at the Society Island hotspot, we removed the axial dipole term from the 1900, 1950, and 2000 IGRF models and found that the three associated "transitional" south VGPs resided within the same Australian patch. Applying these non-axial dipole field models to sites throughout Australasia, we again found the synthetic VGPs to lie along a narrow north-south line through western Australia. In fact, VGPs associated with the modern-day non-dipole field for the same Australasian sites run in a similar fashion through Australia. These findings suggest strongly that the location of the modeled VGPs is not simply fortuitous, due to the current orientation of the geocentric equatorial dipole. Rather they suggest strongly that the flux pattern involved is far more complex, yet stationary, and most likely due to physical variations of the core-mantle boundary region beneath Australasia. Given this correspondence between recorded transitional paleomagnetic data and modeled geomagnetic data, we propose that the onset of an event or reversal attempt involves the near-vanishing of the axial dipole, leaving a residual field whose source is the pattern of flux fixed to the mantle about the surface of the core. Since it appears that the basic features of this pattern are long-lived, serious investigation of global field changes associated with the next geomagnetic event may now be possible.
DE: 1513 Geomagnetic excursions
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
DE: 8115 Core processes (1507)
SC: U
MN: 2003 Fall Meeting