HR: 15:10h
AN: U42A-06    [PDF]
TI: Do The Paleomagnetic Records Tell Us Something About The Next Occurrence of a Field Reversal?
AU: * Valet, J
EM: valet@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussieu, Paris, 75252 France
AU: Herrero-Bervera, E
EM: herrero@soest.hawaii.edu
AF: SOEST Institute ofGeophysics and Planetology, Univserity of Hawaii, 1608 East West Road, Honolulu, HI 96822 United States
AB: It has been occasionnally repeated that the present collapse of the geomagnetic field would predict the future occurrence of a field reversal. The historical field variations represent a very short period of time but the archeomagnetic records tell us that a more or less regular decrease of the field has effectively been going on over the past 1 kyr. Yet this feature depends on the geographical location as a result of the competitive effects of the dipole and non dipole components. Prior to this period (roughly from 1500 to 1000yr BP) there was a field recovery which occurred more or less at a similar rate. Further back in time the field intensity changes revealed by the sedimentary records seem to exhibit large amplitude variations with time scales of a few thousand years. The closest major collapse of the field occurred 38-40 ka ago during the Laschamp event but the most detailed records indicate that other large fluctuations followed until the present period. The last major and worldwide field reversal occurred 780 kyrs ago. In this case as for other reversals, the paleomagnetic records converge to indicate a long-term decrease of the dipole prior to the transition. However this process does not appear to be regular and all detailed records (from sediments as well as from volcanics)show the existence of short-term fluctuations occurring on the millenial scale. In addition the rate of changes appears to be faster during the field recovery which immediatley follows the reversals than during the preceeding decrease of the dipole. In other words, it is evidently necessary to deal with a long time sequence (at least a few tens of thousand years) to ascertain the issue of the collapse. Thus the existing database for the archeomagnetic and paleomagnetic field tells us that no prediction can be made regarding the next occurrence of a geomagnetic reversal from the present collapse of the field.
DE: 1521 Paleointensity
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
SC: U
MN: 2003 Fall Meeting