Late Weichselian geomagnetic ‘reversal’ as a possible example of the reinforcement syndrome

Abstract

A LATE Weichselian geomagnetic reversal has been reported^1,2 from Sweden. Mörner and Lanser³ believed the Swedish reversed palaeomagnetic record to be a “real dipole magnetic reversal of greatest significance for global correlations” and to have been established and well dated in Canada, the North Atlantic and New Zealand and tentatively recognised in Czechoslovakia, the Northern Pacific, the Gulf of Mexico, Japan and France. Noël⁴ has described further palaeomagnetic results from two Swedish varved-clay cores as accurately tracing the annual behaviour of the geomagnetic event and delimiting its initiation and termination. Recognition of the event in lavas and deep sea, continental shelf, varved-clay and lake sediments has been cited as confirming the reality of the event. That previous research, particularly in Sweden, has concentrated on palaeomagnetic measurements at numerous, different late Weichselian localities. Because of the difficulties in correlating between localities, interpreting palaeomagnetic records in coarse grained sediments and deciphering coring and sedimentological complexities in single cores, we have instead studied one carefully selected site in detail. We have come to the conclusion that Swedish late Weichselian palaeomagnetic data do not record a reversal or excursion of the geomagnetic field, but demonstrate that the Swedish geomagnetic field has been of normal polarity since 13,000 yr BP. The Swedish late Weichselian reversal had thus become an example of Watkins'⁵ “reinforcement syndrome”.