Apparent correlation of palaeomagnetic intensity and climatic records in deep-sea sediments

Most reports of a correlation between Pleistocene climate and geomagnetic field intensity rely strongly on the assumption that sediment natural remanent magnetic (NRM) intensity provides a record of geomagnetic field strength and is not sensitive to local changes in properties of the sediment. Critical assessment of relevant data presented here and elsewhere from deep-sea sediment cores shows that a pronounced dependence of NRM intensity on sediment composition can occur which implies that this assumption is unlikely to be generally valid. As sediment composition often reflects varying depositional conditions induced by climatic change, the significance of correlations proposed between Pleistocene palaeomagnetism and climatic indicators in deep-sea sediments may be less dramatic than sometimes supposed

Brunhes Epoch Geomagnetic Secular Variation on Marion Island: Contribution to Evidence for a Long-Term Regional Geomagnetic Secular Variation Maximum

A paleomagnetic study of 30 lavas from Marion Island, situated on the Indian-Atlantic ridge yields a value for Brunhes epoch secular variation with confidence limits so broad that no distinction can be made with present geomagnetic field behavior. When combined with similar results from the nearby Crozet Islands, however, data for over 100 separate lavas become available for analysis, facilitating an estimate of regional secular variation with narrow confidence limits. The result, which suggests that Brunhes epoch geomagnetic secular variation in this region was (at the 95 percent confidence level) higher than at present, could be explained if the present secular variation maximum south of South Africa persisted during at least the past half million years. It is concluded that values of Brunhes epoch geomagnetic secular variation may depend not only on latitude, experimental methods, and coverage of the geological interval involved, but also on proximity to long term isoporic foci. Incidental results for the survey include detection of excursions attributable to non-dipole behavior in some instances, and possible dipole tilting in other cases. © 1974, Society of Geomagnetism and Earth, Planetary and Space Sciences. All rights reserved