Geomagnetic field intensity during the last 60,000 years based on 10Be and 36Cl from the Summit ice cores and 14C

Based on 10Be, 36Cl and 14C records we reconstruct past changes in the geomagnetic field intensity under the assumption that radionuclide records are mainly influenced by changes in their production rates. Subsequent comparison of these records with independent geomagnetic field reconstructions allows us to assess the reliability of our approach and to identify periods where our method or the geomagnetic field reconstructions might be problematic. The geomagnetic field derived from the 10Be-flux to Summit in Central Greenland agrees well with independent geomagnetic field intensity reconstructions. However, compared to independent palaeomagnetic data the radionuclide record suggests increased geomagnetic field intensities especially for the period from 20,000 to 30,000 years BP. 36Cl from the GRIP ice core agrees well with the 10Be record for the last ice age and hence also the reconstructed geomagnetic field. Based on the tree-ring radiocarbon record it is possible to reconstruct geomagnetic field intensity changes during the Holocene. A comparison of radiocarbon-based and independent geomagnetic field reconstructions indicates that changes in the carbon cycle significantly influenced the atmospheric radiocarbon concentration before 10,000 years BP.