Reconstruction of the geomagnetic field between 20 and 60 kyr BP from cosmogenic radionuclides in the GRIP ice core

Abstract

A pure physical model for the simulation of cosmic ray particle interactions with the Earth’s atmosphere was used to investigate the effects of a changing geomagnetic field on the production rates of cosmogenic nuclides. Analytical dependencies of the production rates of 3H, 7Be, 10Be, 14C and 36Cl on geomagnetic field intensity were developed. Applying those relations to the 10Be and 36Cl fluxes measured in the GRIP ice core, the geomagnetic field intensity for the period between 20 and 60 kyr BP was reconstructed. Comparison with remnant magnetism records from marine sediment cores shows excellent agreement. This validates the use of cosmogenic nuclides in ice cores to reconstruct geomagnetic field variations.