The Impact of Geomagnetic Spikes on the Past Production Rates of 14C and 10Be

Abstract:

Archeomagnetic studies in the Near East report the occurrence of strong rises of geomagnetic intensity in this region ca. 980 BC and 890 BC. Here we seek corroborative evidence of such 'spike' events, lasting over only a very few decades, in the records of the past production rates of the cosmogenic nuclides ¹⁴C and ¹⁰Be. Our forward modeling strategy rests on global, time-dependent, geomagnetic spike field models feeding state-of-the-art models of cosmogenic nuclide production. We find that spike models with an energy budget in line with our current understanding of large-scale flow at Earth’s core surface fail to produce a visible imprint in the cosmonuclide records. Spike models able to reproduce the intensity levels reported in the Near East are at variance with this understanding, yet their computed impact on the production rate of ¹⁰Be intriguingly shows hints of what is measured in polar ice cores, albeit with a time shift of 3 to 4 decades. Their imprint on the record of ¹⁴C is less obvious, presumably because its production is more sensitive to changes in the dipole moment rather than in the geometrical configuration of the geomagnetic field. These preliminary results stress the need for further studies devoted to the occurrence, timing, and dynamical origin of extreme geomagnetic field intensity variations, and their possible imprint on the past production of cosmogenic radionuclides.