Polar ice-cores unravel the formation of a UV window during magnetic field collapse ~ 42 ka BP

Dr. SANJEEV DASARI , Guillaume Paris, Julien Charreau, Alexis Lamothe, Joel Savarino

During geomagnetic excursions (GEs), compromised magnetic field and increased cosmic-ray bombardment can deplete the ozone layer forming ‘UV window(s)’ in the Earth’s atmosphere. Here, using triple sulfur-isotope systematics in polar ice-core sulfate record spanning 600 years of the Laschamp GE, we provide direct evidence of the formation of a UV window. Several events of UV-induced anomalous ice-core sulfate were detected under background conditions in Antarctica concomitant with the evolution of paleomagnetic intensity, with a distinct peak observed between ≈ 41.7 ka BP and ≈ 41.6 ka BP corresponding to the weakest magnetic field phase. The timing and amplitude of these events unequivocally confirm the existence of a UV window in the southern hemisphere during the LGE. However, such geochemical imprints were not detected in discrete sub-sampled northern polar ice-core record. We postulate that, among other possibilities, non-uniformity in excursion behaviour at the Earth’s surface could be modulating this geochemical imprint.