Reduced geomagnetic shielding increased UV-B radiation at Earth’s surface during the Laschamps Event

Timothy J Heaton , Eloise Wilkinson-Rowe, Linn Cecile Krüger, Edouard Bard, Christine S Lane, Amy McGuire, T Matthew Robson, Takeshi Nakagawa, Alistair Seddon

Exposure to excess UV-B radiation can harm organisms through DNA damage and oxidative stress, and has likely been a key ecological and evolutionary driver throughout Earth’s history. Here, we show UV-B at Earth’s surface was significantly increased during the Laschamps Event, the last major geomagnetic excursion ca. 41ka BP. During the Laschamps, we find significant and prolonged (lasting >600yrs) increases in UV-B absorbing compounds in subfossil Pinus Diploxylon pollen (e.g., 31% [95% CI 19-44] increase compared to 1.3ka BP). Furthermore, we identify a significant (negative) broader linear relationship (p<0.001) between UV-B absorbing compounds and the geomagnetic dipole moment extending over the past 65ka. Our results demonstrate an empirical link between surface UV-B and geodynamo strength, important for understanding our past and mitigating our potential future.