Reconstructions of UV-B radiation across the Laschamps Geomagnetic Excursion

Stratospheric ozone provides protection from excess quantities of UV-B radiation (ultraviolet-B, 280-315 nm) reaching the Earth’s surface. Solar variability, geomagnetic reversals and volcanic eruptions can weaken ozone layer protection and expose organisms to increased UV-B radiation, with potentially major implications for evolutionary processes in the past. Despite its importance, knowledge about the variations in surface UV-B radiation remains limited due to the difficulties of reconstructing UV-B radiation from ancient sediment records.

As shown in the video above,  a reversal of the Earth’s geomagnetic field which occurred ~41-42,000 years ago (the Laschamps Excursion), provides a striking ‘natural experiment’ for which to investigate the past dynamics of surface UV-B radiation. New palaeoclimate modelling evidence indicates that the weakening of the geomagnetic field strength in the lead-up to the Laschamps Excursion caused elevated levels of UV-B at the Earth’s surface, resulting in widespread climate shifts, vegetation changes and even extinctions, but the effects of Laschamps will remain highly controversial without empirical reconstructions of UV-B radiation at this time period.

Here we will use a new approach to reconstruct UV-B radiation across the Laschamps Excursion using the biomolecular changes measured in fossil pollen grains. Our approach will represent the first attempt to generate synchronous reconstructions of past UV-B radiation for a geological event from three sediment cores, which are representative of temperate and tropical latitudes. We will also develop a new spectroscopy-based automated technique to effectively quantify biochemical variations in pollen grains. In addition to resolving the specific knowledge gaps around the environmental conditions of Laschamps, the project will stand as an important milestone in the development of a novel chemical proxy for understanding the effects of UV-B radiation on life on Earth in other periods of Earth’s history.

PI: Alistair Seddon