INVITED: THE SIBERIAN TRAPS, STRATOSPHERIC OZONE, UV-B FLUX AND MUTAGENESIS

The spores and pollen of terrestrial land plants can increase their investment in UV-B screening pigments when exposed to elevated levels of UV-B radiation. Here, we report an increase in UV-B protecting pigments from a historical record of the spores of Lycopodium magellanicum growing in South Georgia and exposed to a progressive thinning of stratospheric ozone and a corresponding increase in UV-B radiation. Our data records a strong three fold linear increase in the concentration of UV-B protecting pigments in response to a 14% thinning of the ozone column. Our results were obtained using micro FT-IR analysis of sporopollenin, which is readily preserved in the fossil record. Therefore, this newly identified response offers a potential tool for investigating natural changes in the stratospheric ozone layer and UV-B flux over geological time.

We are initially targeting the Permo-Triassic boundary for further investigation, as recent work has suggested a global collapse in the stratospheric ozone due to the emplacement of the Siberian Traps. This hypothesis can now be thoroughly tested using a combined approach, involving the examination of extant plants subjected to experimentally manipulated UV-B radiation, the geochemical study of fossil spores and pollen and the long-term modelling of stratospheric ozone.