Proxy reconstruction of ultraviolet-B irradiance at the Earth’s surface, and its relationship with solar activity and ozone thickness

Abstract

Solar ultraviolet-B (UV-B) irradiance that reaches the Earth’s surface acts as a biotic stressor and has the potential to modify ecological and environmental functioning. The challenges of reconstructing ultraviolent (UV) irradiance prior to the satellite era mean that there is uncertainty over long-term surface UV-B patterns, especially in relation to variations in solar activity over centennial and millennial timescales. Here, we reconstruct surface UV-B irradiance over the last 650 years using a novel UV-B proxy based on the chemical signature of pollen grains. We demonstrate a statistically significant positive relationship between the abundance of UV-B absorbing compounds in Pinus pollen and modelled solar UV-B irradiance. These results show that trends in surface UV-B follow the overall solar activity pattern over centennial timescales, and that variations in solar output are the dominant control on surface level UV-B flux, rather than solar modulated changes in ozone thickness. The Pinus biochemical response demonstrated here confirms the potential for solar activity driven surface UV-B variations to impact upon terrestrial biotas and environments over long timescales.

Pollen‐chemistry variations along elevation gradients and their implications for a proxy for UV‐B radiation in the plant‐fossil record

“…These findings also agree with previous results both from other latitudinal/ altitudinal correlation studies (e.g. Willis et al, 2011;Bell et al, 2018;Jardine et al, 2016;Lomax et al, 2012Lomax et al, , 2008, as well as temporal calibrations through time (Jardine et al, 2020(Jardine et al, , 2016, and laboratory based studies (e.g. Rozema et al, 2001).…”

“…Excess ultraviolet-B radiation (UV-B, ultraviolet, 280-315 nm) is known to induce a stress response in plants and has effects on the biosphere at the level of genes, species, and ecosystems (Neale et al, 2021). Although the Montreal Protocol has been successful in both reducing the abundance of ozone-depleting substances in the atmosphere and allowing the subsequent recovery of stratospheric ozone (Solomon et al, 2016), there is widespread interest in understanding how variations in atmospheric-ozone concentrations, and the associated changes in UV-B radiation, have affected plant and ecosystem functioning in the geological past (Jardine et al, 2020(Jardine et al, , 2016Lomax et al, 2008;Rozema, Blokker, Mayoral Fuertes, & Broekman, 2009;Rozema et al, 2001;Willis, Bennett, & Birks, 2009). Yet despite the fact that UV-B is an essential variable for understanding dynamics of the Earth system, quantitative reconstructions of UV-B radiation beyond the instrumental record have remained elusive.…”

“…An emerging technique has proposed to use the chemical response of pollen grains as a tool to reconstruct the UV-B radiation received by plants (Jardine et al, 2020(Jardine et al, , 2016Lomax et al, 2008;Rozema et al, 2009;Willis et al, 2011). Pollen-grain exines are made of sporopollenin, a complex biomolecule, which is partially composed of phenolic building blocks within a long-chain fatty-acid matrix (Leeuw, Versteegh, & Bergen, 2006;Li, Phyo, Jacobowitz, Hong, & Weng, 2019).…”

Ozone Layer Evolution in the Early 20th Century

“…The proxy-based reconstructions of total ozone are not available at the moment, but there is some progress in this direction. One possible approach is to retrieve surface UV-B radiation level at the surface from the analysis of UV-B absorbing objects in the plants or spores [37][38][39][40]. However, it is not clear how to separate the influence of stratospheric ozone variations from the spectral solar irradiance variability, which is not well constraint on long-term time scales [17].…”

Sporopollenin chemistry and its durability in the geological record: an integration of extant and fossil chemical data across the seed plants

“…2011; Lomax & Fraser 2015; Jardine et al . 2016, 2017, 2020a; Seddon et al . 2017, 2019; Bell et al .…”