title: Pollen and spores as biological recorders of past ultraviolet irradiance.
abstract: Solar ultraviolet (UV) irradiance is a key driver of climatic and biotic change. Ultraviolet irradiance modulates stratospheric warming and ozone production, and influences the biosphere from ecosystem-level processes through to the largest scale patterns of diversification and extinction. Yet our understanding of ultraviolet irradiance is limited because no method has been validated to reconstruct its flux over timescales relevant to climatic or biotic processes. Here, we show that a recently developed proxy for ultraviolet irradiance based on spore and pollen chemistry can be used over long (105years) timescales. Firstly we demonstrate that spatial variations in spore and pollen chemistry correlate with known latitudinal solar irradiance gradients. Using this relationship we provide a reconstruction of past changes in solar irradiance based on the pollen record from Lake Bosumtwi in Ghana. As anticipated, variations in the chemistry of grass pollen from the Lake Bosumtwi record show a link to multiple orbital precessional cycles (19-21 thousand years). By providing a unique, local proxy for broad spectrum solar irradiance, the chemical analysis of spores and pollen offers unprecedented opportunities to decouple solar variability, climate and vegetation change through geologic time and a new proxy with which to probe the Earth system.
authors.affiliation: School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK.
authors.forename: Phillip E
authors.initials: PE
authors.lastname: Jardine
authors.affiliation: School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK.|Geography, Department of Social Sciences, Oxford Brookes University, Oxford OX3 0BP, UK.
authors.forename: Wesley T
authors.initials: WT
authors.lastname: Fraser
authors.affiliation: Agriculture and Environmental Science, University of Nottingham, Sutton Bonington Campus, Leicestershire, LE12 5RD, UK.
authors.forename: Barry H
authors.initials: BH
authors.lastname: Lomax
authors.affiliation: Department of Earth Sciences &Engineering, Imperial College London, South Kensington, London SW7 2AZ, UK.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Sephton
authors.affiliation: Department of Geological Sciences, The University of Texas at Austin, 1 University Station C9000, Austin, Texas 78712, USA.
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Shanahan
authors.affiliation: MARUM,University of Bremen, Leobener Str., D-28359 Bremen, Germany.
authors.forename: Charlotte S
authors.initials: CS
authors.lastname: Miller
authors.affiliation: School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK.|Palaeoecology &Landscape Ecology, Institute of Biodiversity &Ecosystem Dynamics (IBED), University of Amsterdam, 1090 GE Amsterdam, The Netherlands.
authors.forename: William D
authors.initials: WD
authors.lastname: Gosling
mesh_terms: D005580:Fossils; D016014:Linear Models; D006109:Poaceae / Q000254:growth & development; D011058:Pollen / Q000737:chemistry* / Q000528:radiation effects; D017550:Spectroscopy, Fourier Transform Infrared; D014466:Ultraviolet Rays