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Spore chemistry is at the centre of investigations aimed at producing a proxy record of harmful ultraviolet radiation (UV-B) through time. A biochemical proxy is essential owing to an absence of long-term (century or more) instrumental records. Spore cell material contains UV-B absorbing compounds that appear to be synthesised in variable amounts dependent on the ambient UV-B flux. To facilitate these investigations we have developed a rapid method for detecting variations in spore chemistry using combined thermochemolysis gas chromatography-mass spectrometry and micro-Fourier transform infrared spectroscopy. Our method was tested using spores obtained from five populations of the tropical lycopsid Lycopodium cernuum growing across an altitudinal gradient (650-1981 m a.s.l.) in S.E. Asia with the assumption that they experienced a range of UV-B radiation doses. Thermochemolysis and subsequent pyrolysis liberated UV-B pigments (ferulic and para-coumaric acid) from the spores. All of the aromatic compounds liberated from spores by thermochemolysis and pyrolysis were active in UV-B protection. The various functional groups associated with UV-B protecting pigments were rapidly detected by micro-FTIR and included the aromatic C[double bond, length as m-dash]C absorption band which was exclusive to the pigments. We show increases in micro-FTIR aromatic absorption (1510 cm(-1)) with altitude that may reflect a chemical response to higher UV-B flux. Our results indicate that rapid chemical analyses of historical spore samples could provide a record ideally suited to investigations of a proxy for stratospheric O3 layer variability and UV-B flux over historical (century to millennia) timescales.

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Silicate weathering is the primary control of atmospheric CO2 concentrations on multiple timescales. However, tracing this process has proven difficult. Lithium isotopes are a promising tracer of silicate weathering. This study has reacted basalt sand with natural river water for ~9 months in closed experiments, in order to examine the behaviour of Li isotopes during weathering. Aqueous Li concentrations decrease by a factor of ~10 with time, and d 7 Li increases by ~19‰, implying that Li is being taken up into secondary phases that prefer 6 Li. Mass balance using various selective leaches of the exchangeable and secondary mineral fractions suggest that ~12-16% of Li is adsorbed, and the remainder is removed into neoformed secondary minerals. The exchangeable fractionation factors have a D 7 Liexch-soln =-11.6 to-11.9‰, while the secondary minerals impose D 7 Lisecmin-soln =-22.5 to-23.9‰. Overall the experiment can be modelled with a Rayleigh fractionation factor of a = 0.991, similar to that found for natural basaltic rivers. The mobility of Li relative to the carbon-cycle-critical cations of Ca and Mg changes with time, but rapidly evolves within one month to remarkably similar mobilities amongst these three elements. Th evolution shows a linear relationship with d 7 Li (largely due to a co-variation between aqueous [Li] and d 7 Li), suggesting that Li isotopes have the potential to be used as a tracer of Ca and Mg mobility during basaltic weathering, and ultimately CO2 drawdown.

SummaryThe biopolymer sporopollenin present in the spore/pollen walls of all land plants is regarded as one of the most recalcitrant biomacromolecules (biopolymers), providing protection against a range of abiotic stresses. This long-term stability is demonstrated by the near-ubiquitous presence of pollen and spores in the fossil record with spores providing the first evidence for the colonization of the land.Here, we report for the first time chemical analyses of geologically unaltered sporopollenin from Pennsylvanian (c. 310 million yr before present (MyBP)) cave deposits.Our data show that Pennsylvanian Lycophyta megaspore sporopollenin has a strong chemical resemblance to extant relatives and indicates that a co-polymer model of sporopollenin formation is the most likely configuration.Broader comparison indicates that extant sporopollenin structure is similar across widely spaced phylogenetic groups and suggests land plant sporopollenin structure has remained stable since embryophytes invaded land.

Current attempts to develop a proxy for Earth's surface ultraviolet-B (UV-B) flux focus on the organic chemistry of pollen and spores because their constituent biopolymer, sporopollenin, contains UV-B absorbing pigments whose relative abundance may respond to the ambient UV-B flux. Fourier transform infrared (FTIR) microspectroscopy provides a useful tool for rapidly determining the pigment content of spores. In this paper, we use FTIR to detect a chemical response of spore wall UV-B absorbing pigments that correspond with levels of shade beneath the canopy of a high-latitude Swedish birch forest. A 27% reduction in UV-B flux beneath the canopy leads to a significant (p<0.05) 7.3% reduction in concentration of UV-B absorbing compounds in sporopollenin. The field data from this natural flux gradient in UV-B further support our earlier work on sporopollenin-based proxies derived from sedimentary records and herbaria collections

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