Abstract
Excessive acid rainfall associated with emplacement of the Siberian Traps magmatic province is increasingly accepted as a major contributing factor to the end-Permian biosphere crisis. However, direct proxy evidence of terrestrial acidification is so far not available. In this paper, we seek to determine the probability that relative proportions of extractable monophenolic components from soil-derived organic matter in marine sediments provide a molecular proxy for estimating soil acidity. Intermittently low and high ratios of vanillic acid to vanillin detected in latest Permian and earliest Triassic deposits of the southern Alps, Italy, support concepts of pulses of severe acidification (pH <4) during the main phase of the biosphere crisis.
Highlights
Three-dimensional chemistry-climate simulations underlined the plausibility that both acid rainfall and ozone-layer breakdown could have contributed to the global biosphere crisis and associated extinctions at the end of the Permian Period (Black et al, 2014)
Induced by massive acidic and halogenic gas emissions related to the Siberian Traps magmatism, modeled pulses of acid rain with pH values as low as 2 appear to be intense across the Northern Hemisphere, whereas increased UV-B radiation resulting from stratospheric ozone destruction would occur on a more global scale
Concrete evidence for chronic environmental mutagenesis caused by increased UV-B flux may be provided by the worldwide proliferation of tetrads of lycopsid microspores in end-Permian palynological records (Visscher et al, 2004)
Summary
Three-dimensional chemistry-climate simulations underlined the plausibility that both acid rainfall and ozone-layer breakdown could have contributed to the global biosphere crisis and associated extinctions at the end of the Permian Period (Black et al, 2014). A significant intermediate step in various enzymatic decomposition pathways of lignin and other polymerized plant phenolics is the common production of vanillin (Bugg et al, 2011) This monophenolic aldehyde (4-hydroxy3-methoxybenzaldehyde) may be converted to vanillic acid (4-hydroxy-3-methoxybenzoic acid) by aldehyde-oxidase enzymes (e.g., Crawford et al, 1982) and to protocatechuic acid (3,4-dihydroxybenzoic acid), before soil microbes accomplish aromatic ring cleavage. Bacterial culture studies have confirmed that enzymatic oxidation of vanillin and other aromatic and aliphatic aldehydes is a pH-sensitive process, generally with optimum pH values above 5 (e.g., Kunc, 1971) In view of this sensitivity, analysis of variations in relative proportions of vanillin and vanillic acid extracted from SOM may offer the possibility to detect major changes in soil acidity. Results of the additional analyses are detailed in the GSA Data Repository
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