PP51F-06:
Variation of Atmospheric Oxygen in the Phanerozoic Recorded By δ13c of Terrestrial Organic Matter

Friday, 19 December 2014: 9:15 AM
Karlis Muehlenbachs1, Ralf Tappert2, Ryan McKellar1, Alex P Wolfe1, Michelle Tappert1 and Martin Schoell3,4, (1)University of Alberta, Edmonton, AB, Canada, (2)University of Innsbruck, Institute of Mineralogy and Petrography, Innsbruck, Austria, (3)Retired, Washington, DC, United States, (4)GasConsult International Inc., Berkeley, CA, United States
Abstract:
One important factor controlling the δ13C of C3 plants is pO2 and thus δ13C of fossil terrestrial organic matter is a proxy for ancient pO2 once variations of δ13C of the atmosphere and paleo pCO2 are corrected for. We reconstructed pO2 since the emergence of land plants in the Ordovician following the approach of Tappert et al. [1], and using the published δ13C record of fossil resins (amber), coals and dispersed terrestrial organic matter. For most of this time, atmospheric pO2 was considerably lower (pO2 ~ 10-21%) compared to today (pO2 = 21%). Secular variations in pO2 must reflect changing amounts of burial of organic matter and sulfides. We observe a strong correlation between pO2 calculated from land plants, and the strontium and lithium isotopic compositions of marine carbonates. The marine Sr isotope record reflects secular changes of continental weathering and climate driven by tectonic activity. Synchronicity of pO2 with the marine strontium isotope record implies that tectonic processes, including orogeneses and the formation of associated sedimentary basins, not only control the rate of weathering and volume of sedimentation, but also the amount and proportion of the biomass that is buried on geological timescales.