Experimental and Temporal Observations on the Occurrence and Abundance of Pyrogenic PAH Relative to Atmospheric Oxygen Levels

Details Experimental and Temporal Observations on the Occurrence and Abundance of Pyrogenic PAH Relative to Atmospheric Oxygen Levels Experimental and Temporal Observations on the Occurrence and Abundance of Pyrogenic PAH Relative to Atmospheric Oxygen Levels

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.v43c1437s&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #V43C-1437

Mathematics

Logic

0315 Biosphere/Atmosphere Interactions

Scientific paper

The Phanerozoic record of atmospheric O2 is based on a global mass balance of several dynamic geochemical cycles, with error margins reflecting such complexity. The potential for accurately determining the record of atmospheric O2 may significantly improve with the proposed method, which relies on a direct relationship between atmospheric oxygen, fuels, and fire products. The interaction between combustion and atmospheric-oxygen level during biomass burning events is investigated by comparing the occurrence and abundance of pyrogenic polycyclic aromatic hydrocarbons (PAH) from experimentally-produced, modern, Triassic, and Carboniferous chars. The combustion process consumes O2 directly from the atmosphere and thermally alters organic matter to produce chars. PAH that develop through combustion, and are preserved within chars, are expected to be more abundant at times of elevated atmospheric O2, which facilitates biomass burning efficiency. To investigate the hypothesized relationship in the geologic record, PAH have been extracted from chars of three periods - modern, Triassic, and Carboniferous - relating to 21%, 15%, and 35% atmospheric O2, respectively (Berner and Canfield, 1989). Surface samples of modern chars that developed in controlled burns set by National Park Service personnel in a mixed conifer-deciduous forest were collected at Zion National Park, Utah. Triassic fusain from Petrified Forest National Park, AZ, and Carboniferous fusain from Joggins Fossil Cliffs, Nova Scotia, were collected from floodplain- and coastal plain-deposited mudstone and sandstone. Target PAH shown to be uniquely pyrogenic include: phenanthrene, anthracene, fluoranthene, pyrene, benz(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, indeno(1,2,3-cd)pyrene, and benzo(ghi)perylene. The abundance of PAH from modern chars at Zion National Park, Triassic fusain from Petrified Forest National Park, and Carboniferous fusain from Joggins Fossil Cliffs seem to reflect differences in atmospheric oxygen levels. These temporal trends are compared to experimentally-derived pyrogenic PAH produced in a combustion apparatus with different levels of oxygen.

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