Constraints on carbon accumulation rate and net primary production in the Lopingian (Late Permian) tropical peatland in SW China

During the Permian, peatland, as represented in extensive coal deposits, was a major component of the global carbon cycle. Carbon storage in peatland is a balance between decay and net primary production (NPP), which in turn are sensitive to variations in the concentration of atmospheric CO2 and O2. To evaluate peatland carbon storage and NPP during the Lopingian, a period thought to be characterised by higher atmospheric O2 and CO2 than modern levels, spectral analyses of geophysical data from a 15.1 m thick Lopingian (Upper Permian) coal in southwestern China were conducted to define the time frame of temporal carbon accumulation in tropical peatland. The result shows that the mineral matter content (ash yield) of the coal was possibly influenced by 123 ka (eccentricity), 35.6 ka (obliquity) and 21.2 ka (precession) Milankovitch periodicities. Using this timeframe and an understanding of carbon loss during coalification, the Lopingian tropical peatland carbon accumulation rate is calculated to be 61.1–73.0 g C/m2/yr which is expected to correspond to a NPP of 611–1460 g C/m2/yr respectively. A comparison between the predicted Pennsylvanian (Late Carboniferous) NPP and modern values indicates that the Permian NPP calculated is consistent with geochemical and paleobotanical models, supporting a proposal that productivity was mainly controlled by temporal atmospheric O2 and CO2 levels.