ibclogo XVI International Botanical Congess


Abstract Number: 4718
Session = 12.16.7


WHAT REGULATES THE OXYGEN CONTENT OF THE ATMOSPHERE?


Tim Lenton, Institute of Terrestrial Ecology, Edinburgh, EH26 0QB, UK.


The continuous charcoal record and the results of combustion experiments indicate that the oxygen content of the atmosphere has varied remarkably little over Phanerozoic time. A new model of the coupled cycles of P, N, C and O is used to test various feedback mechanisms proposed to account for this stability. Ocean-based mechanisms buffer declining oxygen but switch off when rising oxygen removes anoxia from the ocean. Rising oxygen increases fire frequency and directly suppresses land plant growth. These effects can regulate against increasing oxygen by suppressing the biological amplification of rock weathering, which determines the input of the limiting nutrient, phosphorus to the Earth system and hence, ultimately, the flux of organic carbon burial and the corresponding source of oxygen. When the model is forced with paleo-data, oxygen is regulated close to 21% of the atmosphere.


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