COPSE reloaded: An improved model of biogeochemical cycling over Phanerozoic time

The 'COPSE' (Carbon, Oxygen, Phosphorus, Sulphur and Evolution) biogeochemical model predicts the coupled histories and controls on atmospheric O-2, CO2 and ocean composition over Phanerozoic time. The forwards modelling approach utilized in COPSE makes it a useful tool for testing mechanistic hypotheses against geo-chemical data and it has been extended and altered a number of times since being published in 2004. Here we undertake a wholesale revision of the model, incorporating: (1) elaboration and updating of the external forcing factors; (2) improved representation of existing processes, including plant effects on weathering and ocean anoxia; (3) inclusion of additional processes and tracers, including seafloor weathering, volcanic rock weathering and Sr-87/Sr-86; (4) updating of the present-day baseline fluxes; and (5) a more efficient and robust numerical scheme. A key aim is to explore how sensitive predictions of atmospheric CO2, 02 and ocean composition are to model updates and ongoing uncertainties. The revised model reasonably captures the long-term trends in Phanerozoic geochemical proxies for atmospheric pCO(2), pO(2), ocean [SO4], carbonate PC, sulphate 8(34)S and carbonate 87Sr/86Sr. It predicts a two-phase drawdown of atmospheric CO2 with the rise of land plants and associated cooling phases in the Late Ordovician and Devonian-early Carboniferous, followed by broad peaks of atmospheric CO2 and temperature in the Triassic and mid-Cretaceous-aalthough some of the structure in the CO2 proxy record is missed. The model robustly predicts a mid-Paleozoic oxygenation event due to the earliest land plants, with 02 rising from 5% to > 17% of the atmosphere and oxygenating the ocean. Thereafter, atmospheric 02 is effectively regulated with remaining fluctuations being a Carboniferous-Permian O-2 peak 26% linked to burial of terrestrial organic matter in coal swamps, a Triassic-Jurassic O-2 minimum 21% linked to low uplift, a Cretaceous O-2 peak 26% linked to high degassing and weathering fluxes, and a Cenozoic PO2 decline.