Evidence for a 35 million years CO2 cyclicity and its connection to Earth’s temperature evolution over the last 420 million years

Global records of atmospheric CO2 and global tropical paleotemperature over the last 420 million years (Myr) have been reconstructed from recently compiled databases of atmospheric CO2 and d18O of low-Mg fossil carbonate of seawater. Time series analysis reveals ~35±5 Myr periodicity in both records with an average amplitude ratio of ~100ppm CO2/1 degree Celcius. Wavelet and cross-wavelet analysis indicate that this cyclicity have been occasionally non-stationary, for instance in the late Carboniferous (~310 Myr) when CO2 and paleotemperature records show no signals at the ~35 Myr waveband. Moreover, the ~35 Myr cyclicity is the strongest common cyclicity in the 5-400 Myr waveband range in both records. From 420 Myr to ~200 Myr, CO2 peaks are followed ~8 million years later by temperature peaks, whereas in the last ~115 Myr, the temperature maxima occur ~5 million years before the CO2 maxima. This change in the time-lag between CO2 and paleotemperature is most likely caused by several non-stationarities in the ~35Myr waveband during the Jurassic and early Cretaceous. The shift in the timing of the CO2-paleotemperature connection suggests that the linkage of carbon cycle with global temperature evolution changed during the Mesozoic (see figure).