Plate Tectonics and Climate during the Cenozoic
15 hours ago Andy May
By Andy May
In this post I examine the proxies used to compare CO2 to temperature from 66 million years ago (Ma) until today and comment on the quality of the comparison. In addition, we look at the Cenozoic plate tectonic events that affected global climate. Figure 1 compares Westerhold et al.’s deep-sea d18O (the Oxygen-18 isotope anomaly, a temperature proxy) to the d13C (the Carbon-13 isotope anomaly), both measurements are from the same fossils, so they can be directly compared. One of the problems with many temperature/CO2 plots is often they are from different sources and locations and due to dating errors and differing temporal resolutions, they are not directly comparable. While d13C is not a direct CO2 estimate, it is related to the CO2 concentration in the deep ocean. Atmospheric and ocean CO2 concentration estimates are compared to d13C in figure 2.
Figure 1. Deep-sea d18O temperature in blue compared to d13C proxies in orange for the Cenozoic. Both temperature and d13C increase upward. Data from (Westerhold, et al., 2020).
Major plate tectonic events are noted in figure 1 and a conversion from d18O to deep sea temperature is given in blue on the left. The highest temperatures in the Cenozoic are from the early Eocene (~56-48 Ma) when deep sea temperature exceeded 12°C higher than today. This was accompanied by a dramatic drop in deep-sea CO2. As already mentioned, d13C is not an estimate of CO2 concentration, but related to it. Proxy estimates of CO2 from Rae, et al. are compared to Westerhold’s d13C estimates in figure 2.
Figure 2. Westerhold’s d13C compared to Rae’s CO2 concentration for the Cenozoic. The d13C data are from (Westerhold, et al., 2020) and the CO2 proxy data are from (Rae, et al., 2021). The two values measure different things and are independent.
The match in figure 2 is not great and both datasets have problems, but the similarities in trends are obvious. The estimates of CO2 concentration reported by Rae, et al. are discontinuous and from a variety of proxies that are dated by many different authors with many different techniques. It is clear from the scatter that the assumption that CO2 is evenly distributed globally is not applicable at this compressed time scale. Notice the PETM (Paleocene-Eocene Thermal Maximum) carbon isotope excursion (CIE) event at ~56 Ma shows up dramatically in both records. This large divergence in the ratio of carbon-13 to carbon-12 is a prominent global rock-record phenomenon and a reliable geological time marker that occurred between 55.6 and 55.4 Ma. Possible reasons for the CIE and the PETM are discussed here. This geological event and the following warm period comprise the most dramatic climatic event in the Cenozoic.
https://wattsupwiththat.com/2025/03/30/plate-tectonics-and-climate-during-the-cenozoic/
