The Eocene-Oligocene transition: a review of marine and terrestrial proxy data, models and model-data comparisons

Abstract

<jats:p>Abstract. The Eocene-Oligocene transition (EOT) from a largely ice-free greenhouse world to an icehouse climate with the first major glaciation of Antarctica was a phase of major climate and environmental change occurring ~34 million years ago (Ma) and lasting ~500 kyr. The change is marked by a global shift in deep sea δ18O representing a combination of deep-ocean cooling and global ice sheet growth. At the same time, multiple independent proxies for sea surface temperature indicate a surface ocean cooling, and major changes in global fauna and flora record a shift toward more cold-climate adapted species. The major explanations of this transition that have been suggested are a decline in atmospheric CO2, and changes to ocean gateways, while orbital forcing likely influenced the precise timing of the glaciation. This work reviews and synthesises proxy evidence of paleogeography, temperature, ice sheets, ocean circulation, and CO2 change from the marine and terrestrial realms. Furthermore, we quantitatively compare proxy records of change to an ensemble of model simulations of temperature change across the EOT. The model simulations compare three forcing mechanisms across the EOT: CO2 decrease, paleogeographic changes, and ice sheet growth. We find that CO2 forcing provides by far the best explanation of the combined proxy evidence, and based on our model ensemble, we estimate that a CO2 decrease of about 1.6× across the EOT (e.g. from 910 to 560 ppmv) achieves the best fit to the temperature change recorded in the proxies. This model-derived CO2 decrease is consistent with proxy estimates of CO2 decline at the EOT. </jats:p>

Biotic community and landscape changes around the Eocene–Oligocene transition at Shapaja, Peruvian Amazonia: Regional or global drivers?

“…34 and 33.2 Ma (Fig. 6), provoked a sustained drop in precipitation, and increased seasonality, with a worldwide onset of drier climatic regimes (Hutchinson et al, 2018;Miller et al, 2020;Westerhold et al, 2020). Both the abundance of pedogenic nodules in the concerned interval of the Shapaja section and the concurrent shift from multistratified rainforest to more open deciduous forest consistently point to the strengthening of seasonal contrast, especially regarding rainfall (see previous sections).…”

Quantifying the Effect of the Drake Passage Opening on the Eocene Ocean

“…This bias is very classical in warm climate reconstructions with GCMs and could be responsible for a discrepancy between absolute SST from our experiments and proxies (see Huber & Caballero, 2011). Studies carried out with more recent versions of GCM, such as CESM and GFDL, show improvements in the representation of this gradient, in particular thanks to a better consideration of cloud physics and other greenhouse gases (Baatsen et al, 2020;Hutchinson et al, 2020;Lunt et al, 2020;Sagoo et al, 2013;Zhu et al, 2019). With close boundary conditions, they reconstruct flatter gradients thanks to~3°C lower SST in equatorial area and up to 2°C to 3°C higher SST at midlatitudes ( Figure S7; Baatsen et al, 2020;Hutchinson et al, 2018).…”

Climate and geological change as drivers of Mauritiinae palm biogeography

“…In contrast, cooler climates, such as those during the late Eocene (c. 40-34 Ma;Hutchinson et al, 2020;Liu et al, 2009;Zachos et al, 2008), are associated with periods of significantly lower pollen diversity (Jaramillo et al, 2006). Such changes in pollen diversity are interpreted to indicate matching species diversity changes in tropical forests.…”