Evolution of continental temperature seasonality from the Eocene greenhouse to the Oligocene icehouse –a model–data comparison

Abstract

Abstract. At the junction of greenhouse and icehouse climate states, the Eocene–Oligocene Transition (EOT) is a key moment in Cenozoic climate history. While it is associated with severe extinctions and biodiversity turnovers on land, the role of terrestrial climate evolution remains poorly resolved, especially the associated changes in seasonality. Some paleobotanical and geochemical continental records in parts of the Northern Hemisphere suggest the EOT is associated with a marked cooling in winter, leading to the development of more pronounced seasons (i.e., an increase in the mean annual range of temperature, MATR). However, the MATR increase has been barely studied by climate models and large uncertainties remain on its origin, geographical extent and impact. In order to better understand and describe temperature seasonality changes between the middle Eocene and the early Oligocene, we use the Earth system model IPSL-CM5A2 and a set of simulations reconstructing the EOT through three major climate forcings: pCO2 decrease (1120, 840 and 560 ppm), the Antarctic ice-sheet (AIS) formation and the associated sea-level decrease. Our simulations suggest that pCO2 lowering alone is not sufficient to explain the seasonality evolution described by the data through the EOT but rather that the combined effects of pCO2, AIS formation and increased continentality provide the best data–model agreement. pCO2 decrease induces a zonal pattern with alternating increasing and decreasing seasonality bands particularly strong in the northern high latitudes (up to 8 ∘C MATR increase) due to sea-ice and surface albedo feedback. Conversely, the onset of the AIS is responsible for a more constant surface albedo yearly, which leads to a strong decrease in seasonality in the southern midlatitudes to high latitudes (>40∘ S). Finally, continental areas that emerged due to the sea-level lowering cause the largest increase in seasonality and explain most of the global heterogeneity in MATR changes (ΔMATR) patterns. The ΔMATR patterns we reconstruct are generally consistent with the variability of the EOT biotic crisis intensity across the Northern Hemisphere and provide insights on their underlying mechanisms.

Drivers of the artiodactyl turnover in insular western Europe at the Eocene–Oligocene Transition

“…These two models are not mutually exclusive and can prevail at different levels and timescales (19). Our results already highlighted that the major environmental disturbances at the EOT (28,29,72,78) coincided with the strong extinction of endemic artiodactyl that led to the Grande Coupure, and that immigrant species and ecological traits considered here were not the drivers of the decline of endemic species in the aftermath of the transition. We here propose that the longevity and extinction probability of species, as well as long-term abiotic changes, may be relevant explanatory factors for the dynamics of European artiodactyls and for the decline of endemic species.…”

“…The Eocene-Oligocene transition marks a period of significant decrease in temperature, sea level, and precipitation (26,28,29,72), and a concurrent increase in seasonality in Europe during the Oligocene (72,75,78). We investigated the impact of these environmental factors over the diversification of European artiodactyl species using the MBD model (55).…”

“…sea surface temperature, sea level, continental fragmentation, atmospheric CO2, and organic carbon), for which regional-scale data were not available. We aim to highlight the importance of regional proxies, as climate and flora variations across the EOT appear to be heterogeneous at the global scale (75,78). In particular, the insular setting of western Europe, surrounded to the south by the warm Tethys Sea, may have tempered the impact of global cooling during the Oligocene (27).…”

Isotopic niche modelling of the Pondaung mammal fauna (middle Eocene, Myanmar) shows microhabitat differences. Insights into paleoecology and early anthropoid primate habitats

“…Studies on different climatic proxies including stable isotope analysis of gastropod shells and mammal teeth from the Pondaung Fm. revealed however that a monsoon-like climate was already present in the Eocene (Licht et al, 2014c;Toumoulin et al, 2022;Huang et al, 2023). With our larger data set, covering some of the localities represented in the previous study by Licht et al (2014c) and more, we will try to test whether the same pattern is present.…”