Evolution of continental temperature seasonality from the Eocene greenhouse to the Oligocene icehouse - A model-data comparison

• Main Authors: Toumoulin, Agathe, Tardif, Delphine, Donnadieu, Yannick, Licht, Alexis, Ladant, Jean-Baptiste, Kunzmann, Lutz, Dupont-Nivet, Guillaume
• Format: Text
• Language: English
• Published: 2021
• Subjects: geo; envir; Antarctic; The Antarctic; Antarc*; Ice Sheet; Sea ice
• Online Access: https://doi.org/10.5194/cp-2021-27; https://cp.copernicus.org/preprints/cp-2021-27/

At the junction of greenhouse and icehouse climate phases, the Eocene-Oligocene Transition (EOT) is a key moment in the history of the Cenozoic climate. Yet, while it is associated with severe extinctions and biodiversity turnovers, terrestrial climate evolution remains poorly resolved. Paleobotanical and geochemical continental records suggest a marked cooling in winter, leading to the development of more pronounced seasons (i.e., increase of the Mean Annual Range of Temperature, MATR) in parts of the Northern Hemisphere. However, this increase of the annual temperature range has been poorly studied by climate models; uncertainties remain about the geographical extent of this phenomenon and the associated climatic processes. Although other components of the climate system vary seasonally (e.g., precipitation, wind), we therefore focus on the seasonality of temperatures only. In order to better understand and describe temperature seasonality patterns from the middle Eocene to 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 to 560 ppm), the Antarctic ice-sheet (AIS) formation, and the associated sea-level decrease (-70 m). Our simulations suggest that seasonality changes across the EOT rely on the combined effects of the different tested mechanisms which result in zonal to regional climate responses. Broad continental areas of increased MATR reflect a strengthening of seasonality (from 4°C to > 10°C increase of the MATR) across the EOT in agreement with MATR and Coldest Month Mean Temperatures (CMMT) changes indicated by a review of existing proxies. pCO2 decrease induces a zonal pattern with alternating increasing and decreasing seasonality bands. In the northern high-latitudes, it results in sea-ice and surface albedo feedback, driving a strong increase in seasonality (up to 8°C MATR increase). Conversely, the onset of the AIS is responsible for a more constant surface albedo, which ...