SEASONALITY AND SEASONAL HYDROLOGICAL CYCLE ANALYSIS OF THE PETM USING CESM1.2

Paleocene-Eocene Thermal Maximum (PETM, ~56 my ago, 170,000 y event) is characterized by negative δ¹³C excursions into the atmosphere. This event has caused global temperature to increase ~5-6 °C, followed by climate responses such as marine acidification, ocean stratification, shoaling of CCD, and stronger hydrological cycle.

The study of the PETM dynamic climate response in terms of the seasonality and hydrological cycle can help understand the warming towards the PETM and to predict anthropogenic-induced climate change. In this research, a state-of-the-art community earth system model (CESM1.2) has been applied to simulate this hyperthermal event with various CO₂ concentration levels (1x, 3x, 6x, an 12x of preindustrial level, 280 ppm) to assess the response of the seasonality to CO₂ radiative forcing. With an increase of atmospheric pCO₂ from pre-PETM to PETM by 840 ppmv the meridional temperature gradient decreases substantially. Seasonality increases in midlatitude continental interior of north America, Asia, South America, Africa and Australia, and decreases in high and low latitude. Maximum seasonality amplifies in western Asia (~5.5 °C) in northern hemisphere and interior Antarctica (~5.6 °C) in southern hemisphere. Maximum precipitation increase is 7.1 and 5.5 mm/s for boreal summer and winter. Snow-albedo effect has a strong control on the decrease of high latitude continental seasonality over Antarctica and Arctic realm, with a hotter summer and cooler winter. The main controlling factor of seasonality changes in mid latitude interior of North America and Asia is the reduced summer soil moisture, which leads to a higher temperature increase in the summer. Tropical continental interior in northern South America, Africa, and Asia has a decrease of seasonality, where summer is cooler than winter, which is due to higher temperature increase in winter from lower precipitation (monsoon), where the temperature difference between summer and winter actually increased.