Atmospheric Stabilization Weakened Proto‐Low‐Level Jet Over the Indian Ocean During the Eocene Hothouse
Year: 2025
Type: article
Abstract: Simulations of the Eocene climate using state‐of‐the‐art Earth system models provide a reference state for the future climate, as the Eocene was one of the warmest geological epoch with high atmospheric carbon dioxide (CO 2 ) concentration and global temperatures comparable to projections for the coming centuries. However, the paleogeographic configuration of the Eocene impact's distinct climate features. Here, we decompose the response of low‐level monsoon dynamics over the Indian Ocean to the early Eocene hothouse using five climate model simulations from the Deep‐time Model Intercomparison Project (DeepMIP). We see a circulation pattern resembling the paleo‐monsoon across all models over the Indian Ocean. Surprisingly, we find low‐level jet (LLJ) forming along the topographic barriers of the Eastern African Rift and the Deccan Plateau, which we refer to as the “Proto‐LLJ.” Based on the analysis of the DeepMIP results, we find a reduction in the Proto‐LLJ strength with elevated CO 2 . Under present‐day conditions, the northward shift of monsoonal LLJ is attributable to the increased land‐sea contrast under global warming. Even though land‐ocean temperature contrasts increased during the Eocene hothouse, Proto‐LLJ weakened due to tropical atmospheric stabilization. This stabilization reduced vertical temperature gradients, suppressed convection, and weakened atmospheric overturning, limiting the upward motion needed to drive strong monsoonal winds under CO 2 ‐induced warming.
DOI: 10.1029/2025pa005244
Institutions: Bjerknes Centre for Climate Research, NORCE Research AS, University of Bristol, Stockholm University, Bolin Centre for Climate Research, The University of Tokyo, UNSW Sydney, Climate Change Research Centre, Institute for Basic Science, IBS Center for Climate Physics, Pusan National University, University of Arizona, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Instytut Nauk Geologicznych, Polish Academy of Sciences, Indian Institute of Tropical Meteorology, Ministry of Earth Sciences, The University of Melbourne
Language: English
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
SDG: Climate action
Open Access status: hybrid
Estimated APC paid: $4,070
Awards: Understanding the interaction between ice sheets, ocean and atmosphere under large scale climate changes of the past, The Arctic cryosphere at the Last Interglacial; an analogue for the future?, SWEET:Super-Warm Early Eocene Temperatures and climate: understanding the response of the Earth to high CO2 through integrated modelling and data, G4423037446, G6158023040, Did ocean circulation changes build the Antarctic ice sheet?
OpenAlex ID: W7117314912