4-7 Paleosol carbonates suggest jet-induced Pliocene rainfall seasonality mediated east Asian C4 expansion

Session: Recent Advances in Soil and Paleosol Science

Presenting Author:

Dan Breecker

Authors:

Da, Jiawei¹, Sun, Chijun², Serach, Lily³, Gallagher, Timothy M.⁴, Lu, Huayu⁵, Huntington, Katharine W.⁶, Feng, Ran⁷, Zhang, Hanzhi⁸, Wang, Hanli⁹, Ji, Shunchuan¹⁰, Sharp, Zachary¹¹, Ji, Junfeng¹², Breecker, Dan¹³

(1) The University of Texas at Austin, Austin, TX, USA, (2) University of California, Davis, Woodland, CA, USA, (3) The University of Texas at Austin, Austin, Texas, USA, (4) Kent State, Kent, OH, USA, (5) Nanjing University, Nanjing, China, (6) U Washington, Seattle, WA, USA, (7) The University of Connecticut, Glastonbury, CT, USA, (8) Nanjing University, Nanjing, China, (9) Nanjing University, Nanjing, China, (10) Yunnan Normal University, Kunming, China, (11) University of New Mexico, Albuquerque, NM, USA, (12) Nanjing University, Nanjing, China, (13) The University of Texas, Austin, TX, USA,

Abstract:

C₄ grassland expansion during the Neogene transformed terrestrial ecosystems. Occurring first in Africa and then on the Indian subcontinent during the Miocene, C₄ vegetation subsequently expanded during the Plio-Pleistocene to higher latitudes. We present paleosol carbonate clumped and triple oxygen isotope evidence suggesting rainfall seasonality controlled extratropical, Plio-Pleistocene C₄ distributions in East Asia. Reconstructed soil water d¹⁸O values vary sinusoidally with an amplitude of up to 3‰ and a frequency aligning with the 1.2-Myr obliquity amplitude modulation cycle. The highest soil water d¹⁸O values occur during the warmest climates, and although D’¹⁷O-constrained changes in evaporation intensity account for some of the variability, the observations cannot be explained without higher rainfall d¹⁸O values during warmer climates. These results indicate that the Chinese Loess Plateau (CLP) received more spring rain during warmer Pliocene intervals when the subtropical westerly jet was positioned further poleward, and more summer rain during cooler climates when the jet was further south. This variability was driven by obliquity and global climate-controlled meridional shifts in the position of the summer rain band, dynamically similar to the annual Meiyu front migration but operating on longer timescales. A similar spatiotemporal pattern in organic carbon d¹³C records indicates that the most C₄-rich ecosystems followed the summer rain band as it oscillated north-south across East Asia. The C₄-rich ecosystems eventually migrated across the southern margin of the CLP during early Pleistocene cooling, probably due to the same westerly jet – summer rain band mechanism. Our model refines the East Asian paleomonsoon concept and explains the enigmatic equatorward migration of extratropical C₄ ecosystems during cooling, which is inconsistent with a direct atmospheric CO₂ control.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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