One and a Half Million Yearlong Aridity During the Middle Eocene in North‐West China Linked to a Global Cooling Episode.

The Eocene record of substantial aridification near Tibet was reported to mimic the global climate cooling trend, overwriting the previously proposed dominant role of the Tibetan Plateau uplift in the aridification (Li et al., 2018, https://doi.org/10.1038/s41467‐018‐05415‐x). Here we present new paleoclimate data from the red clay sequence deposited between 40 and 50 Ma in Altun Shan at the northeastern edge of the Tibetan Plateau. After building an age model using a compilation of magnetostratigraphy and cyclostratigraphy, we demonstrate that our record of magnetic susceptibility in the Altun Shan red clay exhibits variations linked to eccentricity cycles. Our age model allows us to estimate the age of eight short geomagnetic events, cryprochrons, in Altun Shan. Further we show that the aridification interval in Altun Shan coincides with (i) a cooling event recorded in the global oxygen isotope record, (ii) a sea surface temperature record on the east Tasmanian plateau, and (iii) an aridity record in the surrounding sedimentary basins of Central Asia. The middle Eocene aridity and cooling reached its maximum 45.5‐44 Ma. Plain Language Summary: Two notable Eocene climate warming events are extensively discussed in the literatureߝthe middle Eocene climatic optimum and the early Eocene climatic optimum. Here, we report our accurately dated climate proxy record of magnetic parameters from the Altun Shan red clay section at the northeastern part of the Tibetan Plateau that reveals an aridity interval 45.5‐44 Ma. The Altun Shan magnetic susceptibility record, an indicator of aridity vs. moisture intensification intervals, exhibits variations linked to eccentricity cycles. The one and a half million yearlong aridity event in Altun Shan coincides with the aridity in middle Asia and the cooling event that could be observed in the global oxygen isotope compilation and the first appearance of ice‐rafted debris from Greenland and Pan‐Arctic sources, indicating global distribution of aridity and cooling 45.5‐44 Ma. Key Points: A magnetic record of the Eocene section near Tibet reveals a one and a half million yearlong aridityThe aridity interval 45.5‐44 Ma coincides with aridity maximum in inner AsiaThe middle Eocene aridity coincides with cooling registered in oceanic records [ABSTRACT FROM AUTHOR]