Pollen record of climate change during the last deglaciation from the eastern Tibetan Plateau

RESEARCH ARTICLE Pollen record of climate change during the last deglaciation from the eastern Tibetan Plateau Wei Shi1,2, Hanchao JiangID1*, Xue Mao1, Hongyan Xu1 1 State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing, China, 2 College of Earth Sciences, University of Chinese Academy of Sciences, Beijing, China * hcjiang@ies.ac.cn, hanchaojiang@hotmail.com Abstract The eastern Tibetan Plateau (TP) is a climatically sensitive area affected by the Indian Sum- mer Monsoon (ISM). A new pollen record from a lacustrine sediment in Mao County shows that the study area was covered mainly by shrubs and herbs during the last deglaciation, indicating open and sparse forest grasslands. Hydrophilous herbs were mainly dominated by Cyperaceae, Poaceae, Myriophyllum, Polygonum and Typha, and they gradually increased from 18.7 to 16.8 ka, suggesting a transition to a more humid climate. This corre- sponds to climate cooling over the same period. From 16.8 to 14.6 ka, hydrophilous herbs continued to increase, coincident with a general ameliorating trend indicated by δ18O rec- ords from East Asia. Between 14.6 and 14.0 ka, the mean content of hydrophilous herbs reached peak in the sequence, corresponding to relatively high δ18O values during this period. From ~14.0 to 12.9 ka, the abundance of hydrophilous herbs decreased significantly. Over the same period, the Greenland ice core shows a decrease in δ18O and low-latitude cave stalagmites in China record an increase in δ18O. This implies that longitudinal tempera-

ture gradients increased and drove the southward retreat of the ISM, which in turn drove a continuous decrease in the abundance of hydrophilous herbs in the study area. From 12.9 to 11.6 ka, the mean content of hydrophilous herbs decreased to the lowest (8.3%) in the whole sequence, indicating a cold and dry climate in the study area. A positive shift in δ18O records during 11.6–10.6 ka was matched by a significant increase in the abundance of hydrophilous herbs in the study area, indicating a warm and humid climate trending. Hence, the ISM has had a significant impact on the climate of the eastern TP since the onset of deglaciation around ~16.8 ka. 1. Introduction The Cenozoic collision of the Indian and Asian plates resulted in uplift of the Tibetan Plateau (TP) and the formation of a steep eastern margin of the plateau, where the elevation decreases from >5000 m to ~600 m over a distance of ~50 km [Fig 1]. This transitional zone is PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.0232803 May 6, 2020 1 / 12 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Shi W, Jiang H, Mao X, Xu H (2020) Pollen record of climate change during the last deglaciation from the eastern Tibetan Plateau. PLoS ONE 15(5): e0232803. https://doi.org/ 10.1371/journal.pone.0232803 Editor: Broxton W. Bird, Indiana University-Purdue University Indianapolis, UNITED STATES Received: January 2, 2020 Accepted: April 21, 2020 Published: May 6, 2020 Copyright: © 2020 Shi et al. This is an open access article distributed under the terms of the Creative

Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: This work was funded by the National Key Research and Development Program of China (2017YFC1501000), the National Natural Science Foundation of China (41572346) and the National Nonprofit Fundamental Research Grant of China, Institute of Geology, China Earthquake Administration (Grant No. IGCEA1713, IGCEA1906).