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

important turning point in the Northern Hemisphere climate, widely believed to indicate the start of the last deglaciation. This timing is consistent with a study that reported the last degla- ciation started at 18.5 ka and strengthened at ~16.5 ka in the southern TP area [35]. The onset of the Northern Hemisphere deglaciation was induced by an increase in northern summer insolation, which led to an abrupt rise in sea level [36]. 14.6–12.9 ka This period is characterized by the greatest abundance of hydrophilous herbs in the entire sec- tion, showing maximum values between 14.6 and 14.0 ka, and decreasing from ~14.0 to 12.9 ka [Fig 4A]. Correspondingly, δ18O values from the Greenland ice core and cave stalagmite records were relatively high between 14.6 and 14.0 ka. Between 14.0 and 12.9 ka, δ18O values from the Greenland ice core show a decrease trend [Fig 4B] [33], whereas δ18O values in cave stalagmites showed an increase [Fig 4C and 4D] [10, 11]. These imply that the climate in the study area during 14.6–14.0 ka was the most humid and warmest of the entire section, which was consistent with high temperatures in high- and low-latitude regions of the Northern Hemisphere. However, temperatures decreased in high-latitude regions from 14.0 to 12.9 ka and increased in low-latitude regions. Accordingly, longitudinal temperature gradients increased from 14.0 to 12.9 ka in the Northern Hemisphere and consequently drove the south- ward retreat of the ISM circulation. We propose that this resulted in a decrease in hydrophi-

lous herbs from 14.0 to 12.9 ka [Fig 4A], accompanied by drought in the middle Yangtze region, although with some fluctuations [Fig 4F]. These trends were linked to a significant increase in insolation during this period [Fig 4E]. Fig 4. Correlation of (a) the abundance trends of hydrophilous herbs from the Xinmocun section with: (b) the δ18O record from GRIP2 [33], (c) the δ18O record from Hulu cave stalagmites [11], (d) the δ18O record from Haozhu cave stalagmites [10], (e) insolation at 33˚N [32], and (f) the Sr/Ca ratio from Haozhu cave stalagmites [10]. For each time interval, the solid line is linear fitting (a). https://doi.org/10.1371/journal.pone.0232803.g004 PLOS ONE Last deglacial pollen reocord from the eastern TP PLOS ONE | https://doi.org/10.1371/journal.pone.0232803 May 6, 2020 9 / 12