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

one section helps to test each other in reliability of dating results and then to better restrain the chronology of the section. Two new AMS 14C dates (S1 Table) and five published OSL dates [18] (S2 Table) show a good age-depth linear relationship (R2 = 0.97) and reveal a high average sedimentation rate of 1.37 mm/yr [Fig 2C], making it beneficial to study high frequency envi- ronmental changes in the eastern TP [18, 24]. The age of each pollen sample was derived by linear interpolation of seven age dates [Fig 2C]. Fifty-three samples were analyzed and 12,772 spore and pollen grains were identified [Fig 3]. The fern spore and algae varied from 10 to 42 grains with a mean of 25 grains while the ter- restrial pollen varied from 135 to 255 grains with an average of 203 grains. Fifty-nine taxa were identified, and these show a generally stable varying feature. To get better knowledge about ter- restrial vegetation changes, all terrestrial pollen taxa were used to calculate the percentage of each pollen while all pollen and spore taxa were used to calculate the percentage of spores. Shrub and herb pollen (49.5%–72.1%, mean 63.8%) was dominant in all samples, comprising mainly Artemisia, Apiaceae, Cyperaceae, and Compositae. Among the taxa identified, Cypera- ceae, Poaceae, Polygonum, Typha, and Myriophyllum were indicative of a humid environment [25–29, 30]; thus, the total percentage of these taxa was used as a proxy for relative humidity [Fig 3]. Broad-leaved pollen taxa (17.7%–40.9%, mean 27.4%) were dominated by Quercus

(mean 10.2%) and Castanea (mean 9.7%), with minor Betula, Ulmus, Corylus, Carpinus, Casta- nopsis, Alnus, Liquidambar, Pterocarya, Juglans, and Tilia. Fern spores and algae (4.9%–18.1%, mean 11.0%) were dominated by Polypodium and Pediastrum. Conifer pollen (3.1%–19.9%, mean 8.1%) included Pinus, Picea, and Abies. The above taxa reflected an open and sparse for- est grassland that covered the study area during the last deglacial period, which was generally consistent with the results of previous studies [31]. Five pollen zones were identified based on variations in the abundance of the dominant and hydrophilous pollen taxa [Fig 3]. Zone A (9 samples, 18.7–16.8 ka) Shrub and herb pollen in zone A (52.4%–68.2%, mean 63.1%) were dominated by Artemisia (7.7%–32.0%, mean 18.0%), Apiaceae (7.1%–19.6%, mean 12.8%), hydrophilous herbs (4.4%– 18.0%, mean 10.4%), and Compositae (0%–8.5%, mean 3.9%) [Fig 3]. The former two taxa showed a relatively high abundance during the early part of the zone, and the latter two taxa Fig 2. (A) Photograph showing the geomorphic features of the intermountain basins in the Diexi lake region and (B) the Xinmocun lacustrine section (red star). (C) 14C and OSL age versus stratigraphic depth of the Xinmocun section. https://doi.org/10.1371/journal.pone.0232803.g002 PLOS ONE Last deglacial pollen reocord from the eastern TP PLOS ONE | https://doi.org/10.1371/journal.pone.0232803 May 6, 2020 4 / 12