Holocene climate reconstruction based on herbaceous phytolith indices from an AMS 14C-dated peat profile in the Changbai Mountains, northeast China

This study uses new herbaceous phytolith indices to reconstruct the paleoclimate in the Changbai Mountains, NE China. In this study, we collected 52 pairs of herbaceous quadrats and corresponding topsoils: 25 were from the understory (UND) and 7 were from the non-understory (NON) in the Changbai Mountains; whereas the other 20 were from the grassland (GRA) of Songnen Plain for comparing the forest area of the Changbai Mountains. The phytolith analyses of the 104 modern samples provide a guide of using herbaceous phytolith indices as paleoclimate reconstruction. The herbaceous quadrats of the Changbai Mountains contained more long-cell phytoliths and fewer short-cell phytoliths compared to the herbaceous quadrats of the Songnen grassland; and similar situations appeared in the corresponding topsoil phytoliths. The ratio of short cell% to long cell% (S/L) in the topsoil can be used to discriminate grassland (S/L > 1.65) and forest (< 1.65), with discriminant accuracy of 80%. Furthermore, in the forest region, S/L in the topsoil is low for the non-understory (NON) (< 0.46), and relatively high for the understory (UND) (0.46 < S/L < 1.65), probably due to preservation of short-cell phytoliths. The ratio of rondel% to lanceolate% (Ro/La) reflected the same trend as S/L for the forest region: Ro/La < 0.23 indicating NON, and Ro/La > 0.89 indicating UND. Thus, lower S/L and Ro/La ratios may reflect more development of NON in the forest region under relatively warm conditions, whereas higher S/L and Ro/La values indicate better development of UND with cold climates. These two indices (S/L and Ro/La) from a peat profile in the Changbai Mountains were further used to reconstruct the paleoclimate since 7670 a BP. The phytolith analyses of 33 peat samples from the 326-cm long core showed four ordinal clustering zones: Zone I (7670-4060 a BP) with low mean S/L (0.42) and Ro/La (0.78) was characterized as warm. In Zone II (4060-2580 a BP), S/L and Ro/La fluctuated around mean values of 0.47 and 3.40, respectively; indicating cooler climate than Zone I. Zone III (2580-640 a BP) was characterized by the highest mean values of S/L (0.53) and Ro/La (6.97) in the profile, reflecting the coldest condition in the record. In Zone IV (640 a BPemodern), the average values of S/L and Ro/La were 0.31 and 1.14, respectively. Both indices increased initially and then declined, perhaps reflecting the colder climate of the Little Ice Age, followed by a warming period. The climatic patterns of the Changbai Mountains reconstructed from the herbaceous phytolith indices agreed with the Ic index and pollen analysis from the same peat profile, suggesting that these new herbaceous phytolith indices should be applicable in paleoclimate reconstruction. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.