Records of East Asian monsoon activities in Northeastern China since 15.6 ka, based on grain size analysis of peaty sediments in the Changbai Mountains

Abstract

Peatlands provide a widespread terrestrial archive for Holocene study. However, little is known about the grain-size characteristics of peaty sediments and their environmental significance. In order to study these phenomena in detail, two sections from the Hani and Gushantun peatlands in the Changbai Mountain Area were cored and sub-sampled. Based on reliable calibrated AMS 14 C ages, we established grain size variations in the peat cores since 15.6 ka cal. BP. Our results showed that the peaty sediments in the Changbai Mountains are mainly composed of silt. Moreover, the grain size component, which is related to paleoclimate variables, can be classified into three groups based on the "Grain size class vs. standard deviation" method. These sensitive grain size components are <37.0 μm (Component 1 or C1), 37.0-497.8 μm (Component 2 or C2) and >497.8 μm (Component 3 or C3). C1 comprises the finest silt in the peaty sediment and is mainly conveyed by the East Asian winter monsoon (EAWM), whereas C2 is transported into the peatland by surface runoff related to the enhancement of the East Asian summer monsoon (EASM). C3 is conveyed in saltation and bed-load mode by strong surface runoff linked to high-energy flow caused by a strong EASM, and perhaps is an indicator of extreme rainfall events in the Changbai Mountains. Our results suggest that the study region was dominated by a cold/dry environment during the late-glacial period under a strong EAWM. However, there was a marked climatic shift from an EAWM-dominated cold/dry climate to an EASM-dominated more mesic environment during the early Holocene. Increased percentage of C2 in peat cores during the Holocene Optimum (9.0-4.5 ka) indicates abundant rainfall in the study region (even with extreme rainfall events) as a result of a significant enhancement of the EASM. Weak monsoon events occurred at 10.5 ka, 9.2 ka, 8.2 ka, 7.2 ka, 6.2ka, 5.5 ka and 4.2 ka shown by sharp decreases in C2, agreeing with the stalagmite δ 18 O records in China. The results obtained from environmentally sensitive grain-size component records are largely consistent with other palaeoenvironmental records in the East Asian monsoon area, substantiating the regional climate patterns and monsoon evolution since late-glacial time. Because intensity of the East Asian monsoon is likely responsible for the grain-size change in the peat samples, the grain size components in peat samples may be used for reconstructions of past environmental conditions and of variability in the East Asian monsoon.

Transition from a warm and dry to a cold and wet climate in NE China across the Holocene

“…Summer insolation was highest during the early Holocene and decreased since then (Berger and Loutre, 1991). Indeed, there are other records from the region that indicate a wet early Holocene and dry late Holocene (Li et al, 2017), more in-line with the expected evolution of the EASM based on the local insolation. The contrasting response recorded in different proxies and in different regions indicates that the climatic evolution of NE China and especially the EASM across the Holocene remains poorly constrained.…”

“…However, biomarker records are currently lacking from other peats in NE China that span the deglaciation such as the Gushantun peat deposits. Although pollen and grain sizes have been used to reconstruct Holocene climate and vegetation changes in the Gushantun peat (Liu et al, 1989;Zhao et al, 2015;Li et al, 2017), the temperature and paleohydrological variations in this peatland during the Holocene are currently unknown. To provide new information on the paleoclimate history of NE China, and dynamics of the EASM, our study employs high temporal resolution (~100-200 year resolution) paleoclimatic proxies based on the abundance and distribution of GDGTs, similar to that of previous Holocene studies (Zheng et al, 2014(Zheng et al, , 2015(Zheng et al, , 2017.…”

Climate changes recorded by Hani Peat in Northeast China over the past 13.8 cal ka BP

“…With relatively high temporal resolution, its humification, elemental content, organic content, pollen content, stable isotopes and more are all effective paleoclimate proxies, and are useful for studying past climate changes (Gorham, 1991). In China, many peatlands have been used to reconstruct climate changes across different time scales (Xiao et al, 2004;Hong et al, 2003Hong et al, , 2005Hong et al, , 2009Zhou et al, 2010;Lu et al, 2013;Chen et al, 2015;Liu et al, 2015;Zhao et al, 2017;Lei et al, 2017;Li et al, 2017;Xu et al, 2006;Ferret et al, 2012;Zheng et al, 2018). These have greatly improved our understanding of the dynamics of the EASM.…”

“…Hani peatland in Jilin Province of northeast China is one of the few peatlands that remain wellpreserved (C. Schroder et al, 2007). It is situated at the frontal area of the EASM and previous studies have shown that past environmental changes can be reconstructed from pollen, grain size, stable isotopes as well as elemental and organic indicators (Ficken et al, 2000;Zhou et al, 2010;Hong et al, 2005Hong et al, , 2009Hong et al, 2010;Seki et al, 2009;McClymont et al, 2010;Yamamoto et al, 2010;Zheng et al, 2010Zheng et al, , 2011aZheng et al, , b, 2017Zheng et al, , 2018Huang et al, 2013;Wu et al, 2016;Li et al, 2017;Xiao et al, 2017), but its development history, and regional hydrology due to climate changes can still be further elaborated. For example, some records suggest that the precipitation in Hani decreased from the early to late Holocene (Hong et al, 2010;Hong et al, 2009Hong et al, , 2010 while some others suggest it increased gradually (Zheng et al, 2018).…”

“…For example, some records suggest that the precipitation in Hani decreased from the early to late Holocene (Hong et al, 2010;Hong et al, 2009Hong et al, , 2010 while some others suggest it increased gradually (Zheng et al, 2018). In addition, some studies show that the precipitation during the YD had increased in the Hani peatland (Zhou et al, 2010;Hong et al, 2010), while others do not show obvious increases (Li et al, 2017).…”