## 4 Discussion
### Influence of Summer Monsoon on Centennial Timescales  
The Huanghe River flows across the Chinese Loess Plateau, and monsoonal climate is one of the most influential factors controlling this erosion [48; 49]. Modern observations suggest that seasonal changes in water discharge and sediment loads of the Huanghe River were coupled [8], inferring that the massive amount of EASM rainfall plays an important role in sediment delivery and erosion [6]. Because the record of Comp-2 content is characterized by centennial variabilities (Figure 6b), we compared this record to the EASM in high-frequency bands (<500 year). As shown, a good agreement was observed between YDZ-3 Comp-2 and EASM changes (Figure 6c), indicating summer climate is another important factor on centennial timescales, dominating deltaic evolution of the Huanghe River. The agreement may demonstrate that: (1) although erosion mainly occurs in winters, most of the eroded materials are carried by rivers in summers; and (2) monsoonal rainfall could enhance erosion in the catchment during flood periods. Thus, considering YDZ-3 location and the significant relationship between water discharge and regional precipitation [14], the linkage between deltaic evolution and EASM changes can be summarized as follows: When EASM strengthened, total rainfall across the catchments increased, and water discharge  
Figure 6: Correlating YDZ–3 record to various paleoenvironmental proxies on centennial timescales. (**a**) YDZ–3 Comp–2 modal size with the low-frequency (<0.002) component of GSC–12 record [8]; (**b**) YDZ–3 Comp–2 relative percentage (original value, dashed line; 3–point moving average, solid line) with the high-frequency (>0.002) component of GSC–12 record [8]; (**c**) Comparison between YDZ–3 Comp–2 relative percentage and the high-frequency (>0.002) component of Dongge Cave \(\delta^{18}\)O record [50]; (**d**) Comparison between YDZ–3 Comp–2 relative percentage and the high-frequency (>0.002) component of total solar irradiance (TSI) during the Holocene [51]. Noted that data in (**c,d**) are 3–point moving average records. and sediment loads enhanced, resulting in accelerating the progradation of the Huanghe River delta and/or overloaded channels. Moreover, a number of paleoclimatic studies claimed that changes in solar irradiance influenced millennial-scale climates, such as the Bond IRD events [52], Asian monsoon [50; 53], and KC [54], while no persistent phase association was reported between PSL shifts of the Huanghe River and solar activities [8]. Comparing total solar irradiance (TSI) with our proxies of deltaic evolution on centennial timescales, a direct correlation was observed (Figure 6d). Therefore, we proposed that solar activities could be an important factor dominating geomorphological evolution, such as deltaic development of the Huanghe River on centennial timescales via the effect of summer monsoon. Integrating millennial and centennial impacts of Asian monsoon, the natural processes of Holocene delta of the Huanghe River can be identified. On the first order, winter climate over East Asia is the dominant factor in deltaic evolution, which induces erosions in the catchment on millennial timescales. On the second order, summer climate related to monsoonal changes is the dominant factor, which influences the transport of erosional materials to the delta on centennial timescales. Since \(\sim\)2360 yr BP, changes in sedimentary proxies of core YDZ-3 are amplified at a higher frequency (Figures 5 and 6), which could be correlated to the frequent channel shift of the Huanghe River [10; 11; 13]. It is thus inferred that the stability of the delta has decreased significantly, probably responding to the accelerating and strengthening impacts of human activities since the Warring States Period in Chinese history (\(\sim\)2400 yr BP).