## 4 Discussion  
### Correlating Modal-Size Changes to Paleo-Superlobes Shifts  
Typically, deltas can be classified as three types: river-, wave-, or tide-dominated systems [38], and most natural systems are developed between the three end members. This process can be simplified as that a river supplies elastic sediments to the receiving basin more rapidly than marine processes can remove it [8]. In this case, deltaic materials should increase abruptly when a delta starts, and similarly decrease when a superlobe migrates. In the study area, the regional sea level rose up to the highest level at \(\sim\)7000-6000 yr BP [39; 40], and due to sea-level rise stagnation [17; 41], the Huanghe River delta initiated at \(\sim\)6000 \({}^{14}\)C yr BP [10; 11; 13]. Prior to construction of major river dams, the hydrodynamics involved in deltaic erosion were much less than sediment inputs, resulting in progradation of the delta [42; 43; 44]. Core YDZ-3 locates downstream to each PSL, and the drilling site was underwater prior to 1855 AD. Because the delta area is generally dominated by cyclonic tidal and geostrophic flows, the YDZ-3 site can record the major changes of the Huanghe River delta in the Holocene. Due to its distal position, the characterized variability of the unmixed grain-size components can be correlated to the eight intervals of changing channel and chenier development in the Holocene (Figure 5). The basic linkage of this correlation can be summarized as follows: when a superlobe started, the amount of deposited materials increased suddenly, causing fine particles in the sediments to significantly and sharply increase; and in contrast, when a superlobe ceased, the amount of fine-grained materials decreased. Because Comp-2 is the component close to the marine surface sediments [14] and considering the relatively coarse-grained sediments in local rivers [45; 46], the Comp-2 record of modal size and relative percentage was employed for later analysis. Based on changes in Comp-2 modal size, the presence of all the seven PSLs are firstly confirmed in this study (Figure 5), namely 6400-5280 yr BP (PSL-1), 4480-4190 yr BP (PSL-2), 3880-3660 yr BP (PSL-3), 3070-2870 yr BP (PSL-4), 2780-2360 yr BP (PSL-5), 2140-2000 yr BP (PSL-6), and 1940-1780 and 1700-1650 yr BP (PSL-7). The timing of these intervals is close to the original proposal of PSLs [15], but with a clearer age limit for each PSL. Although the precise age of these intervals cannot be checked by a single core, the procedure for identifying PSLs in sedimentary sequences in this study may provide a valuable and effective way in future work. Tuning geomorphological events to a well-dated and directly-linked proxy offers an opportunity to testify climatic influences on deltaic evolution of the Huanghe River on different timescales. The catchment of the Huanghe River is affected by the following climatic systems: (1) EASM carries moisture and induces sediment delivery; (2) Kuroshio Current (KC) modulates winter climate of eastern China; and (3) EAMM associated with the Bond ice-rafting debris (IRD) events dominates erosions in the catchment. In winters, it has been proposed that the reduced cyclone frequency and dust storms in northern China could weaken erosion in the catchment and decrease sediment loads [8]. When sediment loads descend low enough, for example 0.278 \(\times\) 10\({}^{9}\) ton/year, a modern threshold [4], the delta lies close to a silting threshold. The silting threshold is critical, because below the value, river channels become self-adapting, interacting with floods, storm surges, or variations in tidal regime or wave action by enhanced channel erosion and greater potential for avulsion [47]. In this case, if sediment loads suddenly increase, the equilibrium will be disturbed, resulting in overloaded channels or channel avulsion.