## 2 Regional Settings and Methods
### Regional Settings
However, before the last capture of the Huaihe River by the ancient Yellow River entering the sea, the main detritus source of the Subei littoral plain area included northward components of Yangtze River sediments. Since the amount of northward components was small, coastlines remained relatively stable for a long time. Nevertheless, the ancient Yellow River captured the Huaihe River and entered the sea in 1128. This provided a large amount of detritus for the formation of the Subei littoral plain area. A previous study demonstrated that the northern Jiangsu coast was mainly affected by the Yellow River [41]. Major element content changes suggested that northward diffusion of Yangtze River sediments was weak and ranged from the estuary to Rudong County [42]. Montmorillonite content changes indicated that the coast northward from Rudong County to the ancient Yellow River Estuary comprised ancient Yellow River detritus [42]. [PERSON] et al. proposed that the land formation process in the Subei littoral plain area was mainly controlled by Yellow River detritus, which could affect areas as far south as the area near Xinhai Bore [43]. [PERSON] et al. suggested that sediments from the coast southward from Rudong County to the Yangtze River Estuary were dominated by Yangtze River sediments, while sediments from the coast northward from Dafeng County to the ancient Yellow River Estuary were dominated by Yellow River sediments [44]. The sediments between these two counties were mixtures of the sediments of these two large rivers [44]. Based on clay mineral assemblages, [PERSON] et al. proposed that sediments from the coast northward from Rudong County to the ancient Yellow River Estuary were dominated by Yellow River inputs, whereas those from the coast southward from Rudong County to the Yangtze River Estuary were dominated by Yangtze River inputs [45]. As mentioned above, in the Subei littoral plain area, the ranges of influence and mixed areas of these two large rivers remain controversial. Currents Tides and Sediment Transportation  
Fruitful research on tidal currents and sediment transport along the Subei coast has been performed in recent decades. The vast majority of the obtained results have indicated that under the influences of the Yellow sea coastal current (YSCC) and Subei coastal waters (SCWs) in winter, suspended sediments around the ancient Yellow River Estuary are transported to the southeast toward the radial sand ridge, even to areas near the Yangtze River Estuary, and jointly with Yangtze River sediments they are carried toward Jeju Island [46]. However, other studies have demonstrated that there is a northward flow along the Subei coast [47], and this could probably cause sediment flow from the ancient Yellow River Estuary or even from the radial sand ridge and the Yangtze River Estuary northward to Haizhou Bay [48]. [PERSON] et al. also proposed that the tidal residual current flowing northward along the coast could transport sediments into SCWs [49]. [PERSON] et al. [50] also found that there exists a relatively stable northward low-frequency circulation along the Subei coast in summer, which flows northward from the north branch of the Yangtze Estuary to Haizhou Bay, turns east and then flows southeast, and this circulation could probably transport Yangtze River sediments to replenish the Subei coast. [PERSON] et al. also determined that the direction of the coastal current in Subei is upwind in winter, and this could probably provide new ideas to explain the source-sink relationship between the Yangtze River Estuary and Subei littoral plain area, combined with the fate of materials entering the sea from the Yangtze River [51]. In summary, it could be concluded that sediment transportation along the Subei coast and the material contributions of the ancient Yellow River and Yangtze River to the Subei littoral plain area are complex and should be investigated.