Sea-level change as the driver for lake formation in the Yangtze Plain - A review

The Yangtze Plain (floodplains in the middle and lower reaches of the Yangtze River) is a region with numerous lakes, including the three largest freshwater lakes in China, i.e. Poyang Lake (PYL), Dongting Lake (DTL), and Taihu Lake (THL). The formation mechanism of these lakes offers insights into the ongoing debate concerning the interaction between tectonic activity, climate, sea-level, human impact, and Earth-surface processes. Previous studies have usually focused on individual lakes, so there remains no over-arching and consistent framework for lake formation in the region as a whole. Here we review published sedimentary and chronological records on the above three lakes and propose that sea-level change has determined their formation. During the last glacial maximum (LGM; ca 30-20 ka), with a sea-level > 120 m lower than present, a landscape of incised valleys and interfluves prevailed over the entire Yangtze Plain, including the DTL area, which is > 1400 km upstream from the modern river mouth, and there was no large lake on the plain. The lakes emerged in the Holocene, although more precise ages await further investigations. The glacial sea-level lowstand, with concomitant headward incision, was responsible for the extensive deeply incised landscape of the LGM, whereas the Holocene high sea-level, with resultant infilling of the incised valleys, accounted for the formation of lakes. This sea-level forcing hypothesis suggests a more far-reaching influence of sea-level change on the Yangtze Plain, and a closer relationship between Earth-surface processes and glacial interglacial cycles (global climate) than is commonly believed. According to our newly hypothesized climate-controlled geomorphological (CCG) model, it is very likely that similar lake-forming processes could have occurred multiple times during earlier glacial-interglacial cycles, and that this pattern might also have occurred in many other river systems in the eastern coastal areas of China, as well as in other similar river plains worldwide, thus having an important role in shaping modern coastal-plain landscapes. Further work is required to test this CCG model.