Paleotidal regime in the Changjiang (Yangtze) Estuary, the East China Sea, and the Yellow Sea at 6 ka and 10 ka estimated from a numerical model

Two-dimensional paleotidal simulations were carried out to investigate the paleotides and paleotidal currents in the Changjiang (Yangtze) Estuary, the East China Sea, and the Yellow Sea. Calculations were made for 10 ka, 6 ka, and the present. An age of 10 ka corresponds to a period during the last deglaciation when the sea-level was about 45 m below its present level. At that time, the Changjiang Estuary extended southeastward to the East China Sea for about 400 km. The second period, 6 ka, coincides with the maximum Holocene transgression in eastern China. The paleotopography around the Changjiang Estuary was reconstructed for 10 ka and 6 ka using available borehole datasets to remove the Holocene strata. At 10 ka, the spatial distribution of M2 tides was different from today. No amphidrome was present in the Yellow Sea, and the current velocity was generally larger on the continental shelf. Strength and ellipticity of the simulated tidal currents indicated that the northern part of the moribund tidal sand-ridge system in the East China Sea might have been formed at around this period. On the other hand, the tidal field at 6 ka was similar to that at present except for the region within and adjacent to the paleo-Changjiang Estuary. A radial tidal-flow pattern was originated from the estuary mouth, which seemed to have enhanced tides and tidal currents in the estuary.