Simulated characteristics of estuarine fronts in the Changjiang River Delta*

The river plume front between the diluted ocean water and salty ocean water in the Changjiang (Yangtze) River Delta (CRD) is well studied. Comparatively, less is known about the estuarine front in the CRD, which is formed between the riverine freshwater and the diluted ocean water and has the highest magnitude of salinity gradient (SG) in the CRD. Estuarine fronts are of great significance to the riverine material transport in the estuary. Many biogeochemical processes are enhanced in estuarine fronts, which have brought about environmental problems. In this study, the seasonal variations of the estuarine fronts in the CRD were studied in wet (July) and dry (January) seasons in 2017, based on model simulations with high spatiotemporal resolutions using the Finite-Volume Community Ocean Model (FVCOM). The estuarine front included several sharp fronts with a SG >4(/500 m), and was bottom-trapped on the submerged delta front. Seasonal changes mainly occurred off the Jiangsu coast, where a significant estuarine front was formed in July. The estuarine fronts generated around the submerged delta topography were accompanied by the offshore extension of older estuarine fronts, which were diluted and evolved into plume fronts over a tidal cycle. The simulated estuarine fronts had a salinity range of 6 to 22 in the dry season and 6 to 14 in wet season 2017. The estuarine fronts hindered the residual current by altering its flow direction to the southeast.