Hyperpycnal plume at the Yellow River Mouth triggered by dam regulation: In-situ observations

Few hyperpycnal flows have ever been observed in estuarine environments although they are believed to play a critical role in sediment dispersal and carbon burial/export within estuarine and deltaic depositional systems. Here we report the hyperpycnal flows directly observed at the Yellow River (Huanghe) mouth during an artificial flooding event as regulated by large dams in the river basin. Instruments deployed at a mooring station at the river mouth recorded the impulse hyperpycnal events within tidal cycle as indicated by warm and fresh water mass in the bottom layer delivering fine-grained sediment (< 10 micros) with flow velocity as high as 160 cm/s. A dual-frequency echo-sounder recorded large differences in acoustic reflectance between high and low frequency signals, which suggest a thick hyperpycnal layer (~ 4.0 m) corresponding to the impulse hyperpycnal plumes. The observations firstly captured the profile structures of estuarine hyperpycnal plume including velocity, temperature, salinity and sediment. Hyperpycnal plume corresponds the high suspended sediment concentration and fine grain size, which implies that rapid export of riverine particulate organ carbon (POC) was contributed by hyperpycnal plume, presenting significant impacts on estuarine carbon cycle and coastal ecosystem.